Interaction between the components of the catalyst system TiCl4-acetophenone-(iso-C4H9)(3)Al used to catalyze the copolymerization of dienes with olefins at a temperature of -30degreesC, including alternating copolymerization, was studied by EPR spectroscopy. It was assumed that the alternating copolymerization of isoprene with ethylene involves the formation in solution of Ti3+ . mTi(4+) complexes (m greater than or equal to 1) containing a greater number of alkyl ligands than in the case of butadiene copolymerization with propylene.