UV-VIS spectra and photoinitiation behaviors of acylphosphine oxide and bisacylphosphine oxide derivatives in unfilled, light-cured dental resins

Abstract

The aims of this study were to investigate the photoinitiation behaviors of acylphosphine oxide (APO) and bisacylphosphine oxide (BAPO) derivatives in comparison to D,L-camphorquinone (CQ)/tertiary amine (EDAB) system. Fifty six kinds of experimental unfilled, light-cured resins were prepared using APO, BAPO, CQ, EDAB, resin monomers, and adhesive monomers. The measurements of ultraviolet-visible (UV-VIS) spectroscopy, photopolymerization with differential scanning calorimeter (photo-DSC) and degree of conversion (DC) determination were performed. Results showed that the UV-VIS spectra of all APO and BAPO derivatives possessed λmax ranging between 365 and 416 nm. Their photoinitiation behaviors were not influenced by acidic adhesive monomers formulated in unfilled Bis-GMA-based resins (p<0.05). Although BAPO exhibited higher reactivity than CQ/EDAB in unfilled 6-methacryloyloxyhexcyl phosphonoacetate (6-MHPA)/ 2-hydroxyethyl methacrylate (HEMA) and 6-MHPA/glycerol monomethacrylate (GM)-based resins, it was found that there were no statistically significant differences in DC (％) between BAPO [44.2(6.5)-51.2(4.3)] and CQ/EDAB [42.4(4.4)-47.5(3.7)] (p<0.05). It was concluded that APO and BAPO photoinitiators exhibited reactivity comparable to that of CQ/tertiary amine system.

Synthesis of a novel camphorquinone derivative having acylphosphine oxide group, characterization by UV-VIS spectroscopy and evaluation of photopolymerization performance

“…Therefore, it was suggested that upon light irradiation, free radicals were generated by two concurrent and parallel mechanisms in CQ-APO: α-cleavage and hydrogen abstraction reactions. 4,5) , like the photoinitiation mechanism of acylphosphine oxides 7) . In the case of CQ-APO with an electron donating agent such as a tertiary amine, it is also noteworthy that after α-diketone [-C(=O)-C(=O)-] of CQ-APO absorbed the energy of visible rays to convert into an excited state (CQ*-APO), α-hydrogen of tertiary amine would then donate CQ*-APO to form CQ*-APO-amine exciplex (excited state complex).…”

“…In the case of CQ-APO with an electron donating agent such as a tertiary amine, it is also noteworthy that after α-diketone [-C(=O)-C(=O)-] of CQ-APO absorbed the energy of visible rays to convert into an excited state (CQ*-APO), α-hydrogen of tertiary amine would then donate CQ*-APO to form CQ*-APO-amine exciplex (excited state complex). The latter was subsequently decomposed to CQ-APO ketyl radical and free radicals derived from tertiary amines, like the photoinitiation mechanism of camphorquinone 7) . However, unlike an inactivated CQ-ketyl radica l7) , the CQ-APO ketyl radical might undergo C-P cleavage to form free radicals (Fig.…”

“…Photopolymerization time was measured according to a method 7) previously reported. Briefly, a resin sample (8.00±0.25 mg) was weighed in a small aluminum pan.…”

“…Unlike CQ/tertiary amine system, APO does not require accelerators such as tertiary amines, which might cause adverse interaction with acidic adhesive monomers 2,6) . In a recent study 7) , APO and BAPO were found to exhibit similarly high photoinitiation reactivity, as well as comparable photoinitiation ability with CQ/tertiary amine system when irradiated using a dental halogen lamp. However, APO exhibits poor photopolymerization reactivity when irradiated by a blue LED (light emitting diode) dental curing light (420-510 nm, λmax 455 nm) because of differences in light absorption range.…”

“…Figure 1 depicts a schematic illustration of the threestep synthesis of CQ-APO. As all reaction products have a photosensitive group in their structures, a hydrophobic solvent was used and all syntheses were conducted in a dark room which was shielded from ambient light containing ultraviolet light and visible light 7) .…”