Difunctional monomeric and polymeric photoinitiators: Synthesis and photoinitiating behaviors

• First methacrylates with two identical photoinitiating groups; and their polymers.
• PI groups are based on acetophenone, benzophenone and Irgacure 2959.
• Photoinitiation efficiencies were determined using photo-DSC.
• BP-based PIs showed much higher efficiency than BP, even at half-concentration.
• Irgacure 2959-based PIs found to be promising type I photoinitiators.

The first methacrylate monomers with two type I or type II side-chain photoinitiating groups (PI1, PI2 and PI3) are synthesized from reactions of 2-(chloromethyl)acryloyl chloride and 4-hydroxybenzophenone, 4-hydroxyacetophenone or 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone (Irgacure 2959), and polymerized, giving polymeric photoinitiators (PPI1, PPI2 and PPI3). PI1 is also copolymerized with N,N-dimethylaminoethyl methacrylate (DMAEM) to investigate the photoinitiation efficiency of the resulting polymer featuring built-in amine coinitiator. Activities of these photoinitiators together with acetophenone (AP), benzophenone (BP) and Irgacure 2959 are investigated in photopolymerizations of hexane-1,6-diol diacrylate, using photodifferential scanning calorimeter and the kinetic parameters are correlated with the structures of the photoinitiating systems. The results show different photoinitiating activities compared to small molecule commercial analogs: BP-based photoinitiators, PI1, PPI1 and PPI(PI1-co-DMAEM), are found to be particularly efficient compared to BP. The Irgacure 2959-based ones appear to be promising as type I photoinitiators.

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