The influence of small additives of cobalt(II) porphyrin (CoIIPn) on cross-linking radical polymerization of butane-1,4-diol dimethacrylate and its structural analog butane-1,4-diol diacrylate was studied. The kinetics of cross-linking radical polymerization of di(meth)acrylates in the absence and presence of CoIIPn and the diffusional sorption and physical mechanical properties of the resulting polymers were studied. Cobalt(II) porphyrin decreases substantially the polymerization rate and partially suppresses the gel effect. Diacrylate polymerization in the presence of CoIIPn proceeds with an induction period, whose value is determined by the content of CoIIPn. Cobalt(II) porphyrin modifies the structure and properties of the formed cross-linked polymers. In the case of dimethacrylate, this is caused by the catalytic chain transfer reaction, whereas for diacrylate the reason is the reversible inhibition reaction.