Design of new Type I and Type II photoinitiators possessing highly coupled pyrene–ketone moieties

Abstract

New Type I and Type II photoinitiators based on 2,2-dimethoxy-2-phenylacetophenone (DMPA), benzophenone (BP) and thioxanthone (TX) linked to a pyrene (Py) moiety (Py_DMPA, Py_BP, Py_TX) are proposed here for the free radical polymerization of acrylates and the cationic polymerization of epoxides and vinylethers under a Xe–Hg lamp, laser diode at 405 nm or a halogen lamp. Excellent polymerization profiles using Py_DMPA and Py_BP are obtained, i.e. better than those recorded with the reference compounds (DMPA and BP). Specifically, Py_DMPA and Py_BP absorb in the near UV-visible range (360–420 nm range; absorption red-shift ∼15 nm), exhibit huge e values (up to a 90 fold increase) and high photochemical reactivity. The mechanisms analyzed by electron spin resonance, steady state photolysis, fluorescence and laser flash photolysis experiments are discussed for the different initiating systems.