A new photoinitiator for free radical photopolymerization, belonging to the thioxanthone derivatives, was synthesized and characterized. It was found that the compound absorbs over the whole UV–vis spectrum with relatively high absorption coefficients. Fluorescence studies reveal that three different singlet excited states are responsible for this absorption. Phosphorescence and laser flash photolysis evidence the formation of a triplet state from which a photoreduction can occur. Consequently, initiating radicals were formed which are able to initiate the photopolymerization of methyl methacrylate in DMF. Finally, the photopolymerization of acrylates was performed in film at different wavelengths such as 392, 476, 532, and 632 nm, emphasizing the possibility to use this novel photoinitiator when panchromatic irradiation is required.

Acetic acid-based thioxanthone (TXCH2 COOH) was synthesized and characterized and used as a photoinitiator for free radical photopolymerization of methyl methacrylate (MMA) in the absence and presence of a tertiary amine (MDEA) in different solvents. Different absorption properties were observed depending on the solvent. Fluorescence and phosphorescence experiments were also carried out successfully. The fluorescence quantum yield was found to be 0.09 and the phosphorescence lifetime was calculated as 138 ms at 77 K. The photoinitiator undergoes efficient intersystem crossing into the triplet state and the lowest triplet state possesses π-π* configuration. Laser flash photolysis experiments show that transient absorption of TXCH2 COOH is similar to the parent thioxanthone and the triplet lifetime was calculated as 2.3 μs at 630 nm.

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Benzoin, a popular photoinitiator for free radical polymerization of vinyl monomers, was improved by introduction of two methyl thioether substituents. This new benzoin derivative showed an about 50 times higher light absorption in the near-UV spectral region and performed better than the unsubstituted benzoin in polymerization experiments in bulk solutions or films of acrylate monomers when low initiator concentrations are used. Laser flash photolysis, low temperature luminescence experiments and photoproduct studies by mass spectrometry suggest that a slow a-cleavage mechanism (k a ¼ 2.2 Â 10 5 s À1) from the electronic triplet state with a quantum yield of 0.1 is the primary photoreaction to generate the initiating free radicals.

Synthesis of the Benzoxazine based benzophenone (BPBnzx) initiator was achieved and used in free radical photopolymerization of methylmethacrylate (MMA) in the absence and presence of a tertiary amine. The results confirmed that BPBnzx presents a one‐component nature. BPBnzx has better absorption properties compared with BP itself and the one‐component characteristic of the BPBnzx initiator was confirmed by incorporation of the BPBnzx unit into the polymethylmethacrylate (PMMA) main chain, using UV spectroscopy and phosphorescence measurements. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

In this study, a new benzoin-based multi-arm star polymer was synthesized by using ATRP, and characterization was achieved by spectrophotometric and chromatographic methods. Obtained multiarm (Benzoin-PS) m -polyDVB star polymer was employed as a polymeric photoinitiator for polymerization of methacrylates and acrylates. Photophysical properties of this initiator were determined by fluorescence and phosphorescence measurements, the phosphorescence lifetime was calculated as 29 ms hence the lowest triplet state nature was n-π* character, and laser flash photolysis technique was additionally used to get more information about triplet state and triplet lifetime which was calculated as 1.34 ms. Photokinetics of difunctional acrylate such as HDDA was studied with a multi-arm (Benzoin-PS) m -polyDVB star polymeric initiator using Photo-DSC.