Abstract
The photocrosslinking reaction of partially cyclized polyisoprene rubber sensitized with aromatic azido compounds was evaluated by crosslinking efficiency, that is, the number of crosslinks of polymer per one photodecomposed azido group. The number of photodecomposed azido groups was determined by spctrophotometric measurements and the number of crosslinks of polymer was estimated by comparison of the gel fraction characteristic curve with Charlesby's theory of gelation. Bisazido compounds were more effective than mono-azido compounds in this photocrosslinking reaction. At higher bisazide concentration, the most predominant reaction of nitrene, formed by the photolysis of azide, was a coupling reaction which could not contribute to the gelation of the polymer, so the reaction proceeded by a diffusion-controlled process. Consequently, the crosslinking efficiency decreased rapidly with increasing aromatic azide concentration. At 3 wt% azide concentration, favorable resist properties were obtained, but at that time only 7% of the photodecomposed azido group was used effectively for crosslinking reaction. It is important for the design of excellent photopolymer materials to use a polymer which contains an active site such as C=C bond or CH bond for the reaction with nitrene.
