Domain swelling in ARB-type triblock copolymers via self-adjusting effective dispersity

We investigated the domain spacing of an ordered structure formed by polydisperse ARB-type triblock copolymers (triBCPs) with random middle R blocks consisting of A and B monomers. ARB-type triBCPs were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization, and the dispersities of all samples were controlled as narrow as ∼1.2. From the bulk and film morphologies, it was found that the domain swelling increases as the content of middle R blocks increases, which implies that the middle R block even with a small content plays a critical role in dilating the domain spacing. Since the random middle R blocks are energetically neutral, they can be segregated into either A or B blocks. The strong stretching theory (SST) suggests that the dispersities of the resulting constituent blocks are maximized to reduce the elastic energy associated with chain stretching, thereby leading to the dilation of domain spacing.