Effect of Molecular Symmetry on the Self-Assembly Behavior of AB₂ Linear–Branched Block Copolymers

The architecture of a block copolymer plays a pivotal role in tailoring its self-assembly behavior. In this work, discrete AB2 linear–branched block copolymer isomers with identical chemical structures but varying molecular symmetry were prepared and studied. Comparing to AB linear diblock copolymers, linear–branched AB2 counterparts exhibit significantly different assembly behaviors, which can be further regulated by adjusting the relative chain length of two B branches. A minor difference in the chain lengths of the B blocks results in an expansion in domain sizes and enhanced phase stability, while a larger asymmetry triggers phase transitions from a cylindrical structure to various spherical phases. The synergistic effects of the long and short B blocks effectively alleviate packing frustration, leading to a nonmonotonic deflection of the spherical/cylindrical phase boundary. The unique phase behaviors were substantiated by a self-consistent field theory study. This work demonstrates the feasibility and robustness of tailoring assembly behaviors by rational manipulation of chain architecture, providing insights into the underlying mechanism that stabilizes unconventional spherical phases.