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

Abstract

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.