Photochemical Reactions of Poly(4-vinylphenol) Thin Films

The mechanism involved in the photochemical immobilization of poly (4-vinylphenol) (PVP) thin. films was investigated. The films were fabricated by a simple procedure of UV irradiation and solvent extraction. A combination of ellipsometry, IR, and high-resolution X-ray photoelectron spectroscopy (XPS) was used to provide detailed and quantitative analysis of the composition of the photochemical reaction products. Upon irradiation at 260 nm, benzyl and phenoxy radicals are generated in the polymer. In the absence of oxygen, PVP films crosslinked via the combination of the benzyl radicals or phenoxy radicals. At lower irradiation doses, the photochemical process was dominated by cross-linking of the polymer backbone via the combination of benzyl radicals. At higher exposure doses, cross-linked quinoid structures were generated, and the concentration increased with the irradiation time. No oxidation or degradation products were observed. In the presence of oxygen, additional reactions of oxidation and degradation occurred. At lower doses, oxidation at the benzyl position produced the ketone structure evidenced by the drastic increase in the 0 content in the irradiated films. As the irradiation doses increased, further oxidation at the methylene position occurred, and in addition, volatile and degradation products were also generated. This photochemical process was successfully employed to fabricate patterned PVP structures.