Transesterification of Poly(Ethyl--Hydroxy-methacrylate)
Prepared via Reversible Addition Fragmentation Chain
Transfer (RAFT) Polymerization
T. Y. Joan Chiu, Martina H. Stenzel, Thomas P. Davis and Christopher BarnerKowollik
SUPPLEMENTARY INFORMATION
Materials
Ethylhydroxy methacrylate (EHMA)1 was purified by percolating over a
column of basic alumina prior to use. Cumyl dithiobenzoate (CDB) was prepared
using the method described by Oae et al.,2 with n-hexane as the solvent. The purity of
the RAFT agent was close to 99% as verified by 1H-NMR and elemental analysis.3
2,2- Azobis(isobutyronitrile) (AIBN, Aldrich, 99%) was re-crystallized twice from
ethanol prior to use.
1 EHMA was kindly provided by Mr Taizo Matsueda, New Chemicals Development
Dept., Nippon Shokubai Co. Ltd., 1-2-2, Uchisaiwai-Cho, Chiyoda-ku, Tokyo 100,
Japan.
2 Oae, S.; Yagihara, T.; Okabe, T. Tetrahedron 1972, 28, 3203.
3 Feldermann, A.; Coote, M. L.; Davis, T. P.; Stenzel, M. H.; Barner-Kowollik, C. J.
Am. Chem. Soc., 2004, 126, 15915.
RAFT polymerization of EHMA
AIBN (1·10-3 mol L-1) and CDB (5·10-3 mol L-1) were dissolved in EHMA
and then separated into reaction vials, each containing about 2 mL of solution, and
sealed with rubber septa (Aldrich). The reaction mixture was subsequently
deoxygenated by purging with a pure nitrogen stream for 30 min. The deoxygenated,
sealed vials were then placed in a 60 °C water bath and removed at pre-selected
reaction times. The reactions were stopped by quenching in ice bath and the addition
of hydroquinone monomethyl ether. The polymeric material was recovered by
dissolving in chloroform and subsequent precipitation in n-hexane.
1
Intramolecular Transesterification of poly(EHMA)
Dry poly(EHMA) (1·10-3 mol L-1) was dissolved in deuterated DMSO with a
trace of p-toluene sulfonic acid as the catalyst. The reaction mixture was then
transferred into an open top reaction vessel and placed in a 150 °C oil bath with
stirring. Samples were taken at pre-selected times and transferred in a small sealed
vial and dried with molecular sieves – this is crucial as the presence of water in the
sample can appear in the NMR spectra, partially overlapping with the lactone signal.
Analytical Methods
Size Exclusion Chromatography
Molecular weight distributions were measured
via size exclusion chromatography (SEC) on a Shimadzu modular system, comprising
an auto injector, a Polymer Laboratories 5.0 m bead-size guard column (50 x 7.5
mm), followed by three linear PL columns (105, 104 and 103 Å) and a differential
refractive index detector. The eluent was tetrahydrofuran (THF) at 25 ºC with a flow
rate of 1 mL min-1. The system was initially calibrated using narrow polystyrene
standards ranging from 540 to 2·106 g mol-1. The resulting molecular weight
distributions have been recalibrated using the Mark-Houwink parameters for
poly(EHMA) (K = 16.66·10-5 dL g-1, a = 0.62). The Mark-Houwink parameters for
polystyrene read (K = 14.1·10-5 dLg-1 and a = 0.70).
Nuclear Magnetic Resonance Spectroscopy NMR spectra were recorded on Bruker
Avance 300 MHz instrument.
2
poly(EHMA)
PDI=1.5
poly(EHMA)-lactone
PDI=1.5
Transesterification
8h
20
25
30
35
40
retention time / min
Figure S1
45
20
25
30
35
40
45
retention time / min
Full molecular weight distribution before and after transesterification
as described in the Communication. The molecular weight distribution does clearly
not broaden (as would be expected when intermolecular transesterification was
operational), underpinning the notion that intramolecular lactonization is the main
reaction pathway.
3
1.5
60000
-3
1.0
-1
[CDB] = 5.5·10 mol L
-3
-1
[CDB] = 11·10 mol L
o
T = 60 C
-3
-1
[AIBN] = 1·10 mol L
-1
50000
Mn / g mol
PDI
2.0
40000
30000
20000
10000
0
0.0
0.1
0.2
0.3
conversion
Figure S2
Evolution of the number average molecular weight, Mn, vs monomer to
polymer conversion in the cumyl dithiobenzoate mediated EHMA polymerization at
60 °C for two initial CDB concentrations. The molecular weights given are absolute
molecular weights. The dashed lines are linear best fits.
4