Kinetics of copolyurethane network formation

Cure kinetics for the formation of copolyurethane networks of various compositions based on hydroxy-terminated polybutadiene (HTPB), poly(12-hydroxy stearic acid-co-TMP) ester polyol(PEP), and different isocyanates has been studied through viscosity build up during the cure reaction. The viscosity(N)—time (t) plots conform to the equation N = aebt, where a and b are empirical constants, dependent on the composition and the nature of the polyols and the isocyanates. The rate constants (k) for viscosity build up, evaluated from the slopes of dN/dt versus N plots at different temperatures, were found to vary significantly from 0.0073 to 0.25 min−1; and the activation energies for gelation were found to be in the range 20 to 40 kJ mol−1. The results have been interpreted in terms of the dependence of the rate constants on structural characteristics of the prepolymers.