Reaction Kinetics of Hexamethylene Diisocyanate and Polypropylene Glycols

Abstract

The kinetics of the reaction between hexamethylene diisocyanate (HDI) and polypropylene glycols (PPG) of different molecular weights toward the synthesis of polyurethanes with versatile properties was studied using differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). From the dynamic exotherms observed in DSC, it was found that the Kissinger equation modified by an additional temperature term in its frequency factor term was able to accurately describe the isothermal reaction kinetics of all HDI/PPG reactions. The modification can be justified by analyses with the Ozawa method and the modulus observed under DMA measurements. Regardless of the type of PPG used, the frequency factors changed with respect to the degree of conversion and maximized at near 70% conversion. The derivation of the modified kinetic equation is presented. In addition, the empirical equations describing the dependence of the activation energies and frequency factors on the molecular weights of PPG were also derived.