MESOPHASE BEHAVIOR IN THERMOTROPIC POLYETHERS BASED ON THE SEMIFLEXIBLE MESOGEN 1-(4-HYDROXYPHENYL)-2-(2-METHYL-4-HYDROXYPHENYL)ETHANE

A series of thermotropic polyethers consisting of a semiflexible mesogen [1-(4-hydroxyphenyl)-2(2-methyl-4-hydroxyphenyl)ethane] with methylene flexible spacers (n = 4-12) (MBPE-n) has been characterized through thermal analysis, wide-angle X-ray diffraction, small-angle X-ray scattering, polarized light microscopy, and solid-state nuclear magnetic resonance. A mesophase is observed for MBPE-n = odd polyethers on cooling from the isotropic melt and found to be monotropic. Crystallization will follow either on further cooling or on isothermal annealing. MBPE-n = even polyethers exhibit rapid crystallization during cooling, with little cooling-rate dependence. Contributions to the enthalpy and the entropy of mesophase transition from both the semiflexible mesogen and methylene units can be determined. The polymers with n = odd show that the flexible spacers mainly contribute to the thermal transition properties. One can thus conclude that the mesophase in these polyethers results from the coupled action of the methylene units with the semiflexible mesogen. The primary contribution to the order in the mesophase, however, is due to the methylenes.