Thermal behavior of co[poly(ethylene terephthalate)‐p‐oxybenzoate

Abstract

AbstractIn a previous investigation of a co[poly(ethylene terephthalate)‐p‐oxybenzoate] containing 30 mole % oxybenzoate units (referred to as T2/30), Krigbaum and Salaris identified the endotherm at tIII = 244°C as a nematic → isotropic transition. Subsequent investigation revealed that the tIII endotherm disappeared if the polymer is heated to the isotropic melt or dissolved and reprecipitated. The loss of the tIII transition might be due to molecular weight reduction, sequence randomization, or erroneous identification of the transition. Viscosity and high‐field NMR data eliminate the first two explanations. Annealing studies at temperatures higher than those of the earlier work demonstrate that the tIII transition, in fact, represents the melting of crystallites formed during a high‐temperature annealing operation. Moreover, we cannot determine the thermodynamic melting temperature of the copolymer from solid‐state annealing studies. Hence, the principal objective of the study of Krigbaum and Salaris, to compare the enthalpies and entropies of the nematic → isotropic and crystal → isotropic transitions, must be fulfilled in future work.