Kinetic study of the polymerization of α‐d‐styrene and/or styrene by homogeneous catalysis. Part II

Initial rates of polymerization using the (C5H5)2TiCl2Al(C2H5)2Cl homogeneous catalyst system, were determined for homo and copolymerizations of styrene, styrene‐α‐C14, α‐d‐styrene, p‐methylstyrene, and m‐methylstyrene. Homopolymerization rates of styrene as a function of Al/Ti ratio indicate three rate maxima of apparently equal magnitude near Al/Ti ratios of 3.0, 11.0, and 16.0. Copolymerizations of gE; 97.5% α‐d‐styrene and styrene as a function of Al/Ti ratio yielded no rate maxima but appeared to be a linear function of the Al/Ti ratio employed. α‐d‐Styrene yielded higher initial polymerization rates than styrene under all tested experimental conditions. These rate increases as a function of monomer deuteration at the α position are related to a higher concentration of active centers. A reaction scheme is proposed in which the predominant mode of formation of active centers occurs via alkylation of titanium but by a cationic mechanism. The observed isotope effect with the use of α‐d‐styrene is related to the stability of the cationically formed active centers. Destruction of these active centers is is suggested to result in either an α‐alkylated new monomer and/or low molecular weight oligomers. An isotopically controlled unimolecular decomposition step is suggested as a mode of termination and/or destruction of potential active centers resulting in divalent titanium; probably (C2H5)2Ti. The predominant mode of termination and/or destruction of active centers appears to occur by a bimolecular mechanism which is related to the experimentally observed monomer dependence of the initial rate of polymerization.