Correlation of the thermal properties of main-chain liquid crystalline polymers with the symmetry and anisometry of their mesogens

摘要

Full Paper: Several series of liquid crystalline polyaroyl-bis(oxyarylates) with oligomethylene (n = 6 and 10) and oligooxyethylene (n = 2; 3: 4 and 6) spacers were synthesized. The structure of their mesogenic groups was varied by replacement of central or terminal units by those with reduced symmetry. The polymers were investigated by methods, such as differential scanning calorimetry, polarizing optical microscopy and in some selected cases by X-ray diffraction methods using synchrotron radiation. An absence of transesterification during measurements at elevated temperatures was proved by C-13 NMR spectroscopy. The formation of smectic melts was demonstrated for all the polymers with high symmetry of the mesogenic group. A lower symmetry leads to a decrease of crystallinity of the polymers and to the appearance of a nematic phase in their melts. Comparative analyses of their thermal properties were made in order to determine the contribution of each single unit of the mesogenic groups on the thermal properties of the polymers. References: 25