Tandem RAFT-ATRP synthesis of polystyrene - Poly(methyl methacrylate) bottlebrush block copolymers and their self-assembly into cylindrical nanostructures

A polystyrene - poly(methyl methacrylate) (PSPMMA) bottlebrush block copolymer with asymmetric branches was synthesized by grafting from a symmetrical backbone containing a novel dual vinyl initiation system and characterized by atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS). The block copolymer backbone was prepared by sequential reversible addition-fragmentation chain transfer (RAFT) copolymerization of solketal methacrylate (SM) and 2-(bromoisobutyryl)ethyl methacrylate (BIEM). From the poly- (BIEM) segment, PMMA branches of 26 units were grafted by atom transfer radical polymerization (ATRP). Solketal groups were then subjected to hydrolysis and functionalized with a RAFT agent. Subsequently, from RAFT sites of the poly(SM) segment, polystyrene branches of 45 units were grafted to yield the final bottlebrush block copolymer. The resulting polymer was found to have a vertically oriented cylindrical morphology by AFM with an average cylinder diameter of 45 nm; morphology was also confirmed by SAXS analysis.