Abstract: The complex constants(K)of acrylonitrile, methyl acrylate, methyl methacrylate and butyl methacrylate with ethylaluminium sesquichloride have been evaluated by UV spectrum method.They are dependent upon the e values of acrylic monomers;K=27.5 exp(1.39e)and have the values of 123, 82.6, 50 and 17.5 l/mole, respectively. The rates of alternating copolymerization of acrylic monomers with conjugated dienes in the presence of ethylaluminium sesquichloride increase with increasing K and the diffrence of e values between two monomers. It is shown that for donor-acceptor monomers the polar effect of monomer plays an important role in the copolymerization.