Polymers Having Stable Radicals : Electrochemical and Chemical Behaviors of the Polymer Having Nitroxyls.

As a part of this series on polymers having stable radicals, evaluation of oxidation-reduction potentials by polarography and oxidative reactivities toward hydrazine and hydrazobenzene has been dealt with on nitroxyl stable radicals. Poly (4-methacryloyloxy-2, 2, 6, 6-tetramethylpiperidine-1-oxyl) (III) as a polymer having stable radicals, and its prototypes, 4-oxy-2, 2, 6, 6-tetramethylpiperidine-1-oxyl (I) and 4-isobutyroyloxy-2, 2, 6, 6-tetramethylpiperidine-1-oxyl (II), have been employed for purpose of the study. The electrode reactions of (I) in a range of pH. 8.0-10.1 in aqueous media were observed to be quasi-reversible and the reduction half-wave potentials (E_) being between 0.120-0.200 V (vs. SCE) depending on pH.. In the other pH. regions, the reactions seemed to be irreversible and the reduction halfwave potentials depended uPon pH. as well. In addition, polarographic data in a non-aqueous medium ensured that all the nitroxyls (I), (II) and (III) might have the same redox potential values. The oxidation reactions, using (I), (II), and (III), on hydrazine and hydrazobenzene have been performed, of which extent was pursued spectrophotometrically. From the kinetics, it was elucidated that, (1) the reactions were bimolecula, (2) the rate determinant steps were in the first hydrogen abstraction and, (3) the reactions with hydrazine were reaction controlled (ΔE ; 11.2-11.3 Kcal/mol) while the reactions with hydrazobenzene were diffusion controlled (ΔE ; 5.9-3.9 Kcal/mol). Thermodynamic analysis indicated that the case of reaction with hydrazobenzene differed mechanistically whether the reactant was monomeric (II)or polymeric (III) (ΔS^‡ : -17.9 e. u., (II) ; -21.8 e.u., (III), at 20℃ in THF)and that a steric hindrance presumably took place in the latter

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