Method for producing vanillin (meth)acrylate

Abstract

The present invention relates to an improved process for the preparation of vanillin (meth)acrylate and its derivatives or structurally related compounds in high purity. The present invention further relates to ethyl vanillin (meth)acrylate, which offers improved crosslinking efficiency at room temperature and is particularly suitable for paints / varnishes and coatings.

Description

[Technical Field]

[0001] The present invention relates to a novel method for producing vanillin (meth)acrylate and its derivatives or structurally related compounds in high purity. The method is resource-efficient and therefore particularly suitable for large-scale synthesis. Furthermore, the present invention relates to ethyl vanillin (meth)acrylate, which can be advantageously applied in paints / varnishes and / or coatings.

[0002] Background of the Invention Polymer latexes or polymer dispersions are widely used in water-based coatings. Drying the polymer latex or polymer dispersion results in the formation of a film through coalescence, which provides the desired mechanical and physical properties. One method for improving the properties of the film formed by the water-based composition is to include a cross-linkable polymer. The cross-linkable polymer may be self-cross-linking or may rely on the involvement of a cross-linking agent that reacts with the polymer.

[0003] Current coating materials include polymers containing carbonyl groups, such as vanillin (meth)acrylate, which can be cured by the addition of a crosslinking agent to yield coatings that are relatively solvent resistant.

[0004] Vanillin (meth)acrylate (VAL(M)A), the (meth)acrylic acid ester of vanillin (4-hydroxy-3-methoxybenzaldehyde), is currently an important natural resource. Vanillin is useful not only for its bioavailability but also because it is a multifunctional molecule, with the carbonyl moiety enabling further reactivity and various post-functionalization steps. From a chemical standpoint, vanillin (meth)acrylate can be described as a (meth)acrylic acid ester of a phenol derivative. Therefore, the synthesis of VAL(M)A requires the use of either (meth)acrylic acid chloride (or halides in general) or (meth)acrylic anhydride. Both routes have been described in the literature, with a recent example being WO 2017 / 007883.

[0005] VAL(M)A can be used in the production of organic polymers, such as thermosetting polymers, as a monomer or comonomer for polymer production and as a reactive diluent for polymer production. Unsaturated polyester resins (UPRs) and vinyl ester resins (VERs) are thermosetting polymers widely used in fiber-reinforced composites. For example, the global market for UPRs is approximately 5,000 kilotons and continues to grow. Vinyl ester resins (VERs) are widely used as matrix materials for advanced polymer composites due to their excellent corrosion and degradation resistance, high glass transition temperature, high strength-to-weight ratio, and low cost. Until recently, petrochemicals were the source of choice for producing the general-purpose monomers for vinyl ester resins. However, continued use of these non-renewable resources raises concerns about environmental pollution and the depletion of non-renewable resources. Furthermore, petroleum-based monomers such as styrene are widely used as reactive diluents for both vinyl ester resins and unsaturated polyesters. However, these reactive diluents are often considered hazardous air pollutants (HAPs) and volatile organic compounds (VOCs). Unsaturated polyester resins (UPR) and vinyl ester resins (VER) are typically mixed with styrene (up to 50% of the total amount) as a reactive diluent before being cured by free radical polymerization. However, styrene has significant drawbacks due to health, safety, and environmental concerns. Additionally, styrene is derived from petroleum, a non-renewable resource. There is a need for a styrene alternative that overcomes one or more of the drawbacks associated with the prior art.

[0006] To develop sustainable and environmentally friendly vinyl ester resins, increasing efforts have been made to identify renewable building blocks to replace the petroleum-derived components of these resins. Several renewable resources (e.g., cellulose, starch, and natural oils) have been utilized to produce novel biomonomers. However, most of these biomonomers are aliphatic or alicyclic, which results in low structural rigidity and thermal stability of the polymers (see, for example, M. Fache, et al., Green Chem 2014, 16, 1987).

[0007] In recent years, bio-based phenolic compounds, such as lignin model compounds and aromatic compounds derived from cashew nut shell liquid, have attracted attention as high-performance vinyl ester resins that exhibit properties comparable to or better than those of petroleum-based commercial products. Vanillin, originally an extract of vanilla plantifolia beans, is one of the most widely used flavors in foods, fragrances, beverages, and pharmaceuticals (see, for example, C. Brazinha, et al., Green Chem 2011, 13, 2197). Certain vanillin derivatives have been used as renewable building blocks for high-performance polymers, primarily due to their rigid aromatic structure. Wood contains approximately 30% lignin, one of the most abundant raw materials in nature. Because vanillin can be mass-produced from this lignin, bioresources can be used to manufacture novel polymeric materials.

[0008] Vanillin has already been modified into methacrylated derivatives for use in vinyl ester resins, for example as coating materials, by Stöglich esterification of vanillin with methacrylic acid (E. Renbutsu, et al., Carbohyd Polym 2007, 69, 697), by esterification of vanillin with methacryloyl chloride (R.J. Patel, et al., Der Pharma Chemica 2013, 5, 63), or by reaction of vanillin with methacrylic anhydride (Stanzione et al., Chemsuschem 2012, 5, 1291).

[0009] Although the synthesis from (meth)acrylic anhydride and vanillin in the presence of a catalyst is known, the subsequent workup of the crude reaction mixture does not have a technically satisfactory solution. The methods described in the art include the use of inert conditions, liquid-liquid extraction steps using organic solvents (which are expensive, toxic, and environmentally unfriendly), chromatographic purification steps, and drying steps using desiccants.

[0010] However, for the large-scale production of VAL(M)A and its derivatives, a non-toxic, environmentally friendly, and at the same time cost-effective work-up is essential.

[0011] Given the above, there is an urgent need for improved methods for the production of VAL(M)A (and its derivatives and structurally related compounds) that allow for large-scale, high-purity, and resource-efficient production.

[0012] A further object of the present invention is to provide monomers suitable for improving the properties of the above-mentioned coating materials. More specifically, it is desirable that such monomers can be processed into dispersions or polymers, such as emulsion polymers, with very low residual monomer content. It is also desirable that the resulting polymers can be crosslinked using commonly applied crosslinking reagents, i.e., diamines and / or dihydrazides (e.g., ADH) and / or blocked crosslinking reagents, such as blocked hydrazides, as described in U.S. Patent Application Publication No. 2014 / 0228509.

[0013] Summary of the Invention The above problems have been solved by the methods and compounds / compositions according to the present invention.

[0014] More specifically, the present invention provides a compound of general formula (I): [ka] [In the formula, R 2 is -H, -OMe, -OEt, or -O-C3~OC 10alkyl, branched alkyl or alkenyl; R 3 is H, Me, Et, or -C3 to C 10 alkyl or alkenyl, R 4 is -Me or -H], [ka] [In the formula, R 2 is as defined above, R 3 is -H, -Me, -Et, or -C3 to C 10 an alcohol of the formula (III) and an activated (meth)acrylic acid derivative (III). [ka] [In the formula, R 4 is as defined above, R 1 is F, Cl, Br, I, —O(CO)C(CH2)CH3, —O(CO)C(CH2)H], wherein the (meth)acrylate of general formula (I) is obtained from the crude reaction mixture by precipitation from an aqueous medium.

[0015] Furthermore, the inventors have surprisingly found that if the process is carried out in the presence of at least one polymerization inhibitor, this polymerization inhibitor co-precipitates with the (meth)acrylate of formula (I), making further (additional) stabilization before storage or shipping unnecessary. The present invention therefore provides stabilized (meth)acrylates of formula (I), which can be obtained by the above-mentioned process carried out in the presence of at least one polymerization inhibitor.

[0016] In addition to the above, the present inventors have surprisingly found that the cross-linking of the compounds of formula (IV) or (V) can be achieved using commonly applied cross-linking reagents (i.e., diamines and / or dihydrazides (such as ADH) and / or blocked cross-linking reagents such as blocked hydrazides). [ka] It has been found that the crosslinking properties of polymers containing (meth)acrylate monomers of the formula (I) can be significantly improved over their methoxy analogues (i.e., vanillin (meth)acrylate).

[0017] Therefore, the present invention provides a compound of formula (IV) or formula (V): [ka] The present invention also relates to (meth)acrylates of the formula:

[0018] In the context of the present invention, the (meth)acrylate of formula (IV) and (V) is referred to as ethyl vanillin (meth)acrylate or EVAL(M)A.

[0019] Detailed Description of the Invention The present inventors have unexpectedly found that a highly pure VAL(M)A derivative can be easily and resource-savingly produced by esterifying an alcohol of general formula (II) with an activated (meth)acrylic acid derivative (III) and isolating the VAL(M)A derivative by simple precipitation from an aqueous medium. This method is particularly suitable for large-scale production, i.e., on the scale of several kilograms to several tons.

[0020] When the crude reaction mixture comes into contact with an aqueous medium, no two-phase mixture or sticky oil / oil droplets form. Instead, the VAL(M)A-derived product crystallizes surprisingly quickly in aqueous media, and the precipitation step produces a purification effect, since no accumulation of impurities or other undesirable compounds (coprecipitation) occurs in the VAL(M)A-derived product. Particularly surprising is the high purity of the aforementioned product, which is obtained regardless of the purity or quality of the starting materials, and in particular, regardless of the purity of the (meth)acrylic anhydride (i.e., the content of (meth)acrylic anhydride in the (meth)acrylic anhydride starting material).

[0021] In the context of the present invention, the terms "VAL(M)A derivative" and "VAL(M)A derived product" are used interchangeably and refer to vanillin (meth)acrylate, its derivatives, and compounds of the general formula (I): [ka] "Structurally similar or structurally related compounds" means compounds that are structurally similar or structurally related to the compounds of the formula (I).

[0022] In a preferred embodiment of the present invention, R 3 is hydrogen or methyl. 3 It is particularly preferred that is hydrogen.

[0023] The term "(meth)acrylate" is understood to mean both esters of methacrylic acid and esters of acrylic acid.

[0024] The inventors have found that during the deposition step according to the method of the present invention (a) The product crystallizes and therefore automatically separates from the reaction mixture; (b) the catalyst (which may be present in the reaction mixture) and derivatives resulting from the catalyst originally used remain in the aqueous phase and are therefore separated from the product; (c) quenching of excess or unreacted activated (meth)acrylic acid derivative (III); (d) By-products from the quenching process (e.g., (meth)acrylic acid, hydrogen chloride / hydrogen halide) remain in the aqueous phase; (e) useful and does not require the use of potentially toxic or harmful organic solvents; and (e) The inhibitor used during the reaction (which may be present in the reaction mixture) coprecipitates and therefore remains in the VAL(M)A-derived product. found.

[0025] Preferably, the (meth)acrylate of formula (I) is vanillin (meth)acrylate (VAL(M)A) or ethyl vanillin (meth)acrylate (EVAL(M)A).

[0026] The aqueous medium used in the precipitation step of the method according to the invention can be selected from pure or demineralized water, aqueous alcohol solutions, aqueous ammonia solutions, aqueous alkali (earth) metal hydroxide solutions, and aqueous alkali (earth) metal bicarbonate and carbonate solutions. The aqueous alcohol solutions are preferably aqueous methanol / ethanol solutions (1% to 70% by weight, preferably 30% to 70% by weight).

[0027] The bicarbonate and carbonate solutions are advantageously saturated. The concentration of the ammonia solution may be between 0.1 mol / l and 16.5 mol / l. The concentration of the alkaline (earth) metal hydroxide solution may be between 0.01 mol / l and 1.0 mol / l.

[0028] Advantageously, the precipitation step is carried out at a pH between 7 and 12, preferably between 7 and 9.

[0029] The amount of aqueous medium used in the precipitation step is ideally 1 to 20 times, preferably 5 to 10 times, the weight of the alcohol (II) initially used. To initiate precipitation, the crude reaction mixture can be poured into the aqueous medium, or the aqueous medium can be added to the crude reaction mixture.

[0030] The activated (meth)acrylic acid derivative (III) used in the present invention is preferably (meth)acrylic anhydride. The activated (meth)acrylic acid derivative (III) used in the reaction can be present in an amount of 0.9 to 2.0 equivalents, preferably 1.0 to 1.8 equivalents, and most preferably 1.2 to 1.6 equivalents relative to the amount of the alcohol of general formula (II).

[0031] The reaction of the alcohol of general formula (II) with the activated (meth)acrylic acid derivative (III) can be carried out under solvent-free conditions, preferably in the presence of at least one catalyst and / or at least one stabilizer (polymerization inhibitor).

[0032] The catalyst can be advantageously selected from the group consisting of alkali metal salts (such as hydroxides, halides, triflates, and perchlorates), alkaline earth metal salts (such as hydroxides, halides, triflates, and perchlorates), zinc salts (such as hydroxides, halides, triflates, and perchlorates), rare earth metal salts (such as halides, triflates, and perchlorates), lithium alkoxides, sulfuric acid, lithium or sodium methacrylate, amino-substituted pyridines such as 4-(dimethylamino)pyridine, or mixtures thereof. The aforementioned metal salts can be used in anhydrous or hydrated form. Preferred amounts of catalyst are 0.1 to 10 mol %, especially 5 mol %, (based on the alcohol) for lithium alkoxides, sodium hydroxide, or magnesium chloride; 0.1 to 2 wt %, especially 0.5 wt %, for sodium methacrylate; and 0.1 to 1 wt %, especially 0.3 to 0.4 wt %, for sulfuric acid (based on the total reactant weight). Preferred lithium alkoxide catalysts are LiOMe, LiOEt, LiOPr, LiOiPr, LiOBu, and LiOiBu. Sulfuric acid can be used in concentrated or diluted form. Preferably, it is applied in an amount of 0.01% to 1.0% by weight based on the reaction weight. Ion exchange resins such as Amberlyst can also be used for catalysis.

[0033] Preferred catalysts for the process according to the invention are lithium methoxide, magnesium chloride, sodium hydroxide, sodium (meth)acrylate, sulfuric acid, or mixtures thereof.

[0034] To prevent undesired polymerization of the (meth)acrylate, a polymerization inhibitor (stabilizer) can be used in the process according to the invention. In the context of the present invention, the terms "(polymerization) inhibitor" and "stabilizer" are used synonymously.

[0035] Advantageously, these processes are carried out in the presence of an inhibitor composition comprising or consisting of at least one phenolic polymerization inhibitor.

[0036] Advantageously, the process of the present invention is carried out in the presence of at least one polymerization inhibitor selected from the group consisting of hydroquinone, a hydroquinone ether, such as hydroquinone monomethyl ether or di-tert-butylcatechol, phenothiazine, N,N'-(diphenyl)-p-phenylenediamine, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, p-phenylenediamine, methylene blue, or a sterically hindered phenol, with the amount of stabilizer at the start of the reaction being adjusted to 0 to 5000 ppm, preferably 1000 to 3000 ppm, based on the amount of product theoretically expected at complete conversion.

[0037] Preferably, the polymerization inhibitor is selected from hydroquinone monomethyl ether, 2,4-dimethyl-6-tert-butylphenol, 2,6-di-tert-butyl-4-methyl-phenol, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (e.g., IRGANOX 1076), and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, and mixtures thereof. These inhibitors co-precipitate with the product (meth)acrylate of general formula (I), which means that spontaneous polymerization in the final product can be avoided.

[0038] The reaction of the alcohol of general formula (II) with the activated (meth)acrylic acid derivative (III) is carried out at a temperature of 0 to 130° C., preferably 80 to 100° C., and most preferably 85 to 95° C. The reaction usually takes 3 to 5 hours to reach complete conversion, but may take 1 to 24 hours.

[0039] Preferably, the activated (meth)acrylic acid derivative (III) is used in its commercially available stabilized form (for example VISIOMER® MAAH), stabilized with the inhibitors outlined above.

[0040] Preferably, the activated (meth)acrylic acid derivative (III) is used in its commercially available stabilized form (e.g., VISIOMER® MAAH) together with either 2000 ppm±200 ppm of 2,4-dimethyl-6-tert-butylphenol or 1000 ppm±200 ppm of 2,4-dimethyl-6-tert-butylphenol, thereby already introducing one stabilizer into the reaction mixture and, as outlined, also into the final product.

[0041] An additional inhibitor may be added. Preferably, the amount of stabilizer added at the start of the reaction is adjusted to be 0 to 1000 ppm relative to the amount of product theoretically expected at complete conversion, and most preferably, the amount of stabilizer added at the start of the reaction is adjusted to be 150 to 1000 ppm relative to the amount of product theoretically expected at complete conversion.

[0042] Prior to precipitating the (meth)acrylate of general formula (I) from the aqueous medium, the crude reaction mixture can be contacted with methanol. If this intermediate step is performed, methanol is preferably added at a temperature of 60°C to 80°C. The amount of methanol added can be calculated and is 1 to 5 equivalents relative to the residual (meth)acrylic anhydride present in the reaction mixture at the end of the reaction.

[0043] In one embodiment of the invention, the alcohol of general formula (II) is vanillin and the (meth)acrylate of general formula (I) is vanillin (meth)acrylate. In a different embodiment, the alcohol of general formula (II) is ethyl vanillin and the (meth)acrylate of general formula (I) is ethyl vanillin (meth)acrylate.

[0044] In a further aspect, the present invention provides stabilized (meth)acrylates of formula (I), i.e. (meth)acrylates of general formula (I) [ka] [In the formula, R 2 is -H, -OMe, -OEt, or -O-C3~OC 10 alkyl, branched alkyl or alkenyl; R 3 is H, Me, Et, or -C3 to C 10 alkyl or alkenyl, R 4 is -Me or -H] and at least one polymerization inhibitor, wherein the composition comprises: General formula (II) [ka] [In the formula, R 2 and R 3 is as defined above] and an activated (meth)acrylic acid derivative (III) [ka] [In the formula, R 1 are F, Cl, Br, I, -O(C=O)C(CH3)(CH2), -O(C=O)C(H)(CH2), R 4 is as defined above], which is carried out in the presence of at least one polymerization inhibitor as described above; precipitating the (meth)acrylate of general formula (I) from the crude reaction mixture by precipitation from an aqueous medium together with at least one inhibitor; The present invention provides a composition that can be obtained by:

[0045] Suitable (meth)acrylates of formula (I) are as defined above. In a preferred embodiment of the present invention, R 3 is hydrogen or methyl. 3 is hydrogen. Vanillin(meth)acrylate and ethyl vanillin(methacrylate), as well as 4-acetylphenyl(meth)acrylate (formulas (VI) and (VII) respectively) and 4-formylphenyl(meth)acrylate (formulas (VIII) and (VIX) respectively) are particularly preferred.

[0046] [ka]

[0047] Suitable inhibitors are as defined above. Advantageously, 2,4-dimethyl-6-tert-butylphenol (Topanol A), p-methoxyphenol (MEHQ), 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl and / or combinations thereof are used.

[0048] The inhibitors used in the present method are preferably applied in an amount of 0 to 5000 ppm total, preferably 1000 to 3000 ppm.

[0049] The stabilized (meth)acrylate of formula (I) thus obtained (i.e., a composition comprising a (meth)acrylate of general formula (I) and at least one stabilizer) has a stabilizer content of 400 ppm to 2000 ppm. In total, the stabilizer concentration in the product is 30% to 80% of the initial stabilizer concentration during the reaction.

[0050] The inventors have unexpectedly found that the crosslinking properties of polymers comprising EVAL(M)A monomers of formula (IV) or (V) with commonly applied crosslinking reagents (i.e., diamines and / or dihydrazides (such as ADH) and / or blocked crosslinking reagents such as blocked hydrazides) can be significantly improved over vanillin (meth)acrylate. As shown in comparative experiments, crosslinking at room temperature is more efficient for polymers incorporating EVAL(M)A instead of VAL(M)A, as experiments on EVAL(M)A-based polymers / films show an increased crosslink density.

[0051] Therefore, the present invention also provides a compound of formula (IV) or formula (V) [ka] (Meth)acrylates of the formula (I) are also included.

[0052] The compounds of formula (IV) and (V) are obtainable by the process according to the invention. As is evident from the above, the present invention also relates to stabilized (meth)acrylates of formula (IV) or formula (V), which are obtainable by the process described above.

[0053] The compounds and compositions according to the invention or obtainable by the process of the invention, respectively, are particularly suitable as comonomers and reactive diluents for the preparation of (emulsion) polymers (UPR, VER), as described, for example, in WO 94 / 025433, WO 2010 / 026204, DE 102013223876 A1, EP 0016518 A1, DE 4237030 A1, WO 2009 / 146995, EP 2246403 A1, US 9394460 A1 and WO 2018063095.

[0054] Furthermore, the compounds and compositions according to the invention or obtainable by the method of the invention, respectively, are particularly suitable as comonomers in crosslinking poly(meth)acrylate binders with functionalized monomers such as acetone monomer, diacetone acrylamide (DAAM), acetoacetoxyethyl (meth)acrylate (AAE(M)A) monomer, butyl acetoacetate (BAA) monomer or mixtures thereof, thereby making the compounds according to the invention suitable comonomers for (partial) replacement or addition to common carbonyl-containing compounds (such as DAAM) used in current and commonly established formulations.

[0055] Polymer emulsions (sometimes called "latexes") are film-forming agents commonly used in the coatings and paints industries. These water-dispersible polymer compositions typically contain an organic polymer binder phase dispersed in an aqueous solvent phase. These polymer emulsions can be cured / crosslinkable under room temperature conditions (typically around 20°C to 30°C). The polymer binder phase of such emulsions is typically composed of a polymer or copolymer with photocurable functional groups, such as vinyl groups. Common examples of such binders include polyacrylates or polymethacrylates. Crosslinking agents are typically added to such compositions to increase the hardness of the final coating. This is achieved by increasing the crosslink density. Aside from increased hardness, other benefits of increased crosslink density include, but are not limited to, improved resistance of the coating to water and chemical solvents (acids, bases), cleanability, and (wet) abrasion resistance.

[0056] Crosslinking can be achieved using commonly applied crosslinking reagents, i.e., diamines and / or dihydrazides (such as ADH) and / or blocked crosslinking reagents, such as blocked hydrazides as described, for example, in U.S. Patent Application Publication No. 2014 / 0228509. [Brief explanation of the drawings]

[0057] [Figure 1] FIG. 1 is a diagram showing the swelling behavior of a crosslinked film.

[0058] The present invention will now be described by way of non-limiting examples and exemplary embodiments.

[0059] Example [ka]

[0060] Example 1a: Synthesis of vanillin methacrylate (VALMA) (R 1 =O(CO)C(CH2)CH3, R 2 =OMe, R 3 =H, R 4 =Me) Vanillin (989 g, 6.5 mol, 1.00 equiv.) and methacrylic anhydride (1402 g, 9.1 mol, 1.40 equiv.) were mixed with 4-methoxyphenol (1.43 g, 0.011 mol, 0.001 equiv.) and lithium methoxide (12.34 g, 0.32 mol, 5 mol%). The resulting mixture was heated to 90-100°C to obtain a homogeneous solution. Air was constantly bubbled through the reaction mixture during the reaction. After 4 hours, methanol (346 g) was added, and the mixture was stirred at elevated temperature for an additional 30 minutes. Water (5 L) was then added, resulting in the precipitation of a colorless crystalline solid. The solid was filtered, optionally washed with water, and dried. Yield: 1200 g (84%).

[0061] The as-obtained product already contains sufficient amounts of the coprecipitated inhibitors 4-methoxyphenol and 2,4-dimethyl-6-tert-butylphenol (derived from methacrylic anhydride) and does not need to be additionally stabilized with a polymerization inhibitor.

[0062] [ka]

[0063] 13 C{ 1 H}NMR is based on the literature.

[0064] Reference: Stanzione, JF, III, Sadler, JM, La Scala, JJ and Wool, RP (2012), Lignin Model Compounds as Bio‐Based Reactive Diluents for Liquid Molding Resins. ChemSusChem, 5: 1291-1297. doi:10.1002 / cssc.201100687 GC (area%): Purity >97% (vanillin methacrylate). Residual methacrylic anhydride <0.1, residual methacrylic acid <0.2 Inhibitor content: 2,4-dimethyl-6-tert-butylphenol 1360 ppm, 4-methoxyphenol 488 ppm

[0065] Example 1b: Synthesis of vanillin methacrylate (VALMA) (R 1 =O(CO)C(CH2)CH3, R 2 =OMe, R 3 =H, R 4 =Me) Vanillin (800 g, 5.26 mol, 1.00 eq.) and methacrylic anhydride (1135 g, 7.37 mol, 1.40 eq.) are mixed with 4-methoxyphenol (1.16 g, 0.009 mol, 0.001 eq.) and sodium methacrylate (4 g, 0.037 mol, 0.007 eq.). The resulting mixture is heated to 90°C to obtain a homogeneous solution. Air is constantly bubbled through the reaction mixture during the reaction. After 6 hours, the mixture is poured into water (2 L) and stirred to precipitate a colorless crystalline solid. The solid is filtered, optionally washed with water, and dried. Yield: 850 g (74%)

[0066] The as-obtained product already contains sufficient amounts of the coprecipitated inhibitors 4-methoxyphenol and 2,4-dimethyl-6-tert-butylphenol (derived from methacrylic anhydride) and does not need to be additionally stabilized with a polymerization inhibitor.

[0067] The analytical data are in good agreement with the purity of VALMA obtained in Example 1a.

[0068] Inhibitor content: 2,4-dimethyl-6-tert-butylphenol 742 ppm, 4-methoxyphenol 253 ppm

[0069] Example 1c: Synthesis of vanillin methacrylate (VALMA) (R 1 =O(CO)C(CH2)CH3, R 2 =OMe, R 3 =H, R 4 =Me) Vanillin (4944.9 g, 32.5 mol, 1.00 equiv.) and methacrylic anhydride (7014.3 g, 45.5 mol, 1.40 equiv.) were mixed with 4-methoxyphenol (7.16 g, 0.057 mol, 0.001 equiv.) and lithium methoxide (61.72 g, 1.62 mol, 5 mol%). The resulting mixture was heated to 90°C to obtain a homogeneous solution. Air was constantly bubbled through the reaction mixture during the reaction. The reaction was monitored by GC, and after 1 hour, consumption of the starting material was nearly complete (at which point the reaction could be stopped). After 4.5 hours, methanol (2082.6 g) was added and the mixture was stirred at elevated temperature for an additional 2 hours. The reaction mixture was then allowed to cool to room temperature. The crude material was poured into water and stirred vigorously, resulting in the precipitation of a colorless crystalline solid. The product was separated from the mother liquor by filtration, washed with water, and dried. Yield: 6149g (86%).

[0070] Note: Additional product can be obtained by delayed precipitation into the mother liquor or by extraction of the mother liquor. Extraction can be carried out with common organic solvents.

[0071] The as-obtained product already contains sufficient amounts of the coprecipitated inhibitors 4-methoxyphenol and 2,4-dimethyl-6-tert-butylphenol (derived from methacrylic anhydride) and does not need to be additionally stabilized with a polymerization inhibitor.

[0072] GC (area%): Purity >98% (vanillin methacrylate). Residual methacrylic anhydride <0.2, residual methacrylic acid <0.1 Water content (Karl Fischer): <0.1% by weight Inhibitor content: 2,4-dimethyl-6-tert-butylphenol 848 ppm, 4-methoxyphenol 205 ppm

[0073] Example 2: Synthesis of ethyl vanillin methacrylate (EVALMA) (R 1 =O(CO)C(CH2)CH3, R 2 =OEt, R 3 =H, R 4 =Me) Ethyl vanillin (200 g, 1.20 mol, 1.00 equiv.) and methacrylic anhydride (259 g, 1.68 mol, 1.40 equiv.) were mixed with 4-methoxyphenol (0.281 g, 0.002 mol, 0.001 equiv.) and lithium methoxide (2.30 g, 0.06 mol, 5 mol%). The resulting mixture was heated to 90-100°C to obtain a homogeneous solution. Air was constantly bubbled through the reaction mixture during the reaction. After 3.5 hours, methanol (47.7 g) was added, and the mixture was stirred at elevated temperature for an additional 30 minutes. Water (2 L) was then added, resulting in the precipitation of a colorless crystalline solid. The solid was filtered, optionally washed with water, and dried. Yield: 268.8 g (95%)

[0074] The as-obtained product already contains sufficient amounts of the coprecipitated inhibitors 4-methoxyphenol and 2,4-dimethyl-6-tert-butylphenol (derived from methacrylic anhydride) and does not need to be additionally stabilized with a polymerization inhibitor.

[0075] [ka]

[0076] GC (area%): Purity >97% (ethyl vanillin methacrylate). Residual methacrylic anhydride <0.1, residual methacrylic acid <0.2 Inhibitor content (double determination): 2,4-dimethyl-6-tert-butylphenol 693 ppm and 727 ppm; 4-methoxyphenol 6 ppm and 20 ppm

[0077] Example 3: Synthesis of 4-acetylphenyl methacrylate (R 1 =O(CO)C(CH2)CH3, R 2 =H, R 3 =Me, R 4 =Me) 4-Hydroxyacetophenone (300 g, 2.20 mol, 1.00 equiv.) and methacrylic anhydride (475.6 g, 3.09 mol, 1.40 equiv.) were mixed with 2,4-dimethyl-6-tert-butylphenol (0.45 g, 0.002 mol, 0.001 equiv.) and magnesium chloride (5.20 g, 2.5 mol%). The resulting mixture was heated to 90-100°C to obtain a homogeneous solution. Air was constantly bubbled through the reaction mixture during the reaction. After 3 hours, methanol (35.2 g) was added, and the mixture was stirred at elevated temperature for an additional 30 minutes. The mixture was then poured into water (4 L), resulting in the precipitation of a colorless crystalline solid. The solid was filtered, optionally washed with water, and dried. Yield: 328.1 g (74%)

[0078] The as-obtained product already contains coprecipitated 2,4-dimethyl-6-tert- in sufficient amounts and does not need to be additionally stabilized with a polymerization inhibitor.

[0079] [ka]

[0080] GC (area%): Purity >98% (vanillin methacrylate). Residual methacrylic anhydride <0.1, residual methacrylic acid <0.1 Inhibitor content: 2,4-dimethyl-6-tert-butylphenol 404 ppm

[0081] Example 4: Synthesis of 4-formylphenyl methacrylate (R 1 =O(CO)C(CH2)CH3, R 2 =H, R 3 =H, R 4 =Me) 4-Hydroxybenzaldehyde (200 g, 1.63 mol, 1.00 equiv.) and methacrylic anhydride (353.5 g, 2.29 mol, 1.40 equiv.) were mixed with 2,4-dimethyl-6-tert-butylphenol (0.31 g, 0.002 mol, 0.001 equiv.) and lithium methoxide (3.10 g, 5 mol%). The resulting mixture was heated to 90-100°C to obtain a homogeneous solution. Air was constantly bubbled through the reaction mixture during the reaction. After 4.5 h, methanol (86.5 g) was added, and the mixture was stirred at elevated temperature for an additional 30 min. The mixture was then poured into aqueous ethanol (2 L, 70:30). Upon cooling, a colorless crystalline solid precipitated. The solid was filtered, optionally washed with water, and dried. The product was a liquid at room temperature.

[0082] GC (area%): Purity >95%. Residual methacrylic anhydride <0.1, residual methacrylic acid <0.2.

[0083] The as-obtained product already contains sufficient amounts of the coprecipitated inhibitor 2,4-dimethyl-6-tert-butylphenol and does not need to be additionally stabilized with a polymerization inhibitor.

[0084] [ka]

[0085] 1 H NMR and 13 C{ 1H}NMR is based on the literature.

[0086] Reference: M. Eing, BT Tuten, JP Blinco, C. Barner-Kowollik, Chem. Eur. J. 2018, 24, 12246 Inhibitor content after recrystallization: 2,4-dimethyl-6-tert-butylphenol 80 ppm

[0087] Inhibitor Content: Synthetic procedures starting from methacrylic anhydride typically contain inherent inhibitors due to the starting material. The methacrylic anhydride used in the above experiments typically already contains 2,4-dimethyl-6-tert-butylphenol (2000 ± 200 ppm). Therefore, adding additional inhibitors during the synthesis is not necessary, although adding additional inhibitors, such as 4-methoxyphenol, is possible. Naturally, the inhibitor content of the final product depends heavily on the yield, purity, and precise workup procedure (washing, amount of water, basic or acidic conditions, recrystallization, etc.). In the case of solid products, the uneven distribution of inhibitors within the solid must also be taken into account. Surprisingly, however, sufficient amounts of inhibitor remain in the product for all products and various workup conditions.

[0088] When the crude reaction mixture resulting from the reaction of alcohol with activated methacrylic acid species is poured into or mixed with purified water, most of the 2,4-dimethyl-6-tert-butylphenol remains in the final product. Given the weight gain of the product, the inhibitor concentration (ppm) will naturally be lower if no additional inhibitor is added. In the above example, the following calculations and measurements are made: [Table 1-1] [Table 1-2]

[0089] In fact, 2,4-dimethyl-6-tert-butylphenol is largely preserved during the reaction and remains to a considerable extent in the product after simple aqueous workup. While almost no residual inhibitor is found in the aqueous wash phase, some amounts are lost along with organic by-products such as methacrylic acid and methyl methacrylate. On the other hand, the inhibitor is lost when the product is recrystallized in organic solvents (see, for example, Example 4).

[0090] That is, surprisingly a) When the activated and stabilized (meth)acrylic acid derivative is reacted with an alcohol as described above, it is not necessarily necessary to add an additional inhibitor.

[0091] b) When the crude reaction mixture is worked up by simply mixing it with an aqueous medium, the inhibitor originating from the stabilized (meth)acrylic acid derivative is largely preserved and remains in the product.

[0092] c) Work-up procedures known in the literature, such as recrystallization, chromatographic purification steps, etc., reduce the final inhibitor concentration in the product and require separate addition of inhibitor.

[0093] d) For VALMA and EVALMA: With respect to the inhibitor concentration [ppm] of the activated and stabilized (meth)acrylic acid component used, the inhibitor concentration in the product will be 30% to 80% of the initial concentration.

[0094] Preparation of dispersion, subsequent crosslinking with adipic acid dihydrazide (ADH), and film formation Example 1: Synthesis of dispersion using ethyl vanillin methacrylate (1.35 mol%) Butyl acrylate-co-methyl methacrylate, ethyl vanillin methacrylate, methacrylic acid BuA-co-MMA-EVALMA-MAS=53.49-42.77-2.74-1(weight%) Ethyl vanillin methacrylate (21.9 g) was dissolved in butyl acrylate (BuA, 427.9 g) and methyl methacrylate (342.2 g). This solution was emulsified (Ultra-Turrax, 3 min, 4000 rpm) with methacrylic acid (8 g), ammonium persulfate (APS, 2.4 g), and Disponol FES 32 (0.6 g, 30%) in water (718.4 g). Water (470 g) and Disponil DES 32 (0.6 g, 30%) were added to a 2 L glass reactor equipped with a temperature controller and a blade stirrer, heated to 80°C, and mixed with APS (0.6 g) dissolved in water (10 g). After 5 min, the first emulsion was added over 240 min (optional intervals). After complete addition of the emulsion, the mixture was further stirred at 80°C for 1 h. After cooling to room temperature, the dispersion was filtered using a 125 μm mesh filter. The as-prepared dispersion had a solids content of 40 ± 1 wt%, a pH of 2.1, a viscosity of 9 mPa·s, an rDNC value of 100 nm, and a minimum film formation temperature of 3.4 °C. Before further reprocessing, the dispersion was adjusted to pH = 9 by adding aqueous ammonia (25%).

[0095] Example 2: Synthesis of a dispersion using ethyl vanillin methacrylate (2.72 mol%) Butyl acrylate-co-methyl methacrylate, ethyl vanillin methacrylate, methacrylic acid BuA-co-MMA-EVALMA-MAS=52-41.56-5.45-1(weight%) This dispersion was synthesized according to the procedure set forth in Example 1, except that 43.6 g of ethyl vanillin methacrylate, 416.0 g of butyl acetate, 332.5 g of methyl methacrylate, and 8 g of methacrylic acid were used. The as-prepared dispersion had a solids content of 40±1 wt %, a pH value of 2.0, a viscosity of 9 mPa·s, an rDNC value of 112 nm, and a minimum film formation temperature of 5.3°C. Before further reprocessing, the dispersion was adjusted to pH=9 by the addition of aqueous ammonia (25%).

[0096] Example 3: Synthesis of dispersion using vanillin methacrylate (1.35 mol%) Butyl acrylate-co-methyl methacrylate, vanillin methacrylate, methacrylic acid BuA-co-MMA-VALMA-MAS=53.58-42.87-2.59-1(weight%) This dispersion was synthesized according to the procedure set forth in Example 1, except that 20.72 g of vanillin methacrylate, 428.64 g of butyl acetate, 342.72 g of methyl methacrylate, and 8 g of methacrylic acid were used. The as-prepared dispersion had a solids content of 40±1 wt%, a pH value of 2.0, a viscosity of 8 mPa s, an rDNC value of 111 nm, and a minimum film formation temperature of 4.4°C. Before further reprocessing, the dispersion was adjusted to pH=9 by the addition of aqueous ammonia (25%).

[0097] Example 4: Synthesis of dispersion using vanillin methacrylate (2.72 mol%) Butyl acrylate-co-methyl methacrylate, vanillin methacrylate, methacrylic acid BuA-co-MMA-VALMA-MAS=52.17-41.7-5.14-1(weight%) This dispersion was synthesized according to the procedure set forth in Example 1, except that 41.1 g of vanillin methacrylate, 417.4 g of butyl acetate, 333.6 g of methyl methacrylate, and 8 g of methacrylic acid were used. As prepared, the dispersion had a solids content of 40±1 wt %, a pH value of 1.9, a viscosity of 8 mPa·s, an rDNC value of 122 nm, and a minimum film formation temperature of 6.9°C. Before further reprocessing, the dispersion was adjusted to pH=9 by the addition of aqueous ammonia (25%).

[0098] Crosslinking of dispersions with adipic acid dihydrazide (ADH) All dispersions were crosslinked with an equimolar amount of ADH. An aqueous solution of ADH (15%) was added to the stirred dispersions, followed by stirring for 2 hours. The films were dried at room temperature.

[0099] Solvent uptake The solvent uptake of the prepared coating was measured using methyl isobutyl ketone (MIBK). A sample of the dispersion coating (A) was immersed and swollen in MIBK at room temperature for 4 hours. The sample was then removed from the solvent, excess solvent removed, and weighed. The sample was then dried at 140°C for 1 hour and reweighed (B). The difference in weight between (A) and (B) is the weight loss, which corresponds to the amount of solvent uptake.

[0100] The swelling relates to the weight of the sample after removing all the soluble parts (B), which is referred to as the true swelling.

[0101] [Table 2]

[0102] Figure 1 shows the swelling behavior of the crosslinked film.

[0103] As evident from the swelling experiments of VALMA and EVALMA films, the absolute difference between the true swelling values ​​of the uncrosslinked and crosslinked films varies significantly depending on the monomer applied: EVALMA results in a more significant decrease in the true swelling values ​​of the as-prepared films (1.35 mol%: Δ(uncrosslinked:crosslinked) = -1918%, 2.72 mol%: Δ(uncrosslinked:crosslinked) = -1472%) compared to VALMA-based films (1.35 mol%: Δ(uncrosslinked:crosslinked) = -1655%, 2.72 mol%: Δ(uncrosslinked:crosslinked) = -1040%).

[0104] Crosslinked films incorporating EVALMA-based polymers consistently show lower true swelling values ​​compared to films incorporating VALMA-based polymers. At both the applied molar concentrations of 1.35 mol% and 2.72 mol%, EVALMA shows lower true swelling values ​​for crosslinked films (265% and 164%) compared to VALMA (270% and 168%).

[0105] Therefore, it is clear that cross-linking of the polymer with, for example, ADH is more efficient when ethyl vanillin methacrylate is used instead of vanillin methacrylate. The same applies to the comparison between ethyl vanillin acrylate and vanillin acrylate.

Claims

1. General formula (I) 【Chemistry 1】 [In the formula, R ２ is —H, —OMe, —OEt, or —O—C ３ ~O-C １０ alkyl, branched alkyl or alkenyl; R ３ is H, Me, Et, or -C ３ ~C １０ alkyl or alkenyl, R ４ is -Me or -H], 【Chemistry 2】 [In the formula, R ２ and R ３ is as defined above] and an activated (meth)acrylic acid derivative (III) 【Transformation 3】 [In the formula, R ４ is as defined above, R １ is -O(CO)C(CH ２ ) CH ３ , -O(CO)C(CH ２ )H], wherein the reaction of the alcohol of the general formula (II) with the activated (meth)acrylic acid derivative (III) is carried out under solvent-free conditions, and the (meth)acrylate of the general formula (I) is obtained from the crude reaction mixture by precipitation from an aqueous medium, 10. A method according to claim 9, wherein the aqueous medium used in the precipitation step is selected from pure or demineralized water, aqueous alcohol solutions, aqueous ammonia solutions, aqueous alkali(earth) metal hydroxide solutions, and aqueous alkali(earth) metal bicarbonate and carbonate solutions.

2. The precipitation step is carried out at a pH of 7 to 12, and / or 2. The method according to claim 1, wherein the amount of the aqueous medium used in the precipitation step is 1 to 20 times the weight of the alcohol (II) initially used.

3. 3. The method according to claim 1 or 2, wherein the alcohol of general formula (II) is vanillin and the (meth)acrylate of general formula (I) is vanillin (meth)acrylate, or the alcohol of general formula (II) is ethyl vanillin and the (meth)acrylate of general formula (I) is ethyl vanillin (meth)acrylate.

4. 4. The process according to claim 1, wherein the reaction of the alcohol of general formula (II) with the activated (meth)acrylic acid derivative (III) is carried out in the presence of at least one catalyst, which is selected from the group consisting of alkali metal salts, alkaline earth metal salts, zinc salts, rare earth metal salts, lithium alkoxides, sulfuric acid, lithium or sodium methacrylate, amino-substituted pyridines, or mixtures thereof.

5. 5. The process according to claim 1, wherein the reaction of the alcohol of general formula (II) with the activated (meth)acrylic acid derivative (III) is carried out in the presence of lithium methoxide, magnesium chloride, sodium hydroxide, sodium (meth)acrylate, sulfuric acid, or a mixture thereof.

6. 6. The process of claim 4 or 5, wherein the catalyst is present in an amount of 0.1 to 10 mol % (based on the alcohol) for lithium alkoxide, sodium hydroxide, or magnesium chloride; 0.1 to 2 wt % for sodium methacrylate; or 0.1 to 1 wt % (based on the total reactant weight) for sulfuric acid.

7. 7. The process according to claim 1, wherein the activated (meth)acrylic acid derivative (III) used in the reaction is present in an amount of 0.9 to 2.0 equivalents relative to the amount of the alcohol of general formula (II).

8. A method described in any one of claims 1 to 7, wherein the activated (meth)acrylic acid derivative (III) used in the reaction is present in an amount of 1.0 equivalent to 1.8 equivalents relative to the amount of alcohol of general formula (II).

9. A method described in any one of claims 1 to 8, wherein the activated (meth)acrylic acid derivative (III) used in the reaction is present in an amount of 1.2 to 1.6 equivalents relative to the amount of alcohol of general formula (II).

10. 10. The process according to claim 1, wherein the reaction of the alcohol of general formula (II) with the activated (meth)acrylic acid derivative (III) is carried out at a temperature between 0°C and 130°C.

11. The method according to claim 1, wherein the reaction of the alcohol of general formula (II) with the activated (meth)acrylic acid derivative (III) is carried out at a temperature of 80°C to 100°C.

12. The method according to claim 1, wherein the reaction of the alcohol of general formula (II) with the activated (meth)acrylic acid derivative (III) is carried out at a temperature of 85°C to 95°C.

13. 13. The process of claim 1, wherein the crude reaction mixture is contacted with methanol prior to precipitating the (meth)acrylate of general formula (I) from the aqueous medium.

14. The method according to any one of claims 1 to 13, wherein the reaction of the alcohol of general formula (II) with the activated (meth)acrylic acid derivative (III) is carried out in the presence of at least one polymerization inhibitor selected from the group consisting of hydroquinone, hydroquinone ether, phenothiazine, N,N'-(diphenyl)-p-phenylenediamine, 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, p-phenylenediamine, methylene blue, and sterically hindered phenols, with the amount of stabilizer at the start of the reaction being adjusted to 0 to 5000 ppm relative to the amount of the product theoretically expected at complete conversion.

15. The method of claim 1, wherein the activated (meth)acrylic acid derivative (III) contains 1800 ppm to 2200 ppm of 2,4-dimethyl-6-tert-butylphenol.

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