INFLUENCE OF BACKBONE RIGIDITY ON THE THERMOTROPIC BEHAVIOR OF SIDE-CHAIN LIQUID-CRYSTALLINE POLYMERS SYNTHESIZED BY RING-OPENING METATHESIS POLYMERIZATION

The effect of backbone flexibility on the mesomorphic behavior of side -chain liquid crystalline polymers synthesized by ring-opening metathe sis polymerization was investigated. The synthesis of norbornene and c yclobutene monomers containing a p-nitrostilbene moiety as the mesogen ic group and polymerization of these monomers to produce side-chain li quid crystalline polymers with low polydispersities and defined molecu lar weights was accomplished. The relatively rigid poly(norbornene)s d isplayed enantiotropic nematic mesomorphism with glass transitions fro m 44 to 64 degrees C and isotropization temperatures between 108 and 1 21 degrees C, whereas the more flexible poly(butadiene)s showed enanti otropic smectic A mesomorphism with glass transition temperatures from 14 to 31 degrees C and isotropization temperatures between 74 and 111 degrees C. A diblock copolymer containing a 1:1 mixture of the poly(n orbornene) and poly(butadiene) also exhibited a smectic A mesophase, c learly demonstrating the dominance of the poly(butadiene) backbone. Th e dependence of the degree of polymerization and flexible spacer lengt h on the phase transitions of these systems was determined, demonstrat ing stabilization of the mesophase by both increasing molecular weight and flexible spacer length.