Structure-reactivity relationships of novel α-hydroxyketone-functionalized cyclopolymerizable and cyclopolymeric photoinitiators

Three novel monomeric photoinitiators (I2959-NTBDA, I2959-NDAA and I2959-NAA) with 1,6-heptadiene structure and based on 2-hydroxy-4 '-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) and the photoinitiating cyclocopolymer of the first (M-n = 28000 D has six-membered rings in the backbone) are synthesized and characterized by NMR, FTIR, UV-Vis spectrometry and thermogravimetry. I2959-NTBDA is synthesized from reaction of tert-butyl alpha-bromomethacrylate with amine functionalized I2959; cleavage of tert-butyl groups gives I2959-NDAA. Synthesis of I2959-NAA involves reaction of allylamine derivative of I2959 and acryloyl chloride. These photoinitiators have lambda(max) (269-280 nm) and epsilon values (13700-17300 M-1 cm(-1)) similar to I2959. The chemical mechanism investigated by electron spin resonance (ESR) and steady state photolysis confirms generation of isopropyl ketyl radicals. Structure-reactivity relationships of the monomeric photoinitiators studied during polymerizations of 2-hydroxyethyl methacrylate (HEMA), poly(ethylene glycol) diacrylate (PEGDA, M-n = 575 D) and trimethylol propane triacrylate (TMPTA) show the order of reactivity I2959-NDAA > I2959-NTBDA > I2959-NAA, indicating that both electronic and steric effects of PI structures are effective. The migration stability of the residual I2959-NTBDA in the cured film is much higher than that of I2959 due to incorporation into the network structure, indicating their potential for producing environmentally friendly materials.