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Upon exposure to UV light, bis[2-(o-chlorophenyl)-4,5-diphenylimidazole] (o-C1--HABI) in solid polymer matrices such as bromo-and chloromethylated polystyrene (BCMS) and chloromethylated polystyrene (CMS) generates 2-(o-chlorophenyl)-4,5-diphenylimidazolyl radical which rapidly abstracts a hydrogen atom from the polymer to produce the polymer radicals which eventually initiate crosslinking reaction of the polymer films. Efficiency of crosslink formation and relative efficiency in producing the polymer radicals were evaluated from the measurements of the gel fraction of solid films and of fluorescence intensity of the imidazole; both the efficiencies are higher in BCMS than in CMS, suggesting that a high sensitivity of crosslink formation is mainly due to high efficiency in producing the polymer radicals. Furthermore, by the application of a magnetic field, the efficiency of crosslink formation of BCMS/o-CI-HABI was found to decrease slightly.

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