Photoinitiated RAFT polymerization of vinyl acetate

Abstract

A photoinitiation process was investigated to develop a rapid and well-controlled RAFT polymerization method applied to vinyl acetate (VAc) using methyl (ethoxycarbonothioyl)sulfanyl acetate (MESA) and bis(2,4,6-trimethylbenzoyl)phenylphosphine oxide as the RAFT agent and photoinitiator, respectively. MESA was selected as the photochemically inert RAFT agent to minimize photolysis of the thiocarbonylthio groups during polymerization. Poly(vinyl acetate) with a prespecified well-controlled molecular weight (MW) and a narrow MW distribution was successfully synthesized. The polymerization reaction proceeded as a living polymerization and was remarkably rapid compared with approaches that use thermally initiated processes with a very short induction period. A detailed kinetic study of the mechanism underlying the polymerization reaction, however, revealed that the chain ends containing xanthate moieties were not perfectly stable upon UV-irradiation, and they generated radicals via homolytic cleavage. This reaction appeared to proceed by a combination of a degenerative transfer RAFT mechanism and a dissociation-combination mechanism. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012