Kinetics of anionic polymerization of o-methylstyrene in 2-methyltetrahydrofuran and tetrahydrofuran

Abstract

The kinetics of anionic polymerization of o-methylstyrene were investigated in 2-methyltetrahydrofuran (MTHF) at 25°C with Li⁺, Na⁺, K⁺ and Cs⁺ as gegenions in the presence and absence of an electric field. Conductance studies showed that the dissociation constants K vary remarkably with the gegenion and that the lithium and sodium salts are dissociated to larger extents than the respective polystyryl salts. The free ion rate constant k^″_p was ≈ 2 × 10⁴ M^–1 s^–1, which was smaller than that of polystyrene. From the conductivity data, the field effect was concluded to be due to an increase in k^″_p with increase of the field strength as in other systems. The k^″_p reached a limiting value of ≈3 × 10⁴ M^–1 s^–1 above 3 kV/cm. The ion pair rate constants k^′_p were 2, 1, 16 and 30 M^–1 s^–1 for Li⁺, Na⁺, K⁺ and Cs⁺, respectively. Comparison with polystyrene systems led to the conclusion that the behaviour of poly(o-methylstyryl) salts are due to steric hindrance effects of the methyl group in the ortho position. The field-accelerating effects reflected in the k^″_p term as in other systems are smaller than that of polystyrene systems. This is discussed in terms of the ortho effect. The kinetics of the caesium salt of poly(o-methylstyrene) were also studied in tetrahydrofuran (THF) at 25°C. The results are compared with those in MTHF.