Liquid crystal comb polymer with polar mesogenic and aliphatic side groups - I. Preparation and structural properties

A liquid crystal comb polymer of potential interest for electro-optical applications has been synthesized and characterized. The polymer has a polyacrylamide main chain and two different types of side group, built up of 4'-undecanoyloxy-4-cyanobiphenyl groups (68 mol%) and of shorter aliphatic groups (32 mol%). The two types of side group occur randomly along the polymer's main chain. The preparation steps and the liquid crystalline structure of the resulting copolymer are compared with those of a homopolymer whose side groups ( built up of 4'-undecanoyloxy-4-cyanobiphenyl groups) are all identical. X-ray diffraction shows that the polymers display different mesophases over different temperature ranges. However, the homopolymer exhibits two smectic phases (SmC(2) and SmA(2)), while the new copolymer exhibits a SmC(2) phase and a nematic mesophase at higher temperature. The mesophase thermal stability of the copolymer is significantly lower than that of the homopolymer.