A general kinetic reaction network has been suggested for the gradual chain growth polyaddition process for the synthesis of linear chain polyurethane. Based on the results from the kinetic investigation of the reactions of model aromatic/aliphatic isocyanates and alcohols and hydroxyethers, some methods were set forth to provide rate-constant values for the reactions included in this network. Model equations were derived from the collision theory, giving dependencies of reaction rate constant values on the molecular weights of the reacting substances. It was found that it was the structure of the reactants that had the most significant effect on the rate of carbamate-yielding reactions; the effects derived from temperature, catalyst, and size of reacting molecules follow.