EP3976720A1

EP3976720A1 - Coating composition with phosphazene catalyst

Info

Publication number: EP3976720A1
Application number: EP20725723.9A
Authority: EP
Inventors: Ralf Grottenmueller; Theresa LORENZ
Original assignee: Merck Patent GmbH
Current assignee: Merck Patent GmbH
Priority date: 2019-05-24
Filing date: 2020-05-20
Publication date: 2022-04-06
Also published as: WO2020239556A1

Abstract

The present invention relates to new silazane containingcoating compositions which contain a phosphazene catalyst. The coating compositions are particularly suitable for the preparation of functional coatings on various base material substrates to provideimproved physical and chemical surface propertiesthereto.The phosphazene catalyst allows a fast and efficient curing of the silazane containing coating composition under ambient conditionsto provide a cured solid functional coating.

Description

Coating Composition with Phosphazene Catalyst

Technical field The present invention relates to new silazane containing coating

compositions which comprise a phosphazene catalyst. The coating compositions are particularly suitable for the preparation of functional coatings on various base material substrates to provide improved physical and chemical surface properties such as, in particular, improved

mechanical resistance and durability (including improved surface hardness, improved scratch resistance, improved abrasion resistance and/or improved smoothness); improved wetting and adhesion properties

(including hydro- and oleophobicity, easy-to-clean effect and/or anti-graffiti effect); improved chemical resistance (including improved corrosion resistance (e.g. against solvents, acidic and alkaline media and corrosive gases) and/or improved anti-oxidation effect); improved optical effects (improved light fastness); and improved physical barrier or sealing effects. The phosphazene catalyst allows a fast and efficient curing of the silazane containing coating composition under ambient conditions to provide a cured solid functional coating.

Beyond that, further beneficial surface properties may be obtained or may be improved by functional coatings which are prepared from the silazane containing coating composition according to the present invention such as, e.g. antistatic effect, anti-staining effect, anti-fingerprint effect, anti-fouling effect and/or anti-microbial effect.

Furthermore, the coating compositions show high adhesion to various substrate surfaces and they allow an easy application by user-friendly coating methods so that functional surface coatings with various film thicknesses may be obtained in an efficient and easy manner under mild conditions. The present invention further relates to a method for preparing a coated article using said silazane containing coating composition and to a coated article which is prepared by said method. A functional coating is formed on the surface of a base material of the article, thereby improving one or more of the above-mentioned specific surface properties. Beyond that, the present invention relates to the use of a phosphazene compound for catalyzing the curing of a silazane-containing polymer. Background of the invention

Polymers with silazane repeating units -[SiR2-NR’-] are typically referred to as polysilazanes. If all substituents R and R’ are hydrogen, the material is called perhydropolysilazane (PHPS) and, if at least one of R and R’ is an organic moiety, the material is called organopolysilazane (OPSZ). PHPS and OPSZ are used for a variety of functional coatings to impart certain properties to surfaces, such as e.g. anti-graffiti effect, scratch resistance, corrosion resistance or hydro- and oleophobicity. Hence, silazanes are widely used for functional coatings for various applications.

Whilst polysilazanes are composed of one or more different silazane repeating units, polysiloxazanes additionally contain one or more different siloxane repeating units. Polysiloxazanes combine features of polysilazane and polysiloxane chemistry and behavior. Polysilazanes and polysiloxa- zanes are resins that are used for the preparation of functional coatings for different types of application. They can be crosslinked by hydrolysis, for example, by reaction with moisture from the air. This leads to an increasing molecular weight and to a solidification or curing of the material. For this reason, the terms“curing” and“crosslinking” and the corresponding verbs “cure” and“crosslink” are interchangeably used as synonyms in the present application when referred to silazane based polymers such as e.g. poly silazanes and polysiloxazanes. Typically, both polysilazanes and polysiloxazanes are liquid polymers which become solid at molecular weights of ca. > 10,000 g/mol. In most applica tions, liquid polymers of moderate molecular weights, typically in the range from 2,000 to 8,000 g/mol, are used. For preparing solid coatings with the above-mentioned properties from such liquid polymers, a curing step is required which is carried out after applying the material on a substrate, either as a pure material or as a formulation. The curing should be as fast as possible. As long as the coating is liquid, some defect formation of the film can occur. For example, the liquid coating may reflow and cause some film thickness variations or the wet film is sensitive to absorption of air-born impurities (e.g. dust) which stick on the wet surface. Another disadvantage is a delay time in the processing of the substrates until the coating is dry. In general, it is possible to speed up the drying time by applying higher temperatures, radiation or an atmosphere with higher humidity. Flowever, in some cases (like for example architectural coatings) the curing has to take place at ambient conditions.

There are several catalyst types known to accelerate the curing of silazanes or siloxazanes at ambient conditions (see WO 2004/039904 A1 , WO 2007/028511 A2 and WO 2018/100027 A1 ). For example, metal salts or organometallic compounds of e.g. boron, palladium, or aluminum are very efficient. Flowever, these compounds only catalyse the Si-N to Si-0 conversion and not Si-FH hydrolysis. Amines and especially strong amines, such as e.g. DBU [1 ,8-diazabicyclo(5.4.0)undec-7-ene], are known to catalyse Si-N conversion as well as Si-FH hydrolysis, too. Flowever, they sometimes form turbid films and bubbles in thick coatings and the shelf-life of silazane amine formulations is limited. Although, various types of catalysts or additives for silazane or siloxazane curing are known, there is still a need for further reduction of curing time for functional coating applications in the industry. Object of the invention

Hence, it is an object of the present invention to overcome the

disadvantages in the prior art and to provide new coating compositions for preparing functional surface coatings which allow a fast and efficient curing under ambient conditions. It is a further object of the present invention to reduce the“dry-to-touch” time at ambient conditions for functional surface coating compositions.

It is a further object of the present invention that the coating compositions are particularly suitable for the preparation of functional surface coatings on various base materials to provide improved physical and chemical surface properties such as, in particular, improved mechanical resistance and durability (including improved surface hardness, improved scratch resistance, improved abrasion resistance and/or improved smoothness); improved wetting and adhesion properties (including hydro- and

oleophobicity, easy-to-clean effect and/or anti-graffiti effect); improved chemical resistance (including improved corrosion resistance (e.g. against solvents, acidic and alkaline media and corrosive gases) and/or improved anti-oxidation effect); improved optical effects (improved light fastness); and improved physical barrier or sealing effects.

Beyond that, it is desirable to obtain additional or further improve beneficial surface properties such as, e.g. antistatic effect, anti-staining effect, anti fingerprint effect and/or anti-fouling effect.

Moreover, it is an object of the present invention to provide new coating compositions which, in addition to the above-mentioned advantages, are clear, homogeneous and storage-stable formulations, which can be applied by conventional coating methods and which can be easily cured to functional surface coatings under ambient conditions or at elevated temperatures of up to 150°C.

It is a further object of the present invention to provide a method for preparing coated articles and coated articles which are prepared by said method showing the above-mentioned advantages. A functional coating is formed on the surface of a base material of the article, thereby improving one or more of the above-mentioned specific surface properties. Finally, it is an object of the present invention to provide compounds which can be used to catalyze the curing of silazane-containing polymers. Such catalyst compounds shall be colorless, miscible with PHPS and OPSZ without spontaneously reacting and non-toxic. In addition, they shall allow the formation of cured films from silazane-containing polymers, which stay clear without any turbidity.

Summary of the invention

The present inventors have surprisingly found that the above objects are solved, either individually or in any combination, by a coating composition, comprising:

(i) a silazane-containing polymer; and

(ii) a phosphazene compound. It was found that phosphazene compounds are highly efficient catalysts for the curing of silazane-containing polymers. For example, the curing of liquid OPSZ to a dry-to-touch coating is finished within one hour under ambient conditions. There are several further advantages of phosphazenes compared to known catalysts: They are colorless, which is important for clear coats, they are miscible with PFIPS as well as with OPSZ, they do not react with PHPS and OPSZ, which guarantees long shelf-life of pre-mixed formulations, and they are non-toxic. In addition, they form cured films from silazane-containing polymers, which stay clear without any turbidity. Beyond that, they show synergistic effects with other types of curing catalysts.

The coating compositions of the present invention are clear, homogeneous and storage-stable formulations, which can be applied by conventional coating methods such as e.g. spray coating, dip coating, spin coating, slit or slot coating, inkjet printing or other coating methods, and which can be easily cured to functional surface coatings under ambient conditions or at elevated temperatures of up to 150°C.

In addition, a method for preparing a coated article is provided, wherein the method comprises the following steps:

(a) applying a coating composition according to the present invention to a surface of an article; and

(b) curing said coating composition to obtain a coated article.

Moreover, a coated article is provided, which is obtainable or obtained by the above-mentioned preparation method.

The present invention further relates to the use of a phosphazene compound for catalyzing the curing of a silazane-containing polymer. Preferred embodiments of the invention are described in the dependent claims. Brief description of the figures

Figure 1 shows FT-IR spectra of Example 4:

Durazane 1800 (raw material, uncured)

Durazane 1800 with BEMP, cured at 25°C and 50% relative humidity for 24 h

Durazane 1800 with AI(AcAc)3, cured at 25°C and 50% relative humidity for 24 h

Durazane 1800 with DBU, cured at 25°C and 50% relative humidity for 24 h

Detailed description

Definitions

The term“polymer” includes, but is not limited to, homopolymers, copolymers, for example, block, random, and alternating copolymers, terpolymers, quaterpolymers, etc., and blends and modifications thereof. Furthermore, unless otherwise specifically limited, the term“polymer” shall include all possible configurational isomers of the material. These configurations include, but are not limited to isotactic, syndiotactic, and atactic symmetries. A polymer is a molecule of high relative molecular mass, the structure of which essentially comprises the multiple repetition of units (i.e. repeating units) derived, actually or conceptually, from molecules of low relative mass (i.e. monomers). Typically, the number of repeating units is higher than 10, preferably higher than 20, in polymers. If the number of repeating units is less than 10, the polymers may also be referred to as oligomers. The term“monomer” as used herein, refers to a molecule which can undergo polymerization thereby contributing constitutional units (repeating units) to the essential structure of a polymer.

The term“homopolymer” as used herein, stands for a polymer derived from one species of (real, implicit or hypothetical) monomer.

The term“copolymer” as used herein, generally means any polymer derived from more than one species of monomer, wherein the polymer contains more than one species of corresponding repeating unit. In one embodiment the copolymer is the reaction product of two or more species of monomer and thus comprises two or more species of corresponding repeating unit. It is preferred that the copolymer comprises two, three, four, five or six species of repeating unit. Copolymers that are obtained by copolymerization of three monomer species can also be referred to as terpolymers. Copolymers that are obtained by copolymerization of four monomer species can also be referred to as quaterpolymers. Copolymers may be present as block, random, and/or alternating copolymers.

The term“block copolymer” as used herein, stands for a copolymer, wherein adjacent blocks are constitutionally different, i.e. adjacent blocks comprise repeating units derived from different species of monomer or from the same species of monomer but with a different composition or sequence distribution of repeating units.

Further, the term“random copolymer” as used herein, refers to a polymer formed of macromolecules in which the probability of finding a given repeating unit at any given site in the chain is independent of the nature of the adjacent repeating units. Usually, in a random copolymer, the sequence distribution of repeating units follows Bernoullian statistics. The term“alternating copolymer” as used herein, stands for a copolymer consisting of macromolecules comprising two species of repeating units in alternating sequence. The term“polysilazane” as used herein, refers to a polymer in which silicon and nitrogen atoms alternate to form the basic backbone. Since each silicon atom is bound to at least one nitrogen atom and each nitrogen atom to at least one silicon atom, both chains and rings of the general formula -[SiR¹R²-NR³-]m (silazane repeating unit) occur, wherein R¹ to R³ may be hydrogen atoms, organic substituents or heteroorganic substituents; and m is an integer. If all substituents R¹ to R³ are hydrogen atoms, the polymer is designated as perhydropolysilazane, polyperhydrosilazane or inorganic polysilazane (-[SiH2-NH-]_m). If at least one substituent R¹ to R³ is an organic or heteroorganic substituent, the polymer is designated as

organopolysilazane.

The term“polysiloxazane” as used herein, refers to a polysilazane which additionally contains sections in which silicon and oxygen atoms alternate. Such sections may be represented, for example, by -[0-SiR⁷R⁸-]_n, wherein R⁷ and R⁸ may be hydrogen atoms, organic substituents, or heteroorganic substituents; and n is an integer. If all substituents of the polymer are hydrogen atoms, the polymer is designated as perhydropolysiloxazane. If at least one substituents of the polymer is an organic or heteroorganic substituent, the polymer is designated as organopolysiloxazane.

The term“functional coating” as used herein refers to coatings which impart one or more specific properties to a surface. Generally, coatings are needed to protect surfaces or impart specific effects to surfaces. There are various effects which may be imparted by functional coatings. For example, mechanical resistance, surface hardness, scratch resistance, abrasion resistance, anti-microbial effect, anti-fouling effect, wetting effect (towards water), hydro-and oleophobicity, smoothening effect, durability effect, antistatic effect, anti-staining effect, anti-fingerprint effect, easy-to-clean effect, anti-graffiti effect, chemical resistance, corrosion resistance, anti oxidation effect, physical barrier effect, sealing effect, heat resistance, fire resistance, low shrinkage, UV-barrier effect, light fastness, and/or optical effects.

The term“cure” means conversion to a crosslinked polymer network (for example, through irradiation or catalysis). Preferred embodiments

The present invention relates to a coating composition, comprising:

(i) a silazane-containing polymer; and

(ii) a phosphazene compound.

Phosphazene compound

Phosphazenes are a class of chemical compounds in which a phosphorus atom is covalently linked to a nitrogen atom by a double bond and to three other atoms or radicals by single bonds, which are preferably amino substituents. The compounds are unusually stable examples of the phosphorene class of molecules and have a remarkable proton affinity. As such, they are one of the eminent examples of neutral, organic superbases. Phosphazenes are also known as iminophosphoranes and phosphine imides. Phosphazene bases are strong non-metallic non-ionic and low- nucleophilic bases. They are stronger bases than regular amine or amidine bases such as e.g. HCinig’s base or DBU.

In a preferred embodiment of the present invention the phosphazene compounds comprises at least one phosphorus atom and at least four nitrogen atoms, wherein said nitrogen atoms are bound to said phosphorus atom. It is preferred that the phosphazene compound comprises at least one N=P double bond, preferably one, two, three or four N=P double bonds. It is preferred that the phosphazene compound has a molecular weight in the range from 150 to 1 ,000 g/mol, preferably in the range from 180 to 900 g/mol, more preferably in the range from 200 to 800 g/mol, and most preferably in the range from 220 to 750 g/mol. In a preferred embodiment of the present invention, the phosphazene compound is represented by one of the following Formulae (A), (B) or (C):

R-[N=P(NR^laR^lb)₂]n-(NR^N ₂) Formula (A) RN=P(NR^laR^lb)3.m(N=P(NR"₂)3)m Formula (B)

[P⁺(N=P(NR"₂)3)4]X Formula (C) wherein in Formula (A): R represents an alkyl group having 1 to 16, preferably 1 to 8, more preferably 1 to 4, carbon atoms, or R represents

P⁺(NR"₂)3X-, wherein X is one or more selected from F, Cl and Br;

R^la and R^lb represent at each occurrence independently from each other an alkyl group having 1 to 4 carbon atoms, or R^la and R^lb together form with the adjacent nitrogen atom a heterocyclic ring system comprising 2 to 7, preferably 3 to 5, more preferably 4, carbon atoms, or both R^la together form with the adjacent nitrogen atoms a heterocyclic ring system

comprising 1 to 6, preferably 2 to 4, more preferably 3, carbon atoms, and R^lb represents an alkyl group having 1 to 4 carbon atoms;

R" represents an alkyl group having 1 to 4 carbon atoms, or both R" together form with the adjacent nitrogen atom a heterocyclic ring system comprising 2 to 7, preferably 3 to 5, more preferably 4, carbon atoms; and n is an integer from 1 to 10, preferably from 1 to 8, more preferably from 1 to 4; wherein in Formula (B): R represents an alkyl group having 1 to 16, preferably 1 to 8, more preferably 1 to 4, carbon atoms;

R^la and R^lb represent at each occurrence independently from each other an alkyl group having 1 to 4 carbon atoms, or R^la and R^lb together form with the adjacent nitrogen atom a heterocyclic ring system comprising 2 to 7, preferably 3 to 6, more preferably 4, carbon atoms, or both R^la together form with the adjacent nitrogen atoms a heterocyclic ring system

R" represents at each occurrence independently from each other an alkyl group having 1 to 4 carbon atoms, or both R" together form with the adjacent nitrogen atom a heterocyclic ring system comprising 2 to 7, preferably 3 to 5, more preferably 4, carbon atoms;

and m is 2 or 3; and wherein in Formula (C): R" represents at each occurrence independently from each other an alkyl group having 1 to 4 carbon atoms, or both R" together form with the adjacent nitrogen atom a heterocyclic ring system comprising 2 to 7, preferably 3 to 5, more preferably 4, carbon atoms; and X is one or more selected from F, Cl and Br. The phosphazene compound according to Formula (A) contains n

[N=P(NR^laR^lb)2] repeating units, which are each linearly linked to one another. The structural elements R and (NR^N2) form the start point and end point of the linearly linked repeating units, respectively. In a more preferred embodiment of Formula (A): R is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl, or R represents

P⁺(NR^N ₂)3X-, wherein X is Cl or Br; R^la and R^lb are at each occurrence independently from each other selected from methyl, ethyl propyl and butyl, or R^la and R^lb together form with the adjacent nitrogen atom a heterocyclic ring system comprising 4 carbon atoms, or both R^la together form with the adjacent nitrogen atoms a heterocyclic ring system comprising 3 carbon atoms, and R^lb is selected from methyl, ethyl, propyl and butyl; R" is selected from methyl, ethyl, propyl and butyl, or both R" together form with the adjacent nitrogen atom a heterocyclic ring system comprising 4 carbon atoms; and n is an integer from 1 to 4. In a more preferred embodiment of Formula (B): R is selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and octyl; R^la and R^lb are at each occurrence independently from each other selected from methyl, ethyl, propyl and butyl, or R^la and R^lb together form with the adjacent nitrogen atom a heterocyclic ring system comprising 4 carbon atoms, or both R^la together form with the adjacent nitrogen atoms a heterocyclic ring system comprising 3 carbon atoms and R^lb is selected from methyl, ethyl, propyl and butyl; R" is at each occurrence independently from each other selected from methyl, ethyl, propyl and butyl, or both R" together form with the adjacent nitrogen atom a heterocyclic ring system comprising 4 carbon atoms; and m is 2 or 3.

In a more preferred embodiment of Formula (C): R" is at each occurrence independently from each other selected from methyl, ethyl, propyl and butyl, or both R" together form with the adjacent nitrogen atom a

heterocyclic ring system comprising 4 carbon atoms; and X is Cl or Br.

It is particularly preferred in Formula (A) and/or Formula (B) that R is selected from -CH₃, -CH2CH3, -CH2CH2CH3, -CH(CH₃)2, -CH2CH2CH2CH3, -CH₂CH(CH₃)2, -CH(CH₃)CH₂CH₃, -C(CH₃)3, and -C(CH3)2CH₂C(CH₃)3.

It is particularly preferred in Formula (A) and/or Formula (B) that R^la and R^lb are selected from -CH3, -CH2CH3, -CFI2CFI2CFI3 and -CH(CH3)2, or R^la and R^lb together form a -CH2CH2CH2- bridge or -CH2CH2CH2CH2- bridge so that a heterocyclic ring system is formed with the adjacent nitrogen atom, or both R^la together form a -CH2CH2CH2- bridge or -CH2CH2CH2CH2- bridge which forms a heterocyclic ring system with the adjacent nitrogen atoms and R^lb is selected from -CH₃, -CH2CH3, -CH2CH2CH3 and -CH(CH₃)2.

It is particularly preferred in Formula (A), Formula (B) and/or Formula (C) that R" is selected from -CH₃, -CH2CH3, -CH2CH2CH3 and -CH(CH₃)2, or both R" together form a -CFI2CFI2CFI2- bridge or -CFI2CFI2CFI2CFI2- bridge which forms a heterocyclic ring system with the adjacent nitrogen atom.

In a most preferred embodiment of the present invention, the phosphazene compound is selected from:

Silazane-containing polymer

In a preferred embodiment of the present invention, the silazane-containing polymer comprises a repeating unit M¹ which is represented by the following Formula (1 ):

-[SiR¹R²-NR³-] (1 ) wherein R¹, R² and R³ are the same or different from each other and independently selected from hydrogen, an organic group, a heteroorganic group, or a combination thereof. Suitable organic and heteroorganic groups for R¹, R² and R³ include alkyl, alkylcarbonyl, alkenyl, cycloalkyl, aryl, arylalkyl, alkylsilyl, alkylsilyloxy, arylsilyl, arylsilyloxy, alkylamino, arylamino, alkoxy, alkoxycarbonyl, alkylcarbonyloxy, aryloxy, aryloxycarbonyl, arylcarbonyloxy, arylalkyloxy, and the like, and combinations thereof (preferably, alkyl, alkenyl, cycloalkyl, aryl, arylalkyl, alkoxy, aryloxy, arylalkyloxy, and combinations thereof); the groups preferably having from 1 to 30 carbon atoms (more preferably, 1 to 20 carbon atoms; even more preferably, 1 to 10 carbon atoms; most preferably, 1 to 6 carbon atoms (for example, methyl, ethyl or vinyl)). The groups can be further substituted with one or more substituent groups such as halogen (fluorine, chlorine, bromine, and iodine), alkoxy, alkoxycarbonyl, amino, carboxyl, hydroxyl, nitro, trialkoxysilyl, and the like, and

combinations thereof.

In a preferred embodiment, R¹ and R² are the same or different from each other and independently selected from hydrogen, alkyl having 1 to 30

(preferably 1 to 20, more preferably 1 to 10, most preferably 1 to 6) carbon atoms, alkenyl having 2 to 30 (preferably 2 to 20, more preferably 2 to 10, most preferably 2 to 6) carbon atoms, or aryl having 2 to 30 (preferably 3 to 20, more preferably 4 to 10, most preferably 6) carbon atoms, wherein one or more hydrogen atoms bonded to carbon atoms may be replaced by fluorine; and R³ is selected from hydrogen, alkyl having 1 to 30 (preferably 1 to 20, more preferably 1 to 10, most preferably 1 to 6) carbon atoms, alkenyl having 2 to 30 (preferably 2 to 20, more preferably 2 to 10, most preferably 2 to 6) carbon atoms, or aryl having 2 to 30 (preferably 3 to 20, more preferably 4 to 10, most preferably 6) carbon atoms, wherein one or more hydrogen atoms bonded to carbon atoms may be replaced by fluorine, OR’ or Si(OR’)3, wherein R’ is selected from alkyl having 1 to 30 (preferably 1 to 20, more preferably 1 to 10, most preferably 1 to 6) carbon atoms.

In a more preferred embodiment, R¹ and R² are the same or different from each other and independently selected from hydrogen, methyl, ethyl, propyl, butyl, pentyl, hexyl or phenyl, wherein one or more hydrogen atoms bonded to carbon atoms may be replaced by fluorine; and R³ is selected from hydrogen, methyl, ethyl, propyl, butyl, pentyl, hexyl, vinyl or phenyl, wherein one or more hydrogen atoms bonded to carbon atoms may be replaced by -F, -OCH₃, -OCH2CH3, -OCH2CH2CH3, -OCH(CH₃)2,

-Si(OCH₃)3 or -Si(OCH₂CH₃)3.

Most preferably, R¹, R² and R³ are the same or different from each other and independently selected from the list consisting of -H, -CH3, -CH2CH3, -CH2CH2CH3, -CH(CH₃)2, -CH=CH2, and -ObHd, wherein one or more hydrogen atoms bonded to carbon atoms may be replaced by fluorine.

In a preferred embodiment of the present invention, the silazane-containing polymer comprises a repeating unit M² which is represented by the following Formula (2):

-[SiR⁴R⁵-NR⁶-] (2) wherein R⁴, R⁵ and R⁶ are the same or different from each other and independently selected from hydrogen, an organic group, a heteroorganic group, or a combination thereof.

Suitable organic and heteroorganic groups for R⁴, R⁵ and R⁶ include alkyl, alkylcarbonyl, alkenyl, cycloalkyl, aryl, arylalkyl, alkylsilyl, alkylsilyloxy, arylsilyl, arylsilyloxy, alkylamino, arylamino, alkoxy, alkoxycarbonyl, alkylcarbonyloxy, aryloxy, aryloxycarbonyl, arylcarbonyloxy, arylalkyloxy, and the like, and combinations thereof (preferably, alkyl, alkenyl, cycloalkyl, aryl, arylalkyl, alkoxy, aryloxy, arylalkyloxy, and combinations thereof); the groups preferably having from 1 to 30 carbon atoms (more preferably, 1 to 20 carbon atoms; even more preferably, 1 to 10 carbon atoms; most preferably, 1 to 6 carbon atoms (for example, methyl, ethyl or vinyl)). The groups can be further substituted with one or more substituent groups such as halogen (fluorine, chlorine, bromine, and iodine), alkoxy, alkoxycarbonyl, amino, carboxyl, hydroxyl, nitro, trialkoxysilyl, and the like, and

combinations thereof. In a preferred embodiment, R⁴ and R⁵ are the same or different from each other and independently selected from hydrogen, alkyl having 1 to 30 (preferably 1 to 20, more preferably 1 to 10, most preferably 1 to 6) carbon atoms, alkenyl having 2 to 30 (preferably 2 to 20, more preferably 2 to 10, most preferably 2 to 6) carbon atoms, or aryl having 2 to 30 (preferably 3 to 20, more preferably 4 to 10, most preferably 6) carbon atoms, wherein one or more hydrogen atoms bonded to carbon atoms may be replaced by fluorine; and R⁶ is selected from hydrogen, alkyl having 1 to 30 (preferably 1 to 20, more preferably 1 to 10, most preferably 1 to 6) carbon atoms, alkenyl having 2 to 30 (preferably 2 to 20, more preferably 2 to 10, most preferably 2 to 6) carbon atoms, or aryl having 2 to 30 (preferably 3 to 20, more preferably 4 to 10, most preferably 6) carbon atoms, wherein one or more hydrogen atoms bonded to carbon atoms may be replaced by fluorine, OR” or Si(OR”)3, wherein R” is selected from alkyl having 1 to 30 (preferably 1 to 20, more preferably 1 to 10, most preferably 1 to 6) carbon atoms.

In a more preferred embodiment, R⁴ and R⁵ are the same or different from each other and independently selected from hydrogen, methyl, ethyl, propyl, butyl, pentyl, hexyl or phenyl, wherein one or more hydrogen atoms bonded to carbon atoms may be replaced by fluorine; and R⁶ is selected from hydrogen, methyl, ethyl, propyl, butyl, pentyl, hexyl, vinyl or phenyl, wherein one or more hydrogen atoms bonded to carbon atoms may be replaced by -F, -OCH₃, -OCH2CH3, -OCH2CH2CH3, -OCH(CH₃)2,

-Si(OCH₃)₃ or -Si(OCH₂CH₃)3.

Most preferably, R⁴, R⁵ and R⁶ are the same or different from each other and independently selected from the list consisting of -H, -CH3, -CH2CH3, -CH2CH2CH3, -CH(CH₃)2, -CH=CH2, and -ObHd, wherein one or more hydrogen atoms bonded to carbon atoms may be replaced by fluorine.

In a preferred embodiment of the present invention, the silazane-containing polymer comprises a repeating unit M³ which is represented by the following Formula (3):

-[SiR⁷R⁸-0-] (3) wherein R⁷ and R⁸ are the same or different from each other and

independently selected from hydrogen, an organic group, a heteroorganic group, or a combination thereof.

Suitable organic and heteroorganic groups for R⁷ and R⁸ include alkyl, alkylcarbonyl, alkenyl, cycloalkyl, aryl, arylalkyl, alkylsilyl, alkylsilyloxy, arylsilyl, arylsilyloxy, alkylamino, arylamino, alkoxy, alkoxycarbonyl, alkylcarbonyloxy, aryloxy, aryloxycarbonyl, arylcarbonyloxy, arylalkyloxy, and the like, and combinations thereof (preferably, alkyl, alkenyl, cycloalkyl, aryl, arylalkyl, alkoxy, aryloxy, arylalkyloxy, and combinations thereof); the groups preferably having from 1 to 30 carbon atoms (more preferably, 1 to 20 carbon atoms; even more preferably, 1 to 10 carbon atoms; most preferably, 1 to 6 carbon atoms (for example, methyl, ethyl or vinyl)). The groups can be further substituted with one or more substituent groups such as halogen (fluorine, chlorine, bromine, and iodine), alkoxy, alkoxycarbonyl, amino, carboxyl, hydroxyl, nitro, trialkoxysilyl, and the like, and

combinations thereof. In a preferred embodiment, R⁷ and R⁸ are the same or different from each other and independently selected from hydrogen, alkyl having 1 to 30 (preferably 1 to 20, more preferably 1 to 10, most preferably 1 to 6) carbon atoms, alkenyl having 2 to 30 (preferably 2 to 20, more preferably 2 to 10, most preferably 2 to 6) carbon atoms, or aryl having 2 to 30 (preferably 3 to 20, more preferably 4 to 10, most preferably 6) carbon atoms, wherein one or more hydrogen atoms bonded to carbon atoms may be replaced by fluorine. In a more preferred embodiment, R⁷ and R⁸ are the same or different from each other and independently selected from hydrogen, methyl, ethyl, propyl, butyl, pentyl, hexyl or phenyl, wherein one or more hydrogen atoms bonded to carbon atoms may be replaced by fluorine. Most preferably, R⁷ and R⁸ are the same or different from each other and independently selected from the list consisting of -H, -Chh, -CH2CH3, -CH2CH2CH3, -CH(CH₃)2, -CH=CH2, and -ObHd, wherein one or more hydrogen atoms bonded to carbon atoms may be replaced by fluorine. It is preferred that the silazane-containing polymer comprises a repeating unit M¹ and a further repeating unit M², wherein M¹ and M² are silazane repeating units which are different from each other.

It is also preferred that the silazane-containing polymer comprises a repeating unit M¹ and a further repeating unit M³, wherein M¹ is a silazane repeating unit and M³ is a siloxane repeating unit.

It is also preferred that the silazane-containing polymer comprises a repeating unit M¹, a further repeating unit M² and a further repeating unit M³, wherein M¹ and M² are silazane repeating units which are different from each other and M³ is a siloxane repeating unit. In one embodiment, the silazane-containing polymer is a polysilazane which may be a perhydropolysilazane or an organopolysilazane. Preferably, the polysilazane contains a repeating unit M¹ and optionally a further repeating unit M², wherein M¹ and M² are silazane repeating units which are different from each other.

In an alternative embodiment, the silazane-containing polymer is a polysiloxazane which may be a perhydropolysiloxazane or an

organopolysiloxazane. Preferably, the polysiloxazane contains a repeating unit M¹ and a further repeating unit M³, wherein M¹ is a silazane repeating unit and M³ is a siloxane repeating unit. Preferably, the polysiloxazane contains a repeating unit M¹, a further repeating unit M² and a further repeating unit M³, wherein M¹ and M² are silazane repeating units which are different from each other and M³ is a siloxane repeating unit.

Preferably, the silazane-containing polymer is a copolymer such as a random copolymer or a block copolymer or a copolymer containing at least one random sequence section and at least one block sequence section. More preferably, the silazane-containing polymer is a random copolymer or a block copolymer.

It is preferred that the silazane-containing polymer has a mixed polycyclic, linear and/or branched-chain structure. The silazane-containing polymers have a molecular weight distribution.

Preferably, the silazane-containing polymers used in the present invention have a mass average molecular weight M_w, as determined by GPC, of at least 1 ,000 g/mol, more preferably of at least 1 ,200 g/mol, even more preferably of at least 1 ,500 g/mol. Preferably, the mass average molecular weight M_w of the silazane-containing polymers is less than 100,000 g/mol. More preferably, the molecular weight M_w of the silazane-containing polymers is in the range from 1 ,500 to 50,000 g/mol. Preferably, the weight ratio of the silazane-containing polymer to the phosphazene compound in the coating composition of the present invention is in the range from 99.99 : 0.01 to 95.0 : 5.0, more preferably in the range from 99.9 : 0.1 to 98.0 : 2.0.

Further components

It is preferred that the coating composition of the present invention comprises one or more solvents. Suitable solvents are organic solvents such as, for example, aliphatic and/or aromatic hydrocarbons, which may be halogenated, such as 1 -chloro-4-(trifluoromethyl)benzene, esters such as ethyl acetate, n-butyl acetate or tert-butyl acetate, ketones such as acetone or methyl ethyl ketone, ethers such as tetrahydrofuran or dibutyl ether, and also mono- or polyalkylene glycol dialkyl ethers (glymes), or mixtures thereof.

Moreover, the coating composition according to the present invention may comprise one or more additives, preferably selected from the list consisting of additives influencing evaporation behavior, additives influencing film formation, adhesion promoters, anti-corrosion additives, cross-linking agents, dispersants, fillers, functional pigments (e.g. for providing functional effects such as electric or thermal conductivity, magnetic properties, etc.), optical pigments (e.g. for providing optical effects such as color, refractive index, pearlescent effect, etc.), particles reducing thermal expansion, nanoparticles, adhesion promoters, rheological modifiers (e.g. thickeners), surfactants (e.g. wetting and leveling agents or additives for improving hydro- or oleophobicity and anti-graffiti effects), viscosity modifiers, and other kinds of resins or polymers such as e.g. epoxy resins, phenol resins, siloxanes, polyurethanes, or polyesters. Nanoparticles may be selected from nitrides, titanates, diamond, oxides, sulfides, sulfites, sulfates, silicates and carbides which may be optionally surface-modified with a capping agent. Preferably, nanoparticles are materials having a particle diameter of < 100 nm, more preferably < 80 nm, even more preferably < 60 nm, even more preferably < 40 nm, and most preferably < 20 nm. The particle diameter may be determined by any standard method known to the skilled person.

In a particularly preferred embodiment of the present invention, the coating composition further comprises one or more solvents and optionally one or more additives.

It is possible to further accelerate the curing of the coating composition by the addition of one or more further catalysts. Examples of useful further catalysts are Lewis acids such as boron-, aluminum-, titanium-, tin- or zinc- alkyls, aryls or carboxylates, Bronsted acids such as carboxylic acids, bases such as primary, secondary or tertiary amines or phosphazenes, or metal salts such as Pd, Pt, Al, B, Sn or Zn salts of carboxylates,

acetylacetonates or alkoxylates. If silazanes having both Si-H and Si- CH=CH2 groups are used, well known hydrosilylation catalysts such as Pt or Pd salts or complexes can be used. If silazanes having only Si-CH=CH2 or both Si-H and Si-CH=CH2 groups are used, UV or thermal radical initiators like peroxides or azo compounds can be used. In a preferred embodiment, the coating composition according to the present invention comprises one or more of the above-mentioned catalysts.

It is to be understood that the skilled person can freely combine the above- mentioned preferred, more preferred, particularly preferred and most preferred embodiments relating to the coating composition and definitions of its components in any desired way. Method

The present invention further relates to a method for preparing a coated article, wherein the method comprises the following steps:

(b) curing said coating composition to obtain a coated article.

In a preferred embodiment, the coating composition, which is applied in step (a), is previously provided by mixing a silazane-containing polymer with a phosphazene compound, wherein the silazane-containing polymer and the phosphazene compound are defined as indicated above for the coating composition according to the present invention. It is preferred that the mixing of the silazane-containing polymer with the phosphazene com- pound takes place at room temperature, preferably at a temperature in the range from 20 to 25°C.

Preferably, the coating composition, which is applied in step (a), is a homogeneous liquid having a viscosity in the range from 2 to 1 ,000 mPas. The viscosity of the composition may be adjusted by the type and content of solvent as well as the type, ratio and molecular weight of the silazane- containing polymer and further additives, if any.

It is preferred that the coating composition is applied in step (a) by an application method suitable for applying liquid compositions to a surface of an article. Such methods include, for example, wiping with a cloth, wiping with a sponge, dip coating, spray coating, flow coating, roller coating, slit coating, slot coating, spin coating, dispensing, screen printing, stencil printing or ink-jet printing. Dip coating and spray coating are particularly preferred. The coating composition of the invention may be applied to the surface of various articles such as, for example, buildings, dentures, furnishings, furniture, sanitary equipment (toilets, sinks, bathtubs, etc.), signs, signboard, plastic products, glass products, ceramics products, metal products, wood products and vehicles (road vehicles, rail vehicles, watercrafts and aircrafts). It is preferred that the surface of the article is made of any one of the base materials as described below.

Typically, the coating composition is applied in step (a) as a layer in a thickness of 1 pm to 1 cm, preferably 10 pm to 1 mm, to the surface of the article. In a preferred embodiment, the coating composition is applied as a thin layer having a thickness of 1 to 200 pm, more preferably 5 to 150 pm and most preferably 10 to 50 pm. The curing of the coating in step (b) may be carried out under various conditions such as e.g. by ambient curing, thermal curing and/or irradiation curing. The curing is optionally carried out in the presence of moisture, preferably in the form of water vapor. For this purpose, a climate chamber may be used.

Ambient curing preferably takes place at temperatures in the range from 10 to 40°C. Thermal curing preferably takes place at temperatures in the range from > 40 to 200°C, preferably from 100 to 150°C. Irradiation curing preferably takes place with IR irradiation or UV irradiation. Preferred IR irradiation wavelengths are in the range from 7 to 15 pm or from 1 to 3 pm for substrate absorption. Preferred UV irradiation wavelengths are in the range from 200 to 300 nm (short wavelength range).

Preferably, the curing in step (b) is carried out under ambient conditions, in a climate chamber or in a furnace. Preferably, the curing time for step (b) is from 10 sec to 24 h, more preferably from 1 min to 12 h, still more preferably from 2 min to 6 h, and most preferably from 5 min to 60 min, depending on the coating

composition and coating thickness.

After curing in step (b), the silazane-containing polymer is crosslinked to form a coating on the surface of the article. Without wishing to be bound to any theory, it is assumed that during the curing Si-N and Si-H bonds of the silazane-containing polymer are converted to Si-0 bonds.

The coating obtained by the above method forms a rigid and dense functional coating which is excellent in adhesion to the surface and imparts at least one of the following improved properties to the article: improved mechanical resistance and durability (including improved surface hardness, improved scratch resistance, improved abrasion resistance and/or improved smoothness); improved wetting and adhesion properties

(including hydro- and oleophobicity, easy-to-clean effect and/or anti-graffiti effect); improved chemical resistance (including improved corrosion resistance (e.g. against solvents, acidic and alkaline media and corrosive gases) and/or improved anti-oxidation effect); improved optical effects

(improved light fastness); and improved physical barrier or sealing effects.

Article Moreover, a coated article is provided, which is obtainable or obtained by the above-mentioned preparation method. By said preparation method a functional coating is formed on the surface of a base material of the article, thereby improving one or more of the following specific surface properties: mechanical resistance and durability (including surface hardness, scratch resistance, abrasion resistance and/or smoothness); wetting and adhesion properties (including hydro- and oleophobicity, easy-to-clean effect and/or anti-graffiti effect); chemical resistance (including corrosion resistance (e.g. against solvents, acidic and alkaline media and corrosive gases) and/or anti-oxidation effect); optical effects (light fastness); and physical barrier or sealing effects. Preferred base materials, to which the coating composition of the present invention is applied, include a wide variety of materials such as, for example, metals (such as iron, steel, silver, zinc, aluminum, nickel, titanium, vanadium, chromium, cobalt, copper, zirconium, niobium, molybdenum, ruthenium, rhodium, silicon, boron, tin, lead or manganese or alloys thereof provided, if necessary, with an oxide or plating film); plastics (such as polymethyl methacrylate (PMMA), polyurethane, polyesters (PET), polyallyldiglycol carbonate (PADC), polycarbonate, polyimide, polyamide, epoxy resin, ABS resin, polyvinyl chloride, polyethylene (PE), polypropylene (PP), polythiocyanate, or polytetrafluoroethylene (PTFE)); glass (such as fused quartz, soda-lime-silica glass (window glass), sodium borosilicate glass (Pyrex®), lead oxide glass (crystal glass), aluminosilicate glass, or germanium-oxide glass); and construction materials (such as brick, cement, ceramics, clay, concrete, gypsum, marble, mineral wool, mortar, stone, textiles or wood and mixtures thereof).

The base materials may be treated with an adhesion promoter to enhance the adhesion of the functional coating. Such adhesion promoters are, for instance, silanes, siloxanes, or silazanes. If plastic materials are used, it may be advantageous to perform a pretreatment by flaming, corona or plasma treatment which might improve the adhesion of the functional coating. If construction materials are used, it may be advantageous to perform a precoating with lacquers, varnishes or paints such as, for example, polyurethane lacquers, acrylic lacquers and/or dispersion paints. Use

The present invention further relates to the use of a phosphazene compound for catalyzing the curing of a silazane-containing polymer.

It is preferred that the phosphazene compound comprises at least one phosphorus atom and at least four nitrogen atoms, wherein said nitrogen atoms are bound to said phosphorus atom. It is preferred that the phosphazene compound comprises at least one N=P double bond, preferably one, two, three or four N=P double bonds.

Further preferred phosphazene compounds are defined as described above for the coating composition of the present invention. Here, especially the phosphazene compounds represented by one of the Formulae (A), (B) and (C) are particularly preferred.

The present invention is further illustrated by the examples following hereinafter which shall in no way be construed as limiting. The skilled person will acknowledge that various modifications, additions and alternations may be made to the invention without departing from the spirit and scope of the present invention.

Examples Example 1 100 g Durazane 1500 rapid cure was mixed with 0.5 g BEMP [2-tert-

Butylimino-2-diethylamino-1 ,3-dimethylperhydro-1 ,3,2-diazaphosphorine] for 2 h. Then a wet film of 10 pm thickness was applied by doctor blade coating on a glass plate. The substrate with the silazane coating was stored at ambient conditions of 25°C and 50% relative humidity. In time periods of 15 min the film was checked, if it is dry-to-touch. After 45 min the film was dry-to-touch. A reference experiment using pure Durazane 1500 rapid cure was made and the dry-to-touch time was 1 h:45min. Another reference experiment using pure Durazane 1500 rapid cure mixed with 0.5% DBU (1 ,8-diazabicyclo[5.4.0]undec-7-ene) was made and the dry-to-touch time was 60 min.

Example 2

A similar experiment was made with Durazane 1500 slow cure instead of Durazane 1500 rapid cure.

100 g Durazane 1500 slow cure was mixed with 0.5 g BEMP [2-tert- Butylimino-2-diethylamino-1 ,3-dimethylperhydro-1 ,3,2-diazaphosphorine] for 2 h. Then a wet film of 10 pm thickness was applied by doctor blade coating on a glass plate. The substrate with the silazane coating was stored at ambient conditions of 25°C and 50% relative humidity. In time periods of 15 min the film was checked, if it is dry-to-touch. After 80 min the film was dry-to-touch. A reference experiment using pure Durazane 1500 slow cure was made and the dry-to-touch time was 420m in. Another reference experiment using Durazane 1500 slow cure mixed with 0.5% DBU (1 ,8- diazabicyclo[5.4.0]undec-7-ene) was made and the dry-to-touch time was 90 min. Another reference experiment using Durazane 1500 slow cure mixed with 0.5% AI(AcAc)3 (aluminum acetylacetonate) was made and the dry-to-touch time was 210 min.

Example 3

To demonstrate the synergistic effects of phosphazenes with other curing catalysts, mixtures with titanium diisopropoxide bis(acetylacetonate) (TDI(ACAC)2 ), a well-known catalyst for siloxane curing and Durazane 1033 were tested.

Mixtures of Durazane 1033 and 0.5% Catalyst were prepared and applied by blade coating at a wet film thickness of 50 pm on a glass plate. The films were stored for 4 h and 16 h under controlled conditions of 25°C and 50% relative humidity and then the Shore A Nano hardness was measured (equipment: Shore A Nano, Q-tec GmbH Germany). As reference, the pure Durazane 1033 without any catalyst was used (see Table 1 ).

Catalyst A: 1 ,8-Diazabicyclo[5.4.0]undec-7-ene

Catalyst B: Titanium diisopropoxide bis(acetylacetonate)

Catalyst C: 2-tert-Butylimino-2-diethylamino-1 ,3-dimethylperhydro-1 ,3,2- diazaphosphorine

Table 1 : Shore A Nano hardness of Durazane 1033 films

‘material is liquid, hardness measurement is not possible Example 4 To demonstrate the faster hydrolysis rate of a silazane containing coating composition by addition of a phosphazene, the phosphazene BEMP (2 -tert- butylimino-2-diethylamino-1 ,3-dimethylperhydro-1 ,3,2-diazaphosphorine) was compared to DBU (1 ,8-diazabicyclo[5.4.0]undec-7-ene) and AI(AcAc)3 (aluminum acetylacetonate).

1 g of Durazane 1800 (available from MERCK KGaA, Germany) was mixed with 0.5 weight-% BEMP, 0.5 weight-% DBU or 0.5 weight-% AI(AcAc)3. All three mixtures were coated on a glass plate by doctor blade coating with a dry-film thickness of 10 pm and cured at ambient conditions of 25°C and 50% relative humidity for 24h. The cured films were analyzed by FT-IR to check the conversion of Si-N and Si-H bonds.

As shown in the FT-IR (see Figure 1 ), the most complete conversion of Si- N (signal at 1140-1190 cm^-1) to Si-0 (signal at 980-1080 cm^-1) was achieved by AI(AcAc)3. Flowever, AI(AcAc)3 shows only insufficient conversion of Si-H (signal at 2100-2170 cm ¹). Both, DBU and BEMP show complete conversion of Si-H. Flowever, the conversion of Si-N is higher for BEMP as for DBU.

Claims

1. A coating composition, comprising:

(i) a silazane-containing polymer; and

(ii) a phosphazene compound.

2. The coating composition according to claim 1 , wherein the

phosphazene compound comprises at least one phosphorus atom and at least four nitrogen atoms, wherein said nitrogen atoms are bound to said phosphorus atom.

3. The coating composition according to claim 1 or 2, wherein the

phosphazene compound comprises at least one N=P double bond, preferably one, two, three or four N=P double bonds.

4. The coating composition according to one or more of claims 1 to 3, wherein the phosphazene compound is represented by one of the following Formulae (A), (B) or (C):

R-[N=P(NR^laR^lb)₂]n-(NR^N2) Formula (A)

RN=P(NR'^aR'^b)3.m(N=P(NR"₂)3)m Formula (B)

[P⁺(N=P(NR"₂)3)₄]X- Formula (C) wherein in Formula (A): R represents an alkyl group having 1 to 16, carbon atoms, or R represents P⁺(NR^N2)3X , wherein X is one or more selected from F, Cl and Br;

R^la and R^lb represent at each occurrence independently from each other an alkyl group having 1 to 4 carbon atoms, or R^la and R^lb together form with the adjacent nitrogen atom a heterocyclic ring system comprising 2 to 7 carbon atoms, or both R^la together form with the adjacent nitrogen atoms a heterocyclic ring system comprising 1 to 6 carbon atoms, and R^lb represents an alkyl group having 1 to 4 carbon atoms;

R" represents an alkyl group having 1 to 4 carbon atoms, or both R" together form with the adjacent nitrogen atom a heterocyclic ring system comprising 2 to 7 carbon atoms; and

n is an integer from 1 to 10;

wherein in Formula (B): R represents an alkyl group having 1 to 16 carbon atoms;

R" represents at each occurrence independently from each other an alkyl group having 1 to 4 carbon atoms, or both R" together form with the adjacent nitrogen atom a heterocyclic ring system comprising 2 to 7 carbon atoms; and

m is 2 or 3; and

wherein in Formula (C): R" represents at each occurrence independently from each other an alkyl group having 1 to 4 carbon atoms, or both R" together form with the adjacent nitrogen atom a heterocyclic ring system comprising 2 to 7 carbon atoms; and

X is one or more selected from F, Cl and Br.

5. The coating composition according to one or more of claims 1 to 4, wherein the phosphazene compound has a molecular weight in the range from 150 to 1 ,000 g/mol.

6. The coating composition according to one or more of claims 1 to 5, wherein the silazane-containing polymer comprises a repeating unit M¹ represented by Formula (1 ):

-[SiR¹R²-NR³-] (1 ) wherein R¹, R² and R³ are the same or different from each other and independently selected from hydrogen, an organic group, a heteroorganic group, or a combination thereof.

7. The coating composition according to claim 6,

wherein the silazane-containing polymer further comprises a repeating unit M² represented by Formula (2):

8. The coating composition according to claim 6 or 7,

wherein the silazane-containing polymer further comprises a repeating unit M³ represented by Formula (3):

-[SiR⁷R⁸-0-] (3) wherein R⁷ and R⁸ are the same or different from each other and independently selected from hydrogen, an organic group, a

heteroorganic group, or a combination thereof.

9. The coating composition according to one or more of claims 1 to 8, wherein the weight ratio of the silazane-containing polymer to the phosphazene compound in the coating composition is in the range from 99.99 : 0.01 to 95.0 : 5.0.

10. The coating composition according to one or more of claims 1 to 9, wherein the composition further comprises one or more solvents and optionally one or more additives.

11. A method for preparing a coated article, wherein the method

comprises the following steps:

(a) applying a coating composition according to one or more of claims 1 to 10 to a surface of an article; and

(b) curing said coating composition to obtain a coated article.

12. A coated article, obtainable by the method according to claim 11.

13. Use of a phosphazene compound for catalyzing the curing of a

silazane-containing polymer.

14. The use according to claim 13, wherein the phosphazene compound comprises at least one phosphorus atom and at least four nitrogen atoms, wherein said nitrogen atoms are bound to said phosphorus atom.

15. The use according to claim 13 or 14, wherein the phosphazene

compound comprises at least one N=P double bond, preferably one, two, three or four N=P double bonds.