Novel Low-Cytotoxic and Highly Efficient Type I Photoinitiators for Visible LED-/Sunlight-Induced Photopolymerization and High-Precision 3D Printing

The development of photoinitiators (PIs) combining high initiation ability, low-toxicity, and availability for high-precision 3D printing is a key challenge and an urgent problem to be solved nowadays in photopolymerization. In this study, carbazole chalcone glyoxylate oxime ester derivatives (denoted as Cs, C1-C5) containing both glyoxylate and oxime ester moieties with good light absorption properties in the visible range have been designed as type I PIs for the free radical photopolymerization (FRP) of trimethylolpropane triacrylate (TMPTA) and ethoxylated trimethylolpropane triacrylate (ETPTA) under 405 nm and 450 nm light-emitting diodes (LEDs) as well as sunlight irradiation. The reaction properties and mechanism of Cs are firstly predicted by molecular modeling/molecular design, which anticipate that C5 could exhibit the best photoinitiation ability, this structure being more prone to decarboxylation. Subsequent experimental results clearly show that the photoinitiation ability of C5 outperforms that of the benchmark commercial PIs (methyl benzoylformate (MBF), diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide (TPO)), and phenylbis (2,4,6-trimethylbenzoyl)-phosphine oxide (BAPO) under the same conditions. Compared to TPO, the photoinitiation ability of C5 improved by 40 %, 132 %, and 47 % exposed to LED@405 nm, LED@450 nm, and sunlight. In addition, C5 is successfully applied to 3D printing for the manufacture of large-scale and high-resolution object. The photochemical mechanism of C5 is systematically and comprehensively analyzed using a combination of steady state photolysis, decarboxylation reaction, fluorescence experiments, and electron spin resonance-spin trapping (ESR-ST) technology. It is found that both glyoxylate and oxime ester in C5 are highly active and capable of undergoing decarboxylation reactions to produce CO2 and free radicals, which is consistent with the results predicted by molecular modeling. Furthermore, the low-toxicity of C5 is evidenced by cytotoxicity assays. The comprehensive molecular modeling and experimental approach adopted in this research has led to the development of novel PIs that are highly efficient and low-toxic, and can be used for high-precision 3D printing, which offers broad application prospects in the fields of environmental sustainability, visible light curing, and biomedical science.

Lignin Derivative as Visible-Light Photo-Initiating System for the Development of Biocide Materials under Light Irradiation

The design of a new visible-light methacrylated-based kraft lignin photosensitizer (MAcL) of iodonium salt (Iod) for the free-radical polymerization (FRP) of polyethylene glycol dimethacrylate (PEGDMA) under LEDs@405, 455, 470, 505, and 530 nm is reported. As demonstrated by laser flash photolysis (LFP) and electron paramagnetic resonance spin-trapping (EPR ST) experiments, the combination of MAcL with an electron acceptor (Iod) and trimethylolpropane tris(3-mercaptopropionate) (TT) used as a crosslinker, leads to the formation of highly efficient initiating radicals, i.e., thyil and carbon-centred radicals, promoting thus the FRP of PEGDMA. The final methacrylate conversions of PEGDMA are very high and range from 80 to 95% under LED@530 nm and LED@405 nm, respectively. For the first time, MAcL is also used as a biocide agent as it produces singlet oxygen when exposed to visible light. The resulting photoinduced bio-based materials incorporating MAcL demonstrate tremendous antibacterial properties against Staphylococcus aureus (S. aureus), inducing 100% bacterial death.

Application of surface-modified functional packaging in food storage: A comprehensive review

Innovations in food packaging systems could meet the evolving needs of the market; emerging concepts of non-migrating technologies reduce the negative migration of preservatives from packaging materials, extend shelf life, and improve food quality and safety. Non-migratory packaging activates the surface of inert materials through pretreatment to generate different active groups. The preservative is covalently grafted with the resin of the pretreated packaging substrate through the graft polymerization of the monomer and the coupling reaction of the polymer chain. The covalent link not only provides the required surface properties of the material for a long time but also retains the inherent properties of the polymer. This technique is applied to the processing for durable, stable, and easily controllable packaging widely. This article reviews the principles of various techniques for packaging materials, surface graft modification, and performance characterization of materials after grafting modification. Potential applications in the food industry and future research trends are also discussed.

Naphthalene-Based Oxime Esters as Type I Photoinitiators for Free Radical Photopolymerization

In order to discuss the polymerization effect from the substituted position and methoxy group of Type I photinitiators, a series of naphthalene-based oxime esters was designed and synthesized. Compared to the 2-naphthalene-substituted compound, the UV absorption region of the 1-naphthalene-based compound was greatly improved. In addition, the methoxy substitution exhibited longer absorption characteristics than did the methoxy-free one. The photochemical reaction behavior of these novel compounds was also studied by photolysis, cyclic voltammetry (CV), and electron spin resonance (ESR) experiments. Finally, the initiation abilities of naphthalene-based oxime esters toward trimethylolpropane triacrylate (TMPTA) monomer were conducted through the photo-DSC instrument under UV and a 405@nm LED lamp. Remarkedly, the naphthalene-based oxime ester (NA-3) that contains 1-naphthalene with o-methoxy substituent showed the rather red-shifted absorption region with the highest final conversion efficiency under UV (46%) and 405@nm LED (41%) lamp irradiation.

Naphthoquinone-based Imidazolyl Esters as Blue-Light-Sensitive Type I Photoinitiators

In this work, a series of Type I photoinitiators (PIs) based on the naphthoquinone scaffold were designed and synthesized for the first time, in order to induce photopolymerization under visible...

Effects of the number and position of methoxy substituents on triphenylamine-based chalcone visible-light-absorbing photoinitiators

Five visible-light-absorbing triphenylamine-based chalcone photoinitiators (CY1–CY5) have been synthesized for application in free radical photopolymerization.

Effect of the Steric Hindrance and Branched Substituents on Visible Phenylamine Oxime Ester Photoinitiators: Photopolymerization Kinetics Investigation through Photo-DSC Experiments

In this work, free radical photopolymerization (FRP) kinetics for series of different phenylamine oxime ester structures (DMA-P, DEA-P, DMA-M, TP-2P, TP-2M and TP-3M) was investigated. Steric hindrance and branched substituents were prepared to realize the corresponding electronic and photopolymerization effects. The photophysical, electrochemical, thermal properties and radical concentration were investigated by UV-visible spectroscopy, cyclic voltammetry (CV), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and electron paramagnetic resonance (EPR). Furthermore, the structure-reactivity relationships were also studied in detail through photo-DSC experiment. We demonstrate that the introduction of alkyl chains and/or numbers of oxime esters affects significantly the photoreactivity. Under the same weight ratio of formulation and irradiated condition, TP-3M containing three oxime esters in its structure and methyl group in the periphery exhibits the highest double-bond conversion efficiency. TP-3M-based formulation also shows a wide operation window under different contents and light intensities. Importantly, the photoreactivity of the TP-3M-based system was found to be better than the commercial photoinitiator (OXE-01) under LED@405 nm at a low concentration. This work could provide some significance to the design of oxime esters with enhanced photoreactivity.

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

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.