Etude de radicaux libres forméas par irradiation ultraviolette de l'amidon: Application aux réctions de photodégradation et de photogreffage

General investigations of radical processes in starch were carried out. ESR experiments showed that UV irradiation of starch, both in photosensitized and unphotosensitized experiments, results in chain scission and radical generation on the glucosidic ring. It was shown that benzophenone, deoxybenzoin and derivatives ( 2a – d ) are efficient sensitizers. The ESR spectra were interpreted by assuming superposition of three signals; they were ascribed to radicals formed by chain scission and hydrogen abstraction. In addition photodegradation processes of starch in the presence and absence of photosensitizers were investigated. The amount of chain scissions was followed under various experimental conditions and appeared as a function of the initiator. Moreover, oxygen was shown to enhance the yield of chain scissions: this was explained through the formation of peroxide functions at C 1 ‐position. UV light induced grafting of a vinyl monomer onto starch was also investigated. It appeared that chemical grafting can easily be achieved through a radical reaction. Moreover, the percentages of grafting and degradation were strongly dependent on the photoinitiator. The whole results gave the possibility to select an efficient initiator of the grafting reaction. In the case of methyl methacrylate, α,α‐dimethoxydeoxybenzoin ( 2a ) appears to be the most efficient initiator. However, previous works as well as the present work suggest that the grafting efficiency is strongly dependent on the three components: substrate, monomer, and initiator.