Catechol-containing polymers

Abstract

The invention relates to a polymer of formula (I): R1, R2 = H or C1 to C4 alkyl groups, with H being preferred, and wherein R1 and R2 can be the same or different, R3, R4 = H or OH, preferably with R3 ≠ R4, wherein A is selected from a unit of formulae (IIa), (IIIa), (IVa), (Va). Unit of formula (IIa) with R5 = H or CH3 and p = 1 bis 6; unit of formula (IIIa), unit of formula (IVa), a unit of formula (Va) wherein n = 5 to 4000 and the polymer (I) contains units A which are the same or different.

Description

[0001] Catechol-containing polymers

[0002] The present invention relates to polymers of formula (I) containing 1,2-dihydroxybenzene derivatives, a process for their preparation, compositions containing the polymers and their use.

[0003] Polymers containing derivatives of 1,2-dihydroxybenzene are of particular interest for academic and industrial research and applications, since it has been shown that this structure can impart special adhesion properties.

[0004] The inspiration for this structure came from mussels, which exhibit industrially unmatched adhesion properties (e.g., underwater adhesion or adhesion to surfaces coated with polytetrafluoroethylene (PTFE)). These adhesion properties are attributed to the presence of 1,2-dihydroxybenzene derivatives within mussel proteins (cf. Angew. Chem. Int. Ed. 2019, 58, 696–714).

[0005] Numerous efforts have already been made to obtain a synthetic polymer with similar adhesion properties. Dopamine, a derivative of 1,2-dihydroxybenzene, is often used for this purpose. This derivative possesses an amine group that can react with methyl methacrylate, for example. Such a molecule could then react with itself or with other monomers to form a polymer containing 1,2-dihydroxybenzene derivatives within the repeating unit. One such synthesis is described, for example, in Journal of Applied Polymer Science 2003;89:1078-84.

[0006] Another possibility for preparing polymers containing derivatives of 1,2-dihydroxybenzene is to prepare the monomer dihydroxystyrene, which can then react with itself or with other monomers such as styrene or methacrylic derivatives, as described, for example, in WO 2021 / 127079.

[0007] A disadvantage of such approaches is that a synthetic derivative of 1,2-dihydroxybenzene must first be prepared, which is usually very complicated to synthesize and purify. Furthermore, when polymerizing derivatives of 1,2-dihydroxybenzene that contain polymerizable vinylic double bonds (e.g., acrylates, methacrylates, styrene derivatives, etc.), it is necessary to protect the phenolic OH groups, as otherwise undesirable side reactions such as branching and / or crosslinking of the polymer occur during polymerization (see Progress in Polymer Science, Volume 38, Issue 1, January 2013, Pages 236-270, Fig. 19). This results in large amounts of waste due to the numerous additional reaction steps.

[0008] US 4,499,243 describes 1,2-dihydroxybenzenes for use in isoprene and butadiene rubber compounds. The study investigates radical crosslinking reactions of polyisoprene masterbatches with resorcinol, hydroquinone, and catechol, carried out with various vulcanization accelerators and elemental sulfur. Vulcanization of the polymers with elemental sulfur leads to improved properties of the tires, belts, and hoses produced with them.

[0009] Another possibility for producing polymers containing 1,2-dihydroxybenzene derivatives is the use of pre-polymerized monomers bearing active esters, such as the ester of pentafluorophenol. When such polymers are reacted with, for example, dopamine, a transesterification occurs, yielding a polymer functionalized with 1,2-dihydroxybenzene derivatives. However, no protecting groups for the phenolic hydroxy groups are required in the synthesis (cf. Angewandte Chemie International Edition 2006;45:908-12). However, this approach has disadvantages, since the active esters of the monomers must first be formed, which is a laborious process.

[0010] The task was therefore to produce polymers containing derivatives of 1,2-dihydroxybenzene that offer several advantages over the state of the art: They should offer increased or at least equivalent adhesion properties to certain surfaces or under certain conditions, such as underwater. Such surfaces include, for example, PTFE-coated surfaces. Furthermore, the polymers should be less complex to produce and should not require complex purification. For example, no protecting group chemistry should be necessary. Furthermore, they should exhibit high atom economy.

[0011] Surprisingly, it was found that this task can be solved by polymers of the formula (I) with R 1 , R 2 = H or Ci- to C4-alkyl groups, where H is preferred, and where R 1 and R 2 may be the same or different, and R 3 , R 4 = H or OH, preferably with R3 R 4 . A is selected from a unit of the formulas (lla), (IIIa), (IVa), (Va), namely a unit of the formula (lla) with R 5 = H or CH3 and p = 1 to 6, preferably p = 2, a unit of the formula (IIIa)

[0012] (Illa), a unit of the formula (IVa) or a unit of the formula (Va) wherein n = 5 to 4000, preferably 5 to 3000, particularly preferably 2000, preferably 8 to 850 for (Ha) and 15 to 1500 for (IIIa), (IVa), (Va), and the polymer (I) contains units A which are the same or different. Consequently, the polymer (I) can contain units selected from one of the four units (Ila), (IIIa), (IVa), (Va). It is also possible for the polymer (I) to comprise two or more units selected from (Ila), (IIIa), (IVa), (Va). Preferably, the units of the polymer (I) are selected from the units (Ha), (IIIa), (IVa). Furthermore, the polymer (I) can contain further comonomers or copolymers.

[0013] In one embodiment of the invention, the polymer (I) consists of units A which are identical or different.

[0014] The polymers (I) according to the invention exhibit increased or at least equivalent adhesion properties to prior art materials on various surfaces or under certain conditions, such as underwater or on difficult-to-bond substrates. Examples of such surfaces include PTFE-coated surfaces, low-energy plastics such as polyethylene and polypropylene, or difficult-to-bond substances such as polyamides. It may be advantageous for the polymer (I) to contain block-arranged copolymers, for example to improve solubility or handling, as well as for better compatibility in compositions according to the invention. The copolymers are preferably selected from poly(meth)acrylates, polyacrylonitrile, or polystyrene.

[0015] For the same reason, the units (I1a), (IIIa), (IVa), and (Va) can have defined molecular weights. The molecular weight is preferably in the range of 1000-1,000,000 g / mol, particularly preferably 2000-500,000, and most preferably 3000-75,000 g / mol.

[0016] The number average molecular weight is determined according to DIN 55672-1 using gel permeation chromatography in tetrahydrofuran as eluent and polystyrene for calibration.

[0017] The polymer (I) may contain further functional groups such as aliphatic hydroxyl groups, amines, thiols, carboxyl groups, or C=C double bonds. The further functional groups may be arranged randomly or blockwise in the polymer (I). The further functional groups are preferably distributed randomly.

[0018] In a preferred embodiment of the invention, a polymer (I) is prepared by the addition of a monomer of formula (VI) to a polymer selected from (IIb), (II Ib), (IVb), (Vb). The monomer (VI) is 1,2-dihydroxybenzene or a derivative thereof, namely with R 1 , R 2 = H or Ci- to C4-alkyl groups, where H is preferred, and where R 1 and R 2 may be the same or different, R 3 , R 4 = H or OH, preferably with R 3 R 4 .

[0019] The addition takes place to a polymer of formula (llb) with R 5 = H or CH3 and p = 1 to 6, preferably p = 2, to obtain a polymer of the formula

[0020] (I) containing A = (lla), or to a polymer of formula (III b) to obtain a polymer of formula (I) containing A = (IIIa), or to a polymer of formula (IVb) to obtain a polymer of formula (I) containing A = (IVa), or to a polymer of formula (Vb) to obtain a polymer of formula (I) containing A = (Va). Index n has the same meaning as already indicated above.

[0021] The advantage of this process is that the preparation of polymer (I) is less complex than the state of the art. For example, neither complex purification nor the use of protecting groups is required. The addition reaction ensures high atom economy, as no byproducts or leaving groups are formed. Furthermore, monomers (VI) such as 1,2-dihydroxybenzene are readily available industrially; extensive synthetic steps for preparation of the addition reaction are not required.

[0022] The polymers (I1a) are, for example, derivatives of a poly(meth)acrylate esterified with methylalkylenol. A methylalkylenol is, for example, 3-methyl-3-buten-1-ol. The polymers (IIIb), (IVb), (Vb) are, for example, polyisoprenes and random or block copolymers of polyisoprene.

[0023] The polymers (Hb), (IIIb), (IVb), and (Vb) can be liquid or solid. As solids, they can be crystalline or amorphous. The polymers (Hb), (IIIb), (IVb), and (Vb) can be linear or branched in their structure. These polymers are preferably linear. Consequently, the polymers (I) according to the invention can be linear or branched in their structure. The polymers according to the invention are preferably linear.

[0024] The double bonds of the polymers (Hb), (IIIb), (IVb), (Vb) can be protonated under suitable conditions, for example acid catalysis, to form a stable carbocation, which can then add to the aromatic structure of the monomer (VI) in an electrophilic aromatic substitution.

[0025] Also according to the invention is a polymer which contains a radical A which is selected from (Ha), (IIIa), (IVa), (Va) or mixtures thereof.

[0026] It is further preferred that the addition of the monomer of formula (IV) takes place with 1 to 100 mol% of the C=C double bonds of the polymers (IIb), (IIIb), (IVb), and (Vb). The term "C=C double bond" encompasses all ethylenic double bonds present in the polymers. A degree of functionalization of 3-80 mol%, particularly preferably 5-60 mol%, is preferably obtained.

[0027] In the reaction of polymers (IIb), (IIIb), (IVb), (Vb) with monomer (VI), the ratio of monomer (VI) to the C=C double bonds of the polymers plays a critical role with regard to the subsequent degree of functionalization. It may be necessary to use a molecular excess of (VI) to achieve the highest possible functionalization. Typically, molar ratios of C=C double bonds of polymers (IIb), (IIIb), (IVb), (Vb) to (VI) of 1:0.1 - 1:20 are used, preferably 1:0.1 - 1:3, particularly preferably 1:0.2 - 1:2.

[0028] The addition preferably takes place catalytically, particularly preferably in the presence of at least one acid. Suitable acids are acids with a pKa value at room temperature < 4, such as sulfuric acid, para-toluenesulfonic acid, hydrochloric acid, acidic ion exchangers, or Lewis acids such as indium(III) trifluoromethanesulfonate. The amount of catalyst used is critical to the success of the reaction. Typically, 0.01–50 mol% of catalyst per C=C double bond is used, preferably 0.1–15 mol%.

[0029] The addition can take place in solvent or in bulk. "In bulk" means that no solvents are added. The reaction is preferably carried out in bulk. Suitable organic solvents for the addition are selected from aprotic solvents such as dichloromethane, toluene, benzene, tetrahydrofuran, hexane, ganic acid, decane, diethyl ether, and the like, as well as protic solvents such as methanol, ethanol, acetone, and the like. When using solvents, preference is given to using aprotic solvents, particularly tetrahydrofuran, dichloromethane, or aliphatic hydrocarbons such as hexane or decane.

[0030] The addition reaction can take place at different temperatures. Preference is given to higher temperatures in the range of 40-180°C, more preferably 110-180°C. After the polymer (I) according to the invention has been prepared, the product should, if necessary, be separated from unreacted monomer (VI). This purification can be carried out by drying the reaction mixture and then washing it in a solvent in which the product or reactants cannot be dissolved, for example methanol or water. Likewise, precipitation of the product in an organic solvent in which the product is poorly soluble or insoluble, for example methanol, is possible. Another method for purifying the product is by extracting the unreacted monomer (VI) with aqueous, basic solutions, for example dilute sodium hydroxide solution or sodium bicarbonate solution, followed by drying the organic phase.It is also possible to purify the product by distillation / sublimation, preferably using a vacuum.

[0031] The product is preferably purified by drying the reaction mixture and then adding a selective solvent which removes either the product or unreacted reactants and the catalyst, preferably alkanols with 1 to 4 C atoms, in particular methanol.

[0032] Also preferably, the product is purified by distillation / sublimation to remove the remaining monomer (III) from the reaction mixture.

[0033] It may be necessary to purify the product by washing and drying / sublimation in two separate steps.

[0034] This invention also relates to the preparation of the polymers (I) according to the invention. For this purpose, the above-described addition process of the monomers (VI) to the polymers selected from (IIIb), (IIIb), (IVb), and (Vb) is carried out. The process according to the invention is carried out as described above.

[0035] A further subject matter are compositions comprising at least one polymer (I) or at least one polymer (I) prepared according to the invention. The polymer (I) is preferably present in a range from 1 to 50 wt. %, based on the total weight of the composition. Preference is given to 1 to 30 wt. %, particularly preferably 3 to 15 wt. The polymers of formula (I) are suitable for improving adhesion.

[0036] The compositions can be adhesives or sealants, coating materials, foams, or lubricants. Adhesives are defined in DIN EN 923:2008-06. Sealants, also called sealing compounds, are materials – generally elastic, applied in liquid to viscous form or as flexible profiles or sheets – used to seal buildings or facilities against water, atmospheric influences, or aggressive media. Example: Bitumens (asphalt), synthetic resins, foams, putties, etc. as well as (especially for joint sealants) silicones, acrylates and polysulfides (RÖMPP editorial team, Sealants, RD-04-01300 (2002) in Böckler F., Dill B., Eisenbrand G., Faupel F., Fugmann B., Gämse T., Matissek R., Pohnert G., Rühling A., Schmidt S., Sprenger G., RÖMPP [Online], Stuttgart, Georg Thieme Verlag, [August 2022] https: / / roempp.thieme.de / lexicon / RD-04-01300).Coating materials include varnishes, paints, and similar products; they are listed in DIN ISO 4618. Foams are described in DIN 7726:1982-05. Lubricants are a collective term for substances that reduce friction and (mechanical) stress on machine parts moving against or against each other. They thereby reduce energy consumption and material wear and also act as coolants (see RÖMPP editorial team, Lubricants, RD-19-01091 (2002) in Böckler F., Dill B., Eisenbrand G., Faupel F., Fugmann B., Gämse T., Matissek R., Pohnert G., Rühling A., Schmidt S., Sprenger G., RÖMPP [Online], Stuttgart, Georg Thieme Verlag, [August 2022] https: / / roempp.thieme.de / lexicon / RD-19-01091).

[0037] The compositions may contain common additives. Depending on the application, the person skilled in the art will be familiar with the addition of appropriate additives.

[0038] In certain applications, for example in the adhesive and sealant sector and in coating materials, the compositions according to the invention can be either chemically curing, physically curing or a combination of both.

[0039] In the case of chemically curing compositions, it is preferred if the polymers (I) according to the invention form a covalent bond with at least one other constituent of the composition during curing, i.e., are reactively incorporated into the composition. These other constituents are selected, for example, from epoxides, polyurethanes, polysilicones, or vulcanizing substances. The polymer (I) forms the covalent bond in particular via the other functional groups, such as aliphatic hydroxyl groups, amines, thiols, carboxyl groups, or C=C double bonds.

[0040] The polymers (I) according to the invention are preferably used in adhesives and sealants to improve adhesion to metallic surfaces, mineral surfaces, wet surfaces, glass, wood, silicone, polyolefins (polyethylene, polypropylene, and mixtures thereof), rubber, and Teflon. Particular preference is given to using them on metallic surfaces, mineral surfaces, wet surfaces, as well as silicone, polyolefins, and Teflon.

[0041] In coating materials or foams, it is conceivable that the polymers (I) of the invention are used to improve adhesion properties and wetting. The polymers of the invention are preferably used to improve adhesion to metallic surfaces, mineral surfaces, wet surfaces, glass, wood, silicone, polyolefins (especially polyethylene, polypropylene, and mixtures thereof), rubber, and Teflon. Particular preference is given to using them on metallic surfaces, mineral surfaces, wet surfaces, as well as silicone, polyolefins, and Teflon.

[0042] When using the compositions of the invention in the field of adhesives and sealants, as well as coating materials, it is conceivable that the composition of the invention be used both as a primer and in the main composition. When using the compositions of the invention in lubricants, it is conceivable that the polymers (I) of the invention are used to improve the tribological properties by adhering to the wear parts and thus providing better, permanent protection against wear. Preferred materials for these wear parts are, for example, metals or plastics such as polyaryletherketones, especially polyetheretherketone, or polyamide.

[0043] The invention further relates to the use of the polymer (I) according to the invention or of a polymer (I) prepared by the process according to the invention to improve adhesion. In particular, the use is in adhesives or sealants, in coating materials, in foams, or in lubricants. This use involves the use of the previously described compositions, whose properties apply analogously to the use.

[0044] Where percentages are given, they are in weight % unless otherwise stated. Where average values, e.g., average molecular weights, are given, they are the number average unless otherwise stated. Where material properties, such as viscosities or similar, are given, they are the material properties at 25°C and 1013 hPa unless otherwise stated. Where chemical (molecular) formulas are used in the present invention, the specified indices can represent both absolute numbers and average values. In the case of polymeric compounds, the indices preferably represent average values.

[0045] Examples

[0046] Polymer used: A linear polyisoprene produced by anionic polymerization with n-butyllithium was used for the examples.

[0047] Molecular weight Mn = 7500 g / mol, dispersity 1.10.

[0048] Attempt 1:

[0049] 7.0 g of polyisoprene (approx. 0.1 mol of double bond) was weighed into 100 mL of THF along with 33 g of catechol (0.3 mol) and 3.44 g of para-toluenesulfonic acid (0.02 mol, 10 mol% based on the double bond) and then heated under reflux for 48 hours under a nitrogen atmosphere. The solvent was then removed using a rotary evaporator, and the remaining substance was washed several times with methanol to remove excess catechol and catalyst. The remaining polymer residue was dried in a vacuum oven and analyzed for conversion by 1 H NMR. Catechol functionalization of 1.4% of the double bonds was observed. Experiment 2:

[0050] 7.0 g of polyisoprene (approx. 0.1 mol double bond) was weighed into 100 mL of THF along with 55 g of catechol (0.5 mol), and 1.96 g of concentrated sulfuric acid (0.02 mol, 10 mol% based on the double bond) and then heated to reflux under a nitrogen atmosphere for 48 hours. The solvent was then removed using a rotary evaporator, and the remaining substance was washed several times with methanol to remove excess catechol and catalyst. The remaining polymer residue was dried in a vacuum oven and analyzed for conversion by 1 H NMR. Catechol functionalization of 8.3% of the double bonds was observed.

[0051] Attempt 3:

[0052] 7.0 g of polyisoprene (approximately 0.1 mol of double bond) was mixed with 44 g of catechol (0.4 mol) and melted at 120 °C. Subsequently, 0.17 g of para-toluenesulfonic acid (1 mmol, 1 mol% based on the double bond) was added and heated to reflux under a nitrogen atmosphere for 4 hours. The crude product was analyzed for conversion by 1 H NMR. Catechol functionalization of 100% of the double bonds was observed.

[0053] Attempt 4:

[0054] 7.0 g of polyisoprene (approximately 0.1 mol of double bond) was mixed with 44 g of catechol (0.4 mol) and melted at 120 °C. Subsequently, 0.05 g of sulfuric acid (0.5 mmol, 0.5 mol% based on the double bond) was added and heated to reflux under a nitrogen atmosphere for 4 hours. The crude product was analyzed for conversion by 1 H NMR. Catechol functionalization of > 90% of the double bonds was observed.

Claims

Patent claims 1 . Polymer of formula (I) R 1 , R 2 = H or Ci- to C4-alkyl groups, where H is preferred, and where R 1 and R 2 may be the same or different, R 3 , R 4 = H or OH, preferably with R 3 R 4 , where A is selected from a unit of the formulas (IIa), (IIIa), (IVa), (Va), with a) a unit of the formula (IIa) with R 5 = H or CH3 and p = 1 to 6, b) a unit of the formula (IIIa) (Illa), c) a unit of formula (IVa) or d) a unit of formula (Va) wherein n = 5 to 4000 and the polymer (I) contains units A which are the same or different, prepared by addition of a monomer of formula (VI) with R 1 , R 2= H or Ci- to C4-alkyl groups, where H is preferred, and where R 1 and R 2 may be the same or different, R 3 , R 4 = H or OH, preferably with R 3 R 4 , a1) to a polymer of formula (Hb) with R 5 = H or CH3 and p = 1 to 6, to obtain a polymer of formula (I) containing A = (Ha), or b1) to a polymer of formula (IIIb) to obtain a polymer of formula (I) containing A = (IIIa), or c1) to a polymer of formula (IVb) to obtain a polymer of formula (I) containing A = (IVa), or d1) to a polymer of formula (Vb) to obtain a polymer of formula (I) containing A = (Va), wherein the addition is carried out catalytically, preferably in the presence of at least one acid.

2. Polymer according to claim 1, characterized in that the units (Ha), (IIIa), (IVa), (Va) each have a number-average molecular weight, determined according to DIN 55672-1, in the range of 1000-1,000,000 g / mol.

3. Polymer according to one of the preceding claims, characterized in that polymer (I) contains block-arranged copolymers, which are preferably selected from poly(meth)acrylate, polyacrylonitrile or polystyrene.

4. Polymer according to one of the preceding claims, characterized in that R 2 = H.

5. Polymer according to one of the preceding claims, characterized in that p = 2.

6. Polymer according to one of the preceding claims, characterized in that it contains a radical A which is selected from (Ha), (IIIa), (IVa), (Va) or mixtures thereof.

7. Polymer according to one of claims 1 to 6, characterized in that 1 to 100 mol% of the C=C double bond of the polymers (lib), (II I b), (IVb) or (Vb) have reacted with (VI).

8. Process for the preparation of polymers of formula (III) according to any one of the preceding claims by addition of a monomer of formula (VI) with R 1 , R 2 = H or Ci- to C4-alkyl groups, where H is preferred, and where R 1 and R 2 may be the same or different, R 3 , R 4 = H or OH, preferably with R 3 R 4 , a) to a polymer of formula (Hb) with R 5 = H or CH3 and p = 1 to 6, to obtain a polymer of formula (I) containing A = (IIa), or b) to a polymer of formula (IIIb) to obtain a polymer of formula (I) containing A = (IIIa), or c) to a polymer of formula (IVb) to obtain a polymer of formula (I) containing A = (IVa), or d) to a polymer of formula (Vb) to obtain a polymer of formula (I) containing A = (Va), wherein the addition is carried out catalytically, preferably in the presence of at least one acid.

9. Compositions containing at least one polymer of formula (I) according to one of claims 1 to 7 or prepared according to claim 8.

10. Use of a polymer of formula (I) according to one of claims 1 to 7 or prepared according to claim 8 for improving adhesion.

11. Use according to claim 10 in adhesives or sealants, in coating materials, in foams or in lubricants.

12. Composition according to claim 9 or use according to any one of claims 10 or 11, wherein the polymer (I) forms a covalent bond to at least one further component of the composition during curing.

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