title: Photoinduced Acrylate Polymerization: Unexpected Reduction in Chain Branching.
abstract: The branching stemming from midchain radical formation in n-butyl acrylate polymerization is investigated via melt-state (13) C NMR measurements. The dependence of the degree of branching (DB) on the monomer conversion of the system is examined for photoinduced polymerizations, revealing a steady increase in branching with conversion. For polymerization at moderate light intensities, an increase in branching from 0.03% to 0.37% is observed for polymerizations at 60 °C, which is fivefold below the level of branching observed in thermally initiated polymerizations under otherwise identical reaction conditions. The reason for this overall reduction in branching remains momentarily unclear; yet, a strong dependence of branching on light intensity is observed. While polymerization under a 1 W LED lamp results at almost full monomer conversion in branching degrees of 0.22%, polymerization under a 400 W lamp yields 1.81% of chain branches.
authors.affiliation: Polymer Reaction Design Group, Institute for Materials Research (IMO), Universiteit Hasselt, Agoralaan Building D, B-3590, Diepenbeek, Belgium.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Wenn
authors.affiliation: Nuclear Magnetic Resonance Spectroscopy Group, Institute for Materials Research (IMO), Universiteit Hasselt, Agoralaan Building D, B-3590, Diepenbeek, Belgium.
authors.forename: Gunter
authors.initials: G
authors.lastname: Reekmans
authors.affiliation: Nuclear Magnetic Resonance Spectroscopy Group, Institute for Materials Research (IMO), Universiteit Hasselt, Agoralaan Building D, B-3590, Diepenbeek, Belgium.|IMEC Associated Lab IMOMEC Wetenschapspark 1, 3590, Diepenbeek, Belgium.
authors.forename: Peter
authors.initials: P
authors.lastname: Adriaensens
authors.affiliation: Polymer Reaction Design Group, Institute for Materials Research (IMO), Universiteit Hasselt, Agoralaan Building D, B-3590, Diepenbeek, Belgium.|IMEC Associated Lab IMOMEC Wetenschapspark 1, 3590, Diepenbeek, Belgium.
authors.forename: Thomas
authors.initials: T
authors.lastname: Junkers
mesh_terms: D000179:Acrylates / Q000138:chemical synthesis / Q000737:chemistry*; D007700:Kinetics; D008027:Light; D009682:Magnetic Resonance Spectroscopy; D058105:Polymerization / Q000528:radiation effects*; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: D000179:Acrylates; D011108:Polymers; C032490:n-butyl acrylate; C036658:acrylic acid
keywords: NMR spectroscopy; acrylates; kinetics (polym.); midchain radicals; photopolymerizations