Curing reaction of unsaturated (epoxy) polyesters based on different aliphatic glycols

Abstract

The cure behavior of the unsaturated (epoxy) polyesters based on different aliphatic glycols with styrene initiated by various types of organic peroxides or the mixture of an acid anhydride/organic peroxide has been studied by means of differential scanning calorimetry. unsaturated polyesters (UP) prepared from cyclohex-4-ene-1,2-dicarboxylic anhydride, maleic anhydride, and suitable aliphatic glycol: ethylene glycol or 1,4-butanediol or 1,6-hexanediol and unsaturated epoxy polyesters (UEP) obtained by chemical modification of UP were dissolved in vinyl monomer (styrene). The styrene solutions of polyesters were subjected to the cure reaction with suitable curing agent. The different organic peroxides: diacyl peroxide: benzoyl peroxide (BPO), dialkyl peroxide: dicumyl peroxide (DCP), and alkyl hydroperoxide: cumene hydroperoxide (CHP) were used. In addition, to cure the UEP, the mixture of the stoichiometric ratio of an acid anhydride (tetrahydrophthalic anhydride or hexahydrophthalic anhydride)/organic peroxide were applied. The curing characteristic such as: temperature of the cure initiation (Tonset), peak maximum temperature (Tmax), final cure temperature (Tend), the heat generated during the cure reaction (ΔH) were evaluated. It has been found that the course of the cure reaction of studied polyesters with styrene significantly depended on their structure and used initiating system. The presence of both carbon–carbon double bonds and epoxy groups in polyester backbone led to obtain more cross-linked materials where the copolymerization, thermal curing of epoxy groups with hydroxyl or carboxyl groups and polyaddition reaction of epoxy to anhydride groups have been expected. The use of BPO allowed to cure the polyesters at relatively lower temperatures with higher exothermic effect compared to DCP and CHP which was directly connected with lower thermal stability and significant higher ΔH values obtained during decomposition of diacyl peroxide used. In addition, the curing exotherm peak of polyesters based on glycol containing more –CH2– units with styrene was shifted to a bit higher temperatures which was probably due to lower molecular mobility of polyester’s chain caused the production of less stiff network structure.