ABSTRACT:In aqueous solutions, 2,3-butanedione (biacetyl: BA) served as a sensitizer for the photopolymerization of acrylamide (AA). The presence of inorganic salts such as KSCN, KSeCN, and NaN3 increased not only the rate of polymerization but also the molecular weight of the polymer. On the other hand, Na2SeO3 increased the rate of polymerization markedly with apparently normal kinetic behavior. In the absence of any salt, the triplet excited state of BA was shown to act as a degradative chain transfer agent as well as a photo-sensitizer. The mechanism of this characteristic photosensitized polymerization is discussed. KEY WORDSPhotopolymerization / Sensitizer / Acrylamide / 2,3-Butanedione / Biacetyl / Triplet Excited State / Inorganic Anion / Degradative Chain Transfer / The photopolymerization of vinyl monomers sensitized by organic carbonyl compounds has been investigated by many workers.1 Most of these studies were carried out in organic solvents. 2,3-Butanedione (Biacetyl: BA), an a-diketone soluble both in water and organic media, was used as an efficient sensitizer for the polymerizations of monomers such as styrene and methyl methacrylate. 2 -5 But there has been little study on BA-sensitized polymerization in an aqueous medium. Recently, Encina and his coworkers 6 reported that in the polymerization of N-vinyl-2-pyrrolidone and vinyl acetate, BA was a poor initiator and relatively high photoinitiation efficiencies were achieved only in the presence of methanol or water, by which BA was solvated giving a hydroxy-substituted alkanone effective at 300 nm irradiation.We studied the photopolymerizations of vinyl monomers such as acrylonitrile, styrene, methyl methacrylate, and acrylamide (AA) sensitized by organic dyes 7 and metal complexes.8-14 In a previous paper, 13 we reported the photopolymerization of AA sensitized by the [Co(NH 3 ) 6 ]Cl 3 or [Co(enh]Cl 3 (en: ethylenediamine)-KSCN system in aqueous medium. These metal complexes alone could not initiate the photopolymerization of AA, but could sensitize the polymerization markedly in the presence of KSCN.We thus studied such effects of inorganic salts on the photopolymerizations in aqueous solutions. BA is soluble in water and has a relatively unique property of exhibiting phosphorescence as well as fluorescence in a fluid solution at room temperature. Then, the effects of inorganic salts on the photopolymerization of AA sensitized by BA were studied kinetically and spectroscopically.Contrary to the normal kinetic behavior of radical polymerization, 15 the addition of some 565