Glass transition temperature profile of the curing reaction of unsaturated polyester resin

Abstract

The curing reaction of unsaturated polyester/styrene system was investigated by differential scanning calorimetry (DSC). Between gelation and vitrification (where 7g of the curing system equals to the curing temperature), the propagation of the curing reaction is kinetically controlled whilst the termination reaction is diffusion controlled. After vitrification, both the propagation and termination reactions are diffusion controlled. The variation of Tg during the curing reaction was calculated from the curing profile obtained from DSC measurements by using an empirical equation developed in a previous work. The experimental data indicated that there exist a critical point such that the time-temperature shifts of Tg vs. ln(cure time) data at different cure temperatures formed a master curve between critical point and vitrification at an arbitrary reference temperature and yielded a single Arrhenius activation energy. These results indicated that polymerization between critical point and vitrification was Tg dependent only.