WO2018154505A1 - Methods for grafting acrylates onto polymer surfaces - Google Patents

Abstract

Methods of grafting an acrylate coating onto a substrate, and articles comprising a substrate with an acrylate coating are disclosed. The acrylate coatings can be formed by applying a first coating layer comprising at least one acrylate monomer and a Type II photoinitiator onto a first surface area of the substrate; and irradiating the first coating layer to form a first polymeric layer, wherein the polymer coating includes the first polymeric layer. The methods can be performed in open air, at room temperature, at ambient pressure, or without de- aerating the compounds, and the resulting acrylate coatings exhibit improved adhesive properties to the substrate.

Description

METHODS FOR GRAFTING ACRYLATES ONTO POLYMER SURFACES

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Patent Application Serial No. 62/463,152 filed February 24, 2017. The related application is incorporated herein in its entirety by reference.

BACKGROUND

[0001] The present disclosure relates to methods for grafting acrylate coatings onto substrates, and articles containing substrates having such acrylate coatings. In particular, methods are described for photografting a plurality of acrylate monomers onto a polymer surface at room temperature and pressure.

[0002] The phenomenon of peeling is observed with coatings that are physisorbed and not chemisorbed onto the substrate. Physisorption is known to result in poorer adhesion, since it does not involve a chemical linkage between the adsorbent and the adsorbate. However, the typical procedures for generating chemisorbed coatings are often complex processes that require two or more of the following: surface pre-activation; elaborate post-polymerization purification steps; long reaction times of up to a few hours; above ambient temperatures; high vacuum;

controlled atmosphere; oxygen-excluding apparatuses; or specific equipment.

[0003] Thus, it would be desirable to identify new methods for grafting acrylate coatings onto a substrate through chemisorption without such complex processes.

BRIEF DESCRIPTION

[0004] The present disclosure relates to simple, versatile, and rapid methods for chemical binding of acrylate polymer coatings to substrates that are substrate independent, do not require surface pre-activation and that can be conducted at room temperature and pressure, in open air without the need for a controlled atmosphere, without the de-aeration of the chemicals, with or without a solvent, or with conventional equipment. The methods generate acrylate-based coatings that are chemisorbed onto the surface of a substrate yielding a durable functionalization. The reaction takes place via a photo-induced process in the presence of a Type II photoinitiator, which is able to react with the surface of the substrate to generate radicals that initiate the polymerization of acrylate monomers constituting the coating formulation. The reaction results in a polymer matrix (i.e., the coating), which is covalently bonded to the substrate

(chemisorption). The process does not require surface pre-activation, elaborate post- polymerization purification steps, long reaction times, temperatures above ambient temperature, high vacuum, a controlled atmosphere, or specific equipment.

[0005] The method of grafting a polymer coating onto a substrate can comprise applying a first coating layer comprising at least one acrylate monomer and a Type II photoinitiator onto a first surface area of the substrate; and irradiating the first coating layer to form a first polymeric layer, wherein the polymer coating includes the first polymeric layer.

[0006] If desired, steps of the applying and the irradiating can be repeated, so the polymer coating is built up of multiple layers. Each layer can be the same or different from the other layers. In particular embodiments, the polymer coating is built up of at least two polymeric layers. The second polymeric layer can be formed by applying a second coating mixture onto the first irradiated layer, and irradiating the second coating mixture to form a second polymeric layer. The polymer coating is then made up of the first and second polymeric layers. The two polymeric layers can be made from the same coating mixture, or different coating mixtures. These process steps can be performed while at room temperature, at ambient pressure, in open air, or without the de-aeration of the chemicals.

[0007] The applied coating mixture can also be described as a coating layer, and both the coating layer and the coating mixture can be described in terms of monomers that are present within the coating mixture and used to form the coating layer. The coating layer can comprise at least one acrylate monomer having the structure of Formula (1) as further disclosed herein. In specific embodiments, the coating layer/mixture comprises at least of the following acrylate monomers: a hydroxyethyl methacrylate (HEM A); a butyl acrylate (BuA); a methyl

methacrylate (MM A); or acrylic acid (AA).

[0008] In some embodiments, the Type II photoinitiator can comprise a benzophenone. The Type II photoinitiator can comprise at least one of a thioxanthone, a xanthone, or a quinone. The Type II photoinitiator can be present in an amount sufficient to provide about 0.0025 grams to about 1 gram of the Type II photoinitiator per square centimeter of the first surface area of the substrate (i.e. the area of the substrate to be coated with the priming solution).

[0009] The coating mixture/layer can be irradiated by exposing the coating mixture/layer to ultraviolet (UV) radiation. In particular embodiments, the coating mixture is irradiated by exposing the coating layer to UV radiation through the substrate.

[0010] The substrate generally has a surface with abstractable hydrogen atoms. The substrate can be polymeric, such as a polycarbonate or a polypropylene. The substrate can also be transparent to visible and ultraviolet radiation, and/or can be flexible. In particular embodiments, the substrate comprises at least one of a polycarbonate, a poly(methyl methacrylate), a poly(ethylene terephthalate), or a polyolefin.

[0011] In preferred embodiments, there is no need for pre-activating the substrate surface, treating the surface of the substrate prior to applying the coating mixture, or post polymerization purification steps.

[0012] In further embodiments, the method can include washing the coated substrate in a solvent after irradiating the coating mixture/layer. This washing step can remove ungrafted polymer chains that remained on the surface of the substrate.

[0013] Also disclosed are articles with a surface area having an acrylate coating grafted thereto, wherein the acrylate coating is covalently bonded to a surface area of the article. The articles can be made using the methods/processes described herein. The substrates described above can be further processed to obtain the article, for example, by changing the shape of the substrate after the acrylate coating has been grafted thereupon. The article can be a part for infra-red reflectors, haptics devices, self-cleaning devices, sensors (for example, biosensors), photochromic devices, displays, data storage devices, security devices (for example,

anticounterfeiting devices), optical films, robotic devices, or microfluidic devices, and/or devices used for similar applications.

[0014] Also disclosed are polymer coating compositions, comprising at least one acrylate monomer and a Type II photoinitiator.

[0015] These and other non-limiting characteristics are more particularly described below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0017] The following is a brief description of the drawings, which are presented for the purposes of illustrating the exemplary embodiments disclosed herein and not for the purposes of limiting the same.

[0018] FIG. 1 is a flow chart illustrating an exemplary method of grafting an acrylate coating onto a substrate according to the present disclosure.

[0019] FIG. 2 is a side cross-sectional view illustrating a coating mixture that has been applied onto a first surface area of the substrate to form a coating layer, according to an exemplary embodiment of the present disclosure. [0020] FIG. 3 is a diagram illustrating an exemplary method of grafting an acrylate coating onto a first surface area of a substrate according to the present disclosure.

[0021] FIG. 4 is an optical microscopy image in bright field of the cross-section of an untreated 8010MC PC film. The bar at bottom right indicates a length of 200 micrometers (μιη).

[0022] FIG. 5 is an optical microscopy image in UVB light of the cross-section of an untreated 8010MC PC film. The bar at bottom right indicates a length of 200 μιη.

[0023] FIG. 6 is an optical microscopy image in bright field of the cross-section of an 8010MC PC film coated with an acrylate coating formed according to the present disclosure. The bar at bottom right indicates a length of 200 μιη.

[0024] FIG. 7 is an optical microscopy image in UVB of the same acrylate coating shown in FIG. 6. The bar at bottom right indicates a length of 200 μιη.

[0025] FIG. 8 is a Fourier transform infrared (FT-IR) spectra of an untreated 8010MC PC film (the lighter-toned line with an inflection point at 3,363 inverse centimeters (cm ¹), and the same film after grafting with a coating mixture according to the present disclosure (darker- toned line with a zero-slope between about 3,500 cm^"1 and about 3,100 cm^"1).

[0026] FIG. 9 is an optical microscopy image in bright field of the cross-section of an 8010MC PC film coated with only HEMA (i.e. without a Type II photoinitiator), as described in Example 3. The bar at bottom right indicates a length of 200 μιη.

[0027] FIG. 10 is an optical microscopy image UVB light of the same coated film as shown in FIG. 9. The bar at bottom right indicates a length of 200 μιη.

[0028] FIG. 11 is an optical microscopy image in bright field of the cross-section of the surface of an 8010MC PC film solvent-casted with polyHEMA as described in Example 4. The bar at bottom right indicates a length of 100 μιη.

[0029] FIG. 12 is a Fourier Transform Infrared (FT-IR) spectra of the same solvent- casted film as shown in FIG. 11.

[0030] FIG. 13 is a transmission electron microscopy (TEM) image of an 8010MC PC film solvent-casted with polyHEMA. The bar at bottom right indicates a length of 200 μιη. The distance indicated by the arrow is 266 nanometers (nm).

[0031] FIG. 14 is a TEM image of an 8010MC PC film photografted with an acrylate coating mixture according to the present disclosure. The bar at bottom right indicates a length of 5 μιη. The value at the center is 6 μιη. The value at top right is 26 μιη. The value below the top right value is 20 μιη. [0032] FIG. 15 is an optical microscopy image in bright field of the cross-section of an 8010MC PC film coated with a coating mixture and irradiated for 1.5 seconds according to the present disclosure. The bar at bottom right indicates a length of 100 μιη.

[0033] FIG. 16 is an optical microscopy image in bright field of the cross-section of an 8010MC PC film coated with the same coating mixture as in FIG. 15, but irradiated for 3 seconds according to the present disclosure. The bar at bottom right indicates a length of 100 μιη.

[0034] FIG. 17 is an optical microscopy image in bright of the cross-section of an 8010MC PC film coated with the same coating mixture as in FIGS. 15 and 16, but irradiated for 7 seconds according to the present disclosure. The bar at bottom right indicates a length of 100 μιη.

[0035] FIG. 18 is an optical microscopy image taken under ultraviolet B (UVB) light of the cross-section of an 8010MC PC substrate with an acrylate coating comprising poly(butyl acrylate) according to the present disclosure. The bar at bottom right indicates a length of 100 μηι. The top value is 36.87 μιη. The bottom value is 47 μιη.

[0036] FIG. 19 is an FT-IR spectra of the untreated 8010MC PC film (the lighter toned line with the lower peak at about 2,968 cm^"1), and the poly(butyl acrylate)-grafted PC film (the darker-toned line with the higher peak at about 2,964 cm^"1) as shown in FIG. 18.

[0037] FIG. 20 is an optical microscopy image taken under UVB light of the cross- section of an 8010MC PC substrate grafted with an acrylate coating comprising poly(methyl methacrylate) according to the present disclosure. The bar at bottom right indicates a length of 100 μηι. The top value is 5.71 μιη. The bottom value is 6.41 μιη.

[0038] FIG. 21 is an FT-IR spectra of the untreated substrate (the darker-toned line with the lower peak at about 3,041 cm^"1), and the poly(methyl methacrylate)-grafted substrate (the lighter-toned line with the higher peak at about 3,058 cm^"1) as shown in FIG. 21.

[0039] FIG. 22 is an optical microscopy image taken under UVA light of the cross- section of an 8010MC PC substrate grafted with an acrylate coating comprising poly(acrylic acid) according to the present disclosure. The bar at bottom right indicates a length of 100 μιη. The top value is 12.11 μιη. The bottom value is 17.82 μιη.

[0040] FIG. 23 is an FT-IR spectra showing the untreated substrate (the darker toned line with the lower peak at about 2,968 cm^"1), and the poly(acrylic acid)-grafted substrate (the lighter-toned line with the higher peak at about 2,968 cm^"1) as shown in FIG. 22.

[0041] FIG. 24 is an optical microscopy image taken under UVB light of the cross- section of a polypropylene substrate coated with a coating mixture comprising hydroxyethyl methacrylate monomers according to the present disclosure. The bar at bottom right indicates a length of 100 μιη. The value at the top is 10.69 μιη.

[0042] FIG. 25 is an FT-IR spectra showing the untreated substrate (the darker toned line with an approximately zero-slope between about 3,500 cm^"1 and about 3,000 cm^"1), and the substrate with an acrylate coating (the lighter-toned line with an inflection point at about 3,405 cm^"1) as shown in FIG. 24.

[0043] FIG. 26 is an optical microscopy image taken under UVB light of the cross- section of a polypropylene substrate coated with a coating mixture comprising butyl acrylate monomers according to the present disclosure. The bar at bottom right indicates a length of 100 μηι. The value at bottom is 1.75 μιη.

[0044] FIG. 27 is an FT-IR spectra showing the untreated substrate (the darker toned line with no associated peak at about 1,736 cm^"1), and the substrate treated with an acrylate coating (the lighter-toned line with an associated peak at about 1,736 cm^"1) as shown in FIG. 26.

[0045] FIG. 28 is an optical microscopy image taken under UVB light of the cross- section of a polypropylene substrate with an acrylate coating comprising poly(methyl methacrylate) according to the present disclosure. The bar at bottom right indicates a length of 100 μπι.

[0046] FIG. 29 is a FT-IR spectra showing the untreated substrate (the darker-toned line with no associated peak at about 1,734 cm^"1), and the substrate treated with an acrylate coating (the lighter-toned line with an associated peak at about 1,734 cm^"1) as shown in FIG. 28. The value at top is 2.14 μιη.

[0047] FIG. 30 is an optical microscopy image taken under UVB light of the cross- section of a polypropylene substrate with an acrylate coating comprising poly(acrylic acid) according to the present disclosure. The bar at bottom right indicates a length of 100 μιη.

[0048] FIG. 31 is an FT-IR spectra showing the untreated substrate (the darker toned line with no associated peak at about 1,702 cm^"1), and the substrate treated with an acrylate coating (the lighter-toned light with an associated peak at about 1,702 cm^"1) as shown in FIG. 30.

DETAILED DESCRIPTION

[0049] The present disclosure can be understood more readily by reference to the following detailed description of desired embodiments and the examples included therein. In the following specification and the claims which follow, reference will be made to a number of terms which shall be defined to have the following meanings. Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the embodiments selected for illustration in the drawings, and are not intended to define or limit the scope of the disclosure. In the drawings and the following description below, it is to be understood that like numeric designations refer to components of like function. In the following specification and the claims which follow, reference will be made to a number of terms, which shall be defined to have the following meanings.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present invention. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

[0051] The singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. The term "or" means "and/or" unless clearly indicated otherwise by context.

[0052] As used in the specification and in the claims, the term "comprising" can include the embodiments "consisting of and "consisting essentially of." The terms "comprise(s)," "include(s)," "having," "has," "can," "contain(s)," and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that require the presence of the named components/steps and permit the presence of other components/steps. However, such description should be construed as also describing devices or methods as "consisting of and "consisting essentially of the enumerated components/steps, which allows the presence of only the named components/steps, and excludes other components/steps.

[0053] A list comprising "at least one of means that the list is inclusive of each element individually, as well as combinations of two or more elements of the list, and combinations of at least one element of the list with like elements not named.

[0054] Numerical values in the specification and claims of this application should be understood to include (i) numerical values which are the same when reduced to the same number of significant figures and (ii) numerical values which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.

[0055] Numerical values should be understood to include numerical values, which are the same when reduced to the same number of significant figures and numerical values, which differ from the stated value by less than the experimental error of conventional measurement technique of the type described in the present application to determine the value.

[0056] All ranges disclosed herein are inclusive of the recited endpoint and

independently combinable (for example, the range of "2 to 10 grams" is inclusive of the endpoints, 2 grams and 10 grams, and all the intermediate values).

[0057] The term "about" can be used to include any numerical value that can vary without changing the basic function of that value. When used with a range, "about" also discloses the range defined by the absolute values of the two endpoints, e.g. "about 2 to about 4" also discloses the range "of 2 to 4." The term "about" can refer to plus or minus 10% of the indicated number.

[0058] Compounds are described using standard nomenclature. For example, any position not substituted by any indicated group is understood to have its valency filled by a bond as indicated, or a hydrogen atom. A dash ("-") that is not between two letters or symbols is used to indicate a point of attachment for a substituent. For example, the aldehyde group -CHO is attached through the carbon of the carbonyl group.

[0059] The term "aliphatic" refers to a linear or branched array of atoms that is not aromatic. The backbone of an aliphatic group is composed exclusively of carbon. The aliphatic group can be substituted or unsubstituted. Exemplary aliphatic groups include, but are not limited to, methyl, ethyl, isopropyl, hexyl, and cyclohexyl.

[0060] The term "aromatic" refers to a radical having a ring system containing a delocalized conjugated pi system with a number of pi-electrons that obeys Hiickel's Rule. The ring system can include heteroatoms such as nitrogen, sulfur, selenium, silicon and oxygen, or can be composed exclusively of carbon and hydrogen. Aromatic groups are not substituted. Exemplary aromatic groups include, but are not limited to, phenyl, pyridyl, furanyl, thienyl, naphthyl and biphenyl.

[0061] The term "hydroxyl" refers to a radical of the formula -OH, wherein the oxygen atom is covalently bonded to a carbon atom.

[0062] The term "carboxy" or "carboxyl" refers to a radical of the formula -COOH, where the carbon atom is covalently bonded to another carbon atom. A carboxyl group can be considered as having a hydroxyl group, although a carboxyl group can participate in certain reactions differently from a hydroxyl group.

[0063] The term "alkyl" refers to a radical composed entirely of carbon atoms and hydrogen atoms which is fully saturated. The alkyl radical can be linear, branched, or cyclic.

[0064] The term "amino" refers to a radical of the formula -NR₂, where each R is alkyl. [0065] The term "acrylate group" refers to a radical of the formula CH2=CH-CO-0-.

[0066] The term "copolymer" refers to a molecule derived from two or more structural units or monomeric species, as opposed to a homopolymer, which is a molecule derived from only one structural unit or monomer.

[0067] The term "polycarbonate" as used herein refers to a polymer comprising residues of one or more monomers, joined by carbonate linkages.

[0068] The term "substituted" refers to at least one hydrogen atom on the named radical being substituted with another functional group, such as halogen, -OH, -CN, or -N0₂. An exemplary substituted alkyl group is hydroxyethyl.

[0069] The term "crosslink" and its variants refer to the formation of a stable covalent bond between two oligomers/polymers. This term is intended to encompass the formation of covalent bonds that result in network formation, or the formation of covalent bonds that result in chain extension. The term "cross -linkable" refers to the ability of an oligomer/polymer to form such stable covalent bonds.

[0070] The present disclosure refers to "polymers." A polymer is a substance made up of large molecules composed of multiple repeating units chained together, the repeating units being derived from a monomer. The term "polymer" can refer to the substance or to an individual large molecule in the substance, depending on the context. One characteristic of a polymer is that different molecules of the polymer will have different lengths, and the polymer is described as having a molecular weight that is based on the average value of the chains (e.g. weight- average or number- average molecular weight). The art also distinguishes between an "oligomer" and a "polymer", with an oligomer having only a few repeating units, while a polymer has many repeating units. For purposes of this disclosure, the term "oligomer" refers to molecules having a weight- average molecular weight of less than 5,000 g/mol, and the term "polymer" refers to molecules having a weight-average molecular weight of 5,000 g/mol or more, as measured by gel permeation chromatography (GPC) using polycarbonate molecular weight standards. These molecular weights are measured prior to any ultraviolet (UV) exposure.

[0071] The term "thin film" refers to a film with a thickness of at most 0.6 millimeters.

[0072] The terms "room temperature" and "ambient temperature" refer to a temperature of about 20°C to about 25 °C.

[0073] The terms "room pressure" and "ambient pressure" refer to an atmospheric pressure of about 95 kilopascal (kPa) to about 105 kPa.

[0074] The term "open air" refers to air naturally found within the Earth's troposphere. Generally, open air comprises, by volume, about 78% nitrogen, about 21% oxygen, about 1% argon, about 0.04% carbon dioxide, and small amounts of other gases. Open air can further include about 0.001 mass% to about 5 mass% of water vapor.

[0075] The present disclosure refers to a "Type II photoinitiator". A Type II

photoinitiator is a molecule that, in its triplet excited state, can abstract a hydrogen atom from a hydrogen-atom donor, producing an initiating radical. In other words, the photoinitiator must react with a second molecule present in the mixture. In contrast, a Type I photoinitiator undergoes a homolytic bond cleavage, such that the photoinitiator molecule itself splits into two radicals, each of which can initiate a polymerization reaction.

[0076] Continuing now, the present disclosure relates to methods for forming a coating/layer on the surface of a substrate, wherein the coating/layer is formed from or contains an acrylate polymer to functionalize the surface of the substrate. In conventional methods, these acrylate monomers are polymerized directly on the surface to be functionalized. This conventional reaction takes place in the presence of a Type I photoinitiator that, under ultraviolet (UV) light, undergoes a homolytic bond cleavage, resulting in radicals that induce

polymerization of the vinyl groups of the acrylate monomers in the coating formulation. In these processes, the surface of the substrate does not take part in the polymerization, yielding a physisorbed coating.

[0077] However, acrylate-based coatings are often plagued by peeling, or delamination, which consists of the premature detachment of the coating from the substrate, inducing a loss of the function the coating was designed to have, thus reducing its lifespan. This is particularly so for polymeric substrates. Thus, solving the problem of coating delamination is of paramount importance for having a durable functionalization.

[0078] The present disclosure relates to acrylate coatings and methods of photografting one or more acrylate monomers onto a substrate. The acrylate coatings are prepared from a coating mixture comprising at least one acrylate monomer that is applied to a substrate to form a coating layer. More particularly, the acrylate coatings are prepared by irradiating a coating layer containing at least one acrylate monomer and a Type II photoinitiator. When the coating layer is exposed to the appropriate wavelength and intensity of light, the Type II photoinitiator induces a reaction with the surface of the substrate and with the acrylate monomers, forming an acrylate polymer matrix that is chemically attached to the substrate. The present disclosure also relates to articles having such acrylate coatings made using the methods described herein. These articles can be useful in applications such as infra-red reflectors, haptics, self-cleaning applications, sensors/biosensors, photochromies, displays, data storage, anticounterfeiting/security, optical films, robotics (e.g. controlling friction of the surface), and microfluidics. [0079] Generally, the methods of the present disclosure include (a) applying a coating layer comprising one or more acrylate monomers to a surface of a substrate, and then (b) irradiating the coating layer with UV light to induce photopolymerization of the acrylate monomers. The operation of the Type II photoinitiator also induces radicals upon the surface of the substrate, which then participate in the polymerization process with the acrylate monomers. The acrylate coatings are thereby covalently bound (i.e. chemisorbed) to the surface of the substrate, and exhibit improved adhesion properties. Furthermore, the processes disclosed herein can be performed in open air, at room temperature, at ambient pressure, and without de- aerating the chemical components. Notably, the methods can be performed in an oxygen- containing atmosphere such as open air. Thus, the use of an inert atmosphere (e.g. nitrogen or argon) is not needed.

[0080] FIG. 1 illustrates an exemplary method of grafting an acrylate coating onto a substrate according to one embodiment of the present disclosure. The method begins at step S 100.

[0081] At step S 120, a coating mixture is applied to a first surface area of a substrate, to form a coating layer. As discussed further below, the coating mixture comprises at least one acrylate monomer. In particular embodiments, the coating mixture comprises a plurality of acrylate monomers. In specific embodiments, the coating mixture comprises a Type II photoinitiator.

[0082] The coating mixture can be applied to one or more different surfaces of the substrate, or to only a portion of a surface of the substrate, depending on the desired area to be grafted with the acrylate coating. The coating mixture can be applied directly to the substrate, with no intervening layers in between. In particular embodiments, the coating layer can be formed by dip-coating or flow-coating the coating mixture onto a first surface area of the substrate. In further embodiments, the coating mixture can be applied while at room

temperature, at ambient pressure, in open air, or without de-aerating the chemicals.

[0083] Before being coated with the coating mixture, the substrate can first be prepared by rinsing the substrate with demineralized water and dried with compressed air to constant weight. In some embodiments, the substrate or a portion of the substrate can be treated with a basic solution that enriches the substrate surface with hydrogen atoms through hydrolysis of carbonate bonds. The base/hydrolyzing agent can be, for example, at least one of potassium hydroxide, sodium hydroxide, or any other suitable base. The basic solution generally has a pH of greater than 7 to 14. The substrate can be treated by, for example, exposing the surface area of the substrate to the basic solution for a time period of about 30 seconds to about 300 seconds. In particular embodiments, the substrate can be treated by placing the substrate in a solution comprising the base and a solvent, wherein the hydrolyzing agent is about 0.1 wt% to about 10 wt% of the solution. The solvent can be water. However, the pre-treatment does not include pre-exposure to any photoinitiators.

[0084] FIG. 2 is a side cross-sectional view 100 illustrating a first coating layer 135 that has been formed by applying a coating mixture to a first surface area 122 of a substrate 120, as described in step S 120. As seen here, the first coating layer 135 is directly contacting the substrate 120. Generally, the substrate 120 can have at least a first surface with a first surface area 122 and a second surface 124 opposite the first surface, although the substrate 120 can be provided in many shapes and sizes.

[0085] Referring back to FIG. 1, at step S 140, the coating layer on the substrate is irradiated to form the acrylate coating. The layer can be irradiated by exposure to ultraviolet (UV) light at an appropriate wavelength and in an appropriate dosage that brings about the desired amount of photopolymerization and crosslinking of the acrylate monomers for the given application. The irradiation should reach the substrate-coating interface, permitting the photoinitiator to cause the formation of covalent bonds between the substrate and the acrylate polymers formed during the irradiation. The irradiation can be uniform over the entire coated area of the coating layer on the substrate or on only a portion of the coated area to result in a polymer coating located in only the irradiated portion. The resulting acrylate coating is chemisorbed onto the substrate.

[0086] In particular embodiments, the coating mixture/layer is directly exposed to UV light. In other embodiments, the coating layer is not directly exposed to UV light. Rather, in such embodiments, a second surface of the substrate is exposed to the UV light, and the coating layer is irradiated by UV light transmitted through the substrate. This can occur when the substrate 120 is transparent to visible light/UV radiation. This also permits the irradiation to reach the substrate-coating interface.

[0087] The exposure time of the coating mixture to the photoactivating radiation will be dependent on the application and the particular properties of the substrate (e.g., % light transmittance). In particular embodiments, the coating mixture can be irradiated for about 1 second to about 1 hour, depending on the irradiation system. In more specific embodiments, the irradiation time is about 1 second to about 1 minute, or about 1 second to about 10 seconds.

[0088] The irradiation can be accomplished by using a UV-emitting light source such as a mercury vapor, High-Intensity Discharge (HID), or various UV lamps. For example, commercial UV lamps are sold for UV curing from manufacturers such as Excelitas, Heraeus Noblelight, and Fusion UV. Non-limiting examples of UV-emitting light bulbs include mercury bulbs (H bulbs), or metal halide doped mercury bulbs (D bulbs, H⁺ bulbs, and V bulbs). Other combinations of metal halides to create a UV light source are also contemplated. Exemplary bulbs could also be produced by assembling the lamp out of UV-absorbing materials and considered as a filtered UV source. A mercury arc lamp is not used for irradiation. An H bulb has strong output in the range of 200 nm to 320 nm. The D bulb has strong output in the 320 nm to 400 nm range. The V bulb has strong output in the 400 nm to 420 nm range.

[0089] It can also be advantageous to use a UV light source where the harmful wavelengths (those that cause polymer degradation or excessive yellowing) are removed or not present. Equipment suppliers such as Excelitas, Heraeus Noblelight, and Fusion UV provide lamps with various spectral distributions. The light can also be filtered to remove harmful or unwanted wavelengths of light. This can be done with optical filters that are used to selectively transmit or reject a wavelength or range of wavelengths. These filters are commercially available from a variety of companies such as Edmund Optics or Praezisions Glas & Optik GmbH. Bandpass filters are designed to transmit a portion of the spectrum, while rejecting all other wavelengths. Longpass edge filters are designed to transmit wavelengths greater than the cut-on wavelength of the filter. Shortpass edge filters are used to transmit wavelengths shorter than the cut-off wavelength of the filter. Various types of material, such as borosilicate glass, can be used as a long pass filter. Schott and/or Praezisions Glas & Optik GmbH, for example, have the following long pass filters: WG225, WG280, WG295, WG305, and WG320, which have cut-on wavelengths of about 225, 280, 295, 305, and 320 nm, respectively. These filters can be used to screen out the harmful short wavelengths while transmitting the appropriate wavelengths for the crosslinking reaction. An exemplary lamp is a high pressure 200 watt mercury vapor short arc, used in combination with a light guide. A filter and an adjustable spot collimating adapter (for spreading the light beam over a large surface) can also be used. Of course, protective equipment to protect the user can also be used.

[0090] In particular embodiments, the coating layer is exposed to light that includes UVA light wavelengths with an intensity of 30.5 milliwatts per centimeter squared (mW/cm²) at a distance of 23 centimeters (cm) from the light source. Ultraviolet A (UVA) refers to wavelengths of 320 nm to 390 nm. This irradiation can be accomplished using a Collimated EXFO Omnicure™ S2000 lamp.

[0091] In step S 160, the coated substrate 210 is washed to remove unbound acrylate polymer chains from the surface of the substrate 220. In particular embodiments, the substrate 210 can be sonicated in a solvent, such as isopropyl alcohol (IPA). The substrate 210 can be washed for about 1 minute to about 60 minutes. The substrate 210 can be dried afterwards by compressed air to constant weight. It should be noted that this step S 160 is optional, and does not need to be performed.

[0092] At S200, the methods end with a substrate having one or more surface areas covered with an acrylate coating. The resulting coating containing an acrylate polymer can have a thickness of about 10 nanometers (nm) to about 30 micrometers (μιη), or 50 nm to 1 micrometer, though other thicknesses can be made.

[0093] FIG. 3 is a diagram illustrating one exemplary method of grafting a polymer coating 250 onto a substrate 220 according to one embodiment of the present disclosure.

Starting at the far left, a first surface area 222 of the substrate 220 is dipped into a coating mixture 230 contained within a vessel 210. In the middle, the dipped substrate 220 has a first surface area 235 with the coating mixture thereon and a second surface area 224 that does not have coating mixture thereon. At the far right, after exposure to UV radiation, the first surface area now has a polymeric coating 250 chemisorbed onto the substrate 220. The second surface area 224 remains uncoated.

[0094] The methods described herein are simple and versatile and can be used to generate polymer coatings from acrylates, with the polymer coatings being covalently bonded to the surface of the substrate. The methods can be performed in the presence of oxygen, so the use of oxygen-excluding devices and inert atmospheres is not needed. The methods described herein can be performed without pre-activating the surface of the substrate, treating the surface of the substrate with other substances prior to applying the coating layer (e.g., plasma treatment, or acid/base application, or coating with a thin layer of a hydrogen-rich material like polydopamine or polyphenols); or post polymerization purification steps.

[0095] In particular embodiments of the present disclosure, the substrate upon which the acrylate polymer coating is formed is a polymeric substrate. The substrate can comprise a polycarbonate or a blend containing a polycarbonate, e.g. LEXAN™ 8040 or LEXAN™ 8010. Other suitable substrates can include poly(methyl methacrylate) (PMMA); poly(ethylene terephthalate) (PET); polycarbonate copolymers such as polycarbonate-poly siloxane copolymers or LEXAN™ CFR; and polyolefins such as polypropylene. Generally, the substrate should have hydrogen atoms at its surface that can be extracted.

[0096] The substrate can be in the form of a molded article, a sheet, or a film. The substrate can be formed by a variety of known processes, such as casting, profile extrusion, film and/or sheet extrusion, sheet-foam extrusion, injection molding, blow molding, thermoforming, and the like. The substrate itself can be a component of an article, such that the article comprises a substrate to be coated with an acrylate coating.

[0097] The coating mixture used in the present disclosure can include a Type II photoinitiator. When exposed to UV light, the Type II photoinitiator reacts with the surface of the substrate to generate radicals that initiate the polymerization of the acrylate monomers in the coating layer. Hydrogen atoms are abstracted from the substrate surface and from the grafted acrylate coating as the reaction proceeds. In particular embodiments, the Type II photoinitiator can comprise at least one of a benzophenone, a thioxanthone, a xanthone, or a quinone.

[0098] Benzophenones are also known as diphenylmethanone, diphenylketone, or benzoyl benzene. Benzophenones have the general structure of Formula (i), where each W is independently alkyl, carboxyl, hydroxyl, or amino, and m and n are independently integers of 0

Formula (i)

to 2. Exemplary benzophenone Type II photoinitiators include benzophenone (m=n=0);

3,3',4,4'-Benzophenonetetracarboxylic dianhydride (m=n=2); 4,4'- bis(diethylamino)benzophenone; 4,4'-bis(dimethylamino)benzophenone; 4,4'- dihydroxybenzophenone; 4-(dimethylamino)benzophenone; 2,5-dimethylbenzophenone (m=0, n=2); 3,4-dimethylbenzophenone (m=0, n=2); 3-hydroxybenzophenone (m=0, n=l); 4- hydroxybenzophenone; 2-methylbenzophenone; and 3-methylbenzophenone. The Type II photoinitiator can be about 0.1 wt% to about 20 wt% of the coating mixture based on the total weight of the coating mixture.

[0099] Thioxanthones and xanthones are compounds that contain a structure of Formula

(ii),

Formula (ii)

wherein X is sulfur or oxygen. The thioxanthone/xanthone can have substituents such as alkyl; halogen; and alkoxy. Exemplary thioxanthone Type II photoinitiators include thioxanthone; 1- chloro-4-propoxythioxanthone; 2-chlorothioxanthone; 2,4-diethylthioxanthone; 2- isopropylthioxanthone; 4-isopropylthioxanthone; and 2-mercaptothioxanthone.

[0100] Quinones generally have a fully conjugated cyclic dione structure. Exemplary quinone Type II photoinitiators include anthraquinone; anthraquinone-2- sulfonic acid;

camphorquinone; 2-ethylanthraquinone; and phenanthrenequinone.

[0101] The coating mixture used to form the coating layer also contains at least one acrylate monomer in addition to the Type II photoinitiator. In particular embodiments, when exposed to UV light, the Type II photoinitiator initiates polymerization of the acrylate monomers, forming a polymer matrix containing an acrylate polymer that is chemically bonded to the surface area of the substrate (i.e. chemisorption).

[0102] The acrylate monomer(s) used in the coating mixture have the structure of Formula (1):

Formula (I)

wherein Ri, R₂, R₃, and R₄ are each independently hydrogen, alkyl, or substituted alkyl.

[0103] Examples of acrylate monomers that can be used in the present disclosure include methacrylates (R₂=CH ); hydroxyethyl methacrylate (HEMA) (Ri=-CH₂CH₂OH; R₂=CH ;

R₃=R₄=H); butyl acrylate (BuA) (Ri=-CH₂CH₂CH ; R₂=R₃=R₄=H); methyl methacrylate (MMA) (Ri=R₂=CH ; R₃=R₄=H); and acrylic acid (AA) (Ri=R₂=R₃=R₄=H). Combinations of such monomers are also contemplated.

[0104] Acrylate monomers generally are in liquid form at room temperature. As a result, the monomer itself, or mixture of multiple monomers, can act as a solvent in the coating mixture that is applied to the surface of the substrate. Where the acrylate monomers are provided with an inhibitor such as 4-methoxyphenol (MEHQ), the monomers can be first prepared by removing the inhibitor. For example, in some embodiments, the acrylate monomers are first passed through basic alumina to remove the inhibitor. However, removal of inhibitor is not necessary for the methods of the present disclosure, and is an optional step. The coating mixture can comprise about 10 wt% to about 99 wt% of acrylate monomers (by solids).

[0105] If desired, the acrylate monomers can be mixed/dissolved with a solvent to form the coating mixture. In particular embodiments, the solvent can be about 1 wt% to about 60 wt% of the coating mixture, or about 40 wt% to about 60 wt% of the coating mixture based on the total weight of the coating mixture. The solvent can comprise at least one of an alcohol (for example, ethanol or isopropyl alcohol); an alkane; or water.

[0106] If desired, an oxygen scavenger can also be added to the coating mixture. In specific embodiments, the oxygen scavenger can be about 0.1 wt% to about 10 wt% of the coating mixture, including about 0.5 wt% to about 5 wt% of the coating mixture. The oxygen scavenger can comprise at least one of ascorbic acid, sodium hydrogen carbonate, hydrazine, phenyl hydrazine, a phosphite, a sulfite, tin 2-ethylhexanoate, or glucose. The oxygen scavenger is optional, and does not need to be present.

[0107] Articles can also be formed with a grafted polymer (acrylate) coating thereon. The substrate itself can be considered an article, or the substrate can be further processed into an article. For example, the shape of the substrate could be altered after the polymer coating has been applied to obtain the desired article.

[0108] As mentioned above, the polymer coating can be formed from more than one layers. This can be done by sequentially applying coating layer(s) to a first polymeric layer to abstract hydrogen atoms from the first polymeric layer. The second coating layer is then irradiated to form a second polymeric layer. In this way, multiple polymeric layers can be built up, for example, 2 to 10 layers, or 2 to 5 layers. Two-layer coatings can be useful for certain applications such as infra-red reflection.

[0109] In such methods, after the first polymeric layer is formed, a second coating mixture is applied to the first polymeric layer to form a second coating layer. The second coating layer does not have to be applied to the entirety of the first polymeric layer unless it is desired to do so. The first coating mixture (used to form the first polymeric layer) and the second coating mixture can be the same or different.

[0110] The second coating mixture is then irradiated to form a second polymeric layer. The first polymeric layer and the second polymeric layer together form a polymer coating. It is noted that the application of the second coating layer causes abstraction of hydrogen atoms from the first polymeric layer, so the second polymeric layer is covalently bonded (i.e. chemisorbed) to the first polymeric layer and through the polymeric layer to the substrate.

[0111] The following examples are provided to illustrate the coatings and methods of the present disclosure. The examples are merely illustrative and are not intended to limit the disclosure to the materials, conditions, or process parameters set forth therein.

EXAMPLES

[0112] Materials and Instrumentation: [0113] Unless stated otherwise, all the operations were conducted in plain air and without de-aerating the chemicals. The abbreviation "PC" is used for polycarbonate.

Isopropanol (IPA, 99.5%, Acros), potassium hydroxide (85%, Acros), hydroxyethyl

methacrylate (HEMA, 97%, Fischer Scientific), acrylic acid (AA, 98%, Acros), methyl methacrylate (MMA, 99%, Acros), butyl acrylate (BuA, 98%, Merck), benzophenone (BP, 99%, Acros), ascorbic acid (99%, Acros), azobisisobutyronitrile (AIBN, 98%, Acros), and basic alumina (99%, Sigma- Aldrich) were used as received. PC sheets (Lexan 8010MC, 0.175 mm gauge thickness, SABIC), PC slabs (injection molded Lexan LS I Resin, 3 mm gauge thickness, SABIC), and PP slabs (Moplen F1000HC, SABIC) were cut to 2.5x2.5 cm pieces.

[0114] The UV treatment was carried out with a C211 benchtop conveyer equipped with two 1300 300 watt lamps kept at approximately 5 cm from the substrate. All experiments were carried out with a fixed belt speed (0.3 seconds of exposure per pass), where the number of passes determined the total amount of radiation applied. Sonication was conducted with a FB 11207 Sonicator. All FTIR images were taken with a Perkin Elmer Spectrum One FTIR spectrometer between 4,000 and 600 cm^"1. Light microscopy imaging was carried out with an Olympus BX60 microscope. Images were viewed under normal light conditions or UV illumination. TEM images were taken using a FEI Tecnai T12 microscope. SEM images were taken using a 7800F microscope. Molecular weight measurements were carried out on an Agilent 1100 series GPC with a PLgel 5 μιη minimax-C 250x4.6 mm column, using 0.01 LiBr in DMF as eluent and calibrated with PMMA standards.

[0115] General Procedure for the Surface Photografting:

[0116] The polycarbonate (PC) substrate was rinsed with demineralized water and dried with compressed air to constant weight. The substrate was then coated (by dip-coating or flow- coating) with a solution of benzophenone (BP) and the monomer, placed face-down in a Petri dish, UV-treated for a given amount of time, sonicated in a solvent for 30 minutes at room temperature and 660 wat using the pulse mode, and dried with compressed air to constant weight. In some cases, the PC surface was pretreated; a solvent and/or ascorbic acid were added to the monomer/BP mixture; and the inhibitor was removed from the monomer prior to the experiment.

[0117] Polymerization of HEMA with AIBN:

[0118] 15 milliliters (mL) of HEMA were placed in a 100 mL round bottom flask equipped with a cooler. The HEMA was passed through a glass filter containing 10 g of basic alumina to remove the inhibitor. 0.8 grams of AIBN were added after which the mixture was stirred and heated with an oil bath. The AIBN was completely dissolved when the reaction mixture reached 40°C. The mixture was heated until it reached 75°C, after which the heating bath was removed. At this point, the reaction mixture was opaque and an increased viscosity was observed. 20 mL of tetrahydrofuran (THF) were added and the resulting mixture was poured into a beaker containing 200 mL hexane, which caused the polymer to precipitate. The mixture was filtered and the collected white solid (polyHEMA) was oven dried. 13.2 grams of polyHEMA were obtained.

[0119] Inventive Formulations:

[0120] Table 1 shows the various coating layer com positions used in the Examples:

Table 1. Compositions of coating layer mixtures.

Example 1

[0120] An 8010MC PC sheet was dip-coated in a solution containing 10 wt% BP and 90 wt% HEMA. The sheet was then exposed to UV light for 4.5 seconds (equivalent to 15 passes in the UV device), sonicated in IPA, and dried. The observation via the optical microscope of the film cross-section revealed the presence of a coating on both faces as seen in FIG. 6 and FIG. 7. As seen in FIG. 8, FT-IR confirmed that the coatings were composed of polyHEMA.

Example 2

[0121] An 8010MC PC sheet was flow-coated with a solution containing 10 wt% BP and 90 wt% HEMA. The sheet was then exposed to UV light for 4.5 seconds (equivalent to 15 passes in the UV device), sonicated in IPA, and dried. The observation via the optical microscope of the substrate cross-section as well as the analysis of the surface by FT-IR revealed the presence of a polyHEMA coating on both faces similar to the one of Example 1. Example 3

[0122] An 8010MC PC sheet was dip-coated in HEMA only, exposed to UV light for 4.5 seconds (equivalent to 15 passes in the UV device), sonicated in IPA, and dried. As seen in FIG. 9 and FIG. 10, no coating was observed under the microscope or signals referable to polyHEMA were detected by FT-IR, indicating that the UV photons alone do not induce the grafting of HEMA. This indicates the need for the presence of the Type photoinitiator to cause

polymerization of the monomer.

Example 4

[0123] The polyHEMA prepared via AIBN-initiated polymerization (see above) was dissolved in IPA, and then solvent-casted onto an 8010MC PC sheet. The resulting coated sample was subjected to sonication in IPA for 30 minutes, and dried with compressed air to constant weight. As illustrated in FIG. 11 and FIG. 12, when the sample was analyzed by optical microscopy and FT-IR, no polyHEMA could be detected on the surface. This is a strong indication that sonication in IPA is able to remove the unbound chains from the surface. When analyzed by TEM, the coating-substrate interface of the PC with solvent-casted polyHEMA and the one obtained from photografting (Example 1) turned out to be different. While the former showed a sharp interface between PC and polyHEMA (as seen in FIG. 13), a diffusion layer was present in the layer (as seen in FIG. 14). In other words, pre-prepared polyHEMA was not physisorbed onto the substrate, whereas the photografted polyHEMA was physisorbed.

Example 5

[0124] An 8010MC PC sheet was dip-coated in HEMA only for the usual amount of time, sonicated in IPA for 30 minutes, and dried with compressed air to constant weight A layer on the top of the PC surface similar to the diffusion layer in Example 4 was observed by TEM, although no trace of HEMA was detected in it via FT-IR. This indicates that HEMA alone has the ability to diffuse into the PC and modify its morphology, but does not interact with the substrate strongly enough to survive the rinsing procedure, similar to polyHEMA in the solvent- casting experiment of Example 4.

Example 6

[0125] In a series of three experiments, 8010MC PC sheets were dip-coated in a solution containing 10 wt% BP and 90 wt% HEMA. The sheets were then exposed to UV light for 1.5 seconds, 3 seconds, or 7.5 seconds (equivalent to 5, 10, and 25 passes in the UV device, respectively), sonicated in IPA, and dried. The observation under the optical microscope of the films' cross-section showed that the coating thickness is positively correlated with the UV exposure time. As seen in FIGS. 15-17, the coating thickness (distinguished from the substrate by a dashed-line) increases as the UV exposure is increased from 1.5 seconds, to 3 seconds, and to 7.5 seconds in FIGS. 15, 16, and 17 respectively.

Example 7

[0126] An 8010MC PC sheet was dip-coated in a solution containing 10 wt% BP and 90 wt% HEMA. The HEMA was passed beforehand through basic alumina for removing the inhibitor. The sheet was then exposed to UV light for 4.5 seconds (equivalent to 15 passes in the UV device), sonicated in IPA, and dried. A slightly greater grafting density was obtained with respect to Example 1. This indicates the desirability of removing any inhibitor.

Example 8

[0127] An 8010MC PC sheet was placed in a 2 wt% solution of KOH in water for up to 120 seconds to enrich the PC surface with hydrogen atoms via hydrolysis of the carbonate bond. The substrate was then rinsed with demineralized water and dried with compressed air. Next, the substrate was dip-coated in a solution containing 10 wt% BP and 90 wt% HEMA. The sheet was then exposed to UV light for 4.5 seconds (equivalent to 15 passes in the UV device), sonicated in IPA, and dried. A slightly greater grafting density was obtained with respect to Example 1. This indicates the desirability of using a basic solution prior to applying the coating mixture.

Example 9

[0128] An 8010MC PC sheet was dip-coated in a solution containing 10 wt% BP, 89 wt% HEMA and 1 wt% of ascorbic acid. The sheet was then exposed to UV light for 4.5 seconds (equivalent to 15 passes in the UV device), sonicated in IPA, and dried with compressed air. A slightly greater grafting density was obtained with respect to Example 1. This indicates the desirability of using an oxygen scavenger in the coating mixture.

Example 10

[0129] An 8010MC PC sheet was dip-coated in a solution containing 99 wt% HEMA and 1 wt% in ascorbic acid. The sheet was then exposed to UV light for 4.5 seconds (equivalent to 15 passes in the UV device), sonicated in IPA, and dried. The observation via the optical microscope of the substrate cross-section as well as the analysis of the surface by FT-IR revealed that grafting did not take place.

Example 11

[0130] An LS I plaque was flow-coated with a solution containing 10 wt% BP and 90 wt% HEMA. The sheet was then exposed to UV light for 4.5 seconds (equivalent to 15 passes in the UV device), sonicated in IPA, and dried. The observation via the optical microscope of the substrate cross-section as well as the analysis of the surface by FT-IR revealed the presence of a coating similar to the one of Example 1.

Example 12

[0131] An 8010MC PC sheet was dip-coated in a solution containing 10 wt% BP, 48 wt% BuA (passed beforehand through basic alumina to remove the inhibitor), 1 wt% ascorbic acid, and 41 wt% isopropyl alcohol. The sheet was then exposed to UV light for 4.5 seconds (equivalent to 15 passes in the UV device), sonicated in IPA, and dried. The observation via the optical microscope of the substrate cross-section as well as the analysis of the surface by FT-IR revealed the presence of a polyBuA coating (as seen in FIG. 18 and FIG. 19).

Example 13

[0132] An 8010MC PC sheet was dip-coated in a solution containing 10 wt% BP, 35 wt% MMA (passed beforehand through basic alumina to remove the inhibitor), 1 wt% ascorbic acid, and 54 wt% of isopropyl alcohol. The sheet was then exposed to UV light for 4.5 seconds (equivalent to 15 passes in the UV device), sonicated in IPA, and dried. The observation via the optical microscope of the substrate cross-section as well as the analysis of the surface by FT-IR revealed the presence of a polyMMA coating (as seen in FIG. 20 and FIG. 21).

Example 14

[0133] An 8010MC PC sheet was dip-coated in a solution containing 10 wt% BP, 46 wt% AA (passed beforehand through neutral alumina to remove the inhibitor), 1 wt% ascorbic acid, and 43 wt% in water. The sheet was then exposed to UV light for 4.5 seconds (equivalent to 15 passes in the UV device), sonicated in IPA, and dried. The observation via the optical microscope of the substrate cross-section as well as the analysis of the surface by FT-IR revealed the presence of a poly(acrylic acid) coating (as seen in FIG. 22 and FIG. 23). Example 15

[0134] A polypropylene (PP) plaque was dip-coated in a solution containing 10 wt% BP, 89 wt% HEMA (passed beforehand through basic alumina to remove the inhibitor), and 1 wt% ascorbic acid. The sheet was then exposed to UV light for 4.5 seconds (equivalent to 15 passes in the UV device), sonicated in IPA, and dried. The observation via the optical microscope of the substrate cross-section as well as the analysis of the surface by FT-IR revealed the presence of a polyHEMA coating (as seen in FIG. 24 and FIG. 25). A lower grafting density was obtained with respect to Example 1.

Example 16

[0135] A PP plaque was dip-coated in a solution containing 10 wt% BP, 48 wt% BuA (passed beforehand through basic alumina to remove the inhibitor), 1 wt% ascorbic acid, and 41 wt% isopropyl alcohol (IPA). The sheet was then exposed to UV light for 4.5 seconds

(equivalent to 15 passes in the UV device), sonicated in IPA, and dried. The observation via the optical microscope of the substrate cross-section as well as the analysis of the surface by FT-IR revealed the presence of a poly(butyl acrylate) coating (as seen in FIG. 26 and FIG. 27). A lower grafting density was obtained with respect to Example 12.

Example 17

[0136] A PP plaque was dip-coated in a solution containing 10 wt% BP, 35 wt% MMA (passed beforehand through basic alumina to remove the inhibitor), 1 wt% ascorbic acid and 54 wt% IPA. The sheet was then exposed to UV light for 4.5 seconds (equivalent to 15 passes in the UV device), sonicated in IPA, and dried. The observation via the optical microscope of the substrate cross-section as well as the analysis of the surface by FT-IR revealed the presence of polyMMA coating (as seen in FIG. 28 and FIG. 29). A lower grafting density was obtained with respect to Example 13.

Example 18

[0137] A PP plaque was dip-coated in a solution containing 10 wt% BP, 46 wt% AA

(passed beforehand through neutral alumina to remove the inhibitor), 1 wt% ascorbic acid, and

43 wt% IPA. The sheet was then exposed to UV light for 4.5 seconds (equivalent to 15 passes in the UV device), sonicated in IPA, and dried. The observation via the optical microscope of the substrate cross-section as well as the analysis of the surface by FT-IR revealed the presence of polyAA coating (as seen in FIG. 30 and FIG. 31). A lower grafting density was obtained with respect to Example 14.

[0138] Set forth below are non-limiting aspects of the present disclosure.

[0139] Aspect la: A method of grafting a polymer coating onto a substrate, the method comprising: applying a first coating layer comprising at least one acrylate monomer and a Type II photoinitiator onto a first surface area of the substrate; and irradiating the first coating layer to form a first polymeric layer, wherein the polymer coating includes the first polymeric layer.

[0140] Aspect lb: A method of grafting a polymer coating onto a substrate, the method comprising: applying a coating mixture that comprises a Type II photoinitiator and one or more acrylate monomers to a surface of the substrate, and then irradiating the coating mixture to form the acrylate coating.

[0141] Aspect 2: The method of aspect 1, wherein oxygen is not excluded during the application of the first coating layer or the irradiation of the first coating layer.

[0142] Aspect 3: The method of any of aspects 1 to 2, further comprising washing the first surface area of the substrate with a basic solution prior to applying the first coating layer.

[0143] Aspect 4: The method of any of aspects 1 to 3, wherein the first coating layer is irradiated with ultraviolet radiation for at most 1 minute.

[0144] Aspect 5: The method of any of aspects 1 to 4, wherein the first coating layer is applied to the first surface area of the substrate by dip-coating or flow-coating.

[0145] Aspect 6: The method of any of aspects 1 to 5, wherein the at least one acrylate monomer comprises at least one of hydroxyethyl methacrylate, butyl acrylate, methyl methacrylate, or acrylic acid.

[0146] Aspect 7: The method of any of aspects 1 to 6, wherein the Type II photoinitiator comprises at least one of a benzophenone, a thioxanthone, a xanthone, or a quinone.

[0147] Aspect 8: The method of any of aspects 1 to 7, wherein a coating mixture is applied to form the first coating layer.

[0148] Aspect 9: The method of aspect 8, wherein the at least one acrylate monomer is about 10 wt% to about 99 wt% of the coating mixture based on the total weight of the coating mixture.

[0149] Aspect 10: The method of any of aspects 8 to 9, wherein the Type II

photoinitiator is about 0.1 wt% to about 20 wt% of the coating mixture based on the total weight of the coating mixture.

[0150] Aspect 11: The method of any of aspects 8 to 10, wherein the coating mixture further comprises an oxygen scavenger. [0151] Aspect 12: The method of aspect 11, wherein the oxygen scavenger is about 0.1 wt% to about 10 wt% of the coating mixture based on the total weight of the coating mixture.

[0152] Aspect 13: The method of any of aspects 1 to 12, wherein the substrate has a surface with abstractable hydrogen atoms.

[0153] Aspect 14: The method of aspect 13, wherein the substrate is at least one of transparent or flexible.

[0154] Aspect 15: The method of any of aspects 13 to 14, wherein the substrate comprises a polycarbonate, poly(methyl methacrylate), poly(ethylene terephthalate), polypropylene, a polyolefin, or a combination comprising ate least one of the foregoing.

[0155] Aspect 16: The method of any of aspects 1 to 15, further comprising: applying a second coating layer comprising at least one acrylate monomer and a Type II photoinitiator onto the first polymeric layer; and irradiating the second coating layer to form a second polymeric layer; wherein the polymer coating includes the first polymeric layer and the second polymeric layer.

[0156] Aspect 17: An article made according to the method of any of aspects 1 to 16, wherein the polymer coating is covalently bonded to the first surface area of the substrate.

[0157] Aspect 18: The article of aspect 17, wherein the article is a part for infra-red reflectors, haptics devices, self-cleaning devices, sensors, biosensors, photochromic devices, displays, data storage devices, anticounterfeiting, devices, security devices, optical films, robotic devices, or micro fluidic devices.

[0158] Aspect 19: A polymer coating composition, the composition comprising:

at least one acrylate monomer; and a Type II photoinitiator.

[0159] Aspect 20: The composition of aspect 19, further comprising a solvent or an oxygen scavenger.

[0160] The present disclosure has been described with reference to exemplary embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the present disclosure be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims

CLAIMS What is claimed is:

1. A method of grafting a polymer coating onto a substrate, the method comprising: applying a first coating layer comprising at least one acrylate monomer and a Type II photoinitiator onto a first surface area of the substrate; and

irradiating the first coating layer to form a first polymeric layer,

wherein the polymer coating includes the first polymeric layer.

2. The method of claim 1, comprising not excluding oxygen during the applying the first coating layer or the irradiating of the first coating layer.

3. The method of any of claims 1 to 2, further comprising washing the first surface area of the substrate with a basic solution prior to applying the first coating layer.

4. The method of any of claims 1 to 3, wherein the first coating layer is irradiated with ultraviolet radiation for at most 1 minute.

5. The method of any of claims 1 to 4, wherein the first coating layer is applied to the first surface area of the substrate by dip-coating or flow-coating.

6. The method of any of claims 1 to 5, wherein the at least one acrylate monomer comprises at least one hydroxyethyl methacrylate, butyl acrylate; methyl methacrylate, or acrylic acid.

7. The method of any of claims 1 to 6, wherein the Type II photoinitiator comprises at least one of a benzophenone, a thioxanthone, a xanthone, or a quinone.

8. The method of any of claims 1 to 7, wherein the applying the first coating layer comprises applying a coating mixture onto the first surface area of the substrate to form the first coating layer.

9. The method of claim 8, wherein the at least one acrylate monomer is about 10 wt% to about 99 wt% of the coating mixture based on the total weight of the coating mixture.

10. The method of any of claims 8 to 9, wherein the Type II photoinitiator is about 0.1 wt% to about 20 wt% of the coating mixture based on the total weight of the coating mixture.

11. The method of any of claims 8 to 10, wherein the coating mixture further comprises an oxygen scavenger.

12. The method of claim 11, wherein the oxygen scavenger is about 0.1 wt% to about 10 wt% of the coating mixture based on the total weight of the coating mixture.

13. The method of any of claims 1 to 12, wherein the substrate has a surface with abstractable hydrogen atoms.

14. The method of claim 13, wherein the substrate is at least one of transparent or flexible.

15. The method of any of claims 13 to 14, wherein the substrate comprises at least one of a polycarbonate, poly(methyl methacrylate), poly(ethylene terephthalate), polypropylene, or a polyolefin.

16. The method of any of claims 1 to 15, further comprising:

applying a second coating layer comprising at least one acrylate monomer and a Type II photoinitiator onto the first polymeric layer; and

irradiating the second coating layer to form a second polymeric layer;

wherein the polymer coating includes the first polymeric layer and the second polymeric layer.

17. An article made according to the method of any of claims 1 to 16, wherein the polymer coating is covalently bonded to the first surface area of the substrate.

18. The article of claim 17, wherein the article is a part for infra-red reflectors, haptics devices, self-cleaning devices, sensors, biosensors, photochromic devices, displays, data storage devices, anticounterfeiting, devices, security devices, optical films, robotic devices, or microfluidic devices.

19. A polymer coating composition, the composition comprising: at least one acrylate monomer; and

a Type II photoinitiator.

20. The composition of claim 19, further comprising a solvent or an scavenger.