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.