Chemorheology of polyurethane systems as predicted from Monte Carlo simulations of their evolutive molecular weight distribution

The chemorheological models used for the description of thermoset polyurethanes are too often specific to a given formulation. This paper discusses the application of a more generic modeling approach which describes the evolutive rheological behavior of a polyurethane reactive mixture from a set of fitted monomer characteristic parameters and its calculated molecular weight distribution (MWD) at a given conversion level. The MWD is evaluated numerically from stochastic simulations. Once the adjusted parameters are obtained, the model becomes applicable at any starting formulation using a liquid prepolymer built from the same monomer. The linear viscoelastic properties were obtained from MWDs using the double reptation mixing rule. The mixing rule was adapted to include a contribution of Rouse’s relaxation times to account for short chains species, as those encountered in the beginning of the polymerization reaction. This procedure was successfully applied to two different difunctional thermoset polymeric systems that included either hydroxy-terminated polybutadiene or polypropylene glycol.