Photoinitiators and use thereof

Abstract

The present invention relates to compounds having the general formula (I) wherein R1 is linear or branched C1 to C4 alkyl, -(C=0)-CH3, -CH2-CF3 or -CH2-C6H5 and R2 is -H or -OR3, wherein R3 is C1 to C4 alkyl, -(C=0)-CH3, -CH2-CF3 or -CH2-C6H5.(I)

Description

Technical Field

[0001] This invention relates to the field of photoinitiators. Background Technology

[0002] The choice of photoinitiator is crucial in the curing process of photoreactive resins. When exposed to UV or visible light, the photoinitiator absorbs the light and forms a substance that initiates polymerization. For free radical photopolymerization, these substances are free radicals.

[0003] Based on the chemical mechanism of free radical formation, there are two types of photoinitiators. Norrish type I photoinitiators form free radicals by breaking chemical bonds when irradiated. On the other hand, Norrish type II photoinitiators react with a second molecule (called a co-initiator) in the excited state to form free radicals that initiate polymerization through electron and proton transfer. Both type I and type II photoinitiators are used for UV curing, with type II photoinitiators being more commonly used in the visible light range, except for diacyldialkylgermanium compounds.

[0004] Due to the short wavelength of UV light, UV curing is most effective for thin, transparent coatings. However, it is not suitable for dark, colored, or composite materials, as well as thicker layers, because these conditions can hinder complete curing with UV light. In such cases, visible light is typically used for irradiation, especially for applications requiring deeper curing, such as light-cured dental filling composites.

[0005] Ivocerin (bis(4-methoxybenzoyl)diethylgermanane) is a photoinitiator commonly used in various polymerization processes, particularly in dental materials such as dental composites, adhesives, and sealants. Ivocerin is typically activated at wavelengths from 390 nm to 445 nm.

[0006] WO 2023 / 186782 discloses tetrakis(2,6-dimethoxybenzoyl)germanane as a photoinitiator that can be activated at wavelengths up to 480 nm.

[0007] US 2019 / 0194362 A1 discloses polymerizable compositions containing acyltin compounds as photoinitiators.

[0008] US 2021 / 0261578 A1 discloses aromatic acyl germanium and acyl tin compounds suitable as photoinitiators for free radical polymerization, particularly for the production of dental materials.

[0009] US 2023 / 0364832 A1 discloses the use of acyl tin photoinitiators, particularly tetrakis(2,4,6-trimethylbenzoyl)stanane, in the preparation of UV-absorbing silicone hydrogel contact lenses.

[0010] Radebner, J et al., Chemistry 2018, 24, 8281-8285, disclosed tetraacryltinane as a photoinitiator that exhibits maximum absorbance at approximately 400 nm and low cytotoxicity.

[0011] Mitterbauer, M et al. (Macromol Mat Eng 2017, 302, 1600536) disclosed tetrakis(2,4,6-trimethylbenzoyl)stanane as a photoinitiator that can be activated at wavelengths up to 550 nm. However, the results showed that tetrakis(2,4,6-trimethylbenzoyl)stanane exhibits rather low stability.

[0012] One object of the present invention is to provide a stable compound that overcomes the disadvantages of photoinitiators known in the art and exhibits effective absorbance at long wavelengths. Summary of the Invention

[0013] This invention relates to compounds having the general formula (I).

[0014] (I),

[0015] R1 is a straight-chain or branched C1 to C4 alkyl, -(C=O)-CH3, -CH2-CF3 or -CH2-C6H5, and R2 is -H or -OR3, wherein R3 is a C1 to C4 alkyl, -(C=O)-CH3, -CH2-CF3 or -CH2-C6H5.

[0016] Surprisingly, compounds of general formula (I) exhibit a significantly wider absorption range for visible light compared to known storage-stable photoinitiators. This allows for polymerization initiation with higher wavelengths of light and enables greater curing depths. The compounds of this invention can be cleaved by light up to 560 nm. This is unexpected, as germanium-based photoinitiators with similar structures can only cleave at wavelengths up to 480 nm (see WO 2023 / 186782). On the other hand, structurally similar tin-alkyl photoinitiators show significantly reduced stability compared to the compounds of this invention (see Example 5 below). This improved stability of the compounds of this invention is not only advantageous but practically essential for their use as photoinitiators in most polymerization processes.

[0017] Furthermore, the compounds of the present invention are characterized by very high absorption extinction coefficients in the visible light range. Therefore, they are already effective as photoinitiators for visible light-induced photopolymerization at low concentrations.

[0018] Another aspect of the invention relates to a composition comprising at least one compound according to the invention as a photoinitiator and at least one free radical polymerizable monomer.

[0019] The compounds of this invention generate free radicals upon exposure to radiation. Therefore, these compounds can be used as photoinitiators to initiate free radical polymerization processes. Together with one or more free radical polymerizable monomers in the composition, they can be used to produce polymers.

[0020] Another aspect of the invention relates to a kit comprising at least one container containing at least one compound of the invention and at least one additional container containing at least one free radical polymerizable monomer of the invention.

[0021] Therefore, another aspect of the present invention relates to a method for preparing a polymer, the method comprising the step of exposing a composition according to the invention to electromagnetic radiation with wavelengths up to 560 nm.

[0022] Another aspect of the invention relates to the use of compounds or compositions according to the invention in the preparation or repair of dental restorations, prostheses, dentures, inlays, high inlays, crowns or bridges; as dental materials, preferably as dental cements, filling composites or veneer materials; as light-curing compositions for 3D printing; and for the curing of highly filled or colored formulations or very thick layers.

[0023] Another aspect of the present invention relates to the use of the compounds according to the invention as photoinitiators. Attached Figure Description

[0024] Figure 1 The following are examples of acetonitrile solutions of tetra(2,6-dimethoxybenzoyl)stanane (1), tetra(2,6-dimethoxybenzoyl)germanane (V1), tetra(2,4,6-trimethylbenzoyl)stanane (V2), and ivocerin (V3) (concentration 1 × 10⁻⁶). - 3 UV / Vis spectrum of M).

[0025] Figure 2 1×10 -3 Stability of compounds M, 1, V1, V2 and V3, in acetonitrile solutions (with 200 ppm H2O), with the absorbance of each compound at its maximum absorbance changing over time, normalized to 100% on day 0.

[0026] Figure 3 1×10 -3Steady-state photolysis experiments of chloroform solutions of compounds M 1, V1, V2 and V3 were conducted. During irradiation with a 460 nm LED (130 mW / cm²), the absorbance of each compound at its maximum absorbance changed over time, with the initial values ​​normalized to 100%. Detailed Implementation

[0027] According to a preferred embodiment of the invention, the straight-chain or branched C1 to C4 alkyl group is methyl or ethyl.

[0028] According to another preferred embodiment of the invention, R1 and / or R3 are methyl groups.

[0029] According to another preferred embodiment of the invention, R1 is methyl and R2 is -H or -OCH3.

[0030] Particularly preferred is that the compound of the present invention is tetrakis(2,6-dimethoxybenzoyl)tinane having formula (II).

[0031] (II)

[0032] The compounds of the present invention can be synthesized, for example, by derivatizing a potassium intermediate obtained by reacting tetra(trimethylsilyl)stanane with potassium tert-butoxide (KOtBu) with an acyl fluoride according to formula (III) according to the method of Haslinger, C. et al. ChemPhotoChem 2022,6, e202200108.

[0033] (III)

[0034] Tetra(trimethylsilyl)stanane was synthesized as described in Buerger, H.; and Goetze, U. Angew. Chem., Int. Ed. Engl. 1968, 7 (3), 212-13. Acyl fluorides could be synthesized as described in Kaduk, C. et al. Lett. Pept. Sci. 1996, 2 (5), 285-288. Since these reactions are sensitive to moisture, the Schlenk technique is preferred.

[0035] Another aspect of the invention relates to a composition comprising at least one compound according to the invention as a photoinitiator and at least one free radical polymerizable monomer.

[0036] A "free radical polymerizable monomer" (also known as a free radical monomer or radical monomer) is a compound that can undergo a free radical polymerization process, which involves the formation of covalent bonds between monomer units by using free radicals (especially those formed by photoinitiators).

[0037] According to a preferred embodiment of the invention, the composition comprises 0.001 wt% to 10 wt%, preferably 0.01 wt% to 8 wt%, more preferably 0.01 wt% to 6 wt%, more preferably 0.01 wt% to 5 wt%, more preferably 0.01 wt% to 4 wt%, more preferably 0.01 wt% to 3 wt%, and more preferably 0.01 wt% to 2 wt% of at least one compound according to the invention. In a particularly preferred embodiment of the invention, the composition comprises 0.01 wt% to 2 wt% of at least one compound according to the invention.

[0038] According to another preferred embodiment of the invention, the composition comprises at least one additional photoinitiator selected from the group consisting of type I initiators and / or type II initiators. Type I initiators may be selected from the group consisting of, but are not limited to, acylgermanium compounds, (bis)acylphosphine oxides, and α-hydroxy ketones. Type II initiators may be selected from the group consisting of, but are not limited to, camphorquinone, benzophenone, thioxanone, and similar compounds.

[0039] The compositions of the present invention comprise at least one free-radical polymerizable monomer. The at least one monomer may comprise two or more, preferably two to three free-radical polymerizable groups. The multifunctional monomer has cross-linking properties.

[0040] Hydrolyzed stable monomers, such as hydrolyzed stable mono(meth)acrylates, such as mesitylene methacrylate or 2-(alkoxymethyl)acrylate (e.g. 2-(ethoxymethyl)acrylate, 2-(hydroxymethyl)acrylate), N-mono- or -N,N-disubstituted acrylamides (e.g. N-ethylacrylamide, N,N-dimethylacrylamide, N-(2-hydroxyethyl)acrylamide or N-methyl-N-(2-hydroxyethyl)acrylamide), N-monosubstituted methacrylamides (e.g. N-ethylmethacrylamide or N-(2-hydroxyethyl)methacrylamide), and N-vinylpyrrolidone or allyl ethers, can also be advantageously used as monomers that can be free radically polymerized.

[0041] Preferred examples of hydrolyzable crosslinking monomers are urethanes of 2-(hydroxymethyl)acrylic acid with diisocyanates (e.g., 2,2,4-trimethylhexamethylene diisocyanate or isophorone diisocyanate), crosslinked pyrrolidones (e.g., 1,6-bis(3-vinyl-2-pyrrolidone)hexane), or commercially available bisacrylamides such as methylene or ethylidene bisacrylamides, bis(meth)acrylamides (e.g., N,N′-diethyl-1,3-bis(acrylamido)propane, 1,3-bis(methacrylamido)propane, 1,4-bis(acrylamido)butane, or 1,4-bis(acryloyl)piperazine), which can be synthesized by reacting the corresponding diamine with (meth)acryloyl chloride. Monomers that are liquid at room temperature are preferred and can be used as diluent monomers. In addition to these hydrolyzable monomers, all other monomers based on acrylates and methacrylates are also suitable.

[0042] Low-shrinkage, free-radical ring-opening polymerizable monomers, such as monofunctional or polyfunctional (i.e., multifunctional) vinylcyclopropanes or bicyclocyclopropane derivatives (preferably those described in DE 196 16 183 C2 or EP 1 413 569 A1), or cyclic allyl sulfides (preferably those described in US 6,043,361 and US 6,344,556), can also be used as free-radical polymerizable binders. These can also be advantageously used in combination with the di(meth)acrylate crosslinkers listed above. Preferred ring-opening polymerizable monomers are vinylcyclopropanes, such as 1,1-di(ethoxycarbonyl)- or 1,1-di(methoxycarbonyl)-2-vinylcyclopropane, or esters of 1-ethoxycarbonyl- or 1-methoxycarbonyl-2-vinylcyclopropane carboxylic acids with ethylene glycol, 1,1,1-trimethylolpropane, 1,4-cyclohexanediol, or resorcinol. Preferred bicyclopropane derivatives are methyl or ethyl 2-(bicyclo[3.1.0]hex-1-yl)acrylate and their disubstituted products at the 3-position, such as methyl or ethyl (3,3-bis(ethoxycarbonyl)bicyclo[3.1.0]hex-1-yl)acrylate. Preferred cyclic allyl sulfides are addition products of 2-(hydroxymethyl)-6-methylene-1,4-dithionecycloheptane or 7-hydroxy-3-methylene-1,5-dithionecyclooctane with 2,2,4-trimethylhexamethylene-1,6-diisocyanate or asymmetric hexamethylene diisocyanate trimers (from Bayer's Desmodur® VP LS2294).

[0043] Further preferred free-radical polymerizable monomers are vinyl esters, vinyl carbonates, and vinyl urethanes. Additionally, styrene, styrene derivatives, divinylbenzene, unsaturated polyester resins, and allyl compounds or free-radical polymerizable polysiloxanes (which may be produced from suitable methacryloxysilanes such as 3-(methacryloyloxy)propyltrimethoxysilane, and described, for example, in DE 199 03 177 C2) may also be used as free-radical polymerizable monomers. Styrene derivatives refer to those in which the phenyl group (rather than the vinyl group) of styrene is surrounded by a simple group (e.g., C1 to C2). 10 Compounds that are monosubstituted or polysubstituted with alkyl, Cl, Br, OH, CH3O, CHO, C2H5O, COOH or carboxylic acid ester groups.

[0044] Furthermore, mixtures of the above-mentioned monomers with acidic monomers that are capable of free radical polymerization (also known as binder monomers) can also be used as binders that are capable of free radical polymerization. Preferred acidic monomers are polymerizable carboxylic acids, such as maleic acid, acrylic acid, methacrylic acid, 2-(hydroxymethyl)acrylic acid, 4-(meth)acryloyloxyethyl trimellitic anhydride, 10-methacryloyloxydecylmalonic acid, N-(2-hydroxy-3-methacryloyloxypropyl)-N-phenylglycine, or 4-vinylbenzoic acid.

[0045] Free radical polymerizable phosphonic acid monomers, particularly vinylphosphonic acid, 4-vinylphenylphosphonic acid, 4-vinylbenzylphosphonic acid, 2-methacryloyloxyethylphosphonic acid, 2-methacrylamidoethylphosphonic acid, 4-methacrylamido-4-methyl-pentylphosphonic acid, 2-[4-(dihydroxyphosphono)-2-oxabutyl]-acrylic acid or 2-[2-dihydroxyphosphono)-ethoxymethyl]-ethyl acrylate or 2,4,6-trimethylphenyl acrylate, are particularly suitable as adhesive monomers.

[0046] In addition, acidic polymerizable phosphate esters, particularly 2-methacryloyloxypropyl phosphate or dihydrogen phosphate, 2-methacryloyloxyethyl phosphate or dihydrogen phosphate, 2-methacryloyloxyethyl phenyl phosphate, pentaerythritol pentamethacryloyl phosphate, 10-methacryloyloxydecyl phosphate, pentaerythritol pentamethacryloyl phosphate, mono-(1-acryloylpiperidin-4-yl) phosphate, 6-(methacrylamido)hexyl phosphate and 1,3-bis(N-acryloyl-N-propylamino)propyl-2-yl phosphate, are suitable as binder monomers.

[0047] In addition, polymerizable sulfonic acids are also suitable as adhesive monomers, especially vinyl sulfonic acid, 4-vinylphenyl sulfonic acid or 3-(methacrylamido)propyl sulfonic acid.

[0048] Thiol-olefin resins containing a mixture of monofunctional or polyfunctional thiol compounds and difunctional or polyfunctional unsaturated monomers (especially allyl or norbornene compounds) are particularly suitable as adhesives that can be cured by addition polymerization.

[0049] Examples of monofunctional or polyfunctional thiol compounds are o-dimercaptobenzene, m-dimercaptobenzene, or p-dimercaptobenzene, as well as thioglycolic acid esters or 3-mercaptopropionates of ethylene glycol, propylene glycol, or butanediol, hexanediol, glycerol, trimethylolpropane, or pentaerythritol. Preferred polyfunctional thiol compounds for the production of thiol-ene resins include thiocyanuric acid derivatives.

[0050] Examples of difunctional or polyfunctional allyl compounds are esters of allyl alcohol with dicarboxylic or tricarboxylic acids (e.g., malonic acid, maleic acid, glutaric acid, succinic acid, adipic acid, sebacic acid, phthalic acid, terephthalic acid, or gallic acid), as well as monofunctional or trifunctional allyl ethers, such as diallyl ethers, α,ω-bis[allyloxy]alkanes, resorcinol or hydroquinone diallyl ethers and pyrogallol triallyl ethers, or other compounds such as 1,3,5-triallyl-1,3,5-triazine-2,4,6-(1H,3H,5H)-trione, tetraallylsilane, or tetraallyl orthosilicate.

[0051] Examples of difunctional or polyfunctional norbornene compounds are Diels-Alder addition products of cyclopentadiene or furan with difunctional or polyfunctional (meth)acrylates, and esters and carbamates of 5-norbornene-2-methanol or 5-norbornene-2-ol with dicarboxylic acids or polycarboxylic acids (e.g., malonic acid, maleic acid, glutaric acid, succinic acid, adipic acid, sebacic acid, phthalic acid, terephthalic acid or gallic acid), with diisocyanates or polyisocyanates (e.g., hexamethylene diisocyanate or its cyclic trimer, 2,2,4-trimethylhexamethylene diisocyanate, toluene diisocyanate or isophorone diisocyanate).

[0052] According to a preferred embodiment of the present invention, at least one free radical polymerizable monomer is a monofunctional (meth)acrylate or a polyfunctional (meth)acrylate.

[0053] The multifunctional (meth)acrylate is preferably a di(meth)acrylate, and more preferably selected from the group consisting of urethane di(meth)acrylate, alkyl di(meth)acrylate, polyether- and polyester di(meth)acrylate or epoxy (meth)acrylate.

[0054] Other preferred (meth)acrylates are selected from the group consisting of: meth (meth)acrylates, ethyl (meth)acrylates, n-propyl (meth)acrylates, isopropyl (meth)acrylates, n-butyl acrylate, isobutyl acrylate, tert-butyl (meth)acrylates, n-pentyl (meth)acrylates, isopentyl (meth)acrylates, n-hexyl (meth)acrylates, isohexyl (meth)acrylates, cyclohexyl (meth)acrylates, phenyl (meth)acrylates, octyl (meth)acrylates, and isooctyl (meth)acrylates. Esters, 2-octyl (meth)acrylates, 2-ethylhexyl (meth)acrylates, decyl (meth)acrylates, lauryl (meth)acrylates, 2-propylheptyl (meth)acrylates, stearyl (meth)acrylates, isobornyl acrylate, benzyl (meth)acrylates, octadecyl acrylate, nonyl acrylate, dodecyl acrylate, isophoryl (meth)acrylates, 2-alkylalkanol (meth)acrylates (wherein the 2-alkylalkanol has a molar average number of carbon atoms of 12 to 32), and any combination or mixture thereof.

[0055] According to a particularly preferred embodiment of the invention, the composition comprises 1 wt% to 99 wt%, preferably 5 wt% to 95 wt%, more preferably 10 wt% to 90 wt%, and even more preferably 15 wt% to 85 wt% of at least one free radical polymerizable monomer.

[0056] According to another preferred embodiment of the invention, the composition of the invention may further contain at least one organic or inorganic filler or fiber or additive, preferably pigment, dye and / or stabilizer.

[0057] The compositions according to the invention may advantageously contain one or more organic or preferably inorganic fillers. Fibrous fillers and, in particular, particulate fillers are preferred.

[0058] Nanofibers, glass fibers, polyamide fibers, and carbon fibers are preferred fibrous fillers. Nanofibers refer to fibers with a length of less than 100 nm. Fibrous fillers are particularly suitable for the production of composite materials.

[0059] Preferred inorganic fillers are amorphous spherical nanoparticle-based fillers based on oxides, such as fumed silica or precipitated silica, ZrO2 and TiO2 or SiO2, Al2O3, mixed oxides of ZrO2 and / or TiO2, lithium disilicate, fine fillers (e.g., quartz, glass ceramics, or glass powder), and radiopaque fillers (e.g., ytterbium trifluoride, nanoparticle tantalum pentoxide, or barium sulfate). Preferred inorganic fillers also include phosphates such as hydroxyapatite and tricalcium phosphate, nitrides such as silicon nitride, and metals such as titanium, iron, and copper. Ytterbium trifluoride preferably has a particle size of 200 nm to 800 nm.

[0060] Particulate fillers preferably have a particle size of 0.01 μm to 15 μm. Nanoparticle fillers preferably have a particle size of 10 nm to 100 nm, and fine fillers preferably have a particle size of 0.2 μm to 5 μm. Non-transmissive fillers, unless they are nanoparticle fillers, preferably have a particle size of 0.2 μm to 5 μm.

[0061] Unless otherwise specified, all particle sizes are weight-average particle sizes (D50 values), with particle size determination in the range of 0.1 μm to 1000 μm preferably performed by static light scattering, for example using an LA-960 static laser scattering particle size distribution analyzer (Horiba, Japan). Here, a laser diode with a wavelength of 655 nm and an LED with a wavelength of 405 nm are used as light sources. Using two light sources with different wavelengths makes it possible to measure the entire particle size distribution of the sample in a single measurement, wherein the measurement is performed as a wet method. For this purpose, a 0.1% to 0.5% aqueous dispersion of the packing is prepared, and its scattered light is measured in a flow cell. The scattered light analysis used to calculate the particle size and particle size distribution is performed according to Mie theory in accordance with DIN / ISO 13320. The measurement of particle size in the range of 5 nm to 0.1 μm is preferably performed by dynamic light scattering (DLS) from the aqueous particulate dispersion, preferably using a He-Ne laser with a wavelength of 633 nm, a scattering angle of 90°, and a temperature of 25 °C, for example using Malvern Zetasizer Nano ZS (Malvern Instruments, Malvern UK).

[0062] Particle sizes smaller than 0.1 μm can also be determined by SEM or TEM microscopy. Transmission electron microscopy (TEM) is preferably performed using a Philips CM30 TEM at an accelerating voltage of 300 kV. For sample preparation, droplets of the particle dispersion are applied onto a 50 Å thick copper mesh (300 mesh width) coated with carbon, and then the solvent is evaporated. The particles are counted and the arithmetic mean is calculated.

[0063] To improve the bonding between the filler particles and the crosslinked polymer matrix, surface modification of the filler is preferred. For SiO2-based fillers, surface modification with methacrylate-functionalized silanes is preferred, and 3-methacryloyloxypropyltrimethoxysilane is particularly preferred. For surface modification of non-silicate fillers such as ZrO2 or TiO2, functionalized acidic phosphates, such as 10-methacryloyloxydecyl phosphate dihydrogen ester, can also be used.

[0064] Furthermore, the compositions according to the invention may contain additional additives and solvents. Additives are preferably selected from stabilizers, chain transfer agents, UV absorbers, dyes or pigments, rheology modifiers, and lubricants. Preferred solvents are water, ethanol, acetone, ethyl acetate, and mixtures thereof.

[0065] Another aspect of the invention relates to a kit comprising at least one container containing at least one compound of the invention and at least one additional container containing at least one free radical polymerizable monomer of the invention.

[0066] The kit of the present invention comprises at least two containers, wherein one of the containers contains at least one compound of the present invention, and the other container contains at least one free-radical polymerizable monomer of the present invention. Furthermore, the kit may also include instructions regarding the use of the components in the polymerization reaction.

[0067] Another aspect of the present invention relates to the use of the compounds according to the invention as photoinitiators.

[0068] The compounds and / or compositions of this invention can be used in a variety of technical fields. They can be used in inks, coatings, and varnishes for curable printing processes (e.g., screen printing, flexographic printing, and offset printing); in adhesives and sealants to ensure rapid curing, strong adhesion, and improved performance; in wood coatings for furniture, flooring, and wood surfaces to achieve rapid curing and enhanced durability; in the electronics and optics fields for manufacturing electronic components (e.g., printed circuit boards (PCBs), semiconductor devices, and optical films) to achieve precise curing processes and reliable performance; in the automotive industry for the production of automotive coatings (e.g., paints, varnishes, and topcoats) to provide rapid curing, scratch resistance, and UV protection; and in the packaging industry as packaging materials. Inks and coatings on packaging materials (such as cartons, labels, films, and plastics) to ensure efficient and high-quality printing and surface protection; in medical and dental applications, in dental composites, orthodontic adhesives, and other medical devices requiring rapid curing, biocompatibility, and high-performance properties; in curable ink formulations for 3D printing technology to achieve rapid layer-by-layer curing of resin-based materials; in the textile industry, in inks and coatings for textile printing to ensure vibrant colors, rapid curing, and excellent wash resistance; and in cosmetics and personal care products, in formulations of curable nail gels and coatings for manicures and toenails to achieve rapid drying and long-lasting effects. The compounds and compositions of the present invention are particularly preferred for dental applications and 3D printing.

[0069] Therefore, other aspects of the invention relate to the use of compounds or compositions according to the invention in inks, coatings, varnishes, curable printing processes (preferably offset printing), adhesives, sealants, electronics, optics, automotive industry, packaging industry, medical applications, dental applications (e.g., for the preparation or repair of dental restorations, prostheses, dentures, inlays, high inlays, crowns or bridges, dental materials, preferably as dental cements, filling composites or veneers), for the preparation of bone materials, 3D printing processes or the textile industry.

[0070] Another aspect of the invention relates to a method for preparing a polymer, the method comprising the step of exposing a composition according to the invention to electromagnetic radiation with wavelengths up to 560 nm.

[0071] One of the main advantages of the compounds of this invention is that they can be cleaved using light up to 560 nm, thus allowing for greater curing depth. Another advantage is the stability of the compounds of this invention in the dark regarding their decomposition.

[0072] According to another preferred embodiment of the invention, the composition is exposed to electromagnetic radiation in the wavelength range of 320 nm to 560 nm, preferably 430 nm to 560 nm, more preferably 470 nm to 560 nm, more preferably 480 nm to 560 nm, and more preferably 490 nm to 560 nm.

[0073] However, the present invention is further illustrated in the following embodiments, but is not limited thereto.

[0074] Example

[0075] Example 1

[0076] Synthesis of 2,6-dimethoxybenzoyl fluoride

[0077] Because the reaction involves moisture-sensitive compounds, trace amounts of oxygen and moisture were removed during the reaction. The synthesis of 2,6-dimethoxybenzoyl fluoride was carried out according to Kaduk, C. et al. Lett. Pept. Sci. 1996, 2 (5), 285-288.

[0078]

[0079] 2,6-Dimethoxybenzoic acid (1.154 g, 5.5 mmol, 1 eq.) was dried under high vacuum (HV) and 25 mL of dry DCM (dichloromethane) was added. The suspension was cooled to 0 °C in an ice bath. Diethylaminosulfur trifluoride (DAST, 1.12 g, 5.8 mmol, 1.05 eq.) was added dropwise over 5 minutes to obtain a clear solution. After stirring at 0 °C for 1 hour, the solution was poured into an ice-cold saturated NH4Cl solution. The aqueous phase was extracted three times with 25 mL of DCM each time, and the combined organic phases were dried over Na2SO4 and filtered. The solvent was removed under vacuum, and the beige solid was dried under high vacuum. The product was characterized by nuclear magnetic resonance spectroscopy.

[0080] Yield: 1.15g (99%)

[0081] Characterization: Beige solid

[0082] Melting point: 65.9°C to 67.1°C

[0083] 1 H-NMR (400 MHz, CDCl3): δ 7.41 (t, J = 8.5 Hz, 1H, Ar), 6.59 (dd, J =8.5, 1.0 Hz, 2H, Ar), 3.87 (s, 6H, CH3).

[0084] 13 C NMR (101 MHz, CDCl3): δ 159.28, 157.31, 153.83, 133.98, 104.03, 56.29.

[0085] 19 F-NMR (376 MHz, CDCl3): δ 53.64.

[0086] Synthesis of tetra(trimethylsilyl)stanane

[0087] Since the reaction also involves moisture-sensitive compounds, trace amounts of oxygen and moisture were removed during the reaction. The synthesis of tetra(trimethylsilyl)stanane was carried out according to Buerger, H.; and Goetze, U.Angew. Chem., Int. Ed. Engl. 1968, 7 (3), 212-13.

[0088]

[0089] Lithium foil (1.99 g, 288 mmol, 10 eq.) was cut into small pieces and suspended in 59 mL of dry THF (tetrahydrofuran) in a Schlenk flask. TMSCl (trimethylchlorosilane; 22.5 mL, 180 mmol, 6.25 eq.) was mixed with SnCl4 (3.4 mL, 28 mmol, 1 eq.) and filled into a dropping funnel fitted to the Schlenk flask. The flask was cooled to -78 °C, and the TMSCl / SnCl4 mixture was added dropwise over 50 minutes. The reaction mixture was stirred overnight while reaching room temperature. The black suspension was heated to reflux for 3 hours, cooled to room temperature, and filtered through a Celite® filter to obtain a clear solution. The liquid was quenched with 50 mL of cooled 1 N H2SO4, and the aqueous phase was washed three times with 25 mL of diethyl ether each. The combined organic phases were washed three times with 25 mL of water each and dried over Na2SO4. The solvent was evaporated under vacuum to give a gray solid. Dissolve it in diethyl ether, filter, and evaporate the solvent again under vacuum. Store the white solid at 4°C under argon atmosphere.

[0090] Yield: 1.49g (13%)

[0091] Characterization: White solid

[0092] Melting point: 181.3°C to 199.1°C

[0093] 1 ¹H NMR (400 MHz, benzene-d6, ppm): δ 0.41 – 0.33 (s, 27H).

[0094] 119 Sn NMR (149 MHz, benzene-d6, ppm): δ -664.06.

[0095] 29 Si NMR (79 MHz, benzene-d6, ppm): δ -9.69 (s, 4Si).

[0096] Synthesis of tetra(2,6-dimethylbenzoyl)stanane (1)

[0097] The synthesis of tetra(2,6-dimethoxybenzoyl)stanane was carried out under orange light to exclude wavelengths below 520 nm, and even trace amounts of oxygen and moisture were removed during the reaction using the Schlenk technique. This reaction is based on Marschner, C.; Eur. J. Inorg. Chem. 1998, 221-226 and Haslinger, C. et al. ChemPhotoChem 2022, 6,e202200108.

[0098]

[0099] Tetra(trimethylsilyl)stanane (500.8 mg, 1.22 mmol, 1 eq.) and dried KOtBu (potassium tert-butoxide; 150.5 mg, 1.34 mmol, 1.1 eq.) were weighed into a dry brown glass vial in a glove box. 12.5 mL of dried DME (dimethoxyethane) was added and the mixture was stirred for 2 hours. Via... 119 Sn-NMR confirmed the potassium intermediate. Simultaneously, 2,6-dimethoxybenzoyl fluoride (914.2 mg, 4.98 mmol, 4.1 eq.) was dissolved in 6.7 mL of dry DME in another dry brown glass vial. Both solutions were cooled to 0 °C, and then the (TMS)4Sn / KOtBu solution was added dropwise to the fluoride solution. A deep red suspension formed after the addition, which was allowed to reach room temperature overnight. The next day, an orange suspension appeared, and the solvent was evaporated under vacuum. The orange residue was extracted with 18 mL of DCM, centrifuged, and the solution reduced to 2 mL. Furthermore, the precipitate was transferred to 75 mL of cold n-pentane, centrifuged, and dried at HV. Other byproducts were separated using rapid chromatography, where impurities were first eluted with PE:EE 1:1, and the pure product was eluted with pure EE. The final product was dried at HV.

[0100] Yield: 169.1 mg (9%)

[0101] Characterization: Orange solid

[0102] Rf: 0.21 (pure EE)

[0103] 1 H NMR (400 MHz, CDCl3, ppm): δ 7.10 (t, J = 8.4 Hz, 4H, Ar-H), 6.39 –6.30 (m, 8H, Ar-H), 3.83 (s, 24H, -OCH3).

[0104] 13 C NMR (101 MHz, CDCl3, ppm): δ 236.73 (C=O), 158.02, 133.14, 121.85,103.76, 55.91 (-OCH3).

[0105] 119 Sn NMR (149 MHz, CDCl3, ppm): δ -547.04.

[0106] Example 2

[0107] V1 Synthesis

[0108] The synthesis of tetra(2,6-dimethoxybenzoyl)germanane (V1) was carried out according to Haslinger, C. et al. ChemPhotoChem 2022, 6, e202200108.

[0109] Example 3

[0110] V2 Synthesis

[0111] The synthesis of tetra(2,4,6-trimethylbenzoyl)stanane (V2) was carried out according to Mitterbauer, M. et al. Angew. Chem. Int. Ed. 2018, 57, 12146.

[0112] Compound V3 was provided courtesy of Ivoclar AG.

[0113] Example 4

[0114] UV / Vis Measurement

[0115] The absorbance of a photoinitiator determines the wavelength at which it can be broken down to initiate free radical polymerization. Longer wavelengths can penetrate deeper into the formulation, thus allowing for the curing of thicker layers.

[0116] UV / Vis measurements were performed using 1×10 -3 The reaction was carried out using acetonitrile solutions of PI (photoinitiator) 1 and V1 to V3 in M ​​and quartz cuvettes (10 mm long).

[0117] Table 1. Maximum absorption in acetonitrile and its corresponding extinction coefficient.

[0118]

[0119] According to Table 1, compared to V1 to V3, 1 shows the highest absorption at the highest wavelength and the highest extinction coefficient at its maximum value. Furthermore, 1 can be fragmented using light up to 550 nm because it has the longest tail absorption toward longer wavelengths (see Table 1). Figure 1 ).

[0120] Example 5

[0121] Optical-DSC Experiment

[0122] To determine the initiation kinetics and further completion of the photopolymerization process, photo-DSC experiments were performed using a 0.1 mol% PI solution of hexanediol diacrylate (HDDA) containing 500 ppm 2,6-di-tert-butyl-4-methylphenol (BHT) as a stabilizer. These experiments allowed the determination of parameters such as double bond conversion (DBC) and polymerization rate (R). p ), the time to reach 95% heat flux (t) 95 ) and the time to reach the maximum heat flux (t) max Curing was performed using a 460nm LED (10.0mW / cm²) and a 400nm LED (10.3mW / cm²). Samples were irradiated at 25°C for 300 seconds, in triplicate.

[0123] To compare PIs (1, V1, V2) with four chromophores with PIs (V3) with only two chromophores, an adjuvant formulation using twice the molar amount of V3 (0.2 mol%) was investigated.

[0124] Table 2. Photo-DSC results of HDDA solution containing 0.1 mol% PI and 500 ppm BHT at 25 °C for 300 seconds under irradiation at 400 nm and 10.3 mW / cm².

[0125]

[0126] Table 3. Photo-DSC results of HDDA solution containing 0.1 mol% PI and 500 ppm BHT at 25 °C for 300 seconds under irradiation at 460 nm and 10.0 mW / cm².

[0127]

[0128] For the 460nm experiment, 1 produced the highest DBC (Table 3), even surpassing 2x V3, which had the best DBC in the 400nm experiment (Table 2). Comparing R... p For most PIs, Ri at 460 nm is higher than that at 400 nm. p Increase (1, V2) or remain similar (V1), except for V3, where R for longer wavelengths p Lower. Regarding R at 460nm p The best result is obtained by 1, followed by V2.

[0129] With DBC and R p Similarly, at 400nm, the t of all PI max The values ​​are also very similar. At 400 nm, t... 95The results were quite unexpected, as 1 required the shortest time; although all PIs achieved results within a similar range. In the experiment at 460nm, t... max The values ​​also show a greater difference here, again showing that 1 has the best result so far (2.9 seconds), as it is almost a second faster than V1 (3.8 seconds) and V2 (3.9 seconds).

[0130] Example 6

[0131] Stability studies in solution

[0132] The stability of PI in solution or formulation is crucial for further applications, as it is generally impossible to store it under inert, anhydrous conditions below room temperature. Using acetonitrile with a water content of 200.3 ppm as the solvent, a concentration of 1 × 10⁻⁶ was obtained. -3 Solutions of M1 and reference PIs V1, V2, and V3 were prepared. Based on these concentrations, the molar ratio of water to PI was calculated to be 8.7:1. The solutions were placed in quartz glass cuvettes, purged with argon gas, and sealed with Teflon caps and paraffin films. The cuvettes were stored at room temperature protected from light, except for UV / Vis measurements performed after days 0, 1, 2, 3, 4, 7, 9, and 14. The maximum absorbance measured for each compound during the study period was plotted against time, with the absorbance of the first measurement on day 0 normalized to 100%.

[0133] Table 4. PI in solution (1×10⁻⁶) -3 The change in the maximum absorbance of M in acetonitrile containing 200.3 ppm H2O over 14 days, with day 0 normalized to 100%.

[0134]

[0135] Table 5. Decomposition rate during light-protected storage, expressed as a percentage decrease in absorbance per day.

[0136]

[0137] The absorbance of V2, which has the lowest stability, decreases by more than 80% within one day (Table 4). Figure 2 Other PIs, V1, V3, and 1, exhibited good stability over two weeks and likely even longer. The absorbance percentage of 1 remained as high as that of V3, making it the first Sn-based PI to be as stable as commercially available photoinitiators. Table 6 provides a better comparison of decomposition rates, with V1 exhibiting the lowest decomposition rate, followed by 1 and V3, whose decomposition rates were similar.

[0138] Example 7

[0139] Steady-state photolysis

[0140] Steady-state photolysis experiments were conducted to investigate photobleaching behavior. These experiments revealed the rate of compound degradation during irradiation, thereby indicating the rate of free radical generation.

[0141] The sample was dissolved in chloroform to obtain 1×10 -3 Solution M. Accurately pipette 2 mL into a cuvette, and throughout the experiment, it is crucial to stir the solution using a small magnetic stir bar suitable for the cuvette and a magnetic stirrer under the cuvette holder. Record the spectrum of pure chloroform as background. Irradiate each sample for 900 seconds using a 460 nm LED (130 mW / cm²), recording the UV / Vis spectrum every 5 seconds.

[0142] Table 6. Decomposition rate during 460nm LED irradiation, expressed as % of absorbance per second.

[0143]

[0144] Table 6 shows the decomposition rate (R) during 460nm LED irradiation. d 460nm The highest value is shown for 1, followed by V2, both of which are Sn-based photoinitiators (also shown in...). Figure 3 (in the middle). This indicates that these compounds can initiate the curing of the formulation most quickly. Furthermore, both compounds exhibit good photobleaching behavior, meaning that there is no significant residual absorbance after irradiation, thus producing colorless polymers.

[0145] Example 8

[0146] Curing depth

[0147] The curing depth of a formulation is an important parameter because it depends on the wavelength of the light used, as well as the amounts of photoinitiator and filler used. Therefore, these experiments compared two similar formulations that differed only in the photoinitiator compound.

[0148] The formulations used in all the following experiments consisted of 0.1 mol% PI (1 or V2), 500 ppm BHT as a stabilizer, UDMA (urethane dimethacrylate) and D3MA (decanediol dimethacrylate) as monomers (molar ratio 1:1), and 10 wt% dental glass as filler. To determine the curing depth, a Teflon mold with a glass plate at the bottom was used in conjunction with a green laser pointer (532 nm, 80 mW / cm²). The Teflon mold was completely filled with the formulation, and the laser pointer was placed under the glass plate to directly irradiate the formulation for a period of time. After irradiation, the liquid formulation was removed, and the resulting polymer was washed with acetone and dried. The final polymer was characterized by its height and mass using a precision balance and thrust gauge.

[0149] Table 7. Experimental results of curing depth of V2 and 1 at different irradiation times using a 532nm laser pointer and 80mW / cm², in terms of height and mass.

[0150]

[0151] For each point in Table 7, the formulation containing 1 achieved more polymerization than the formulation containing V2, both in terms of height and mass. Therefore, it can be shown that 1 is more reactive than V2 at 532 nm. The greatest difference can be seen in the mass at short irradiation times, particularly from 30 to 90 seconds. For longer irradiation times, starting from 120 seconds, the height and mass parameters of the two initiators tend to be similar, but 1 still surpasses V2.

Claims

1. A compound having the general formula (I) (I)， R1 is a straight-chain or branched C1 to C4 alkyl, -(C=O)-CH3, -CH2-CF3 or -CH2-C6H5, and R2 is -H or -OR3, wherein R3 is a C1 to C4 alkyl, -(C=O)-CH3, -CH2-CF3 or -CH2-C6H5.

2. The compound according to claim 1, wherein the straight-chain or branched C1 to C4 alkyl group is methyl or ethyl.

3. The compound according to claim 1 or 2, wherein R1 and / or R3 are methyl groups.

4. The compound according to any one of claims 1 to 3, wherein R1 is methyl and R2 is -H or -OCH3.

5. A composition comprising at least one compound according to any one of claims 1 to 4 and at least one free radical polymerizable monomer.

6. The composition according to claim 5, wherein the composition comprises 0.001 wt% to 10 wt%, preferably 0.01 wt% to 8 wt%, more preferably 0.01 wt% to 6 wt%, more preferably 0.01 wt% to 5 wt%, more preferably 0.01 wt% to 4 wt%, more preferably 0.01 wt% to 3 wt%, more preferably 0.01 wt% to 2 wt% of at least one compound according to any one of claims 1 to 4.

7. The composition according to claim 5 or 6, wherein the composition comprises at least one additional photoinitiator selected from the group consisting of type I initiators and / or type II initiators.

8. The composition according to any one of claims 5 to 7, wherein the at least one free radical polymerizable monomer is a monofunctional (meth)acrylate and / or a polyfunctional (meth)acrylate.

9. The composition according to claim 8, wherein the polyfunctional (meth)acrylate is a di(meth)acrylate, preferably selected from the group consisting of urethane di(meth)acrylate, alkyl di(meth)acrylate, epoxy-, polyether-, or polyester di(meth)acrylate.

10. The composition according to any one of claims 5 to 9, wherein the composition comprises 1 wt% to 99 wt%, preferably 5 wt% to 95 wt%, more preferably 10 wt% to 90 wt%, and even more preferably 15 wt% to 85 wt% of the at least one free radical polymerizable monomer.

11. The composition according to any one of claims 5 to 10, wherein the composition further comprises at least one organic or inorganic filler or fiber or additive, preferably pigment, dye and / or stabilizer.

12. Use of the compound according to any one of claims 1 to 4 or the composition according to any one of claims 5 to 11 in inks, coatings, varnishes, curable printing processes (preferably offset printing), adhesives, sealants, electronics, optics, automotive industry, packaging industry, medical applications, dental applications, for the preparation of bone materials, 3D printing processes, or textile industry.

13. Use of the compound according to any one of claims 1 to 4 as a photoinitiator.

14. A method for preparing a polymer, comprising the step of exposing the composition according to any one of claims 5 to 11 to electromagnetic radiation with a wavelength up to 560 nm.

15. The method of claim 14, wherein the composition is exposed to electromagnetic radiation in the wavelength range of 320 nm to 560 nm, preferably 430 nm to 560 nm, more preferably 470 nm to 560 nm, more preferably 480 nm to 560 nm, and even more preferably 490 nm to 560 nm.

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