Hydrogen-bonding-mediated formation of supramolecular rod-coil copolymers exhibiting hexagonal columnar and bicontinuous cubic liquid crystalline assemblies

The preparation and characterization of the supramolecular rod-coil copolymers directed by molecular recognition of 4,4'-bipyridine and 4-[poly(propyleneoxy)propyloxy]-4'-bis(biphenyl carboxylic acid) with degrees of polymerization (DP) of poly(propylene oxide) coil of eight (P-8-HP), 10 (P-10-HP), 15 (P-15-HP), 17 (P-17-HP), 21 (P-21-HP), 27 (P-27-HP) and 34 (P-34-HP) are described. The introduction of poly(propylene oxide) (PPO) coils with different lengths into the rodlike polymeric system induces a rich variety of self-assembled microstructures. In the crystalline phase, the supramolecular rod-coil copolymers with DP of PPO 8-17 organize into a microphase-separated monolayer lamellar structure. In contrast, the supramolecular rod-coil copolymers with DP of PPO 21-34 exhibit a hexagonal columnar crystalline phase. A dramatic phase change after crystalline melting of the polymers is observed with the variation of the coil length. The supramolecular rod-coil copolymers P-8-HP and P-10-HP display a bicontinuous cubic mesophase with Ia3d symmetry, while the supramolecular rod-coil copolymers P-15-HP, P-17-HP, and P-21-HP with a medium length of PPO coil exhibit a hexagonal columnar mesophase. Further increasing the length of coil, as in the case of P-27-HP and P-34-HP, suppresses liquid crystallinity and induces only crystalline polymers.