Kinetic and chemorheological modeling of the vitrification effect of highly reactive poly(urethane-isocyanurate) thermosets

The cure kinetics and chemorheology of a highly reactive poly(urethane-isocyanurate) was characterized by DSC and parallel plate rheometry. The cure kinetics were modeled with a modified autocatalytic approach. The relationship between the transition temperature (Tg) of the urethane and isocyanurate networks as a function of conversion was obtained with DSC analysis. Even at low curing temperatures (T < 70 °C), the viscosity increased sharply as a function of conversion. For higher curing temperatures (T > 90 °C), the parallel plate configuration was not suitable to resolve how the viscosity evolved as a function of conversion. The damping factor as a function of frequency showed that it was possible to discern the vitrification and gelation phenomena during cure. The experimental data were modeled using an improved phenomenological model which contemplated the chemoviscosity contribution of the urethane and isocyanurate networks. The model was used to predict the chemorheological behavior at elevated temperatures and to obtain the temperature, time viscosity (TTV) diagrams.