PRIMARY PHOTOPROCESSES OF CR(VI) IN REAL-TIME HOLOGRAPHIC RECORDING MATERIAL - DICHROMATED POLY(VINYL ALCOHOL)

The primary photoprocesses of Cr(VI) in poly(vinyl alcohol) have been studied under various experimental conditions. Aqueous solution and po lymer films of dichromated poly(vinyl alcohol) (DCPVA) have been irrad iated, and the quantum yield values were determined for the photoreduc tion of Cr(VI) to Cr(III) at different pH values. Thermal and photoche mical evolution of Cr(V), Cr(III), and polymer radical in DCPVA films was monitored at room temperature using real-time ESR spectrometry. Sp in-trapping experiments with N-tert-butyl-alpha-phenylnitrone (PBN) ga ve evidence for the formation of radical adduct from the polymer matri x. Effect of pH of the coating solution and concentration of dichromat e on the photochemical evolution of intermediates were observed. Possi ble involvement of all intermediate species from Cr(VI) has been discu ssed. On the basis of our experimental findings, a suitable mechanism has been suggested, involving the electron transfer from the polymer m atrix to Cr(VI) leading to the formation of Cr(V) and polymer radical, which further undergoes reaction to produce Cr(III) and a cross-linke d polymer matrix.