KR20140038538A - Polyimide-coated fillers - Google Patents

Abstract

Filled polyimide shaped articles or parts are produced, with reduced pore content, containing polyimide-coated filler particles. Filler particles are coated with a polyimide precursor that is end-capped, and the coating is then imidized. Coated filler particles can also be combined with additional polyimide precursors, which are then imidized in a conventional manner. The resulting composites are used to form shaped parts or parts useful for, for example, aerospace, transportation, and material handling and processing equipment applications.

Description

Polyimide-coated filler {POLYIMIDE-COATED FILLERS}

This application claims 35 U.S.C. from US Provisional Application No. 61 / 501,926, filed June 28, 2011 and US Provisional Application No. 61 / 501,930, filed June 28, 2011. We claim priority under § 119 (e) and claim its benefits, each of which is incorporated by reference in its entirety as part of this specification for all purposes.

FIELD OF THE INVENTION The present invention relates to fillers for use with and in compositions of polyimide resins, wherein the resulting systems of compositions of filled polymers and / or polyimide resins can be used to produce parts with low pore content.

Due to the unique performance of the polyimide composition under stress and at high temperatures, the polyimide composition is useful for making articles such as parts and shapes for the automotive, aerospace, and semiconductor industries.

However, various factors can cause performance degradation of articles made from polyimide compositions. Such articles often contain voids, which can degrade their properties, especially thermal stability. In addition, such articles are often manufactured by isostatic pressing techniques to obtain high densities, but it is necessary to machine the metal from the surface of the part when isostatic pressing occurs in molten tin-bismuth metal. . Articles made from polyimide resins may also suffer from service related issues such as galvanic corrosion of stainless steel housings that may occur when bushings made of graphite-filled polyimide resins are operated in a salt spray environment.

Therefore, there is still a need for polyimide resins, especially filled polyimide resins, which exhibit improved properties such as lower pore content and / or cause fewer problems during service.

In one embodiment, (a) coating the particles of particulate filler material with a polyimide precursor comprising an end-capping agent; And (b) imidating the polyimide precursor coating to produce particles of the polyimide-coated particulate filler material, thereby providing a method of making a coated particulate filler material.

In another embodiment, (a) coating a particle of particulate filler material with a polyimide precursor comprising an end-capping agent; (b) imidating the polyimide precursor coating to produce particles of the polyimide-coated particulate filler material; (c) combining the polyimide-coated particles with an additional polyimide precursor; And (d) imidating additional polyimide precursors to prepare a filled polyimide composition, a method of making a filled polyimide composition is provided herein.

In further embodiments, provided herein are polyimide-coated particulate filler materials. In another embodiment, provided herein is a polyimide-coated particulate filler material wherein the polyimide in the coating contains an end-capping agent.

In yet another embodiment, provided herein is a composition of a polyimide polymer and a polyimide-coated particulate filler material. In another embodiment, in the polyimide-coated particulate filler material of such a composition, the polyimide in the coating contains an end-capping agent.

In one embodiment of the method of the invention, the method comprises the steps of: (a) coating particles of particulate filler material with a polyimide precursor comprising an end-capping agent; And (b) imidating the polyimide precursor coating to produce particles of the polyimide-coated particulate filler material. This method provides a polyimide-coated particulate filler material; In a preferred form of such material, the polyimide in the coating contains an end-capping agent.

In another embodiment of the method of the invention, the method comprises the steps of: (a) coating particles of particulate filler material with a polyimide precursor comprising an end-capping agent; (b) imidating the polyimide precursor coating to produce particles of the polyimide-coated particulate filler material; (c) combining the polyimide-coated particles with an additional polyimide precursor; And (d) imidizing the additional polyimide precursor to prepare the filled polyimide composition. This method provides a composition of a polyimide polymer and a polyimide-coated particulate filler material; In a preferred form of such a composition, the polyimide in the coating contains an end-capping agent.

Polyimide resin

As used herein, polyimide resins are prepared from polyimide precursors. Precursors for polyimide resins include polymers in which at least about 80% of the linking groups between repeating units are imide groups. In one embodiment, at least about 90% of the linking groups between repeating units, and in further embodiments, at least about 98% are imide groups. The precursor for the polyimide resin may be an aromatic polyimide, which is at least about 60 to about 100 mol%, preferably at least about 70 mol%, and more preferably at least about 80 mol% of the repeat units of the polymer chain thereof Organic polymers having the structure represented by Formula I:

(I)

Wherein R ¹ is a tetravalent aromatic radical and R ² is a divalent aromatic radical, as described below. Polyimide precursors as used to prepare polyimide resins further include polyamic acid, polyamic esters, or polyamic acid esters, which may be imidized to produce the corresponding polyimide, as described below.

As used herein, a polyimide precursor or resin can be represented by the structure of formula (I):

(I)

Wherein R ¹ is a tetravalent aromatic radical and R ² is a divalent aromatic radical, as described below. The structure of formula I represents an aromatic polyimide.

Suitable polyimide precursors or resins for use in the present invention are, for example, by reacting monomeric aromatic diamine compounds, including derivatives thereof, with monomeric aromatic tetracarboxylic acid compounds, including derivatives thereof. Tetracarboxylic acid compounds may thus be tetracarboxylic acids themselves, the corresponding dihydrides, or derivatives of tetracarboxylic acids such as diester diacids or diester diacid chlorides. The reaction of the aromatic diamine compound with the aromatic tetracarboxylic acid compound produces a corresponding polyamic acid ("PAA"), polyamic ester, polyamic acid ester, or other reaction product depending on the choice of starting material, which is "polyimide Precursor ". Typically aromatic diamines are polymerized with dianhydrides preferentially over tetracarboxylic acids, and in such reactions catalysts are often used in addition to solvents. Nitrogen-containing bases, phenols or amphoteric materials can be used as such catalysts.

As an example of a polyimide precursor, polyamic acid is a mixture of aromatic diamine compounds and aromatic tetracarboxylic acid compounds, generally having a high boiling point such as pyridine, N-methylpyrrolidone, dimethylacetamide, dimethylformamide or mixtures thereof. In an organic polar solvent which is a solvent, it can be obtained by polymerizing preferably in substantially equimolar amounts. The amount of all monomers in the solvent can range from about 5 to about 40 weight percent, from about 6 to about 35 weight percent, or from about 8 to about 30 weight percent, based on the combined weight of monomers and solvent. The temperature for the reaction is generally about 100 ° C. or less, and may range from about 10 ° C. to 80 ° C. The polymerization reaction time is generally in the range of about 0.2 to 60 hours.

Subsequently, the imidization, i.e., ring closure in the polyimide precursor, to produce the polyimide resin from the polyimide precursor may be subjected to heat treatment (e.g., described in US Pat. No. 5,886,129), chemical dehydration or these Both, and subsequent removal of condensates (typically water or alcohol). For example, the ring closure may be accomplished by a cyclization agent such as pyridine and acetic anhydride, picoline and acetic anhydride, 2,6-lutidine and acetic anhydride, and the like.

In various embodiments of the polyimide resins so obtained, at least about 60 to 100 mole percent, or at least about 70 mole percent, or at least about 80 mole percent of the repeating units of the polymer chain thereof have a polyimide structure represented by formula (I) Has:

(I)

Wherein R < ¹ > is a tetravalent aromatic radical derived from a tetracarboxylic acid compound; R ² is typically a divalent aromatic radical derived from a diamine compound which can be represented as H ₂ NR ² -NH ₂ .

Diamine compounds as used to prepare polyimide precursors or resins, and / or as used in the present invention to prepare coated polyimide or polyimide compositions, are represented by structures H ₂ NR ^2- NH ₂ . May be one or more aromatic diamines, wherein R ² is a divalent radical containing at least one aromatic ring; Optionally, the at least one aromatic ring may contain one or more (but typically only one) heteroatoms, wherein the hetero atoms are, for example, -N-, -O-, or -S-. Such R ² groups where R ² is a biphenylene group are also included herein. Aromatic diamine compounds as used for such purposes include diamine compounds comprising at least one in-chain aromatic ring, including derivatives thereof.

Examples of suitable aromatic diamines are also known as 2,6-diaminopyridine, 3,5-diaminopyridine, 1,2-diaminobenzene, 1,3-diaminobenzene (m-phenylenediamine or "MPD"). ), 1,4-diaminobenzene (also known as p-phenylenediamine or "PPD"), 2,6-diaminotoluene, 2,4-diaminotoluene, 4,4'-diaminodi Phenyl ether, 3,4'-diaminodiphenyl ether, naphthalenediamine, 3,3'-diaminodiphenyl ether, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane , 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 2,2-bis (4 -Aminophenoxyphenyl) propane, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- (3-aminophenoxy) phenyl] sulfone, 4,4'-bis (4-aminophenoxy ) Biphenyl, 4,4'-bis (3-aminophenoxybiphenyl, 4,4'-diaminobiphenyl ( Also known as jidine), 3,3'-dimethyl-4,4'-diaminobiphenyl (also known as 3,3'-dimethylbenzidine), 3,3'-diaminodiphenylphosphine , 4,4'-diaminodiphenylphosphine, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,3'-diaminodiphenylsulfide, 4,4'-di Aminodiphenylsulfide, 3,3'-diaminodiphenylsulfone, and 4,4'-diaminodiphenylsulfone are included without limitation.

These aromatic diamines may be used alone or in combination. In one embodiment, the aromatic diamine is 4,4'-diaminodiphenyl ether (also known as "ODA" or "oxydianiline"). In one embodiment, the aromatic diamine compound is 1,4-diaminobenzene (also known as p-phenylenediamine or "PPD"), 1,3-diaminobenzene (m-phenylenediamine or "MPD" "Also known as"), or mixtures thereof.

Aromatic tetracarboxylic acid compounds suitable for use in preparing polyimide precursors or resins and / or used to prepare coated polyimide or polyimide compositions include aromatic tetracarboxylic acids, acid anhydrides thereof, and their Salts, and esters thereof, can be included without limitation. An aromatic tetracarboxylic acid compound can be represented by the general formula (II):

≪ RTI ID = 0.0 &

Wherein R ¹ is a tetravalent aromatic group and each R ³ is independently hydrogen or lower alkyl (eg, normal or branched C ₁ -C ₁₀ , C ₁ -C ₈ , C ₁ -C ₆ or C ₁ ˜C ₄ ) group. In various embodiments, the alkyl group is a C ₁ to C ₃ alkyl group. In various embodiments, the tetravalent organic group R ¹ can have a structure represented by one of the following formulas:

Examples of suitable aromatic tetracarboxylic acids include 3,3 ', 4,4'-biphenyltetracarboxylic acid, 2,3,3', 4'-biphenyltetracarboxylic acid, pyromellitic acid, 2, 3,6,7-naphthalenetetracarboxylic acid and 3,3 ', 4,4'-benzophenonetetracarboxylic acid are included without limitation. The aromatic tetracarboxylic acids may be used singly or in combination. In one embodiment, the aromatic tetracarboxylic acid compound is aromatic tetracarboxylic dianhydride. Examples include 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride ("BPDA"), pyromellitic dianhydride ("PMDA"), 3,3,4,4'-benzophenonetetra Carboxylic acid dianhydride, 1,4,5,8-naphthalene tetracarboxylic dianhydride, 2,3,6,7-naphthalene tetracarboxylic dianhydride, 1,4,5,8-naphthalene tetracarboxylic Acids, 2,3,6,7-naphthalenetetracarboxylic acids, and mixtures thereof are included without limitation.

In one embodiment, suitable polyimide resins are from 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride ("BPDA") as aromatic tetracarboxylic acid compounds and p- as aromatic diamine compounds. It can be prepared from polyamic acid resulting from a mixture of phenylenediamine ("PPD") and m-phenylenediamine ("MPD"). In another embodiment, the aromatic diamine compound is a p- phenylenediamine Min is greater than 60% to about 85 mol% mol m- phenylenediamine Min less than about 15% to 40% by mole of the mole of the same. Such polyimide resins are described in US Pat. No. 5,886,129, which is incorporated by reference in its entirety as part of this specification for all purposes, and the repeating units of such polyimide resins are also generally represented by the structures Can:

(III)

Wherein from about 60 to about 85 mole% of the R ² groups are p -phenylene radicals:

ego,

From about 15 to about 40 mole% of the m -phenylene radical:

to be.

In an alternative embodiment, suitable polyimide resins are 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride ("BPDA") as the dianhydride derivatives of tetracarboxylic acid compounds, and as diamine compounds. It can be prepared from polyamic acid produced from 70 mol% p-phenylenediamine and 30 mol% m-phenylenediamine.

In another embodiment, suitable polyimide resins are pyromellitic dianhydrides as dianhydride derivatives of tetracarboxylic acid compounds, and 4,4′-diaminodiphenyl as diamine compounds, represented by the structure represented by Formula IV. It can be prepared from polyamic acid resulting from ether ("ODA"):

(IV)

In a further embodiment, suitable polyimide resins are 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride ("BPDA") as a dianhydride derivative of a tetracarboxylic acid compound, and as a diamine compound. It can be prepared from 4,4'-diaminodiphenyl ether ("ODA").

During or after the formation of the polyimide precursor or resin by the reaction of the aforementioned components, the reactive component or polyimide precursor or resin itself may be contacted with an end-capping agent (also known as a chain terminator). The end-capping agent is a monofunctional molecule that reacts with the reactive ends of the polymer chains to provide new non-reactive end groups or moieties on that chain. Numerous molecules are known for use as end-capping agents during or after the formation of polyimide resins, and one example of such a suitable molecule is 4-phenylethynylphthalic anhydride, “4, as represented by the structure of formula (V). -PEPA ":

(V)

Other end-capping agents suitable for use in the present invention in connection with the formation of polyimide precursors or resins, or suitable for reaction with polyimide precursors or resins, can be represented by the structure of Formula VI:

(VI)

Wherein a is 0 to 5; b is 0 to 4;

R8 and R9 are each independently halogen (eg F, Cl or Br); Hydrocarbon-based radicals such as linear or branched C1 to C10 (or C1 to C4) alkyl radicals; Linear or branched C1 to C10 (or C1 to C4) alkoxy radicals; C6 to C20 (or C6 to C12) aryl radicals; Or substituted with C6 to C20 (or C6 to C12) aryloxy radicals [or halogens (eg F, Cl or Br) and / or other hetero atoms such as O, S and / or P Any one of these radicals] is independently selected from the group consisting of;

X is a linking group to a polyimide precursor or resin (NH 2, CHO, isocyanate, anhydride, carboxylic acid, ester, acyl halide, or primary amine, anhydride, dark acid, to form a stable covalent bond to the polyimide backbone, Or groups such as those comprising any other group reactive with any of the amic esters).

Methods of making end-capping agents as described above, and methods of making polyimide precursors such as polyamic acid, or polyimide resins using the same, are described in U.S. Pat. Which is incorporated by reference in its entirety).

Polyimide resins, such as those prepared from the aforementioned precursors, are preferably infusible polymers, which are polymers that do not melt (ie, liquefy or flow) below the temperature at which they decompose. Typically, articles such as parts and shaped articles made from compositions of insoluble polymers, such as polyimide resins, are described in, for example, US Pat. No. 4,360,626, which is incorporated by reference in its entirety as part of this specification for all purposes. Much like a powder metal is formed from similar parts and shaped articles, it is formed under heat and pressure.

Filler

In various embodiments thereof, the particulate filler material is coated with a polyimide precursor. In another embodiment, the filler material coated with the imidized coating combines with the polyimide resin to form a polyimide composition, altering properties compared to the unfilled polyimide resin alone; For example, one or more of the following properties are imparted: lower coefficient of thermal expansion, higher strength properties; Heat dissipation or heat resistance properties, corona resistance electrical conductivity and / or reduced wear or friction coefficient. Examples of such particulate filler materials include graphite powder, carbon fibers, carbon filaments [ie, average diameters of about 70 to about 400 nm, average lengths of about 5 to about 100 μm and aspect ratios (ie, length divided by diameter). Fibers of more than about 50], carbon black, carbon nanotubes, graphite whiskers, diamond powder, clay, muscovite mica, synthetic mica, talc, boron nitride, glass fibers, ceramic fibers, boron fibers, glass beads And whiskers, aramid fibers, metal fibers, ceramic fibers, inorganic whiskers (eg, titanium dioxide whiskers), silica, silicon carbide, silicon oxide, alumina, magnesium powder, titanium powder, silver powder, copper powder, aluminum powder, and Nickel powders are included without limitation. Examples of clays that can be used as fillers in the present invention include laponite, bentonite, montmorillonite, hectorite, kaolinite, dickite, nacrite, halosite, saponite , Nontronite, beidelite, volhonskoite, sauconite, magadite, medmonite, kenmonite, Vermiculite, serpentine group, attapulgite (also known as palygorskite), kulkeite, alliteite, sepiolite, allophane and imogolite Included without limitation.

In one embodiment, the average particle size of the particulate filler material is in the range between any two of the following values, and optionally includes both: 0.001, 0.01, 0.05, 0.1, 0.25, 0.5, 1, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, and 100 μm. In one embodiment, the average particle size of the filler ranges from about 0.001 to about 100 μm. In another embodiment, the average particle size of the filler is in the range of about 1 to about 20 μm. In another embodiment, the particulate filler material comprises nanoparticles, ie particles having at least one dimension less than about 100 nm (0.1 μm). Mixtures of fillers can be used, for example graphite powder and kaolinite, or graphite powder and titanium dioxide whiskers.

In one embodiment, the filler as used to form the coated filler in the present invention, or a composition therefrom, comprises graphite powder or graphite whiskers. Graphite is typically included as part of a polyimide composition to improve wear and friction properties and to control the coefficient of thermal expansion (CTE). Thus, the amount of graphite used in the polyimide composition for that purpose is chosen to match the CTE of the bonded part. In one embodiment, the amount of graphite used in the composition in the process of the present invention is the combined weight of the graphite present and all the polyimide resins (ie, the polyimide resin component in addition to the coating on the filler particles formed from the polyimide resin). From about 47 to about 58 weight percent based on weight percent.

Graphite is commercially available in a variety of forms, such as fine powders, and can vary widely but have an average particle size that often ranges from about 5 to about 75 micrometers. In one embodiment, the average particle size ranges from about 5 to about 25 micrometers. In another embodiment, the graphite used in the present invention comprises less than about 0.15% by weight reactive impurities such as ferric sulfide, barium sulfide, calcium sulfide, copper sulfide, barium oxide, calcium oxide, and copper oxide It contains what is selected from.

Graphite suitable for use in the present invention may be natural graphite or synthetic graphite. Natural graphites generally have a wide range of impurity concentrations, while synthetically produced graphites with low concentrations of reactive impurities are commercially available. Graphite containing unacceptably high concentrations of impurities can be purified by any of a variety of known treatments, including, for example, chemical treatment with mineral acid. For example, treatment of non-pure graphite with sulfuric acid, nitric acid or hydrochloric acid at elevated or reflux temperatures can be used to reduce impurities to a desired level.

The polyimide resin component may be present in the composition obtained from the process of the present invention in an amount ranging from about 95% to about 30% by weight based on the combined weight of all components in the composition. The polyimide-coated filler component may be present in an amount ranging from 5% to 70% by weight based on the combined weight of all components in the composition. Other materials may also be present in the composition. For example, it may be a pigment, an antioxidant, and other additives known to be used with the polyimide resin.

Preparation of Polyimide-Coated Fillers

In one embodiment of the method of the invention, the method comprises the steps of: (a) coating particles of particulate filler material with a polyimide precursor comprising an end-capping agent; And (b) imidating the polyimide precursor coating to produce particles of the polyimide-coated particulate filler material. An end-capped polyimide precursor, which is a polyimide precursor comprising an end-capping agent, is a polyimide precursor reacted with an end-capping agent as described above.

In one embodiment, coating the particles of particulate filler material with an end-capped polyimide precursor comprises (i) contacting the particles of particulate filler material to a solution comprising the polyimide precursor to form a suspension, wherein the polyimide The weight ratio of particles of the precursor to the particulate filler material is about 4: 1 to about 6: 1; (ii) heating the suspension under reflux to coat the particles with a polyimide precursor; And, optionally, (iii) recovering the coated filler particles. Next, the polyimide precursor coated on the particles of particulate filler material can be imidized in the manner described above, which will produce polyimide-coated particles of particulate filler material. For example, to provide coated particles, particles of particulate filler material to be coated may be incorporated into the heel of an imidizer. If desired, the polyimide-coated particles of the particulate filler material can then be recovered.

As mentioned above, 4-phenylethynyl phthalic anhydride (4-PEPA) is one example of an end-capping agent suitable for use in the present invention. It has been widely used by NASA as end-capping agent for its high temperature aerospace resins ( Polymer 2000, 41, 5073). Since the chemical crosslinking of phenylethynyl end groups occurs at much higher temperatures than the conversion of polyamic acid to polyimide, the end groups will be free-flowing during the process, which will result in a denser portion with less voids. . As used in the processes described herein, the end-capping agents are used in amounts ranging from about 5% to about 15% by weight, based on the combined weight of the end-capping agent and the polyimide precursor.

The particles of particulate filler material form a suspension of filler particles in a solution of the end-capped polyimide precursor and the suspension is heated at reflux for about 2 to about 4 hours in one embodiment, thereby the end-capped polyimide Coated with precursors. Suitable reflux times to achieve an effective coating will depend, for example, on the solvent (s), the concentration of the end-capped polyimide precursor, and the amount of filler particles. Suitable solvents for the end capped polyimide precursors include N, N-dimethylformamide, N, N-dimethylacetamide, tetrahydrofuran (THF), dimethyl sulfoxide, 1-methyl-2-pyrrolidinone (Also known as N-methyl pyrrolidone, or “NMP”), tetramethylurea, m-cresol and the like are included without limitation. Such solvents may be used alone or in combination with other solvents such as benzene, benzonitrile, dioxane, xylene, toluene, and cyclohexane. The end capped polyimide precursor is present in an amount ranging from about 6% to about 14% by weight, based on the combined weight of the end capped polyimide precursor and the solvent; In one embodiment, in an amount ranging from about 8 to about 12 wt%, in another embodiment, in an amount from about 9 wt% to about 11 wt%, or in another embodiment, in an amount of about 10 wt% .

The particulate filler material may be added to the end capped polyimide precursor solution or dispersed in a solvent or solvent mixture, for example N-methylpyrrolidone + pyridine, to facilitate handling and preventing aggregation. have. In one embodiment, the filler is present in the suspension in an amount ranging from about 10 to about 30 weight percent, based on the weight of the filler plus any added solvent + end capped polyimide precursor solution together; In further embodiments, the filler is present in an amount ranging from about 15 to about 25 weight percent, or in an amount ranging from about 18 to about 22 weight percent. In suspension, the weight ratio of filler to end capped polyimide precursor is from about 4: 1 to about 6: 1.

The particles of particulate filler material, then coated with the end capped polyimide precursor, can be separated by filtration and dried if desired. Prior to using the coated filler particles, such as incorporating the coated filler particles into the polyimide component of the composite, the coating is imidized as described above, so that when the filler particles are added during the formation of the bulk polyimide component, Will remain on the filler particles.

Another embodiment includes combining (eg, by mixing) particles of a polyimide-coated, particulate filler material with an additional polyimide precursor; And additional steps of preparing the filled polyimide composition by imidizing the additional polyimide precursor. In such embodiments, forming a composition containing the polyimide resin and the particulate filler material comprises mixing the polyimide-coated filler particles with an additional (bulk) polyimide precursor to the required level, followed by The mid precursor is imidized as described above.

Articles such as parts and shaped articles can be made from either type of composition, that is, one is coated with particles of particulate filler material with a polymer precursor that is imidized to form a coating, and the other is an additional polyimide After the precursor has been applied to or mixed with the so formed coating, further applied or further mixed precursor is imidated to form the composition.

Thus, provided herein are particulate filler materials coated with a polyimide polymer; In a further alternative embodiment, a particulate filler material is provided, wherein the polyimide polymer comprises an end-capping agent represented by the structure of Formula VI shown above. Thus, also provided herein are compositions comprising (a) a polyimide-coated particulate filler material, and (b) a polyimide polymer; In another embodiment, a composition is provided wherein the polyimide polymer in the coating contains an end-capping agent represented by the structure of Formula VI shown above.

Product Formation and End Use

As with articles made from other insoluble polymer materials, articles such as parts and / or shaped articles made from compositions made by the methods of the present invention are described in US Pat. No. 4,360,626, which is part of this specification for all purposes. And the application of heat and pressure, as described in its entirety herein). In some embodiments, the higher density and lower pore content is at low pressure, for example, a pressure of at least about 6.9 MPa (0.5 ton / in ² ), or a pressure of at least about 13.8 MPa (1 ton / in ² ), or A pressure of at least about 27.6 MPa (2 ton / in ² ), or a pressure of at least about 41.4 MPa (3 ton / in ² ), but a pressure of at least about 137.9 MPa (10 ton / in ² ), or about 110.3 MPa (8 ton / in ² ) or less, or about 82.7 MPa (6 ton / in ² ) or less, or about 55.2 MPa (4 ton / in ² ) or less; Or by forming directly at a pressure ranging from about 6.9 MPa (0.5 ton / in ² ) to about 68.9 MPa (5 ton / in ² ). Such lower pressures (eg, compression molding at 1 ton / in ² ) at 13.8 MPa (compared to ¹ ton / in ² ) are compared to puck molded at greater than 10 up to about 509.5 to 500 in. It can even provide a density improvement (increase) of the compression molded puck. The physical properties of articles molded from the compositions made by the methods of the present invention can be further improved by sintering, which can typically be carried out at temperatures in the range from about 300 ° C to about 450 ° C.

Articles made from coated particles, or from compositions made by the process of the present invention, have a comparable poly that includes filler particles that are not coated with end-capped polyimide, as described for the process of the present invention. Lower pore content compared to the mid composition. Such articles include, for example, parts and shaped articles useful in aerospace, transportation, and material handling and processing equipment applications.

Articles made from the compositions or particles produced by the process of the invention may be used in aerospace applications, such as aircraft engine parts, such as bushings (eg, variable stator vane bushings), bearings, washers (eg, thrust washers). , Seal rings, gaskets, wear pads, splines, wear strips, bumpers, and slide blocks. These components for aerospace applications can be used for reciprocating piston engines, and in particular for all types of aircraft engines, such as jet engines. Other examples of aerospace applications include turbochargers; Shrouds, aircraft subsystems such as thrust reversers, nacelle, flap systems and valves, and aircraft fasteners; Airplane spline couplings used to drive generators, hydraulic pumps, and other equipment; A tube clamp for an aircraft engine for attaching hydraulic lines, hot air lines, and / or electrical lines to an engine housing; Control linkage components, door mechanisms, and rocket and satellite components.

Such articles are also useful for transportation applications, for example as parts in vehicles such as, but not limited to, automobiles, recreational vehicles, off-road vehicles, military vehicles, commercial vehicles, farm and construction equipment and trucks. Do. Examples of vehicle parts include automobiles and other types of internal combustion engines; Other vehicle subsystems such as exhaust gas recirculation systems and clutch systems; Fuel systems (eg bushings, seal rings, band springs, valve seats); Pumps (eg, vacuum pump vanes); Transmission parts (eg, thrust washers, valve seats, and seal rings such as seal rings in continuously variable transmissions), transaxle parts, drive-train parts, non-aircraft jet engines; Engine belt tensioner; Rubbing blocks in ignition distributors; Powertrain applications (e.g. exhaust components, variable valve systems, turbochargers (e.g. ball bearing retainers, wastegate bushings, air intake modules); driveline applications (e.g. manual and dual clutch transmissions, transfer cases) seal rings, thrust washers and fork pads in a transfer case; seal rings and thrust washers for heavy-duty off-road transmissions and hydraulic motors; all-terrain vehicles; Bushings, buttons, and rollers for continuously variable transmissions in " ATV " and snowmobiles; and chain tensioners for snowmobile gear cases; brake systems (e.g., wear pads, valve components for antilock brake systems); door hinge bushings; Gear stick rollers; wheel disc nuts, steering systems, air conditioning systems; suspension systems; intake and exhaust systems; piston rings; and shock absorbers are limited Included without.

Such articles also include material handling equipment and material processing equipment such as injection molding machines and extrusion equipment (eg, insulators, seals, bushings and bearings for plastic injection molding and extrusion equipment), conveyors, belt presses and tenter frames; ; And films, seals, washers, bearings, bushings, gaskets, wear pads, seal rings, slide blocks and push pins, glass handling parts such as clamps and pads, seals in aluminum casting machines, valves (eg valve seats, Spools, gas compressors (eg piston rings, poppets, valve plates, labyrinth seals), hydraulic turbines, metering devices, electric motors (eg bushings, washers, thrust plugs), handheld tools Small-motor bushings and bearings for instrument motors and fans, torch insulators, and other applications where low wear is desirable.

Such articles may also be used in the manufacture of beverage cans such as bushings of body makers forming can shapes, vacuum manifold parts, and shell press bands and plugs; In the steel and aluminum rolling mill industry as bushings and mandrel liners; In gas and oil exploration and refining equipment; And textile machines (eg bushings for weaving machines, ball cups for knitting looms, wear strips for textile finishing machines).

In some applications, parts or other articles made from the composition are in contact with the metal for at least a portion of the time that the device in which it is present is assembled and normally used.

Example

The advantageous properties and effects of the compositions of the invention can be seen in the Examples (Example 1) as described below. The embodiments of these compositions on which these examples are based are merely representative, and the choice of these embodiments to illustrate the invention is that materials, components, reactants, components, formulations or specifications not described in these examples practice the invention. It is not intended to be exhaustive or to exclude the scope of the appended claims and their equivalents, which are not suitable for the present disclosure. The importance of the examples is better understood by comparing the results obtained from the examples with the results obtained from certain experimental runs, which are designed to serve as control experiments (Control A to Control C).

In the examples the following abbreviations are used: "BPDA" is defined as 3,3 ', 4,4'-biphenyltetracarboxylic anhydride, "cm" is defined in centimeters, and "Comp." Is compared Defined as an example, "ESCA" is defined by Electron Spectroscopy, "eV" is defined by electron volts, "Ex." Is defined by Examples, and "FSSG" is free sinter specific gravity (free sintered specific gravity), "ft" is defined in feet, "g" is defined in grams, "h" is defined as time, "IEP" is defined as isoelectric point, and "in" is defined as Defined in inches, "L" defined in liters, "m" defined in meters, "ml" defined in milliliters, "mm" defined in millimeters, "MPa" defined in megapascals , "MPD" is defined as m-phenylenediamine, "NMP" is defined as N-methyl pyrrolidone, "PAA" is defined as polyamic acid, "PEPA" is phenylethynylphthalic anhydride "PPD" is defined as p-phenylenediamine, "PSD" is defined as particle size distribution, "psi" is defined as pounds per square inch, "rpm" is defined as revolutions per minute and , "TEM" is defined by transmission electron microscopy, "ToF-SIMS" is defined by Time-of-Flight Secondary Ion Mass Spectrometry, and "% by weight" is defined as weight percent ( Percent) and "μm" are defined in micrometers.

material.

4-phenylethynylphthalic anhydride (4-PEPA) was provided by CRISKEV Company, Inc., Lenex, Kansas, USA. 3,3 ', 4,4'-biphenyltetracarboxylic anhydride was obtained from Mitsubishi Gas Chemical Co., Inc. (Tokyo, Japan). M-phenylenediamine and p-phenylenediamine were obtained from DuPont (Wilmington, Delaware, USA). The graphite used was synthetic graphite with a maximum ash content of 0.05% and a median particle size of about 8 micrometers.

Way.

The dried polyimide resin was subjected to ASTM E8 (2006), "Standard Tensile Test Specimen-Flat Non-Machine Tension Bar" for Powder Metal Products at room temperature and 690 MPa (50 ton / in ^2, 100,000 psi) molding pressure. It was manufactured as a tension bar by direct molding according to the Standard Tension Test Specimen for Powdered Metal Products-Flat Unmachined Tensile Test Bar. The tension bar was sintered at 405 ° C. for 3 hours with nitrogen purging.

X-ray tomography was used to examine the compacted solid puck for the presence of voids and agglomerates. In order to produce an X-ray tomography puck, 15-20 mg samples of raw resin powder were placed in a stainless steel die and 13.8 MPa (2000) with a dwell time of 10 seconds on a Carver® press. psi) to produce a 5.1 mm by 0.76 mm (0.2 in by 0.03 in) disc, referred to herein as a "puck".

The surface area of the particles was measured by the BET (Brunauer, Emmett and Teller, 1938) method.

Particle size distribution (PSD) was determined using a Malvern Mastersizer. As reported, “d (x) = z” indicates that the fraction of particles × (eg, 0.50, 0.90) has a diameter of less than z.

Polyimide coatings were characterized using several surface analysis techniques: IEP measurement (where isoelectric point is the pH when the particulate surface is not charged with an electrical charge), electron spectroscopy for chemical analysis (ESCA), time-of-flight secondary Ion mass spectroscopy (ToF-SIMS), optical microscopy, and transmission electron microscopy (TEM).

Production Example 1

This preparation describes the preparation of 4-PEPA end-capped polyamic acid.

Polyamic acid was prepared from BPDA, PPD, and MPD. The reaction vessel was a 500 ml three necked flask equipped with a condenser, an overhead stirrer, a thermocouple, and a nitrogen purge. 5.13 g of PPD and 2.20 g of MPD were added to the vessel along with 225 ml of NMP. The contents were stirred and heated to 55 ° C. using an oil bath and a heating mantle. To prepare a 15% PEPA end-capped polymer, 16.91 g (0.0575 moles) of BPDA and 5.03 g (0.0203 moles) of 4-PEPA were added along with 25 ml of NMP. The temperature was then increased to 70 ° C. and maintained at 70 ° C. for 2 h. To prepare a 10% PEPA end-capped polymer, 17.90 g (0.0608 mole) BPDA and 3.36 g (0.0135 mole) 4-PEPA were used instead. Similarly, for 5% PEPA end-capped polymers, 18.90 g (0.0642 moles) of BPDA and 1.68 g (0.0068 moles) of 4-PEPA were used.

Production Example 2

This preparation describes the preparation of graphite coated with PEPA end-capped polyimide.

Coating was done in a 1 L three-necked flask equipped with a condenser, overhead stirrer, thermocouple, 20 ml Dean-Stark trap, and nitrogen purge. 10% PEPA end-capped PAA was prepared as in Preparation Example 1. 1.95 g of end-capped PAA (10% solids loading) in NMP, and 50 ml NMP were added to the flask. Then 50 grams of graphite was slowly added to the flask with stirring at 150 rpm. 70 ml pyridine was added to the flask to completely wet the graphite and prevent its aggregation. The flask contents were stirred and heated to 160 ° C. for 4 h using an oil bath and heating mantle. After cooling to room temperature, the resulting suspension was added to 2 L acetone and filtered through 0.45 micron nylon membrane. The solid was washed with acetone and dried overnight at 120 ° C. under vacuum. In this preparation 59.06 g (98.5% yield) of graphite with 15% by weight coating of PEPA end-capped polyimide were obtained.

The specific surface area and particle size distribution of the coated graphite so prepared were comparable to the uncoated graphite, indicating uniform encapsulation with little particle agglomeration. As measured by BET, the coated graphite has a surface area of 14 m ² / g, while the uncoated graphite has a surface area of 11.3 m ² / g. PSD of coated graphite in water is d (0.50) = 12 μm and d (0.90) = 23 μm micrometer, whereas PSD of uncoated graphite in pyridine is d (0.50) = 8-13 μm and d (0.90) = 20 μm.

Further evidence for well encapsulated graphite is provided by IEP measurements. The IEP of the coated graphite has a pH of 2.6, while the laboratory-made neat polyimide has a pH of 2-3 with an IEP and an uncoated graphite has a pH of 4.3. Imide coatings on the graphite surface were also confirmed by ESCA and ToF-SIMS. As measured by ESCA, the percentages of C, O, and N are in Table 1 below. The coated graphite contained the following species: carbon, oxygen, nitrogen as CN, designated as {C- (C, H), C- (O, N), (O, N) -C = O}, and π → π *. The presence of a π → π * transition indicates the presence of a conjugated carbon functional group. There is clearly a carbon peak at ˜286 eV and ˜289 eV which is characteristic of polyimide coatings. ToF-SIMS showed that imide is present on the graphite surface and there is almost complete overlap between the carbon-graphite and the imide domain.

Coated graphite was also examined by light microscopy and TEM. Optical microscopy showed little particle agglomeration, a thin coating of polyimide encapsulates graphite, and there was some free polyimide granules. TEM represented a graphite / polyimide composite that penetrated each other in a coating layer in which graphite was separated into basic structural units wrapped with a polymer.

Production Example 3

This preparation describes the preparation of graphite coated with nonfunctionalized PAA by the use of spray drying techniques that result in aggregated particles.

A coating of nonfunctionalized PAA was applied to the graphite using standard spray drying techniques. The graphite suspended in a solution of PAA in N-methyl pyrrolidinone (NMP) was spray dried to produce PAA-coated graphite particles. Graphite was of the same type as used in Preparation Example 2, and PAA was prepared from BPDA, PPD, and MPD as in Preparation Example 1, but without end-capping. The composition of the suspension is provided in Table 2.

Spray drying was performed in a 3 ft diameter, 15 ft ³ volume, pilot spray dryer. The dryer was supplied with dry nitrogen heated to 175 ° C. The solution was metered into the spray-dry nozzle using a peristaltic pump. The slurry was sprayed into the volume of the dryer using spray system SU4, a dual fluid nozzle, supplied with 0.28 MPa (40 psig) N ₂ . An 88 ° C. aerosol was released from the dryer into an 8 ft ² bag filter, which removed entrained solids from the spent dry gas. Solids-lean dry gas came out of the bag filter at 71-77 ° C. and was treated through a venturi scrubber before venting.

PSD was determined in heptane and the results are provided in Table 2 below. Value [d (90) / d (10)] ^{(1 / 2.56)} represents the width of the particle size distribution. Samples were also characterized by optical microscopy. Samples from each of the three runs were well handled in terms of particle flow. However, there was significant agglomeration of the graphite particles, which often spand several hundred micrometers. In addition, for Run 1 samples, it was not even clear that a coating had been formed.

Example 1, Control A to Control C

Example 1 and Controls A to C show improved density in such pucks when the polyimide resin pucks are compacted at low tonnage and the resin contains graphite coated with PEPA-end-capped polyimide Prove that.

Polyimide resins were prepared using the coated graphite prepared in Preparation Example 2, and polyamic acid (PAA) prepared from BPDA, PPD, and MPD. The amount of PAA added to the imidization instrument was reduced in view of the polyimide already present on the filler. For tension bars made under standard compression molding conditions (689.45 MPa (50 ton / in ² , 100,000 psi)) (designated as control A), the FSSG density (as determined by ASTM method D-792) is 1.6833 g / Cm 3 (4.8% void) —typical for laboratory prepared polyimides made from BPDA, PPD, and MPD as disclosed in US Pat. No. 5,886,129, which is incorporated by reference in its entirety for all purposes. , Contained 50% by weight of uncoated graphite. However, when the puck was formed by compression molding at low tonnage (13.8 MPa (1 ton / in ² , 2000 psi)) (designated as Example 1), the density was dramatically improved by PEPA end-capped coating. The pucks of Example 1 had a density of 1.7245 g / cm 3, which is 98% of theoretical density.

Puck formed under standard compression molding conditions (509.5 MPa (50 ton / in ² , 100,000 psi)) so that the pucks formed from laboratory prepared polyimide containing 50% uncoated graphite had a density (Control B); By compression molding at low tonnage (689.5 MPa (1 ton / in ² , 2000 psi)), the puck formed from this composition has a density of 1.6043 g / cm 3 (control C). Add to, X-ray tomography showed no large voids or agglomeration at all in the Example 1 polyimide parts prepared using PEPA-functionalized coatings on graphite. The results are summarized in Table 3.

In addition to the sales companies referred to elsewhere herein, various materials suitable for use in the methods of the present invention may be prepared by methods known in the art and / or by Alfa Aesar, Massachusetts, USA. Fisher Scientific (Fairon, NJ), Sigma-Aldrich (St. Louis, Missouri, USA), < RTI ID = 0.0 > Or from a source such as Stanford Materials, Aliso Viejo, CA.

In this specification, unless the context clearly dictates otherwise or is contrary to the context of use, it is to be understood that the embodiment of the subject matter includes, departs from, comprises, comprises, One or more features or elements in addition to those explicitly described or described may be present in the embodiments. However, alternative embodiments of the present subject matter may be described or described as consisting essentially of certain features or elements, where features or features that significantly change the operating principle or distinctive features of the embodiments. The element is not present in the embodiment. Additional alternative embodiments of the present subject matter may be described or described as consisting of certain features or elements, in which only those features or elements are specifically described or described. This exists.

When a range of numerical values is mentioned or established herein, the range includes the endpoint and all individual integers and fractions within that range, and also to form a subgroup of a larger group of values within the stated range. Each of the narrower ranges formed therein by the end points and all possible various combinations of integers and fractions inside includes the same extent as if each of these narrower ranges were explicitly mentioned. When a range of numerical values is described herein as being greater than the stated values, the ranges are nevertheless finite, and the ranges are defined at their upper limits by values operable within the context of the invention disclosed herein. Boundaries are made. When a range of numerical values is referred to herein as being below a stated value, the range is nonetheless bounded at its lower limit by a non-zero value.

In this specification, unless expressly stated otherwise or indicated to the contrary in the context of use,

(a) the list of compounds, monomers, oligomers, polymers and / or other chemicals includes derivatives of members of the list, and also includes any combination of two or more of each member and / or any of its respective derivatives;

(b) the amounts, sizes, ranges, formulations, parameters and other quantities and characteristics mentioned herein are not necessarily to be precise when specifically modified by the term " about ", and also include tolerances, conversion factors, rounding, a measurement error, etc., and the inclusion of values outside thereof having functional equivalents and / or operability equivalents with those described in the context of the present invention, are approximated and / May be larger or smaller).

Claims (24)

As a method of preparing a filled polyimide composition,
(a) coating the particles of particulate filler material with a polyimide precursor comprising an end-capping agent;
(b) imidating the polyimide precursor coating to produce particles of the polyimide-coated particulate filler material;
(c) combining the polyimide-coated particles with an additional polyimide precursor; And
(d) imidizing the additional polyimide precursor to produce a filled polyimide composition. The method of claim 1, wherein (a) coating the particles of particulate filler material comprises (i) contacting the particles of particulate filler material to a solution comprising the polyimide precursor to form a suspension, wherein the polyimide precursor to particles of The weight ratio is about 4: 1 to about 6: 1; And (ii) heating the suspension under reflux. The method of claim 1, wherein the end-capping agent is represented by the structure of Formula VI:
(VI)

Wherein a is 0 to 5; b is 0 to 4; and R 8 and R 9 are each independently selected from the group consisting of halogen and hydrocarbon-based radicals; X is a linking group to a polyimide precursor or resin. The method of claim 1, wherein the end-capping agent comprises 4-phenylethynylphthalic anhydride. The method of claim 1, wherein the polyimide precursor comprises a polyamic acid prepared from an aromatic diamine compound and an aromatic tetracarboxylic acid compound,
(a) Aromatic diamine compounds include 2,6-diaminopyridine, 3,5-diaminopyridine, 1,2-diaminobenzene, 1,3-diaminobenzene, 1,4-diaminobenzene, 2, 6-diaminotoluene, 2,4-diaminotoluene, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, naphthalenediamine, 3,3'-diaminodiphenyl ether , 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene , 1,3-bis (3-aminophenoxy) benzene, 2,2-bis (4-aminophenoxyphenyl) propane, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- ( 3-aminophenoxy) phenyl] sulfone, 4,4'-bis (4-aminophenoxy) biphenyl, 4,4'-bis (3-aminophenoxybiphenyl, 4,4'-diaminobiphenyl , 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-diaminodiphenylphosphine, 4,4'-diaminodiphenylfo Pin, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,3'-diaminodiphenylsulfide, 4,4'-diaminodiphenylsulfide, 3,3'-di Aminodiphenylsulfone, and 4,4'-diaminodiphenylsulfone, and mixtures thereof;
(b) the aromatic tetracarboxylic acid compound is 3,3 ', 4,4'-biphenyltetracarboxylic acid, 2,3,3', 4'-biphenyltetracarboxylic acid, pyromellitic acid, 2 , 3,6,7-naphthalenetetracarboxylic acid, 3,3 ', 4,4'-benzophenonetetracarboxylic acid, 3,3', 4,4'-biphenyltetracarboxylic dianhydride, pi Romellitic dianhydride, 3,3,4,4'-benzophenonetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetra Carboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, and mixtures thereof. The method of claim 1, wherein the polyimide precursor is selected from the group consisting of polyamic acid produced from 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and a mixture of p-phenylenediamine and m-phenylenediamine; Or polyamic acid produced from pyromellitic dianhydride and 4,4'-diaminodiphenyl ether. The particulate filler material of claim 1, wherein the particulate filler material is graphite powder, carbon fiber, carbon filament, carbon black, carbon nanotubes, graphite whisker, diamond powder, clay, muscovite mica, synthetic mica, talc, boron nitride Glass fibers, ceramic fibers, boron fibers, glass beads, whiskers, aramid fibers, metal fibers, ceramic fibers, inorganic whiskers, silica, silicon carbide, silicon oxide, alumina, magnesium powder, titanium powder; Silver powder, copper powder, aluminum powder, nickel powder, and mixtures thereof. The method of claim 1, wherein the average particle size of the particulate filler material is from about 0.001 μm to about 100 μm. The method of claim 1, further comprising forming an article from the filled polyimide composition. An article formed according to the method of claim 9. A method of making a coated particulate filler material,
(a) coating the particles of particulate filler material with a polyimide precursor comprising an end-capping agent; And
(b) imidating the polyimide precursor coating to produce particles of the polyimide-coated particulate filler material. The method of claim 11, wherein (a) coating the particles of particulate filler material comprises (i) contacting the particles of particulate filler material to a solution comprising the polyimide precursor to form a suspension, wherein the polyimide precursor to particles of The weight ratio is about 4: 1 to about 6: 1; And (ii) heating the suspension under reflux. The method of claim 11, wherein the end-capping agent is represented by the structure of Formula VI:
(VI)

Wherein a is 0 to 5; b is 0 to 4; R ⁸ and R ⁹ are each independently selected from the group consisting of halogen and hydrocarbon-based radicals; X is a linking group to a polyimide precursor or resin . The method of claim 11, wherein the end-capping agent comprises 4-phenylethynylphthalic anhydride. The method of claim 11, wherein the polyimide precursor comprises a polyamic acid prepared from an aromatic diamine compound and an aromatic tetracarboxylic acid compound,
(a) Aromatic diamine compounds include 2,6-diaminopyridine, 3,5-diaminopyridine, 1,2-diaminobenzene, 1,3-diaminobenzene, 1,4-diaminobenzene, 2, 6-diaminotoluene, 2,4-diaminotoluene, 4,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl ether, naphthalenediamine, 3,3'-diaminodiphenyl ether , 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene , 1,3-bis (3-aminophenoxy) benzene, 2,2-bis (4-aminophenoxyphenyl) propane, bis [4- (4-aminophenoxy) phenyl] sulfone, bis [4- ( 3-aminophenoxy) phenyl] sulfone, 4,4'-bis (4-aminophenoxy) biphenyl, 4,4'-bis (3-aminophenoxybiphenyl, 4,4'-diaminobiphenyl , 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-diaminodiphenylphosphine, 4,4'-diaminodiphenylfo Pin, 3,3'-diaminobenzophenone, 4,4'-diaminobenzophenone, 3,3'-diaminodiphenylsulfide, 4,4'-diaminodiphenylsulfide, 3,3'-di Aminodiphenylsulfone, and 4,4'-diaminodiphenylsulfone, and mixtures thereof;
(b) the aromatic tetracarboxylic acid compound is 3,3 ', 4,4'-biphenyltetracarboxylic acid, 2,3,3', 4'-biphenyltetracarboxylic acid, pyromellitic acid, 2 , 3,6,7-naphthalenetetracarboxylic acid, 3,3 ', 4,4'-benzophenonetetracarboxylic acid, 3,3', 4,4'-biphenyltetracarboxylic dianhydride, pi Romellitic dianhydride, 3,3,4,4'-benzophenonetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7-naphthalenetetra Carboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, and mixtures thereof. 12. The polyimide precursor of claim 11, wherein the polyimide precursor is selected from the group consisting of polyamic acid produced from 3,3 ', 4,4'-biphenyltetracarboxylic dianhydride and a mixture of p-phenylenediamine and m-phenylenediamine; Or polyamic acid produced from pyromellitic dianhydride and 4,4'-diaminodiphenyl ether. The particulate filler material of claim 11, wherein the particulate filler material comprises graphite powder, carbon fiber, carbon filament, carbon black, carbon nanotubes, graphite whiskers, diamond powder, clay, dolomite, synthetic mica, talc, boron nitride, glass fiber, ceramic fiber, Boron fibers, glass beads, whiskers, aramid fibers, metal fibers, ceramic fibers, inorganic whiskers, silica, silicon carbide, silicon oxide, alumina, magnesium powder, titanium powder; Silver powder, copper powder, aluminum powder, nickel powder, and mixtures thereof. The method of claim 11, wherein the average particle size of the particulate filler material is from about 0.001 μm to about 100 μm. The method of claim 11, further comprising forming an article from the polyimide-coated particulate filler material. An article formed according to the method of claim 19. Particulate filler material coated with a polyimide polymer. The particulate filler material of claim 21, wherein the polyimide polymer comprises an end-capping agent represented by the structure of the formula: A composition comprising (a) a polyimide-coated particulate filler material and (b) a polyimide polymer. The composition of claim 23, wherein the polyimide polymer in the coating comprises an end-capping agent represented by the structure of: