Macromolecular thiolysis of oxiranes: End-group modification of RAFT prepared homopolymers
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Chain end modification of low molecular weight, RAFT-prepared polystyrene and poly(N,N-diethylacrylamide) by reaction with a range of small molecule epoxides is described. Two different routes are examined—initial dithioester end-group cleavage yielding the thiol-terminated polymer followed by catalytic thiolysis of the oxiranes and a one-pot procedure involving hydride cleavage of the dithioester end groups in the presence of an epoxide. High degrees of functionalization (>80%) are observed via the first route in the presence of ZnCl2 with molecular weight distributions remaining unimodal and narrow. However, with DBU as catalyst significant amounts of coupled species are observed. In contrast, the one-pot route, at least with poly(N,N-diethylacrylamide), resulted in essentially quantitative degrees of functionalization as evidenced by 1H NMR spectroscopy and qualitatively by FTIR spectroscopy. The effect of the newly introduced alcohol-functional end groups on the lower critical solution temperature of poly(N,N-diethylacrylamide) is demonstrated with cloud points tunable from ca. 27 to 47 °C.
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