A kinetic study was made of alternating copolymerization of styrene with methyl methacrylate in the presence of diethyl aluminium chloride, initiated by UV exposure in bulk and in tetrachloroethylene solutions. Molar ratios of methyl methacrylate: styrene = 1·2; [diethyl aluminium chloride]:[methyl methacrylate] = 0.5. It was shown that the rate of copolymerization is proportional to the intensity of initiating UV exposure to 0·5. Copolymer molecular weight remains constant up to 20–25% conversion. The reaction order with overall monomer concentration is 1·5. The average life time of active centres τ=0·65±0·32 sec was measured using the rotating sector method. It was shown that molecular weights of the copolymers formed are practically independent of reaction rate for the conventional range of rates of initiation because of strong chain transfer to the monomer. The constant of chain transfer to the monomer was calculated C m=(2·3±0·2)×10 −3 mole/l/·sec. It was established that copolymerization of the styrene-methyl methacrylate-diethyl aluminium chloride system is a radical chain process, characterized by a short life time of active centres, bimolecular chain termination, high rate of propagation and hig rate of self-transfer.