Polymeric coatings and coating method

Polymeric coatings and methods of forming polymeric coatings are described. In a method of forming a polymeric coating a first layer is deposited on a substrate. The first layer includes at least one highly soluble diamine component. A second layer is formed on the substrate to contact the first layer. The second layer includes paraformaldehyde and an aromatic diamine including two primary amine groups. Once formed, the first and second layers are heated. Heating causes the components of the first and second layers to cure. For example, the paraformaldehyde from the second layer diffuses into the first layer and reacts via hemiaminal-type chemistry with the high soluble diamine component. The coatings may be substantially homogenous or comprise a compositional gradient in thickness or along the substrate plane depending on deposition methods and other processing parameters.

BACKGROUND

The present disclosure relates to polymeric materials, and more specifically, to polymeric materials for coatings and composite materials and processes for forming coatings and composite materials.

SUMMARY

According to one embodiment of the present disclosure, a method includes depositing a first layer on a substrate. The first layer comprises at least one compound selected from the following:

A second layer is deposited on the substrate, the first and second layers contact each other. The second layer comprises paraformaldehyde and an aromatic diamine including two primary amine groups. Once deposited on the substrate, the first and second layers are heated. The order of deposition for the first and second layers is not particularly limited and the second layer may be deposited on the substrate before the first layer. Additionally, in some embodiments, either of the first and second layers may cover only a portion of the substrate.

According to another embodiment, a coating method includes forming a primer film on a substrate. The primer film is formed from a primer solution including at least one compound selected from the following:

In this embodiment, a precursor film is formed over the primer film. The precursor film formed from a precursor solution including paraformaldehyde and an aromatic diamine including two primary amine groups. After the primer film and the precursor film are formed, the primer film and the precursor film are heated to a temperature between 50° C. and 200° C.

According to yet another embodiment, a polymeric coating is formed by a method comprising depositing a first layer on a substrate. The first layer includes at least one compound selected from the following:

The method further comprises depositing a second layer on the substrate. The first and second layers contact each other. The second layer comprises paraformaldehyde and a first aromatic diamine including two primary amine groups. After deposition, the first and second layers are heated.

DETAILED DESCRIPTION

With reference now toFIG. 1, a polymeric coating150is formed on a substrate100. Substrate100, for graphical convenience, is depicted as a single, flat surface. However, substrate100is not particularly limited in shape, morphology, or composition. In some specific example embodiments, substrate100can be an optically flat glass substrate, a carbon fiber, a carbon fabric, a metal sheet, a printed circuit board, a silicon wafer, or a porous material. The substrate may be a reinforcing portion for a composite material. In most, but not necessarily all embodiments, it will be preferable for the polymeric coating150to adhere strongly to substrate100. Adhesion between coating150and substrate100may be aided by inclusion of an adhesion promoting layer105, but adhesion promoting layer105is optional and may be included or excluded depending on intended end use and/or the specific materials selected for substrate100and polymeric coating150.

InFIG. 1, a process of forming a polymeric coating150on substrate100(with the optional adhesion promoting layer105disposed thereon) begins by forming a primer film110on substrate100. Primer film110is formed from a primer solution109including one or more highly soluble diamine component (also referred to as a “HSDA component” or “HSDA”). The composition of the primer solution109and the highly soluble diamine component(s) within primer solution109are discussed further below. In an example, 4-amino benzylamine may be the HSDA component in primer solution109. The primer solution109may include an organic solvent.

InFIG. 1, adhesion promoting layer105is not depicted on the substrate after its initial formation, but the adhesion promoting layer105may be present during later processing steps and/or in the final product if initially present.

The primer film110can be formed on substrate100by physical application of the primer solution109to the substrate100in a process such as dip coating, spin coating, brush coating, roll coating, blade coating, knife coating, spray coating, and/or intaglio-type printing. The primer film110can be formed to cover all or only a portion of the surface of substrate100. Similarly, thickness (in a direction orthogonal to surface of substrate100) of the primer film110can be constant or varying over the substrate100.

After primer film110is formed, a precursor film120is formed over the primer film110. The precursor film120can be formed by physical application of a polymeric precursor solution119(also referred to as “precursor solution119”) in a process such as dip coating, spin coating, brush coating, roll coating, blade coating, knife coating, spray coating, and/or intaglio-type printing. The precursor film120can be formed to cover all or only a portion of the primer film110. Thickness (in a direction orthogonal to surface of substrate100) of the precursor film120can be constant or varying. The composition of the polymeric precursor solution119is discussed further below, but, in general, the polymeric precursor solution119includes paraformaldehyde (PF) and an aromatic diamine component (also referred to as an “ADA component” or “ADA”). In this context, paraformaldehyde is a polyacetal OH(CH2O)mH (wherein m is typically in a range of 8-100). In a specific example, 4,4′-oxydianiline (ODA) can be used as the aromatic diamine component. The precursor solution119may also include an organic solvent.

After the precursor film120is formed, a second primer film110can optionally be formed over the precursor film120. That is, a three or more layer coating (i.e., primer film110/precursor film120/primer film110) can be formed on the substrate100. The process used for forming the second primer film110over the precursor film120can be the same type of process used to form the initial primer film110or a different type process can be used. For example, dip coating can be used to form the initial primer film110on the substrate100and spray coating can be used to form the second primer film110over the precursor film120. Similarly, the primer solution109used for forming the primer films110can be varied for each layer, though in each instance the primer solution109contains one or more highly soluble diamine component.

The thickness of each primer film110can be the same or each film may have a different thickness. The coverage ratio for each primer film110formed on the substrate10can be the same or different. That is, for example, the initial primer film110may cover the entirety of the surface of substrate100and the second primer film110may cover only a portion of the precursor film120. The second primer film110may be formed on the underlying precursor film120in an arbitrary pattern, such as might be supplied in conjunction with a 3D printing process or the like.

After the second primer film110is formed, another precursor film120can optionally be formed. The process used to form the second precursor film120can be same type of process used to form the initial precursor film120or may be a different type process. For example, blade coating can be used to form the initial precursor film120and intaglio-type printing can be used to form the second precursor film120(that is, the fourth layer in a four layer coating). The composition of the precursor solution119can be varied for each precursor film120, though in each instance paraformaldehyde and an aromatic diamine component are present.

As depicted inFIG. 1, a plurality of primer films110and precursor films120can optionally be formed on substrate100. The number of each of the films in the stack is not particularly limited though overall film quality of the coating150may be poor for very thick coatings and this may serve as a practical upper limit on the number of films in some instances. Furthermore, while each primer film110and precursor film120inFIG. 1is depicted as having substantially the same thickness, this is not required. For example, each primer film110may be approximately 100 nm thick when formed and each precursor film120may be 200 nm thick when formed. As discussed above, each primer film110can also have a thickness that is independently set from the other primer films110. Similarly, each precursor film120can also have a thickness that is independently set from the other precursor films120. Furthermore, while depicted inFIG. 1as being deposited in a one-to-one ratio in a fully alternating manner, a primer film110may be formed directly on another primer film110and a precursor film120may be formed directly on another precursor film120. This stacking of the same film-types directly upon one another may be used, for example, as a means to provide different layer thicknesses in the coating film stack without varying the composition of solutions or the processes used in forming the individual films.

In some embodiments, a precursor film120may be the initial film formed on the substrate100rather than a primer film110. Likewise, the capping layer (the last film in the coating stack) can be a primer film110rather than a precursor film120. That is, order of formation of primer film(s)110and precursor film(s)120can be varied without limitation.

After a film stack including at least one primer film110and at least one precursor film120is formed on the substrate100, the film stack is cured, by heating or other processes of extending chemical bonding in a polymer system, to form the coating150. The curing process will be discussed further below, but, in general, it includes formation of a crosslinked resin material through hemiaminal-type chemistry. Depending on relative amounts and disposition of components in the primer films110and the precursor films120, the resultant coating150can be a substantially homogenous polymeric coating, a polymeric coating with a compositional gradient along the thickness direction, or a polymeric coating having a 3D-type physical and/or compositional patterning along the substrate100plane and/or in the thickness direction above the substrate100plane.

As noted, substrate100is depicted inFIG. 1as a single, flat surface, but substrate100is not particularly limited in shape, morphology, or composition. Substrate100, for example, may be formed of insulating materials, conductive materials, semiconductor materials, silicon, metals, carbon fiber, wood, plastic, or various combinations of materials. Substrate100may itself be polymeric or include polymeric layers. Substrate100my comprise stacked or otherwise mixed layers of various materials, such as a crystalline silicon wafer having patterned and unpatterned layers of metal, insulators, and semiconductor material disposed thereon. In addition, substrate100may have surface topography including, for example, local peaks and valleys relative to an average substrate plane, mesas, trenches, lines, spaces, pillars, holes, or other features disposed on or in the substrate100. Substrate100may also have an outer surface that is bent, spherical, concave, convex, or otherwise non-planar. Substrate100may be a fabric, a felt, a mesh, or a scaffold (reinforcement) material for a composite component. For example, substrate100may comprise carbon fibers and/or carbon nanotubes.

Adhesion Promoting Layer

As described above, an adhesion promoting layer105can be used to promote adhesion between the first film110(or a second film120, if first in the coating stack) and the substrate100. The adhesion promoting layer105may be a distinct film applied to substrate100by, for example, a vapor deposition process such as physical vapor deposition, chemical vapor deposition, atomic layer deposition, or the like, or a physical application process such as one of those suggested for forming the first film110. The adhesion promoting layer105can also be formed by conversion or modification of a portion of substrate100. In some embodiments, the adhesion promoting layer105may be the residue or result of a surface treatment process such as a plasma treatment process or cleaning process which causes the surface of the substrate100to be modified in some manner. For example, partial oxidation of substrate100to form an oxide film on the surface of substrate100.

Primer Solution

The primer solution109used in forming primer film110may include one or more materials which may be described as a highly soluble diamine component. The highly soluble diamine component includes two primary amine groups per molecule and is readily soluble in an organic solvent. The HSDA component is characterized by its relatively quick reaction with paraformaldehyde to form a polymeric material. The speed of the reaction of the HSDA and paraformaldehyde may be such that it would be difficult to handle or otherwise process a mixture of HSDA and paraformaldehyde before substantial polymerization (gelation) occurs. The reaction rate of HSDA and paraformaldehyde may be substantial even at room temperature (25° C.). As such, while the primer solution109can include a solvent, it typically does not include paraformaldehyde because gelation of the mixture would severely limit storage lifetime of the primer solution109and/or cause difficulty in the processing used to form the primer film110. Non-limiting examples of HSDA components are provided below:

Possible HSDA components include 4-aminobenzylamine and p-xylylenediamine and the condensation products of 4-aminobenzylamine with 1,4-butanediol diacrylate or trimethylolpropane triacrylate. As used above, the structural notation (—CH2—)0,1indicates the methylene group may be present (1) or absent (0) at the specific location depicted. Thus, the amino end group may be directly bonded to the aromatic ring. In this context, each end group can be independent of the other end groups in the molecule.

The highly soluble diamine component(s) may be present at a concentration between 1 and 100 wt %. As noted, the primer solution109may include a solvent. The solvent can be any suitable solvent. Preferred solvents include dipolar aprotic solvents such as, for example, N-methyl-2-pyrrolidone (NMP), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), propylene carbonate (PC), and propylene glycol methyl ether acetate (PGMEA). Most preferably, the solvent is NMP.

The viscosity of the primer solution can be varied by changing the concentration and/or the selection of particular HSDA components. For instance, 4-amino benzylamine and p-xylylenediamine are liquid at room temperature, but the condensation products of 4-amino benzylamine with 1,4-butanediol diacrylate or trimethylolpropane triacrylate are viscous oils. However, each of these materials quickly solubilize in NMP (or other organic solvents). A higher viscosity for the primer solution109may be useful for certain coating processes such as dip coating, spin coating, or other physical application techniques such as brush coating, roll coating, or intaglio-type printing because higher viscosity materials will be more likely to maintain substrate coverage after being applied. A lower viscosity for the primer solution109may be useful for certain coating processes such as spray-on coating, inkjet printing, or other processes requiring the primer solution109to pass through narrow openings, channels, or pores. In general, primer solution109viscosity may be lowered by increasing relative solvent content and/or selecting lower viscosity components over higher viscosity components. In general, primer solution109viscosity may be increased by decreasing relative solvent amounts and/or increasing amounts of higher viscosity components.

Precursor Solution

The precursor solution119includes paraformaldehyde (PF), at least one monomer having two primary aromatic amine groups, and optionally a solvent. The precursor solution119may include a single aromatic diamine (ADA) component or a mixture of two or more ADA component types. The precursor solution119may optionally include a diluent-type monomer component having only one primary aromatic amine group. The inclusion of diluent-type components can be used to control crosslink density of cured resins materials. The ratio of paraformaldehyde to primary aromatic amine groups will generally be greater than one and may be set with consideration of the expected relative amount of primary amine groups in the HSDA of the primer solution109(or more specifically, the amount of HSDA in primer film(s)110formed from the primer solution109).

A non-limiting group of exemplary monomers including two primary aromatic amine groups which can be used as ADA components can be described by the formula (1):

wherein L′ is a divalent linking group. The L′ divalent linking group can be selected from the group consisting of *—O—*, *—S—*, *—N(R′)—*, *—N(H)—*, *—R″—*, and combinations thereof, wherein R′ and R″ independently comprise at least 1 carbon, and here each “*” starred bond indicates a point of attachment to an aromatic ring. In an embodiment, R′ and R″ are independently selected from the group consisting of methyl, ethyl, propyl, isopropyl, phenyl, and combinations thereof. Other possible L′ divalent linking groups include methylene (*—CH2-*), isopropylidenyl (*—C(Me)2-*), and fluorenylidenyl:

The precursor solution119at time of application to substrate100may include oligomers resulting from polymerization of the ADA monomer(s) initially present in precursor solution119. The precursor solution119may be specifically processed to cause partial polymerization of solution components before application to substrate100or partial polymerization may be an unintended or unavoidable consequence of storage and/or handling prior to application. Partial polymerization of precursor solution119prior to application may improve film forming qualities in some instances by increasing solution viscosity. Low temperature storage for precursor solution119prior to application may be used to limit pre-application polymerization and improve solution shelf life.

As noted, precursor solution119may include one or more diluent-type monomer. A diluent monomer includes only a single primary aromatic amine group rather than two. As such, the diluent-type monomer can be included to control the degree/extent of crosslinking in the final coating150. While discussed here in the context of inclusion in the precursor solution119, a diluent-type monomer may also, or instead, be included in primer solution109.

As noted, the precursor solution119may include a solvent. The solvent can be any suitable solvent. Preferred solvents include dipolar aprotic solvents such as, for example, N-methyl-2-pyrrolidone (NMP), dimethylsulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMA), propylene carbonate (PC), and propylene glycol methyl ether acetate (PGMEA). Most preferably, the solvent is NMP.

Coating Process

FIG. 2depicts formation of a polymeric coating on a substrate. For simplicity, only one primer film110and one precursor film120is depicted as being disposed on substrate100. Primer film110includes a highly soluble diamine (HSDA)220, which is highly soluble diamine component as described above. Precursor film120includes an aromatic diamine (ADA)210, which is an aromatic diamine component as described above, paraformaldehyde, and solvent. In state (a) depicted inFIG. 2, the films are discrete and film components have not substantially diffused or otherwise mixed. In some embodiments, state (a) will be short-lived because mixing of layers may occur nearly instantaneously upon application of the second film (e.g., film120) on the first film (e.g., film110). That is, depending on such factors as the application methods, solvent loadings, and the miscibility of different components, substantial mixing of layers may occur during application of the second film (e.g., film120) in the stack.

State (b) inFIG. 2depicts a region230between film110and film120that is an interfacially mixed region in which components from the adjacent films are found. For example, region230may include paraformaldehyde, solvent, ADA210, and HSDA220. The size of region230may depend in part on the length of time the films110and120have been in contact and/or the coating method used to form the films. Components in the adjacent films will tend to diffuse from areas of high concentration to low concentration. In general, lower molecular weight components will be expected to migrate more quickly than higher molecular weight components. Heat also promotes diffusion of components, but in this instance heat also promotes polymerization reactions amongst the available components. The incorporation of various components into polymer chains (increasing molecular weight) will tend to hinder diffusion between the films. As such, the degree of mixing (size of region230) may be alterable by varying processing temperature, with high temperatures (e.g., ˜200° C.) possibly limiting the extent of mixing between layers depending on relative rates of polymerization (vitrification) and component diffusion.

State (b) ofFIG. 2depicts films110and120before substantial curing of film components has occurred. In state (c) ofFIG. 2, an initial curing reaction has occurred. Film120has been converted to region260containing a hemiaminal dynamic covalent network (HDCN)240. Here, available primary aromatic amine groups begin to react with paraformaldehyde. Polymers result from this reaction when at least one of the reactants has a second primary aromatic amine that is available for reaction. In a similar manner to film120, film110converts to region270containing a HDCN240. In general, the conversion of film110into a region270containing HDCN240requires the transport/diffusion of paraformaldehyde from film120into film110.

In state (c), region230also contains HDCN material. The material of region230in state (c) may include a HDCN240(type 1) formed solely by reaction of ADA210with paraformaldehyde, a HDCN240(type 2) formed solely by reaction HSDA220and paraformaldehyde, and a HDCN240(type 3) formed by a mixed reaction of ADA210and HSDA220with paraformaldehyde. All three types of HDCN240may be present in region230.

FIG. 3depicts an exemplary reaction scheme for forming polymeric coating on a substrate.FIG. 3specifically depicts formation of HDCN240(type 3) incorporating both an aromatic diamine (ADA210) from film120and a highly soluble diamine (HSDA220) from film110. In this instance, the ADA210is ODA and HSDA220is 4-amino benzylamine.

In state (d) ofFIG. 2, HDCN240is converted polyhexahydrotriazine (PHT)250. In state (d) region230may include a PHT250(type 1) having ADA210as a precursor, a PHT250(type 2) having HSDA220as a precursor, and a PHT250(type 3) having both ADA210and HSDA220as precursors. All three types of PHT250may be present in region230. As noted,FIG. 3depicts an exemplary reaction scheme for forming polymeric coating on a substrate.FIG. 3specifically depicts formation of PHT250(type 3) incorporating both an aromatic diamine (ADA210) from film120and a highly soluble diamine (HSDA220) from film110. Depending on processing temperature HDCN240may be only transiently, if at all, present.

Compositionally Homogenous and Gradient Coatings

FIG. 4Adepicts a homogenous polymeric coating formed on a substrate. InFIG. 4A, coating150formed on substrate100corresponds to a condition in which the materials of film120and film110(see state (a) inFIG. 2) become intimately mixed before or during the conversion of ADA210and HSDA220. The resultant coating150is substantially homogenous. The mixing necessary for obtaining a homogenous coating150may occur during the initial deposition of film120on to film110and/or may be considered to result from an exaggerated version of state (b) in which region230subsumes all of film110and film120by eventual diffusion (or other mixing) of components. It should be noted that while a progression from state (a) to state (d) depicted inFIG. 2occurs in sequence for purposes of explanation, formation of a homogenous coating150as depicted inFIG. 4Ais not necessarily a continuation of the sequence depicted inFIG. 2, but rather a homogenous coating150is an end state variant resulting from selection of processing and compositional parameters to provide substantial mixing of the film110and film120components at some point during the coating process rather than only partial mixing.

Material410of coating150in general corresponds to polymeric material of the region230depicted in state (c) or (d) ofFIG. 2. That is, material410can be a mixture of types 1 to 3 of HDCN240or mixtures of types 1 to 3 of PHT250.

FIG. 4Bdepicts a polymeric coating formed on a substrate with a compositional gradient along the thickness direction. InFIG. 4B, coating150formed on substrate100corresponds in general to state (c) or state (d) depicted inFIG. 2. Material430of coating150is rich in polymeric material primarily derived from polymerization of highly soluble diamine monomers (e.g., HSDA220) from the primer film110. The HSDA component reacts with paraformaldehyde from precursor film120. Material430is not necessarily exclusively derived from HSDA monomers, but the HSDA-derived polymer fraction in material430predominates over the ADA-derived polymer fraction in material430. As was the case in the homogenous coating depicted inFIG. 4A, material410inFIG. 4Bcan be a mixture of types 1 to 3 of HDCN240or mixtures of types 1 to 3 of PHT250. Material420of coating150is rich in polymeric material primarily derived from polymerization of aromatic diamine monomers (e.g., ADA210) from a precursor film120with paraformaldehyde (also from precursor film120). The material420is not necessarily exclusively derived from ADA monomers, but the ADA-derived polymer fraction in material420predominates over the HSDA-derived polymer fraction in material420.

As noted in the discussion ofFIG. 1, the film stack used to form coating150may include several primer films110and precursor films120stacked in an alternating manner. As such, a coating150having a compositional gradient as depicted inFIG. 4Bcan include several alternating portions of materials420and430with interposed portions of material410. The relative thicknesses of these portions may be varied by control of the initial thicknesses of the primer films110and the precursor films120and other processing parameters like curing temperature and times, solvent loadings, and paraformaldehyde loadings. In some instances, the thickness of material410may be negligible when inter-film mixing of ADA and HSDA monomers is negligible. And as noted with respect toFIG. 4A, distinct phases corresponding to material420and material430may be absence from coating150when inter-film mixing of ADA and HSDA monomers is substantial.

Film Stacking and 3D Printing

Physical properties of coating150can be varied according to the selection of specific monomer components and their proportions. For example, PHT materials derived from ADA components, such as ODA, can have a high modulus and a high glass transition temperature. PHT materials derived from HSDA components can have a lower modulus and a lower glass transition temperature in comparison. Thus, a gradient coating including alternating material430and material420can have alternating layers of relatively flexible material and relatively stiff material. This sort of arrangement may be advantageous in coating applications requiring both durability and hardness. In addition, the alternating materials in a gradient coating150may be useful in optical coating applications.

FIG. 1depicts as an optional process the repeated formation of primer films110and precursor films120in a multiple layer stack prior to curing into a coating150. Another processing sequence achieving somewhat similar results would be to form a single primer film110and a single precursor film120, cure this pair to form a first coating150, then repeat the process by forming another primer film110and precursor film120on the previously formed first coating150. The second pair of films can then be cured to form another coating150over the first coating150. This, in effect, treats the first coating150as a part of substrate100and repeats the initial processing depicted inFIG. 1.

A related processing sequence would be to form at least one primer film and at least one precursor film120each over the entirety of substrate100, then to selectively heat only portions of the films thus formed. Only the portions selected for heating would substantially cure, and uncured (or low cure) portions of the films could be removed with solvent(s). Selective heating could be provided, for example, by exposure to light or other radiation or by a thermal printing apparatus.

As previously noted, it is not required that either of primer film110or precursor film120completely cover the substrate100when formed. Rather either film can be selectively deposited onto the substrate100. That is, one or both of these films can be selectively disposed on substrate100in an arbitrary pattern. For example, substrate100may be a metal plate or a silicon wafer having a substantially flat surface. In one process, primer film110could be coated over the entire surface of substrate100, then precursor film120could be selectively deposited over primer film110in a desired pattern. The film stack thus formed could then be heated and cured. Those portions of primer film110beyond the diffusion distance of paraformaldehyde provided by the patterned precursor film120would not cure to polyhemiaminal or poly(hexahydrotriazine) material. The uncured portions of primer film110could be removed by solvent. The process could be repeated to build a patterned structure on substrate100in a layer-by-layer process. In another, process each of primer film100and precursor film120could be selectively deposited on the substrate100in a desired pattern, then the patterned stack could be cured. This process could also be repeated to build a patterned structure on substrate100in a layer-by-layer process.

Properties of Coating Materials

Various materials were prepared by curing a HSDA component with a particular ADA component (4,4′-oxydianiline (ODA)). The first column of Table 1 depicts the structure of the HSDA component. The second column is the percentage (wt %) of HSDA in the mixture with ODA (that is, the percentage of total combined weight of HSDA and ODA in the mixture). In preparing these materials, an excess of paraformaldehyde was used. HSDA and ODA were dissolved in NMP. The third column is the temperature at which the resulting materials lost 5% of initial mass as determined in a thermogravimetric analysis. The fourth column is the glass transition temperature (Tg) of the resultant material as determined by differential scanning calorimetry.

Incorporation of HSDA components in the resultant PHT network affects the thermal properties of the resultant material as the crosslinking density varies. While these materials can be prepared by simple mixing of components, in general, HSDA components react very quickly (gelation time of about 1 minute or less at 50° C.) in the presence of paraformaldehyde. Fast curing times may be desirable in some situations, but not always when requirements such as handling, storage, and processing windows are considered.

The gelation time of ODA/paraformaldehyde/NMP solutions is about 1-2 hours at 50° C. The gelation time of typical HSDA/paraformaldehyde/NMP solutions is about 1 minute at 50° C. Without paraformaldehyde, the HSDA component will be substantial stable and can be stored and/or processed. Higher viscosity HSDA components, such as those depicted in Table 1, can be prepared. Higher viscosity solutions may be preferred for some coating processes such as dip coating or spraying as it may allow for more stable coverage of substrate materials.

Example Dip-Coating Process and Coatings

A primer-type solution was prepared by mixing approximately 1 gram of 4-amino benzylamine, 0.75 gram trimethylolproprane triacrylate, and 1.7 gram of NMP. The mixture was stirred for 4 hours at 50° C. Substantially complete conversion of the acrylate was confirmed by1H NMR.

A precursor-type solution was prepared by mixing approximately 2 grams of ODA, 1.1 grams of paraformaldehyde, and 15 mL of NMP. The solution was stirred until clear (about 15 minutes), then stored at 0° C. until use.

A substrate (e.g., a metal screen) was dipped into the primer-type solution previously prepared. The substrate was then dipped into the precursor-type solution previously prepared. These steps can be repeated to prepare a thicker film. After 10 to 30 seconds at elevated temperature (e.g., 50° C.) gelation of the material disposed on the substrate was observed (by visual inspection).

The coated substrate was then subjected to thermal processing: 50° C. for 1 hour, 50° C. to 200° C. for +1 hour, and 200° C. for 1 hour. The coating on the substrate thus formed was subjected to dynamic mechanical analysis (DMA).

FIG. 5depicts DMA measurement results for a polymeric coating formed on a substrate (a metal screen in these examples). A temperature sweep (50° C. to 250° C.) DMA measurement for different samples is depicted. The storage modulus (E′) is on the left-side axis and the tangent of the phase lag (δ) between stress and strain is on the right-side axis. A “1 dip” coating (consisting of a single dip in each of the primer-type solution and the precursor-type solution before thermal processing) is depicted by the solid lines. A “2 dips” coating (consisting of two sequential dips in each of the primer-type solution and the precursor-type solution before thermal processing) is depicted by dashed lines.FIG. 5depicts a single glass transition temperature (Tg) for each coating type (“1 dip” and “2 dips”) evidencing the formation of a homogenous coating in each instance.

Example Spray-Coating Process and Coatings

A primer-type solution was prepared by mixing approximately 1 g of 4-aminobenzylamine, 0.8 g 1,4-butanediol diacrylate, and 1.8 g NMP. The mixture was stirred at 50° C. for 4 hours. The conversion of acrylate was checked for completeness by1H NMR and the solution was diluted with additional solvent before transfer to a storage reservoir of a first spraying apparatus.

A precursor-type solution was prepared by mixing approximately 2 g of ODA, 1.1 g paraformaldehyde, and 15 mL NMP. The solution was sealed and heated to 50° C. After approximately 15 min at 50° C., the sealed solution became clear and was then transferred a storage reservoir of a second spraying apparatus.

Layers were sprayed successively on to a glass substrate (distance between the substrate and spray apparatus nozzle being about 15 cm; spraying pressure approximately 25 psi). The layers were sprayed on the glass substrate in this order: 1) primer-type solution, then 2) precursor-type solution until a total of eight layers (4 of each type) were deposited on the substrate. After 30 seconds, the sprayed on solutions vitrified. The glass substrate was then transferred on a hot plate for curing. The following thermal treatment was used: 50° C. for 1 hour, 50° C. to 110° C. 1 hour, 110° C. for 1 hour, 110° C. to 200° C.+1 hour, 200° C. for 1 h after which the coated substrate was allowed to cool down to room temperature (25° C.). A piece of the resultant film was scrapped for the surface of the substrate with a blade then this piece was subjected to thermal analysis.FIG. 6depicts differential scanning calorimetry (DSC) analysis of the material formed by this method.FIG. 6shows that by DSC the polymeric material formed in the manner described above had glass transition temperature (Tg) of approximately 160° C.