A novel mathematical model is presented on the methylolation of melamine with formaldehyde at 48 C and pH 9.0. The model assumes an instantaneous hydration/dehydration of formaldehyde and the methylolation mechanism of Gordon et al. (J Appl Polym Sci 1966, 10, 1153). The 24 kinetic constants were adjusted to experimental measurements by Tomita(J Polym Sci 1977, 15, 2347). The model predicts the evolutions of the comonomers and the nine methylolated species. This is the first article of a series that aims at developing a detailed model for the industrial synthesis of melamine-formaldehyde resins. (c) 2007 Wiley Periodicals, Inc.