Thermally activated pyrrole chalcone free radical photoinitiator with excellent stability to sunlight

Abstract

Chalcone photoinitiator, (2E,6E)-2,6-bis((1H-pyrrol-2-yl)methylene)cyclohexan-1-one (E,E-BPC) efficiently initiated the polymerization of acrylate monomer in the presence of triethanolamine(TEOA), however, it was found that its isomer (2E,6Z)-2,6-bis((1H-pyrrol-2-yl)methylene)cyclohexan-1-one (E,Z-BPC) with TEOA didn’t work. For E,Z-BPC isomerizing back to be E,E-BPC by heating, E,Z-BPC/TEOA was developed to be thermally activated for free radical photopolymerization. Moreover, E,Z-BPC was thermodynamically stable at room temperature under sun-light irradiation in the presence of TEOA owing to its intra-molecular hydrogen bonding of N–H⋯O=C not only preventing E,Z-BPC from isomerizing back to be E,E-BPC at room temperature but also weakening the ability to abstract hydrogen of carbonyl on E,Z-BPC under sunlight irradiation. This thermally activated initiating system based on chalcone with excellent stability stability to sun-light, which was reported firstly, made photopolymerization formulations used conveniently in the way of preparation, storage and application.