The effect of chain architecture on the phase behavior of A₄B₄ miktoarm block copolymers

In this work, we systematically synthesized well-defined miktoarm (polystyrene)₄-(polylactic acid)₄ ((PS)₄-(PLA)₄) block copolymers (BCPs) having 4 pairs of PS and PLA arms. 4-Arm epoxy core material was used as an end capping agent for linear PS synthesized via anionic polymerization, and the PLA blocks were grown from the hydroxyl groups created from the epoxy groups. As control samples, the linear PS-b-PLA BCPs were also prepared and the molecular weights of PS and PLA blocks were exactly matched to those of PS and PLA arms, in order to compare the phase segregation behaviors between the linear and miktoarm architectures. From the measurement of the order-disorder transition temperature, it was observed that miktoarm stars significantly enhance the phase segregation compared to linear counterparts without increased domain spacing, due to the junction constraints of the miktoarm architecture that lead to the reduction in translational entropy.