Photopolymerization Of Acrylates Research Articles

Second Generation Zwitterionic Aza‐Diarylethene: Photoreversible CN Bond Formation, Three‐State Photoswitching, Thermal Energy Release, and Facile Photoinitiation of Polymerization

AbstractDiarylethenes are a well‐studied and optimized class of photoswitches with a wide range of applications, including data storage, smart materials, or photocontrolled catalysis and biological processes. Most recently, aza‐diarylethenes have been developed in which carbon‐carbon bond connections are replaced by carbon‐nitrogen connections. This structural elaboration opens up an entire new structure and property space expanding the versatility and applicability of diarylethenes. In this work, we present the second generation of zwitterionic aza‐diarylethenes, which finally allows for fully reversible photoswitching and precise control over all three switching states. High‐yielding photoswitching between the neutral open form and a zwitterionic Z isomer is achieved with two different wavelengths of light. The third zwitterionic E isomeric state can be reached in up to 87 % upon irradiation with a third wavelength. Its high energy content of >10 kcal/mol can be released thermally by deliberate solvent change as trigger mechanism, rendering aza‐diarylethenes into interesting candidates for molecular solar thermal energy storage (MOST) applications. The third state also serves as locking state, allowing to toggle light‐responsiveness reversibly between thermally labile and thermally stable switching. Further, irradiation of the zwitterionic states leads to highly efficient photopolymerization of methyl acrylate (MA), directly harnessing the unleashed chemical reactivity of our aza‐diarylethene in a materials application.

Second Generation Zwitterionic Aza-Diarylethene: Photoreversible CN Bond Formation, Three-State Photoswitching, Thermal Energy Release, and Facile Photoinitiation of Polymerization.

Diarylethenes are a well-studied and optimized class of photoswitches with a wide range of applications, including data storage, smart materials, or photocontrolled catalysis and biological processes. Most recently, aza-diarylethenes have been developed in which carbon-carbon bond connections are replaced by carbon-nitrogen connections. This structural elaboration opens an entire new structure and property space expanding versatility and applicability of diarylethenes. In this work, we present the second generation of zwitterionic aza-diarylethenes, which finally allows for fully reversible photoswitching and precise control over all three switching states. High-yielding photoswitching between the neutral open form and a zwitterionicZisomer is achieved with two different wavelengths of light. The third zwitterionicEisomeric state can be reached up to 87% upon irradiation with a third wavelength. Its high energy content of >10 kcal/mol can be released thermally by deliberate solvent change as trigger mechanism, rendering aza-diarylethenes into interesting candidates for molecular solar thermal energystorage (MOST) applications. The third state further serves as locking state, allowing to toggle light-responsiveness reversibly between thermally labile and thermally stable switching. Further, irradiation of the zwitterionic states leads to highly efficient photopolymerization of methyl acrylate (MA),directly harnessing the unleashed chemical reactivity of aza-diarylethene in materials applications.

Mechanochromic Displays Based on Photoswitchable Cholesteric Liquid Crystal Elastomers

AbstractStimuli responsive optical materials are attractive for many areas, from healthcare to art design. However, creating intricate color‐changing patterns for visual information is still a challenge. This work describes the preparation of mechanochromic structural colored intricate pictures imprinted in cholesteric liquid crystal elastomers by using a chiral isosorbide molecular photoswitch. The photoswitch contains a photoisomerizable cinnamate moiety and was incorporated in a main chain liquid crystal oligomer with photopolymerizable acrylate end groups. After coating, the structural colored film was irradiated with ultraviolet (UV) light in air causing E/Z isomerization of the cinnamate units leading to a redshift of the structural color of the film. A grayscale photomask was used to spatially control the photoisomerization reaction and imprint colorful pictures such as portraits and landscapes, in the cholesteric liquid crystal films with high resolution. Photopolymerization in a nitrogen atmosphere led to a mechanochromic cholesteric liquid crystal elastomer with striking structural colors that blueshift upon strain. The sharp details of the patterns were preserved even under deformation and the system returned to the initial state upon strain removal. Our work offers a simple photoswitch approach to prepare stimuli responsive optical polymers imprinted with color‐changing pictures of unprecedented complexity.

Mechanochromic Displays Based on Photoswitchable Cholesteric Liquid Crystal Elastomers.

Stimuli responsive optical materials are attractive for many areas, from healthcare to art design. However, creating intricate color-changing patterns for visual information is still a challenge. This work describes the preparation of mechanochromic structural colored intricate pictures imprinted in cholesteric liquid crystal elastomers by using a chiral isosorbide molecular photoswitch. The photoswitch contains a photoisomerizable cinnamate moiety and was incorporated in a main chain liquid crystal oligomer with photopolymerizable acrylate end groups. After coating, the structural colored film was irradiated with ultraviolet (UV) light in air causing E/Z isomerization of the cinnamate units leading to a redshift of the structural color of the film. A grayscale photomask was used to spatially control the photoisomerization reaction and imprint colorful pictures such as portraits and landscapes, in the cholesteric liquid crystal films with high resolution. Photopolymerization in a nitrogen atmosphere led to a mechanochromic cholesteric liquid crystal elastomer with striking structural colors that blueshift upon strain. The sharp details of the patterns were preserved even under deformation and the system returned to the initial state upon strain removal. Our work offers a simple photoswitch approach to prepare stimuli responsive optical polymers imprinted with color-changing pictures of unprecedented complexity.

Hybrid direct ink writing of bioglass-calcite-carbon composite scaffolds supported by novel silicone-based emulsions

70S30C (70 mol% SiO2, 30 % CaO) bioglass is one of the most promising bioceramics for bone tissue engineering. We discuss the feasibility of 70S30C bioglass/calcite/carbon composites derived from novel silicone-based emulsions, leading to highly porous lattice scaffolds. These are produced by direct ink writing (DIW) 3D printing, followed by ceramic conversion at 700 °C in flowing nitrogen. The emulsions consisted of droplets of concentrated calcium nitrate aqueous solution incorporated into blends of H44 commercial polysiloxane and photocurable acrylate resin. This formulation offered unprecedented opportunities in both synthesis and shaping. Specifically, the homogeneous dispersion of the CaO precursor in silicone enabled a uniform SiO2/CaO distribution, favoring the formation of a glass matrix. Additionally, the acrylate component and water content allowed for tuning of the microstructure both immediately after printing and upon firing. Photopolymerization of acrylates consolidated the printed bodies (configuring a ‘hybrid DIW’) after extrusion, while water evaporation enhanced gas evolution during ceramic conversion, promoting pore interconnectivity.

Antimicrobial Coatings Based on a Photoreactive (Meth)acrylate Syrup and Ferulic Acid-The Effectiveness against Staphylococcus epidermidis.

A novel photopolymerizable (meth)acrylate oligomer syrup modified with ferulic acid (FA) was verified as an antimicrobial coating binder against a biofilm of Staphylococcus epidermidis. A solution-free UV-LED-initiated photopolymerization process of aliphatic (meth)acrylates and styrene was performed to prepare the oligomer syrup. The influence of ferulic acid on the UV crosslinking process of the varnish coatings (kinetic studies using photo-DSC) as well as their chemical structure (FTIR) and mechanical (adhesion, hardness), optical (gloss, DOI parameter), and antibacterial properties against S. epidermidis were investigated. The photo-DSC results revealed that FA has a positive effect on reducing the early occurrence of slowing processes and has a favorable effect on the monomer conversion increment. It turned out, unexpectedly, that the more FA in the coating, the greater its adhesion to a glass substrate and hardness. The coating containing 0.9 wt. part of FA exhibited excellent antimicrobial properties against S. epidermidis, i.e., the bacterial number after 24 h was only 1.98 log CFU/mL. All the coatings showed relatively high hardness, gloss (>80 G.U.), and DOI parameter values (30-50 a.u.).

Tailored bond characteristics in additively manufactured resin bond grinding wheels: achieving optimal performance, high abrasive concentration, and cost efficiency

AbstractThis research study addresses the issues with additive manufacturing of high abrasive concentration as well as highly affordable resin-bond grinding wheels. High-concentration resin bond grinding wheels are high-demand cutting tools that provide high-efficiency grinding operation for a broad range of ferrous and nonferrous metals. Adding a high concentration of abrasive grains into the blend while using high-temperature acrylic resins as a bond material has encountered some difficulties during digital light processing (DLP), such as insufficient flow of material resulting from the high inherent viscosity of the pure resin and less printability due to their dark color, which become worse by adding a high volume of abrasive grains. An engineered bond material achieved through the mechanical alloying of acrylate photopolymers with tailored properties has been discovered during this research study, taking advantage of reduced price, excellent grinding performance, and high grain concentration. The experimental grinding operations comprising medium and high material removal rates were carried out to prove the supreme properties of the SiC- and diamond-printed grinding wheels toward having high accuracy besides a high-quality finished surface. Mechanical characterization including tensile test and grinding performance examination comprising tool wear, cutting force, surface quality, and surface integrity were conducted on the printed and ground parts. The results showed that integrating 14.6 Wt% of Resin A (with higher thermal resistance and viscosity) into the wheel’s composition could contribute to the fabrication of a high-performance grinding wheel, besides having a reliable, fast, and feasible printing process. Furthermore, On-machine and out-of-machine measurements on the ground surface signified that the composition with the highest Resin B concentration (GW-H) offered up to 2 times higher mechanical properties, 33–50% lower grinding forces, 25–50% improved surface qualities, 2–3 times extended tool life span, and less interval dressing operation compared to the grinding wheel containing the lowest Resin B concentration (GW-L).

Novel amphipathic photoinitiating systems utilizing ethyl violet for acrylate and thiol-based click photopolymerization under 630 nm and 450 nm LED

We conducted the first-ever investigation on the use of amphipathic triphenylmethane dyes ethyl violet (EV), in combination with iodonium salts (Iod) and sodium tetraphenylborate (STPB), as novel visible light photoinitiating systems (PISs), for initiating oil-based photopolymerization of acrylate and thiol-ene, as well as water-based photopolymerization, under 630 nm and 450 nm light-emitting diodes (LED) irradiation. The polymerization kinetics verified the efficient initiation of the EV/STPB/Iod system under two light sources. Differential scanning calorimetry (DSC) and thermal imaging tests further confirmed the crucial role of light in the polymerization process. The potential photolysis mechanism of these systems containing EV was explored through steady-state photolysis, liquid chromatography-mass spectrometry (LC-MS), and electron spin resonance (ESR). This research not only offers a viable approach for developing PISs used for LED photopolymerization technology but also contributes to the development of water-based photopolymerization.

Aryl structural effect on the photoinitiation abilities of aryl glycine derivatives for polymerization upon exposure to blue light

AbstractThe design and development of photoinitiating systems applicable to visible light delivered from light‐emitting diodes (LEDs) have attracted increasing attention owing to the wide application of photopolymerization. In this study, four aryl glycine derivatives are designed and synthesized, and their applicability as visible light‐sensitive photoinitiators is thoroughly investigated. Specifically, the photoinitiation mechanism of these aryl glycine derivatives, when combined with iodonium salt, is investigated using steady‐state photolysis, fluorescence, and electron paramagnetic resonance spin trapping techniques. It is revealed that radicals can be generated from aryl glycine derivatives/iodonium salt combinations upon exposure to blue LEDs (410 and 445 nm) to induce free radical photopolymerization (FRP) of (meth)acrylates. Additionally, besides FRP, a photobase generator based on one of the investigated aryl glycine derivatives is synthesized and demonstrates the capability to initiate epoxy‐thiol polymerization under light irradiation. The remarkable photolatent characteristics demonstrate the significant potential in broadening the application of aryl glycine derivatives in controlled photopolymerization processes.

New Application of Multiresonance Organic Delayed Fluorescence Dyes: High-Performance Photoinitiating Systems for Acrylate and Epoxy Photopolymerization and Photoluminescent Pattern Preparation.

The primary focus of photopolymerization research is to advance highly efficient visible photoinitiating systems (PISs) as alternatives to conventional ultraviolet (UV) photoinitiators. We developed four multiresonance emitters (BIC-pCz, BNO1, BO-DICz, and TPABO-DICz) to sensitize iodonium salt (Iod) and initiate free-radical and cationic photopolymerization under visible light for the first time. The TPABO-DICz/Iod system achieved a double-bond conversion of over 70% within just 4 s of exposure to green light (520 nm), while the BNO1/Iod system achieved a double-bond conversion exceeding 50% with 10 s of exposure to red light (630 nm). The photochemical properties were studied through thermodynamic research, steady-state photolysis, and electron spin resonance. Photolithography techniques were employed to fabricate photoluminescent films and micrometer-scale patterns utilizing the blue-emitting BIC-pCz dye, showcasing the potential of photolithography in the production of photoluminescent pixels. Additionally, the BIC-pCz/Iod and TPABO-DICz/Iod systems have been employed to rapidly fabricate photoluminescent polymer patterns using a digital-light-processing 3D printer with a low-intensity light (3.2 mW cm-2). These multiresonance emitters show exceptional photosensitizing effects and can act as fluorescent dyes in photoluminescent patterns, highlighting the potential of utilizing photopolymerization for OLED applications.

Novel D-π-A hemicyanine dye as photoinitiators for insitu hydrogel formation and DLP printing.

The field of biofabrication imposes stringent requirements on the polymerization activity and biosafety of photopolymeric hydrogel systems. In this investigation, we designed and synthesized four hemicyanine dyes with a D-π-A structure specifically tailored for biofabrication purposes. These novel dyes, incorporating carbazole (CZ), triphenylamine (TPA), anthracene (AN), and benzodithiophene (BDT) as electron donors, along with heterocyclic salt (IN) as electron acceptors, were prepared using a straightforward synthesis method. The absorption maxima of ANIN, CZIN, and TPAIN exceeded 500 nm, rendering them suitable co-initiators for the free radical photopolymerization of acrylates under green-red light exposure facilitated by light-emitting diodes (LEDs) and the co-initiator iodonium salt (ION). Notably, CZIN and TPAIN, due to their robust dye absorption and efficient electron transfer to ION, functioned as high-performance photosensitizers. Meanwhile, BDTIN, with its strong and broad absorption range (400-600 nm), enhanced the accuracy of visible light photopolymerization. These dyes exhibit characteristics such as facile synthesis, heightened photo stability, and non-toxicity and also demonstrate the ability to discern the alkalinity of a solution to some extent. Furthermore, we explored the application of these hemicyanine dyes in 3D printing, showing potential to enhance printing resolution in DLP 3D printing (digital light process 3D printing).

Leveraging the Activated Monomer Mechanism to Create Grafted Polymer Networks in Epoxide–Acrylate Hybrid Photopolymerizations

Hybrid epoxide–acrylate photopolymerization enables the temporal structuring of polymer networks for advanced material properties. The ability to design polymer network architectures and to tune mechanical properties can be realized through the control of the cationic active center propagation reaction (active chain end mechanism) relative to the cationic chain transfer reaction (activated monomer mechanism). Grafted polymer networks (GPNs) can be developed through the covalent bonding of epoxide chains to acrylate chains through hydroxyl substituents, making hydroxyl-containing acrylates a promising class of chain transfer agents. This work demonstrates the formation of these GPNs and explores the physical properties obtained through the control of hydroxyl content and hybrid formulation composition. The GPNs exhibit a lower glass transition temperature than the neat epoxide network and result in a more homogeneous network. Further investigations of hydroxyl-containing acrylates as chain transfer agents will generate a wider range of physical property options for photopolymerized hybrid coatings, sealants, and adhesives.

Designing unimolecular photoinitiator by installing NHPI esters along the TX backbone for acrylate photopolymerization and their applications in coatings and 3D printing

Developing efficient and long wavelength sensitive unimolecular photoinitiators (PIs) is still facing a great challenge. In this work, a series of thioxanthone-based N-hydroxyphthalimide esters (TX-NHPIEs) were synthesized by installing NHPIEs along the TX backbone and characterized. The investigated TX-NHPIEs have a 60 nm redshift and demonstrate sterling initiating efficiency for free radical photopolymerization (FRP) under LED@450 nm light irradiation compared with the commercialized isopropylthioxanthone (ITX). Real-time 1Hnuclear magnetic resonance (1H NMR), electron spin resonance (ESR), decarboxylation and gas chromatograph-mass spectrometer (GC–MS) experiments and density functional theory (DFT) reveal that TX-NHPIEs can generate one alkyl radical and one N-centered iminyl radical, which can initiate FRP directly and indirectly, respectively. In other words, TX-NHPIEs absorb one photon and can generate two active radicals, which break through the limitations of common PIs. TX-NHPIE-Cpe demonstrates the highest initiating efficiency, and its application in coatings and 3D printing was also studied, indicating TX-NHPIEs have broad potential applications in photopolymerization processes.

The flexural strength of 3D-printed provisional restorations fabricated with different resins: a systematic review and meta-analysis

BackgroundThree-dimensional (3D) printing technology has revolutionized dentistry, particularly in fabricating provisional restorations. This systematic review and meta-analysis aimed to thoroughly evaluate the flexural strength of provisional restorations produced using 3D printing while considering the impact of different resin materials.MethodsA systematic search was conducted across major databases (ScienceDirect, PubMed, Web of Sciences, Google Scholar, and Scopus) to identify relevant studies published to date. The inclusion criteria included studies evaluating the flexural strength of 3D-printed provisional restorations using different resins. Data extraction and quality assessment were performed using the CONSORT scale, and a meta-analysis was conducted using RevMan 5.4 to pool results.ResultsOf the 1914 initially identified research articles, only 13, published between January 2016 and November 2023, were included after screening. Notably, Digital Light Processing (DLP) has emerged as the predominant 3D printing technique, while stereolithography (SLA), Fused Deposition Modeling (FDM), and mono-liquid crystal displays (LCD) have also been recognized. Various printed resins have been utilized in different techniques, including acrylic, composite resins, and methacrylate oligomer-based materials. Regarding flexural strength, polymerization played a pivotal role for resins used in 3D or conventional/milled resins, revealing significant variations in the study. For instance, SLA-3D and DLP Acrylate photopolymers displayed distinct strengths, along with DLP bisacrylic, milled PMMA, and conventional PMMA. The subsequent meta-analysis indicated a significant difference in flexure strength, with a pooled Mean Difference (MD) of − 1.25 (95% CI − 16.98 - 14.47; P < 0.00001) and a high I2 value of 99%, highlighting substantial heterogeneity among the studies.ConclusionsThis study provides a comprehensive overview of the flexural strength of 3D-printed provisional restorations fabricated using different resins. However, further research is recommended to explore additional factors influencing flexural strength and refine the recommendations for enhancing the performance of 3D-printed provisional restorations in clinical applications.

Coumarin derivatives as dual photo/thermal initiators for free radical polymerization and 3D printing

In this study, five coumarin derivatives were developed and synthesized to serve as visible light photoinitiators for the free radical photopolymerization of acrylates upon near-UV or visible light.

Efficient reduction of photopolymerization shrinkage stress through microporous particles templated from Pickering emulsion droplets

Photopolymerization of acrylate based resin is a rapid, efficient and low-energy curing process that is achieving wide applications in many industrial fields. However, the volumetric shrinkage and the shrinkage stress of the cured resin have long been the major factor reduces adhesion strength of UV curable coatings onto the substrate. In this paper, the Pickering emulsion template method is employed to prepare elastic microporous particles with well-defined surface and internal structures and these microporous particles are thus added into the UV curable resin formulation to verify their capability to reduce polymerization stress through the microporous structure. The gel point time of UV-curable materials is delayed by 11 s with 1.5 wt% addition of the microporous particles and the double bond conversion at the gel point is subsequently increased. By real time MIR-photo-rheology and 3D line scanning laser confocal measurement, it is found that addition of microporous particles into the resin formulation can reduce the volume shrinkage of the resin by 61.2 % with only 1.5 wt% microporous particles, while the excellent mechanical and thermal properties of the cured resin is basically maintained.

Fabrication of a Novel Fluorescein Embedded Photocomposite Based on Interpenetrating Polymer Network (IPN) and Its Application in 4D Printing

AbstractWith the rapid development of the 3D printing technique, the concept of 4D has emerged, defining time as the fourth dimension. This concept allows for changes in the appearance, function, or other properties of 3D printed objects in response to certain controlled external stimuli over time. In this work, a new photocomposite containing fluorescein based is designed on an interpenetrating polymer network (IPN) system, this system can be generated by the simultaneous photopolymerization of acrylate and epoxide monomers under visible LED@405 nm irradiation. Unexpectedly, combining the reversible fluorometric turn‐on property of fluorescein and the deformation of the IPN in the presence of water, the 3D flower structure printed from this photocomposite would demonstrate a novel dual responsive behavior with both fluorescence and shape changes when it is exposed to water for a short time. This work would present a novel functional photocomposite material and also expand the application prospect of 4D printing.

Novel bis-chalcone-based carbazole derivative photoinitiators for visible light polymerization with good photobleaching and biocompatibility

Four novel bis-chalcone-based carbazole derivative photoinitiators (2E,5E)-2,5-bis((9-phenyl-9H-carbazol-3-yl)methylene)cyclopentan-1-one (KZA), 2,5-bis((E)-4-(9H-carbazol-9-yl)benzylidene)cyclopentan-1-one (KZB), (2E,5E)-2,5-bis((9-ethyl-9H-carbazol-3-yl)methylene)cyclopentan-1-one (KZC) and (2E,5E)-2,5-bis((5-(9-ethyl-9H-carbazol-3-yl)thiophen-2-yl)methylene)cyclopentan-1-one (KZD) were successfully designed and synthesized. Their maximum absorption wavelengths were 440 nm, 405 nm, 446 nm and 500 nm, respectively, and they all had high molar extinction coefficients. Furthermore, three-component photoinitiation system including bis-chalcone/iodonium/amine could quickly and efficiently trigger the photopolymerization of acrylates. For example, PEGDA coatings could cure in 10 s and the CC bond conversion exceeded 90 % in the end. Then we also conducted photosteady-state degradation, fluorescence quenching, cyclic voltammetry and ESR experiments to investigate the mechanisms of photopolymerization. Besides, all four bis-chalcones showed good photobleaching and biocompatibility, which was suitable for use in 3D printing and deep coating curing. For instance, the LCD 3D printer successfully printed clear and photobleached objects with KZD/iodonium/amine system. All these excellent properties indicated the industrial application potential of the four carbazole derivatives in visible light curing.

Photopolymerization of Poly(Hydroxyethyl Acrylate) (PHEA): Experimental Parameters-Viscoelastic Properties Relationship

The activity of the photoinitiator system, based on triethanolamine (TEOA) and methylene blue (MB), on the photopolymerization of hydroxyethyl acrylate (HEA) monomer under very soft irradiation conditions, was evaluated. A remarkable difference in the polymerization kinetics of a set of PHEA experiments was underlined according to TEOA/MB concentrations, as well as the solutions pH. Indeed, the complex viscosity (η*), storage modulus (G'), and loss modulus (G") of the resulting polymers were potentially dependent on these experimental parameters despite comparable values of monomer conversion.

Photoinitiating Ability of Pyrene–Chalcone‐Based Oxime Esters with Different Substituents

AbstractWith the rapid development of new irradiation setups as well as the ongoing interest in 3D printing, photopolymerization is extensively studied during the last decades. In photopolymerization, a photoinitiator and/or photosensitizer play(s) a crucial role in the photoinitiation step as this component absorbs light, thus creating the initiating species. In this study, a series of 17 chalcone‐based oxime esters (OXEs) featuring the pyrene chromophore are designed, synthesized, and studied for their photoinitiation properties upon irradiation with visible light. Precisely, their photoinitiation abilities are examined during the free radical photopolymerization of acrylates under the irradiation of light‐emitting diode (LED) at 405 nm. In the series of oxime esters, five of them demonstrate excellent photoinitiation abilities. Their thermal initiation abilities are also examined. To improve their photoinitiation abilities, these type I photoinitiators are also tested as type II photoinitiators in two‐component photoinitiating systems using bis‐(4‐tert‐butylphenyl)iodonium or ethyl 4‐(dimethylamino)benzoate as additives. In this process, the OXE‐B/iodonium system shows the best photopolymerization. To develop the use of these chalcone‐based oxime esters, the best OXE is used as a monocomponent photoinitiating system in 2D laser writing at 405 nm. The design of composites using glass fibers or carbon fiber as fillers is also examined.