Photocrosslinking reaction of vinyl-functional polyphenylsilsesquioxane sensitized with aromatic bisazide compounds

fPhotochemical reactions of aromatic azide groups were applied for a novel photosensitive silicone ladder polymer, that is, partially vinyl-substitute d polyphenylsilsesquioxane sensitized with aromatic bisazide compounds as a photocrosslinker. The photocrosslinking reaction in this system was invest igated from the viewpoint of the efficiency of the photocrosslinker, that i s, the ratio of the photocrosslinker consumed for crosslinking. The numbers of photodecomposed azide groups and crosslinks in the polymer were determi ned by Fourier transform infrared measurements. At a higher bisazide concen tration, the predominant reaction of nitrenes formed as the intermediary ra dical by the photolysis of azide was a coupling reaction that could not con tribute to the gelation of the polymer. The ratio of the bisazide compound consumed for crosslinking showed the highest value at its concentration of 3 wt % ( and decreased with the addition of a larger amount. The semiempiri cal molecular orbital calculations were applied to the theoretical analysis of the photoreaction of nitrenes using phenylnitrene as a model structure. The calculation results indicated that the coupling reaction of nitrenes s hould proceed more easily than the photocrosslinking reaction in N-2 atmosp here, and the fact that the oxidation of nitrenes should proceed exclusivel y in the atmosphere including O-2 agreed with the experimental results. (C) 2001 John Wiley & Sons, Inc.