Highly water-soluble and migration stable photoinitiators from meso-2,3-dimercaptosuccinic acid

Abstract

A facile route to prepare highly water-soluble and migration stable Type I and Type II photoinitiators is reported. The mono- or doubly 2-hydroxy-4′-(2-hydroxyethoxy)-2 methylpropiophenone (I2959), 1-hydroxycyclohexyl phenyl ketone (I184) and benzophenone (BP) functionalized meso-2,3-dimercaptosuccinic acid (DMSA) salts with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) or sodium counterion (DMSA-I2959-DBU, DMSA-I184-Na, DMSA-BP-Na, DMSA-BP-DBU) are synthesized in one-pot thiol-Michael addition reaction. Although DMSA-I2959-DBU and DMSA-I184-Na have higher water solubility (e.g. 16 times higher than that of I2959 for the first one) than I2959 and I184, BP functionalized PIs are not stable in water. The synthesized photoinitiators have similar or higher λmax compared to the commercial ones they are synthesized from. The decomposition mechanism and the radical generations are investigated by steady state photolysis and electron spin resonance (ESR). They show reasonable photoinitiating reactivity towards (meth)acrylic double bonds except the I184-based one. The higher migration stability of photoinitiators (DMSA-I2959-DBU has ∼4 times higher than that of I2959), is due to their and unreactive photodecomposition byproducts’ high molecular weight.