Organometallic vs organic photoredox catalysts for photocuring reactions in the visible region

2020

Catalysts

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Metal complexes are used in numerous chemical and photochemical processes in organic chemistry. Metal complexes have not been excluded from the interest of polymerists to convert liquid resins into solid materials. If iridium complexes have demonstrated their remarkable photochemical reactivity in polymerization, their high costs and their attested toxicities have rapidly discarded these complexes for further developments. Conversely, copper complexes are a blooming field of research in (photo) polymerization due to their low cost, easy syntheses, long-living excited state lifetimes, and their remarkable chemical and photochemical stabilities. Copper complexes can also be synthesized in solution and by mechanochemistry, paving the way towards the synthesis of photoinitiators by Green synthetic approaches. In this review, an overview of the different copper complexes reported to date is presented. Copper complexes are versatile candidates for polymerization, as these complexes are now widely used not only in photopolymerization, but also in redox and photoassisted redox polymerization processes.

Section: Complexes With Elongated Excited State Lifetimes: the Basismentioning

confidence: 99%

Section: Complexes With Elongated Excited State Lifetimes: the Basismentioning

confidence: 99%

Recent Advances on Copper Complexes as Visible Light Photoinitiators and (Photo) Redox Initiators of Polymerization

Noirbent

2020

Catalysts

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“…a white polymer totally soluble in the solvent. However, analyses by 1 H and 13 C nuclear magnetic resonance (NMR) as well as infrared (IR) spectroscopy revealed that a single ring-opening reaction occurred, letting the cyclopropane group unchanged (See Scheme 2). This mechanism is consistent with those previously reported by Mülhaupt and co-workers concerning the cationic polymerization of 1,3dioxolane monomers.…”

Section: Ferrocenium Salts Used As Photoinitiators Of Polymerizationmentioning

confidence: 99%

“…In this field, the superiority of the metal-based photoinitiators compared to the purely organic ones has been clearly established. [13] This is attributable to the long-living excited state lifetimes of metal complexes, providing more time for the different additives to react with the photosensitizers. [14] In this field, remarkable works on photopolymerization have notably been developed as soon as 2010 [15] with ruthenium-based photocatalysts and iridium complexes in 2011.…”

Section: Introductionmentioning

confidence: 99%

Recent advances on iron-based photoinitiators of polymerization

European Polymer Journal

2020

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With regards to the environmental and safety concerns raised nowadays by the polymer industry, polymerization processes requiring light as the activation source are currently knowing a revival of interest after decades of disinterest. Recent progresses in photopolymerization are notably sustained by the development of new polymerization application namely 3D and 4D printing enabling an unprecedented access to structures of incredible complexity. Parallel to the manufacturing process, the polymer material itself and its composition are also facing numerous questions concerning their environmental and human health impacts. Beyond the monomers, the different additives introduced in the resin can also be potentially toxic so that a great deal of efforts is currently done to develop new photoinitiators with a toxicity assessed as being insignificant. In this field, iron-based metal complexes are candidates of choice due to the clinical demonstration of their very low toxicities. Among iron complexes, ferrocene is among the most widely studied iron-based metallocene. Due to its unique and reversible electrochemical properties as well as their absorption centred in the visible range, numerous photoinitiators have been developed with ferrocene or its oxidized form i.e. ferrocenium. Parallel to this, the remarkable electrochemical properties of ferrocenium made it an excellent candidate for its incorporation in photoinitiating systems. However, interest for iron-based photoinitiators was not limited to ferrocene and ferrocenium, and Schiff base complexes were also successfully used as initiators of polymerization. In this review, an overview of the different iron-based photoinitiating systems reported to date is presented. More precisely, if iron-based photoinitiators are developed since 50 years, a special focus will be done on photoinitiators designed for recent polymerization conditions, namely, under visible light and low light intensity.

“…Oxygen inhibition is a major drawback for polymerization, especially when liquid monomers are used due to the facile oxygen diffusion inside the resins. At present, examples of visible light photoredox catalysts for polymerization activatable under low light intensity still remain scarce, despite the possibility to initiate a polymerization with such compounds while significantly reducing the energy consumption [25]. Given that organic and organometallic photoredox catalysts of polymerization have been developed since 2010, availability of metal-based photocatalysts remains extremely low [11,25].…”

Section: Introductionmentioning

confidence: 99%

Recent Advances on Visible Light Metal-Based Photocatalysts for Polymerization under Low Light Intensity

2019

Catalysts

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In recent years, polymerization processes activated by light have attracted a great deal of interest due to the wide range of applications in which this polymerization technique is involved. Parallel to the traditional industrial applications ranging from inks, adhesives, and coatings, the development of high-tech applications such as nanotechnology and 3D-printing have given a revival of interest to this polymerization technique known for decades. To initiate a photochemical polymerization, the key element is the molecule capable to interact with light, i.e., the photoinitiator and more generally the photoinitiating system, as a combination of several components is often required to create the reactive species responsible for the polymerization process. With the aim of reducing the photoinitiator content while optimizing the polymerization yield and/or the polymerization speed, photocatalytic systems have been developed, enabling the photosensitizer to be regenerated during the polymerization process. In this review, an overview of the photocatalytic systems developed for polymerizations carried out under a low light intensity and visible light is provided. Over the years, a wide range of organometallic photocatalysts has been proposed, addressing both the polymerization efficiency and/or the toxicity, as well as environmental issues.