Effect of increasing NCO/OH molar ratio on the physicomechanical and thermal properties of isocyanate terminated polyurethane prepolymer

The study investigates the effect of increasing NCO/OH molar ratio on the physico-mechanical and thermal properties of isocyanate terminated polyurethane prepolymer. The prepolymer was prepared using methylene diphenyl diisocyanate and difunctional polypropylene glycol. The NCO/OH molar ratio has been varied from 1.2:1 to 3:1. The formation of the prepolymer was confirmed by FTIR spectroscopy. The results reveal that the viscosity, weight average molecular weight and curing time of the prepolymer decreased with increase in NCO/OH molar ratio. When NCO/OH molar ratio increased, the tensile strength of the polyurethane film increased, while percent elongation decreased due to increase in hard segment content. The glass transition temperature of the prepolymer decreased with increase in NCO/ OH molar ratio of the prepolymer. Keywords: Polyurethane Prepolymer, Viscosity, Molecular Weight, Curing Time, Glass Transition Temperature.