MESOGEN CONFORMATION CHANGES IN THERMOTROPIC POLYESTERS AT PHASE-TRANSITIONS

Mesogen conformations in thermotropic polyesters with alternating meso gens and poly(methylene) spacers were investigated by IR spectroscopy with polarized and unpolarized light. The selective deuteration of ter ephthaloyl-bis(p-oxybenzoate) mesogens gave a possibiity of assigning part of the IR bands to terephthalic or to oxybenzoic fragments. It is shown that in the liquid crystalline melt the mesogen conformation is planar, but in the semicrystalline state it is mainly nonplanar. Diff erences in mesogen conformations of polymers containing an even or an odd number of methylene units in the spacer are detected. Thus, LC ord ering seems to affect not only the conformation of the spacer but also the conformation of the mesogen.