Combining thio-bromo Click chemistry and raft polymerization: a powerful tool for preparing functionalized multiblock and hyperbranched polymers

Article abstract of DOI:10.1021/ma902154h

An experiment was conducted to prove that RAFT-prepared polymers can serve as convenient masked macromolecular thiols suitable for thio-bromo reactions. Homopolymers were prepared by RAFT polymerization using 4-cyanopentanoic acid dithiobenzoate (CPADB) a

Full text of DOI:10.1021/ma902154h

20 Macromolecules 2010, 43, 20–24
DOI: 10.1021/ma902154h
Scheme 1. Model Reactions Used To Evaluate the Combination of
Combining Thio-Bromo “Click” Chemistry and RAFT
Polymerization: A Powerful Tool for Preparing
Functionalized Multiblock and Hyperbranched
Polymers
RAFT and Thio-Bromo “Click” Reaction
Jiangtao Xu, Lei Tao, Cyrille Boyer, Andrew B. Lowe,* and
Thomas P. Davis*
Centre for Advanced Macromolecular Design (CAMD), School
of Chemical Sciences and Engineering, The University of
New South Wales, Sydney NSW 2052, Australia
Received September 28, 2009
Revised Manuscript Received November 17, 2009
“Click” chemistry, first described in 2001 by Kolb, Finn, and
Sharpless,1 has been applied in a range of areas of chemistry,
materials, and biology over the past decade.2 An excellent
example of such chemistry, the copper-catalyzed alkyne-azide
cycloaddition (CuAAC),3 has been employed in the synthesis of a
broad diversity of functional materials, nanoparticles, and bio-
conjugates.4 The orthogonality of CuAAC chemistry has also
allowed the reaction to be combined with other efficient chemistries
such as Diels-Alder cycloadditions5 and the coupling of
aldehydes and hydroxylamines (oxime bond formation).6 In
addition to CuAAC chemistry, a series of thiol-based reactions
have recently been highlighted as powerful “click” chemistries
and include the thiol-ene/yne7-9 and thiol-isocyanate10 reactions.
A particularly attractive feature of such reactions is the large
number of cheap, commercially available, thiols, enes, ynes, and
isocyanates, including multifunctional species.
Controlled radical polymerization techniques, and especially
reversible addition-fragmentation chain transfer (RAFT)
polymerization,11 have rapidly developed as facile and convenient
approaches to controlled architecture and topology block, graft,
star, hyperbranched, telechelic, multifunctional, and cyclic
(co)polymers and as a simple route to new highly functional
materials when combined with the above-mentioned “click”
chemistries.8,12 Recently, Percec and co-workers reported the
nucleophilic thio-bromo “click” reaction and specifically high-
lighted the base-mediated thioetherification of thioglycerol with
R-bromoesters to prepare a new class of poly(thioglycerol-2-
propionate) (PTP) dendrimers13 and dendritic macromolecules.14
Such reactions were rapid and proceeded with near-quantitative
conversion and were shown to be compatible with a range of
functional thiols.
Herein we highlight that RAFT-prepared (co)polymers can
serve as convenient masked macromolecular thiols suitable for
thio-bromo reactions. The in situ aminolysis ofthiocarbonylthio
end groups in the presence of R-bromoesters serves as a con-
venient route to ω-thioether-functionalized homopolymers. We
demonstrate that such chemistry can be extended to prepare
functionalized multiblock and hyperbranched polymers. A model
reaction (Scheme 1) was first examined to evaluate the general
reaction rates and efficiencies.
For model polymeric studies we synthesized three short
homopolymers: poly(methyl acrylate) (PMA) (Mn,GPC=560 Da,
Mn,NMR = 970 Da, PDI = 1.10, denoted PMA1000), PMA
(Mn,GPC =4100 Da, Mn,NMR =4580 Da, PDI=1.08, denoted
PMA4500), and poly(N-isopropylacrylamide) (PNIPAAm)
(Mn,GPC =1010 Da, Mn,NMR =1750 Da, PDI=1.07, denoted
PNIPAAm1750). Homopolymers were prepared by RAFT po-
lymerization using 4-cyanopentanoic acid dithiobenzoate
(CPADB) as the chain transfer agent, yielding homopolymers
with dithiobenzoate groups at the ω-termini that can be readily
cleaved to thiols via aminolysis. The generated thiol can subse-
quently react with many functionalities, including maleimide,
pyridyl disulfide, and enes.8,15 In our work, we utilized the in situ
generated thiol for subsequent reaction with two model
R-bromoesters: methyl 2-bromopropionate (MBP) and ethyl
2-bromoisobutyrate (EBiB) (Scheme 1).
The aminolysis of PMA4500 in the presence of MBP was
performed using hexylamine/triethylamine (TEA) as the cleavage
agent and base, respectively, in a molar ratio PMA4500/hexyla-
mine/TEA/MBP=1/1/2/2 in acetonitrile at a concentration of
0.027 mol/L. The red color of the initial polymer solution faded
completely within 30 min, after which an aliquot was withdrawn
for GPC analysis. For comparison, the aminolysis of PMA4500
in the absence of MBP was performed as a control. The
experimentally measured GPC traces are shown in Figure 1. A
small shift to lower retention time was observed for the MBP-
modified PMA4500 as well as the appearance of a small fraction
of coupled products compared to the parent PMA4500 homo-
polymer. In contrast, a distinctive bimodal molecular weight
distribution was observed for the control experiment with the
large peak at lower retention time due to the presence of coupled
PMA4500 chains. These model reactions indicate that the thio-
bromo reaction is kinetically preferred over the competing
reaction of disulfide formation. Such tandem reactions, i.e.,
aminolysis followed by thio-bromo substitution, proceed rea-
sonably quickly and are essentially complete within ∼30 min. The
aminolysis/thio-bromo sequence with PNIPAAm1750 gave
similar results: uniform and unshifted GPC curves (Figure S1
in the Supporting Information) and rapid reaction time (∼30
min). However, a longer reaction time of ca. 3 h was required to
obtain high yields of the thioether product from the aminolysis of
PMA4500 in the presence of EBiB.
*Corresponding authors. E-mail: a.lowe@unsw.edu.au (A.B.L.);
t.davis@unsw.edu.au (T.P.D.).
pubs.acs.org/Macromolecules
Published on Web 12/07/2009
r 2009 American Chemical Society

Communication
Macromolecules, Vol. 43, No. 1, 2010 21
To verify successful cleavage/thioether formation, PMA1000
was aminolyzed in the presence of MBP orEBiB and the products
analyzed by ESI mass spectrometry (ESI MS). As shown in
Figure 2, the main series of peaks in all three traces exhibits an
interval of 86.01 mass units, which corresponds to the methyl
acrylate (MA) repeat unit. The main peak, for example m/z=
904.39 in Figure 2A,D, can be attributed to PMA with a degree of
polymerization of 7 and a ω-dithiobenzoate end-group catio-
nized by Naþ. The absence of any other peaks indicates the high
purity of the homopolymer. After aminolysis in the presence of
MBP (Figure 2B,E) or EBiB (Figure 2C,F), the masses of the
main series of peaks both matched with the predicted structures
of polymer 1 or 3, respectively, as indicated in Scheme 1. How-
ever, small amounts of impurities are observed as indicated by
peaks P1 in Figure 2F and P3 in Figure 2E and are attributed to
the presence of cyclic thiolactone16 end-groups cationized by
Naþ, while P2 in Figure 2F is attributed to unreacted thiol end-
groups cationized by Naþ. On the basis of these observations, the
end-group functionality can be semiquantitatively calculated to
be ∼80% based on the intensities of the main peaks and
impurities as seen in the ESI MS spectra. This value is supported
by NMR (Figure S2 in the Supporting Information), in which the
calculated degree of end-group modification from the aminolysis/
thio-bromo reaction of PMA4500 and EBiB is ∼73%. The
aminolysis/thio-bromo sequence of PNIPAAm1750 with MBP
gave better results (Figure S3 in the Supporting Information)
with no detectable undesirable end-groups but was accompanied
by the appearance of AIBN initiator-derived chain peaks16a
cationized by Naþ and main product cationized by Hþ (Figure
S3D). Employing the semiquantitative calculation, the degree of
ω-functionality was determined to be g95%.
These model reactions suggested that the thio-bromo “click”
reaction between an in situ generated thiol from RAFT-synthe-
sized homopolymers and an R-bromoester can be rapid and
efficient with appropriate substrates. Extending this modification
approach, we applied the method to prepare functionalized
hyperbranched polymers from AB2 macromonomers. Two novel
RAFT agents 6 and 7 (Scheme 2) bearing two bromoesters in the
R group fragment were designed and synthesized by a similar
procedure to one we have previously reported.15a After MA
homopolymerization with 6 or 7, novel AB2 macromonomers 8
or 9, bearing ω-dithiobenzoate and R-bis bromoester end-groups,
were obtained. The ω-dithiobenzoate end-groups were cleaved,
via aminolysis, to the corresponding thiol that then reacted
intermolecularly with the R-bromoester terminal groups on other
polymer chains yielding a hyperbranched structure via a step-
growth polycondensation process.
The MA RAFT homopolymerizations were well controlled
by the novel dithiobenzoates 6 and 7 as indicated by linear
pseudo-first-order kinetic plots, the linear increase in the num-
ber-average molecular weights with conversion, and low poly-
dispersity indices (Mw/Mn < 1.2) (see Figures S4 and S5 in the
Supporting Information).
Figure 1. GPC traces for PMA4500 (Mn,GPC =4100 Da, Mn,NMR
=
4580 Da, PDI=1.08) before (solid) and after (dashed and dash-dotted)
aminolysis in the absence (dashed) and presence (dash-dotted) of
methyl 2-bromopropionate (MBP). Aminolysis conditions: [PMA4500]/
[hexylamine]/[TEA]/[MBP] = 1/1/2/2, [PMA4500] = 0.027 mol/L; room
temperature; solvent: acetonitrile.
The aminolysis of the AB2 macromonomers, 8 or 9, was
monitored by GPC. Multimodal GPC curves (Figure 3) consistent
Figure 2. ESI-MS spectra of polymer PMA1000 (A), aminolysis products of PMA1000 in the presence of MBP (B) and EBiB (C), and their respective
partial enlargements (D, E, and F). Aminolysis conditions: [PMA4500]/[hexylamine]/[TEA]/[MBP] = 1/1/2/2, [PMA4500] = 0.027 mol/L; room
temperature; solvent: acetonitrile.

22 Macromolecules, Vol. 43, No. 1, 2010
Scheme 2. One-Pot Preparation of Multiblock and Hyperbranched Polymers
Communication
with growth toward high molecular weight were observed as
aminolysis progressed. Obviously, the increase of molecular
weight in the macromonomer 8 system was much quicker than
in the case of macromonomer 9. After 30 min, the reaction
involving macromonomer 8 was essentially complete, as evi-
denced by the near-constant molecular weight at subsequent
sampling times, whereas the molecular weight in the macromo-
nomer 9 system steadily increased. Static light scattering (SLS)
was employed to measure the absolute weight-average molecular
weight (Mw), yielding Mw ∼ 72230 for 10, derived from macro-
monomer 8, and Mw ∼ 64360 for 11, formed from macromono-
mer 9. The Mw values as determined by GPC, calibrated with
narrow molecular weight distribution polystyrene standards,
were 30 300 (Mw/Mn =2.01) for 11, which is much lower than
the value determined by SLS (64360), indicating that the final
product structure is hyperbranched. It is interesting to note that
the GPC-measured Mw for 10 was 68760 (Mw/Mn=1.83), which
is close to the value measured by SLS, suggesting that 10 is not
hyperbranched, but a linear multiblock or lightly branched
species. This supposition is borne out qualitatively when the
viscosities of aqueous solutions of 10 and 11, at identical
concentrations, are compared. Visually, the solution of 10 is
noticeably more viscous than that of 11, which is consistent with a
linear vs hyperbranched species of similar molecular weight and
concentration in aqueous solution.
The formation of a hyperbranched vs linear/lightly branched
species from 9 and 8 respectively can be rationalized as follows:
While the R-bromoester functional groups in both 8 and 9 are
initially equally reactive, theybecome potentially disparate after a
couple of condensation reactions with R-bromoester functional-
ity now, potentially, located at a chain termini and pendant along
the chain with the later suffering from steric crowding effects.
As such, the formation of a linear vs hyperbranched structure
is a direct reflection of the relative rates of reaction of the
R-bromoester functional groups, as these different locations,
toward substitution. In the case of macromonomer 8, the high

Communication
Macromolecules, Vol. 43, No. 1, 2010 23
ESI MS. Two novel AB2 macromonomers bearing ω-dithiobenzoate
and R-double bromoester end-groups were utilized to prepare
functionalized and defined multiblock/lightly branched and
hyperbranched polymers. Excess R-bromoester functionalities
could be modified easily to other functionalities on the periphery
of these multiblock/lightly branched and hyperbranched struc-
tures and provide potential anchoring points for graft polymeriza-
tions via ATRP/SET-LRP or other metal-catalyzed living radical
processes.
Acknowledgment. The authors acknowledge the receipt of
Discovery Grants from the Australian Research Council (ARC).
T.P.D. is also thankful for a Federation Fellowship from the
ARC.
Supporting Information Available: Experimental details.
This material is available free of charge via the Internet at
http://pubs.acs.org.
References and Notes
(1) Kolb, H. C.; Finn, M. G.; Sharpless, K. B. Angew. Chem., Int. Ed.
2001, 40, 2004–2021.
Figure 3. GPC traces (RI signal) monitoring aminolysis of AB2 macro-
(2) (a) Moses, J. E.; Moorhouse, A. D. Chem. Soc. Rev. 2007, 36, 1249–
1262. (b) Amblard, F.; Cho, J. H.; Schinazi, R. F. Chem. Rev. 2009, 109,
4207–4220. (c) Barner-Kowollik, C.; Inglis, A. J. Macromol. Chem.
Phys. 2009, 210, 987–992. (d) Barner, L. Adv. Mater. 2009, 21, 2547–
2553. (e) Best, M. D. Biochemistry 2009, 48, 6571–6584. (f) Wang, Z.;
Cohen, S. M. Chem. Soc. Rev. 2009, 35, 1315–1329.
monomers: (A) AB2 macromonomer 8 (Mn,GPC=7830 Da, Mn,NMR
=
9100 Da, PDI=1.10); (B) AB2 macromonomer 9 (Mn,GPC=5390 Da,
Mn,NMR=6050 Da, PDI=1.10) at different time points. Aminolysis
conditions: [macromonomers]0/[hexylamine]0/[TEA]0 = 1/1/2; room
temperature; solvent: acetonitrile.
(3) (a) Rostovtsev, V. V.; Green, L. G.; Fokin, V. V.; Sharpless, K. B.
Angew. Chem., Int. Ed. 2002, 41, 2596–2599. (b) Vestberg, R.;
Malkoch, M.; Kade, M.; Wu, P.; Fokin, V. V.; Sharpless, K. B.;
Drockenmuller, E.; Hawker, C. J. J. Polym. Sci., Part A: Polym.
Chem. 2007, 45, 2835–2846. (c) Lutz, J.-F. Angew. Chem., Int. Ed.
2007, 46, 1018–1025. (d) Tornoe, C. W.; Christensen, C.; Meldal, M.
J. Org. Chem. 2002, 67, 3057–3064. (e) Joralemon, M. J.; O'Reilly,
R. K.; Matson, J. B.; Nugent, A. K.; Hawker, C. J.; Wooley, K. L.
Macromolecules 2005, 38, 5436–5443. (f) O'Reilly, R. K.; Joralemon,
M. J.; Hawker, C. J.; Wooley, K. L. J. Polym. Sci., Part A: Polym.
Chem. 2006, 44, 5203–5217.
(4) (a) A Virtual Issue of Macromolecules: “Click Chemistry in Macro-
molecular Science.”Macromolecules 2009, 42, 3827-3829. (b) Fournier,
D.; Hoogenboom, R.; Schubert, U. S. Chem. Soc. Rev. 2007, 36, 1369–
1380. (c) Hawker, C. J.; Wooley, K. L. Science 2005, 309, 1200–1205.
(d) Franc, G.; Kakkar, A. Chem. Commun. 2008, 5267–5276. (e) Bock,
V. D.; Hiemstra, H.; van Maarseveen, J. H. Eur. J. Org. Chem. 2005, 1,
5267–5276. (f) de Graaf, A. J.; Kooijman, M.; Hennink, W. E.; Mastrobattista,
E. Bioconjugate Chem. 2009, 20, 1281–1295.
reactivity of the secondary R-bromoester functionality, as evi-
denced in the model reaction, favors reaction at the chain termini,
and hence formation of a linear/lightly branched species, with
steric effects due to the polymer backbone significantly, reducing
the reactivity of pendent R-bromoester functionality. However,
with macromonomer9, the difference in reactivity between chain-
end and pendant R-bromoester groups is not as dramatic. From
the model reaction with EBiB it is clear that the thio-bromo
reaction is slow, at least relative to MBP, requiring >20 h of
reaction time to reach high yields. Clearly, the reactivity of the
already sterically hindered tertiary R-bromoester is little affected
by being located at a chain terminus or as a pendant functional
group. As such, it appears that if the spacer between the polymer
backbone and the pendant functionality is short, then in an AB2
macromonomer with an inherent high reactivity between A and B
that the formation of a linear/lightly branched polymer is favored
whereas a low reactivity between A and B tends to favor the
formation of a hyperbranched species.15a,17
(5) (a) Gacal, B.; Akat, H.; Balta, D. K.; Arsu, N.; Yagci, Y. Macro-
molecules 2008, 41, 2401–2405. (b) Meng Shi; Wosnick, J. H.; Ho, K.;
Keating, A.; Shoichet, M. S. Angew. Chem., Int. Ed. 2007, 46, 6126–
6131.
It should also be noted that in any typical ABn polymerization
intramolecular cyclization is always a potential, undesirable side
reaction. However, in this present work, provided optimized
conditions are used, no cyclic structures could be identified from
the GPC curves (Figure 3).
The excess bromoester functionality in the multiblock/lightly
branched or hyperbranched structures can be proven by 1H
NMR spectroscopy (Figure S6). After aminolysis, the protons
(1, 2, 3) associated with the dithiobenzoate disappeared completely,
while the methine proton (6) in the monomer repeat unit close to
the thiocarbonylthio group moved to a lower chemical shift, and
the integration of overlapped peaks 4 and 5 decreased. After post-
treatment of the aminolysis product 10 with excess benzyl
mercaptam (Figure S6C in the Supporting Information), a
further decrease in the integration of peaks 4 and 5 verified the
presence of bromoester functionality after aminolysis.
(6) Gilmore, J. M.; Scheck, R. A.; Esser-Kahn, A. P.; Joshi, N. S.;
Francis, M. B. Angew. Chem., Int. Ed. 2006, 45, 5307–5311.
(7) See for example: (a) Becer, C. R.; Hoogenboom, R.; Schubert,
U. S. Angew. Chem., Int. Ed. 2009, 48, 4900–4908. (b) Dondoni, A.
Angew. Chem., Int. Ed. 2008, 47, 8995–8997. (c) Hoyle, C. E.; Lee,
T. Y.; Roper, T. J. Polym. Sci., Part A: Polym. Chem. 2004, 42, 5301–
5338. (d) Koehn, M. J. Peptide Sci. 2009, 15, 393–397.
(8) See for example: (a) Killops, K. L.; Campos, L. M.; Hawker, C. J.
J. Am. Chem. Soc. 2008, 130, 5062–5064. (b) Campos, L. M.; Killops,
K. L.; Sakai, R.; Paulusse, J. M. J.; Damiron, D.; Drockenmuller, E.;
Messmore, B. W.; Hawker, C. J. Macromolecules 2008, 41, 7063–
7070. (c) Carioscia, J. A.; Schneidewind, L.; O'Brien, C.; Ely, R.;
Feeser, C.; Cramer, N.; Bowman, C. N. J. Polym. Sci., Part A: Polym.
Chem. 2007, 45, 5686–5696. (d) Li, Q.; Zhou, H.; Wicks, D. A.; Hoyle,
C. E. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 5103–5111.
(e) Chan, J. W.; Hoyle, C. E.; Lowe, A. B. J. Am. Chem. Soc. 2009,
131, 5751–5753. (f) Chan, J. W.; Zhou, H.; Hoyle, C. E.; Lowe, A. B.
Chem. Mater. 2009, 21, 1579–1585. (g) David, R. L. A.; Kornfield,
J. A. Macromolecules 2008, 41, 1151–1161. (h) Chen, G.; Amajjahe,
S.; Stenzel, M. H. Chem. Commun. 2009, 1198–1200. (i) Gu, W.; Chen,
G.; Stenzel, M. H. J. Polym. Sci., Part A: Polym. Chem. 2009, 47,
5550–5556. (j) Jone, M. W.; Mantovani, G.; Ryan, S. M.; Wang, X.;
Brayden, D. J.; Haddleton, D. M. Chem. Commun. 2009, 5272–5274.
In conclusion, thio-bromo “click” reactions between in situ
generated thiolsobtained by the aminolysis of RAFT-synthesized
polymers and R-bromoesters was simulated by a model reaction
and the products characterized by GPC, NMR spectroscopy, and

24 Macromolecules, Vol. 43, No. 1, 2010
Communication
(k) Nurmi, L.; Lindqvist, J.; Randev, R.; Syrett, J.; Haddleton, D. M.
Chem. Commun. 2009, 2727–2729.
(12) (a) Niels, A.; Rueben, P.; Klumperman, B. Macromoleules 2009, 42,
3014–3018. (b) Ladmiral, V.; Legge, T. M.; Zhao, Y.; Perrier, S.
Macromoleules 2008, 41, 6728–6732. (c) Li, M.; De, P.; Gondi,
S. R.; Sumerlin, B. S. Macromol. Rapid Commun. 2008, 29, 1172–
1176. (d) Goldmann, A. S.; Quemener, D.; Millard, P.-E.; Davis, T. P.;
Stenzel, M. H.; Barner-Kowollik, C.; Mueller, A. H. E. Polymer 2008,
49, 2274–2281. (e) Yang, L.; Zhou, H.; Shi, G.; Wang, Y.; Pan, C.-Y.
J. Polym. Sci., Part A: Polym. Chem. 2008, 46, 6641–6653.
(f) Zhang, X.; Lian, X.; Liu, L.; Zhang, J.; Zhao, H. Macromoleules
2008, 41, 7863–7869.
(13) Rosen, B. M.; Lligadas, G.; Hahn, C.; Percec, V. J. Polym. Sci.,
Part A: Polym. Chem. 2009, 47, 3931–3939.
(14) Rosen, B. M.; Lligadas, G.; Hahn, C.; Percec, V. J. Polym. Sci.,
Part A: Polym. Chem. 2009, 47, 3940–3948.
(15) (a) Xu, J.; Tao, L.; Liu, J.; Bulmus, V.; Davis, T. P. Macromoleules
2009, 42, 6893–6901. (b) Jia, Z.; Wong, L.; Davis, T. P.; Bulmus, V.
Biomacromolecules 2009, 9, 3106–3113.
(16) (a) Xu, J.; He, J.; Fan, D.; Wang, X.; Yang, Y. Macromoleules
2006, 39, 8616–8624. (b) Llauro, M.; Loiseau, J.; Boisson, F.; Delolme,
(9) (a) Boyer, C.; Bulmus, V.; Davis, T. P. Macromol. Rapid Commun.
2009, 30, 493–497. (b) Boyer, C.; Granville, A.; Bulmus, V.; Davis, T. P.
J. Polym. Sci., Part A: Polym. Chem. 2009, 47, 3773–3794.
(10) (a) Li, H.; Yu, B.; Matsushima, H.; Hoyle, C. E.; Lowe, A. B.
Macromolecules 2009, 42, 6537–6542. (b) Shin, J.; Matsushima, H.;
Chan, J. W.; Hoyle, C. E. Macromolecules 2009, 42, 3294–3301.
(11) (a) Chiefari, J.; Chong, Y. K.; Ercole, F.; Krstina, J.; Le, T. P. T.;
Mayadunne, R. T. A.; Meijs, G. F.; Moad, G.; Moad, C. L.;
Rizzardo, E.; Thang, S. H. Macromolecules 1998, 31, 5559–5562.
(b) Lowe, A. B.; McCormick, C. L. Prog. Polym. Sci. 2007, 32, 283–
351. (c) Perrier, S.; Takolpuckdee, P. J. Polym. Sci., Part A: Polym.
Chem. 2005, 43, 5347–5393. (d) Barner, L.; Davis, T. P.; Stenzel, M. H.;
Barner-Kowollik, C. Macromol. Rapid Commun. 2007, 28, 539–559.
(e) York, A. W.; Scales, C. W.; Huang, F. Q.; McCormick, C. L.
Biomacromolecules 2007, 8, 2337–2341. (e) Inglis, A. J.; Sinwell,
S.; Davis, T. P.; Stenzel, M. H.; Barner-Kowollik, C. Macromolecules
2008, 41, 4120–4126. (f) Postma, A.; Davis, T. P.; Evans, R. A.; Li, G.;
Moad, G.; O'Shea, M. S. Macromolecules 2006, 39, 5293–5306.
(g) Xu, J.; He, J.; Fan, D.; Tang, W.; Yang, Y. Macromoleules 2006,
39, 3753–3759. (h) Xu, J.; Boyer, C.; Bulmus, V.; Davis, T. P. J. Polym.
Sci., Part A: Polym. Chem. 2009, 47, 4302–4313. (i) Tao, L.; Liu, J.;
Tan, B. H.; Davis, T. P. Macromoleules 2009, 42, 4960–4962. (j) Boyer,
C.; Bulmus, V.; Davis, T. P.; Ladmiral, V.; Liu, J.; Perrier, S. Chem. Rev.
2009, 109, 5402–5436.
ꢀ
F.; Ladaviere, C.; Claverie, J. J. Polym. Sci., Part A: Polym. Chem.
2004, 42, 5439–5462.
(17) (a) Trollsas, M.; Atthoff.; Claesson, H.; Hedrick, J. L. Macromo-
˚
lecules 1998, 31, 3439–3445. (b) Trollsås, M.; Hedrick, J. L. Macro-
molecules 1998, 31, 4390–4395. (c) Trollsas, M.; Kelly, M. A.;
Claesson, H.; Siemens, R.; Hedrick, J. L. Macromolecules 1999, 32,
4917–4924.