WO2017093759A1

WO2017093759A1 - Functionalisation method for metal oxide particles

Info

Publication number: WO2017093759A1
Application number: PCT/GB2016/053813
Authority: WO
Inventors: Alan Taylor; Géraldine Gabrielle DURAND; Nadia SID; Marta ÁLVAREZ TIRADO; Stephen MYCOCK
Original assignee: The Welding Institute
Priority date: 2015-12-02
Filing date: 2016-12-02
Publication date: 2017-06-08
Also published as: GB201810582D0; GB201521301D0; GB2559942A

Abstract

A method of functionalising a metal oxide substrate, having pendant hydroxyl groups wherein the substrate pendant OH groups are reacted with a functional alkoxy silane in the presence of a catalyst in an alcohol - liberating condensation reaction. The method is carried out in the absence of water and hence avoiding hydrolysis. The silane may be a trialkoxy alkyl silane, such as a silane wherein the alkyl group for subsequent reaction with resin precursor monomer. The metal oxide is for instance a particulate material. The invention minimises agglomeration and allows very high concentration suspensions to be produced and blended into other liquid products.

Description

FUNCTIONALISATION METHOD FOR METAL OXIDE PARTICLES

Field of the Invention

The present invention relates to a novel functionalization method for metal oxide particles.

Background to the Invention

Methods of functionalising metal oxide particles with silane coupling agents (silanes) are widely known, for example US2010233060A1 , Posthumus et al Journal of Colloid and Interface Science 269 (2004) 109-1 16, US2008063868A1 , Rosen & Gu Langmuir 201 1 , 27, 10507-10513, US6051672. However, these reactions involve water and are difficult to control. Side reactions can occur which result in by-products or silsesesquioxane formation (Bauer et al, Macromol. Chem. Phys. 2003, 204, 375-383). When two different silanes are present homocondensation as opposed to heterocondensation can occur which leads to a multitude of different reaction products.

Organosilsesquioxanes are silicon-oxygen based frameworks having the general formula (RSiOi_.5)_n, in which n is an even number greater than 4. These compounds are well-known and have the potential to offer good mechanical properties, for example as coatings with good abrasion resistance, and can be formulated to have good chemical resistance. These and other properties render the organosilsesquioxanes useful as protective coatings for a wide variety of substrates, particularly polymer-based materials, such as acrylic polymers and polycarbonates, which are routinely used as alternatives to glass in many situations where the weight, tendency to shatter or expense of glass contraindicates its use.

We described a novel process for the production of these compounds in our previous patent application published as WO2007/050387. The processes described therein involved controlled hydrolysis of silane monomers particularly including organofunctional trialkoxy silanes. WO'387 allowed improvement to reaction times described compared to the prior art.

Functionalising agents such as hexamethyl disilazane have also been used to treat surfaces, for instance, of metal oxides. Such reagents do not require preliminary hydrolysis to activate them, nor do they require the presence of catalyst. Furthermore monomeric silazanes with reactive substituents on organic groups linked to the silicon atoms are not available.

Summary of the Invention

The present invention relates to a method of functionalising a metal oxide substrate having pendant hydroxyl groups, wherein the pendant hydroxyl groups are reacted with an organofunctional alkoxy silane in the presence of a catalyst in an alcohol - liberating condensation reaction, wherein the reaction is non- hydrolytic, carried out in the substantial absence of water.

The present invention avoids hydrolysis by excluding water. Since hydrolysis does not take place the polymerisation of the silanes and other side reactions are avoided. Instead the hydroxyl groups on the metal oxide particles are forced to react avoiding potential side reactions involving silsesquioxane formation.

The method defined herein allows inorganic particles to be produced that have properties allowing incorporation into organic resin compositions in higher amounts than in the prior art. This advantageously improves certain characteristics such as durability of articles or coatings formed from the resin compositions. The resin compositions are less viscous than those of the prior art, which allows them to be processed more easily.

The present invention additionally allows different functionalities to be introduced onto the metal oxide particles. Accordingly, the present invention also provides a metal oxide substrate comprising a multiplicity of pendant siloxane substituents of general formula: I I

I I I I I I

/ / / / / / / /

wherein R^A and R^B are different and are independently selected from alkyl, alkenyl, and alkynyl, optionally substituted by one or more groups, preferably one group, selected from halide, amido, epoxy, acrylate, methacrylate, styrene, anhydride, ester, phosphino, amino, aryl, mercapto, cyanate and mixtures thereof; and / / / represents the metal oxide substrate. Preferably R^A and R^B are different and are independently selected from alkyl, alkenyl, and alkynyl, optionally substituted by one or more groups, preferably one group, selected from acrylate, methacrylate, epoxy, halide, cyanate, aryl and mercapto.

Detailed Description of the Invention

The present invention is a method of functionalising a metal oxide substrate.

By "functionalising" is meant introducing an organic R group. The R groups are introduced by reacting the metal oxide substrate with an organofunctional alkoxysilane. The organofunctional alkoxysilane has at least one pendant organic group R which introduces the functionality.

The method of this invention is substantially non-hydrolytic. By this is meant that there is little or no water present in the reaction medium. Steps are taken to exclude water, by, for instance, use of starting metal oxides that are available in water-free form, or by synthesising oxides in a preliminary step that is water-free. More importantly the functionalisation reaction does not utilise water to take place. The reaction takes place in a solvent which is not water. The solvent is preferably selected from alcohols, ethers, acetates, tetrahydrofuran, hydrocarbons and mineral spirits.

The process is carried out in the presence of a suitable catalyst. The catalyst is of the type used for transesterification. Suitable catalysts include:

(i) tin-based catalysts, preferably dibutyl tin dilaurate or tin (II) octanate;

(ii) phosphate based catalysts, preferably an alkyl acid phosphate catalyst;

(iii) sulphonic acid catalysts.

The reaction sequence is analogous to the catalysed condensation reactions widely practiced in the preparation of room temperature vulcanising silicone rubbers, of which an example reaction sequence is shown below. Catalysts suited for such condensation reactions are used in the present invention: O

I

1

R— ^■Si— ^■R

1

R OR' R O R

1 1 [Sn] 1 1 1

¹— Si— OH + R'O— Si— OR'—► -0— -Si- — o— ^■Si— -o— -Si

I I 1 1

1 1 1 1

R OR' R O R

1

Polymer Silicic acid crosslinker 1

R— ^■Si— ^■R

1

O

The substrate is preferably in the form of metal oxide particles. The particles may for instance have a diameter in the range 10-1000nm. The particles preferably exist as primary particles with little or no agglomeration or aggregation. Commercially available metal oxide particles may agglomerate and form larger particles, in which case they are preferably broken down before further reaction in the process of the present invention.

The organofunctional alkoxy silane may have general formula R₍₄-n₎(OR¹)_nSi wherein n is 1 -3, R is the organofunctional ligand and typically consists of an Ci_-6, preferably C_1-3 alkyl linker group and a terminal atom or organic group which provides the functionality.

Suitable examples of group R¹ include methyl, ethyl and propyl.

Examples of the group R include (cyclo)alkyl, alkenyl and alkynyl, optionally substituted with one or more groups selected from halide, amido, epoxy, methacrylate, styrene, anhydride, ester, phosphino, amino, aryl, mercapto and cyanate groups, and mixtures thereof. Preferred R groups are selected from (cyclo)alkyl and alkenyl groups, optionally substituted with one or more groups, preferably one group, selected from epoxy, vinyl, methacrylate, mercapto, aryl and cyanate groups.

n is preferably 3.

The reaction preferably takes place according to the following reaction scheme:

+ m HO-R¹

wherein A is a metal oxide particle.

The metal oxide may be selected from silica, alumina, titania, ITO, AZO, ZnO, and Al₂0₃-Si0₂. As mentioned above, the metal oxide should be provided in a water-free form. Suitable starting materials in particulate form are available as pyrogenic materials but require suspending in an suitable water free, organic vehicle.

Preferably, the metal oxide is silica.

Silica particles may be formed by pyrogenic methods or via solution methods such as according to the following reaction:

R²OH

Si (OEt)₄ + 2H₂O [sj I— |₄QI— I ^Si02 ^{+ 4Et0H} wherein Et is ethyl and R² is lower alkyl, for instance Ci_-6 alkyl, preferably ethyl. This reaction scheme advantageously avoids agglomeration of the particles as mentioned above.

The process of the present invention may involve the use of a single type of organofunctional alkoxy silane, having the formula RSi(OR¹)₃. Alternatively, two or more different organofunctional alkoxy silanes may be used, for instance differing in the nature and/or number of organic groups R and/or the nature and/or number of the alkoxy groups OR¹.

Other reactives such as silazanes may be included in addition to the functional alkoxy silane(s) for instance to increase hydrophobicity and hence water repellence. These silazanes can be used in combination with the organofunctional alkoxy silane to develop dually functionalised metal oxides.

By way of example, a mixture of functional alkoxy silanes may be used having different R groups. Preferably, two or more organofunctional alkoxy silanes used in combination are each trialkoxy silanes, such as R^ASi(OR¹)₃, R^BSi(OR⁴)₃, etc., the R^A and R^B groups being selected from the groups defined above for R to provide particular mechanical and/or chemical properties in the final product. In this regard, the present invention is not limited to the use of two different types of organofunctional alkoxysilane, but may involve the use of more than two different types of the organofunctional alkoxy silane, provided that adequate control over the process is maintained so as to achieve the desired level of incorporation of the different R groups into the final product.

It is believed that this is the first time that anybody has successfully reacted organofunctional alkoxy silanes having two different R groups (R^A and R^B) with metal oxide particles. In prior art processes wherein silanes are hydrolysed to react the generation of hydroxyl groups on the silicon atom of the silane leads to competitive hydrolysis, condensation of silanes and silsesquioxane formation. The polymer chains can bridge between particles leading to uncontrolled agglomeration. In the present invention by contrast, reaction with the metal oxide particles is not overly influenced by the nature of the R group and so a particulate substrate retains its structure and primary physical characteristics.

Two successive reactions with different organofunctional alkoxy silanes may be carried out to produce first and second generation functionalised metal oxide particles. For instance, metal oxide particles may be functionalised with a first organofunctional alkoxy silane to produce a first generation functionalised metal oxide substrate. The pendant R groups on the functionalised metal oxide particles may then be reacted in a subsequent reaction with another organofunctional alkoxy silane, with a different R group, to produce a second generation functionalised metal oxide substrate.

By way of example, first organofunctional alkoxy silane may have an R group including an epoxy functionality, and these may react with amine groups of a second organofunctional alkoxy silane to produce the second generation substrate.

As mentioned above, and in addition or alternatively to the use of first organofunctional alkoxy silanes having different R and/or OR¹ group, the process may involve the use of organofunctional alkoxy silane, differing in the number of groups OR¹. In particular, organofunctional alkoxy silanes having the general formula R⁶ _4-nSi(OR⁵)_n, in which n is 1 , 2 or 3, preferably n is 3, R⁶ is an organic group, for instance selected from those groups given for R above, and the R⁶ groups are the same or different to one another, and the R⁵ groups are the same or different to one another and the same or different to R¹ of the first organofunctional alkoxy silane, and mixtures of such monomer precursors, may be used in addition to the first organofunctional alkoxy silane, RSi(OR¹)₃. In the following, these additional silanes are termed "second organofunctional alkoxy silane".

In addition, or alternatively, the process may involve the use of organofunctional alkoxy silanes having fewer OR¹ groups than the first organofunctional alkoxy silanes but the same R group, for instance having a formula selected from R₂Si(OR¹)₂ (n=2) and R₃SiOR¹ (n=3), and mixtures thereof.

In the context of any of the second organofunctional alkoxy silanes mentioned above, the groups R⁶ and R⁵ are as defined above for R and R¹ , respectively of the first organofunctional alkoxy silane. For clarity, however, the groups R⁶ and/or R⁵ in the second organofunctional alkoxy silanes may be the same as or different to the groups R and/or R¹ in the first organofunctional alkoxy.

Suitable examples of first organofunctional alkoxy silane and second organofunctional alkoxy silanes include:

(i) (alkyl)alkoxysilanes such as Ci_-6 alkyl-trimethoxysilanes, -tri- ethoxysilanes, -tri-isoproxysilanes, -tri-n-propoxysilanes, and -tributoxysilanes, dialkyl-dimethoxysilanes, -di-ethoxysilanes, -di-iso-propoxysilanes, -di-n-propoxy- silanes and -di-butoxysilanes, and tri-Ci_-6alkyl-monomethoxysilanes, monoethoxysilanes, and -monobutoxysilanes, for instance selected from methyltrimethoxysilane, ethyltriethoxy-silane, n-propyltri-n-propoxysilane, butyltnbutoxysilane, dimethyldimethoxysilane, diethyldiethoxysilane, di-iso-propyl- di-iso-propoxysilane, dibutyldibutoxysilane, tri-methylmethoxysilane, triethylethoxysilane, tri-n-propyl-n-propoxysilane, and tributylbutoxysilane, or phenyltriCi-₄alkoxysilane such as phenyltrimethoxy-silane, diphenyldiethoxysilane or triphenylalkoxysilane, such as triphenylmethoxysilane;

(ii) (alkyl)alkoxysilanes having an isocyanato group such as 3- isocyanatopropyltrimethoxysilane, 3-isocyanatopropyl-triethoxysilane, 3- isocyanatopropylmethyldimethoxysilane, 3-isocyanatopropylethyldiethoxysilane, 3- isocyanatopropyl-dimethyl-iso-propoxysilane, 3-isocyanatopropyldiethyl- ethoxysilane, 2-isocyanatoethyldiethylbutoxysilane, di(3- isocyanatopropyl)diethoxysilane, di(3-isocyanatopropyl)-methylethoxysilane, and ethoxytriisocyanatosilane;

(iii) (alkyl)alkoxysilanes having an epoxy group such as 3- glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltri-ethoxysilane, 3- glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethydiethoxysilane, 3- glycidoxypropyldi-methyl ethoxysilane,2-(3,4-epoxycyclohexyl)ethyltrimethoxy- silane, and 3,4-epoxybutyltrimethoxysilane;

(iv) (alkyl)alkoxysilanes having a carboxyl group such as carboxymethyltriethoxysilane and carboxymethylethyldi-ethoxysilane;

(v) alkoxysilanes having an acid anhydride group such as 3- (triethoxysilyl)-2-methpropylsuccinic anhydride;

(vi) (alkyl)alkoxysilanes having an acid halide group such as 2-(4- chlorosulphonylphenyl)ethyltriethoxysilane;

(vii) (alkyl)alkoxysilanes having an amino group such as N-2-(aminoethyl)-3- aminopropyltriethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane, and N-phenyl-3-aminopropyltrimethoxysilane;

(viii) (alkyl)alkoxysilanes having a thiol group such as 3-mercaptopropyl- trimethoxy-silane, 3-mercaptopropyltri-ethoxysilane, 2- mercaptoethyltriethoxysilane, and 3-mercaptopropylmethyldimenthoxysilane;

(ix) (alkyl)alkoxysilanes having a vinyl group such as vinyltrimethoxysilane, vinyltriethoxysilane, and vinyl-methyldiethoxysilane;

(x) (alkyl)alkoxysilanes having an acrylate or methacrylate group such as 3- methacryloxy-propyltrimethoxysilane, 3-methacryloxyproply-triethoxysilane, 3- methacryloxypropylmethyldimethyl-silane and 3-acryloxypropyltriethoxysilane;

(xi) (alkyl)alkoxysilanes having a halogen atom such as triethoxyfluorosilane, 3-chloropropyltrimethoxysilane, 3-bromoalkylalkoxysilane, and 2-chloroethylmethyldimethoxy-silane;

(xii) (alkyl)alkoxysilanes having an halogenated alkyl ligand such as (3,3,3- trifluoropropyl)trimethoxysilane and 1 H, 1 H,2H,2H-perfluorodecyltriethoxysilane; and

(xiii) (alkyl)alkoxysilanes employing an alkoxy group as a functional group such as isopropyltri-isopropoxysilane and tri-isopropylisopropoxysilane.

In the above compounds the alkyl group may be replaced by cycloalkyl group or an alkenyl group, and may optionally be substituted preferably with a (meth)acrylate group or an epoxy group.

The present reaction is carried out in the presence of a solvent which is not water. Organofunctional alkoxysilane is added to metal oxide particles in said solvent and a suitable catalyst is added. The reaction is carried out for around 18 hours at a temperature of around 65°C. Solvent is then removed. The product can be characterised by weighing, NMR and microscopy, e.g. TEM. Determination of the non-volatile content of the product shows that surface functionalisation has taken place. Determination of the particle size allows assessment of bridging between particles. If there is no change in particle size then silsesquioxane formation can be assumed not to have taken place. Contact angles and surface energy can be calculated to further characterise the product.

The selection of reactive functional groups R is made according to which resin compositions the products are intended to be incorporated. For instance,

(i) groups R comprising acrylate groups render the functionalised metal oxide suitable for incorporation into a resin that is acrylate resin; or

(ii) groups R comprising epoxy groups make the product suitable for epoxy resins; or

(iii) groups R comprising mercapto groups make the product suitable for an acrylate resin.

The hydrophilic/hydrophobic character of the R groups(s) will determine the behaviour of the final product when exposed to water. This behaviour can be modified by appropriate selection of solvent in the reaction with silane. For example, the tendency towards the repulsion of water of an aliphatic hydrocarbon R can be changed by the use of a protic solvent, such as alcohol, compared to an aprotic one, such as tetrahydrofuran.

The product is then ready for use, for instance as or in a coating composition, or in bulk form, or it may be further modified prior to use. For instance, the product may be cross-linked (or cured) and/or modified to include further organic character and/or dehydrated. Solvent may be added to the composition, to improve shelf-life.

The invention allows production of particulate functionalised metal oxide having desirable suspension and redispersion properties. It is found that the primary particles remain of substantially the same size when particle size is determined, e.g. by dynamic light scattering and agglomeration is avoided. The particles may be covered and redispersed into solvent at will, returning low viscosity non-agglomerated characteristics. The R groups introduce points of chemical reactivity. When water is present in the system, as in the prior art, unintended reactions may occur with the R groups. For example, when isocyanate silanes are hydrolysed there is a competing reaction between the alkoxy groups and the isocyanate groups for the water. The greater hydrolysis rate of the R group compared to the (OR¹) group results in loss of the isocyanate reactivity. This is avoided in the present invention.

Cross-linking, or curing, of the product may be achieved through the pendent organic R groups.

Cross-linking of the organic groups R may be achieved by any of the conventional means, for instance by the use of suitable cross-linking reagents or processing conditions, or both. For example, epoxy-containing R groups may be cross-linked, or further polymerised, using reagents which act as accelerators or hardeners, for instance amines, or using Lewis acids.

The properties of a final resin product incorporating the functional metal oxide may be further adjusted through the use of additives conventional in the art.

The present invention can be used to incorporate metal oxides into organic resin compositions, i.e. compositions containing resins or resin precursors, such as monomers, oligomers or polymers. Such compositions form a further aspect of the invention. Such resin compositions have been found to have a lower viscosity compared to the prior art. The present invention can also be used to provide the following properties: fire resistance, surface finish, hardness, low energy surfaces, anti-graffiti surfaces, corrosion resistance and barrier properties. When the R groups are epoxy groups, for instance, the functionalised metal oxide particles can be incorporated into an epoxy resin. Such compatibility allows higher concentration of metal oxide particles to be incorporated. When more of the metal oxide particle is incorporated in this manner these properties are improved, e.g. a higher fire resistance is expected with higher amounts of metal oxide particles.

The composition of the invention may be a coating composition and may be applied to a substrate by any conventional means, for example dipping, spraying, roll coating or brushing. The composition may be applied to a wide variety of substrates, and is particularly suitable for coating polymeric substrate materials having relatively low melting points, for example of 150°C or lower. Examples of such polymeric substrate materials include thermoplastic materials and thermosetting materials such as polycarbonates, polyesters such as polyacrylates and polyterephthalates, polyurethanes, and polyacrylics. The enhanced scratch/abrasion and chemical resistance imparted to these materials by way of the coatings of the present invention allows them to be considerably more widely utilised than they are at present.

A coating composition according to the invention may also be used to coat substrates selected from glass, metals including soft metals such as aluminium, brass and silver, ceramic materials, and natural materials such as leather and wood, or synthetic substitutes for these materials. It finds particular use as a coating for glass, and glass substitutes. For example, it may be used to coat building or vehicle, windows and windscreens, e.g. for automobile, aircraft and trains; spectacle lenses; camera lenses; protective visors; optical filters and light casings, e.g. headlamp clusters; compact discs; display screens, e.g. in personal computers and mobile phones; and to protect white goods, e.g. refrigerators and washing machines, and brown goods e.g. audiovisual equipment.

The resin compositions may also be used to produce materials which find use as bulk materials rather than as coatings. In this case, the composition material may be shaped, for instance by moulding, or otherwise formed into a wide variety of different articles.

When used to form a bulk article, the functionalised metal oxide nanoparticles are incorporated into an organic resin composition using conventional mixing methods. The resin is then processed according to standard methods, e.g. casting. It finds particular use in the production of transparent glazing for automotive or aerospace applications when incorporated into castable polymers such as acrylic or aliphatic polycarbonate prior to the polymerisation step and subsequently participating in the network formation during polymerisation. Incorporation of the functionalised metal oxide nanoparticles improves abrasion resistance, solvent resistance. Transparency of the glazing is not compromised if the metal oxide nanoparticles remain below about 80nm in diameter.

Other examples of bulk articles include films such as polyimide or polyester whose barrier properties are improved by the incorporation of appropriate functionalised metal oxide particles which chemically bind into the organic matrix.

Furthermore, incorporation of the functionalised metal oxide particles into the organic matrix of fibre composite can yield performance enhancements. When epoxy functionalised silica particles are incorporated into an epoxy resin composition which is then subsequently used in a fibre reinforced matrix, an improvement in hardness and stiffness results as does an enhancement of the thermal properties, specifically a retardation of the thermal degradation.

The invention allows production of metal oxide particles having dual functionality, e.g. having an R group capable of cross-linking into a bulk organic matrix and a water- or other liquid-repellent R group. The surface of a coating or bulk material containing the functionalised metal oxide particles can demonstrate very high levels of repellence towards water or even other liquids.

In the examples below illustrate the present invention and the properties ascertained. The measurement methods used are described below:

Analytical Methods

pH - The pH of the metal oxide nanoparticle suspensions were measured using a pH meter 24 hours after the completion of the preparation step.

The non-volatile content (NVC) was determined gravimetrically, an aliquot of the suspension was weighed in a glass bottle. The sample was then heated in air in an oven at 65 °C for at least 18 hours or until no further weight loss was measured. The weight of the residual material is then expressed as a percentage of the weight of the original aliquot after accounting for the weight of the glass bottle.

The silica content was determined gravimetrically using a Netzsch STA 449 F3 simultaneous thermal analyser. The nanoparticle suspension was dried at 65°C for at least 18 hours or until no further weight loss was measured. The solid residue was then loaded into the STA 449 and heated in a flowing air atmosphere at l O /min to Ι ΟΟΟ . All samples exhibited an initial weight loss due to trapped volatiles, weight losses varied between 3-5% of the initial sample weight. All volatile related losses were completed by ~\ 50°C. The sample weight at Ι ΟΟΟ as a percentage of the sample weight at 150°C was defined as the silica content.

The size of the nanoparticles in suspension was measured using a Malvern Instrument Nanosizer. Data on the particle size as a function of intensity, number and volume was recorded. The derivative Z_average term was used to compare the different particles.

The hydrophobicity of the metal oxide nanoparticles was measured using a Kruss DSA100. The nanoparticles were deposited onto a borosilicate glass slide by dipping the slide into the prepared suspension and then withdrawing at 100mm/min. The coated slide was dried at ~\ 50 °C for one hour in air, allowed to cool and the water contact angle was measured using distilled water in the DSA100. The reported water contact angle (WCA) value is the average of at least three separate water drops per sample.

The viscosity of nanoparticle / resin mixtures was measured using a Brookfield viscometer.

Example 1

Metal oxide nanoparticle synthesis - TSS4

In vessel A, 84. Og of tetrethoxysilane and 150.0g of industrial methylated spirit where thoroughly mixed together. In a separate container, vessel B, 375.0g of industrial methylated spirit, 12.0g of 25% ammonium hydroxide and 15.0g of deionised water were thoroughly mixed. The contents of vessel A were slowly added to vessel B to ensure homogenous mixing.

The mixture was then heated at 65°C for 3 hrs, the ammonia was then removed by evaporation. In a rotorvap chamber 60% (by weight) of the volatiles were removed and replaced with fresh industrial methylated spirit. To ensure no residual ammonia this step was repeated

Example 2

Metal oxide nanoparticle synthesis - TSS5

In vessel A, 29. Og of tetrethoxysilane and 150.0g of industrial methylated spirit where thoroughly mixed together. In a separate container, vessel B, 350g of industrial methylated spirit, 22.5g of 25% ammonium hydroxide and 77. Og of deionised water were thoroughly mixed. The contents of vessel A were slowly added to vessel B to ensure homogenous mixing.

The mixture was then heated at 65°C for 3 hrs, the ammonia was then removed by evaporation. In a rotorvap chamber 60% (by weight) of the volatiles were removed and replaced with fresh industrial methylated spirit. To ensure no residual ammonia this step was repeated.

The properties of the nanoparticles produced in examples 1 and 2 are given in table 1 , below.

Example 3

Preparation of single functionalised metal oxide nanoparticles

To prepare functionalised nanoparticles a series of mixtures were prepared. These preparations were mixtures of a an organofunctional alkoxy silane, one of the metal oxide suspensions prepared in examples 1 and 2 and, optionally, dibutyltin dilaurate (DBTL) as catalyst. Each mixture was heated for 18hours at 65°C under reflux. The details of each experiment are given in Table 2, below.

Where:

NPTMS - N-propyltrimethoxysilane

MPTMS - Methacryloxypropyl trimethoxysilane

HMDS - Hexamethyldisilazane

FAS - 1 H,1 H,2H,2H-Perfluorooctyltriethoxysilane

GPTS - 3-Glycidoxypropyltrimethoxysilane

VTMS - Vinyltrimethoxysilane

INV - According to the invention

REF - Reference

The properties of these nanoparticles are given in table 3, below.

Comparing the results of 3.1 (no catalyst) and 3.5, which use the same silane, it may be seen that the presence of catalyst is important for achieving changes in non-volatile content (i.e. weight increase due to derivatisation) and water contact angle. This particle size is still low for the product of the invention indicating little agglomeration/aggregation of the particles and so a retention of the primary particle character. Other R groups impact the water contact angle, hydrophobic groups, giving high water contact angles which are expected to lead to good water repellency (example 3.6 in particular). The level of silane and catalyst affects the extent of functionalization as shown by the results of examples 3.2 and 3.3. Example 4

Preparation of dual functionalised metal oxide particles using trialkoxysilanes

To prepare dual functional nanoparticles using a series of mixtures of organofunctional trialkoxysilanes were prepared. These preparations were mixtures of the metal oxide suspension prepared in example 1 , together with n- propyltrimethoxysilane and methacryloxypropyl trimethoxysilane and dibutyltin dilaurate. In the first preparation, a reaction vessel was charged with 186.5g of the TSS4 suspension as produced in example 1 , 4.0g n-propyltrimethoxsilane and 0.49g of dibutyltin dilaurate. This mixture was heated for 18hours at 65°C under reflux and then 4.0g of methacryloxypropyl trimethoxysilane was added and the mixture was heated for 18hours at 65°C under reflux.

In the second preparation, a reaction vessel was charged with 186.5g of the TSS4 suspension as produced in example 1 , 4.0g methacryloxypropyl trimethoxysilane and 0.49g of dibutyltin dilaurate. This mixture was heated for 18hours at 65 °C under reflux and then 4.0g of n-propyltrimethoxysilane was added and the mixture was heated for 18hours at 65 °C under reflux.

In the third preparation, a reaction vessel was charged with 186.5g of the TSS4 suspension as produced in example 1 , 4.0g methacryloxypropyl trimethoxysilane, 4.0g of n-propyltrimethoxysilane and 0.49g of dibutyltin dilaurate. This mixture was heated for 18hours at 65°C under reflux.

The details of each experiment are given in Table 4, below.

The properties of these nanoparticles are given in Table 5, below.

These results show that for silanes having the same OR¹ groups and the same number of such groups per molecule in the first and second silane, and where the R groups are lower alkyl and methacyloyloxy substituted alkyl, respectively, it makes little difference to the products in terms of particle size and water-contact angle, whether the silanes are reacted sequentially, and in which order, or whether they are reacted in admixture. The WCA values are similar to those of the single reagent MPTMS (example 3.2) i.e. the surface is not particularly water-repellent.

Example 5

Preparation of dual functionalised metal oxide particles using different functionalisation agents

To prepare dual functional nanoparticles using different functionalisation agents a series of mixtures were prepared. A reaction vessel was charged with 186.5g of the TSS4 suspension as produced in example 1 , methacryloxypropyl trimethoxysilane and dibutyltin dilaurate. This mixture was heated for 18hours at 65°C under reflux and then hexamethyldisilazane was added and the mixture was heated for 18hours at 65°C under reflux, the evolved ammonia was then removed by evaporation. In a rotorvap chamber 60% (by weight) of the volatiles were removed and replaced with fresh industrial methylated spirit. To ensure no residual ammonia this step was repeated.

The details of each experiment are given in Table 6, below.

The properties of these nanoparticles are given in table 7, below.

Example Appearance pH NVC Si0₂ DLS WCA age

(%) content ^aver

(°)

(nm)

(%)

5.1 Single phase Translucent, 7.64 6.82 68.64 50.2 43.5 liquid blue haze

5.2 Single phase Translucent, 7.6 5.63 74.12 47.9 106.1 liquid blue haze

5.3 Single phase Translucent, 7.8 4.89 79.39 48.3 88.8 liquid blue haze The results show that higher levels of functionalised metal oxide product are produced where higher ratio of organofunctional alkoxy silane to disilazane is used (higher NVC values for 5.1 vs 5.3). All products produce non-agglomerated particulate product.

Example 6

Preparation of functionalised metal oxide particles using aminofunctional trialkoxysilanes

To prepare amino-functionalised nanoparticles a series of mixtures were prepared. These preparations were mixtures of the metal oxide suspension prepared in example 1 , together with aminopropyltriethoxysilane (APTEOS) and dibutyltin dilaurate as catalyst. Each mixture was heated for 18hours at 65°C under reflux, the evolved ammonia was then removed by evaporation. In a rotorvap chamber 60% (by weight) of the volatiles were removed and replaced with fresh industrial methylated spirit. To ensure no residual ammonia this step was repeated.

The details of each preparation are given in Table 8, below.

The characteristics of the resultant materials of these preparations are given in Table 9, below.

This example indicates that the amine group on the organofunctional silane has a significant impact on agglomeration and aggregation of the particles. This is well known to those practiced in the art. The lack of water and, consequentially, hydrolysis of the alkoxy groups is seen to have little impact on the ability of the aminosilanes to promote particle-particle interaction.

Example 7

Preparation of functionalised metal oxide particles using aminofunctional trialkoxysilanes and silazane

To prepare dual functional nanoparticles using different functionalisation agents (i.e. organofunctional alkoxy silanes) a series of mixtures were prepared. These preparations were mixtures of the metal oxide suspension prepared in example 1 , together with aminopropyltriethoxysilane, hexamethyldisilazane and dibutyltin dilaurate.

In the first preparation, a reaction vessel was charged with 186.5g of the TSS4 suspension as produced in example 1 and 6.0g of hexamethyldisilazane. This mixture was heated for 18hours at 65°C under reflux, the evolved ammonia was then removed by evaporation. In a rotorvap chamber 60% (by weight) of the volatiles were removed and replaced with fresh industrial methylated spirit. To ensure no residual ammonia this step was repeated. To this mixture 2.0g of aminopropyltriethoxysilane and 0.46g of dibutyltin dilaurate, as catalyst, were added. This mixture was heated for 18hours at 65°C under reflux.

In the second preparation, a reaction vessel was charged with 186.5g of the

TSS4 suspension as produced in example 1 and 2.0g of aminopropyltriethoxysilane and 0.46g of dibutyltin dilaurate. This mixture was heated for 18hours at 65°C under reflux. To this mixture 6.0g of hexamethyldisilazane was added and this mixture was heated for 18hours at 65°C under reflux, the evolved ammonia was then removed by evaporation. In a rotorvap chamber 60% (by weight) of the volatiles were removed and replaced with fresh industrial methylated spirit. To ensure no residual ammonia this step was repeated.

In the third preparation, a reaction vessel was charged with 186.5g of the TSS4 suspension as produced in example 1 , 6.0g of hexamethyldisilazane, 2.0g of aminopropyltriethoxysilane and 0.46g of dibutyltin dilaurate. This mixture was heated for 18hours at 65°C under reflux, the evolved ammonia was then removed by evaporation. In a rotorvap chamber 60% (by weight) of the volatiles were removed and replaced with fresh industrial methylated spirit. To ensure no residual ammonia this step was repeated. The details of each preparation are given in Table 10, below.

The characteristics of the resultant materials of these preparations are given in Table 1 1 , below.

The preliminary reaction of metal oxide with disilazane provides some improvement compared to example 6 for subsequent functionalization by amino functional silane, indicating a reduction in the availability of surface silanols which can be used to bridge between particles to enable agglomeration. Example 7.3 indicates that the silazane reacts more rapidly that the aminosilane, but unless full coverage is achieved the residual silanols can still allow undesirable particle- particle aggregation.

Example 8

Primary particle character retention after solvent removal and re-dilution

The nanoparticles prepared in examples 1 , 3.2 and 3.5 were treated in a rotorvap to remove the solvent and volatiles. The NVC of the residual syrup like liquid was determined and the syrup was then diluted using industrial methylated spirit or tetrahydrofuran to its original concentration. After mixing and stirring to ensure dispersion, the reconstituted suspensions were visually examined, the NVC of the liquid portion of the preparation determined and the particle size measured. The results of these tests are given in Table 12, below. Example Nanoparticle NVC post Appearance after NVC of liquid DLS

preparation solvent re-dilution phase Zaverage (ΠΓΠ) after dilution

method removal

8.1 Example 1 52.1 Two phases, 0.08 17.34

REF precipitated solid

and transparent

liquid

8.2 Example 3.2 50.2 Single liquid 7.49 24.37

INV phase

8.3 Example 3.5 51 .7 Single liquid 7.36 34.38

INV phase

These results show that the functionalised metal oxide particle suspension produced in the invention may be concentrated or diluted, while remaining stable and handlable.

Example 9

Incorporation of nanoparticles into an organic acrylate resin

The nanoparticles prepared in examples 1 and 3.2 and a commercially available fumed silica (A200 from Evonik Industries) were incorporated into an acrylate organic resin composition (SR494 from Sartomer)

The viscosity of various formulations with different loading levels of the nanoparticles is given in Table 13, below.

Nanoparticle loading Example 9.1 Example 9.2 Comparative level by weight (%) example 9.3

Nanoparticles from Nanoparticles from Aerosil

Example 1 (REF) Example 3.2 (INV)

0 280 280 280

0.5 234 - 356

1 244 - 399

2 254 - 959

5 382 - 147600

7.5 1010 - 1729000

8.0 2500 738 -

10 55740 748 -

25 1202

50 1864

75 2048

Very high concentrations of particles produced in the invention can be produced that have viscosities allowing easy handling.

Example 10

Incorporation of nanoparticles into an organic epoxy resin

The nanoparticles prepared in examples 1 and 3.7 and a commercially available fumed silica (A200 from Evonik Industries) were incorporated into an epoxy organic resin composition (3,4-epoxycyclohexylmethyl 3,4 epoxycyclohexanecarboxylate from Sigma Aldrich)

The viscosity of various formulations with different loading levels of the nanoparticles is given in Table 14, below. Nanoparticle loading Example 9.1 Example 9.2 Comparative level by weight (%) REF INV example 9.3

Nanoparticles Nanoparticles from Aerosil from Example 1 Example 3.7

0 384 384 384

1 406 410 666

2 408 421 918

5 623 589 2150

7.5 685 689 4060

10 781 758 1 1500

20 48850 1009 1000000

The resin compositions containing functionalised metal oxide produced by the present invention at high levels are of a viscosity allowing easy handling.

Example 1 1

Solvent removal from functionalised nanoparticle suspension prior to mixing with organic resins.

The nanoparticles prepared in example 3.2.5 were treated in a rotorvap to remove the solvent and volatiles. The NVC of the residual syrup was 70.5%, this syrup was then added to the acrylate formulation described in example 9 to give a nanoparticle loading level of 75% by weight. The resulting mixture was a transparent single phase liquid. This shows that production of useful compositions with high particulate solids loadings is easy and convenient.

Claims

1 . A method of functionalising a metal oxide substrate, having pendant hydroxyl groups wherein the substrate pendant OH groups are reacted with organofunctional alkoxy silanes in the presence of a catalyst in an alcohol - liberating condensation reaction, wherein the reaction is non-hydrolytic, carried out in the substantial absence of water.

2. A method according to claim 1 , wherein the substrate is in the form of metal oxide particles, preferably having a Z-average diameter by DLS in the range 10-

1000nm.

3. A method according to claim 1 or claim 2, wherein the silane includes an organofunctional trialkoxysilane.

4. A method according to any of claims 1 -3, wherein the organofunctional alkoxysilane has general formula R₍₄-n₎(OR¹)_nSi wherein n is 1 -3, R¹ is alkyl and R is a group selected from alkyl, alkenyl and alkynyl, optionally substituted with one or more groups selected from amido, methacrylate, styrene, epoxy, anhydride, ester, phosphino, amino, halide, cyanate, aryl, mercapto, and mixtures thereof.

5. A method according to claim 4, wherein R is selected from alkyl, haloalkyl and alkoxylated alkyl groups and is preferably selected from methyl, ethyl, octyl, octadecyl, phenyl and tri-fluropropyl.

6. A method according to claim 4, wherein R is selected from ligands which contain methacrylate, epoxy, mercapto, amino, vinyl, isocyanate functionalities.

7. A method according to claim 4, wherein each R¹ is the same and is Ci_-4 alkyl, preferably ethyl.

8. A method according to any preceding claim, wherein the metal oxide is selected from silica, alumina, titania, ITO, AZO, ZnO, and AI₂O₃-SiO₂, preferably silica.

9. A method according to any preceding claim, wherein the catalyst is selected from:

(i) tin-based catalysts, preferably dibutyl tin dilaurate or tin (II) octanoate;

(ii) phosphate based catalysts, preferably an alkyl acid phosphate catalyst;

(iii) sulphonic acid catalysts.

10. A method according to any preceding claim, wherein the reaction is carried out in the presence of a solvent selected from alcohols, ethers, acetates, tetrahydrofuran, hydrocarbons and mineral spirits.

1 1 . A method according to any preceding claim according to the following scheme:

+ m HO-R¹

wherein A represents a metal oxide particle.

12. A method according to any preceding claim, wherein the pendant OH groups are reacted with two or more different organofunctional alkoxy silanes, preferably each silane having the formula defined in claim 4.

13. A method according to claim 12, wherein first and second organofunctional alkoxy silanes are reacted with the metal oxide in sequential steps.

14. A method according to any preceding claim, wherein the metal oxide is in the form of silica particles, which are formed in a preliminary step according to the following reaction: R²OH

Si (OEt)₄ + 2H₂O [sj I— |₄QI— I ^Si02 ^{+ 4Et0H} wherein Et is ethyl and R² is C_1-4 alkyl.

15. A method according to any preceding claim comprising a subsequent step of reacting the R group with a coreactive group on a resin molecule or precursor thereof.

16. A functionalised metal oxide substrate obtainable by the method according to any preceding claim.

17. A metal oxide substrate comprising a multiplicity of siloxane bonds of general formula:

wherein R^A and R^B are different and are independently selected from alkyl, alkenyl, and alkynyl, optionally substituted by one or more groups selected from acrylate, methacrylate, epoxy, halide, cyanate, aryl, mercapto, amido, styrene, anhydride, ester, phosphino, amino, and mixtures thereof.

18. A particulate functionalised metal oxide having the formula

+ m HO-R¹

wherein A is a metal oxide particle, R¹ is alkyl, and the or each R is a group selected from alkyl, alkenyl, alkynyl, optionally substituted by one or more groups selected from halide, amido, epoxy, methacrylate, styrene, anhydride, ester, phosphino, amino, aryl, mercapto, cyanate, and mixtures thereof.

19. A composition comprising the particulate functionalised metal oxide of claim 18, or the functionalised metal oxide substrate of claim 16 or claim 17 in suspension in a liquid.

20. A composition according to claim 19, further comprising resin or resin precursor co-reactive with the group R, R^A and/or R^B, as the case may be, on the functionalised metal oxide.

A composition according to claim 20, wherein:

(i) groups R, R^A or R^B comprise acrylate groups and the resin is an acrylate resin; or

(ii) groups R, R^A or R^B comprise epoxy groups and the resin is an epoxy resin; or

(iii) groups R, R^A or R^B comprise mercapto groups and the resin is an acrylate resin.

22. A method of coating a product comprising coating the composition of any of claims 19-21 onto the product.

23. A method according to claim 22, wherein the product is aluminium glass, composite, textile, wood, titanium, steel or stainless steel.

24. A method of:

(i) improving abrasion resistance; and/or

(ii) increasing hydrophobicity; and/or

(iii) anti-microbially enhancing; and/or

(iv) increasing durability; and/or

(v) providing fire resistance

of a product, comprising coating on it or incorporating within it a functionalised metal oxide substrate obtainable by the method of any of claims 1 -15.

25. A method according to claim 24, wherein the product is an aircraft wing or wind turbine.