DE102008047006A1 - Light-curing compositions - Google Patents

Abstract

The present invention relates to light-curing compositions comprising free-radically polymerizable vinyl compounds and daylight-sensitive radical initiators of the formulas (I) and / or (II) and optionally further additives, such as fillers, pigments, solvents, and their use as a coating material for technical, optical and medical applications. $ F1

Description

The The present invention relates to photocurable or photohardenable Compositions containing radically polymerizable compounds, in particular vinyl compounds and daylight-sensitive radical initiators and optionally further additives such as fillers, Pigments, solvents and their use as a coating material for technical, optical and medical applications. Moreover, the invention relates cured products made from the compositions including their production process. After all The invention also relates to those used as radical initiators new compounds as such and a process for their preparation.

photoinitiators absorb radiation in the UV or in the visual range and set in this way the polymerization initiating species for Available. In the case of a radical polymerization These are free radicals. Generally, radical photoinitiators (Radical initiators), based on the chemical mechanism of Radical formation divided into two classes. Norrish type I photoinitiators form due to radiation due to unimolecular bond breaking free radicals. The counterpart undergo Norrish Type II Photoinitiators, after exposure to radiation a bimolecular Reaction, wherein the photoinitiator with a second molecule (the coinitiator) and initiating the polymerization Species by electron and proton transfer or directly by Hydrogen abstraction forms. Norrish type I and II photoinitiators are used in curing with UV light. For now are almost exclusively Norrish type II photoinitiators for polymerization by irradiation with visual Light used.

Characteristic of the curing by radiation in the UV range is the high reaction rate. This type of curing is used for example for coatings of various substrates such as wood. Such an example of UV-curable coatings of materials with Norrish type I photoinitiators, such as diethoxyphenylacetophenone or acrylicphosphine oxides, is disclosed in U.S. Pat EP 1247843 described. Furthermore, the describes WO 01/51533 a UV-curable wood-plating material using acrylphosphine oxides, α-hydroxyalkylphenones or α-dialkoxyacetophenones as photoinitiators.

UV curing can be used for all transparent coatings with low layer thicknesses. However, it reaches its limits with an admixture of pigments and at higher layer thicknesses. Such photopoly-reactive compounds therefore cure only incompletely by UV radiation. If a deeper through cure is desired, such as in the photohardening of dental materials to be used as a dental filling, visible light may be used for irradiation which has a higher penetrating power. A photoinitiator that can be used for such purposes is a combination of α-diketones and amino coinitiators. Such a system is used in the GB 1,408,265 described. Examples in which dental materials and photoinitiators are used are in US 4,457,818 , or in the US 4,525,256 in which camphorquinone is preferably used. Camphorquinone has an absorption maximum of 468 nm, which explains the intense yellow color. This may be to the disadvantage that the materials cured by camphorquinone-amine systems as photoinitiators have an undesirable visible yellow tinge. Another system which initiates radical polymerization of dental materials by radiation in the visual field is based on acylgermanium compounds and is disclosed in US Pat US 2008/0076847 described.

It Thus it can be seen that the initiator systems known in the prior art are not able, in any case, a sufficiently fast and complete curing of the desired To ensure materials. Rather, the well-known Compounds which by means of short-wave light (UV range) the polymerization providing initializing species, the disadvantage that the short-wave radiation achieves only a small penetration depth. This is especially true when used in systems with fillers problematic. In addition, no systems were available by means of visible light (daylight) and without coinitiators polymerization initiating species in a simple manner Make available. So there was still the urgent Need to provide new easier yet more powerful Initiators that are activated efficiently by visible light can.

Of the The present invention therefore an object of the invention, a new Initiator for radical polymerization available which upon irradiation with visible light (i.e., long-wave Daylight) a sufficiently fast and complete Curing the desired materials even without Co-initiator and the aforementioned negative side effects guaranteed.

These Task was surprising by the present invention according to the appended claims solved.

The new photoinitiators for radical polymerization according to the invention, the formulas (I) and (II), wherein the compounds of the formula (I) to the monomers and those of the formula (II) to the dimers Structures acts. The dimeric structures are approximate same efficiency in the initiator effect, but also have even less diffusibility, which is more practical Relevance can be.

worin in den Formeln (I) und (II) jeweils unabhängig voneinander
X = S, CHR⁴, O, oder NR⁴ darstellt;
R¹ und R² jeweils unabhängig voneinander H, lineares oder verzweigtes C1-C20-Alkyl; Thioalkyl; Aryl; oder Heteroaryl sind, wobei R¹ und R² auch miteinander verbunden sein können unter Bildung von gesättigten oder ungesättigten Cyclen oder Heterocyclen;
R³ = H, lineares oder verzweigtes C1-C20-Alkyl; Thioalkyl; Aryl; Heteroaryl ist;
R⁴ = H, lineares oder verzweigtes C1-C20-Alkyl, wobei der Alkylsubstituent cyclische Teilstrukturen aufweisen kann; Acyloxy; Aryl; oder Heteroaryl ist;
A eine aliphatische, aromatische oder heteroaromatische Verbindungsgruppe ist.Formulas (I) and (II):

wherein in the formulas (I) and (II) each independently
X = S, CHR ⁴ , O, or NR ⁴ ;
R ¹ and R ^{2 are} each independently H, linear or branched C ¹ -C 20 alkyl; thioalkyl; aryl; or heteroaryl, wherein R ¹ and R ^{2 may} also be linked together to form saturated or unsaturated cyclics or heterocycles;
R ³ = H, linear or branched C ¹ -C 20 -alkyl; thioalkyl; aryl; Heteroaryl is;
R ⁴ = H, linear or branched C 1 -C 20 -alkyl, where the alkyl substituent may have cyclic substructures; acyloxy; aryl; or heteroaryl;
A is an aliphatic, aromatic or heteroaromatic compound group.

• a. mindestens eine radikalisch polymerisierbare Verbindung, insbesondere Vinylverbindung; und
• b. mindestens eine Verbindung der Formel (I) und/oder der Formel (II) als Radikalinitiator.

The polymerization initiators according to formula (I) or (II) according to the invention are used in light-curing or photocurable composition. These compositions include:

• a. at least one radically polymerizable compound, in particular vinyl compound; and
• b. at least one compound of formula (I) and / or formula (II) as a radical initiator.

The The invention further relates to the cured product which by photocuring this composition with visible Light is available, as well as the light curing process for producing such a cured product as such.

Furthermore In particular, the invention relates to the use of the compounds of the formula (I) and / or the formula (II) as a radical initiator for the radical polymerization.

After all The invention also relates to a new production method for the compounds of the formula (I) and / or of the formula (II).

The substituent R ¹ in formulas (I) and (II) may preferably be varied as follows: R ¹ = H, C ¹ -C 20 alkyl; Aryl, wherein aryl may be a mono- to tri-substituted phenyl substituent, a monosubstituted to trisubstituted naphthalene substituent; Substituents may be halogen, preferably chloro, alkoxy, C 1 -C 20 alkyl, aminoalkyl, diaminoalkyl, acylamino, nitro, cyano, alkoxycarbonyl, wherein alkoxy = C 1 -C 10 alkyl is attached to a monovalent oxygen substituent; acyloxy; Dialkylamino = one or two C1-C10 alkyl bonded to a divalent nitrogen atom; Acylamino = C1-C10 alkanoyl or substituted benzoyl or naphthoyl bonded to an amino nitrogen.

The substituent R ² in the formulas (I) and (II) may preferably be varied as follows: R ² = H, C ¹ -C 20 -alkyl; Aryl, wherein aryl may be a mono- to tri-substituted phenyl substituent, a monosubstituted to trisubstituted naphthalene substituent; Substituents may be halogen, preferably chloro, alkoxy, dialkylamino, acylamino, methyl, nitro, cyano, alkoxycarbonyl, wherein alkoxy = C1-C10 alkyl is attached to a monovalent oxygen substituent; acyloxy; Dialkylamino = one or two C1-C10 alkyl bonded to a divalent nitrogen atom, acylamino = C1-C10 alkanoyl or substituted benzoyl or naphthoyl bonded to an amino nitrogen; Heteroaryl, wherein preferably a mono- to tetra-substituted pyridine substituent, substituted thiazyl, oxazyl and imidazyl substituents are used.

The substituent R ³ in the formula (I) may preferably be varied as follows: R ³ = H, C ¹ -C 20 -alkyl, preferably a mono- to quintuply-substituted phenyl radical, a monosubstituted to trisubstituted naphthalene substituent; Substituents are selected from halogen, preferably chloro, methoxy, methyl, nitro, cyano, alkoxycarbonyl, where alkoxy = C1-C10 alkyl is attached to a monovalent oxygen substituent gene; acyloxy; Dialkylamino = one or two C1-C10 alkyl bonded to a divalent nitrogen atom, acylamino = C1-C10 alkanoyl or substituted benzoyl or naphthoyl bonded to an amino nitrogen. Single and multiple condensation products between a cyclic thiohydroxamic acid and a substituted benzene-1,2-, 1,3- or 1,4-dicarboxylic acid or a naphthalene di-, tri-, tetracarboxylic acid can also be mentioned as R ³ . Furthermore, R ³ may be a heteroaromatic radical, wherein the term heteroaroamtisch preferably refers to pyridine, pyrrole, thiophene and furan and derivatives thereof.

The substituent R ⁴ in the formulas (I) and (II) can preferably be varied as follows: R ⁴ = H, C 1 -C 10 -alkyl, where from C ³ the alkyl chain can be linear or branched or the alkyl substituent can have cyclic substructures, Phenyl, one to five times substituted phenyl groups.

The ring group X in the formulas (I) and (II) can preferably be varied as follows, but is particularly preferred X = S. Formula (I) is exemplified below.

at A of the compounds of the formula (II) is preferably a pyridine, Pyrrole, thiophene, furan, thiazole, oxazole or imidazole group or a derivative thereof or a mono- to tetra-substituted or unsubstituted phenylene group.

Preferred embodiments of the invention have compounds of the formula (I) or (II) in which X = S. In addition, R ¹ , R ² , R ³ and R ⁴ are preferably independently of one another H, C ¹ -C 20 -alkyl, aryl or heteroaryl; where aryl is a monosubstituted to trisubstituted phenyl substituent or a monosubstituted to trisubstituted naphthalene substituent, the substituents being selected from halogen, in particular chlorine, C 1 -C 10 -alkoxy, C 1 -C 20 -alkyl, aminoalkyl, C 1 -C 10 -alkyl, Mono- or dialkylamino, acylamino, nitro, cyano, alkoxycarbonyl; and heteroaryl is substituted or unsubstituted pyridine, pyrrole, thiophene or furan. Further, A is preferably a pyridine, pyrrole, thiophene, furan, thiazole, oxazole or imidazole group or a derivative thereof, or a mono- to tetra-substituted or unsubstituted phenylene group. The definition of the substituents on the phenylene group corresponds to the definition given above. R ² in formula (I) or (II) is particularly preferably not H, since in these compounds (ie in which R ^{2 is} C ¹ -C 20 -alkyl, aryl or heteroaryl as defined above) a surprisingly higher sensitivity in the visible range of Light occurs. The reason for this is assumed to be a bathochromic shift of the longest wavelength absorption maximum of the chromophore (eg of the thiazole-2 (3H) chromophore) at alkyl and in particular aryl substituent R ² and a higher sensitivity in the visible range associated therewith.

Further preferred are compounds of formula (I) wherein X is S, R ¹ is C 1 -C 4 alkyl, R ^{2 is} phenyl or a phenyl radical having another ortho, meta or para substituent, said Substituent is selected from methoxy, C 1 -C 4 alkyl, amino, dialkylamino, acylamino and chlorine; or R ¹ and R ^{2 form} an unsaturated cycle; R ³ = phenyl or a phenyl radical having another ortho, meta or para substituent selected from methoxy, C 1 -C 4 alkyl, amino, dialkylamino, acylamino and chloro. Unsaturated cyclics formed by R ¹ and R ² are especially phenyl, indene, coumarone (benzofuran), indole, thionaphthene (benzothiophene), naphthalene which may be substituted. Particularly suitable substituents are halogen, preferably chlorine, C 1 -C 10 -alkoxy, C 1 -C 20 -alkyl, aminoalkyl, C 1 -C 10 -mono- or -dialkylamino, acylamino, nitro, cyano, alkoxycarbonyl.

All particularly preferred compounds according to the invention are represented by the following formulas (III) - (V). The compounds (III) and (IV) are particularly suitable for the photopolymerization with pure blue light of the wavelength from about 380-500 nm.

In the formulas (III) to (V), R ^{5 represents} chlorine, alkoxy, C 1 -C 20 -alkyl, aminoalkyl, diaminoalkyl, acylamino, nitro, cyano, alkoxycarbonyl, wherein: alkoxy = C 1 -C 10 -alkyl to a monovalent oxygen -Substituenten bound; acyloxy; Dialkylamino = one or two C1-C10 alkyl bonded to a divalent nitrogen atom; Acylamino = C1-C10 alkanoyl or substituted benzoyl or naphthoyl bonded to an amino nitrogen. Further, X = O, S, CHR ⁴ , NR ⁴ , preferably S, and n ranges from 1 to 4. R 4 is as defined above for the formulas (I) and (II).

Examples of the invention in which X is NR ⁴ are as follows (formulas (VI) and (VII)):

The polymerization initiators according to formula (I) or (II) according to the invention, which can be activated by the irradiation with visible light, are prepared according to the methods Acta Cryst. (2005). E61, o1738-01741 ; Eur. J. Org. Chem. (1999). 1275-1290 ; or Synlett 2000, 371-373 accessible.

worin X, R¹ und R² wie oben definiert sind, mit einem Carbonsäurechlorid bzw. Bis(carbonsäurechlorid) einer der beiden folgenden Formeln

umfasst, worin R³ wie oben dfiniert ist, und ebenfalls Teil der Erfindung ist. Im folgenden wird die Synthese beispielhaft für die bevorzugte Ausführungsform mit X = S, d. h. unter Einsatz von N-Hydroxythiazolthionen als Edukt, beschrieben. Analoges gilt aber auch für die anderen oben genannten Definitionen von X.In addition, the polymerization initiators of the formula (I) or (II) according to the invention can be prepared by a novel process which comprises reacting the free N-hydroxy compound of the following formula

wherein X, R ¹ and R ^{2 are} as defined above, with a carboxylic acid chloride or bis (carboxylic acid chloride) of one of the following two formulas

wherein R ^{3 is} as defined above and is also part of the invention. In the following, the synthesis is described by way of example for the preferred embodiment with X = S, ie using N-hydroxythiazolethiones as starting material. The same applies to the other definitions of X above.

The formation of the compound of the formula (I) or the formula (II) depends on the molar ratios of the starting materials used. At an approximately 1: 1 molar ratio of N-hydroxythiazolethione to carboxylic acid chloride, the compounds of formula (I) result in an approximately 2: 1 molar ratio of N-Hydroxythiazolthion to bis (carboxylic acid chloride) results in the compounds of formula (II). The reaction takes place in an alkaline aqueous / organic medium (preferably alkali metal carbonate in acetone) in a temperature range from 10 ° to 50 ° C., preferably at ambient temperature (about 20 ° C.). The starting materials are either commercially available or can be prepared by methods known to those skilled in the art.

advantage Compared to the known methods is the use of the free N-Hydroxythiazolthione instead of their salts, since the free Acids generally as a product of thiazole thione synthesis incurred and in contrast to most hygroscopic alkali metal salts are neither hygroscopic nor basic. Consequently, draws In particular, the new procedure is characterized by a higher Efficiency and easier handling of the starting materials.

The according to the invention after polymerization Formula (I) or (II) exhibit high through-cure Cure degree or high penetration depth and are can be used in a wide technical field. About that In addition, they have some significant advantages compared to already known UV and VIS photoinitiators. This includes that the new initiators metal-free, easy to synthesize and with, but in particular also be used without amine coinitiators can. The photoinitiators are indicated for the Uses in amounts of 0.001 to 20 wt .-%, preferably 0.01 to 1 wt .-% and particularly preferably from 0.01 to 0.1 wt .-%, weighed in based on the monomer system. It can the photoinitiators, thanks to their good solubility, are simple be stirred into the system used, resulting in a uniform Distribution of the initiators and the transparency of the polymer guaranteed.

The Photopolymerization can be done by solar radiation, or by known methods of photopolymerization, ie by irradiation by means of light sources showing the required wavelengths emit sufficiently. Suitable wavelengths are 300 <λ <780 nm, preferably 350 <λ <600.

The new compound can act as a photoinitiator for photopolymerizable unsaturated compounds are used. Such compounds For example, unsaturated monomers such as esters of (Meth) acrylic acid, e.g. Methyl, ethyl, n- or tert-butyl, Isooctyl, hydroxyethyl, glycidyl or tetrahydrofufuryl (meth) acrylate, Ethylene glycol di (meth) acrylate, neopentyl di (meth) acrylate, trimethylolpropane tri (meth) acrylate; Pentaerythritol tetra- (meth) acrylate or pentaerythritol (meth) acrylate; Acrylonitrile, (meth) acrylonitrile, (Meth) acrylamide, N-substituted (meth) acrylamides; Vinyl esters like z. Styrene, alkylstyrenes, halostyrenes, divinylbenzene, vinylnaphthalene, N-vinylpyrrolidone, vinyl chloride; Allyl compounds such as diallyl phthalate, Diallyl maleate, triallyl isocyanurate, triallyl phosphate, or ethylene glycol diallyl ether, and the mixture of such unsaturated monomers.

photopolymerizable Compounds are also unsaturated oligomers or Polymers and their mixtures with unsaturated monomers. These include thermoplastic resins, the unsaturated ones Groups such as maleic acid esters, fumaric acid, allyl groups or acrylic or methacrylic groups. Examples of such Oligomers are unsaturated polyesters, unsaturated Acrylic resins and polyether acrylate oligomers. examples for Polyunsaturated compounds are especially the acrylates or methacrylates of diols and polyols z. Hexamethylenedi (meth) acrylate, Trimethylenepropane tri (meth) acrylate, or pentaerythritol tetra (meth) acrylate.

Of Furthermore, a polymerization in the usual way in emulsion, in reverse emulsion, in bulk or in solution become. As solvent can water, aqueous organic solvents, pure organic solvents, Solvent mixtures or ionic liquids be used. When using a transparent apparatus or a high-pressure stable light source, the polymerization can also be carried out in supercritical carbon dioxide. The polymerization may in particular under for the radical Polymerization typical conditions are carried out. The exact conditions are uncritical and may vary from Professional in the usual way.

The invention further relates to the use of the above-described composition which comprises at least one free-radically polymerizable compound, in particular vinyl compound; and at least one compound of formula (I) and / or formula (II) as a radical initiator, as a coating material for technical, optical, medical applications and in photolithography. Photohardening is of particular importance for printing inks since the drying time of the binder decisively influences the production speed of the product. Likewise, the photocuring of surface coatings, as obtained in the coating of sheets, or plastic parts of any kind, another field of application. Also Here, the advantage is that by the irradiation with visible light (blue light) initializes the hardening and thus can be dispensed with the irradiation of harmful to humans UV rays. Also, a photoinitiator according to the present invention which provides by visible light the polymerization-initializing species is suitable for use in photolithography. Here, a substrate is coated with photopolymerizable monomers and irradiated certain areas of the substrate with visible light. Subsequently, the uncured fractions are rinsed out by means of solvents. In this way, with the help of the new photoinitiator three-dimensional structures can be constructed, as used for example in printing plates, or in a partial coating of silicon wafers. The light-curing compositions used for various purposes may contain fillers such as silica, gypsum, pigments, dyes, fibers, flow control agents or blowing agents, or other conventional additives, other than the photopolymerizable compounds and the corresponding photoinitiator.

The Invention is further illustrated by the following examples:

Application examples:

1. Synthesis of the compounds of formula (I) and (II):

The preparation of the compounds of formula (I) and (II) according to the invention according to the following general schemes:

For the preferred embodiment X = S (ie using an N-hydroxythiazolethione as starting material), the synthesis proceeds as follows:

A solution of N-hydroxythiazolethione (1.00 mmol) in an adequate volume of acetone is combined with K ₂ CO ₃ (3 mmol) and stirred at 20 ° C for 10 min. To the reaction mixture was added dropwise a carboxylic acid chloride (1.1 mmol). The reaction mixture is stirred at 20 ° C. Water is added to the resulting suspension, the phases are separated and the aqueous phase is extracted successively with diethyl ether and with ethyl acetate. The organic phase is combined with the organic extracts and washed with 2 M NaOH, and with saturated aqueous NaCl solution. The organic phase is separated, dried with MgSO ₄ and concentrated under reduced pressure. The residue obtained is recrystallized from CH ₂ Cl ₂ / Et ₂ O / pentane.

2. Use of the compounds according to formula (I) and (II) as a photoinitiator:

It in a Schlenk flask 2 g of monomer and 0.5 wt .-% ethylene glycol dimethacrylate (EGDMA) as a crosslinker and stirred until, until a homogeneous solution has emerged. To the polymerization is added to the monomer solution with 0.07 wt .-% (1.4 mg / 0.0039 mmol) of 5- (4-methoxyphenyl) -4-methyl-2-thioxo-2,3-dihydro-1,3-thiazol-3-yl-benzoate stirred and the polymer direct sunlight exposed. After just a few minutes, the curing is so far advanced that a solid polymer has arisen.

• ^a) Polymerisation in Lösung mit Toluol als LM
• ^f) festes Polymer
• ⁿ⁾ Polymerniederschlag
• ^*) Aushärtung nach Belichten mit Sonnenlicht bei direkter Sonneneinstrahlung im Monat Mai

The results are shown in the following Table 1. Tab. 1: Application examples Monomer (100% by weight) EGDMA (% by weight) Initiator (wt%) Curing * (min.) hydroxyethyl methacrylate 0.5 0.07 3-6 ^f) vinyl acetate 0.5 0.07 15 ^f) 1-vinyl-2-pyrolidone 0.5 0.07 5-10 ^f) styrene 0.5 0.07 8-10 ^f) methacrylic acid 0.5 0.07 5 ^f) acrylonitrile 0.5 0.07 20-30 ⁿ⁾ Styrene + maleic anhydride ^a) 0.5 0.07 30 ⁿ⁾

• ^a) Polymerization in solution with toluene as LM
• ^f) solid polymer
• ⁿ⁾ polymer precipitate
• ^*) Curing after exposure to sunlight in direct sunlight in the month of May

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - EP 1247843 [0003]
• WO 01/51533 [0003]
• GB 1408265 [0004]
• US 4457818 [0004]
• US 4525256 [0004]
• US 2008/0076847 [0004]

Cited non-patent literature

• - Acta Cryst. (2005). E61, o1738-01741 [0025]
• Eur. J. Org. Chem. (1999). 1275-1290 [0025]
• Synlett 2000, 371-373 [0025]

Claims (12)

A light-curing composition comprising a. at least one radically polymerizable compound; and b. at least one compound of the formula (I) and / or of the formula (II) as free-radical initiator,

wherein in formulas (I) and (II) each independently represent X = S, CHR ⁴ , O, or NR ⁴ ; R ¹ and R ^{2 are} each independently H, linear or branched C ¹ -C 20 alkyl; thioalkyl; aryl; or heteroaryl, wherein R ¹ and R ^{2 may} also be linked together to form saturated or unsaturated cyclics or heterocycles; R ³ = H, linear or branched C ¹ -C 20 -alkyl; thioalkyl; aryl; Heteroaryl is; R ⁴ = H, linear or branched C 1 -C 20 -alkyl, where the alkyl substituent may have cyclic substructures; acyloxy; aryl; or heteroaryl; A is an aliphatic, aromatic or heteroaromatic compound group. A composition according to claim 1 wherein X is S and / or R ¹ , R ² , R ³ and R ^{4 are} independently H, C ¹ -C 20 alkyl, aryl or heteroaryl; where aryl is a monosubstituted to trisubstituted phenyl substituent or a monosubstituted to trisubstituted naphthalene substituent, the substituents being chlorine, C1-C10-alkoxy, C1-C20-alkyl, aminoalkyl, C1-C10-mono- or dialkylamino, acylamino, nitro, cyano, alkoxycarbonyl; and heteroaryl means substituted or unsubstituted pyridine, pyrrole, thiophene or furan; and A is a pyridine, pyrrole, thiophene, furan, thiazole, oxazole or imidazole group or a derivative thereof or a substituted or unsubstituted phenylene group. A composition according to claim 1 and / or 2, wherein in the formula (I) X = S, R ¹ = C ¹ -C ⁴ alkyl, R ² = phenyl or a phenyl radical with another ortho, meta or para -terminated substituent, wherein the substituent is selected from methoxy, C 1 -C 4 alkyl, amino, dialkylamino, acylamino and chloro; or R ¹ and R ^{2 form} an unsaturated cycle; R ³ = phenyl or a phenyl radical having another ortho, meta or para substituent selected from methoxy, C 1 -C 4 alkyl, amino, dialkylamino, acylamino and chloro. Use of the composition according to any one of the claims 1 to 3 as a coating material for technical, optical, medical applications as well as in photolithography. Hardened product, which is light-cured The composition according to any one of claims 1 to 3 Visible light is available. Process for producing a cured A product which comprises curing the composition according to a of claims 1 to 3 by exposure to Includes daylight. Use of the product according to claim 5 as dental material, Printing ink, varnish, or surface coating. Use of the compound of formula (I) and / or of the formula (II) as defined in any one of claims 1 to 3 is defined as a radical initiator for the radical Polymerization. Compound of the formula (I)

wherein X represents S, CHR ⁴ , O, or NR ⁴ ; R ¹ and R ^{2 are} each independently H, linear or branched C ¹ -C 20 alkyl; thioalkyl; aryl; or heteroaryl, wherein R ¹ and R ^{2 may} also be linked together to form saturated or unsaturated cyclics or heterocycles; R ³ = linear or branched C ¹ -C 20 -alkyl; thioalkyl; aryl; Heteroaryl is; R ⁴ = H, linear or branched C 1 -C 20 -alkyl, where the alkyl substituent may have cyclic substructures; acyloxy; aryl; or heteroaryl; with the proviso that (a) R ^{2 is} not H when X = S; and (b) not simultaneously X = S, R ¹ = methyl, R ² = p-methoxyphenyl and R ³ = phenyl. Compound of the formula (II),

wherein X represents S, CHR ⁴ , O, or NR ⁴ ; R ¹ and R ^{2 are} each independently H, linear or branched C ¹ -C 20 alkyl; thioalkyl; aryl; or heteroaryl, wherein R ¹ and R ^{2 may} also be linked together to form saturated or unsaturated cyclics or heterocycles; R ⁴ = H, linear or branched C 1 -C 20 -alkyl, where the alkyl substituent may have cyclic substructures; acyloxy; aryl; or heteroaryl; A is an aliphatic, aromatic or heteroaromatic linking group, provided that R ^{2 is} not H when X = S. Process for the preparation of the compound of formula (I) or (II)

wherein R ¹ , R ² , R ³ and A are as defined in any one of claims 1 to 3, which is the reaction of a free N-hydroxy compound of the following formula

with a carboxylic acid chloride or a bis (carboxylic acid chloride) according to one of the following two formulas

includes. The method of claim 11, wherein X = S.