CONFORMATIONAL BEHAVIOR OF THE SPACER IN A LIQUID-CRYSTALLINE MAIN-CHAIN POLYMER IN ITS NEMATIC AND GLASSY STATES

NMR investigations of a liquid crystalline main-chain polyether are presented. This glass-forming polymer consists of the aromatic mesogen 1-(4-hydroxy-4'-biphenylyl)-2-(4-hydroxyphenyl)butane (TPB) linked through a perdeuterated decylene spacer. At higher temperatures in the nematic mesophase the conformational behavior of the alkyl group is consistent with the alternate trans model, predicted by calculations of Yoon. At lower temperatures in the glassy state the hydrocarbon chain is found to be an extended chain containing an increased amount of trans conformers. This change in the conformational statistics is accompanied by reduced conformational mobility in the glassy state. Evidence for two glass transitions is presented, one being associated with the freezing of the mesogens and the other, at the lower temperature, being due to freezing of the spacer mobility.