A series of Type I photoinitiators (PIs) based on a nitrocarbazole scaffold are developed and examined for the first time as photoinitiators for visible light photopolymerization. Three oxime esters (OXE-M, OXE-V, OXE-P) varying by the terminal groups (acetyl, acryloyl and benzoyl) attached via the oxime ester group are originally prepared. As a result of this, the three PIs exhibit excellent photoinitiation abilities in the presence of acrylate monomers upon LED@ 405 nm irradiation. Markedly, OXE-M exhibits a better performance than the benchmark Type I phosphine-oxide (diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide TPO). Chemical mechanisms supporting the polymerization process with these PIs are investigated by steady state photolysis, molecular orbital calculations and real-time Fourier transformed infrared spectroscopy. After the cleavage of N─O bond and decarboxylation, free radicals are generated to initiate the free radical polymerization efficiently. Free radical photopolymerization of OXE-M is applied in direct laser write and 3D printing. Interestingly, OXE-M exhibits thermal initiation behaviors in monomers and can be used as dual photo and thermal initiators. The highly opaque feature of carbon fibers makes it difficult for light penetration, so dual photo/thermal curing are used here to prepare carbon fiber composites.

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Nitro-Carbazole Based Oxime Esters as Dual Photo/Thermal Initiators for 3D Printing and Composite Preparation

https://hal.archives-ouvertes.fr/hal-03160625/document

Photopolymerization and 3D/4D applications using newly developed dyes: Search around the natural chalcone scaffold in photoinitiating systems

Organic dye-based photoinitiating systems for visible-light-induced photopolymerization

Silver nanoparticles (AgNPs) play a crucial role in biology and medical research as their extensive and efficient antibacterial activity and high electrical and thermal conductivity. However, the generation of them with a certain morphology under mild conditions (under air, solvent-free, room temperature, etc.,) is still a huge challenge. Herein, a simple one-step method is proposed to generate AgNPs in situ at room temperature under air by combining the photopolymerization process with the formation process of AgNPs within a few minutes. In detailed, 12 different dyes based on 2,5-diethylene-cyclopentan-1-one were first synthesized and used as high-performance type II photoinitiator. When using in conjunction of bis-(4-tert-butylphenyl) iodonium hexafluorophosphate (Iod) and ethyl 4-dimethylaminobenzoate (EDB), they can effectively boost the free radical photopolymerization (FRP) of polyethylene glycol diacrylate (PEG-DA) and the cationic photopolymerization (CP) of 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (EPOX) upon irradiation with LED@405 nm. Furthermore, all the formulations containing/without AgNPs can be successfully used to perform the direct laser write experiment. However, even if all of the obtained 3D patterns exhibited reversible swelling performance and shape-memory effects caused by swelling and dehydration for the access to 4D printing, the presence of AgNPs will affect these properties.

https://hal.archives-ouvertes.fr/hal-03230219/document

In situ generation of Ag nanoparticles during photopolymerization by using newly developed dyes‐based three‐component photoinitiating systems and the related 3D printing applications and their shape change behavior

/pdf/recent-advances-on-visible-light-phenothiazine-based-3mu1m5ma.pdf

Recent advances on visible light Phenothiazine-based photoinitiators of polymerization

Radical initiation upon LED light irradiation is discussed herein as well as its application in additive manufacturing. The ability of manufacturing complex structures, freedom of design, low energy consumption, fast prototyping, and excellent spatial resolution are the main benefits of the 3D printing technology by photopolymerization. Therefore, the 3D printing of composites through photopolymerization processes is developing rapidly in the academia and industry, and has been a turning point of additive manufacturing (AM). In the present review, an overview of radical initiation with LEDs (i.e., the photopolymerization LED technology, the photoinitiating systems, and the polymerizable media) and of the main 3D printing methods by photopolymerization, materials, and their applications in different fields has been carried out. As a challenging topic, the issue of light penetration in a filled matrix for the access to composites is discussed, including the light transmittance of the composite, the mismatch of the refractive index between the filler and the monomer, the factors of the filler, and the adverse influence of low light penetration on the 3D printing process. In particular, the popular applications of 3D printing by photopolymerization in biomedical science, electronic industry, materials for adsorption, and 4D printing are discussed. Overall, this review gives an overview of the 3D printing of polymer matrix composites through photopolymerization processes as a benchmark for future research and development.

Radical photoinitiation with LEDs and applications in the 3D printing of composites.

Two fac-rhenium tris-carbonyl complexes bearing a π-accepting pyridoannelated N-heterocyclic carbene (NHC) ligand with general formula Re(CO)3(pyipy)X, where pyipy is 2-pyridil-imidazo[1,5-a]pyridi...

Rhenium(I) N-Heterocyclic Carbene Complexes in Photoinitiating Systems for Polymerization upon Visible Light: Development of Photosensitive Resins for 3D and 4D Applications

Yijun Zhang

Papers

Radical photoinitiation with LEDs and applications in the 3D printing of composites.

Rhenium(I) N-Heterocyclic Carbene Complexes in Photoinitiating Systems for Polymerization upon Visible Light: Development of Photosensitive Resins for 3D and 4D Applications

Preparation of Iron Filler-Based Photocomposites and Application in 3D Printing