The influence of H-donors on the photodecomposition of selected water-soluble photoinitiators

Evidence is presented which shows that aqueous solutions of 4-(trimethylammoniummethyl)benzophenone chloride, BP2, are photochemically stable within experimental conditions applied. However, in aqueous solutions of BP2 which contain compounds capable of H-atom donation, then BP2 undergoes rapid decomposition. In terms of the enhancement of photodecomposition, the observed order is poly(vinyl alcohol) > propan-2-ol > ethanol > propan-1-ol > glucose > 1,3-propanediol > 1,2-ethanediol > methanol.

By contrast, 4-(sulphomethyl)benzil sodium salt, BZ1, is rapidly photodecomposed when irradiated in aqueous solution even in the absence of additional H-atom donors.

Information is given which shows that various monomers have the ability to reduce the level of photodecomposition of aqueous solutions of BP2 which contain propan-2-ol. Thus, 2-hydroxyethyl acrylate> 2-hydroxypropyl acrylate > acrylic acid in terms of reducing the extent of photodecomposition. In addition, details are presented regarding the concentration dependence of this photodecomposition process with regard to the presence of 2-hydroxyethyl acrylate. Finally, aspects of the photodecomposition of BP2 and BZ1, present in regenerated cellulose film, are considered.