Photochemistry in polymer solids. VI. Photoreaction of benzophenone in poly(vinyl alcohol) matrix.

HORIE Kazuyuki, ANDO Harumi, MORISHITA Keiko, MITA Itaru

doi:10.11454/photogrst1964.47.345

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高分子固体中の光化学　ＶＩ　　ベンゾフェノンとポリビニルアルコールマトリックスとの光反応
コウブンシコタイチュウノコウカガク 6 ベンゾフェノントポリビニルア
Photoreaction of Benzophenone in Poly (vinyl alcohol) Matrix
ベンゾフェノンとポリビニルアルコールマトリックスとの光反応

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The phosphorescence decay of benzophenone in poly (vinyl alcohol) (PVA) film (250 μm thickness) excited by a 10-ns nitrogen laser pulse at 337 nm was measured at -196-140°. The phosphorescence decays exponentially for T<Tr (-100°) and T>T_g (85°), but deviates from single exponential type for T_r< T< Tg (Fig. 2). The deviation is attributed to the diffusion-controlled hydrogen abstraction (k_a) of benzophenone triplet for PVA matrix. The phosphorescence intensity φ(t) is given to decay as eq.(b) with A= 4πRDN and B= 4R² (πD) ^1/2N.<BR>k_a=4πRDN (1+R/√πDt) =A+B/√t (a)<BR>lnφ(t) =-(k₀+A [PVA]) t-2B [PVA] t1/2 (b)<BR>The curve fitting for the experimental phosphorescence decay with eq.(b) gives the values of 1/τ=k₀+A [PVA] and B, which are shown in Fig. 3. The breaks at T_g=85°C, Tβ =30°C, and the appearance of B at Tγ=-100°C clearly reflect the change in molecular motions of the matrix PVA.<BR>In order to know the net quantum yield for the benzophenone disappearance, Y, by hydrogen abstraction in PVA, the change in UV spectra of benzophenone in the PVA film was followed during continuous irradiation of 365 nm UV light (Fig. 6). The values of Y are 0.02-0.08 for T<T_g suggesting the predominant occurrence of backward reaction of benzophenone ketyl radical in the cage for the temperature range below T_g

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