Crystallization Modes of Poly(3-dodecylthiophene)-based Block Copolymers Depend on Regioregularity

Conjugated block copolymers (BCPs) can self-assemble into highly ordered nanostructures in a melt state. However, when cooled below the melting temperature, crystal growth can disrupt the self-assembled structure and produce a poorly-ordered fibrillary texture. Here, we demonstrate that crystallization modes of poly(3-dodecylthiophene) (P3DDT)-based BCPs can be tuned through regioregularity (RR) and morphology. When cylindrical BCP structure is formed, crystal growth tends to break through the morphology even with low RR, showing both “break-out” and “template” crystallization modes. In contrast, when lamellar structure is formed, crystal growth remains confined by the second block domain with high RR. This morphology-dependent behavior is attributed to geometric compatibility of P3DDT crystal growth and the self-assembled symmetry: In a lamellar phase, the P3DDT chain orientations at the block interface are compatible with crystal growth, and both the alkyl-stacking and π-π growth directions are unrestricted within a lamellar sheet. In a cylindrical phase, the radial orientation of P3DDT chains at the block interface is not compatible with crystal growth, and the hexagonal close-packed symmetry only allows for one direction of unrestricted crystal growth.