A general model for interfacial polymerization is proposed and solved numerically. The model takes into account diffusion and reaction of monomers, presence of unreacted functional groups on the growing polymer, and solubility effects. The formation of a polyamide film in composite separation membranes is taken as an example. The evolution of the concentrations of the polymer and unreacted moieties are followed explicitly, thus enabling the calculations of the limiting thickness and the asymmetric distribution of density and charge in the resulting film. Such knowledge is important for the prediction of rejection and transport properties of the film. The effects of reaction kinetics, monomer concentrations, and hydrodynamic conditions on the properties of the film are analyzed, and a number of analytical correlations are developed. (C) 2003 Wiley Periodicals, Inc.