Kinetics of anionic polymerizations of styrene and its m- and p-derivatives: Hammett's relations

Abstract

The kinetics of anionic polymerizations of styrene, m-methylstyrene, p-isopropylstyrene, and p-methylstyrene were investigated in tetrahydrofuran (THF) at 25°C with Cs⁺ as gegenion in the presence and absence of an electric field. Anionic polymerizations of m- and p-methylstyrenes in 2-methyltetrahydrofuran (MTHF) with Na⁺ as gegenion were also studied. The ion-pair rate constants k^′_p, the free ion rate constants k^″_p and the dissociation constants K of the styrene derivatives were generally smaller in both solvents than those of styrene. Conductance studies showed that the K values of the caesium salts are practically the same in THF. It was found that the free anions of these living polymers in MTHF are half as reactive as in THF. The field acceleration effect was hardly perceptible in THF. Following earlier studies of the field effect, the solvation ability of ethereal solvents to free carbanions was concluded to decrease along the series dimethoxyethane (DME) > THP ≃ MTHF > THF. A value of (12 ± 2)× 10⁴ M^–1 s^–1 was attributed to the “desolvated” free ion rate constant for living polystyrene. Hammett's relations of the two systems Cs⁺/THF and Na⁺/MTHF were examined for k_p, k^′_p, k^″_p, and K, independently. The reactivity constants ρ for k_p and K were dependent on systems whereas those for k^″_p were not.