A novel thermotropic behavior of a mesogen-jacketed liquid crystal polymer

A mesogen-jacketed liquid crystal polymer, poly {2,5-bis[(4'-hexyloxyphenyl) oxycarbonyl]styrene} (PHPCS) with number-averaged molecular weight of 1.28 x 10(5) and polydispersity of 1.48 was prepared via 2, 2, 6,6-tetramethyl-piperidinyloxy mediated free radical polymerization. The thermotropic behavior was studied by a combination of differential scanning calorimetry, thermogravimetry, polarized optical microscope and wide-angle X-ray diffraction. PHPCS was not crystalline over the entire temperature region studied. On heating, PHPCS first became an isotropic melt at glass transition temperature (T-g) and then a mesophase at temperatures much higher than T-g. On subsequent cooling, the formed ordered phase disappeared above T-g Contrary to theoretical predictions and previous experimental observations, the transition from isotropic melt to liquid crystalline phase was an endothermic process and the order-disorder transition took place with concurrence of heat release.