Dual Photo Research Articles

The Preparation of Copolymers Derived from Thiol‐ene/Cationic Systems by Using a Coupling Agent

AbstractA bifunctional monomer with methacrylate and epoxycyclohexyl groups linked by a tetramethyldisiloxane moiety was used as a coupling agent for dual photo and thermally polymerizable Thiol‐Ene/cationic systems. The thiol‐ene system included a tetrafunctional thiol, a trifunctional acrylate and a radical photoinitiator while the cationic system comprised a difunctional epoxycyclohexyl monomer and a cationic photoinitiator. It was found that in a first stage the methacrylate group of the coupling agent reacted with the components of the thiol‐ene system rendering a polysulfide with pendant epoxycyclohexyl groups. In a second stage these pendant groups copolymerized with the epoxy monomer by means of a thermal treatment at 120 °C. When the obtained polymers were analyzed by DMA, an increase in the storage modulus was noticed in comparison with the polymers where no coupling agent was added.

Development of Hybrid Polymeric Materials Based on Thiol‐Ene/Cationic Formulations

AbstractNovel materials were prepared from dual photo and thermal polymerization of hybrid thiol‐ene/cationic systems. In the first stage, the thiol‐ene system proceeded to high conversions, while the cationic photopolymerization was inhibited. The formation of sulfides during this stage was the main factor for the inhibition of the cationic photopolymerization of the epoxy monomers. Once those sulfides were formed, they reacted with the oxonium‐terminated growing polyether chains to form trialkylsulfonium salts. These salts promoted the thermal polymerization of the epoxy monomers in the second stage. The viscoelastic properties of the resulting polymers were measured by DMA.magnified image

3D Image Recording on Photopolymer Films Containing Molecular Composites of a New s-Triazine Monomer and Acrylate Monomer by Dual Photopolymerization

Three dimensional (3D) image recording on photopolymer film was explored using a mixture of s-triazine diepoxy (SEP) and ethylene glycol phenyl ether acrylate (PA) as a monomer to induce cationic and radical polymerization during the holographic recording. The photopolymer films were sensitive to a visible light source and polymerized upon excitation with a visible laser. 3D image was recorded on the photopolymer film by holographic recording using a 491 nm laser. The film containing a molecular composite of SEP and PA showed high diffraction efficiency via dual photo polymerization. Within 10 min of recording the image formation was vivid. In this way 3D screw and a letter image with large viewing angle were obtained onto the photopolymer film. The images were stable for longer than 3 month at RT and 5 hr at 85 degrees C, when read by a visible light.

Dual photo‐ and thermally initiated cationic polymerization of epoxy monomers

AbstractSelective inhibition of the photoinitiated cationic ring‐opening polymerization of epoxides by dialkyl sulfides has provided dual systems that can be “activated” by UV irradiation and then subsequently be polymerized by the application of heat. It is proposed that dialkyl sulfides terminate the initial or growing polyether chains at an early stage to form stable trialkylsulfonium salts. These systems are dormant at room temperature but on thermolysis, the sulfonium salts are capable of reinitiating ring‐opening polymerization. These dual photo‐ and thermal cure systems have potential applications in adhesives, potting resins, and composites. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6750–6764, 2006

Photoelectrochemical reaction mechanisms The reduction of benzophenone and 4-halobenzophenones

Abstract The dual photo- and electro-chemical activation of benzophenone and the 4-halobenzophenones, 4-XC6H4COOPh (X  F, Cl) in acetonitrile solution using channel electrode methodology is reported. In the cases of benzophenone and 4-fluorobenzophenone one-electron reduction leads to the formation of the corresponding radical anions which are stable in the absence of light. Irradiation using light of wavelength 325 nm induced significant photocurrents to pass; this was interpreted in terms of a light-induced disproportionation reaction, initially generating the parent material and the corresponding di-anion, with the latter ultimately leading to the formation of the corresponding alcohols, C6H5CH(OH)Ph and FC6H4CH(OH)Ph. The processes are shown to follow DISP2 mechanisms, in which there is both a significant fraction of back reaction (conproportionation) and also quenching of the photo-excited state of the radical anion by the parent material. In contrast, the reduction of 4-chlorobenzophenone at − 1.61 V (vs. Ag) was found to be accompanied by only tiny photo-currents on irradiation with light of wavelength 325 nm.

Comparison of bone mineral density between athletic and non-athletic Chinese male adolescents.

For the evaluation of the effect of exercise on bone mineral density of adolescent athletes, twenty-nine Chinese male adolescent athletes, each of whom had regular training in his major sport which included baseball, swimming, judo and middle/long-distance running for one to six years and eight age-matched non-athletic controls were included in this study. Bone mineral density (BMD) was measured in all study subjects using dual photo absorptiometry at the second to fourth lumbar spines (L2-4) and the right femoral neck (FN). The results revealed the following: (1) the combined group of athletes had significantly greater BMD of L2-4 (1.08 +/- 0.09 g/cm2) than the control group (0.99 +/- 0.08 g/cm2) and a tendency for greater BMD of FN (1.15 +/- 0.13 g/cm2) than the control group (1.09 +/- 0.13 g/cm2); (2) judo majors had significantly greater BMD of L2-4 than baseball majors (P < 0.05), swimming majors (P < 0.01), track majors (P < 0.05) and controls (P < 0.005); (3) baseball majors had significantly greater BMD of L2-4 than controls (P < 0.05) and greater BMD of FN than swimming majors (P < 0.05), judo majors (P < 0.05), track majors (P < 0.005) and controls (P < 0.005); (4) body weight and body mass index (BMI) had good correlation with BMD of L2-4 and FN in control group, (5) in the combined group of athletes, weight and BMI were only strongly linked to BMD of FN, and not to BMD of L2-4. There was no good correlation between BMI and BMD of L2-4 and FN in any group of athletes. We concluded that (1) physical activity during adolescence may contribute significantly towards increasing BMD of athletes and (2) the training type may provide a specific stimulus for increasing BMD at specific localized sites experienced in training.

Photoelectrochemical reduction of meta-halonitrobenzenes and related species

Dual photo- and electro-chemical activation of m-chloronitrobenzene and m-bromonitrobenzene in acetonitrile solution leads to halide loss through a photo-ECE mechanism. This proceeds via absorption of visible light by the radical anions [X-C6H4NO2]˙–, which is followed by fragmentation forming the C6H4NO2 aryl radical. The latter reacts with the solvent system forming nitrobenzene which is further reduced at the electrode with the generation of [C6H5NO2]˙–. Reduction of m-iodonitrobenzene leads to iodide loss without the need for irradiation. However, this process is accelerated by visible light. In contrast the dual activation of p-cyanonitrobenzene, p-dinitrobenzene, phenyl 4-nitrophenyl sulfone, methyl 4-nitrophenyl sulfone, phenyl 4-nitrophenyl sulfoxide or methyl 4-nitrophenyl sulfoxide failed to induce the leaving of any substituent suggesting that the process may be selective to halo-compounds.

Photoelectrochemical reduction of p-halonitrobenzenes

A detailed and comparative mechanistic study of the photoelectrochemical dehalogenation of the four p-halonitrobenzenes, X-C6H4-NO2(X = F, Cl, Br or I) in acetonitrile solution is reported. In the case of p-iodonitrobenzene, iodide loss is accomplished by electrochemical reduction alone. The formation of I– is shown to take place via an ECE process with the ultimate generation of the radical anion of nitrobenzene. Dual photo- and electro-chemical activation of p-chloronitrobenzene and p-bromonitrobenzene leads to halide loss through a photo-ECE mechanism. This proceeds via absorption of light by the radical anions, [X-C6H4-NO2]˙–, which is followed by fragmentation forming the ˙C6H4NO2 aryl radical. The latter is shown to react with the solvent system forming nitrobenzene which is further reduced at the electrode with the generation of [C6H4-NO2]˙–. The aryl radical is demonstrated to be able to undergo (partial) recombination with added Br– or Cl–. The effectiveness of different electronic transitions in the radical ions, [X-C6H4-NO2]˙–(X = Br, Cl) towards dehalogenation are compared; both radical anions-exhibit transitions centred near 330 and 470 nm in the near UV–VIS part of the spectrum. For the chloro-compound only the former band is effective in stimulating chloride release, whereas for the bromo-compound the excitation of either band causes bromide loss. The long wavelength band of the latter is quantified as being some 5.6 times more effective towards fragmentation on a per photon absorbed basis and this is rationalised using spin selection rules. No loss of fluoride from [F-C6N4-NO2]˙– was observed at any wavelength in the visible region of the spectrum.