The melt state reaction of the diglycidyl ether of Bisphenol A with Bisphenol A is investigated with respect to modeling the reaction rate. Both linear chain addition and branching are considered within the general model as well as the probability for unreactive site formation in the branching reaction path. Through the use of Fourier transform infrared spectroscopy, the epoxide concentration is monitored using the 913-cm-1 band. The phenol mode at 1592 cm-1 provides the necessary second parameter as an internal thickness band for the application of the nonlinear regression technique. Two modifications of a general model are evaluated for the A + B --> C and A + C --> C type reaction systems. The results of the regression analysis are in close agreement under different considerations of unreactive site probability. Catalysis effects upon the branching reaction are found to be negligible for model accuracy for the stoichiometric samples. The activation energy calculated from the rate constants determined is in excellent agreement with those reported in the literature.