Description:BACKGROUND
FIELD OF THE DISCLOSURE
Various embodiments of the disclosure relate generally to epoxy vitrimers. More specifically, various embodiments of the disclosure relate to epoxy vitrimers and transparent, hydrophobic, conductive coatings comprising the epoxy vitrimers.
DESCRIPTION OF THE RELATED ART
Thermosets are covalently cross-linked polymer networks that, unlike thermoplastics, cannot be reprocessed by melting, or dissolving in solvents. Thermosetting polymers or thermosets are widely used in industrial applications such as coatings, adhesives, and fiber-reinforced polymer composites for high-performance applications due to their superior mechanical strength, chemical resistance, and thermal stability. A key limitation of thermosets lies in their defining characteristic of intractable three-dimensional structure, which, while beneficial for performance, renders them non-recyclable and non-processable, contributing to significant material waste.
Epoxy polymers, a subclass of thermosets, are quite diverse in their chemical properties. Epoxy resins can be readily synthesized from various unsaturated precursors through oxidation reactions or via nucleophilic substitution reactions, such as with epichlorohydrin, due to which a wide range of resins are available, such as epoxidized soybean oil, epoxidized polyisoprene, and diglycidyl ether of bisphenol A (DGEBA) for epoxy polymer formation. Furthermore, epoxy resins are highly reactive and can engage in crosslinking reactions with a broad range of functional groups, such as thiols, amines, carboxylic acids, and anhydrides to form epoxy polymer.
Epoxy polymers are extensively utilized due to their exceptional chemical resistance, mechanical properties, electrical insulation, and strong adhesion, making them indispensable in high-performance applications such as aerospace. However, despite their versatility and widespread use, conventional epoxy polymers are irreversible thermosets that cannot be repaired, reshaped, or recycled. This inherent limitation presents significant environmental challenges, particularly due to the accumulation of epoxy polymer waste.
Vitrimerization is an emerging technology for converting thermoset polymers into reprocessable polymers. Vitrimers are covalently crosslinked polymer networks in which dynamic covalent bond exchange allows topological rearrangements. At a temperature below a material-dependent vitrimer transition temperature (Tᵥ), the vitrimers retain thermoset-like dimensional and chemical stability, while above Tᵥ, bond exchanges permit reprocessing, reshaping, and self-healing. This dual behaviour combines the mechanical robustness and solvent resistance of thermosets with the reconfigurability and recyclability of thermoplastics, enabling applications in coatings, insulating materials, high-performance composites, and electronic packaging. However, to replace conventional epoxy polymers with epoxy vitrimers in demanding applications such as aerospace, stringent quality standards must be met. Novel vitrimers must be meticulously engineered to match or surpass the properties of the conventional epoxy resins.
Thermally activated covalent adaptable networks (CANs) can be broadly classified into two categories, associative CANs, where bond formation and bond breaking occur simultaneously, and dissociative CANs, where bond breaking precedes bond reformation. The associative CANs, such as those based on transesterification, disulfide metathesis, silyl ether exchange, acetal exchange, imine exchange, and boronic ester metathesis are particularly advantageous because the network backbone remains intact during bond exchange. This ensures a constant crosslink density, preventing sudden liquefaction or degradation upon heating, and allows vitrimers to maintain mechanical strength and dimensional stability while enabling flow and reprocessability at elevated temperatures.
Despite the benefits of associative CANs, epoxy vitrimer systems face challenges in achieving certain properties. There is a growing need to develop epoxy vitrimers that exhibit transparency, hydrophobicity, and self-healing ability, while retaining high glass transition temperatures, chemical resistance, and mechanical robustness. Addressing these challenges requires careful molecular design of the resin, crosslinker, and initiator system, along with optimization of the dynamic bond exchange chemistry.
Limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of described systems with some aspects of the present disclosure, as set forth in the remainder of the present application and with reference to the drawings.
SUMMARY
According to embodiments of the present disclosure, an epoxy vitrimer is provided. The epoxy vitrimer comprises an epoxy unit formed by a reaction between an epoxy resin and an initiator, wherein the initiator is selected from 1-(3-aminopropyl)imidazole (API), 2-propylimidazole, 2,4,6-tris(dimethylaminomethyl)phenol, N,N-dimethylbenzylamine, 2-methyl imidazole, 1,2-dimethylimidazole, 2-ethyl-4-methyl-1H-imidazole, benzyl triethyl ammonium chloride, boron trichloride, boron trifluoride monoethyl amine, 2-phenylimidazole (2-PI), 2-undecylimidazole (2-UI), 1-butyl-3-methylimidazolium salts, 1-cyanoethyl-2-methylimidazole, and combinations thereof. The epoxy vitrimer further comprises a dynamic crosslinker configured to form a covalent adaptive network with the epoxy unit through silyl ether exchange alone, or in combination with one or more mechanisms selected from transesterification, disulfide exchange reaction, imine formation, thiol-ene vinyl reactions, and transcarbamoylation.
In another embodiment, a transparent, hydrophobic coating comprising an epoxy vitrimer is provided. The epoxy vitrimer comprises an epoxy unit formed by a reaction between an epoxy resin and an initiator, and a dynamic crosslinker. The initiator is selected from 1-(3-aminopropyl)imidazole, 2-propylimidazole, 2,4,6-tris(dimethylaminomethyl)phenol, N,N-dimethylbenzylamine, 2-methyl imidazole, 1,2-dimethylimidazole, 2-ethyl-4-methyl-1H-imidazole, benzyl triethyl ammonium chloride, boron trichloride, boron trifluoride monoethyl amine, 2-phenylimidazole (2-PI), 2-undecylimidazole (2-UI), 1-butyl-3-methylimidazolium salts, 1-cyanoethyl-2-methylimidazole, and combinations thereof. The dynamic crosslinker is configured to form a covalent adaptive network with the epoxy unit through silyl ether exchange alone, or in combination with one or more mechanisms selected from transesterification, disulfide exchange reaction, imine formation, thiol-ene vinyl reactions, and transcarbamoylation. An electrically conducting nanoparticle is dispersed in the coating. The nanoparticle is selected from silver nanowires, silver nanoparticles, gold nanowires, copper nanowires, metal meshes, metal oxide nanoparticles, indium tin oxide nanoparticles, zinc oxide nanoparticles, aluminum-doped zinc oxide nanoparticles, gallium-doped zinc oxide nanoparticles, carbon nanotubes, conducting polymers, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) and combinations thereof. The coating has an optical density in a range of 50% to 90%.
In yet another embodiment, a method of forming a transparent, hydrophobic coating on a substrate is provided. The method comprises the steps of (i) applying to the substrate a coating composition comprising an epoxy vitrimer to form a first substrate. The epoxy vitrimer comprises an epoxy unit formed by a reaction between an epoxy resin and an initiator, and a dynamic crosslinker. The initiator is selected from 1-(3-aminopropyl)imidazole, 2-propylimidazole, 2,4,6-tris(dimethylaminomethyl)phenol, N,N-dimethylbenzylamine, 2-methyl imidazole, 1,2-dimethylimidazole, 2-ethyl-4-methyl-1H-imidazole, benzyl triethyl ammonium chloride, boron trichloride, boron trifluoride monoethyl amine, 2-phenylimidazole (2-PI), 2-undecylimidazole (2-UI), 1-butyl-3-methylimidazolium salts, 1-cyanoethyl-2-methylimidazole, and combinations thereof. The dynamic crosslinker is configured to form a covalent adaptive network with the epoxy unit through silyl ether exchange alone, or in combination with one or more mechanisms selected from transesterification, disulfide exchange reaction, imine formation, thiol-ene vinyl reactions, and transcarbamoylation. The method further comprises (ii) curing the first substrate at a temperature in a range of 80°C to 140°C to form the transparent, hydrophobic coating on the substrate.
BRIEF DESCRIPTION OF DRAWINGS
FIG. 1 is a flow chart that illustrates a method of preparing an epoxy vitrimer, in accordance with an exemplary embodiment of the disclosure;
FIG. 2 is a representative reaction scheme, in accordance with an exemplary embodiment of the disclosure;
FIG. 3 is a flow chart that illustrates a method of forming a coating on a substrate, in accordance with an exemplary embodiment of the disclosure;
FIG. 4 depicts an image demonstrating electrical conductivity of a coating in accordance with an exemplary embodiment of the disclosure;
FIG. 5 depicts an image of contact angle measurements on various substrates, in accordance with an exemplary embodiment of the disclosure; and
FIG. 6 depicts an image demonstrating transparency of a coated substrate, in accordance with an exemplary embodiment of the disclosure.
Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description of exemplary embodiments is intended for illustration purposes only and is, therefore, not intended to necessarily limit the scope of the present disclosure.
DETAILED DESCRIPTION OF EMBODIMENTS
The following description illustrates some exemplary embodiments of the disclosed disclosure in detail. Those of skill in the art will recognize that there are numerous variations and modifications of this disclosure that are encompassed by its scope. Accordingly, the description of a certain exemplary embodiment should not be deemed to limit the scope of the present disclosure.
The term “comprising” as used herein is synonymous with “including,” or “containing,” and is inclusive or open-ended and does not exclude additional, unrecited elements, or process steps.
As used herein, the term 'and combinations thereof' refers to the possibility that the listed components may be employed individually or in any combination with one or more of the other listed components.
All numbers expressing quantities of ingredients, property measurements, and so forth used in the specification are to be understood as being modified in all instances by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth herein are approximations that may vary depending upon the desired properties sought to be obtained.
These and other features and advantages of the present disclosure may be appreciated from a review of the following detailed description of the present disclosure, along with the accompanying figures in which like reference numerals refer to like parts throughout.
As used herein, the term “copolymer” refers to a polymer derived from more than one species of monomer, where the copolymer includes repeating units of each of the monomers.
As used herein, the term “blend” refers to a mixture of two or more polymers or copolymers that have been blended together to create a new material with different physical properties.
As used herein, the term “epoxy polymer” refers to a thermosetting polymer obtained from one or more monomers or resins containing oxirane (epoxide) groups, which are cured or crosslinked through reaction with a hardener, such as an amine, a carboxylic acid, or other suitable curing agents, to form a three-dimensional crosslinked network. The epoxy polymer is hereinafter also referred to as a “conventional epoxy”.
The term "elastic modulus" of a material is defined as the gradient of the stress-strain curve of the material in the elastic deformation region and is a measure of the stiffness of the material. The unit of elastic modulus is the Pascal (Pa). Stiffer materials have higher values of elastic modulus. The elastic modulus is otherwise known as the "modulus of elasticity" or "Young's modulus".
As used herein, the term “cycle life” refers to a number of times a polymer may be recycled without adversely affecting its mechanical or thermal properties.
Plastic “recycling” refers to a process whereby useful products may be produced from waste plastics after reprocessing, or melting the waste plastics. However, after recycling, the recycled polymer usually possesses inferior properties compared to its virgin counterparts. The extent of degradation may depend on degradation during use, cycle life, and the severity of conditions applied during reprocessing.
Vitrimers are a class of polymers containing reversible dynamic covalent bonds that can reorganize upon application of external stimuli such as heat, light, chemical agents, and/or pH.
Epoxy vitrimers of the present disclosure, form associative CANs, which means that existing covalent bonds are only broken when new ones are formed on application of heat. The formation of CANs through a dynamic crosslinker renders the epoxy vitrimers recyclable, repairable, or processable.
According to embodiments of the present disclosure, an epoxy vitrimer is provided. The epoxy vitrimer comprises an epoxy unit formed by a reaction between an epoxy resin and an initiator, wherein the initiator is selected from 1-(3-aminopropyl)imidazole, 2-propylimidazole, 2,4,6-tris(dimethylaminomethyl)phenol, N,N-dimethylbenzylamine, 2-methyl imidazole, 1,2-dimethylimidazole, 2-ethyl-4-methyl-1H-imidazole, benzyl triethyl ammonium chloride, boron trichloride, boron trifluoride monoethyl amine, 2-phenylimidazole (2-PI), 2-undecylimidazole (2-UI), 1-butyl-3-methylimidazolium salts, 1-cyanoethyl-2-methylimidazole, and combinations thereof. The epoxy vitrimer further comprises a dynamic crosslinker configured to form a covalent adaptive network with the epoxy unit through silyl ether exchange alone, or in combination with one or more mechanisms selected from transesterification, disulfide exchange reaction, imine formation, thiol–ene vinyl reactions, and transcarbamoylation.
FIG. 1 is a flow chart 100 that illustrates a method of preparing an epoxy vitrimer through exemplary steps 102 through 104, according to embodiments of the present disclosure. At step 102, a homogeneous solution is prepared comprising an epoxy resin, a dynamic crosslinker and an initiator.
The epoxy resin comprises at least one epoxide group, and comprises a monomer or an oligomer. As used herein, the term “at least one” refers to having one, or more than one. The epoxy resin, in one embodiment, is a glycidyl type resin obtained by condensation reaction of a diol, diacid, or diamine with epichlorohydrin. In some embodiments, the epoxy resin may contain some rigidity by having phenylene rings in the molecule. In other embodiments, the epoxy resin may contain some flexibility by having linear or branched alkylene or poly(alkyleneoxide) unit in the molecule. Non-limiting examples of epoxy resins include diglycidyl ether of bisphenol A (DGEBA), diglycidyl ether of bisphenol F, hydrogenated bisphenol A diglycidyl ether, tetraglycidyl methylene dianiline, pentaerythritol tetraglycidyl ether, trimethylol triglycidyl ether, tetrabromo bisphenol A diglycidyl ether, or hydroquinone diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, butylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, bisphenol A polyethylene glycol diglycidyl ether, bisphenol A polypropylene glycol diglycidyl ether, 4,4’-methylenebis(N, N-diglycidylaniline), tetraglycidyl diaminodiphenyl methane, or combinations thereof. In one embodiment, the epoxy resin comprises 4,4’-methylenebis(N, N-diglycidylaniline), diglycidyl ether of bisphenol A (DGEBA), tetraglycidyl diaminodiphenyl methane, diglycidyl ether of bisphenol F, or combinations thereof.
As used herein, the term ‘dynamic crosslinker’ refers to a component in a vitrimer network that introduces dynamic covalent bonds into the network, enabling bond-exchange reactions above vitrimer transition temperature while maintaining a stable, crosslinked network below this temperature. The dynamic crosslinker comprises an aminosilane, an epoxy silane, a vinyl silane, an acrylic silane, a vinyl-(meth)acryloxy silane, an alkyl silane, an alkyl-bridged silane, an aryl silane, a sulphur-functionalized silane, a polymeric silane, or a hybrid silane. In some embodiments, the dynamic crosslinker is selected from 3-aminopropyltriethoxysilane (APTES), 3-(trimethoxysilyl)propyl methacrylate (TMSPMA), 3-(triethoxysilyl)propyl acrylate, 3-(triethoxysilyl)propyl methacrylate, 3-glycidyloxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyl-/methacryloxy-silane hybrid, methyltriethoxysilane, phenyltriethoxysilane, 4,4'- bis-3-(triethoxysilyl)-propyl)-tetrasulfide (TESPT), bis[3-(triethoxysilyl)propyl] disulfide (TESPD), bis[triethoxysilyl]ethane (BTSE), silyl-terminated polymers, silane-functionalized glycidyl methacrylate copolymer, trialkoxysilane-functionalized polyurethane, and trialkoxysilane-functionalized epoxy. In one embodiment, the dynamic crosslinker is 4,4'- bis-3-(triethoxysilyl)-propyl)-tetrasulfide (TESPT).
The initiator is as described previously herein.
It is believed that the epoxy vitrimer in this disclosure is prepared through a chain-growth ring-opening polymerization mechanism. In chain-growth ring-opening polymerization mechanism, nucleophilic initiators such as imidazoles, or tertiary amines attack the epoxide ring of the epoxy resin to generate reactive species that propagate along the chain, thereby incorporating the initiator into the polymer backbone as a structural element of the vitrimer network. The initiators, as used herein, advantageously accelerate the chain initiation and/or chain propagation process. As the initiators (i.e., reaction centers) are distributed uniformly throughout the network, this mechanism yields improved dimensional stability, reduced susceptibility to creep, and greater control over polymeric network uniformity compared to conventional epoxy systems. As used herein, the term “susceptibility to creep” refers to the tendency of an epoxy polymer to undergo time-dependent, permanent deformation when subjected to a constant load or stress at a given temperature. As used herein, the term “dimensional stability” refers to the ability of a polymeric material to maintain its shape, size, and structural integrity when subjected to variations in temperature, stress, or chemical environment.
In the present system, the initiator units serve as uniformly distributed reaction centers that participate directly in epoxy ring-opening, while simultaneously engaging with a single dynamic crosslinker to form a single CAN, or multiple CANs. The term “multiple, as used herein, refers to more than one. The uniform spatial distribution reduces phase separation and network inhomogeneity in the resulting vitrimers. Such structural uniformity not only enhances thermal and mechanical reliability but also creates a robust platform for extending vitrimer performance into functional domains such as transparency, self-healing, and hydrophobicity, in addition to the recyclability typical of CAN-based materials. The factors that may influence chain-growth polymerization include the type and concentration of initiator, epoxy resin, crosslinker and process conditions such as reaction temperature and curing time, all of which may determine initiation efficiency, propagation rate, and the resulting vitrimer architecture.
In epoxy systems (for example, conventional epoxy and/or epoxy vitrimers) where multifunctional amines or carboxylic acids act as curing agents and initiate epoxide ring opening, the mechanism is through step-growth polymerization. In such systems, initiation and dynamic exchange are separate processes where the acid or amine initiates curing, and a later-added catalyst (such as zinc salts) facilitates the CAN dynamics in the case of vitrimers. The curing agent and/or catalyst typically remains a distinct entity within the network rather than being structurally integrated into the polymer backbone. In epoxy vitrimers, instability often arises from heterogeneous multiphase morphologies caused by uneven distribution of reactive centers or multiple crosslinkers. While such systems produce robust thermosets, they suffer from less control over network distribution, potential inhomogeneity of dynamic centers, and consequently greater risk of creep or compromised functional properties such as transparency and dimensional stability.
The initiator and the dynamic crosslinker are added to the epoxy resin, which is typically in liquid form. In some embodiments, the initiator and the dynamic crosslinker may be dissolved individually, or together, in a solvent such as ethanol, methanol, or acetone prior to addition to the epoxy resin. In certain embodiments, the epoxy resin may be heated to a temperature of up to about 80 °C to reduce a viscosity of the liquid epoxy resin before introducing the dynamic crosslinker and the initiator. The homogeneous solution may further comprise a second solvent. Non-limiting examples of second solvents include ethanol, methanol, or acetone. The inclusion of solvents is optional, and when employed, it is typically removed during processing so as not to affect the final properties of the vitrimer network.
At step 102, the dynamic crosslinker and the initiator are added to the liquid epoxy resin with constant mixing to obtain the homogeneous solution, as in a one-pot synthesis. Mixing may be performed using any apparatus or method known in the art, such as manual mixing in a beaker using a spatula, magnetic stirrers, high-shear mixing, rotor-stator mixing, and the like. The formation of the homogeneous solution is facilitated by mechanical agitation for a period of time while gradually heating the solution to a temperature ranging from 70 to 80 °C. Once a homogeneous solution is obtained, it is subjected to vacuum degassing to remove any dissolved gases.
Without wishing to be bound by theory, it is believed that at step 102, the ring-opening polymerization of the epoxy units initiates at ambient temperature. At this stage, the reaction proceeds slowly, primarily forming oligomeric or partially reacted species. Heating, for example, from 70°C to up to 80 °C, accompanied by agitation at this step and curing at a subsequent step, accelerates both the propagation and crosslinking processes, thereby driving the reaction toward completion and establishing the vitrimer network. In this way, the vitrimer formulation maintains sufficient pot life for handling, mixing, and degassing, while controlled heating ensures the desired crosslink density and incorporation of dynamic covalent linkages within the final material. As used herein, the term ‘curing’ refers to the crosslinking of a polymer or vitrimer that occurs upon heating the composition to a temperature above 80 °C, at which significant crosslinking reactions take place. Completion of curing may be assessed by monitoring the disappearance of the oxirane absorption peak at approximately 912 cm⁻¹ in Fourier Transform Infrared (FTIR) spectroscopy.
In some embodiments, a weight ratio of the epoxy unit to the dynamic crosslinker in the epoxy vitrimer is in a range of 99.5:0.5 to 80:20. In preferred embodiments, the weight ratio of the epoxy unit to the dynamic crosslinker in the epoxy vitrimer is at a ratio of 90:10.
At step 104, the homogenous solution is cured to form the epoxy vitrimer. During curing, the extent of reaction or a degree of dynamic crosslinking increases between the epoxy resin, the dynamic crosslinker, and the initiator to form the crosslinked, epoxy vitrimer. The homogenous solution, in liquid or semi-liquid form in step 102, solidifies in step 104 on crosslinking to form the epoxy vitrimer.
The homogeneous solution is poured into a mold, in one embodiment, at step 104 of curing. However, other processing methods such as casting, filament coiling, continuous molding or molding between film coatings, infusion, pultrusion, resin transfer molding or RTM, reaction injection molding (or RIM) or any other methods known to those skilled in the art, as described in “Epoxy Polymers: New Materials and Innovations,” edited by J. P. Pascault and R. J. Williams, Wiley-VCH, Weinheim 2010, may be employed.
As is known in the art, curing generally requires time, where the speed of curing is dependent on the particular epoxy resin, dynamic crosslinker, and the initiator employed. The step 104 of curing is accelerated by applying heat. In one embodiment, curing is achieved by subjecting the homogeneous solution to a temperature of above 80 °C. In certain embodiments, the curing is carried out at a temperature in the range of above 80 °C to about 150 °C with the curing process completed within 1 hour (as indicated by the disappearance of the oxirane absorption peak at approximately 912 cm⁻¹ in FTIR), depending on the formulation and desired crosslinking density. In certain embodiments, curing agents and/or accelerants may be employed as known in the art.
It is a particular advantage of the disclosure that the epoxy vitrimer has a lower curing time when compared to a standard epoxy polymer formed from a similar resin but without the dynamic crosslinker and the initiator. Furthermore, because the standard epoxy polymer proceeds through a step-growth mechanism, its curing typically requires multiple stages at different temperatures. In one embodiment, curing is performed at a temperature of 120°C for a period of less than 1 hour.
The epoxy vitrimer has a vitrimer transition temperature in a range of 80 °C to 180 °C. In preferred embodiments, vitrimer transition temperature is in a range of 90 °C to 120 °C. As discussed previously, a vitrimer functions as a thermoset below its transition temperature, whereas above this temperature it becomes reprocessable and, in the present case, demonstrates self-healing behaviour.
In many applications where replacement of conventional epoxy polymers is required, it is expected that the vitrimer exhibit properties that are at least comparable to, or better than, those of the conventional epoxy polymer, irrespective of the additional advantages inherently provided by the vitrimer. In one embodiment, the epoxy vitrimer has a Young’s modulus within ±20% of a Young’s modulus of a standard epoxy polymer prepared from the same epoxy resin.
In some embodiments, the epoxy vitrimer has a Shore hardness measured at an ambient temperature. The ambient temperature corresponds to a range of about 20 °C to 40 °C, i.e., a temperature below the vitrimer transition temperature. As used herein, the term Shore hardness refers to the resistance of the material to indentation, determined using a durometer in accordance with ASTM D2240 or an equivalent standardized method. The hardness value is typically reported on the Shore D scale for rigid thermosetting polymers. In certain embodiments, the epoxy vitrimer exhibits a Shore D hardness within ±10% of the Shore D hardness of a standard epoxy polymer prepared from the same epoxy resin. In other embodiments, the epoxy vitrimer exhibits a Shore D hardness within ±2% to ±3% of the Shore D hardness of the corresponding standard epoxy polymer. By way of example, in some embodiments, the epoxy vitrimer has a Shore D hardness in the range of 70 to 85, which is comparable to the Shore D hardness of conventional epoxy polymers. Such measurements demonstrate that, under service conditions, the epoxy vitrimer provides hardness comparable to conventional epoxy polymers, while additionally offering reprocessability and self-healing behaviour at elevated temperatures.
The formation of the epoxy vitrimer, as outlined in the method illustrated in FIG. 1, can be better understood through a representative reaction, in accordance with the embodiments of the disclosure. A reaction scheme 200, as shown in FIG. 2, illustrates one possible mechanism by which the representative reaction may proceed. It is understood that alternative pathways, intermediates, or mechanisms could also account for the observed results, and the invention is not limited to the mechanism depicted below.
In the reaction scheme 200, as shown in FIG. 2, the initiator is 1-(3-aminopropyl) imidazole, epoxy resin is diglycidyl ether of bisphenol A (DGEBA), and the dynamic crosslinker is 4,4'- bis-3-(triethoxysilyl)-propyl)-tetrasulfide (TESPT). Referring to FIG. 2, the reaction initiates with the nucleophilic attack by primary amine functional group of the initiator 1-(3-aminopropyl) imidazole on the less substituted carbon of the asymmetric epoxide ring present in the epoxy resin (DGEBA). The ring-opening reaction occurs via the lone pair electrons on the nitrogen atom of the amine group, resulting in the formation of intermediate [I].
Subsequently, a proton transfer from the protonated amine (NH⁺) to the negatively charged oxygen (O⁻) of the opened epoxide ring occurs, forming secondary hydroxyl groups to form intermediate [II]. The intermediate [II] corresponds to the epoxy unit described herein. As used herein, the term “epoxy unit” refers to a structural moiety derived from the epoxy resin through ring-opening reaction of the epoxide group with the initiator, and forms part of the crosslinked network in the resulting epoxy vitrimer.
The hydroxyl functionalities of the intermediate [II] play a crucial role in vitrimer formation. Specifically, the electrophilic oxygen of the generated hydroxyl group nucleophilically attacks the electron-deficient silicon centre of 4,4'- bis-3-(triethoxysilyl)-propyl)-tetrasulfide, initiating a silyl ether formation through intermediate [II]. During silyl ether formation, one of the ethoxy groups attached to silicon acts as a leaving group, resulting in the formation of a silyl ether bond as shown by intermediate [III]. This reaction introduces dynamic covalent linkages into the vitrimer network through silyl ether exchange mechanisms, establishing a single dynamic exchangeable network within the epoxy vitrimer system. A second covalent adaptive network is formed through disulfide exchange between the disulfide bonds (intermediate [III]) of the same chain, or between different chains (not shown).
As described previously, the inventive epoxy vitrimer comprises an epoxy unit formed from an epoxy resin and an initiator. The dynamic crosslinker is configured to form CANs with the epoxy unit through silyl ether exchange reaction and in certain embodiments a second covalent adaptive network.
Table 1 provides representative examples of dynamic crosslinkers that may be employed in the present disclosure, together with the types of covalent adaptable networks (CANs) they form in the corresponding epoxy vitrimers, in addition to silyl ether exchange. .

Dynamic crosslinker Type of CANs
3-(aminopropyl)triethoxysilane Imine Formation
3-(trimethoxysilyl)propyl methacrylate (TMSPMA) Transesterification
vinyltrimethoxysilane Thiol–ene vinyl reaction
bis[3-(triethoxysilyl)propyl] disulfide/tetrasulphide Disulfide Exchange
Trialkoxysilane-functionalized urethane/epoxy Transcarbamoylation
vinyl-/methacryloxy-Silane Hybrids (e.g., MEMO from Evonik)
Si-O-Si dynamic bond

Table 1

The mechanical properties of the epoxy vitrimer may be characterized in terms of tensile strength. As used herein, the term “tensile strength” is defined as the maximum tensile load a material can withstand before it breaks. The tensile strength is determined using a tensile test and the tensile strength corresponds to the highest point of the stress-strain curve plotted from the test. In one embodiment, the epoxy vitrimer has a tensile strength within ±10% of a tensile strength of a standard epoxy polymer prepared from the same epoxy resin. The tensile strength of the inventive epoxy vitrimer is in a range of 40 MPa to 80 MPa.
The degradation temperature is an important parameter to consider when processing or manufacturing polymers, as it can affect the properties of the polymer and may even limit its range of applications. As used herein, the term “degradation temperature” refers to a maximum temperature at which a polymer can be used without undergoing damaging chemical changes. In one embodiment, the inventive epoxy vitrimer has a degradation temperature of 250°C, or above 250°C. The inventive epoxy vitrimer maintains its mechanical properties and dimensional stability even at elevated temperatures, owing to its higher degradation temperature. This makes the epoxy vitrimer more resistant to thermal degradation and aging, ensuring a longer service life and improved durability across various applications.
The relaxation time is another important parameter with a view to the processability of vitrimers, influencing, for example, a time required for a material to be shaped, or recycled. Stress relaxation tests are typically performed using a dynamic mechanical analyzer to determine the relaxation time, and are described in further detail in the Examples section.
An activation energy Ea may be calculated using Arrhenius equation: τ(T) = τ0 exp (Ea/RT) at a given time. The presence of CAN in the inventive epoxy vitrimer lowers the activation energy when compared to a standard epoxy polymer prepared from the same epoxy resin. Lower activation energy facilitates faster and more efficient reprocessing and/or self-healing at lower temperatures. As will be appreciated, the covalent adaptive networks present in the inventive vitrimer are dynamic in nature and the networks may be broken and re-formed on application of heat. As a result, the inventive vitrimer may be processed, or repaired (self-healable) post-formation.
In some embodiments, the epoxy vitrimer is recyclable. In some embodiments, recycling the epoxy vitrimer corresponds to recycling the epoxy vitrmer along with epoxy polymers. The epoxy polymers include virgin epoxy polymers, post-consumer recycled (PCR) epoxy polymers, post-industrial recycled (PIR) epoxy polymers, or combinations thereof. Post-consumer recycled (PCR) plastics refer to plastic waste generated by consumers, or after-use plastic products. The post-industrial recycled (PIR) plastics are derived from plastic waste produced during industrial and manufacturing processes.
In accordance with embodiments of the present disclosure, a method of recycling the epoxy vitrimer is provided. The method comprises heating the epoxy vitrimer dispersed in a solvent to a temperature of 200°C, or less than 200°C for a period of time in a range of 2 to 10 hours. Examples of solvents include dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidone (NMP) and the like.
The terms “self-repairing” or “self-healing” refer to the ability of a material to eliminate or reduce defects in the material. A material that exhibits self-healing is said to be self-healable. In one embodiment, scratches on a surface of the epoxy vitrimer can be repaired through heat treatment at a temperature in a range of 150 to 180 ° C. The surface self-heals after the application of heat within a period of less than about 12 hours, preferably less than about 6 hours.
The epoxy vitrimers may be reprocessed or self-healed multiple times without degradation of their mechanical properties when compared to processing epoxy polymers made from similar epoxy resins but without the dynamic crosslinkers.
According to embodiments of the disclosure, a coating composition comprising the epoxy vitrimer is provided. The epoxy vitrimer, is as described previously.
FIG. 3 is a flowchart 300 outlining a method of forming a transparent, hydrophobic coating on a substrate. The flow chart 300 illustrates exemplary steps 302 through 304, according to embodiments of the present disclosure. At step 302, the method comprises applying, onto a substrate, a coating composition comprising the epoxy vitrimer to form a first substrate. The substrate may include, without limitation, a metal, a ceramic, a glass, polyethylene terephthalate (PET), or a polymer. In one embodiment, the substrate is PET. In addition to these general classes of materials, the disclosure also contemplates specific applications where such substrates are employed. Non-limiting examples of such substrates include an aircraft wing, an aircraft fuselage, a cockpit window, a display panel, a photovoltaic panel, architectural glass, a smart window, a medical device housing, an automotive body panel, and a windshield. The transparency of a coating may be expressed in terms of optical density (OD) measured using a UV–Visible spectrophotometer. OD is calculated as the negative logarithm of transmittance, where transmittance is defined as the ratio of transmitted light intensity to the incident light intensity. The coating exhibited an optical density in a range of 50 to 90% transparency, depending on film thickness and substrate. Such levels of transparency ensure that the coating remains visibly clear while still incorporating conductive and protective functionalities. For example, a thinner coating (thickness ~50 μm) displayed higher transparency with lower OD values, while relatively thicker films (~150 μm) showed increased OD, corresponding to reduced transparency.
The coating composition comprising the epoxy vitrimer may be applied onto the substrate by any suitable technique known in the art. Examples of such techniques include, but are not limited to, spray coating, dip coating, spin coating, roll coating, blade coating, and screen printing. In certain embodiments, the coating is applied as a uniform thin film on the substrate.
In some embodiments, the coating is formulated to be electrically conductive while maintaining optical transparency and surface hydrophobicity. For example, aeroplanes are known to experience charge accumulation during flight. Use of a conductive coating can be envisaged to minimize charge buildup by facilitating lightning protection and static charge dissipation. This may be achieved by incorporating conducting nanoparticles in an amount and dispersion that is effective to impart electrical conductivity without significantly compromising light transmission. As used herein, the term “nanoparticles” refers to particles having at least one dimension in the nanometer range, typically less than 100 nanometers (nm). “Nanowires” are a special case of nanoparticles having elongated nanostructures with diameters in the nanometer range and lengths extending from hundreds of nanometers to several micrometers. By virtue of their nanoscale dimensions, such nanoparticles impart unique functional properties to a coating. In particular, their size being smaller than the wavelength of visible light allows the coating to maintain optical transparency, while their intrinsic electrical characteristics contribute to imparting conductivity to the coating. The conducting nanoparticle is selected from silver nanowires, silver nanoparticles, gold nanowires, copper nanowires, metal meshes, metal oxide nanoparticles, indium tin oxide nanoparticles, zinc oxide nanoparticles, aluminum-doped zinc oxide nanoparticles, gallium-doped zinc oxide nanoparticles, carbon nanotubes, conducting polymers, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) polymer, and combinations thereof. In some embodiments, the conducting nanoparticles are dispersed in the coating composition. In yet another embodiment, the conducting nanoparticles are disposed on the first substrate prior to step 304. In one such embodiment, the nanoparticles are applied by spraying onto the first substrate.
A concentration of nanoparticles in the coating may range from about 1 weight percent to about 15 weight percent, based on the total weight of the coating.
At step 304, the first substrate is cured to form the coating. The curing may be accomplished by thermal treatment, ultraviolet (UV) irradiation, or by chemical curing agents, depending on the specific composition employed. In certain embodiments, thermal curing is carried out at a temperature above 80 °C to about 180 °C within a period of 1 hour, optionally under an inert atmosphere to minimize oxidative degradation. In other embodiments, UV curing may be employed using photoinitiators, with exposure intensities and durations selected to achieve complete crosslinking while preserving optical transparency of the coating. The curing process establishes the covalent adaptable network (CAN) structure of the vitrimer.
Conventional epoxy-based coatings degrade over time or exhibit aging due to deterioration in epoxy structure or bonding between epoxy chains on prolonged exposure to environmental factors and stress. The drawbacks of conventional epoxy-based coatings are addressed in the present disclosure by employing epoxy vitrimers that may be re-processed, or self-healed on application of heat. In accordance with embodiments of the present disclosure, the coating is self-healable.
In one embodiment, scratches or mar on a surface of the coatings formed according to the method as shown in FIG.3, can be repaired on heat treatment at a temperature above vitrimer transition temperature in a range of 80 to 180 ° C. The coatings self-heal after the application of heat within a period of less than about 6 hours, preferably less than 4 hours, more preferably less than 1 hour. In one embodiment, the epoxy vitrimer, and coating comprising the epoxy vitrimer have a self-healing efficiency of 85%, or greater than 85%. As used herein, the term self-healing efficiency is defined as the ratio of defects on a specimen after self-healing to a ratio of defects on the specimen before self-healing. The self-healing may be analyzed using micro-computed tomography techniques, which may reveal internal as well as external (surface, such as mar or scratches) defects.
Due to hydrophobic nature of the coating, the coating may be applied to protect surfaces from water damage, corrosion, and fouling, and also to enhance the performance and durability of coated materials in wet or harsh environments. Overall, the combination of hydrophobicity, reprocessability, self-healing capability, optical transparency, and electrical conductivity in the coating renders the present disclosure a promising solution for imparting water repellency and protective functionality across a wide range of applications.

EXAMPLES
EXAMPLE 1
Preparation of epoxy vitrimer
In a 50 milliliter (ml) beaker, about 0.98 gram (g) of 4,4'- bis-3-(triethoxysilyl)-propyl)-tetrasulfide (TESPT), corresponding to 11 mole% epoxy function, was blended with diglycidyl ether of bisphenol A (DGEBA) epoxy resin (Lapox ARL-135LV from Atul Ltd. having an epoxy equivalent weight of 169 to 185 g/eq and a viscosity of 1,000 to 1,500 mPa·s at 25 °C). About 2.4 mol% of 1-(3-aminopropyl)imidazole (API) was added to the above mixture, and the mixture was mechanically agitated with gradual heating between 70 and 80°C to form a homogenous solution. The homogenous solution was vacuum degassed until no more gas evolved and was quickly poured into a Teflon-coated mould (35.0 × 12.7 × 3.2mm3) preheated at 120°C for curing. Curing was carried out by placing the mould in a hot air oven at 120°C for one hour to obtain vitrimer sample (Sample 2). The formation of the epoxy vitrimer was confirmed by Fourier Transform Infrared (FTIR) spectra. The Si-O stretch remained at 1080 cm-1 while the characteristic peaks of the epoxy group (C-O stretching of the oxirane ring at 912 cm-1) disappeared upon vitrimer formation.
For comparison of properties, a conventional epoxy polymer was prepared using the diglycidyl ether of bisphenol A (DGEBA) epoxy resin (Lapox ARL-135LV from Atul Ltd.), together with an amine-based hardener (Lapox AH-411 from Atul Ltd.), and referred to as Sample 1.

Mechanical testing
According to ASTM D638 (type V) stress-strain properties of the samples (namely, Sample 1 and Sample 2) were measured using Universal Testing Machine at room temperature. The testing parameters were load cell: 5 kN, preload force: 0.1 N, cross head speed: 1 mm/minute, gauge length: 15mm, number of Samples: 3 per batch for consistency, sample dimension: 50 mm length x 3.21 mm width x 3.17 mm thickness.
The sample was placed between clamps of the Universal Testing Machine - Tensile Testing Module such that the edges of the sample were parallel to the direction of the load. The grips were then tightened to hold the sample securely within the jig. The sample was then pulled apart at a tensile speed of 1 mm/min until it broke. The epoxy vitrimer sample (Sample 2) designed with dynamic covalent bonds, exhibited a tensile strength of ~59.9 MPa, comparable to the tensile strength of conventional epoxy (Sample 1), which had a tensile strength of 60.2 MPa.
From the stress–strain data obtained according to ASTM D638, Young’s modulus was determined as the slope of the initial linear region of the stress–strain curve. The epoxy vitrimer (Sample 2) exhibited a Young’s modulus of about 745.04 MPa, while conventional epoxy (Sample 1) had a value of 845.41 MPa. These results indicate that the incorporation of dynamic covalent bonds in the vitrimer matrix did not adversely affect the stiffness of the material.
Shore D hardness testing was performed on the prepared samples. Sample 2, corresponding to the epoxy vitrimer, exhibited a Shore D hardness of 84, whereas Sample 1, corresponding to the comparative epoxy polymer, exhibited a Shore D hardness of 86. The hardness value of the epoxy vitrimer was therefore within ±10% of that of the standard epoxy polymer.
Self-healing test
The self-healing capability of the synthesized epoxy vitrimer was evaluated by inducing controlled mechanical damage in the form of surface scratches with millimetre-scale depth on the cured samples. The damaged specimens were subsequently subjected to thermal annealing in a hot air oven at 150 °C for 24 hours, a temperature above the vitrimer transition temperature (Tᵥ), to activate dynamic bond exchange. This thermal treatment facilitated the autonomous repair of the induced defects, attributed to the associative nature of the covalent adaptive network (CAN), enabling topological rearrangement and stress relaxation.
Recyclability test
To evaluate the reprocessability and mechanical recyclability of the vitrimer, Sample 2 was mechanically ground into a fine powder using a standard milling process. The resulting particulate matter was transferred into a pre-heated mold and subjected to compression molding in a Santec hydraulic press under the following conditions: 200 °C and 5 MPa for 10 minutes. Under these conditions, the vitrimer powder exhibited melt-flow behaviour attributable to dynamic bond exchange, enabling reformation into a monolithic structure without significant loss of mechanical integrity. These results demonstrate that the vitrimer is capable of undergoing multiple reshaping cycles and mechanical recycling.
The thermal and dynamic mechanical properties of the epoxy vitrimer (Sample 2) were evaluated in comparison to a conventional epoxy (Sample 1). Dynamic mechanical analysis (DMA) was carried out using a TA Instruments Q-800 in dual cantilever mode. Rectangular specimens (35.0 × 12.7 × 3.2 mm³) were aligned without preloading, and stress relaxation tests were conducted at a heating rate of 3 °C/min under a constant strain of 0.02%. Relaxation modulus (E(t)) was recorded as a function of time at isothermal conditions ranging from 140 °C to 190 °C in 10 °C intervals, with representative temperatures of 150 °C, 160 °C, 170 °C, and 180 °C.
The typical relaxation time (τ) was defined according to the Maxwell model as the time at which the relaxation modulus decreased to approximately 37% (1/e) of its initial value (E₀). For Sample 2, τ values were determined to be 466.3 s, 196 s, 86.7 s, and 36.7 s at 150 °C, 160 °C, 170 °C, and 180 °C, respectively. Faster relaxation at higher temperatures is attributed to accelerated dynamic bond exchange, whereas slower relaxation at lower temperatures arises from reduced segmental mobility and partially frozen dynamic bonds. Stress relaxation data were fitted to the Arrhenius equation:
ln(τ)=ln(τ_0) +E_a/RT
where Eₐ represents the activation energy of bond exchange, T is the absolute temperature, τ₀ is the characteristic relaxation time, and R is the universal gas constant. Linear fitting of ln(τ) versus 1000/T yielded a straight line with an adjusted R² value of 0.99731, confirming Arrhenius-type behaviour. The calculated activation energy of the vitrimer system was 134.67 kJ/mol, higher than reported values for silyl ether–hydroxyl exchange, likely due to the presence of dual dynamic crosslinking mechanisms and increased crosslink density.
The topology freezing transition temperature (Tᵥ), also referred to as the vitrimer transition temperature, was calculated using:
η=⅓E^' τ
where η is the viscosity, E′ is the storage modulus, and τ is the relaxation time. Tᵥ is generally defined as the temperature at which the vitrimer viscosity reaches approximately 10¹² Pa·s. For the epoxy vitrimer (Sample 2), Tᵥ was determined to be approximately 95 °C. Below Tᵥ, the network topology is kinetically frozen due to slow bond exchange, whereas above Tᵥ, dynamic network rearrangements are activated.
Differential scanning calorimetry (DSC) was performed using a DSC Q-250 (TA Instruments) to determine the glass transition temperature (Tg) and to assess curing completeness. Approximately 3.5 to 5 mg of sample was placed in an aluminum crucible, and thermograms were recorded over 40–200 °C in sequential heating–cooling–heating cycles at 10 °C/min. Tg values were obtained from the second heating cycle. No residual exothermic peak was observed, confirming complete curing of the vitrimer network. Sample 2 exhibited a Tg of approximately 120 °C, comparable to Sample 1, which had a Tg value of 129 °C, indicating that dynamic crosslinkers did not adversely affect bulk thermal properties.
Thermogravimetric analysis (TGA) was conducted using a TGA Q-500 (TA Instruments) to assess thermal decomposition. Approximately 10–15 mg of sample was heated from 40 °C to 600 °C at 10 °C/min under a nitrogen atmosphere. Sample 2 displayed an onset decomposition temperature of approximately 328.5 °C, compared to 323 °C for Sample 1, confirming that the vitrimer maintains thermal stability comparable to or exceeding conventional epoxy while providing dynamic bond exchange functionality. These combined results demonstrate that the epoxy vitrimer exhibits excellent thermal and temperature-dependent mechanical stability, alongside reprocessability and self-healing potential.
EXAMPLE 2
Preparation of coating composition and coatings therefrom
An epoxy vitrimer precursor solution was prepared by stoichiometrically combining diglycidyl ether of bisphenol A (DGEBA) with 4,4'- bis-3-(triethoxysilyl)-propyl)-tetrasulfide (TSPTE) under controlled mixing conditions to ensure homogeneity. The resultant formulation was subsequently drop-cast onto clean glass substrates (dimensions: 75 mm × 26 mm × 1 mm. The coated glass was subjected to a temperature of 80 °C for 25 to 40 minutes, enabling the formation of an intermediate network structure. In the second step, electrically conducting silver nanowire (AgNWs) suspensions were spray-coated onto the semi-cured coated glass. About 1.0 mL of AgNWs solution was deposited on the glass substrate. The coated glass sample was then subjected to final curing at 120 °C for 1 hour, facilitating complete crosslinking of the vitrimer matrix and robust embedding of the AgNWs into the polymer network, referred to as Sample 3.

Adhesion studies
To evaluate the mechanical robustness and interfacial adhesion of the developed coating to the substrate (Sample 3), a Scotch tape peel test was carried out following a standardized protocol. A commercially available pressure-sensitive adhesive tape (3M Scotch Tape) was firmly applied to the coated surface of the glass substrate (Sample 3), prepared as described in Example 2, to ensure uniform contact across the adhesion area. The tape was subsequently peeled off manually at a 90° angle relative to the substrate plane, using a consistent and steady pulling force. The surface was visually inspected for evidence of delamination, cracking, or residue transfer. To ensure reproducibility, the test was performed in triplicate, providing a qualitative assessment of the coating’s adhesion performance under peel stress. The Scotch tape test serves as an effective method to demonstrate the adhesion strength of the coating. The coating remained stable after the tape adhesion test, which is attributed to the macroscopic crosslinks imparted by the polymer network. This robust adhesion highlights the potential of the coating to be spray-applied onto diverse substrates, including both conductive (e.g., metals) and non-conductive (e.g., plastics, glass) materials.
Conductivity studies
The electrical conductivity of thin films is typically evaluated by measuring their sheet resistance, often using a four-point probe method to minimize contact resistance errors. In this method, a known current is passed through the outer probes, and the resulting voltage drop across the inner probes is measured, from which sheet resistance is calculated. Sample 3 exhibited a sheet resistance of 212 ohms per square (Ω/sq) and an electrical conductivity of 258.2 Siemens per meter (S/m), highlighting its efficacy in electrostatic charge dissipation (ECD) applications. The dynamic nature of the vitrimer network preserved the electrical pathways, as confirmed by the electrical conductivity studies. Overall, the coating (Sample 3) exhibited multifunctional performance in terms of mechanical resilience, self-healing, reprocessability, hydrophobicity, and electrical conductivity.
The conductive nature of the coating (Sample 3) was further verified through a simple electrical circuit demonstration, in which the coated glass substrate was incorporated into a circuit consisting of a power source and a light-emitting diode (LED) or bulb. When the circuit was closed, the LED illuminated successfully, as shown in FIG. 4. This confirmed that the AgNWs formed a well-aligned and interconnected conductive network across the vitrimer surface, thereby enabling efficient current flow and circuit completion.
Hydrophobicity or water repellence studies
The hydrophobicity and water repellence of Sample 3 were evaluated using sessile drop contact angle measurement. Coatings prepared according to the procedure described in Example 2 were tested using a Kyowa Contact Angle Goniometer under ambient laboratory conditions. A 2 μL droplet of deionized water was dispensed onto the coated surface using a precision micro-syringe. High-resolution images of the droplet profile were captured immediately after deposition, and the static contact angle was determined using image analysis software integrated with the goniometer. Contact angles greater than 90° were considered indicative of hydrophobic behaviour.
Sample 3 exhibited hydrophobic properties as confirmed by contact angle measurements, as shown in FIG. 5. A 2.0 μL droplet of deionized water remained spherical on the coated surfaces and slid off readily. FIG. 5 includes image 500 that highlights water droplets on various substrates. The coating applied to glass, PET, and metal substrates demonstrated large water contact angles. The average contact angle was determined from the left and right profiles of the droplet and was measured as (a) 103.2° on glass, (b) 104.1° on PET, (c) 103.95° on metal, and (d) 107.85° on glass substrate coated with epoxy vitrimer containing nanowires. These results demonstrated that the coatings were hydrophobic and capable of providing water resistance and corrosion protection. The epoxy vitrimer coatings also retained their hydrophobic properties after reprocessing, owing to the dynamic exchange of covalent bonds in the vitrimer network.
Optical transparency
The transparency of the vitrimer coating was visually demonstrated by placing a printed logo beneath the coated substrate. FIG. 6 includes image 600 where the logo remained clearly visible through the coating, confirming both the transparency of the coating and the non-obstructive arrangement of the embedded AgNWs.
The measured OD values confirmed that the coating is suitable for applications requiring both conductivity and optical clarity, such as display panels, touchscreens, and transparent electrodes.
It is to be understood that the above description is intended to be illustrative, and not restrictive. Furthermore, many other embodiments will be apparent to those of skill in the art upon reading and understanding the above description. Although the present disclosure has been described with reference to specific exemplary embodiments, it will be recognized that the disclosure is not limited to the embodiments described, but can be practiced with modification and alteration within the scope of the appended claims.
, Claims:CLAIMS
I/We Claim:
1. An epoxy vitrimer comprising:
an epoxy unit formed by a reaction between an epoxy resin and an initiator, wherein the initiator is selected from 1-(3-aminopropyl)imidazole, 2-propylimidazole, 2,4,6-tris(dimethylaminomethyl)phenol, N,N-dimethylbenzylamine, 2-methyl imidazole, 1,2-dimethylimidazole, 2-ethyl-4-methyl-1H-imidazole, benzyl triethyl ammonium chloride, boron trichloride, boron trifluoride monoethyl amine, 2-phenylimidazole (2-PI), 2-undecylimidazole (2-UI), 1-butyl-3-methylimidazolium salts, 1-cyanoethyl-2-methylimidazole, and combinations thereof; and
a dynamic crosslinker configured to form a covalent adaptive network with the epoxy unit through silyl ether exchange alone, or in combination with one or more mechanisms selected from transesterification, disulfide exchange reaction, imine formation, thiol–ene vinyl reactions, and transcarbamoylation.
2. The epoxy vitrimer as claimed in claim 1, wherein the epoxy resin is selected from diglycidyl ether of bisphenol A (DGEBA), diglycidyl ether of bisphenol F, hydrogenated bisphenol A diglycidyl ether, tetraglycidyl methylene dianiline, pentaerythritol tetraglycidyl ether, trimethylol triglycidyl ether (TMPTGE), tetrabromo bisphenol A diglycidyl ether, hydroquinone diglycidyl ether, ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, butylene glycol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,4-butanediol diglycidyl ether, 1,6-hexanediol diglycidyl ether, cyclohexanedimethanol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, polytetramethylene glycol diglycidyl ether, resorcinol diglycidyl ether, neopentyl glycol diglycidyl ether, bisphenol A polyethylene glycol diglycidyl ether, bisphenol A polypropylene glycol diglycidyl ether, 4,4’-methylenebis(N, N-diglycidylaniline) (MDGA), tetraglycidyl diaminodiphenyl methane (TGDDM), and combinations thereof.
3. The epoxy vitrimer as claimed in claim 1, wherein the dynamic crosslinker comprises an amino-silane, an epoxy silane, a vinyl silane, an acrylic silane, a vinyl-(meth)acryloxy silane, an alkyl silane, an alkyl-bridged silane, an aryl silane, a sulphur-functionalized silane, a polymeric silane, or a hybrid silane.
4. The epoxy vitrimer as claimed in claim 3, wherein the dynamic crosslinker is selected from 3-aminopropyltriethoxysilane (APTES), 3-(trimethoxysilyl)propyl methacrylate (TMSPMA), 3-(triethoxysilyl)propyl acrylate, 3-(triethoxysilyl)propyl methacrylate, 3-glycidyloxypropyltrimethoxysilane, vinyltrimethoxysilane, vinyl-/methacryloxy-silane hybrid, methyltriethoxysilane, phenyltriethoxysilane, 4,4'- bis-3-(triethoxysilyl)-propyl)-tetrasulfide (TESPT), bis[3-(triethoxysilyl)propyl] disulfide (TESPD), bis[triethoxysilyl]ethane (BTSE), silyl-terminated polymers, silane-functionalized glycidyl methacrylate copolymer, trialkoxysilane-functionalized polyurethane, and trialkoxysilane-functionalized epoxy.
5. The epoxy vitrimer as claimed in claim 1, wherein a weight ratio of the epoxy unit to the dynamic crosslinker in the epoxy vitrimer is in a range of 99.5:0.5 to 80:20.
6. The epoxy vitrimer as claimed in claim 1, wherein the epoxy vitrimer has a vitrimer transition temperature in a range of 80 °C to 180 °C.
7. The epoxy vitrimer as claimed in claim 1, wherein the epoxy vitrimer has a tensile strength which is within ±10% of a tensile strength of a standard epoxy polymer derived from the same epoxy resin.
8. The epoxy vitrimer as claimed in claim 1, wherein the epoxy vitrimer has a Shore D hardness which is within ±10% of a Shore D hardness of a standard epoxy polymer derived from the same epoxy resin.
9. The epoxy vitrimer as claimed in claim 1, wherein the epoxy vitrimer has a curing time of 1 hour, or less than 1 hour.
10. A coating composition comprising an epoxy vitrimer as claimed in claim 1.
11. A transparent, hydrophobic coating comprising:
an epoxy vitrimer, the epoxy vitrimer comprising;
an epoxy unit formed by a reaction between an epoxy resin and an initiator, wherein the initiator is selected from 1-(3-aminopropyl)imidazole, 2-propylimidazole, 2,4,6-tris(dimethylaminomethyl)phenol, N,N-dimethylbenzylamine, 2-methyl imidazole, 1,2-dimethylimidazole, 2-ethyl-4-methyl-1H-imidazole, benzyl triethyl ammonium chloride, boron trichloride, boron trifluoride monoethyl amine, 2-phenylimidazole (2-PI), 2-undecylimidazole (2-UI), 1-butyl-3-methylimidazolium salts, 1-cyanoethyl-2-methylimidazole, and combinations thereof, and
a dynamic crosslinker configured to form a covalent adaptive network with the epoxy unit through silyl ether exchange alone, or in combination with one or more mechanisms selected from transesterification, disulfide exchange reaction, imine formation, thiol–ene vinyl reactions, and transcarbamoylation; and
an electrically conducting nanoparticle dispersed in the coating, wherein the nanoparticle is selected from silver nanowires, silver nanoparticles, gold nanowires, copper nanowires, indium tin oxide nanoparticles, metal meshes, metal oxide nanoparticles, zinc oxide nanoparticles, aluminum-doped zinc oxide nanoparticles, gallium-doped zinc oxide nanoparticles, carbon nanotubes, conducting polymers, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) and combinations thereof, and wherein the coating has an optical density in a range of 50% to 90%.
12. The coating as claimed in claim 11, wherein the coating is self-healable.
13. The coating as claimed in claim 11, wherein the conducting nanoparticle is silver nanowires.
14. A method (300) of forming a transparent, hydrophobic coating on a substrate, the method comprises the steps of:
(i) applying to the substrate a coating composition (302) comprising an epoxy vitrimer to form a first substrate, wherein the epoxy vitrimer comprises an epoxy unit and a dynamic crosslinker, wherein the epoxy unit is formed by a reaction between an epoxy resin and an initiator, wherein the initiator is selected from 1-(3-aminopropyl)imidazole, 2-propylimidazole, 2,4,6-tris(dimethylaminomethyl)phenol, N,N-dimethylbenzylamine, 2-methyl imidazole, 1,2-dimethylimidazole, 2-ethyl-4-methyl-1H-imidazole, benzyl triethyl ammonium chloride, boron trichloride, boron trifluoride monoethyl amine, 2-phenylimidazole (2-PI), 2-undecylimidazole (2-UI), 1-butyl-3-methylimidazolium salts, 1-cyanoethyl-2-methylimidazole, and combinations thereof, and wherein the dynamic crosslinker is configured to form a covalent adaptive network with the epoxy unit through silyl ether exchange alone, or in combination with, one or more mechanisms selected from transesterification, disulfide exchange reaction, imine formation, thiol–ene vinyl reactions, and transcarbamoylation; and
(ii) curing the first substrate (304) at a temperature in a range of 80°C to 140°C to form the transparent, hydrophobic coating on the substrate.
15. The method (300) as claimed in claim 14, wherein an electrically conducting nanoparticle is dispersed in the coating composition, or disposed on the first substrate prior to step (ii), to form an electrically conductive coating.
16. The method (300) as claimed in claim 15, wherein the electrically conducting nanoparticle is selected from silver nanowires, silver nanoparticles, gold nanowires, copper nanowires, indium tin oxide nanoparticles, metal meshes, metal oxide nanoparticles, zinc oxide nanoparticles, aluminum-doped zinc oxide nanoparticles, gallium-doped zinc oxide nanoparticles, carbon nanotubes, conducting polymers, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), and combinations thereof; and
17. The method (300) as claimed in any of the claims 14-16, wherein the substrate comprises a metal, a ceramic, a glass, polyethylene terephthalate, or a polymer.
18. The method (300) as claimed in any of the claims 14-17, wherein the substrate is selected from an aircraft wing, an aircraft fuselage, a cockpit window, a display panel, a photovoltaic panel, architectural glass, a smart window, a medical device housing, an automotive body panel, and a windshield.