Sequence Effects on Block Copolymer Self-Assembly through Tuning Chain Conformation and Segregation Strength Utilizing Sequence-Defined Polypeptoids

Polymers with precise sequence control offer the possibility of tuning segregation strength with comonomer sequence instead of chemical identity. We have synthesized polystyrene-b-polypeptoid block copolymers with different sequences of comonomers in the polypeptoid block, where nonpolar phenyl side chains are incorporated to tune compatibility with polystyrene. Using small-angle X-ray scattering, we see that these materials self-assemble into lamellae with domain spacings and order–disorder transition (ODT) temperatures varying with sequence, despite identical composition. The variation in the ODT suggests that sequence control at the monomer level alters segregation strength, and by comparing domain spacings and SCFT simulations, we find that the main driving force is likely chain conformational effects that localize comonomers at the block–block interface. However, trends seen in the ODT are not captured by SCFT simulations or effective χ parameters (measured in the disordered phase by approximating the copolypeptoid as a uniform block). The disagreement between measured thermodynamic properties and coarse-grained approaches like SCFT and effective χ points to the importance of molecular-scale effects in sequence-defined materials.