The photopolymerization behavior and reaction kinetics of ethylhexyl methacrylate (EHMA) and ethylene glycol dimethacrylate (EGDMA) monomers in styrene-butadiene-styrene block copolymer (SBS) were studied. For both monomers, di- and tetrafunctional, reaction diffusion was found to be the only mechanism of termination when the polymerization is carried out in this polymeric medium, that is, reaction diffusion controls the termination reaction from the beginning of the reaction. The polymerization of EGDMA in polystyrene and polybutadiene showed similar behavior to that in SBS. Also, the relationship between the individual rate constants k(t) and k(p) was studied, and a constant ratio of these kinetic constants was found.