Towards new NIR dyes for free radical photopolymerization processes.

The use of cheap and safe near-infrared (NIR) light is still the subject of intense research efforts but remains a huge challenge due to the associated low photon energy (wavelength from 0.78 to 2.5 µm). In this study, a series of 17 NIR dyes mainly based on a well-established cyanine scaffold is proposed. Remarkably, 11 of them were never synthesized before. Markedly, noncharged structures, negatively charged cyanine bearing Na+ as counter cation, and positively charged cyanines bearing (B(Ph)4 -) or (I-) as counter anions were examined as promising NIR light photoinitiating systems. Excellent photoinitiating abilities were found for some reported dyes when used in combination with iodonium salt and amine. Markedly, photothermal effects with a huge heater behavior were also observed for different NIR dye structures. Interestingly, the synthesis of interpenetrating polymer networks (IPNs, e.g., for the polymerization of acrylate/epoxy monomer blends) can also be carried out upon NIR light with the proposed systems.

NIR Sensitizer Operating under Long Wavelength (1064 nm) for Free Radical Photopolymerization Processes.

Free radical polymerization upon near-infrared (NIR) light is still the subject of intense research efforts and remains a huge challenge particularly for long wavelengths (>1000 nm). In this study, a NIR sensitizer operating upon long wavelength (1064 nm) is proposed for an efficient polymerization of acrylate monomers. A new three-component photoinitiating system is developed comprising the NIR sensitizer in combination with an Iodonium salt (Iod) and an amine. Remarkably, the NIR sensitizer (IR 1064) absorbing strongly in all the near infrared region (700-1200 nm) offers the possibility to use a broad range of irradiation wavelengths, i.e., examples are provided at 785 and 1064 nm. Such long wavelengths are characterized by many advantages such as a deeper penetration of light and therefore a better curing of the monomer but it is also much safer than UV light. Excellent performance is observed for the three-component IR 1064/Iod/Amine system under air: high conversion of acrylate functions associated with a fast polymerization time. The use of IR 1064 as NIR sensitizer with a broad NIR absorption is-to the best of current knowledge-never proposed in the literature. The photoinitiating performances are studied using real-time Fourier transform infrared spectroscopy.

High Performance Redox Initiating Systems Based on the Interaction of Silane with Metal Complexes: A Unique Platform for the Preparation of Composites.

Currently, Redox Initiating Systems (RISs) of Free Radical Polymerization (FRP) are mainly based on the interaction of aromatic amines with peroxides (e.g., dibenzoyl peroxide (BPO)) that can be both toxic and unstable. In the present work, we aim to replace these hazardous substances in new RIS that can be peroxide-free and amine-free. Our redox two components (2K) initiating system is based on diphenylsilane (DPS) as reducing agent combined with different metal complexes (Mn(acac)2, Cu(AAEMA)2 or Fe(acac)3) as oxidizing agents. For the new proposed RIS, an excellent reactivity is found for the polymerization of benchmark methacrylate monomers under mild conditions (redox polymerization done under air and at room temperature); remarkably, it is also possible to finely control the gel time. Different techniques (optical pyrometry, Real-Time FTIR spectroscopy, Cyclic Voltammetry and Electron Spin Resonance (ESR)) were used to follow the polymerization processes but also to shed some light on the new redox chemical mechanisms.

New Synthetic Route to an Highly Efficient Photoredox Catalyst by Mechanosynthesis.

Photoredox catalysis based on the [Cu(neo)(DPEphos)]BF4 copper complex allowed getting a significant improvement of the polymerization performances (e.g., thick samples, coatings...) compared to that obtained with other benchmarked photoinitiators in both cationic (CP) and free radical polymerizations (FRP). Nevertheless, as for other copper complexes classically used as photoinitiators in polymer science, the synthesis of these complexes is carried out in a solvent; this fact remains an obstacle to their widespread use because of the cost associated with the use of a solvent and the complex synthesis procedure. In the present study, on the contrary, an outstanding efficient mechanosynthesis of [Cu(neo)(DPEphos)]BF4-purity ≥95% outranking the previous Cu(I) mechanosynthesis-allowed (i) to divide the synthesis time by 170-fold (as only 5 min is necessary to get the complex), (ii) to lower the environmental impact and cut the synthetic costs associated with solvent usage, and (iii) to access a new Cu(I) complex with a counteranion that is impossible to introduce under the traditional chemistry methods (e.g., I-). Reactivities of the mechanosynthesized copper complexes in resins (FRP and CP) confirmed the very high purity of the obtained copper complex by 1H nuclear magnetic resonance spectroscopy and high-resolution electrospray ionization mass spectrometry.

Simultaneous analysis of organochlorine pesticides and polychlorinated biphenyls in air samples by using accelerated solvent extraction (ASE) and solid-phase micro-extraction (SPME) coupled to gas chromatography dual electron capture detection.

An analytical method associating accelerated solvent extraction (ASE) and solid-phase micro-extraction (SPME) in immersion mode combined with gas chromatography dual electrons capture detectors (SPME-GC-2ECD) has been developed and studied for the simultaneous determination of 19 organochlorine pesticides (OCPs) and 22 polychlorinated biphenyls (PCBs) in air samples (active and XAD-2 passive samplers). Samples were extracted with ASE with acetonitrile using the following conditions: temperature, 150 °C; pressure, 1500 psi; static, 15 min; cycles, 3; purge, 300 s; flush, 100 %. Extracts were reduced to 1 mL, and 500 µL of this extract, filled with deionised water, was subject to SPME extraction. Experimental results indicated that the proposed method attained the best extraction efficiency under the optimised conditions: extraction of PCB-OCP mixture using 100-µm PDMS fibre at 80 °C for 40 min with no addition of salt. The performance of the proposed ASE-SPME-GC-2ECD methodology with respect to linearity, limit of quantification and detection was evaluated by spiking of XAD-2 resin with target compounds. The regression coefficient (R (2)) of most compounds was found to be high of 0.99. limits of detection (LODs) are between 0.02 and 4.90 ng m(-3), and limits of quantification (LOQs) are between 0.05 and 9.12 ng m(-3) and between 0.2 and 49 ng/sampler and 0.52 and 91 ng/sampler, respectively, for XAD-2 passive samplers. Finally, a developed procedure was applied to determine selected PCBs and OCPs in the atmosphere.

Concomitant evaluation of atmospheric levels of polychlorinated biphenyls, organochlorine pesticides, and polycyclic aromatic hydrocarbons in Strasbourg (France) using pine needle passive samplers.

In this study, pine needles were used as cost-effective and reliable passive bio-monitors to concomitantly evaluate atmospheric concentrations of three classes of persistent organic pollutants, polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), and polycyclic aromatic hydrocarbons (PAHs). The extraction of persistent organic pollutants (POPs) from needle samples was performed. Eleven PCBs, 11 OCPs, and 15 PAHs were detected and followed through time in needle samples from three sites in the Strasbourg region. The urban and rural sites were more exposed to PCBs than the suburban site. The highest concentration of PCBs was found at the urban site, but the largest number of congeners (10) was detected at the rural site. PCB 189 and 156 were the predominant congeners in the rural site and PCB 70 in the urban site. For OCPs, the rural site displayed the highest concentrations (up to 22.9 ng g(-1)) and number of compounds investigated (9). The high concentration of γ- and ß-hexachlorocyclohexane (HCH) at that time in the urban site was the reason for this result. γ- and ß-HCH were the two predominant compounds in all samples. The suburban and urban sites were the most exposed with PAHs with pyrene, phenanthrene, and acenaphthene being the three predominant compounds in these sites. No specific trend in terms of time was apparent for PCBs and OCPs. However, higher concentrations were detected for some compounds in the first sampling, especially for PAHs, and this is attributed to variations in meteorological conditions (e.g., temperature, wind, rain) and variable inputs from both identified and unidentified sources.

Recent Developments of Versatile Photoinitiating Systems for Cationic Ring Opening Polymerization Operating at Any Wavelengths and under Low Light Intensity Sources.

Photoinitiators (PI) or photoinitiating systems (PIS) usable in light induced cationic polymerization (CP) and free radical promoted cationic polymerization (FRPCP) reactions (more specifically for cationic ring opening polymerization (ROP)) together with the involved mechanisms are briefly reviewed. The recent developments of novel two- and three-component PISs for CP and FRPCP upon exposure to low intensity blue to red lights is emphasized in details. Examples of such reactions under various experimental conditions are provided.