Influence of number of functional groups of hyperbranched polyol on cure kinetics and physical properties of polyurethanes

Curing of polyurethane prepolymer with three hyperbranched polyol was studied using FTIR spectroscopy. The disappearance of the strong isocyanate absorption peak was followed with time and temperature to determine the reaction kinetics. It was shown that all the hyperbranched polyols followed the second order kinetic equation and the reaction rate enhanced with increase in the number of the functional groups of the hyperbranched polyol. Activation energy, activation enthalpy, and activation entropy were also measured. The swelling character of the polyurethanes was investigated with the help of gel fraction, degree of crosslinking, and average molecular weight between crosslinks. Atomic force microscopy indicated phase separated morphology of the cured polyurethanes. The thermal, mechanical, and thermomechanical properties were enhanced when the number of the functional groups in the hyperbranched polyols was increased.