EFFECTIVE FUNCTIONALITY AND INTRAMOLECULAR REACTIONS OF POLYISOCYANATES AND POLYOLS

A gel point bracketing method has been developed for the determination of the weighted average functionality (“effective functionality”) of reactants involved in polycondensation reactions. Its principle lies in the coincidence of gel point and completion of reaction, where the ratio of the reactants is not stoichiometric. With this method, Stockmayer's gel equation is applicable to reactants containing arbitrary distribution of functional groups of equal or unequal reactivity. For a given polycondensation system, the effect of dilution on the gel point is in excellent agreement with a modified gel equation which accounts for intramolecular reactions. Furthermore, it is shown that the extent of intramolecular reactions depends both on dilution and on the effective functionality. Explicit relations have been obtained which allow the calculation of the extent of intramolecular reactions. It is concluded that cyclization in polyol-polyisocyanate systems is negligibly small, over a large range of concentrations, when the functionality of both reactants approaches the value of two. © 1969, American Chemical Society. All rights reserved.