The effects of molecular weight dispersity on block copolymer self-assembly

Abstract

The influence of dispersity in the molecular weight distributions in the core forming block for block copolymer (BCP) self-assembly is analyzed via an automated flow synthesis approach. Polystyrenes with increasing dispersity in the core forming block are synthesized from reversible addition-fragmentation chain transfer (RAFT) polymerization with an average degree of polymerization (DPn) of 15 and 50 and dispersities between 1.10 and 1.45. After chain extension of these polymers with hydroxy ethyl acrylate, the residual BCPs were subjected to nanoaggregate formation via continuous flow mixing. Nanoaggregates were carefully analyzed with an ensemble of dynamic light scattering (DLS), scanning transmission electron microscopy (STEM) and small angle neutron scattering (SANS). With an increase in the dispersity of the core forming polymer block, the overall dispersity of the nanoparticles was reduced, demonstrating that lower polymer dispersities are not necessarily more advantageous to form uniform nanostructures. This unravels the fundamental role of molecular weight distribution shape in polymer self-assembly and introduces a new tool for tuning particle properties, specifically via continuous flow processes.