Phase transformation and self-assembly behavior of supramolecular rod-comb block copolymers

We investigated the self-assembly behavior of a series of supramolecular rod-comb block copolymer complexes made by the hybridization of rod-coil diblock copolymers of poly (2,5-di(2-ethylhexyloxy)-1,4-phenylene vinylene)-b-poly(2- vinyl pyridine) (PPV-b-P2VP_f) with different volume fractions, f, of the P2VP coils and an anionic surfactant, dodecyl benzenesulfonic acid (DBSA), that selectively interacts with the P2VP to form the side-chain comb teeth. The resulting hybrids show hierarchically ordered structures at multiple length scales, forming so-called structure-in-structure morphology. Notably, for PPV-b-P2VP_0.56(DBSA)_x, the larger-scale structure changes from a lamellar phase, to a broken lamella, and eventually to a hexagonally packed strip phase with increasing DBSA molar ratio (x) to P2VP monomer unit. Furthermore, simultaneous SAXS and WAXS measurements showed that the order-disorder transition temperatures of larger-scale structures in the PPV-P2VP_0.56(DBSA) rod-comb systems were higher than those associated with the pristine PPV-P2VP_0.56 polymers. The large-scale structure of PPV-P2VP_0.56(DBSA) exists at temperatures around 210 °C even though the rod-rod interaction between PPV blocks disappear at ∼120°C, signifying that the formation of the P2VP(DBSA) lamellar mesophase plays a critical role in forming the large-scale hexagonally packed strip structures.