Free Radical Photopolymerization Research Articles

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 diethacrylate (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.

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 diethacrylate (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.

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).

The role of the terminal benzene derivatives in triphenylamine‐based oxime esters for free radical photopolymerization

In this study, we investigate the effect of terminal benzene derivatives in triphenylamine‐based oxime esters on their photoreactivity. Five novel oxime esters ( Miko series) that containing different benzene derivatives as terminal groups, were synthesized. The electronic properties of the substituents on the benzene ring range from electron‐donating to electron‐withdrawing. Specifically, a methoxy benzene for Miko‐MOB, tert‐butyl benezene for Miko‐t‐Bu, chloro benzene for Miko‐CB, trifluoromethyl benzene for Miko‐TFM, and nitro benzene for Miko‐NB. Additionally, a compound with benzene only as the terminal substituent (TP‐1) was selected for comparision. All the new compounds exhibited higher molar extinction coefficients than TP‐1. Additionally, the steady‐state photolysis and electron spin resonance (ESR) properties would decrease from the electron‐donating substitutes to electron‐withdrawing substitutes. Finally, these oxime esters are utilized in Type I photoinitiating systems for the free radical polymerization of trimethylolpropane triacrylate (TMPTA) under UV or LED@405 nm light irradiation conditions. Among all formulations, Miko‐MOB demonstrated the highest double bond conversion efficiency under both UV and LED@405 nm light irradiation. Thus, terminal benzene derivatives in oxime esters play an important role in tuning the optical and photochemical reaction performance, offering significant value for the design strategy of such photoinitiators.

Coumarin based glyoxylate photoinitiators for free radical and cationic Photopolymerizations with UV-Visible LED irradiation

High-performance photoinitiators (PIs) play a crucial role in ultraviolet–visible (UV–Vis) photopolymerization. In this study, three coumarin-3-oxoacetic acid methyl esters (COAEs) which demonstrate significant UV–Vis absorption within the 300–500 nm range were synthesized and studied. Real-time fourier transform infrared (RT-FTIR) and photo-differential scanning calorimetry (photo-DSC) experiments demonstrated that these PIs can function as Type I and Type II PIs for initiating free radical polymerization (FRP) of acrylate monomers. Additionally, they can serve as photosensitizers for iodonium salts and sulfonium salts, enabling cationic photopolymerization (CP) of epoxy and oxetane monomers. Remarkably, even at low concentrations of 0.01 wt%, they can effectively initiate the deep curing of Tri-(propylene glycol) diacrylate (TPGDA) to a depth of approximately 9 cm after 5 min of irradiation with a 415 nm or 450 nm LED light source. Furthermore, the COAEs exhibit satisfactory photobleaching properties, making them suitable for colorless applications in photopolymerization. The photochemical and photophysical properties of the COAEs were thoroughly investigated using absorption spectroscopy, electron spin resonance, cyclic voltammetry experiments, and photoinduced decarboxylation experiments to elucidate the photoinitiation mechanism. Cytotoxicity experiments revealed that COAE-N exhibited good cytocompatibility. Therefore, the exceptional polymerization properties of COAEs offer promising prospects for FRP and CP applications. Additionally, their efficient photobleaching characteristics make them highly suitable for deep photopolymerization applications. Moreover, the low cytotoxicity of COAEs suggests significant potential for biomedical applications such as dental restoration.

Photobleachable coumarin-thioester derivatives with low cytotoxicity as visible-light photoinitiators for free radical and cationic photopolymerization

The development of photoinitiators is suffering from deep color, low solubility, and biotoxicity caused by the introduction of large-conjugated structures, also the complex synthetic procedures constrain the application of photoinitiators. To overcome this issue, nine kinds of coumarin thioester photoinitiators (CTEs) have been delicately designed and synthesized through a simple, metal-free two-step reaction. CTEs with excellent light absorption properties in the visible light range can be used not only as a type I photoinitiator but also as a type II photoinitiator, and sensitizer in the cationic photoinitiating system. CTEs effectively initiate the photopolymerization of tripropylene glycol diacrylate (TPGDA) under the irradiation of 405 nm LED, and the double bond conversions are similar to or better than those of commercial photoinitiators. Also, the cationic photopolymerization of bisphenol A diglycidyl ether (BADGE) is successfully initiated by CTEs/IOD systems. Notably, the epoxy group conversion initiated by 6O-CTE/IOD reaches 72.1 %, surpassing that of the commercial photoinitiating system. The photoinitiating mechanism of CTEs is proposed and supported by theoretical calculations. Furthermore, the bond cleavage abilities of CS bonds endow CTEs with photobleaching properties. The colorless cured film initiated by 6O-CTE was obtained under only 15 s irradiation, indicating their application prospects of CTEs in colorless photopolymerization. More importantly, the cytotoxicity of CTEs is much lower than that of commercial photoinitiator TPO. This work provides new insight into the design of biocompatible photoinitiators with a photobleaching property for LED photopolymerization.

Novel High-Performance Glyoxylate Derivative-Based Photoinitiators for Free Radical Photopolymerization and 3D Printing with Visible LED.

Investigations concerning the glyoxylate moiety as a photocleavable functional group for visible light photoinitiators, particularly in the initiation of free radical photopolymerization remain limited. This study introduces nine innovative carbazole-based ethyl glyoxylate derivatives (CEGs), which are synthesized and found to exhibit excellent photoinitiation abilities as monocomponent photoinitiating systems. Notably, these structures demonstrate robust absorption in the near-UV/visible range, surpassing the commercial photoinitiators. Moreover, the newly developed glyoxylate derivatives show higher acrylate function conversions compared to a benchmark photoinitiator (MBF) in free radical photopolymerization. Elucidation of the photoinitiation mechanism of CEGs is achieved through a comprehensive analysis involving the decarboxylation reaction and electron spin resonance spin trapping. Furthermore, their practical utility is confirmed during direct laser writing and 3D printing processes, enabling the successful fabrication of 3D printed objects. This study introduces pioneering concepts and effective strategies in the molecular design of novel photoinitiators, showcasing their potential for highly advantageous applications in 3D printing.

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.

Naphthoquinone-imidazolyl derivatives-based oxime esters as photoinitiators for blue LED-induced free radical photopolymerization

In this study, we report the successful design and synthesis of nine novel oxime esters based on the naphthoquinone-imidazolyl scaffold and serving as photoinitiators to trigger photopolymerization processes under visible light. In the presence of acrylate monomers and upon irradiation at 405 nm with a LED, these photoinitiators showed remarkable photoinitiating abilities. Newly developed photoinitiators exhibited a multifunctional photoinitiating ability since these structures could act both as Type I photoinitiators or in multicomponent systems, with an improvement of the monomer conversions in the second case. This performance enhancement was notably evidenced in two-component systems comprising the new compounds in combination with either an iodonium salt or an amine. This enhancement of the monomer conversion can be assigned to favorable interactions between the dyes and the different additives, enabling to improve the free radical generation. The underlying chemical mechanisms that govern the radical chemistry during the different photopolymerization processes were explored through a series of systematic experiments. To end, usefulness of these photoinitiators was confirmed by the successful production of 3D objects using the Direct Laser Write method. This suggests promising applications of these photoinitiators in 3D printing technologies.

Photoinitiators from bio-sourced naphthoquinone – the application of naphthoquinone-based vitamins K1 and K3 in free radical photopolymerization

Two common bio-sourced naphthoquinone derivatives, vitamin K1 (phylloquinone) and vitamin K3 (menadione), were employed in free radical photopolymerization under LED light exposure at 405 nm.

Coumarin Derivatives as Dual Photo/Thermal initiators for Free Radical Polymerization and 3D Printing

In this study, five coumarin derivatives (Coums) were developed and synthesized to serve as visible light photoinitiators for the free radical photopolymerization of acrylates upon irradiation with a 405 nm...

Mechanochromic and ionic conductive cholesteric liquid crystal elastomers for biomechanical monitoring and human-machine interaction.

Cholesteric liquid crystal elastomers (CLCEs) that combine rubbery elasticity with structural colour from self-assembled helical nanostructures are of paramount importance for diverse applications such as biomimetic skins, adaptive optics and soft robotics. Despite great advances, it is challenging to integrate electrical sensing and colour-changing characteristics in a single CLCE system. Here, we report the design and synthesis of an ionic conductive cholesteric liquid crystal elastomer (iCLCE) through in situ Michael addition and free-radical photopolymerization of CLCE precursors on silane-functionalized polymer ionic liquid networks, in which robust covalent chemical bonding was formed at the interface. Thanks to superior mechanochromism and ionic conductivity, the resulting iCLCEs exhibit dynamic colour-changing and electrical sensing functions in a wide range upon mechanical stretching, and can be used for biomechanical monitoring during joint bending. Importantly, a capacitive elastomeric sensor can be constructed through facilely stacking iCLCEs, where the optical and electrical dual-signal reporting performance allows intuitive visual localization of pressure intensity and distribution. Moreover, proof-of-concept application of the iCLCEs has been demonstrated with human-interactive systems. The research disclosed herein can provide new insights into the development of bioinspired somatosensory materials for emerging applications in diverse fields such as human-machine interaction, prostheses and intelligent robots.

Triphenylamine-substituted BODIPY dye based photoinitiators for free radical and cationic photopolymerization under visible LED irradiation and application in 3D printing

Until now the photopolymerization process is largely dependent on the hazardous UV or near UV light irradiation. Herein this work, a series of boron dipyrromethene (BODIPY) derivatives substituted by electron-donating triphenylamine moiety on different positions were introduced and investigated thoroughly. Markedly, their photoinitiation abilities under mild conditions, e.g. visible LEDs irradiation and room temperature, were examined for the first time. In combination with an iodonium salt and an amine as the co-initiators, these BODIPY dyes could form three-component photoinitiating systems (PISs) for the purpose to initiate both the free radical polymerization of acrylate monomers and cationic polymerization of epoxy monomers. Interestingly, under the irradiation of LED@405 nm, LED@530 nm or LED@660 nm, some of these BODIPYs-based PISs could conduct high monomeric conversion and rapid photopolymerization rates, as reflected by the relevant photopolymerization kinetics. Then the notable photochemical reactivity of these BODIPY dyes was examined by both steady state photolysis and fluorescence quenching experiments, and theoretical calculation was also performed on them in details. Finally, photocuring 3D printing technique was applied to the acrylate/epoxy mixture resin, as the result the BODIPYs-based PISs demonstrated great potential to fabricate truly three-dimensional objects in macroscopic scale with excellent spatial resolution.

Study on the photoinitiation mechanism of carbazole-based oxime esters (OXEs) as novel photoinitiators for free radical photopolymerization under near UV/visible-light irradiation exposure and the application of 3D printing

In this work, twenty-two oxime esters bearing different functional groups and based on carbazole as the chromophore were designed and synthesized as Type I photoinitiators. Interestingly, all structures mentioned in this work have never been reported before (even for their synthesis). These oxime esters were found to have good light absorption properties in the UV–visible range, and especially at 405 nm which is a reference wavelength in photopolymerization. Noticeably, several structures showed better photoinitiation abilities than the benchmark photoinitiator i.e. diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), evidencing the interest of these structures. In order to investigate the photoinitiation mechanism of the two series of oxime esters differing by the position of the photocleavable groups, electronic absorption spectra were determined by molecular modeling and density functional theory calculations. Photopolymerization abilities of the different oxime esters and release of CO2 during the polymerization experiments were determined by Real-Time Fourier Transformed Infrared (RT-FTIR). Active free radicals were characterized by mean of Electron Spin Resonance Spin Trapping (ESR-ST) experiments. On the basis of these different complementary experiments, chemical mechanisms occurring during photopolymerization could be proposed. Experimental results showed that the decarboxylation reaction occurring subsequent to the photocleavage of oxime esters had a beneficial effect on the photoinitiation ability. Finally, 3D printed objects were successfully obtained by using oxime esters exhibiting the best photoinitiating abilities.

Synthesis and properties of acyldiphenylphosphine oxides photoinitiators carrying ferrocene group for free radical photopolymerization

Thick film curing has become a research hotspot in photocuring systems, among which designing and synthesizing visible light initiators is particularly important. Herein, two new visible light initiators of (diphenylphosphoryl)(ferrocene-1-yl)methanone (FEPO) and ferrocene-1,1′-diylbis((diphenylphosphoryl)methanone) (FSPO) were designed and synthesized from diphenylphosphine oxide reacting with ferrocenecarboxaldehyde and 1,1′-ferrocenedicarboxaldehyde, respectively. FEPO and FSPO possess good solubility in different solvents and acrylic monomers. The UV-Vis spectrums of FEPO and FSPO showed that they exhibit a wide absorption range of 300–670 nm, and the maximum absorption wavelengths are about 494 nm and 505 nm, with a molar extinction coefficient of around 1226 M⁻¹cm⁻¹ and 299 M⁻¹cm⁻¹, suggesting that they are likely to be visible light photoinitiator (PI). The addition of N-phenylglycine (NPG) significantly improved the curing efficiency of FEPO and FSPO, the degree of double bond conversion (DC) of FSPO increased from 27 % to 48 % under the irradiation of LED@480 nm, while, under the irradiation of LED@405 nm, the DC of FEPO/NPG is about 52 %. Moreover, the curing depth of FEPO/NPG/trimethylolpropane triacrylate (TMPTA) (1.75 cm) was about 1.8 times that of diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO)/TMPTA (0.98 cm) after irradiating for 5 min. In addition, FEPO can be used in laser cladding deposition (LCD) 3D printers with light-emitting diode (LED)@405 nm. Using steady-state photolysis and electron spin resonance spin-trapping studies, the photocuring mechanism was examined. Additionally, photoinitiators (PIs) also exhibit superior biocompatibility performance demonstrated by cytotoxicity assays, suggesting they might be utilized in 3D printing in biological materials and coatings for food packaging.

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.

Nanocomposite Hydrogel Films Based on Sequential Interpenetrating Polymeric Networks as Drug Delivery Platforms.

In this study, novel materials have been obtained via a dual covalent and ionic crosslinking strategies, leading to the formation of a fully interpenetrated polymeric network with remarkable mechanical performances as drug delivery platforms for dermal patches. The polymeric network was obtained by the free-radical photopolymerization of N-vinylpyrrolidone using tri(ethylene glycol) divinyl ether as crosslinker in the presence of sodium alginate (1%, weight%). The ionic crosslinking was achieved by the addition of Zn2+, ions which were coordinated by the alginate chains. Bentonite nanoclay was incorporated in hydrogel formulations to capitalize on its mechanical reinforcement and adsorptive capacity. TiO2 and ZnO nanoparticles were also included in two of the samples to evaluate their influence on the morphology, mechanical properties and/or the antimicrobial activity of the hydrogels. The double-crosslinked nanocomposite hydrogels presented a good tensile resistance (1.5 MPa at 70% strain) and compression resistance (12.5 MPa at a strain of 70%). Nafcillin was loaded into nanocomposite hydrogel films with a loading efficiency of up to 30%. The drug release characteristics were evaluated, and the profile was fitted by mathematical models that describe the physical processes taking place during the drug transfer from the polymer to a PBS (phosphate-buffered saline) solution. Depending on the design of the polymeric network and the nanofillers included, it was demonstrated that the nafcillin loaded into the nanocomposite hydrogel films ensured a high to moderate activity against S. aureus and S. pyogenes and no activity against E. coli. Furthermore, it was demonstrated that the presence of zinc ions in these polymeric matrices can be correlated with the inactivation of E. coli.

Preparation of nitro‐phenothiazine‐based oxime esters as dual photo/thermal initiators for 3D printing

AbstractNowadays, photopolymerization has spanned across all academic and industrial applications due to its appealing features such as energy saving, environmentally‐friendly polymerization conditions, high monomer conversions, rapid polymerization kinetics and so on. Photoinitiator (PI), as a crucial component of the photoinitiating system (PIS) are capable of interacting with light efficiently, enabling to generate initiating species in mono or multicomponent systems. In this work, 13 phenothiazine‐based oxime esters (OXEs) (never reported before) were synthesized and their photoinitiation abilities for the free radical photopolymerization (FRP) of acrylates were examined upon irradiation with LED@405 nm. Parallel to their photochemical reactivities, their abilities to initiate thermal polymerization processes were also investigated. Finally, these OXEs exhibited excellent photo/thermal initiation performances, demonstrating their dual initiation properties. Phenothiazine‐based oxime esters can be used as PIs in 3D printing as well as thermal initiator in the manufacturing of carbon fiber composites.

Synthesis and photochemistry of flavonol camphorsulfonates photoinitiator with different substituents

In this study, we synthesized five novel flavonol camphorsulfonates (HFSs) photoinitiators using a flavonol scaffold as the chromophore. These HFSs demonstrated photoinitiating properties in both one-component (Norrish Type I) and two-component photoinitiating systems, with high final reaction function conversion and excellent polymerization rates of acrylates in free radical photopolymerization. Additionally, HFSs exhibited thermal stability in thermogravimetric tests. To explain the photoinitiating mechanisms, we used various complementary approaches, including real-time FT-IR spectroscopy, UV–Vis absorption spectroscopy, fluorescence spectroscopy, analysis of photolysis products, cyclic voltammetry, free radical capture experiments and molecular modelling calculations.

Synthesis and properties of acyldiphenylphosphine oxides photoinitiators carrying triphenylamine or pyrene group for free radical photopolymerization

AbstractTwo new photoinitiators of acyldiphenylphosphine oxides carrying triphenylamine (NHPO) or pyrene group (BHPO) were designed and synthesized with diphenylphosphine oxide reacting with 4‐(diphenylamino) benzaldehyde or 1‐pyrenecarboxaldehyde. The solubility of NHPO is about 13.7 wt% in TMPTA, which is higher than that of (2,4,6‐trimethylbenzoyl) diphenylphosphine oxide (TPO) (about 12.5 wt%). The UV–Vis spectrum of NHPO and BHPO revealed that their maximum absorption wavelengths have redshifted to 397 and 419 nm, respectively, with a molar extinction coefficient of around 19,057 and 24,257 M−1 cm−1, suggesting that they are likely to be effective photoinitiators when exposed to light from LEDs. According to real‐time Fourier transform infrared spectroscopies, the degree of double bond conversion of NHPO reached 65%, which was higher than that of TPO (about 45%), showing that NHPO had substantially better photoinitiated properties than TPO. Using steady‐state photolysis and electron spin resonance spin‐trapping studies, the photocuring mechanism was examined, and it was discovered that the NHPO and BHPO had produced two free radicals. Additionally, NHPO exhibited superior biocompatibility performance as demonstrated by cytotoxicity assays and had a low migration rate of only 0.23%, as determined by migration. As a result, NHPO might be utilized in coatings for food packaging.