Polymerization of liquid-crystalline monomers having a Schiff-base structure

Vinyl monomers having a Schiff-base structure were synthesized and their thermal and photopolymerization behavior was explored for different phases of the monomers. It was found that conversion of the monomers increased with temperature in the nematic phase, while it decreased in the isotropic phase. This result suggests that the polymerization behavior may be affected by the molecular alignment. Arrhenius plots for the initial rates of photopolymerization showed a straight line, while those of thermal polymerization changed in slope at the nematic-isotropic phase transition temperature. For MBEA, the number-average molecular weight of the polymer produced by thermal polymerization in the nematic phase was higher than that in the isotropic phase. For ABBA, it was observed that birefringence partially remained in the polymer produced in the nematic phase, although polymer produced by solution polymerization showed no liquid-crystalline phase. In addition, the orientation of the crosslinked polymer obtained by photopolymerization was better than that of the polymer produced by thermal polymerization. (C) 1999 Elsevier Science Ltd. All rights reserved.