A kinetic-thermodynamic model is presented to predict the total porosities of macroporous copolymer networks formed by free-radical crosslinking copolymerization of styrene (S) and commercial divinylbenzene (DVB, a mixture of meta and para DVB isomers and ethylstyrene). The kinetic part of the model predicts, based upon the method of moments, the concentration of the reacting species, the gel, and sol properties as a function of the monomer conversion. The thermodynamic part of the model describes the phase equilibria between the gel and separated phases during the S-DVB copolymerization and predicts the volume of the separated phase, which is the pore volume of the crosslinked material, as a function of the monomer conversion. Calculation results show that the porosity of S-DVB networks increases as the polymer-diluent interaction parameter increases, or as the initial monomer concentration decreases. Porosity also increases on increasing the DVB content of the monomer mixture. Both the polymerization temperature and the initiator concentration affect significantly the kinetics of S-DVB copolymerization. However, the final porosity of S-DVB copolymers is largely insensitive to the amount of the initiator and to the polymerization temperature. All calculation results are in accord with the experimental data published previously. (C) 1999 John Wiley & Sons, Inc.