Rose Bengal photopolymerization

Fig. 9 Top Rose-bengal-stained fluorescence images of photograft-polymerized regions of Models Ay B and C as a function of photopolymerization time or copolymer composition of CMS (see Fig. 8 legend). These indicate that stem-chain length (Model A), daughter-chain length (Model B) and daughter-chain density (Model C) are well-controlled. Bottom Change in fluorescence intensity as a fimction of photopolymerization time or copolymer composition of CMS CMS Chloromethyl styrene...

The patent and open literature were searched for examples of dye sensitized photopolymerization in which a common monomer (acrylamide), and one of several common dyes (thionine, T methylene blue, MB or rose bengal, RB) were used in combination with a stated concentration of an activator. The polymerization conditions (monomer concentration, light intensity absorbed, and extent conversion) were stated in each case chosen for inclusion. The relative photospeed of the system was calculated based on several corrections to the raw data. We here define the relative photospeed of a composition as the inverse of the exposure time t needed to effect some fixed percentage of monomer conversion. 

The use of dye-sensitized initiation in polymerization dates to 1949 when Bamford and Dewar observed that some vat dyes could sensitize the photopolymerization of styrene. This was quickly followed up hy Gerald Oster s discovery " in 1954 that the polymerization of acrylonitrile and of acrylamide could be photoinitiated by fluorescein, rose bengal, and similar dyes, in the presence of reducing agents (such as phenylhydrazine, ascorbic acid) and oxygen. Remarkably, the amount of dye required for the photoinitiation event was extremely small ( 0.1% of the weight of monomer), and the quantum yield of monomer consumption was in excess of 4000 monomer units per photon. " ... 

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