THERMOTROPIC HYDROCARBON MAIN-CHAIN LIQUID-CRYSTALLINE POLYMERS BASED ON A BIPHENYL MESOGEN - SYNTHESIS AND CHARACTERIZATION

A new homologous series of hydrocarbon oligomers having biphenyl mesogenic units and polymethylene spacers in the main chain were prepared by a carbon-carbon coupling reaction. Polymers with number-average molecular weights in the range of 4000-6000 have been obtained. Homopolymers with spacer units varying from 6 to 10 methylene units and equimolar copolymers with 6/8, 6/10, and 8/10 methylene spacers were found to exhibit smectic mesophases. The effect of the variation of the lengths of the methylene spacers on liquid crystalline properties is discussed. In general, increasing the length of the methylene spacers is accompanied by a decrease in the isotropization temperature. An alternating odd-even effect in transition temperatures is also observed, with the even members having higher isotropization temperatures than the odd members. Two different X-ray diffraction patterns for odd- and even-membered homopolymers were observed for unoriented samples.