A potential new RAFTClick reaction or a cautionary note on the use of diazomethane to methylate RAFT-synthesized polymers

Article abstract of DOI:10.1071/CH10471

It has been found that diazomethane undergoes a facile 1,3-dipolar cycloaddition with both dithiobenzoate RAFT agents and the dithiobenzoate end-groups of polymers formed by RAFT polymerization. Thus, 2-cyanoprop-2-yl dithiobenzoate on treatment with diaz

Full text of DOI:10.1071/CH10471

RESEARCH FRONT
Full Paper
CSIRO PUBLISHING
www.publish.csiro.au/journals/ajc
Aust. J. Chem. 2011, 64, 433–437
A Potential New RAFT Click Reaction or a Cautionary
]
Note on the Use of Diazomethane to Methylate
RAFT-synthesized Polymers-
A B
,
A B
,
A
Ming Chen,
Graeme Moad,
and Ezio Rizzardo
A
CSIRO Materials Science and Engineering, Bag 10, Clayton South, Vic. 3169, Australia.
Corresponding authors. Email: ming.chen@csiro.au, graeme.moad@csiro.au
B
It has been found that diazomethane undergoes a facile 1,3-dipolar cycloaddition with both dithiobenzoate RAFT agents
and the dithiobenzoate end-groups of polymers formed by RAFT polymerization. Thus, 2-cyanoprop-2-yl dithiobenzoate
on treatment with diazomethane at room temperature provided a mixture of stereoisomeric 1,3-dithiolanes in near
quantitative (495%) yield. A low-molecular-weight RAFT-synthesized poly(methyl methacrylate) with dithiobenzoate
end-groups underwent similar reaction as indicated by immediate decolourization and a quantitative doubling of
molecular weight. Higher-molecular-weight poly(methyl methacrylate)s were also rapidly decolourized by diazomethane
and provided a product with a bimodal molecular weight distribution. Under similar conditions, the trithiocarbonate group
does not react with diazomethane.
Manuscript received: 21 December 2010.
Manuscript accepted: 1 February 2011.
Introduction
with the thiocarbonylthio end-group of RAFT-synthesized
polymers in more detail.
Diazomethane is routinely used in polymer chemistry to
methylate the carboxylic acid functionality in polymers or
copolymers (e.g. those containing acrylic or methacrylic acid
units[1]). This treatment facilitates characterization by gel per-
meation chromatography (GPC) and NMR spectroscopy.
In recent years, reversible addition–fragmentation chain trans-
fer (RAFT) polymerization, one of the most effective processes
for reversible deactivation radical polymerization,[2] has been
successfully applied to a large range ofmonomers including those
with unprotected carboxylic acid groups.[3–8] The RAFT process
involves performing a radical polymerization in the presence
of certain thiocarbonylthio compounds (S¼C(Z)–SR) known as
RAFT agents. The RAFT agents provide living characteristics to
the polymerization. The products of RAFT polymerization are
themselves (macro-)RAFT agents and possess the S¼C(Z)S– and
R groups as chain ends (Scheme 1).
In an experiment where diazomethane was used to methylate
RAFT-synthesized poly(methacrylic acid) with dithiobenzoate
end groups, we observed, in addition to the expected methyla-
tion, that the (initially pink) polymer was decolourized and
developed a bimodal molecular weight distribution with forma-
tion of a new peak with double the predicted molecular weight.
This observation led us to examine the reaction of diazomethane
The reaction between diazoalkanes and thiocarbonyl com-
pounds was first reported in 1920 by Staudinger et al.[9] who
investigated the reaction between diphenyldiazomethane and
various diaryl thioketones and commented that diphenyldiazo-
methane reacted only slowly with dithiobenzoates. Scho¨nberg
et al.[10] extended this study to many diazoalkane–thiocarbonyl
compound pairs. Depending on the reaction conditions and
the specific reactants, 1,3-dithiolanes, thiiranes or alkenes
were observed among the reaction products. However, the
precise mechanism of the reaction remained unclear until
Huisgen et al. isolated a thiadiazole intermediate (2) from the
reaction of thiobenzophenone (1) and diazomethane at ꢀ788C
(Scheme 2).[11]
It was proposed[11] that diazomethane reacted with 1 in 1:1
stoichiometry at ꢀ788C by 1,3-cycloaddition, producing the
2,5-dihydro-2,2-diphenyl-1,3,4-thiadiazole (2). The thiadiazole
2 then eliminated N2 in a 1,3-cycloreversion at ꢀ458C, affording
thiobenzophenone S-methylide (3). The reactive methylide 3
was not isolable but intercepted in situ by another molecule of 1
or a second dipolarophile, d¼e, giving rise to the cycloadducts 4
or 5 respectively. Among the many dipolarophiles (e.g. C¼S,
C¼O, C¼C, and CꢁC), thiocarbonyl compounds appeared to
be more reactive toward 3, as evidenced by the formation
of 1,3-dithiolane 4 in 95% yield even when 1 was treated
with excess diazomethane at 208C (the original conditions
used by Scho¨nberg). In competition with cycloaddition, or
S
S R Initiator
R Px
S
S
Monomer ϩ
C
Z
C
Z
Scheme 1.
yThis paper is dedicated to the memory of Professor Athelstan L. J. Beckwith whose innovation and enthusiasm have inspired several generations of free radical
chemists.
Ó CSIRO 2011
10.1071/CH10471
0004-9425/11/040433

RESEARCH FRONT
434
M. Chen, G. Moad, and E. Rizzardo
Ph
Ph
S
THF/Ϫ78°C
N
N
Ph C
S
ϩ CH2N2
2
1
2
THF/Ϫ45°C
ϪN2
Ph
Ph
Ph
Ph
Ph
Ph
Ph
Ph
S
S
ϩ
S
ϩ
S
Ph
S
Ph2C
S
Ph
Ph
Ϫ
Ϫ
CH2
ϩ
C
C
Ph
CH2
S
S
Ph
Ph
3b
6
7
Ϫ(S)
Ph
3a
4
dϭe
Ph
Ph
Ph
S
8
d
e
5
Scheme 2.
in the absence of intercepting reagents, the ylide 3 also under-
went a head-to-head dimerization, to yield the 1,4-dithiane 6, or
irreversible electrocyclization to give the thiirane 7. On heating
or after extended reaction times, the latter (7) extruded sulfur
to give 1,1-diphenylethylene (8). The mechanism for reactions
between other thiocarbonyl compounds and diazo compounds
(including that of diazomethane with dithioesters[12–14]) was
presumed to be analogous.
The Reaction between Diazomethane and Polymers
with Dithiobenzoate End-groups
A series of poly(methyl methacrylate) (PMMA) with narrow
molecular weight distributions (Mw/Mno1.2) and average
molecular weights (Mn) in the range ,2000–80000 were syn-
thesized by RAFT polymerization using the dithiobenzoate
RAFT agent 9. Treatment of dichloromethane solutions of these
polymers with diazomethane at 208C gave rapid decolouriza-
tion. The molecular weight distributions of the isolated poly-
mers were determined by GPC (Fig. 1). The chromatograms
showed that the lowest-molecular-weight PMMA sample
had quantitatively doubled in molecular weight. The higher-
molecular-weight PMMA samples each provided a product with
a bimodal molecular weight distribution, with the formation of a
higher-molecular-weight component approximately twice that
of the original PMMA (Table 1, Fig. 1).
By analogy with the chemistry observed for ‘small molecule’
dithiobenzoates, we propose that the higher-molecular-weight
component comprises PMMA chains joined by a 1,3-dithiolane
linkage (15, Scheme 4). This structure results from 1,3-
cycloaddition between ylide end-group 14 and the dithiobenzo-
ate end-group 13. The fraction of the higher-molecular-weight
component observed decreases with an increase in the molecular
weight of the precursor PMMA. The proportion of this compo-
nent (Imono) was roughly estimated from a comparison of the
corresponding GPC traces (Table 1).
Results and Discussion
The Reaction of Diazomethane with Dithiobenzoates
When diazomethane was slowly introduced into a red solution
of 2-cyanoprop-2-yl dithiobenzoate (9) in dichloromethane at
208C, a brisk evolution of nitrogen was observed and the solution
rapidly decolourized. Two 1,3-dithiolane stereoisomers, 10 and
11, were isolated from the reaction mixture by column chro-
matography in yields of 53 and 42% respectively. The proposed
mechanism is shown in Scheme 3. The near-quantitative yield of
10 þ 11 suggests that the reaction of 9 with the intermediate ylide
12 is substantially faster than the reaction of 9 with diazo-
methane. The identity of products was established by NMR
spectroscopy. For the symmetrical trans-isomer 10, the 5-H2
protons are identical, giving rise to a singlet signal at d 4.51 in
the 1H NMR spectrum, whereas the spectrum of the cis-isomer
11 shows an AB pattern for the 5-H2 protons at d 3.91 and 4.62
with J ¼ 8.8 Hz. Characterization of this compound by mass
spectrometry posed a challenge, because the dithiolanes tend to
fragment when ionized. The electron impact (EI) mass spectra
showed only a weak molecular ion for the dithiolanes, in addition
to several much more intense fragment ions.
The dithiolanes appear indefinitely stable at ambient tem-
perature but isomerize, decompose or both on heating at ele-
vated temperatures. For example, on heating in a melting point
apparatus, an initially colourless sample of 10 was observed to
turn red at ,1708C before meting at 180–1818C. Similarly, a
sample of 11 was observed to turn red at ,1848C before melting
at 188–1898C. Samples of pure 10 or 11 heated in [D5]chloro-
benzene at 4908C in an NMR tube underwent isomerization to a
mixture of 10 and 11 with noticeable reaction being observed
after 30 min. At higher temperatures, conversion to 9 and
unidentified by-products was observed, which may indicate that
the formation of the dithiolanes is reversible. The dithiolane 10
was completely decomposed by heating at 1058C for 18 h.
One explanation for coupling not being quantitative is that
the precursor polymer is contaminated by dead chains (i.e.
without dithiobenzoate ends). Dead chains may be produced
by termination or by irreversible chain transfer to initiator,
solvent or monomer. If the initial RAFT agent is completely
consumed, the number of dead chains formed by termination
(Dc) should be approximately equal to the number of initiator-
derived chains, and can be estimated using Eqn 1
2df ½ACHNꢂ0ð1 ꢀ eꢀk t
Þ
d
Dc ¼
ð1Þ
½RAFTꢂ0 þ 2df ½ACHNꢂ0ð1 ꢀ eꢀk t
Þ
d
where f is the initiator efficiency (,0.5), d is the number
of chains formed by radical–radical termination (2 for dispro-
portionation, 1 for combination and ,1.67 for PMMA), t is
time and kd is the rate constant for initiator decomposition
(2.15 ꢃ 10ꢀ5 sꢀ1 for 1,10-azobis(cyclohexanecarbonitrile)

RESEARCH FRONT
Potential New RAFT–‘Click’ Reaction
435
S
C
CH
C
3
CH
S
S
S
S
95%
NC
NC
S
S
NC
NC
S
S
2
S
ϩ CH2N2
5
ϩ
5
3
CN
9
10, 53%
11, 42%
9
ϪN2
ϩ
S
S
N
S
C
S
C
N
CH2
CN
CN
12
Scheme 3.
The Reaction between Diazomethane
and Trithiocarbonates
Similar experiments with diazomethane and either small-
molecule or polymeric trithiocarbonate compounds were per-
formed using similar reaction conditions. The solution retained
the yellow colour attributable to the trithiocarbonate chromo-
phore and no change was detected by NMR. This is consistent
with the trithiocarbonates being poorer dipolarophiles than
dithiobenzoate.
A New RAFT–‘Click’ Reaction?
There has been recent interest in the direct transformation
of RAFT end groups by the ‘Click’ reaction.[19] One process
investigated by Barner-Kowollik and coworkers[20–28] is the
hetero-Diels–Alder reaction with suitable dienes. It may be
possible to make use of the chemistry described in the present
paper to provide a method to functionalize polymers with
dithiobenzoate ends. Mloston et al.[12] have reported that the
thiadiazole intermediates formed by reaction of phosphono-
dithioformates with diazomethane are stable at ꢀ658C and can
be quantitatively converted to the ylide on warming to ꢀ358C.
This ylide could be trapped by various small molecule
dipolarophiles.[12]
105
104
Molecular weight
103
Fig. 1. Molecular weight distributions of reversible addition–fragmentation
chain transfer (RAFT)-synthesized poly(methyl methacrylate) before (—) and
after (----) treatment with diazomethane.
The proposed process is shown in Scheme 5. The low-
temperature reaction with diazomethane forms the thiadiazole;
the ylide can then be generated by warming the reaction mixture
to react with a dipolarophile (A¼B) (Scheme 5). This dipolaro-
phile may be a RAFT agent or a macro-RAFT agent, providing a
route to block copolymers.
The cycloaddition of RAFT agents (S¼C(Z)–SR) with
diazomethane is facilitated by electron-withdrawing Z and
requires a dithiobenzoate (or more active RAFT agent). The
hetero-Diels–Alder reaction examined by Barner-Kowollik and
coworkers[20–28] showed a similar but more pronounced trend.
The reaction of the ylide is both more facile and less selective
and, based on the work of Mloston et al.,[12] a wide variety of
dipolarophiles, including trithiocarbonates, can be used.
(ACHN) at 908C) (Table 1). The incidence of irreversible chain
transfer should be negligible for the polymerization conditions
used.
The finding that the fraction of uncoupled chains (Imono
)
appears significantly greater than the estimated fraction of dead
chains in the PMMA indicates that there must be another
explanation.
A second explanation is that intramolecular electrocycliza-
tion of the polymeric ylide 14 to give thiirane 16 (Scheme 4)
competes with intermolecular coupling between 13 and 14.
The intramolecular electrocyclic ring closure becomes more
competitive for higher-molecular-weight PMMA because the
probability of the dithiobenzoate end-group 13 encountering
the ylide 14 is reduced by the end-group concentration and
the rate of end-group diffusion is lower (the solutions for the
higher-molecular-weight polymers were also significantly more
viscous).
Sasso et al.[18] reported the diazomethane methylation of a
RAFT-synthesized polymer. However, the dithiobenzoate ends
had been previously removed by amine treatment and no
unexpected reactions were reported.
Conclusions
The interaction of diazomethane and thiocarbonylthio RAFT
agents and macroRAFT agents has been studied. Diazomethane
undergoes an extremely facile reaction with dithiobenzoates,
though not with trithiocarbonates and, most likely, less active
RAFT agents. This study suggests some limitations on the direct
use of diazomethane to esterify polymers formed by RAFT

RESEARCH FRONT
436
M. Chen, G. Moad, and E. Rizzardo
Table 1. The molecular weights of reversible addition fragmentation chain transfer (RAFT)-synthesized poly(methyl methacrylate) (PMMA), the
]
proportion of dead chains in that polymer, and the fraction of uncoupled chains after reaction with diazomethane
9 ꢃ 103 M
Time [h]
Conversion [%]
Mn
Mn
Mn calc.C
Mn calc.D
Mw/Mn
DcE [%]
ImonoF [%]
A
B
Sample
PMMA-1
181.0
–
16
–
46
–
2100
3500
2300
3850
1900
1900
1.16
1.17
1.07
1.12
1.06
1.12
1.08
1.16
1.06
1.14
1.08
1.17
1.2
–
–
,0
–
PMMA-1-diazo
PMMA-2
–
9300
–
45.25
–
6
63
–
8900
9800
8800
12200
23000
40400
73300
2.5
–
PMMA-2-diazo
PMMA-3
–
14800
11800
19600
25900
36500
41000
58100
80400
104700
16200
13000
21500
28400
40000
44900
63600
88000
114500
25
–
45.25
–
16
–
85
–
12500
–
4.6
–
PMMA-3-diazo
PMMA-4
21
–
11.31
–
4
50
–
29200
–
6.7
–
PMMA-4-diazo
PMMA-5
–
38
–
11.31
–
8
83
–
48300
–
11.1
–
PMMA-5-diazo
PMMA-6
–
38
–
5.656
–
10
–
84
–
91900
–
22.6
–
PMMA-6-diazo
48
AMolecular weight in polystyrene equivalents.
BMolecular weight in PMMA equivalents from universal calibration with Mark–Houwink–Sakaruda parameters of K ¼ 11.4 ꢃ 108 g Lꢀ1, a ¼ 0.716
(PMMA),[15] and K ¼ 9.44 ꢃ 108 g Lꢀ1, a ¼ 0.719 (polystyrene).[16]
CTheoretical molecular weights calculated using the expression
½MMAꢂ0x
Mn
¼
where x is the fractional monomer conversion, [RAFT]0 and [MMA]0 are the initial concentrations and MRAFT and MMMA the molecular weights of the initial
MMMA þ MRAFT
½RAFTꢂ0
RAFT agent and of MMA respectively.
DTheoretical molecular weights calculated using the expression:[4,17]
½MMAꢂ0x
Mn
¼
MMMA þ MRAFT
Þ
t
½RAFTꢂ0 þ 2df ½ACHNꢂ0ð1 ꢀ eꢀk
d
where f is the initiator efficiency (0.5), d is the number of chains formed by radical–radical termination (1.67 for PMMA) and kd is the rate constant for initiator
decomposition (2.15 ꢃ 10ꢀ5 sꢀ1 for 1,10-azobis(cyclohexanecarbonitrile) (ACHN) at 908C).
EProportion of the dead chains Dc calculated using Eqn 1.
FProportion of uncoupled chains Imono based on relative intensity peaks in the gel permeation chromatograph (GPC) traces shown in Fig. 1 and the following
assumptions: (a) the higher-molecular-weight peak is formed by coupling of two chains; (b) the peak intensity is proportional to the molecular weight.
S
Z
S
S
S
S
C S
S
S
CH2N2
13
Pn
ϩ
SϪ
Ϫ
S C
14
N
Ϫ
CH2
N
N
ϩ
S
A
Nϩ
CH2
13
S
S
B
A
S
B
Z
S
15
Z
Z
S
S
Pn
Z
S
Pn
Pn
Pn
S
S C CH2
16
S
ZЈ
S
Qn
ZЈ
Z
S
Scheme 4.
S
Qn
S
Pn
S
polymerization with dithiobenzoate (or (macro)RAFT agents
with similar or greater activity). Reaction of a polymer with
trimethylsilyldiazomethane[29] is likely to be subject to similar
complications as those observed with direct treatment with
diazomethane. Treatment of the polymer with methyl iodide and
tetramethylammonium hydroxide[30] may be complicated with
conversion of the thiocarbonylthio end-group to a thiol end and
subsequent formation of a coupled product by disulfide forma-
tion. It is recommended that the end-groups be removed from
such RAFT-synthesized polymers before methylation. A variety
of procedures are now available for this.[19]
The present work also suggests a new ‘Click’ reaction for
end-functionalizing RAFT-synthesized polymers by sequential
treatment of a polymer with diazomethane (or other diazo-
compound) and a dipolarophile (A¼B; Scheme 5). When the
dipolarophile isa macro-RAFT agent, theproductwill bea block
copolymer. This process will be the subject of future work.
Scheme 5.
Experimental Section
1,10-Azobis(cyclohexanecarbonitrile) (Vazo88, DuPont) was
used as received. Methyl methacrylate (MMA; Aldrich)
was purified by vacuum distillation and then flash distilled
before use. Solutions of diazomethane in diethyl ether[31] and
2-cyanopropan-2-yl dithiobenzoate[32] were prepared as repor-
ted previously (CAUTION! Diazomethane is toxic and poten-
tially explosive. For safe handling procedures, see ref. [31]).
Melting points were obtained with an Electrothermal
melting point apparatus and are uncorrected. Positive-ion EI
mass spectra were run on a ThermoQuest MAT95XL mass
spectrometer using ionization energy of 70 eV. 1H and 13C NMR
spectra were recorded on a Bruker AV400 spectrometer

RESEARCH FRONT
Potential New RAFT–‘Click’ Reaction
437
(1H, 400.13 MHz; 13C, 100.63 MHz) at 258C in deuterated
solvents as stated. Proton chemical shifts are expressed in parts
per million (d scale) downfield from tetramethylsilane and
are referenced to the residual protonated NMR solvent signal.
Carbon chemical shifts are expressed in parts per million (d
scale) downfield from tetramethylsilane and are referenced to
the carbon resonance of the NMR solvent spectra.
[3] J. Chiefari, Y. K. Chong, F. Ercole, J. Krstina, J. Jeffery, T. P. T. Le,
R. T. A. Mayadunne, G. F. Meijs, C. L. Moad, G. Moad, E. Rizzardo,
S. H. Thang, Macromolecules 1998, 31, 5559. doi:10.1021/MA9804951
[4] G. Moad, E. Rizzardo, S. H. Thang, Aust. J. Chem. 2005, 58, 379.
doi:10.1071/CH05072
[5] G. Moad, E. Rizzardo, S. H. Thang, Aust. J. Chem. 2006, 59, 669.
doi:10.1071/CH06250
[6] G. Moad, E. Rizzardo, S. H. Thang, Acc. Chem. Res. 2008, 41, 1133.
doi:10.1021/AR800075N
[7] G. Moad, E. Rizzardo, S. H. Thang, Polymer 2008, 49, 1079.
doi:10.1016/J.POLYMER.2007.11.020
[8] G. Moad, E. Rizzardo, S. H. Thang, Aust. J. Chem. 2009, 62, 1402.
doi:10.1071/CH09311
[9] H. Staudinger, J. Siegwart, Helv. Chim. Acta 1920, 3, 833. doi:10.1002/
HLCA.19200030178
[10] A. Scho¨nberg, B. Koenig, E. Singer, Chem. Ber. 1967, 100, 767.
doi:10.1002/CBER.19671000310
[11] R. Huisgen, I. Kalvinsch, X. Li, G. Mloston, Eur. J. Org. Chem. 2000,
Molecular weights of polymer were characterized by GPC
performed in tetrahydrofuran (THF, 1.0 mL minꢀ1) at 308C
using a Waters GPC instrument with a Waters 2414 refractive
index detector, a series of four Polymer Laboratories PLGel
columns (3 ꢃ 5 mm Mixed-C and 1 ꢃ 3 mm Mixed-E) and
Empower software. The GPC was calibrated with narrow poly-
dispersity polystyrene standards (Polymer Laboratories Easi-
Cal, molecular weight from 264 to 256000). PMMA molecular
weights are based on application of universal calibration and
Mark–Houwink–Sakaruda parameters of K ¼ 11.4 ꢃ 108 g Lꢀ1
(polystyrene).[16]
,
2000, 1685.
a ¼ 0.716 (PMMA),[15] and K ¼ 9.44 ꢃ 108 g Lꢀ1, a ¼ 0.719
[12] G. Mloston, K. Urbaniak, M. Gulea, S. Masson, A. Linden,
H. Heimgartner, Helv. Chim. Acta 2005, 88, 2582. doi:10.1002/HLCA.
200590198
Synthesis of 1,3-Dithiolane 10 and 11. An ethereal solution
of diazomethane was added dropwise to a dichloromethane
solution (2 mL) of the dithiobenzoate 9 (221 mg, 1.00 mmol)
at 208C until the red colour of the reaction mixture had vanished.
The solution was evaporated to dryness, and purified by column
chromatography on silica gel (Kieselgel-60, 230–400 mesh)
with ethyl acetate/n-hexane 10:90 (v/v) as eluent to afford the
two stereoisomers of the 1,3-dithiolane, 10 (121 mg, 53%) and
11 (96 mg, 42%). Both products were recrystallized from a
mixture of dichloromethane and methanol.
10. Mp: 180–1818C. dH (400.13 MHz, C6D5Cl) 0.93 (s, 6H),
1.23 (s, 6H), 4.51 (s, 2H), 7.08–7.16 (m, 6H), 7.80 (bs, 4H). dC
(100.63 MHz, C6D5Cl) 27.60, 28.89, 30.98, 39.88, 85.45, 123.86,
125.82, 126.02, 127.29, 128.10, 128.30, 129.12, 129.32, 131.93,
135.32. m/z (EI-MS) 456.1 (2, Mþ), 388.0 (12), 356.1 (14), 256.0
(100), 210.0 (29), 167.0 (24), 121.0 (80), 77.0 (15).
11. Mp: 188–1898C. dH (400.13 MHz, C6D5Cl) 1.00 (s, 6H),
1.34 (s, 6H), 3.91 (d, 1H, J 8.8), 4.62 (d, 1H, J 8.8), 6.88–6.94
(m, 4H), 6.99–7.04 (m, 2H), 7.36 (bd, 4H, J 7.7). dC
(100.63 MHz, C6D5Cl) 28.08, 29.39, 33.30, 39.97, 85.33,
123.03, 125.83, 126.03, 126.97, 128.10, 128.30, 128.60,
129.13, 129.32, 130.94, 137.97. m/z (EI-MS) 456.1 (2, Mþ),
388.1 (16), 356.1 (8), 256.1 (85), 210.1 (23), 167.0 (28), 121.0
(100), 77.1 (20).
[13] J. M. Beiner, D. Lecadet, D. Paquer, A. Thuillier, J. Vialle, Bull. Soc.
Chim. Fr. 1973, 1979.
[14] G. Mloston, J. Romanski, E. B. Rusanov, A. N. Chernega, Y. G.
Shermolovich, Zh. Org. Khim. 1995, 31, 1027.
[15] R. A. Hutchinson, J. H. McMinn, D. A. Paquet, S. Beuermann,
C. Jackson, Ind. Eng. Chem. Res. 1997, 36, 1103. doi:10.1021/
IE9604031
[16] R. A. Hutchinson, S. Beuermann, D. A. Paquet, Jr, J. H. McMinn,
Macromolecules 1997, 30, 3490. doi:10.1021/MA970176U
[17] Y. K. Chong, G. Moad, E. Rizzardo, M. A. Skidmore, S. H. Thang,
Macromolecules 2007, 40, 9262. doi:10.1021/MA071100T
[18] B. Sasso, M. Dobinson, P. Hodge, T. Wear, Macromolecules 2010, 43,
7453. doi:10.1021/MA1011683
[19] G. Moad, E. Rizzardo, S. H. Thang, Polym. Int. 2011, 60, 9.
doi:10.1002/PI.2988
[20] A. J. Inglis, S. Sinnwell, T. P. Davis, C. Barner-Kowollik, M. H.
Stenzel, Macromolecules 2008, 41, 4120. doi:10.1021/MA8002328
[21] S. Sinnwell, A. J. Inglis, T. P. Davis, M. H. Stenzel, C. Barner-
Kowollik, Chem. Commun. 2008, 2052. doi:10.1039/B718180A
[22] S. Sinnwell, C. V. Synatschke, T. Junkers, M. H. Stenzel, C. Barner-
Kowollik, Macromolecules 2008, 41, 7904. doi:10.1021/MA8013959
[23] S. Sinnwell, M. Lammens, M. H. Stenzel, F. E. Du Prez, C. Barner-
Kowollik, J. Polym. Sci. A Polym. Chem. 2009, 47, 2207. doi:10.1002/
POLA.23299
[24] S. Sinnwell, A. J. Inglis, M. H. Stenzel, C. Barner-Kowollik,
Macromol. Rapid Commun. 2008, 29, 1090. doi:10.1002/MARC.
200800233
Synthesis of PMMA by RAFT Polymerization
Solutions of 9, ACHN (4.5 mg, 1.84 ꢃ 10ꢀ3 M), MMA (6.552 g,
6.552 M) in benzene (3 mL) were transferred to an ampoule
which was degassed through three freeze–pump–thaw cycles,
sealed under vacuum, and heated at 908C for the stated time. The
polymers were then precipitated twice into n-hexane (100 mL),
filtered, and washed with n-hexane (50 mL) to give the poly-
mers. The polymerization conditions and conversions are
summarized in Table 1.
[25] L. Nebhani, S. Sinnwell, A. J. Inglis, M. H. Stenzel, C. Barner-
Kowollik, L. Barner, Macromol. Rapid Commun. 2008, 29, 1431.
doi:10.1002/MARC.200800244
[26] A. J. Inglis, S. Sinnwell, M. H. Stenzel, C. Barner-Kowollik, Angew.
Chem. Int. Ed. Engl. 2009, 48, 2411. doi:10.1002/ANIE.200805993
[27] L. Nebhani, P. Gerstel, P. Atanasova, M. Bruns, C. Barner-Kowollik,
J.Polym. Sci.APolym. Chem.2009, 47, 7090. doi:10.1002/POLA.23756
[28] L. Nebhani, S. Sinnwell, C. Y. Lin, M. L. Coote, M. H. Stenzel,
C. Barner-Kowollik, J. Polym. Sci. A Polym. Chem. 2009, 47, 6053.
doi:10.1002/POLA.23647
[29] L. Couvreur, C. Lefay, J. Belleney, B. Charleux, O. Guerret,
S. Magnet, Macromolecules 2003, 36, 8260. doi:10.1021/MA035043P
[30] L. Hutson, J. Krstina, C. L. Moad, G. Moad, G. R. Morrow, A. Postma,
E. Rizzardo, S. H. Thang, Macromolecules 2004, 37, 4441. doi:10.1021/
MA049813O
Acknowledgement
The provision of a Julius Career Award to M.C. by the CSIRO Office of the
Chief Executive (OCE) Science Team is acknowledged.
References
[1] A. Katchalsky, H. Eisenberg, J. Polym. Sci., Polym. Phys. Ed. 1951, 6,
145. doi:10.1002/POL.1951.120060202
[31] F. Arndt, in Organic Synthesis (Collective Vol. 2) (Ed. A. H. Blatt)
1943, pp. 165–167 (Wiley: New York).
[2] A. D. Jenkins, R. I. Jones, G. Moad, Pure Appl. Chem. 2010, 82, 483.
doi:10.1351/PAC-REP-08-04-03
[32] S. H. Thang, Y. K. Chong, R. T. A. Mayadunne, G. Moad, E. Rizzardo,
Tetrahedron Lett. 1999, 40, 2435. doi:10.1016/S0040-4039(99)00177-X