Naphthyl-based acylphosphine oxide photoinitiators with high effiency and low migration
Graphical abstract
Introduction
Light curing was widely used in coating, adhesive, ink, electronic packaging, 3D printing, food packaging and biomedical fields due to its efficiency, applicability, safety and environmental friendly properties [[1], [2], [3], [4], [5], [6], [7]]. Photoinitiators (PIs) are one of the most important components in the light curing system [8]. Among them, the acylphosphine oxide compounds exhibit excellent reactivity for UV and near-UV light irradiation [[9], [10], [11], [12]]. With the exposure of light, PIs (ground state) could convert to the transition state (radical or cation). And the latter is able to trigger certain monomer to polymer [13]. During the process, the matching of PIs and light is essential to achieve excellent conversion of monomer. Taking account of the safe usage and good light output, light-emitting diodes (LEDs) have been chosen as the light source. And the LEDs giving irradiation of near-UV or visible light [[14], [15], [16], [17]] are preferred. Accordingly, great efforts have been made in the design of PIs with long wavelength of light absorption. For example, Henne and Wolf et al. synthesized several acyl oxides and acyl sulfide with light absorption up to 600 nm [18,19]. In our previous work, by introducing of diethyl amino group into the acyl group, an acyl phosphine compound was synthesized. This compound exhibited red-shifted absorption spectrum with high absorption molar absorption coefficients [20].
Besides the absorption of long wavelength light, the migration of PIs is another issue that should be noticed. Migration means the transfer of unreacted species to the surface of materials. Such transfer is very important in food packaging and would confine the application of light curing in this field and other materials in direct contact with human body [21]. However, as reported by Cai et al., the newly synthesized initiating agents commonly possessed severe migration after photopolymerization [22]. Xiao et al. synthesized naphthalimide based methacrylated PIs for the photo-initiated polymerization under visible light [23]. Although the PIs exhibited high light curing efficiency, higher migration of PIs was also detected. From this point of view, reducing of the migration of PIs in light curing materials needs to be solved urgently.
In order to lower the migration and improve the absorption properties and curing efficiency of PIs, a series of monoacylphosphine oxides containing different naphthyl groups was designed and synthesized (N1-N4 in Fig. 1). The performances of these PIs in the FRP of TMPTA have been evaluated and compared with traditional photoinitiator (TPO). The migrations of PIs from the cured sample were also discussed.
Section snippets
Materials and characterization
The following compounds (Fig. 2) were used without pretreatment in this study: TPO and diphenylphosphine oxide (DPO) were supplied by Qingdao Fusilin Chemical Science &Technology Co., Ltd. (Qingdao, China). 1-naphthaldehyde, 2-naphthaldehyde, 2-methoxy-1-naphthaldehyde, 6-methoxy-2-naphthaldehyde, dichloromethane (DCM) and ethyl acetate (EA) and TMPTA were purchased from Aladdin Industrial Corporation (Shanghai, China). Active manganese dioxide (MnO2) was synthesized in our laboratory [24].
Synthesis of naphthyl-based acylphosphine oxide photoinitiators
The
Synthesis of naphthyl-based acylphosphine oxide photoinitiators
Naphthyl-based acylphosphine oxide photoinitiators (N1 ∼ N4) were synthesized according to Scheme 1. After the completion of reaction, the products were obtained by flash column chromatography on silica gel. However, N4 could not be isolated successfully. Results of TLC analysis suggested that N4 decomposed quickly during the isolation process (Fig. S10). According to literatures, acylphosphine oxides suffer the solvolytic cleavage of carbon-phosphorus bond and the existence of ortho-substitute
Conclusion
In summary, a series of naphthyl-based acylphosphine oxide compounds were designed and synthesized to obtain the photoinitiators with red-shifted absorption, high curing effiency and low migration. As expected, N1 ∼N3 possessed higher molar absorption coefficients and better initiating activity than the commercial one (TPO). Migration results showed that the mobility of N1 ∼N3 in polymerized TMPTA is much lower than that of TPO, especially for N3. Therefore, this study give good candidates for
Author statement
Yaoyal Liu: Synthesized compound N2, N3; analysis their properties; write the manuscript.
Tingting Wang: Synthesized compound N1, N2; analysis their properties.
Chuanbao Xic: made contributions with the migration analysis of N1–N3.
Xiujuan Tian: made contributions with the FTIR analysis.
Liang Song: revised the manuscript critically for important intellectual content.
Lei Liu: revised the manuscript critically for important intellectual content.
Zhongwei Wang: discussed and interpretation the results
Data availability
The raw/processed data required to reproduce these findings cannot be shared at this time due to legal/ethical reasons.
Declaration of Competing Interest
None.
Acknowledgements
This work was founded by National Natural Science Foundation of China (Grant No. 21103099, 21676285 and 21306214), Basic Research Projects in Science and Technology Program of Qingdao (13-1-4-242-jch), Qingdao Indigenous Innovation Program (No. 15-9-1-76-jch) and Research Foundation of Qingdao Fusilin Chemical Science &Technology Co., Ltd. (FSL-RF 2016).
References (29)
- et al.
Monomer-to-polymer conversion and micro-tensile bond strength to dentine of experimental and commercial adhesives containing diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide or a camphorquinone/amine photo-initiator system
J. Dent.
(2013) - et al.
Photopolymerization upon LEDs: new photoinitiating systems and strategies
Polym. Chem.
(2015) - et al.
A novel acyl phosphine compound as difunctional photoinitiator for free radical polymerization
Prog. Org. Coat.
(2019) - et al.
Low migration type I photoinitiators for biocompatible thiol-ene formulations
Eur. Polym. J.
(2017) - et al.
Chemical aspects of self-etching enamel-dentin adhesives: asystematic review
Dent. Mater.
(2005) - et al.
On the photolysis of acylphosphine oxides: 1. laser flash photolysis studies with 2,4,6-trimethylbenzoyldiphenylphosphine oxide
Polymer
(1985) - et al.
Effect of addition of cellulose nanocrystals to wood coatings on color changes and surface roughness due to accelerated weathering
J. Coat. Technol. Res.
(2015) - et al.
Coating performance and characteristics for UV-curable aliphatic urethane acrylate coatings containing norrish type I photoinitiators
JCT Res.
(2006) Advances in Electronic Packaging Technologies by Ultra-Small Microvias, Super-Fine Interconnections and Low Loss Polymer Dielectrics
(2009)- et al.
High-performance 3D printing of hydrogels by water-dispersible photoinitiator nanoparticles
J. Appl. Sci. Eng.
(2016)
Photoinitiators: a food safety review
Food Addit. Contam. Part A Chem. Anal. Control Expo. Risk Assess.
Effect of different photoinitiators and reducing agents on cure efficiency and color stability of resin-based composites using different LED wavelengths
J. Dent.
Photoinitiated polymerization: advances, challenges, and opportunities
Macromolecules
Rational design of acyldiphenylphosphine oxides as photoinitiators of radical polymerization
Macromolecules
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Yaoyao Liu and Tingting Wang contributed equally to this work.