functionality but not though the NMP functionality—hence
potentially allowing access to an orthogonally reactive CRP
initiator. Further work is exploring the application of this novel
NMP–RAFT initiator and in particular in the one pot preparation
of block copolymers.
purification procedures. Current work is exploring this method
for the synthesis of novel polymer architectures and functional
materials. It is proposed that the universal nature of this chem-
istry allows for access to a wider range of RAFT/MADIX agents
using facile, efficient and high yielding strategies.
We have also applied this chemistry as a strategy for the post-
functionalisation and grafting of polymers. For example, a
poly(styrene-co-chloromethylstyrene) (MNn MR ¼ 10 600, Mw/Mn
¼ 1.13, with 12.1% functional monomer incorporation) was
prepared using reported NMP procedures (120 1C, bulk, 100
equiv.) and 2,2,5-trimethyl-3-(1-phenylethoxy)-4-phenyl-3-aza-
hexane as an initiator.10 This polymer was isolated and then
modified to incorporate a RAFT initiator through the reactive
chloro functionality in the side chain (evidence of complete
conversion, by halide analysis and also shift of the methylene
signal in the 1H NMR spectrum from d 4.5 to 4.7). This RAFT
macro initiator, 17, (MNn MR ¼ 11 700, Mw/Mn ¼ 1.15) was then
utilised to polymerise tert-butyl acrylate (tBuA) (60 1C, dioxane,
100 equiv., 0.1 equiv. AIBN) to afford a diblock graft copolymer
(MNn MR ¼ 28 300, Mw/Mn ¼ 1.23). This highlights the scope of
this chemistry to enable access to novel block and graft copoly-
mers, which are perhaps inaccessible using conventional strate-
gies, via a post-polymerisation CTA functionalisation and
subsequent polymerisation strategy.
The authors would like to acknowledge the EPSRC and the
Department of Chemistry for funding for J.S. and the Royal
Society and Downing College for funding for R.K.O.R. Alan
Dickerson (University of Cambridge) is thanked for elemental
analysis.
Notes and references
z Typical experimental procedure. To a round bottomed flask, equipped
with a stirrer bar, was added thiol, solvent and base. The mixture was
allowed to stir and the CS2 added and then the alkyl halide. The reaction
was then monitored by TLC (with reaction times ranging from 1 min to
13 h. The reaction mixture was filtered and solvent removed under vacuum
to afford a yellow oil/solid which was purified by column chromatography.
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Rizzardo and S. H. Thang, Macromolecules, 1998, 31, 5559; (b) Y. K.
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All the CTAs in this work have been characterised fully by
1H, 13C NMR spectroscopy, IR, MS and elemental analysis (see
ESIw). A selection of the CTAs were also utilised in RAFT/
MADIX polymerisations to highlight their purity and effective-
ness in mediating the controlled polymerisation of a wide range
of monomers (Table 1 and ESIw). In particular CTA 1a which
was isolated directly from the reaction mixture (after filtration
and removal of solvent) was utilised in the polymerisation of
styrene and compared to results for the purified initiator 1.
Table 1 highlights that in the synthesis of dithiocarbonate CTA
1a no purification of the reaction mixture is required before
utilisation as CTA for the polymerisation of styrene, given the
high yield of the reaction.
4 Y. Q. Wang, Z. M. Ge, X. L. Hou, T. M. Cheng and R. T. Li,
Synthesis, 2004, 5, 675.
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Chem., 2002, 40, 4498; (b) M. Hales, C. Barner-Kowollik, T. P.
Davis and M. H. Stenzel, Langmuir, 2004, 20, 10809.
Overall this chemistry has been demonstrated to be both
versatile and efficient for the synthesis of novel and previously
reported RAFT agents. This methodology can be readily tailored
to allow for the high yielding synthesis of dithiocarbamates,
xanthates and trithiocarbonate CTAs. The significant advantage
of this strategy over existing methods is the wide range of CTAs
accessible via mild reaction conditions and without difficult
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Table 1 Polymers formed by RAFT/MADIX polymerisations using
CTAs synthesised in this study
Time/ Mn,th
h
/
Mn,GPC
/
Mw/
Conversion
(%)
CTA Monomer
g molꢁ1 g molꢁ1 Mn
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and C. Barner-Kowollik, Macromol. Chem. Phys., 2003, 204, 1160;
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Mori, H. Ookuma, S. Nakano and T. Endo, Macromol. Chem.
Phys., 2006, 207, 1005; (d) D. Wan, K. Satoh, M. Kamigaito and
Y. Okamoto, Macromolecules, 2005, 38, 10397.
9 (a) N. Azizi, F. Aryanasab and M. R. Saidi, Org. Lett., 2006, 8,
5275; (b) D. Chaturvedi and S. Ray, Tetrahedron Lett., 2006, 47,
1307; (c) R. N. Salvatore, S. Sahab and K. W. Jung, Tetrahedron
Lett., 2001, 42, 2055.
1a
1
2
3
8
11
10
6
9
16
tBuA
tBuA
24
24
22.5
40
2.75 29 200
13
22.5
21.5
21.5
4
25 400
25 400
8000
24 000
24 500
7300
1.18
1.18
1.18
1.13
1.30
1.43
1.32
1.17
1.12
1.08
499
499
77
Styrene
Styrenea
MMA
VAc
7200
7300
69
39 300
8700
5700
13 100
13 600
12 400
499
499
46
97
98
8900
9100
12 600
12 800
12 300
NVCa
tBuA
tBuA
tBuA
97
10 D. Benoit, V. Chaplinski, R. Braslau and C. J. Hawker, J. Am.
Chem. Soc., 1999, 121, 3904.
a
Polymerisation run in 1 : 1 monomer : dioxane.
ꢀc
This journal is The Royal Society of Chemistry 2008
Chem. Commun., 2008, 4183–4185 | 4185