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

Abstract

Several series of liquid crystalline poly[aroyl‐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 13C 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.

Main-Chain Liquid Crystalline Elastomers: Monomer and Cross-Linker Molecular Control of the Thermotropic and Elastic Properties

“…The alignment of the mesogens forces the elongation of the chain, and because the polymer is a periodic structure containing the mesogen−siloxane sequence, the preferential orientation of the mesogens favors the existence of a positional order (microsegregation), thus generating a smectic phase at low temperatures. The results also show that the molecular symmetry of the mesogen influences the stability of the smectic mesophase against the nematic phase, as observed by Billibin …”

“…The results also show that the molecular symmetry of the mesogen influences the stability of the smectic mesophase against the nematic phase, as observed by Billibin. 49 Characterization of the Elastomers Prepared with the Various Monomers M0-M3. As mentioned above, the synthesis of the main chain LCEs was performed according to the onestep procedure.…”