The oxidizing process and the oxygen-binding lifetime of 5, 10, 15, 20-tetra (o-pivalamidophenyl)-porphyrinato cobalt (II) (TPPCo) complexed with poly (vinylimidazole-co-fluoropentyl methacrylate) (PFIm) were studied, and the mechanism and dynamics of irreversible oxidation of TPPCo were discussed. The TPPCo displayed a reversible change in the UV-visible absorption spectrum from the deoxy form (λmax = 530 nm) to the oxygen-binding one (λmax = 548 nm) with an isosbestic point at 538 nm, in response to the partial oxygen pressure of the atmosphere. But the active TPPCo complex in the membrane was slowly changed, via the irreversible oxidation reaction in the open atmosphere, to the TPPCo(III) complex without the oxygen-binding ability, which could be monitored by the UV-visible absorption at λmax = 548 nm. In the solid membrane state, water molecules in air may attack the TPPCo-bound dioxygen to yield a hydrodioxy radical and TPPCo(III), which is the main reason that diminishes the oxygen-binding ability of the TPPCo complex and that of the membrane. The half-lifetime (τ) of the TPPCo complex as an oxygen carrier was measured by allowing the TPPCo-PFIm membrane to stand in dry air (environmental humidity 10%), in laboratory air (humidity ca. 50%), and in a water vapor atmosphere (humidity 95%) at room temperature, respectively. The decrease course of the active TPPCo complex approximately follows the first-order kinetics and gives the t values. The τ value of the PFIm-TPPCo complexed membrane was as long as ca. 250 days even in the water vapor-saturated atmosphere. Under the same laboratory air condition, the lifetime of the PFIm-TPPCo membrane was much longer (ca. 13 times) than that of the reference non-fluoro membrane such as the membrane of TPPCo complexed with poly(octyl methacrylate-co-vinylimidazole). The hydrophobic property of the PFIm polymer is considered to suppress the irreversible oxidation of the active TPPCo carriers caused by water molecules and to significantly prolong the operational lifetime of the TPPCo complex membrane.
|ジャーナル||Acta Polymerica Sinica|
|出版ステータス||Published - 2003 2月|
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