Cure kinetics, microheterogeneity, and mechanical properties of the high‐temperature cure of vinyl ester resins

Abstract

AbstractA kinetic model has been developed that is based on the irreversible thermodynamic fluctuation theory, in which the conversion of comonomers is a function of the curing relaxation time, reaction time, and reaction temperature. This modified model permits a better prediction of the course of the high‐temperature cure reaction of vinyl ester (VE) resins under isothermal conditions. The microheterogeneity in cured resins was investigated through the measurement of the residual heat of isothermally cured samples with differential scanning calorimetry and through the observation of the fracture surfaces of samples under different cure conditions with scanning electron microscopy (SEM). The SEM photographs demonstrated the existence of clusters of microgels of about 20 μm in samples isothermally cured at 80°C for 3 h. The results of the dynamic mechanical thermal analysis of postcured samples verified the microheterogeneity in the cured samples and showed that the glass‐transition temperatures were not affected by the curing conditions. The effect of postcuring on the conversions of VE and styrene varied with the different cure schedules. The postcure for a sample isothermally cured at 80°C increased the tensile strength and flexural strength. On the contrary, the postcure for samples isothermally cured at 120°C reduced the tensile strength and flexural strength. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1124–1133, 2004