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 pr esented. This glass-forming polymer consists of the aromatic mesogen 4 -hydroxy-4'-biphenylyl)-2-(4-hydroxyphenyl)butane (TPB) linked through a perdeuterated decylene spacer. At higher temperatures in the nemati c mesophase the conformational behavior of the alkyl group is consiste nt with the alternate trans model, predicted by calculations of Yoon. At lower temperatures in the glassy state the hydrocarbon chain is fou nd to be an extended chain containing an increased amount of trans con formers. This change in the conformational statistics is accompanied b y reduced conformational mobility in the glassy state. Evidence for tw o glass transitions is presented, one being associated with the freezi ng of the mesogens and the other, at the lower temperature, being due to freezing of the spacer mobility.