Nergis Arsu

Synthesis and characterization of UV-curable vinyl ether functionalized urethane oligomers

Vinyl ether functional group bearing urethane-based oligomers were synthesized by reacting toluene (2,4-2,6) diisocyanate (TDI) with 4-hydroxybutyl vinyl ether (HBVE) and three different diols, namely poly(ethylene glycol), poly(propylene glycol) and α-ω-hydroxy terminated organofunctional poly(dimethyl siloxane). The structures of the oligomers were characterized by FTIR. All resins, except the poly(ethylene glycol) containing one, were successfully polymerized cationically by UV irradiation in the presence of a diaryliodonium photoinitiator and isopropyl thioxanthone (ITX) photosensitizer. Physical properties of UV-cured films such as gel content, solvent resistance, stress–strain and water absorption behaviors, were examined. The stress–strain tests showed that PDMS containing oligomer gives better tensile strength and elongation values when compared with PPG containing one. The curing process was followed quantitatively by monitoring the disappearance of vinyl ether groups by real-time infrared spectroscopy. The reactivity of PDMS containing oligomer was found higher than PPG containing one. In addition, thermal gravimetric analysis of PDMS containing polymeric films gave higher char yield due to their silicone containing structure.

Photoinitiated polymerization of methyl methacrylate by phenacyl type salts

Phenacyl onium salts, namely N-phenacyl-N,N-dimethylanilinium-N,N-diethyldithiocarbamate (Ia), phenacyl-triphenylphosphonium-N,N-diethyldithiocarbamate (II), 1-phenacyl pyridinium-N,N-diethyldithiocarbamate (III), are shown to be efficient photoinitiators for polymerization of methyl methacrylate (MMA). Plausible mechanism of the photoinitiation involves both free radical and zwitterionic processes. Phenacyl radicals formed from the homolytic cleavage of carbon heteroatom bond initiates the free radical polymerization while Lewis bases formed from homolytic cleavage followed by electron transfer or heterolytic cleavage responsible for the zwitterionic initiation. The capability of the salts to act as initiators for the polymerization of multifunctional monomer, trimethylolpropane trimethacrylate (TMPTMA), was also demonstrated.

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.

Magnetic and spin effects in the photoinitiation of polymerization

Application of a moderate external magnetic field increases the efficiency of triplet photoinitiators of polymerization. The reasons for this observation are briefly outlined. Such well-documented magnetic and spin effects as the magnetic isotope effect (MIE) and chemically induced dynamic nuclear and electron polarization (CIDNP and CIDEP) have been observed under the photolysis of photoinitiators. CIDEP results are emphasized. The study of CIDEP under the photolysis of initiators allows the detection and identification of free radicals of initiators and the spin multiplicity of the reacting photoinitiator (triplet or singlet). The transfer of the spin polarization of the initiator free radical to monomers is a promising technique for following radical reaction pathways. The results of a CIDEP study of the sensitized decomposition of phosphine oxide photoinitiators are presented.

Use of 2-(N-methyl-N-phenylamino)-1-phenylethanol as synergist in UV-curing applications

2-(N-Methyl-N-phenylamino)-1-phenylethanol in formulations was used as an aminoalcohol to help reduce the effect of oxygen inhibition and to act as synergist with a Type II initiator. When the aminoalcohol in the formulation containing Trimethylolpropane triacrylate (TMPTA) is replaced by the NMDEA at the 10% level, the same amount of cure is obtained after one pass as when 1% aminoalcohol is used. It was found that the aminoalcohol was efficient at reducing oxygen inhibition and act as an excellent synergist for isopropylthioxanthone.

Photoinitiated polymerization of ethyl cyanoacrylate by phosphonium salts

The photoinitiated polymerization of ethyl cyanoacrylate (ECA) by benzyl triphenylphosphonium hexafluoroantimonate (BP+) and (anthracen-9-ylmethyl)triphenylphosphonium hexafluoroantimonate (MAP+) was studied. Zwitterionic and free radical mechanisms which involved homolytic and heterolytic decomposition of the phosphonium salts are discussed. The anthracene-sensitized photopolymerization of ECA was also demonstrated. Die photoinitiierte Polymerisation von Cyanacrylsaureethylester (ECA) mit Benzyltriphenylphosphoniumhexafluorantimonat (BP+) und (Anthracen-9-ylmethyl)triphenylphosphoniumhexafluorantimonat (MAP+) als Photoinitiatoren wurde untersucht. Ein zwitterionischer sowie ein radikalischer Mechanisms, einschlieslich der homolytischen und heterolytischen Zersetzung der Phosphoniumsalze, werden diskutiert. Die mit Anthracen initiierte Photopolymerisation von ECA wurde ebenfalls untersucht

Critical Exponents of Photoinitiated Gelation at Different Light Intensities

A photo-differential scanning calorimetric (Photo-DSC) technique was used to study the photoinitiated radical polymerization of a 75% epoxy diacrylate (EA) and 25% tripropyleneglycoldiacrylate (TPGDA) mixture with 2-mercaptothioxanthone (TX-SH) as photoinitiator by using different light intensities. Photopolymerization reactions were carried out under identical conditions of temperature and initiator concentration. It was observed that all conversion curves during gelation at various UV light intensities present good sigmoidal behavior as predicted by the percolation model. Observations around the critical time, called the glass transition point (tg), taken for polymerization to reach the maximum rate (Rp max) show that the gel fraction exponents β obeyed the universal percolation picture. On the other hand, Rp max, t g, and final conversion values were found to be dependent on the UV light intensity.

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.

Modification of multiwall carbon nanotube by thiol-ene click chemistry

Abstract Thiol-ene click chemistry was used for the preparation of polystyrene grafted multiwall carbon nanotubes (MWCNTs) via the thermal initiation method. The thiol end-functional PSt (PSt-SH) was prepared by the nucleophilic substitution reaction of the bromide end groups of PSt obtained by atom transfer radical polymerization. PSt-SH grafted to the surface of the MWCNTs by thiol-ene click chemistry via the thermal initiation method.

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.