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  • C08G73/00—Macromolecular compounds obtained by reactions forming a linkage containing nitrogen with or without oxygen or carbon in the main chain of the macromolecule, not provided for in groups C08G12/00 - C08G71/00
  • C08G73/06—Polycondensates having nitrogen-containing heterocyclic rings in the main chain of the macromolecule
  • C08G73/10—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
  • C08G73/1003—Preparatory processes
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  • C08G73/10—Polyimides; Polyester-imides; Polyamide-imides; Polyamide acids or similar polyimide precursors
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Definitions

• This disclosure relates to fillers for use with, and in compositions of, polyimide resins, wherein the resulting systems of filled polymers and/or compositions of polyimide resins can be used to produce parts with lowered void content.
• Such articles often contain voids, which can compromise their properties, especially thermal stability.
• such articles are often made by isostatic pressing techniques to obtain high density, but when the isostatic pressing occurs in molten tin-bismuth metal, the metal needs to be machined off the surface of the part.
• Articles fabricated from a polyimide resin can also suffer service related problems, such as the galvanic corrosion of a stainless steel housing that can occur where a bushing made of graphite- filled polyimide resin is operated in a salt spray environment.
• a process for preparing a coated particulate filler material by (a) coating particles of a particulate filler material with a polyimide precursor that comprises an end-capping agent; and (b) imidizing the polyimide precursor coating to produce particles of a polyimide-coated particulate filler material.
• a process for preparing a filled polyimide composition by (a) coating particles of a particulate filler material with a polyimide precursor that comprises an end- capping agent; (b) imidizing the polyimide precursor coating to produce particles of a polyimide-coated particulate filler material; (c) combining the polyimide-coated particles with additional polyimide precursor; and (d) imidizing the additional polyimide precursor to prepare a filled polyimide composition.
• a polyimide-coated particulate filler material there is provided herein a polyimide-coated particulate filler material.
• a polyimide-coated particulate filler material wherein the polyimide in the coating contains an end-capping agent.
• a composition of a polyimide polymer and a polyimide-coated particulate filler material there is provided herein a composition of a polyimide polymer and a polyimide-coated particulate filler material.
• the polyimide in the coating contains an end-capping agent.
• a process for preparing a coated particulate filler material by (a) coating particles of a particulate filler material with a polyimide precursor that comprises an end-capping agent; and (b) imidizing the polyimide precursor coating to produce particles of a polyimide-coated particulate filler material.
• This process provides a polyimide-coated particulate filler material; and, in a preferred form of such material, the polyimide in the coating contains an end-capping agent.
• a process for preparing a filled polyimide composition by (a) coating particles of a particulate filler material with a polyimide precursor that comprises an end-capping agent; (b) imidizing the polyimide precursor coating to produce particles of a polyimide-coated particulate filler material; (c) combining the polyimide-coated particles with additional polyimide precursor; and (d) imidizing the additional polyimide precursor to prepare a filled polyimide composition.
• This process provides a composition of a polyimide polymer and a polyimide-coated particulate filler material; and, in a preferred form of such composition, the polyimide in the coating contains an end-capping agent.
• a polyimide resin is prepared from a polyimide precursor.
• a precursor for a polyimde resin includes a polymer in which at least about 80% of the linking groups between repeat units are imide groups. In one embodiment, at least about 90%, and, in a further embodiment, at least about 98%, of the linking groups between repeat units are imide groups.
• a precursor for a polyimide resin can be an aromatic polyimide, which includes an organic polymer in which about 60 to about 100 mol%, preferably about 70 mol% or more, and more preferably about 80 mol% or more of the repeating units of the polymer chain thereof have a structure as represented by the following Formula (I):
• a polyimide precursor as used to make a polyimide resin includes a polyamic acid, a polyamic ester, or a polyamic acid ester that can undergo imidization to produce the corresponding polyimide, as further described below.
• a polyimide precursor or resin as used herein, can be represented by the structure of the following Formula ( I) :
• R 1 is a tetravalent aromatic radical and R 2 is a divalent aromatic radical, as described below.
• the structure of Formula I is representative of an aromatic polyimide.
• a polyimide precursor or resin suitable for use herein may be synthesized, for example, by reacting a monomeric aromatic diamine compound (which includes derivatives thereof) with a monomeric aromatic tetracarboxylic acid compound (which includes derivatives thereof) , and the tetracarboxylic acid compound can thus be the tetracarboxylic acid itself, the corresponding dianhydride, or a derivative of the tetracarboxylic acid such as a diester diacid or a diester diacidchloride.
• the reaction of the aromatic diamine compound with an aromatic tetracarboxylic acid compound produces the corresponding polyamic acid ("PAA") , polyamic ester, polyamic acid ester, or other reaction product according to the selection of starting materials, which are referred to herein as "polyimide precursors".
• PAA polyamic acid
• polyamic ester polyamic acid ester
• polyimide precursors polyamic acid ester
• An aromatic diamine is typically polymerized with a dianhydride in preference to a tetracarboxylic acid, and in such a reaction a catalyst is frequently used in addition to a solvent.
• a nitrogen-containing base, phenol or an amphoteric material can be used as such a catalyst.
• a polyamic acid can be obtained by polymerizing an aromatic diamine compound and an aromatic tetracarboxylic acid compound, preferably in substantially equimolar amounts, in an organic polar solvent that is generally a high-boiling solvent such as pyridine, N-methylpyrrolidone, dimethylacetamide,
• the amount of all monomers in the solvent can be in the range of about 5 to about 40 wt%, in the range of about 6 to about 35 wt%, or in the range of about 8 to about 30 wt%, based on the combined weight or monomers and solvent.
• the temperature for the reaction is generally not higher than about ioo°C, and may be in the range of about io°C to 8o°C.
• the time for the polymerization reaction generally is in the range of about 0.2 to 60 hours.
• Imidization to produce a polyimide resin from a polyimide precursor i.e. ring closure in the polyimide precursor
• ring closure can then be effected through thermal treatment (e.g. as described in U.S. Patent 5,886,129), chemical dehydration or both, followed by the elimination of a condensate (typically, water or alcohol) .
• ring closure can be effected by a cyclization agent such as pyridine and acetic anhydride, picoline and acetic anhydride, 2,6-lutidine and acetic anhydride, or the like.
• polyimide structure as represented by the following Formula (I) :
• R 1 is a tetravalent aromatic radical derived from the tetracarboxylic acid compound
• R 2 is a divalent aromatic radical derived from the diamine compound, which may typically be represented as H 2 N-R 2 -NH 2 .
• a diamine compound as used to prepare a polyimide precursor or resin, and/or as used herein to prepare a coated polyimide or a polyimide composition may be one or more of the aromatic diamines that can be represented by the structure H 2 N-R 2 -NH 2 , wherein R 2 is a divalent radical containing at least one aromatic ring; optionally, at least one aromatic ring can contain one or more (but typically only one) heteroatoms, a heteroatom being, for example, -N-, -0-, or -S-. Also included herein are those R 2 groups wherein R 2 is a biphenylene group.
• An aromatic diamine compound as used for such purpose includes a diamine compound (which includes derivatives thereof) comprising at least one in-chain aromatic ring.
• aromatic diamines include without limitation: 2,6-diaminopyridine, 3, 5-diamino pyridine, 1,2-diaminobenzene, 1,3- diaminobenzene (also known as m-phenylenediamine or "MPD"), 1,4- diaminobenzene (also known as p-phenylenediamine or "PPD”), 2,6- diaminotoluene, 2,4-diaminotoluene, 4,4-diaminodiphenyl ether, 3,4 - diaminodiphenyl ether, naphthalenediamines, 3,3 -diaminodiphenyl ether, 3,3'-diaminodiphenylmethane, 4,4'-diaminodiphenylmethane, i,4-bis(4- aminophenoxy)benzene, i,3-bis(4-aminophenoxy)benzene, i,
• aromatic diamines can be employed singly or in combination.
• the aromatic diamine is 4,4'-diaminodiphenyl ether (also known as "ODA” or “oxydianiline”).
• the aromatic diamine compound is 1,4-diaminobenzene (also known as p- phenylenediamine or "PPD”), 1,3-diaminobenzene (also known as m- phenylenediamine or "MPD”), or mixtures thereof.
• Aromatic tetracarboxylic acid compounds suitable for use to prepare a polyimide precursor or resin, and/or as used to prepare a coated polyimide or a polyimide composition may include without limitation aromatic tetracarboxylic acids, acid anhydrides thereof, salts thereof and esters thereof.
• An aromatic tetracarboxylic acid compound may be as represented by the general Formula (II):
• R 1 is a tetravalent aromatic group and each R 3 is independently hydrogen or a lower alkyl (e.g. a normal or branched Q-Q o , Q-Cg, Q-Cg or Q ⁇ C 4 ) group.
• the alkyl group is a Q to C 3 alkyl group.
• the tetravalent organic group R 1 may have a structure as represented by one of the following formulae:
• aromatic tetracarboxylic acids examples include without limitation 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.
• the aromatic tetracarboxylic acids can be employed singly or in combination.
• the aromatic tetracarboxylic acid compound is an aromatic tetracarboxylic dianhydride.
• Examples include without limitation 3,3',4,4'-biphenyltetracarboxylic dianhydride ("BPDA”), pyromellitic dianhydride (“PMDA”), 3,3,4,4 -benzophenonetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic dianhydride, 2,3,6,7- naphthalenetetracarboxylic dianhydride, 1,4,5,8-naphthalenetetracarboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, and mixtures thereof.
• BPDA 3,3',4,4'-biphenyltetracarboxylic dianhydride
• PMDA pyromellitic dianhydride
• 3,3,4,4 -benzophenonetetracarboxylic dianhydride 1,4,5,8-naphthalenetetracarboxylic dianhydride
• a suitable polyimide resin may be prepared from polyamic acid produced from 3,3 ,4,4'-biphenyltetracarboxylic dianhydride ("BPDA") as the aromatic tetracarboxylic acid compound, and from a mixture of p-phenylenediamine (“PPD”) and m-phenylenediamine (“MPD”) as the aromatic diamine compound.
• BPDA 3,3 ,4,4'-biphenyltetracarboxylic dianhydride
• PPD p-phenylenediamine
• MPD m-phenylenediamine
• the aromatic diamine compound is greater than 60 to about 85 mol%
• R 2 groups wherein from about 60 to about 85 mol% of the R 2 groups are p-phenylene radicals:
• a suitable polyimide resin may be prepared from polyamic acid produced from 3,3',4,4'-biphenyltetracarboxylic dianhydride ("BPDA") as a dianhydride derivative of the tetracarboxylic acid compound, and 70 mol% p-phenylenediamine and 30 mol% m- phenylenediamine as the diamine compound.
• BPDA 3,3',4,4'-biphenyltetracarboxylic dianhydride
• a suitable polyimide resin may be prepared from from polyamic acid produced from pyromellitic dianhydride as a dianhydride derivative of the tetracarboxylic acid compound, and 4,4 - diaminodiphenyl ether ("ODA”) as the diamine compound, represented by the structure shown in Figure (IV).
• ODA 4,4 - diaminodiphenyl ether
• a suitable polyimide resin may be prepared from 3,3',4,4'-biphenyltetracarboxylic dianhydride (“BPDA”) as a dianhydride derivative of the tetracarboxylic acid compound, and 4,4'-diaminodiphenyl ether (“ODA”) as the diamine compound .
• BPDA 3,3',4,4'-biphenyltetracarboxylic dianhydride
• ODA 4,4'-diaminodiphenyl ether
• an end-capping agent also known as a chain terminator
• an end-capping agent also known as a chain terminator
• an end-capping agent is a mono functional molecule that will react with the reactive end of a polymer chain to furnish on that chain a new, non-reactive end group or moiety.
• an end-capping agent also known as a chain terminator
• Numerous molecule are known for use as an end-capping agent during or after formation of a polyimide resin, and one example of a suitable such molecule is 4-phenylethynylphthalic anhydride, "4-PEPA", as represented by the structure of the following Formula (V),
• R8 and R9 is each independently selected from the group consisting of halogen (such as F, Cl or Br); a hydrocarbon-based radical such as a linear or branched Ci to C10 (or Ci to C4) alkyl radical; a linear or branched Ci to Cio (or Ci to C4) alkoxy radical; a C6 to C20 (or C6 to C12) aryl radical; or a C6 to C20 (or C6 to C12) aryloxy radical [or versions of any one of those radicals substituted with a halogen (e.g. F, Cl or Br) and/or with other hetero atoms such as O, S and/or P] ; and
• halogen such as F, Cl or Br
• a hydrocarbon-based radical such as a linear or branched Ci to C10 (or Ci to C4) alkyl radical; a linear or branched Ci to Cio (or Ci to C4) alkoxy radical; a C6 to C20 (or C6 to C12)
• X is a linking group to the polyimide precursor or resin (formed by a group such as those including NH2, CHO, an isocyanate, an anhydride, a carboxylic acid, an ester, an acyl halide, or any other group reactive with either a primary amine, an anhydride, an amic acid or an amic ester to form a stable covalent linkage to a polyimide backbone).
• a process for preparing an end-capping agent as described above, and for using it to prepare a polyimide precursor, e.g. a polyamic acid, or a polyimide resin is described in U. S. Patent 5,138,028 (which is by this reference incorporated in its entirety as a part hereof for all purposes).
• a polyimide resin as provided from a precursor as described above, is preferably an infusible polymer, which is a polymer that does not melt (i. e. liquefy or flow) below the temperature at which it decomposes.
• articles such as parts and shapes prepared from a composition of an infusible polymer such as a polyimide resin are formed under heat and pressure, much like powdered metals are formed into similar parts and shapes (as described, for example, in U.S. 4,360,626, which is by this reference incorporated in its entirety as a part hereof for all purposes).
• particulate filler material is coated with a polyimide precursor.
• filler material coated with an imidized coating is incorporated with a polyimide resin to form a polyimide composition to modify properties versus an unfilled polyimide resin alone; for example to impart one or more of the following: a lowered coefficient of thermal expansion, high strength properties; heat dissipation or heat resistance properties, corona resistance electric conductivity and/or reduced wear or coefficient of friction.
• Examples of such a particualte filler material include without limitation graphite powder, carbon fibers, carbon filaments [i. e. fibers having mean diameter about 70 to about 400 nm, mean length about 5 to about 100 ⁇ and an aspect ratio (i. e.
• clays that can be used as fillers herein include without limitation laponite, bentonite, montmorillonite, hectorite, kaolinite, dickite, nacrite, halloysite, saponite, nontronite, beidellite, volhonskoite, sauconite, magadite, medmonite, kenyaite, vermiculite, serpentines, attapulgite (also known as palygorskite), kulkeite, alletite, sepiolite, allophane, imogolite.
• the average particle size of the particualte filler material is in a range that is between, and optionally includes, any two of the following values: o.ooi, o.oi, 0.05, 0.1, 0.25, 0.5, 1, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, and 100 um. In one embodiment, the average particle size of the filler is in a range from about 0.001 to about 100 ⁇ . In another
• the average particle size of the filler is in a range from about 1 to about 20 um.
• the particulate filler material comprises nanoparticles, i.e. particles having at least one dimension less than about 100 nm (0.1 ⁇ ).
• Mixtures of fillers can be used, for example, graphite powder and kaolinite, or graphite powder and titanium dioxide whiskers.
• a filler as used herein to form a coated filler, or a composition therefrom includes graphite powder or graphite whiskers.
• Graphite is typically incorporated as a part of a polyimide composition to improve wear and frictional characteristics, and to control the coefficient of thermal expansion (CTE).
• CTE coefficient of thermal expansion
• the amount of graphite used in a polyimide composition for such purpose is thus chosen to match the CTE of the mating components.
• the amount of graphite used in a composition in the processes hereof is from about 47 to about 58 wt%, based on the combined weight of the graphite and all polyimide resin present therein (i.e.
• Graphite is commercially available in a variety of forms as a fine powder, and may have a widely varying average particle size that is, however, frequently in the range of from about 5 to about 75 microns. In one embodiment, the average particle size is in the range of from about 5 to about 25 microns. In another embodiment, graphite as used herein contains less than about 0.15 weight percent of reactive impurities, such as those selected from the group consisting of ferric sulfide, barium sulfide, calcium sulfide, copper sulfide, barium oxide, calcium oxide, and copper oxide.
• Graphite as suitable for use herein can be either naturally occurring graphite or synthetic graphite. Natural graphite generally has a wide range of impurity concentrations while synthetically produced graphite is commercially available having low concentrations of reactive impurities. Graphite containing an unacceptably high concentration of impurities can be purified by any of a variety of known treatments including, for example, chemical treatment with a mineral acid. Treatment of impure graphite with sulfuric, nitric or hydrochloric acid, for example, at elevated or reflux temperatures can be used to reduce impurities to a desired level.
• the polyimide resin component can be present in a composition obtained from the processes hereof in an amount ranging from about 95 wt% to about 30 wt% based on the combined weight of all components in the composition.
• the polyimide-coated filler component can be present in an amount ranging from 5 wt% to 70 wt%, based on the combined weight of all components in the composition.
• Other materials may also be present in the composition. For instance, these may be pigments, antioxidants and other additives known for used in connection with polyimide resins.
• a process for preparing a coated particulate filler material by (a) coating particles of a particulate filler material with a polyimide precursor that comprises an end-capping agent; and (b) imidizing the polyimide precursor coating to produce particles of a polyimide-coated particulate filler material.
• a polyimide precursor that comprises an end-capping agent, an end-capped polyimide precursor is a polyimide precursor that has been reacted with an end-capping agent, as described above.
• coating particles of a particulate filler material with an end-capped polyimide precursor is performed by (i) contacting a solution comprising the polyimide precursor with particles of the particulate filler material, thereby forming a suspension wherein the weight ratio of polyimide precursor to particles of particulate filler material is in the range of about 4:1 to about 6:1 ; (ii) heating the suspension under reflux, thereby coating the particles with the polyimide precursor; and, optionally, (iii) recovering the coated filler particles.
• the polyimide precursor that is coated on the particles of particulate filler material can then be imidized in the manner described above, which will produce polyimide-coated particles of particulate filler material.
• the particles of particulate filler material to be coated can be incorporated into the heel of the imidizer. If desired, the polyimide-coated particles of particulate filler material can then be recovered.
• 4-Phenylethynyl phthalic anhydride is one example of an end-capping agent suitable for use herein. It has been widely used by NASA as an end-capping agent for its high temperature aerospace resins [Polymer 2000, 41, 5073] .
• the chemical cross-linking of the phenylethynyl end groups occurs at much higher temperatures than the conversion of polyamic acid to polyimide, so the end-groups will be free- flowing during processing which should result in a denser part with fewer voids.
• an end-capping agent is used in an amount in the range of between about 5 wt% and about 15 wt% based on the combined weight of the end-capping agent and the polyimide precursor together.
• the particles of particualte filler material are coated with the end- capped polyimide precursor by formation of a suspension of the filler particles in a solution of the end-capped polyimide precursor, and heating the suspension at reflux, in one embodiment for about two to about 4 hours.
• the appropriate refluxing time to achieve effective coating will depend, for example, on the solvent(s), the concentration of the end-capped polyimide precursor, and the amount of the filler particles.
• Suitable solvents for the endcapped polyimide precursor include without limitation: N,N- dimethylformamide, ⁇ , ⁇ -dimethylacetamide, tetrahydrofuran (THF), dimethyl sulfoxide, i-methyl-2-pyrrolidinone (also known as N-methyl pyrrolidone, or "NMP"), tetramethylurea, m-cresol, and the like.
• NMP N-methyl pyrrolidone
• tetramethylurea m-cresol, and the like.
• solvents can be used alone or in combination with other solvents such as benzene, benzonitrile, dioxane, xylene, toluene, and cyclohexane.
• the endcapped polyimide precursor is present in an amount in the range of about 6 wt% to about 14 wt%, based on the combined weight together of the endcapped polyimide precursor and the solvent; in one embodiment, it is present in an amount in the range of about 8 to about 12 wt%, and, in another, in an amount of about 9 wt% to about 11 wt%, or in another about 10 wt%.
• the particulate filler material can be added to the endcapped polyimide precursor solution neat, or dispersed in a solvent or mixture of solvents, such as N-methylpyrrolidone plus pyridine, for ease of handling and preventing agglomeration.
• the filler is present in the suspension in an amount in the range of about 10 to about 30 wt%, based on the combined weight together of filler plus any added solvent plus endcapped polyimide precursor solution; in further embodiments, the filler is present in an amount in the range of about 15 to about 25 wt%, or an amount in the range of about 18 to about 22 wt%.
• the weight ratio of filler to endcapped polyimide precursor is between about 4:1 and about 6:1.
• the endcapped polyimide precursor coated particles of particulate filler material can then be isolated by filtration and, if desired, dried.
• the coating is imidized as described above, so that the coating will be maintained on the filler particles when they are added during the formation of the bulk polyimide component.
• Another embodiment involves the additional steps of combining (such as by mixing) the polyimide-coated particles of particulate filler material with additional polyimide precursor; and imidizing the additional polyimide precursor to prepare a filled polyimide composition.
• forming a composition that contains a polyimide resin and a particulate filler material involves mixing polyimide-coated filler particles with additional (bulk) polyimide precursor at a desired level, and the polyimide precursor is then imidized as described above.
• Articles such as parts and shapes can be made from either type of composition, viz: one in which particles of particulate filler material have been coated with a polymer precursor that is imidized to form the coating, and another in which additional polyimide precursor is applied to, or mixed with, the coating so formed followed by imidizaton of the further-applied or further-mixed precursor, thus forming a composition.
• a particulate filler material coated with a polyimide polymer there is thus provided herein a particulate filler material coated with a polyimide polymer; and in a further alternative embodiment, there is provided a particualte filer material wherein the polyimde polymer comprises an end-capping agent represented by the structure of Formula VI, shown above.
• articles such as parts and/or shapes fabricated from a composition prepared by a process hereof may be made by techniques involving the application of heat and pressure such as those described in U.S. Patent No. 4,360,626 (which is by this reference incorporated in its entirety as a part hereof for all purposes).
• higher density and lower void content can be achieved by direct forming at low pressure for example, at a pressure of about 0.5 ton/in 2 or more, or a pressure of about 1 ton/in 2 or more, or a pressure of about 2 ton/in 2 or more, or a pressure of about 3 ton/in 2 or more, and yet a pressure of about 10 ton/in 2 or less, or a pressure of about 8 ton/in 2 or less, or a pressure of about 6 ton/in 2 or less, or a pressure of about 4 ton/in 2 or less; or a pressure in the range of about 0.5 ton/in 2 to about 5 ton/in 2 .
• Such lower pressures e.g.
• pressing at 1 ton/in 2 may even give improvements (increases) in density in pressed pucks as compared to pucks that were pressed at above 10 up to about 50 ton/in 2 .
• Physical properties of articles molded from a composition prepared by a process hereof can be further improved by sintering, which may typically be performed at a temperature in the range of from about 300°C to about 450°C.
• Articles fabricated from coated particles or from a composition prepared by a process hereof exhibit lower void content over comparable polyimide compositions comprising filler particles that have not been coated with end-capped polyimide, as described for the processes hereof.
• Such articles include parts and shapes that are useful, for example, in aerospace, transportation, and materials handling and processing equipment applications.
• Articles fabricated from particles or a composition prepared by a process hereof are useful in aerospace applications such as aircraft engine parts, such as bushings (e.g. variable stator vane bushings) , bearings, washers (e.g. thrust washers), seal rings, gaskets, wear pads, splines, wear strips, bumpers, and slide blocks.
• aerospace application parts may be used in all types of aircraft engines such as reciprocating piston engines and, particularly, jet engines.
• Other examples of aerospace applications include without limitation: turbochargers; shrouds, aircraft subsystems such as thrust reversers, nacelles, flaps systems and valves, and aircraft fasteners; airplane spline couplings used to drive generators, hydraulic pumps, and other equipment; tube clamps for an aircraft engine to attach hydraulic, hot air, and/or electrical lines on the engine housing; control linkage
• Such articles are also useful in transportation applications, for example, as components in vehicles such as but not limited to automobiles, recreational vehicles, off-road vehicles, military vehicles, commercial vehicles, farm and construction equipment and trucks.
• vehicular components include without limitation: automotive and other types of internal combustion engines; other vehicular subsystems such as exhaust gas recycle systems and clutch systems; fuel systems (e.g., bushings, seal rings, band springs, valve seats) ;pumps (e.g. vacuum pump vanes) ;
• transmission components e.g. thrust washers, valve seats, and seal rings such as seal rings in a continuously variable transmission
• transaxle components e.g. thrust washers, valve seats, and seal rings such as seal rings in a continuously variable transmission
• transaxle components drive- train components, non-aircraft jet engines
• engine belt tensioners e.g. rubbing blocks in ignition distributors
• powertrain applications e.g. emission components, variable valve systems, turbochargers (e.g. ball bearing retainers, wastegate bushings), air induction modules
• driveline applications e.g.
• seal rings, thrust washers and fork pads in manual and dual clutch transmissions, transfer cases) seal rings and thrust washers for heavy- duty off-road transmissions and hydraulic motors
• bushings, buttons, and rollers for continuous variable transmissions in all-terrain vehicles ("ATVs") and snowmobiles and chain tensioners for snowmobile gear cases
• brake systems e.g. wear pads, valve components for anti-lock braking systems
• door hinge bushings gear stick rollers
• wheel disc nuts, steering systems, air conditioning systems suspension systems
• intake and exhaust systems piston rings
• shock absorbers shock absorbers.
• Such articles are also useful in material handling equipment and materials processing equipment, such as injection molding machines and extrusion equipment (e.g. 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 (e.g. valve seats, spools), gas compressors (e.g. piston rings, poppets, valve plates, labyrinth seals), hydraulic turbines, metering devices, electric motors (e.g. bushings, washers, thrust plugs), small-motor bushings and bearings for handheld tools appliance motors and fans, torch insulators, and other applications where low wear is desirable.
• injection molding machines and extrusion equipment e.g. insulators, seals, bushings and bearings for plastic injection molding and extrusion equipment
• Such articles are also useful in the manufacture of beverage cans, for example, bushings in body makers that form the can shape, 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 in textile machinery (e.g. bushings for weaving machines, ball cups for knitting looms, wear strips for textile finishing machines).
• a part or other article prepared from a composition hereof is in contact with metal at least part of the time when the apparatus in which it resides is assembled and in normal use.
• compositions hereof may be seen from an example (Example l), as described below.
• Example l The embodiments of these compositions on which the examples are based are representative only, and the selection of those embodiments to illustrate the invention does not indicate that materials, components, reactants, ingredients, formulations or specifications not described in these examples are not suitable for practicing the inventions herein, or that subject matter not described in these examples is excluded from the scope of the appended claims and equivalents thereof.
• the significance of the examples is better understood by comparing the results obtained therefrom with the results obtained from certain trial runs that are designed to serve as control experiments (Controls A ⁇ C).
• BPDA 3,3',4,4'-biphenyltetracarboxylic anhydride
• Cm centimeter(s)
• Comp is defined as comparative
• ESA Electron Spectroscopy for Chemical Analysis
• eV electron volt(s)
• Ex is defined as example(s)
• FSSG is defined as free sintered specific gravity
• ft is defined as foot or feet
• g is defined as gram(s)
• h is defined as hour(s)
• IEP is defined as isoelectric point
• in is defined as inch
• L is defined as liter(s)
• m is defined as meter(s)
• MmL is defined as milliliter(s)
• mm is defined as millimeter(s)
• MPa is defined as megapascal(s)
• MPD is defined as m-phenylenediamine
• NMP megapascal
• Dried polyimide resin was fabricated into tensile bars by direct forming according to ASTM E8 (2006), "Standard Tension Test Specimen for Powdered Metal Products-Flat Unmachined Tensile Test Bar", at room temperature and 50 ton/in 2 (100,000 psi, 690 MPa) forming pressure.
• the tensile bars were sintered at 405°C for 3 hours with a nitrogen purge.
• X-ray tomography was used to examine pressed solid pucks for the presence of voids and agglomerates. To prepare a puck for X-ray
• the polyimide coating was characterized using several surface analytical techniques: IEP determination (here, the isoelectric point is the pH at which a particular surface carries no net electrical charge), Electron Spectroscopy for Chemical Analysis (ESCA), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), optical microscopy, and transmission electron microscopy (TEM). .
• IEP determination here, the isoelectric point is the pH at which a particular surface carries no net electrical charge
• ESA Electron Spectroscopy for Chemical Analysis
• ToF-SIMS Time-of-Flight Secondary Ion Mass Spectrometry
• TEM transmission electron microscopy
• 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 3-neck flask equipped with a condenser, overhead stirrer, thermocouple, and nitrogen purge. 5.13 g of PPD and 2.20 g of MPD were added to the vessel with 225 mL of NMP. Contents were stirred and heated to 55°C using an oil bath and heating mantle.
• To prepare polymer with 15 % PEPA end-caps 16.91 g (0.0575 moles) of BPDA and 5.03 g (0.0203 moles) of 4-PEPA were added with 25 mL of NMP. The temperature was then increased to 70 °C and held at 70 °C for 2 h.
• This preparation describes the preparation of graphite coated with
• the coating was carried out in a 1 L 3-neck 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 1. 1.95 g of the end-capped PAA, in NMP (10 % solids loading), and 50 mL NM P were added to flask. 50 grams of graphite was then added slowly to the flask while stirring at 150 rpm. 70 mL pyridine was added to the flask to fully wet the graphite and prevent its agglomeration. The flask contents were stirred and heated to i6o°C for 4 h using an oil bath and heating mantle.
• the specific surface area and the particle size distribution of the coated graphite so prepared were comparable to uncoated graphite, implying a uniform encapsulation with little particle agglomeration.
• the surface area of the coated graphite was 14 m 2 /g while the uncoated graphite has a surface area of 11.3 m 2 /g as measured by BET.
• the IEP of the coated graphite was pH 2.6, while lab- prepared neat polyimide has an IEP of pH 2-3 and the uncoated graphite has an IEP of pH 4.3.
• the imide coating on the graphite surface was also confirmed by ESCA and ToF-SIMS.
• the percentage of C, O, and N as measured by ESCA is in Table 1 below.
• the existence of the ⁇ * transition indicated the presence of conjugated carbon functional group.
• the coated graphite was also examined by optical microscopy and TEM.
• Optical microscopy revealed almost no particle agglomeration, a thin coating of polyimide encapsulating the graphite, and some free polyimide granules.
• the TEM revealed an interpenetrated graphite/polyimide composite at the coating layer where the graphite is separated into basic structural units encased by polymer.
• This preparation describes the preparation of graphite coated with unfunctionalized PAA by use of a spray drying technique, which results in agglomerated particles.
• PAA-coated graphite particles were produced by spray drying graphite suspended in a solution of PAA in N- methyl pyrrolidinone (NMP).
• NMP N- methyl pyrrolidinone
• the graphite was the same type used in Preparation 2, and the PAA was prepared from BPDA, PPD, and MPD as in Preparation 1, but without end-capping.
• the compositions of the suspensions are given in Table 2.
• Spray drying was done in a 3 ft diameter, 15 ft 3 volume, pilot spray dryer. The dryer was supplied with drying nitrogen heated to i75°C.
• a peristaltic pump was used to meter feed solutions to the spray-drying nozzle.
• a Spraying Systems SU4 dual fluid nozzle supplied with 40 psig (0.28 MPa) N 2 was used to spray slurries into the volume of the dryer.
• PSD was determined in heptane and results are presented in the following Table 2.
• the value [d(9o)/d(io)] '56 ⁇ is an indicator of the breadth of the particle size distribution.
• Samples were also characterized by optical microscopy. The samples from each of the three runs handled well in terms of particle flow. However, there was significant agglomeration of the graphite particles, with agglomerates often hundreds of micrometers across. Also, for Run 1 samples, it was unclear whether a coating had even formed.
• Example 1 and Controls A ⁇ C demonstrate the density improvement in polyimide resin pucks when such pucks are pressed at low tonnage and the resin contains graphite coated with PEPA-end-capped polyimide.
• a polyimide resin was prepared using the coated graphite prepared in
• Preparation 2 and polyamic acid (PAA) prepared from BPDA, PPD, and
• Example 1 (4.8% voids) which is typical of laboratory prepared polyimide prepared from BPDA, PPD, and MPD as disclosed in U.S. Patent No. 5,886,129 (which is by this reference incorporated in its entirety as a part hereof for all purposes), and containing 50 wt% uncoated graphite.
• Example 1 when pucks were formed by pressing at low tonnage (1 ton/ in 2 , 2000 psi), designated Example 1, there was a dramatic improvement in density with the PEPA end-capped coating.
• the Example 1 pucks had a density of 1.7245 g/cm 3 which is 98% of the theoretical density.
• range includes the endpoints thereof and all the individual integers and fractions within the range, and also includes each of the narrower ranges therein formed by all the various possible combinations of those endpoints and internal integers and fractions to form subgroups of the larger group of values within the stated range to the same extent as if each of those narrower ranges was explicitly recited.
• range of numerical values is stated herein as being greater than a stated value, the range is nevertheless finite and is bounded on its upper end by a value that is operable within the context of the invention as described herein.
• range of numerical values is stated herein as being less than a stated value, the range is nevertheless bounded on its lower end by a non-zero value.

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