A Norrish II type photoinitiator and its application in dental materials

Abstract

The present invention discloses a Norrish type II photoinitiator and its application in dental materials, relating to the technical field of organic synthesis. The structural formula of the Norrish type II photoinitiator is shown as follows. Among them, R1 is hydrogen, methoxy, or fluorine; R2 is hydrogen or methacryloxymethyl; R3 is methoxy or methacryloxy; when R2 is hydrogen, R3 can only be methacryloxy. This Norrish type II photoinitiator can jointly form a photoinitiating system with camphorquinone and iodide salt, and has a lower carbon-hydrogen bond dissociation energy compared with common amine initiators such as ethyl 4-dimethylaminobenzoate, and can be used to synthesize photo-curing dental resin materials with excellent properties. #imgabs0#

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, and in particular to a Norrish II type photoinitiator and application thereof in dental materials. Background Art

[0002] Lignin is widely present in nature, and its reserves are second only to cellulose. It is the most abundant natural aromatic polymer in nature, and has the advantages of low price, non-toxicity, and renewable, but it has not been effectively utilized so far. In recent years, the demand for obtaining fine chemicals or energy from sustainable materials has continued to increase, and related research on the conversion of lignin into high-value-added chemicals has received widespread attention. At present, a large number of studies have been conducted on the depolymerization of lignin, and the obtained phenolic compounds can be used in the production of polymers, antioxidants, resins, drugs or pesticides to replace traditional fossil fuel resources. The aromatic rings in lignin are connected by CC bonds (5-5, β-5, β-β, β-1) and CO bonds (4-O-5, α-O-4, β-O-4), of which β-O-4 accounts for about 50% of the covalent bond connection structure. The chemical degradation of β-O-4 lignin usually includes two steps: oxidation of β-O-4 benzyl alcohol to benzophenone and cleavage of the CO bond.

[0003] Since the first discovery of light-curable dental resin materials in 1975, photoinitiated free radical polymerization has been widely used in dental resin-based composites. At present, dental composites are mainly composed of organic resin matrix (monomer, photoinitiator system and stabilizer), inorganic filler and coupling agent. The polymerization reaction of dental composites is initiated by the free radicals produced by the photoinitiator system after irradiation with dental light curing lamp. Under the irradiation of blue light, the initiator molecule absorbs hydrogen (proton) to become acetyl free radicals, the initiator and the electron in the initiator exchange, and the co-initiator molecule becomes an alkyl free radical. The free radical combines with the carbon-carbon double bond of the monomer for "chain growth". The camphorquinone (CQ) / aromatic amine (such as ethyl 4-dimethylaminobenzoate EDB) system is the most mature, and the free radical is initiated by the hydrogen transfer mechanism. However, EDB has some disadvantages, such as poor color stability over time (yellowing color), inherent cytotoxicity and genotoxicity, instability of acidic dental resins and sensitivity to oxygen inhibition. Therefore, finding a new photoinitiator system for methacrylate dental resins has become a hot issue.

[0004] Recently, the Lalevée research group has demonstrated that sulfates / sulfonates are good co-initiators, and the photoinitiator system formed by combining with iodosulfonates and camphorquinone has good polymerization performance (J.Kirschner, F.Szillat, M.Bouzrati-Zerelli, JM Becht, JE Klee, J.Lalevée, Sulfinates and sulfonates as highperformance co-initiators in CQ based systems: Towards aromatic amine-free systems for dental restorative materials, Dent. Mater. 2020, 36(2)187-196); piperonyl compounds or germanium hydrides with CH bonds have also been shown to be new hydrogen donors (AG Moreira, CE Cuevas-Suárez, WL de O. da Rosa, AOO gliari, CL Petzhold, E. Piva, FAO gliari, Gd SLima, Piperonyl methacrylate: Copolymerizable coinitiator for adhesive compositions, J. Dent. 2018, 79 31-38); The research group also developed new hydrogen donors with methacrylates based on sesamol, 6-hydroxy-3-kumaranone and 5-hydroxy-2(3H)-benzofuranone (E.Sprick, JM Becht, B.Graff, JP Salomon, T.Tigges, C.Weber, J.Lalevée, New hydrogen donors for amine-freephotoinitiating systems in dental materials, Dent.Mater.2021,37(3)382-390).Hammoud et al. proposed that oxime ester (OXE) be used as an initiating group. The NO bond is cleaved under light to produce iminoacyl and acyloxy radicals, which can obtain high polymerization rate and good final conversion rate (F. Hammoud, Z. Lee, B. Graff, A. Hijazi, J. Lalevée, Y. Chen, J. Novel phenylamine-based oxime ester photoinitiators for LED-induced free radical, cationic, and hybrid polymerization, J. Poly. Sci. 2021, 59(15), 1711-1723).

[0005] However, there is no report in the prior art on the application of lignin derivatives in the synthesis of photocurable materials, especially in the field of photocurable dental materials. Summary of the invention

[0006] The invention provides a Norrish II type photoinitiator. The Norrish II type photoinitiator can form a photoinitiator system together with camphorquinone and iodine salt. The Norrish II type photoinitiator has a lower carbon-hydrogen bond dissociation energy (BDE(CH2)) than that of commonly used amine initiators such as ethyl 4-dimethylaminobenzoate (EDB), and can be used for synthesizing a light-cured dental resin material with excellent performance.

[0007] The specific technical solutions adopted are as follows:

[0008] A Norrish II type photoinitiator, the structural formula of which is shown in formula (I):

[0009]

[0010] Among them, R1 is hydrogen, methoxy or fluorine; R2 is hydrogen or methacryloxymethyl; R3 is methoxy or methacryloxy; when R2 is hydrogen, R3 can only be methacryloxy.

[0011] Preferably, the structural formula of the Norrish II type photoinitiator is any one of the compounds shown in the following formula:

[0012]

[0013] Norrish II type photoinitiator generally refers to an initiator that absorbs light energy and then reacts with the co-initiator in the excited state through bimolecular reaction to form active free radicals through hydrogen abstraction reaction or electron / proton transfer. This type of photoinitiator is based on the reaction of the triplet excited state with the hydrogen donor to produce initiating free radicals.

[0014] Free radical polymerization is divided into two types: a cleavage reaction mechanism (Norrish I type) and a hydrogen abstraction reaction mechanism (Norrish II type); the Norrish II type photoinitiator provided by the present invention is a derivative of β-O-4 lignin, and has the hydrogen supply capacity required by the co-initiator; the initiation system in the present invention belongs to the Norrish II type, and under light, camphorquinone (CQ) absorbs visible light to form an excited state CQ*, which forms a common excited state with the Norrish II type photoinitiator, and the hydrogen of the Norrish II type photoinitiator is transferred to CQ to generate C free radicals and C-OH free radicals respectively, and the C free radicals are transferred to the monomer to initiate monomer polymerization.

[0015] The present invention also provides a method for preparing the Norrish II type photoinitiator, and the method for preparing the Norrish II type photoinitiator is one of method 1 or method 2:

[0016] Method 1 includes the following steps:

[0017] Step (1.1), in an alkaline environment, using compound 1 and a phenol compound as raw materials to react in an organic solvent, and after the reaction, post-treating the product solution to prepare intermediate 1;

[0018] Step (1.2), in an alkaline environment, reacting the intermediate 1 and methacryloyl chloride as raw materials in an organic solvent at room temperature, and after the reaction, post-treating the product solution to obtain the Norrish II type photoinitiator;

[0019] Method 2 includes the following steps:

[0020] Step (2.1), in an alkaline environment, using compound 1 and a phenol compound as raw materials to react in an organic solvent, and after the reaction, post-treating the product solution to prepare intermediate 1;

[0021] Step (2.2), in an alkaline environment, using intermediate 1 and formalin as raw materials to react at room temperature in a mixed solvent system, and obtaining intermediate 2 through post-treatment;

[0022] Step (2.3), in an alkaline environment, reacting the intermediate 2 and methacryloyl chloride as raw materials in an organic solvent at room temperature, and after the reaction, post-treating the product solution to obtain the Norrish II type photoinitiator;

[0023] In method 1 and method 2, the structural formula of the compound 1 is: The definition of R1 is the same as that in formula (I); the phenol compound is hydroquinone or 4-methoxyphenol.

[0024] Preferably, in step (1.1), step (2.1) and step (2.2), potassium carbonate is added to the reaction raw materials to achieve an alkaline environment; in step (1.2) and step (2.3), triethylamine is added to the reaction raw materials to achieve an alkaline environment.

[0025] Preferably, in step (1.1) and step (2.1), the reaction temperature is 90-95°C and the reaction time is 1-10h; in step (2.2), the reaction time is 1-10h; in step (1.2) and step (2.3), the reaction time is 12-36h.

[0026] Preferably, in step (1.1) and step (2.1), the organic solvent is acetone, acetonitrile or N,N-dimethylformamide; in step (2.2), the mixed solvent is at least two of acetone, ethanol, acetone and methanol; in step (1.2) and step (2.3), the organic solvent is dichloromethane, chloroform or dichloroethane.

[0027] Preferably, in step (1.1) and step (2.1), the molar ratio of compound 1 to the phenol compound is 1:1-2; in step (1.2), the molar ratio of intermediate 1 to methacryloyl chloride is 1:1-3; in step (2.2), the molar ratio of intermediate 1 to formalin is 1:1-10; in step (2.3), the molar ratio of intermediate 2 to methacryloyl chloride is 1:1-3.

[0028] The present invention also provides application of the Norrish II type photoinitiator in dental materials.

[0029] Specifically, the present invention provides a light-curing dental resin material, comprising the following raw material components in weight percentage: 0.5%-1.5% of the Norrish II type photoinitiator; 0.2%-1% of camphorquinone, 0.5%-1.5% of iodine salt, 63%-73% of main monomer; and 24%-34% of diluent monomer.

[0030] The iodine salt is diphenyl iodine hexafluorophosphate, 4,4'-ditolyl iodine hexafluorophosphate or diphenyl ammonium iodine hexafluorophosphate; adding the iodine salt to the two-component initiator system can significantly increase the polymerization rate and the final conversion rate, because more active benzene free radicals are generated and the number of free radicals is increased;

[0031] The main monomer includes at least one of bisphenol A-glycidyl methacrylate (Bis-GMA), urethane dimethacrylate (UDMA), and ethoxylated bisphenol A dimethacrylate (Bis-EMA);

[0032] The diluent monomer includes at least one of triethylene glycol dimethacrylate (TEGDMA), hydroxyethyl methacrylate (HEMA), and ethylene glycol dimethacrylate (EDMA).

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) Compared with commonly used amine initiators such as ethyl 4-dimethylaminobenzoate (EDB), the Norrish II photoinitiator provided by the present invention has a lower carbon-hydrogen bond dissociation energy (BDE(CH)), which indicates that it can efficiently provide hydrogen to the co-initiator camphorquinone and has good co-initiator behavior;

[0035] (2) The synthesis method of the Norrish II type photoinitiator provided by the present invention is simple to operate, has mild reaction conditions, and the synthetic raw materials are economical and readily available. Lignin is widely present in nature, is environmentally friendly, has higher economic benefits, and has less environmental pressure in production;

[0036] (3) The present invention applies the Norrish II type photoinitiator to dental photocurable resin materials, which has not been reported in the prior art. When the Norrish II type photoinitiator is used to synthesize photocurable dental resin materials, it has a high double bond conversion rate and a high polymerization rate. The synthesized photocurable dental resin materials have good bleaching properties, good color stability, good curing depth, and good biocompatibility, and have broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The curves showing the change of carbon-carbon double bond conversion rate over time for the control group 1 and the experimental groups 5-7 in Example 8;

[0038] Figure 2 The graph is a curve showing the change in carbon-carbon double bond conversion rate over time for the control group 1 and the experimental groups 1-4 in Example 8. DETAILED DESCRIPTION

[0039] The present invention is further illustrated below in conjunction with the examples and accompanying drawings. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer.

[0040] In the following examples, the flash column chromatography process uses 70-230 mesh silica gel for column chromatography separation, and the eluent is a mixture of ethyl acetate and petroleum ether in a volume ratio of 1:1. The eluate containing the target compound is collected, concentrated and dried to obtain the target product.

[0041] Example 1 Synthesis of Norrish II Photoinitiator HDA

[0042]

[0043] (1) In a dry round-bottom flask, hydroquinone 2a (11 mmol, 1.1 eq), potassium carbonate (14 mmol, 1.4 eq), compound 1a (10 mmol, 1.0 eq) and acetone (40 mL) were added in sequence, the mixture was heated to 90-95° C. and refluxed for 5 hours, cooled to room temperature, the mixed product was filtered, concentrated to obtain a crude product, and purified by flash column chromatography to obtain intermediate 1 (HDa) with a yield of 60%;

[0044] (2) HDa (2.31 mmol, 1.0 eq) and triethylamine (TEA, 2.77 mmol, 1.2 eq) were dissolved in dichloromethane (DCM, 1 M), and methacryloyl chloride 4a (2.54 mmol, 1.1 eq) was added dropwise at 0°C. The reaction was heated to room temperature and stirred for 24 hours. After concentration, the crude product was purified by flash column chromatography to obtain Norrish II type photoinitiator HDA with a yield of 72%;

[0045] HDa, pale yellow solid, 1 H NMR (500MHz, CDCl3): δ7.98(d,J=7.4Hz,2H),7.61(t,J=7.4Hz,1H),7.49(t,J =7.8Hz,2H),6.83–6.79(m,2H),6.77–6.73(m,2H),5.51(s,1H),5.22(s,2H).

[0046] HDA, light yellow powder, 1 H NMR (500MHz, CDCl3): δ8.03–7.99(m,2H),7.66–7.61(m,1H),7.51(t,J=7.8Hz,2H),7.06–7.03(m, 2H),6.99–6.94(m,2H),6.34–6.31(m,1H),5.74(p,J=1.3Hz,1H),5.27(s,2H),2.08–2.04(m,3H).

[0047] Example 2 Synthesis of Norrish II Photoinitiator HDB

[0048]

[0049] (1) In a dry round-bottom flask, hydroquinone 2a (11 mmol, 1.1 eq), potassium carbonate (14 mmol, 1.4 eq), compound 1b (10 mmol, 1.0 eq) and acetone (40 mL) were added in sequence, the mixture was heated to 90-95° C. and refluxed for 5 hours, cooled to room temperature, the mixed product was filtered, concentrated to obtain a crude product, and purified by flash column chromatography to obtain intermediate 1 (HDb) with a yield of 57%;

[0050] (2) HDb (3.34 mmol, 1.0 eq) and triethylamine (TEA, 4.01 mmol, 1.2 eq) were dissolved in dichloromethane (DCM, 1 M), and methacryloyl chloride 4a (3.67 mmol, 1.1 eq) was added dropwise at 0°C. The reaction was heated to room temperature and stirred for 24 hours. After concentration, the crude product was purified by flash column chromatography to obtain Norrish II type photoinitiator HDB with a yield of 49%;

[0051] HDb, light yellow powder, 1 H NMR (500MHz, CDCl3): δ7.92 (dd, J=7.8, 1.8Hz, 1H), 7.56–7.51 (m, 1H), 7.05 (t, J=7.5 Hz,1H),7.00(d,J=8.4Hz,1H),6.81–6.71(m,4H),5.18(d,J=0.7Hz,2H),3.95(s,3H).

[0052] HDB, light yellow oil, 1 H NMR (500MHz, CDCl3): δ7.92 (dd, J=7.8, 1.7Hz, 1H), 7.56–7.48 (m, 1H), 7.09–6.98 (m, 4H ),6.94–6.88(m,2H),6.31(s,1H),5.72(s,1H),5.22(s,2H),3.93(s,3H),2.04(s,3H).

[0053] Example 3 Synthesis of HDC

[0054]

[0055] (1) In a dry round-bottom flask, hydroquinone 2a (11 mmol, 1.1 eq), potassium carbonate (14 mmol, 1.4 eq), compound 1c (10 mmol, 1.0 eq) and acetone (40 mL) were added in sequence, the mixture was heated to 90-95° C. and refluxed for 5 hours, cooled to room temperature, the mixed product was filtered, concentrated to obtain a crude product, and purified by flash column chromatography to obtain intermediate 1 (HDc) with a yield of 32%;

[0056] (2) HDc (0.47 mmol, 1.0 eq) and triethylamine (TEA, 0.56 mmol, 1.2 eq) were dissolved in dichloromethane (1 M), and methacryloyl chloride 4a (0.52 mmol, 1.1 eq) was added dropwise at 0°C. The reaction was heated to room temperature and stirred for 24 hours. After concentration, the crude product was purified by flash column chromatography to obtain Norrish II type photoinitiator HDC with a yield of 50%;

[0057] HDc, white powder, 1 H NMR (500MHz, CDCl3): δ8.00 (d, J = 8.6Hz, 2H),

[0058] 6.97(d,J=8.7Hz,2H),6.84(dd,J=8.9,1.5Hz,2H),6.75(d,J=8.8Hz,2H),5.16(s,2H),3.89(s,3H).

[0059] HDC, white powder, 1 H NMR (500MHz, CDCl3): δ7.99 (d, J = 8.8Hz, 2H),

[0060] 7.06–7.01(m,2H),6.96(t,J=9.4Hz,4H),6.32(s,1H),5.73(s,1H),5.20(s,2H),3.88(s,3H),2.04(s,3H).

[0061] Example 4 Synthesis of Norrish II Photoinitiator HDD

[0062]

[0063] (1) In a dry round-bottom flask, hydroquinone 2a (11 mmol, 1.1 eq), potassium carbonate (14 mmol, 1.4 eq), compound 1d (10 mmol, 1.0 eq) and acetone (40 mL) were added in sequence, the mixture was heated to 90-95° C. and refluxed for 5 hours, cooled to room temperature, the mixed product was filtered, concentrated to obtain a crude product, and purified by flash column chromatography to obtain HDd with a yield of 34%;

[0064] (2) HDd (1.65 mmol, 1.0 eq) and triethylamine (TEA, 1.98 mmol, 1.2 eq) were dissolved in dichloromethane (1 M), and methacryloyl chloride 4a (1.82 mmol, 1.1 eq) was added dropwise at 0°C. The reaction was heated to room temperature and stirred for 24 hours. After concentration, the crude product was purified by flash column chromatography to obtain Norrish II type photoinitiator HDD with a yield of 38%;

[0065] HDd, white powder, 1 H NMR (500MHz, CDCl3): δ7.99 (td, J=7.8, 1.7Hz,

[0066] 1H),7.62–7.56(m,1H),7.29(t,J=7.6Hz,1H),7.19(dd,J=11.0,8.5Hz,1H),6.86–6.73(m,4H),5.17(d,J=3.3Hz,2H),4.75(s,1H).

[0067] HDD, white powder, 1 H NMR (500MHz, CDCl3): δ8.00 (td, J=7.6, 1.8Hz,

[0068] 1H),7.60(ddd,J=15.3,5.2,1.8Hz,1H),7.33–7.25(m,1H),7.20(dd,J=11.0,8.4Hz,1H),7.07–7. 02(m,2H),6.97–6.92(m,2H),6.32(s,1H),5.76–5.71(m,1H),5.22(d,J=3.3Hz,2H),2.05(s,3H).

[0069] Example 5 Synthesis of Norrish Type II Photoinitiator HDE

[0070]

[0071] (1) In a dry round-bottom flask, hydroquinone 2a (11 mmol, 1.1 eq), potassium carbonate (14 mmol, 1.4 eq), compound 1e (10 mmol, 1.0 eq) and acetone (40 mL) were added in sequence, the mixture was heated to 90-95° C. and refluxed for 5 hours, cooled to room temperature, the mixed product was filtered, concentrated to obtain a crude product, and purified by flash column chromatography to obtain HDe with a yield of 48%;

[0072] (2) HDe (2.30 mmol, 1.0 eq) and triethylamine (TEA, 2.76 mmol, 1.2 eq) were dissolved in dichloromethane (1 M) and methacryloyl chloride 4a (2.52 mmol, 1.1 eq) was added dropwise at 0°C. The reaction was heated to room temperature and stirred for 24 hours. After concentration, the crude product was purified by flash column chromatography to obtain Norrish II type photoinitiator HDE with a yield of 16%;

[0073] HDe, white powder, 1 H NMR (500MHz, CDCl3): δ8.05 (ddd, J=8.9,5.2,

[0074] 2.5Hz,2H),7.19–7.13(m,2H),6.88–6.70(m,4H),5.16(s,2H).

[0075] HDE, white powder, 1 H NMR (500MHz, CDCl3): δ8.08–8.02(m,2H),7.21–7.15(m,2H),7.07–7.02(m,2H) ,6.97–6.92(m,2H),6.32(s,1H),5.75–5.72(m,1H),5.20(s,2H),2.05(s,3H).

[0076] Example 6 Synthesis of Norrish II-type photoinitiator HDF

[0077]

[0078] (1) In a dry round-bottom flask, hydroquinone 2a (11 mmol, 1.1 eq), potassium carbonate (14 mmol, 1.4 eq), compound 1c (10 mmol, 1.0 eq) and acetone (40 mL) were added in sequence, the mixture was heated to 90-95° C. and refluxed for 5 hours, cooled to room temperature, the mixed product was filtered, concentrated to obtain a crude product, and purified by flash column chromatography to obtain intermediate 1 (HDc) with a yield of 32%;

[0079] (2) In acetone / ethanol (50 mL, 1:1 v / v), intermediate 1 (HDc, 2.62 mmol, 1.0 eq) and potassium carbonate (2.88 mmol, 1.1 eq) were added, and the mixture was stirred at room temperature for 5 minutes. Formalin (40 wt%, 1.1 mL, 10.5 mmol) was then added and stirred at room temperature for 2.5 hours. After the reaction was completed, 40 mL of water was added, and the mixture was extracted with DCM. The organic layers were mixed, dried, concentrated, and purified by flash column chromatography to obtain intermediate 2 (referred to as compound 2c) with a yield of 47%;

[0080] (3) Compound 2c (1.25 mmol, 1.0 eq), triethylamine (2.99 mmol, 2.4 eq), dichloromethane (5 mL) and methacryloyl chloride 4a (2.75 mmol, 2.2 eq) were mixed and stirred at 0°C for 15 minutes, then heated to room temperature and stirred for 24 hours. The mixture was concentrated and the crude product was purified by flash column chromatography to obtain HDF with a yield of 25%.

[0081] Compound 2c, white powder, 1 H NMR (500MHz, CDCl3): δ8.06–8.02(m,2H),6.96–6.92(m,2H),6.78–6.74(m,2H),6.71– 6.65(m,2H),5.39(dd,J=6.3,4.1Hz,1H),5.11(s,1H),4.16–4.04(m,2H),3.87(s,3H).

[0082] HDF, white powder, 1 H NMR (500MHz, CDCl3): δ8.15–8.11(m,2H),7.00–6.94(m,4H),6.91–6.88(m,2H),6.30(s,1H),6.08(s,1H),5.73–5.71(m,1H), 5.60(dd,J=7.2,3.8Hz,1H),5.58–5.57(m,1H),4.76–4.55(m,2H),3.87(s,3H),2.03(t,J=1.3Hz,3H),1.90(t,J=1.4Hz,3H).

[0083] Example 7 Synthesis of Norrish II Photoinitiator HDG

[0084]

[0085] (1) To a dry round-bottom flask, 4-methoxyphenol 3a (11 mmol, 1.1 eq), potassium carbonate (14 mmol, 1.4 eq), acetone (30 mL) and compound 1c (10 mmol, 1.0 eq) were added in sequence, the mixture was heated to 90-95°C, stirred for 5 hours, and then the crude product was filtered, concentrated and purified by flash column chromatography to obtain intermediate 1 (referred to as compound 3b) with a yield of 47%.

[0086] (2) Compound 3b (4.53 mmol, 1.0 eq) and potassium carbonate (4.98 mmol, 1.1 eq) were added to acetone / ethanol (50 mL, 1:1 v / v), and the mixture was stirred at room temperature for 5 minutes. Formalin (40 wt%, 1.1 mL, 10.5 mmol) was then added and stirred at room temperature for 2.5 hours. After the reaction was completed, 40 mL of water was added, and the mixture was extracted with DCM. The organic layers were mixed, dried, concentrated, and purified by flash column chromatography to obtain compound 3c with a yield of 62%;

[0087] (3) Compound 3c (2.80 mmol, 1.0 eq), triethylamine (3.37 mmol, 1.2 eq), dichloromethane (5 mL) and methacryloyl chloride (3.08 mmol, 1.1 eq) were mixed and stirred at 0°C for 15 minutes, then heated to room temperature and stirred for 24 hours. Sodium chloride was added to the mixture and extracted with DCM. The organic layer was dried and concentrated to obtain a crude product, which was purified by flash column chromatography to obtain HDG with a yield of 70%.

[0088] Compound 3b, white powder, 1 H NMR (500MHz, CDCl3): δ8.06–8.02(m,2H),6.95–6.91(m,2H),6.86–6.82(m,2 H),6.79–6.74(m,2H),5.40(dd,J=6.3,4.2Hz,1H),3.86(s,3H),3.72(s,3H).

[0089] Compound 3c, white powder, 1 H NMR (500MHz, CDCl3): δ8.01–7.97(m,2H),6.98–6.93(m,2H),6.91–6.86(m,2H),6.84–6.79(m,2H),5.16(s,2H),3.87(s,3H),3.75(s,3H).

[0090] HDG, white solid, 1 H NMR (500MHz, CDCl3): δ8.17–8.08(m,2H),6.95(dd,J=8.9,4.0Hz,2H),6.86–6.80(m,2H),6.78–6.74(m,2H),6.07 (s,1H),5.58–5.55(m,1H),5.52(dd,J=7.1,3.9Hz,1H),4.74–4.55(m,2H),3.87(s,3H),3.72(s,3H),1.90(s,2H).

[0091] Example 8 Preparation of light-cured dental resin material

[0092] Preparation of the system of the experimental group: The light-curing dental resin material was prepared according to the raw material composition in Table 1. Bis-GMA and TEGDMA were mixed in a round-bottom flask at room temperature with magnetic stirring (~30 min), and then the initiator (CQ), the Norrish II type photoinitiator prepared in Example 1-7 and the iodine salt were added to the flask, and magnetic stirring was performed at room temperature (~2 h) to prepare the light-curing dental resin materials in the experimental groups 1-7.

[0093] Preparation of the control group system: Bis-GMA and TEGDMA were mixed in a round-bottom flask at room temperature with magnetic stirring (~30 min), and then the initiator (CQ) and the co-initiator (EDB) were added to the flask and magnetic stirring was performed at room temperature (~2 h) to prepare the light-curing dental resin material in control group 1.

[0094] Table 1 Raw material composition of light-curing dental resin materials

[0095]

[0096] The properties of the light-cured dental resin materials in the control group 1 and the experimental groups 1-7 were tested:

[0097] (1) The conversion rate of polymerized double bonds was detected by total attenuation Fourier transform infrared spectrometer. The light-curable dental resin materials in experimental groups 1-7 and control group 1 were deposited on polypropylene film, and the sample volume was controlled by a mold (4 mm in diameter and 1 mm in thickness). The polymerization was carried out in air at room temperature using a blue LED dental visible light curing lamp. 1638 cm -1 The methacrylate double bond content at 1725 cm -1 The carbon group at (peak area) was used as the internal standard to calculate the polymerization double bond conversion rate DC; the results are shown in Table 2. Figure 1 and Figure 2 As shown, after curing for 20 seconds, except for experimental group 2 and experimental group 3, whose DC was significantly lower than EDB, the other experimental groups showed good curing performance, such as the conversion rates of experimental group 5, experimental group 6 and experimental group 7 were 72.53%, 74.47% and 73.01% respectively (vs. control group ~ 71.99%). All systems reached the maximum conversion rate (Rp) within 5 seconds and almost completed photopolymerization within 10 seconds. The maximum conversion rate (Rpmax) of experimental group 2, experimental group 6 and experimental group 7 was not statistically different from that of the control group. Among them, the Rpmax of experimental group 2 and experimental group 7 was better, which were 41.93% / s and 40.11% / s respectively (vs. control group ~ 37.76% / s).

[0098] Table 2. Polymerization conversion rate and conversion rate of control group 1 and experimental groups 1-7

[0099]

[0100]

[0101] (2) Density functional theory M06-2X / 6-311G (d, p) method was used to calculate the carbon-hydrogen bond dissociation of Norrish II type photoinitiator and triplet energy of 4-dimethylaminobenzoic acid ethyl ester. The carbon-hydrogen bond dissociation energy of each experimental group was lower than that of the control group, so the experimental groups all had good co-initiator behavior.

[0102] (3) Bleaching test: The light-curing dental resin materials in the experimental groups 1-7 and the control group 1 were irradiated with a dental light-curing lamp for 100 seconds, and then their bleaching properties were tested using a spectrophotometer. The specimen radius was 7.5 mm and the thickness was 1 mm. At the same time, the color stability of the samples was tested with reference to ISO4049:2009 and ISO7491 guidelines. The samples were circular specimens (radius 7.5 mm, thickness 1 mm, light curing time: 80 seconds on each side). The disc-shaped specimens of each group were randomly divided into 3 groups. The specimens of the first group (Gr. 1) were at 37±2 ℃ oven for 7 days; the second group of specimens (Gr.2) were dried in a 37±2℃ oven and in a distilled water bath for 7 days (water depth: 10±3mm above the specimens); after the third group of specimens were dried in an oven at 37±2℃ for 24 hours, half of the specimens were wrapped with aluminum foil (foil wrapped side: Gr.3a; non-wrapped side: Gr.3b) and placed under strong light (150000±15000Lux) irradiation and a distilled water bath (37±2℃) for 24 hours, the aluminum foil was removed after 24 hours, and the specimens were returned to the 37±2℃ oven to dry for 5 days.

[0103] The bleaching property and color stability are shown in Table 3. The b* value indicates the chromaticity. The smaller the b* value, the better the bleaching performance. The b* value of experimental group 4 is significantly smaller than that of the control group, indicating that experimental group 4 has ideal bleaching property. The bleaching properties of experimental groups 3, 5 and 6 are similar to those of the control group. △E1, △E2 and △E3 respectively represent the color stability under different scenarios; the absorption of water has little effect on the color stability of experimental groups 2-3 and 5-7, which is similar to the control group (△E1). Short-term strong light combined with water absorption has little effect on the color stability of experimental groups 1 and 5 (△E2). Short-term strong light has the same effect on the color stability of the experimental group and the control group (△E3).

[0104] Table 3. Bleaching performance and color stability of control group 1 and experimental groups 1-7

[0105]

[0106] (4) Cure depth test: The cure depth was tested with reference to ISO4049:2009 guidelines. The dental light curing lamp was used to irradiate one end of the uncured specimen for 20 seconds (radius 2 mm, thickness 10 mm). The uncured material was removed with a plastic knife. The height of the cylinder of the cured part was measured with an electronic vernier caliper. The cure depth was calculated. The results are shown in Table 4. All experimental groups were able to achieve a cure depth similar to or better than that of the control group. The cure depths of experimental groups 1-3 and experimental group 5 were significantly better than that of the control group.

[0107] Table 4. Depth of cure of control group 1 and experimental groups 1-7

[0108]

[0109] (5) Cytotoxicity test: The CCK-8 test of mouse fibroblasts (L929 cells) was used to test the cytotoxicity of the extract of the light-cured dental resin material after curing. The extract was prepared according to the ISO1099312 guideline (sample surface area / culture medium volume = 1.25 cm 2 / mL) was prepared, and the optical density (OD) at 450nm was measured by a microplate reader after the cells and the extract were cultured for 24h, 48h, 72h and 96h; the results are shown in Table 5. Under the same co-culture time, the in vitro cytotoxicity of the experimental group was similar to that of the control group.

[0110] Table 5. Relative growth rate (RGR) of control group 1 and experimental groups 1-7

[0111]

[0112] The above-described embodiments provide a detailed description of the technical solutions of the present invention. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A Norrish II type photoinitiator, characterized in that The structural formula of the Norrish II type photoinitiator is any one of the compounds shown in the following formula:

2. The method for preparing the Norrish II type photoinitiator according to claim 1, characterized in that: The preparation method of the Norrish II type photoinitiator is one of method 1 or method 2: Method 1 includes the following steps: Step (1.1), in an alkaline environment, using compound 1 and a phenol compound as raw materials to react in an organic solvent, and after the reaction, post-treating the product solution to prepare intermediate 1; Step (1.2), in an alkaline environment, reacting the intermediate 1 and methacryloyl chloride as raw materials in an organic solvent at room temperature, and after the reaction, post-treating the product solution to obtain the Norrish II type photoinitiator; Method 2 includes the following steps: Step (2.1), in an alkaline environment, using compound 1 and a phenol compound as raw materials to react in an organic solvent, and after the reaction, post-treating the product solution to prepare intermediate 1; Step (2.2), in an alkaline environment, using intermediate 1 and formalin as raw materials to react at room temperature in a mixed solvent system, and obtaining intermediate 2 through post-treatment; Step (2.3), in an alkaline environment, reacting the intermediate 2 and methacryloyl chloride as raw materials in an organic solvent at room temperature, and after the reaction, post-treating the product solution to obtain the Norrish II type photoinitiator; In method 1 and method 2, the structural formula of the compound 1 is: The phenol compound is hydroquinone or 4-methoxyphenol.

3. The method for preparing the Norrish II type photoinitiator according to claim 2, characterized in that: In step (1.1), step (2.1) and step (2.2), potassium carbonate is added to the reaction raw materials to achieve an alkaline environment; in step (1.2) and step (2.3), triethylamine is added to the reaction raw materials to achieve an alkaline environment.

4. The method for preparing the Norrish II type photoinitiator according to claim 2, characterized in that: In step (1.1) and step (2.1), the reaction temperature is 90-95°C and the reaction time is 1-10h; in step (2.2), the reaction time is 1-10h; in step (1.2) and step (2.3), the reaction time is 12-36h.

5. The method for preparing the Norrish II type photoinitiator according to claim 2, characterized in that: In step (1.1) and step (2.1), the organic solvent is acetone, acetonitrile or N,N-dimethylformamide; in step (2.2), the mixed solvent is at least two of acetone, ethanol, acetone and methanol; in step (1.2) and step (2.3), the organic solvent is dichloromethane, chloroform or dichloroethane.

6. The method for preparing the Norrish II type photoinitiator according to claim 2, characterized in that: In step (1.1) and step (2.1), the molar ratio of compound 1 to the phenol compound is 1:1-2; in step (1.2), the molar ratio of intermediate 1 to methacryloyl chloride is 1:1-3; in step (2.2), the molar ratio of intermediate 1 to formalin is 1:1-10; in step (2.3), the molar ratio of intermediate 2 to methacryloyl chloride is 1:1-3.

7. Use of the Norrish II type photoinitiator according to claim 1 in dental materials.

8. A light-curing dental resin material, characterized in that: The invention comprises the following raw material components in weight percentage: 0.5%-1.5% of the Norrish II type photoinitiator according to claim 1; 0.2%-1% of camphorquinone; 0.5%-1.5% of iodine salt; 63%-73% of main monomer; and 24%-34% of diluent monomer.

9. The light-curing dental resin material according to claim 8, characterized in that: The iodine salt is diphenyl iodine hexafluorophosphate, 4,4'-ditolyl iodine hexafluorophosphate or diphenyl ammonium iodine hexafluorophosphate; The main monomer includes at least one of bisphenol A-glycidyl methacrylate, polyurethane dimethacrylate, and ethoxylated bisphenol A dimethacrylate; The diluent monomer includes at least one of triethylene glycol dimethacrylate, hydroxyethyl methacrylate, and ethylene glycol dimethacrylate.

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