Chain growth polymerization mechanism in polyurethane-forming reactions

Abstract

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.