Kinetic Model for the Reaction of Ipdi and Macrodiols: Study on the Relative Reactivity of Isocyanate Groups

The kinetics of the bulk polymerization reaction of 1-iso-cyan-a-to-3-isocyanato methyl-3,5,5-trimethylcyclohexane or isophorone diisocyanate (IPDI) with poly(oxytetramethylene) glycol (POTM) was studied by 13C nuclear magnetic resonance (13C-NMR). The difference of reactivity of the NCO groups in this unsymmetrical diisocyanate was taken into account for the determination of the kinetics constants. A kinetic model using several chemical species is proposed. These are differentiated by their isocyanate or hydroxyl terminal functions. A second order reaction mechanism was used and modified to include catalysis by the urethane groups formed and the substitution effect. The kinetics constants were calculated by a numerical resolution, using the fourth order Runge-Kutta method.