Photodecomposition of copolymers between 9-anthrylmethylmethacrylate and methymethacrylate by XeF excimer laser irradiation

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Abstract

Laser photodecomposition of copolymer films (9-anthrylmethylmethacrylate and methylmethacrylate polymerized at various ratios) and polymethylmethacrylate (PMMA) film doped with 9-anthrylmethylisobutylate (AMIB) (model compound of the copolymer) was studied using an XeF excimer laser (351 nm) with variation of the irradition fluence and pulse number. As the laser fluence (F) is increased, the etch rate for films with high dopant concentrations increases linearly with log F. For films with lower dopant concentrations, a steep increase in the etch rate is obtained at higher fluence. The molecular weight distribution of the fragments of the irradiated films was studied using high performance liquid chromatography (HPLC). For copolymer films, the higher molecular weight fraction is produced via photocrosslinking of anthryl groups in the polymer and the lower molecular weight fraction is generated via the simultaneous degradation of the polymer. However, for the dopant-dispersed films, the higher molecular weight fraction is not produced and only decomposition of the polymer occurs. Photodecomposition and photoablation of PMMA are caused by highly excited anthracene molecules attained via two or three multiphoton excitations. It is revealed that photothermal mechanism via multiphoton excitation has an important role in the photocrosslinking of the copolymer.

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