Effect of Amine Structure on Photoreduction of Hydrogen Abstraction Initiators

Abstract

The photocuring rates of acrylate monomers initiated by abstraction type photoinitiators (benzophenone, isopropylthioxanthone, and N-methylmaleimide) and a series of structurally different tertiary amine combinations are reported. Photo-DSC results confirm that transferable hydrogens on tertiary amines are essential for efficient acrylate polymerization. Laser flash photolysis experiments were carried out to define the electron/proton transfer reactions which occur between excited triplet states of the photoinitiators and tertiary amines. In the case of N-methylmaleimide, an intermediate radical anion was detected for amines with no readily transferable proton. This confirms that the photoreduction of the triplet state of N-substituted maleimides by tertiary amines occurs by an electron/proton transfer when the tertiary amine electron donor has a transferable proton.