SYNTHESIS POLYETHERSULFONE-BASED AMPHIPHILIC BLOCK COPOLYMERS & DEVELOPMENT OF SINGLE-ION CONDUCTORS FOR LITHIUM ION BATTERIES By Hui Zhao A DISSERTATION Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Chemistry 2012
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SYNTHESIS POLYETHERSULFONE-BASED AMPHIPHILIC BLOCK COPOLYMERS & DEVELOPMENT OF SINGLE-ION CONDUCTORS FOR
LITHIUM ION BATTERIES
By
Hui Zhao
A DISSERTATION
Submitted to Michigan State University
in partial fulfillment of the requirements for the degree of
DOCTOR OF PHILOSOPHY
Chemistry
2012
ABSTRACT
SYNTHESIS POLYETHERSULFONE-BASED AMPHIPHILIC BLOCK COPOLYMERS & DEVELOPMENT OF SINGLE-ION CONDUCTORS FOR
LITHIUM ION BATTERIES
By
Hui Zhao
Polyethersulfone (PES) membranes often foul easily because of their
hydrophobicity, and addition of amphiphilic PES block copolymers to
membrane formulations may help overcome this problem. This dissertation
explores the synthesis and aggregation properties of relevant amphiphilic ABA
block copolymers, where PES is the hydrophobic B block and poly(2-
hydroxyethyl methacrylate) or poly(2-hydroxypropyl methacrylate) are the
hydrophilic A blocks. 1H nuclear magnetic resonance (NMR) spectroscopy,
Fourier transform infrared spectroscopy (FT-IR) and thermogravimetric
analysis (TGA) confirm the block copolymer synthesis, and 1H NMR spectra
and TGA also provide consistent data on copolymer compositions.
Aggregation behavior of the copolymers in solvent/non-solvent mixture is
studied using NMR and dynamic light scattering (DLS).
Lithium ion batteries are now ubiquitous, but concentration polarization is
still a problem in the currently used battery electrolytes, especially in
high-current applications. Immobilizing anions and having lithium cations
contribute to most of the ionic conductivity is a good solution to address this
problem. This work aims to create nanoparticle-containing electrolytes using
silica nanoparticles modified with polyanions that have Li+ as the counterion.
Anion mobility is restricted by the polyanion polymer backbones, which is
further immobilized by the nanoparticles. The polyelectrolyte-grafted
nanoparticles were synthesized by surface atom transfer radical
polymerization (ATRP) of monomers from initiator-grafted silica nanoparticles.
To prepare a lithium-ion conductor, the polyelectrolyte-grafted nanoparticles
were blended with polyethyleneglycol (PEG) oligomer. Because the anions are
immobile, lithium is the only ion that conducts current. AC impedance shows
that the best conductivity is from a Bis(trifluoromethanesulfonyl)imide (TFSI)
analogue monomer around 10-6
S/cm, which is in the same range as a
monolayer-grafted silica nanoparticle system using similar TFSI analogue
structure. A proposed model shows that the multilayer-grafted nanoparticles
only have outermost layer of lithium cations accessible to the solution,
because of the low solubility of polyelectrolytes in the PEG solvent.
Direct modification of PEG via alkyne-azide or thiol-ene click chemistry as
single lithium ion conductor. To make sure 1,2,3-triazole or sulfur structure
from click chemistry is not impeding lithium transport, we synthesize
1,2,3-triazole and sulfur containing PEGs via step growth polymerization.
Conductivity measurement of lithium perchlorate with triazole containing PEG
or sulfur containing PEG shows similar data as the pure PEG, which proves
that click chemistry could be applied in the development of single-ion
conductors for Lithium Ion Batteries.
Copyright by HUI ZHAO
2012
v
ACKNOWLEDGEMENTS
Dr. Gregory Baker – for his patience, encouragement, advice and intellectual
generosity
Dr. Merlin Bruening – for much appreciated advice and discussions on my
research project
Dr. William Wulff, Dr. Milton Smith and Dr. Babak Borhan– for being my
committee member
Many people, past and present, in the lab, Qin Yuan, Sampa Saha, Tomas
Many people, in the department, in particular, Daniel Holms, Kathryn Severin
for their help on the instruments.
Finally, I would like to thank my family for their love and support.
vi
TABLE OF CONTENTS
LIST OF TABLES ............................................................................................ viii
LIST OF FIGURES ............................................................................................ x
LIST OF SCHEMES ....................................................................................... xiv
Chapter 1 Introduction ....................................................................................... 1 Part I: Synthesis of Polyethersulfone (PES)-Based Amphiphilic Block Copolymers ..................................................................................................... 1 Part II: Synthesis of Comb-Polyethyleneoxide (PEO) via Click Chemistry- New polymers for Possible Lithium Ion Conductors ....................................... 3 References ..................................................................................................... 8
Introduction ................................................................................................... 10 Polysulfone Materials and Their Application as Water Treatment Membranes ............................................................................................... 10 Block Copolymers ..................................................................................... 13 Polysulfone-Based Amphiphilic Copolymers ............................................ 17 Self-assembly of Block Copolymers ......................................................... 22 Block Copolymers as Phase Inversion Membrane Materials ................... 24 Unique Aspects of Self-assembly of Polysulfone-Based Block Copolymers .................................................................................................................. 27
Results and Discussion ................................................................................ 29 Purification of Hydroxypropyl Methacrylate (HPMA) Isomers .................. 30 Synthesis of PES with Hydroxyl End Groups ........................................... 33 Synthesis of a PES Macroinitiator and Use of a Model Compound to Explore the ATRP Catalytic System ......................................................... 36 Polymerization from a PES Macroinitiator ................................................ 42 GPC Analysis of HEMAn-PESm-HEMAn and HPMAn-PESm-HPMAn Block Copolymers ..................................................................................... 47 Infrared Spectra of the Block Copolymers ............................................... 53 TGA of the Block Copolymers .................................................................. 57 Critical Water Content (CWC) Values of PES and PES-based Block Copolymers ............................................................................................... 63 Aggregation of Block Copolymers in Dilute Solutions-NMR and DLS Studies ...................................................................................................... 72
Chapter 3 Use of the Nanoparticles and Click Chemistry in the Development of Single-ion Conductors for Lithium Ion Batteries ............................................ 102
Introduction-Ion Conduction in Lithium Ion Batteries ................................. 102 Results and Discussion .............................................................................. 106
Single-ion Conductors Containing Nanoparticles with Immobilized Anions ................................................................................................................ 106 Single-ion Conductors Prepared Using Nanoparticles Modified by Grafting of Polyanions .......................................................................................... 109 Towards Click Chemistry for Synthesizing Single-ion Conductors with a High Density of Lithium Ion PEO ............................................................ 113
Table 2.1. Different conditions for synthesis of PES and the molecular weights and PDI values of the resulting polymer. ......................................................... 33
Table 2.2. Block Copolymers with their Molecular Weights and PDI Values. ......
Table 2.3. PDIs of various copolymers as determined from GPC data or calculated using equation (2) ........................................................................................... 52
Table 2.4. PolyHEMA Content in Copolymer Samples as Calculated from NMR Spectra and TGA under nitrogen ..................................................................... 60
Table 2.5. PolyHPMA Content in Copolymer Samples as calculated from NMR spectra and TGA. ............................................................................................. 63
Table 2.6. Commercial Polyethersulfones and their Molecular Weights, PDI Values and Terminal Groups. ........................................................................... 64
Table 2.7. Solubility Parameters of Several Solvents and Polymers at 25 oC. ......................................................................................................................... 68
Table 2.8. Evolution of the proton NMR signals from HEMA22-PES34-HEMA22 with increasing of D2O content in the DMSO-d6 solvent. ............................................................................................................. 75
Table 2.9. DLS particle sizes and particle volume percentages for aggregates of HEMA22-PES34-HEMA22 formed in NMP/water mixtures. The mixtures contained 1 mg/mL HEMA22-PES34-HEMA22. .............................................. 77
Table 2.10. DLS particle sizes and particle volume percentages for aggregates of HEMA22-PES34-HEMA22 formed in NMP/water mixtures. The mixtures contained 10 mg/mL HEMA22-PES34-HEMA22 ............................................ 79
ix
Table 2.11. DLS particle sizes and particle volume percentages for aggregates of HEMA22-PES34-HEMA22 formed in NMP/water mixtures. The mixtures contained 30 mg/mL HEMA22-PES34-HEMA22. ............................................ 80
Table 2.12. Polystyrene standards used to calibrate the results of GPC in DMF. ......................................................................................................................... 84
Table 3.1. Lithium transference numbers for several lithium salts in battery solvents. ......................................................................................................... 105
Table 3.2. Particle weight percentages and O/Li for electrolytes prepared from Si-C5NTfLi dispersed in PEGDME-500. ........................................................ 108
Table 3.3. Particle weight percentages and O/Li ratios for electrolytes prepared from Si-TfMALi dispersed in PEGDME-500. ................................................. 110
x
LIST OF FIGURES
Figure 2.1. Equilibrium morphologies in AB diblock copolymers.. ................... 24
Figure 2.2. Phase inversion membranes made from PSf (upper left: SEM top view, upper right: edge view, NMP solvent), and PES (bottom: SEM edge view DMAc solvent). ................................................................................................. 26
Figure 2.3. SEM images of membranes prepared by phase inversion of poly(styrene)-co-poly(4-vinylpyridine). Peinemann’s work. Edge view (left), top view (right). Scale bars correspond to 500 nm.. .............................................. 27
Figure 2.4. Proton NMR 500 MHz spectra of an HPMA isomer mixture (bottom) and purified 2-hydroxypropyl methacrylate (top) in deuterated chloroform.. ... 32
Figure 2.5. ProtonNMR 500 HMz spectra of bisphenol sulfone (bottom) and BisphenolS-I (top) in deuterated DMSO... ..................................................... 37
Figure 2.6. ATRP kinetic plot for polymerization of HEMA using BisphenolS-I as an initiator and CuBr/PMDETA as the catalyst in DMF, the initial monomer concentration was 2 M... .................................................................................. 38
Figure 2.7. ATRP kinetic plot for polymerization of HEMA using ethyl bromoisobutyrate as an initiator and CuCl/CuCl2/PMDETA as the catalyst in NMP, the initial monomer concentration was 2 M... ........................................ 40
Figure 2.8. ATRP kinetic plot for polymerization of HEMA using ethyl BisphenolS-I as the initiator and CuCl/CuCl2/PMDETA as the catalyst in NMP, the initial monomer concentration was 2 M... .................................................. 41
Figure 2.9. ATRP kinetic plot for polymerization of HEMA using a PES macroinitiator and CuCl/CuCl2/PMDETA as the catalyst in NMP, the initial monomer concentration was 1.3 M... .............................................................. 42
Figure 2.10. Proton NMR 500 MHz spectra of (a) NMP, (b) HEMA26-PES42- HEMA26 and (c) macroinitiator in DMSO-d6... ............................................... 44
Figure 2.11. Gel-permeation chromatograms of (a) PES51 and (b) the copolymer HEMA9-PES51-HEMA9... .............................................................. 47
xi
Figure 2.12. Gel-permeation chromatograms of (a) PES42 (b) copolymer HEMA13-PES42-HEMA13 and (c) HEMA26-PES42-HEMA26... ................... 49
Figure 2.13. Gel-permeation chromatograms of (a) PES34 and (b) HEMA22- PES34-HEMA22... ........................................................................................... 50
Figure 2.14. An ABA block copolymer with monodisperse A block and polydisperse (PDI=2.0) B blocks... .................................................................. 51
Figure 2.15. Gel-permeation chromatograms of (a) PES42, (b) HPMA12- PES42-HPMA12 and (c) HPMA26-PES42-HPMA26... ................................... 53
Figure 2.16. IR spectra of (a) PES, (b) polyHEMA and (c) HEMA22-PES34- HEMA22... ........................................................................................................ 54
Figure 2.17. IR spectra of (a) HEMA9-PES51-HEMA9, (b) HEMA13-PES42- HEMA13, (c) HEMA26-PES42-HEMA26 and (d) HEMA22- PES34-HEMA22....
Figure 2.18. IR Spectra of (a) PES, (b) polyHPMA and (c) HPMA12-PES42- HPMA12... ........................................................................................................ 56
Figure 2.19. IR spectra of (a)HPMA12-PES42-HPMA12 and (b) HPMA26- PES42-HPMA26... ........................................................................................... 57
Figure 2.20. TGA data for PES and several polyHEMA-co-PES-co-polyHEMA samples heated under air (samples were held at 120 oC until the weight was constant (~ 3 hours) before heating at 10 oC/min) (a) PES, (b) HEMA9-PES51- HEMA9, (c) HEMA13-PES42-HEMA13, (d) HEMA26-PES42-HEMA26 and (e) HEMA22-PES34-HEMA22... ........................................................................... 58
Figure 2.21. TGA data for PES, polyHEMA and polyHEMA-co-PES-co- polyHEMA samples heated under nitrogen (samples were held at 120 oC until weight was constant (~ 3 hours) before heating at 10 oC/min). (a) PES, (b) polyHEMA, (c) HEMA9-PES42-HEMA9, (d) HEMA13-PES42-HEMA13, (e) HEMA26-PES42-HEMA26 and (f) HEMA22-PES34-HEMA22... .................... 59
xii
Figure 2.22. TGA data for PES and polyHPMA-co-PES-co-polyHPMA samples heated under air (samples were held at 120 oC until the weight was constant (~ 3 hours) before heating at 10 oC/min) (a) PES, (b) HPMA12-PES42- HPMA12 and (c) HPMA26-PES42-HPMA26... ............................................... 61
Figure 2.23. TGA data for PES and polyHPMA-co-PES-co-polyHPMA samples heated under nitrogen (samples were held at 120 oC until weight was constant (~ 3 hours) before heating at 10 oC/min) (a) PES, (b) polyHPMA, (c) HPMA12- PES42-HPMA12 and (d) HPMA26-PES42-HPMA26... ................................... 62
Figure 2.24. Room-temperature critical water content (CWC) values of different PES materials in four solvents (NMP, DMF, DMSO, DMAc) (a) Ultrason 2020 P from BASF, (b) Ultrason 6020 P from BASF, (c) Veradel 3600 RP from Solvay, (d) Veradel 3000 RP from Solvay and (e) PES synthesized at MSU Mn=10,000, PDI=2.0. (Each data point is an average from three independent samples, and the data points often obscure the error bars.).. .......... .................................................................................................................................................... 65
Figure 2.25. Room-temperature CWC values for several PES samples in NMP. (1) Ultrason 6020P, (2) Veradel 3000RP, (3) Ultrason 2020P, (4) Veradel 3600RP and (5) home-made PES. (Each data point is an average from three independent samples, and the data points often obscure the error bars.).. ......... .................................................................................................................................................... 70
Figure 2.26. Room-temperature CWC values in NMP for (a) PES, (b) HPMA26 -PES42-HPMA26 and (c) HEMA22-PES34-HEMA22. (Each data point is an average from three independent samples, and the data points often obscure the error bars.).. ............................................................................................... 71
Figure 2.27. Proton NMR 500 MHz Spectra of HEMA22-PES34-HEMA22 in DMSO-d6/D2O co-solvents with varying amounts of water... ......................... 73
Figure 2.28. DLS size distributions for HEMA22-PES34-HEMA22 (1 mg/mL at 25 oC) dissolved in NMP and NMP/water co-solvents with different volume ratios... ............................................................................................................. 76
Figure 2.29. DLS size distributions for HEMA22-PES34-HEMA22 (10 mg/mL at 25 oC) dissolved in NMP and NMP/water co-solvents with different volume ratios... ............................................................................................................. 78
xiii
Figure 2.30. DLS size distributions for HEMA22-PES34-HEMA22 (30 mg/mL at 25 oC) dissolved in NMP and NMP/water co-solvents with different volume ratios... ............................................................................................................. 80
Figure 3.1. Schematic diagram of a lithium ion battery containing a metal oxide cathode and a graphite anode. The figure also shows redox reaction during discharge... .................................................................................................... 103
Figure 3.2. Concentration polarization during discharge of a lithium ion battery... ......................................................................................................... 104
Figure 3.3. Temperature-dependent conductivity of electrolytes containing different fractions of Si-C5NTfLi dispersed in PEGDE-500. These results were obtained by Fadi Asfour, and I repeated some of the measurements... ....................................................................................................................... 108
Figure 3.4. Temperature-dependent conductivity of electrolytes containing different fractions of Si-TfMALi dispersed in PEGDE-500. The various fractions of particles (see Table 3.3) lead to the different O/Li ratios shown in the figure... ....................................................................................................................... 110
Figure 3.5. Temperature-dependent conductivity for (a) Si-C5NTfLi at O/Li 425 and (b) Si-TfMALi at O/Li 32, both samples contain ~19 wt% modified particles... ....................................................................................................... 111
Figure 3.6. Kinetics of step-growth polymerization between dipropargyl and diazido tetraethylene glycol... ........................................................................ 122
Figure 3.7. Conductivities of mixtures of LiClO4 with pure PEO (black squares) and triazole-containing PEO (red circles) at different ratios of PEO to LiClO4. The O/Li ratios in the mixture were determined from the masses of LiClO4 and PEO added, and these ratios only include the O atoms from PEO. Measurements occurred at 90 oC... ............................................................... 124
Figure 3.8. Conductivities of mixtures of LiClO4 with pure PEO (black squares) and thioether-PEO (red circles) at different ratios of PEO to LiClO4. The O/Li ratios in the mixture were determined from the masses of LiClO4 and PEO added, and these ratios only include the O atoms from PEO. Measurements occurred at 90 oC... ........................................................................................ 125
xiv
LIST OF SCHEMES
Scheme 1.1. Structure of the ABA amphiphilic block copolymers synthesized in this study... ..................................................................................................... 2
Scheme 1.2. Small molecule model (BisphenolS-I) initiator used to explore ATRP catalytic systems for synthesis of block copolymers. This molecule mimics the structure of PES macroinitiators... ................................................... 2
Scheme 1.3. Grafting of polyelectrolytes to nanoparticles to create single-ion conductors... ...................................................................................................... 4
Scheme 1.4. Monolayer-modified silica nanoparticles for single ion conductors... ...................................................................................................... 6
Scheme 2.1. Chemical Structures of Bisphenol A Polysulfone (PSf) and Polyethersulfone (PES)... ................................................................................ 12
Scheme 2.2. Reactions invovled in ATRP... ..................................................... 14
Scheme 2.3. Possible architectures of copolymers synthesized from two monomers, A and B... ...................................................................................... 16
Scheme 2.4. Structure of the block copolymer synthesized by Jo... ............... 18
Scheme 2.5. PSf-based amphiphilic block copolymer prepared by Moore et al. for formation of membranes... .......................................................................... 19
Scheme 2.6. PSf-based amphiphilic block copolymers synthesized by Wang el al for use as membrane additives... ................................................................. 20
Scheme 2.7. PSf-based graft copolymer prepared by Yi... ............................. 21
Scheme 2.8. PES-based graft copolymer synthesized by Yi et al... ............... 21
Scheme 2.9. Protocol for making phase-inversion membranes... ................... 25
xv
Scheme 2.10. Selective reaction of triphenylmethyl chloride with the primary alcohol in hydroxypropyl methacrylate mixtures and subsequent isolationof 2-hydroxypropyl methacrylate.......................................................................... 30
Scheme 2.11. Synthesis of hydroxyl terminated polyethersulfone (PES)... .... 34
Scheme 2.12. Mechanism of etherification in synthesis of PES... .................. 35
Scheme 2.13. Synthesis of a macroinitiator from OH-terminated PES... ........ 36
Scheme 2.14. Synthesis of BisphenolS-I... .................................................... 37
Scheme 2.15. Characteristic protons for calculation of copolymer composition from NMR spectra... ......................................................................................... 85
Scheme 2.16. Characteristic protons for calculation of copolymer composition from NMR spectra... ......................................................................................... 86
Scheme 3.2. Method for determining the Li+ content of PEO-based electrolytes... .................................................................................................. 107
Scheme 3.3. Silica nanoparticles prepared by grafting lithiated poly (trifluoromethane sulfonic aminoethyl-methacrylate) (Si-TfMALi) from the surface... ........................................................................................................ 109
Scheme 3.4. Proposed qualitative conformations of monolayer Si-C5NTfLi (top) and multilayer Si-TfMALi (bottom) at 30 oC and at 80 oC... ........................... 112
Scheme 3.5. Proposed single-ion conductors prepared by synthesis of PEO containing alkene or alkyne groups and subsequent attachment of anions to these groups via click chemistry... ................................................................. 114
Scheme 3.6. Polysulfone structures synthesized by Bielawski’s et al for proton-conduction... ....................................................................................... 115
xvi
Scheme 3.7. Polyacrylate structures prepared by Martwiset et al. for formation of membranes that exhibit proton conductivity at 200 oC... ........................... 116
Scheme 3.8. Poly(ether ether ketone) prepared by Gao et al for reaction with 3-mercaptopropyltrimethoxysilane via click chemistry... ............................... 117
Scheme 3.9. The thioether and triazole structures that result from (a) thiol-ene and (b) alkyne-azido click chemistry, respectively... ..................................... 117
Scheme 3.10. (a) Scheme of ideal lithium transport in an electrolyte material and (b) scheme of lithium transport if the click functionality (triazole or thioether) impedes Li+ transport... .................................................................................. 118
Scheme 3.11. (a) Monomers synthesized to prepare triazole-containing PEO, (b) monomers to that will react to give sulfur-containing PEO... ................... 119
Scheme 3.12. Two methods for synthesis of dipropargyl tetraethylene glycol... ....................................................................................................................... 120
Scheme 3.13. Synthesis of several step-growth polymerization monomers via the ditosyl derivative... .................................................................................. 121
Scheme 3.14. Synthesis of diallyl tetraethylene glycol.. ............................... 121
Scheme 3.15. Step-growth polymerization of diazido and dipropargyl tetraethylene glycol... ..................................................................................... 122
Scheme 3.16. Step-growth polymerization of dithiol and diallyl tetraethylene glycol... ........................................................................................................... 123
1
Chapter 1. Introduction
There are two parts to this dissertation: chapter 2 describes the synthesis of
polyethersulfone (PES)-based block copolymers that are relevant to
membrane modification, and chapter 3 explores potential single-ion
conductors based on comb-polyethyleneoxide (PEO) materials. Such
conductors are important elements of lithium ion batteries. Below I briefly
summarize the two projects, and each chapter contains a more extensive
introduction.
Part I: Synthesis of Polyethersulfone (PES)-Based Amphiphilic Block
Copolymers
Polyethersulfone (PES) is widely employed in water-treatment membranes
because of its chemical and thermal stability. However, the hydrophobic nature
of PES may cause severe fouling problems.2 The introduction of ABA block
copolymers (Scheme 1.1) into PES membranes sometimes greatly improves
their filtration properties.3 A PES B block facilitates incorporation into the
membrane, and hydrophilic A blocks can create more wettable surfaces that
resist fouling.
2
O Om
nhydrophobic block
SO O
O
OH
hydrophilic block
polyethersulfone (PEO)
O Om
OH
poly(hydroxylethyl methacrylate)polyHEMA
poly(2-hydroxylpropyl methacrylate)polyHPMA
Scheme 1.1. Structure of the ABA amphiphilic block copolymers synthesized
in this study. (For interpretation of the references to color in this and all other
figures, the reader is referred to the electronic version of this dissertation.)
Scheme 1.2. Small molecule model (BisphenolS-I) initiator used to explore
ATRP catalytic systems for synthesis of block copolymers. This molecule
mimics the structure of PES macroinitiators.
Our synthesis of ABA copolymers relies on ATRP from PES macroinitiators.
To explore atom transfer radical polymerization (ATRP) catalyst systems for
polymerization, BisphenolS-I served as a model compound for the PES
macroinitiator (Scheme 1.2). NMR characterization is much simpler with this
3
small molecule than a polymer. We tested different combinations of metal
catalyst and ligand, and CuCl/CuCl2/N,N,N′,N′,N′′-pentamethyldiethylene
triamine (PMDETA) proved effective for controlled polymerization of
2-hydroxyethyl methacrylate (HEMA) and 2-hydroxypropyl methacrylate
(HPMA). This catalyst system enabled synthesis of polyHEMA-PES-
polyHEMA and polyHPMA-PES-polyHPMA on a 10-20 g scale. Fourier
and 1H NMR show successful synthesis of these block copolymers. Dynamic
light scattering studies reveal copolymer aggregates (radii of 60 nm) in 20 vol%
water in N-methylpyrrolidone. These copolymers may prove valuable in
membrane modification, and we have delivered them to Pall Corporation for
their investigation.
Part II: Synthesis of Comb-Polyethyleneoxide (PEO) via Click Chemistry-
New Polymers for Possible Lithium Ion Conductors
When a lithium ion battery discharges, electrons flow from the anode to the
cathode through the external circuit. Simultaneously, inside the cell lithium
cations formed at the anode migrate and intercalate into the cathode. Ideally,
lithium ions carry all the current within the cell. Typical values of the Li+
transference number (tLi+, the fraction of the current carried by Li+) in
electrolytes range from 0.2-0.3, however, which indicates the anion is the
dominant species in carrying current. Since a low tLi+ limits a battery’s power
density and often affects the chemical stability of electrolytes, development of
4
electrolytes with near-unity lithium-ion transference numbers is important.
Scheme 1.3. Grafting of polyelectrolytes to nanoparticles to create single-ion
conductors.1
In research for my MS thesis, I investigated several nanoparticle systems
where Li+ is a counterion to anionic groups immobilized on grafted polymers
(Scheme 1.3). Nanoparticle-containing electrolytes were prepared by mixing
the purified particles and low-molecular weight (~500 g/mol) polyethylene
glycol dimethyl ether (PEGDME-500). Movement of the anions was largely
restricted because of the surface-anchored polymer backbones, so Li+
became the only ion conducting current.
The MS thesis explored four different polymer structures (Scheme 1.3) with
the aim of improving the ionic conductivity of the nanoparticles/PEGDME-500
blend. The first grafted polymer, poly(lithium styrene sulfonate) was initially
synthesized from sodium styrene sulfonate monomer, and lithium exchange
5
gave poly(lithium sulfonate styrene). In a second case, polyethylene glycol
methyl ether methacrylate (PEGMA) was copolymerized with the styrene
sulfonate, to facilitate transport of lithium cations and increase the miscibility of
the particles with PEGDME-500. The third structure used phosphonates, which
have two lithium counterions per monomer, to increase the lithium content.
The room temperature conductivity of these electrolytes was 10-7
S/cm. This is
several orders of magnitude lower than the conductivity of electrolytes
employed in current lithium ion batteries, and one or two orders of magnitude
lower that current single-ion conductors.
To further improve the conductivity, the fourth structure was inspired by
lithium bis(trifluoromethane sulfonyl) imide (LiTFSI). High conductivity
correlates with the dissociation of Li+ from the anion, and therefore anions such
as ClO4-, PF6
- and bis(trifluoromethylsufonyl amide) (TFSI) are commonly used
in electrolytes. We synthesized a polymerizable analogue of TFSI and grew the
corresponding polymers from silica nanoparticles. The maximum conductivity,
10-6
S/cm, occurred at an oxygen to lithium ratio of 32. The O in this ratio
comes exclusively from ether oxygens in PEGDME-500, and Li comes from the
amount of the lithium cations in the electrolytes. The value of O/Li is a common
measure of the lithium concentration in the electrolytes.
6
Scheme 1.4. Monolayer-modified silica nanoparticles for single ion
conductors.4
We expected much higher conductivity than 10-6
S/cm, because the
polyelectrolyte constitutes 70~90 wt% of the polymer grafted particles. This
high polyelectrolyte content should supply a large amount of free lithium cations
to contribute to a high conductivity. A previous group member, Fadi Asfour,
investigated monolayer-coated silica nanoparticles as single-ion conductors
(Scheme 1.4), and these materials mixed with PEGDME-500 also have a
conductivity of 10-6
S/cm.4 A possible explanations for the low conductivity with
a dense layer of polyelectrolyte on the particle surface is that not all of the
lithium cations have access to the solvent (PEGDME-500). Most of the
polyelectrolytes are buried near the silica surface and do not contribute to
conductivity.
We then planned to directly modify the PEO structure to obtain a single ion
conductor via alkyne-azido or thiol-ene click chemistry. Chapter 3 describes
synthesis of PEO derivatives with click functionalities in the polymer backbone.
The conductivity with these materials mixed with salts is similar to data with
pure PEO, suggesting that using click chemistry in the synthesis of lithium ion
7
electrolytes is feasible. The triazole and thioether groups do not limit
conductivity.
8
REFERENCES
9
REFERENCES
1. Zhao, H. Master Thesis, 2011, MSU.
2. Beyer, M.; Lohrengel, B.; Nghiem, L. D., Membrane fouling and chemical cleaning in water recycling applications. Desalination 2010, 250 (3), 977-981.
3. Zhou, H., Brunelle, J., Moore, D., R., Zhang, L., Misner, M., J., Chen, X., Ma, M., Block copolymer membranes and associated methods for making the same. US Patent, 123033 A1, 2011.
4. Asfour, F. Ph.D Dissertation, 2004, MSU.
10
Chapter 2. Synthesis of Polyethersulfone (PES)-Based Amphiphilic Block Copolymers
1. Introduction
This chapter describes the synthesis of new polysulfone-based block
copolymers and preliminary studies on their solubility and phase-segregation
properties. To put this work in context, in this introduction I first discuss the
importance of polysulfone materials in water-treatment membranes.
Polysulfone block copolymers can serve as additives to make these
membranes more hydrophilic and reduce fouling. Thus, section 1.2 describes
block copolymers in general, and section 1.3 presents specific literature
examples of the synthesis of polysulfone-based block copolymers. In section
1.4, I provide a brief description of the self-assembly of block copolymers, and
section 1.5 of the introduction mentions a specific application of block
copolymer self-assembly, the formation of nanoporous structures. Finally,
section 1.6 discusses challenges in the self-assembly of polysulfone-based
copolymers.
1.1. Polysulfone Materials and Their Application as Water Treatment
Membranes
Polysulfone (PSf) and polyethersulfone (PES) constitute an important class
of engineering thermoplastics that is widely used to manufacture membranes
with relatively high chemical, thermal and mechanical stability. Broadly
speaking, polysulfone refers to all sulfone-containing polymers, so both
bisphenol A polysulfone and polyethersulfone (PES) are polysulfone materials.
11
In all polysulfones, but especially PES, the aromatic rings in the polymer
backbone are electronically deactivated by the adjacent sulfone (-SO2) groups.
Additionally, the repeating aromatic rings cause steric hindrance to rotation
around the polymer backbone, and both of these factors make PES unusually
stable.
Bisphenol A polysulfone or poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene
oxy-1,4-phenylene(1-ethylethylidene)-1,4-phenylene) (Scheme 2.1) has a
glass transition temperature (Tg) of around 185 oC. Polyethersulfone (PES) or
poly(oxy-1,4-phenylenesulfonyl-1,4-phenylene) has an even higher Tg of 220
oC (Scheme 2.1).
1
Because of its high Tg, PES can retain dimensional stability at temperature
as high as 200 oC.
2 As a high-temperature-resistant resin, PES is also flame
retardant, certified for UL94-V0 (burning stops within 10 seconds on a vertical
specimen; drips of particles allowed as long as they are not inflamed).2
12
Scheme 2.1. Chemical Structures of Bisphenol A Polysulfone (PSf) and
Polyethersulfone (PES).
Membranes made of PES show wide pH tolerance (1 to 13); excellent
resistance to oxidants, including chlorine employed in water treatment (i.e., <
50 ppm); and stability at high temperature (operation at 75 oC and limited
exposure to temperature up to 125 oC).
3 Because of this stability, PES is
widely used to create water treatment membranes for applications such as
wastewater purification and seawater desalination (removal of salt and other
minerals from saline water).
PES shows excellent chemical and water resistance, partly because of its
hydrophobicity. However, this means that it also exhibits a low wettability.
Water contact angles on PES range from 53o to 60
o, and these values are
higher than contact angles on both cellulose (36.9o) and aromatic polyamide
(36.9o) membranes.
4 Recent research correlated low surface wettability with
increased non-specific adsorption of naturally occurring organic matter (NOM)
on the membrane.5 Such adsorption is a major cause of chronic fouling of
membranes during water treatment. Fouling causes a significant increase in
hydraulic resistance and leads to a permanent flux decline or a need for higher
transmembrane pressures.5
Blending of hydrophobic PES with hydrophilic polymers should increase
wettability and decrease fouling propensity.6 However, blends suffer from
long-term instability due to migration of the hydrophilic molecules to the
13
surface. Amphiphilic block copolymers can potentially increase hydrophilicity
and avoid such instability. The next section describes some general methods
for the synthesis of block copolymers, whereas section 1.3 gives specific
examples of the synthesis of polysulfone-based block copolymers.
1.2. Block Copolymers
The synthesis of block copolymers has been studied extensively, and
several authors reviewed this subject.7 Advances in polymer synthetic
chemistry in recent decades, especially in controlled radical polymerization,
have enabled access to a wide range of block copolymer compositions and
architectures.
In a conventional free radical polymerization, decomposition of an initiator
generates a radical that starts the polymerization of a vinyl monomer (e.g.
methylacrylate, methyl methacrylate and styrene). Because of the high
reactivity of radicals with monomers, propagation is very rapid. Since initiation
is not instantaneous, this rapid propagation makes the lengths of polymer
chains inhomogeneous. Additionally, radicals in solution undergo coupling
reactions that terminate chain growth and further broaden the molecular
weight distribution.
Attainment of narrower molecular weight distributions requires slower
propagation rates and termination reactions through controlled or living
polymerization techniques. Three criteria define such techniques: (1) fast
initiation in which the polymer chains start to propagate at the same time; (2)
14
homogeneous propagation to ensure that the chains grow at the same rate;
and (3) minimal termination. The case of zero termination corresponds to the
definition of a ‘living’ polymerization. In reality, no system is completely
“living”, but many are highly controlled. Atom Transfer Radical Polymerization
(ATRP) is one of the most common controlled radical polymerization
techniques. Scheme 2.2 shows the ATRP mechanism.8
Scheme 2.2. Reactions invovled in ATRP.8
In this scheme, PnX is the initiating alkyl halide/macromolecular species;
kact is the rate constant of activation through radical formation; kdeact is the
rate constant for the reverse reaction, which gives a dormant chain; Mtm
represents the transition metal species in oxidation state m; and L is the
metal-binding ligand. ATRP uses halide derivatives as initiators (bromo or
chloro groups), and Cu(I) is the most widely used catalyst, although other
metal species such as Ru(II), Fe(II), Cr(III), and Os(II) can also catalyze the
polymerization.9,10
Ligands (typically amine derivatives) chelate the Cu(I) to
increase its solubility in organic solvents and tune its catalytic properties.
Oxidation of the Cu(I)/L complex occurs with homo-cleavage of the carbon
halide bond to form carbon radicals, and the radical initiates the polymerization.
However, kact is typically two to four orders smaller than kdeact, so PnX serves
15
as a reservoir of radical initiators (Scheme 2.2), and the radical concentration
at any given time is low. The propagation rate is kp[Pn*][M] (kp is the
propagation rate constant, [Pn*] is the concentration of radicals, and [M]
concentration of monomers). Equally important, the termination rate is
kt[Pn*][Pn*] (kt is the termination reaction constant). Thus, the propagation rate
is first order with respect to the radical concentration, but the termination rate is
second order. The low radical concentration gives rise to a slow, controlled
first-order propagation reaction, while the second-order termination reaction is
nearly negligible.
16
Scheme 2.3. Possible architectures of copolymers synthesized from two
monomers, A and B.
Scheme 2.3 shows the common copolymer structures synthesized from two
types of repeating units, A and B. In linear polymers A and B may appear
randomly, in an alternating pattern or in blocks, and the resulting polymers are
17
termed random, alternating, and block copolymers, respectively. In some
cases, blocks containing a single repeating unit may branch out from the
polymer main chain to give a graft copolymer. If the blocks branch out from a
common location on the main chain, the structure is a star copolymer. Because
ATRP gives polymers with low polydispersity and minimal termination, it is
particularly useful for synthesizing block copolymers by sequential synthesis of
the different blocks.
Amphiphilic block copolymers contain with both hydrophobic and hydrophilic
blocks. Based on different categories of hydrophilic blocks, there are three
kinds of amphiphilic block copolymers: non-ionic copolymers, such as
Synthesis of ABA block copolymers: polyHEMA-co-PES-co-polyHEMA.
In a 250 mL Schlenk flask, the PES macroinitiator (15 g, 1.5 mmol), HEMA (20
g, 0.154 mol) and PMDETA (0.60 mL, 2.9 mmol) were dissolved in NMP (120
mL). (The stirred mixture occasionally required heating to obtain a
homogeneous solution.) After two freeze-pump-thaw cycles, the flask was
refilled with nitrogen, CuCl2 (0.108 g, 0.8 mmol) was added and the solution
was stirred until the Cu species dissolved. After two freeze-pump-thaw
cycles, the flask was refilled with nitrogen and CuCl (0.078 g, 0.8 mmol) was
added to the flask under N2. The flask was heated in a 40 °C oil bath. The
reaction was monitored by 1H NMR and when the polymerization reached the
desired HEMA conversion, the solution was opened to the air to quench
polymerization reaction. The polymer was precipitated by addition of the
solution into 300 mL of saturated disodium ethylenediaminetetraacetate (EDTA)
solution, and the copolymer was recovered as a fine powder. Suction filtration
required 5-6 hours to recover the product. The air-dried product was dissolved
in DMSO, precipitated in water, and after a second precipitation from DMSO,
90
the polymer was dried under vacuum at 90 °C for 24 h. Synthesis of
polyHPMA-co-PES-co-polyHPMA occurred similarly.
Free Radical Polymerization of Hydroxyethyl Methacrylate (HEMA). A
Schlenk flask was charge with 15 mL dry THF, 4 g of HEMA (0.031 mol) and
0.43 g azobisisobutyronitrile (2.6 mmol). After one freeze-pump-thaw cyle, the
flask was put onto a 70 °C oil bath. After an overnight reaction, NMR
spectroscopy of the reaction solution showed that the conversion was 100%,
and the flask was opened to air to quench the reaction. PolyHEMA precipitated
onto the bottom of the flask, and the solid product was dried under vacuum at
70 °C. 3.56 g product was recovered (90% yield).
91
APPENDIX A
92
Appendix A1. 1H NMR 500 MHz spectrum of HEMA9-PES51-HEMA9 in
DMSO-d6.
93
Appendix A2. 1H NMR 500 MHz spectrum of HEMA13-PES42-HEMA13 in
DMSO-d6.
94
Appendix A3. 1H NMR 500 MHz spectrum of HEMA26-PES42-HEMA26 in
DMSO-d6.
95
Appendix A4. 1H NMR 500 MHz spectrum of HEMA22-PES34-HEMA22 in
DMSO-d6.
96
Appendix A5. 1H NMR 500 MHz spectrum of HPMA12-PES42-HPMA12 in
DMSO-d6.
97
Appendix A6. 1H NMR 500 MHz spectrum of HPMA26-PES42-HPMA26 in
DMSO-d6.
98
REFERENCES
99
REFERENCES
1. Meier-Haack, J.; Vogel, C.; Butwilowski, W.; Lehmann, D., Sulfonated poly(ether sulfone)s for fuel cells by solvent-free polymerization. Pure and Applied Chemistry 2007, 79 (11), 2083-2093. 2. Locatelli, F. R., C.; Tetta, C. , Polyethersulfone: membranes for multiple clinical Applications. Karer AG: Basel, 2003. 3. Zeeman; Zydney, A. L. M. D., INC. New York, Microfiltration and ultrafiltration: principles and applications. 1996. 4. Perry, R. H. G., D. W.; Eds McGraw-Gill: New York, 1997, Perry's chemical engineer's handbook, 7th ed. 1997. 5. Beyer, M.; Lohrengel, B.; Nghiem, L. D., Membrane fouling and chemical cleaning in water recycling applications. Desalination 2010, 250 (3), 977-981. 6. Peyravi, M.; Rahimpour, A.; Jahanshahi, M.; Javadi, A.; Shockravi, A., Tailoring the surface properties of PES ultrafiltration membranes to reduce the fouling resistance using synthesized hydrophilic copolymer. Microporous and Mesoporous Materials 2012, 160 (0), 114-125. 7. (a) Schacher, F. H.; Rupar, P. A.; Manners, I., Functional block copolymers: nanostructured materials with emerging applications. Angewandte Chemie-International Edition 2012, 51 (32), 7898-7921; (b) Moad, G.; Rizzardo, E.; Thang, S. H., Radical addition-fragmentation chemistry in polymer synthesis. Polymer 2008, 49 (5), 1079-1131; (c) Braunecker, W. A.; Matyjaszewski, K., Controlled/living radical polymerization: features, developments, and perspectives. Progress in Polymer Science 2007, 32 (1), 93-146. 8. Matyjaszewski, K. W., J.-S. 1996. 9. Matyjaszewski, K., Atom transfer radical polymerization (ATRP): current Status and future perspectives. Macromolecules 2012, 45 (10), 4015-4039. 10. di Lena, F.; Matyjaszewski, K., Transition metal catalysts for controlled
100
radical polymerization. Progress in Polymer Science 2010, 35 (8), 959-1021. 11. Owen, S. C.; Chan, D. P. Y.; Shoichet, M. S., Polymeric micelle stability. Nano Today 2012, 7 (1), 53-65. 12. Jo, W. H. K., T.; Hwang, I. C.; Kwon, N. H. Novel amphiphilic block copolymer, method for manufacturing the same and polymer electrolyte membrane using the same. 2010. 13. Zhou, H., Brunelle, Daniel, J., Moore, D., R., Zhang, L., Misner, M., J., Chen, X., Ma, M., Block copolymer membranes and associated methods for making the same. US Patent, 123033 A1, 2011. 14. Wang, J. Y.; Xu, Y. Y.; Zhu, L. P.; Li, J. H.; Zhu, B. K., Amphiphilic ABA copolymers used for surface modification of polysulfone membranes, Part 1: Molecular design, synthesis, and characterization. Polymer 2008, 49 (15), 3256-3264. 15. Yi, Z. A.; Zhu, L. P.; Xu, Y. Y.; Zhao, Y. F.; Ma, X. T.; Zhu, B. K., Polysulfone-based amphiphilic polymer for hydrophilicity and fouling-resistant modification of polyethersulfone membranes. Journal of Membrane Science 2010, 365 (1-2), 25-33. 16. Yi, Z.; Zhu, L. P.; Cheng, L.; Zhu, B. K.; Xu, Y. Y., A readily modified polyethersulfone with amino-substituted groups: Its amphiphilic copolymer synthesis and membrane application. Polymer 2012, 53 (2), 350-358. 17. Bates, F. S.; Fredrickson, G. H., Block copolymer thermodynamics - theory and experiment. Annual Review of Physical Chemistry 1990, 41, 525-557. 18. Fredrickson, G. H.; Bates, F. S., Dynamics of block copolymers: theory and experiment. Annual Review of Materials Science 1996, 26, 501-550. 19. Kim, J. K.; Yang, S. Y.; Lee, Y.; Kim, Y., Functional nanomaterials based on block copolymer self-assembly. Progress in Polymer Science 2010, 35 (11), 1325-1349. 20. Ichikawa, T.; Yoshio, M.; Hamasaki, A.; Kagimoto, J.; Ohno, H.; Kato, T., 3D Interconnected ionic nano-channels formed in polymer films: self-Organization and polymerization of thermotropic bicontinuous cubic liquid crystals. Journal of the American Chemical Society 2011, 133 (7), 2163-2169. 21. Nunes, S. P., Recent advances in the controlled formation of pores in membranes. Trends in Polymer Science 1997, 5 (6), 187-192.
101
22. Smolders, C. A.; Reuvers, A. J.; Boom, R. M.; Wienk, I. M., Microstructures in phase-inversion membranes .1. formation of macrovoids. Journal of Membrane Science 1992, 73 (2-3), 259-275. 23. Amirilargani, M.; Mohammadi, T., Synthesis and characterization of asymmetric polyethersulfone membranes: effects of concentration and polarity of nonsolvent additives on morphology and performance of the membranes. Polymers for Advanced Technologies 2011, 22 (6), 962-972. 24. Peinemann, K. V.; Abetz, V.; Simon, P. F. W., Asymmetric superstructure formed in a block copolymer via phase separation. Nature Materials 2007, 6 (12), 992-996. 25. Nunes, S. P.; Sougrat, R.; Hooghan, B.; Anjum, D. H.; Behzad, A. R.; Zhao, L.; Pradeep, N.; Pinnau, I.; Vainio, U.; Peinemann, K. V., Ultraporous films with uniform nanochannels by block copolymer micelles assembly. Macromolecules 2010, 43 (19), 8079-8085. 26. Widin, J. M.; Schmitt, A. K.; Schmitt, A. L.; Im, K.; Mahanthappa, M. K., Unexpected Consequences of block polydispersity on the self-Assembly of ABA triblock copolymers. Journal of the American Chemical Society 2012, 134 (8), 3834-3844. 27. Percec, V.; Clough, R. S.; Grigoras, M.; Rinaldi, P. L.; Litman, V. E., Reductive dehalogenation versus substitution in the polyetherification of 4,4'-dihalodiphenyl sulfones with bisphenolates. Macromolecules 1993, 26 (14), 3650-3662. 28. Tang, W.; Kwak, Y.; Braunecker, W.; Tsarevsky, N. V.; Coote, M. L.; Matyjaszewski, K., Understanding Atom transfer radical polymerization: Effect of ligand and initiator structures on the equilibrium constants. Journal of the American Chemical Society 2008, 130 (32), 10702-10713. 29. Xia, J.; Matyjaszewski, K., Controlled/“living” radical polymerization. atom transfer radical polymerization using multidentate amine ligands. Macromolecules 1997, 30 (25), 7697-7700. 30. Lynd, N. A.; Meuler, A. J.; Hillmyer, M. A., Polydispersity and block copolymer self-assembly. Progress in Polymer Science 2008, 33 (9), 875-893.
102
Chapter 3. Use of Nanoparticles and Click Chemistry in the Development of Single-ion Conductors for Lithium Ion Batteries
This chapter describes research aimed at developing single-ion conductors
for lithium ion batteries. The introduction first discusses why single-ion
conductors are important for decreasing concentration polarization and related
voltage losses during battery discharge. Subsequently, I first present work on
nanoparticles coated with immobilized anions as part of single-ion conductors.
This work follows up previous studies by Fadi Asfour and shows that
nanoparticles with grafted polyanions have a higher lithium conterion weight
fraction than nanoparticles coated with only monolayers of anion. However,
because the conductivity of these nanoparticle-PEO electrolytes is not high
enough for battery applications, subsequent work aims toward using click
chemistry to modify PEO directly and create single-ion conductors. These
studies show that the presence of triazole or thioether groups does not limit
conductivity. Thus, click chemistry may provide a useful method for introducing
immobile anions in PEO to create single-ion conductors.
1. Introduction- Ion Conduction in Lithium Ion Batteries
In discharge of a lithium ion battery, electrons flow from the anode to the
cathode through the external circuit, while inside the cell, lithium cations
formed at the anode migrate to the cathode and intercalate into the cathode
material with reduction at the cathode (Figure 3.1). The electrolyte usually
contains a lithium salt dissolved in a solvent, and ideally Li+ ions are the only
current carriers in this region. When anions carry a significant fraction of the
103
current, concentration polarization occurs, and the battery loses voltage.1
Figure 3.1. Schematic diagram of a lithium ion battery containing a metal
oxide cathode and a graphite anode. The figure also shows redox reaction
during discharge.
Figure 3.2 illustrates the concentration polarization. At the anode, only part
of the Li+ formed by oxidation migrates away to carry current, so Li
+
accumulates. Additionally, anions migrate toward the anode and collect there.
At the cathode, more Li+ is intercalated with reduction than can migrate to the
cathode due to current, so Li+ is depleted. Anions migrate away from the
cathode and are also depleted in this region. These accumulation and
depletion zones decrease the potential drop at the cathode-solution interface
104
and increase the potential drop at the anode-solution interface to decrease the
battery voltage. If the discharge is slow enough, diffusion will help dissipate the
concentration polarization, but at fast discharge, concentration polarization is a
serious problem. Moreover, the low conductivity in the depleted region near the
cathode increases the ohmic potential drop, which leads to heating and an
additional loss of battery voltage. The effective voltage during discharge is V
(cell voltage) - Vp (polarization voltage), and the voltage needed to charge the
cell is V+Vp. Of course, power output is directly proportional to discharge
voltage.
Figure 3.2. Concentration polarization during discharge of a lithium ion battery.
The lithium ion transference number (tLi+) is the fraction of current in solution
carried by Li+. For electrolytes with only one cation and one anion, the sum of
the cation and anion transference numbers must equal 1. Typical Li+
transference numbers in PEO-based electrolytes range from 0.2 to 0.4 (Table
3.1), showing that the anion is the dominant current-carrying species. Thus,
concentration polarization during discharge may be severe as more Li+ ions
105
form at the anode than can migrate away, and more Li+ enters the cathode
than migrates there. Electrolytes with Li+ transference numbers close to 1 are
highly desirable for decreasing concentration polarization.
Synthesis of dithiol tetraethylene glycol: In a 250 mL round bottom flask,
20.1 g ditosyl tetraethylene glycol (0.04 mol), 40 mL of ethanol, and 6.1 g of
thiourea (0.08 mol) were added to 30 mL of deionized water. The solution was
purged with nitrogen for 15 minutes, and the flask was fitted with a condenser.
After reflux for 15 h, a solution of 4 g NaOH (0.1 mol) in 40 mL deionized water
was added, and after another 2 h of reflux, the flask was placed in an ice bath.
Fifteen mL of concentrated HCl solution was added to neutralize the solution,
and the product was then extracted in dichloromethane (3 x 50 mL). The
133
combined dichloromethane solution was dried over MgSO4, solvent was
removed by rotary evaporation, and vacuum distillation gave 4 g of dithiol
tetraethylene glycol (0.025 mol, 62%) as colorless oil. See Appendix 12 for the
1H NMR spectrum.
Synthesis of diallyl tetraethylene glycol: In a 500 mL round bottom flask,
11.6 g of dihydroxyl tetraethylene glycol (0.06 mol) and 14 g of powderized
KOH (0.25 mol) were dissolve in 200 mL of acetone. After placing the flask in
an ice bath, 10 mL of allyl bromide (0.12 mol) was slowly added over 10
minutes. The ice bath was then removed, and the mixture was allowed to react
at room temperature overnight. Acetone was removed using rotary
evaporation, and the product was dissolved in 300 mL dichloromethane.
Deionized water was used to wash the dichloromethane solution (3 x 80 mL),
the organic layer was dried using MgSO4, and solvent was removed by rotary
evaporation. Silica column chromatography (hexane/ethyl acetate 9/1) gave
10.84 g (0.042 mol, 70% yield) of product. See Appendix 10 for the 1H NMR
spectrum.
Thiol-ene Step growth polymerization: 6.46 g diallyl tetraethylene glycol
(0.024 mol), 5.36 g dithiol tetraethylene glycol (0.024 mol) were dissolved with
100 mL dichloromethane in a 250 mL round bottom flask. The solution was
purged with nitrogen for 30 minutes and was done in a 50 oC oil bath for 24 h.
To work up the reaction, the mixture was put under rotovac to remove residual
solvent. The product was dissolved in 100 mL chloroform and added dropwise
134
to 200 mL diethyl ether with strong stirring. Product was obtained as a light
yellow viscous oil, which was dissolved in chloroform and precipitated in ether
again. Polymer product was dried under vacuum as viscous oil (11.5 g, 97.3%).
GPC: Mn=6,700, Mw=7,400, PDI=1.1. See Appendix 14 for the 1H NMR
spectrum.
135
APPENDIX B
136
Appendix B1. 1H NMR spectrum of ditosyl tetraethyleneglycol in CDCl3.
137
Appendix B2. 13
C NMR spectrum of ditosyl tetraethyleneglycol in CDCl3.
138
Appendix B3. FT-IR spectrum of ditosyl tetraethyleneglycol.
139
Appendix B4. 1H NMR spectrum of diazido tetraethyleneglycol in CDCl3.
140
Appendix B5. 13
C NMR spectrum of diazido tetraethyleneglycol in CDCl3.
141
Appendix B6. FT-IR spectrum of diazido tetraethyleneglycol.
142
Appendix B7. 1H NMR spectrum of dipropargyl tetraethyleneglycol in CDCl3.
143
Appendix B8. 13
C NMR spectrum of dipropargyl tetraethyleneglycol in CDCl3.
144
Appendix B9. FT-IR spectrum of dipropargyl tetraethyleneglycol.
145
Appendix B10. 1H NMR spectrum of diallyl tetraethyleneglycol in CDCl3.
146
Appendix B11. FT-IR spectrum of diallyl tetraethyleneglycol.
147
Appendix B12. 1H NMR spectrum of dithiol tetraethyleneglycol in CDCl3.
148
Appendix B13. 13
C NMR spectrum of dithiol tetraethyleneglycol in CDCl3.
149
Appendix B14. 1H NMR spectrum of dithiol tetraethyleneglycol in CDCl3.
150
Appendix B15. FT-IR spectrum of dithiol tetraethyleneglycol.
151
Appendix B16. FT-IR spectrum of thioether-PEO.
152
Appendix B17. 1H NMR spectrum of triazole-PEO in CDCl3.
153
Appendix B18. FT-IR spectrum of triazole-PEO.
154
REFERENCES
155
REFERENCES
1. Zhao, H. Single ion conductors based on polyelectrolyte grafted nanoparticles. Michigan State University, 2011.
2. Matsumoto, K.; Endo, T., Synthesis of networked polymers with lithium counter cations from a difunctional epoxide containing poly(ethylene glycol) and an epoxide monomer carrying a lithium sulfonate salt moiety. Journal of Polymer Science Part A: Polymer Chemistry 2010, 48 (14), 3113-3118.
3. Sun, X.-G.; Kerr, J. B., Synthesis and Characterization of Network Single Ion conductors based on comb-branched polyepoxide ethers and lithium bis(allylmalonato)borate. Macromolecules 2005, 39 (1), 362-372.
4. Snyder, J. F.; Hutchison, J. C.; Ratner, M. A.; Shriver, D. F., Synthesis of comb polysiloxane polyelectrolytes containing oligoether and perfluoroether side chains. Chemistry of Materials 2003, 15 (22), 4223-4230.
5. Asfour, F. Molecularly Reinforced Polymers and Self-assembled Nanocomposites for Secondary Lithium Batteries. Michigan State University, 2004.
6. (a) Aravindan, V.; Gnanaraj, J.; Madhavi, S.; Liu, H. K., Lithium-Ion conducting electrolyte salts for lithium batteries. Chem.-Eur. J. 2011, 17 (51), 14326-14346; (b) Meyer, W. H., Polymer electrolytes for lithium-ion batteries. Adv. Mater. 1998, 10 (6), 439.
7. Kolb, H. C.; Finn, M. G.; Sharpless, K. B., Click chemistry: Diverse chemical function from a few good reactions. Angew Chem Int Edit 2001, 40 (11), 2004.
8. Hoyle, C. E.; Bowman, C. N., Thiol–ene click chemistry. Angewandte Chemie International Edition 2010, 49 (9), 1540-1573.
9. Norris, B. C.; Li, W.; Lee, E.; Manthiram, A.; Bielawski, C. W., ‘Click’-functionalization of poly(sulfone)s and a study of their utilities as proton conductive membranes in direct methanol fuel cells. Polymer 2010, 51 (23), 5352-5358.
156
10. Martwiset, S.; Yavuzcetin, O.; Thorn, M.; Versek, C.; Tuominen, M.; Coughlin, E. B., Proton conducting polymers containing 1H-1,2,3-triazole moieties. Journal of Polymer Science Part A: Polymer Chemistry 2009, 47 (1), 188-196.
11. Gao, S.; Zhao, C.; Na, H., Chemically stable hybrid polymer electrolyte membranes prepared by silane-crosslinking and thiol-ene click chemistry. Journal of Power Sources 2012, 214 (0), 285-291.
12. Lonergan, M. C.; Nitzan, A.; Ratner, M. A.; Shiriver, D. F., Dynamically disordered hopping, glass transition, and polymer electrolytes. The Journal of Chemical Physics 1995, 103, 3253-3261.
13. Johansson, P.; Tegenfeldt, J.; Lindgren, J., Modelling amorphous lithium salt–PEO polymer electrolytes: ab initio calculations of lithium ion–tetra-, penta- and hexaglyme complexes. Polymer 1999, 40 (15), 4399-4406.
14. Chen, Y.; Baker, G. L., Synthesis and Properties of ABA Amphiphiles. The Journal of Organic Chemistry 1999, 64 (18), 6870-6873.
15. Linford, R. G., Application of electroactive polymers. Chapman & Hall: London, 1993.
16. Wen, S. J.; Richardson, T. J.; Ghantous, D. I.; Striebel, K. A.; Ross, P. N.; Cairns, E. J., FTIR characterization of PEO+LiN(CF3SO2)(2) electrolytes. J Electroanal Chem 1996, 408 (1-2), 113-118.
17. Gujadhur, R.; Venkataraman, D.; Kintigh, J. T., Formation of aryl nitrogen bonds using a soluble copper(I) catalyst. Tetrahedron Letters 2001, 42 (29), 4791-4793.