Dual versatility of triazolium-based cyclic carbonate inimer: From homopolymerization to on-demand thermally activated initiating site

Article abstract of DOI:10.1021/ma201589r

A new triazolium-based cyclic carbonate monomer was prepared by nucleophilic addition of the 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5- ylidene N-heterocyclic carbene to a six-membered cyclic carbonate ring bearing a free carboxylic acid group. A sim

Full text of DOI:10.1021/ma201589r

NOTE
pubs.acs.org/Macromolecules
Dual Versatility of Triazolium-Based Cyclic Carbonate Inimer: From
Homopolymerization to On-Demand Thermally Activated
Initiating Site
Olivier Coulembier,* Sꢀebastien Moins, and Philippe Dubois
Center of Innovation and Research in Materials and Polymers (CIRMAP), Laboratory of Polymeric and Composite Materials,
University of Mons (UMONS), Place du Parc 23, Mons 7000, Belgium
S Supporting Information
b
ver the past decades, associations of complementary poly-
merization techniques have attracted considerable attention
Scheme 1. Synthesis of 1-Type Monomers Adapted from
Ref 8a
O
since they allow the preparation of materials generated from
monomers that polymerize either by different mechanisms or
from disparate catalysts. To date, block,1 brushlike,2 grafted,3
star-shaped,4 miktoarm,5 and cross-linked copolymers6 have
been prepared by various strategies employing dual initiators
or chain-ends/dangling groups transformations. Subsequently,
inimers and functional monomers bearing an active initiator
as a pendent group have also been developed.7 In 2008, Hedrick
et al. demonstrated the feasibility to produce a six-membered
cyclic carbonate ring bearing different esters as easily obtained
fromthe2,2-bis(methylol)propionic acid(Scheme1, stepsi tovi).8
Since ring-opening polymerization (ROP) mediated by metal-
free organocatalytic systems has recently emerged as a tremen-
dous research area,9 and because the ROP of cyclic carbo-
nates provides narrowly dispersed polymers of predictable
molecular weights and end-group fidelity,10 some of us demon-
strated that cyclic carbonate ring bearing a reversible additionÀ
fragmentation chain transfer (RAFT) function might be easily
prepared and polymerized in the absence of metal residue.11
Whatever the origin of the side group present on the cyclic carbo-
nate ring, the approach developed by Hedrick requires the esteri-
fication of a six-membered cyclic carbonate ring bearing free
carboxylic acid group, 1, with a suitable ROH alcohol (Scheme 1,
steps i to vi).
In order to shortcut the preparation of functionalized cyclic
carbonates, an improved two-step route featuring a cyclic carbo-
nate functionalized by a pentafluorophenyl ester group has then
been developed by the same group (Scheme 1, steps vii to viii).12
The elevated cost of production of such versatile ester inter-
mediate prompted us to investigate the direct protection of 1
by an equimolar amount of 1,3,4-triphenyl-4,5-dihydro-1H-1,2,
4-triazol-5-ylidene since such triazolium carbene is known to
react quantitatively with free carboxylic acid functions at room
temperature.13 Since carboxylic acid/triazolium adduct is an
efficient initiating system for the ROP of [R,S]-β-butyrolactone
(BL) at high temperature,13c the preparation of such triazolium
ester cyclic carbonate, 2, is of interest since the triazolium function
might act as either thermally removable protecting group of 1 or
“catalyst” for the ROP of BL at elevated temperature.
a Conditions: (i) BnBr, DMF, KOH, 100 °C, 15 h; (ii) triphosgene,
pyridine, CH2Cl2, À78 f 0 °C; (iii) H2, Pd/C, EtOAc, rt, 24 h;
(iv) (COCl)2, THF, rt, 1 h; (v) ROH, DCC, THF, rt, 16 h; (vi) ROH,
NEt3, rt, 3 h; (vii) (C6F5O)2CO, CsF, 20 h; (viii) ROH, Nu.
and carboxylic acid at elevated temperature, then a one-pot
process might be expected for the preparation of model copoly-
mers composed by a polycarbonate backbone grafted by poly-
ester chains.
To date, a large variety of selected functionalized cyclic carbo-
nate monomers have been polymerized by using a catalytic
system composed by an equimolar mixture of 1-(3,5-bis(trifluo-
romethyl)phenyl)-3-cyclohexyl-2-thiourea (TU) and 1,8-diazabicyclo-
[5.4.0]undec-7-ene (DBU).8,11,12 Despite its very high ROP
activity, DBU (and by correlation 1,5,7-triazabicyclo[4.4.0]dec-
5-ene, TBD) causes at high temperature some degradation when
exposed to polylactide (PLA) chains and more especially if that
base is in the presence of carboxylic acid residues.14 Fearing an
even faster degradation on PBL chains by transesterification, the
TU/DBU association has been ruled out. Alternatively, some
of us demonstrated that the association of fluorinated tertiary
We reasoned that if the triazolium ester cyclic carbonate 2
is stable at rt and if the catalytic system designed for its
(co)polymerization is compatible with free triazolium carbene
Received: May 19, 2011
Revised:
August 8, 2011
Published: August 22, 2011
r
2011 American Chemical Society
7493
dx.doi.org/10.1021/ma201589r Macromolecules 2011, 44, 7493–7498
|

Macromolecules
NOTE
alcohols and (À)-sparteine provides narrowly dispersed poly-
carbonates of predictable molecular weights.15 Even if such
system is less active, its compatibility regarding free triazolium
carbene and carboxylic acid group is expected without any
damage on PBL chains.16 However, to broaden the scope of
the tertiary alcohol catalysts family, the fluorinated tertiary alco-
hol species was replaced by a simple phenol derivative also
known to activate carbonyl compounds (such as carbonate) by
hydrogen bonding.17
In a first attempt, p-chlorophenol (CP) was surveyed as
organocatalyst for the ROP of commercially available trimethy-
lene carbonate (TMC). Polymerizations were conducted using
an alcohol initiator, such as benzyl alcohol (BnOH), with (À)-
sparteine (S) as a cocatalyst base. The ROP of TMC was
evaluated both in CH2Cl2 ([TMC]0 ∼ 2 M at 23 and 50 °C)
and in bulk (90 °C) for a [TMC]/[BnOH]/[S]/[CP] ratio of
100:1:5:5, and relative conversions were determined by using
SEC analysis (Table 1; a typical 1H NMR spectrum is shown in
Figure 1 and confirms the expected structure and end-group
fidelity).
controlled process (Figure 1, inset). While SEC chromatograms
show Gaussian distribution of molecular weights for each sample
and since the plot of MnSEC versus conversions reveals that
polymer chains grow regularly (for temperatures comprised
between 23 and 90 °C), the competition of recently revealed
active chain end (ACE) propagating mechanism is of well minor
importance to the expected activated monomer mechanism
(AM) (Scheme 2).18
In the frame of this research, the CP/S catalytic complex has
then been used for the copolymerization of TMC and function-
alized cyclic carbonate 2. The molecule 2 is obtained as afore-
mentioned by the nucleophilic reaction between cyclic carbonate
1 and triazolium carbene in THF at room temperature (rt)
(Scheme 3). Evolution of the reaction is followed by FT-IR
analysis. After 3 h of reaction, the nucleophilic addition of the
triazolium carbene to the carboxylic acid group is proved quan-
titative since the recrystallized and dried product does not show
the wide initial ν(CdO) vibration band characterizing the
ÀCOOH group of 1 (∼1700 cmÀ1). Moreover, the as-obtained
adduct keeps safe the ν(ÀOC(O)OÀ) band of the carbonate
Clearly, higher temperature in bulk state provides high TMC
conversions and predictable molecular weights with reasonable
narrow dispersities (^M = Mw/Mn). A comparison between the
measured molecular weights (MnSEC) of PTMC samples and
determined conversions shows a linear fit consistent with a
Scheme 2. Illustration of ACE and AM Mechanisms for the
ROP of TMC Catalyzed by CP/S Catalytic Complex
Table 1. Molecular Characteristic Features of PTMC Ob-
tained at Different Temperatures and Using a CP/S Catalytic
Complex
entry temp (°C) polym time (h) conv (%)a MnSEC (g/mol)a
^
M
a
1
2
3
4
5
23
1.5
19
3
13
31
70
86
500
1300
3400
6800
8350
1.02
1.14
1.09
1.24
1.33
50
90
22
2
4
a As determined by SEC in THF/NEt3 at 35 °C using PS standards.
Figure 1. 1H NMR spectrum of representative PTMC obtained by a CP/S catalytic complex (entry 5, Table 1). Inset: evolution of MnSEC to
conversions determined at different temperatures.
7494
dx.doi.org/10.1021/ma201589r |Macromolecules 2011, 44, 7493–7498

Macromolecules
NOTE
function at 1750 cmÀ1, attesting for the selectivity of the
nucleophilic addition to the prejudice of the nucleophilic sub-
stitution of the cyclic carbonate from the carbene unit. Addi-
1 and triazolium carbene are totally dissociated (Figure 2). In
correlation with the nature of the bond linking the two partners
within the adduct, i.e., hydrogen bond, the variation of enthalpy
recorded for such adduct thermal dissociation is of about 67 J/g,
significantly lower than the one recorded for the covalent
methanol adduct (∼215 J/g) and in agreement with theory.20
Finally, and prior to any copolymerization with TMC, the
reactivity of the carboxylic-type carbene group of the carbonate
adduct 2 has been assessed in anionic ROP of BL monomer
(Scheme 4).
tionally, a new band shows up between 1650 and 1550 cmÀ1
,
confirming the presence of the triazolium aromatic groups
(Figure S1 in Supporting Information). In the H NMR spec-
1
trum, the nonequivalence of both methylene carbonate protons
attests for the cyclic structure of the monomer 2, confirming
that free triazolium carbene does not cause any damage on cyclic
carbonate monomer in THF in presence of carboxylic acid
functions (at least at rt). It is also worth noting that the
theoretical ratio of the proton integration ([CH3]/[CH2]/
[Har] = 3:4:15) fits well with the experimental one, i.e.,
3:4.2:15.1, attesting then for the completeness of the reaction
(Figure S2).
The cyclic carbonate carbene adduct 2 has then been eval-
uated with respect to thermal stability. As already performed on
other carbene adducts,19 a modulated differential scanning
calorimetry (M-DSC) analysis of 2 has been carried out under
nitrogen. Similarly to the 5-methoxy-1,3,4-triphenyl-4,5-dihy-
dro-1H-1,2,4-triazol-5-ylidene obtained by covalent association
between methanol and free triazolium carbene, the cyclic carbo-
nate 2 presents its first endothermic transition at ca. 103 °C. Such
a temperature corresponds to the point for which both carbonate
Practically, the anionic polymerization of BL has been
carried out in bulk at 90 °C for an initial monomer-to-initiator
molar ratio ([BL]0/[2]0) of 70. After 40 min reaction time
1
(conversion ∼ 0.62; DPth = 44), the H NMR analysis of the
precipitated product attests for the effective polymerization of BL
(Figure S3). While a negligible signal of backbiting crotonization
is observed in the resolution limit of the 1H NMR spectroscopy
(at around 5.75 ppm), the presence of the cyclic carbonate end-
group is clearly visible between 4.1 and 4.6 ppm. By comparing
the intensities of methylene butyrate repeating units (∼2.4 ppm)
and methylene carbonate end-group protons (∼4.1À4.6 ppm),
an experimental DP of 49 is estimated. Such DPexp is in good
accordance with the theoretical DP of 44. The control over
the polymerization has finally been attested for by a narrow
^
of 1.21 as determined by SEC. This combined set of data
M
Scheme 3. Synthesis of Triazolium Ester Cyclic Carbonate 2
demonstrates end-group fidelity, predictable molecular weights
(particularly for targeted DPs lower than 40), and the selectivity
of the carbene catalyst for the lactone polymerization. It is worth
Scheme 4. Polymerization of BL from Cyclic Carbonate 2
Figure 2. Temperatures and enthalpies of carbene adducts destructurations.
7495
dx.doi.org/10.1021/ma201589r |Macromolecules 2011, 44, 7493–7498

Macromolecules
NOTE
Scheme 5. One-Pot Two-Step Procedure for the Preparation of Poly(carbonate)-graft-Poly(butyrolactone) (PC-g-PBL)
Copolymers
The ability of the cyclic carbonate 2 to copolymerize with
TMC from a CP/S catalytic complex has then been investigated
using 11-bromo-1-undecanol (11-BU) as alcohol initiator
(Scheme 5). Because of possible reaction between free carbene
and chlorinated solvents,19a the copolymerization has been
performed in toluene at 35 °C for a total monomer concentration
of 2 M ([11-BU]0/[TMC]0/[2]0 = 1:45:5). In order to slightly
improve the kinetics recorded and presented in Table 1, a 10-fold
excess of CP/S complex has been used regarding the alcohol
initiator content ([11-BU]0/[CP]0/[S]0 = 1:10:10). As attested
by SEC analysis, 44.25 h is sufficient to completely consume both
comonomers and generate a controlled P(TMC-co-2) copoly-
mer (MnSEC = 4100 g molÀ1; ^M = 1.19; Figure 3). The as-
obtained P(TMC-co-2) has then been used to initiate the ROP of
BL monomer from the dangling triazolium functions present on
the polycarbonate backbone (Scheme 5). At this stage, two
thermally on-demand polymerizations were performed at 90 °C:
(i) the first copolymerization was realized by using an initial
[BL]0/[11-BU]0 of 60 ([BL]0 ∼ 2M) and (ii) the second one
1
after evaporation of the toluene ([BL]0/[11-BU]0 = 150). H
NMR analysis attests for the effective ROP of BL by the
appearance of characteristic signals of butyrate repeating units
observed at 2.5 and 5.2 ppm (Figure 4). Molecular parameters of
both poly(carbonate)-graft-poly([R,S]-butyrolactone) (PC-g-PBL)
copolymers are gathered in Table 2.
Figure 3. Representative size exclusion chromatography traces of P-
(TMC-co-2) (in gray) and PC-g-PBL1 (in black).
noting that polymerizations targeting higher conversions (DPs
ranging from 50 to 100) tended to show broadening in the ^M
(data not shown here). Moreover, for these DPs, an important
amount of crotonate was observed, consistent with typical pro-
ton abstraction reactions leading to a second mode of polymer-
ization. The loss of control and end-group fidelity at the high
targeted DPs is fully consistent with that observed by Duda,
Coates, and also some of us.21
While 1 h is required to lead to 20% conversion in BL when the
copolymerization is performed in solution (PC-g-PBL 1), poly-
merization conducted in bulk conditions increases the propaga-
tion kinetics and conversions up to 99% are obtained within
45 min (PC-g-PBL 2). Whatever the experimental conditions, a
relatively good accordance between experimental and calculated
DPs is observed (by taking into account the inherent experi-
1
mental error of the H NMR spectroscopy). Moreover, SEC
7496
dx.doi.org/10.1021/ma201589r |Macromolecules 2011, 44, 7493–7498

Macromolecules
NOTE
Figure 4. 1H NMR spectrum of PC-g-PBL 2 (Table 2) in CDCl3.
Table 2. Molecular Characteristic Features of PC-g-PBL Obtained after BL ROP from P(TMC-co-2)
samplea
polym time (min)
conv (%)b
DPthPBL
DPexpPBLc
MnSEC copo (g/mol)d
^
M
d
PC-g-PBL 1
PC-g-PBL 2
60
45
20
99
12
17
6200
8600
1.32
1.26
150
160
a Sample 1 refers to the copolymer obtained after polymerization of BL in presence of toluene; sample 2 was obtained after polymerization in bulk.
b As determined by gravimetry. c As determined by 1H NMR in CDCl3. d As determined in THF/NEt3 at 35 °C by using PS calibration.
analyses attest for the controlled behavior of both copolymer-
izations by ^M varying from 1.26 to 1.32 (Figure 3). Since PC-g-
PBL 1 and 2 are mainly different by the length of PBL chain
(5 side chains per backbone and DP of side chain is 3 for 1 and
32 for 2), the small variation of experimental molecular weight
determined by SEC is probably due to the variation of hydro-
dynamic volumes between those two copolymers different in
terms of topology. As expected, no degradation of the poly-
carbonate backbone has been observed neither during the
thermal activation of the triazolium adduct nor after the BL
polymerization. More importantly, if 45 min is required to
polymerize BL from dangling triazolium functions of P(TMC-
co-2) for a DP of 32 and in the presence of CP and S, it might
be concluded that very limited interactions between free car-
bene and CP take place during the polymerization of BL. Indeed,
40 min is necessary to generate a PBL of a DP 44 from BL ROP
initiated from 2 without CP and S (all other experimental
conditions identical).
’ ASSOCIATED CONTENT
S
Supporting Information. Figures S1ÀS3 and experi-
b
mental details. This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: olivier.coulembier@umons.ac.be.
’ ACKNOWLEDGMENT
This work was supported by the European Commission and
Rꢀegion Wallonne FEDER program (Materia Nova) and OPTI2-
MAT program of excellence, by the Interuniversity Attraction
Pole program of the Belgian Federal Science Policy Office (PAI
6/27), and by FNRS-FRFC. O.C. is an FNRS Research Associate.
In conclusion, a new triazolium-based cyclic carbonate
monomer has been prepared by nucleophilic addition of
the 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene N-
heterocyclic carbene to a six-membered cyclic carbonate ring
bearing a free carboxylic acid group. That new inimer may act as
an active initiator for the ROP of BL and is also easily poly-
merized by an organocatalytic complex based on (À)-sparteine
and p-chlorophenol. The complementarity of triazolium and
sparteine/p-chlorophenol active species allowed the genera-
tion of controlled poly(carbonate)-graft-poly(butyrolactone)
copolymers.
’ REFERENCES
(1) (a) Bougard, F.; Jeusette, M.; Mespouille, L.; Dubois, Ph.;
Lazzaroni, R. Langmuir 2007, 23, 2339–2345. (b) Coulembier, O.;
Degꢀee, Ph.; Cammas-Marion, S.; Guꢀerin, Ph.; Dubois, Ph. Macromole-
cules 2002, 35, 9896–9903. (c) Spasova, M.; Mespouille, L.; Coulembier,
O.; Paneva, D.; Manolova, N.; Rashkov, I.; Dubois, Ph. Biomacromole-
cules 2009, 10, 1217–1223. (d) Bernaerts, K.; Schacht, E.; Goethals, E.;
Du Prez, F. J. Polym. Sci., Polym. Chem. 2003, A1, 3206–3217.
(e) Mespouille, L.; Vachaudez, M.; Suriano, F.; Gerbaux, P.; Van Camp,
W.; Coulembier, O.; Degꢀee, Ph.; Flammang, R.; Du Prez, F.; Dubois, Ph.
React. Funct. Polym. 2008, 68, 990–1003. (f) Paneva, D.; Mespouille, L.;
7497
dx.doi.org/10.1021/ma201589r |Macromolecules 2011, 44, 7493–7498

Macromolecules
NOTE
Manolova, N.; Degꢀee, Ph.; Rashkov, I.; Dubois, Ph. Macromol. Rapid
Commun. 2007, 28, 2151–2158.
(2) Lee, H.-I.; Jakubowski, W.; Matyjaszewski, K.; Yu, S.; Sheiko,
S. S. Macromolecules 2006, 39, 4983–4989.
(3) (a) Mespouille, L.; Degꢀee, Ph.; Dubois, Ph. Eur. Polym. J. 2005,
41, 1187–1195. (b) Theryo, G.; Jing, F.; Pitet, L. M.; Hillmyer, M. A.
Macromolecules 2010, 43, 7394–7397.
(4) Heise, A.; Trollsas, M.; Magbitang, T.; Hedrick, J. L.; Franck,
C. W.; Miller, R. D. Macromolecules 2001, 34, 2798–2804.
(5) (a) Rieger, J.; Coulembier, O.; Dubois, Ph.; Bernaerts, K. V.; Du
Prez, F. E.; Jꢀer^ome, R.; Jꢀer^ome, C. Macromolecules 2005, 38, 10650–
10657. (b) Babin, J.; Taton, D.; Brinkmann, M.; Lecommandoux, S.
Macromolecules 2008, 41, 1384–1392.
(6) (a) Mespouille, L.; Coulembier, O.; Paneva, D.; Degꢀee, Ph.;
Rashkov, I.; Dubois, Ph. Chem.—Eur. J. 2008, 14, 6369–6378.
(b) Mespouille, L.; Coulembier, O.; Paneva, D.; Degꢀee, Ph.; Rashkov,
I.; Dubois, Ph. J. Polym. Sci. 2008, 46, 4997–5013. (c) Wiltshire, J. T.;
Qiao, G. G. Macromolecules 2006, 39, 4282–4285.
(7) (a) Voccia, S.; Jꢀer^ome, C.; Detrembleur, Ch.; Leclꢁere, Ph.;
Gouttebaron, R.; Hecq, M.; Gilbert, B.; Lazzaroni, R.; Jꢀer^ome, R. Chem.
Mater. 2003, 15, 923–927. (b) Hutchison, J. B.; Stark, P. F.; Hawker,
C. J.; Anseth, K. S. Chem. Mater. 2005, 17, 4789–4797. (c) Coulembier,
O.; Degꢀee, Ph.; Gerbaux, P.; Wantier, P.; Barbaud, Ch.; Flammang, R.;
Guꢀerin, M.; Dubois, Ph. Macromolecules 2005, 38, 3141–3150. (d) Zhao,
Y.; Perrier, S. Macromolecules 2006, 39, 8603–8608.
(8) Pratt, R. C.; Nederberg, F.; Waymouth, R. M.; Hedrick, J. L.
Chem. Commun. 2008, 114–116.
(9) Dove, A. P. In Handbook of Ring-Opening Polymerization; Dubois,
Ph., Coulembier, O., Raquez, J.-M., Eds.; Wiley-VCH Verlag GmbH &
Co. KGaA: Weinheim, 2009; p 357.
(10) Kiesewetter, M. K.; Shin, E. J.; Hedrick, J. L.; Waymouth, R. M.
Macromolecules 2010, 43, 2093–2107.
(11) Mespouille, L.; Nederberg, F.; Hedrick, J. L.; Dubois, Ph.
Macromolecules 2009, 42, 6319–6321.
(12) Sanders, D. P.; Fukushima, K.; Coady, D. J.; Nelson, A.;
Fujiwara, M.; Yasumoto, M.; Hedrick, J. L. J. Am. Chem. Soc. 2010, 132,
14724–14726.
€
(13) (a) Bourissou, D.; Guerret, O.; Gabbai, F. P.; Bertrand, G.
Chem. Rev. 2000, 100, 39–91. (b) Cowman, J. A.; Clyburne, J. A. C.;
Davidson, M. G.; Harris, R. L. W.; Howard, J. A. K.; K€upper, P.; Leech,
M. A.; Richards, S. P. Angew. Chem., Int. Ed. 2002, 41 (8), 1432–1434.
(c) Coulembier, O.; Delva, X.; Hedrick, J. L.; Waymouth, R. M.; Dubois,
Ph. Macromolecules 2007, 40, 8560–8567.
(14) Coulembier, O.; Moins, S.; Raquez, J.-M.; Meyer, F.; Mespouille,
L.; Duquesnes, E.; Dubois, Ph. Polym. Degrad. Stab. 2011, 96, 739–744.
(15) Coulembier, O.; Sanders, D. P.; Nelson, A.; Horn, H.; Rice, J.;
Fujiwara, M.; Dubois, Ph.; Hedrick, J. L. Angew. Chem., Int. Ed. 2009,
48 (28), 5170–5173.
(16) Coulembier, O.; Hedrick, J. L.; Nelson, A.; Rice, J. E.; Sanders,
D. P. Method of Ring-Opening Polymerization, and Related Composi-
tions and Articles. US 20100305300A1, 2010.
(17) Pihko, P. M. Angew. Chem., Int. Ed. 2004, 43, 2062–2064 and
references therein.
(18) Delcroix, D.; Martin-Vaca, B.; Bourissou, D.; Navarro, Ch.
Macromolecules 2010, 43, 8828–8835.
(19) (a) Nyce, G.; Csihony, S.; Waymouth, R. M.; Hedrick, J. L.
Chem.—Eur. J. 2004, 10, 4073–4079. (b) Coulembier, O.; Delcourt, C.;
Dubois, Ph. Open Macromol. J. 2007, 1, 1–5.
(20) Steiner, T. Angew. Chem., Int. Ed. 2002, 41, 48–76.
(21) (a) Duda, A. J. Polym. Sci., Part A: Polym. Chem. 1992,
30, 21–29. (b) Rieth, L. R.; Moore, D. R.; Lobkovsky, E. B.; Coates,
G. W. J. Am. Chem. Soc. 2002, 124, 15239–15248. (c) Coulembier, O.;
Lohmeijer, B. G. G.; Dove, A. P.; Pratt, R. C.; Mespouille, L.; Culkin,
D. A.; Benight, S. J.; Dubois, Ph.; Waymouth, R. M.; Hedrick, J. L.
Macromolecules 2006, 39, 5617–5628.
7498
dx.doi.org/10.1021/ma201589r |Macromolecules 2011, 44, 7493–7498