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

Photochemistry and Radical Chemistry under Low Intensity Visible Light Sources: Application to Photopolymerization Reactions:

The search for radical initiators able to work under soft conditions is a great challenge, driven by the fact that the use of safe and cheap light sources is very attractive. In the present paper, a review of some recently reported photoinitiating systems for polymerization under soft conditions is provided. Different approaches based on multi-component systems (e.g., photoredox catalysis) or light harvesting photoinitiators are described and discussed. The chemical mechanisms associated with the production of free radicals usable as initiating species or mediators of cations are reported

Microstructural evolution and mechanical properties of SnAgCu alloys

Lead containing solder paste is now considered as an environmental threat. In order to eliminate this undesirable environmental impact associated to their production, a family of lead-free solder joint, Sn-3.8Ag-0.7Cu, is proposed. Microstructural and mechanical data of this solder joint have been acquired and compared with the most common used SnPb solder paste. The evolution of the microstructure as well as the failure mode and the mechanical properties of SnAgCu solder joint are discussed as a function of strain rate, annealing treatments, and testing temperature. Tensile tests have been performed, at temperatures ranging from –50 to +150 °C, on bulk samples. Changes of the mechanical properties of bulk tested samples are actually correlated with microstructural changes, as shown by transmission electronic microscopy investigations

In Silico Design of Nitrocoumarins as Near-UV Photoinitiators: Toward Interesting Opportunities in Composites and 3D Printing Technologies

In this research, 31 nitrocoumarins (including 27 structures never reported in the literature) were designed through molecular orbital calculations and synthesized as high-performance near-UV–visible light photoinitiators of polymerization for a better understanding of their structure/reactivity/efficiency relationship. Based on their photoinitiating abilities examined during the free-radical polymerization (FRP) of acrylates, different coumarins examined in this work can be classified into three main categories: (1) very reactive ones (Coum6,7,11,12&26); (2) moderately reactive nitrocoumarins (Coum1,2,16,20,21,23,25,27&28); and (3) nitrocoumarins of low reactivity (Coum3,4,5,8,9,10,13,14,15,17,18,19,22,24,29,30&31). Different techniques were used in order to understand their photoinitiating abilities as well as the associated chemical mechanisms. The real-time Fourier transform infrared technique has been used to follow the polymerization profiles (reactive function conversion (FCs) vs irradiation time). Different two- and three-component photoinitiating systems based on nitrocoumarin/iodonium salt (or N-phenylglycine (NPG) or ethyl 4-(dimethylamino)benzoate) and nitrocoumarin/iodonium salt/NPG were examined for the FRP of acrylates or/and the cationic polymerization of epoxides upon irradiation with a light-emitting diode at 405 nm as an unharmed and inexpensive irradiation source. Moreover, cyclic voltammetry, fluorescence spectroscopy, UV–visible spectroscopy, and electron spin resonance techniques were also used to provide a full picture of the involved chemical mechanisms. Excellent polymerization performances (i.e., high final reactive FCs and also great rates of polymerization (Rp)) were obtained using these derivatives. Some applications in three-dimensional printing and composite synthesis are reported to highlight the interest of the proposed structures in modern technologies

In-silico based development of photoinitiators for 3D printing and composites: Search on the coumarin scaffold

In this work, the in-silico rational design of new photoinitiators by molecular modeling for specific wavelength (here 405 nm) and specific applications (3D printing, composites) is reported. A large number of (keto)coumarin derivatives were investigated by molecular modeling and their synthesis and more detailed photochemical investigations are based on obtaining structures having both excellent predicted light absorption properties @ 405 nm and high excited state energy levels (to ensure high photochemical reactivity). More particularly, four new families of coumarins were designed (4 of the 19 proposed coumarins were never synthesized (N2,M6,T1,T6)): the first family is based on Nitrocoumarins (N1-N6), the second one on Methoxybenzene-based coumarins and Ethoxycoumarins (M1-M6), the third one on Thiophene-based coumarins (T1-T6) and the last family studied concerns Alkyne-based coumarin (A1). The purpose of this work concerns the study of the photoinitiating ability of these compounds in different monomers for different polymerization processes (free radical, cationic) using FTIR technique. The different compounds reported in this work are very efficient to initiate the free radical polymerization of (meth)acrylates but also the cationic polymerization of epoxides upon mild irradiation conditions using a Light Emitting Diode (LED) at 405 nm as visible light source. Nitrocoumarins were identified as the best candidates for photoinitiation among the different families of coumarins investigated in this work. More precisely, nitrocoumarins are characterized by very good polymerization profiles, great final reactive function conversions (FC) and also high rates of polymerization (Rp). The electrochemical and pho-tochemical properties of the different compounds were also studied to get a deeper insight into the photo-chemical mechanisms supporting the initiation process. A full picture of the involved photochemical mechanisms is provided. Thanks to the astounding polymerization initiating ability of these coumarins, their use in 3D printing applications can be worthwhile. Remarkably, using these compounds, the preparation of photo-composites was possible even in difficult light penetration conditions resulting from the presence of fibers inside the resins

Household LED irradiation under air: cationic polymerization using iridium or ruthenium complex photocatalysts:

Household LED bulbs are used to promote the ring-opening photopolymerization of epoxides in the presence of a photocatalyst (here tris(2-phenylpyridine)iridium [Ir(ppy)(3)] or tris(1,10-phenanthroline)ruthenium(II) [Ru(phen) (3) (2+) ] complex) and a silyl radical source. Remarkably, even under this very soft irradiation (light intensity lower than 10 mW/cmA(2)), excellent polymerization profiles are obtained i.e., this is the first reported use of such very convenient irradiation devices for photopolymerization processes. The role of the silane and other hydrogen donors is outlined

Silyloxyamines as sources of silyl radicals: ESR spin-trapping, laser flash photolysis investigation, and photopolymerization ability:

Two silyloxyamines derived from 8-(pentamethyldisilyloxy)-julolidine and diethyl 3-(pentamethyldisilyloxy)-aniline are proposed as new sources of silyl radicals. The decomposition mechanism, excited state processes and the radical generation are explored by steady state photolysis, laser flash photolysis (LFP), electron spin resonance (ESR), and MO calculations. The Si-Si bond cleavage is clearly demonstrated. The formation of a radical cation on the amine moiety is also observed. Moreover, these compounds work as efficient Type I and Type II photoinitiators (PI) of free radical photopolymerization (FRP). Copyright (C) 2010 John Wiley & Sons, Ltd

Structural Effects in the Indanedione Skeleton for the Design of Low Intensity 300−500 nm Light Sensitive Initiators

International audienceNewly synthesized indanedione derivatives combined with an iodonium salt, N-vinylcarbazole, amine, phenacyl bromide, or 2,4,6-tris- (trichloromethyl)-1,3,5-triazine have been used as photoinitiating systems upon very low visible light intensities: blue lights (e.g., household blue LED bulb at 462 nm) or even a halogen lamp exposure. One of them (ID2) is particularly efficient for cationic, radical and thiol−ene photopolymerizations as well as for the synthesis of interpenetrated polymer networks (IPNs). It can be useful to overcome the oxygen inhibition. ID2 based photoinitiating systems can also be selected for the reduction of Ag+ and the in situ formation of Ag(0) nanoparticles in the synthesized polymers. The (photo)chemical mechanisms are studied by electron spin resonance spin trapping, fluorescence, cyclic voltammetry, laser flash photolysis, and steady state photolysis techniques