Contributions to the photochemistry of poly(4-vinylpyridine) and its ionic derivatives in the presence of water

Films of poly(4-vinylpyridine), poly(N-carboxyethyl-4-vinylpyridine) and poly(N-allyl-4-vinylpyridine) chloride were exposed at a radiation spreading between about 250 and 270 nm, and the photochemical processes were monitored by spectroscopic methods. Reaction mechanisms considering: (i) a double role of the water molecule, to form water–pyridine ring hydrogen bonds and to accept hydrogen atoms, (ii) the scission of CH methine bonds in units with photoexcited pyridine rings, (iii) the scission of N+C bonds in betaine units, and (iv) crosslinks appearing by recombination of carbon macroradicals or by the addition of methine groups to allyl groups, were found to explain the photocrosslinking of the three polymers. Their properties of crosslinking photoresists were observed by AFM and the best ones were found for the polymer with N-allyl-pyridinium chloride units.