Photoinitiator Research Articles

In vitro analysis of composition profiles of resins for 3D printing of dentures.

This study aimed to investigate the resin compounds from CAD-CAM 3D-printed denture resins, focusing on the identification and classification of free monomers and other components. The primary objective was to determine the chemical profile of these 3D-prinding resin materials. Four 3D-printed denture resins, two base materials (1: DentaBASE, Asiga Ltd., Alexandria, NSW, Australia; 2: DENTURETEC, SAREMCO Dental AG), and two tooth-colored materials (1: DentaTOOTH, Asiga Ltd.; 2: CROWNTEC (SAREMCO Dental AG), were analyzed using high-performance liquid chromatography and mass spectrometry (HPLC-MS). Data analysis was processed including peak alignment and normalization to an ethanol blank, resulting in detailed identification of compounds in the resin. Out of 5,208 detected compounds in the resin, 63 were retained after applying filtering criteria for further analysis, categorized into methyl methacrylate (MMA) and derivatives (31), photo initiators (8), UV stabilizers (1), and other additives (23). Sample 2B exhibited the highest number of resin compounds (62), including the most MMA derivatives and additives. MMA accounted for over 69% in abundance across samples, with unique additives such as ethyl-4-dimethylaminobenzoate and bis(acryloyloxymethyl) tricyclo [5.2.1.02,6] decane (TCD-DI-HEA) identified. Variations in the resin composition distribution and abundance highlighted differences in resin formulations. Within the limits of this in vitro, exploratory study, unpolymerized 3D-printed denture resins were analyzed, and various resin compounds in 3D-printed denture resins, including MMA, photo initiators, UV stabilizers, and additives, were identified along with significant variability between samples. While 3D-printing enhances efficiency and customization, further investigation is needed to better understand and assess the long-term intraoral effects and their effectiveness in complete dentures. This study provides insights into the chemical composition of 3D-printed denture resins, highlighting variability in resin compound profiles. Understanding these materials is essential for ensuring biocompatibility and performance. The findings support the need for further research and standardized testing to guide clinicians in the safe and effective use of 3D-printed dentures.

Vat photopolymerization printing by thermal polymerisation utilising carbon nanotubes as photothermal converters

ABSTRACT Traditional printing compositions for stereolithography (SLA), a vat photopolymerization technology, rely on light-sensitive photoinitiators (PIs) to initiate cross-linking reactions. Here, we propose a new approach for printing in which the polymerisation occurs locally with carbon nanotubes (CNTs), which function as photothermal converters combined with low-cost thermal initiators (TIs). The irradiation is performed at near-infrared (NIR), which enables deep light penetration, and polymerisation in black compositions, thus increasing the printing throughput. We demonstrate the control over polymerisation kinetics, printing resolution and cure depth, achieving very large printable layer thickness. The CNT photoconvertors can be used in both nonaqueous and aqueous systems, while the latter addresses the limited availability of water-soluble PIs for printing in water. The CNT enables dual use, initiating polymerisation and printing composite materials. This approach presents an advancement in SLA-based technologies, avoiding the use of conventional PIs and thus broadening the scope of 3D printing applications.

Biocompatibility and performance of new generation dental composites

Dental composites have undergone significant advancements in recent years, with new-generation materials being developed to improve both biocompatibility and mechanical performance. These innovations have led to the increased use of dental composites in restorative dentistry, particularly in both anterior and posterior restorations. Biocompatibility remains a key concern, as the release of unreacted monomers, such as bisphenol A glycidyl methacrylate (Bis-GMA), can cause local tissue irritation or systemic effects. Modern composites aim to reduce these risks by incorporating alternative resin systems and advanced photo initiators. Nanotechnology has further enhanced the performance of these materials by improving mechanical strength and wear resistance, but questions about the safety of nanoparticles and their long-term biological effects continue to be explored. In addition to biocompatibility, the mechanical properties of new-generation composites have been significantly optimized. The introduction of bulk-fill composites allows for deeper polymerization and faster placement, reducing clinical procedure times while maintaining high mechanical integrity. Polymerization shrinkage, a common issue in traditional composites, has been minimized in newer formulations, reducing the risk of marginal gaps and microleakage. The effectiveness of different light-curing units, such as light-emitting diode (LED) versus halogen lights, plays a crucial role in achieving optimal polymerization depth, especially in posterior restorations where light penetration can be limited. Long-term clinical outcomes depend on several factors, including material choice, placement technique, and patient adherence to oral hygiene. Despite the improvements in composite materials, the longevity of restorations still faces challenges such as wear, fracture, and degradation over time. Continued research into the safety, effectiveness, and clinical performance of new-generation composites is essential to ensuring patient safety and enhancing the durability of restorations in the future. These advancements promise to address many of the limitations seen in earlier dental materials while offering superior performance and patient satisfaction.

Novel Ketone Derivatives Involving Triphenylamine Electron‐Donating Group as Low Migration Photoinitiators for Visible Light Radical Polymerization and 3D Printing

AbstractGiven the ongoing advancements in photopolymerization technology, there is an imperative need to develop novel free radical photoinitiators (PIs) with long‐wavelength absorbance and low migration. To meet the demand for visible light photopolymerization, four novel ketone derivatives photoinitiators (PHMOs) were synthesized in this study via a one‐step reaction. By constructing the push‐pull structure, the maximum absorption wavelength of the new PIs was red‐shifted to the vicinity of 400 nm, satisfying the requirement of visible excitation. The one‐component photoinitiation effect of PHMOs under visible light was comparable to that of Irgacure 1173, among which the photopolymerisation performance of PHMO‐2 was significantly superior to that of 1173. The photopolymerization effect of the two‐component photoinitiaton system composed by the addition of hydrogen donor was significantly improved. PHMO‐1 was successfully used in 3D printing to produce well‐defined printed products. The photolysis mechanism of PHMOs was investigated by steady‐state photolysis and electron spin resonance test. In addition, PHMOs had good solubility, thermal stability and good biosafety. Attributed to the presence of double bonds, PHMOs had low migration. These excellent properties indicated that PHMOs had desirable potential applications in the field of visible light polymerization.

Protective Coatings Based on the Organosilicon Derivatives of Fatty Acids Obtained by the Thiol-Ene Click Reaction.

This article describes the synthesis of a hydrophobic protective coating for concrete based on a silane derivative of fatty acids. The coating was obtained through a thiol-ene click addition reaction using methyl oleate and 3-mercaptopropyltrimethoxysilane in the presence of the photoinitiator 2,2-dimethoxy-2-phenylacetophenone (DMPA). This reaction proved to be more efficient compared with other tested (photo)initiators, considering the double bond conversion of oleate. The coating was applied to concrete using two methods: immersion and brushing. Both methods exhibited similar consumption of methyl oleate-based silane (UVMeS) at approximately 20 g/m2. The hydrophobic properties of the coatings were evaluated based on the contact angle, which for the modified surfaces was above 93°, indicating their hydrophobic nature. The penetration depth of the silane solution into the concrete was also studied; it was 5-7 mm for the immersion method and 3-5 mm for the brushing method. The addition of tetraethoxysilane (TEOS) to the silane solution slightly improved the barrier properties of the coating.

Occurrences and migration characteristics of photoinitiators in paper food packaging: Implication for human exposure

Photoinitiators (PIs), as an important component of UV inks, are widely used in the printing of paper food packaging. Nevertheless, there is limited information concerning the identification of PIs in food packaging and their potential migration rules under natural storage condition. In this study, 23 target PIs detected in paper food packaging were dominated by benzophenones (BZPs), followed by amine co-initiators (ACIs), thioxanthones (TXs) and phosphine oxides (POs). The concentration of ΣPIs ranged between 48.3 and 1.11 × 105 ng/g. Meanwhile, the concentration of ΣPIs were found to be significantly higher in Corrugated paper compared to Polyethylene (PE) coated paper, Composite paper and White card paper. Benzophenone (BP) was found as the dominant PI congener in Corrugated paper, with the concentration ranging from 923-3.66 × 104 ng/g. The migration quantity of ΣPIs increased in a time-dependent manner in the first 13 days and then eventually reached equilibrium. Low temperatures had a certain inhibitory effect on the migration of PIs from paper packaging to food. Under high exposure scenario, the EDIs of ΣPIs for children, adolescents, and adults were 31.4 ng/(kg bw·day), 17.2 ng/(kg bw·day), and 14.4 ng/(kg bw·day), respectively, all of which did not exceed the reference dose, indicating that dietary intake of PIs does not pose any health risks to the human body.

Light-matter interaction during and post polymerization in self-written polymer waveguide integrated with optical fibers

Self-written polymer waveguide is a polymer interconnection structure often integrated with optical fibers. The structure is fabricated by photopolymerization, through which a photon beam initiates a polymerization reaction to change liquid monomer into a solid polymer. During light-matter interaction photoinitiator molecules are excited to the singlet and then to the third state to form free radicals by attaching to the adjacent monomer molecules. The free radicals in turn form polymer chains and cross-linked structures. Photo-induced polymerization leads to a raised refractive index of the monomer and forms an optical waveguide. The change is permanent to allow the process of self-focusing and self-trapping of the propagation light beam and hence guide it to the aligned optical fiber. In this article, light matter interaction during polymer waveguide fabrication and post polymerization has been investigated. A photopolymer system of acrylate-based monomer, co-initiator amine and photo initiator is used to study the absorption of the monomer mixture at the spectral range of 450–550 nm. Then photobleaching was investigated after waveguide fabrication. The optical transmission efficiency of the polymer bridge increases as absorption ceases within the polymer structure such that optical loss reduces from 1.1 dB to about 0.65 dB.

Evaluating the embryotoxicity of benzophenone-based photoinitiators in stem cells and zebrafish embryos

Benzophenones (BPs) are widely used as photoinitiators (PIs) or printing inks in food packaging, which may migrate into foods. However, the toxicity information of some BP analogues, such as 4,4′-bis(diethylamino)-benzophenone (DEAB), 4-phenylbenzophenone (4-PBP), 4 (hydroxymethyl)benzophenone (4-HMBP), those are used as PIs is lacking. Developmental toxicity is a health concern associated with PIs exposure. Recently, alternative non-in vivo methods have been proposed to evaluate the concerned chemicals or better understand the modes of action of certain toxicological endpoints. In this study, using in silico methods, we predicted that BP, DEAB, 4-PBP and 4-HMBP might exhibit developmental toxicity. However, we found that only DEAB is strong embryotoxic and disturbs the early differentiation of mouse embryonic stem cells into three germ layers and cardiomyocytes. DEAB treatment also prevented cardiomyocyte differentiation in human induced pluripotent stem cells (hiPSCs) on day 10. However, BP, 4-PBP and 4-HMBP had no similar effects on cardiomyocyte differentiation on day 10. Transcriptomic analysis revealed that treatment with DEAB significantly decreased the mRNA levels of differentiation-related transcription factors SOX17 and FOXA1, in hiPSCs on day 4. Furthermore, DEAB treatment caused tail malformations and yolk sac edema in zebrafish embryos. To conclude, DEAB may be embryotoxic because it disturbs the early differentiation of stem cells. Further studies are warranted to better understand the health effects of DEAB exposure.

Effect of Melamine Formaldehyde Resin Encapsulated UV Acrylic Resin Primer Microcapsules on the Properties of UV Primer Coating.

Ultra-Violet (UV) coatings are widely adaptable of substrates and produce low emissions of volatile organic compounds. UV coatings can extend service life by adding self-healing microcapsules that restore integrity after sustaining damage. In this study, UV coating was used as a core material; microcapsules were produced and added to the UV coating to enhance its self-healing property, providing a good protection for both the UV coating and the substrate. UV primer microcapsules were prepared with UV primer as the core material and melamine formaldehyde resin as the wall material. The UV primer containing more than 98.0% solids content was mainly composed of epoxy acrylic resin, polyester acrylic resin, trihydroxy methacrylate, trimethyl methacrylate, and photo initiator. The preparation process of the UV primer microcapsules was optimized. Further, the UV coating was prepared with better UV primer microcapsules, and the effects of the UV primer microcapsules alongside the comprehensive properties of the coating were studied. The best preparation process for the UV primer microcapsules was as follows: the wall-core mass ratio was 1:0.50, Triton X-100 and Span-20 as emulsifiers with an HLB value of 10.04, the microcapsule reaction temperature was 70 °C, and the reaction time of the was 3.0 h. When the quantity of the UV primer microcapsules increased in the coating, color difference ΔE of the coating increased, gloss decreased, transmittance decreased, elongation at break increased and then decreased, roughness increased, and self-healing rate first increased and then decreased. When the addition of the UV primer microcapsules reached 2.0%, the color difference ΔE of the coating was 1.71, the gloss was 106.63 GU, the transmittance was 78.80%, the elongation at break was 3.62%, the roughness was 0.204 μm, and the self-healing rate was 28.56%, which were the best comprehensive properties of the UV primer. To improve the comprehensive properties of the UV coatings, the UV coatings were modified by a microcapsule technology, which gave the UV coatings a better self-healing property. The application range of microcapsules for the UV coatings was broadened. Based on the previous research of microcapsules in UV coatings, the results further refined the study of the effects of adding self-healing microcapsules to UV coatings using the UV coating itself as the core material.

Push-Pull Carbazole-Based Dyes: Synthesis, Strong Ultrafast Nonlinear Optical Response, and Effective Photoinitiation for Multiphoton Lithography.

The present work reports on the ultrafast nonlinear optical (NLO) properties of a series of D-π-Α and D-A push-pull carbazole-based dyes and establishes a correlation between these properties and their efficiency for potential photonic and optoelectronic applications such as multiphoton lithography (MPL). The ultrafast NLO properties of the studied dyes are determined by two distinct experimental techniques, Z-scan and pump-probe optical Kerr effect (OKE), employing 246 fs laser pulses at 515 nm. The results indicate that chemical functionalization of the carbazole moiety with various strong electron-donating and/or electron-withdrawing groups, such as benzene, styrene, 4-bromostyrene, nitrobenzene, trimethyl isocyanurate, methyl, and indane-1,3-dione, can result in a controlled and significant enhancement of the NLO absorptive and refractive responses. In the context of potential applications, the efficiency of carbazole-based organic materials as photoinitiators (PIs) for MPL applications is demonstrated. The fabricated woodpile microstructure using chemically functionalized carbazole as a PI demonstrates improvements in both feature size and MPL efficiency compared to that using unfunctionalized carbazole as a PI. This is attributed to the efficient charge transfer resulting from chemical functionalization, which leads to a substantial increase (approximately 1 order of magnitude) in the values of the imaginary part of the second-order hyperpolarizability (Imγ) and the two-photon absorption cross section (σ). The achieved feature size of 280 nm is comparable to that obtained with other widely used PIs in MPL applications. Additionally, owing to the strong NLO properties of the studied functionalized carbazole, they could also be promising candidates for further applications in photonics and optoelectronics.

Cyclo‐Bis(Acyl)phosphine Oxides as Efficient Photoinitiators for Radical Polymerization

AbstractAcyclic acylphosphine oxides have been extensively utilized in industrial applications as typical photoinitiators (PIs). In this study, we demonstrate the efficiency of their cyclic analogues, cyclo‐bis(acyl)phosphine oxides (CBAPOs), as efficient PIs. We present the isolation and X‐ray crystallographic characterization of CBAPOs. These compounds exhibit a long maximum absorption wavelength ranging between 415 and 420 nm, extending well into the near 500 nm region. Radical trapping experiments suggest that CBAPOs undergo homolytic P−C(O) bond α‐cleavage. Steady‐state photolysis conducted with LED light at 390 nm, monitored by UV‐Vis spectroscopy, confirms the gradual decay of CBAPOs over time. Additionally, all CBAPOs are capable of initiating radical polymerization under irradiation at 365 nm. Notably, one of the CBAPOs (4a) demonstrates comparable photoinitiating efficiency to one of commercially available bis(acyl)phosphine oxides (Irgacure 819).

Capsanthin-iodonium salt system for free radical photopolymerization under LED irradiation

The current photoinitiator (PI) is effective under mercury lamps but exhibits limited selectivity towards different radiation sources, which hinders its compatibility with eco-friendly LED lighting and raises concerns about toxicity and deep coloration. Capsanthin (Cap), with its strong photo-absorption in the 400–500 nm range, utilizes its conjugated structure to align the PI's absorption wavelength with the LED's emission spectrum. This study introduced Cap as a natural photosensitizer (PS) for free radical photopolymerization under LED irradiation. The Cap-based initiation system demonstrated promising photoinitiating capabilities under a 405 nm LED, achieving over 50 % double bond conversion in polymerized monomers. Furthermore, the system's photobleaching properties were exceptional, and its cytotoxicity was significantly lower than that of traditional PIs, such as benzoin methyl ether. The Cap's photochemical behavior under LED irradiation was explored, investigating its photoinitiating capacity and mechanism through fluorescence, photolysis, and electron paramagnetic resonance techniques. This research is vital for developing bio-based photoinitiating systems for photopolymerization in LED light environments.

Tribological, mechanical, and thermal properties of nano tricalcium phosphate and silver particulates reinforced Bis-GMA/TEGDMA dental resin composites

The proposed study is based on fabricating a hybrid dental composite of nano tricalcium phosphate and silver nanoparticles with resin matrix. Silver nanoparticles (20 wt%) and tricalcium phosphate (0–4 wt%) were incorporated in Bis-GMA/TEGDMA resin matrix. Photo initiator and accelerator were also employed for the polymerization of dental composites. Wear or tribology analysis of dental composites was performed on pin on disc setup. Physical, thermal, and mechanical properties were investigated under ASTM parameters. Void, water solubility, and sorption increased with an increment of filler loading. Maximum polymerization shrinkage 3.85 ± 0.02 % and depth of cure 2.57 ± 0.12 mm indicated by control sample TAg0. Taguchi L25 orthogonal array was used as a design of experiment (DOE) for wear analysis. TGA revealed the thermal stability in the form of: TAg0 > TAg1 > TAg2 > TAg3 > TAg4 in the range of 22–100 ̊C. In conclusion, the direct restorative material composed by the hybrid showed good mechanical and physical properties and potential thermal results, widening the scope of Ag and tricalcium phosphate in the dental composites.

Nail salon dust reveals alarmingly high photoinitiator levels: Assessing occupational risks

Photoinitiators (PIs) are chemical additives that generate active substances, such as free radicals to initiate photopolymerization. Traditionally, polymerization has been considered a green technique that seldomly generates contaminants. However, many researches have confirmed toxicity effects of PIs, such as carcinogenicity, cytotoxicity, endocrine disrupting effects. Surprisingly, we found high levels of PIs in indoor dust. Our analysis revealed comparable levels of PIs in dust from printing shops (geometric mean, GM: 1.33 ×103 ng/g) and control environments (GM: 874 ng/g), underscoring the widespread presence of PIs across various settings. Alarmingly, in dust samples from nail salons, PIs were detected at total concentrations ranging from 610 to 1.04 × 107 ng/g (GM: 1.87 ×105 ng/g), significantly exceeding those in the control environments (GM: 1.43 ×103 ng/g). Nail salon workers' occupational exposure to PIs through dust ingestion was estimated at 4.86 ng/kg body weight/day. Additionally, an in vitro simulated digestion test suggested that between 10 % and 42 % of PIs present in ingested dust could become bioaccessible to humans. This is the first study to report on PIs in the specific environments of nail salons and printing shops. This study highlights the urgent need for public awareness regarding the potential health risks posed by PIs to occupational workers, marking an important step towards our understanding of environmental pollution caused by PIs.

Carbene-mediated gelatin and hyaluronic acid hydrogel paints with ultra adhesive ability for arthroscopic cartilage repair

In articular cartilage defect, particularly in arthroscopy, regenerative hydrogels are urgently needed. It should be able to firmly adhere to the cartilage tissue and maintain sufficient mechanical strength to withstand approximately 10 kPa of arthroscopic hydraulic flushing. In this study, we report a carbene-mediated ultra adhesive hybrid hydrogel paints for arthroscopic cartilage repair, which combined the photo initiation of double crosslinking system with the addition of diatomite, as a further reinforcing agent and biological inorganic substances. The double network consisting of ultraviolet initiated polymerization of hyaluronic acid methacrylate (HAMA) and carbene insertion chemistry of diazirine-grafted gelatin (GelDA) formed an ultra-strong adhesive hydrogel paint (H2G5DE). Diatomite helped the H2G5DE hydrogel paint firmly adhere to the cartilage defect, withstanding nearly 100 kPa of hydraulic pressure, almost 10 times that in clinical arthroscopy. Furthermore, the H2G5DE hydrogel supported cell growth, proliferation, and migration, thus successfully repairing cartilage defects. Overall, this study demonstrates a proof-of-concept of ultra-adhesive polysaccharide hydrogel paints, which can firmly adhere to the articular cartilage defects, can resist continuous hydraulic pressure, can promote effective cartilage regeneration, and is very suitable for minimally invasive arthroscopy.

Typ‐I‐Photoinitiator auf der Basis nachhaltiger Kohlenstoffpunkte

AbstractNachhaltige Kohlenstoffpunkte, die an der Oberfläche Oximestergruppen enthalten, welche einer homolytischen Bindungsspaltung folgen, zeigen ein Potential als Photoinitiatoren für die traditionelle freie radikalische Photopolymerisation. Die Kohlenstoffpunkte wurden nach einem solvothermalen Verfahren aus nachhaltigem Furfural, welches über Lignocellulose erhältlich ist, hergestellt. Aldehydgruppen der Oberfläche reagierten mit Hydroxylamin zu dem entsprechendem Oxim, während die Reaktion mit Benzoylchlorid zu einem bio‐basierten Typ I Photoinitiator (CD‐PI) führte, welcher nachhaltige Kohlenstoffpunkte enthält. Die Fähigkeit zur Photoinitiierung wurde unter UV‐Bestrahlung bei 365 nm mit dem traditionellen Photoinitiator (PI) Ethyl (2,4,6‐trimethyl benzoyl) phenyl phosphinat (TPO‐L) mittels Echtteit FTIR Spektroskopie verglichen. Die auf einem Gemisch von Urethandimethacrylat (UDMA) und Tripropylenglykoldiacrylat (TPGDA) basierte Photopolymerzusammensetzung führte unter Verwendung von CD‐PI oder TPO‐L zu einem ähnlichen Endumsatz von etwa 70 %. Dennoch erschien das vernetzte Material im Fall der Zusammensetzungen, die mit CD‐PI verarbeitet wurden, homogen, während jene, die mit TPO‐L hergestellt wurden, heterogen waren, was durch die beiden Glasübergangstemperaturen gezeigt wurde. Außerdem war die Migrationsgeschwindigkeit von CD‐PI in den gehärteten Proben geringer im Vergleich zu jenen Proben für die TPO‐L als PI eingesetzt wurde.

Type I Photoinitiator Based on Sustainable Carbon Dots.

Sustainable carbon dots comprising surficial oxime ester groups following homolytic bond cleavage exhibit potential as photoinitiators for traditional free radical photopolymerization. Carbon dots were made following a solvothermal procedure from sustainable furfural available from lignocellulose. Surficial aldehyde moieties reacted with hydroxylamine to the respective oxime while reaction with benzoyl chloride resulted in a biobased Type I photoinitiator comprising sustainable carbon dot (CD-PI). Photoinitiating ability was compared with the traditional photoinitiator (PI) ethyl (2,4,6-trimethyl benzoyl) phenyl phosphinate (TPO-L) by real-time FTIR with UV exposure at 365 nm. Photopolymer composition based on a mixture of urethane dimethacrylate (UDMA) and tripropylene glycol diacrylate (TPGDA) resulted in a similar final conversion of about 70 % using either CD-PI or TPO-L. Nevertheless, it appeared homogeneous in the case of compositions processed with CD-PI, while those made with TPO-L were heterogeneous as shown by two glass transition temperatures. Moreover, the migration rate of CD-PI in the cured samples was lower in comparison with those samples using TPO-L as PI.

Low-migration, deep photocuring thiobarbituric acid-based one-component visible photoinitiators for high-efficiency photopolymerization

The practical applications of thiobarbiturates in medicinal chemistry exemplifies their exceptional biosafety, which is crucial for developing high-efficiency photopolymerization and low-migration photoinitiators (PIs). In this study, five novel D-π-A visible PIs (ANs) were designed and synthesized via using aniline derivatives as the electron donor (D) and thiobarbituric acid as electron acceptor (A). EPR and steady-state photolysis display that the conjugated structure can be destroyed by intramolecular electron/proton transfer, leading to photobleaching. Real-time infrared (FT-IR) analyses have confirmed effective polymerization of 1,6-hexanediol diacrylate (HDDA) initiated by ANs and ANs/N-methyldiethanolamine (MDEA) under illumination. The experimental molar extinction coefficient (ε) aligns with the oscillator strength (f) calculated via DFT, while the high ε and f of AN-5 facilitate electron transfer and free radical generation, resulting in improved initiation efficiency. The conversion rate of independent initiating polymerization exhibits an impressive 78 %. Moreover, colorless polymer columns initiated by AN-5 and AN-5/MDEA display curing depths of 45 mm and 50 mm, along with photobleaching rates reaching up to 98.7 % and 100 %, respectively. Especially, AN-5 exhibits the mere 0.2 % extraction rate from polymerization films under illumination (60 min). These results indicated the great potential of thiobarbituric acid-based ANs in deep-curing materials, food packaging.

Efficient and safe coumarin-carbazole-based oxime esters for one/two-photon polymerization of LEDs/NIR light

Photocuring has developed rapidly in recent years owing to its unique “5E” characteristics, especially in the industrial and manufacturing fields, where photoinitiators (PIs) are essential components of the polymerization system. However, most PIs have limited applications in fields that directly contact the human body, such as food packaging or biomedicine, due to migration stability and toxicity. Here, four oxime esters were designed as PIs by using coumarin-carbazole as the conjugate structure, and their properties were optimized by multisite modification of the molecular structure. First, substituents with different electronic properties were introduced at the 4-position of coumarin. The introduction of electron-withdrawing trifluoromethyl redshifted the molecule and better matched the light-emitting diode (LED) emission spectra (i.e., 365–450 nm). In addition, the introduction of long and branched alkyl chains on carbazole increased the solubility of the four PIs. The initiation efficiency of the PIs was improved by inserting long or cyclized alkyl chains at the α-position of C = N double bond. The experimental results demonstrated that these four PIs are superior to the commercial oxime ester OXE 02 in terms of light absorption and initiation ability under LED irradiation. The migration stability and cytocompatibility of these PIs were validated, ensuring a green and safe application in photocuring applications. Furthermore, these PIs exhibited a considerable writing speed and remarkable nanopatterning capabilities under 780 nm laser in two-photon polymerization. These outstanding properties indicated their great potential for applications in diverse areas of photocuring, especially in food packaging, bio-3D printing, tissue engineering, and nano-additive manufacturing.

Coffee ring-free inkjet printing using UV-curable quantum dot-acrylate solution for high resolution displays

We report the coffee ring-free inkjet printing using a UV curable quantum dot (QD)-acrylate coating solution. The main objective of this study is to utilize UV curable acrylate monomers to prevent formation of coffee rings and hence to obtain uniform QD patterns using inkjet printing. For the UV curing reaction, cyclohexylmethacrylate (CHMA) was selected as the acrylate monomer, 1-[4-(phenylthio)phenyl]-1,2-octanedione 2-(o-benzoyloxime) (OXE-01), 2-isopropylthioxanthone (ITX), and 2,2-dimethoxy-2-phenylacetophenone (DMPA) were tested as photoinitiators (PIs), and pentaerythritol triacrylate (PETA) was used as a crosslinker. When the QDs were used with CHMA monomers without UV curing, inkjet printing resulted in the formation of coffee rings or cracks during monomer evaporation. However, UV curing with ITX as a PI produced inkjet droplets with uniform surfaces owing to the balance between evaporation and UV curing rates. By optimizing the compositions of the monomer, PI, and crosslinker, we successfully obtained uniform QD patterns on the micrometer scale using inkjet printing. We also demonstrated that this technique could be applied to inkjet printing of the 400 ×100 μm patterned epoxy molds. These results will be useful for the inexpensive and rapid fabrication of high-resolution QD displays using inkjet printing.