AbstractControlled two step block copolymerization of styrene, methyl methacrylate and ethyl acrylate with aliphatic and aromatic disulphides under UV irradiation took place in bulk and in THF solution. In the first step of the polymerization, the most reactive system was ethyl acrylate with aromatic disulphides.The molecular weights and yields of polymerizations increased with reaction time. The macromolecules were terminated by primary. SR radicals and by combination of two macroadicals which was observed by NMR spectroscopy. Aninsignificant portion of uninitiated photopolymerization was detected only for MMA. In the second step of polymerization, the purified macroinitiators from the first step reacted with additional monomers to form block copolymers with a small quantity of unreacted macroinitiator. The molecular weights of copolymers increased, the bonding segments between the blocks being detected by1H NMR. The overall reaction is an insertion of monomers between two thiyl groups.