Direct evidence for transesterification and randomization in a mixture of homopolyesters of poly(Hba) and poly(hna) above 450 °c

Preparation of blends of the homopolymers of 4-hydroxybenzoic acid (HBA) and 6-hydroxy- 2-naphthoic acid (HNA) has been investigated via compression molding at temperatures up to 460 °C and pressures up to 8 kpsi. It has been found that 1:1 mixtures of finely divided powders of the homopolymers when compression molded under these conditions can transesterify rapidly to form a 1:1 random copolyester. When mixtures of lowMn homopolymers (3-5K) were molded, the conversion to the 1:1 random copoly- ester was nearly complete. However, for mixtures of high Mn homopolymer (>30K) only partial conversion to the random copolyester was observed in the brief time available for processing before degradation reactions ensue. Presumably, the limited conversion is due to the higher viscosity of the melt or the much lower concentration of end groups which act to limit transesterification. © 1990, American Chemical Society. All rights reserved.