Polyurethane and unsaturated polyester hybrid networks: Chemorheological and dielectric study for the resin transfer molding process (RTM)

The kinetic, rheological and dielectric behavior of a polyurethane‐unsaturated polyester hybrid system was studied with a view to control the RTM process. The kinetics of the polyurethane reaction (which governs the viscosity evolution during injection) was satisfactorily modeled with a simple second order model. The rheological study enabled complex viscosity and gelation time (tanδ crossover) at different curing temperatures to be obtained. Furthermore, dielectric data and viscosity measurements have been interpreted with respect to kinetics. It was shown that the modified percolation law equation suggested by Macosko et al. can be used to describe the viscosity as a function of temperature and extent of reaction by using a temperature and conversion dependent critical exponent. Dielectric properties such as ionic conductivity were related to viscosity with a Stockes based equation, and to conversion with an empirical equation.