UCO2M-UMR CNRS n°6011 Université du Maine LCOM-Chimie des Polymères Faculté des Sciences et Techniques THESE Présentée en vue de l’obtention du grade de DOCTEUR Spécialité: Chimie et Physicochimie des Polymères par Nitinart SAETUNG Synthetic- and natural rubber-based telechelic polyisoprenes: preparation and use for block copolymers via RAFT polymerization Soutenue le 25 novembre 2010, devant le jury composé de: Mme Pranee PHINYOCHEEP Assoc. Professeur, Mahidol University, Thaïlande Rapporteur M. Christophe BOISSON Directeur de Recherche-HDR CNRS, Université Lyon 1 Rapporteur Mme Sophie BISTAC Professeur, Université de Haute Alsace, Mulhouse Présidente M. Frédéric PERUCH Chargé de Recherche-HDR CNRS, Université de Bordeaux 1 Examinateur Mme Irène CAMPISTRON Ingénieur CNRS à l’Université du Maine Co-encadrante Mme Sagrario PASCUAL Maître de Conférences, Université du Maine Co-encadrante M. Laurent FONTAINE Professeur, Université du Maine Directeur M. Jean-François PILARD Professeur, Université du Maine Co-directeur
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UCO2M−UMR CNRS n°6011 Université du Maine LCOM−Chimie des Polymères Faculté des Sciences et Techniques
THESE
Présentée en vue de l’obtention du grade de
DOCTEUR Spécialité: Chimie et Physicochimie des Polymères
par
Nitinart SAETUNG
Synthetic- and natural rubber-based telechelic polyisoprenes:
preparation and use for block copolymers via RAFT polymerization
Soutenue le 25 novembre 2010, devant le jury composé de:
Mme Pranee PHINYOCHEEP Assoc. Professeur, Mahidol University, Thaïlande Rapporteur M. Christophe BOISSON Directeur de Recherche-HDR CNRS, Université Lyon 1 Rapporteur Mme Sophie BISTAC Professeur, Université de Haute Alsace, Mulhouse Présidente M. Frédéric PERUCH Chargé de Recherche-HDR CNRS, Université de Bordeaux 1 Examinateur Mme Irène CAMPISTRON Ingénieur CNRS à l’Université du Maine Co-encadrante Mme Sagrario PASCUAL Maître de Conférences, Université du Maine Co-encadrante M. Laurent FONTAINE Professeur, Université du Maine Directeur M. Jean-François PILARD Professeur, Université du Maine Co-directeur
For my grandparents For my parents For my family members For my teachers
The present thesis is the result of my PhD research at the Université du Maine,
France. I will never forget this time in my life and, most importantly, the people I met here
and who helped me to create, develop and finish this thesis. First of all, I would like to
acknowledge the financial support from Prince of Songkla University, Thailand and from the
French Ministry of Education and Research. Taking this opportunity, I would like to express
my sincere gratitude to Assistance Professor Dr. Orasa PATARAPAIBOOLCHAI for her
advice and recommendation letter that brought me study for a Ph.D. at Université du Maine.
I would like to thank my advisor: Professor Laurent FONTAINE for giving me an
opportunity to do my PhD work within his group, as well as for his support and professional
guidance during my PhD period. Professor Laurent has been a wonderful advisor, providing
me with support, encouragement, patience and an endless source of ideas. His breadth of
knowledge and his enthusiasm for research inspires me. I thank him for the countless hours
he has spent with me, discussing everything from research to career choices, reading my
manuscript and correcting my presentation.
I would also like to thank Professor Jean-François PILARD, my Ph. D. co-advisor.
Professor Jean-François has been a great advisor. His enthusiasm for research and his vision
for the future have been an inspiration. He has given me support and encouragement and his
advice about my research have greatly enhanced the work. I thank him for his assistance and
for all the support provided to both me and to my husband, Anuwat SAETUNG.
I would like to express my sincere gratitude to Dr. Irène CAMPISTRON, whose
enthusiasm for the controlled oxidative and metathesis degradations of natural rubber and
her knowledge of the subject has helped me understand many aspects of controlled
degradation of natural rubber, especially the metathesis degradation that was foreign to me
beforehand, and for correcting my manuscript. Most importantly, I would like to thank her for
her encouragement, patience and also much assistance in my personal life for the past 4
years.
I am extremely grateful to Dr. Sagrario PASCUAL for the time spent discussing the
results related to living radical polymerization, especially RAFT polymerization that was new
to me at the start of this thesis. Most importantly, I would like to thank her for her
encouragement and for having confidence in me and my abilities and for finding the time to
read through the manuscripts and correct my manuscript.
Next, I would like to thank members of my thesis committee, Assoc. Professor Pranee
PHINYOCHEEP, Professor Sophie BISTAC, Dr. Christophe BOISSON and Dr. Frédéric
PERUCH who have been generous with their time and have assisted with the successful
completion of this work. I would especially like to thank to Professor Sophie BISTAC for her
help with preliminary wedge tests.
I am grateful to Dr. Jean-Claude SOUTIF for his assistance and useful discussions on
MALDI-TOF MS over the last year. Furthermore, I would especially like thank to Madame
Evette SOUTIF, his wife, for all the love, kindness and help offered to my family throughout,
in particular to my daughter, Alisa SAETUNG. Evette took care of my daughter like she was
her own granddaughter.
Many thanks to Mme Cécile CHAMIGNON and Mme Amélie DURAND for help
interpreting liquid 1H NMR spectra and 13C NMR spectra. I would also like to thank to Dr.
Monique BODY for the analysis of solid-state 13C NMR spectra of my samples.
I am greatly indebted to Dr.Véronique MONTEMBAULT, Dr. Michel THOMAS and
Dr. Charles COUGNON, Anita LOISEAU, Jean-Luc MONEGER and Aline LAMBERT for
their guidance and helpful in providing advice many times during my work here. I would
especially like thank to Dr. Fédéric GOHIER and his wife, Dr. Stephanie LEGOUPY, for
their kindness and support shown to my family throughout by lending me their baby clothes
and baby accessories for the past 4 years.
I am also grateful to Professor Jean-Claude BROSSE, Dr. Daniel DEROUET and
Dr. Albert LAGUERRE for their helpful, guidance and support for my study here.
Thank you all friends in LCOM laboratory, Chuanpit, Faten, Hoa, Sandie, Charles,
Dao, Ekasit, Ekkawit, Hien, Jean-Marc, Martin and Rachid for their friendship and good
atmosphere in laboratory. I would like to give special thanks to Martin for his helpful
discussions related to living radical polymerization and also for helping me to improve my,
English. I would also like to give special thanks to Chuanpit for her help in my personal life,
especially during my first year in France, and thanks to Faten for her help improving my
French.
Finally, I would like to thank my grandparents, my family for all their advice, support
and love. I am very lucky to have such wonderful family members. I especially thank my
wonderful husband, Anuwat SAETUNG who is my best friend and turn to ‘soul-mate’. He has
kept me happy and positive throughout the Ph.D. process, and I thank him for all his patience,
support, encouragement and love. I truly thank Anuwat for sticking by my side, even during
the difficult days. Most importantly, I am very lucky to have a wonderful daughter, Alisa
SAETUNG who was an inspiration during my graduate Ph. D. studies, and in future always
will be.
Synthetic- and natural rubber-based telechelic polyisoprenes: preparation and use for block copolymers via RAFT polymerization ABSTRACT: The aim of this research work is to develop new strategies to synthesize well-
defined block copolymers from natural rubber (NR) based telechelic polyisoprene (PI) by
reversible addition-fragmentation chain transfer (RAFT) polymerization. The tert-butyl
acrylate (t-BA) has been chosen as comonomer which is further modified to obtain acrylic
acid (AA) units. To target such block copolymers, two original synthetic routes have been
developed to target NR-based PIs which are further employed as macromolecular chain
transfer agents (macroCTAs) for the RAFT polymerization of t-BA.
In the first approach, a trithiocarbonate functionalized telechelic cis-1,4-PI was synthesized
via the oxidative degradation of NR followed by reductive amination and amidation. The
microstructure of the functionalized PI is strictly cis-1,4. The end-functionality was
determined by 1H-NMR spectroscopy and clearly demonstrated that telechelic cis-1,4-PI
chains carry the trithiocarbonate moiety. We demonstrated that the chain extension of the
trithiocarbonate functionalized cis-1,4-PI starting block resulted in an efficient block
copolymer formation. PI-b-P(t-BA) diblock copolymer presents an unimodal SEC trace and
polydispersity index equal to 1.76. The copolymer has a nM equal to 26,000 g.mol-1 as
determined by SEC and a nDP (PI) equal to 62 and a nDP (P(t-BA)) equal to 87 as
determined by 1H NMR spectroscopy.
In the second approach, a well-defined α,ω-bistrithiocarbonyl-end functionalized telechelic
cis-1,4-polyisoprene was synthesized via functional metathesis degradation from NR in the
presence of second generation Grubbs catalyst (GII) and a bistrithiocarbonyl-end
functionalized olefin as CTA. Formation of telechelic natural rubber occurs rapidly in a
single-step process. The nM was equal to 8,200 g. mol-1 as determined by SEC after 4h of
reaction at 25 °C. A perfectly bifunctional telechelic PI was obtained using a ratio of
[NR]0/[GII] 0/[CTA]0 to 100/1/2 at 25°C. Moreover, the difunctional telechelic PI has a strictly
cis-1,4-microstructure. It was successfully used as macroCTA for the RAFT polymerization
of t-BA to form well-defined P(t-BA)-b-PI-b-P(t-BA) triblock copolymer. The final
copolymer has a nM equal to 23,300 g.mol-1, PDI equal to 1.50 as determined by SEC and a
nDP (PI) equal to 80 and nDP (P(t-BA)) equal to 100 as determined by 1H NMR
spectroscopy.
Finally, the tert-butyl ester groups of the P(t-BA) blocks were chemically cleaved to acrylic
acid groups using iodotrimethylsilane at room temperature in order to get PI-b-PAA diblock
and PAA-b-PI-b-PAA triblock copolymers. The thermal properties of block copolymers
before and after dealkylation of tert-butyl ester groups have been investigated by DSC and
I. General strategies to synthesize block copolymers.................................................. ...........5 I.1 Synthesis of well-defined linear AB diblock copolymers...................................... ............6 I.2 Synthesis of well-defined ABA triblock copolymers............................................. ............8
II. Synthesis of block copolymers based on polyisoprene.......................................... ..........11 II.1 Using anionic polymerization.............................................................................. ..........11
II.1.1 Synthesis of AB diblock copolymers............................................................ ..........12 II.1.2 Synthesis of ABA triblock copolymers.......................................................... ..........19
II.2.1.1 Synthesis of AB diblock copolymers......................................................... ..........23 II.2.1.2 Synthesis of ABA triblock copolymers................................................... ..........30
II.2.2 Reversible Addition-Fragmentation Chain transfer Polymerization (RAFT).............32 II.3 Using a combination of various polymerizations................................................... ........36
II.3.1 Synthesis of AB diblock copolymers.............................................................. ........36 II.3.2 Synthesis of ABA triblock copolymers........................................................... ........39
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
General conclusion...............................................................................................129
General introduction
General introduction
- 1 -
In the 20th century, natural polymers such as cellulose, cotton and rubber have attracted
considerable attention from polymer scientists. Increasing environmental consciousness
and demands of consumers have created significant opportunities for improved materials
and development of new preparation methods. Developing polymers from renewable
resources will support environmental request. The current challenge of polymers from
renewable resources is a growing area of reseach.1
Natural rubber (NR) is a polymer of great interest for use in producing new polymeric
materials as it is a polymer which comes form a renewable resource. Moreover, it is well
known that NR consists of a long sequence of cis-1,4-polyisoprene that provides the
material with unique and special properties, including good elastomeric properties, low
glass transition temperature, excellent flexibility, good “green” strength and building tack.2
Due to its excellent properties, polymer scientists have developed new synthetic routes to
obtain polyisoprene with very similar structure.3 The polymerization using Ziegler-Natta
catalysts leads to PIs with 98% of cis-1,4-polyisoprene units.4 However, these synthetic PIs
showed different properties from NR, especially in terms of processability. The living
anionic polymerization5 leads to PIs with 95% of cis-1,4-polyisoprene units, 1% of trans-
1,4-polyisoprene units and 4% of 3,4-polyisoprene units. The controlled/living radical
polymerizations (CRPs)6 of isoprene gave 80% of 1,4-polyisoprene, between 5% and 15%
of 3,4-polyisoprene and between 5% and 15% of 1,2-polyisoprene depending on the
reaction conditions. The microstructure influences the properties of the polyisoprene; for
example, the trans-1,4-polyisoprene has a higher degree of crystallinity and a higher glass
transition temperature than the cis-1,4-polyisoprene.7 Therefore, the synthesis of telechelic
strictly cis-1,4-polyisoprene from natural rubber (TNR) will give rise to original polymers
and copolymers with new potential applications. The most widely used methods to produce
TNR derivatives are controlled oxidative degradation8 or metathesis degradation.9
[1] Joseph, S.; John, M.; Pothen, L.; Thomas, S., Raw and Renewable Polymers. In Polymers-Opportunities and Risks II, Eyerer, P.;
Weller, M.; Hubner, C., Eds. Springer Berlin: Heidelberg, 2010; Vol. 12, p 55-80. [2] Morton, M., Rubber Technology. Van Nostrand Reinhold: New York, 1973. p 152. [3] Puskas, E. J.; Gautriaud, E.; Deffieux, A.; Kennedy, P. J., Prog. Polym. Sci. 2006, 31, 533-548. [4] Van Amerongen G, J., Transition Metal catalyst systems for polymerization Butadiene and Isoprene. In Elastomer Stereospecific
polymerization, Johnson, L. B.; Goodman, M., Eds. American chemical society: Washington, D.C., 1966; Vol. 52, p 136-152. [5] Young, N. R.; Quirk, R. P.; Fetters, J. L., Anionic Polymerizations of Non-Polar Monomers Involving Lithium. In Anionic
polymerization, Fetters, J. L.; Luston, J.; Quirk, R. P.; Vass, F.; Young, N. R., Eds. Springer-Verlag NewYork Heidelberg Berlin, 1984; Vol. 56, p 53.
[6] Jitchum, V.; Perrier, S., Macromolecules 2007, 40, 1408-1412. [7] Kent, E. G.; Swinney, F. B., I&EC Product Research and Development 1966, 5, 134-138. [8] Nor, H. M.; Ebdon, J. R., Prog. Polym. Sci. 1998, 23, 143-177. [9] Ivin, K. J.; Mol, J. C., Olefin metathesis and metathesis polymerisation. Academic Press: London, 1997. p 375.
General introduction
- 2 -
Oxidative degradation of NR has been widely used in our laboratory to develop precursors
for thermoplastic elastomers,10 biomaterials11 and polyurethane materials.12-15 In addition,
we have also developed a method for the preparation of TNR in a single-step process via
the metathesis degradation of cis-1,4-polyisoprene.16 Therefore, it is possible to prepare
functional TNR by combining chain cleavage reaction of NR with a post-functionalization
reaction to form original block copolymers with new potential applications. To best of our
knowledge, no work has been previously reported on the synthesis of telechelic cis-1,4-
polyisoprene from natural rubber as precursor for CRPs in order to obtain well-defined
block copolymers. Among CRP techniques, Reversible Addition/Fragmentation chain
transfer (RAFT) polymerization17 is recognized as one of the most versatile method for the
synthesis of block copolymers since it is effective for a wide range of monomers and thus
leads to a wide range of block copolymers.
The objective of this research work is to develop new strategies to synthesize well-defined
diblock copolymers and triblock copolymers from NR-based cis-1,4-PI by RAFT
polymerization in order to obtain new polymeric materials. In this work, the tert-butyl
acrylate (t-BA) has been chosen as a comonomer. To target such block copolymers, new
synthetic routes (Figure 1) are developed to prepare NR-based cis-1,4-PI which could
further be employed as macromolecular chain transfer agent (macroCTAs) for the RAFT
polymerization of t-BA. In the first approach, the PI-macroCTA was synthesized via the
oxidative degradation of NR followed by reductive amination and amidation. In the second
approach, the PI-macroCTA was synthesized via one-pot metathesis degradation from NR.
In order to compare the properties of final block copolymers, the preparation of synthetic
PI-macroCTAs has also been performed by RAFT polymerization.
Scheme I-21. Synthesis of PI-b-PLA block copolymer by the combination of living
anionic polymerization and controlled coordination-insertion polymerization.76
Recently, Carpentier and coworkers77 reported the synthesis of a well-defined PI-b-PLA
diblock copolymer by a combination of living anionic polymerization of isoprene and the
stereoselective ring-opening polymerization of rac-lactide. The copolymer was synthesized
by a two-step sequential procedure.76,78-79 The first step involves the living anionic
polymerization of isoprene, followed by addition of ethylene oxide to end-capped
polymers (PI-OH). In the second step, an aluminium (1, Scheme I-22A) or yttrium (2,
Scheme I-22B) organometallic moiety is grafted onto PI-OH to get PI-O-[Al] or PI-O-[Y]
macroinitiators. The polymerization of rac-lactide with the macroinitiator PI-O-[Y]
occurred under much milder conditions (THF, 20 °C, 1 h) than those required for
PI-O-[Al] (toluene, 70 °C, 96 h). Moreover, the PI-O-[Al] macroinitiator undergoes an
isotactic PLA block as the PI-O-[Y] macroinitiator undergoes a heterotactic PLA block.
The resulting PI-b-PLA copolymers with an isotactic or a heterotactic PLA segment have
nM ≈ 13,600 g.mol-1and polydispersity index of 1.19 determined by SEC.
Chapter I : Literature on block copolymers based on PI
- 38 -
A)
OH
n R-Y[X2]
Me-Al[X'2]
O
n
Y[X2]
O
n
Al[X'2]
O
n
O
O O
O
O
O
OO
H
m
O
n
O
O O
O
O
O
OO
H
m
1. D,L-lactide
2. H+
PI b (het D,L PLA)
THF
20 °C
PI b (iso D,L PLA)
1. D,L-lactide
2. H+
toluene
70 °C
p q
t-Bu O
t-Bu
N N
O t-Bu
t-Bu
Al
Me
t-Bu
t-Bu
N
O Y O
t-Bu
t-BuO
THF
RMe
R = N(SiHMe2)2
B)
1
2
1
2
Scheme I-22. Synthesis of PI-b-PLA block copolymers by a combination of living anionic
polymerization and controlled organometallic-insertion polymerization: A) using an
aluminium based organometallic, and B) using an yttrium based organometallic.77
Miura and Miyake80 investigated the synthesis of polydimethylsiloxane-b-polyisoprene
diblock copolymers by the combination of anionic ring-opening polymerization (AROP) of
hexamethylcyclotrisiloxane (D3) and NMP of isoprene (Scheme I-23). In the first step, an
alkoxyamine (A, Scheme I-23) was treated with Li powder in ether (B, Scheme I-23)
suitable for the AROP of D3. The resulting functional PD3 was employed for the
polymerization of isoprene in bulk at 120 °C in order to obtain PD3-b-PI diblock
copolymer. Characteristics of the copolymer were determined by SEC ( nM = 10,100
g.mol-1, PDI = 1.15) and 1H NMR spectroscopy ( nM = 13,000 g.mol-1). In addition, the
PD3-b-PI was also used as a macroinitiator to prepare PD3-b-PI-b-PS triblock copolymers.
Chapter I : Literature on block copolymers based on PI
- 39 -
BrO N
PhLi, ether
RTLi
O N
Ph(+ LiBr)
D3
O N
PhCH3
m
n
D3
O N
Ph
CH3m
D3, THF
RT
n120 °C
D3 :
(A) (B)
SiO
SiO
Si
O
m
Scheme I-23. Synthesis of PD3-b-PI block copolymer by combination of AROP and
NMP.80
II.3.2 Synthesis of ABA triblock copolymers
The synthesis of ABA triblock copolymers based on isoprene and styrene by a
combination of anionic polymerization and atom transfer radical polymerization81-82
(ATRP) has been described by Matyjaszewski et al.83. The macroinitiator, polystyrene-b-
polyisoprene containing a 2-bromoisobutyryl bromide (BriBBr) chain-end (PS-b-PI-Br)
(Scheme I-24A) was prepared by anionic polymerization. For that, styrene was first
polymerized in toluene at −30°C using BuLi as initiator in dry box. Afterward, isoprene
was added to the solution. The living PS-b-PI−Li+ was chain extended with styrene epoxide
and then terminated by addition of BriBBr (Scheme I-24B). The macromolecular
characteristics of PS-b-PI-Br were determined by SEC ( nM = 16,800 g.mol-1 and
PDI = 1.03). The copolymer composition was determined by 1H NMR spectroscopy ( nDP
(PS) = 58 and nDP (PI) = 160). The PS-b-PI-Br was then used to initiate the
polymerization of styrene by ATRP in bulk at 110 °C using copper bromide (I) complexed
with N, N, N’, N’, N’’-pentamethyldiethylenetriamine (PMDETA) as a catalytic system to
form PS-b-PI-b-PS triblock copolymer. The resulting triblock copolymer had a number-
average molecular weight nM = 32,800 g.mol-1 and a PDI of 1.20.
Chapter I : Literature on block copolymers based on PI
- 40 -
+ s BuLi30 °C
LiPSTHF,
LI30 °C
PS b PITHFH2C CH
O
LIPS b PI CH2 CH O BrPS b PI CH2 CH O C
OBrBr C
O
CuBr, PMDETA, 110 °CPS b PI b PS
A)
BrPS b PI CH2 CH O C
OB)
m
n
x
Scheme I-24. Synthesis of PS-b-PI-b-PS block copolymer by combination of anionic
polymerization and ATRP: A) PS-b-PI-Br diblock copolymer, and B) PS-b-PI-b-PS
triblock copolymers.83
Chapter I : Literature on block copolymers based on PI
- 41 -
Conclusion
Well-defined block copolymers based on polyisoprene and other polymers can be
synthesized either by anionic polymerization, controlled/living radical polymerization or a
combination of various polymerizations. Of these techniques, controlled/living radical
polymerization methods have numerous advantages over the anionic polymerization as the
reactions can be performed under less stringent conditions and they can be applied to a
wide range of functional monomers. These advantages drive us to use controlled/living
radical polymerization and more precisely the RAFT polymerization to synthesize block
copolymers based on polyisoprene as NMP necessitates high temperatures for some
monomers such as styrene and the challenging synthesis of difunctional initiators. The
polyisoprene block is often obtained starting from the isoprene monomer but it can also be
obtained from a biomacromolecule, cis-1,4-polyisoprene, or so called natural rubber (NR).
In this case, telechelics from natural rubber (TNR) are necessary to synthesize block
copolymers. The transformation of NR into TNR can be obtained by chain cleavage
reaction of NR with a functionalization.
In this work, we propose two strategies to prepare AB diblock copolymers based on PI
using the RAFT process:
− starting from synthetic isoprene monomer,
− starting with TNR obtained by oxidative chain cleavage of NR and then chemically
modified by coupling reaction with a RAFT agent.
These PIs are used as macromolecular chain transfer agents (macroCTAs), and then chain
extended with t-BA using RAFT polymerization to make AB diblock copolymers. In
addition, we will demonstrate the synthesis of ABA triblock copolymers based on PI
obtained from a functional metathesis degradation of NR. Such degradation leads to
difunctional PI-macroCTAs which were employed for the RAFT polymerization of t-BA
to form ABA triblock copolymers.
Chapter I : Literature on block copolymers based on PI
- 42 -
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[29] Jerome, R.; Fayt, R.; Ouhadi, T., Prog. Polym. Sci. 1984, 10, 87. [30] Binder, W. H.; Sachsenhofer, R., Macromol. Rapid Commun. 2007, 28, 15-54. [31] Bellas, V.; Rehahn, M., Macromol. Rapid Commun. 2007, 28, 1415-1421. [32] Fetters, L. J.; Lustofi, J.; Quirk, R. P., Adv. Polym. Sci. 1984, 56, 1. [33] Hadjichristidis, N.; Iatrou, H.; Pispas, S.; Pitsikalis, M., J. Polym. Sci., Part A:
Polym. Chem. 2000, 38, 3211-3234. [34] Pispas, S.; Hadjichristidis, N., Macromolecules 2000, 33, 6396-6401. [35] Kaditi, E.; Pispas, S., J. Polym. Sci., Part A: Polym. Chem. 2010, 48, 24-33. [36] Quirk, R. P.; Corona-Galvan, S., Macromolecules 2001, 34, 1192-1197. [37] Pispas, S., The Journal of Physical Chemistry B 2006, 110, 2649-2655. [38] Narita, T.; Terao, K.; Dobashi, T.; Nagasawa, N.; Yoshii, F., Colloids and Surfaces
B: Biointerfaces 2004, 38, 187-190. [39] Morton, M., Anionic Polymerization: Principles and Practice. Academic Press: New
531. [44] Varshney, S. K.; Hautekeer, J. P.; Fayt, R.; Jerome, R.; Teyssie, P., Macromolecules
1990, 23, 2618-2622. [45] Ünal, I., H.; Price, C.; Budd, P. M.; Mobbs, R. H., Eur. Polym. J. 1994, 30, 1037-
1041. [46] Huang, H.; Remsen, E. E.; Kowalewski, T.; Wooley, K. L., J. Am. Chem. Soc. 1999,
121, 3805-3806. [47] Lu, Z.; Liu, G.; Liu, F., J. Appl. Polym. Sci. 2003, 90, 2785-2793. [48] Tasis, D.; Pispas, S.; Galiotis, C.; Bouropoulos, N., Mater. Lett. 2007, 61, 5044-5046. [49] Lu, Z.; Xu, H.; Li, Y.; Hu, Y., J. Appl. Polym. Sci. 2006, 100, 1395-1402. [50] Batra, U.; Russel, W. B.; Pitsikalis, M.; Sioula, S.; Mays, J. W.; Huang, J. S.,
Macromolecules 1997, 30, 6120-6126. [51] Varshney, S. K.; Kesani, P.; Agarwal, N.; Zhang, J. X.; Rafailovich, M.,
Macromolecules 1999, 32, 235-237. [52] Davis, K. A.; Matyjaszewski, K., Adv. Polym. Sci. 2002, 159, 1. [53] Hawker, C. J.; Bosman, A. W.; Harth, E., Chem. Rev. 2001, 101, 3661-3688. [54] Moad, G.; Rizzardo, E.; Thang, S. H., Polymer 2008, 49, 1079-1131. [55] Wootthikanokkhan, J.; Tongrubbai, B., J. Appl. Polym. Sci. 2003, 88, 921-927. [56] Gopalan, P.; Li, X.; Li, M.; Ober, C. K.; Gonzales, C. P.; Hawker, C. J., J. Polym.
Sci., Part A: Polym. Chem. 2003, 41, 3640-3656. [57] Wegrzyn, J. K.; Stephan, T.; Lau, R.; Grubbs, R. B., J. Polym. Sci., Part A: Polym.
Chem. 2005, 43, 2977-2984. [58] Greene, A. C.; Grubbs, R. B., J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 6342-
6352. [59] Iovu, M. C.; Craley, C. R.; Jeffries-El, M.; Krankowski, A. B.; Zhang, R.;
Kowalewski, T.; McCullough, R. D., Macromolecules 2007, 40, 4733-4735. [60] Iovu, M. C.; Jeffries-El, M.; Sheina, E. E.; Cooper, J. R.; McCullough, R. D.,
Polymer 2005, 46, 8582-8586. [61] Benoit, D.; Harth, E.; Fox, P.; Waymouth, R. M.; Hawker, C. J., Macromolecules
2000, 33, 363-370.
Chapter I : Literature on block copolymers based on PI
- 44 -
[62] Murthy, K. S.; Ma, Q.; Remsen, E. E.; Tomasz, K.; Wooley, L. K., J. Mater. Chem. 2003, 13, 2785.
[63] Huang, H.; Kowalewski, T.; Wooley, K. L., J. Polym. Sci., Part A: Polym. Chem. 2003, 41, 1659-1668.
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[65] Benoit, D.; Chaplinski, V.; Braslau, R.; Hawker, C. J., J. Am. Chem. Soc. 1999, 121, 3904-3920.
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[67] Yin, X.; Hoffman, A. S.; Stayton, P. S., Biomacromolecules 2006, 7, 1381-1385. [68] Jitchum, V.; Perrier, S., Macromolecules 2007, 40, 1408-1412. [69] Chiefari, J.; Chong, Y. K.; Ercole, F.; Krstina, J.; Jeffery, J.; Le, T. P. T.;
Mayadunne, R. T. A.; Meijs, G. F.; Moad, C. L.; Moad, G.; Rizzardo, E.; Thang, S. H., Macromolecules 1998, 31, 5559-5562.
[70] Wood, M. R.; Duncalf, D. J.; Rannard, S. P.; Perrier, S., Org. Lett. 2006, 8, 553-556. [71] Germack, D. S.; Wooley, K. L., J. Polym. Sci., Part A: Polym. Chem. 2007, 45,
4100-4108. [72] Lai, J. T.; Filla, D.; Shea, R., Macromolecules 2002, 35, 6754-6756. [73] Germack, D. S.; Wooley, K. L., Macromol. Chem. Phys. 2007, 208, 2481-2491. [74] Bartels, J. W.; Billings, P. L.; Ghosh, B.; Urban, M. W.; Greenlief, C. M.; Wooley,
K. L., Langmuir 2009, 25, 9535-9544. [75] Devasia, R.; Bindu, R. L.; Borsali, R.; Mougin, N.; Gnanou, Y., Macromolecular
Symposia 2005, 229, 8-17. [76] Schmidt, S. C.; Hillmyer, M. A., Macromolecules 1999, 32, 4794-4801. [77] Amgoune, A.; Thomas, C. M.; Balnois, E.; Grohens, Y.; Lutz, P. J.; Carpentier, J.-F.,
Macromol. Rapid Commun. 2005, 26, 1145-1150. [78] Wang, Y.; Hillmyer, M. A., Macromolecules 2000, 33, 7395-7403. [79] Zalusky, A. S.; Olayo-Valles, R.; Wolf, J. H.; Hillmyer, M. A., J. Am. Chem. Soc.
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Chapter II
Synthesis of block copolymers based
on PI by RAFT process
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 45 -
Introduction
As mentioned in the previous chapter, the successful polymerization of isoprene via the
RAFT process was reported by Perrier et al.1 and by Wooley et al.2-3 Moreover, these
groups demonstrated the ability of RAFT polymerization to prepare AB diblock
copolymers and ABC triblock copolymers. For instance, Perrier et al.1 have prepared well-
defined poly(tert-butyl acrylate)-b-polyisoprene (P(t-BA)-b-PI) and polystyrene-b-
polyisoprene (PS-b-PI) block copolymers. In this study,1 P(t-BA) or PS is first prepared
and then used as a molecular chain transfer agent (macroCTA) to chain extend with
isoprene in order to prepare P(t-BA)-b-PI or PS-b-PI block copolymers. Moreover,
Wooley et al.2 have reported the RAFT polymerization of isoprene to target PI and chain
extended the PI-macroCTA with styrene to form PI-b-PS diblock copolymer. The same
group3 also reported the preparation of P(t-BA)-b-PI-b-PS triblock copolymers via RAFT
polymerization. In this case, P(t-BA) is synthesized first followed by RAFT
polymerization of isoprene. The resulting P(t-BA)-b-PI is then used as a macroCTA for
the RAFT polymerization of styrene.
The aim of the research work described in this chapter is to develop synthetic routes to
obtain well-defined block copolymers based on PI and P(t-BA) via RAFT polymerization.
These copolymers may find applications as compatibilizers for polymer blends,4 surface
modifiers5 and adhesive applications when the tert-butyl group is cleaved in order to form
acrylic acid.
Herein, PI-b-P(t-BA) diblock copolymer was prepared via RAFT polymerization. The
method of synthesis differs from the work by Wooley. et al3 as the blocks are prepared in
the reverse order. In this work, well-defined polyisoprene is first synthesized by RAFT
polymerization using S-1-dodecyl-S’-(α-α’-dimethyl-α’’-acetic acid) trithiocarbonate6 (1,
Scheme II-1) as a chain transfer agent. The resulting PI was used as macroCTA to mediate
the RAFT polymerization of t-BA to form PI-b-P(t-BA) block copolymers.
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 46 -
I. Synthesis and characterization of polyisoprene
RAFT polymerization of isoprene was carried out using S-1-dodecyl-S’-(α-α’-dimethyl-
α’’-acetic acid) trithiocarbonate (1, Scheme II-1) and tert-butyl peroxide (t-bp) as initiator
at 125 °C for 25h. Monomer conversion was determined via gravimetry and calculated to
be 49 % conversion.
C12H25S
S
SOH
O
1
C12H25S
S
SO
OH
x y z
0.2 eq t-bp
125 °C, 25h
190 eq1 eq
+
2
Scheme II-1. Synthesis of polyisoprene via RAFT polymerization of isoprene in bulk at
125 °C ([I]0/([1]0/([t-bp]0=190/1/0.2).
The resulting polymer was characterized by 1H NMR spectroscopy and 13C NMR
spectroscopy (Figure II-1) . 1H NMR spectroscopy of a representative polymer (Figure II-
1A) revealed the presence of polyisoprene resonances arising from all three major repeat
unit isomers.7-8 Peaks at 5.84-5.67 ppm, at 5.12 ppm, 4.98-4.81 ppm and at 4.75-4.61 ppm
are corresponding to methine protons, 11 (1,2-polyisoprene, -HC=CH2), methine protons,
MM and MmacroCTA are the initial concentration of t-BA monomer, the initial concentration of polyisoprene macroCTA, the molecular weight of t-BA monomer and the molecular weight of the polyisoprene macroCTA respectively. cNumber-average molecular weight measured by size exclusion chromatography (SEC) calibrated with polystyrene standards. dPolydispersity index measured by SEC.
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
- 52 -
9 10 11 12 13 14 15 16 17 18
Retention time (mins)
PI
PI-b-P(t-BA)_1.5h
PI-b-P(t-BA)_2.5h
PI-b-P(t-BA)_3.25h
PI-b-P(t-BA)_4h
Figure II-3. Overlaid SEC traces of PI-macroCTA and PI-b-P(t-BA) diblock
copolymers synthesized via RAFT polymerization of t-BA in bulk at 60 °C
([t-BA] 0/[PI-macroCTA]0/[AIBN] 0 = 250/1/0.2).
The molar composition of the diblock copolymer was determined by comparing the
integral of the ethylenic proton, 7 (Figure II-4A) , of the 1,4-polyisoprene backbone (set
equivalent to the degree of polymerization of 81) at resonance at 5.12 ppm to the methine
proton, 23 (Figure II-4A), of P(t-BA) resonances at 2.4-2.1 ppm on the 1H NMR spectrum
of the copolymer (Figure II-4A) . It was found that the diblock copolymer contains 47% of
P(t-BA) for 53% of 1,4-polyisoprene. Therefore, the number-average degree of
polymerization )DP( n of PI is equal to 90 and the nDP of P(t-BA) is equal to 72. Finally,
the molar composition of the diblock copolymer is equal to 55.5% of PI and 44.5% of
P(t-BA).
Chapter II : Synthesis of block copolymers based on PI by RAFT polymerization
Figure III-2. 13C NMR spectrum of α-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene (4,
Scheme III-1).
The reaction between the in situ formed carboxylic chloride of the RAFT agent (3, Scheme
III-1) and the α-amino group of functionalized polyisoprene (2, Scheme III-1) was further
studied by MALDI-TOF MS analysis by using dithranol as matrix with silver
trifluoroacetate as added salt. Figure III-3 shows an enlargement from 800 to 1400 g mol-1
of the MALDI-TOF-MS spectrum of α-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene.
There are two sets of peaks separated by an identical peak-to-peak mass increment, which
is equal to the molecular weight of the isoprene repeating unit (68 Da). Here, the two sets
of molecular ions are labelled as A’ and B’ (Figure III-3) in ascending order of m/z
magnitude. Each peak of set A’ is higher in intensity than the corresponding peak of set B’,
separated by 16 in m/z corresponding to the presence of an epoxide unit in the main chain.
These epoxide units come from the uncomplete oxidative chain cleavage reaction used to
prepare the initial carbonyl telechelic cis-1,4-polyisoprene and have been previously
observed25,41. The fragment ion at m/z = 814.62 of series A’ (Figure III-2) corresponds to
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 67 -
a polymer chain consisting of n =9 isoprene units ionized by a hydrogen atom with a
sulfonium (EG1, Scheme III-2) at one chain-end and a ketone group (EG2, Scheme III-2)
at the other chain-end. The theoretical mass calculated with the equation (1) is 814.65 Da
(monisotopic peak) in good agreement with the experimental values of 814.62 Da,
confirming the formation of such a structure. The occurrence of fragmentation during
ionization in the MALDI-TOF analysis of dithiocarbamate-terminated polymers has
already been reported42-46. A fragmentation pathway involving the protonation of the
trithiocarbonyl group followed by the heterolytic cleavage of S-C(S)S group could
occurred (Scheme III-2). This cleavage leads to the formation of the sulfonium species
(EG1, Scheme III-2) and a neutral molecule (5, Scheme III-2). This is in a good
agreement with the analysis in negative mode, which did not show C12H25 nor
C12H25SCS species. Each peak value was calculated according to the following equation
(1):
Mcal = MEG + nMisoprene (1)
where MEG is the mass of the end groups (⊕S-C6H11NO, EG1 and C3H5O, EG2) with an
average molecular mass = 202.09,) in the telechelic cis-1,4-polymer, Misoprene is the mass of
isoprene unit (molecular mass = 68) and n is the number of repeating units.
m
ONHC12H25S
S
SO
m
ONHS
Ouν+ C13H26S2
EG1
19 kV
EG2H
4 4' 5
Scheme III-2. End groups observed during MALDI-TOF MS measurements.
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 68 -
Figure III-3. MALDI-TOF mass spectrum of α-trithiocarbonyl-ω-carbonyl-cis-1,4-
polyisoprene
The data obtained from 1H NMR spectroscopy and MALDI TOF mass spectrometry
provide evidence for the formation of the new α-trithiocarbonyl-ω-carbonyl-cis-1,4-
polyisoprene with a number-average molecular weight ( nM ) of 12,000 g mol-1and
polydispersity index of 1.60 as determined by SEC. The number-average degree of
polymerization equal to 62 ( nM = 4650 g mol-1) was calculated from 1H NMR spectrum
by comparing the integration of methylene protons of the chain-ends at 2.43 ppm (12,
Figure III-1) to the integration of the methine proton of the isoprene backbone at 5.12
ppm (9, Figure III-1) . The different nM values between SEC and 1H NMR spectroscopy
are attributed to the fact that polystyrene standards calibration was used to determine the
average molecular weights.
The average trithiocarbonyl functionality )( nf of α-trithiocarbonyl-ω-carbonyl-cis-1,4-
polyisoprene was determined by 1H NMR spectroscopy, by comparing the integration of
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 69 -
the methylene protons at 2.43 ppm (12, Figure III-1) with the one of the methylene
protons at 3.25 ppm (3, Figure III-1) . The integration of their respective peaks showed
complete trithiocarbonate functionality by 1H NMR spectroscopy (Figure III-1) that
agrees with a 1:1 theoretical ratio. Therefore, α-trithiocarbonyl-ω-carbonyl-cis-1,4-
polyisoprene can subsequently be used as a monofunctional macroCTA for the chain
extension reaction in order to form diblock copolymers.
II. Synthesis of PI-b-P(t-BA) diblock copolymer
We investigated the synthesis of a PI-b-P(t-BA) diblock copolymer using a purified α-
trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene (4, Scheme III-3) as a macromolecular
chain transfer agent (macroCTA). The reaction was performed in toluene at 60 oC and
AIBN was used as an initiator ([t-BA] 0/[macroCTA]0/[AIBN] 0 = 250/1/0.2) (6, Scheme
III-3) . Monomer conversion was determined by following the disappearance of the vinyl
peaks of t-BA at the range of 6.40 to 5.60 ppm in comparison with methyl protons of
anisole used as an internal standard at 3.75 ppm by 1H NMR spectroscopy. Table III-1
shows that the t-BA conversion increases with time and reaches 39% after 5h. Moreover,
the number-average molecular weights of the block copolymer increase with t-BA
conversion. SEC traces in Figure III-4 shows a shift towards higher number-average
molecular weights indicating that the α-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene
(4, Scheme III-3) was extended into a block copolymer. Moreover, the SEC traces of the
so obtained block copolymers are unimodals illustrating that the polymerization of the
second block underwent chain transfer quantitatively. The molar composition of block
copolymer (S-4, Table III-1) was analyzed by 1H-NMR spectroscopy. The number
average degree of polymerization )DP( n of PI was equal to 62 and that of P(t-BA) was
equal to 87 as calculated by comparing the integral of the ethylenic proton, (8, Figure III-
5) of the polyisoprene backbone at 5.12 ppm to the methine proton, (4, Figure III-5) of
P(t-BA) at 2.4-2.1 ppm on the 1H NMR spectrum of the copolymer (Figure III-5) . The
data obtained from SEC and 1H NMR spectroscopy provide additional evidence for the
formation of the AB diblock copolymer based on the cis-1,4-polyisoprene from natural
rubber.
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 70 -
m
OC12H25
S
S
SO
NH
4
60 °C, toluene
O O
0.2 eq. AIBN
m
OC12H25
S
S
SO
NH
O O
k
6
250 eq.
Scheme III-3. Synthesis of PI-b-P(t-BA) by RAFT polymerization using α-trithiocarbonyl-
ω-carbonyl-cis-1,4-polyisoprene as macroCTA.
Table III-1. Synthesis of AB diblock copolymers via RAFT polymerization of tert-butyl
acrylate (t-BA) using the PI as macroCTA and AIBN as initiator at 60°C in toluene.
Copolymer
Reaction time
(h)
conv.a
(%)
b,calnM
(g mol-1)
c,SECnM
(g mol-1)
PDId
S-1 1 2 12 640 13 000 1.55
S-2 2 4 13 280 13 500 1.55
S-3 4 21 18 720 19 000 1.55
S-4 5 39 24 480 26 000 1.76 aMonomer conversion determined using 1H NMR spectroscopy. bNumber average molecular weight
calculated using: calcnM , = (conversion (%)×[M] 0/[MacroCTA]0×MM)+MmacroCTA where [M]0, [MacroCTA]0, MM and MmacroCTA are the initial concentration of t-BA monomer, the initial concentration of ∝-trithicarbonyl-ω-carbonyl-cis-1,4-polyisoprene macroCTA, the molecular weight of t-BA monomer and the molecular weight of the ∝-trithiocarbonyl-ω-carbonyl-cis-1,4-polyisoprene macroCTA respectively. cNumber average molecular weight measured by size exclusion chromatography (SEC) calibrated with polystyrene standards. dPolydispersity index measured by SEC.
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 71 -
Figure III-4. Overlaid SEC traces using UV detection at a wavelength of 309 nm of PI
A typical RAFT polymerization. A typical procedure is given for the polymerization of
tert-butyl acrylate (t-BA) mediated by the α-trithiocarbonyl-ω-carbonyl-cis-1,4-
polyisoprene. (4, Scheme III-1) used as macromolecular chain transfer agent (macroCTA)
and using AIBN as initiator ([t-BA] 0/[macroCTA]0/[AIBN] 0 = 250/1/0.2). A magnetic stir
bar was charged to a Schlenk tube together with the macroCTA (0.4337 g, 0.093 mmol), t-
BA (2.976 g, 23.25 mmol), AIBN (0.0030 g, 0.018 mmol), toluene (0.8 mL, 20% v/v) and
anisole (0.17 mL, 5% v/v). Then, the reaction mixture was deoxygenated by bubbling with
argon for 15 min. The polymerization was initiated (t = 0) by immersion in a thermostated
oil bath at 60°C. Samples were withdrawn from the reaction mixture via a degassed
syringe for conversion monitoring (by 1H NMR spectroscopy) and molecular weight
analysis (by SEC). At the end of reaction, the polymer solution was concentrated under
vacuum using rotary evaporation and was purified by a series of precipitations from
dichloromethane (minimum volume) into an ice cold 1:1 mixture of water and methanol.
The copolymer was separated by filtration and dried under vacuum until constant weight. It
was then further analyzed by 1H NMR spectroscopy, 13C NMR spectroscopy and SEC. 1H NMR (CDCl3): δ (ppm) 5.12 (br, polyisoprene backbone -C(CH3)=CH), 3.25 (t, chain-
Chapter III : Synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes and their use to prepare block copolymers via RAFT polymerization
- 77 -
References [1] Mohanty, A. K.; Misra, M.; Hinrichsen, G., Macromol. Mater. Eng 2000, 276-277,
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Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 79 -
One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprenes
and their use to prepare block copolymers by RAFT polymerization.
Publication accepted in Macromolecules, DOI: 10.1021/ma102406w
Graphical abstract
n
C12H25S S
OS
O
OS S
C12H25
O
S
C12H25S S
S
S SC12H25
SqO O O O
m m
1) Grubbs II catalyst
2) t-butyl acrylate/ AIBN
+
P(t-BA)-b-PI-b-P(t-BA) triblock copolymer
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 80 -
ABSTRACT : We investigate the one-pot synthesis of a new α,ω-bistrithiocarbonyl-end
functionalized telechelic cis-1,4-polyisoprene (PIp) via metathesis degradation from
natural rubber (NR) in the presence of the Grubbs second generation catalyst (GII) and a
bistrithiocarbonyl-end functionalized olefin as a chain transfer agent (CTA). When the
metathesis degradation of the NR of 2x106 g mol-1 molecular weight is performed in
toluene at 25 °C using the ratio of [Ip]0/[GII] 0/[CTA] 0 = 100/1/1, a cis-1,4-polyisoprene of
14,000 g mol-1 after 4h is obtained. The functionality estimated by 1H NMR spectroscopy
is equal to 1.5±0.1. The structure of telechelic cis-1,4-polyisoprene was confirmed by
combination of 1H NMR, 13C NMR spectroscopy and FTIR. The influence of the CTA
concentration was investigated. It was found that using concentrations of catalyst
([Ip] 0/[GII] 0/[CTA] 0 of 100/1/2 and 100/1/5 lead to form a perfectly telechelic cis-1,4-
polyisoprene with a functionality of 2 with no significant difference in nM values
(approximately 6,400 g mol-1) and in polydispersity indices (∼1.70). The new well-defined
α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprenes were used
successfully as macromolecular chain transfer agents (macroCTA) to mediate the RAFT
polymerization of t-BA using AIBN as the initiator ([t-BA] 0/[macroCTA]0/[AIBN] 0 =
500/1/0.4) in toluene at 60 °C leading to well-defined P(t-BA)-b-PIp-b-P(t-BA) triblock
Telechelic unsaturated polymers are good candidates to obtain block copolymers with a
wide range of applications. For instance, block copolymers containing polyisoprene (PIp)
as a constituent have found applications as nanofibers1, thermoplastic elastomers,2 pressure
sensitive adhesives,3-4 and biocompatible materials.5-6 The PIp block is essentially
synthesized by living anionic polymerization of isoprene (Ip),7-16 by controlled/living
radical polymerization (CRP) of isoprene,17-27 or ring-opening metathesis polymerization
of 1,5-dimethyl-1,5-cyclooctadiene.28 The cis-1,4-polyisoprene block can be obtained from
natural rubber (NR) which is a biomacromolecule and a renewable resource. It is well
known that strictly cis-1,4-microstructure of NR provides unique and special properties,
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 81 -
including good elastomeric properties, very low glass transition temperature, excellent
flexibility, good “green” strength and building tack. Therefore, the synthesis of telechelic
cis-1,4-polyisoprene from NR (TNR) opens new synthetic routes to develop materials
based on a biopolymer from a renewable resource. The block copolymers obtained from
NR can lead to new materials with properties suitable for a number of potential
applications including microemulsion elastomers29 for the paint industry, adhesives3-4 and.
nanoporous materials.30 The transformation of NR into TNR can be obtained by combining
chain cleavage reaction of NR with a postfunctionalization reaction. The most widely used
methods to produce TNR derivatives are controlled oxidative degradation,
photodegradation or metathesis degradation.31 Our group has focused on selective
degradation of synthetic cis-1,4-polyisoprene using well-controlled oxidative chain
cleavage reaction leading to new carbonyl telechelic cis-1,4-polyisoprene32 and the
chemical modification of carbonyl end-groups has led to the development of new
hydroxyl6,33 and amino telechelic polyisoprenes.34 The hydroxyl telechelic polyisoprene
was engaged as a precursor in the synthesis of linear polyurethanes for biological
materials6 and foams applications.35-36 However, this technique requires several steps to
obtain the precursor of the desired products. Alternatively, we have also developed a
method for the preparation of acetoxy-telechelic polyisoprene in a single-step process via
the metathesis degradation of cis-1,4-polyisoprene.37-38 To the best of our knowledge, no
study has been reported on the single-step synthesis of telechelic cis-1,4-polyisoprene
suitable to be employed as precursors for controlled/living radical polymerizations (CRPs)
in order to obtain block copolymers. Among CRP techniques,39 Reversible
Addition/Fragmentation chain Transfer (RAFT) polymerization40 is recognized as one of
the most versatile method for the synthesis of block copolymers since it is compatible with
a wide range of unprotected polar monomers41 including acrylic acid.42 The most common
RAFT chain transfer agent (CTA) contains thiocarbonylthio groups that are easily removed
or modified by a variety of methods.43
Herein, we have investigated the one-pot synthesis of original telechelic cis-1,4-
polyisoprenes (PIp) through a metathesis degradation of NR using Grubbs second
generation catalyst and a bistrithiocarbonyl-end functionalized olefin as a CTA (2, Scheme
IV-1A ). The resulting PIp were used as difunctional macroCTAs to mediate the
polymerization of tert-butyl acrylate to form ABA triblock copolymers via the RAFT
process. To the best of our knowledge, no previous studies have been reported on the one-
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 82 -
pot synthesis of α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene
suitable to be used in RAFT polymerization.
n
[Ru]
+
[Ru]O
S SC12H25
O
S+
C12H25S S
OS
O
OS S
C12H25
O
S
p6
3
5'
4
5
B)
[Ru] [Ru]
m m'
C12H25S S
OS
O
n
p'6'
C12H25S S
OS
O
[Ru]
n'
+
7
C12H25S S
OS
O
OS S
C12H25
O
Sq
NN
Ru
PCy3
Ph
Cl
Cl
[Ru]Ph
:
[Ru]Ph
1. (COCl)2, 20 °C
HO OH1
2
C12H25S S
OHS
O
C12H25S S
OS
O
OS S
C12H25
O
S2.
Toluene, 25 °C
15 min.
A)
[Ru]O
S SC12H25
O
S33'
C12H25S S
OS
O Ph
+
Scheme IV-1. A) Synthesis of a bistrithiocarbonyl-end functionalized CTA and, B)
synthesis of α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene from
NR via metathesis degradation.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 83 -
I. Functional Metathesis Degradation.
Herein, we investigated the synthesis of α,ω-bistrithiocarbonyl-end functionalized
telechelic cis-1,4-polyisoprene via metathesis degradation of NR using Grubbs second
generation catalyst (GII) and a bistrithiocarbonyl-end functionalized olefin (2) as the CTA
(Scheme IV-1). The difunctional CTA was reacted with Grubbs II catalyst in a
stoichiometrical ratio in toluene-d8 at 25 °C and the resulting product analyzed by 1H NMR
spectroscopy (Figure IV-1) and 2D-correlation spectroscopy (COSY) (Figure IV-2). New
peaks were observed in 1H NMR spectrum (Figure IV-1) at 5.35 ppm and 4.14 ppm that
are attributed to the olefinic proton, 1’([Ru]=CHCH2OC(O)-R) and to aliphatic proton, 2’
([Ru]=CHCH2OC(O)-R), respectively. In addition, new peaks were found at 4.36 ppm, at
5.87-5.80 ppm and at 6.15-6.10 ppm corresponding to 2’’ (Ph-CH=CHCH2OC(O)-R), to 4
(Ph-CH=CHCH2OC(O)-R), and to 4’ (Ph-CH=CHCH2OC(O)-R), respectively. COSY
two-dimensional NMR experiment was used to confirm these structures. In the COSY
spectrum (Figure IV-2), the signal at 4.14 ppm corresponding to aliphatic proton 2’ is
correlated with the signal centred at 5.35 ppm, corresponding to the olefinic proton, 1’. We
can also observe the correlation between the signals 6.15-6.10 ppm and 5.87-5.80 ppm,
corresponding to alkenes proton 4’ and 4, with the signal at 4.36 ppm, corresponding to
aliphatic proton 2” . Thus it was confirmed that the Grubbs II catalyst reacts with
difunctional CTA (2, Scheme IV-1A) to result in the new ruthenium carbene molecule (3,
Scheme IV-1A). This new catalyst (3, Scheme IV-1A) undergoes the metathesis
degradation at 25 °C with double bonds of NR (4, Scheme IV-1B) to form α,ω-
Therefore, the one-pot degradation and functionalization reactions can continuously take
place in a catalytic fashion.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 84 -
[Ru]
C12H25S
S
SO
O O
OS
S
SC12H25
O
OS
S
SC12H25
[Ru]
Ph
+
+
C12H25S
S
SO
O
Ph1
2
3
2'
2"
4
1'
4'
25 °C
Toluene-d8
4.55.05.56.06.57.07.5 ppm
4.55.05.56.06.57.07.5 ppm
4.55.05.56.06.57.07.5 ppm192021 ppm
192021 ppm
192021 ppm
1
1'
3
2
2'
2"44'
1'
Figure IV-1. 1H NMR spectra (toluene-d8), A) the resulting mixture solution between
CTA and Grubbs II catalyst, B) CTA, and C) Grubbs II catalyst.
A)
B)
C)
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 85 -
[Ru]
C12H25S
S
SO
O O
OS
S
SC12H25
O
OS
S
SC12H25
[Ru]
Ph
+
+
C12H25S
S
SO
O
Ph1
2
3
2'
2"
4
1'
4'
25 °C
Toluene-d8
ppm
4.04.55.05.56.06.57.0 ppm
4.0
4.5
5.0
5.5
6.0
6.5
7.0
2'
2"44'
1'
2'
2"
4
4'
1'
Figure IV-2. COSY spectrum (toluene-d8) of the resulting mixture solution between CTA
and Grubbs II catalyst.
A first attempt for the preparation of telechelic NR (entry A-2, Table IV-1) was
performed in toluene using Grubbs II catalyst and bistrithiocarbonyl-end functionalized
olefin (2, Scheme IV-1A) as the CTA. The reaction was carried out at room temperature
for 4h with a ratio [Ip]0/[GII] 0/[CTA] = 100/1/1. The resulting polymer was characterized
by 1H NMR spectroscopy (Figure IV-3) and 2D-correlation spectroscopy (COSY) (Figure
IV-4) . An intense signal corresponding to vinylic protons at 5.16 ppm (4,
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 86 -
-(CH3)C=CHCH2-) was observed in 1H NMR spectroscopy (Figure IV-3). This result
indicates that telechelic polyisoprenes with 1,4-microstructure are obtained. In addition,
new peeks were also observed at 5.86-5.70 ppm, at 5.60-5.50 ppm, at 5.38-5.28 ppm and at
and 2 (-C(CH3)=CH-CH2OC(O)-) or 6 (-CH=CH-CH2OC(O)-), respectively. COSY two-
dimensional NMR experiment was used to confirm these structures. In the COSY spectrum
(Figure IV-4), the signals centred at 5.78 ppm and at 5.55 ppm corresponding to cis- and
trans-ethylenic protons, 5, are correlated with the signal centred at 4.53 ppm corresponding
to aliphatic proton 6. We can also observe the correlation of the signal at 5.83 ppm, the
signal centred at 5.55 ppm and the signal centred at 5.34 ppm corresponding respectively
to cis- ethylenic proton, 5(cis-), trans- ethylenic proton, 5(trans-) and isoprenic proton, 3,
with the signal centred at 4.62 ppm corresponding to aliphatic protons, 6 and 2. In addition,
we can observe the correlation of the signal at 5.34 ppm corresponding to isoprenic proton,
3 with the signal centred at 4.68 ppm corresponding to aliphatic protons, 2. 13C NMR spectroscopy (Figure IV-5) was used to identify the 1,4-microstructure of
telechelic polyisoprenes. The signals observed at 135.21 (1, -C(CH3)=CH-), 125.02 (2,
-C(CH3)=CH-), 32.2 ppm (3, -CH2C(CH3)=CH-), 26.39 (5, -C(CH3)=CHCH2-), and 23.44
ppm (7, -C(CH3)=CH-) correspond to the cis-1,4- polyisoprene unit. There are no signals at
16.00 (-C(CH3)=CH-) corresponding to the trans-1,4-polyisoprene unit.47 This result
confirmed that the telechelic polyisoprene is a strictly cis-1,4-polyisoprene. By contrast,
the synthesis of telechelic polyisoprene through anionic polymerization,48-49 NMP21 or
RAFT polymerization24-26 gives a mixture of 1,4-addition, 1,2-addition and 3,4-addition
products. On the other hand, the synthesis of telechelic polyisoprene via the Ring-Opening
Metathesis polymerization of 1,5-dimethyl-1,5-cyclooctadiene gives a mixture of telechelic
cis-1,4 and trans-1,4-polyisoprene.28
In order to determine the average functionality )( nf of telechelic cis-1,4-polyisoprene, the
number average polymerization degree (nDP ) of the oligomers determined by 1H NMR
spectroscopy was compared with the nDP determined by SEC. The nDP of cis-1,4-
polyisoprene from 1H NMR spectroscopy was calculated by comparing the relatives
integrations of the methylene protons (2 and 6, Figure IV-3) of the chain-ends at 4.72-
4.50 ppm, with those of the isoprenic protons (4, Figure IV-3) of polyisoprene backbone
at 5.16 ppm. The functionality was then calculated according to equation (1) which is an
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 87 -
adaptation of the equation used by Pham et al.50-51 for hydroxytelechelic polybutadiene
obtained by radical or anionic polymerization.
isopreneM
BSECnM
I
IInf
××
+++=
*,
4
62/)26( 2I (1)
with 2I corresponding to the relative integration of aliphatic protons 2 of isoprene chain-
end unit at 4.72-4.68 ppm (Figure IV-3);
26+I corresponding to the relative integration of aliphatic protons 6+2 of isoprene and
butadiene chain-ends unit at 4.68-4.56 ppm (Figure IV-3);
6I corresponding to the relative integration of aliphatic protons 6 of butadiene chain-end
unit at 4.56-4.50 ppm (Figure IV-3);
4I corresponding to the relative integration of vinylic protons 4 of isoprene backbone unit
at 5.16 ppm (Figure IV-3);
*,SECnM is the number average molecular weight of telechelic cis-1,4-polyisoprene
determined by SEC at 25 °C;
B is Benoît factor value52 of polyisoprene equal to 0.67;
Misoprene is the molar mass of isoprene unit equal to 68 g mol-1.
The resulting functionality for the cis-1,4-polyisoprene telechelic (entry A-2, Table IV-1)
was equal to 1.5±0.1. We believe that under these conditions the low concentration of CTA
gives rise to some active free ruthenium carbene (8, Scheme IV-2), which could be
involved in backbiting reactions leading to the formation of non-functional cyclic products
(8’, Scheme IV-2). Finally, ethyl vinyl ether used to stop the reaction leads to oligomer
vinylic chain-ends (8’’, Scheme IV-2). These reactions limit the functionality of the so-
obtained polyisoprenes.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 88 -
+[Ru]
O
[Ru]O
+
8'
8''
Termination
Backbiting reaction
n
8
[Ru]
qC12H25
S SO
S
O
Scheme IV-2. The formation of non-functional chain-ends.
The evolution of number-average molecular weight of telechelic cis-1,4-polyisoprene with
reaction time is presented in Figure IV-6. It illustrates that metathesis degradation
proceeds in two relatively distinct steps. A very rapid decrease of the molecular weights of
the cis-1,4-polyisoprene, corresponding to a drop from 2×106 g mol-1 to 14,000 g mol-1, is
observed over the first two hours. In the initial stage of the reaction, an active ruthenium
carbene reacts rapidly with the double bonds of the cis-1,4-polyisoprene backbone leading
to a decrease of molecular weight. In addition, the active ruthenium carbene at the chain-
end can also react with the double bonds of cis-1,4-polyisoprene via intermolecular
metathesis reactions. Then, in a second period from 2h to 8h, the molecular weight of the
polymer decreases slowly but continually to form telechelic cis-1,4-polyisoprene with a
final molecular weight of approximately 5,800 g mol-1. This is also proved53-55 by the fact
that at very long reaction times intramolecular metathesis reactions can occur to form
cyclic oligomers. The resulting cyclic oligomers were confirmed by MALDI-TOF MS
analysis (Figure IV-7). The Ag+ ionized MALDI spectrum of oligomers isolated after
precipitation of the higher molecular weight fraction using 2-propranol reveals cyclic
polyisoprenic species. For example, the signal at m/z = 583 corresponds to a cyclic
polyisoprene consisting of n = 7 isoprene units ionized by Ag+ (Mcal = 107 + 7×68 = 583 g
mol-1; where 107 g mol-1 is the mass of silver atom and 68 g mol-1 is the mass of isoprene
unit) This experimental value is good agreement with the theoretical mass calculated (583
Da, monoisotopic peak), confirming the formation of cyclic oligomers via backbiting
reaction.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 89 -
In order to obtain better control of the molecular weight and chain-end functionality of
telechelic cis-1,4-polyisoprene, the effect of changing the ratio of [Ip]0/[GII] 0/[CTA] 0
(entries A-1 to A-4, Table IV-1) was studied. When the ratio of [Ip]0/[GII] 0/[CTA] 0 is
equal to 200/1/1(entry A-1, Table IV-1), it was found that the evolution of the number-
average molecular weight of telechelic cis-1,4-polyisoprene with time followed a similar
two-step profile to that observed for sample A-2 (Table IV-1). During the first stage, a
period of two hours, the nM decreased rapidly from 2×106 g mol-1 to 34,000 g mol-1. After
2h, the nM decreased slowly to form telechelic cis-1,4-polyisoprene with a final
molecular weight of about 10,000 g mol-1 after a period of 8h (Figure IV-6). However, the
final telechelic cis-1,4-polyisoprene has a higher molecular weight corresponding to a
higher initial ratio of [Ip]0/[GII] 0/[CTA] 0. Moreover, the functionality of telechelic cis-1,4-
polyisoprene obtained was unaffected and remained less than 2. In order to form a
perfectly difunctional telechelic cis-1,4-polyisoprene, the influence of the CTA
concentration was investigated. The ratio of [GII]0/[CTA] 0 was set to 1/2 and 1/5, and the
ratio of [Ip]0/[GII] 0 was fixed at 100/1 (entries A-3 and A-4, Table IV-1). We observed
that ratios of [GII]0/[CTA] 0 of 1/2 and 1/5 formed polymers with a chain-end functionality
of 2 as shown by 1H NMR spectrum (Figure IV-3B) with no significant difference in
nM values and in polydispersity indices of the final telechelic cis-1,4-polyisoprene. This is
probably due to the fact that the CTA which have not reacted with the Grubbs II catalyst
may react with the ruthenium carbene at the chain-end (8, Scheme IV-3) leading to
Scheme IV-3. Formation of difunctionalized telechelic cis-1,4-polyisoprene.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 90 -
Table IV-1. Metathesis degradation of NR using Grubbs II catalyst and difunctional chain
transfer agent in toluene at 25 °C after 4h.
Entry
[Ip] 0/[GII] 0/[CTA] 0 SECnM ,
a
(g mol-1)
NMRnM ,
b
(g mol-1)
Functionalityc
PDId
Yield
(%)
A-1 200/1/1 23 000 16 400 1.4±0.1 1.83 78
A-2 100/1/1 10 200e 7 200 1.5±0.1 1.76 76
A-3 100/1/2 8 200e 6 200 2.0±0.1 1.70 76
A-4 100/1/5 8 200 6 400 2.0±0.1 1.67 70 aExperimental number average molecular weight measured by size exclusion chromatography (SEC) calibrated with polystyrene standards at 35 °C, bDetermined by 1H NMR spectroscopy according to nM =
[(I4×68)/(I1/4)] + 848, cDetermined by 1H NMR spectroscopy and using equation (1). dPolydispersity index measured by SEC, eExperimental number average molecular weight measured by size exclusion chromatography (SEC) calibrated with polystyrene standards at 25 °C.
Figure IV-3. 1H NMR spectra of difunctional telechelic cis-1,4-polyisoprenes, A) entry
A-2, Table IV-1 and B) entry A-3, Table IV-1.
A)
B)
5.1=nf
0.2=nf
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 91 -
qO
O
S SCH2H2CS SO
OC11H23
12
345
6C11H23
1
5
S S
ppm
4.24.44.64.85.05.25.45.65.86.0 ppm
4.2
4.4
4.6
4.8
5.0
5.2
5.4
5.6
5.8
6.0
2
6+2
6
3
5(trans-)
5(cis-)
2+6
Figure IV-4. COSY spectrum of the difunctional telechelic cis-1,4-polyisoprene (entry A-
2, Table IV-1).
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
Figure IV-6. Evolution of the telechelic cis-1,4-polyisoprene number-average molecular
weight as a function of reaction time (entries A-1 to A-3, Table IV-1).
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 93 -
573 578 583 588 593 598m/z
a.i.
Figure IV-7. MALDI-TOF mass spectrum of the cyclic polyisoprene oligomers obtained
via backbiting reaction. The insert shows the theoretical distribution at m/z 538.
II. Synthesis of P(t-BA)-b-PIp-b-P(t-BA) triblock copolymers.
We investigated the synthesis of ABA triblock copolymers containing polyisoprene as the
central block using a purified α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-
polyisoprene as macroCTA (7, Scheme IV-4). The P(t-BA)-b-PIp-b-P(t-BA) (9, Scheme
IV-4 ) was prepared from the RAFT polymerization of tert-butyl acrylate using the
difunctional telechelic cis-1,4-polyisoprene (A-3, Table IV-1) as a macroCTA. The
reaction was performed in toluene at 60 oC and AIBN was used as an initiator ([t-BA] 0/[
macroCTA]0/[AIBN] 0 = 500/1/0.4). Monomer conversion was determined by 1H NMR
spectroscopy by following the disappearance of the vinyl protons of t-BA at 6.40 to 5.60
ppm which were compared with methyl protons of anisole used as an internal standard at
3.75 ppm. The macromolecular characteristics of block copolymers were determined by
SEC.
580 650 720 m/z
1000
2000
3000
4000
5000
6000
7000
a.i.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 94 -
After a polymerization time of 5h, the t-BA conversion reaches 26% (Table IV-2). The
block copolymer had a number-average molecular weight of 23,300 g mol-1 and a
polydispersity index of 1.50 by SEC. The SEC trace of the copolymer (Figure IV-8A )
showed the absence of a peak corresponding to the PIp-macroCTA and a unimodal curve,
illustrating that the polymerization of the second block underwent chain transfer
quantitatively. The number average degree of polymerization of the PIp block is equal to
80 and the one of P(t-BA) is equal to 100 as calculated by comparing the integral of the
ethylenic protons 4 of the polyisoprene backbone resonance at 5.14 ppm to the methine
protons 2 of P(t-BA) resonances at 2.4-2.1 ppm on the 1H NMR spectrum of the copolymer
(Figure IV-8B). The data obtained from SEC and 1H NMR spectroscopy provide
additional evidence for the formation of the ABA triblock copolymer based on the cis-1,4-
polyisoprene from NR with the desired topology.
Glass transition temperature (Tg) of PIp-macroCTA and P(t-BA)-b-PIp-b-P(t-BA) triblock
copolymer were investigated by thermal analysis by differential scanning calorimetry
(DSC) under nitrogen at 10 °C/min heating rate. A single Tg of PIp-macroCTA is observed
at −65 °C. Whereas, the P(t-BA)-b-PIp-b-P(t-BA) triblock copolymers show two values of
Tg which the low temperature at −37 °C corresponds to the glass transition temperature of
PIp and the higher temperature at 32 °C corresponds to the glass transition temperature of
P(t-BA) as the Tg of P(t-BA) is equal to 48 °C.56 This is a supplementary proof of the
successful synthesis of P(t-BA)-b-PIp-b-P(t-BA) triblock copolymers.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 95 -
Table IV-2. Synthesis of ABA triblock copolymers via RAFT polymerization of tert-butyl
acrylate (t-BA) using the macroCTA (A-3, Table IV-1) and AIBN as initiator at 60°C in
toluene.
Copolymer
Reaction time
(h)
conv.a
(%)
b,calnM
(g mol-1)
c,SECnM
(g mol-1)
PDId
S-1 2 2 9 080 8 200 1.75
S-2 4 15 17 400 16 000 1.50
S-3 4.5 21 21 240 20 000 1.50
S-4 5 26 24 440 23 300 1.50 aMonomer conversion determined using 1H NMR spectroscopy. bNumber average molecular weight calculated using: Mn,calc = (conversion (%)×[M] 0/[MacroCTA]0×MM)+MmacroCTA where [M]0, [MacroCTA]0, MM and MmacroCTA are the initial concentration of monomer, the initial concentration of difunctional telechelic cis-1,4-polyisoprene macroCTA, the molecular weight of monomer and the molecular weight of the difunctional telechelic cis-1,4-polyisoprene macroCTA respectively. cNumber average molecular weight measured by size exclusion chromatography (SEC) calibrated with polystyrene standards at 35°C. dPolydispersity index measured by SEC.
C12H25S S
OS
O
OS S
C12H25
O
S80
toluene, 60 °C, 5h O O0.4 eq. AIBN,
500 eq.
C12H25S S
S
S SC12H25
S80
O O O O
50 50
7
9
Scheme IV-4. Synthesis of P(t-BA)-b-PIp-b-P(t-BA) by RAFT polymerization using α,ω-
bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene as macroCTA.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 96 -
A)
B)
1.01.52.02.53.03.54.04.55.05.56.0 ppm
3.33.43.5 ppm
1
4
2
3
Figure IV-8. A) Overlaid SEC traces of the telechelic cis-1,4-polyisoprene and of the P(t-
BA)-b-PIp-b-P(t-BA) triblock copolymers, and B) 1H NMR spectrum of P(t-BA)-b-PIp-b-
P(t-BA) triblock copolymers.
6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
Retention time (mins)
P(t-BA)-b-PI-b-P(t-BA)
PI
CH2S S
S
S SCH2
S80O O O O
50 50
C11H23C11H232
3 42
3
1 1
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 97 -
Conclusion
A new α,ω-bistrithiocarbonyl-end functionalized telechelic cis-1,4-polyisoprene was
successfully synthesized in one-pot reaction via metathesis degradation of NR using the
Grubbs II catalyst and a bistrithiocarbonyl-end functionalized olefin as a CTA. The
influence of the Grubbs II catalyst concentration and the CTA concentration were
investigated. The functionality of telechelic cis-1,4-polyisoprene reaches 2 when the ratio
of [GII] 0/[CTA] 0 is equal to 1/2 or/and 1/5 as demonstrated by 1H NMR spectroscopy. The
resulting α,ω-bistrithiocarbonyl-end functionalized telechlelic cis-1,4-polyisoprene was
successfully used as macroCTA for the RAFT polymerization of tert-butyl acrylate to form
P(t-BA)-b-PIp-b-P(t-BA) triblock copolymers. This polymer precursor could be of great
interest in various block copolymers applications especially regarding adhesive properties
which are still in studies currently in our laboratory. This interest is also reinforced by the
fact that such functionalized oligomers are an alternative to few analogues coming from
petroleum origin.
Acknowledgments. The authors wish to thank French Ministry of education and research
and Prince of Songkla University, Thailand for their financial support. Thanks to Dr. Jean-
Claude Soutif for MALDI-TOF MS analysis.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 98 -
Experimental Section
General Characterization. NMR spectra were recorded on a Bruker Avance 400
spectrometer for 1H NMR (400 MHz), 13C NMR (100 MHz). Chemical shifts are reported
in ppm down-field from tetramethylsilane (TMS). Molecular weights and molecular
weight distributions were measured using size exclusion chromatography (SEC) on a
system equipped with a SpectraSYSTEM AS 1000 autosampler, with a Guard column
(Polymer Laboratories, PL gel 5 µm Guard column, 50×7.5 mm) followed by two columns
(Polymer Laboratories, 2 PL gel 5 µm MIXED-D columns, 2×300×7.5) and with a
SpectraSYSTEM RI-150 detector. The eluent used was tetrahydrofuran (THF) at a flow
rate of 1 mL min-1 at 25 °C or 35°C. Narrow molecular weight linear polystyrene standards
(ranging from 580 g mol-1 to 4.83×105 g mol-1) were used to calibrate the SEC. Infrared
spectra were recorded on a Nicolet Avatar 370 DTGS FT-IR spectrometer in the 4000-500
cm-1 range with KBr pellets and controlled by OMNIC software. Matrix-assisted laser
desorption ionization time-of-flight (MALDI-TOF) mass spectra were recorded on a
Bruker Biflex III equipped with a nitrogen laser (lZ337 nm). All mass spectra were
obtained in the linear mode with an acceleration voltage of 19 kV. The delay time was 200
ns. Typically, 100 single-shot acquisitions were summed to give a composite mass
spectrum. All data were reprocessed using the Bruker XTOF software. Thermal transition
of samples was measured by DSC Q100 (TA Instrument) Differential Scanning
Calorimeter equipped with the cooling system that temperature can be decrease to −90°C.
Samples were put in the aluminium capsule and empty capsule was used as inert reference.
All experiments were carried out under nitrogen atmosphere at flow rate 50 mL/min with
weight of sample 5 to 10 mg. Two scans from −80 to 60°C were performed with a heating
and cooling rate of 10°C/min and the glass transition temperature was recorded.
Materials. All chemicals were purchased from Aldrich unless otherwise noted. Oxalyl
benzylidineruthenium (IV) dichloride (99%+) (Grubbs second generation catalyst, GII), 2-
propanol (99%) (Fisher Scientific) and anisole (99%) were used as received.
Dichloromethane (99%+) and methanol (99%) were distilled over CaH2 prior to use. tert-
butyl acrylate (t-BA, 99%) was purified by passing through neutral alumina column to
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 99 -
remove inhibitor. 2,2-Azobis(2-methylpropionitrile) (AIBN, 98%) was recrystallized into
methanol prior to use. NR latex was preserved with ammonia solution 0.7% (w/w) (Dry
rubber content, DRC = 60%, wM = 2×106 g mol-1, Pattani Industrial, Thailand) and non
rubber impurities were removed by urea treatment, nonionic surfactant washing and double
centrifugation followed by coagulation with methanol and dried.44 The RAFT agent, S-1-
dodecyl-S’-(α-α’-dimethyl-α’’-acetic acid) trithiocarbonate, (1, Scheme IV-1A) was
prepared according to a procedure reported in the literature.45 The bistrithiocarbonyl-end
functionalized olefin used as CTA (2, Scheme IV-1A) was synthesized as described
previously.46
Functional Metathesis Degradation Procedure. A general procedure for metathesis
degradation of NR to obtain difunctional telechelic cis-1,4-polyisoprene (7, Scheme IV-
1B) is described. A magnetic stirrer was charged to a dry Schlenk tube fitted with a rubber
septum. A degassed solution of purified NR (0.7 g, 0.0103 mol) dissolved in toluene (20
mL) was added. Separately, a solution of the difunctional CTA (2, Scheme IV-1A)
(0.1606 g, 0.2056 mmol) and Grubbs II catalyst (GII, 0.0873 g, 0.1028 mmol) in toluene (4
mL) was degassed by sparging with argon and stirred for 15 min. The resulting solution of
difunctional CTA and Grubbs II catalyst was transferred into the solution of NR using a
degassed syringe (defining t = 0) at 25 °C. Aliquots were withdrawn from the reaction
solution after 2, 4, 6 and 8 h. When this time had elapsed the metathesis reaction was
quenched by adding ethyl vinyl ether into the reaction solution under an argon atmosphere.
The resulting solution was concentrated under vacuum at room temperature and was
purified by a series of precipitations from dichloromethane (minimum volume) into 2-
propanol (100 mL) at room temperature. The isolated polymer was dried under vacuum to
remove any trace of solvent. It was then further analyzed by 1H NMR spectroscopy, 13C
NMR spectroscopy, FTIR spectroscopy and SEC. Yield: 76%.
backbone, -CH2C(CH3)=CH- and -C(CH3)=CHCH2), 1.70-1.60 (br, polyisoprene
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 100 -
backbone, -C(CH3)=CH, and chain-end -SC(CH3)2C(O)O-), 1.20-1.40 (br, chain-end, -
Then, the reaction mixture was deoxygenated by bubbling with argon for 15 min. The
polymerization was initiated by immersion in a thermostatted oil bath at 60°C. Samples
were withdrawn from the reaction mixture via a degassed syringe for conversion
monitoring (by 1H NMR spectroscopy) and molecular weight analysis (by SEC). At the
end of reaction, the polymer solution was concentrated under vacuum using rotary
evaporation and was purified by a series of precipitations from dichloromethane (minimum
volume) into an ice cold 1:1 mixture of water and methanol. The copolymer was separated
by filtration and dried under vacuum until constant weight. It was then further analyzed by 1H NMR spectroscopy, 13C NMR spectroscopy and SEC.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
- 102 -
References
[1] Liu, G.; Li, Z.; Yan, X., Polymer 2003, 44, 7721-7727. [2] Szwarc, M.; Levy, M.; Milkovich, R., J. Am. Chem. Soc. 1956, 78, 2656-2657. [3] Phillips, J. P.; Deng, X.; Stephen, R. R.; Fortenberry, E. L.; Todd, M. L.;
McClusky, D. M.; Stevenson, S.; Misra, R.; Morgan, S.; Long, T. E., Polymer 2007, 48, 6773-6781.
[4] Sasaki, M.; Fujita, K.; Adachi, M.; Fujii, S.; Nakamura, Y.; Urahama, Y., Int. J. Adhes. Adhes. 2008, 28, 372-381.
5046. [14] Lu, Z.; Xu, H.; Li, Y.; Hu, Y., J. Appl. Polym. Sci. 2006, 100, 1395-1402. [15] Batra, U.; Russel, W. B.; Pitsikalis, M.; Sioula, S.; Mays, J. W.; Huang, J. S.,
Macromolecules 1997, 30, 6120-6126. [16] Varshney, S. K.; Kesani, P.; Agarwal, N.; Zhang, J. X.; Rafailovich, M.,
Macromolecules 1999, 32, 235-237. [17] Gopalan, P.; Li, X.; Li, M.; Ober, C. K.; Gonzales, C. P.; Hawker, C. J., J. Polym.
Sci., Part A: Polym. Chem. 2003, 41, 3640-3656. [18] Wegrzyn, J. K.; Stephan, T.; Lau, R.; Grubbs, R. B., J. Polym. Sci., Part A: Polym.
Chem. 2005, 43, 2977-2984. [19] Greene, A. C.; Grubbs, R. B., J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 6342-
6352. [20] Iovu, M. C.; Jeffries-El, M.; Sheina, E. E.; Cooper, J. R.; McCullough, R. D.,
Polymer 2005, 46, 8582-8586. [21] Benoit, D.; Harth, E.; Fox, P.; Waymouth, R. M.; Hawker, C. J., Macromolecules
2000, 33, 363-370. [22] Cheng, C.; Qi, K.; Khoshdel, E.; Wooley, K. L., J. Am. Chem. Soc. 2006, 128,
6808-6809. [23] Ruehl, J.; Nilsen, A.; Born, S.; Thoniyot, P.; Xu, L. P.; Chen, S.; Braslau, R.,
Polymer 2007, 48, 2564-2571. [24] Jitchum, V.; Perrier, S., Macromolecules 2007, 40, 1408-1412. [25] Germack, D. S.; Wooley, K. L., Macromol. Chem. Phys. 2007, 208, 2481-2491. [26] Germack, D. S.; Wooley, K. L., J. Polym. Sci., Part A: Polym. Chem. 2007, 45,
4100-4108. [27] Bartels, J. W.; Billings, P. L.; Ghosh, B.; Urban, M. W.; Greenlief, C. M.; Wooley,
K. L., Langmuir 2009, 25, 9535-9544. [28] Thomas, R. M.; Grubbs, R. H., Macromolecules 2010, 43, 3705-3709.
Chapter IV : One-pot synthesis of natural rubber-based telechelic cis-1,4-polyisoprene and their use to prepare block copolymers by RAFT polymerization
[30] Hillmyer, M. A., Adv. Polym. Sci. 2005, 190, 137-181. [31] Nor, H. M.; Ebdon, J. R., Prog. Polym. Sci. 1998, 23, 143-177. [32] Gillier-Ritoit, S.; Reyx, D.; Campistron, I.; Laguerre, A.; Singh, R. P., J. Appl.
Isono, Y., J. Appl. Polym. Sci. 2004, 93, 555-559. [45] Lai, J. T.; Filla, D.; Shea, R., Macromolecules 2002, 35, 6754-6756. [46] Mahanthappa, M. K.; Bates, F. S.; Hillmyer, M. A., Macromolecules 2005, 38,
10, 441-446. [54] Ivin, K. J.; Mol, J. C., Olefin metathesis and metathesis polymerisation. Academic
Press: London, 1997. p 375. [55] Bielawski, C. W.; Grubbs, R. H., Prog. Polym. Sci. 2007, 32, 1-29. [56] Fernández-García, M.; Fuente, J. L. d. l.; Cerrada, M. L.; Madruga, E. L., Polymer
2002, 43, 3173-3179.
Chapter V
Thermal properties of block
copolymers based on PI/P(t-BA) and
PI/PAA
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 104 -
Introduction
In order to have a better knowledge on the potential use of previously synthesized well-
defined block copolymers containing polyisoprene (PI) from synthetic- and natural rubber
(NR) with poly(tert-butyl acrylate) (P(t-BA)), the thermal properties of PI macromolecular
chain transfer agent (PI-macroCTAs), PI-b-P(t-BA) diblock copolymers and P(t-BA)-b-PI-
b-P(t-BA) triblock copolymers are studied in the first part. In the second part, the influence
of the PI microstructure on thermal properties was studied. The last part describes the
investigation on the cleavage reaction of the tert-butyl ester units of P(t-BA) to form
poly(acrylic acid) (PAA) and the determination of the thermal properties of resulting block
copolymers based on PI and PAA.
I. Comparison between PI-macroCTA and block copolymers based on
PI/P(t-BA)
In this section, the thermal properties of previous PI-macroCTAs, well-defined PI-b-P(t-
BA) diblock copolymers synthesized from successive RAFT polymerizations of isoprene
and t-BA (2, Scheme V-I) and from oxidative degradation of NR followed by reductive
amination, amidation and RAFT polymerization of t-BA (2’, Scheme V-I) are
investigated. Moreover, thermal analysis of well-defined P(t-BA)-b-PI-b-P(t-BA) triblock
copolymers (5, Scheme V-II) prepared via metathesis degradation of NR followed by the
RAFT polymerization of t-BA are carried out by differential scanning calorimetry (DSC)
and thermogravimetric analysis (TGA). The results are summarized in Table V-1.
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 105 -
A) B)
62
OC12H25
S
S
SO
NH
O O
87
C12H25
S
S
SO
OH
80O O
65
64
and
2 2'
C12H25
S
S
SO
OH
81 4 5
901
0.2 eq AIBN
60 °C, 2.5h250 eq t-BA
62
OC12H25
S
S
SO
NH
1'
62
OC12H25
S
S
SO
NH
O OH
87
iodotrimethylsilane25 °C, 4h
3'
0.2 eq AIBN
60 °C, 4h250 eq t-BA
C12H25
S
S
SO
OH
80O OH
6564
3
iodotrimethylsilane25 °C, 4h
CH2Cl2
CH2Cl2
Scheme V-1. Synthesis of PI-b-PAA diblock copolymers; A) PI block obtained by RAFT
polymerization of isoprene and B) PI block obtained by oxidative degradation of NR
followed by reductive amination and amidation.
80
50
OOOO
50
S
S
SC12H25
S
S
SC12H25
80
50
OHOOHO
50
S
S
SC12H25
S
S
SC12H25
25 °C, 4h
5
6
4
C12H25S S
OS
O
OS S
C12H25
O
S80
0.4 eq AIBN
60 °C, 5h500 eq t-BA
iodotrimethylsilane CH2Cl2
Scheme V-2. Synthesis of PAA-b-PI-b-PAA based on PI block obtained by metathesis
degradation of NR.
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 106 -
Table V-1. Thermal properties of PI-macroCTAs and block copolymers based on PI Glass transition Thermal degradation stage
Entry Sample temperature 1st stage 2nd stage 3rd stage Tg
under a nitrogen atmosphere, at a heating rate of 10 °C/min.
A)
B)
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 113 -
Figure V-6. A) themogravimetric curves, B) first derivatives curve for PI-macroCTA
(entry A-5, Table V-1) and P(t-BA)-b-PI-b-P(t-BA) triblock copolymers (entry A-6,
Table V-1) under a nitrogen atmosphere, at a heating rate of 10 °C/min.
B)
A)
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 114 -
II. Influence of the PI microstructure
In this section, the influence of the PI microstructure on the thermal properties of PI-b-
P(t-BA) diblock copolymers is studied by comparing DSC curves and TGA curves
between PI-b-P(t-BA) diblock copolymer obtained from successive RAFT polymerizations
of isoprene and t-BA (2, Scheme V-1) and PI-b-P(t-BA) diblock copolymer obtained by
oxidative degradation of NR followed by reductive amination and amidation and RAFT
polymerization of t-BA (2’, Scheme V-1).
The Tg value of PI-macroCTA obtained by RAFT polymerization of isoprene (entry A-1,
Table V-1) was noted at −60°C that is a slightly higher than Tg noted (Tg= −64 °C) of PI-
macroCTA obtained by oxidative degradation of NR followed by reductive amination and
amidation (entry A-3, Table V-1). The PI-macroCTA (entry A-1, Table V-1) obtained by
RAFT polymerization of isoprene has a microstructure composed of 90% of 1,4-PI (60%
trans and 40% cis), 4% of 1,2-PI and 6% of 3,4-PI. By contrast, PI-macroCTA (entry A-3,
Table V-1) obtained by oxidative degradation of NR followed by reductive amination and
amidation leads to cis-1,4-PI units. It is well-known that the type of isomeric structures of
PI influences the degree of crystallinity and glass transition temperature of PI.7 Normally,
the Tg of cis-1,4-PI is lower than that of trans-1,4-PI and 3,4-PI due to the fact that the
lower the cis content, the less amount the crystallinity that the polymer can develop.8
However, the various PI microstructures in our work has no significant influence on their
thermal properties. This is probably due to the fact that the NR-based cis-1,4-PI obtained
after NR degradation have a low number-average molecular weight.
The Tg values assigned to the PI backbone of PI-b-P(t-BA) diblock copolymers (entry A-2
and entry A-4, Table V-1) increase from −60 °C to −35 °C and from −64 °C to −40 °C
respectively. This shift toward higher temperatures is expected since the introduction of
rigid P(t-BA) in the block copolymers reduces the mobility of the chains. This reduction of
mobility can also explained the thermal stability of PI-b-P(t-BA) diblock copolymers. It
can be observed that the Tmax (424 °C) in the second stage of PI-b-P(t-BA) diblock
copolymers from PI-macroCTA obtained by RAFT polymerization of isoprene (entry A-2,
Table V-1) is not different to the Tmax (425 °C) observed in the second stage of PI-b-P(t-
BA) diblock copolymers from PI-macroCTA obtained by oxidative degradation of NR
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 115 -
(entry A-4, Table V-1). Thus it can be concluded that the difference in microstructures of
low molecular weight PI has no effect on the thermal stability of the diblock copolymers.
III. Deprotection of t-BA group and thermal stability of resulting block
copolymers based PI/PAA
A number of recent reports have described the preparation of diblock copolymers
containing PI with poly(acrylic acid) (PAA) through the cleavage reaction of the tert-butyl
ester units to form PI-b-PAA. Wooley et al.9 have prepared PI-b-PAA by the hydrolysis of
PI-b-P(t-BA) copolymer precursor by heating the diblock polymers in 1,4-dioxane
containing concentrated HCl at reflux.
Lu et al.10 reported the preparation of microspheres using PI-b-PAA as the surfactant to
disperse a solution of PI-b-P(t-BA) and a P(t-BA) homopolymer (hP(t-BA)) in
dichloromethane. The PI-b-P(t-BA) and the precursor of PI-b-PAA were prepared by
sequential anionic polymerization. The tert-butyl ester groups of the precursor of PI-b-
PAA were removed quantitatively under acidic hydrolysis by treatment with trifluoroacetic
acid in dry dichloromethane to form PI-b-PAA and then used as the surfactant. More
recently Wooley and co-workers11 have investigated the synthesis of amphiphilic shell-
crosslinked (SCK) nanoparticles consisting of a PI core and a PAA shell from P(t-BA)-b-
PI block copolymers prepared via NMP. The cleavage reaction of the tert-butyl ester unit
was performed in toluene/acetic acid using methanesulfonic acid as catalyst at 110 °C. The
same group12 further extended the synthesis of PI-b-P(t-BA) copolymers to the synthesis of
core-shell brush copolymers. A brush copolymer consisting of a PI-b-P(t-BA) diblock
copolymer grafts and a polynorbornene backbone is obtained. The P(t-BA) units are
hydrolysed using HCl to form PAA units that were subsequently crosslinked with 2,2-
(ethylenedioxy)bis(ethylamine) to form a crosslinked brush. Full details of these
experiments were described in pages 15-28 of Chapter I.
Previous well-defined PI-b-P(t-BA) diblock copolymers synthesized from successive
RAFT polymerizations of isoprene and t-BA (2, Scheme V-I) and from oxidative
degradation of NR followed by reductive amination, amidation and RAFT polymerization
of t-BA (2’, Scheme V-I) were treated by iodotrimethylsilane at room temperature.13
After 4h, the excess solvent and reagent were removed and the copolymers were
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 116 -
redissolved in THF. The resulting solutions were dialyzed using nanopure water, followed
by lyophilisation to obtain the white solid product of PI-b-PAA diblock copolymers (3 and
3’, Scheme V-I). In addition, the previous P(t-BA)-b-PI-b-P(t-BA) triblock copolymers (5,
Scheme V-II) prepared via metathesis degradation of NR followed from the RAFT
polymerization of t-BA were treated with iodotrimethylsilane to form PAA-b-PI-b-PAA
triblock copolymers (6, Scheme V-II) following the same conditions as for the preparation
of PI-b-PAA diblock copolymers (3 and 3’, Scheme V-I).
All solid products of PI-b-PAA diblock copolymers and PAA-b-PI-b-PAA triblock
copolymers obtained after lyophilisation are difficult to solubilize in polar solvents
(DMSO (d-6), D2O, pyridine (d-5)) at 25 °C. Due to this problem, ATR-FTIR analysis and 13Carbon Cross-Polarisation (CP) combined with Magic Angle Spinning (MAS) (13C-CP-
MAS) solid-state NMR spectroscopy were used to observe the cleavage of the tert-butyl
groups. The modification of PI-b-P(t-BA) (2 and 2’, Scheme V-I) to PI-b-PAA (3 and 3’,
Scheme V-I) and P(t-BA)-b-PI-b-P(t-BA) (5, Scheme V-II) to PAA-b-PI-b-PAA (6,
Scheme V-II) were confirmed by ATR-FTIR analysis (Figures V-7-9). After deprotection
of the tert-butyl ester, the ATR-FTIR spectra show a broad peak in the region ~2900-3400
cm-1 corresponding to O-H bond stretching vibrations in acrylic acid groups, a broadening
of carbonyl band that shifts from 1730 to 1700 cm-1 and the disappearance of the bands at
1368 and 1392 cm-1 characteristics of the pendant methyl group of tert-butyl acrylate. This
indicates that the tert-butyl groups were successfully cleaved.
Similar results are seen in the ATR-FTIR spectrum of PAA-b-PI-b-PAA triblock
copolymers (Figure V-10). This result confirmed that tert-butyl groups were cleaved to
acrylic acid groups.
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 117 -
Figure V-7. ATR-FTIR spectra of PI-b-P(t-BA) diblock copolymer (2, Scheme V-1) and
PI-b-PAA diblock copolymer (3, Scheme V-1).
Figure V-8. ATR-FTIR spectra of PI-b-P(t-BA) diblock copolymer (2’, Scheme V-1) and
Chapter V : Thermal properties of block copolymers based on PI/P(t-BA) and PI/PAA
- 128 -
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