Coil-helix Block Copolymers Can Exhibit Divergent Thermodynamics

Recent advances in polymer synthesis have led to the development of chiral block copolymers, which are capable of exhibiting several interesting phenomena arising from self-assembly. Several thermodynamic factors play a role in the self-assembly such as the entropy, enthalpy, and fluctuation effects arising from the helical conformation. In particular, thermodynamic properties such as order-disorder transition temperature appear to depend on the particular chemistry of the chiral block. In this work, we utilized a particle-based simulation model to evaluate distinct thermodynamic metrics and to compute the conformational statistics of chiral molecules. Five distinct parameters produce a wide range of helical conformations of varying pitch, resulting in two distinct thermodynamic behaviors. Specifically, we aimed to understand (1) the relationship between the helical conformation and entropy, and (2) the effect of the conformation on the Flory–Huggins interaction parameter, χ, when chemical disparity was introduced. Commonly used conformational metrics for flexible or stiff block copolymers do not capture the effective block repulsion because helical blocks are semiflexible and aspherical. Instead, pitch can quantitatively capture the effective block repulsion. Quite remarkably, the shift in χ for chemically dissimilar block copolymers can switch sign with small changes in the pitch of the helix.