Synthesis and characterization of isocyanate-terminated polyurethane prepolymers

Using statistically designed experiments, seven variables were investigated to determine their effect on the physical and mechanical properties of isocyanate-terminated polyurethane prepolymers. The choice of catalyst (dibutyltin diacetate, T-1, or stannous octoate, T-9) along with the ratio of diol to triol were found to most significantly control the prepolymer properties. Other variables such as reaction temperature, reaction time, and order of polyol addition did not affect the system. In comparing the two catalysts, T-9 was found to be concentration sensitive, yielding low-viscosity prepolymers at the lower catalyst level and higher viscosity, unstable materials at the higher catalyst level. No evidence was found to show concentration sensitivity of T-1. A series of prepolymers based on varying ratios of diol to triol were synthesized, and their physical and mechanical properties are reported.