RAFT iniferter polymerization in miniemulsion using visible light

Abstract

Methodology for the successful implementation of RAFT (4-cyano-4[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanoic acid (CDTPA)) iniferter polymerization of butyl methacrylate in miniemulsion using visible light (green light; λ_max = 530 nm) has been developed. Under suitable conditions, the polymerization proceeds to high conversion with good control/livingness, generating polymeric nanoparticles in the approximate diameter range of 100–200 nm. The surfactant loading is a crucial parameter – if the concentration of free SDS in the aqueous phase is too high, secondary nucleation occurs, leading to ill-defined molecular weight distributions and low polymerization rates. It is proposed that this originates in the phenomenon known as “frustrated entry”, whereby photoinitiation involving the original RAFT agent leads to exit of the thus generated hydrophilic radical, which in turn may lead to secondary nucleation. It is demonstrated that RAFT agents as visible light iniferters provide a useful synthetic route to polymer nanoparticles under benign solvent free conditions.