WO2024008805A1 - Heteroaromatic ketones and their use in radical and cationic polymerization - Google Patents

Abstract

The invention relates to heteroaromatic ketones of formula (I) for radical and cationic polymerization (I), wherein the substituents A, B, C and D can be the same or different and are nitrogen or carbon, while R¹ and R², independently of each other, are hydrogen, deuterium, a C₁-C₁₀ alkyl group or a C₅-C₁₂ aryl group.

Description

HETEROAROMATIC KETONES AND THEIR USE IN RADICAL AND CATIONIC POLYMERIZATION

FIELD OF THE INVENTION

The invention is in the field of polymers and relates to new sensitizers for photoinduced polymerization, their use and a process for carrying out photoinduced polymerization using the new sensitizers

TECHNOLOGICAL BACKGROUND

Free radical polymerizations can essentially be described as the sum of five elementary reactions, the initiation, start, growth and termination reactions via recombination and disproportionation according to the following scheme:

An initiator is used that can thermally decompose into an initiating radical (I»), which, after addition to a monomer M, initiates the polymerization with the formation of polymer radical PT. These can add n monomers, whereby the grown polymer radicals either recombine or disproportionate to the desired polymer.

Here, h is the initiator, I« is an initiator radical, M is the monomer, P' _n and P' _m are the growing polymer radicals with chain lengths n and m. The initiation reaction to form the reactive radicals can take place in different ways. Among other things, the self-initiation of styrene and methyl methacrylate is known, and initiation via redox initiator systems such as hydrogen peroxide or organic peroxides and Fe ²⁺ is also possible. The most common variant of generating radicals is the homolytic cleavage of a thermally unstable compound that has relatively low dissociation energies in the range of 100 to 170 kJ-mol" ¹ . In particular, compounds with OO, SS or N = N units, such as peroxides, diperoxyketals, disulfides and azo derivatives, are used. When these formulations consisting of monomer and initiator are mixed, radical formation can begin at room temperature. Such a mi- Not suitable for applications that require high storage stability of monomer and initiator.

[0004] Alternatively, in addition to the use of thermal energy, light in particular can be used to form radicals, as in J. P. Fouassier, J. Lalevee, Photoinitiators for Polymer Synthesis, Wiley-VCH, Weinheim, 2012 or S. Dadashi-Silab, S. Doran , Y. Yagci, "Photoinduced Electron Transfer Reactions for Macromolecularsyntheses" Chemical Reviews 2016, 776, 10212-10275. The storage stability of such systems consisting of monomer and photoinitiator is significantly better than those based on thermal initiation. Photoinduced polymerizations have the advantage that they can be switched on and off again at the push of a button. This is a big advantage compared to thermal systems, as it leads to a simplification of processes and saving important resources such as energy. This has already been pointed out (C. Schmitz, B. Strehmel, "Laser instead of oven" Color Lack 2018, 724, 40-44.; B. Strehmel, C. Schmitz, K. Cremanns, J. Göttert, "Photochemistry with Cyanines in the Near Infrared: A Step to Chemistry 4.0 Technologies" Chemistry - A European Journal 2019, 25, 12855-12864.; C. Schmitz, B. Strehmel, "NIR LEDs and NIR lasers as feasible alternatives to replace oven processes for treatment of thermal -responsive coatings" Journal of Coatings Technology and Research 2019, 16, 1527-1541.)

The photoinduced generation of radicals to initiate polymerization usually takes place in the presence of so-called photosensitizers or initiators; the terms are used synonymously below. Examples of photoinitiators of types I and II include:

Type I photoinitiators

[0006] The disadvantage, however, is that some of these substances require wavelengths for activation that are significantly below 400 nm, as is the case with benzoin derivatives, hydroxyalkylace tophenone derivatives, sulfonyl ketone derivatives, dithiocarbamates or benzophenone derivatives. This often requires the use of short-wave emitters such as: B. mercury lamps, the use of which is only possible to a limited extent due to legal requirements and is therefore not desirable in new developments for the market. Other compounds such as coumarins react from the singlet state and show a significantly lower effectiveness in combination with iodonium salts, which act as coinitiators. The use of hexarylbisimidazoles is questionable in combination with mercapto compounds because their absorption is also too short-wave. Thioxanthone derivatives are questionable for use in certain systems due to certain factors. These include inadequate fading, which is problematic in commercial applications that require greater depth curing. Furthermore, with thioxanthone the spectral range for excitation is limited to 450 nm, which precludes use in holography with 532 nm excitation, for example.

Phosphine oxide-containing photoinitiators such as BAPO could serve as an alternative because they require a lower amount of energy for activation. However, these substances have recently been classified as questionable, which is why it can be assumed that they will soon no longer be available for practical use. In combination with iodonium salts, these compounds are significantly less effective for developing conjugate acid, compared to the described compounds of the invention. These can only be used for free radical polymerization. The use for controlled radical polymerizations that build polymer using the ATRP process is not directly possible with these compounds.

RELEVANT STATE OF TECHNOLOGY

EP 2007393 A2 (UNIV LOUISIANA) discloses thiazole and thiophene compounds useful in the treatment of inflammatory conditions, autoimmune diseases and cancers.

WO 2009 151957 A1 (3M) relates to an initiator system comprising a diarylalkylamine compound and a sensitizer, and also discloses a curable composition containing the initiator system.

[0010] WO 2017 155042 A1 (UNIV NAGOYA) provides a fluorescent dye that has an absorption maximum and a fluorescence maximum at higher wavelengths, a high fluorescence quantum yield and a high light stability and can be introduced into the various substituents. In a rhodamine dye, the benzene ring is substituted by a thiophene structure and an oxygen atom in the backbone is substituted by a phosphorus-containing group.

US 6,479,706 B1 (ALBEMARLE) relates to new benzophenone derivatives and processes for their production and use. The compounds can have highly active photoinitiation and photopolymerization properties. [0012] CN 106220649 A (CECEP) discloses a compound based on diaryl ketones and the use of the compound for producing organic electroluminescent devices.

TASK TO BE SOLVED

The object of the present invention was therefore, on the one hand, to provide new photoinitiators for the photoinduced radical or cationic polymerization, especially of vinyl monomers, which are free from the disadvantages described. In particular, the new photoinitiators should be harmless from an environmental and health perspective and should initiate polymerization with a sensitivity that enables use in combination with comparatively low-energy UV-VIS light, which can be provided by appropriate LEDs. A generally higher efficiency of photoinitiation is also desired. Finally, the new photoinitiators should also be usable for photocatalytic applications, such as in particular photo-ATRP using metal salts in the ppm range or metal-free photo-ATRP. The compounds used should be able to replace existing solutions based on the use of mercury lamps with LEDs with emission in the UVA and blue spectral range.

DESCRIPTION OF THE INVENTION

in der die Substituenten A, B, C und D jeweils gleich oder verschieden sein können und dabei für Stickstoff oder Kohlenstoff stehen, während R¹ und R² unabhängig voneinander für Wasserstoff, Deuterium, eine C1-C10 Alkyl- oder C5-C12 Arylgruppe stehen. [0014] In a first embodiment, the invention relates to heteroaromatic ketones of the formula (I)

in which the substituents A, B, C and D can each be the same or different and represent nitrogen or carbon, while R ¹ and R ² independently represent hydrogen, deuterium, a C1-C10 alkyl or C5-C12 aryl group .

[0015] Surprisingly, it was found that the new photoinitiators fully fulfill the complex task described at the beginning. They can be used for all commercial applications in which polymerization is initiated with LEDs from UV to far into the visible range. To do this, they are combined with a co-initiator, which puts the system into either an oxidative or reductive mechanism. This forms radicals which initiate the polymerization of vinyl monomers after a controlled or based on free radical polymerization. [0016] Due to the incorporation of the thiophene structures and other heterocyclic elements, there is also a higher effectiveness in terms of the efficiency of photoinitiation. Heterocycles such as B. Thiophene proves to be easier to oxidize and the formation of triplet states is surprisingly more efficient, since the electron return transfer in such systems, which reduces the efficiency of photoinitiation, is of minor importance in the compounds mentioned in this invention.

The compounds mentioned can also be used for photocatalytic applications, such as. B. the photo-ATRP using metal ion catalyst in the ppm range or the metal-free photo-ATRP.

Heteroaromatic ketones

The heteroaromatic ketones according to the invention are new. Preferred species include the following structures: AA, BB, CC, AC, AB and BC:

Manufacturing process

The production of heteroaromatic ketones of the formula (I) is illustrated by the following formula scheme, whereby the starting materials used are either commercially available or can be prepared by the person skilled in the art using the standard methods of organic chemistry:

unter Abspaltung von Chlorwasserstoff mit Dichloraceton umsetzt. Photoinitiatorsysteme A further subject of the present invention therefore relates in particular to a process for producing heteroaromatic ketones of the formula (I), in which substances of the formula (a), (b) and/or (c) are used.

reacted with dichloroacetone with the elimination of hydrogen chloride. Photoinitiator systems

[0021] In order to trigger a photoinitiated radical and/or cationic polymerization, the photoinitiators according to the invention require a substance that is capable of forming radicals after absorbing light and thus starting the chain structure. The task of the initiators is to reduce the amount of energy required to homolytically cleave a bond in the radical generator. A further subject of the present invention therefore relates to photoinitiator systems containing

(a) at least one ketone of formula (I) and

(b) at least one radical generator.

[0022] Suitable radical formers can be derived from onium salts, with iodonium salts being particularly preferred, amines, mercapto compounds, disulfides, hexaarylbisimidazoles, alkyl halides, metal salts and mixtures thereof.

Photoinduced polymerization

A further subject of the present invention relates to a process for the photoinduced polymerization of monomers, comprising the following steps:

(i) providing a monomer suitable for photoinduced polymerization;

(ii) providing a photoinitiator system according to claim 4;

(iii) mixing the components from steps (i) and (ii) as well

(iv) irradiating the mixtures with light in the UV-VIS range.

The monomers suitable for photopolymerization can be selected from the group formed by substances of the formula (II), (III) and/or (IV)

(II) (HD (I) in which the substituents J, K, L, M, N and P can be the same or different and are selected from the group formed by hydrogen, C1-C10 alkyl, C1-C10 alkoxy , Ci-C10 Alkyoxycarbonyl, C1-C10 Alkylsulfonyl, C1-C10 Alkylmercapto, C1-C10 Dialkylphosphonyl, C5-C12 Aryl, C5-C iz Aryloxy, C5-C12 Aryloxycarbonyl, C5-C12 Arylsulfonyl, C5-C12 Arylmercapto, C5-C12 Diarylphosphonyl, halogen, cyano, COOR, OCOR, OSO2R, SO2R, SO3R, PO3R2, PO4R3 and R each represents hydrogen or a C1-C10 alkyl or C5-C12 aryl group. Typical representatives of II are acrylic or methacrylic acid esters with at least one radical polymerizable group Epoxides and oxetanes with at least one cationically polymerizable group are representative representatives of III and IV. As part of the method according to the invention, the mixtures are irradiated with UV-VIS light, ie light with a wavelength in the range from approximately 300 to approximately 550 nm. LEDs which emit light in the specified wavelength range are preferably used for this purpose.

In a preferred embodiment, the photoinitiator systems according to the invention are used together with compounds selected from the group of onium salts, amines, mercapto compounds, disulfides, hexaarylbisimidazoles, alkyl halides, metal salts and mixtures thereof.

Further preferred embodiments are described below:

Ketones of the general formula type AA, AB, AC, BB, BC or CC or mixtures thereof can preferably be used in photopolymer systems in combination with light sources whose emission is in the UV and visible spectral range. Their combination with lasers and LEDs is preferred; LEDs are particularly preferred.

Ketones of the general formula type AA, AB, AC, BB, BC or CC or mixtures thereof are preferably combined with co-initiating components, whereby radicals are formed according to an oxidative mechanism, which cause a free radical polymerization of vinyl monomers of the general structure (II) initiate. Preferred co-initiating components are onium compounds. Lodonium compounds are particularly preferred.

Ketones of the general formula type AA, AB, AC, BB, BC or CC or mixtures thereof are preferably combined with co-initiating components, whereby radicals are formed according to a reductive mechanism, which promote the free radical polymerization of vinyl monomers of the general structure (II) initiate. Preferred co-initiating components here are amines, secondary alcohols, hexaarylbisimidazoles or mercapto compounds, which can also be used in a multiple combination with onium compounds.

Ketones of the general formula type AA, AB, AC, BB, BC or CC or mixtures thereof are preferably combined with co-initiating components which consist of a hexarylbisimidazole and a mercapto compound, with radicals being formed after light excitation, which are the free ones initiate radical polymerization of vinyl monomers of the general structure (II).

Ketones of the general formula type AA, AB, AC, BB, BC or CC or mixtures thereof will preferably initiate a cationic polymerization of monomers in combination with an onium salt.

Ketones of the general formula type AA, AB, AC, BB, BC or CC or mixtures thereof can preferably achieve a controlled radical polymerization of vinyl mono- Activate mers in combination with an alkyl halide, whereby polymer is built up in a controlled manner according to the principle of ATRP.

Ketones of the general formula type AA, AB, AC, BB, BC or CC or mixtures thereof can preferably activate the controlled radical polymerization of vinyl monomers in combination with an alkyl halide and an amine such as PMDETA or TPMA, according to the principle of ATRP controlled polymer is built up. Metal ions in the ppm range can be added to these reaction mixtures, whereby polymer is built up in a controlled manner according to the ATRP principle. CuBrz or FeBrs are particularly preferred.

INDUSTRIAL APPLICABILITY

The invention further relates to the use of ketones of the formula (I) as photoinitiators in photoinduced polymerization for the production of polymers. This applies to applications in image recording and image display such as 2D, 3D or 4D printing, lithography such as computer-to-plate imaging or circuit board production for the production of electronic components. Printing includes applications for the formulation of printing inks in the inkjet sector, UV printing, prosthesis production in medicine or even tooth restoration in the dental sector or the production of prostheses and bone replacements in general for medical applications. These are just a few of the many possible commercial applications.

EXAMPLES

The synthesis of the compounds of general structure I can be carried out using the following instructions:

[0036] H. Hartmann, J. Schumann, A. Kanitz, W. Rogier, Preparation of diarylaminothiophenes as electroluminescent phosphors, 2001, W02001053287.

[0037] K. Eckert, C. Mokry, A. Schröder, H. Hartmann, “Synthesis and solvatochromic properties of 5-dicyanovinyl- and 5-tricyanovinyl-substituted 2-aminothiazoles and 2-aminothiophenes” Phosphorus, Sulfur Silicon Relat. Elem. 1999, 752, 99-114.

[0038] C. Mokry, H. Hartmann, “Preparation and properties of 2-(dialkylamino)-5-(haloacetyl)thiazoles and 4-[2-(dialkylamino)-5-thiazolyl]thiazoles” J. Prakt. Chem./Chem.- Ztg. 1998, 340, 375-380.

example 1

Free radical polymerization

The following structures were produced according to the instructions listed above and can be used as sensitizers for photopolymerization.

[0040] Sensitizers:

Sens-7 Sens-8 Sens-9 The following compounds were used as co-initiators:

rM-1 rM-2

rM-8 Co-4a Co-4b Co-4c Monomers:

rM-1 rM-2

rM-8

Polymerizable formulations for free radical photopolymerization were examined using photo-DSC. A regular photo-DSC setup was used to determine the photoinitiation efficiency of the UV-Vis photoinitiator systems in the monomers. A UV LED array emitting at the specified wavelength was used for all exposure experiments. The generated light was collected with a lens and projected into a Y-fiber, which was connected to the measuring head of the DSC (Q2000 from TA- instrument). The power of each fiber arm was adjusted on the Y-fiber with a strong emitting source (OmniCure HR4000 from TA-Instruments, additionally coupled to the DSC). This realizes a nearly equal intensity of each fiber arm available for simultaneous exposure of both the sample and the reference in the calorimeter. The LED source was synchronized with the DSC through a shutter system placed between the fiber and the lens. It was controlled by an Arduino uno board. The DSC's software controls the event output of this instrument, which acts as a digital switch and handles the modulation ON or OFF. Here, the maximum polymerization rate (/? _p ^max ) and the final degree of conversion (x«) were determined as parameters that describe the reactivity of the system. The intensity of the irradiation was 1W. /? _p ^max was obtained by recording the heat flow in J/s. The values were then divided by the weight of the photopolymer composition and then multiplied by the molecular weight of the monomer used. These values are then divided by the molar heat of polymerization of the monomer, giving the shown values of the polymerization rate R _p in s ^-1 . A numerical integration of these and subsequent multiplication by 100% then gave the conversion of reacting double bonds. The parameters /? can then be derived from both curves. _p ^max and oo (in%) can be determined.

Figure 1 shows a typical experiment for determining reactivity parameters of a free radical photopolymerization, specifically a photo-DSC experiment for determining the photopolymerization rate of a formulation consisting of Sens-1 (0.5% by weight), Co-1a (1% by weight ) and rM-3c (0.5 wt%) when irradiated with an LED that emits at 395 nm.

[0045] Furthermore, the following results were obtained by varying the sensitizer, co-initiator, monomer and irradiation wavelength. Table 1 below summarizes the results for determining the reactivity of photopolymers which contain the general structure I in combination with various co-initiators and monomers or mixtures thereof. Examples 1 to 23 are according to the invention, Examples V1 to V3 serve for comparison.

Table 1

Reactivity of photopolymers

The compounds listed in Figure 1 can still be used for photo-ATRP. For this purpose, the following substances are added to a previously evacuated Schlenk vessel from which the oxygen was expelled with nitrogen: sensitizer of structure I (31.6 mg), EBPA (26.25 pl, 0.150 mmol), Met ⁿ Br _n salt solution as a stock solution in DMF (4.5 pmol) and Ligand L as a stock solution in DMF (20.3 pmol). To this are added monomer (4.51 g [4.8 ml], 45 mmol) and DMF as solvent (4.53 g [4.8 ml]). The reaction mixture is homogenized by continuous stirring and the remaining oxygen is driven off four times using a Schlenk technique. This is followed by four cycles of freezing with liquid nitrogen and subsequent thawing under vacuum and flushing with nitrogen. The now evacuated reaction vessel is irradiated with an LED at 470 nm with a power of 1 W for 6 h. After the reaction time has elapsed, the reaction vessel is ventilated and the LED is switched off to end the reaction. The polymer obtained is precipitated in precooled methanol and dried under vacuum. It will happen again dissolved in THF and precipitated in cooled methanol. It is then dried again under reduced conditions. The polymer obtained is now quantitatively recorded using a gravimetric measurement and characterized with regard to the number average and the dispersity of the molecular weight using a ¹ H-NMR spectrum and a GPC analysis. The following results were obtained.

Example 2 photo-ATRP

The following co-initiators were used for these experiments.

The compilation of the photo-ATRP experiments can be found in Table 2. An LED with a power of 1W was used, which emitted at 470 nm. Examples 24 to 35 are according to the invention, Examples V4 and V5 serve for comparison. Table 2

Experimental setup

Example 3 cationic photopolymerization

cM-2 cM-3 cM-4 The following monomers were used:

cm-2 cm-3 cm-4

When irradiated with an LED (power 10 W), the results listed in Table 3 were obtained. The choice of concentrations corresponds to the conditions from Table 1. The conversion was determined using FTIR. Spectroscopy determined. The irradiation was carried out on a a VERTEX 70 from Bruker. The layer thickness was 40 pm. Examples 36 to 42 are according to the invention, Examples V6 and V7 serve for comparison.

Table 3 Cationic photopolymerization

Claims

PATENT CLAIMS Heteroaromatic ketones of the formula (I)

in which the substituents A, B, C and D can each be the same or different and represent nitrogen or carbon, while R ¹ and R ² independently represent hydrogen, deuterium, a C1-C10 alkyl or C5-C12 aryl group . Ketones of formula (I), characterized in that they are selected from the group formed by the structures AA, BB, CC, AC, AB and BC:

Process for the preparation of heteroaromatic ketones of the formula (I), in which substances of the formula (a), (b) and/or (c) are used

reacted with dichloroacetone with the elimination of hydrogen chloride. Photoinitiator systems containing (a) at least one ketone of formula (I) and (b) at least one radical generator. Photoinitiator systems according to claim 4, characterized in that the free radical generators are selected from the group formed by onium salts, amines, mercapto compounds, disulfides, hexaarylbisimidazoles, alkyl halides, metal salts and mixtures thereof. Process for the photoinduced polymerization of monomers, comprising the following steps: (i) providing a monomer suitable for photoinduced polymerization; (ii) providing a photoinitiator system according to claim 4; (iii) mixing the components from steps (i) and (ii) as well (iv) irradiating the mixtures with light in the UV-VIS range. Method according to claim 5, characterized in that the monomers suitable for photopolymerization are selected from the group formed by substances of the formula (II), (II) and/or (IV)

in which the substituents J, K, L, M, N and P can be the same or different and are selected from the group formed by hydrogen, C1-C10 alkyl, C1-C10 alkoxy, C1-C10 alkyoxycarbonyl, C1- C10 alkylsulfonyl, C1-C10 alkylmercapto, C1-C10 dialkylphosphonyl, C5-C12 aryl, C5-C12 aryloxy, C5-C12 aryloxycarbonyl, C5-C12 arylsulfonyl, C5-C12 arylmercapto, C5-C12 diarylphosphonyl, halogen, cyano, COOR , OCOR, OSO2R, SO2R, SO3R, PO3R2, PO4R3 and R each represents hydrogen or a C1-C10 alkyl or C5-C12 aryl group. Method according to claim 5 and/or 6, characterized in that the mixtures are irradiated with light of a wavelength in the range from approximately 300 to approximately 550 nm. Method according to at least one of claims 6 to 8, characterized in that the photoinitiator systems are used together with compounds which are selected from the group formed by amines, secondary alcohols, mercapto compounds, onium compounds, aryl bisimidazoles, alkyl halides, metal salts and their mixtures. Use of ketones of the formula (I) as photoinitiators in photoinduced polymerization for the production of polymers.