Curing of unsaturated polyester resins: Viscosity studies and simulations in pre‐gel state

The curing of styrene‐unsaturated polyester (UP) resins was studied until gelation. The viscosity and gel points were measured during curing and were correlated with curing temperature, initiator concentration, and accelerator concentration. A gelation model concerning the formation of intra‐crosslinked polymer coils, called microgels, was proposed. The model describes the gelation mechanism in four stages: induction, microgel formation, transition, and macro‐gelation. The kinetic and gelation parameters of the model were experimentally obtained. The gel points and viscosities in the pre‐gel state were simulated by the gelation model for isothermal and nonisothermal curings. Comparisons of the simulation results with experimental data showed good agreement.