Role of Polymer Chain Helicity in Block Copolymer Self-Assembly

While coil–coil and rod–coil block copolymer self-assembly are well understood, the details of how chain conformational asymmetry affects the thermodynamics of self-assembly are still unclear. Here, we use polypeptoid-containing block copolymers to achieve direct control of chain conformation. By incorporating homochiral, bulky side chains, a helical conformation is induced in the polypeptoid block, while a racemic mixture of the same side chains generates an unstructured polypeptoid chain. Block copolymers with a helical polypeptoid chain have increased domain spacings relative to the unstructured counterpart, due to chain stretching penalty and packing frustration. Thermodynamically, the chain conformation is expected to affect the Flory–Huggins parameter χ through an effective coordination number. The interaction parameter between the two chemically distinct blocks, poly(methacrylate) and polypeptoid (helical or unstructured), can be extracted from interfacial segregation of the block copolymers to a homopolymer interface using secondary ion mass spectrometry (SIMS). This polypeptoid-containing system will offer new insights into the effects of chain helicity on the thermodynamic interactions and self-assembled structures of block copolymers.