Photochemistry of polymeric systems. I. Photocrosslinking of polymers and copolymers containing pyridine N‐oxide groups

Vinylpyridine‐N‐oxide units were introduced in polymeric chains in order to study their photocrosslinking. Copolymers of styrene and 4‐vinylpyridine‐N‐oxide were especially synthesized and studied. The methods used for characterization of photocrosslinked films were a “photoresist test” or the measurement of the insolubility and of the swelling ratio. The Cleavage of the N‐oxide bond was responsible for the photocrosslinking. The competitive formation of carbonyl compounds took place and decreased the rate of photocrosslinking. This last reaction is favored by triplet‐state quenchers. The photosensitivity of the copolymers was determined as a function of the wavelength of the radiation used. When the photocrosslinking proceeded, a film of the copolymeric material became transparent in the 280–320‐nm range. Thick films could therefore be completely photocrosslinked when irradiated in this range of wavelength.