REACTION-KINETICS ANALYSIS OF URETHANE POLYMERIZATION TO GELATION

A chemical reaction analysis of a thermosetting, urethane resin formul ated from a triol and a diisocyanate is reported. Population density d istributions of oligomeric molecules, monomer concentration, the cumul ative molar concentration of intramolecular bonds, the resin's average molecular weights, and extent of reaction were determined as a functi on of time. Rate expressions for intermolecular reactions were first o rder with respect to the concentration of each reactant and were propo rtional to the functionality of the irrespective chemical moieties. Ra te expressions for intramolecular reactions were first order with resp ect to the concentration of the reactant and were proportional to the functionality of the limiting chemical moiety on the reactant. The ini tial ratio of the chemical equivalents and effects of dilution were in corporated into numerical simulations. Stanford and Stepto's experimen tal data were analyzed. Gel points and the concentration of intramolec ular bonds were correlated as a function of conversion. Intramolecular reaction rate expressions derived with the aid of Gaussian chain stat istics require the molar concentrations of all chemical isomers of a s pecified chemical composition. The present reaction rate expression al lows chemical isomers to be lumped into a single population density di stribution variable, substantially reducing the dimensions of the simu lation. Numerical results demonstrate that the simplified rate express ion is an excellent approximation.