Effect of Molecular\nSymmetry on the Self-Assembly\nBehavior of AB<sub>2</sub> Linear–Branched Block Copolymers

The\narchitecture of a block copolymer plays a pivotal role in tailoring\nits self-assembly behavior. In this work, discrete AB<sub>2</sub> linear–branched\nblock copolymer isomers with identical chemical structures but varying\nmolecular symmetry were prepared and studied. Comparing to AB linear\ndiblock copolymers, linear–branched AB<sub>2</sub> counterparts\nexhibit significantly different assembly behaviors, which can be further\nregulated by adjusting the relative chain length of two B branches.\nA minor difference in the chain lengths of the B blocks results in\nan expansion in domain sizes and enhanced phase stability, while a\nlarger asymmetry triggers phase transitions from a cylindrical structure\nto various spherical phases. The synergistic effects of the long and\nshort B blocks effectively alleviate packing frustration, leading\nto a nonmonotonic deflection of the spherical/cylindrical phase boundary.\nThe unique phase behaviors were substantiated by a self-consistent\nfield theory study. This work demonstrates the feasibility and robustness\nof tailoring assembly behaviors by rational manipulation of chain\narchitecture, providing insights into the underlying mechanism that\nstabilizes unconventional spherical phases.