Thermodynamic functions of thermotropic polyethers based on the semiflexible mesogen 1‐(4‐hydroxyphenyl)‐2‐(2‐methyl‐4‐hydroxyphenyl)ethane

Abstract

AbstractHeat capacities of a series of thermotropic polyethers consisting of a semiflexible mesogen [1‐(4‐hydroxyphenyl) ‐ 2 ‐ (2 ‐ methyl ‐ 4 ‐ hydroxyphenyl)ethane], with n methylene flexible spacers (n = 4–12) (MBPE‐n) have been measured by DSC and fitted at low temperature to an approximate frequency spectrum, as well as at high temperature to a general equation for the liquid MBPE‐n. The latter equation is: Cp = n(17.33 + 0.04551T) + (280.9 + 0.3839T) where n is the number of methylenes in the polyether spacer. The calculated vibration‐only heat capacities start to show deviations from the measured heat capacities below the melting temperature, reflecting contributions from conformational disorder and motion in methylene spacers. It is suggested that part of this increase in heat capacity can be looked upon as a glass transition of the partially conformationally disordered crystals. Solid state 13C–NMR studies showed similarly that over the range of temperature some of the CC bonds in the spacer are in a rotational state similar to that in the melt. The equilibrium heats of fusion (ΔH) and the changes of heat capacity (ΔCp) for the amorphous polymer at the glass transition temperature, Tg, were determined by WAXD and DSC. Based on the discrepancy of ΔCp it is concluded that these phenylene containing polyethers have a certain amount of rigid amorphous polymer. Thermodynamic functions H, S and G for all of the polyethers have been established.