Synthesis of ABB′ and ABC star copolymers via a combination of NMRP and ROP reactions

Abstract

We report here a facile method to prepare ABB′ and ABC type miktoarm star copolymers by a combination of nitroxide-mediated radical polymerization (NMRP) and ring opening polymerization (ROP). The first two arms were prepared by sequential NMRP of the same or different monomers, e.g. styrene and tert-butyl methacrylate (tBMA). The hydroxyl group was introduced between the two blocks by one-step radical addition to N-(2-hydroxyethyl)maleimide. The attached in-chain hydroxyl group was used to initiate the ring opening polymerization of L-lactide in the presence of DBU, forming the third block of poly(L-lactide). Thermal properties, microphase separation and solution self-assembly of the miktoarm star copolymers were investigated using TGA, DSC and TEM. It was found that the star copolymer underwent microphase separation to form two phases with a lamellar structure in the bulk state. In addition, hollow spheres were formed from ABC copolymer solution when a mixed solvent was used.