Synthesis and Characterization of Hydrophobic-Hydrophilic Segmented and Multiblock Copolymers for Proton Exchange Membrane and Reverse Osmosis Applications Rachael A. VanHouten Dissertation submitted to the faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSPHY In Macromolecular Science and Engineering James E. McGrath, Chair Judy S. Riffle John G. Dillard Richey M. Davis Scott W. Case December 1, 2009 Blacksburg, Virginia Keywords: multiblock copolymer, segmented copolymer, disulfonated poly(arylene ether sulfone)s, proton exchange membrane, reverse osmosis membrane
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Synthesis and Characterization of Hydrophobic-Hydrophilic Segmented and Multiblock Copolymers for Proton Exchange Membrane and
Reverse Osmosis Applications
Rachael A. VanHouten
Dissertation submitted to the faculty of the Virginia Polytechnic Institute and State
University in partial fulfillment of the requirements for the degree of
Synthesis and Characterization of Hydrophilic-Hydrophobic Segmented
and Multiblock Copolymers for Proton Exchange Membrane and
Reverse Osmosis Applications
Rachael A. VanHouten
ABSTRACT
This thesis research focused on the synthesis and characterization of disulfonated
poly(arylene ether sulfone) hydrophilic-hydrophobic segmented and multiblock
copolymers for application as proton exchange membranes (PEMs) in fuel cells or as
reverse osmosis (RO) membranes for water desalination. The first objective was to
demonstrate that synthesizing blocky copolymers using a one oligomer, two monomer
segmented copolymerization afforded copolymers with similar properties to those which
used a previous approach of coupling two preformed oligomers. A 4,4’-biphenol based
hydrophilic block of disulfonated poly(arylene ether sulfone) oligomer of controlled
number average molecular weight (Mn) with phenoxide reactive end groups was first
synthesized and isolated. It was then reacted with a calculated amount of hydrophobic
monomers, forming that block in-situ. Copolymer and membrane properties, such as
intrinsic viscosity, tensile strength, water uptake, and proton conductivity, were
consistent with those of multiblock copolymers synthesized via the oligomer-oligomer
approach.
The segmented polymerization technique was then used to synthesize a variety of
other copolymers for PEM applications. The well known bisphenol phenolphthalein was
iii
explored as a comonomer for either the hydrophilic and hydrophobic blocks of the
copolymer. Membrane properties were explored as a function of block length for both
series of copolymers. Both series showed that as block length increases, proton
conductivity increases across the entire range of relative humidity (30-100%), as does,
water uptake. This was consistent with earlier research which showed that the water self-
diffusion coefficient scaled with block length. Copolymers produced with
phenolphthalein had higher tensile strength, but lower ultimate elongation than the 4,4’-
biphenol based copolymers.
Multiblock copolymers were also synthesized and characterized to assess their
feasibility as RO membranes. A new series of multiblock copolymers was synthesized
by coupling hydrophilic disulfonated poly(arylene ether sulfone) (BisAS100) oligomer
with hydrophobic unsulfonated poly(arylene ether sulfone) (BisAS0) oligomer. Both
oligomers were derived using 4,4´-isopropylidenediphenol (Bis-A) as the bisphenol.
Phenoxide-terminated BisAS100 was end-capped with decafluorobiphenyl and reacted at
relatively low temperatures (~ 100 oC) with phenoxide-terminated BisAS0. Basic
properties were characterized as a function of block length. The initial membrane
characterization suggested these copolymers may be suitable candidates for reverse
osmosis applications, and water and salt permeability testing should be conducted to
determine desalination properties. The latter measurements are being conducted at the
University of Texas, Austin and will be reported separately.
iv
Acknowledgements
I would like to think my advisor, Dr. James E. McGrath, for his continued
guidance throughout my graduate education. His willingness to discuss my research and
help me overcome problems was invaluable for my research. I would also like to thank
my committee members, Drs. Judy S. Riffle, John G. Dillard, Richey M. Davis, and Scott
W. Case for their time and research suggestions.
I am appreciative of all the discussions and support my labmates from past and
present have provided me throughout the years. A special thanks to Dr. Harry Lee, Yu
Chen, Ozma Lane, Dr. Ruilan Guo, Dr. Gwangsu Byun, Dr. Xiang Yu, Dr. Yanxiang Li,
Dr. Abhishek Roy, Dr. Mou Paul, Dr. Gwangyu Fan, and Drs. Melinda and Brian Einsla
for their dedication to help me synthesize better polymers and write better papers. I am
grateful to the staff of the MACR program and MII for helping me with various tasks
throughout my time at Virginia Tech: Laurie, Millie, Angie, Tammy Jo, and Mary Jane.
I am thankful for the love and continued support of my mom, Betty Zeller, and
siblings, Stacy, Katie, and Alex. They have motivated me, encouraged me, and prayed
for me throughout my academic career. I am thankful to everyone at Main Street Baptist
Church and all my friends who have become my extended family away from home. I
would never have made it this far without constant encouragement, support, and prayers
throughout the past 5 ½ years from all my family and friends.
I am indebted to my loving husband and best friend, Desmond, for everything he
has been for me throughout my graduate career. He never gave up hope that I could get
this far and provided all the support he could to help me get here. No one else came close
to the understanding and patience he provided me through the long haul of graduate
v
school. I am excited for the new addition to our family, baby Adeline, and looking
forward to seeing what else our future has in store.
Ultimately, I’m thankful to God. Without Him, I would be lost. He guided and
directed me daily. I owe all my blessings to Him.
vi
ATTRIBUTION
Several colleagues facilitated the research described in the chapters included in this
dissertation. Their contributions are described below.
James E. McGrath is the author’s academic advisor and committee chair. He provided
support and guidance on all of the work.
Ozma Lane aided in proton conductivity measurements for chapter 2 and 3.
Desmond VanHouten assisted with thermal analysis and tensile testing for chapters 2, 3,
4, and 5 and helped with proton conductivity measurements for chapters 3 and 4.
Myoungbae Lee obtained transmission electron microscopy images for chapter 5.
vii
TABLE OF CONTENTS
TABLE OF FIGURES....................................................................................................... xi TABLE OF TABLES ...................................................................................................... xiv 1 Literature Review……………........................................................................................ 1 1.1 Ionomers ..................................................................................................................1 1.2 Fuel Cells .................................................................................................................1 1.3 PEM Fuel Cells ........................................................................................................2 1.4 Materials Used for PEMs.........................................................................................3
1.4.3 Directly Polymerized Sulfonated Monomers to form Sulfonated Poly(arylene ether) Random Copolymers.................................................................17
1.9 Research Objectives...............................................................................................67 2 Synthesis of Segmented Hydrophobic-Hydrophilic, Fluorinated-Sulfonated Block Copolymers for Use as Proton Exchange Membranes ..................................................... 79 2.1 Introduction............................................................................................................79 2.2 Experimental Section .............................................................................................83
2.2.2 Synthesis of Phenoxide-Terminated Hydrophilic Blocks (BPS-100)....... 83 2.2.3 Synthesis of BisSF-BPSH100 Segmented Copolymers ........................... 84 2.2.4 Synthesis of BisSF-BPSH100 Multiblock Copolymer Controls .............. 85
2.2.4.1 Synthesis of Fluorine-Terminated Hydrophobic Blocks (BisSF) ........ 85 2.2.4.2 Synthesis of Phenoxide-Terminated Hydrophilic Blocks (BPS-100) .. 85 2.2.4.3 Synthesis of BisSF-BPS100 Multiblock Copolymers .......................... 86
2.2.5 Characterization of Copolymers ............................................................... 86 2.2.6 Membrane preparation .............................................................................. 87 2.2.7 Determination of water uptake and dimensional swelling........................ 87 2.2.8 Measurement of proton conductivity ........................................................ 88 2.2.9 Tensile testing ........................................................................................... 89
2.3 Results and Discussion ..........................................................................................89 2.3.1 Synthesis of Hydrophilic Oligomers......................................................... 89 2.3.2 Synthesis of BisSF-BPSH100 Segmented Copolymers ........................... 92 2.3.3 Synthesis of BisSF-BPSH100 Multiblock Copolymer Controls .............. 95 2.3.4 Comparison of BisSF-BPSH100 Segmented and Multiblock Copolymer Properties .................................................................................................................. 96
2.4 Conclusions..........................................................................................................100 3 Synthesis and Characterization of Highly Fluorinated-Disulfonated Hydrophobic-Hydrophilic Segmented Copolymers Containing Various Bisphenols for Use as Proton Exchange Membranes..................................................................................................... 105 3.1 Introduction..........................................................................................................106 3.2 Experimental ........................................................................................................108
3.2.1 Materials ................................................................................................. 108 3.2.2 Synthesis of Phenoxide-Terminated Hydrophilic Blocks (BPS-100)..... 108 3.2.3 Synthesis of segmented copolymer with simultaneous formation of hydrophobic segments ............................................................................................ 109 3.2.4 Membrane Preparation............................................................................110 3.2.5 Characterization ...................................................................................... 110 3.2.6 Determination of water uptake and dimensional swelling...................... 111 3.2.7 Measurement of proton conductivity ...................................................... 112 3.2.8 Dynamic Mechanical Analysis ............................................................... 112 3.2.9 Thermal Gravimetric Analysis................................................................ 113 3.2.10 Tensile testing ......................................................................................... 113
3.3 Results and Discussion ........................................................................................113 3.3.1 Synthesis of PhS-BPS100 Segmented Copolymers................................ 113 3.3.2 Comparison of PhF-BPSH100 and BisSF-BPSH100 Segmented Copolymer Properties ............................................................................................. 116
4 Synthesis and Characterization of Hydrophobic-Hydrophilic Segmented Copolymers with Unequal Hydrophobic and Hydrophilic Block Lengths for Use as Proton Exchange Membranes………………………................................................................................ 126 4.1 Introduction..........................................................................................................126 4.2 Experimental ........................................................................................................128
4.2.1 Materials ................................................................................................. 128 4.2.2 Synthesis of Phenoxide-Terminated Hydrophilic Oligomers
4.2.3 Synthesis of segmented copolymer with simultaneous formation of hydrophobic segments ............................................................................ 130
4.2.4 Membrane Preparation............................................................................130 4.2.5 Characterization ...................................................................................... 131 4.2.6 Determination of water uptake and dimensional swelling...................... 131 4.2.7 Measurement of proton conductivity ...................................................... 132 4.2.8 Dynamic Mechanical Analysis ............................................................... 133 4.2.9 Tensile testing ......................................................................................... 133
4.3 Results and Discussion ........................................................................................133 4.3.1 Synthesis of Phenoxide-Terminated Disulfonated Hydrophilic Oligomer
Derived from Phenolphthalein................................................................ 133 4.3.2 Synthesis of BisSF-PhS Segmented Copolymer..................................... 136 4.3.3 Characterization of BisSF-PhSH100 Segmented Copolymer Properties 139
4.4 Conclusions..........................................................................................................144 5 Synthesis and Characterization of Multiblock Copolymers Derived from Bisphenol-A for Application as Reverse Osmosis Membranes ........................................................... 147 5.1 Introduction..........................................................................................................148 5.2 Experimental Section ...........................................................................................152
5.2.1 Materials ................................................................................................. 152 5.2.2 Synthesis of Phenoxide-Terminated Hydrophobic Oligomers
(BisAS0)…… ......................................................................................... 152 5.2.3 Synthesis of Phenoxide-Terminated Hydrophilic Oligomers
(BisAS100)……………………………………………….…………….153 5.2.4 Endcapping of Phenoxide-Terminated Hydrophilic Oligomers with
DFBP…................................................................................................... 154 5.2.5 Synthesis of Hydrophilic-Hydrophobic BisAS100-BisAS0 Multiblock
Copolymers ............................................................................................. 154 5.2.6 Characterization of Copolymers ............................................................. 154 5.2.7 Membrane preparation ............................................................................155 5.2.8 Determination of Ion Exchange Capacity (IEC)..................................... 156 5.2.9 Determination of water uptake and dimensional swelling...................... 156 5.2.10 Transmission Electron Spectroscopy (TEM).......................................... 157 5.2.11 Tensile testing ......................................................................................... 158 5.2.12 Dynamic Mechanical Analysis ............................................................... 158 5.2.13 Differential Scanning Calorimetry.......................................................... 158 5.2.14 Thermal Gravimetric Analysis................................................................ 159 5.2.15 Static Chlorine Exposure ........................................................................ 159
5.3 Results and Discussion ........................................................................................159 5.3.1 Synthesis of Phenoxide-Terminated Hydrophobic (BisAS0) and
Hydrophilic (BisAS100) Oligomers ....................................................... 159 5.3.2 Endcapping of Phenoxide-Terminated Hydrophilic Oligomers with
DFBP……............................................................................................... 164 5.3.3 Synthesis of Hydrophilic-Hydrophobic BisAS100-BisAS0 Multiblock
Copolymers ............................................................................................. 166 5.3.4 Membrane Characterization of BisAS100-BisAS0 Multiblock
Figure 1.1. Electrochemistry for PEMFC. ......................................................................... 3 Figure 1.2. Electrochemistry for DMFC............................................................................ 3 Figure 1.3. Chemical structure of Nafion®. ....................................................................... 5 Figure 1.4. Synthesis of poly(arylene ether sulfone) by nucleophilic aromatic substitution.............................................................................................................................................. 7 Figure 1.5. Side reactions due to water or excess base in SNAR polymerizations. ............ 9 Figure 1.6. Synthesis of poly(arylene ether sulfone) by electrophilic aromatic substituion............................................................................................................................................ 10 Figure 1.7. Synthesis of poly(arylene ether sulfone) by a modified Ullmann Reaction., . 11 Figure 1.8. Examples of post-sulfonated poly(arylene ether sulfone)s. Sulfonic acid group is located in the activated position (ortho to the ether group). (a) Sulfonated poly(ethersulfone) (b) sulfonated polysulfone (c) hexafluorinated sulfonated polysulfone............................................................................................................................................ 12 Figure 1.9. Crosslinking scheme for post-sulfonated UDEL using 1,1’-carbonyldiimidazole (CDI) and diamine as the crosslinking agents. (a) Sulfonic acid groups are activated by CDI (b) N-sulfonylimidazoles are converted to sulfonamides. .. 16 Figure 1.10. Synthesis of monomer grade SDCDPS. .......................................................18 Figure 1.11. Direct polymerization of SDCDPS, DCDPS, and 4,4’-biphenol to form BPSH-35 random copolymer. ........................................................................................... 19 Figure 1.12. Disulfonated poly(arylene ether) random copolymers containing different aryl linkages. ..................................................................................................................... 20 Figure 1.13. Disulfonated poly(arylene ether ketone) random copolymers using (a-b) 5,5’-carbonylbis(2-fluorobenzene-sulfonate) or (c) 1,4-bis(3-sodium sulfonate-4-fluorobenzoyl)benzene as the sulfonated comonomers....................................................23 Figure 1.14. Sulfonated naphthalene diol monomers. (a) 2,7-dihydroxynaphthalene-3,6-sulfonate disodium salt (b) 2,8-dihydroxynaphthalene-6-sulfonate sodium salt and (c) 2,3-dihydroxynaphthalene-6-sulfonate sodium salt.......................................................... 24 Figure 1.15. S-SEBS triblock copolymer. ........................................................................ 26 Figure 1.16. S-SIBS triblock copolymer........................................................................... 28 Figure 1.17. S-HPBS diblock copolymer. ........................................................................ 29 Figure 1.18. P(VDF-co-HFP)-b-SPS diblock copolymer. ................................................ 31 Figure 1.19. Synthesis of PAES-b-SPB multiblock copolymer. ..................................... 32 Figure 1.20. Synthesis of BPS-100:PEPO multiblock copolymer.................................... 35 Figure 1.21. Synthesis of various sulfonated-fluorinated multiblock copolymers. .......... 36 Figure 1.22. BPSH-100:BPS-00 multiblock copolymer with (a) DFBP and (b) HFB linking groups. .................................................................................................................. 41 Figure 1.23. Poly(arylene ether sulfone) multiblock copolymers synthesized using a DFBP coupling agent containing (a) BPS-00 or (b) 6FS hydrophobic oligomer. ............ 42 Figure 1.24. BPSH-100:6FK multiblock copolymer. .......................................................43 Figure 1.25. Synthesis of BPS-100:polyimide multiblock copolymer. ............................ 45 Figure 1.26. Synthesis of BPS-00:SPPP multiblock copolymer. ..................................... 47 Figure 1.27. BPSH-100:PBP multiblock copolymer. .......................................................48
xii
Figure 1.28. Formation of polyurethane segmented copolymer with a diol-based carbamate hard segment.................................................................................................... 50 Figure 1.29. Synthesis of poly(arylene ether ketone) segmented copolymers. ................ 52 Figure 1.30. Synthesis of hydrophobic block with subsequent synthesis of poly(arylene ether ketone) segmented copolymer.,................................................................................ 53 Figure 1.31. Synthesis of segmented block copolymer (BisSF-BPSH100) with simultaneous formation of hydrophobic block (BisSF).................................................... 55 Figure 1.32. World Desalination Capacity by Process, as of June 1999. Membrane processes: reverse osmosis (RO) and electrodialysis (ED); Thermal processes: multistage flash distillation (MSF), multi-effect distillation (ME), and vapor compression (VC) .... 57 Figure 1.33. Schematic of reverse osmosis....................................................................... 58 Figure 1.34. Structures of aromatic (a) polyamide-hydrazine and (b) polyamide copolymers........................................................................................................................ 62 Figure 1.35. Crosslinked fully aromatic polymer. ........................................................... 63 Figure 2.1. Phenoxide-terminated BPS-100 with controlled molecular weight .............. 90 Figure 2.2. 1H NMR spectrum of BPS-100 oligomer...................................................... 91 Figure 2.3. Log (Mn) vs. log (I.V.) for the hydrophilic oligomers................................... 92 Figure 2.4. BisSF-BPSH100 segmented copolymer........................................................93 Figure 2.5. (a) 1H and (b) 19F NMR spectra for BisSF-BPS100 segmented copolymer... 94 Figure 2.6. 13C NMR spectra for BisSF-BPS100 multiblock and segmented copolymers........................................................................................................................................... 95 Figure 2.7. BisSF-BPSH100 multiblock copolymer........................................................ 96 Figure 2.8. Comparison of dimensional swelling data for segmented, multiblock, and random copolymers........................................................................................................... 99 Figure 2.9. Comparison of proton conductivity under partially hydrated conditions for segmented and multiblock copolymers with increasing block length ............................ 100 Figure 3.1. General synthetic scheme for highly fluorinated:disulfonated segmented copolymers...................................................................................................................... 114 Figure 3.2. (a) 1H and (b) 19F NMR spectra for PhF-BPS100 segmented copolymer.... 115 Figure 3.3. 13C NMR spectrum for PhF-BPS100 segmented copolymer and BPS-35 random copolymer .......................................................................................................... 116 Figure 3.4. Comparison of proton conductivity under partially hydrated conditions for BisSF-BPSH100 and PhF-BPSH100 segmented copolymers with increasing block length......................................................................................................................................... 118 Figure 3.5. Comparison of dimensional swelling data for BisSF-BPSH100 and PhF-BPSH100 segmented and BPSH35 random copolymers................................................ 119 Figure 3.6. Thermal gravimetric analysis plots for BisSF-BPSH100 and PhF-BPSH100 copolymers in air............................................................................................................. 120 Figure 3.7. DMA plots for a) BisSF-BPSH100 and b)PhF-BPSH100 segmented copolymers. In a) and b) the closed symbols represent the storage modulus and the open symbols represent the tan delta. ...................................................................................... 121 Figure 4.1. PhS100 phenoxide-terminated hydrophilic oligomers ................................. 135 Figure 4.2. 1H NMR spectrum of PhS100 oligomer....................................................... 135 Figure 4.3. BisSF-PhS100 segmented copolymer .........................................................137 Figure 4.4. Representative (a) 1H and (b) 19F NMR spectra for BisSF-PhS100 segmented copolymer ....................................................................................................................... 138
xiii
Figure 4.5. 13C NMR spectrum for BisSF-PhS100 segmented copolymer..................... 139 Figure 4.6. Comparison of dimensional swelling data for segmented copolymers ....... 140 Figure 4.7. Proton conductivity under partially hydrated conditions for BisSF-PhSH100 segmented copolymers with increasing block length .....................................................141 Figure 4.8. DMA plots for BisSF-PhS100 multiblock copolymers. The solid lines represent the storage modulus and the dashed lines represent the tan δ. ........................ 142 Figure 4.9. Stress vs. Strain curves for BisSF-PhSH100 segmented copolymers .......... 143 Figure 5.1. Phenoxide-terminated BisAS0 with controlled molecular weight .............. 161 Figure 5.2. Aromatic region of a 1H NMR spectrum of BisAS0 oligomer ................... 161 Figure 5.3. Phenoxide-terminated BisAS100 with controlled molecular weight .......... 162 Figure 5.4 2D-COSY spectrum of BisAS100 oligomer ................................................. 162 Figure 5.5. Aromatic regions of a 1H NMR spectrum of BisAS100 oligomer before end-capping reaction .............................................................................................................. 163 Figure 5.6. Log (I.V.) vs. log (Mn) for the hydrophobic and hydrophilic oligomers..... 164 Figure 5.7. DFBP end-capping of phenoxide-terminated BiSA100 oligomer............... 165 Figure 5.8. Aromatic region of a 1H NMR spectrum of BisAS100 endcapped with DFBP......................................................................................................................................... 166 Figure 5.9. Coupling reaction of hydrophilic and hydrophobic oligomers.................... 167 Figure 5.10. Aromatic region of a 1H NMR spectrum for BisAS100-BisAS0 multiblock copolymer ....................................................................................................................... 167 Figure 5.11. Portions of 13C NMR spectra for (a) BisAS100-BisAS0 multiblock and (b) BisAS32 random copolymers ......................................................................................... 168 Figure 5.12. Water uptake (wt%) as a function of block length for BisAS100-BisAS0 multiblock copolymers.................................................................................................... 170 Figure 5.13. Comparison of dimensional swelling data for random and multiblock copolymers...................................................................................................................... 171 Figure 5.14. TEM images of 8k8k and 12k12k BisAS100-BisAS0 multiblock copolymers. (The bright white spot in the middle of the images is a camera artifact.) . 172 Figure 5.15. DMA plot of BisAS100-BisAS0 10k10k multiblock copolymer (black) and BisAS32 random copolymer (grey). Solid lines represent the storage modulus and dashed lines represent tan δ of the copolymers............................................................... 173 Figure 5.16. Thermograms for BisAS100-BisAS0 multiblock copolymers and BisAS32 random copolymer .......................................................................................................... 174 Figure 5.17. Thermal gravimetric analysis plot of BisAS32 random and BisAS100-BisAS0 multiblock copolymers ...................................................................................... 175 Figure 5.18. Stress-strain plots for BisAS copolymers.................................................. 176 Figure 5.19. 1H NMR spectra comparing copolymers before and after exposure to 500 ppm NaOCl for 24 h (pH of 4.5-5.0) (BisAS100-BisAS0 8k8k multiblock copolymer (a) before and (b) after exposure, BisAS32 random copolymer (c) before and (d) after exposure)......................................................................................................................... 177
xiv
TABLE OF TABLES
Table 2.1. Characterization of Hydrophilic Telechelic Oligomers.................................. 91 Table 2.2. Characterization of Hydrophilic and Hydrophobic Telechelic Oligomers for BisSF-BPSH100 Multiblock Copolymers ........................................................................ 96 Table 2.3. Characterization of Segmented and Multiblock BisSF-BPSH100 Copolymers........................................................................................................................................... 97 Table 2.4. Comparison of Tensile Properties for Segmented and Multiblock Copolymers........................................................................................................................................... 98 Table 3.1. Characterization of BisSF-BPSH100 and PhF-BPS100 Segmented Copolymers......................................................................................................................................... 117 Table 3.2. Tensile Properties of BisSF-BPSH100 and PhF-BPSH100 Segmented Copolymers ..................................................................................................................... 122 Table 4.1. Target and Experimental Mn for PhS100 Oligomers.................................... 136 Table 4.2. Characterization of BisSF-PhSH100 Segmented Copolymer ....................... 140 Table 4.3. Tensile Properties of BisSF-PhS Segmented Copolymers ............................ 143 Table 5.1. Characterization of Hydrophobic and Hydrophilic Telechelic Oligomers ... 163 Table 5.2. Characterization of BisAS100-BisAS0 Multiblock Copolymers ................. 170 Table 5.3. Tensile Properties of BisAS Copolymers ...................................................... 176
1
1 Literature Review
1.1 Ionomers
Copolymers which contain ionic groups throughout the polymer backbone have
been termed ionomers.1 The interactions that result from the ionic groups strongly
influence the structure and properties of these copolymer systems.2 Ionomers, employed
as ion-exchange membranes, have found many applications in electro-membrane
processes and separation and purification processes.3 They have the ability to separate
ions and can be used to recover desirable ions from solution, remove unwanted ions, or as
a transportation medium. Examples of these applications include reverse osmosis,
The post-sulfonation of poly(arylene ether sulfone)s has been explored by many
researchers.18,20,21,22 As noted earlier, many methods of post-sulfonation have been
utilized for this process. Although most of the post-sulfonation methods yield ionomers
with similar properties, which largely depend on the degree of sulfonation, there are
advantages and drawbacks among the methods.
S
O
OSO3H
O* *n
O ** S O
O
O
CH3
CH3
HO3S
n
O *
CF3
CF3
* S O
O
O
SO3H n
(a)
(b)
(c)
S
O
OSO3H
O* *n
O ** S O
O
O
CH3
CH3
HO3S
n
O *
CF3
CF3
* S O
O
O
SO3H n
S
O
OSO3H
O* *n
O ** S O
O
O
CH3
CH3
HO3S
n
O *
CF3
CF3
* S O
O
O
SO3H n
(a)
(b)
(c)
Figure 1.8. Examples of post-sulfonated poly(arylene ether sulfone)s. Sulfonic acid group is located in the activated position (ortho to the ether group). (a) Sulfonated
Poly(ether ether ketone)s (PEEK) have also been used extensively to make post-
sulfonated polymers.23,24,25,26,27,28,29 Several problems arise when PEEK is post-
sulfonated. Unlike poly(aryl ether sulfone)s, PEEK dissolves in few solvents because of
its semi-crystalline nature. Some of the early sulfonation work resulted from the desire to
find a solvent to characterize these polymers. Strong acids were used as the solvent.29
However, dissolution and sulfonation of the polymer happened concurrently in strong
acids. Therefore, low levels of random sulfonation were hard to achieve because of the
heterogeneity of the polymer solution during sulfonation. Sulfonation levels as high as
30% could be reached before a homogeneous solution was formed.23,27 Various degrees
of crosslinking and degradation have been reported when a sulfur trioxide/triethyl
phosphate complex28 or chlorosulfonic acid29 were used as the sulfonating agent.
Bailly et al.23 studied the post-sulfonation of PEEK copolymer using two
sulfonation techniques. Various ratios of methanesulfonic acid (MSA) and sulfuric acid
were used as the first sulfonating agent and concentrated sulfuric acid was the second.
The former reaction medium allowed for dissolution and sulfonation to occur separately
because MSA was able to dissolve the polymer without sulfonating it. Although this
medium could be used to produce randomly sulfonated PEEK (SPEEK) with low levels
of sulfonation (5-40 mol%), it would not be useful for sulfonation levels greater than that
because the ratio of MSA to sulfuric acid becomes impractical. A sulfuric acid
concentration of 96.4% as the sulfonating agent resulted in sulfonation of 25-70 mol%.
Although the samples were not characterized in the acid form, SPEEK samples in the
sodium form displayed an increase in Tg as the sulfonation degree increased, much like
15
the SPSF samples. The addition of sodium sulfonate decreased the crystallinity, which
helped to increase the solubility of these copolymers in organic solvents.
Several groups have further studied the post-sulfonation of PEEK using sulfuric
acid, with the focus on characterizing SPEEK for use as a PEM in fuel cell
applications.24,26 SPEEK samples with percent sulfonation of 30–97%, which
corresponds to IEC values of 0.5 to 1.55 meq/g, were achieved. Sample preparation and
pretreatment methods used to prepare the films varied between the research groups, as
did the testing conditions. The highest conductivity measured for SPEEK was 0.11 S/cm.
This was measured for two different samples, one having 96% sulfonation26 and one 60%
sulfonation.24 The former was tested under fully hydrated conditions at 25 oC, while the
later was tested at 100% RH at 150 oC, 6.1 atm. The water uptake of the samples
obtained approached 100% at high sulfonation levels. In some cases, this prevented the
copolymers from being analyzed because their dimensional changes made the
conductivity measurements unreliable.
In order to combat the increased water swelling in sulfonated poly(arylene ether)
copolymers which possess high IEC values, several groups have proposed crosslinking
the membranes to suppress the swelling, while still maintaining high conductivity.20,30
Nolte et al.20 formed crosslinked membranes from post-sulfonated poly(arylene ether
sulfone)s (commercially available UDEL® P-1700) using 1,1’-carbonyldiimidazol and
diamine as the crosslinking agents (Figure 1.9). Because bis-(4-amino-phenyl)-sulfone is
not as reactive as its aliphatic counterparts, the ionomer and crosslinking agents could be
mixed, cast, and then cured at elevated temperatures, which afforded a sulfonated
16
crosslinked membrane. About a 50% decrease in swelling was observed for crosslinked
membranes, while still maintaining acceptable conductivity levels.
SPolymer
O
O
OH NN
NN
O
SPolymer
O
O
NN
SPolymer
O
O
O CO2H2N
N+ + + +
+
SPolymer
O
O
NN
NH2 R NH2 SPolymer
O
O
NH
R NH
S Polymer
O
O
NHN
+ + 2
(a)
(b)
SPolymer
O
O
OH NN
NN
O
SPolymer
O
O
NN
SPolymer
O
O
O CO2H2N
N+ + + +
+
SPolymer
O
O
NN
NH2 R NH2 SPolymer
O
O
NH
R NH
S Polymer
O
O
NHN
+ + 2
SPolymer
O
O
OH NN
NN
O
SPolymer
O
O
NN
SPolymer
O
O
O CO2H2N
N+ + + +
+SPolymer
O
O
OH NN
NN
O
SPolymer
O
O
NN
SPolymer
O
O
O CO2H2N
N+ + + +
++
SPolymer
O
O
NN
NH2 R NH2 SPolymer
O
O
NH
R NH
S Polymer
O
O
NHN
+ + 2
(a)
(b)
Figure 1.9. Crosslinking scheme for post-sulfonated UDEL using 1,1’-carbonyldiimidazole (CDI) and diamine as the crosslinking agents. (a) Sulfonic acid
groups are activated by CDI (b) N-sulfonylimidazoles are converted to sulfonamides.20
Kerres et al.30 crosslinked post-sulfonated UDEL using methods for post-
sulfonating and crosslinking which differed from previous studies. First, UDEL was
post-sulfonated via a metalation procedure.31 This multi-step procedure resulted in a
post-sulfonated UDEL where the sulfonic acid was placed in the deactivated position of
the UDEL backbone (ortho to the sulfone group). The reader is referred to the original
work for a detailed description of this post-sulfonation process.31 The polymer could be
crosslinked by first oxidizing a sulfinated polymer to form a partially
sulfonated/sulfinated polymer, followed by crosslinking between the sulfinate groups
using diiodobutane as an S-alkylation crosslinking agent. Crosslinking the polymer
decreased the water swelling but it also reduced the IEC. This method does not seem
feasible for large scale production due to the many steps needed to form the crosslinked
polymer.
17
1.4.3 Directly Polymerized Sulfonated Monomers to form Sulfonated Poly(arylene
ether) Random Copolymers
Among the limitations of post-sulfonation modification are the ability to fully
control the degree and location of sulfonation, as well as the ability to form a truly
random copolymer. Direct polymerization of sulfonated monomers not only allows
precise levels of sulfonation to be obtained, but also affords a statistical random
distribution of sulfonic acid moieties in the polymer backbone. The position of
sulfonation can be directed using this technique. Unlike in most post-sulfonation
modification reactions, where the sulfonic acid groups are placed in the activated
positions, acid groups could be placed in the more stable, more acidic, deactivated
positions. The degree of sulfonation can be increased to two sulfonic acids per repeat
unit, yielding a polymer with a higher IEC, and potentially higher conductivity, when
hydroquinone (6FP) (Figure 1.14c) showed suitable water uptake and proton
conductivity. Polymers containing 6FP comonomer with 50% disulfonation had water
uptake of 29% (80 oC) and proton conductivity of 1.0 x 10-1 S/cm (80 oC in liquid
water).44 It was proposed that the bulkiness of the 6FP pendent group increased the free
volume between the polymer chains, which increased the water uptake. However, this
led to a higher conductivity for these polymers at elevated temperatures.
23
O
CF3
CF3
O
OO
O
CF3
CF3
O
OSO3H
SO3H
n
n
CF3
CF3
CH3
CH3
X=
O X* O
SO3H
HO3S
O X O *
O
n
O
n
O
O
(a)
CF3
CF3
OO
*
O
O
O
YO* O Y On
n
SO3H
HO3S
Y=
(1-x)
(1-x)
(1-x)
X
X
X
(b)
(c)
O
CF3
CF3
O
OO
O
CF3
CF3
O
OSO3H
SO3H
n
n
CF3
CF3
CH3
CH3
X=
O X* O
SO3H
HO3S
O X O *
O
n
O
n
O
O
(a)
CF3
CF3
OO
*
O
O
O
YO* O Y On
n
SO3H
HO3S
Y=
(1-x)
(1-x)
(1-x)
X
X
X
(b)
(c)
Figure 1.13. Disulfonated poly(arylene ether ketone) random copolymers using (a-b) 5,5’-carbonylbis(2-fluorobenzene-sulfonate) or (c) 1,4-bis(3-sodium sulfonate-4-
fluorobenzoyl)benzene as the sulfonated comonomers.
VanHouten et al.94 synthesized segmented copolymers with a fully sulfonated
hydrophilic block and highly fluorinated hydrophobic segments. These polymers were
compared to polymers made using a multiblock synthetic method reported by Yu et al.76
Simultaneously coupling the hydrophobic segments and hydrophilic block was an
alternate procedure for synthesizing the block copolymer, and it eliminated the need to
synthesize and isolate a separate hydrophobic block before coupling it to the hydrophilic
block, which was utilized previously.
Two precautions were taken to avoid ether-ether interchange. Because of the
decreased reactivity of SDCDPS, the phenoxide-terminated hydrophilic oligomer was
synthesized first, using SDCDPS and BP as the monomers. An excess molar ratio of
55
BP:SDCDPS was used to control the molecular weight. After isolation, the hydrophilic
oligomer was reacted with DFBP and Bis-S monomers in a nucleophilic aromatic
substitution reaction to form a segmented block copolymer (Figure 1.31). Choosing the
highly reactive DFBP as the dihalide for the hydrophobic segments allowed for low
reaction temperatures to be used (90 oC), which eliminated ether-ether interchange during
the coupling reaction. The stoichiometry was controlled such that the DFBP and Bis-S
monomers formed the hydrophobic segments of the copolymer, while also reacting with
the phenoxide-terminated hydrophilic oligomer. The segmented copolymers were
synthesized with equal hydrophilic and hydrophobic molecular weights. The block
lengths ranged from 3000 g/m to 16000 g/mol. The IV data confirmed that high
molecular weight polymer was achieved using this synthetic method. The ability to cast
tough films indicated high molecular weight polymer. When comparing polymers with
similar IEC values, water uptake increased as the block lengths increased, which is
attributed to an increase in the nanophase separated morphology.
OKO S O
O
OSO3K
KO3S
OKn
F
FFFF
F
F F F F
OH S OH
O
O
K2CO3Cyclohexane/NMP4 hrs @ 85 oC
add 36-70 hrs @ 90 oC
OO S O
O
OSO3K
KO3S
n
FFFF
F F F F
FFFF
F F F F
O S O
O
O
Om
x
OKO S O
O
OSO3K
KO3S
OKn
F
FFFF
F
F F F F
OH S OH
O
O
K2CO3Cyclohexane/NMP4 hrs @ 85 oC
K2CO3Cyclohexane/NMP4 hrs @ 85 oC
add 36-70 hrs @ 90 oC36-70 hrs @ 90 oC
OO S O
O
OSO3K
KO3S
n
FFFF
F F F F
FFFF
F F F F
O S O
O
O
Om
x
Figure 1.31. Synthesis of segmented block copolymer (BisSF-BPSH100) with simultaneous formation of hydrophobic block (BisSF).
56
1.5 Water Desalination
Water shortages are a growing concern across the world. Demand continues to
grow for a way to provide fresh water for an estimated 41% of the world that lives in
water-stressed areas.97 Oceans hold 97% of the earth’s water. 98 The quest for an
economically viable way to obtain fresh water from salt water continues because of its
large abundance. The variety of technical processes designed to remove salt from water
is termed “desalination”.
There are two major categories in which desalination of water can be achieved.
These include thermal and membrane processes.98,99 Thermal processes require salt
water to be heated and then condensed in various ways and stages, mimicking the natural
hydrologic cycle. The condensate, which is free of salt, is collected. Thermal processes
include multiple effect distillation, multistage flash distillation, and vapor compression
distillation. Membrane processes remove salt from water by selectively permitting or
prohibiting the passage of certain ions. These processes include electrodyalysis and
electrodyalysis reversal and reverse osmosis.
The two most commonly used methods of those listed are multistage flash
distillation (MSF) and reverse osmosis (RO) (Figure 1.32). As of 2002, MSF systems
accounted for 44% of installed or contracted desalination processes.98 MSF distillation
can effectively produce high quality fresh water from seawater, reducing salt
concentrations of 60,000 to 70,000 ppm total dissolved solids to less than 10 ppm.
However, this method is very expensive because of the large energy requirements to
evaporate and condense the water in multistage distillations. RO is a process used to
desalinate water using a semi-permeable membrane. Plants utilizing RO technology are
57
becoming more popular because the process requires less energy than evaporation, often
10 times less energy is required to produce fresh water using RO technology versus
thermal distillation.97 It can also remove microorganisms and organic contamination in
addition to salt.100 Recent developments in RO technology have allowed new membrane
capacity to surpass the annual additions to the distillation capacity.
44% (MSF)40% (RO)
4% (ME)4% (VC)
3% (other)6% (ED)
44% (MSF)40% (RO)
4% (ME)4% (VC)
3% (other)6% (ED)
Figure 1.32. World Desalination Capacity by Process, as of June 1999. Membrane processes: reverse osmosis (RO) and electrodialysis (ED); Thermal processes: multistage flash distillation (MSF), multi-effect distillation (ME), and vapor
compression (VC)
1.6 Reverse Osmosis
Osmosis occurs when two solutions of varying concentrations are separated by a
semipermeable membrane. Solute from the less concentrated side will pass through the
58
membrane to the more concentrated side in order to form an equilibrium between the two
solutions. This process creates a pressure called osmotic pressure.
Reverse osmosis is a technology used to separate the salt and other impurities
from sea water and brackish water to create fresh water. A semipermeable membrane is
placed between salt water and fresh water, similar to osmosis. However, pressure is
applied to the salt water to overcome the osmotic pressure. This causes the water from
the salt-water side to pass through the membrane to the fresh water side, leaving a more
crosslinked polypiperazineamides (Toray), and crosslinked polyether (Toray) were also
produced. Manufacturers were also exploring polyacrylonitrile (Sumitomo),
polybenzimidazolone (Teijin), and sulfonated polysulfones (DSI, Millipore, Nitto Denko)
for RO membrane materials.
NH
C C NH
NH
C C *NH
*
O O O O
C
NH
O
NH
COOH
x
y N
HC C N
HNH
C C *NH
*
O O O O
C
NH
O
NH
COOH
x
y
Figure 1.35. Crosslinked fully aromatic polymer.
64
Currently, RO filtration units contain aromatic polyamide thin film composites as
their semi permeable membrane (Dow-FilmTec, GE-Osmonics, Nitto Denko-
Hydranautics, etc.)111 Despite some of their inadequacies, aromatic polyamide
membranes are still the state of the art membranes because they are able to reach a 99.9%
salt rejection rate, while still maintaining a reasonable flux.97,112
1.8.3 Sulfonated Aromatic Polymers
Sulfonated aromatic polymers have also been explored for use as RO membranes
since the 1970s. Research began with the exploration of sulfonated poly(phenylene
oxide) and sulfonated polyfurane membranes and progressed to sulfonated
polysulfones.101 Sulfonated membranes maintain a low permeability to salts because the
sulfonate ions allow the anions in the salt to be repelled. Allegrezza et al.113,114 reported
that RO modules utilizing sulfonated polysulfone membranes exhibited high tolerance to
chlorine because they lack the oxidizable amide links present in polyamide membranes.
The sulfonated polysulfone RO modules could also withstand a wide pH range (4-11),
were resistant to fouling, and could be operated at high flux for long periods of time.
Although sulfonated polysulfones had desirable properties, they were synthesized using
post-sulfonation modification procedures,6,13115,116,117,118 which have many drawbacks.
Among the limitations of post-sulfonation modification are the ability to fully control the
degree and location of sulfonation, as well as, side reactions and chain-degradation.9
Over the past decade, research efforts in the McGrath group have been focused on
the direct synthesis of disulfonated poly(arylene ether) random
copolymers.119,120,121,122,123,124 These copolymers were synthesized by a nucleophilic
aromatic substitution reaction of a disulfonated dihalide (3,3’-disulfonated-4,4’-
65
dichlorodiphenylsulfone, SDCDPS), unsulfonated dihalide, and bisphenol to afford
random copolymers, with predetermined degrees of disulfonation based on the
stoichiometric ratio of sulfonated to unsulfonated dihalide. Copolymers with degrees of
sulfonation ranging from zero to 100% disulfonation have been achieved. These
copolymers have excellent oxidative, hydrolytic, and mechanical stability, as well as,
good film forming properties. Disulfonated poly(arylene ether sulfone) random
copolymers derived from SDCDPS, 4,4’-dichlorodiphenylsulfone (DCDPS), and 4,4’-
biphenol (coined BPSxx, where xx represents the degree of sulfonation) have been shown
to have high chlorine tolerance across a broad pH range (4-10).125 Exposure to protein
water or oil/water emulsions resulted in minimal fouling.126 Salt rejection and water
permeability for this type of membrane were correlated to the degree of disulfonation.
Overall, copolymers with higher ion content (BPS40) displayed higher fluxes and lower
salt rejection than copolymers with lower ion content (BPS20).18,127 However, water flux
and salt rejection were also influenced by the structure of the bisphenol used to
synthesize the copolymer and whether the copolymer was in salt or acid form.
Additional synthetic variations have been suggested, which could tailor the
properties of disulfonated poly(arylene ether) copolymers further, making them more
suited for RO applications.112,128 Among these has been crosslinking random copolymers
in order to enhance salt rejection without hindering the flux. Paul et al.112 synthesized
50% disulfonated poly(arylene ether sulfone) random copolymers derived from 4,4’-
biphenol, which had controlled number-average molecular weight (Mn) and reactive
phenoxide end groups. These were used to crosslink the copolymer with tetraglycidyl
bis(p-aminophenyl)methane. Membranes which were cured for 90 minutes had a 97.2%
66
salt rejected compared to 73.4% for BPS-50 uncrosslinked copolymer. Only modest
decreases were observed in water permeability.
67
1.9 Research Objectives
The first objective of this research was to assess if a segmented synthesis
technique, which is simpler in concept than the current technique, could be effectively
used to produce “blocky” ionic copolymers. Chapter 2 describes the synthesis of a
segmented multiblock copolymer comprised of a disulfonated poly(arylene ether sulfone)
hydrophilic block and highly fluorinated poly(arylene ether sulfone) hydrophobic block.
The properties of this copolymer are compared to a multiblock which used a previous
synthetic approach of coupling two preformed oligomers.
The segmented method was studied further using the well known bisphenol
phenolphthalein as a comonomer in either the hydrophobic (chapter 3) or hydrophilic
(chapter 4) block. It is proposed that phenolphthalein may improve proton conductivity
at lower relative humidity because the bulkiness of the monomer increases free volume in
copolymer. The synthesis of segmented copolymers with unequal hydrophobic and
hydrophilic block lengths is also examined in chapter 4.
The final objective was to synthesize novel hydrophilic-hydrophobic multiblock
copolymers derived from Bisphenol-A for potential use as reverse osmosis membranes.
Chapter 5 describes the synthesis of a novel series of poly(arylene ether sulfone)s which
utilized Bisphenol-A as the comonomer in both the hydrophobic and hydrophilic blocks.
68
References
1 Ionomers: Synthesis, Structure, Properties and Applications, Tant, M. R., Mauritz, K. A. and Wilkes, G. L., Eds.; Chapman and Hall: New York, 1997. 2 Eisenberg, A.; Rinaudo, M. Polyelectrolytes and ionomers. Polym. Bull., 1990, 24, 671. 3 Nagarale, R. K.; Gohil, G. S.; Shahi, V. K. Shahi. Recent developments on ion-exchange membranes and electro-membrane processes. Adv. Colloid. Interfac. 2006, 119, 97-130. 4 Winter, M.; Brodd, R.J. What are Batteries, Fuel Cells, and Supercapacitors? Chem.Rev. 2004, 104, 4245-4269. 5 Marsh, G. Membranes fit for a revolution. Materials Today 2003, 6(3), 38-43. 6 Hickner, M.A.; Ghassemi, H.; Kim. Y.S.; Einsla, B.R.; McGrath, J.E. Alternative Polymer Systems for Proton Exchange Membranes (PEMs). Chem. Rev. 2004, 104, 4587-4612. 7 Savadogo, O. Emerging membranes for electrochemical systems: (I) solid polymer electrolyte membranes for fuel cell systems. J. New Mat. Electrochem. Systems 1998, 1, 47-66. 8 Program's Multi-Year Research: Fuel Cells. Department of Energy, 2007. 9 Resnick, P.R.; Grot, W.G.; of E.I. du Pont de Nemours and Company, Wilmington, DE, Sept 12, 1978; U.S. Patent 4,113,585. 10 Mauritz, K.A.; Moore, R.B. State of Understanding of Nafion. Chem. Rev. 2004, 104, 4515-4585. 11 Alberti, G.; Casciola, M. Solid state protonic conductors, present main applications and future prospects. Solid State Ionics 2001, 145, 3-16. 12 Cotter, R. J. Engineering Plastics: A Handbook of Polyarylethers, Gordon & Breach: Basel, Switzerland: 1995. 13Viswanathan, R.; Johnson, B. C.; McGrath, J. E. Synthesis, kinetic observations and characteristics of polyarylene ether sulphones prepared via a potassium carbonate DMAC process. Polymer 1984, 25, 1827-1836. 14 Johnson, R. N.; Farnham, A. G.; Clendinning, R. A.; Hale, W. F.; Merriam, C. N. Poly(aryl ether)s by Nucleophilic Aromatic Substitution. I. Synthesis and Properties. J. Polym. Sci.A1. 1967, 5, 2375-2398.
69
15 Robeson, L.M.; Farnham, A.G.; McGrath, J.E. Synthesis and dynamic mechanical characteristics of poly(arylene ether)s Appl. Polym. Symp. 1975, 26, 373-385. 16 Jurek, M.J.; McGrath, J.E. The synthesis of poly(arylene ethers) via the Ullmann condensation reaction Polym. Prepr. 1987, 28(1), 180-181. 17 Bassin, J. P.; Cremlyn, R. J.; Swinbourne, F. J. Chlorosulfonation of Aromatic and Heteroaromatic Systems, Phosphorous, Sulfur, and Silicon and the Related Elements 1991, 56, 245-275. 18 Noshay, A.; Robeson, L.M. Sulfonated Polysulfone. J. Appl. Polym. Sci. 1976, 20(7), 1885-1903. 19 Roziere, J.; Jones, D.J. Non-Fluorinated Polymer Materials for Proton Exchange Membrane Fuel Cells. Annual Rev. Mater. Res. 2003, 33, 503-555. 20 Nolte, R.; Ledjeff, K.; Bauer, M.; Mülhaupt, R. Partially Sulfonated Poly(arylene ether sulfone) – A Versatile Proton Conducting Membrane Material for Modern Energy Conversion Technologies. J. Membr. Sci. 1993, 83, 211- 220. 21Genova-Dimitrova, P.; Baradie, B.; Foscallo, D.; Poinsignon, C.; Sanchez, J.Y. Ionomeric membranes for proton exchange membrane fuel cell (PEMFC): sulfonated polysulfone associated with phosphatoantimonic acid. J. Membr. Sci. 2001, 185, 59-71. 22 Lufrano, F.; Squadrito, G.; Patti, A.; Passalacqua, E. Sulfonated Polysulfone as Promising Membranes for Polymer Electrolyte Fuel Cells. J. Applied Polym. Sci. 2000, 77, 1250-1257. 23 Bailly, C.; Williams, D.J.; Karasz, F.E.; MacKnight, W.J. The sodium salts of sulphonated poly(aryl-ether-ether-ketone) (PEEK): Preparation and characterization. Polymer 1987, 28, 1009-1016. 24 Bauer, B.; Jones, D.J.; Roziere, J.; Tchicaya, L.; Alberti, G.; Casciola, M.; Massinelli, L.; Peraio, A.; Besse, S.; Ramunni, E. Electrochemical characterisation of sulfonated polyetherketone membranes. J. New Mat. Electr. Sys. 2000, 3, 93-98. 25 Huang, R.Y.M.; Shao, P.; Burns, C.M.; Feng, X. Sulfonation of Poly(Ether Ether Ketone) (Kinetic Study and Characterization. J. Appl. Polym. Sci. 2001, 82, 2651-2660. 26 Kaliaguine, S.; Mikhailenko, S.D.; Wang, K.P.; Xing, P.; Robertson, G.; Guiver, M. Properties of SPEEK based PEMs for fuel cell application. Catal. Today 2003, 82, 213-222. 27 Jin, X.; Bishop, M.T.; Ellis, T.S.; Karasz, F.E. A Sulfonated Poly(aryl Ether Ketone). Brit. Polym. J. 1985, 17, 4-10.
70
28 Litter, M.I.; Marvel, C.S. Polyaromatic Ether-Ketones and Polyaromatic Ether-Ketone Sufonamides from 4-Phenoxybenzoyl Chloride and from 4,4’-Dichloroformyldiphenyl Ether. J. Polym. Sci. Polym. Chem. Ed. 1985, 23, 2205-2223. 29 Bishop, M.T.; Karasz, F.E.; Russo, P.S.; Langley, K.H. Solubility and Properties of a Poly(aryl ether ketone) in Strong Acids. Macromolecules 1985, 18, 86-93. 30 Kerres, J.; Zhang, W.; Cui, Wei. New Sulfonated Engineering Polymers via the Metalation Route. II. Sulfinated/Sulfonated Poly(ether sulfone) PSU Udel and Its Crosslinking. J. Polym. Sci.: Part A: Polym. Chem. 1998, 36, 1441-1448. 31 Kerres, J.; Cui, W.; Reichle, S. New Sulfonated Engineering Polymers via the Metalation Route. I. Sulfonated Poly(ethersulfone) PSU Udel® via Metalation-Sulfination-Oxidation. J. Polym. Sci: Part A: Polym. Chem. 1996, 36, 2421-2438. 32 Robeson, L.M. ; Matzner, M. Flame retardant polyarylate compositions. US Patent 4,380,598, (to Union Carbide) 1983. 33 Ueda, M.; Toyota, H.; Ouchi, T.; Sugiyama, J.I.; Yonetake, K.; Masuko, T.; Teramoto, T. Synthesis and Characterization of Aromatic Poly(ether Sulfone)s Containing Pendant Sodium Sulfonate Groups. J. Polym. Sci.: Part A: Polym. Chem. 1993, 31, 853-858. 34 Wang, F.; Hickner, M.; Ji, Q.; Harrison, W.; Mecham, J.; Zawodzinski, T.A.; McGrath, J.E. Synthesis of Highly Sulfonated Poly(arylene ether sulfone) Random (Statistical) Copolymers Via Direct Polymerization. Macromol. Symp. 2001, 175, 387-395. 35 Sankir, M.; Bhanu, V.A.; Harrison, W.L.; Ghassemi, H.; Wiles, K.B.; Glass, T.E.; Brink, A.E.; Brink, M.H.; McGrath, J.E. Synthesis and Characterization of 3,3’-Disulfonated-4,4’-dichlorodiphenyl Sulfone (SDCDPS) Monomer for Proton Exchange Membranes (PEM) in Fuel Cell Applications J. Appl. Polym. Sci. 2006, 100, 4595-4602. 36 Li, Y.; VanHouten, R.; Brink, A.; McGrath, J.E. Purity Characterization of 3,3’-Disulfonated-4,4’-Dichlorodiphenyl Sulfone (SDCDPS) Monomer by UV-visible Spectroscopy. Polymer, 2008, 49, 3014-3019. 37 Wang, F.; Hickner, M.; Kim, Y.S.; Zawodzinski, T.A.; McGrath, J.E. Direct polymerization of sulfonated poly(arylene ether sulfone) random (statistical) copolymers: candidates for new proton exchange membranes. J. Membr. Sci. 2002, 197, 231-242. 38 Harrison, W.L.; Wang, F.; Mecham, J.B.; Bhanu, V.A.; Hill, M.; Kim, Y.S.; McGrath, J.E. Influence of the Bisphenol Structure on the Direct Synthesis of Sulfonated Poly(arylene ether) Copolymers. I. J. Polym. Sci: Part A: Polym. Chem. 2003, 41, 2264-2276.
71
39 Sumner, M.J.; Harrison, W.L.; Weyers, R.M.; Kim, Y.S.; McGrath, J.E.; Riffle, J.S.; Brink, A.; Brink, M.H. Novel proton conducting sulfonated poly(arylene ether) copolymers containing aromatic nitriles. J. Membr. Sci. 2004, 239, 199-211. 40 Wang, F.; Li, J.; Chen, T.; Xu, J. Synthesis of poly(ether ether ketone) with high content of sodium sulfonate groups and its membrane characteristics. Polymer, 1999, 40, 795-799. 41 Wang, F.; Chen, T.; Xu, J. Sodium sulfate-functionalized poly(ether ether ketone)s. Macromol. Chem. Phys. 1998, 199, 1421-1426. 42 Xing, P.; Robertson, G.P.; Guiver, M.D.; Mikhailenko, S.D.; Kaliaguine, S. Sulfonated Poly(aryl ether ketone)s Containing Naphthalene Moieties Obtained by Direct Copolymerization as Novel Polymers for Proton Exchange Membranes. J. Polym. Sci.: Part A: Polym. Chem., 2004, 42, 2866–2876. 43 Xing, P.; Robertson, G.P.; Guiver, M.D.; Serguei, D.; Mikhailenko, S.K. Synthesis and characterization of poly(aryl ether ketone) copolymers containing (hexafluoroisopropylidene)-diphenol moiety as proton exchange membrane materials. Polymer, 2005, 46, 3257–3263. 44 Liu, B.; Robertson, G.P.; Guiver, M.D.; Sun, Y-M.; Liu, Y-L.; Lai, J-Y.; Mikhailenko, S.; Sulfonated Poly(aryl ether ether ketone ketone)s Containing Fluorinated Moieties as Proton Exchange Membrane Materials. J. Polym. Sci.: Part B: Polym. Phys. 2006, 44, 2299–2310. 45 Gao, Y.; Robertson, G.P.; Guiver, M.D.; Mikhailenko, S.D.; Li, X.; Kaliguine, S. Low-swelling proton-conducting copoly(aryl ether nitrile)s containing naphthalene structure with sulfonic acid groups meta to the ether linkage. Polymer, 2006, 47, 808–816. 46 Gao, Y.; Robertson, G.P.; Guiver, M.D.; Mikhailenko, S.D.; Li, X.; Kaliaguine, S. Synthesis of Poly(arylene ether ether ketone ketone) Copolymers Containing Pendant Sulfonic Acid Groups Bonded to Naphthalene as Proton Exchange Membrane Materials. Macromolecules 2004, 37, 6748-6754. 47 Gao, Y.; Robertson, G.P.; Kim, D-S, Guiver, M.D.; Mikhailenko, S.D.; Li, X.; Kaliaguine, S. Comparison of PEM Properties of Copoly(aryl ether ether nitrile)s Containing Sulfonic Acid Bonded to Naphthalene in Structurally Different Ways. Macromolecules 2007, 40, 1512-1520. 48 Wang, F.; Mecham, J.; Harrison, W.; Hickner, M.; Kim, Y.; McGrath, J.E. Synthesis of sulfonated poly(arylene ether phosphine oxide sulfone)s via direct polymerization. ACS Polym. Mat.: Sci. & Eng. (PMSE) 2001, 84, 913-914.
72
49 Wang, F.; Chen, T.; Xu, J.; Liu, T.; Jiang, H.; Qi, Y.; Liu, S.; Li, X. Synthesis and characterization of poly(arylene ether ketone) (co)polymers containing sulfonate groups. Polymer, 2006, 47, 4148-4153. 50 Higashihara, T.; Matsumoto, K.; Ueda, M. Sulfonated aromatic hydrocarbon polymers as proton exchange membranes for fuel cells. Polymer, 2009, 50, 5341-5357. 51 Noshay, Allen; McGrath, James E. Block Copolymers: Overview and Critical Survey, Academic Press: New York: 1977. 52 Roy, A.; Hickner, M.A.; Yu, X.; Li. Y.; Glass, T.E.; McGrath, J.E. Influence of Chemical Composition and Sequence Length on the Transport Properties of Proton Exchange Membranes. J. Polym. Sci. Part B, 2006, 44, 2226-2239. 53 Shi, Z.; Holdcroft, S. Synthesis and proton conductivity of partially sulfonated poly([vinylidene difluoride-co-hexafluoropropylene]-b-styrene) block copolymers. Macromolecules 2005, 38, 4193-4201. 54 Won, J.; Choi, S.W.; Kang, Y.S.; Ha, H.W.; Oh, I-H.; Kim, H.S.; Kim, K.T.; Jo, W.H. Structural characterization and surface modification of sulfonated polystyrene-(ethylene-butylene)-styrene triblock proton exchange membranes. J. Membr. Sci., 2003, 214, 245-257. 55 Kim, J.; Kim, B.; Jung, B. Proton conductivities and methanol permeabilities of membranes made from partially sulfonated polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene copolymers. J. Membr. Sci. 2002, 207, 129-137. 56 Yang, J-E.; Lee, J-S. Selective modification of block copolymers as proton exchange membranes. Electrochem. Acta 2004, 50, 617-620. 57 Sangeetha, D. Conductivity and solvent uptake of proton exchange membranes based on polystyrene(ethylene-butylene)polystyrene triblock polymer. Eur. Polym. J. 2005, 41, 2644-2652. 58 Fernàndez-Carretero, F.J.; Compañ, V.; Riande, E. Hybrid ion-exchange membranes for fuel cells and separation processes. J. Power Sources 2007, 173, 68-76. 59 Serpico, J.M.; Ehrenberg, S.G.; Fontanella, X.J.; Perahia, D.; McGrady, K.A.; Sanders, E.H.; Kellogg, G.E.; Wnek, G.E. Transport and Structural Studies of Sulfonated Styrene-Ethylene Copolymer Membranes, Macromolecules 2002, 35, 5916-5921. 60 Elabd, Y.A.; Napadensky, E.; Sloan, J.M.; Crawford, D.M.; Walker, C.W. Triblock copolymer ionomer membranes Part I. Methanol and proton transport. J. Membr. Sci. 2003, 217, 227-242.
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61 Elabd, Y.A.; Walker, C.W.; Beyer, F.L. Triblock copolymer ionomer membranes Part II. Structure characterization and its effects on transport properties and direct methanol fuel cell performance. J. Membr. Sci. 2004, 231, 181-188. 62 Elabd, Y.A.; Napadensky, E. Sulfonation and characterization of poly(styrene-isobutylene-styrene) triblock copolymers at high ion-exchange capacities. Polymer 2004, 45, 3037-3043. 63 Elabd, Y.A.; Napadensky, E.; Walker, C.W.; Winey, K.L. Transport Properties of Sulfonated Poly(styrene-b-isobutylene-b-styrene) Triblock Copolymers at High Ion-Exchange Capacities. Macromolecules 2006, 39, 399-407. 64 Gardner, C.L.; Anantaraman, A.V. Measurement of membrane conductivities using an open-ended coaxial probe. J. Electroanal. Chem. 1995, 395, 67-73. 65 Mokrini, A.; Acosta, J.L. Studies of sulfonated block copolymer and its blends. Polymer 2001, 41, 9-15. 66 Mokrini, A.; Del Rìo, C.; Acosta, J.L. Synthesis and characterization of new ion conductors based on butadiene styrene copolymers. Solid State Ionics 2004, 166, 375-381. 67 Zhang, X.; Liu, S.; Liu, L.; Yin, J. Paritally sulfonated poly(arylene either sulfone)-b-polybutadiene for proton exchange membrane. Polymer 2005, 46, 1719-1723. 68 Zhang, X.; Liu, S.; Yin, J. Synthesis and characterization of a new block copolymer for proton exchange membrane. J. Membr. Sci. 2005, 258, 78-84. 69 Leibler, L. Theory of Microphase Separation in Block Copolymers. Macromolecules 1968, 13(6), 1602-1617. 70 Matsen, M.W.; Bates, F.S. Origins of Complex Self-Assembly in Block Copolymers. Macromolecules 1996, 29, 7641-7644. 71 Wang, F.; Kim, Y.; Hickner, M.; Zawodzinski, T.A.; McGrath J.E. Synthesis of Polyarylene Ether Block Copolymers Containing Sulfonate Groups. ACS Polym. Mat.: Sci. & Eng. (PMSE) 2001, 85, 517-518. 72 Ghassemi, H.; McGrath, J.E.; Zawodzinski, T.A. Multiblock sulfonated-fluorinated poly(arylene ether)s for a proton exchange membrane fuel cell. Polymer 2006, 47, 4132-4139. 73 Ghassemi, H.; Zawodzinski, T.A. Multiblock sulfonated-fluorinated poly(arylene ether)s membranes for a proton exchange membrane fuel cell. Prepr. Pap.-Am. Chem. Soc.; Div. Fuel Chem. 2005, 50(2), 531-533.
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74 Yu, X.; Roy, A.; McGrath, J.E. Perfluorinated-sulfonated hydrophobic-hydrophilic multiblock copolymers for proton exchange membranes (PEMs). ACS Polym. Mat.: Sci. & Eng. (PMSE) 2006, 95, 141-142. 75 Yu, X.; Roy, A.; McGrath, J.E. Synthesis and characterization of multiblock copolymers for proton exchanged membranes. Prepr. Pap.-Am. Chem. Soc., Div. Fuel Chem. 2005, 50(2), 577-578. 76 Yu, X.; Roy, A.; Dunn, S.; Yang, J.; McGrath, J.E. Synthesis and Characterization of Sulfonated-Fluorinated, Hydrophilic-Hydrophobic Multiblock Copolymers for Proton Exchange Membranes. Macromol. Symp. 2006, 245-245, 439-449. 77 Yu, X. PhD Dissertation, Virginia Polytechnic Institute and State University, 2008. 78 Yu, X.; Roy, A.; Dunn, S.; Badami, A. S.; Yang, J.; Good, A. S.; McGrath, J. E. Synthesis and Characterization of Sulfonated-Fluorinated, Hydrophilic-Hydrophobic Multiblock Copolymers for Proton Exchange Membranes J. Polym. Sci. Part A: Polym. Chem., 2009, 47, 1038–1051. 79 Lee, H.-S.; Roy, A.; Lane, O.; Dunn, S.; McGrath, J.E. Hydrophilic-hydrophobic multiblock copolymers based on poly(arylene ether sulfone) via low-temperature coupling reactions for proton exchange membrane fuel cells. Polymer 2008, 49, 715-723. 80 Nakabayashi, K.; Matsumoto, K.; Ueda, M. Synthesis and Properties of Sulfonated Multiblock Copoly(ether sulfone)s by a Chain Extender. J. Polym. Sci. Pol. Chem. 2008, 46, 3947-3957. 81 Li, Y.; Roy, A.; Badami, A.S.; Hill, M.; Yang, J.; Dunn, S.; McGrath, J.E. Synthesis and characteristics of partially fluorinated hydrophobic-hydrophilic multiblock copolymers containing sulfonate groups for proton exchange membrane. J. Power Sources 2007, 172, 30-38. 82 Lee, H.-S.; Roy, A.; Badami, A.S.; McGrath J.E. Synthesis and Characterization of Sulfonated Poly(arylene ether) Polyimide Multiblock Copolymers for Proton Exchange Membranes. Macromol. Res. 2007, 15(2), 160-166. 83 Lee, H.; Roy, A.; Lane, O.; Dunn, S.; McGrath, J. E. Segmented Sulfonated Poly(arylene ether sulfone)-b-Polyimide Copolymers for Proton Exchange Membrane Fuel Cells. I. Copolymer Synthesis and Fundamental Properties J. Polym. Sci. Part A. 2007, 45(21), 4879-4890. 84 Genies, C.; Mercier, R.; Sillion, B.; Petiaud, R.; Cornet, N.; Gebel, G.; Pineri, M. Stability study of sulfonated phthalic and naphthalenic polyimide structures in aqueous medium. Polymer 2001, 5097-5105.
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85 Sek, D.; Wanic, A.; Schab-Balcerzak, E. Novel approach to the mechanism of the high-temperature formation of naphthalimides. Polymer 1993, 34(11), 2440-2442. 86 Einsla, B.R.; Hong, Y.-T.; Kim, Y.S.; Wang, F.; Gunduz, N.; McGrath, J.E. Sulfonated Naphthalene Dianhydride Based Polyimide Copolymers for Proton-Exchange-Membrane Fuel Cells. I. Monomer and Copolymer Synthesis. J. Polym. Sci. Pol. Chem. 2004, 42, 862-874. 87 Wang, H.; Badami, A.S.; Roy, A.; McGrath, J.E. Multiblock Copolymers of Poly(2,5-benzophenone and Disulfonated Poly(arylene ether sulfone) for Proton-Exchange Membranes. I. Synthesis and Characterization. J. Polym. Sci. Pol. Chem. 2007, 45, 284-294. 88 Ghassemi, H.; Ndip, G.; McGrath, J.E. New multiblock copolymers of sulfonated poly(4’-phenyl-2,5-benzophenone) and poly(arylene ether sulfone) for proton exchange membranes. Polym. Prepr. 2003, 44(1), 814-815. 89 Ghassemi, H.; Ndip, G.; McGrath J.E. New multiblock copolymers of sulfonated poly(4’-phenyl-2,5-benzophenone) and poly(arylene ether sulfone) for proton exchange membranes. II. Polymer 2004, 45, 5855-5862. 90 Ghassemi H.; McGrath , J.E. Synthesis and properties of new sulfonated poly( p-phenylene) derivatives for proton exchange membranes. I. Polymer 2004, 45(17), 5847-5854. 91 Shin, C.K.; Maier, G.; Andreaus, B.; Scherer, G.G. Block copolymer ionomers for ion conductive membranes. J. Membr. Sci. 2004, 245, 147-161. 92 Zhao, C.; Li, X.; Wang, Z.; Dou, Z.; Zhong, S.; Na, H. Synthesis of block sulfonated poly(ether ether ketone)s (S-PEEKs) materials for proton exchange membrane. J. Membr. Sci. 2006, 280, 643-650. 93 Zhao, C.; Lin, H.; Shao, K.; Li, X.; Ni, H.; Wang, Z.; Na, H. Block sulfonated poly(ether ether ketone)s (SPEEK) ionomers with high ion-exchange capacities for proton exchange membranes. J. Power Sources 2006, 162, 1003-1009. 94 VanHouten, R.A.; Lane, O.; McGrath, J.E. Synthesis of Segmented Hydrophobic:Hydrophilic, Fluorinated:Disulfonated Block Copolymers for use as Proton Exchange Membranes. Prepr. Pap.-Am. Chem. Soc., Div. Fuel Chem. 2008, 53(2), 765-766. 95 Badami, A.S. PhD Dissertation, Virginia Polytechnic Institute and State University, 2007.
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96 Shin, C.K.; Maier, G.; Scherer, G.G. Acid functionalized poly(arylene ether)s for proton-conducting membranes. J. Mebran. Sci. 2004, 245, 163-173. 97 Service, R.F. Desalination Freshens Up Science 2006, 313, 1088-1090. 98 Gleick, P.H. In The World's Water 2001-2002: The Biennial Report on Freshwater Resources, Island Press: Washington, D.C., 2000. 99 Van der Bruggen, B.; Vandecasteele, C. Distillation vs. membrane filtration: overview of process evolutions in seawater desalination. Desalination, 2002, 143, 207-218. 100 Gleick, P.H.; Cooley, H.; Wolff, G.H., With a Grain of Salt: An Update on Seawater Desalination. In The World's Water 2006-2007: The Biennial Report on Freshwater Resources, Island Press: Washington, D.C., 2006. 101 Petersen, R.J. Composite reverse osmosis and nanofiltration membranes. J. Membr. Sci. 1993, 83, 81-150. 102 Loeb, S, Sourirajan, S. Advances in Chemistry Series 1963, 38, 117-132. 103 Glater, J. The early history of reverse osmosis membrane development. Desalination, 1998, 117, 297-309. 104 Amjad, Z., Ed. Reverse Osmosis: Membrane Technology, Water Chemistry, and Industrial Applications; Van Nostrand Reinhold: New York, 1993. 105 Lonsdale, H. K., Podall, H. E., Ed., Reverse Osmosis Membrane Research; Plenum Press: NewYork-London, 1972. 106 Gill, W.N. Review of Reverse Osmosis Membranes and Transport Models Chem. En. Commun. 1981, 12, 279-363. 107 Kurihara, M.; Himeshima, Y. The major developments of the evolving reverse osmosis membranes and ultrafiltration membranes. Polym. J. 1991, 23(5), 513.-520. 108 Lloyd, D.R.; Gerlowski, L.E.; Sunderland, C.D.; Wightman, J.P.; McGrath, J.E.; Igbal, M; Kang, Y. Poly(aryl ether) Membranes for Reverse Osmosis. In: Turbak, Albin F., editor. Synthetic Membranes: Volume 1 Desalination. Washington D.C.: American Chemical Society, 1981. 109 McKinney Jr., R. Properties of aromatic polyamide and polyamide-hydrazide membranes. In: Lonsdale, H. K., Podall, H. E., Eds., Reverse Osmosis Membrane Research. Plenum Press: NewYork-London, 1972. 110 Avlonitis, S.; Hanbury, W.T.; Hodgkiess, T. Chlorine Degradation of Aromatic Polyamides Desalination 1992, 85, 321-334.
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111 Zhang, Z.; Fan, G.; Sankir, M.; Roy, A.; Li, Y.; Park, H.B., Freeman, B.D.; McGrath, J.E. Disulfonated Directly Copolymerized Poly(arylene ether) Random Copolymers: Applications to Chlorine Resistant Reverse Osmosis (RO) or Nanofiltration (NF) Membranes—Part 1 Synthesis San Francisco ACS Meeting, September 2006. 112 Paul, M.; Park, H.B.; Freeman, B.D.; Roy, A.; McGrath, J.E.; Riffle, J.S. Synthesis and crosslinking of partially disulfonated poly(arylene ether sulfone) random copolymers as candidates for chlorine resistant reverse osmosis membranes Polymer 2008, 49, 2243-2252. 113 Allegrezza, Jr., A.E.; Parekh, B.S.; Parise, P.L.; Swiniarski, E.J.; White, J.L. Chlorine Resistant Polysulfone Reverse Osmosis Modules. Desalination, 1987, 64, 285-304. 114 Parise, P.L.; Allegrezza Jr.; A.E.; Parekh, B.S. Super hi-flux CP® chlorine-resistant reverse osmosis modules. Ultrapure Water, 1987, 4(7), 54-65. 115 Johnson, B. C.; Yilgor, I.; Tran, C.; Iqbal, M. Whightman, J. P.; Lloyd, D. R.; McGrath, J. E. Synthesis and Characterization of Sulfonated Poly(arylene ether sulfone)s. J. Polym. Sci.: Polym. Chem. Ed. 1984, 22, 721-737. 116 Lloyd, D.R.; Gerlowski, L.E.; Sunderland, C.D.; Wightman, J.P.; McGrath, J.E.; Iqbal, M.; Kang, K. Poly(aryl ether) Membranes for Reverse Osmosis. In Synthetic Membranes; Turbank, F.T., Eds.; ACS Symposium Series No. 153, American Chemical Society:Washington, D.C., 1981; 1, 327-350. 117 Drzewinski, M.; Macknight, W. J. Structure and properties of sulfonated polysulfone ionomers J. Appl. Polym. Sci. 1985, 30, 4753 – 4770. 118 Quentin, J.P. Sulfonated Polyarylether Sulfones, U.S. 3,709,841, Rhone-Poulenc, January 9, 1973. 119 Hickner, M.A.; Ghassemi, H.; Kim. Y.S.; Einsla, B.R.; McGrath, J.E. Alternative Polymer Systems for Proton Exchange Membranes (PEMs). Chem. Rev. 2004, 104, 4587-4612. 120 Wang, F.; Hickner, M.; Ji, Q.; Harrison, W.; Mecham, J.; Zawodzinski, T.A.; McGrath, J.E. Synthesis of Highly Sulfonated Poly(arylene ether sulfone) Random (Statistical) Copolymers Via Direct Polymerization. Macromol. Symp. 2001, 175, 387-395. 121 Wang, F.; Hickner, M.; Kim, Y.S.; Zawodzinski, T.A.; McGrath, J.E. Direct polymerization of sulfonated poly(arylene ether sulfone) random (statistical) copolymers: candidates for new proton exchange membranes. J. Membr. Sci. 2002, 197, 231-242. 122 Harrison, W.L.; Wang, F.; Mecham, J.B.; Bhanu, V.A.; Hill, M.; Kim, Y.S.; McGrath, J.E. Influence of the Bisphenol Structure on the Direct Synthesis of Sulfonated
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Poly(arylene ether) Copolymers. I. J. Polym. Sci: Part A: Polym. Chem. 2003, 41, 2264-2276. 123 Sumner, M.J.; Harrison, W.L.; Weyers, R.M.; Kim, Y.S.; McGrath, J.E.; Riffle, J.S.; Brink, A.; Brink, M.H. Novel proton conducting sulfonated poly(arylene ether) copolymers containing aromatic nitriles. J. Membr. Sci. 2004, 239, 199-211. 124 Harrison, W.L.; Hickner, M.A.; Kim, Y.S.; McGrath, J.E. Poly(arylene ether sulfone) copolymers and related systems from disulfonated monomer building blocks: synthesis, characterization, and performance - a topical review. Fuel Cells 2005, 5(2), 201-212. 125 Park, H.B.; Freeman, B.D.; Zhang, Z.B.; Sankir, M.; McGrath, J.E. Highly Chlorine-Tolerant Polymers for Desalination. Angewandte Chemie 2008, 47, 6019-6024. 126 Park, H.B.; Freeman, B.D.; Zhang, Z-B.; Fan, G-Y.; Sankir, M.; McGrath, J.E. Water and Salt Transport Behavior through Hydrophilic-Hydrophobic Copolymer Membranes and Their Relations to Reverse Osmosis Membrane Performance. ACS PMSE Preprints 2006, 95, 889-891. 127 Zhang, Z-B.; Fan, G-Y.; Sankir, M.; Park, H.B.; Freeman, B.D.; McGrath, J.E. Synthesis of Di-Sulfonated Poly(arylene ether sulfone) Random Copolymers as Novel Candidates for Chlorine-resistant Reverse Osmosis Membranes. ACS PMSE Preprints 2006, 95, 887-888. 128 Park, H.B.; Freeman, B.D.; McGrath, J.E. Hydrophilic-hydrophobic Nanostructured Polymeric Materials for Desalination. ACS PMSE Preprints 2009, 100, 286-289.
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2 Synthesis of Segmented Hydrophobic-Hydrophilic, Fluorinated-Sulfonated
Block Copolymers for Use as Proton Exchange Membranes
Rachael A. VanHouten, Ozma R. Lane, Desmond J. VanHouten, James E. McGrath*
Macromolecular Science and Engineering, Macromolecular and Interfaces Institute
Figure 2.9. Comparison of proton conductivity under partially hydrated conditions
for segmented and multiblock copolymers with increasing block length
2.4 Conclusions
Segmented copolymers containing highly fluorinated hydrophobic blocks and
100% disulfonated hydrophilic blocks have been successfully synthesized using an
oligomer- two monomer approach. The utilization of low temperature reactions
eliminated randomization by ether-ether interchange, evidenced by 13C NMR. The
properties of these copolymers were in good agreement with the properties of multiblock
copolymers synthesized using a more cumbersome oligomer-oligomer approach.9,10 An
increase in water uptake with increasing block length indicated the formation of well
connected channels as block length increased. Increased conductivity over the entire RH
range was also evidence that a connected hydrophilic morphology developed with
increased block length.
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Acknowledgement. The authors would like to acknowledge the Department of
Energy (DE-FG36-06G016038) and NSF IGERT (DGE-0114346) for funding.
102
References
1 Eisenberg, A. and Kim, J. S. Introduction to ionomers; Wiley: New York, 1998. 2 Ionomers: Synthesis, Structure, Properties and Applications, Tant, M. R., Mauritz, K. A. and Wilkes, G. L., Eds.; Chapman and Hall: New York, 1997. 3 Mauritz, K.A.; Moore, R.B. State of Understanding of Nafion. Chem. Rev. 2004, 104, 4515-4585. 4 Zalbowitz, M.; Thomas, S. “Fuel Cells: Green Power,” Department of Energy, 1999 LA-UR-99-3231. 5 Hickner, M.A.; Ghassemi, H.; Kim. Y.S.; Einsla, B.R.; McGrath, J.E. Alternative Polymer Systems for Proton Exchange Membranes (PEMs). Chem. Rev. 2004, 104, 4587-4612. 6 Resnick, P. R.; Grot, W. G.; of E.I. du Pont de Nemours and Company, Wilmington, DE, Sept 12, 1978; U.S. Patent 4,113,585. 7 Wang, F.; Hickner, M.; Kim, Y.S.; Zawodzinski, T.A.; McGrath, J.E. Direct polymerization of sulfonated poly(arylene ether sulfone) random (statistical) copolymers: candidates for new proton exchange membranes. J. Membr. Sci. 2002, 197, 231-242. 8 Wang, F.; Hickner, M.; Ji, Q.; Harrison, W.; Mecham, J.; Zawodzinski, T.A.; McGrath, J.E. Synthesis of Highly Sulfonated Poly(arylene ether sulfone) Random (Statistical) Copolymers Via Direct Polymerization. Macromol. Symp. 2001, 175, 387-395. 9 Yu, X.; Roy, A.; Dunn, S.; Yang, J.; McGrath, J.E. Synthesis and Characterization of Sulfonated-Fluorinated, Hydrophilic-Hydrophobic Multiblock Copolymers for Proton Exchange Membranes. Macromol. Symp. 2006, 245-245, 439-449. 10 Yu, X.; Roy, A.; Dunn, S.; Badami, A. S.; Yang, J.; Good, A. S.; McGrath, J. E. Synthesis and Characterization of Sulfonated-Fluorinated, Hydrophilic-Hydrophobic Multiblock Copolymers for Proton Exchange Membranes J. Polym. Sci. Part A: Polym. Chem., 2009, 47, 1038–1051. 11 Wang, H.; Badami, A.S.; Roy, A.; McGrath, J.E. Multiblock Copolymers of Poly(2,5-benzophenone and Disulfonated Poly(arylene ether sulfone) for Proton-Exchange Membranes. I. Synthesis and Characterization. J. Polym. Sci. Pol. Chem. 2007, 45, 284-294. 12 Lee, H.; Roy, A.; Lane, O.; Dunn, S.; McGrath, J. E. Segmented Sulfonated Poly(arylene ether sulfone)-b-Polyimide Copolymers for Proton Exchange Membrane Fuel Cells. I. Copolymer Synthesis and Fundamental Properties J. Polym. Sci. Part A. 2007, 45(21), 4879-4890.
103
13 Lee, H.-S.; Roy, A.; Lane, O.; Dunn, S.; McGrath, J.E. Hydrophilic-hydrophobic multiblock copolymers based on poly(arylene ether sulfone) via low-temperature coupling reactions for proton exchange membrane fuel cells. Polymer 2008, 49, 715-723. 14 Roy, A.; Hickner, M.A.; Yu, X.; Li. Y.; Glass, T.E.; McGrath, J.E. Influence of Chemical Composition and Sequence Length on the Transport Properties of Proton Exchange Membranes. J. Polym. Sci. Part B, 2006, 44, 2226-2239. 15 Einsla, M.L.; Kim, Y.S.; Hawley, M.; Lee, H.-S.; McGrath, J.E.; Liu, B.; Guiver, M.D.; Pivovar, B.S. Toward Improved Conductivity of Sulfonated Aromatic Proton Exchange Membranes at Low Relative Humidity. Chem. Mater. 2008, 20(17), 5636-5642. 16 Nakabayashi, K.; Matsumoto, K.; Ueda, M. Synthesis and Properties of Sulfonated Multiblock Copoly(ether sulfone)s by a Chain Extender. J. Polym. Sci. Pol. Chem. 2008, 46, 3947-3957. 17 Shin, C.K.; Maier, G.; Andreaus, B.; Scherer, G.G. Block copolymer ionomers for ion conductive membranes. J. Membr. Sci. 2004, 245, 147-161. 18 Zhao, C.; Li, X.; Wang, Z.; Dou, Z.; Zhong, S.; Na, H. Synthesis of block sulfonated poly(ether ether ketone)s (S-PEEKs) materials for proton exchange membrane. J. Membr. Sci. 2006, 280, 643-650. 19 Zhao, C.; Lin, H.; Shao, K.; Li, X.; Ni, H.; Wang, Z.; Na, H. Block sulfonated poly(ether ether ketone)s (SPEEK) ionomers with high ion-exchange capacities for proton exchange membranes. J. Power Sources 2006, 162, 1003-1009. 20 Noshay, Allen; McGrath, James E. Block Copolymers: Overview and Critical Survey, Academic Press: New York: 1977. 21 McGrath, J.E.; Dunson, D.L.; Mecham, S.J.; Hedrick, J.L. Synthesis and characterization of segmented polyimide-polyorganosiloxane copolymers. Adv. Polym. Sci. 1999, 140, 61-105. 22 Newton, A.B.; Rose, J.B. Relative reactivities of the functional groups involved in synthesis of poly(phenylene ether sulphones) from halogenated derivatives of diphenyl sulphone. Polymer, 1972, 13(10), 465-474.
23 Sankir, M.; Bhanu, V.A.; Harrison, W.L.; Ghassemi, H.; Wiles, K.B.; Glass, T.E.; Brink, A.E.; Brink, M.H.; McGrath, J.E. Synthesis and Characterization of 3,3’-Disulfonated-4,4’-dichlorodiphenyl Sulfone (SDCDPS) Monomer for Proton Exchange Membranes (PEM) in Fuel Cell Applications J. Appl. Polym. Sci. 2006, 100, 4595-4602.
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24 Li, Y.; VanHouten, R.; Brink, A.; McGrath, J.E. Purity Characterization of 3,3’-Disulfonated-4,4’-Dichlorodiphenyl Sulfone (SDCDPS) Monomer by UV-visible Spectroscopy. Polymer, 2008, 49, 3014-3019. 25 Ueda, M.; Toyota, H.; Ouchi, T.; Sugiyama, J.I.; Yonetake, K.; Masuko, T.; Teramoto, T. Synthesis and Characterization of Aromatic Poly(ether Sulfone)s Containing Pendant Sodium Sulfonate Groups. J. Polym. Sci.: Part A: Polym. Chem. 1993, 31, 853-858. 26 Yang, J.; Li, Y.; Roy, A.; McGrath J.E. Viscometric behavior of disulfonated poly(arylene ether sulfone) random copolymers used for proton exchange membranes. Polymer, 2008, 49(24), 5300-5306. 27 Kim, Y. S.; Wang, F.; Hickner, M.; McCartney, S.; Hong, Y. T.; Harrison, W.; Zawodzinski, T. A.; McGrath, J. E. Effect of Acidification Treatment and Morphological Stability of Sulfonate Poly(arylene ether sulfone) Copolymer Proton Exchange Membranes for Fuel Cell Use Above 100 °C. J. Polym. Sci.: Part B: Polym. Phys. 2003, 41, 2816-2828. 28 Zawodzinski, T. A.; Neeman, M.; Sillerud, L. O.; Gottesfeld, S. Determination of water diffusion coefficients in perfluorosulfonate ionomeric membranes J. Phys. Chem. 1991, 95, 6040. 29 Springer, T. E.; Zawodzinski, T. A.; Wilson, M. S.; Gottesfeld, S. Characterization of polymer electrolyte fuel cells using ac impedance spectroscopy J. Electrochem. Soc. 1996, 143, 587.
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3 Synthesis and Characterization of Highly Fluorinated-Disulfonated
Hydrophobic-Hydrophilic Segmented Copolymers Containing Various
Bisphenols for Use as Proton Exchange Membranes
Rachael A. VanHouten, Desmond J. VanHouten, Ozma Lane, James E. McGrath*
Macromolecular Science and Engineering Macromolecules and Interfaces Institute Virginia Tech, Blacksburg, VA 24061
A new series of disulfonated hydrophobic: hydrophilic segmented poly(arylene ether
sulfone) copolymers was synthesized and characterized for potential use as proton
exchange membranes in fuel cell applications. Copolymers comprised of 100%
disulfonated hydrophilic segments and hydrophobic segments derived from the bisphenol
phenolphthalein and decafluorobiphenyl were synthesized using an oligomer-two
monomer approach via a nucleophilic aromatic substitution reaction. The properties of
segmented copolymers derived from phenolphthalein were compared to copolymers
previous synthesized using 4,4’-sulfonyldiphenol (bisphenol-S) to determine the effect
the bisphenol had on conductivity, tensile properties, and thermal behavior of the
membrane. An increase in tensile modulus, strength, and glass transition temperature
was observed for the segmented copolymer derived from phenolphthalein due to the
greater rigidity of the phenolphthalein compared to bisphenol-S. Water uptake for the
two systems increased as block length increased. Proton conductivity also increased
across the entire range of relative humidity for both series. However, copolymers
106
containing bisphenol-S displayed higher overall conductivity when scaled to block
length.
3.1 Introduction
Disulfonated poly(arylene ether sulfone) (PAES) random copolymers have shown
promise for use as materials for proton exchange membranes (PEMs).1,2,3 They produce
membranes which are chemically, thermally, and mechanically stable. When used as
PEMs at moderate temperatures and high relative humidity (RH), they exhibit
conductivities comparable to that of Nafion®, the benchmark polymer used for PEMs at
this time.4,5,6 However, at low RH and higher temperatures, the conductivity of random
disulfonated PAES decreases, and this has been attributed to loss of connectivity in the
hydrophilic domains.
The conductivity at low RH had been improved with hydrophobic-hydrophilic
multiblock copolymers. In particular, our group has focused on systematically
controlling the volume fraction of blocks, the block length and ion exchange capacities
IEC). Synthesis of the multiblock copolymers was achieved by coupling telechelic
wholly aromatic 4,4’-biphenol based disulfonated poly(arylene ether) hydrophilic
oligomers with several fluorinated, nonfluorinated, and polyimide hydrophobic
oligomers.7,8,9 Ion-rich channels have been shown to form by atomic force microscopy
(AFM) and transmission electron microscopy (TEM) when the hydrophobic and
hydrophilic domains of these multiblock copolymers are designed to nano-phase
separate. This has been shown to increase the water self diffusion coefficient in the
hydrophilic phase, which allows for higher conductivity even under partially hydrated
conditions.10 By changing the volume fraction of blocks, block length, and the
107
interaction parameter of the hydrophilic and hydrophobic blocks, the extent of nano-
phase separation can be altered.11,12
This paper is concerned with producing the multiblock copolymers via what has
been suggested to be termed a segmented technique.13 For example, segmented
copolymers have been synthesized using a preformed oligomer which is then directly
reacted with one A-B or two A-A and B-B monomers. For the present system, a
hydrophilic block of disulfonated poly(arylene ether sulfone) oligomer with phenoxide
reactive end groups was first synthesized and isolated (in principle, this might not be
required). It was then reacted with a calculated amount of hydrophobic monomers,
forming that block in-situ. Using the segmented technique, multiblock copolymers were
synthesized in a shorter amount of time because there was no need to synthesize both
oligomers separately before coupling.
One approach for altering the hydrophobic segments of the copolymer is to
employ various bisphenols in the copolymerization. Previous studies13,14 focused on the
use of bisphenol-S as the comonomer in the hydrophobic segments. This bisphenol,
which is economically viable, affords hydrolytically stable amorphous soluble
copolymers, which have manageable water uptake.9,15 This paper describes a series of
segmented copolymers using phenolphthalein as a comonomer in the hydrophobic
segments. Phenolphthalein was chosen as an alternate comonomer because its bulky
nature may increase the free volume of the copolymer,16 possibly allowing for higher
conductivity at lower relative humidity.17 The monomer rigidity may also enhance
mechanical strength. This paper describes the synthesis of segmented copolymers
utilizing phenolphthalein in the hydrophobic segments. The characteristics of these
108
segmented copolymers will also be compared to those of our previously synthesized
segmented copolymers derived from bisphenol-S.
3.2 Experimental
3.2.1 Materials
Decafluorobiphenyl (DFBP) was obtained from Matrix Scientific and dried under
vacuum at room temperature overnight. Bisphenol-S (Bis-S) was purchased from Alfa
Aesar and dried under vacuum at 60 oC for 24 h before use. Monomer grade 4,4’-
biphenol (BP) was obtained from ChrisKev Company, Inc. and dried at 60 oC for 24 h
under vacuum before use. 4,4’-dichlorodiphenylsulfone (DCDPS) was kindly provided
by Solvay Advanced Polymers and used as received to synthesize 3,3’-disulfonated-4,4’-
dichlorodiphenylsulfone (SDCDPS) according to a procedure reported elsewhere.18,19,20
Phenolphthalein was purchased from Sigma Aldrich and was recrystallized from ethanol
and water. The phenolphthalein was dried under vacuum at 90 oC for 24 h prior to use.
N,N-dimethylacetamide (DMAc) and N-methyl-2-pyrrolidone (NMP) (Aldrich) were
vacuum-distilled from calcium hydride onto molecular sieves and stored under nitrogen
before use. Potassium carbonate (K2CO3) was obtained from Aldrich and dried under
vacuum at 120 oC overnight before use. Toluene, cyclohexane, and isopropyl alcohol
were obtained from Aldrich and used as received.
3.2.2 Synthesis of Phenoxide-Terminated Hydrophilic Blocks (BPS-100)
Phenoxide-terminated hydrophilic blocks were synthesized using a previously
published procedure from our laboratory.9 The targeted molecular weights of the blocks
ranged from 5000 to 13000 g/mol. In a typical procedure for an Mn of 5000 g/mol, the
109
following conditions were utilized. BP (4.2789 g, 22.98 mmol), SDCDPS (10.1116 g,
20.58 mmol), and DMAc (72 mL) were added to a three-neck, round-bottom flask,
equipped with mechanical stirrer, Dean-Stark trap, condenser, and N2 inlet. The reaction
bath was set to 85 oC, and the monomers were allowed to dissolve. K2CO3 (3.652 g,
26.43 mmol) and toluene (36 mL) were added to the flask. The temperature of the bath
was increased to 155 oC, and the reaction was allowed to azeotrope water for 4 h.
Toluene was removed from the system by increasing the bath temperature to 180 oC. The
reaction was allowed to proceed for 96 h. After cooling, the solution was filtered to
remove salts and precipitated into acetone. The resulting oligomer was dried at 110 oC
for at least 24 h under vacuum and had an Mn of 4700 g/mol determined by end group
analysis using 1H NMR.
3.2.3 Synthesis of segmented copolymer with simultaneous formation of
hydrophobic segments
The segmented copolymer was synthesized using DFBP and either Bis-S or Ph
monomers to form the hydrophobic block. For a Ph containing segmented copolymer (PhF-
BPSH100) (5K:5K): a 3-neck, round bottom flask, equipped with mechanical stirrer, Dean-
Stark trap, condenser, and N2 inlet was loaded with BPS-100 (5K; 3.1010 g, 0.6164 mmol),
Ph (1.4949 g, 4.6961 mmol), and NMP (31 mL). After dissolution of reactants, K2CO3
(0.844 g, 6.109 mmol) and cyclohexane (6 mL) were added to the reaction solution. The
reaction bath was heated to 110 oC and allowed to azeotrope for 4 h. The cyclohexane was
drained from the system and the bath temperature was lowered to 85 oC. DFBP (1.7750 g,
5.3125 mmol) and NMP (12 mL) were added to the reaction flask. The bath temperature was
raised to 90 oC and the reaction was allowed to proceed for 40 h. The reaction was cooled
110
and precipitated into isopropyl alcohol (1 L). The product was filtered and washed in
deionized water at 60 oC for 12 h and acetone for 12 h. It was dried under vacuum at 110 oC
for 24 h before casting (Figure 3.1). The Bis-S containing segmented copolymers (BisSF-
BPSH100) were synthesized in a similar manner.14
3.2.4 Membrane Preparation
Membranes were cast from a 6 w/v% solution of polymer in DMAc onto a clean
glass plate. Solvent was removed using an IR lamp. The lamp intensity was held at 30-
35 oC for 24 h and then raised to 35-40 oC for an additional 24 h. The film was dried
under vacuum at 110 oC for 24 h. The film was removed from the glass plate by
submersion in water and acidified in boiling 0.5 M H2SO4 for 2 h, followed by 2 h in
boiling deionized water.
3.2.5 Characterization
1H, 19F, and 13C NMR analyses were performed on a Varian Unity 400 MHz
spectrometer. 1H and 19F NMR spectra were obtained from a 1% solution (w/v) of
sample in DMSOd6. 13C NMR spectra were obtained from a 10% solution (w/v) of
sample in DMSOd6. All were run at ambient temperatures. Intrinsic viscosities of the
segmented copolymers were determined using universal calibration size exclusion
chromatography (SEC), (also known as gel permeation chromatography (GPC)). The
experiments were performed on a liquid chromatograph equipped with a Waters 1515
isocratic HPLC pump, Waters Autosampler, Waters 2414 refractive index detector and
Viscotek 270 dual detector. 0.05 M LiBr/NMP was used as the mobile phase. The
column temperature was maintained at 60 oC because of the viscous nature of NMP. Both
111
the mobile phase and sample solution were filtered before introduction to the GPC
system. This procedure has been described in detail.21
3.2.6 Determination of water uptake and dimensional swelling
The water uptake for all membranes was determined gravimetrically. Acidified
membranes were equilibrated in liquid water at room temperature for 24 h. Wet
membranes were removed from the liquid water, blotted dry to remove excess water, and
quickly weighed. Membranes were dried at 110 oC under vacuum for 24 h and weighed
again. Water uptake was calculated according to Equation 3.1 where massdry and masswet
refer to the mass of the dry and wet membranes, respectively. An average of three
samples was used for each measurement.
( )wet dry
dry
mass masswater uptake% 100
mass
−= × 3.1
Percent swelling of the membranes was determined in the in-plane (x and y) and through-
plane (z) directions. Wet measurements were performed after equilibrating membranes
in liquid water for 24 h at room temperature. Membranes were then dried in a convection
oven at 80 oC for 2 h and measured again. Wet and dry measurements in the x and y
direction were performed by sandwiching the membrane between layers of polyethelene
and two glass plates and measuring with a ruler (mm). Wet and dry measurements in the
z direction were performed using a micrometer. Typical sample size was 2.5 x 2.5 cm
squares when wet. Percent swelling was reported for three directions and calculated
112
according to Equation 3.2 where lengthwet,i and lengthdry,i refer to the length (where i
represents the x, y, or z direction) of the dry and wet membrane, respectively.
( )wet,i dry,ii
dry,i
length lengthpercent swelling 100
length
−= × 3.2
3.2.7 Measurement of proton conductivity
Proton conductivity at 30 oC in liquid water was determined in a window cell
geometry22 using a Solartron 1252 + 1287 Impedance/Gain-Phase Analyzer over the
frequency range of 10 Hz to 1 MHz following the procedure reported in the literature.23
In determining proton conductivity in liquid water, membranes were equilibrated at 30 oC
in DI water for 24 h prior to the testing. Proton conductivity under partially hydrated
conditions was performed at 80 oC. Membranes were equilibrated at 80% RH for 8 h in a
humidity-temperature oven (ESPEC, SH-240). The thickness of the film was measured
with a micrometer. Membranes were allowed to equilibrate at 95% RH and each
additional specified RH value for 4 h before each measurement. Thickness
measurements were performed at the lowest RH which was reached.
3.2.8 Dynamic Mechanical Analysis
Dynamic mechanical analysis (DMA) was performed using a TA Instruments
2890 Dynamic Mechanical Analyzer. Salt-form rectangular membrane films measuring
0.35 mm x 4 mm x 25 mm were used for the test in order to observe the Tg before
degradation of the sulfonic acid groups begins. Multi-frequency tension tests were
conducted on the membranes, with an amplitude of 25 µm and a pre-load force of 0.025
N.
113
3.2.9 Thermal Gravimetric Analysis
Thermal gravimetric analysis (TGA) was performed using a TGA Q500 (TA
Instruments) on the membrane specimens to determine the thermal stability of the
copolymers. The samples were dried isothermally in the TGA at 150 oC for 20 min to
remove any residual moisture. The samples were then equilibrated at 30 oC and run at a
heating rate of 10 oC/min. in an air atmosphere.
3.2.10 Tensile testing
The tensile properties of the membranes were measured using an Instron 5500R
equipped with a 200 lb load cell at room temperature and 44-54% RH and a rate of 5
mm/min. Membrane samples were dried under vacuum at 110 oC for 24 h. A dogbone
die measuring 50 mm in length and 4 mm in width was used to stamp out 5 samples for
each membrane. The dogbone samples were then conditioned in a humidity chamber at
44% RH for 48 h prior to testing.
3.3 Results and Discussion
3.3.1 Synthesis of PhS-BPS100 Segmented Copolymers
The phenoxide-terminated hydrophilic blocks were synthesized via a well
understood step growth polymerization. A small molar access of BP to SDCDPS
monomer was used to synthesize oligomers with controlled molecular weight; number-
average molecular weights (Mn) of 5, 7, 10, and 13 kg/mol were targeted. Proton NMR
was used to confirm that the oligomers were phenoxide endcapped and to simultaneously
determine the Mn by end group analysis. Further details of this reaction and Mn
determination are available.14
114
The segmented copolymers were synthesized using an oligomer-two monomer
reaction approach as described earlier. Phenoxide-terminated 100% disulfonated
poly(arylene ether sulfone) oligomers (BPS100) were reacted with Ph and DFPB
monomers in a nucleophilic aromatic substitution reaction to afford the segmented
copolymer (PhF-BPS100) (Figure 3.1). The stoichiometric ratio of DFPB to phenoxide
end groups, from either Ph or BPS100, remained 1:1 for the copolymer series. Whereas,
the stoichiometric ratio of DFBP to Ph was controlled to target block lengths for the
hydrophobic portions (PhF) that were equal to the preformed hydrophilic block lengths.
Since DFBP is highly reactive, low reaction temperatures (90-105 oC) could be used for
the coupling reaction, which minimized ether-ether interchange.
OKO S O
O
OSO3K
KO3S
OKn
F
FFFF
F
F F F F
K2CO3
Cyclohexane/NMP4 hrs @ 110 oC
add 18-85 hrs @ 90-105 oC
Boiling H2SO4 (0.5 M), 2hBoiling H2O, 2h
(Phenolphthalein)
(DFBP)
O
O
OHOH
FFFF
F F F F
O
O
OO
F F F F
OO S O
O
OSO3H
HO3S
On
FFFF
m
x
OKO S O
O
OSO3K
KO3S
OKn
F
FFFF
F
F F F F
K2CO3
Cyclohexane/NMP4 hrs @ 110 oC
add 18-85 hrs @ 90-105 oC
Boiling H2SO4 (0.5 M), 2hBoiling H2O, 2h
(Phenolphthalein)
(DFBP)
O
O
OHOHOKO S O
O
OSO3K
KO3S
OKn
F
FFFF
F
F F F F
K2CO3
Cyclohexane/NMP4 hrs @ 110 oC
K2CO3
Cyclohexane/NMP4 hrs @ 110 oC
add 18-85 hrs @ 90-105 oC18-85 hrs @ 90-105 oC
Boiling H2SO4 (0.5 M), 2hBoiling H2O, 2h
(Phenolphthalein)
(DFBP)
O
O
OHOH
FFFF
F F F F
O
O
OO
F F F F
OO S O
O
OSO3H
HO3S
On
FFFF
m
x
Figure 3.1. General synthetic scheme for highly fluorinated:disulfonated segmented
copolymers
Representative 1H and 19F NMR spectra for the PhF-BPS100 series are shown in
115
Figure 3.2. The absence of peaks at 6.8, 7.05, 7.4, and 7.55 ppm in the 1H NMR signified
a successful coupling reaction had occurred. These peaks would be present if unreacted
hydrophilic oligomer remained due to protons from the terminal BP. There were also no
additional fluorine peaks in the 19F NMR spectrum. The two peaks present were assigned
to fluorines in the chain.
FFFF
F F F F
O
O
OO
F F F F
OO S O
O
O SO3K
KO3S
On
FFFF
m
x
edc
ed
bac
gf
hh
gf
ba
i j
i j
(a)
(b)
FFFF
F F F F
O
O
OO
F F F F
OO S O
O
O SO3K
KO3S
On
FFFF
m
x
edc
ed
bac
gf
hh
gf
ba
i j
i j
FFFF
F F F F
O
O
OO
F F F F
OO S O
O
O SO3K
KO3S
On
FFFF
m
x
edc
ed
bac
gf
hh
gf
ba
i j
i j
(a)
(b)
Figure 3.2. (a) 1H and (b) 19F NMR spectra for PhF-BPS100 segmented copolymer
Carbon NMR spectra for representative PhF-BPS100 segmented copolymer and a
35% disulfonated poly(arylene ether sulfone) random copolymer (BPS-35) are shown in
Figure 3.3. The sharp singlets in the segmented copolymer spectrum suggest the blocky
structure of the copolymer was maintained. Randomization of the backbone would result
in peak splitting similar to that shown in the BPS-35 random copolymer spectrum.
116
PhF-BPS100 7k7k
BPS-35
PhF-BPS100 7k7k
BPS-35
Figure 3.3. 13C NMR spectrum for PhF-BPS100 segmented copolymer and BPS-35
random copolymer
3.3.2 Comparison of PhF-BPSH100 and BisSF-BPSH100 Segmented Copolymer
Properties
The objective for synthesizing the PhF-BPS100 copolymer series was twofold.
Firstly, it allowed further investigation of the segmented synthetic procedure using a
different bisphenol to derive the hydrophobic segments. Secondly, it allowed for
comparisons to be made to an initial series of segmented copolymers14 to determine how
the structure of the bisphenol affects the properties of the copolymer. Properties of the
BisSF-BPSH100 and PhF-BPSH100 segmented copolymers are summarized in Table
3.1. The intrinsic viscosity (I.V.) data confirmed that high molecular weight polymer
was achieved using this synthetic method. Tough ductile transparent films were also cast
from the copolymers, indicating that high molecular weight was achieved. For the
BisSF-BPSH100 segmented copolymer, the water uptake increased and was interpreted
as reflecting the sharper nano-phase separation that occurred as block length increased.
117
Both the BisSF-BPSH100 and PhF-BPSH100 segmented copolymers yielded membranes
with manageable water uptake.
Table 3.1. Characterization of BisSF-BPSH100 and PhF-BPS100 Segmented Copolymers
a Calculated from experimental loading: IEC = (g of Hydrophilic *IEC of BPSH100)/(g of Hydrophobic + g of Hydrophilic)
b IEC was calculated according to 1H NMRc Intrinsic viscosity measured by GPCd Measured in liquid water at 30°Ce Water uptake was calculated through [(Wwet-Wdry) / Wdry] x 100%
Water
Uptakee
Theoreticala Experimentalb %BisSF:BPSH100
3K3K1.6 1.8 0.63 0.10 62
BisSF:BPSH100 5K5K
1.6 1.5 0.50 0.11 51
BisSF:BPSH100 9K9K
1.7 1.5 0.82 0.15 74
PhF:BPSH100 5K5K
1.7 1.7 0.48 0.11 42
PhF:BPSH100 7K7K
1.8 1.8 0.58 0.14 73
PhF:BPSH100 13K13K 1.7 1.7 0.46 0.11 73
IEC
(meq/g)Conductivity
d S/cmIV c
(dL/g)
The conductivity of the BisSF-BPSH100 and PhF-BPSH100 segmented
copolymers as a function of relative humidity is shown in Figure 3.4. At 95 %RH, both
systems of segmented copolymers yielded higher performance than Nafion®. However,
as the relative humidity was decreased the conductivity of the systems fell below
Nafion®. In both the BisSF-BPSH100 and PhF-BPSH100 segmented copolymers, the
conductivity increased with an increase in block length over the entire RH range. The
118
conductivity of the BisSF-BPSH100 segmented copolymers was greater than the PhF-
BPSH100, when comparing similar block lengths despite the PhF-BPSH100 segmented
*Tests run at a heating rate of 5 oC/min in an air atmosphere
(a) (b)
Figure 3.7. DMA plots for a) BisSF-BPSH100 and b)PhF-BPSH100 segmented copolymers. In a) and b) the closed symbols represent the storage modulus and the
open symbols represent the tan delta.
The tensile properties of the membranes are shown in Table 3.2. The PhF-
BPSH100 segmented copolymers exhibited significantly greater tensile moduli and
strength than the BisSF-BPSH100 segmented copolymers. The increase in both the
tensile moduli and strength may reflect the greater rigidity of the phenolphthalein. This
greater rigidity also decreased the elongation of the PhF-BPSH100 segmented
copolymers. However, both segmented copolymers yielded tough films.
122
Table 3.2. Tensile Properties of BisSF-BPSH100 and PhF-BPSH100 Segmented Copolymers
Segmented copolymers containing highly fluorinated hydrophobic blocks and
100% disulfonated hydrophilic blocks have been successfully synthesized using an
oligomer-monomer approach. Tough membranes were produced from BisSF-BPSH100
and PhF-BPSH100 segmented copolymers. The greater rigidity of the phenolphthalein
led to an increase in tensile modulus, strength, and Tg of the PhF-BPSH100 segmented
copolymer series. Further experiments are ongoing to assess whether utilization of the
phenolphthalein in the hydrophilic phase will behave differently.
Acknowledgment. The authors would like to acknowledge the Department of
Energy for funding under DE-FG36-06G016038.
123
References
1 Wang, F.; Hickner, M.; Kim, Y.S.; Zawodzinski, T.A.; McGrath, J.E. Direct polymerization of sulfonated poly(arylene ether sulfone) random (statistical) copolymers: candidates for new proton exchange membranes. J. Membr. Sci. 2002, 197, 231-242. 2 Wang, F.; Hickner, M.; Ji, Q.; Harrison, W.; Mecham, J.; Zawodzinski, T.A.; McGrath, J.E. Synthesis of Highly Sulfonated Poly(arylene ether sulfone) Random (Statistical) Copolymers Via Direct Polymerization. Macromol. Symp. 2001, 175, 387-395. 3 Hickner, M.A.; Ghassemi, H.; Kim. Y.S.; Einsla, B.R.; McGrath, J.E. Alternative Polymer Systems for Proton Exchange Membranes (PEMs). Chem. Rev. 2004, 104, 4587-4612. 4 Kim, Y.S.; Dong, L.; Hickner, M.A.; Pivovar, B.S.; McGrath, J.E. Processing induced morphological development in hydrated sulfonated poly(arylene ether sulfone) copolymer membranes. Polymer 2003, 44, 5729-5736. 5 Kim, Y. S.; Wang, F.; Hickner, M.; McCartney, S.; Hong, Y. T.; Harrison, W.; Zawodzinski, T. A.; McGrath, J. E. Effect of Acidification Treatment and Morphological Stability of Sulfonate Poly(arylene ether sulfone) Copolymer Proton Exchange Membranes for Fuel Cell Use Above 100 °C. J. Polym. Sci.: Part B: Polym. Phys. 2003, 41, 2816-2828. 6 Kim, Y.S.; Sumner, M.J.; Harrison, W.L.; Riffle, J.S.; McGrath, J.E.; Pivovar, B.S. Direct Methanol Fuel Cell Performance of Disulfonated Poly(arylene ether benzonitrile) Copolymers. J. Electrochem. Soc. 2004, 151, A2150-A2156. 7 Yu, X.; Roy, A.; Dunn, S.; Yang, J.; McGrath, J.E. Synthesis and Characterization of Sulfonated-Fluorinated, Hydrophilic-Hydrophobic Multiblock Copolymers for Proton Exchange Membranes. Macromol. Symp. 2006, 245-245, 439-449. 8 Wang, H.; Badami, A.S.; Roy, A.; McGrath, J.E. Multiblock Copolymers of Poly(2,5-benzophenone and Disulfonated Poly(arylene ether sulfone) for Proton-Exchange Membranes. I. Synthesis and Characterization. J. Polym. Sci. Pol. Chem. 2007, 45, 284-294. 9 Lee, H.; Roy, A.; Lane, O.; Dunn, S.; McGrath, J. E. Segmented Sulfonated Poly(arylene ether sulfone)-b-Polyimide Copolymers for Proton Exchange Membrane Fuel Cells. I. Copolymer Synthesis and Fundamental Properties J. Polym. Sci. Part A. 2007, 45(21), 4879-4890. 10 Roy, A.; Hickner, M.A.; Yu, X.; Li. Y.; Glass, T.E.; McGrath, J.E. Influence of Chemical Composition and Sequence Length on the Transport Properties of Proton Exchange Membranes. J. Polym. Sci. Part B, 2006, 44, 2226-2239.
124
11 Leibler, L. Theory of Microphase Separation in Block Copolymers. Macromolecules 1968, 13(6), 1602-1617. 12 Matsen, M.W.; Bates, F.S. Origins of Complex Self-Assembly in Block Copolymers. Macromolecules 1996, 29, 7641-7644. 13 VanHouten, R.A.; Lane, O.; McGrath, J.E. Synthesis of Segmented Hydrophobic:Hydrophilic, Fluorinated:Sulfonated Block Copolymers for Use as Proton Exchange Membranes. Prep. Pap.-Am. Chem. Soc., Div. Fuel Chem. 2008, 53(2), 765-766.
14 VanHouten, Rachael A.; Lane, Ozma. R.; VanHouten, Desmond J.; McGrath, James E. Synthesis of segmented hydrophobic:hydrophilic, fluorinated:sulfonated block copolymers for use as proton exchange membranes. Macromolecules 2009, Submitted. 15 Yu, X.; Roy, A.; Dunn, S.; Badami, A. S.; Yang, J.; Good, A. S.; McGrath, J. E. Synthesis and Characterization of Sulfonated-Fluorinated, Hydrophilic-Hydrophobic Multiblock Copolymers for Proton Exchange Membranes J. Polym. Sci. Part A: Polym. Chem., 2009, 47, 1038–1051. 16 Wang, Zhonggang; Chen, Tianlu; Xu, Jiping. Gas permeabilities of cardo polyoxyarylene membranes. Journal of Applied Polymer Science 2002, 83(4), 791-801. 17 Miyatake, Kenji; Zhou, Hua; Uchida, Hiroyuki; Watanabe, Masahiro. Highly proton conductive polyimide electrolytes containing fluorenyl groups. Chem Commun 2003, 3, 368. 18 Ueda, M.; Toyota, H.; Ouchi, T.; Sugiyama, J.I.; Yonetake, K.; Masuko, T.; Teramoto, T. Synthesis and Characterization of Aromatic Poly(ether Sulfone)s Containing Pendant Sodium Sulfonate Groups. J. Polym. Sci.: Part A: Polym. Chem. 1993, 31, 853-858. 19 Sankir, M.; Bhanu, V.A.; Harrison, W.L.; Ghassemi, H.; Wiles, K.B.; Glass, T.E.; Brink, A.E.; Brink, M.H.; McGrath, J.E. Synthesis and Characterization of 3,3’-Disulfonated-4,4’-dichlorodiphenyl Sulfone (SDCDPS) Monomer for Proton Exchange Membranes (PEM) in Fuel Cell Applications J. Appl. Polym. Sci. 2006, 100, 4595-4602. 20 Li, Y.; VanHouten, R.; Brink, A.; McGrath, J.E. Purity Characterization of 3,3’-Disulfonated-4,4’-Dichlorodiphenyl Sulfone (SDCDPS) Monomer by UV-visible Spectroscopy. Polymer, 2008, 49, 3014-3019. 21 Yang, J.; Li, Y.; Roy, A.; McGrath J.E. Viscometric behavior of disulfonated poly(arylene ether sulfone) random copolymers used for proton exchange membranes. Polymer, 2008, 49(24), 5300-5306.
125
22 Zawodzinski, T. A.; Neeman, M.; Sillerud, L. O.; Gottesfeld, S. Determination of water diffusion coefficients in perfluorosulfonate ionomeric membranes J. Phys. Chem. 1991, 95, 6040. 23 Springer, T. E.; Zawodzinski, T. A.; Wilson, M. S.; Gottesfeld, S. Characterization of polymer electrolyte fuel cells using ac impedance spectroscopy J. Electrochem. Soc. 1996, 143, 587.
126
4 Synthesis and Characterization of Hydrophobic-Hydrophilic Segmented
Copolymers with Unequal Hydrophobic and Hydrophilic Block Lengths for Use
as Proton Exchange Membranes
Rachael A. VanHouten, Desmond J. VanHouten, James E. McGrath*
Macromolecular Science and Engineering Macromolecules and Interfaces Institute Virginia Tech, Blacksburg, VA 24061
Table 4.1. Target and Experimental Mn for PhS100 Oligomers
a. Calculated from 1H NMR
Target Experimentala
7000 650010000 1040013000 1360017000 16800
Molecular Weight(g/mol)
4.3.2 Synthesis of BisSF-PhS Segmented Copolymer
Hydrophilic, PhS oligomers were reacted with DFBP and Bis-S monomers to
form four BisSF-PhS segmented copolymers via a nucleophilic aromatic substitution
reaction (Figure 4.3). This series of polymers will be referred to as BisSF-PhS100 or
BisSF-PhSH100 segmented copolymers to differentiate between copolymers in salt or
acid forms, respectively. Specific copolymers within the series are identified by the Mns
of the oligomers used in the syntheses, i.e. a copolymer with targeted and 9 kg/mol
hydrophobic segments and 13 kg/mol hydrophilic blocks is called 9k13k. These
copolymers were synthesized using a similar method to that described in chapters 3 and
4. The ratio of DFBP to Bis-S monomer was controlled using the Carothers equation to
obtain blocks with desired Mns (often referred to as block length throughout this
discussion) for the hydrophobic segments, which were shorter than the hydrophilic block
lengths. The overall stoichiometric ratio of DFBP to phenolic end groups (from the Bis-S
monomer or PhS100 oligomer) was maintained at 1:1.
137
The targeted ion exchange capacity (IEC) for the series of copolymers was 1.7
meq/g. This ion exchange capacity was targeted so that the copolymers could be more
closely compared to the BisSF-BPSH100 and PhF-BPSH100 copolymers described in
chapter 3 and 4, respectively. Copolymers with unequal hydrophilic and hydrophobic
block lengths needed to be synthesized in order to achieve a comparable IEC to the
aforementioned copolymers because PhS100 oligomers have a lower IEC value than
BPS100 due to the increased molecular weight of the repeat unit. Synthesizing a
copolymer with equal block lengths would have resulted in a theoretical IEC value of
~1.4 meq/g.
F
FFFF
F
F F F F
K2CO3Cyclohexane/NMP4 hrs @ 110 oC
add 15-30 hrs @ 90-110 oC
(DFBP)
O S O
O
O SO3Na
NaO3SO
O
KO n
O
O
OK OH S OH
O
O
(Bis-S)
FFFF
F F F F
OO
F F F F
O
FFm
O
O
O S O
O
O SO3K
KO3SO
O
O n
x
F
S
O
OF
F
FFFF
F
F F F F
K2CO3Cyclohexane/NMP4 hrs @ 110 oC
K2CO3Cyclohexane/NMP4 hrs @ 110 oC
add 15-30 hrs @ 90-110 oC15-30 hrs @ 90-110 oC
(DFBP)
O S O
O
O SO3Na
NaO3SO
O
KO n
O
O
OK OH S OH
O
O
(Bis-S)
FFFF
F F F F
OO
F F F F
O
FFm
O
O
O S O
O
O SO3K
KO3SO
O
O n
x
F
S
O
OF
Figure 4.3. BisSF-PhS100 segmented copolymer
138
In order to confirm the success of the reaction and chemical structure and
sequencing of the segmented copolymers, nuclear magnetic resonance (NMR) was
performed for several nuclides, including 1H, 19F, and 13C. Peaks from protons in both
the hydrophobic and hydrophilic block were able to be assigned (Figure 4.4a). Also the
absence of a peak at 6.75 ppm indicated that no unreacted hydrophilic block remained.
Peaks from residual DFBP monomer were absent from the 19F NMR spectrum (Figure
4.4b). The peaks at -138.2 and -153.8 ppm were assigned to the fluorine in the backbone
of the hydrophobic block. Figure 4.5 shows a portion of a 13C NMR spectrum for a
9k:13k segmented copolymer. The sharp singlets result from the blocky structure in the
copolymer backbone. The shorter sequencing in a random copolymer results in doublets
in the 13C NMR spectrum.
FFFF
F F F F
OO
F F F F
O
FFm
O
O
O S O
O
O SO3K
KO3SO
O
O n
x
F
S
O
OF
feba d
c
g h
cf
e
a
d
bh g
i j
i j
(a)
(b)
FFFF
F F F F
OO
F F F F
O
FFm
O
O
O S O
O
O SO3K
KO3SO
O
O n
x
F
S
O
OF
feba d
c
g h
cf
e
a
d
bh g
i j
i j
(a)
(b)
Figure 4.4. Representative (a) 1H and (b) 19F NMR spectra for BisSF-PhS100 segmented copolymer
139
162 160 158 156 PPM
Figure 4.5. 13C NMR spectrum for BisSF-PhS100 segmented copolymer
4.3.3 Characterization of BisSF-PhSH100 Segmented Copolymer Properties
BisSF-PhSH100 segmented copolymer membranes were characterized for their
application as proton exchange membranes. Transparent, tough, ductile films were able to be
cast from this series of copolymers. Table 4.2 summarizes selected copolymer properties of
the series. The experimental IEC agreed closely with the targeted value (~1.7 meq/g) for the
system. The I.V. of the copolymers suggested high molecular weight copolymer was
synthesized. Conductivity in liquid water (30 oC) was not dependent on block length.
However, water uptake was affected by block length. Copolymers with longer block lengths
sorbed more water than copolymers with shorter block lengths, which has been ascribed to
the formation of co-continuous hydrophilic channels that form with increasing block length.2
This was also observed in dimensional water sorption tests. Figure 4.6 shows water swelling
in the x, y, and z directions. As the block length of the copolymer increases, the z-directional
swelling increases, while only small changes were observed in the x and y directions.
140
Table 4.2. Characterization of BisSF-PhSH100 Segmented Copolymer
a. Calculated from 1H NMR; theoretical IEC for the series is 1.7 meq/gb. GPC performed in 0.05 M LiBr/NMP at 60 oCc. Performed in liquid water at 30 oC
(BisAS0) and fully disulfonated hydrophilic oligomers (BisAS100) and were synthesized
via a nucleophilic aromatic substitution reaction (Figure 5.1 and Figure 5.3, respectively).
A small molar excess of Bis-A to SDCDPS or DCDPS was used to control the molecular
weight of the oligomers, targeting Mns of 4, 6, 8, 10, or 12 kg/mol. Proton NMR was
used to confirm that both series of oligomers were phenoxide-terminated and
simultaneously determine the Mns of the oligomers using end-group analysis. To aide in
160
the assignment of the peaks from 1H NMR, two-dimensional homonuclear correlation
spectroscopy (2-D COSY) experiments were performed. COSY experiments allow spin-
coupled pairs of nuclei to be determined.31 Figure 5.4 depicts a 1H-1H COSY of
BisAS100 oligomer with a Mn of 4 kg/mol. Splitting between protons on adjacent
carbons was determined by examining off-diagonal peaks. Based on the pairing made
using COSY experiments, proper peak assignments were made for BisAS100 oligomer
(Figure 5.5). The terminal protons due to a Bis-A unit at the end of a chain were assigned
to peaks at 6.65 and 6.75 ppm for the hydrophilic and hydrophobic blocks, respectively
(Figure 5.2 and Figure 5.5). Whereas, aromatic protons from a Bis-A unit in the middle
of the chain resulted in peaks at 6.95 and 7.25 ppm for the hydrophilic and 7.22 and 7.0
ppm for the hydrophobic oligomers. By comparing the integration value ratios of main
chain peaks to end-group peaks, Mn was determined. Theoretical and experimental Mn
values are summarized in Table 5.1, along with intrinsic viscosity (I.V.) values measured
by SEC. An increase in I.V. was observed as Mn of the oligomers increased. Log-log
plots of Mn versus intrinsic viscosity for both copolymer series had a linear relationship,
indicating the expected strong correlation between I.V. and Mn for BisAS100 and BisAS0
oligomers (Figure 5.6).
161
K2CO3Toluene/DMAc4 hrs @ 155 oC48 hrs @ 180 oC
+ OH
CH3
CH3
OHCl S Cl
O
O
OK
CH3
CH3
O S O
O
O
CH3
CH3
KO m
K2CO3Toluene/DMAc4 hrs @ 155 oC48 hrs @ 180 oC
+ OH
CH3
CH3
OHCl S Cl
O
O
OK
CH3
CH3
O S O
O
O
CH3
CH3
KO m
Figure 5.1. Phenoxide-terminated BisAS0 with controlled molecular weight
OK
CH3
CH3
O S O
O
O
CH3
CH3
KO m
a b c d a’
a’
d cab
OK
CH3
CH3
O S O
O
O
CH3
CH3
KO m
a b c d a’
a’
d cab
Figure 5.2. Aromatic region of a 1H NMR spectrum of BisAS0 oligomer
162
K2CO3Toluene/DMAc4 hrs @ 155 oC96 hrs @ 180 oC
+
OK
CH3
CH3
O S O
O
O SO3K
KO3SCH3
CH3
KO n
Cl S Cl
O
O SO3Na
NaO3S
OH
CH3
CH3
OH
K2CO3Toluene/DMAc4 hrs @ 155 oC96 hrs @ 180 oC
+
OK
CH3
CH3
O S O
O
O SO3K
KO3SCH3
CH3
KO n
Cl S Cl
O
O SO3Na
NaO3S
OH
CH3
CH3
OH
Figure 5.3. Phenoxide-terminated BisAS100 with controlled molecular weight
ed
bg
ac f ih
ed
bg
a cf
ih
f1 (ppm)
f2 (
ppm
)
ed
bg
ac f ih
ed
bg
a cf
ih
ed
bg
ac f ih
ed
bg
a cf
ih
ed
bg
a cf
ih
f1 (ppm)
f2 (
ppm
)
Figure 5.4 2D-COSY spectrum of BisAS100 oligomer
163
OKO S O
O
O SO3K
KO3S
KO n
c
ab
d
e
i
dca b e f g h i
fhg
OKO S O
O
O SO3K
KO3S
KO n
c
ab
d
e
i
dca b e f g h i
fhg
Figure 5.5. Aromatic regions of a 1H NMR spectrum of BisAS100 oligomer before
end-capping reaction
Table 5.1. Characterization of Hydrophobic and Hydrophilic Telechelic Oligomers
a. Calculated from end group analysis using1H NMRb. SEC results of oligomer in salt form performed in NMP w/0.05 M LiBrc. SEC results of oligomer performed in chloroform
oligomers were coupled to phenoxide-terminated, unsulfonated poly(arylene ether
sulfone) hydrophobic oligomers via a nucleophilic aromatic substitution reaction (Figure
5.9). This series of copolymers will be referred to as BisAS100-BisAS0 multiblock
copolymers. Specific copolymers within the series are identified by the Mns of the
oligomers used in the syntheses, i.e. a copolymer with 4 kg/mol hydrophobic and
hydrophilic blocks is called 4k4k. Multiblock copolymers which had equal Mn for the
BisAS100 and BisAS0 blocks were synthesized using a 1:1 stoichiometry. The aromatic
region of a representative 1H NMR spectrum for a BisAS100-BisAS0 multiblock
copolymer is shown in Figure 5.10. The spectrum indicates successful formation of
multiblock copolymer, as peaks from both hydrophilic and hydrophobic aromatic protons
are present. Completion of the reaction was evidenced by the disappearance of peaks due
to end-group protons which would have resulted if unreacted BisAS0 oligomer remained.
167
O
CH3
CH3
O S O
O
O SO3K
KO3SCH3
CH3
O n
F
F
F
F
FF
F F
F
F
F
F
FF
F F
O O
CH3
CH3
O S O
O
O
CH3
CH3
m
x
OK
CH3
CH3
O S O
O
O
CH3
CH3
KO m
O
CH3
CH3
O S O
O
O SO3K
KO3SCH3
CH3
O n F
F
F
F
F
FF
F F
F
F
F
F
FF
F F
F 24-48 hrs @ 125 oC
K2CO3cyclohexane/DMAc4 hrs @ 110 oC
Addition of hydrophilic BisAS100 oligomer
O
CH3
CH3
O S O
O
O SO3K
KO3SCH3
CH3
O n
F
F
F
F
FF
F F
F
F
F
F
FF
F F
O O
CH3
CH3
O S O
O
O
CH3
CH3
m
x
OK
CH3
CH3
O S O
O
O
CH3
CH3
KO m
O
CH3
CH3
O S O
O
O SO3K
KO3SCH3
CH3
O n F
F
F
F
F
FF
F F
F
F
F
F
FF
F F
F 24-48 hrs @ 125 oC
K2CO3cyclohexane/DMAc4 hrs @ 110 oC
Addition of hydrophilic BisAS100 oligomer
Figure 5.9. Coupling reaction of hydrophilic and hydrophobic oligomers
O
CH3
CH3
O S O
O
O
CH3
CH3
m
x
O
CH3
CH3
O S O
O
O SO3K
KO3SCH3
CH3
O n
F
F
F
F
FF
F F
F
F
F
F
FF
F F
O
a b c d
e
f g h i
e d ca
bf,hg
i
O
CH3
CH3
O S O
O
O
CH3
CH3
m
x
O
CH3
CH3
O S O
O
O SO3K
KO3SCH3
CH3
O n
F
F
F
F
FF
F F
F
F
F
F
FF
F F
O
O
CH3
CH3
O S O
O
O
CH3
CH3
m
x
O
CH3
CH3
O S O
O
O SO3K
KO3SCH3
CH3
O n
F
F
F
F
FF
F F
F
F
F
F
FF
F F
OO
CH3
CH3
O S O
O
O SO3K
KO3SCH3
CH3
O n
F
F
F
F
FF
F F
F
F
F
F
FF
F F
O
a b c d
e
f g h i
e d ca
bf,hg
i
Figure 5.10. Aromatic region of a 1H NMR spectrum for BisAS100-BisAS0 multiblock copolymer
The highly reactive DFBP end-groups on the hydrophilic blocks facilitated the
use of low reaction temperatures (125 oC). Low reaction temperatures are one way to
prevent well known ether-ether interchange reactions33 from occurring. Carbon NMR
168
was used to monitor the possible presence of randomization in the multiblock backbone,
which would arise if ether-ether interchange had occurred. Figure 5.11 shows 13C NMR
spectra of a BisAS100-BisAS0 multiblock copolymer with block Mns of 6 kg/mol and a
BisAS32 random copolymer. The high sequenced backbone of the multiblock copolymer
results in the formation of sharp singlets; whereas, the shorter monomer sequences of the
random copolymer, results in doublets.
(a)
(b)
(a)
(b)
Figure 5.11. Portions of 13C NMR spectra for (a) BisAS100-BisAS0 multiblock and (b) BisAS32 random copolymers
5.3.4 Membrane Characterization of BisAS100-BisAS0 Multiblock Copolymers
Criteria for ideal RO membranes have been identified.34,35 They must be highly
permeable to water (high flux) while maintaining high salt rejection. Resistance to
microbiological attack and fouling by colloidal and suspended material, chemical
stability, and tolerance to chlorine and other oxidants maximizes membrane life. They
require mechanical integrity that is not affected by exposure to high pressures (up to 1200
psig) or high temperatures (25-90 oC). Easy formation of thin films or hollow fibers is
necessary to reduce operation cost.
169
Basic membrane properties for BisAS100-BisAS0 multiblock copolymers were
evaluated to decide if RO testing is warranted. Table 5.2 summarizes some basic
copolymer properties for this series of copolymers. The IEC values for the multiblock
copolymers were obtained by titration and were slightly lower than the theoretical value
of ~1.5 meq/g. However, they were fairly consistent throughout the series and the value
matches closely with that of BisAS32, which makes comparing and contrasting other data
for this series easier. Tough, transparent, flexible films were formed from this series of
copolymers. The copolymers had high I.V. values which indicate high molecular weight
polymer had been formed.
Water sorption plays an important role in RO processes. Park et at.21 showed that
water permeability increased and salt rejection decreased as water uptake increased for
random copolymers synthesized with 4,4’-biphenol. The water uptake values were
dependent on the IEC (degree of sulfonation) of the copolymers. The multiblock copolymers
discussed here had a fixed IEC value. Instead, the changes seen in water uptake were a
function of block length (Figure 5.12). This may affect the trends observed between water
sorbtion and water permeability or salt rejection. Directional swelling may also play a role in
water flux and salt rejection.
Figure 5.13 compares dimensional swelling of random and multiblock copolymers in
(x and y) and through (z) the plane. BisAS32 random copolymer and 12k12k multiblock
copolymer had nearly isotropic swelling. Whereas, 4k4k through 10k10k copolymers had
greater swelling in the z direction. The way the water distributes itself in the copolymer may
affect how salt is rejected.
170
Table 5.2. Characterization of BisAS100-BisAS0 Multiblock Copolymers
a. Calculated from Titrationb. Intrinsic viscosity SEC results of polymer in salt form
performed in NMP w/0.05 M LiBrc. [(mass wet – mass dry)/(mass dry)] x 100
IEC (meq/g)
Copolymer Exp.a
4k4k 1.2 1.82 236k6k 1.3 1.31 348k8k 1.4 1.65 41
10k10k 1.2 1.77 5112k12k 1.2 1.99 59
BisAS32 random
1.3 1.35 17
Water
Uptakec IVb
(dL/g)
R2 = 0.9925
0
10
20
30
40
50
60
70
2 4 6 8 10 12 14
Block Length (kg/mol)
Wat
er U
ptak
e (%
)
Figure 5.12. Water uptake (wt%) as a function of block length for BisAS100-BisAS0 multiblock copolymers
171
0
5
10
15
20
25
30
35
BisAS32 1.3 meq/g
4k4k 1.2 meq/g
6k6k 1.3 meq/g
8k8k 1.4 meq/g
10k10k 1.2 meq/g
12k12k 1.2 meq/g
Sw
ellin
g (%
)
x y z
z
X
y
0
5
10
15
20
25
30
35
BisAS32 1.3 meq/g
4k4k 1.2 meq/g
6k6k 1.3 meq/g
8k8k 1.4 meq/g
10k10k 1.2 meq/g
12k12k 1.2 meq/g
Sw
ellin
g (%
)
x y z
z
X
yz
X
y
Figure 5.13. Comparison of dimensional swelling data for random and multiblock
copolymers
Figure 5.14 compares the nanostructures of 8k8k and 12k12k multiblock
copolymers. Nanophase separation between the hydrophilic (black) and hydrophobic
(grey) domains was evident in both copolymers. The hydrophilic and hydrophobic
pathways that formed in the 12k12k copolymer appeared to be co-continuous. The
hydrophobic pathways in the 8k8k copolymer were highly connected, whereas, the
hydrophilic pathways were shorter ranged. In some places complete segregation of
hydrophilic domain was observed. Increased block length of the copolymers, results in
better hydrophilic channel formation.
172
AKDA
KD AKD
AKDA
KD
Figure 5.14. TEM images of 8k8k and 12k12k BisAS100-BisAS0 multiblock copolymers. (The bright white spot in the middle of the images is a camera artifact.)
The glass transition temperature of the copolymers was determined using DMA.
BisAS100-BisAS0 10k10k was chosen as a representative plot of the multiblock
copolymers and is compared to BisAS32 random copolymer in Figure 5.15. A distinct
transition was observed between 200 and 210 oC from the DMA for all of the block
copolymers, which was attributed to chain relaxation in hydrophobic block. A plateau
was observed after the initial decrease in the storage modulus. The presence of the
sulfonate groups in the hydrophilic blocks led to ionic aggregation, which resulted in a
higher thermal transition for the hydrophilic block as compared to the hydrophobic block.
The exact temperature of the transition of the hydrophilic block could not be obtained
because degradation of the block copolymers occurs at temperatures lower than the
transition temperature, as is shown in the TGA plot (Figure 5.17). Since the random
copolymer had much smaller domains of the hydrophobic and hydrophilic regions, a
single thermal transition is observed in the DMA at 275 oC.
173
0 50 100 150 200 250 300 350102
103
104
10-3
10-2
10-1
100
Sto
rage
Mod
ulus
[MP
a]
Temperature [oC]
Tan δ
Figure 5.15. DMA plot of BisAS100-BisAS0 10k10k multiblock copolymer (black) and BisAS32 random copolymer (grey). Solid lines represent the storage modulus
and dashed lines represent tan δ of the copolymers.
DSC was also used to observe the thermal transitions in the random and
multiblock copolymers, and thermograms are shown in Figure 5.16. Multiblock
copolymers with the longest block lengths, 10k10k and 12k12k, exhibited two Tgs. The
Tg at 190 oC is attributed to the hydrophobic block and the Tg at 270 oC was attributed to
the hydrophilic block. As the Mn of block decreases, the presence of two Tgs was harder
to discern in the thermograms. The Tg of the random copolymer, BisAS32, was hard to
determine using the DSC.
174
50 100 150 200 250 300
Temperature ( oC)
Hea
t Flo
w (
Exo
dow
n)
6k6k8k8k10k10k12k12kBisAS32
Figure 5.16. Thermograms for BisAS100-BisAS0 multiblock copolymers and BisAS32 random copolymer
The results of the TGA are shown in Figure 5.17. The TGA was conducted in an
air atmosphere to assess the oxidative stability of the copolymers. It can be seen that all
of the block copolymers behave similarly and are oxidatively stable up to 375 oC. Two
distinct weight loss regions are also observed, one at 275 oC and the second at 375 oC.
The initial weight loss at 275 oC is attributed to the loss of the sulfonate groups on the
hydrophilic blocks. The main chain degradation leads to the weight loss at 375 oC.
These temperatures were well above temperatures use in RO processes.
175
0
10
20
30
40
50
60
70
80
90
100
0 100 200 300 400 500 600
Temperature ( oC)
Wei
ght (
%)
4k4k
6k6k
8k8k
10k10k
12k12k
BisAS32
Figure 5.17. Thermal gravimetric analysis plot of BisAS32 random and BisAS100-
BisAS0 multiblock copolymers
The tensile properties of the random and multiblock copolymers are summarized
in Table 5.3 and stress-strain plots are shown in Figure 5.18. All of the membranes
synthesized had a tensile strength near 50 MPa. The multiblock copolymers exhibited a
slightly higher tensile strength than the BisAS32 random copolymer. However, the
elongation of the multiblock copolymers was less than the BisAS32 random copolymer.
Despite the differences between the random and multiblock copolymers, all of the
Figure 5.18. Stress-strain plots for BisAS copolymers
It is advantageous for copolymers being used in RO applications to have chlorine
resistance. Chlorine is used as a disinfectant and a bactericide throughout the water
177
treatment process. Currently, sea water is chlorinated to remove algae in order to prevent
RO membranes from fouling.104 The water is then dechlorinated because polyamide
membranes are susceptible to chlorine degradation. The water requires re-chlorination to
kill bacteria so it can be used as drinking water. The development of a membrane which
would not require the dechlorination and rechlorination steps could save money by
decreasing time and costly pre- and post-treatment processes.
Chlorine exposure tests were conducted on this series of membranes to ensure
chlorine tolerance before RO testing is commenced. Membranes were soaked in a 500
ppm solution of NaOCl in water for 24 h. The pH of the solution was adjusted to 4.5-5.0
with HCl. Proton NMR spectra were obtained before and after exposure to the chlorine.
Proton NMR spectra for a sample multiblock and random copolymer are shown in Figure
5.19. No changes were observed after exposure to chlorine indicating acceptable chlorine
tolerance.
(c)
(d)
(a)
(b)
(c)
(d)
(a)
(b)
(a)
(b)
Figure 5.19. 1H NMR spectra comparing copolymers before and after exposure to
500 ppm NaOCl for 24 h (pH of 4.5-5.0) (BisAS100-BisAS0 8k8k multiblock copolymer (a) before and (b) after exposure, BisAS32 random copolymer (c) before
and (d) after exposure)
178
5.4 Conclusions
A series of hydrophilic-hydrophobic poly(arylene ether sulfone) multiblock
copolymers which utilize Bis-A as the bisphenol were synthesized. The 100%
disulfonated hydrophilic oligomers were end-capped with DFBP to facilitate coupling
with phenoxide-terminated hydrophobic oligomers at low temperatures. Copolymers
with equal hydrophilic and hydrophobic block lengths were achieved, ranging from 4k4k
to 12k12k. The copolymers were cast into tough, ductile films. Water sorption was
measured gravimetrically and dimensionally. Both showed that water uptake increases
with increasing block length, despite the copolymers having similar IECs. This was due
to the formation of longer co-continuous hydrophilic pathways that develop within the
copolymer as block length increased. TEM was used to confirm that a nanophase
separated morphology resulted for multiblock copolymers with 8k8k and 12k12k block
lengths. Static exposure to chlorine resulted in no degradation, which indicated these
membranes have high chlorine tolerance making them possible candidates for
desalinating and purifying water. The water would not require the dechlorination steps
used in current desalination units. These copolymers have adequate thermal and
mechanical stability as evidenced by TGA and tensile testing, respectively, to justify
further RO testing. Further characterization is underway to determine if these
membranes are suitable for RO applications.
Acknowledgement. The authors would like to acknowledge Dow FilmTec for
funding.
179
References
1 Service, R.F. Desalination Freshens Up Science 2006, 313, 1088-1090. 2 Gleick, P.H.; Cooley, H.; Wolff, G.H., With a Grain of Salt: An Update on Seawater Desalination. In The World's Water 2006-2007: The Biennial Report on Freshwater Resources, Island Press: Washington, D.C., 2006. 3 Petersen, R.J. Composite reverse osmosis and nanofiltration membranes. J. of Membr. Sci. 1993, 83(1), 81-150. 4 Avlonitis, S.; Hanbury, W.T.; Hodgkiess, T. Chlorine Degradation of Aromatic Polyamides Desalination 1992, 85, 321-334. 5 Light, W.G.; Chu, H.C.; Tran, C.N. Reverse Osmosis TFC Magnum Elements for Chlorinated/Dechlorinated Feedwater Processing. Desalination 1987, 64, 411-421. 6 Allegrezza, Jr., A.E.; Parekh, B.S.; Parise, P.L.; Swiniarski, E.J.; White, J.L. Chlorine Resistant Polysulfone Reverse Osmosis Modules. Desalination, 1987, 64, 285-304. 7 Parise, P.L.; Allegrezza Jr.; A.E.; Parekh, B.S. Super hi-flux CP® chlorine-resistant reverse osmosis modules. Ultrapure Water, 1987, 4(7), 54-65. 8 Lloyd, D.R.; Gerlowski, L.E.; Sunderland, C.D.; Wightman, J.P.; McGrath, J.E.; Iqbal, M.; Kang, K. Poly(aryl ether) Membranes for Reverse Osmosis. In Synthetic Membranes; Turbank, F.T., Eds.; ACS Symposium Series No. 153, American Chemical Society:Washington, D.C., 1981; 1, 327-350. 9 Johnson, B.C.; Yilgor, I.; Tran, C.; Iqbal, M. Whightman, J.P.; Lloyd, D.R.; McGrath, J.E. Synthesis and Characterization of Sulfonated Poly(arylene ether sulfone)s. J. Polym. Sci.: Polym. Chem. Ed. 1984, 22, 721-737. 10 Drzewinski, M.; Macknight, W. J. Structure and properties of sulfonated polysulfone ionomers J. Appl. Polym. Sci. 1985, 30, 4753 – 4770. 11 Quentin, J.P. Sulfonated Polyarylether Sulfones, U.S. 3,709,841, Rhone-Poulenc, January 9, 1973. 12 Hickner, M.A.; Ghassemi, H.; Kim. Y.S.; Einsla, B.R.; McGrath, J.E. Alternative Polymer Systems for Proton Exchange Membranes (PEMs). Chem. Rev. 2004, 104, 4587-4612. 13 Wang, F.; Hickner, M.; Ji, Q.; Harrison, W.; Mecham, J.; Zawodzinski, T.A.; McGrath, J.E. Synthesis of Highly Sulfonated Poly(arylene ether sulfone) Random (Statistical) Copolymers Via Direct Polymerization. Macromol. Symp. 2001, 175, 387-395.
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14 Wang, F.; Hickner, M.; Kim, Y.S.; Zawodzinski, T.A.; McGrath, J.E. Direct polymerization of sulfonated poly(arylene ether sulfone) random (statistical) copolymers: candidates for new proton exchange membranes. J. Membr. Sci. 2002, 197, 231-242. 15 Harrison, W.L.; Wang, F.; Mecham, J.B.; Bhanu, V.A.; Hill, M.; Kim, Y.S.; McGrath, J.E. Influence of the Bisphenol Structure on the Direct Synthesis of Sulfonated Poly(arylene ether) Copolymers. I. J. Polym. Sci: Part A: Polym. Chem. 2003, 41, 2264-2276. 16 Sumner, M.J.; Harrison, W.L.; Weyers, R.M.; Kim, Y.S.; McGrath, J.E.; Riffle, J.S.; Brink, A.; Brink, M.H. Novel proton conducting sulfonated poly(arylene ether) copolymers containing aromatic nitriles. J. Membr. Sci. 2004, 239, 199-211. 17 Harrison, W.L.; Hickner, M.A.; Kim, Y.S.; McGrath, J.E. Poly(arylene ether sulfone) copolymers and related systems from disulfonated monomer building blocks: synthesis, characterization, and performance - a topical review. Fuel Cells 2005, 5(2), 201-212. 18 Park, H.B.; Freeman, B.D.; Zhang, Z.B.; Sankir, M.; McGrath, J.E. Highly Chlorine-Tolerant Polymers for Desalination. Angewandte Chemie 2008, 47, 6019-6024. 19 Park, H.B.; Freeman, B.D.; Zhang, Z-B.; Fan, G-Y.; Sankir, M.; McGrath, J.E. Water and Salt Transport Behavior through Hydrophilic-Hydrophobic Copolymer Membranes and Their Relations to Reverse Osmosis Membrane Performance. ACS PMSE Preprints 2006, 95, 889-891. 20 Zhang, Z-B.; Fan, G-Y.; Sankir, M.; Park, H.B.; Freeman, B.D.; McGrath, J.E. Synthesis of Di-Sulfonated Poly(arylene ether sulfone) Random Copolymers as Novel Candidates for Chlorine-resistant Reverse Osmosis Membranes. ACS PMSE Preprints 2006, 95, 887-888. 21 Park, H.B.; Freeman, B.D.; McGrath, J.E. Hydrophilic-hydrophobic Nanostructured Polymeric Materials for Desalination. ACS PMSE Preprints 2009, 100, 286-289. 22 Paul, M.; Park, H. B.; Freeman, B. D.; Roy, A.; McGrath, J. E.; Riffle, J. S. Synthesis and crosslinking of partially disulfonated poly(arylene ether sulfone) random copolymers as candidates for chlorine resistant reverse osmosis membranes. Polymer 2008, 49, 2243-2252. 23 Roy, Abhishek; Lee, Hae-Seung; McGrath, James E. Hydrophilic–hydrophobic multiblock copolymers based on poly(arylene ether sulfone)s as novel proton exchange membranes – Part B Polymer 2008, 49, 5037-5044. 24 Lee, H.-S.; Roy, A.; Lane, O.; Dunn, S.; McGrath, J.E. Hydrophilic-hydrophobic multiblock copolymers based on poly(arylene ether sulfone) via low-temperature coupling reactions for proton exchange membrane fuel cells. Polymer 2008, 49, 715-723.
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25 Noshay, Allen; McGrath, James E. Block Copolymers: Overview and Critical Survey, Academic Press: New York: 1977. 26 Roy, A.; Hickner, M.A.; Yu, X.; Li. Y.; Glass, T.E.; McGrath, J.E. Influence of Chemical Composition and Sequence Length on the Transport Properties of Proton Exchange Membranes. J. Polym. Sci. Part B, 2006, 44, 2226-2239. 27 Sankir, M.; Bhanu, V.A.; Harrison, W.L.; Ghassemi, H.; Wiles, K.B.; Glass, T.E.; Brink, A.E.; Brink, M.H.; McGrath, J.E. Synthesis and Characterization of 3,3’-Disulfonated-4,4’-dichlorodiphenyl Sulfone (SDCDPS) Monomer for Proton Exchange Membranes (PEM) in Fuel Cell Applications J. Appl. Polym. Sci. 2006, 100, 4595-4602. 28 Li, Y.; VanHouten, R.; Brink, A.; McGrath, J.E. Purity Characterization of 3,3’-Disulfonated-4,4’-Dichlorodiphenyl Sulfone (SDCDPS) Monomer by UV-visible Spectroscopy. Polymer, 2008, 49, 3014-3019. 29 Ueda, M.; Toyota, H.; Ouchi, T.; Sugiyama, J.I.; Yonetake, K.; Masuko, T.; Teramoto, T. Synthesis and Characterization of Aromatic Poly(ether Sulfone)s Containing Pendant Sodium Sulfonate Groups. J. Polym. Sci.: Part A: Polym. Chem. 1993, 31, 853-858. 30 Yang, J.; Li, Y.; Roy, A.; McGrath J.E. Viscometric behavior of disulfonated poly(arylene ether sulfone) random copolymers used for proton exchange membranes. Polymer, 2008, 49(24), 5300-5306. 31 Croasmun, W. R., Carlson, R. M. K., Eds. Two-dimensional NMR spectroscopy : applications for chemists and biochemists; VCH: New York, 1987. 32 Lee, H.-S.; Roy, A.; Lane, O.; Dunn, S.; McGrath, J.E. Hydrophilic-hydrophobic multiblock copolymers based on poly(arylene ether sulfone) via low-temperature coupling reactions for proton exchange membrane fuel cells. Polymer 2008, 49, 715-723. 33 Newton, A. B.; Rose, J.B. Relative reactivities of the functional groups involved in synthesis of poly(phenylene ether sulphones) from halogenated derivatives of diphenyl sulphone. Polymer, 1972, 13(10), 465-474. 34 Amjad, Z., Ed. Reverse Osmosis: Membrane Technology, Water Chemistry, and Industrial Applications; Van Nostrand Reinhold: New York, 1993. 35 Lonsdale, H. K., Podall, H. E., Ed., Reverse Osmosis Membrane Research; Plenum Press: NewYork-London, 1972.
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6 Overall Conclusions
A segmented synthesis technique was used to produce ionomers for use as proton
exchange membranes for fuel cell applications. In previous research, multiblock
copolymers were produced by separately synthesizing the hydrophobic and hydrophilic
oligomers with different telechelic functionality, followed by a coupling reaction between
the two oligomers. While the membranes formed from previous copolymers exhibited
good properties, the synthesis was time consuming. In the segmented approach, a
phenoxide-terminated hydrophilic block was first synthesized. The dihalide and
bisphenol comonomers used to produce the hydrophobic block were then reacted with the
hydrophilic oligomers so the coupling reaction proceeded in tandem with the
hydrophobic block formation. By using highly reactive decafluorobiphenyl as the
dihalide, low reaction temperatures (< 105 oC) could be used, which reduced ether-ether
interchange reactions. This helped ensure the formation of a blocky hydrophobic-
hydrophilic structure throughout the copolymer backbone. This technique was proven
successful by comparing the properties of segmented BisSF-BPS100 copolymers with
BisSF-BPS100 multiblock copolymers having the same block length compositions. Both
synthetic techniques produced copolymers with similar properties.
The segmented approach to synthesizing ionomers was then extended to PhF-
BPS100 and BisSF-PhS100 copolymers. These systems of ionomers produced ductile
membranes that were able to be characterized for use in fuel cell applications. The use of
the segmented technique to produce three different systems of ionomers demonstrated
that it is a suitable technique to produce copolymers with a blocky structure.
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While the segmented copolymers produced in this study did not yield membranes
with better conductivity than Nafion® over the entire RH range, the research produced a
better understanding of how the bisphenol affects copolymer properties. Segmented
copolymers containing phenolphthalein as the bisphenol yielded copolymers with greater
tensile strength due to the enhanced rigidity of the phenolphthalein as compared to
Bisphenol-S or 4,4’-biphenol. The research also gave greater insight into the importance
of the hydrophilic and hydrophobic block length on the membrane properties. Block
length was proven to have a greater impact on the conductivity and water uptake than the
ion exchange capacity of the copolymers.
In this research, multiblock copolymers were also produced for potential use as
reverse osmosis applications. Bisphenol-A was chosen as the bisphenol in the multiblock
synthesis due to the monomer cost. Phenoxide-terminated hydrophobic and hydrophilic
oligomers were initially synthesized. Decafluorobiphenyl was used to end-cap the
hydrophilic oligomers, converting the phenoxide-terminated copolymer to fluorine-
terminated copolymer. This functionality facilitated the use of low temperatures (< 125
oC) for the subsequent coupling reaction with the phenoxide-terminated hydrophobic
oligomer. The system of multiblock copolymers afforded ductile membranes. The
membranes were shown to be resistant to chlorine degradation, which can play an
important role in reverse osmosis applications and the future economics of water
desalination.
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7 Future Research
The next step in assessing the BisAS multiblock copolymers as RO membranes is
to evaluate the salt rejection and water permeability. This is currently being conducted at
University Texas-Austin in conjunction with Prof. Freeman. Based on the results
obtained from these studies several changes can be made to the copolymer to tailor the
properties.
In the current study, copolymers with an IEC of ~1.3 meq/g were synthesized.
Salt rejection and water permeability can be altered by changing the IEC of the
copolymer. This could be done by synthesizing copolymers with unequal hydrophobic
and hydrophilic block lengths. Converting the copolymers into acid form may also
change the membrane properties. It has been shown that the boiling procedure that is
used to convert membranes from salt to acid form alters the morphology of the
copolymers.1 This morphology change could alter the salt rejection and water
permeability of the copolymer even if the backbone chemistry was maintained.
Finally, if the series of copolymers were converted to acid from, it could be tested
for fuel cell applications as well.
185
References
1 Kim, Y. S.; Wang, F.; Hickner, M.; McCartney, S.; Hong, Y. T.; Harrison, W.; Zawodzinski, T. A.; McGrath, J. E. Effect of Acidification Treatment and Morphological Stability of Sulfonate Poly(arylene ether sulfone) Copolymer Proton Exchange Membranes for Fuel Cell Use Above 100 °C. J. Polym. Sci.: Part B: Polym. Phys. 2003, 41, 2816-2828.