High toughness filled films comprising polymers having imidazole groups

Abstract

Disclosed is a filled polymer film comprising a polymer and an inorganic permittivity enhancing additive, the filled polymer film having 12 to 75 weight percent of the inorganic permittivity enhancing additive based on the total weight of the polymer and the inorganic permittivity enhancing additive in the filled polymer film; wherein the polymer comprises an imidazole group; and wherein the filled film toughness of the filled polymer film is 70 to 100 percent of the pure film toughness of a polymer film of the same thickness made of the same polymer but not containing the inorganic dielectric constant enhancing additive.

Description

Background Art

[0001] FIELD OF THE INVENTION The present invention relates to polymer films having improved voltage resistance, which are additionally suitable for addressing higher voltage requirements in automotive, electronic devices, and other applications. In particular, the present invention relates to polymer films having a high dielectric constant (also known as relative permittivity) and methods for making such films.

[0002] Description of the Related Art. The present invention relates to polymer films made from polymers made by polymerizing diamines and diacids; preferably polymer films having residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole and one or more aromatic diamines and one or more aromatic diacid chlorides. Various publications disclose that films and other articles can be made having residues of: p-phenylenediamine (PPD), 5(6)-amino-2-(p-aminophenyl)benzimidazole (DAPBI); and terephthaloyl dichloride (TDC). These include, for example, such publications as: U.S. Pat. Nos. 8,497,344 to Bos and 8,362,192 to De Vos et al.; Longbo et al. in High Performance Polymers [High Performance Polymers] 2017, Vol. 29(I), pp. 58-67; and U.S. Pat. No. 9,193,841 to Lee.

[0003] Furthermore, it is known that the addition of particulate matter to polymeric membranes can significantly reduce the membrane toughness of those loaded or filled membranes. It is believed that the particles do not provide membrane reinforcement because they are merely encapsulated in the membrane, creating a Swiss cheese-like membrane structure similar to a voided membrane, thereby severely reducing its toughness when compared to a polymeric membrane of the same thickness but without the particles or voids.

[0004] The dielectric constant of an insulating material (such as a film) is important in the design of film capacitors and in other devices where it is expected that the film may introduce capacitance into a circuit. Capacitance is the ability of a component or circuit to collect and store energy in the form of an electrical charge. The dielectric constant or relative permittivity of an insulating material (such as a film) is a measure of the ability of the insulating material or film to store electrical energy in an electric field. Films used for electrical insulation typically have a low dielectric constant, while films used for their capacitance (such as in capacitors) are expected to have a high dielectric constant, thereby allowing thinner films to be used in capacitors.

[0005] Therefore, polymer films with high dielectric constants are highly desirable to manufacturers of automobiles and electronic devices due to their increased value per unit weight, which translates into space savings for miniaturization of components. Therefore, any increase in the dielectric constant of such polymer films is of high value, especially if the dielectric enhanced film is a filled film having a film toughness of 70 to 100 percent of that of a neat film of the same thickness and made of the same polymer. Summary of the Invention

[0006] The present invention relates to a filled polymer film comprising a polymer and an inorganic dielectric constant enhancing additive, wherein the polymer comprises imidazole groups;

[0007] The filled polymer film has 12 to 75 weight percent of the inorganic dielectric constant enhancing additive based on the total weight of the polymer and the inorganic dielectric constant enhancing additive in the filled polymer film; and

[0008] wherein the filled film toughness of the filled polymer film is 70 to 100 percent of the pure film toughness of a polymer film of the same thickness made of the same polymer but without the inorganic dielectric constant enhancing additive. Brief Description of the Drawings

[0009] Figure 1 is a graph showing the relationship between the capacitance and the dielectric constant dK of films of various thicknesses.

[0010] Figure 2 is a graph showing that the relative level of the in-plane permittivity (or dielectric constant dK) is affected by the electrical state of the imidazole groups in the polymer, and that dK is relatively stable over a wide frequency range.

[0011] Figure 3 is the chemical structure of the 5(6)-amino-2-(p-aminophenyl)benzimidazole residue or repeating unit in the polymer chain, where the nitrogen in the benzimidazole is fully protonated to the form of a benzimidazolium salt.

[0012] Figure 4 is the chemical structure of the 5(6)-amino-2-(p-aminophenyl)benzimidazole residue or repeating unit in the polymer chain, where the nitrogen in the benzimidazole is considered to be in a "neutral" state; that is, one of the imidazole nitrogens contains a proton and the other imidazole nitrogen has a double bond because it has no salt label.

[0013] Figure 5 is the chemical structure of the 5(6)-amino-2-(p-aminophenyl)benzimidazole residue or repeating unit in the polymer chain, where the nitrogen in the benzimidazole is considered to be in a deprotonated state, and this structure forms a benzimidazolide. Specifically, as used herein, benzimidazolide should be understood as a salt in which one of the nitrogen atoms in the imidazole residue is the anion providing the negative charge (-) for the salt, and some other substance is the cation providing the positive charge for the salt. Detailed Description of the Invention

[0014] The present invention relates to a filled film having high loadings of dielectric enhancing particles, which unexpectedly retains most of the toughness of a pure film of the same thickness and made of the same polymer. A pure film means a film made of a polymer and containing no one or more particulate inorganic dielectric constant enhancing additives. A filled film means a film made of a polymer and further containing one or more particulate inorganic dielectric constant enhancing additives.

[0015] Specifically, the present invention relates to a filled polymer film comprising a polymer and an inorganic dielectric constant enhancing additive, wherein the polymer comprises imidazole groups for high temperature stability. The filled polymer film has from 12 to 75 weight percent of the inorganic dielectric constant enhancing additive based on the total combined weight of the polymer and the inorganic dielectric constant enhancing additive in the filled polymer film. The filled film toughness of this filled polymer film is from 70 to 100 percent of the pure film toughness, wherein the pure film is a polymer film of the same thickness and made of the same polymer but made without any inorganic dielectric constant enhancing additives.

[0016] The filled polymer film preferably has a thickness of from 1 to 50 microns. Films thicker than 50 microns have manufacturing problems because typically these films are cast from solutions having a high percentage amount of solvent, which solvent must be removed. Films thinner than 1 micron become very difficult to manufacture; thin films may be difficult to handle and may be prone to tearing. In some embodiments, the filled polymer film has a thickness of from 1 to 12 microns, while in some other embodiments, the filled polymer film has a thickness of from 1 to 5 microns. In still other embodiments, the filled polymer film has a thickness of from 2 to 25 microns, from 2 to 15 microns, or from 2 to 5 microns.

[0017] The filled polymer film has a dielectric constant of 5.5 or greater at 2 GHz, preferably 5.8 or greater at 2 GHz, which is advantageous because a higher dielectric constant means the film has a higher capacitance. In some embodiments, the filled polymer film has a dielectric constant of at least 6.2 at 2 GHz. In some embodiments, the dielectric constant does not exceed 10 at 2 GHz.

[0018] The relationship between the dielectric constant of the film and its capacitance per area is represented by the following equation:

[0019]

[0020] where C is the capacitance in nF / in 2 2, the dielectric constant dK is dimensionless, A is the area of the film being tested in square inches, 0.2248 is a constant with units of nF / in, and the capacitor film thickness D is measured in inches. If desired, the capacitance in SI units (nF / cm 2)Capacitance calculated: (nF / cm 2 ) = (nF / in 2 ) / 6.45. The dielectric constant dK is dimensionless because it is the ratio of the permittivity of the material to the permittivity of equivalent free space (air).

[0021] Figure 1 Figure is a plot of the capacitance per area of an idealized film of various thicknesses versus the dielectric constant dK using the above equation. For any particular film with a given dK, a thinner film has a higher capacitance than a thicker film.

[0022] The dielectric constant (dK) of any film is conveniently measured on a 25 - micron - thick film sample; however, the dielectric constant does not vary significantly over the required thickness range of approximately 1 to 50 microns.

[0023] In some embodiments, the filled polymer film has a capacitance of at least 15 nF / in 2 ; in some preferred embodiments, the filled polymer film has a capacitance of at least 20 nF / in 2 . It can be appreciated that in order to achieve a thinner film with a higher capacitance, the dK of the material must be increased. Figure 1

[0024] The filled polymer film contains an inorganic dielectric - constant - enhancing additive. An inorganic dielectric - constant - enhancing additive means an inorganic material having a high dielectric constant, typically in the form of a powder or fine particles. Examples of inorganic dielectric - constant - enhancing additives include various titanates, including barium titanate, lead zirconate titanate, barium strontium titanate, and lead lanthanum zirconate titanate. In some embodiments, the inorganic dielectric - constant - enhancing additive includes barium titanate. In some embodiments, the inorganic dielectric - constant - enhancing additive is a single inorganic additive, and in some embodiments, the only inorganic dielectric - constant - enhancing additive is barium titanate. Additional additives that enhance other properties may be added as long as the tensile properties of the film are not negatively affected.

[0025] In some embodiments, the inorganic dielectric - constant - enhancing additive has a particle size range of 0.1 to 3.0 microns. In some embodiments, a particle size range of 0.1 to 1.5 microns may be preferred, while in other embodiments, a particle size range of 0.1 to 1.0 microns may be preferred. In still other embodiments, a particle size range of 0.1 to 0.7 microns may be preferred.

[0026] As used herein, the term "particle size" is the average particle size assigned to the particles by the particle manufacturer / supplier; the average particle can also be determined by visually inspecting a magnified image of the particles, such as using a scanning electron microscope (SEM) method.

[0027] ​In some embodiments, the filled polymer film comprises 30 to 75 weight percent of an inorganic dielectric constant enhancing additive. In some preferred embodiments, the filled polymer film comprises 40 to 75 weight percent of an inorganic dielectric constant enhancing additive; and in some other embodiments, the filled polymer film comprises 50 to 75 weight percent of an inorganic dielectric constant enhancing additive.

[0028] In some embodiments, the filled film toughness of the filled polymer film is 75 to 100 percent of the unfilled film toughness of a polymer film of the same thickness made of the same polymer but without the inorganic dielectric constant enhancing additive. In still other preferred embodiments, the filled film toughness of the filled polymer film is 80 to 100 percent of the unfilled film toughness of a polymer film of the same thickness and made of the same polymer but without the inorganic dielectric constant enhancing additive.

[0029] The polymer of the polymer film contains imidazole groups in the polymer chain; in some preferred embodiments, the polymer of the polymer film has residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole and one or more aromatic diamines and one or more aromatic diacyl chlorides. Although polymers containing DAPBI are exemplified, the polymers useful in the polymer film extend to any polymer film made of a polymer containing imidazole groups, without limitation.

[0030] As used herein, the term "residue" of a chemical substance refers to the portion of the resulting product of the chemical substance in a particular reaction scheme or subsequent formulation or chemical product, regardless of whether the portion is actually obtained from the chemical substance. Thus, a copolymer containing a residue of p-phenylenediamine refers to a copolymer having one or more units of the formula:

[0031]

[0032] And a copolymer containing a residue of terephthaloyl dichloride contains one or more units of the formula:

[0033]

[0034] Similarly, a copolymer containing a residue of DAPBI contains one or more units as shown in Figures 3 to 5 depending on the state of the imidazole group. For example, Figure 3Shows the residue of DAPBI, where the nitrogen in benzimidazole is fully protonated to the form of benzimidazolium salt. Specifically, as used herein, benzimidazolium salt should be understood as such a salt, where one of the nitrogen atoms in the imidazole residue is the cation that provides the positive charge (+) for the salt, and some other substance is the anion (A-) that provides the negative charge for the salt. This is usually the case when an imidazole polymer is treated with an acid to protonate the benzimidazole and form a benzimidazolium salt.

[0035] This is also the chemical structure of the polymer directly after the polymerization of 5(6)-amino-2-(p-aminophenyl)benzimidazole and one or more aromatic diamines with one or more aromatic diacyl chlorides, because this polymerization produces acidic by-products. Typically, the acidic by-product is hydrochloric acid (HCl), as the diacyl chloride is usually one of these monomers. Thus, directly after the polymerization, the DAPBI residue has Figure 3 the chemical structure of, where the anion "A-" is the chloride ion (Cl-) ionically bonded to the imidazole ring. Washing the membrane with water can reduce but not eliminate the amount of ionically bonded chloride ions. If the polymer is recovered and then dissolved in a stronger acid such as sulfuric acid and then formed into a membrane, this chemical structure also exists. In this case, the "A-" anion is the sulfate ion (HSO4-) ionically bonded to the imidazole ring. Washing the membrane with water can reduce but not eliminate the amount of ionically bonded sulfate.

[0036] Figure 4 Shows the residue of DAPBI, where the nitrogen in benzimidazole is considered to be in a "neutral" state; that is, one of the imidazole nitrogens contains a proton and the other imidazole nitrogen has a double bond because it has no salt label. This is the chemical structure of the polymer after neutralizing the acidic by-products generated during polymerization with a typical base.

[0037] Figure 5 Shows the residue of DAPBI, where the nitrogen in benzimidazole also forms a salt, but in this case the nitrogen is considered to be in a deprotonated state, and this structure forms a benzimidazolide. Specifically, as used herein, benzimidazolide should be understood as such a salt, where one of the nitrogen atoms in the imidazole residue is the anion that provides the negative charge (-) for the salt, and some other substance is the cation (C+) that provides the positive charge for the salt. This is the case when an imidazole polymer is treated with a very strong base with a very high pH to deprotonate the benzimidazole and form a benzimidazolide. To generate a negative charge on the imidazole, a very high pH of 13.8 or preferably greater is required. Since the strong base is typically sodium hydroxide, potassium hydroxide, calcium hydroxide or a mixture thereof, the cation (C+) on any one repeating unit can be sodium, potassium or calcium. It has been found that, as shown by Figure 5 the pure membrane or unfilled benzimidazole membrane made of the polymer has a dielectric constant higher than that with Figure 4The pure film in the neutralized imidazole state or the unfilled neutral benzimidazole film shown is 15 to 20 percent higher.

[0038] As used herein, the term "polymer" means a material prepared by polymerizing monomers, end-functionalized oligomers, and / or end-functionalized polymers, whether of the same type or different types. As used herein, the term "copolymer" refers to a polymer prepared from at least two different monomers. For clarity, it should be understood that, unless otherwise indicated, the use of the word "polymer" as used herein may be used interchangeably with "copolymer". In some embodiments, all monomers can be combined and reacted together once to form a polymer. In some embodiments, monomers or different amounts of monomers can be reacted sequentially to form oligomers, which can be further reacted with one or more additional monomers or one or more oligomers to form a polymer. "Oligomer" means a polymer or substance eluted at <3000 MW using a column calibrated with poly(p-phenylenediamine terephthalamide) homopolymer.

[0039] As used herein, "stoichiometric amount" means the amount of a component that theoretically reacts with all of the reactive groups of a second component. For example, "stoichiometric amount" refers to the number of moles of terephthaloyl dichloride required to react with substantially all of the amine groups of an amine component (p-phenylenediamine and DAPBI). Those skilled in the art will understand that the term "stoichiometric amount" refers to a range of amounts typically within 10% of the theoretical amount. For example, the stoichiometric amount of terephthaloyl dichloride used in a polymerization reaction can be 90%-110% of the amount of terephthaloyl dichloride theoretically required to react with all of the p-phenylenediamine and DAPBI amine groups.

[0040] The term "organic solvent" shall be understood herein to include single-component organic solvents or mixtures of two or more organic solvents. In some embodiments, the organic solvent is dimethylformamide, dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), or dimethyl sulfoxide. In some preferred embodiments, the organic solvent is NMP or DMAc. In some embodiments, a solubility enhancer for inorganic salts is added in a suitable amount before or during polymerization to enhance the solubility of the resulting polymer in the amide polar solvent. The term "inorganic salt" refers to a single inorganic salt or a mixture of two or more inorganic salts. In some embodiments, the inorganic salt is sufficiently soluble in the solvent and releases halogen atom-containing ions. In some embodiments, preferred inorganic salts are potassium chloride (KCl), zinc chloride (ZnCl2), lithium chloride (LiCl), or calcium chloride (CaCl2). In certain preferred embodiments, the inorganic salt is LiCl or CaCl2. The amount of inorganic salt added to the solvent for enhancing polymer solubility is preferably removed from the membrane by washing and thus does not cause a significant increase in the dielectric constant of the polymer, and thus for the purposes herein, it should be understood that dielectric constant enhancing additives do not include any inorganic salts added as polymer solubility enhancers. As used with the polymer solution, "solid" means the ratio of the mass of the polymer (on a neutral basis) to the total mass of the solution (i.e., the mass of the polymer plus the solvent).

[0041] In preferred embodiments, the polymer comprises residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole and residues of an aromatic diamine and an aromatic diacyl chloride. In some embodiments, the polymer comprises residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, which forms a salt with sodium, potassium, or calcium cations; and residues of an aromatic diamine and an aromatic diacyl chloride.

[0042] Suitable aromatic diamines include p-phenylenediamine, 4,4'-diaminobiphenyl, 2-methyl-p-phenylenediamine, 2-chloro-p-phenylenediamine, 2,6-naphthalenediamine, 1,5-naphthalenediamine, and 4,4'-diaminobenzanilide. In some embodiments, the preferred aromatic diamine is p-phenylenediamine.

[0043] Suitable aromatic diacyl chlorides include terephthaloyl dichloride, 4,4'-benzoyl dichloride, 2-chloroterephthaloyl dichloride, 2,5-dichloroterephthaloyl chloride, 2-methylterephthaloyl dichloride, 2,6-naphthalene dicarboxylic acid chloride, and 1,5-naphthalene dicarboxylic acid chloride. In some embodiments, the preferred aromatic diacid is terephthaloyl dichloride.

[0044] In a preferred embodiment, the polymer comprises residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole and residues of p-phenylenediamine and terephthaloyl dichloride. In another preferred embodiment, the polymer comprises residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, the imidazole forming a salt with sodium, potassium or calcium cations; and residues of p-phenylenediamine and terephthaloyl dichloride.

[0045] In some embodiments, with respect to the residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole and the residues of aromatic diamine in the polymer film, the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine is from 30 / 70 to 85 / 15. In some embodiments, the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine is from 45 / 55 to 85 / 15. In still other embodiments, 5(6)-amino-2-(p-aminophenyl)benzimidazole is 50 mole percent or more of the total moles of 5(6)-amino-2-(p-aminophenyl)benzimidazole and aromatic diamine residues present in the polymer and the film. Preferably, the aromatic diamine is p-phenylenediamine.

[0046] Likewise, in some embodiments, for the residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole in the polymer film, the imidazole forming a salt with sodium, potassium or calcium cations; and the residues of aromatic diamine, the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine is from 30 / 70 to 85 / 15. In some embodiments, the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine is from 45 / 55 to 85 / 15. In still other embodiments, 5(6)-amino-2-(p-aminophenyl)benzimidazole is 50 mole percent or more of the total moles of 5(6)-amino-2-(p-aminophenyl)benzimidazole and aromatic diamine present. Preferably, the aromatic diamine is p-phenylenediamine.

[0047] Figure 2 It is shown that the relative level of the in-plane permittivity or dK of the pure DABPI-containing film is unexpectedly affected by the electrical state of the imidazole groups in the polymer, and dK is relatively stable over a wide frequency range. Figure 2 It is shown that when the polymer film comprises DAPBI residues of benzimidazolide having the structure as shown in Figure 5 the highest relative in-plane permittivity is achieved; and when the polymer film comprises DAPBI residues of benzimidazolium salt having the structure as shown in Figure 3 the lowest relative in-plane permittivity is achieved. Figure 2 It is further shown the in-plane permittivity of two other sets of data, which are those comprising in the neutral state; i.e., having as shown in Figure 4A polymer film of DAPBI residues of the structure shown in []. These two sets of data provide the in-plane permittivity of a polymer film in which the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine is 70 / 30 (neutral 70 / 30) and a polymer film in which the molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine is 50 / 50 (neutral 50 / 50). As shown, the in-plane permittivity or dK does not change significantly within this molar ratio range.

[0048] The polymerization reaction of 5(6)-amino-2-(p-aminophenyl)benzimidazole, aromatic diamine and aromatic dichloride can be accomplished by means known in the art. See, for example, PCT Patent Application No. 2005 / 054337 and U.S. Patent Application No. 2010 / 0029159. Typically, one or more acyl chlorides and one or more aromatic diamines are reacted in an amide polar solvent (such as N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, dimethylimidazolinone, etc.). In some embodiments, N-methyl-2-pyrrolidone is preferred.

[0049] In some embodiments, a solubility agent for an inorganic salt (such as lithium chloride or calcium chloride, etc.) is added in a suitable amount before or during polymerization to enhance the solubility of the resulting polymer in the amide polar solvent. After the desired degree of polymerization has been reached, the polymer exists in the form of unneutralized solid debris. "Debris" means that the polymer is in the form of a brittle material or gel that easily separates into recognizable individual chunks upon shear. The unneutralized debris contains the polymer, the polymerization solvent, the solubility agent, and the by-product acid (typically hydrochloric acid (HCl)) from the condensation reaction. In the presence of the HCl by-product, the DAPBI residues in the polymer chain have Figure 3 the chemical structure of [], in which the imidazole is protonated.

[0050] After completion of the polymerization reaction, the unneutralized debris can optionally be contacted with a base, which can be an alkaline inorganic compound such as sodium hydroxide, potassium hydroxide, calcium hydroxide, calcium oxide, ammonium hydroxide, etc. The alkaline inorganic compound can be used in an aqueous solution for the neutralization reaction of HCl by-products. If desired, the basic compound can be an organic base such as diethylamine or tributylamine or other amines. Typically, the unneutralized copolymer debris is contacted with an aqueous base solution by washing to convert the acidic by-products to salts (usually sodium chloride salt if sodium hydroxide is the base and HCl is the acidic by-product) and also to remove some of the polymerization solvent. If desired, the unneutralized copolymer debris can optionally be washed one or more times with water first to remove excess polymerization solvent before contacting with the alkaline inorganic compound. Once the acidic by-products in the polymer debris are neutralized, additional water washes can be employed to remove the salts and polymerization solvent. After this washing, the DAPBI residues in the polymer chains have Figure 4 the chemical structure in which the imidazole is in a neutralized state. In some embodiments, the membrane is cast from a polymer solution in which the imidazole is in a neutralized state.

[0051] The molecular weight of the polymer is typically monitored by one or more dilute solution viscosity measurements and is related to the one or more dilute solution viscosity measurements. Thus, relative viscosity (“V rel ” or “η rel ” or “n rel ”) and intrinsic viscosity (“V inh ” or “η inh ” or “n inh ”) dilute solution measurements of the polymer are typically used to monitor the polymer molecular weight. The relative viscosity and intrinsic viscosity of the dilute polymer solution are related according to the following expression

[0052] V inh =ln(V rel ) / C,

[0053] where ln is the natural logarithm function and C is the concentration of the polymer solution. V rel is a dimensionless ratio, so V inh is expressed in units of reciprocal concentration, typically expressed as deciliters per gram (“dl / g”). The polymer typically has an intrinsic viscosity of at least 3 dl / g, preferably at least 5 dl / g or higher. In some embodiments, the intrinsic viscosity can be 6 dl / g or greater.

[0054] A polymer membrane comprising an inorganic dielectric constant enhancing additive and a polymer having residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacyl chloride can be made by a method comprising the following steps:

[0055] a) Forming an isotropic casting solution of a polymer comprising an inorganic dielectric constant enhancing additive, 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacyl chloride in an organic solvent in the presence of a solubilizing salt, the isotropic casting solution having a polymer concentration of 1 to 5 weight percent based on the total amount of polymer, solvent, and solubilizing salt in the isotropic casting solution,

[0056] b) Casting the isotropic casting solution in a laminar flow onto a surface to form a cast film, and

[0057] c) Removing the solvent and the solubilizing salt from the cast film.

[0058] The film can also be made in a similar manner from an isotropic casting solution comprising a polymer containing an imidazole group and an inorganic dielectric constant enhancing additive.

[0059] In some embodiments, the isotropic casting solution of step a) can be formed by dissolving preformed polymer crumbs made from 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacyl chloride in a suitable organic solvent, and the preferred solvent is DMAc. In other words, in this embodiment, it is preferred to polymerize 5(6)-amino-2-(p-aminophenyl)benzimidazole, p-phenylenediamine, and terephthaloyl dichloride at a high solids content (7 weight percent or greater) in NMP / CaCl2 or DMAC / CaCl2, and then separate and optionally wash the polymer crumbs, and then dissolve them in an organic solvent to form a low solids isotropic casting solution. In some cases, if the polymer is later dissolved in a strong acid (such as sulfuric acid), using polymer crumbs in which the by-product HCl has been neutralized can reduce bubble formation. However, the neutralization of the polymer crumbs is optional. Preferably, the polymer is cast from a polymer solution that does not leave sulfur residues in the film; that is, the final film has at most trace amounts of sulfur (less than 0.05 weight percent sulfur). Preferably, the film is made without contact with sulfuric acid or any other sulfur-containing compound.

[0060] In some other embodiments, the isotropic casting solution of step a) can be formed

[0061] i) Polymerizing 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacyl chloride in an organic solvent in the presence of a solubilizing salt to form a polymer solution, and

[0062] ii) Optionally adjusting the amount of solvent in the polymer solution by adding or removing solvent to form an isotropic casting solution having a polymer concentration of 1 to 5 weight percent based on the total amount of polymer, solvent, and solubilizing salt in the isotropic casting solution.

[0063] Regardless of the source of the polymer, the isotropic casting solution has a solid polymer concentration of 1 to 5 weight percent based on the total amount of polymer, solvent, and solubilizing salt in the isotropic casting solution. It is believed that a polymer concentration of less than 1 weight percent requires more solvent than is typically desired or practical in commercial processes, while a polymer concentration greater than 5 weight percent is at or near the upper limit of the solubility of the polymer in DMAc, thus risking the formation of an undesirable gel that is difficult to cast into a film. In a preferred embodiment, the isotropic casting solution has a polymer concentration of 2 to 4 weight percent based on the amounts of polymer, solvent, and solubilizing agent in the isotropic casting solution. In some preferred embodiments, the isotropic casting solution is made by dissolving the polymer in a DMAc / CaCl2 or DMAc / LiCl solvent system, where the solubilizing agent (CaCl2 or LiCl) has a concentration of 0.5 weight percent or greater in the solvent system. In some embodiments, a solubilizing agent concentration of 1.5 weight percent or greater in the solvent system is desired. In some embodiments, the concentration of the solubilizing salt in the solvent system is 2 to 5 weight percent.

[0064] The inorganic dielectric constant enhancing additive is preferably added to the polymer solution via a stock solution. For example, a dilute solution of 0.5 to 1.0 weight percent polymer is first prepared in a solvent or solvent system (preferably DMAc / CaCl2), and a certain amount of the inorganic dielectric constant enhancing additive is added (preferably under high shear mixing) to form a stock solution. Then the desired amount of the stock solution can be added to a polymer solution having a solids content of approximately 3 to 4 weight percent to form a casting solution having a solids content of about 2 to 4 weight percent, where the solids are a combination of the polymer and the inorganic dielectric constant enhancing additive. The final solids concentration of the casting solution should have a viscosity that allows for good pouring and casting into a film. If the viscosity of the casting solution is too thick, additional solvent can be added.

[0065] The isotropic casting solution can further contain additives such as antioxidants, lubricants, UV blockers, colorants, etc.

[0066] After step a) of forming the isotropic casting solution, there follows step b) of casting a layer of the isotropic casting solution onto a surface to form a film. Casting the isotropic casting solution to make a film can be accomplished by a variety of methods. For example, the film can be made by casting the casting solution onto a polished metal surface and calendaring. In some methods, the film can be made continuously by, for example, casting via a film casting die or a doctor blade; or casting the solution onto a surface such as a belt or a rotating roll (or a glass plate), and then optionally additionally doctoring the casting solution to produce a casting film on the surface having a desired or uniform thickness.

[0067] Once the cast film is made, the solvent and solubilizing salt are removed from the cast film in step c). There are many methods for removing the solvent and solubilizing salt from the film; however, the method and rate of solvent removal can determine the structure of the final film. For commercial production, the solvent removal rate needs to be actually as fast as possible without damaging the film. If the solvent is removed too quickly, voids will be generated in the film, and cracks and actual pinholes may form. These cracks and holes can reduce the toughness of the film and / or reduce the breakdown voltage of the film.

[0068] The rate of solvent and solubilizing salt removal depends on matters such as the amount of solvent and solubilizing salt present, the thickness of the film, and the driving force applied to the film. It has been found that it is desirable to control the solvent removal rate in step c) to avoid generating voids in the film. The solvent removal rate can be controlled, for example, by removing the solvent in more than one step, where the driving force in any one step does not generate voids in the film.

[0069] In addition, it may be advantageous to restrict the cast film during the removal of the solvent in step c); for example, using a frame that sandwiches the cast film between a frame and a surface to prevent the film from shrinking during this step.

[0070] The removal of the solvent and solubilizing salt from the cast film in step c) can be accomplished by a variety of methods. The solvent and solubilizing salt can be removed from the cast film by washing the film with an aqueous liquid in one or more stages; or using a combination of washing and drying steps, where each of the washing and drying steps includes one or more stages.

[0071] The solvent and solubilizing salt can be removed from the cast polymer film in step c) by immersing the cast polymer film in one or more water baths and / or applying an aqueous liquid to the film surface with various applicators (spray bars, troughs, etc.), preferably washing the cast film during a countercurrent washing process using water, where each stage has a progressively diluted solvent solution (less and less solvent in the wash water).

[0072] Alternatively, if the solvent can be removed from the cast polymer film in step c) in a drying step, the drying step exposes the film to heat to drive off the solvent from the film. In the drying step, the cast film can be exposed to the heat in an oven or heated gas in an inflation chamber, each of which provides energy to strip the solvent from the cast film.

[0073] Solvent removal from the cast film can be accomplished over a wide temperature range, whether by washing or by applying heat, depending on how quickly the solvent needs to be removed. For example, in an embodiment of the washing process, the solvent can be removed by exposing the cast film to a temperature ranging from room temperature (20 °C) or slightly higher up to the boiling point of the washing liquid. Alternatively, in one embodiment, the solvent can be removed from the cast polymer film by exposing the cast film to a drying step maintained at a temperature of about 35 °C to 280 °C. In some embodiments, the drying step is maintained at a temperature of 80 °C to 150 °C. In other embodiments, it may be desirable for the drying step to be carried out at a temperature of 35 °C to 80 °C; or for the drying to be carried out in multiple stages, where each stage has a higher temperature than the previous stage.

[0074] If a drying stage is used to remove the solvent, the process should additionally include a washing step to remove any solubilized salts that remain, as the salt is undesirable in the final film.

[0075] It has been found that a method particularly useful for manufacturing a film utilizes step c) comprising the following steps:

[0076] c-1) Removing at least a portion of the solvent from the cast film by heating to form an intermediate film, c-2) rinsing the intermediate film with water in a second washing step, and

[0077] c-3) Further removing liquid from the intermediate film in a tension drying step, where the intermediate film is restricted from shrinking to form a film.

[0078] Step c-1) can be carried out as previously described; that is, the solvent can be removed from the cast polymer film by exposing the cast film to a drying step maintained at a temperature of about 35 °C to 280 °C. In some embodiments, the drying step is maintained at a temperature of 80 °C to 150 °C. In other embodiments, it may be desirable for the drying step to be carried out at a temperature of 35 °C to 80 °C; or for the drying to be carried out in multiple stages, where each stage has a higher temperature than the previous stage.

[0079] Following step c-1) is step c-2) of rinsing the intermediate film, which is typically carried out by using an aqueous liquid as the rinsing liquid. It is believed that the rinsing liquid can be effective over a wide temperature range; the rinsing liquid can have a temperature ranging from room temperature (20 °C) or slightly higher up to the boiling point of the rinsing liquid. In some embodiments, the rinsing liquid is maintained at a temperature of 80 °C to 150 °C. In other embodiments, it may be desirable for the rinsing liquid to have a temperature of 35 °C to 80 °C.

[0080] The amount of this washing is determined by the method used. If it is desired to simply remove the solubilized salts, the amount of washing is determined by the desired amount of residual solubilized salts remaining in the intermediate film after washing.

[0081] Since the result of step c-2) is a wet film, step c-3) is then carried out to remove liquid from the washed intermediate film in a tension drying step, where the intermediate film is restricted from shrinking while being exposed to a temperature ranging from room temperature (20 °C) to 280 °C to form the final film.

[0082] In some embodiments, it may be desirable to expose the intermediate film to a temperature of 80 °C to 150 °C in this tension drying step. In other embodiments, it may be desirable to expose the intermediate film to a temperature of 35 °C to 80 °C in this tension drying step. In the tension drying step, the intermediate film can be exposed, for example, to the heat in an oven or the heated gas in an inflation chamber.

[0083] If desired, after or during step c-3), the method for manufacturing the polymer film can further include an optional step in which the film is mechanically stretched axially or biaxially. In some embodiments, the film is stretched at a certain draw ratio. The cross-sectional area of the film is axially stretched or stretched in one direction by 1.2 to 8.0 percent, preferably 1.2 to 4 percent; in some other embodiments, the film is biaxially stretched in two directions by 1.2 to 8.0 percent, preferably biaxially stretched in two directions by 1.2 to 4 percent.

[0084] It has been found that a pure polymer film comprising residues or repeating units containing 5(6)-amino-2-(p-aminophenyl)benzimidazole, where the imidazole is in the deprotonated state as depicted in Figure 5 has an increased dielectric constant in its pure form before the addition of any inorganic dielectric constant enhancing additives, as shown in Figure 2 The dielectric constant of such films is 15 to 20 percent higher than that of a control film having the neutralized imidazole state as shown in Figure 4 Therefore, a filled polymer film in which the imidazole in combination with the inorganic dielectric constant enhancing additive is in the deprotonated state provides a polymer film exhibiting an even higher dielectric constant.

[0085] Preferably, a filled polymer film comprising both an inorganic dielectric constant enhancing additive and residues or repeating units containing 5(6)-amino-2-(p-aminophenyl)benzimidazole, where the imidazole is in the deprotonated state as depicted in Figure 5 has a dielectric constant of 6.3 or greater at 2 GHz, preferably 6.7 or greater at 2 GHz, which is advantageous because a higher dielectric constant means the film has a higher capacitance. In some embodiments, the filled polymer film has a dielectric constant of at least 7.1 at 2 GHz. In some embodiments, the dielectric constant does not exceed 12 at 2 GHz.

[0086] A filled membrane having a residue or repeating unit of 5(6)-amino-2-(p-aminophenyl)benzimidazole, wherein the imidazole is in the deprotonated state as depicted in Figure 5 can be made by washing the membrane in step c) with an alkaline aqueous solution using any of the steps described herein to deprotonate the imidazole and form a polymer membrane having a polymer chain comprising a polymeric imidazolium salt, wherein the cation (C+) is determined by the type of base (e.g., sodium hydroxide, potassium hydroxide, calcium hydroxide, etc.). The alkaline aqueous solution should have a pH of 13.8 or greater. Preferably, the alkaline aqueous solution has a pH of 14 or higher; the alkaline water is preferably an aqueous solution containing sodium hydroxide, potassium hydroxide, calcium hydroxide, or a mixture or buffer thereof. An alkaline washing solution having a pH of 13.8 or greater can be made by dissolving an appropriate amount of base in water.

[0087] If Figure 5 the polymer structure is desired, the washing solution should be in contact with the membrane for a sufficient time to achieve the desired chemical structure, i.e., to deprotonate one nitrogen such that the benzimidazole is in the deprotonated state to form a benzimidazolide salt with sodium, potassium, or calcium cations. Preferably, at least 90 percent of the imidazole residue repeating units in the polymer are deprotonated at one nitrogen, and most preferably at least 95% of the imidazole residue repeating units in the polymer are deprotonated at one nitrogen. The anion provides the negative charge (-) for the salt, while some other substance is the cation that provides the positive charge (C+) for the salt.

[0088] Specifically, at least 90%, and preferably at least 95%, of the DAPBI residue repeating units in the polymer are salts having the structure as shown in Figure 5 .

[0089] These membranes are used in electronic devices that require higher frequencies, lower voltages, and greater currents, specifically in applications that require smaller form factors and lower costs. It is believed that these membranes can provide improved electrical performance in the device, including reduced board size. These membranes have particular use in embedded capacitor applications and in slot linings.

[0090] Test Methods

[0091] The dielectric constant (relative permittivity or dK) and dissipation factor (Df or tan δ) are determined using a rectangular cavity resonator at 2 to 10 GHz (or the provided frequency) in accordance with ASTM2520C, IPC-TM-650 2.5.5.3.

[0092] The capacitance of the membrane is determined using a Hioki IM3536 LCR meter using the method provided with the meter.

[0093] The breakdown voltage of the film was determined according to ASTM D-149.

[0094] The film thickness was measured using a thickness gauge model DR600.

[0095] The film tensile properties (film toughness, modulus, and elongation at break) were measured according to ASTM D-882.

[0096] Reference Example

[0097] A polymer was made as follows. Monomer 5(6)-amino-2-(p-aminophenyl) benzimidazole (DAPBI) and p-phenylenediamine (PPD) were combined in an amount suitable for forming a copolymer with a DABPI / PPD monomer ratio of 70 / 30 with a stoichiometric amount of terephthaloyl dichloride (TCl) in a solvent system comprising an N-methyl-2-pyrrolidone (NMP) solvent and 4.5 weight percent calcium chloride (CaCl2) as a solubility enhancer. These monomers were polymerized to form a copolymer. After polymerization was completed, the copolymer crumbs were recovered, ground, and washed with sodium hydroxide to neutralize the byproduct hydrochloric acid. The crumbs were then filtered and dried. The copolymer had an intrinsic viscosity of about 6.4 dl / g.

[0098] Example 1

[0099] The film was made from a solution comprising a polymer, an inorganic dielectric constant enhancing additive, and a solvent system. The polymer was the copolymer of the reference example. The inorganic dielectric constant enhancing additive was barium titanate. The specific barium titanate used in the example was Bespa BTC-4FB and Bespa BTC-5B available from Nippon Chemical Industrial Co., Ltd. Bespa BTC-4FB contains barium titanate particles having a particle size of about 0.5 microns, while Bespa BTC-5B barium titanate particles have a particle size of about 1.0 microns. The solvent system was dimethylacetamide (DMAc) having 4 weight percent lithium chloride.

[0100] Nine solutions were prepared by weighing each of the components as described in Table 1 into 250 mL glass jars. Item A was a control that did not contain an inorganic dielectric constant enhancing additive and made a pure film. Items 1-4 were made with 0.5μ particles, while items 5-8 were made with 1.0μ particles.

[0101] The glass jars were then placed in an industrial paint shaker and mixed (for about 2 to 8 hours) until a homogeneous mixture was observed. Each of these solutions was then cast onto a glass plate using a doctor blade set to a 381 μm gap. The cast solutions were then heated in a nitrogen-purged oven at 90 °C for 45 minutes to remove the solvent. After removal from the oven, the glass plates with the cast pre-films were immersed (washed) in a deionized water bath at room temperature for 60 minutes to remove the lithium chloride solubility enhancer. The cast pre-films were then removed from the glass plates and fixed in a stationary frame. Once fixed, it was immediately placed in a vacuum oven at 120 °C for 60 minutes to fully form the film and then allowed to cool. The film and the frame were cooled to room temperature before the film was removed from the stationary frame. The film was trimmed and measured. All films were approximately 7 inches by 7 inches square and had a thickness of approximately 9 μm. The properties of the resulting films are shown in Tables 2 and 3.

[0102] Table 1

[0103]

[0104] Table 2

[0105]

[0106] * Tensile strength and tensile modulus are normalized with respect to thickness

[0107] Table 3

[0108]

[0109]

[0110] When compared to the pure film as a control, the filled films retain greater than 90% of the toughness of the pure film. Specifically, when the particle loading of barium titanate particles in the filled films is in the particle size range of approximately 0.5 to 1.0 microns and is 13 to 30 weight percent, the filled films unexpectedly retain 93.1% to 96.9% of the toughness of the pure film. The filled films further have an improved relative permittivity (dielectric constant).

[0111] Example 2

[0112] This example demonstrates the properties of filled films having a particulate loading that varies over a wide range. Filled films containing 0.5 μ barium titanate particles were produced by preparing a dispersion of the desired amounts of polymer, solvent system, and inorganic dielectric constant enhancing additive, and then casting the dispersion onto a glass substrate. First, a polymer stock solution was formed by dissolving the polymer in a solvent system of dimethylacetamide (DMAc) and 4.5 wt.% calcium chloride (CaCl2). The relative amounts of solvent and polymer were used such that the polymer stock solution had 2.5 wt.% polymer in DMAc.

[0113] Then, various polymer dispersions for casting films having different concentrations of barium titanate were prepared by combining the polymer stock solution, additional DMAc solvent, and 0.5 μ barium titanate particles. To ensure a uniform dispersion even at high particle concentrations, a predispersion of 50 wt.% DMAc, 40 wt.% polymer stock solution, and 10 wt.% barium titanate particles was mixed using a high-shear mixer. This predispersion was then combined with additional amounts of the polymer stock solution, followed by additional mixing, to form a polymer dispersion (casting solution) having a nominal 3.5 wt.% polymer and a concentration of additive barium titanate particles for making the film that varied from 30 to 80 weight percent.

[0114] Each casting solution was cast onto a glass plate using a doctor blade. The casting solution on the glass plate was then heated on a hot plate at 80 °C for 5 minutes to remove the solvent and form a cast film on the glass plate. The glass plate and the cast film were then removed from the oven and allowed to cool to room temperature, after which they were washed in a deionized water bath at room temperature for 60 minutes to remove any solubility enhancers. The cast film was then removed from the glass plate and fixed in a stationary frame. Once fixed, the film and the frame were placed in a nitrogen-purged oven at 120 °C for 60 minutes. The film and the frame were then cooled to room temperature before the filled film was removed from the frame. The filled film was then trimmed to form a square film sample of approximately 12 inches × 12 inches. The properties of the resulting filled films are shown in Tables 4 and 5. Item A (the pure film of Example 1) was used as a control.

[0115] When compared to the pure film used as a control, the filled films having a particulate loading of 30 to 75 weight percent unexpectedly retained 76% to 98% of the toughness of the pure film. The filled films further had an improved relative permittivity (dielectric constant).

[0116] Table 4

[0117]

[0118] Table 5

[0119]

[0120]

[0121] Example 3

[0122] This example demonstrates that the filled film can have a preferred capacitance of at least 15 nF / in 2 or higher. Filled film samples with 50 and 60 weight percent of 0.5 micron barium titanate particles were prepared in a manner similar to Example 2; the filled film had a nominal thickness of 2 microns. Three-inch diameter circles were cut from the film samples and then sputter-coated with gold palladium (AuPd) on both sides and then tested for capacitance. The characteristics of the filled film are shown in Table 6.

[0123] Table 6

[0124]

[0125] Example 4

[0126] This example further demonstrates the capacitance and breakdown voltage characteristics of some filled film samples. Film samples with 50 weight percent barium titanate particles were prepared and tested according to Example 3; however, three different film samples were made from barium titanate particles with three different particle size diameters (i.e., 0.6 microns, 0.3 microns, and 0.15 microns). The filled film had a nominal thickness of 2 microns. The characteristics of the film are shown in Table 7.

[0127] Table 7

[0128]

[0129]

[0130] Example 5

[0131] This example demonstrates a filled polymer film in which an inorganic dielectric constant enhancing additive is added to a polymer having an imidazole group (where the imidazole is in the deprotonated state). Example 2 was repeated; however, instead of washing the film with deionized water, the film was washed with an aqueous sodium hydroxide wash solution having a pH of 14. This provided a polymer film in which the nitrogen in benzimidazole was considered to be in the deprotonated state (this structure forms benzimidazolide), where at least 95% of the imidazole residue repeating units in the polymer are salts as Figure 5 depicted. In this specific demonstration, the benzimidazolide is a salt in which one nitrogen in the imidazole residue is the anion providing the negative charge (-) for the salt, and the positive charge of the salt is provided by the sodium cation. Table 8 compares that of Example 2 and has as Figure 4The dK values of the neutralizing imidazole membranes (designated as Ex. 2) and the predicted dK ranges of the benzimidazolide membranes (designated as Ex. 5) shown in [reference] demonstrate the improved relative permittivity (dielectric constant) of the filled membranes made with benzimidazolides.

[0132] Table 8

[0133]

Claims

1. A filled polymer film comprising a polymer and an inorganic dielectric constant enhancing additive, wherein the polymer comprises imidazole groups; the filled polymer film has from 12 to 75 weight percent of the inorganic dielectric constant enhancing additive based on the total weight of the polymer and the inorganic dielectric constant enhancing additive in the filled polymer film; and wherein the filled film toughness of the filled polymer film is 70 to 100 percent of the pure film toughness of a polymer film of the same thickness made of the same polymer but without the inorganic dielectric constant enhancing additive.

2. The filled polymer film according to claim 1, wherein, The filled polymer film comprises 30 to 75 weight percent of the inorganic dielectric constant enhancing additive.

3. The filled polymer film according to claim 2, wherein, The filled polymer film comprises 40 to 75 weight percent of the inorganic dielectric constant enhancing additive.

4. The filled polymer film according to claim 3, wherein, The filled polymer film comprises 50 to 75 weight percent of the inorganic dielectric constant enhancing additive.

5. The filled polymer film according to any one of claims 1 to 4, wherein, The filled film toughness is 75 to 100 percent of the pure film toughness of a polymer film of the same thickness made of the same polymer but without the inorganic dielectric constant enhancing additive.

6. The filled polymer film according to claim 5, wherein, The filled film toughness is 80 to 100 percent of the pure film toughness of a polymer film of the same thickness made of the same polymer but without the inorganic dielectric constant enhancing additive.

7. The filled polymer film according to any one of claims 1 to 6, wherein, The filled polymer film has a thickness of 2 to 25 microns.

8. The filled polymeric membrane according to claim 7, wherein, The filled polymer film has a thickness of 2 to 10 microns.

9. The filled polymer film according to claim 8, wherein, The filled polymer film has a thickness of 2 to 5 microns.

10. The filled polymer film according to any one of claims 1 to 9, wherein, For a 25-micron-thick sample, the filled polymer film has a dielectric constant of at least 5.8 or greater at 2 GHz.

11. The filled polymer film according to claim 10, wherein, For a 25-micron-thick sample, the filled polymer film has a dielectric constant of at least 6.2 or greater at 2 GHz.

12. The filled polymer film according to any one of claims 1 to 11, wherein, The inorganic dielectric constant enhancing additive comprises barium titanate.

13. The filled polymer film according to any one of claims 1 to 12, wherein, The inorganic dielectric constant enhancing additive is a single inorganic additive.

14. The filled polymer film according to any one of claims 1 to 13, wherein, The polymer comprising imidazole groups comprises 5(6)-amino-2-(p-aminophenyl)benzimidazole.

15. The filled polymer film according to claim 14, wherein, The polymer comprises residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacyl chloride.

16. The filled polymeric membrane according to claim 15, wherein, The aromatic diamine is p-phenylenediamine.

17. The filled polymeric film according to claim 15 or 16, wherein, The aromatic diacyl chloride is terephthaloyl dichloride.

18. The filled polymer film according to any one of claims 15 to 17, having a molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine of 30 / 70 to 85 / 15.

19. The filled polymer film according to claim 18, having a molar ratio of 5(6)-amino-2-(p-aminophenyl)benzimidazole to aromatic diamine of 45 / 55 to 85 / 15.

20. The filled polymer film according to any one of claims 14 to 18, comprising 50 mole percent or more of 5(6)-amino-2-(p-aminophenyl)benzimidazole.

21. The filled polymeric membrane according to any one of claims 14 to 20, wherein, The polymer comprises residues of 5(6)-amino-2-(p-aminophenyl)benzimidazole, an aromatic diamine, and an aromatic diacyl chloride, and the polymer is in the form of a polymer having a polymer chain comprising a salt having formula I, wherein C+ is a sodium, potassium, or calcium cation.

22. The polymer film according to claim 21, wherein, At least 90% of the imidazole residue repeating units in the polymer are salts having the formula I.

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