An ESR Study of the Curing Reaction of Unsaturated Polyester with Vinyl Monomers and the Thermal Behavior of the Cured Polymers

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Abstract
The curing reaction of an unsaturated polyester (BAPM), prepared by polycondensation of Bisphenol A-di-(2-hydroxypropyl)ether and maleic anhydride, with vinyl monomers was investigated by IR and ESR. Thermal properties of the resulting polymer were studied by DSC and TMA. For the curing reaction of BAPM with styrene initiated with the cobalt naphthalate/1-hydroxycyclohexyl hydroperoxide system, the copolymerization process could be satisfactorily analyzed by the Mayo-Lewis integral equation for the usual homogeneous copolymerization. The reaction mixtures contained long-lived polymer radicals, the ESR spectra of which gave important information on the curing reaction. The DSC and TMA results showed that a microphase separation occurred in the cured polymer from BAPM and styrene. The phase separation was accelerated by treatment at -3°C. However, heat treatment above 150°C eliminated the phase separation. These phenomena were also confirmed by TEM examination.