Influence of Residual Polyesterification Catalysts on the Curing of Polyesters

Abstract

Unsaturated polyesters are synthesized by means of polyesterification, often with catalysts like strong acids, metal oxides and metal-organic salts. Most often, the catalysts used cannot be separated from the bulk of the polyester. Also, some organic or inorganic additives – called fillers – which are used with the polyester in order to decrease cost, affect the curing of the polyester. In this work the effect of residual catalyst on the curing of unsaturated polyester is studied. Unsaturated polyesters were prepared using propylene glycol with a 10% molar excess over stoichiometry and a mixture of dicarboxylic acids, namely maleic acid (unsaturated) adipic acid (saturated) and phthalic anhydride (saturated) at a molar ratio 1:2:2. Lead dioxide, p-toluenesulfonic acid and zinc acetate were used as catalysts, at 0.1% w/w. After the polyesterification, the polymers were diluted with styrene at a proportion of 100:30 w/w. The resins were cured by using MEKP (methylethylketone peroxide) as initiator and CoNp (cobalt naphthenate) as accelerator. Catalysts affect the final color of the polyester. The kinetics of curing of the resins was studied by DSC analysis based on the exothermic peak due to the double bonds breaking to give crosslinked macromolecules. The heat released ΔH is decreased by the presence of catalyst, while activation energy, the frequency factor and the order of reaction are increased.