Feyza Karasu

Thioxanthone hydroquinone-O,O'-diacetic acid: photoinitiator or photostabilizer?

A photoinitiator for free-radical polymerization based on a thioxanthone chromophore containing two acetic acid functions was synthesized and characterized. Photophysical studies such as fluorescence, phosphorescence, and laser flash photolysis in addition to photopolymerization of acrylates were performed to elucidate the radical generation mechanism involving intramolecular electron transfer from the triplet state followed by decarboxylation. We found that the position of the acetic acid substituent is critical for the photoreactivity. In most solvents and acrylic monomers, if the acetic acid functionality is at the 1-position, the singlet excited states are deactivated rapidly before electron transfer can occur, resulting in negligible photoreactivity. The excited-state deactivation probably involves intramolecular H-bonding deactivation. The intramolecular H-bonding is disrupted by solvents that support intermolecular H-bonding, such as DMF and DMSO, leading to efficient intramolecular photoreaction.

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.

LED-cured self-replenishing hydrophobic coatings based on interpenetrating polymer networks (IPNs)

LED-cured IPN-based coatings bearing hydrophobic functional groups have been developed in order to obtain hydrophobic self-replenishing surfaces with improved mechanical properties. Acrylate/epoxide combinations have been chosen to achieve two different Tgs: a lower one to provide sufficient mobility for self-replenishing behavior and a higher one for sufficient hardness. Detailed characterizations of the mechanical and morphological properties of the IPN coatings, in the absence and presence of covalently bonded fluorinated dangling chains, have been performed. Finally, the self-replenishing behavior of these networks with intrinsic hardness has been investigated. This new approach, which is based on IPN and LED technologies could offer self-replenishing functionality for industrial applications, namely in the automotive or aerospace industry.