title: Quantifying photoinitiation efficiencies in a multiphotoinitiated free-radical polymerization.
abstract: Online size exclusion chromatography-electrospray ionization-mass spectrometry (SEC/ESI-MS) is employed for quantifying the overall initiation efficiencies of photolytically generated radical fragments. In a unique experiment, we present the first quantitative and systematic study of methyl-substituted acetophenone-type photoinitiators being employed in a single cocktail to initiate the free-radical polymerization of methyl methacrylate (MMA) in bulk. The photoinitiators are constituted of a set of two known and four new molecules, which represent an increasing number of methyl substituents on their benzoyl fragment, that is, benzoin, 4-methylbenzoin, 2,4-dimethylbenzoin, 2,4,6-trimethylbenzoin, 2,3,5,6-tetramethylbenzoin, and 2,3,4,5,6-pentamethylbenzoin. The absolute quantitative evaluation of the mass spectra shows a clear difference in the initiation ability of the differently substituted benzoyl-type radical fragments: Increasing the number of methyl substituents leads to a decrease in incorporation of the radical fragments.
authors.affiliation: Preparative Macromolecular Chemistry, Institut für Technische, Chemie und Polymerchemie, Karlsruhe Institute of Technology, KIT, Engesserstr. 18, 76128 Karlsruhe, Germany.
authors.forename: Dominik
authors.initials: D
authors.lastname: Voll
authors.forename: Andrea
authors.initials: A
authors.lastname: Hufendiek
authors.forename: Thomas
authors.initials: T
authors.lastname: Junkers
authors.forename: Christopher
authors.initials: C
authors.lastname: Barner-Kowollik
mesh_terms: D002850:Chromatography, Gel; D005609:Free Radicals / Q000737:chemistry*; D020366:Methylmethacrylate / Q000737:chemistry*; D055668:Photochemical Processes; D058105:Polymerization / Q000528:radiation effects; D021241:Spectrometry, Mass, Electrospray Ionization
chemical_list: D005609:Free Radicals; D020366:Methylmethacrylate