A study on hybrid oligomeric type II photoinitiator

Abstract

AbstractPreparing tailor-made hybrid photoinitiator (PI) for specific applications continues to gain momentum. The hybrid PIs comprising both H-abstraction chromophore and coinitiator moiety are the candidate materials with energy-saving and environment-protection in the photo-curing field. So two oligomeric photoinitiators (OMKs) containing benzophenone (BP) and aliphatic tert-amines chromophore in the main-chain (OMK-2) or side-chain (OMK-1) were synthesized and characterized respectively. Photophysical investigation showed that the absorption maxima of OMKs were around 340 nm, red shifted about 5-10 nm compared to BP. Their initiation efficiencies were found to be higher than that of BP and 4,4’-bis(dimethylamino)benzophenone(MK) respectively. The reaction proceeds via a simple electron-transfer/proton-transfer mechanism. Dynamic NMR data reveal that H-abstraction reacts predominantly via alpha H of aliphatic tertamines, as might be expected on the basis of the lower ionization potential and bond dissociation energy of aliphatic amines compared to aromatic amines. The reaction mechanism of H-abstraction was confirmed by using radical scavenger 2,2,6,6-tetramethylpiperidin-1-oxy(TEMPO), which acts as a probe under photolysis reaction conditions. The volatility and migration were tested under simulated conditions, the result show that OMKs exhibited very low volatility and significantly reduced migration compared to the low molecular analogs. Results showed that the OMKs are the promising candidate as higher efficient PIs with low volatile organic compounds (VOCs) emission and reduced migration. They are suitable for environmental-friendly formulations.