Rationally Leveraging Polymer Chain-Length Heterogeneity for Robust Structural Engineering

The inherent uncertainty of chain length in synthetic polymers casts doubt on the explicit understanding of fundamental principles. This study quantitatively assesses the critical role of chain-length distribution in the self-assembly process, aiming to identify the point at which discernible discrepancies begin to emerge. By blending discrete diblock copolymers of varying sizes, chain-length nonuniformity can be pre-cisely regulated while the average composition remains constant. Introducing a minor heterogeneity leads to an expansion of lattice dimension, while a phase transition occurs as the difference exceeds a threshold. Interestingly, a transition from the Frank- Kasper sigma phase to the body-centered cubic phase was triggered by enlarging the size difference of the corona block, while introducing heterogeneity in the core block stabilized the hexagonally close-packed spheres. A self-consistent field theory calculation reveals that the synergy between the long and short chains effectively releases packing frustration, leading to substantial changes in the free-energy landscape and stabilizing unconventional phases otherwise inaccessible. This work calls particular at-tention to the importance of chain-length heteroge-neity and provides a robust approach to finely tuning the phase behavior and physical properties of block copolymers without altering their chemical composition.