Aqueous interpenetrating polymer network

Abstract

The present invention relates to a process for making a sprayable aqueous colloidal suspension wherein the colloidal suspension comprises an interpenetrating polymer network comprising a polyurethane network and a polyacrylic acid network, the process comprises the steps of: a) preparing a polyurethane prepolymer composition by mixing at a reaction temperature from about 50 DEG C to about 120 DEG C: i. An aliphatic isocyanate having at least two isocyanate groups per molecule; ii. A diol; iii. A polyol having at least one acid group per molecule; and iv. A polyurethane polymerization catalyst; b) cooling the polyurethane prepolymer composition to a temperature below the reaction temperature and then adding an alkylamine to form a neutralized polyurethane prepolymer composition; and then c) adding the following components to the neutralized polyurethane prepolymer composition while mixing: i. Water; ii, a polyurethane chain extender; iii. Crosslinking an acrylic monomer; and iv. A radical initiator wherein a non-crosslinked acrylic monomer is also added in step b) or step c) to form an aqueous colloidal suspension.

Description

[0001] Related applications

[0002] This application claims priority to Australian Provisional Patent Application No. 2022903771 filed on December 9, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to sprayable aqueous dispersions of interpenetrating polymer networks and films or coatings formed therefrom. Background Art

[0004] Surfaces treated with superhydrophobic coatings or membranes have shown great potential as next-generation self-cleaning surfaces. Superhydrophobic surfaces can be used in many applications, including as anti-corrosion treatments, to prevent moisture degradation of composite materials, to prevent biofouling of surfaces frequently submerged in water, in oil-water separation processes, for drag reduction and anti-icing coatings, and more recently, as antiviral and antibacterial surfaces.

[0005] Superhydrophobic coatings have been an area of intense research over the past two decades, but despite significant efforts, they still need to realize their full commercial potential. The commercialization of superhydrophobic surfaces has typically been hampered by poor mechanical durability and the use of hazardous chemicals during the manufacturing process. While ultra-robust superhydrophobic coatings with excellent wear resistance based on interpenetrating polymer networks (IPNs) are now achievable, the synthesis of IPNs still relies on organic solvents such as acetone and xylene, which are characterized as volatile organic compounds (VOCs) by environmental protection agencies in Europe and the United States. VOCs not only pose an environmental and health hazard to employees at manufacturing sites, but also significantly increase manufacturing costs in order to avoid releasing VOCs into the environment and to meet various stringent health and safety requirements.

[0006] In addition, if the method for forming super-hydrophobic coating is improved, its commercialization potential can be further promoted. At present, IPN based coating is formed by casting process usually, wherein the precursor of IPN dispersion or two polymer systems is poured on the surface, ostensibly dried and / or solidified (may include heating step) after forming coating. However, not all surfaces or materials are suitable for this process. For example, external aircraft wall panels (its anti-icing performance may benefit from super-hydrophobic coating) may not be suitable for heating (due to material used), or too large to heat when there is no special equipment, or shape projection to such an extent that cannot cast. Although other processes such as spraying can improve the application of super-hydrophobic coating in many surfaces, known problem is that the synthesis of IPN is sensitive to complete gelation (this is undesirable when attempting to obtain sprayable dispersion), and the sprayable dispersion obtaining IPN particles may be difficult to achieve.

[0007] Therefore, there is a need for an environmentally friendly superhydrophobic coating formulation comprising an IPN in the form of an aqueous dispersion that still maintains high mechanical resistance and excellent abrasion resistance, but with a low contaminant content. The environmentally friendly superhydrophobic coating formulation is preferably sprayable to easily apply the coating to a wider range of surface materials. It is also preferred that the aqueous dispersion can be dried under ambient conditions to form a coating on the surface.

[0008] It is an object of the present invention to at least partially satisfy at least one of the above needs.

[0009] An object of the present invention is to overcome or ameliorate one or more shortcomings of the prior art, or at least provide a useful alternative. SUMMARY OF THE INVENTION

[0011] The present invention is directed to reducing the use of pollutants, particularly volatile organic solvents, that are commonly used to produce polymer-based coatings. In particular, the present invention is directed to providing methods for producing aqueous interpenetrating polymer network dispersions capable of forming superhydrophobic coatings that are preferably robust and / or durable and at least comparable to coatings formed from organic solvent-based interpenetrating polymer network dispersions.

[0012] In a first aspect of the present invention, there is provided a method for preparing a sprayable aqueous colloidal suspension, wherein the colloidal suspension comprises an interpenetrating polymer network comprising a polyurethane network and a polyacrylic acid network, the method comprising the steps of:

[0013] a) preparing a polyurethane prepolymer composition by mixing the following components at a reaction temperature of about 50° C. to about 120° C.:

[0014] i. an aliphatic isocyanate having at least two isocyanate groups per molecule;

[0015] ii. diols;

[0016] iii. a polyol having at least one acid group per molecule; and

[0017] iv. polyurethane polymerization catalyst;

[0018] b) cooling the polyurethane prepolymer composition to a temperature below the reaction temperature, and then adding an alkylamine and a dispersion medium to form a neutralized polyurethane prepolymer composition, wherein the dispersion medium is selected from water or a non-crosslinked acrylic monomer; and then

[0019] c) adding the following components to the neutralized polyurethane prepolymer composition while mixing:

[0020] i. if the dispersion medium of step b) is a non-crosslinked acrylic acid monomer, water; or if the dispersion medium of step b) is water, a non-crosslinked acrylic acid monomer;

[0021] ii. polyurethane chain extender;

[0022] iii. cross-linking acrylic acid monomers; and

[0023] iv. free radical initiators,

[0024] To form an aqueous colloidal suspension.

[0025] The following options may be used in conjunction with the first aspect, alone or in any suitable combination.

[0026] The aliphatic isocyanate of the method of the present invention may include an aliphatic diisocyanate or an aliphatic triisocyanate. Preferably, the isocyanate is an aliphatic diisocyanate. More preferably, the isocyanate is isophorone diisocyanate (IPDI).

[0027] The method of the first aspect of the present invention uses a polyol in which each molecule has been substituted with at least one acid group. The acid group replaces a hydroxyl group. It can be a triol, tetraol, or pentanol in which at least one hydroxyl group is substituted with an acid group. The acid group can be any suitable ionizable acid group, such as a carboxyl group, a sulfate group, a phosphate group, or a nitrate group. Preferably, the polyol has one carboxylic acid group per molecule. More preferably, the polyol is 2,2-bis(hydroxymethyl)propionic acid (DMPA).

[0028] The method of the first aspect of the present invention also uses a diol, which is an organic moiety having two hydroxyl groups. The hydroxyl group can be a terminal hydroxyl group (i.e., located at the end of the longest organic chain). The diol can be an oligomer or a polymer. It can be an oligomeric diol or a polymeric diol. Preferably, the diol is a polyether diol. More preferably, the diol is poly(tetramethylene ether) glycol.

[0029] The polyurethane polymerization catalyst of the present invention can be any suitable catalyst capable of initiating polyurethane polymerization. Preferably, the polyurethane catalyst is dibutyltin dilaurate.

[0030] The alkylamine of the first aspect is added to neutralize the acid groups provided by the acid-substituted polyol. The alkylamine can be a dialkylamine or a trialkylamine. Preferably, the alkylamine is a trialkylamine. More preferably, the trialkylamine is triethylamine (TEA).

[0031] The polyurethane chain extender of the first aspect of the present invention can be any suitable compound capable of reacting with the NCO-terminated polyurethane prepolymer. It can contain at least one hydroxyl group or at least one amine group, or a combination thereof. Those skilled in the art will appreciate that the chain extender must have at least two groups capable of reacting with isocyanate groups to form crosslinks. It can be a diol, a polyol, a diamine, a triamine, or a tetramine. It can be the same or different diols or polyols described herein. In a preferred embodiment, it can be a diamine, a triamine, or a tetramine. Preferably, it is a triamine. More preferably, the triamine is diethylenetriamine (DETA).

[0032] The first aspect of the present invention also includes a non-crosslinked acrylic acid monomer, a crosslinked acrylic acid monomer and a free radical initiator. The non-crosslinked acrylic acid monomer can be an acrylate or a methacrylate. Preferably, the non-crosslinked acrylic acid monomer is a methacrylate. More preferably, the non-crosslinked acrylic acid monomer is methyl methacrylate. The crosslinked acrylic acid monomer can be a diol di(meth)acrylate, a triol tri(meth)acrylate, a tetraol tetra(meth)acrylate or a pentanol penta(meth)acrylate. Preferably, the crosslinked acrylic acid monomer is a triol tri(meth)acrylate. More preferably, the crosslinked acrylic acid monomer is trimethylolpropane trimethacrylate (TRIM). The free radical initiator can be any suitable initiator capable of initiating acrylic acid polymerization. In a preferred embodiment, it is 2,2'-azobis(2-methylpropionitrile) (AIBN).

[0033] The inventors believe that the relative proportions of certain reactants contribute to the advantages of the present invention. Preferably, the inventors have found that the following relative molar ratios are most important in producing the stable aqueous dispersions described herein:

[0034] - a ratio of aliphatic isocyanate to diol of 1:1 to 5:1, or about 2:1 to 3:1, especially 3:1;

[0035] - a ratio of aliphatic isocyanate to polyol having at least one acid group per molecule of 2:1 to 6:1, in particular 4:1;

[0036] - a ratio of aliphatic isocyanate to total hydroxyl groups (ie the sum of polyols and diols) of 1:1 to 2:1, in particular about 1.4:1;

[0037] - the ratio of non-crosslinking monomer to crosslinking monomer is 10:1 to 50:1;

[0038] - a ratio of polyols having at least one acid group per molecule to diols of 1:1 to 10:1, in particular 6:1 to 8:1;

[0039] - a ratio of total pendant acid groups to alkylamines of about 1:1; and

[0040] The ratio of hard segments (ie the sum of aliphatic isocyanate, polyol having at least one acid group per molecule and polyurethane chain extender) to soft segments (ie diol) is 1:2 to 1:20, in particular 1:3 to 1:5.

[0041] The reaction temperature of step a) of the first aspect can be from about 50°C to about 120°C, or from about 70°C to about 100°C, or from about 80°C to 90°C, for example, about 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C, or any range therein. In a preferred embodiment, the reaction temperature is about 90°C.

[0042] The method for first aspect can also be included in step a) and step b) between the waiting time.In other words, once the reactant of step a) is mixed and is heated to temperature of reaction, just can keep a period of time under this temperature of reaction, to guarantee that complete reaction or at least sufficient reaction occurs.Waiting or reaction times can be about 2 hours to about 6 hours, or about 2 hours to 4 hours, or 3 hours to 5 hours, for example, about 2,2.5,3,3.5,4,4.5,5,5.5 or 6 hours or any scope therein.In one embodiment, the reaction times is about 4 hours.Similarly, the method for first aspect can also be included in step b) and step c) between about 10 minutes to about 1 hour, or about 20 minutes to 40 minutes, or about 25 minutes to 50 minutes, for example, about 10,5,20,25,30,35,40,45,50,55 or 60 minutes waiting time. Likewise, the method of the first aspect may further comprise a waiting period of at least 2 hours, e.g., from about 4 hours to 24 hours, or from about 2 hours to 12 hours, or from about 6 hours to 12 hours, e.g., about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 or 24 hours, after step c) before applying the sprayable aqueous colloidal suspension.

[0043] The colloidal dispersion formed by the method of the first aspect is advantageously sprayable. That is, the dispersion is suitable for application to a surface via a spraying device. Therefore, the sprayable dispersion should not contain any large agglomerates that would not pass through the spraying device. Although the dispersion may be sprayable, this does not preclude the dispersion from being applied using other methods known in the art, such as casting, roller coating, spin coating, etc.

[0044] Therefore, in one embodiment of the present invention, there is provided a method for preparing a sprayable aqueous colloidal suspension, wherein the colloidal suspension comprises an interpenetrating polymer network, and the interpenetrating polymer network comprises a polyurethane network and a polyacrylic acid network, the method comprising the steps of:

[0045] a) mixing isophorone diisocyanate, polyether diol, 2,2-bis(hydroxymethyl)propionic acid (DMPA) and a polyurethane catalyst, heating to a temperature of 70° C. to 90° C., and maintaining the temperature for about 4 hours while mixing to form a polyurethane prepolymer composition;

[0046] b) cooling the polyurethane prepolymer composition to a temperature of about 50° C. to 60° C., and then adding the trialkylamine, methacrylate, and water to form a neutralized polyurethane prepolymer composition; and

[0047] c) adding triamine, methyl methacrylate, and 2,2'-azobis(2-methylpropionitrile) (AIBN) to the neutralized polyurethane prepolymer composition while mixing to form an aqueous colloidal suspension.

[0048] In another embodiment of the present invention, there is provided a method for preparing a sprayable aqueous colloidal suspension, wherein the colloidal suspension comprises an interpenetrating polymer network, and the interpenetrating polymer network comprises a polyurethane network and a polyacrylic acid network, the method comprising the steps of:

[0049] a) mixing an aliphatic diisocyanate, poly(tetramethylene ether) glycol, 2,2-bis(hydroxymethyl)propionic acid (DMPA), and a polyurethane catalyst, heating to a temperature of about 90° C., and maintaining the temperature for about 3-5 hours while mixing to form a polyurethane prepolymer composition;

[0050] b) cooling the polyurethane prepolymer composition to a temperature of less than or about 60° C., and then adding triethylamine, methyl methacrylate, and water to form a neutralized polyurethane prepolymer composition; and

[0051] c) adding triamine, trimethylolpropane trimethacrylate, and 2,2'-azobis(2-methylpropionitrile) (AIBN) to the neutralized polyurethane prepolymer composition while mixing to form an aqueous colloidal suspension.

[0052] In another embodiment of the present invention, there is provided a method for preparing a sprayable aqueous colloidal suspension, wherein the colloidal suspension comprises an interpenetrating polymer network, and the interpenetrating polymer network comprises a polyurethane network and a polyacrylic acid network, the method comprising the steps of:

[0053] a) mixing an aliphatic diisocyanate, poly(tetramethylene ether) glycol, 2,2-bis(hydroxymethyl)propionic acid (DMPA), and a polyurethane catalyst, heating to a temperature of about 90° C., and maintaining the temperature for about 3-5 hours while mixing to form a polyurethane prepolymer composition;

[0054] b) cooling the polyurethane prepolymer composition to a temperature of less than or about 60° C. and then adding triethylamine to form a neutralized polyurethane prepolymer composition; and

[0055] c) adding methyl methacrylate, water, triamine, trimethylolpropane trimethacrylate, and 2,2'-azobis(2-methylpropionitrile) (AIBN) to the neutralized polyurethane prepolymer composition while mixing to form an aqueous colloidal suspension.

[0056] In a second aspect of the present invention, there is provided a method for preparing a coating comprising an interpenetrating polymer network, the method comprising the steps of:

[0057] a) spraying the aqueous colloidal suspension of the first aspect onto a surface to produce a coated surface; and

[0058] b) applying a particulate solid to the coating surface, wherein substantially the entire surface of the particulate solid is hydrophobic.

[0059] The following options may be used in conjunction with the second aspect, alone or in any suitable combination.

[0060] In a preferred embodiment, application of the particulate solid is by spraying, although other suitable application methods may be used.

[0061] The method for second aspect can also comprise a time period between applying aqueous colloidal suspension to produce coating surface and granular solid being applied to coating surface.This time period can make the coating surface part drying, thereby with immediately granular solid being applied to coating surface and comparing, this can improve the adhesive force between coating surface and the granular solid.As those skilled in the art will recognize, the coating surface at least partially dry required time can depend on a series of environmental factors, comprise the existence of temperature and humidity, air flow and / or direct sunlight in the zone of for example dry coating.Therefore, required this time period can be variable.In some embodiments, this time period can be for approximately 1 minute to approximately 240 minutes, for example, approximately 1 minute to 60 minutes, or approximately 5 minutes to 30 minutes, or approximately 10 minutes to 75 minutes, or approximately 30 minutes to 90 minutes, or approximately 40 minutes to approximately 100 minutes, or approximately 60-90 minute, or approximately 60-75 minute. In some embodiments, the granular solid of coating surface can be applied to the coating surface for at least 1 minute.For example, about 1,2,3,4,5,6,7,8,9,10,15,20,25,30,35,40,45,50,55,60,65,70,75,80,85,90,95,100,110,120,130,40,150,160,170,180,190,200,210,220,230 or 240 minutes.In other embodiments, may need longer time period.The granular solid that is applied to the coating surface can be embedded in the coating surface at least in part, that is to say, at least a portion of granular solid is not wetted by the coating surface, and is accessible at the surface.In some embodiments, granular solid can be embedded in the surface basically or embed in the surface fully.

[0062] In a third aspect of the invention there is provided a coating produced by the method of the second aspect.

[0063] BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings.

[0065] Figure 1 Shown is a waterborne PU-PMMA IPN system that has formed non-sprayable aggregates.

[0066] Figure 2 A stable waterborne PU-PMMA IPN system that remains dispersed in an aqueous environment is shown.

[0067] Figure 3 Shown is a waterborne polyurethane system that has formed non-sprayable aggregates.

[0068] Figure 4Results from an optimization study of spray volume and spray distance for the APUA system to produce durable coatings are shown: (a, b) light transmission change of the coating under hard wear conditions; and (c, d) change in haze value percentage with wear cycles.

[0069] Figure 5 The abrasion resistance of the waterborne PU-PMMA IPN coating was measured using a rotating platform abrasion tester with two CS-10 (Calibrase, USA) abrasive wheels (the abrasive wheel surfaces had been re-ground with a 150-grit grinding wheel) at 60 RPM according to the ASTM D4060 Taber standard. The load on each wheel was 250 g.

[0070] Figure 6 Fourier transform infrared (FTIR) spectra comparing aqueous suspensions described herein to solvent-based formulations are shown as a) uncured dispersions and b) cured coatings.

[0071] Figure 7 Shown are time-based analysis of waterborne poly(urethane-acrylate) reactions: (a, b, and c) spectra depicting comparative analysis of APUA systems at time intervals of 0 h, 2 h, and 8 h; (d, e, and f) relative intensities representing the reduction of intermediate water-isocyanate linkages, utilization of diethylenetriamine, reduction of free amines, and formation of long chains and crosslinks in the APUA systems over time, respectively.

[0072] Figure 8 Shown are the superhydrophobic properties of APUA-F-SiO2 coatings with different APUA curing times evaluated via (a) hard abrasion and (b) soft abrasion.

[0073] Figure 9 A comparative waterborne polyurethane system is shown that has formed a non-sprayable gel.

[0074] definition

[0075] This manual uses the following abbreviations:

[0076] AIBN: 2,2'-azobis(methylpropionitrile)

[0077] APUA: Waterborne poly(urethane-acrylate) system

[0078] DBTDL: Dibutyltin dilaurate

[0079] DETA: Diethylenetriamine

[0080] DMPA: 2,2-bis(hydroxymethyl)propionic acid

[0081] IPDI: Isophorone diisocyanate

[0082] IPN: Interpenetrating polymer network

[0083] MMA: Methyl Methacrylate

[0084] PMMA: polymethyl methacrylate

[0085] POLYOL: Polytetramethylene ether glycol (also known as PolyTHF)

[0086] PU: polyurethane

[0087] SHS: Super Hydrophobic Surface

[0088] TEA: triethylamine

[0089] TRIM: trimethacrylate

[0090] VOC: Volatile Organic Compounds

[0091] To facilitate a better understanding of the present invention disclosed herein, the following definitions are provided. These definitions are intended to be general and are not intended to limit the scope of the present invention to these terms or definitions. Unless otherwise defined, all technical and scientific terms used herein have the same meanings as those understood by one of ordinary skill in the art to which the present invention pertains.

[0092] As used herein, the term "alkyl" refers to a hydrocarbon group derived from an alkane, which may be linear, branched, or cyclic. For example, "methyl" refers to a radical derived from methane.

[0093] As used herein, the term "alkenyl" refers to a hydrocarbon group derived from an alkene, which may be linear, branched, or cyclized. For example, "vinyl" refers to a free radical derived from ethylene.

[0094] As used herein, the term "interpenetrating polymer network" refers to "a polymer comprising two or more networks that are at least partially interlaced on the molecular scale but are not covalently bonded to each other and will not separate unless the bonds are broken" (see IUPAC Gold Book http: / / goldbook.iupac.org / I03117.html, which is incorporated herein by reference in its entirety). The skilled person will recognize that the interweaving of networks generally requires that the two networks be formed in the presence of each other (simultaneously or sequentially). The skilled person will also recognize that a mixture of two or more preformed polymer networks is not an IPN, but can be described as a polymer mixture. Similarly, the skilled person will recognize that a polymer material comprising a polymer network and one or more linear or branched polymers (wherein the polymer network is penetrated on a molecular scale by at least a portion of the linear or branched polymers) is not an IPN, but can be described as a semi-IPN. Semi-IPNs can, at least in theory, be divided into a polymer network and a linear or branched polymer, which distinguishes them from true IPNs, as true IPNs cannot be separated without cleaving chemical bonds.

[0095] As used herein, the term "network" (when applied to a polymer chain or system) or "polymer network" refers to a polymer system (which may be linear or branched) comprising intramolecular or intermolecular covalent bonds. These covalent bonds, which may be referred to as crosslinks, connect at least a portion of the polymer system to itself, thereby forming a network. Crosslinks may be formed within a single polymer chain (i.e., intramolecularly) or between identical polymer chains (i.e., intermolecularly). As will be apparent to one skilled in the art, a "polymer network" comprising at least a portion of crosslinks will typically be "thermosetting" (i.e., once formed and cured, thermosetting polymers will no longer melt or flow upon reheating) because covalent crosslinks can only be broken by breaking chemical bonds. On the other hand, linear or branched polymer chains tend to be thermoplastic (i.e., thermoplastics melt or flow above the glass transition temperature, solidify below the glass transition temperature, and can be reheated and cooled multiple times) because there are no permanent bonds between the polymer chains.

[0096] As used herein, the term "polyacrylate" refers to a polymer chain or network formed from monomers containing a C=CC=O structure (ie, formed from acrylate monomers, which contain a C=CC=O moiety).

[0097] As used herein, the term "polyurethane" refers to a polymer chain or network formed by organic units joined by divalent carbamate (or urethane) linkages of the structure -NH-(C=O)-O-.

[0098] As used herein, the term "superhydrophobic" refers to a surface of a material having a water contact angle of at least 150°.

[0099] The terms "colloid" or "colloidal suspension," as used interchangeably herein, refer to a mixture in which one substance composed of microscopically dispersed insoluble particles is suspended in another substance. For example, microscopic particles comprising a polymer-based system (e.g., IPN) can be dispersed in a liquid such as water.

[0100] As used herein, the term "comprising" means "including." Variations of the word "comprising," such as "including" and "comprising," have correspondingly varying meanings. As used herein, the terms "comprising" and "including" are non-exclusive. As used herein, the terms "comprising" and "including" do not imply that the specified items represent a substantial portion of a whole.

[0101] The transitional phrase "consisting of" excludes any element, step, or ingredient not specified. If included in a claim, such phrase would close the claim to materials other than those listed, except for impurities normally associated with the listed materials. When the phrase "consisting of" appears in a clause in the body of a claim, rather than immediately following the preamble, it limits only the elements listed in that clause; other elements are not excluded from the claim as a whole.

[0102] The transitional phrase "consisting essentially of" is used to qualify a composition, process, or method as including other materials, steps, features, components, or elements in addition to those literally disclosed, so long as they do not materially affect the basic and novel characteristics of the claimed invention. The term "consisting essentially of" occupies a middle ground between "comprises / comprising" and "consisting of."

[0103] If applicants define an invention or a portion thereof using open-ended terms such as "comprising" or "including," it should be readily understood that (unless otherwise indicated) the description should be interpreted as also describing the invention as "consisting essentially of" or "consisting of." In other words, with respect to the terms "comprising," "consisting of," and "consisting essentially of," when any of these three terms is used herein, the presently disclosed and claimed subject matter may include the use of either of the other two terms. Thus, in some embodiments not expressly recited, any instance of "comprising" may be replaced with "consisting of" or "consisting essentially of."

[0104] Furthermore, unless expressly stated to the contrary, "or" is inclusive, not exclusive. For example, a condition A or B is satisfied by any of the following: A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), and both A and B are true (or exist).

[0105] In addition, the indefinite articles "a" and "an" appearing before an element or component of the invention are intended to be non-limiting with respect to the number of instances of that element or component. Thus, "a" or "an" should be understood to include one or at least one, and the singular form of the element or component also includes the plural form unless the number is obviously intended to be singular.

[0106] Except in the operating examples or where otherwise indicated, all numbers used herein expressing amounts of ingredients or reaction conditions should be understood to be modified in all instances by the term "about." These examples are not intended to limit the scope of the invention. In the following text or where otherwise indicated, "%" shall mean "percentage by weight"; "ratio" shall mean "ratio by weight"; and "parts" shall mean "parts by weight."

[0107] As used herein, the terms "predominantly" and "substantially" shall mean greater than 50% by weight unless otherwise indicated.

[0108] As used herein, the terms "about," "approximately," and "substantially" when referring to numbers in a series of numbers should be understood to refer to a range of -10% to +10% of the referenced number, preferably a range of -5% to +5% of the referenced number, more preferably a range of -1% to +1% of the referenced number, and most preferably a range of -0.1% to +0.1% of the referenced number. Furthermore, when referring to numerical ranges, these terms should be interpreted as supporting claims directed to any number or subset of numbers within that range. For example, a disclosure of 1-10 should be understood to support ranges of 1-8, 3-7, 1-9, 3.6-4.6, 3.5-9.9, 8-10, etc.

[0109] As used herein, "wt. %" refers to the weight of a particular component relative to the total weight of the referenced composition. Likewise, "% v / v" refers to the volume of a particular component relative to the volume of the referenced composition.

[0110] The entire disclosures of the patents, patent documents, and publications cited herein are incorporated by reference in their entirety, as if each were individually incorporated. DETAILED DESCRIPTION

[0111] The following description provides a sufficiently detailed description of exemplary embodiments of the present invention to enable one of ordinary skill in the art to practice the present invention. The features or limitations of the various embodiments described do not necessarily limit other embodiments of the present invention or the present invention as a whole. Therefore, the following detailed description does not limit the scope of the present invention, which is defined solely by the claims.

[0112] The present invention described herein relates to an improved method for forming a super-hydrophobic coating. More specifically, the present invention relates to a method for forming a super-hydrophobic coating comprising an IPN. Typically, polymer-based coatings (including IPN-based coatings) are produced by dispersing polymers (or monomers or precursors or their particles) in organic solvents, wherein organic solvents are typically classified as VOCs. For hydrophobic polymers that are not easily dispersed in aqueous environments, such as polyurethanes, this is especially true. As the global regulation of VOCs increases, resulting in a more expensive method utilizing VOCs, the inventors have developed a method for eliminating or at least significantly reducing the use of VOCs in IPN-based polymer coating methods.

[0113] The inventors have previously described methods for utilizing organic solvents to form a colloidal suspension of IPN particles that, when applied as a coating to a surface, renders the surface superhydrophobic (WO 2017 / 193157A1, which is incorporated herein by reference in its entirety). As will be apparent from the description below, the present water-based IPNs offer significant improvements over these previous methods because the organic solvents (i.e., m-xylene and acetone) are effectively replaced with water, thereby providing an improved method by eliminating or significantly reducing VOCs. Advantages of the present improved methods include reduced costs due to reduced solvent costs and VOC emission mitigation requirements, improved health outcomes, reduced potential for adverse outcomes for manufacturing workers, and reduced environmental impact of VOC emissions, thereby contributing to atmospheric carbon levels.

[0114] Colloidal dispersions

[0115] To produce a superhydrophobic coating, a method includes the following initial steps: forming a colloidal dispersion (or interchangeably referred to as a suspension) in which the colloidal particles comprise, consist of, or consist essentially of an IPN. In theory, any two or more cross-linkable polymer networks can be used to form the colloidal IPN particles. However, in particularly preferred embodiments, the colloidal IPN particles comprise, contain, or consist essentially of two polymer networks: one polymer network based on urethane linkages (i.e., polyurethane) and one polymer network based on acrylic or methacrylic monomers (i.e., polyacrylate or polymethacrylate). The two polymer networks are intertwined on a molecular scale, or at least partially intertwined on a molecular scale. By "intertwined," it is meant that the two polymer networks (the polyurethane network and the polyacrylate or polymethacrylate network) cannot be separated (or at least theoretically cannot be separated) without breaking or cleaving the covalent bonds. Notably, this differs from a semi-interpenetrating polymer network, in which one of the polymer systems is not cross-linked and, therefore, can, at least theoretically, be separated from the cross-linked system. It is expected that the skilled artisan will recognize the difference between interpenetrating polymer networks (IPNs) and semi-interpenetrating polymer networks (semi-IPNs).

[0116] Advantageously, the colloidal IPN particles are stably suspended in an aqueous liquid. The aqueous liquid can contain, consist of, or consist essentially of water. It can be 100% v / v water, or it can be 99, 98, 97, 96, 95, 94, 93, 92, 91, or 90% v / v water (i.e., it can contain or consist of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10% v / v of another liquid). As will be appreciated by those skilled in the art, some of the reactants added to the reaction mixture to form the colloidal IPN particles may be formulated with or include an organic solvent, the use of which may introduce small amounts of organic solvent as impurities into the aqueous colloidal suspension. In preferred embodiments, the aqueous liquid is at least 98% v / v water, at least 99% v / v water, or approximately 100% v / v water.

[0117] The method of the present invention for preparing an aqueous colloidal suspension is carried out in a single vessel (i.e., a "one-pot process"). The method generally comprises three steps: (1) forming a polyurethane prepolymer composition; (2) neutralizing the polyurethane prepolymer composition and dispersing the neutralized prepolymer composition; and (3) forming a colloidal aqueous suspension by simultaneously forming a crosslinked polyacrylic acid network and a crosslinked polyurethane network. The method of the present invention is described using two alternative synthetic routes, wherein the dispersion medium in step (2) above is either water or a non-crosslinked monomer. Each step is described in more detail below.

[0118] Polyurethane prepolymer composition

[0119] The first step of the present invention involves forming a polyurethane prepolymer composition. The prepolymer is based on urethane chemistry, which means it contains diols, polyols, and isocyanates with at least two isocyanate groups per molecule. By "prepolymer," it is meant that this step results in the formation of short-chain polyurethane polymers terminated with isocyanate groups at one, both ends (for linear prepolymers), or both ends (for branched prepolymers) (i.e., the prepolymer remains reactive). These prepolymers are then extended and cross-linked to form a network. In this regard, this first polyurethane polymerization step is not intended to proceed to completion and form a fully cured network, but rather to produce a composition comprising a reactive polyurethane prepolymer. A prepolymer can be defined as an intermediate molecular weight state that can be further polymerized by reactive groups to form a fully cured, high molecular weight state, and is formed from a monomer system that has reacted together. In other words, one would expect that the prepolymer composition would contain reactive short-chain polymers (also known as NCO-terminated polymers) and may contain unreacted components or monomers (because the reaction was stopped or slowed before the polymerization reaction was completed). Alternatively, the reaction can be controlled by providing a molar excess of the isocyanate-containing reactants to ensure the formation of an NCO-terminated prepolymer.

[0120] The isocyanates used in the present invention are aliphatic isocyanates. As those skilled in the art will recognize, isocyanates (i.e., compounds having at least one -N=C=O group) generally fall into one of two categories: aliphatic isocyanates or aromatic isocyanates. Aromatic isocyanates are compounds in which the isocyanate group is directly attached to an aromatic ring. For example, TDI (toluene diisocyanate; either 2,4-TDI or 2,6-TDI, or a mixture thereof) is a well-known aromatic isocyanate based on a toluene (i.e., aromatic ring) moiety. Similarly, aliphatic isocyanates are compounds in which the isocyanate group is directly attached to a linear, branched, or cyclic aliphatic chain, which can be saturated or unsaturated. Aromatic isocyanates are known to be more reactive than aliphatic isocyanates, but this results in sensitivity to water (or more generally, moisture), which reacts with aromatic isocyanates. Because the polyurethane prepolymer in this step terminates with at least one isocyanate group, and water is added before the polyurethane is fully polymerized, highly reactive aromatic isocyanates are not suitable for use in the present invention. The aliphatic isocyanate may have 2 isocyanate groups per molecule, or it may have 3, 4, or 5 isocyanate groups per molecule. For example, the aliphatic isocyanate may be isophorone diisocyanate (IPDI), 1,6-hexamethylene diisocyanate (HDI), trimethylhexamethylene diisocyanate (TMDI), 4,4'-diisocyanatodicyclohexylmethane (hydrogenated MDI, or HDI), or 1,6-hexamethylene diisocyanate (HDI). 12In a preferred embodiment, the aliphatic isocyanate is isophorone diisocyanate (IPDI).

[0121] The diol used in the present invention can be any suitable compound having two hydroxyl groups connected by an organic moiety. It can be an alkane diol (for example, that is, the organic moiety can be an alkanediyl group, which can be linear, branched, cyclic, or can have two or all of these structures). For example, it can be an alkane α, ω-diol (that is, the hydroxyl group is located at the terminal carbon atom of the longest carbon chain of the general formula HO-R-OH), wherein the alkane is a linear alkane (that is, it can be a alkane of the general formula HO(CH2) n OH, wherein n can be 2-12, or 2-10, 2-6, 3-8 or 4-6, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, optionally greater than 12). It can be polymeric. It can be a polyester diol, such as poly(tetramethylene ether) glycol (PolyTHF or PTME), or polyethylene glycol, or any other suitable polymeric diol. Polymeric diols are generally graded by average molecular weight, for example, PTME650 can refer to a composition comprising poly(tetramethylene ether) glycol having an average molecular weight of about 650 Da. Thus, the average molecular weight of the polymeric glycol used in the present invention can be from about 75 Da to about 3000 Da, or from about 100 Da to about 2500 Da, or 150-2000 Da, 200-1500 Da, 500-1000 Da, 650-2000 Da, 1000-3000 Da or 1500-2000 Da, for example, about 75 Da, 100 Da, 125 Da, 150 Da, 175 Da, 200 Da, 250 Da, 300 Da, 350 Da, 400 Da, 500 Da, 550 Da, 600 Da, 750 Da, 800 Da, 900 Da, 1000 Da, 1500 Da, 1750 Da, 2000 Da, 2500 Da, 3000 Da, 3500 Da, 4000 Da, 5000 Da, 5500 Da, 6000 Da, 7500 Da, 8000 Da, 9000 Da, 10000 Da, 15 ... In some embodiments, the diol is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, or 400 Da, or any range therein. In a preferred embodiment, the diol is poly(tetramethylene ether) glycol, which has the general formula HO-[C4H8O] n-H, wherein n can be 2-40, such as 2-10, 3-12, 5-20, 7-15, 10-30, or 20-40, such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, or 40. As will be appreciated by those skilled in the art, since polymeric glycols are obtained based on an "average molecular weight," it is possible that the PolyTHF (or other polymeric glycol) obtained and used in this step can contain chains with more than one value of n (e.g., a PolyTHF composition having an average molecular weight of 225 can contain chains with n values of 2, 3, and 4).

[0122] The polyol used in the present invention can be any suitable compound that each molecule contains more than two hydroxyls.Its each molecule can have 3,4,5,6,8,10,12,15,17,20 or more than 20 hydroxyls.In some embodiments, polyol can have 3 (triol), 4 (tetraol) or 5 (amyl alcohol) hydroxyls.However, in the present invention, at least one hydroxyl of polyol is replaced by acid group (for example carboxyl, i.e.-COOH).Each molecule of acid-substituted polyol of the present invention can comprise 1,2,3,4 or more acid groups, and each acid group all replaces hydroxyl.For example, " acid-substituted triol" of the present invention (and as described herein) can comprise two hydroxyls and an acid group (replacing the 3rd hydroxyl) or a hydroxyl and two acid groups (replacing second and the 3rd hydroxyl).In other words, although compound may only have two hydroxyls, if it also comprises acid group, then still can be regarded as " triol" of the present invention. In this regard, the acid-substituted polyols of the present invention provide dual functionality: each hydroxyl group reacts with an isocyanate group to form a urethane linkage (i.e., it is incorporated into the polyurethane chain); and at least one acid group provides a polar, ionizable site to aid in the dispersion of the polyurethane prepolymer in an aqueous liquid (as described in more detail below). It will be appreciated by those skilled in the art that polyurethane chains are typically hydrophobic and tend to aggregate in polar environments (e.g., in aqueous liquids). However, the addition of polar, ionizable side groups to the polyurethane chains reduces the hydrophobicity of the polyurethane chains and enables the polyurethane to be dispersed in aqueous liquids (also known as "waterborne polyurethanes"). Typically, the polar side groups are ionizable, so that the acid groups can be ionized for more effective dispersion in aqueous liquids. For example, the acid groups can be carboxyl groups, sulfate groups, phosphate groups, nitrate groups, or any other suitable ionizable acidic groups. In a preferred embodiment, the acid groups can be carboxyl groups, and the polyol can contain one acid per molecule. For example, the polyol may be 2,2-bis(hydroxymethyl)propionic acid (DMPA), 2,2-bis(hydroxymethyl)butanoic acid (DMBA), or any other suitable acid-substituted polyol. In a preferred embodiment, the polyol is 2,2-bis(hydroxymethyl)propionic acid (DMPA).

[0123] In the present invention, the molar ratio of polyol to diol can be from about 1:1 to about 10:1, or from about 5:1 to 10:1 or from 3:1 to 7:1, such as about 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1 or 10:1, or any range therein, based on the average molecular weight of the diol (which can be an oligomeric diol). In a preferred embodiment, the molar ratio of polyol to diol can be from 6:1 to 8:1. In addition, since the molecular weight of polyol is generally lower than that of diol (generally an oligomeric diol), the weight ratio of polyol to diol can be from about 0.05 to about 0.5, or from about 0.2-0.5, 0.3-0.5, 0.1-0.4, 0.1-0.3 or 0.2-0.4, such as about 0.05, 0.1, 0.2, 0.3, 0.4 or 0.5, or any range therein. Preferably, the weight ratio of polyol to diol can be about 0.1-0.2. More preferably, the weight ratio of polyol to diol can be about 0.15. The molar ratio of isocyanate to polyol can be about 6:1 to 2:1, or about 5:1 to 3:1, such as about 6:1, 5:1, 4:1, 3:1 or 2:1, or any range therein. It can be seen that the molar ratio of isocyanate to diol can be about 1:1 to 5:1, or about 2:1 to 4:1, such as about 1:1, 2:1, 3:1, 4:1 or 5:1. In a preferred embodiment, the molar ratio of isocyanate to polyol can be about 4:1, and the molar ratio of isocyanate to diol can be about 3:1. As recognized by the technician, polyurethane generally comprises a hard segment (comprising isocyanate material, polyol and chain extender) and a soft segment (generally comprising oligomeric diols), and balancing the relative proportions of hard segment and soft segment can enable the technician to adjust the physical properties of the polyurethane. For example, if a polyurethane has too many soft segments, it may be too soft or pliable to act as a coating; similarly, a polyurethane with too many hard segments may be too brittle or stiff to act as a coating. In this regard, one can adjust the ratio of hard segments to soft segments to achieve the desired material and physical properties. In one embodiment, the inventors have found that a molar ratio of the hard segment components (i.e., isocyanate, polyol, and chain extender) to the soft segment components (i.e., diol) of about 1:2 to 1:20 is particularly suitable for achieving a durable coating. Therefore, in one embodiment of the present invention, the ratio of hard segments to soft segments can be about 1:3 to 1:10, or about 1:5 to 1:15, or about 1:10 to 1:20, for example, about 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or 1:20. In a preferred embodiment, the ratio of hard segments to soft segments is 1:3 to 1:5.

[0124] The molar ratio of isocyanate to the sum of the moles of hydroxyl groups, i.e., the molar ratio of isocyanate to the total moles of polyols and diols, can be from about 1:1 to about 2:1, or from about 1:1 to about 1.4:1, or from about 1.2:1 to about 1.5:1, or from about 1.5:1 to about 1.8:1, for example, about 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, or 2:1. In a preferred embodiment, the molar ratio of isocyanate to the total moles of polyols and diols is about 1.4:1. The isocyanate can be present in a molar excess relative to the sum of the hydroxyl groups. It can be present at a molar concentration of about 101% to about 120%, or about 101-110%, 101-105%, 105-120%, 110-120%, or 105-110%, such as about 101%, 102%, 103%, 104%, 105%, 106%, 107%, 108%, 109%, 110%, 115%, or 120%, compared to the sum of the molar concentrations of the polyol and diol.

[0125] The polyurethane prepolymer composition of the present invention includes a polyurethane polymerization catalyst. The polyurethane polymerization catalyst can be added to a mixture containing an aliphatic isocyanate, a diol, and a polyol. Suitable catalysts include metal-based catalysts, such as catalysts based on tin, bismuth, zirconium, aluminum, or a mixture of any two or more thereof. The catalyst can be a carboxylate, such as laurate, stearate, acetate, or other carboxylate. The metal can also be bonded to one or more (usually two) alkyl groups, such as a C1-C6 alkyl group. Therefore, suitable catalysts include dibutyltin dilaurate and dibutyltin diacetate. Other catalysts include tertiary amine catalysts, such as 1,4-diazabicyclo[2.2.2]octane (Dabco), diazabicyclononane (DBN), diazabicycloundecane (DBU), 2,2'-bis(dimethylamino)diethyl ether, benzyldimethylamine, N,N-dimethylcyclohexylamine, etc. In a preferred embodiment, the polyurethane polymerization catalyst can be dibutyltin dilaurate. The polyurethane catalyst can be added to a final concentration in the reaction mixture of about 50 ppm to about 500 ppm, or about 100-300, 300-500, or 200-400 ppm, such as about 50, 75, 100, 150, 200, 250, 350, 400, 450, or 500 ppm. In a preferred embodiment, the polyurethane catalyst is added to a final concentration in the reaction mixture of about 100 ppm.

[0126] The resulting catalytic reaction mixture (comprising an aliphatic isocyanate, a diol, a polyol, and a polyurethane polymerization catalyst) is then heated at a suitable temperature and for a suitable time to allow partial polymerization of the catalytic reaction mixture to occur, thereby forming a polyurethane prepolymer composition. As will be appreciated by those skilled in the art, the appropriate temperature will depend on the precise nature of the catalytic reaction mixture components (particularly the specific aliphatic isocyanate, diol, polyol, and polyurethane polymerization catalyst used), as well as the amount of time for which heating is performed. In this regard, those skilled in the art will recognize that some optimization of the temperature and reaction time may be required to produce a prepolymer composition having desired properties (e.g., average molecular weight and viscosity). Typically, the temperature will be below the optimal curing temperature of the polyurethane composition, as a slower reaction rate allows for better control of the prepolymer product. However, the temperature should not be so low as to prevent any substantial reaction from occurring. For example, polyurethanes can typically be cured at temperatures between about 120°C and about 150°C, however, the catalytic reaction mixture of the present invention can advantageously be heated at temperatures below 120°C. For example, the temperature can be below about 110°C, or below about 100°C, or below about 90°C, or below about 80°C, or below about 70°C, or below about 60°C, and above about 50°C. It can be from about 50°C to about 120°C, or from about 55°C to about 110°C, or from about 60°C to about 120°C, or from about 70°C to about 100°C, or from about 80°C to about 110°C, or from about 90°C to about 100°C, or from about 50°C to about 70°C, or from about 60°C to about 80°C, or it can be about 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C or 120°C, or any range therein. In a preferred embodiment, the temperature is from about 70°C to about 100°C, or about 80°C, or about 90°C. The catalytic reaction mixture can be heated from room temperature to the desired reaction temperature. The heating can be performed at a rate of about 1°C / min, or about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20°C / min, or any range thereof. The catalytic reaction mixture can be maintained at the reaction temperature for a suitable period of time to produce a polyurethane prepolymer composition having desired properties (e.g., molecular weight and / or viscosity). The reaction mixture can be maintained at the reaction temperature until it no longer flows. The time can be about 30 minutes to about 6 hours, for example, 30 minutes to 1 hour, 45 minutes to 2 hours, 1-4 hours, 2-5 hours, or 3-6 hours, for example, about 30, 35, 40, 45, 50, 55, 60 minutes, or about 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, or 6 hours, or any range thereof.In a preferred embodiment, the time is from about 3 hours to about 5 hours, or about 4 hours.

[0127] Therefore, in a preferred embodiment of the present invention, a polyurethane prepolymer composition is produced by preparing a catalytic reaction mixture. The catalytic reaction mixture comprises: isophorone diisocyanate (IPDI) as an aliphatic isocyanate; poly(tetramethylene ether) glycol (PolyTHF) as a diol; 2,2-bis(hydroxymethyl)propionic acid (DMPA) as an acid-substituted diol; and dibutyltin dilaurate as a polyurethane polymerization catalyst, wherein: the ratio of DMPA to PolyTHF is about 6:1 to 8:1; the molar ratio of IPDI to hydroxyl groups is about 2:1 to about 4:1; and the amount of catalyst is about 0.1% v / v. The catalytic reaction mixture is then heated to a reaction temperature of 70°C to 100°C with stirring for about 3-5 hours to form the polyurethane prepolymer composition.

[0128] Neutralized polyurethane prepolymer composition

[0129] The second step of the inventive method comprises neutralizing the polyurethane prepolymer composition of the first step. In particular, the ionizable acidic side groups incorporated into the polyurethane prepolymer are treated with alkali and converted into anions, making the polyurethane prepolymer dispersible in water. For example, when the ionizable acidic side groups are carboxyl groups, these groups are converted into carboxylate ions after adding a neutralizing agent. This step also includes adding a non-crosslinked acrylic acid monomer or water as a dispersion medium. The inventors surprisingly discovered that adding a dispersion medium (either water or a non-crosslinked acrylic acid monomer) in this step reduces the occurrence of precipitation or large agglomerated particles that may form in the water-dispersible polyurethane dispersion and the water-dispersible polyurethane-polyacrylic acid interpenetrating polymer network. Without being bound by theory, the inventors believe that this effect is observed because the addition of the dispersion medium ensures that the neutralizing agent is fully mixed in the reaction mixture before polymerization, thereby preventing one or both polymerization systems from precipitating when other reactants are added.

[0130] Before adding the neutralizing agent, the polyurethane prepolymer composition is cooled to a temperature below the reaction temperature. The composition can be cooled to a temperature that is at least 5°C, or at least 10°C, or at least 20°C, or at least 30°C, or at least 40°C lower than the reaction temperature. For example, if the reaction temperature is 80°C, the composition can be cooled to a temperature of about 75°C, or about 70°C, or about 65°C, or about 60°C, or about 55°C, or about 50°C, or about 45°C, or about 40°C, or any range thereof, before adding the neutralizing agent. For example, if the reaction temperature is 90°C, the composition can be cooled to a temperature of about 85°C, or about 80°C, or about 75°C, or about 70°C, or about 65°C, or about 60°C, or about 55°C, or about 50°C, or any range thereof, before adding the neutralizing agent. In one embodiment, the polyurethane prepolymer composition is cooled from about 80°C to about 60°C before adding the neutralizing agent.

[0131] Once cooled, a neutralizing agent is added to the polyurethane prepolymer composition while stirring to form a neutralized polyurethane prepolymer composition.

[0132] The neutralizing agent can be any suitable base. It can be an organic base. It can be an amine, for example, it can be ammonia. It can be an alkylamine. It can be a trialkylamine of the general formula R3N, wherein each R can independently be an alkyl group (i.e., methyl, ethyl, butyl, propyl, pentyl or hexyl) having a length of 1 to 6 carbon atoms. Each alkyl group can be straight-chain, or can be branched. Each alkyl group can further be substituted by at least one group selected from hydroxyl, amine or halogen. For example, it can be triethylamine (TEA), or it can be dimethylethanolamine (DMEA), or it can be any other suitable organic amine base. It can be an inorganic base, for example, it can be sodium hydroxide or potassium hydroxide, or it can be any other suitable inorganic base. In a preferred embodiment, the neutralizing agent is triethylamine (TEA).

[0133] The neutralizing agent may be added in an amount suitable to ionize all, substantially all, or at least half of the acidic side groups. The neutralizing agent may be in stoichiometric excess relative to the acidic side groups present in the prepolymer. The neutralizing agent may be added in an amount of 100%, 105%, 110%, 120%, 150%, or 200% of the moles of acidic side groups present in the polyurethane prepolymer, or any range therein.

[0134] During this step, water is also added in one reaction scheme (hereinafter referred to as "Scheme I") to form a neutralized polyurethane (i.e., NCO-terminated) prepolymer composition. The amount of water added can be sufficient to dilute the solids content of the neutralized NCO-terminated prepolymer composition by at least 5%, or at least 10%, or at least 20%, or at least 30%, or at least 40%, or at least 50%, or at least 75%, or at least 100%, or at least 150%, or at least 200%, or any range therein. As one skilled in the art will appreciate, the amount of water added can be optimized, depending on factors such as the viscosity of the prepolymer composition, the reaction rate of the polymerization reaction, the molecular weight of the prepolymer, and the concentration of residual monomers. The water is added to provide an aqueous solvent system in which the interpenetrating polymeric network can be dispersed. "Aqueous" means that the solvent contains water, is primarily water, is essentially water, or is at least 50% water. In other words, during and after the formation of the interpenetrating polymeric network, the most abundant solvent is water. While other solvents may be present, the most abundant solvent should be water.

[0135] Alternatively, in another reaction scheme (hereinafter referred to as "Route II"), a non-crosslinked acrylic monomer is added to the neutralized polyurethane prepolymer composition as a dispersion medium instead of water. The non-crosslinked acrylic monomer contains only one carbon-carbon double bond. The non-crosslinked acrylic monomer can be acrylic acid or methacrylic acid. For example, it can be a (meth)acrylate, (meth)acrylamide, (meth)acrylic acid, or some other non-crosslinked acrylic monomer (e.g., an alkoxy methacrylate). In a preferred embodiment, the non-crosslinked acrylic monomer is methyl methacrylate.

[0136] In any of the above synthesis routes, the polyurethane prepolymer composition is uniformly neutralized due to the addition of the neutralizing agent and the dispersing medium.

[0137] Once the neutralizing agent and dispersion medium (non-crosslinked acrylic monomer or water) have been added, the reaction mixture can be mixed. It can be stirred. It can be maintained at the temperature at which it was cooled after step a), or it can be cooled to room temperature (i.e., about 20-25° C.), or it can be heated to a temperature of up to 120° C. The neutralized polyurethane prepolymer composition can be stirred and / or heated for a suitable period of time to ensure complete or substantially complete homogenization. This period of time can be 1-120 minutes, or 5 minutes to 60 minutes, or 20-80 minutes, for example, about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, or 120 minutes.

[0138] Polyacrylic acid system and polyurethane chain extension

[0139] The third step in producing the aqueous colloidal suspension of the present invention is to form the acrylic polymer system and simultaneously expand and complete the polyurethane system. As will be appreciated by those skilled in the art, by simultaneously forming the polyacrylic polymer network while further reacting with the polyurethane prepolymer and expanding into a network, the two polymer systems (i.e., the polyacrylic system and the polyurethane system) are interpenetrating and can only be separated by breaking the chemical bonds (i.e., an interpenetrating polymer network is formed by the two polymer network systems).

[0140] In this step, a polyurethane chain extender, a crosslinking acrylic monomer, and a free radical initiator, along with water (in Route I) or a non-crosslinking monomer (in Route II), are added to the neutralized polyurethane prepolymer composition. As will be appreciated by those skilled in the art, and as discussed in detail below, the inventors understand that each polyurethane chain extender molecule reacts with the NCO end groups of at least two separate polyurethane prepolymers to form a single crosslinked polyurethane network, while the free radical initiator initiates the polymerization of acrylic acid, resulting in each crosslinking acrylic monomer molecule reacting with two or more crosslinking or non-crosslinking acrylic monomer molecules to form a crosslinked polyacrylic acid network.

[0141] The polyurethane chain extender can be any suitable compound capable of reacting with the NCO-terminated polyurethane prepolymer to complete the formation of the polyurethane network. As is known to those skilled in the art, polyurethane chain extenders are typically low molecular weight compounds that react with diisocyanates to increase the molecular weight of the polyurethane and increase the block length of the hard segment. The polyurethane chain extender can contain at least two hydroxyls or at least two amine groups. Typically, the polyurethane chain extender can be any suitable diol (i.e., containing two hydroxyls) or diamine (i.e., containing two amine groups). It can be an aliphatic diol or diamine, or it can be an aromatic diol or diamine. The chain extender can be the same or different diols added during the formation of the polyurethane prepolymer. The diol can be as described above. The diamine can be any suitable compound having two amine groups connected by an organic moiety. It can be an alkane diamine (e.g., the organic moiety can be an alkane diyl, which can be linear, branched, cyclic, or can have two or all of these structures). For example, it can be an alkane α,ω-diamine (that is, the amine group is located at the terminal carbon of the longest carbon chain of the general formula H2N-R-NH2), wherein the alkane is a straight chain alkane (it can be of the general formula H2N(CH2) nNH2, wherein n may be 2-12, or 2-10, 2-6, 3-8 or 4-6, for example 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, optionally greater than 12. It may also be a triamine, wherein the organic moiety comprises a secondary amine group in the chain. For example, it may be a compound of the general formula H2N-R-NH-R-NH2, wherein the two R groups may have the same or different alkyl chain lengths. For example, it may be diethylenetriamine (H2N-CH2CH2-NH-CH2CH2-NH2), dipropylenetriamine (H2N-CH2CH2CH2-NH-CH2CH -2 Alternatively, each R group may be an alkenyl chain, an alkynyl chain, or an aryl group. Each R group may be further substituted with any suitable free radical (e.g., including alkyl, alkenyl, alkynyl, aryl, halogen, cycloalkyl, hydroxyl, carboxyl, cyano, sulfate, isocyanate, or amido groups). In a preferred embodiment, the polyurethane chain extender may be diethylenetriamine (DETA). The chain extender may be added in a molar excess over the available isocyanate groups on the prepolymer. As will be appreciated by those skilled in the art, the available isocyanate groups on the prepolymer are inversely proportional to the size of the polyurethane prepolymer: the longer the initial polymerization step (i.e., the formation of the polyurethane prepolymer described above), the more isocyanate groups are available to react with the diol or polyol (thus forming a longer prepolymer), and therefore, the fewer isocyanate groups are available to react with the chain extender, and vice versa. The chain extender may be added in an amount of about 100% or 105% or 110% or 120% or 150% or 200% of the molar concentration of available isocyanate groups on the polyurethane prepolymer.

[0142] Crosslinking acrylic monomers contain at least two carbon-carbon double bonds. As the skilled artisan will recognize, acrylic monomers (crosslinked or non-crosslinked) polymerize via free radical addition reactions involving carbon-carbon double bonds. Thus, if acrylic monomers have two (or more) carbon-carbon double bonds (as is the case with the crosslinking acrylic monomers required by the present invention), these monomers have two (or more) sites that can polymerize (i.e., react with another monomer). When these monomers are incorporated into an acrylic polymer, they will branch and crosslink with other acrylate chains (hence the use of the term "crosslinking acrylic monomer"). For the purposes of the present invention, such crosslinking is necessary to produce an interpenetrating polymer network; if one of the polymer systems is not crosslinked (i.e., consists of completely linear or branched polymer chains without crosslinks), it does not meet the definition of an interpenetrating polymer network, but would be described as a semi-interpenetrating polymer network (as defined in the IUPAC Gold Book - see https: / / goldbook.iupac.org / terms / view / S05598, which is incorporated herein by reference in its entirety), or described as a polymer blend. The crosslinking acrylic monomer can be a (meth)acrylate or a (meth)acrylamide. If it is an ester, it can be an ester of a diol, triol, tetraol, pentanol or other polyol, that is, it can be a diester, triester, tetraester or pentaester, etc. If it is an amide, its structure can be HN((=O)C-CH=CH2)2, N((=O)C-CH=CH2)3 or other similar structures. In a preferred embodiment, the crosslinking acrylic monomer is trimethylolpropane trimethacrylate (TRIM) ([H2C=C(CH3)CO2CH2]3CC2H5).

[0143] As mentioned above, and as the skilled person understands, acrylic monomers require a free radical initiator to begin polymerization. Once polymerization is begun, the free radical polymerization reaction will continue on its own until the monomer is exhausted, or two free radicals react, thereby forming a complete polymeric network. The free radical initiator can be an azo initiator, an azo ester initiator, a peroxide initiator, a peroxydicarbonate initiator or some other suitable initiator. Usually it will be a thermal initiator (i.e., an initiator activated by heat), but it can also be an initiator, a redox initiator or some other suitable initiator types that are UV activated in some cases. If it is a thermal initiator, its 10-hour half-life temperature can be from about 40 to about 100°C, or about 40-70°C, 40-60°C, 50-80°C, 60-80°C, 75-100°C, 60-90°C, or 50-70°C, for example, about 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100°C. It should be appreciated that the half-life of an initiator may depend in part on the medium in which it is measured. The above 10-hour half-life temperature can be measured in toluene or in the polymerization mixture. Suitable initiators include 2,2'-azobis(2-methylpropionitrile) (AIBN), 4,4'-azobis(4-cyanovaleric acid), benzoyl peroxide, lauroyl peroxide, and potassium persulfate. In a preferred embodiment of the present invention, the initiator is 2,2'-azobis(2-methylpropionitrile) (AIBN). The free radical initiator may be present in a molar ratio of about 2% relative to the total amount of the non-crosslinking monomer and the crosslinking monomer. It may be present in an amount of about 0.5% to about 5%, or about 1-5%, 2-5%, 0.5-2%, 0.5-1% or 1-3%, for example, about 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.

[0144] In the acrylic network, the ratio of non-crosslinking monomer to crosslinking monomer can be from about 10:1 to about 50:1 (i.e., from about 10:1 to about 50:1, or from about 10:1 to 40:1, 10:1 to 30:1, 10:1 to 20:1, 20:1 to 50:1, 30:1 to 50:1, or 15:1 to 30:1, for example, about 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, 20:1, 25:1, 30:1, 35:1, 40:1, 45:1, or 50:1), based on the number of moles of polymerizable groups. In this context, for example, if the ratio of non-crosslinking monomer to crosslinking monomer is 2:1 on a molar basis, and the crosslinking monomer has two polymerizable olefinic groups per molecule (for example, if it is a dimethacrylate), then the ratio of non-crosslinking monomer to crosslinking monomer will be 1:1 based on the moles of polymerizable groups.

[0145] After the polyurethane chain extender, crosslinking acrylic monomer, and free radical initiator are added, the reaction mixture is stirred. The reaction mixture may be heated (if the free radical initiator is a thermal initiator), or exposed to UV light (if the free radical initiator is a UV-activated initiator), or some other conditions that result in activation of the initiator and polymerization of the acrylic network. For example, when AIBN is used as the free radical initiator, the reaction mixture may be heated to a temperature of about 40 to about 100° C., or about 40-70° C., 40-60° C., 50-80° C., 60-80° C., 75-100° C., 60-90° C., or 50-70° C., such as about 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100° C., or any range thereof. Advantageously, because the reaction mixture contains water as the most abundant solvent, there is no need to pressurize the reaction vessel because the heating is carried out at or below the boiling point of water (i.e., below 100° C.). Reaction mixture can be kept at this temperature for about 2 to about 24 hours, or about 2-6 hour, 4-10 hour, 6-12 hour, 5-15 hour, 7-14 hour, 10-20 hour or 12-24 hour, for example about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 or 24 hours, or any scope wherein.It is estimated that the time that temperature and reaction mixture keep at this temperature will be enough to guarantee that the remaining reaction components (comprising acrylic acid monomer and NCO-terminated polyurethane prepolymer) react completely or substantially completely or significantly completely.Therefore, the required relative temperature and time of any concrete mixture can depend on the reactive species existing.Technician can optimize these parameters.In some cases, can before starting acrylic acid polymerization, reaction mixture is degassed, to remove oxygen. This can be achieved by sparging, for example with nitrogen, helium or other oxygen-free gases, or by continuous freeze-thaw cycles (e.g., 2, 3 or 4 such cycles) or by any other suitable method. In some cases, the acrylic acid polymerization reaction can be carried out in the dark, i.e., in the absence of visible light and / or UV radiation, and optionally in the absence of all electromagnetic radiation.

[0146] The polyurethane prepolymer composition, as well as the neutralized polyurethane prepolymer composition alone or the aqueous colloidal suspension, may have a solids content of about 5% w / v to about 50% w / v, or about 5-40% w / v, 10-30% w / v, 10-20% w / v, 30-50% w / v, or 7-15% w / v, such as about 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48, or 50% w / v. In this context, "solids content" refers to the weight of all materials in 100 mL of solution, excluding solvent. Thus, "solids" may not actually be in solid form.

[0147] coating

[0148] In some cases, the interpenetrating polymer network can be formed by the dispersion of particles in an aqueous solvent, wherein the particles comprise the interpenetrating polymer network or are composed of the interpenetrating polymer network. It can be a colloidal dispersion. The average particle size of the particles of the dispersion can be from about 200nm to about 1000nm, or from about 200-500nm, 500-1000nm, 300-700nm, for example, from about 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950 or 1000nm. In some cases, it can be smaller, for example, as low as about 10nm. For example, it can be from about 10 nm to about 200 nm, or from about 10-100 nm, 10-50 nm, 20-200 nm, 50-200 nm, 100-200 nm, 20-50 nm or 50-100 nm, for example, about 20, 30, 40, 50, 60, 70, 80, 90, 100, 150 or 200 nm. The particles can be monodisperse or polydisperse. Their particle size distribution can be wide or narrow. The ratio of weight average particle size to number average particle size can be from about 1 to about 10 or larger, or from about 1-5, 1-2, 2-10, 5-10 or 2-5, for example, about 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 6, 7, 8, 9 or 10. Therefore, it should be understood that the dispersion comprises or contains a solidified interpenetrating polymer network in the form of colloidal particles dispersed in an aqueous solvent. When applied to a surface, the aqueous solvent can evaporate and the colloidal interpenetrating polymer network particles can adhere to the surface and to each other, leaving a coated surface that is slightly roughened due to the shape and size of the attached colloidal particles. In this regard, the skilled artisan will understand that the method is not about solidifying the polymer on the surface to form a two-polymer system (whether an interpenetrating polymer network, a semi-interpenetrating polymer network, or a polymer blend), but rather about drying and then attaching the colloidal particles comprising, containing, or consisting of the solidified interpenetrating polymer network to the surface to form a film or coating.

[0149] Advantageously, the colloidal dispersions of the present invention are both stable and sprayable. The inventors have discovered that the specific order, timing, and amounts of reactants used (as described above) affect the size of the dispersed particles and the overall stability of the dispersion, and importantly, whether the resulting dispersion is sprayable or whether larger agglomerates are formed that prevent the dispersion from being applied using spray equipment. For example, if the non-crosslinking acrylic monomer is added in the third step (i.e., along with the crosslinking acrylic monomer and free radical initiator) rather than in the second step, the resulting dispersion forms larger agglomerates and is not sprayable (see Examples below and Figure 1 and Figure 2). The inventors understand that the present invention is the first to report a stable, sprayable water-based PU-PMMA IPN dispersion, which is a major technical challenge and the present invention has now solved this problem.

[0150] Dispersion can be free of, substantially free of large particles (such as sediment by-products) that block the spraying device. Dispersion can also have a suitable viscosity so that it can be sprayed evenly without excessive pressure. For example, its viscosity can be lower than about 1000cP, or lower than about 500, 200, 100 or 50cP. Therefore, it is possible to spray by using any suitable device or equipment, and the colloidal dispersion is applied to the surface. In one embodiment, the colloidal dispersion is applied using an artist's spray gun with a pressure of about 2-4 bar (bar), or preferably with a pressure of about 3 bar, and at a distance of about 15-25cm or about 20cm from the surface. However, these variables can be optimized according to the specific characteristics of the colloidal suspension to be sprayed. Although colloidal dispersion can be sprayed, it is also possible that the alternative method applied to the surface is suitable. For example, methods such as wiping, roller coating, spin coating, dip coating, drip coating, electrostatic spinning or some other suitable methods can also be used.

[0151] Once the colloidal dispersion is applied to a surface, it can be allowed to dry, thereby forming a coating or film on the surface. The drying time will depend on a range of conditions, including, but not limited to, the thickness of the coating, the presence of other solvents (except water), and the relative humidity and temperature of the drying. Drying can be carried out at any suitable temperature. It will typically be carried out at ambient temperature, for example, at about 20-25°C, but can also be carried out at elevated temperatures, for example, from about 25°C to about 80°C, or from about 25-50°C, 25-35°C, 35-60°C, 40-70°C, or 50-80°C. For example, it can be carried out at about 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, or 80°C. Suitable conditions are 20-25°C and 40-60% relative humidity. It is expected that the skilled person can optimize the drying conditions. Preferably, the coating is dried at ambient conditions.

[0152] The surface can be any suitable surface. It can be a metal surface, a polymer surface, a wooden surface, a glass surface, a ceramic surface, a synthetic surface or some other surface, or a combination of any two or more of these surfaces. The resulting dried coating can serve as a protective coating. It can also serve as a base coat for subsequent coatings.

[0153] In one embodiment, the particulate material can be applied to the coating after the coating has partially dried. For example, it can be sprayed onto the coating. The particulate material can be applied in the form of a suspension, or it can be applied in the form of dry particles. The suspension can be in a volatile solvent, or it can be in an aqueous solvent. The concentration of the particulate material in the suspension can be from about 1% w / v to about 10% w / v, or about 1-5% w / v, 1-2% w / v, 2-10% w / v, 5-10% w / v, or 2-5% w / v, for example, about 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10% w / v. The particulate material can be applied to the coating after the colloidal suspension has been applied to the surface to form the coated surface for a period of time. The time period can be about 10-100 minutes, or it can be about 10-40 minutes, or about 40-60 minutes, or about 50-75 minutes, or 70-100 minutes, for example, about 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 minutes. This time should be enough to partially dry the coating, but preferably not enough to completely dry the coating. After the particulate solid is applied, the resulting composite solid can be allowed to completely dry. In this context, "completely" means that the residual solvent content is less than about 5% by weight, or less than about 4%, 3%, 2% or 1% by weight. Without being bound by theory, it is believed that the hydrophobic particles provide nano-roughness to the film surface, and the nano-roughness combined with the micro-roughness caused by the colloidal particles provides super-hydrophobicity to the coating.

[0154] The granular material can be a granular solid. Its average particle size can be from about 2 nm to about 20 nm, or from about 2-10 nm, 2-5 nm, 5-20 nm, 10-20 nm, or 5-10 nm, for example, about 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nm. It can be an inorganic granular solid. The particles of the granular solid can have organic and inorganic regions. The granular solid can be hydrophobic. It can be a ceramic. It can be titanium dioxide. It can be iron oxide. It can be a hydrophobic ceramic, such as hydrophobic silica. It can be silica with organic groups grafted onto the particle surface. It can be fumed silica, such as hydrophobic fumed silica. Mixtures of any two or more of these particles can also be used. It can be fumed silica with hydrophobic groups on the surface. The hydrophobic group can be an alkyl group, such as a C1 to C18 linear or branched alkyl group, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, hexyl, octyl, isooctyl, decyl, dodecyl, tetradecyl, or hexadecyl group. It can be a fluoroalkyl group, such as a perfluoroalkyl group. It can be a fluorinated, perfluorinated, or partially perfluorinated form of any of the above alkyl groups. Any two or more of the above hydrophobic groups can be present. For example, the surface of the fumed silica can have fluoroalkyldialkylsiloxy groups. The alkyl group can be any of the above alkyl groups, and the fluoroalkyl group can be any of the above fluoroalkyl groups. For example, the particulate solid can comprise a fumed silicate having 1H,1H,2H,2H-perfluorooctyldimethylsiloxy groups on its surface. It should be noted that "1H,1H,2H,2H-perfluorooctyl" refers to F3C(CF2)5(CH2)2-. The organic group can be present on substantially the entire surface of the particle. When being applied to film, hydrophobic granular solid can be partially wetted by polymer mixture, or it can be fully wetted by polymer mixture.Can wet the partial surface of granular solid particles.Can be before polymer solidification and / or drying, wet granular solid, thereby when solidifying, hydrophobic solid part or at least part embed in the film surface.Embedded particle can have wear resistance.Embedded particle can partially embed in the film surface, part is exposed in the surrounding environment, or they can embed in the film surface fully.In the embodiment that granular solid partly embeds coating surface, estimate that at least a portion of granular solid is directly contactable (that is, granular solid is not fully wetted or completely surrounded by coating surface) at the surface.

[0155] The suspension of particulate material and the dispersion of interpenetrating polymer network particles can each be stable. They can be independently stable for at least about 1 week or at least about 2, 3, 4, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 or 52 weeks or longer. In one embodiment, the dispersion of the present invention is stable for at least 12 months. As will be appreciated by those skilled in the art, environmental conditions such as temperature and humidity, as well as factors such as the material of the storage container or the light source, can affect the stability of the formulation during storage. In this context, the term "stable" means that when the dispersion is stored without stirring, after the shelf life, at room temperature (i.e., about 15-25° C.) and a relative humidity of about 10% to about 60%, the difference between the particle concentration in the upper half of the dispersion and the particle concentration in the lower half of the dispersion is less than about 10%, or less than about 8%, 6%, 4%, 2% or 1%, i.e., the dispersion remains uniform or substantially uniform. As will be appreciated by the skilled artisan, if the temperature and / or relative humidity are reduced, the dispersion is expected to remain sprayable for at least 12 months; similarly, if the temperature and / or relative humidity are increased, the dispersion may not remain stable for up to 12 months. For the avoidance of doubt, it is expected that the aqueous dispersion of the present invention can be stored under laboratory conditions, at room temperature and variable relative humidity, in a glass container, and exposed to light, for at least 12 months and remain sprayable after this storage period.

[0156] Thus, the resulting composite membrane can comprise an interpenetrating polymer network and can have a surface layer containing particulate solids. In this context, a "surface layer" can be the top 20% or 10% or 5% or 2% of the membrane. The surface layer can comprise the interpenetrating polymer network and the particulate solids. It can comprise the particulate solids at least partially embedded in the interpenetrating polymer network. The composite network can be hydrophobic. It can be superhydrophobic. It can have a lotus effect surface. It can exhibit Cassie-Baxter wetting properties. Its WCA can be at least about 150°, or at least about 155°, 160°, or 165°, for example, about 150°, 155°, 160°, 165°, or 170°. Its sliding angle can be less than about 20°, or less than about 15°, 10°, or 5°, for example, about 5°, 10°, 15°, or 20°. It can maintain these values after abrasion. It can maintain these properties after at least 50, or at least 60, 70, 80, 90, 100, 150, 200, 250, 300, 400, 500, 750, or 1000 abrasion cycles. These properties can be defined as in ASTM D4060. At 354 nm and 3.3 mW / cm 2The film can be exposed to UV light for at least 1000 minutes, or at least about 1500, 2000, 2500 or 3000 minutes, and it can still keep these characteristics. After soaking in strong mineral acid for at least 6 hours, or at least 12, 18 or 24 hours, it can still keep these characteristics. After soaking in oil for at least 6 hours, or at least 12, 18 or 24 hours, it can still keep these characteristics. The film is substantially transparent to visible light when thickness is up to 1mm. Its light transmittance under 600nm can be at least about 50%, or at least about 55%, 65% or 70%. The thickness of the film can be about 10 microns to 50 microns (microns), or about 10-30, 20-50, 20-30 or 20-40 microns, for example, about 10, 15, 20, 25, 30, 35, 40, 45 or 50 microns. The thickness of the film can be measured by any suitable means known in the art, such as handheld coating thickness gauges etc.

[0157] The super-hydrophobic film of the present invention can be used for any super-hydrophobicity is the field of advantage, and / or wear resistance and / or durability are the field of advantage.For example, they can be used to reduce the drag coefficient of water vehicles, or reduce ocean fouling, or reduce the corrosion of the body immersed in water, particularly metal body.They can also be used as the coating on electronic equipment, solar panels, glass surfaces, to reduce droplet adhesion (for example, for windshield), for medical equipment so that surface self-cleaning, and for other applications.The super-hydrophobic film of the present invention is that base material forms a useful protective coating, thus improves the resistance to wear and chemical attack.Advantageously, compared with the coating produced with organic solvent (even if organic solvent has been replaced by water), film of the present invention or coating provide at least identical or improved mechanical and chemical properties.

[0158] In a specific embodiment, the present invention relates to a stable, aqueous PU-PMMA colloidal IPN system that self-assembles into a hierarchical, ultra-robust coating during a spray deposition process. This IPN coating can serve as a platform for superhydrophobic nanostructures capable of maintaining a highly dewetting Cassie-Baxter state through mechanical, chemical, and light-induced stresses. These superhydrophobic coatings maintained a pristine lotus leaf dewetting surface (WCA>150°, SA<10°) after 250 rotational abrasion cycles, finger wipe recovery, prolonged immersion in concentrated acid and oil contaminants, and prolonged high-intensity UVC exposure. In addition, the composite interface exhibited excellent optical properties, with a net transmittance loss of 14.8%. These findings provide a PU-PMMA IPN platform with excellent mechanical and chemical properties and ease of application for the synthesis of highly durable and transparent self-cleaning coatings, providing a starting step for many practical applications.

[0159] This paper describes a method for producing highly durable, sprayable, superhydrophobic coatings based on microscale and nanoscale textures, where the microscale texture is provided by colloidal interpenetrating polymer network particles and the nanoscale texture is provided by hydrophobic particulate solids. The sprayable coatings are prepared in aqueous solutions, eliminating the use of volatile organic compounds (VOCs) in known methods. This makes the process more cost-effective and safer, while achieving coatings with durability and physical properties at least equivalent to those produced with volatile solvents.

[0160] Example

[0161] The present invention will be described below with reference to examples which are provided for illustration purposes only; it is not intended that the present invention be limited to only the examples provided herein.

[0162] As described above, it has been advantageously discovered that stable, sprayable APUA IPN dispersions can be produced by either a) adding water and a neutralizing agent to an NCO-terminated polyurethane prepolymer (i.e., Route I synthesis); or b) adding a non-crosslinkable acrylic monomer along with a neutralizing agent separately to the other acrylic system reactants as a medium for dispersing the NCO-terminated prepolymer (i.e., Route II synthesis), as summarized in Scheme 1 below.

[0163]

[0164] It is believed that adding a non-crosslinkable acrylic monomer separately to the other acrylic components, or adding water to effectively dilute the NCO-terminated polyurethane prepolymer, will reduce the formation of precipitates or agglomerates. This is believed to be due to the fact that the addition of the dispersant (either water or non-crosslinkable acrylic monomer) before the addition of the reactive polymerizing agent may completely neutralize the polyurethane NCO-terminated prepolymer. For comparison, see Figure 1 (PU-PMMA IPN system formed without using a dispersion medium) and Figure 2 (The PU-PMMA IPN system is formed by adding a non-crosslinkable acrylic monomer as a dispersion medium and a neutralizer before adding water and the remaining acrylic reagent.) Without being bound by theory, it is expected that these agglomerates are caused by the following reasons: one of the polymer network systems (most likely the polyurethane system) forms faster than the other polymer system (most likely the acrylic system), thus forming large particles. The inventors have noticed that the same phenomenon can be observed when using only a water-based polyurethane system without adding an acrylic system (see Figure 3), which indicates that co-formed acrylic systems can maintain colloidal particles at a dispersible size, provided that the non-crosslinking acrylic monomer is dispersed in the polyurethane prepolymer prior to polymerization—this can be achieved by using the non-crosslinking monomer as a dispersion medium or by adding water to slow the kinetics of the parallel polymerization reaction. For illustrative purposes, examples of these synthetic routes and their characterization are provided below.

[0165] Example 1 - Aqueous Colloidal Dispersion (Synthesis Route 1)

[0166] To synthesize a water-based IPN dispersion containing a polyurethane network and a polyacrylic acid network (i.e., PU-PMMA IPN dispersion), a general example includes mixing isophorone diisocyanate (IPDI, Sigma-Aldrich), 2,2-bis(hydroxymethyl)propionic acid (DMPA, Sigma-Aldrich), polytetramethylene ether glycol (POLYOL, Sigma-Aldrich, Mn=2000), and dibutyltin dilaurate (DBTDL, Sigma-Aldrich, 95%) together and reacting them at 80°C to obtain an NCO-terminated prepolymer, which is then cooled to 60°C and triethylamine (TEA, Sigma-Aldrich) is added to neutralize the ionic centers. Water was then added to the neutralized NCO-terminated prepolymer as a dispersion medium, followed by the chain extender diethylenetriamine (DETA, Sigma-Aldrich) and PMMA precursors methyl methacrylate (MMA, Sigma-Aldrich, 99%), trimethylolpropane trimethacrylate (TRIM, Sigma-Aldrich, 90%), and 2,2′-azobis(2-methylpropionitrile) solution (AIBN, Sigma-Aldrich, 0.2 M in toluene) to obtain an aqueous PU-PMMA IPN dispersion.

[0167] Those skilled in the art will recognize that the molar ratios of the various reactants are most relevant to the stability of the aqueous suspensions of the present invention and the properties of the resulting films or coatings. In this example, the inventors discovered that the optimal relative molar ratios of the reactants are: IPDI:POLYOL from about 8:1 to about 9:1; IPDI:DETA from about 1.5:1 to about 3:1; IPDI:DMPA from about 3:1 to about 4:1; and DMPA:POLYOL from about 2:1 to about 3:1. The inventors discovered that colloidal particles comprising or consisting of PU-PMMA IPNs dispersed in an aqueous solvent, when produced using the methods of the present invention at the aforementioned concentrations and relative ratios, remain well dispersed and stable at room temperature, without agglomerating larger particles that would be unsuitable for spray coating. This stability was observed over extended periods, with samples of the aqueous suspension remaining sprayable approximately one year after formulation.

[0168] Example 2 - Aqueous Colloidal Dispersion (Synthesis of Route II)

[0169] In another method for synthesizing a water-based IPN dispersion containing a polyurethane network and a polyacrylic acid network (i.e., a PU-PMMA IPN dispersion), an isocyanate-terminated prepolymer was first prepared in a 100 mL round-bottom flask by reacting 3.34 g of isophorone diisocyanate (IPDI, Sigma-Aldrich, 98%), which constitutes the hard segment, with 3.74 g of pre-melted polytetramethylene ether glycol (POLYOL, Sigma-Aldrich, average Mn = 2000), which provides the soft segment, and 0.54 g of 2,2-bis(hydroxymethyl)propionic acid (DMPA, Sigma-Aldrich, 98%), which contains hydrophilic carboxyl groups, in the presence of a catalyst, dibutyltin dilaurate (DBTDL, Sigma-Aldrich, 95%). The reaction was allowed to proceed at 90°C for 4 hours with a constant stirring rate of 500 rpm. In addition to adding methyl methacrylate (MMA, Sigma-Aldrich, 99%) as a dispersion medium to achieve a flowing viscosity, an equimolar concentration of triethylamine (TEA, Sigma-Aldrich, >99%) was added to the reaction mixture to neutralize all carboxylic acid groups. The reaction was allowed to proceed to 60°C until all solids were visually dissolved, yielding a neutralized NCO-terminated prepolymer. Furthermore, 0.91 g of the polyurethane crosslinker diethylenetriamine (DETA, Sigma-Aldrich, 99%), 0.24 g of the polypropylene glycol (PPMA) crosslinker trimethylolpropane trimethacrylate (TRIM, Sigma-Aldrich, 90%), 0.12 g of the PPMA initiator 2,2'-azobis(2-methylpropionitrile) solution (AIBN, Sigma-Aldrich, 0.2 M in toluene), and 80 mL of deionized water as a dispersion medium were added to the reaction mixture. The reaction mixture was maintained at a constant stirring rate of 500 rpm to 70° C. for 8 hours to obtain a 90 mL batch of a sprayable water-based IPN dispersion having a solids content of 15%.

[0170] It is noteworthy that in this synthesis method, the molar ratios of the components are the same as described above for the synthesis of Route 1.

[0171] Example 3 - Characterization

[0172] As discussed below, the dispersions obtained from these two synthesis methods were further characterized.

[0173] coating

[0174] In preliminary tests, the aqueous dispersion obtained via Route 1 above was sprayed onto a 3 cm x 3 cm glass surface using an artist's airbrush. Specifically, 1.2 mL of the aqueous dispersion was sprayed at a pressure of 3 bar and a distance of 20 cm from the substrate. After a finger wipe test, the sprayed coating remained on the surface (i.e., the applied dispersion was not removed by manual wiping shortly after application), indicating that the dispersion was firmly attached to the glass surface. Visually, it also appeared to be similar to compositions previously obtained using VOC-based solvent systems (such as those described in WO 2017 / 193157).

[0175] As the skilled artisan will recognize, the main challenge in using waterborne coatings and adhesives is substrate wetting during the coating process. Conventional solvent-based PU-PMMA systems do not cause substrate wetting due to the use of highly volatile organic compounds (VOCs), which evaporate much faster at standard temperature and pressure (SATP). The vaporization enthalpy of acetone (ΔH vap )=31kJ mol -1 , the vaporization enthalpy of xylene (ΔH vap )=42kJ mol -1 , compared with the vaporization enthalpy of water in the aqueous poly(urethane-acrylate) system (ΔH vap )=44kJ mol -1 . In addition, using Raoult's law, the vapor pressure of the acetone-xylene mixture at SATP is 19.58 kPa, which is 600% higher than the vapor pressure of water (3.17 kPa). This indicates that the evaporation rate of the solvent-based PU-PMMA system is significantly higher. In addition, the evaporation of the water-based dispersion is further hindered by the ambient relative humidity of 30%-50% compared to the solvent-based system. The inventors found that by establishing a balance between the deposition of the sprayable colloid and the evaporation of the dispersion medium, the over-wetting of the substrate can be alleviated, which ensures that the fluid does not gradually accumulate on the substrate. The use of a spray gun and nozzle for coating manufacture, combined with optimized spraying parameters, helps to prevent substrate wetting by maintaining a small droplet size while ensuring the durability of the coating.

[0176] Spray Optimization-Wear Analysis

[0177] Since the cured APUA coating is completely wetted by water, the spray volume and spray distance were optimized by studying the changes in optical properties induced by abrasion instead of water contact measurements.

[0178] By making the coated sample withstand hard rotating platform wear tester, this tester is based on ASTM D4060 Taber standard, has two CS-10 wheels (width is 12.7mm, diameter is 51.7mm, Calibrase, the U.S.) and 250g loading on each grinding wheel, for different spraying volumes and spraying distances, the durability of APUA coating is evaluated. Make the sample carry out up to 800 wear cycles at a speed of 60rpm, while measuring optical properties at three different positions of wear track, for quantitative analysis of wear damage. Before each measurement, with the predetermined interval of 0, 100, 200, 400 and 800 wear cycles, use compressed air flow to remove residual material, and then use vacuum to continuously remove dust and debris during the wear process. Because different spraying parameters cause the difference of deposited material to be quite large, therefore according to ASTM D 1003 standard, with TH-100 haze meter (CHNSpec Technology, China) replace traditional weight loss and Taber wear cycle functional relationship measurement transmittance and haze value.

[0179] As the skilled artisan will recognize, transmittance is defined as the percentage of light that passes through a sample, while haze is a measure of the fraction of light that is scattered by an angle greater than 2.5° from the incident source as it passes through an object. The transmittance and haze values of the APUA coating were plotted as a function of hard abrasion at predetermined intervals of 0, 100, 200, 400, and 800 abrasion cycles, see Figure 4 As can be seen, an initial decrease in transmittance of the APUA coating is observed before 100 cycles, indicating an increase in surface roughness due to surface damage caused by abrasion, which is further supported by the increase in haze values in the same range. When abrasion continues for up to 800 cycles, an increase in transmittance is observed, accompanied by a decrease in haze values, indicating that the glass substrate is exposed due to the removal of the coating caused by abrasion, see Figure 4 (a) and 4(c). In addition, the optimization plots for spray volume and spray distance show that a spray volume of 0.5 mL and a spray distance of 10-15 cm showed less change in transmittance and haze values after 100 hard wear cycles, in contrast, a spray volume of 1.0-1.5 mL and a spray distance of 20 cm showed an increase in transmittance and a decrease in haze at 800 cycles compared to 100 cycles due to the removal of the damaged coating. This is expected as it is known that an increase in spray volume increases surface roughness, leading to a higher number of wear points, while an increase in spray distance results in a thinner coating, both of which make the coating susceptible to increased wear damage. The transmittance of the unworn coating produced at a spray distance of 20 cm increased by 1% and the haze decreased by 15% compared to the spray distance of 10 cm, further indicating that increasing the spray distance reduces the coating thickness, participating Figure 4(b) and 4(d).

[0180] Figure 5 The relatively high durability performance of the sprayed APUA coating was demonstrated in

[15] , which was produced using optimized parameters (spray distance 10 cm, spray volume 0.5 mL) and subjected to 1000 hard cyclic abrasion cycles. Qualitatively, the results of this test showed that the coating formed from the water-based PU-PMMA IPN dispersion remained intact until at least 250 cycles, with some small degradation visible at 500 cycles and significant degradation at 1000 cycles, although a small piece of coating material was clearly removed after 1000 cycles (see

[15] ). Figure 5 This indicates that the coating is beginning to fail. However, this result is consistent with more common VOC-based IPN coatings.

[0181] Spectral analysis

[0182] To investigate the successful transition from a solvent-borne PU-PMMA IPN system (as described in WO 2017 / 193157 A1) to a water-borne poly(urethane-acrylate) APUA system, comparative spectroscopic analyses of uncured dispersions and cured coatings from both systems were performed.

[0183] As those skilled in the art will appreciate, Fourier transform infrared spectroscopy (FTIR) techniques, such as transmission, reflection, and attenuated total reflectance (ATR), are commonly used to study the formation of polyurethanes, the presence of hydrogen bonding in urethane and urea-based formulations, and to investigate the reaction kinetics of the system. The chemical composition and successful synthesis of the APUA system were investigated by comparative analysis of uncured suspensions and cured coatings of the APUA and solvent-based PU-PMMA IPN systems using FTIR in attenuated total reflectance mode (FTIR-ATR, using diamond crystals, Bruker-Alpha, USA). All measurements were obtained for uncured samples by drop-casting the colloidal suspension onto an ATR crystal. For cured samples, spray-deposited samples were prepared using an artist's airbrush (nozzle diameter 0.3 mm) onto 25 × 25 mm microscope glass slides. Each formulation was sprayed at a pressure of 3 bar, a spray distance of 10 cm, a spray angle of 90°, and a spray volume of 0.5 mL. A 24-hour cure time was ensured to allow for evaporation of all solvent and stabilization of internal polymer stresses before measurements were taken. Control spin-coated samples were prepared to investigate artifacts caused by the roughness of the sprayed samples; no significant differences were observed in the spectral analysis. Furthermore, a time-dependent study of the APUA reaction system was performed by acquiring spectral information for cured samples at predetermined intervals, with an initial time of 0 h representing the formation of the neutralized NCO-terminated prepolymer, followed by the addition of water, PU crosslinker, and remaining PMMA precursor. The measurement results were recorded at intervals of 0h, 2h, 4h, and 8h. Since the data obtained for the 2h and 4h samples were similar, FTIR spectra were plotted for the APUA-0h, APUA-2h, and APUA-8h samples. Each signal is in the range of 400-4000cm -1 The spectral data were acquired using 24 scans, with each sample scanned three times. The spectral data were plotted and analyzed in OriginPro 2020b.

[0184] In addition to the presence of hydrogen bonding, the unique peaks of the uncured dispersions specific to the solvents used, and the similarity of the peaks of the cured coatings specific to urethane, acrylate, and urea linkages, indicate the successful synthesis of the APUA system, see Figure 6 (a). It is noteworthy that for the cured coating, although the formation of NCO-terminated prepolymers and the presence of the catalyst DBTDL accelerate the formation of urethane bonds and limit isocyanate-water side reactions, the presence of the diamine chain extender leads to the formation of a large number of urea linkages caused by isocyanate-amine reactions. In addition, the bifurcated hydrogens of urea have a strong affinity for forming high-strength, ordered hydrogen bonds at room temperature, which is manifested by the shift of free carbonyl and NH stretching vibrations to lower wavenumbers due to the weakening of CO and NH bonds caused by hydrogen bonding. Shifts as high as 150 cm have been previously reported. -1Comparing the uncured dispersions of the two systems, the solvent-based PU-PMMA dispersion showed characteristic peaks of acetone and m-toluene, as shown at 2967 cm -1 CH3 asymmetric stretching vibration, 2871cm -1 CH3 symmetric stretching vibration, 1713cm -1 Carbonyl (CO) stretching vibration, 1362 cm -1 Symmetric deformation of CH3, 1221cm -1 The CCC asymmetric stretching vibration and 1090 cm -1 In contrast, the uncured aqueous poly(urethane-acrylate) dispersion exhibits characteristic peaks of water, such as 2900–3700 cm -1 The broad area of ​​3300cm -1 The peak at 1640 cm corresponds to the OH stretching vibration. -1 The peak at corresponds to the hydrogen-bonded OH bending vibration.

[0185] In contrast, the cured coatings from the solvent-based and APUA systems showed high similarity, with characteristic peaks of urethane and urea appearing in the following regions: -NH stretching vibration 3150-3500 cm -1 , CH stretching vibration 2700-3000cm -1 , and CO stretching vibration 1600-1800cm -1 , see Figure 6 (b) and (c). For the APUA system, the characteristic peak of ethyl carbamate appears at 1729 cm -1 The stretching vibration of the free carbonyl group (C=O) is 1533 cm -1 is the amide II (N–H) bending vibration, and 3300 cm -1 The hydrogen-bonded NH stretching vibrations at around 3500 cm indicate the presence of hydrogen-bonded urea and urethane linkages. -1 A very weak shoulder peak corresponds to the stretching vibration of free NH, and a double peak is located in the region of 1700-1730 cm-1, of which 1704 cm -1 The peak at 1729 cm -1 H-bonded carbonyl (C–O···H–N) stretching vibration near the free carbonyl peak, 1621 cm -1 The peak at represents the high-intensity ordered hydrogen-bonded carbonyl (C–O···N–H) stretching vibration of urea, which is consistent with the stretching of the free carbonyl of urea at 1687 cm -1 In comparison, there are 66cm -1 In addition, the peak shift of 2255cm of APUA system -1The disappearance of the isocyanate peak of IPDI and the 2235cm peak of TDI in the solvent-derived system -1 The disappearance of NCO stretching indicates that the isocyanate is completely converted into urethane and urea. -1 Overlapping CH stretching vibration at 1729 cm -1 The free carbonyl CO stretching peak at 1447 cm -1 The CH bending vibration at 1062 cm and the 1062 cm- -1 All the peaks indicate the presence of PMMA in the system. Table 1 shows all the characteristic peaks of the uncured dispersions and cured coatings of the solvent-borne PU-PMMA and water-borne poly(urethane-acrylate) systems.

[0186] Table 1: Comparative analysis of the vibration frequencies of uncured dispersions and cured coatings of conventional solvent-based PU-PMMA and water-based poly(urethane-acrylate) systems. All vibration frequencies are expressed in ν ～ (cm -1 ) and obtained experimentally using FTIR.

[0187]

[0188]

[0189] The solvent-based and APUA systems also showed some significant differences, including: (i) hydrogen-bonded urea (1621 cm -1 ) and hydrogen bonded urethane (1729cm -1 ) connection ratio, (ii) hydrogen bonding urethane (1704cm -1 ) linked to free urethane (1729 cm-1), and (iii) the proportion of methylene (2851 cm-1) -1 ) and methyl (2936cm -1 ) ratio.

[0190] Further testing was performed using the above aqueous dispersion (obtained via Route II), which was then sprayed onto the surface of a 25 mm x 25 mm glass microscope slide using an artist's airbrush. Specifically, 0.5 mL of the aqueous dispersion was sprayed at a pressure of 3 bar, a spray angle of 90°, and a distance of 10 cm from the substrate. The dispersion was then left to cure for 24 hours to evaporate any solvent and stabilize stresses within the polymer before measurement. Spin-coated samples were prepared to investigate artifacts caused by the roughness of the sprayed samples; no significant differences were observed in the spectral analysis.

[0191] To further understand the chemical composition of waterborne poly(urethane-acrylate) systems and their similarities to solvent-borne PU-PMMA curing systems, the time-dependent reaction kinetics were investigated by acquiring spectra at time intervals of 0 h, 2 h, 4 h, and 8 h, which are designated APUA-0 h, APUA-2 h, APUA-4 h, and APUA-8 h, respectively. The initial time, t = 0 h, corresponds to the formation of the neutralized NCO-terminated prepolymer and the addition of the PU chain extender diethylenetriamine, the PMMA initiator AIBN, the crosslinker TRIM, and the dispersion medium, deionized water. Due to the similarity in the spectral information obtained for the APUA-2 h and APUA-4 h samples, the FTIR spectra of APUA-0 h, APUA-2 h, and APUA-8 h were plotted and analyzed. Figure 7 (a) It was observed that the APUA-8h sample had a strong 1062cm -1 The peaks correspond to the PMMA backbone swaying, which indicates that the MMA is fully polymerized after the reaction is completed. The delay in PMMA formation is attributed to the presence of hydroquinone monomethyl ether (MEHQ) in the MMA monomer, which acts as an inhibitor that delays the conversion of MMA to PMMA. In addition, three major regions also show obvious changes in peaks over time for urethane and urea formation. They are: (i) 1300-1800 cm-1 corresponding to carbonyl stretching vibration -1 region, (ii) 2900–3700 cm corresponding to NH stretching vibration -1 region, and (iii) 2800–3000 cm-1 corresponding to CH stretching vibration -1 Region, as described below.

[0192] 1.CO region: depends on hydrogen bonding ability, polyurethane is at 1610-1760cm -1 The carbonyl region shows a strong carbonyl absorption band in the range of 1600-1610 cm-1. The interpretation of the carbonyl region is challenging for waterborne poly(urethane-acrylate) systems because after the formation of the neutralized NCO-terminated prepolymer, diamines and water are added simultaneously, and diamines and water show high reactivity with isocyanates. The presence of triamines (TEA) further increases the complexity, which catalyzes the isocyanate-alcohol reaction and accelerates the formation of polyurethanes. In addition, even in the absence of a catalyst, isocyanates and water react readily at room temperature to form urethane linkages, while the addition of a primary amine (DETA) results in a considerably higher reaction rate between isocyanate-amines compared to isocyanate-water. For APUA-0h and APUA-2h samples, the 1610-1680 cm-1 -1 The broad carbonyl peak (at 1637 cm -1), indicating the presence of ordered hydrogen-bonded ureas in the system, which is attributed to the amine-isocyanate reaction and the intermediate carbamate linkage formed by the isocyanate-water side reaction. However, since the more nucleophilic diethylenetriamine is also present in the system in addition to the formation of broad polymer chains, it is understandable that the carbamate linkages are rearranged to form new ethyl carbamate or urea compounds via transcarbamylation, as shown below: 1637 cm -1 Peak disappears, 1621cm -1 The ordered hydrogen-bonded urea peak appears at the peak, and the hydrogen-bonded ethyl carbamate peak at 1704 cm-1 is closely related to the peak at 1725 cm-1. -1 The relative intensity of the free urethane peak at Figure 7 (b) and (d). The higher thermal stability of isocyanate-based ureas than urethane linkages further explains the dissociation of urethane groups when DETA is added to the reaction system. The shift of ordered hydrogen-bonded ureas to lower wavenumbers, while the increase in hydrogen-bonded urethanes, is attributed to the increased polymer network and crosslinking between PU and PMMA, resulting in stronger hydrogen bonding. Stronger hydrogen bonding results in restricted vibrational motion recorded at lower absorption frequencies.

[0193] 2.NH area: except 1199cm -1 CN stretching vibration at 889 cm -1 In addition to the NH stretching vibration at 3367 cm, the APUA-0h sample also -1 There is a broad and strong peak corresponding to the stretching vibration of the free amine at t = 0 h, which indicates that diethylenetriamine was added at t = 0 h, see Figure 7 (c). In contrast, APUA-8h at 3300 cm -1 The peak at 3367 cm-1 of APUA-0h is relatively narrow and has a significantly reduced intensity, indicating that the chain extender DETA is used to generate hydrogen bonded amide linkages via amine-isocyanate reactions. -1 Peak at 3330cm of APUA-2h -1 and 3300cm of APUA-8h -1 displacement, combined with APUA-0h at 1558 cm -1 Towards APUA-2h 1541cm -1 and APUA-8h's 1533cm -1 The displacement further indicates that the hydrogen bonding strength in the waterborne poly(urethane-acrylate) system increases as the reaction proceeds. In addition, the value of amide connection is slightly higher when the reaction is completed, indicating that the increase in chain length and cross-linking in the system leads to an increase in the number of amide groups per unit volume, see Figure 7 (e).

[0194] 3. CH region: CH stretching vibration appears at 2800-3000 cm -1 There are multiple peaks in this region, indicating that there are both methyl (CH3) and methylene (CH2) in the APUA system. -1 and 2851cm -1 The peaks at 2936 cm-1 correspond to the asymmetric and symmetric stretching vibrations of CH2, respectively, while the peaks at 2936 cm-1 correspond to the asymmetric and symmetric stretching vibrations of CH2, respectively. -1 The peak at 1447 cm corresponds to the CH3 asymmetric stretching, while the CH3 symmetric stretching vibration peak is masked by the high intensity CH2 peak. -1 In addition to the peaks corresponding to overlapping CH bending vibrations at 1370 cm- -1 The CH bending peak further confirms the presence of methyl groups in the system. Time-based reaction analysis shows that the symmetric methylene stretching vibration increases over time compared to the asymmetric methyl stretching vibration, see Figure 7 (f) As time goes by, the increase of CH2 groups per unit volume of APUA preparation indicates that the chain extension and cross-linking in the system lead to the formation of interpenetrating long chains between polyurethane and PMMA. In addition, as the reaction proceeds, the -1 The appearance of asymmetric stretching vibration peak of methylene further indicates the existence of long-chain CH2 molecules in the system.

[0195] Example 4 - Superhydrophobicity

[0196] In order to evaluate the superhydrophobicity of the waterborne poly(urethane-acrylate) system, a layer of low surface energy fluorinated silica nanoparticle suspension was spray-deposited on the cured APUA surface. It is reported that the optimal curing time for solvent-borne PU-PMMA system is 20 minutes under SATP conditions, but for the APUA system, due to the delayed evaporation of water and the penetration of F-SiO2 nanoparticles in the still wet APUA layer, no superhydrophobic state was observed for the coating made with a 20 minute curing time. Therefore, the superhydrophobicity of the waterborne poly(urethane-acrylate) system was studied by varying the curing time of the APUA layer (25-40 minutes with a fixed interval of 5 minutes). In addition, the water contact angle (θ W CA ), the durability of the APUA-F–SiO2 superhydrophobic coating was evaluated.

[0197] It was observed that for all APUA samples with curing time of 25-40 min, the surface showed superhydrophobic state, and the initial θ W CAThe angle of curing time is greater than 150°, which indicates that a curing time of at least 25 min is required to obtain an APUA-based superhydrophobic coating. In addition, the sample with a curing time of 25 min also exhibited a superhydrophobic Cassie-Baxter state in up to 100 hard cyclic wear cycles and 200 soft cloth linear wear cycles, but it was observed that the performance deteriorated with increasing curing time, see Figure 8 Since the ΔH of water vap The expected superior performance of the higher, longer cure time samples was replaced by the high performance of the 25 min sample because the optimized spray volume of the APUA system was reduced by 300% compared to the traditional solvent-based PU-PMMA system, resulting in a shortened optimized cure time.

[0198] Example 5-Comparative Example

[0199] To demonstrate that not all aqueous dispersions of polyurethane / polyacrylic acid IPNs are sprayable, the inventors prepared aqueous dispersions disclosed in Yan, et al. (2017) Journal of Materials, Processing and Design, Vol 1, No. 1, pp. 1-9 (herein incorporated by reference in its entirety).

[0200] In this comparative example, the inventors prepared a prepolymer composition in an aqueous environment based on the method of Yan et al. (although some similar substitutions were made due to unavailable chemicals). In this method, the following steps were performed to form a prepolymer polyurethane composition, with the only changes being the use of 1,1,1-tris(hydroxymethyl)propane (instead of polyether 310) and dimethylolpropionic acid (instead of dimethylolbutanoic acid), which the inventors believe are suitable chemical substitutes:

[0201] (a) IPDI (aliphatic diisocyanate) was added to a mixture of polyether 218 (diol), 1,1,1-tris(hydroxymethyl)propane (triol) and dimethylolpropionic acid (a polyol with one acid group) and heated to above 85°C with stirring for 4 hours; then

[0202] (b) After heating, the reaction mixture was cooled to 70°C and hydroxyethyl acrylate (non-crosslinking monomer) was added, followed by continuous stirring for 1 hour. Ethylenediamine (chain extender) was then added, followed by triethylamine (alkylamine) and water to a final solids content of 25%.

[0203] This formulation resulted in a very hard gel that settled to the bottom of the reaction vessel, which the inventors were unable to remove or disperse in hydroxyethyl acrylate or water as suggested in the method of Yan et al. Figure 9 A photograph of the gelled prepolymer is shown, and the inverted Schott bottle clearly shows the undispersed prepolymer. From these results it is clear that the composition of Yan et al. is not sprayable (an advantage of the present invention).

[0204] The inventors attribute this hard gelation to the addition of TRIOL in the first step of the reaction, which leads to the formation of a network, thus causing gelation. Based on their experience, the inventors concluded that the precipitate formed by the gelation precursor could not be dispersed, which is why it is observed here. The inventors also note that this is consistent with the above discussion of Figures 1 to 3 The results discussed are similar, i.e., simultaneous acrylic polymerization and polyurethane chain extension can reduce the aggregation and gelation of polyurethane systems, thus leading to Figure 2 The dispersion seen in .

[0205] This comparative example further demonstrates that the order of reactant addition, particularly including the dispersion medium and neutralizing agent to ensure complete neutralization of the polyurethane prepolymer prior to polymerization of the polymer system, is important in forming sprayable aqueous particle dispersions comprising an interpenetrating polymer network and that not all mixtures comprising a urethane reactant and an acrylate reactant inherently form sprayable dispersions.

[0206] This comparative example further verifies the ease of synthesis of the aqueous PU-PMMA dispersion described herein.

[0207] Although the present invention has been described with reference to specific embodiments, it will be appreciated by those skilled in the art that the present invention may be embodied in many other forms, and in particular, the features of any one of the various described embodiments may be provided in any combination to any other described embodiment. Various modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the invention. It will be understood that the present invention is not intended to be unduly limited by the illustrative embodiments and examples set forth herein, which are presented by way of example only, and that the scope of the invention is intended to be limited only by the claims set forth herein as follows.

Claims

1. A method for preparing a sprayable aqueous colloidal suspension, wherein the colloidal suspension comprises an interpenetrating polymer network comprising a polyurethane network and a polyacrylic acid network, the method comprising the steps of: a) preparing a polyurethane prepolymer composition by mixing the following components at a reaction temperature of about 50° C. to about 120° C.: i. an aliphatic isocyanate having at least two isocyanate groups per molecule; ii. diols; iii. a polyol having at least one acid group per molecule; and iv. polyurethane polymerization catalyst; b) cooling the polyurethane prepolymer composition to a temperature lower than the reaction temperature, and then adding an alkylamine and a dispersion medium to form a neutralized polyurethane prepolymer composition, wherein the dispersion medium is selected from water or a non-crosslinked acrylic monomer; and then c) adding the following components to the neutralized polyurethane prepolymer composition while mixing: i. if the dispersion medium of step b) is a non-crosslinked acrylic monomer, water; or if the dispersion medium of step b) is water, a non-crosslinked acrylic monomer; ii. polyurethane chain extender; iii. cross-linking acrylic acid monomers; and iv. free radical initiators, to form the aqueous colloidal suspension.

2. The method according to claim 1, wherein the aliphatic isocyanate is an aliphatic diisocyanate.

3. The method of claim 2, wherein the aliphatic diisocyanate is isophorone diisocyanate (IPDI).

4. The process according to any one of claims 1 to 3, wherein the polyol is a triol, a tetraol or a pentanol, and at least one hydroxyl group has been substituted with an acid group.

5. The method of any one of claims 1 to 4, wherein the polyol has one carboxylic acid group per molecule.

6. The method of claim 5, wherein the polyol is 2,2-bis(hydroxymethyl)propionic acid (DMPA).

7. The method of any one of claims 1 to 6, wherein the diol is an oligomeric diol or a polymeric diol.

8. The method of claim 7, wherein the diol is poly(tetramethylene ether) glycol.

9. The method of any one of claims 1 to 8, wherein the polyurethane catalyst is dibutyltin dilaurate.

10. The process according to any one of claims 1 to 9, wherein the alkylamine is a trialkylamine. The method according to claim 10 , wherein the trialkylamine is triethylamine (TEA).

12. The method of any one of claims 1-11, wherein the polyurethane chain extender is a diamine, a triamine, or a tetraamine.

13. The method of claim 12, wherein the triamine is diethylenetriamine (DETA).

14. The method according to any one of claims 1 to 13, wherein the non-crosslinking acrylic monomer is an acrylate or a methacrylate.

15. The method of claim 14, wherein the non-crosslinking acrylic monomer is methyl methacrylate.

16. The method according to any one of claims 1 to 15, wherein the cross-linking acrylic monomer is diol di(meth)acrylate, triol tri(meth)acrylate, tetraol tetra(meth)acrylate, or pentanol penta(meth)acrylate.

17. The method of claim 16, wherein the cross-linking acrylic monomer is trimethylolpropane trimethacrylate (TRIM).

18. The method of any one of claims 1 to 17, wherein the free radical initiator is 2,2'-azobis(2-methylpropionitrile) (AIBN).

19. The method according to any one of claims 1 to 18, wherein: The molar ratio of the aliphatic isocyanate to the polyol having at least one acid group per molecule is from 2:1 to 6:1, or about 4:1; and The molar ratio of the aliphatic isocyanate to the diol is from 1:1 to 5:1, or from about 2:1 to 3:1, or about 3:1; and The molar ratio of the non-crosslinking monomer to the crosslinking monomer is 10:1 to 50:

1.

20. The method of any one of claims 1-19, wherein the reaction temperature is from about 70°C to about 100°C, or about 90°C.

21. The method of claim 20, wherein the temperature of step b) is less than or about 60°C.

22. The method according to any one of claims 1 to 21, further comprising: a waiting time of about 2 hours to about 6 hours between step (a) and step (b); and / or A waiting time between step (b) and step (c) of about 10 minutes to about 1 hour; and / or A waiting time of about 4 hours to about 24 hours follows step (c).

23. A method for preparing a coating comprising an interpenetrating polymer network, the method comprising the steps of: a) spraying the aqueous colloidal suspension according to any one of the preceding claims onto a surface to produce a coated surface; and b) applying a particulate solid to the coating surface, wherein substantially the entire surface of the particulate solid is hydrophobic.

24. The method of claim 23, wherein the applying is performed by spraying.

25. The method of claim 23 or 24, further comprising a period of time between applying the aqueous colloidal suspension to produce a coated surface and applying a particulate solid to the coated surface.

26. The method of claim 25, wherein the time period is 10-100 minutes.

27. The method of any one of claims 23-26, wherein the particulate solid is at least partially embedded in the coated surface.

28. A coating produced by the method of any one of claims 23 to 27.

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