GEL-PERMEATION CHROMATOGRAPHIC ANALYSIS OF POLYURETHANE PREPOLYMER SYNTHESIS KINETICS .2. THE EFFECTS OF STOICHIOMETRY AND TYPE OF DIISOCYANATE

The kinetics of formation of polyurethane prepolymers is studied by an analytical technique which involves reactive quenching of the isocyan ate, separation of the oligomeric species by GPC, and measurement by U V absorbance of the quenched moieties. The precision of the kinetic pa rameters and the ratios of the oligomers are determined. The effect of changes in reactant stoichiometry on the ratio of oligomers is measur ed and compared to the value predicted by an equation from Flory. Tolu ene diisocyanate is shown to give fewer high oligomers than predicted, while methylene diphenylene diisocyanate gives nearly the predicted v alues. Tetramethylxylene diisocyanate gives more high oligomers than p redicted, an unexpected but possibly important result. Catalyst is sho wn to increase the reaction rate of the last by more than 200 times. ( C) 1994 John Wiley & Sons, Inc.