Double-twisted helical lamellar crystals in a synthetic main-chain chiral polyester similar to biological polymers

A twisted helical lamellar crystal in one of the first of few chiral main-chain liquid crystalline polyesters was studied. The polymer, PET(R*)-9, was synthesized from (R)-(-)-4′-{ω-[2-(p-hydroxy-o-nitrophenyloxy)-1- propyloxy]-1-nonyloxy}-4-biphenyl carboxylic acid. PET(R*)-9 double-twisted lamellae were crystallized from the melt rather than in solution, indicating that the structure was an intrinsic character of the chiral polymer and not a result of solvent interaction. The helical crystals had a regular orthorhombic unit cell structure, identical to that of the flat lamellar crystals. The molecular chain folding was along the b-axis in both flat and helical lamellar crystals, indicating that the chain folding was toward the less ordered state.