| Abstract: | The kinetics of formation of polyurethane prepolymers is studied by an analytical technique which involves reactive quenching of the isocyanate, separation of the oligomeric species by GPC, and measurement by UV absorbance of the quenched moieties. The precision of the kinetic parameters and the ratios of the oligomers are determined. The effect of changes in reactant stoichiometry on the ratio of oligomers is measured and compared to the value predicted by an equation from Flory. Toluene diisocyanate is shown to give fewer high oligomers than predicted, while methylene diphenylene diisocyanate gives nearly the predicted values. Tetramethylxylene diisocyanate gives more high oligomers than predicted, an unexpected but possibly important result. Catalyst is shown to increase the reaction rate of the last by more than 200 times. © 1994 John Wiley & Sons, Inc. |
