Control of gel time and exotherm behaviour during cure of unsaturated polyester resins

The curing behaviour of an unsaturated polyester resin has been studied by gel time and pseudo-adiabatic exotherm measurements. The gel time corresponded closely with the initial rise in exotherm temperature. Incorporation of tert-butyl catechol inhibitor increased the gel time in a linear fashion and the exotherm was similarly delayed. An increase in the concentrations of initiator (either methyl ethyl ketone peroxide or acetyl acetone peroxide) or cobalt octoate accelerator decreased the gel time in a reciprocal fashion and increased the rate of polymerization. These results are fitted to a theoretical model for inhibition and initiation.