The cationic copolymerizations of 1- and 2-vinylnaphthalenes with α-methylstyrene were carried out with titanium as an initiator in dichloromethane at various temperatures. The monomer reactivity ratios, r₁ and r₂, and the values of activation enthalpy and entropy differences have been determined. In the relationship between in ln r and 1/T, the ln r₁ was proportional to 1/T but ln r₂ was markedly decreased above -60℃ for 1-vinylnaphthalene and α-methylstyrene system. For 2-vinylnaphthalene and α-methylstyrene system, the ln r₁ and r₂ were proportional to 1/T. It were found that the reactivity of α-methylstyrene to 1- and 2-vinylnaphthalene and cations was greater than that of styrene and the reactivity of 2-vinylnaphthalene to α-methylstyryl cation was greater than that of 1-vinylnaphthalene at -75 and -60℃. The steric effect of methyl group in α-methylstyrene appears to be less important than the inductive effect and the peri-hydrogen effect in 1-vinylnaphthalene appears to be more important than the effect of π-conjugation of 1-naphthyl group. From the values of activation enthalpy (ΔH*)and entropy (ΔS*) differences, we can deduce that the copolymerizations of 1-and 2-vinylnaphthalene to α-methylstyryl cation are enthalpic controlled reaction at -75and -60℃ and entropic controlled reaction above -50℃.