Effect of N-phenylmaleimide on a novel chemically bonded polymerizable photoinitiator comprising the structure of planar N-phenylmaleimide and benzophenone for photopolymerization

A novel chemically bonded polymerizable photoinitiator 4-[(4-maleimido)phenoxy]benzophenone (MPBP) comprising the structure of planar N-phenylmaleimide (NPMI) and benzophenone (BP), compared with the physical mixtures of NPMI/BP or NPMI/4-hydroxybenzophenone, was investigated to disclose the mutual influence between NPMI and BP. A BP derivative, 4-phenoxylbenzophenone, was selected as the model compound. Electron spin resonance spectra of such photoredox systems indicated MPBP and BP possess the same initiation mechanism. The large red-shifted pi-pi* absorption of MPBP should be because of the phenoxyl group in MPBP but not the maleimide group. The photopolymerization of methyl methacrylate (MMA) and 1,6-hexanediol diacrylate (HDDA) initiated by those systems, using the unsaturated tertiary amine N,N-dimethylaminoethyl methacrylate (DMAEMA) as the coinitiator (H donor), was studied through dilatometry and photo-differential scanning calorimetry. The results showed that MPBP was more efficient for the photopolymerization of MMA and HDDA than its physical mixture counterpart. The high efficiency of MPBP may be mainly because of the interaction between NPMI and BP group but not the phenoxyl group alone. A certain amount of NPMI can accelerate the photopolymerization when added to the formulations, but too much NPMI will eventually decrease the photoefficiency. (c) 2006 Society of Chemical Industry.