Thermodynamics and kinetics of one-step curing process for vinyl ester-unsaturated polyester resin in low shrinkage

Abstract

Vinyl ester-unsaturated polyester resin (VER) with adipic acid presented the lowest shrinkage and highest flexural strength among VER with CaCO3, polymer vinyl acetate (PVAc), or adipic acid after curing. The Gibbs free energy change of adipic acid/VER specimen was the highest among pure VER, CaCO3/VER, PVAc/VER, and adipic acid/VER, indicating the lowest polymerization spontaneity of adipic acid/VER. Semiquantitative Fourier transform infrared proved that adipic acid did not consume during the curing process. With the presence of adipic acid, traditional two-step curing process of VER glue changed to a one-step curing process with a slower reaction rate constant via the analysis of the curing kinetics. 1H nuclear magnetic resonance and dynamic differential scanning calorimetry (DSC) show the existence of hydrogen bonding between VER and adipic acid. The network structure formed by hydrogen bonding of VER and adipic acid inhibited the cross-linking between unsaturated polyester and styrene, leading to the decrease of curing degree of adipic acid/VER. Thermogravimetric was applied to demonstrate the thermal decomposition behavior of adipic acid for VER, identifying the inefficient curing of adipic acid/VER characterized by DSC.