Effect of Peak Exotherm Temperature on the Degree of Cure of Unsaturated Polyester Resins in Copolymerization with Styrene

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Abstract
In order to prepare full-cured resin by room temperature curing, the effect of the peak exotherm temperature on the degree of cure was investigated by using three types of unsaturated polyester resins including bisphenol-type, iso-type, and G-type resins. The degree of cure was examined by Barcol hardness, the conversion of styrene, and the conversion of fumarate double bond. In the resin cured with the methyl ethyl ketone peroxide (MEKP)/cobalt naphthenate (Co-naph)/dimethyl aniline (DMA) system or the MEKP/Co-naph system at 25°C, the degree of cure was influenced by the peak exotherm temperature, and there was an optimum region that ranged from 90 to 160°C. The resins cured at the lower peak exotherm temperature have decreased degrees of cure, but they could be cured completely by postcure at 100°C for 2 hr, because a sufficient amount of peroxide had remained unreacted in the resin after the room temperature cure. The degree of cure of the resin cured at the higher peak exotherm temperature decreases with an increase in the peak exotherm temperature, and the degree of the cure was not greatly increased by postcure because the amount of residual peroxide was limited.