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Abstract: The reactions of aminyl and aminoalkyl radicals, derived from primary or secondary amines toward two reactants – a double bond (methylacrylate MA) and a phenol (hydroquinone methylether HQME) – were investigated for the first time through Laser Flash Photolysis (LFP). The aminoalkyl radicals were directly observed and studied by LFP; their structure was confirmed by ESR spin trapping experiments. The reactivity of the aminyl radical was also monitored by LFP using an indirect method. Compared to aminyl radicals, the addition of aminoalkyl radicals to MA is very efficient (rate constant: 0.7–1.7×107 M−1s−1 vs. <105 M−1s−1) whereas the interaction with HQME is rather low (<5×105 M−1s−1 vs. 1.1×108 M−1s−1). Quantum mechanical calculations allow a discussion of the aminyl vs. aminoalkyl radical reactivity. [Copyright &y& Elsevier]

The free radical polymerization of low viscosity methacrylate blends upon a LED irradiation at 405 nm under air is carried out using Cu(I)/iodonium salt/tin(II) organic derivative as photoinitiating systems. The system exhibits a high reactivity; where tin derivative plays a crucial role. It operates through a catalytic cycle in which Cu(I) is regenerated and can be used at low concentrations (0.1-0.3 wt %). Remarkable performances are achieved. At first, a final methacrylate conversion of 82% after 40 s in 1.4 mm thick samples is obtained for an irradiance of 35 mW/cm2 whereas such a conversion is only reached only when using a Cu(I)/iodonium salt system under a 200 mW/cm2 light exposure. Second, a 55% conversion is still obtained after 150 s under a very low irradiance (2.5 mW/cm2). Third, almost tack-free thick samples (1.4 mm) under air are produced upon sunlight exposure (65% of conversion for the 1.4 mm thick sample after 90 s of irradiation). Fourth, the photocuring of clear samples as thick as 9 cm (and presumably even more) with an impressive homogeneity through the entire polymerizable medium is feasible; the photopolymerization of 8.5 cm thick filled samples is also realized. Fifth and last, a lateral polymerization beyond the irradiated area is demonstrated with unprecedented extensions of 8 mm (tin(II) = 1.3%) and 28 mm (tin(II) = 8%), which allows polymerization reactions to occur in shadowed areas. The chemical mechanisms are studied by steady state photolysis and ESR-spin trapping experiments. The subsequent role of the hydroperoxides (ROOH) formed during the polymerization reaction is a key point i.e. for the polymerization in shadowed areas (thick and filled samples), these latent species (ROOH) will be generated from the oxygen inhibition and can diffuse for a full curing of the samples through a ROOH/Cu(I) redox initiation. [ABSTRACT FROM AUTHOR]

Three new triphenylamine derivatives bearing formyl groups were synthesized and tested for their suitability as photo-initiators for multi-photon lithography. The efficiency of the photo-polymerization was tested by two different setups and for a variety of applications. Based on their broad fabrication window, the well-defined 3D prints in the sub-micron range (resolution and aspect ratio), the solubility, we demonstrate these photo-initiators are a viable alternative to standard photo-initiators. [ABSTRACT FROM AUTHOR]

Novel functionalized ketones (K_PY) incorporating one/two pyrene moieties or a pyridinium chromophore for radical and/or cationic polymerization under soft irradiation conditions (Xe–Hg lamp, halogen lamp) are proposed. These compounds exhibit red-shifted absorptions and enhanced molar extinction coefficients (e.g. for near visible lights (395 nm), the absorption can be increased by a factor of 20). The ability of the various K_PY/amine couple in the radical polymerization of an acrylate (up to 75% conversion) and the different K_PY/diphenyliodonium salt system in the cationic polymerization of an epoxide (up to 70% conversion) is often better than that of reference compounds. These structures are also very efficient to overcome the oxygen inhibition. Molecular orbital calculations, ESR experiments and laser flash photolysis allow an investigation of the absorption properties, the excited state processes and the involved initiation mechanisms. [ABSTRACT FROM AUTHOR]

Abstract: In this work, 29Si nuclear magnetic resonance and Fourier-transformed infrared spectroscopy were combined to study the hydrolysis and polycondensation of γ-aminopropyltriethoxysilane (γ-APS), both in the liquid sol state and in the film state. γ-APS sols were prepared in methanol or ethanol solvent in the pH range from 5.7 to 11 and deposited. The aim of the present study was to get the most complete picture in regard to the chemical events and time scale of these events. Transesterification reactions between γ-APS and methanol result in faster kinetics in methanol compared to ethanol. γ-APS films were deposited on aluminium and dried at ambient conditions (23°C, 55% relative humidity). The silane films reached a chemical equilibrium in a couple of minutes (natural pH of 11) to 1h (pH 7) depending on the pH of the silane solution. From a practical perspective, the results obtained here might give some clues to define an optimized schedule for the application of γ-APS coupling agent to metals. [Copyright &y& Elsevier]

Abstract: A polystyrene-block-poly(ethylene oxide) (PS-b-PEO) copolymer is synthesised in an original manner by nitroxide mediated polymerization of styrene from a PEO macroalkoxyamine. Minor amounts of side products are unavoidably present in the final polymer, including: traces of macroalkoxyamine, PEO-b-PS-b-PEO triblock copolymer—a product of the recombination of PEO-b-PS macro-radical during the initial stage of the polymerization—and hPS—a product of thermal initiation. These species do not represent more than a little percentage of the total composition. They are hardly detectable with classical SEC. We use liquid chromatography at critical conditions (LC-CC), 2D chromatography and LC-CC-NMR to get an exhaustive description of the chemical composition distributions (CCD) and of the molar mass distributions (MMD) of all the minor species quoted above. The results are consistent with the synthesis route and prove the accuracy of the LC-CC based techniques in analysing even very small amounts of species. [Copyright &y& Elsevier]

This investigation presents the use of a photoredox catalyst "G1" as a photoinitiating system for free radical/cationic hybrid polymerization under mild irradiation conditions. The G1 system (G1/iodonium salt/ N -vinylcarbazole), can simultaneously initiate the free radical and cationic polymerization reactions upon exposure to a visible (405 nm) light from a Light Emitting Diode (LED) source. The multicomponent G1 system is able to simultaneously generate radical and cationic species through a catalytic photoredox process. The curing of thin samples (25 μm), thick samples (1.4 mm) as well as the manufacture of hybrid system/glass fibers composites (˜2 to 4 mm thickness) was realized and the influence of the ratio of cationic/radical monomer blends on the polymerization kinetics was studied. The use of G1 in visible light photoinitiating system for the access to composites and 3D printing experiments was particularly outlined. G1 was also shown to have low levels of migration from the cured materials. When compared to reference materials ("F1", a similar copper complex and an anthracene derivative, dibutoxy anthracene), G1 showed better polymerization efficiency. The initiation efficiency was investigated through the real-time Fourier transform infrared (RT-FTIR) spectroscopy and optical pyrometry. Dynamical Mechanical Analysis has been used to determine the glass temperature transition of the cured hybrid system as a complementary technique. [ABSTRACT FROM AUTHOR]

Photopolymerization under near-infrared (NIR) light is challenging due to the low energy of the absorbed photon but, if successful, presents significant advantages. For example, this lower energy wavelength is safer than UV light that is currently the standard photocuring light source. Also, NIR allows for a deeper light penetration within the material and therefore resulting in a more complete curing of thicker materials containing fillers for access to composites. In this study, we report the use of three-component systems for the NIR photopolymerization of methacrylates: (1) a dye used as a photosensitizer in the NIR range, (2) an iodonium salt as a photoinitiator for the free radical polymerization of the (meth)acrylates, and (3) a phosphine to prevent polymerization inhibition due to the oxygen and to regenerate the dye upon irradiation. Several NIR-absorbing dyes such as a cyanine borate and a silicon–phthalocyanine are presented and studied. Systems using borate dyes resulted in methacrylate monomer conversion over 80% in air. We report three types of irradiation system: low-power LED at 660 and 780 nm as well as a higher power laser diode at 785 nm. The excellent performance reported in this work is due to the crucial role of the added phosphine. [ABSTRACT FROM AUTHOR]

ABSTRACT The first use of a new mechanosynthesized copper complex (Cu(acac)(2dppba)) as a initiator for the redox and redox photoactivated polymerization of methacrylates under air is proposed. This paper (i) describes the mechanosynthesis of this complex, (ii) outlines the relative efficiency of the complex for redox polymerization (mechanosynthesized product vs. solvent synthesized product), (iii) follows the polymerization enhancement under a 405 nm light, and (iv) demonstrates the high performance of this complex in near infrared photoactivated redox polymerization where a completely colorless polymer is obtained (unprecedented under NIR irradiations, 785 nm, here). The light activated polymerization exhibit higher conversions, better time controls (activation control) and higher surface conversions than redox polymerization. The mechanosynthesis is well characterized by two solvent-free methods (visual color change and Electron Spin Resonance) and two solvent-based methods (high resolution-electrospray ionization-mass spectrometry (HR-ESI-MS) and UV-vis spectrometry). The involved mechanisms are discussed. Mechanosynthesis of copper complexes opens new perspectives for copper (photo)redox polymerization catalysts as the environmental impact and economical costs of the complex synthesis are significantly reduced. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3646-3655 [ABSTRACT FROM AUTHOR]

Aconitum karacolicum from northern Kyrgyzstan (Alatau area) contains about 0.8–1% aconitine as well as other aconite derivatives that have already been identified. In this paper, we compare several methods for the further purification of an Aconitum karacolicum extract initially containing 80% of aconitine. Reverse-phase flash chromatography, reverse-phase semi-preparative HPLC, centrifugal partition chromatography (CPC) and recrystallization techniques were evaluated regarding first their efficiency to get the highest purity of aconitine (over 96%) and secondly their applicability in a semi-industrial scale purification process (in our case, 150 g of plant extract). Even if the CPC technique shows the highest purification yield (63%), the recrystallization remains the method of choice to purify a large amount of aconitine as i) it can be easily carried out in safe conditions; ii) an aprotic solvent is used, avoiding aconitine degradation. Moreover, this study led us to the identification of lappaconitine in Aconitum karacolicum , a well-known alkaloid never found in this Aconitum species. [ABSTRACT FROM AUTHOR]

Abstract: Light-emitting electrochemical cells (LECs) based on a semiconducting polymer blended with lithium salt and novel polyelectrolytes have been studied. Random copolymers of poly(ethylene glycol) methyl ether methacrylate have been developed in order to increase their glass transition temperature (T g) above room temperature. Devices have been optimized and successfully turned on upon heating. Cooling devices under applied voltage bias down to room temperature leads to frozen PN junctions. The relaxation of these junctions over voltage-free storage is studied. The higher the T g, the longer the shelf-life of the junctions. This research opens the route to room temperature stable organic PN junctions for use in organic electronic devices such as light-emitting diodes, photovoltaic solar cells and other organic electronic devices. [Copyright &y& Elsevier]

Abstract: Low sample recovery may represent an important drawback in liquid chromatography at the critical adsorption point (LC-CAP) if the critical eluent is not carefully fitted to the system. So far, this problem was often overlooked and only few experimental examples can be found in literature. We showed that in the case of polystyrene (PS) in a tetrahydrofuran (THF)/n-hexane critical mixed eluent, PS with molar masses higher than 100kgmol−1 were not eluted from a tandem of two columns packed by bare silica gels with 30nm and 100nm pore size, respectively. The polymer trapped within the columns was well recovered after injection of a small volume of pure THF as demonstrated using 2D chromatography. We studied PS conformations by means of small angle neutron scattering and found that the THF/n-hexane critical eluent is in fact a theta solvent for PS. By replacing it by a CH2Cl2/n-hexane critical mixture, which is a good solvent for PS, the limits of reduced sample recovery was displaced towards far higher molar masses. Thus, thermodynamic quality of eluent – theta or good solvent – plays an important role on the phenomenon of sample recovery. [Copyright &y& Elsevier]

Rectifying antennas are often prensented as a potentiel technological breakthrough for energy harvesting. First theorized in the 1970's, the downsizing of an antenna coupled with a rectifier has become technologically achievable with the progresses of fabrication techniques such as electron beam or photolithography. However, reaching infrared or visible region of the electromagnetic spectra still entails challenges on the integration of a rectifier operating in the terahertz range. New bottom up approaches are likely to bring a promising solution to this issue. To improve our understanding of the key points of rectifying antennas' design for the infrared and visible light, and the challenges of device fabrication, this work reviews the progresses of this technology, going back from the first historical RF energy harvesting systems and covering the most innovative trends to this date. [ABSTRACT FROM AUTHOR]