Macromolecular thiolysis of oxiranes: end-group modification of RAFT prepared homopolymers

Abstract

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.