Effect of composition and polyesterification catalysts on the optical properties of cured polyesters

Unsaturated polyesters based on ethylene glycol have been synthesized using a variety of anhydride, saturated and unsaturated dicarboxylic acids and various catalysts. The structure of the polyesters and the effect of the different compositions on the colour of cured polyesters are studied by FTIR, DSC and colorimetry. The structure of cured polyesters greatly depends on the isomerization of maleic acid to fumaric acid during polyesterification. The colour of unsaturated polyesters cured with the most common curing system (MEKP as initiator and CoNp as accelerator) is firstly influenced by the curing accelerator CoNp via the d–d transitions of the transition metal cobalt. Secondly, the composition of the dicarboxylic acids and anhydride used in the polyesterification influences the colour of the polyesters which depends especially on the isomerization of maleic acid. The cured maleate polyesters have more unreacted double bonds and more polar structure because of the presence of carbonyl groups, compared to the corresponding fumarate polyesters, and this structure affects the colour. The residual catalysts from the polyesterification have minor influence on the colour of cured polyesters. Copyright © 2002 Society of Chemical Industry