A linear-chained epoxy resin was formulated from phenyl glycidyl ether and nadic methyl anhydride catalyzed by benzyldimethylamine. Intermolecular polymerizations were modeled as a parallel set of propagation reactions. Fourier-transform infrared spectroscopy was used to determine the concentrations of the oxirane, anhydride, and ester moieties within the resin as a function of time for two isothermal cures. Data analyses yielded the propagation rate constant as a function of temperature and the initiator’s concentration, including contributions from impurities within the resin. Results compared favorably with measurements on fractionated resins, using gel permeation chromatography. Population density distributions are described by Poisson molar distributions for this resin.