Determination of rate constants of initiation and propagation in the cationic polymerization of α-methylstyrene with CF3SO3H and H2SO4

The polymerization of α-methylstyrene with CF₃SO₃H and H₂SO₄ as initiators was studied at 30°C in dichloroethane by the stopped-flow/rapid-scan spectroscopic technique. The propagating cation shows λ_max at 336–340 nm. The initiation process and the early stage of propagation were analyzed kinetically on the basis of the cation formation and monomer consumption by taking into account the equilibrium monomer concentration. The rate of initiation with CF₃SO₃H was found to be proportional to the concentrations of CF₃SO₃H and monomer, but the initiation with H₂SO₄ is not proportional to the H₂SO₄ concentration. The rate constant of initiation was estimated to be (2 ± 1)·10³ 1.mol^?1.s^?1 with CF₃SO₃H, and similar values were found with H₂SO₄. The rate constant of propagation is 3.10⁴ 1.mol^?1.s^?1 with CF₃SO₃H as initiator and 10⁶ ? 10⁷ 1.mol^?1.s^?1 with H₂SO₄ as initiator. These k_p values are close to that obtained previously in the radiation polymerization. Finally, λ_max values of the propagating cation, obtained by the stopped-flow technique, were collected.