Reinvestigation of the Mechanism of the Free Radical Polymerization Photoinitiation Process by Camphorquinone–Coinitiator Systems: New Results

Abstract

AbstractSummary: Comparative studies of photoinitiation processes using camphorquinone (CQ) and benzophenone (BP) as light absorbers were performed. The experimental results show that after the transformation of (phenylthio)acetic acid (PTAA) into its tetrabutylammonium salt (PTAA AS), a substantial decrease of the polymerization photoinitiation ability for the CQ–PTAA AS pair in comparison to the CQ–PTAA pair is observed. The mechanism of the photoinitiated polymerization for the tested photoredox pair was clarified based on laser flash photolysis experiments obtained using benzophenone as an electron acceptor and (phenylthio)acetic acid and its tetrabutylammonium salt as electron donors in solution in MeCN. It is documented and deduced that the photoreduction of benzophenone in the presence of (phenylthio)acetic acid and its tetrabutylammonium salt occurs by a photoinduced electron transfer process, while for CQ as initiator, the free radicals are formed by hydrogen atom abstraction by the triplet state of camphorquinone.Schematic of the transients formed after an electron‐transfer process for benzophenone–PTAA and benzophenone–PTAA AS pairs.magnified imageSchematic of the transients formed after an electron‐transfer process for benzophenone–PTAA and benzophenone–PTAA AS pairs.