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The simulation of polymer-forming reactions can be a powerful tool to reduce the time and cost of developing new polymer formulations; formulations that can be potentially both more sustainable and less costly. A critical aspect of advancing such simulations is the reduction in the number of fitted parameters, and more specifically, the identification of fundamentally-correct parameters that can be applied to a range of reactions as opposed to parameters specific to each reaction. This paper presents an innovative approach focusing on the frequency factor of the Arrhenius equation resulting in insight to how this frequency factor is a characterization of mass transfer that can be broadly applied to a range of similar reactions. The result is a reduction in the number of fitted parameters needed for simulation and providing a more fundamental, efficient, and robust method to simulate thermoset polymerization reactions. Impacts of mass transfer limitations due to the large increase of resin viscosities during thermoset polymer reactions were reflected in the frequency (pre-exponential) factor of Arrhenius equation. By representing the frequency factor as the sum of viscosity-dependent and a viscosity-independent terms to account the impact of inter- and intra-molecular diffusion/movement of the reacting moieties in the resin, the same pre-exponential factor was able to be used for catalytic and non-catalytic paths. Impacts of catalysts were reflected in lower activation energies. Temperature profiles of urethane gel reactions were used to characterize the reactivities of different polyols based on the fractional content of primary (versus secondary) hydroxyl moieties. This approach the simulation results of reaction temperature show good agreement with the experimental data.

The reaction of polyol and isocyanate monomers to form polyurethanes is commonly presented in reaction chemistry that implies a step-growth mechanism for the polymerization. However, viscosity versus temperature profiles of both experimental studies and gel-forming simulation studies indicate that the degree of polymerization resulting from the reactions varies considerably from reactions with catalysts compared with those without catalysts. An extension of a simulation based solely on step-growth mechanisms to simulations that include chain growth via an active catalytic complex provides viscosity and temperature profiles that are consistent with the range of experimental data. The results indicate that as catalytic mechanisms dominate the kinetics chain growth mechanisms also overwhelm step growth mechanisms. Based on this mechanism, the choice of catalysts can impact both the rate of reaction and degree of polymerization length; both being of high importance in engineering urethane foams.

One of the obstacles to displacing petroleum-based polyols with soy-based polyols in rigid urethane foam formulations is foam shrinkage, especially at displacements greater than 50%. The shrinkage is a result of partial vacuums forming in the closed-cell foam as reaction temperatures dissipate. It was hypothesized that the shrinkage was in part due to inadequate curing of the foam which was due to lower maximum-attained temperatures during the near-adiabatic foaming process. Foam formulation studies were performed to evaluate the correlation of peak temperature foam shrinkage. Two approaches were evaluated to increase peak temperatures: (a) preheating of the monomers prior to reaction and (b) use of bio-based glycerol as a co-reagent to increase the mixture hydroxyl number and respective maximum temperatures. The results show that as the maximum reaction temperature increases, foam shrinkage decreases. Both preheating and use of a glycerol co-reagent were effective for increasing peak temperatures and decreasing shrinkage. Experimental results were supplemented with a simulation of the foaming process to better understand the fundamental phenomena and to evaluate the effectiveness of the simulation to evaluate approaches to better utilize bio-based monomers in thermoset polymers.