Modulating Regioregularity of Poly(3-hexylthiophene)-based Amphiphilic Block Copolymers To Control Solution Assembly from Nanowires to Micelles

In selective solvents, poly(3-hexylthiophene) (P3HT)-based block copolymers (BCPs) assemble into one-dimensional nanowires (NWs) due to strong π–π stacking interactions of the P3HT block. Herein, we report the effect of P3HT regioregularity (RR) on the assembly of P3HT-based amphiphilic BCPs in solution. We synthesized a series of P3HT-block-poly(2-vinylpyridine) (P3HT-b-P2VP) copolymers with similar molecular weights and P3HT volume fractions but with different RRs, ranging from 55% to 95%, and studied their assembly in tetrahydrofuran/n-butanol mixtures. P3HT-b-P2VP copolymers with high RR (>80%) crystallized into well-ordered NWs with core widths consistent with fully extended P3HT chains. In BCP nanostructures with decreasing RR, more flexible P3HT chains produced gradual increases in the width of the NWs, from 12 to 24 nm. Eventually, a morphological transition to spherical micelle structures was observed at 55% RR. The structural differences were visualized by incorporating Au nanoparticles, which locate at the interface of P3HT and P2VP blocks, onto the NWs and imaging the resulting hybrid nanostructures by transmission electron microscopy. In addition, the crystalline behaviors of the assembled nanostructures were determined using differential scanning calorimetry and grazing incidence X-ray scattering. We elucidated important relationships between the solution assembly behaviors and the crystalline interactions of conjugated semicrystalline–coil BCPs, which will guide design of future versatile BCP nanostructures.