WO2007140939A1

WO2007140939A1 - Hydroxy-aromatic compound, process for its preparation, and use as cross-linking agent

Info

Publication number: WO2007140939A1
Application number: PCT/EP2007/004874
Authority: WO
Inventors: Van Rudolfus Antonius Theodorus Maria Benthem
Original assignee: Dsm Ip Assets B.V.
Priority date: 2006-06-02
Filing date: 2007-06-01
Publication date: 2007-12-13

Abstract

The invention relates to a process for the preparation of a hydroxy-aromatic compound. The process comprises the step of bringing a starting compound according to formula (I) together with an alkanol hemiacetal according to formula (II) to form a reaction mixture. The reaction mixture is then brought to conditions whereby the hydroxy-aromatic compound is formed. Formula (I), wherein R4 is a C1 - C20 alkyl group, aryl group, aralkyl group or cycloalkyl group. Formula (II), wherein R8 is a C1-C12 alkyl group, aryl group, aralkyl group or cycloalkyl group and wherein R12 is H1 a C1-C12 alkyl group, aryl group, aralkyl group or cycloalkyl group. The hydroxy-aromatic compounds obtained from the process can be used as cross -linking agents in elastomers, coatings, EPDM and TPV.

Description

HYDROXY-AROMATIC COMPOUND, PROCESS FOR ITS PREPARATION. AND

USE AS CROSS-LINKING AGENT

The present invention relates to a hydroxy-aromatic compound; the invention further relates to a process for the preparation of a hydroxy-aromatic compound; the invention moreover relates to the use of a hydroxy-aromatic compound, in particular as cross-linker.

Hydroxy-aromatic compounds and their use as cross-linker in materials such as coatings or elastomers are known; a widely used example of such a hydroxy-aromatic compound is a phenol-formaldehyde resin.

A disadvantage of phenol-formaldehyde resins is that their use is associated with health risks relating to the emission of formaldehyde during resin preparation, resin curing and in end products.

It is the objective of the present invention to reduce or even eliminate the said disadvantage while still providing a compound suitable for use as cross-linker in materials such as coatings or elastomers.

The objective is achieved by a hydroxy-aromatic compound according to formula (III), (IV), (V), and/or (Vl):

wherein:

• R₄ is a Ci-C₂₀ alkyl group, aryl group, aralkyl group or cycloalkyl group;

• n is an integer having a value of O, 1 , 2, or 3;

R₆ is methyl or a C₂-C₁₂ alkyl group. R₆ is preferably methyl.

An advantage of the hydroxy-aromatic compounds according to the invention is that a desired functionality - e.g. as cross-linker - is combined with a reduction of associated health risks as compared to the known compounds. The invention relates to a closely related group of hydroxy-aromatic compounds. One important characteristic of the compounds is that they comprise at least one hydroxy-aromatic moiety; this is defined herein as an -OH group that is directly attached to an aromatic ring. Another important characteristic of the compounds is that said hydroxy-aromatic moiety is substituted on the para-location and on at least one ortho-location.

The para-substitution of the hydroxy-aromatic compounds according to the invention is indicated in the formulas (III), (IV)₁ (V) and (Vl) by means of R₄. According to the invention, R₄ is a C₁ - C₂o akyl group, aryl group, aralkyl group or cycloalkyl group. In one preferred embodiment, R₄ is a C₉ alkyl group. An advantage of the para-substitution is that it can increase the compatibility and/or solubility of the hydroxy-aromatic compound with alkyl compounds or olefinic compounds or polymers such as various oils and polymers like for example PE, PP, EPDM.

The ortho-substitution of the hydroxy-aromatic compounds according to the invention is a -C(R₇)CO₂Re group, whereby R₇ is either -OH or an ortho-linked para-substituted hydroxy-aromatic moiety. Through this linking of hydroxy-aromatic moieties, an oligomeric structure with a repeating unit is encompassed within the invention, as reflected in formula (IV). Since it was found that the effectiveness of the compound according to the invention as cross-linking agent is the highest when the overall molecular weight of the compound according to the invention is not very high, it is preferred that the repeating unit - as indicated by 'n' in formula (IV) - does not repeat itself more than 10 or 5, preferably not more than 3 times. As can be seen in the formulas, a value of n of O in (IV) is possible, as this leads to formula (III). At certain values of n, the compound according to formula (IV) can be regarded as being a resin. The term resin is herein understood to have the same meaning as it has to a skilled person in thermosetting chemistry, namely as a low molecular weight polymer having reactive groups. The term low molecular weight means a molecular weight typical for an oligomer and lying between a few hundred g/mole, e.g. 200, and a few thousand g/mole, e.g. 3,000. Ideally the number of reactive groups per molecule is at least two. These reactive groups form the chemical handles to connect the polymer chains together through covalent cross-link bonds, via a chemical reaction. The process of cross-linking is mostly referred to as "cure", "hardening" or "vulcanisation". A resin may be present in the form of a solution, e.g. an aqueous solution, or as such. -A-

The invention further relates to a process for the preparation of a hydroxy-aromatic compound, in particular a hydroxy-aromatic compound according to any one of the formulas (III), (IV)₁ (V), or (Vl). The said process comprises the steps of: • bringing a starting compound according to formula (I) together with an alkanol hemiacetal according to formula (II) to form a reaction mixture, wherein: o formula (I) is:

wherein R₄ is a C₁ - C₂o alkyl group, aryl group, aralkyl group or cycloalkyl group; formula (II) is:

-O R₆

«12- -o- -OH

H (II) wherein R₆ is a C₁-C₁₂ alkyl group, aryl group, aralkyl group or cycloalkyl group and wherein R₁₂ is H, a C₁-C₁₂ alkyl group, aryl group, aralkyl group or cycloalkyl group; bringing the reaction mixture to conditions whereby the hydroxy-aromatic compound is formed.

In the process according to the invention, a reaction mixture is formed by bringing together raw materials. The raw materials comprise a starting compound according to formula (I). Such compounds are as such known. In formula (I), R₄ refers to a C₁ - C₂₀ or preferably C₁-C₁₂ alkyl group, aryl group, aralkyl group or cycloalkyl group. The compound according to formula (I) may be one single compound but is understood to also comprise the meaning of a mixture of two or more compounds falling within the scope of the formulas as defined above. In a preferred embodiment, the compound of formula (I) is nonylphenol.

The raw materials further comprise an alkanol hemiacetal according to formula (II). In formula (II), R₆ is a C₁-C₁₂ alkyl group, aryl group, aralkyl group or cycloalkyl group and R₁₂ is H, a C₁-C₁₂ alkyl group, aryl group, aralkyl group or cycloalkyl group. Preferably R₆ and R₁₂ are C₁-C₁₂ alkyl groups. Examples thereof are methyl, ethyl, propyl, butyl, pentyl, hexyl, and heptyl. R₆ and R₁₂ are in particular a methyl group or an ethyl group. The compound according to formula (II) may be one single compound but is understood to also comprise the meaning of a mixture of two or more compounds falling within the scope of the formulas as defined above. Examples of preferred compounds according to formula (II) are methylglyoxylate methanol hemiacetal (GMHA™, DSM Fine Chemicals, Linz); ethylglyoxylate ethanol hemiacetal (GEHA™, DSM Fine Chemicals, Linz); ethylglyoxylate methanol hemiacetal; butylglyoxylate butanol hemiacetal; butylglyoxylate methanol hemiacetal; butylglyoxylate ethanol hemiacetal; isopropylglyoxylate isopropanol hemiacetal; propylglyoxylate propanol hemiacetal; cyclohexylglyoxylate methanol hemiacetal and 2-ethylhexylglyoxylate methanol hemiacetal.

The bringing together of the raw materials to form the reaction mixture may be accomplished by simply mixing them; it may be beneficial to do this in the presence of a solvent. It may thus be beneficial to execute the reaction step according to the invention in a solvent or dispersant. As solvents, those compounds are suitable in which the reactants dissolve sufficiently to let the reaction take place. Examples of such solvents are water and various organic solvents. Depending on the specific compound or compounds of formula (I) and (II), it may well be possible to use one or more of the reactants as solvent; in such a case, it can be possible to forego on the use of a solvent that is essentially a non-reactant and to execute the reaction step in bulk. In particular, many of the compounds according to formula (II) are a liquid at temperatures between 10⁰C and 100⁰C and can act as dispersant/solvent as well as reactant.

The molar ratio between the raw materials that are brought together in the reaction mixture may vary between wide limits. The molar ratio between the alkanol hemiacetal compound of formula (II) (A) and the starting compound of formula (I) (H), herein referred to as the A/H ratio, preferably lies between about 0.1 and about 10. The molar ratio A/H is preferably at least 0.1 , 0.2, 0.3, 0.4, 0.5 or 0.6 and preferably at most 10, 9, 8, 7, 6, 5, 4, 3, or 2.

If the molar A/H ratio lies above 1 , then this will generate a preference towards the formation of compounds of formula (IV) and in particular (III). If the molar A/H ratio lies below 1 , then this will generate a preference towards the formation of compounds of formula (Vl) and in particular (V).

Once the reaction mixture is formed, it should be brought to conditions whereby the hydroxy-aromatic compound can be formed, i.e. in a reaction step. Although the reaction step may proceed spontaneously once the respective compounds have been brought together, it may be useful to bring the compounds together in the presence of a catalyst in order to accelerate the reaction. As catalyst, preferably an acid is used; in particular, a Lewis or a Brønstedt type of acid is preferred - such as for example sulphuric acid - whereby the pH is reduced to between 0 and 5, preferably to between 1 and 4, in particular to between 2 and 3. Suitable examples of acid catalysts are sulphuric acid, nitric acid, hydrochloric acid, phosphoric acid, boric acid, tetrafluoroboric acid, paratoluene sulphonic acid, methane sulphonic acid, formic acid, ammonium sulphate, ammonium chloride, ammonium nitrate, aluminum sulphate, aluminum chloride, zirconium (IV) chloride, titanium (IV) chloride, zinc chloride, stannic chloride, stannous chloride, boron trifluoride etherate.

The temperature in the reaction step of present process can vary within wide limits, and preferably lies between 10°C and 100⁰C. More preferably the process is carried out at between 40⁰C and 9O⁰C. The pressure in the present process preferably is between 0.005 MPa and 1.0 MPa, preferably between 0.02 MPa and 0.2 MPa; most preferably, the pressure is atmospheric. The time needed for completion of the reaction step may vary within wide limits and is primarily determined by the time needed to achieve the end result of the reaction step, i.e. the formation of a resin. As is known, factors like the temperature and the nature and amount of catalyst strongly influence the time needed to achieve the desired end result. In practice, the reaction step could be completed in a time lying between 5 minutes and 180 minutes. Furthermore, it is noted that the length of time of the reaction step can have an influence on the specific type of hydroxy-aromatic compound that is formed. For example, an increase in duration of the reaction step will favour the formation of a compound of formula (IV) over a compound of formula (III); likewise, an increase in duration of the reaction step will favour the formation of a compound of formula (Vl) over a compound of formula (V). Thus, it can be easily seen that routine experiments with the A/H ratio in combination with reaction temperature and time can lead to the preferred formation of the desired hydroxy-aromatic compound.

The hydroxy-aromatic compounds according to the invention have as a specific benefit that they may be favourably used as cross-linking agent. The invention thus also relates to the use of a hydroxy-aromatic compound of formula (III), (IV), (V)₁ or (Vl) as cross-linking agent in coatings or in natural or synthetic elastomers. It may be desirable or even necessary to use, in conjunction with the said hydroxy- aromatic compounds, a catalyst in order to achieve the desired cross-linking.

As is known, a cross-linking action can be achieved through various types of chemical processes. One such process involves a cationic mechanism, in which preferably a free non-aromatic -OH or -OR group is involved; if this mechanism is desired of necessary, as is often the case in the cross-linking of elastomers, then the compounds of formula (III) and (IV) are particularly suitable.

Another known process through which cross-linking may be achieved involves the ring-opening of epoxy groups, e.g. in epoxy resins. An epoxy resin, as is known, is an oligomeric or polymeric material comprising at least two oxygen- containing three-membered ring structures, often in the form of glycidyl ether moieties. The oxygen-containing three-membered ring serves as location for further reactions, commonly referred to as curing or cross-linking. The term epoxy resins is in practice also used for the cured / cross-linked polymers, even thought practically all or even all of the oxygen-containing three-membered ring structures that were present have reacted away. It was found that in the cross-linking of epoxy resins, aromatic hydroxy groups are particularly effective; thus, compounds of formula (III), (IV), (V) and (Vl) are particularly suitable for this purpose. One well-known example of the use of epoxy- based resins is in coatings for cans; the compounds of formula (III), (IV), (V) and (Vl) are particularly suitable as cross-linking agent for this type of coating. An acidic or base catalyst may be beneficial.

Elastomers, both natural as well as synthetic, are known as such. Some well-known synthetic examples include SBR (styrene-butadiene rubber) and EPDM (terpolymer of ethylene, propylene and a diene monomer). Elastomers undergo a cross-linking step, also referred to as vulcanisation step, in order to be suitable for their final use. It was found that the hydroxy-aromatic compounds according to the invention can be used favourably as cross-linking agent with which the cross-linking step is done. The compounds may be used in the usual manner, e.g. by mixing with the elastomer and subjecting the resulting mixture to a heat treatment, possibly in combination with mechanical kneading and possibly with the aid of a cross-linking catalyst, said catalyst preferably being an oil-soluble Lewis or Brønstedt acid. Preferably, the elastomer to be vulcanised is EPDM. In a preferred embodiment of the invention, a hydroxy-aromatic compound of formula (III) or (IV) is used as cross-linking agent in thermoplastic elastomer compositions; these compositions contain as is known a thermoplastic polymer and an elastomer component whereby the elastomer component is the component that is to be vulcanised. The resulting materials is typically referred to as thermoplastic vulcanisate (TPV). Preferred thermoplastic elastomer compositions are those that contain blends of polyolefinic materials such as polyprolylene with EPDM; such compositions are as such known. The amount of hydroxy-aromatic compound to be used for vulcanisation is in first approximation comparable to the amount of the known phenol-formaldehyde resin that would be used, and preferably varies between 0.02 and 10 wt.% relative to the amount of elastomer.

2,6-bis(hydroxy(metoxycarbonyl)methyl)-4-nonyl-phenol is prepared in the following manner. A reactor is filled with 400 grams of Methanol. At room temperature, 22 grams of 4-nonyl-phenol (0,10 moles) is added. As catalyst 10 grams Sulfuric acid is added. The mixture is heated to 60 °C. Within ^ΛA hour 30 grams (0,25 moles) Glyoxylic acid methyl ester hemi acetal (GMHA) is dosed to the mixture. The reaction mixture is kept at 60 ⁰C for 10 hours. The solvent methanol is distilled off. 500 ml of Toluene and 200 ml of water are added and layer separation takes place. The organic layer is washed once more with 200 ml water. From the organic layer the toluene is distilled of, resulting in a high viscous oil. The oil is identified by H-NMR and Mass spectrometry as 2,6-bis(hydroxy(metoxycarbonyl)methyl)-4-nonyl-phenol.

Claims

1. Process for the preparation of a hydroxy-aromatic compound, comprising the steps of:

• bringing a starting compound according to formula (I) together with an alkanol hemiacetal according to formula (II) to form a reaction mixture, wherein: o formula (I) is:

R₄ (I) wherein R₄ is a C₁ - C₂o alkyl group, aryl group, aralkyl group or cycloalkyl group; o formula (II) is:

C O R₆

R₁₂- -O- -OH

H (II) wherein R₆ is a C₁-Ci₂ alkyl group, aryl group, aralkyl group or cycloalkyl group and wherein R₁₂ is H, a Ci-C₁₂ alkyl group, aryl group, aralkyl group or cycloalkyl group;

• bringing the reaction mixture to conditions whereby the hydroxy-aromatic compound is formed.

Process according to claim 1 , wherein the molar ratio between the starting compound according to formula (I) and the alkanol hemiacetal according to formula (II) in the reaction mixture lies between 0.3 and 1.5. Hydoxy-aromatic compound according to formula (III):

wherein Me is methyl and wherein R₄ is a C₁ - C₂o alkyl group, aryl group, aralkyl group or cycloalkyl group.

Hydroxy-aromatic compound according to formula (IV):

wherein Me is methyl, n is an integer having a value of 1 , 2 or 3, and wherein R₄ is a C₁ - C_2O alkyl group, aryl group, aralkyl group or cycloalkyl group.

5. Hydroxy-aromatic compound according to formula (V):

wherein Me is methyl and wherein R₄ is a C₁ - C₂₀ alkyl group, aryl group, aralkyl group or cycloalkyl group.

6. Hydroxy-aromatic compound according to formula (Vl):

7. Use of a hydroxy-aromatic compound according to any one of claims 3 - 6 as cross-linking agent in elastomers or in coatings.

8. Use of a hydroxy-aromatic compound according to any one of claims 3 - 4 as cross-linking agent in EPDM or in TPV.