The free radical copolymerization of styrene and other vinyl monomers to produce cross-linked, network polymers is of technological importance in the production of ion-exchange resins, packings for gas-liquid and gel permeation chromatography, cross-linked latex polymers, and other products. The principal multifunctional cross-linking monomers which are used in this connection are ethylene glycol dimethacrylate and divinylbenzenes, and accurate values for reactivity ratios in their reactions with bifunctional monomers are essential for the design of copolymerization processes and products.