Demet Karaca Balta

One‐Component Thioxanthone Acetic Acid Derivative Photoinitiator for Free Radical Polymerization

Acetic acid–based thioxanthone (TXCH2COOH) 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 TXCH2COOH is similar to the parent thioxanthone and the triplet lifetime was calculated as 2.3 μs at 630 nm.

Universality in gelation of epoxy acrylate with various photoinitiators: a photo differential scanning calorimetric study

Photo-differential scanning calorimetric (Photo-DSC) technique was used to study the gelation of P-3038 (epoxy acrylate (EA) 75% and tripropyleneglycoldiacrylate (TPGDA) 25%) in the presence of various thioxanthone-based initiators, namely, thioxanthone (TX), 5-thia-naphtacene-12-one (TX-NP), 2-(carboxymethoxy) thioxanthone (TX-OCH2COOH), 2-thioxanthone-thioacetic acid (TX-SCH2COOH), and 2-mercaptothioxanthone (TX-SH). Photopolymerization reactions were performed under identical conditions of temperature, initiator concentration, and UV light intensity. Photo-DSC technique allowed us to monitor the gelation, without disturbing the system mechanically, and to test the universality of the gelation as a function of some kinetic parameters like initiator concentration. During gelation, it was observed that all conversion curves present a good sigmoidal behavior by predicting to employ percolation model. Observations around the glass transition point, t g shows that the gel fraction exponents β obeyed the percolation picture. On the other hand, t g was found to be much higher for the crosslinked networks obtained with TX-OCH2COOH and TX-SCH2COOH initiators than those with the other initiators.

“Mono” and “bifunctional” aromatic esterificated benzophenone photoinitiators for free radical polymerization

Aromatic esterificated benzophenone derivatives, benzoic acid 4-benzoyl-phenyl ester (BPBz) and bis-benzoic acid 4-benzoyl-phenyl ester (BisBPBz) were simply synthesized and characterized. The triplet states of the photoinitiators were determined by laser flash photolysis and phosphorescence spectroscopy. The photodecomposition of the initiators was performed by UV light; the increase in the absorption spectra was attributed to the decreasing number of ester groups which led to an increase in ketone groups according to the Photo-Fries rearrangement of aromatic esters. The photoinitiation capabilities for methyl methacrylate (MMA) polymerizations were investigated under air and nitrogen atmospheres. Ester-functional benzophenone photoinitiators were found to be more effective than benzophenone (BP) in the presence of a co-initiator for photoinduced free radical polymerization of MMA. The kinetics of photopolymerization for different formulations which consist of multifunctional acrylates was also studied using the Real-Time Fourier Transform infrared spectroscopy (RT-FTIR) method. The film properties of these formulations were investigated after curing of films by Mini-UV-Cure equipment.

Photodimerization of thioxanthone–anthracene: formation of monochromophoric Type II initiator

Abstract Thioxanthone–anthracene (TX-A) was previously synthesized and used as an initiator for the polymerization of acrylates and methacrylates in air atmosphere. Photodimerization of TX-A was carried out in benzene under light irradiation of >350 nm, and dimer (diTX-A) formation was followed by UV–vis, fluorescence and phosphorescence spectroscopy. The conjugation of anthracene was destroyed after dimerization, and the thioxanthone group was left behind. Therefore, the typical thioxanthone absorption spectrum was seen at 380 nm. TX-A itself does not have phosphorescence emission; however, diTX-A displayed phosphorescence emission spectrum similar to thioxanthone. IR and 1H NMR spectrophotometric techniques also helped to determine the structure of diTX-A. Furthermore, photopolymerization of methyl methacrylate (MMA) in the presence of dimer (diTX-A) was another proof of the photodimerization of TX-A. diTX-A initiated polymerization of MMA as good as thioxanthone in the nitrogen atmosphere and displayed typical Type II initiator behaviour.