A novel mathematical model is presented for the reaction between melamine (M) and formaldehyde (F) at pH = 9.0 and at temperatures between 38 and 90 degrees C. It is based on a kinetic scheme that includes reversible methylolations, irreversible formation of (unsubstituted) methylene bridges, reversible formation of (unsubstituted) ether bridges, instantaneous dissolution of M, and instantaneous equilibrium for the hydration/dehydration of F. The model predicts the distributions of molecular weights and functionalities of the evolving ME resin. Arrhenius expressions were adjusted for the seven kinetic constants on the basis of measurements reported in the first part of this series. Even though the final products contain thousands of different Molecular species, 21 of them Constitute more than 90% of the total weights. During the initial period with negligible condensation, the undissolved M distorts the distributions of molecular weights and functionalities; but the reversibility of methylolations corrects for Such distortion prior to the effective start of condensation. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 1017-1029, 2009