Characterization of Kinetic Mechanisms of Three-component Photoinitiator Systems for Visible-light Free Radical Polymeri
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1060-LL02-05
Characterization of Kinetic Mechanisms of Three-component Photoinitiator Systems for Visible-light Free Radical Polymerizations Dongkwan Kim, and Jeffrey W Stansbury Craniofacial Biology, University of Colorado at Denver and Health Sciences Center, Aurora, CO, 80045 ABSTRACT Three-component photoinitiator systems generally include a light-absorbing photosensitizer (PS), an electron donor and an electron acceptor, which is usually an onium salt. To investigate the key factors involved with visible-light free radical polymerizations of threecomponent photoinitiators, we used thermodynamic feasibility and kinetic considerations with three-component photoinitiator systems containing either rose bengal (RB) or fluorescein (FL) as the photosensitizer. The Rhem-Weller equation was used to verify the thermodynamic feasibility for the photo-induced electron transfer reaction. Using the thermodynamic feasibility, we suggest three different kinetic mechanisms, which are i) photo-reducible series mechanism, ii) photooxidizable series mechanism and iii) parallel-series mechanism. INTRODUCTION Recently, three-component photoinitiator systems have emerged as an attractive alternative because a number of investigators have illustrated that the kinetic effectiveness of a two-component electron/proton transfer initiator system can be improved by the addition of third component [1-3]. Three-component initiator systems generally include a photosensitizer (PS), which is typically a dye; an electron donor; and a third component, which is usually an electron acceptor such as an iodonium or sulfonium salt. Three-component systems have consistently been found to be faster, more efficient, and more sensitive than their two-component counterparts [1-3]. To investigate the key factors involved with visible-light free radical polymerizations of three-component photoinitiators, we used thermodynamic feasibility and kinetic considerations with three-component photoinitiator systems containing either rose bengal (RB) or fluorescein (FL) as the photosensitizer. The Rhem-Weller equation [4] was used to verify the thermodynamic feasibility for the photo-induced electron transfer reaction. Using the thermodynamic feasibility, we suggest three different kinetic mechanisms, which are i) photoreducible series mechanism, ii) photo-oxidizable series mechanism and iii) parallel-series mechanism. To characterize the different kinetic mechanisms, the rates of polymerization were measured by photo-differential scanning calorimeter (Photo-DSC). EXPERIMENT Materials. The organic dyes rose bengal (RB) and fluorescein (FL) were purchased from Aldrich Chemical Company and were used as received. The monomer 2hydroxyethylmethacrylate (HEMA) was obtained from Aldrich and was used as a model monomer system. Triethylamine (TEA) and N-methydiethanolamine (MDEA) were purchased from Aldrich and were used as electron donors (DH). Diphenyliodonium chloride (DPI) and
triphenylsulfonium hexafluoroarsenate (TPS) were purchased from Aldrich and Alfa Aesar, respec
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