Tribological polymer compositions

Abstract

A resin composition [composition (C)] suitable for use in the preparation of molded articles subject to friction and wear, the composition comprising : - 65.0 to 98.0 wt% of an aromatic poly(amide-imide) [polymer (PAI)], based on the total weight of composition (C); - 0.1 to 5.0 wt% of a ultra-high molecular weight silicone polymer [polymer (UHMW SIL)]; based on the total weight of composition (C); - 0.0 to 30.0 wt% of a graphite, based on the total weight of composition (C); - 0.0 to 30.0 wt% of at least one filler selected from the group consisting of TiO2, ZrO2, SiO2, reinforcing fibers or mixtures thereof, based on the total weight of composition (C).

Description

SSPU 2024 / 043- 1 -Tribological polymer compositionsReference To Related ApplicationsThis application claims priority from US patent application Nr 63 / 725343 filed on 2024-11-26, the whole content of this application being incorporated herein by reference for all purposes.Technical Field

[0001] The present invention relates to an aromatic polyimide polymer, in particular an aromatic polyamide-imide polymer composition having a good balance of processability and tribological properties, to a process for its manufacture and to its use for the manufacture of tribological articles.Background Art

[0002] Thermoplastics are increasingly displacing metals in many tribological materials such as radial and axial bearings, engines, gears, and seal rings. These tribological materials are used in many automotive and industrial applications which require materials having the strength and wear resistance found in lubricated metals. Internally lubricated polymers are replacing metals in these applications because of their ease of fabrication, higher performance, lower or little dependence on external lubrication, and lower overall cost.

[0003] Considerable effort has already been directed towards developing improved tribological materials.

[0004] It is known that a variety of materials may be added to polymeric matrix materials to provide or enhance their tribological properties. However, the selection of additives to improve tribological properties has been and continues to be difficult, as an additive that provides or enhances one desirable tribological property such as wear or coefficient of friction (COF) reduction, may degrade another desirable characteristic, such as render the processing by extrusion of the polymeric material difficult.

[0005] For example, polyimides have been compounded with a variety of lubricants including graphite, molybdenum sulfide, bismuth nitride and others to improve wear resistance under severe conditions. Compositions comprising polyimides and graphite, together with fluoropolymers, haveSSPU 2024 / 043- 2 - found wide acceptance for use in a variety of applications requiring good friction and wear properties.

[0006] A key driver for this type of materials exploration is supply chain. With ongoing evolution of regulatory restrictions on fluorinated materials, continuity of supply, even for application spaces not subject to such restrictions, is a concern. There is thus a continuous need for new polymeric compositions based on new combinations of polymeric matrix materials and additives having good tribological properties over a wide range of operating conditions while retaining the processing ability of the polymeric matrix material.Summary of invention

[0007] The present invention relates to a composition [composition (C)] comprising:65.0 to 98.0 wt% of an aromatic poly(amide-imide) [polymer (PAI)], based on the total weight of composition (C);0.1 to 5.0 wt% of an ultra-high molecular weight silicone polymer [polymer (IIHMW SIL)]; based on the total weight of composition (C);0.0 to 30.0 % wt% of a graphite, based on the total weight of composition (C) ;0.0 to 30.0 wt% of at least one filler selected from the group consisting of TiO2, ZrO2 SiC>2, reinforcing fibers or mixtures thereof, based on the total weight of composition (C).

[0008] Another specific object of the present invention is an article comprising composition (C).

[0009] The Applicant has found that certain amounts of ultra-high molecular weight silicone polymer provide compositions having good tribological properties and which are easy to process by extrusion. In particular, the inventive composition (C) exhibits good mechanical properties such as high tensile modulus.Description of Invention

[0010] For the purposes of the present description:- the use of parentheses before and after symbols or numbers identifyingSSPU 2024 / 043- 3 - compounds, chemical formulae or parts of formulae has the mere purpose of better distinguishing those symbols or numbers from the rest of the text and hence said parentheses can also be omitted;- the expression “comprising” should be understood as meaning “comprising at least one”;- the expression “a” or “an” should be understood as meaning “at least one”;- the expression such as “Object P comprises at least the elements p1 , p2... pi” should also be understood as encompassing explicitly the embodiment wherein Object P consists essentially of the elements p1 , p2 ... pi;-“essentially” in this context means that some impurities, undesired species, unintentional compounds or the like could be present in Object P without impacting its targeted function and effect in the framework of the present invention;-the expression “comprised between ... and ...” or “from... to...” and the like should be understood as including the limits;- the adjective “aromatic” denotes any mono- or polynuclear cyclic group (or moiety) having a number of IT electrons equal to 4n+2, where n is 1 or any positive integer.

[0011] For the purpose of the present invention, “aromatic polyamide-imide polymer [polymer (PAI)]” is intended to denote any polymer comprising more than 50 mol% of recurring units comprising at least one aromatic ring, at least one imide group, as such or in its amic acid form, and at least one amide group which is not included in the amic acid form of an imide group [recurring units (RPAI)].

[0012] The recurring units (RPAI) are advantageously chosen among those of formula:SSPU 2024 / 043- 4 -kpAi'b kpAI-a(amic acid form)(imide form) wherein :Ar is a trivalent aromatic group. Preferably Ar is selected from the group consisting of following structures:and corresponding optionally substituted structures, with X being -O-, - C(O)-, -CH2-, -C(CH3)2-, -C(CF3)2-, -(CF2)q-, with q being an integer from 1 to 5 ;R is a divalent aromatic group. Preferably, R is selected from the group consisting of following structures:and corresponding optionally substituted structures, with Y being -O-, -S-, -SO2-, -CH2-, -C(O)-, -C(CH3)2-, -C(CF3)2-, -(CF2)q, q being an integer from 1 to 5.

[0013] Preferably, the aromatic polyamide-imide comprises more than 50 mol% of recurring units (RPAI) comprising an imide group in which the imide groupSSPU 2024 / 043- 5 - is present as such, like in recurring units (RpAi-a), and / or in its amic acid form, like in recurring units (RpAi-b).

[0014] Recurring units (RPAI) are preferably chosen from recurring units (I), (m) and (n), in their amide-imide (a) or amide-amic acid (b) forms :wherein the attachment of the two amide groups to the aromatic ring as shown in (l-b) will be understood to represent the 1 ,3 and the 1 ,4 polyamide-amic acid configurations;wherein the attachment of the two amide groups to the aromatic ring as shown in (m-b) will be understood to represent the 1 ,3 and the 1 ,4 polyamide-amic acid configurations; and(n)n-b(amide-imide form) . . .f.(amide-amic acid form) wherein the attachment of the two amide groups to the aromatic ring as shown in (n-b) will be understood to represent the 1 ,3 and the 1 ,4 polyamide-amic acid configurations.SSPU 2024 / 043- 6 -

[0015] More preferably, the polymer (PAI) comprises more than 90 mol% of recurring units (RPAI). Still more preferably, it contains no recurring unit other than recurring units (RPAI). Polymers commercialized by Syensqo Specialty Polymers USA, L.L.C, as TORLON® polyamide-imides comply with this criterion.

[0016] In polymer (PAI) typically 90% or more, even 92% to 95% of the amic acid groups are imidized.

[0017] Polymer (PAI) may conveniently have an intrinsic viscosity (measured at 25°C using NMP as solvent and 0.5 wt% polymer concentration) of 0.45 to 0.95 dL / g).

[0018] The total weight of polymer (PAI), based on the total weight of composition (C), is at least 65.0 wt%, at least 67.5 wt%, preferably at least 68.0 wt%.

[0019] The weight of polymer (PAI), based on the total weight of composition (C), is advantageously no more than 98.0 wt%, no more than 97.5 wt%, no more than 97.0 wt%.

[0020] Composition (C) comprises 0.1 to 5.0 wt% of an ultra-high molecular weight silicone polymer [polymer (UHMW SIL)]. Without intending to be limited by theory, it is believed that polymer (UHMW SIL) can, among other things, improve the processing of the composition, such as by providing better processing ability during extrusion and molding. Further, due to its ultra-high molecular weight, it is also believed that polymer (UHMW SIL) is less likely to migrate or diffuse to the surface of the composition, which further minimizes the likelihood of phase separation.

[0021] For the purpose of the invention, the expression ’’ultra-high molecular weight” when used to identify silicone polymers refers to polymers having a weight average molecular weight of 100,000 g / mol or more, 200,000 g / mol or more, even 500,000 g / mol or more, preferably of 800,000 g / mol or more. The weight average molecular weight is up to 2,500,000 g / mol. The molecular weight is conveniently from 800,00 to 2,500,000 g / mol, preferably from 1 ,000,000 to 2,000,000 g / mol. The weight average molecular weight may be measured using gel permeation chromatography (GPC) analysis. Chloroform at 25 °C can be used as eluent. SuitableSSPU 2024 / 043- 7 - conditions are a flow rate of 1 mL / min using a WGE SEC / GPC chromatograph equipped with four in-line detectors (Rl, VI, UV, MALS) and two Agilent PLgel 5 pm columns. Molecular weights can be calculated by the standard calibration method using polystyrene standards as known in the art.

[0022] Polymer (LIHMW SIL) may also have a relative high kinematic viscosity, such as 100,000 centistokes (cSt) or more, 300,000 cSt or more, or even 1 x 106cSt or more. The kinematic viscosity may be in the range 1 x 106to 50 x 1 o6cSt, preferably from 10 x 1 o6to 50 x 1 o6cSt.

[0023] Any of a variety of ultra-high molecular weight silicone polymers may generally be employed in composition (C). Polymer LIHMW SIL a macromolecular polymer formed primarily from R3SiOi / 2 and SiO4 / 2 units, wherein R is a functional or nonfunctional organic group. Suitable organofunctional groups ("R") may include, for instance, alkyl (e.g. , methyl, ethyl, propyl, butyl, etc.), aryl (e.g., phenyl), cycloalkyl (e.g., cyclopentyl), arylenyl, alkenyl, cycloalkenyl (e.g. , cyclohexenyl), alkoxy groups (e.g., methoxy), etc., as well as combinations thereof. These polymers are also known as "MQ" resin, in which M identifies the units RsSiOi / 2 and Q the SiO4 / 2 units. Such resins are generally prepared by chemically linking MQ resin molecules having a low weight average molecular weight (such as less than 100,000 g / mol) with polysiloxane linkers.

[0024] Polymer (UHMW SIL) is at least 0.1 wt.%, at least 0.2 wt%, preferably at least 0.5 wt% with respect to the total weight of composition (C). The amount of polymer (UHMW SIL) does not exceed 5.0 wt%, generally it does not exceed 3.0 wt%, preferably does not exceed 2.5 wt%, it does not exceed 2.0 wt%, and even more preferably it does not exceed 1 .5 wt% of the weight of polymer composition (C).

[0025] Polymer (UHMW SIL) may be provided in the form of a masterbatch that includes a carrier resin. Polymer (UHMW SIL) may constitute 30.0 wt% to 70.0 wt% of the masterbatch, typically 40.0 wt% to 60.0 wt% of theSSPU 2024 / 043- 8 - masterbatch. Any of a variety of carrier resins may be employed, such as polyolefins (ethylene polymer, propylene polymers, etc.), polyamides, etc.

[0026] Advantageously the carrier resin is a polyamide, more advantageously polyamide PA6.

[0027] When polymer (IIHMW SIL) is in the form of a masterbatch composition (C) will comprise no more than 5.0 wt%, typically no more than 4.0 wt%, preferably no more than 3.5 wt% of the weight of polymer composition (C) of the carrier resin.

[0028] Some non-limiting examples of ultra-high molecular weight silicone polymer masterbatches that may be employed include, for instance, those available from Polymer Dynamix under the trade designation EverGlide®, specifically EverGlide® MB 1950.

[0029] Composition (C) may further comprise a graphite filler. Such graphite may be either natural or synthetic. Intercalated graphite, which has been modified by exchanging ions between laminas or by inserting organic matters, may also be used within the context of the present invention.

[0030] Graphite suitable for use in composition (C) is generally spherical or flaky. The graphite is preferably present in the form of fine particles. The graphite fine particles have advantageously a particle diameter of 250 pm or less, advantageously an average particle diameter of 40 to 50 pm.

[0031] The weight percent of graphite in polymer composition (C), when graphite is present, is generally at least 1 .0 wt%, preferably at least 5.0 wt%, based on the total weight of composition (C).The weight percent of the graphite is generally at most 30.0 wt%, preferably at most 25.0 wt%, more preferably at most 22.5 wt%, based on the total weight of composition (C).

[0032] Excellent results were obtained when graphite was used in an amount of 8.0 wt% to 22.5 wt% weight percent, based on the total weight of composition (C).

[0033] Composition (C) may optionally comprise a filler selected from the group consisting of TiO2, ZrO2 and SiO2, reinforcing fibers or mixtures thereof.

[0034] The term “filler” may include surface treated, non-treated and core / shell structured fillers or a mixture thereof. The term “surface treated filler”SSPU 2024 / 043- 9 - intends to denote fillers obtained by heat treatment, chemical treatment by using for example silanes or phosphonate or plasma treatment of the surface of said filler. The term “core / shell structured filler” is intended to include fillers which are composed of a core selected from the group of consisting of TiO2, ZrO2 and SiO2 or mixtures thereof, generally made up of between a few hundred and a few thousand atoms and surrounded by an organic outer layer of ionic or non-ionic surfactant molecules, such as notably silanes e.g. amino functionalized silanes or surrounded by an additional inorganic outer layer including notably metal oxide compounds.

[0035] Among inorganic oxide fillers, TiO2 is preferred. Surface treated TiO2 is more preferred.

[0036] Inorganic oxide fillers selected from the group of consisting of TiO2, ZrO2 and SiO2 are preferably present in the form of fine particles with a D50 particle size value of at least 100 nm, more preferably at least 200 nm and at most 500 nm, preferably of at most 450 nm. The filler can advantageously be TiO2 with a D50 particle size value from 400 to 500 nm. The D50 value of the particle size of the filler is measured via light scattering techniques (dynamic or laser) using the respective equipment coming for example from the company Malvern (Mastersizer Micro or 3000) or using screen analysis according to DIN 53196.

[0037] The filler may be selected among reinforcing fibers. Notable examples of suitable reinforcing fibers include glass fibers, carbon fibers, boron fibers, metal fibers, ceramic fibers, talc-glass fibers, calcium silicate fibers like wollastonite micro-fibers, silicon carbide fibers, metal borides fibers and mixtures thereof. Carbon fibers and glass fibers are preferred.

[0038] When composition (C) comprises a filler, the filler is generally present in an amount of at most 30.0 wt%, preferably at most 25.0 wt%, more preferably at most 15.0 wt% based on the weight of composition (C). Composition (C) may comprise the filler in an amount of at least 0.5 wt%, even at least 1 .0 wt%, based on the weight of composition (C). One or more fillers of different types selected from the list provided above may be present in composition (C) in a combined weight of at most 30.0 wt%.SSPU 2024 / 043- 10 -

[0039] The composition (C) of the present invention can further comprise at least one additive (AD) selected from those known in the art to further improve tribological properties, thermal conductivity, creep strength and fracture resistance, high temperature dimensional stability, or fatigue resistance of composition (C).

[0040] Composition (C) may comprise:68.0 to 90.0 wt% of polymer (PAI), based on the total weight of composition (C) ;0.1 to 1 .0 wt% of polymer (LIHMW SIL); based on the total weight of composition (C);5.0 to 22.5 % wt% of a graphite, based on the total weight of composition (C) ;0.0 to 15.0 wt% of at least one filler selected from the group consisting of TiO2, ZrO2 SiO2 or mixtures thereof, based on the total weight of composition (C).

[0041] Another advantageous composition (C) comprises:90.0 to 97.5 wt% of polymer (PAI), based on the total weight of composition (C) ;0.1 to 1 .0 wt% of polymer (LIHMW SIL); based on the total weight of composition (C);0.0 to 30.0 % wt% of a graphite, based on the total weight of composition (C) ;0.5 to 5.0 wt% of at least one filler selected from the group consisting of TiO2, ZrO2 SiO2 or mixtures thereof, based on the total weight of composition (C).

[0042] Still another advantageous composition (C) comprises:65.0 to 68.5 wt% of polymer (PAI), based on the total weight of composition (C);0.1 to 1 .0 wt% of polymer (UHMW SIL); based on the total weight of composition (C);0.0 to 10.0 % wt% of a graphite, based on the total weight of composition (C);SSPU 2024 / 043- 11 -10.0 to 30.0 wt% of at least one filler selected from the group consisting of reinforcing fibers, preferably glass or carbon fibers, based on the total weight of composition (C).

[0043] Another aspect of the present invention concerns a process for manufacturing the polymer composition (C) as above described, which comprises mixing :65.0 to 98.0 wt% of an aromatic poly(amide-imide) [polymer (PAI)], based on the total weight of composition (C);0.1 to 5.0 wt% of a ultra-high molecular weight silicone polymer (IIHMW SIL); based on the total weight of composition (C);0.0 to 30.0 % wt% of a graphite, based on the total weight of composition (C); and0.0 to 30.0 wt% of at least one filler selected from the group consisting of TiO2, ZrO2, SiO2 or mixtures thereof, based on the total weight of composition (C).

[0044] Advantageously, the process comprises mixing by dry blending and / or melt compounding polymer (PAI), polymer (IIHMW SIL), optionally graphite and / or optionally a filler selected from TiO2, ZrO2, SiO2 and reinforcing fibers, as well as any further optional additive.

[0045] Preferably, mixing is by melt compounding. Examples of suitable devices to melt compound the polymer composition of the invention are screw extruders. Thus, polymer (PAI), polymer (UHMW SIL), optionally graphite and / or optionally a filler selected from TiO2, ZrO2, SiC>2, reinforcing fibers as well as any further optional additive, are advantageously fed in powder or granular form in an extruder and the composition is extruded into strands and the strands are chopped into pellets. Alternatively, extrudate may be cut at the die face, using a rotating blade, into pellets.

[0046] In a most preferred embodiment, polymer (PAI), polymer (UHMW SIL), optionally graphite and / or optionally a filler selected from TiO2, ZrO2, SiC>2, reinforcing fibers, as well as any further optional additive as detailed above are melt compounded in a twin-screw extruder.SSPU 2024 / 043- 12 -

[0047] The composition (C) can be further processed following standard methods for injection moulding, extrusion, blow moulding, foam processing, compression molding, casting, coating and the like. Finished articles comprising the composition (C) as described above can undergo postfabrication operations such as post-curing.

[0048] Another object of the invention is an article comprising the composition (C) as described above.

[0049] The total weight of the composition (C), based on the total weight of the article, is advantageously above 50 wt%, preferably above 80 wt%; more preferably above 90 wt%; more preferably above 95 wt% and more preferably above 99 wt%. If desired, the article may consist of the composition (C).

[0050] Advantageously, the article is an injection moulded article, an extrusion moulded article, a shaped article, a coated article or a casted article.

[0051] Non limiting examples of articles include bearing articles such as radial and axial bearings for auto transmission, bearings used in dampers, shock absorbers, bearings in any kind of pumps, e.g. acid pumps, or hydraulically actuated seal rings for clutch components.

[0052] In a particular embodiment, the article is a bearing article. For the purpose of the present invention, the term “bearing article” refers to articles with a bearing surface that are subjected to relatively high loads, relatively high speeds, or both. “Bearing articles” and “bearings,” as used herein, refers to any article(s) having a surface that interacts with a surface in relative motion, for example, by sliding, pivoting, oscillating, reciprocating, rotating, or the like. Examples of such articles include, but are not limited to, thrust bearings, sleeve bearings, journal bearings, thrust washers, rub strips, bearing pads, needle bearings, ball bearings, including the balls, valve seats, piston rings, valve guides, compressor vanes, and seals, under dynamic conditions.

[0053] The bearing article can consist of several parts, wherein at least one of said parts, and possibly all of them, consist of the composition (C). When at least one part of a multi-part bearing article consists of a material otherSSPU 2024 / 043- 13 - than the polymer composition (e.g. metal or steel) [hereinafter, the other part], the weight of said other part, based on the weight of the bearing article, is usually less than 90 wt%, and is often less than 50 wt%, or even less than 10 wt%. In accordance with the present invention, a certain preferred bearing article is a single part consisting of the composition (C). Another preferred bearing article consists of several parts consisting of the composition (C).

[0054] All definitions and preferences provided in respect of the inventive composition (C) apply to the process for preparing the composition (C), to the process for preparing an article comprising the composition (C) as well as to the article itself.

[0055] The Applicant has found that the composition (C) of the present invention is effective in providing articles having good mechanical properties and ease of extrusion molding.

[0056] Further object of the present invention is the use of LIHMW SIL to improve processing ability or to lubricate compositions comprising a polymer (PAI), optionally a graphite and / or at least one filler selected from the group consisting of TiO2, ZrO2 SiC>2, reinforcing fibers; in particular compositions comprising 65.0 to 98.0 wt% of polymer (PAI); 0.0 to 30.0 wt% of a graphite; and 0.0 to 30.0 wt% of at least one filler selected from the group consisting of TiO2, ZrO2 SiC>2, reinforcing fibers or mixtures thereof, based on the total weight of composition (C). LIHMW SIL is used in an amount of 0.1 to 5.0 wt% based on the total weight of composition (C).

[0057] Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

[0058] The invention will now be described in more details with reference to the following examples, whose purpose is merely illustrative and not intended to limit the scope of the invention.

[0059] Raw materialsSSPU 2024 / 043- 14 -

[0060] Polymer PAI: Torlon® 4000T is an aromatic polyamide-imide polymer commercially available from Syensqo Specialty Polymers USA, LLC.

[0061] TiO2 : Obtained as Ti-Pure™ R-900, median particle size of 410 nm.

[0062] PTFE : Polytetrafluoroethylene powdered resin, obtained as Algoflon® L203 R PTFE micronized powder from Syensqo Specialty Polymers Italy SpA, average particle size is 5.0 pm.

[0063] UHMW SIL: EverGlide® MB1950 silicone masterbatch in PA6 containing 50 wt% UHMW silicone, obtained from Polymer Dynamix.

[0064] Graphite : Graphite 4735 from Superior Graphite Company.

[0065] General description of the compounding process of the aromatic polyamide-imide polymer compositions

[0066] A dry blend of PAI polymer with the desired amounts of PTFE, UHMW SIL, TiO2, and / or graphite was first prepared by tumble blending. The preblended mixture was then fed into the pilot-scale twin screw extruder, using conventional processing techniques. The extrudate was cut into pellets, either via stranding or at the die face, for later evaluation via injection molding.

[0067] The thus obtained pellets of the polymer compositions were next dried for 4 hours in a desiccated air oven at 149°C and were then injection molded into ASTM D1708 microtensile and flex bars. The molded parts were thermally cured for 17 days after molding. The different polymer compositions are summarized in Table 1 . The examples were generated while holding the screw design constant, and experiments were conducted using the same pilot-scale extruder; compounding conditions were held as constant as possible, with minor variations in screw speed and feed rate from day-to-day. While holding as many factors constant as possible and changing only the formulation, it was found that compositions containing UHMW SIL behaved similarly in terms of observed torque and die pressure to the compositions containing PTFE. Furthermore, the reference compositions, which did not contain UHMW SIL or PTFE, resulted in higher torque and consequently higher die pressure compared withSSPU 2024 / 043- 15 - compositions containing LIHMW SIL or PTFE. This is indicative of lower melt viscosity and therefore the lubricating effect of the additives.Table 1

[0068] Mechanical tests were performed according to ASTM standards and carried out at ambient temperature (23 °C). Table 2 below summarizes the standard and conditions used for each test.Table 2

[0069] Mechanical properties for the different compositions are given in Table 3.Table 3SSPU 2024 / 043- 16 -

[0070] These data demonstrate that mechanical performance is maintained regardless of whether HMW SIL or PTFE are utilized. This highlights that the additives do not detract from the mechanical properties which make polymer PAI desirable in the target application space, while at the same time the additives positively impact the polymer PAI processing ability.

Claims

SSPU 2024 / 043- 17 -1. A composition [composition (C)] comprising :65.0 to 98.0 wt% of an aromatic poly(amide-imide) polymer [polymer (PAI)], based on the total weight of composition (C) ;0.1 to 5.0 wt% of an ultra-high molecular weight silicone polymer [polymer (LIHMW SIL)]; based on the total weight of composition (C);0.0 to 30.0 wt% of a graphite, based on the total weight of composition (C) ;0.0 to 30.0 wt% of at least one filler selected from the group consisting of TiO2, ZrO2 SiC>2, reinforcing fibers or mixtures thereof, based on the total weight of composition (C).

2. Composition (C) according to claim 1 which comprises:- 68.0 to 90.0 wt% of polymer (PAI);- 0.1 to 1.0 wt% of polymer (UHMW SIL);- 5.0 to 22.5 wt% of a graphite;- 0.0 to 15.0 wt% of at least one filler selected from the group consisting of TiO2, ZrO2 SiO2 or mixtures thereof.

3. Composition (C) according to claim 1 which comprises:- 90.0 to 97.5 wt% of polymer (PAI);- 0.1 to 1.0 wt% of polymer (UHMW SIL);- 0.0 to 30.0 wt% of a graphite;- 0.5 to 5.0 wt% of at least one filler selected from the group consisting of TiO2, ZrO2 SiO2 or mixtures thereof.

4. Composition (C) according to any one of claims 1 to 3, wherein the filler is TiO2.

5. Composition (C) according to claim 1 which comprises:- 65.0 to 68.5 wt% of polymer (PAI);- 0.1 to 1.0 wt% of polymer (UHMW SIL);- 0.0 to 10.0 wt% of a graphite;- 10.0 to 30.0 wt% of at least one filler selected from the group consisting of reinforcing fibers, preferably glass or carbon fibers.SSPU 2024 / 043- 18 -6. Composition (C) according to any one of claims 1 to 5 wherein [polymer (PAI)] is a polymer comprising more than 50 mol% of recurring units comprising at least one aromatic ring, at least one imide group, as such or in its amic acid form, and at least one amide group which is not included in the amic acid form of an imide group [recurring units (RPAI)], said recurring units (RPAI) being selected from the group consisting of :pAI-a(amic acid form)(imide form) wherein:Ar is a trivalent aromatic group; preferably Ar is selected from the group consisting of following structures :corresponding optionally substituted structures, with X being -O-, -C(O)-, - CH2-, -C(CF3)2-, -(CF2)q-, with q being an integer from 1 to 5 ;R is a divalent aromatic group; preferably R is selected from the group consisting of following structures:SSPU 2024 / 043- 19 -corresponding optionally substituted structures, with Y being -O-, -S-, -SO2- , -CH2-, -C(O)-, -C(CF3)2-, -(CF2)q, q being an integer from 1 to 5.

7. Composition (C) according any one of claims 1 to 6, wherein polymer (IIHMW SIL) is a silicone polymer having a weight average molecular weight from 800,00 to 2,500,000 g / mol, preferably from 1 ,000,000 to 2,000,000 g / mol, measured using gel permeation chromatography (GPC) using chloroform at 25°C as eluent and polystyrene standards.

8. A process for manufacturing polymer composition (C) according to any one of claims 1 to 7, which comprises mixing :65.0 to 98.0 wt% of an aromatic poly(amide-imide) polymer [polymer (PAI)], based on the total weight of composition (C) ;0.1 to 5.0 wt% of a ultra-high molecular weight silicone polymer [polymer (IIHMW SIL)], based on the total weight of composition (C);0.0 to 30.0 wt% of a graphite, based on the total weight of composition (C) ;0.0 to 30.0 wt% of at least one filler selected from the group consisting of TiO2, ZrO2 SiC>2, reinforcing fibers or mixtures thereof, based on the total weight of composition (C).

9. The process according to claim 8, wherein polymer (UHMW SIL) is added in the form of a masterbatch, the masterbatch comprising polymer (UHMW SIL) and a carrier resin, preferably the masterbatch comprising polymer (UHMW SIL) in an amount of 30.0 wt% to 70.0 wt% with respect to the weight of the masterbatch.SSPU 2024 / 043- 20 -10. The process of claim 8 or 9 wherein mixing is made by melt compounding.

11. An article comprising composition (C) according to any one of claims 1 to 7.

12. The article according to claim 11 which is a bearing article.

13. The article of claim 11 which is selected from the group consisting of thrust bearings, sleeve bearings, journal bearings, thrust washers, rub strips, bearing pads, needle bearings, ball bearings, including the balls, valve seats, piston rings, valve guides, compressor vanes, and seals.

14. A process for the manufacturing of an article according to claims 11 to 13 comprising injection moulding, extrusion, blow moulding, foam processing, compression molding, casting and coating of the composition (C) according to any one of claim 1 to 7.

15. Use of a ultra-high molecular weight silicone polymer [polymer (UHMW SIL)] to improve the processing ability or to lubricate a composition comprising an aromatic poly(amide-imide) polymer [polymer (PAI)].

16. Use according to claim 15 in which 0.1 to 5.0 wt% polymer (UHMW SIL) is used.

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