Browsing by Author "Hirohara, Hideo"

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    Kinetics of Anionic Polymerization of o-Methylstyrene in 2-Methyltetrahydrofuran and Tetrahydrofuran
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (1), 1972) Hirohara, Hideo; Nakayama, Masatoshi; Kawabata, Ryoichi; Ise, Norio
    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.
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    Kinetics of Anionic Polymerizations of Styrene and Its m- and p-Derivatives: Hammett’s Relations
    (Journal of the Chemical Society : Faraday Transaction - I. The Chemical Society, London. 1972, 68 (1), 1972) Hirohara, Hideo; Nakayama, Masatoshi; Ise, Norio
    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 kp, k′p, k″p, and K, independently. The reactivity constants ρ for kp and K were dependent on systems whereas those for k″p were not.