Photoinitiated Free Radical Polymerizations of Styrene and Methyl Methacrylate by Triphenylsulfonium Salts

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Abstract
Triphenylsulfonium salts with anions such as C1− (1), Br− (2), I− (3), and BF4 − (4) were prepared, and the photoistiation ability of these compounds was investigated. Compounds (1), (2), and (4) initiated the photopolymerization of styrene and -mefiyl metGcrylate. These polymerizations were inhibited by the addition of benzoquinone as a radical scavenger. The overall polymerization rate was proportional to the square root of the concentration of the sulfonium salt employed and first order to the monomer concentration. Further, copolymerization of styrene and methyl methacrylate by (2) showed a typical monomer reactivity ratio of free radical polymerization. The above results indicate that these photopolymerizations proceed through a free radical mechanism. In addition, the photoinitiation ability of these compounds increased in the order (2) > (1) > (4). This result suggested the possibility of initiation of rgdical-polymerization by the phenyl radical which was generated from a one-electron transfer mechanism. On the other hand, Compound (3) did not initiate photopolymerization of styrene or methyl methacrylate.