How to process polyimide

Abstract

1. A method of treating a polyimide, comprising the steps of: providing a polyimide to be treated; and contacting the polyimide to be treated with a fluid to obtain a treated polyimide, the polyimide comprising first repeat units derived from pyromellitic dianhydride (PMDA) and second repeat units derived from 4,4'-oxodianiline (4,4'-ODA); the fluid being a supercritical fluid, 10.0 mN m under the conditions of the contacting step. -1 Methods are disclosed that include a liquid, or mixtures thereof, having the following surface tensions: Polyimides obtainable by the methods of the invention, molded polyimide products comprising the polyimides of the invention, and articles comprising the molded polyimide products of the invention are also disclosed.

Description

[Technical field]

[0001] The present invention relates to a method for processing polyimides, polyimides obtainable by the method of the present invention, molded polyimide products comprising the polyimides of the present invention, and articles comprising the molded polyimide products of the present invention. [Background technology]

[0002] Polyimides are well known as durable, high-performance polymers that find application in areas such as aerospace, automotive, and oil and gas industries. Typical properties of polyimide materials include heat resistance, lubricity, dimensional stability, chemical resistance, and creep resistance. Such known polyimides are described, for example, in U.S. Pat. Nos. 3,249,588, 3,179,631, and 4,755,555, and have been commercially available for many years, such as DuPont's Vespel® SP product range and Saint-Gobain performance plastics' Meldin® 7000 product range, which comply with ASTM standard D6456-10 (Standard Specification for Finished Parts Made from Polyimide Resins).

[0003] Continuing engineering challenges faced in sectors such as aerospace, automotive, and heavy industry indicate that it would be desirable to provide polyimide materials with improved mechanical properties, especially at higher temperatures. From an environmental and economic standpoint, it would also be desirable to provide processes that allow for a reduction in the use of volatile organic compounds (VOCs) and also allow for the recovery and reuse of a large portion of the chemicals used in the processing of polyimide materials. Summary of the Invention

[0004] The present invention aims to provide a solution to the problems discussed above. In particular, the present invention relates to a method of treating a polyimide, comprising the steps of: preparing a polyimide to be treated; and contacting the polyimide to be treated with a fluid to obtain a treated polyimide, the polyimide comprising first repeat units derived from pyromellitic dianhydride (PMDA) and second repeat units derived from 4,4'-oxodianiline (4,4'-ODA); the fluid being a supercritical fluid, 10.0 mN m under the conditions of the contacting step. -1 The present invention provides a method for treating a polyimide comprising the steps of: mixing the treated polyimide with an additive to obtain a polyimide mixture;

[0005] The present invention also provides a method for molding the treated polyimide of the present invention or the polyimide blend of the present invention to obtain a molded polyimide article.

[0006] The present invention also provides treated polyimides, polyimide blends, and molded polyimide articles obtainable by the methods of the present invention.

[0007] The present invention also provides a 100m 2 g -1 Also provided is a polyimide having a BET specific surface area of ​​greater than 100 nm, the polyimide comprising a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA), the polyimide being free of an encapsulated filler or comprising an encapsulated filler in an amount of 20 wt % or less based on the weight of the polyimide.

[0008] The present invention also provides a 70m 2 g -1Also provided is a polyimide having a BET specific surface area of ​​greater than 100 nm, wherein the polyimide comprises a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA), and the treated polyimide comprises an encapsulated filler in an amount of 20 wt% to 60 wt% based on the weight of the polyimide.

[0009] The present invention also provides a directly cast crystalline polyimide article, the polyimide comprising first repeat units derived from pyromellitic dianhydride (PMDA) and second repeat units derived from 4,4'-oxodianiline (4,4'-ODA), the directly cast crystalline polyimide article comprising: - Contains no encapsulated fillers, contains between 0 wt% and 0.5 wt% additives based on the weight of the polyimide, and has a tensile strength of 80.0 MPa or greater; or - containing 10 wt% to 20 wt% of an encapsulated filler, based on the weight of the polyimide, containing 0 wt% to 0.5 wt% of an additive, based on the weight of the polyimide, and having a tensile strength of 63.0 MPa or greater; or - containing 20 wt% to 60 wt% of an encapsulated filler, based on the weight of the polyimide, containing 0 wt% to 2.0 wt% of an additive, based on the weight of the polyimide, and having a tensile strength of 50.0 MPa or greater; or - containing 10 wt% to 20 wt% of an encapsulated filler, based on the weight of the polyimide, containing 5 wt% to 15 wt% of an additive, based on the weight of the polyimide, and having a tensile strength of 52.5 MPa or more; or - containing 20wt%-60wt% of an encapsulated filler based on the weight of the polyimide, containing 10wt%-20wt% of an additive based on the weight of the polyimide, and having a tensile strength of 39.5MPa or more; Directly molded crystalline polyimide products are also provided.

[0010] The present invention also provides a hot isostatically pressed crystalline polyimide product, a ram extruded (optionally subsequently hot isostatically pressed) crystalline polyimide product, or a hot compression molded crystalline polyimide product, wherein the polyimide comprises a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA), and the hot isostatically pressed crystalline polyimide product, the ram extruded (optionally subsequently hot isostatically pressed) crystalline polyimide product, or the hot compression molded crystalline polyimide product is - Contains no encapsulated fillers, contains between 0 wt% and 0.5 wt% additives based on the weight of the polyimide, and has a tensile strength of 87.0 MPa or greater; or - containing 10 wt% to 20 wt% of an encapsulated filler, based on the weight of the polyimide, containing 0 wt% to 0.5 wt% of an additive, based on the weight of the polyimide, and having a tensile strength of 66.0 MPa or greater; or - containing 20 wt% to 60 wt% of an encapsulating filler, based on the weight of the polyimide, containing 0 wt% to 2.0 wt% of an additive, based on the weight of the polyimide, and having a tensile strength of 52.5 MPa or greater; or - containing 10 wt% to 20 wt% of an encapsulated filler, based on the weight of the polyimide, containing 5 wt% to 15 wt% of an additive, based on the weight of the polyimide, and having a tensile strength of 49.5 MPa or more; or - Contains no encapsulated fillers, contains 10 wt% to 20 wt% additives based on the weight of the polyimide, and has a tensile strength of 59.0 MPa or greater; or - containing 20wt%-60wt% of an encapsulated filler based on the weight of the polyimide, containing 10wt%-20wt% of an additive based on the weight of the polyimide, and having a tensile strength of 39.5MPa or more; Also provided are hot isostatically pressed, ram extruded (optionally followed by hot isostatic pressing), or hot compression molded crystalline polyimide products.

[0011] The present invention also provides articles comprising the molded polyimide products of the present invention.

[0012] The present invention provides several advantages. The method of the present invention allows for reduced use of volatile organic compounds, improved recovery of residual liquid medium from the polymerization process (e.g., greater than 90% solvent recovery), reuse of fluids after the contacting step, and convenient removal of impurities (e.g., acetic anhydride and phthalic anhydride and their acid derivatives, which may be present as residual end-capping agents from the polymerization process). The polyimides with increased SSA of the present invention have advantages in that they can be better compressed when processed into molded products under the influence of forces, resulting in higher achievable density in the parts, improved tensile strength, and improved high temperature mechanical properties. The molded polyimide products of the present invention may have better high temperature mechanical properties than VESPEL SP and Meldin 7000 grades. The present application provides crystalline molded polyimide products that may have better properties than amorphous products, for example, may absorb less water than amorphous products. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention provides a method for treating polyimide, comprising the steps of: Providing a polyimide to be treated; contacting the polyimide to be treated with a fluid to obtain a treated polyimide; Including, the polyimide comprises a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA); The fluid is a supercritical fluid, and the flow rate is 10.0 mN m -1 The method includes providing a liquid, or a mixture thereof, having the following surface tension:

[0014] The polyimide to be treated comprises a first repeat unit derived from PMDA and a second repeat unit derived from 4,4'-ODA. Polyimides comprising a first repeat unit derived from PMDA and a second repeat unit derived from 4,4'-ODA are known in the art and are described, for example, in U.S. Pat. Nos. 3,249,588 and 3,179,631.

[0015] In general, any polyimide to be treated that comprises a first repeat unit derived from PMDA and a second repeat unit derived from 4,4'-ODA is suitable for use as the polyimide to be treated in the method of the present invention.

[0016] The polyimide to be treated may have a number average molecular weight of, for example, 10 to 500 kDa, 100 to 600 kDa, 200 to 700 kDa, 300 to 800 kDa, 400 to 900 kDa, or 500 to 1000 kDa.

[0017] The polyimide to be treated may have a weight average molecular weight of, for example, 10 to 500 kDa, 100 to 600 kDa, 200 to 700 kDa, 300 to 800 kDa, 400 to 900 kDa, or 500 to 1000 kDa.

[0018] The polyimide to be treated may have a polydispersity index of, for example, 0.8 to 1.0, 0.9 to 1.1, or 1.0 to 1.2.

[0019] The relative molar amounts of PMDA and 4,4'-ODA repeat units in the polyimide to be treated are not particularly limited. Typically, the molar ratio of PMDA:4,4'-ODA is in the range of 1:1.1 to 1.1:1. Preferably, the molar ratio of PMDA:4,4'-ODA is in the range of 1:1.07 to 1.07:1. More preferably, the molar ratio of PMDA:4,4'-ODA is in the range of 1:1.05 to 1.05:1. Even more preferably, the molar ratio of PMDA:4,4'-ODA is in the range of 1:1.03 to 1.03:1. Most preferably, the molar ratio of PMDA:4,4'-ODA is in the range of 1:1.01 to 1.01:1, or about 1:1.

[0020] The polyimide to be treated may further comprise further repeat units in addition to the repeat units derived from PMDA and 4,4'-ODA. Suitable further repeat units include those derived from dianhydride monomers, such as 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3',4,4'-diphenyltetracarboxylic dianhydride, 1,2,5,6-naphthalenetetracarboxylic dianhydride, 2,2',3,3'-diphenyltetracarboxylic dianhydride, 2,2-bis-(3,4-dicarboxyphenyl)-propane dianhydride, bis-(3,4-dicarboxyphenyl)-sulfone dianhydride, bis-(3,4-dicarboxyphenyl)-ether dianhydride, 2,2-bis-(2,3 ... 1,1-bis-(2,3-dicarboxyphenyl)-propane dianhydride, 1,1-bis-(3,4-dicarboxyphenyl)-ethane dianhydride, bis-(2,3-dicarboxyphenyl)-methane dianhydride, bis-(3,4-dicarboxyphenyl)-methane dianhydride, 3,4,3',4'-benzophenone tetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride (BTDA), or diphenyl tetracarboxylic dianhydride (BPDA), or mixtures thereof. Suitable additional repeat units include those derived from 4,4'-diaminodiphenylpropane, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylamine, benzidine, 4,4'-diaminodiphenyl sulfide, 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl ether, bis-(4-aminophenyl)diethylsilane, bis-(4-aminophenyl)-phenylphosphine oxide, bis-(4-aminophenyl)-N-methylamine, 1,5-diaminonaphthalene, 3,3'-dimethyl-4,4'-diaminobiphenyl, 3,3'-dimethoxybenzidine, 1,4-bis-(p-aminophenoxy)-benzene, 1,3-bis-(p-aminophenoxy)-benzene, m-phenylenediamine (MPD), p-phenylenediamine (PPD), or any mixture thereof.

[0021] The polyimide to be treated preferably does not contain any further repeating units in addition to the repeating units derived from PMDA and 4,4'-ODA.Therefore, the polyimide to be treated preferably is a copolymer of PMDA and 4,4'-ODA.The term poly(PMDA-co-4,4'-ODA) used herein refers to the copolymer of PMDA and 4,4'-ODA that does not contain any further repeating units in addition to the repeating units derived from PMDA and 4,4'-ODA.

[0022] The polyimide to be treated may include end-capping units, such as units derived from phthalic anhydride or acetic anhydride, preferably acetic anhydride. Such end-capping units are not additional repeat units.

[0023] The polyimide to be treated is typically not a gel. The polyimide to be treated is typically not an aerogel.

[0024] The polyimide to be treated is typically in powder form, the term powder as used herein refers to any form in which the polyimide exists as a plurality of particles, including, for example, dry powders as well as wet agglomerates comprising the polyimide to be treated.

[0025] As used herein, a wet aggregate comprising a polyimide to be treated typically comprises the polyimide to be treated and a liquid medium, which may include liquids used in the preparation of the polyimide to be treated (e.g., liquids used in the preparation methods disclosed in U.S. Pat. Nos. 3,249,588, 3,179,631, and / or 4,755,555, or any combination of such liquid(s)), such as solvents, washing liquids, virgin chemicals including, for example, monomers and end-capping agents, and the like.

[0026] When in powder form, the polyimide to be treated typically has a particle size characterized by a volume median diameter (Dv50) of 10 to 80 μm. Preferably, the particle size may be characterized by a Dv50 of 20 to 70 μm. More preferably, the particle size may be characterized by a Dv50 of 25 to 60 μm. As described elsewhere herein, the polyimide to be treated may include an encapsulated filler. The above typical, preferred, more preferred, even more preferred, and most preferred particle sizes apply to embodiments in which the polyimide to be treated includes an encapsulated filler, and to embodiments in which the polyimide to be treated does not include an encapsulated filler. The Dv50 values ​​referred to herein are typically measured by laser diffraction in deionized water in accordance with ISO13320:2009.

[0027] The polyimide to be treated may include an encapsulated filler. In embodiments in which the polyimide to be treated includes an encapsulated filler, the encapsulated filler is typically graphite.

[0028] The filler particles encapsulated within the polyimide to be treated typically have a Dv90 of 2.0 to 10.0 μm, preferably 3 to 9 μm, more preferably 4.0 to 8.0 μm, and most preferably 5.0 to 7.0 μm.

[0029] The amount of encapsulated filler present in the polyimide to be treated is typically 5 to 60 wt %, for example 10 to 20 wt % or 35 to 45 wt %, preferably 12 to 18 wt % or 37 to 43 wt %, more preferably 14 to 16 wt % or 39 to 41 wt %, and most preferably about 15 wt % or about 40 wt %, based on the weight of the polyimide to be treated.

[0030] The polyimides to be treated can be prepared by methods known in the art, such as those described in U.S. Pat. Nos. 3,249,588, 3,179,631, and 4,755,555, or by methods analogous to such known methods.

[0031] As used herein, the contacting step refers to the step of the method of the present invention in which the polyimide to be treated is contacted with a fluid to obtain a treated polyimide. The term "contacting step conditions" typically refers to the temperature and pressure under which the polyimide to be treated is contacted with the fluid.

[0032] The contacting step may be carried out subsequent to the preparation of the polyimide to be treated. Known preparation methods (e.g., those disclosed in U.S. Pat. Nos. 3,249,588, 3,179,631, and / or 4,755,555) typically include a step of precipitating the polyimide. Following the step of precipitating the polyimide, known precipitating methods typically include a step of washing the polyimide, a step of drying the polyimide under vacuum, and / or a step of heating the polyimide (e.g., to a temperature above 160° C.). At the time of carrying out the contacting step in the method of the present invention, the polyimide to be treated has typically not been subjected to a step of drying the polyimide under vacuum and / or a step of heating the polyimide (e.g., to a temperature above 160° C.) for a time sufficient to remove substantially all liquid medium from the polyimide to be treated. In this context, liquid medium refers to liquids used in the preparation of the polyimide to be treated (e.g., liquids used in the preparation methods disclosed in U.S. Pat. Nos. 3,249,588, 3,179,631, and / or 4,755,555, or any combination of such liquid(s)), such as solvents, cleaning solutions, unused chemicals (including, for example, monomers and end-capping agents), etc. Removal of substantially all liquid medium in this context refers to removing liquid medium to the extent that said liquid medium is present in an amount of 25.0 wt % or less, 15.0 wt % or less, 10.0 wt % or less, 5.0 wt % or less, such as 2.5 wt % or less, 1 wt % or less, 0.8 wt % or less, 0.6 wt % or less, 0.4 wt % or less, 0.2 wt % or less, or 0.1 wt % or less based on the weight of the polyimide to be treated.

[0033] The contacting step may be performed substantially immediately after the polyimide to be treated is prepared, or the contacting step may be performed at an interval after the polyimide to be treated is prepared. In this context, reference to the prepared polyimide may refer to the time when the deposition step is completed, the time when the washing step is completed, or the time when the step of drying the polyimide (e.g., under vacuum conditions) is completed. In embodiments in which the contacting step is performed at an interval after the polyimide to be treated is prepared, the interval may be, for example, 1 year or less, 6 months or less, 4 months or less, 2 months or less, 1 month or less, 2 weeks or less, 1 week or less, 72 hours or less, 48 ​​hours or less, 24 hours or less, 12 hours or less, 6 hours or less, 4 hours or less, 3 hours or less, 2 hours or less, 1 hour or less, 45 minutes or less, 30 minutes or less, 20 minutes or less, 10 minutes or less, or 5 minutes or less. The polyimide to be treated may be in the form of a wet aggregate as described herein for the duration of the interval.

[0034] The contacting step may be carried out under any suitable conditions, provided that the fluid contacted with the polyimide to be treated is a supercritical fluid and / or a fluid having a desired low surface tension (e.g., 10.0 mNm -1 As described below or elsewhere herein, this is intended to include liquids having a pH of 10 or higher. One of ordinary skill in the art will be able to determine the appropriate conditions for any particular fluid.

[0035] The contacting step may for example be carried out at a pressure of from 5 to 500 bar, typically from 25 to 400 bar, preferably from 50 to 300 bar, more preferably from 100 to 200 bar, even more preferably from 140 to 160 bar, or most preferably at about 150 bar.

[0036] The contacting step may be carried out at a temperature of, for example, 20 to 200°C, typically 40 to 150°C, preferably 60 to 100°C, more preferably 70 to 90°C, even more preferably 75 to 85°C, and most preferably about 80°C.

[0037] The duration of the contacting step is not particularly limited. Those skilled in the art can easily select a suitable duration, for example, based on the batch size. The duration of the contacting step can be, for example, 1 minute or more, 5 minutes or more, 10 minutes or more, 20 minutes or more, 30 minutes or more, 45 minutes or more, 1 hour or more, 2 hours or more, 3 hours or more, 4 hours or more, or 5 hours or more. The duration of the contacting step can be, for example, 24 hours or less, 12 hours or less, 6 hours or less, 4 hours or less, 3 hours or less, 2 hours or less, 1 hour or less, 45 minutes or less, 30 minutes or less, 20 minutes or less, 10 minutes or less, or 5 minutes or less. The duration can be within a range between any applicable combination of the upper and lower limits above.

[0038] The contacting step may include flowing the fluid over the polyimide to be treated. The contacting step may include immersing the polyimide to be treated in the fluid.

[0039] In embodiments where a fluid is flowed over the polyimide to be treated, the duration may be determined by a combination of the flow rate of the fluid and the desired amount of fluid to be contacted with the polyimide to be treated. In embodiments where the polyimide to be treated is present in an aggregate comprising polyimide particles and a liquid medium, the desired amount of fluid is typically determined based on the combined mass of the polyimide particles and the liquid medium. For example, the ratio of the mass of the fluid to be contacted with the polyimide to be treated to the combined mass of the polyimide particles and the liquid medium may typically range from 1:1 to 25:1, preferably 2:1 to 20:1, more preferably 4:1 to 15:1, even more preferably 6:1 to 10:1, and most preferably about 8:1. The liquid medium may include liquids used in the preparation of the polyimide to be treated (e.g., liquids used in the preparation methods disclosed in U.S. Pat. Nos. 3,249,588, 3,179,631, and / or 4,755,555, or any combination of such liquid(s)), such as solvents, washings, unused chemicals (e.g., monomers and end-capping agents), and the like.

[0040] In the embodiment where a fluid is flowed over the polyimide to be treated, the flow rate of the fluid is not particularly limited. Those skilled in the art can easily select an appropriate flow rate based on, for example, the batch size and the desired amount of fluid to be contacted with the polyimide to be treated. The flow rate of the fluid can be, for example, 0.5 kg of fluid per minute or more, 1 kg of fluid per minute or more, 2 kg of fluid per minute or more, 3 kg of fluid per minute or more, 4 kg of fluid per minute or more, 5 kg of fluid per minute or more, 6 kg of fluid per minute or more, 7 kg of fluid per minute or more, 8 kg of fluid per minute or more, 9 kg of fluid per minute or more, 10 kg of fluid per minute or more, or 25 kg of fluid per minute or more. The flow rate of the fluid may be, for example, 50 kg fluid per minute or less, 30 kg fluid per minute or less, 15 kg fluid per minute or less, 12 kg fluid per minute or less, 10 kg fluid per minute or less, 9 kg fluid per minute or less, 8 kg fluid per minute or less, 7 kg fluid per minute or less, 6 kg fluid per minute or less, 5 kg fluid per minute or less, 3 kg fluid per minute or less, 2 kg fluid per minute or less, or 1 kg fluid per minute or less. The flow rate may be within a range between any applicable combination of the above upper and lower limits, for example, 25-50 kg fluid per minute, and will ultimately be determined by the batch size and / or the size of the plant utilized to perform the extraction.

[0041] Suitable devices for contacting a solid with a fluid are known in the art, and one of ordinary skill in the art would be able to select an appropriate device. For example, in embodiments in which the fluid comprises a supercritical liquid, a supercritical extraction device may be used. Suitable supercritical extraction devices are commercially available and are well known in areas such as decaffeinating coffee and extracting cannabidiol from cannabis.

[0042] A "fluid" as referred to herein is a fluid that is contacted with the polyimide to be treated in the contacting step, unless the context indicates otherwise. Fluids include supercritical fluids or low surface tension liquids. As used herein, the term "low surface tension liquid" refers to a fluid that is less than 10.0 mNm under the conditions of the contacting step. -1As used herein, the term "supercritical fluid" refers to a liquid having a surface tension below 0.15. As used herein, the term "supercritical fluid" refers to a substance at a temperature and pressure above its critical point, which is the highest temperature and pressure at which both the gas and liquid phases of the substance can coexist.

[0043] The fluid used in the contacting step may comprise a low surface tension liquid. As used herein, the term "surface tension" when used to describe a liquid refers to the liquid-air surface tension. The surface tension of the liquid under the conditions of the contacting step may be determined experimentally according to the procedure described in Chenet al.; Measuring Surface Tension of Liquids at High Temperature and Elevated Pressure; J. Chem. Eng. Data 2008, 53, 742-744, or as described by JR Brock and RB Bird (AICHE Journal 1, 174 (1955)), DI Hakim, D. Steinberg, and LI Stiel, (Ind. Eng. Chem. Fundam. 10, 174 (1971)), C. Miqueu, D. Broseta, J. Satherley, B. Mendiboure, J. Lachaise, and A. Gracia, (Fluid Phase Equil. 172, 169 (2000)), or Y.-X. Zuo and EH Stenby, (Can. J. Chem. Eng. 75, 1130 (1997)).

[0044] A low surface tension liquid is 10.0 mNm under the conditions of the contacting step. -1 Typically, under the conditions of the contacting step, the surface tension is 8.5 mNm -1 % or less, preferably 8.5 or less, more preferably 6.0, even more preferably 4.5 or less, even more preferably 2.0 or less, and most preferably 1.0 or less.

[0045] When the contacting step is performed over a range of temperatures and / or pressures, a liquid is considered to have a particular surface tension under the conditions of the contacting step if the liquid has that particular surface tension at temperatures and / or pressures within the range of temperatures and / or pressures over which the contacting step is performed.

[0046] Suitable substances that are supercritical fluids include methane, ethane, ethylene, carbon dioxide, nitrous oxide, and mixtures thereof.

[0047] Suitable materials for the low surface tension liquid include methane, ethane, ethylene, carbon dioxide, nitrous oxide, and mixtures thereof.

[0048] Typically the fluid comprises supercritical CO2 and / or low surface tension liquid CO2. Preferably, the fluid comprises supercritical CO2, i.e. the fluid comprises supercritical CO2 and the temperature of the contacting step is 31.0°C or higher and the pressure of the contacting step is 73.8 bar or higher (i.e. the contacting step is performed above the critical point of CO2). More preferably, the fluid comprises supercritical CO2 and the conditions of the contacting step include a temperature of 60-100°C and a pressure of 100-200 bar. Even more preferably, the fluid comprises supercritical CO2 and the conditions of the contacting step include a temperature of 70-90°C and a pressure of 140-160 bar. Most preferably, the fluid comprises supercritical CO2 and the conditions of the contacting step include a temperature of about 80°C and a pressure of about 150 bar.

[0049] When the fluid comprises low surface tension liquid CO2, the conditions of the contacting step typically include a temperature of -40.0°C or greater and a pressure of 10.0 bar or greater, for example a temperature of -40.0°C or greater and less than 31.0°C, and a pressure of 10.0 bar or greater and less than 73.8 bar.

[0050] In addition to the supercritical fluid and / or low surface tension liquid, the fluid may further comprise a co-solvent, which is easily removed by the process or by subsequent drying. Suitable co-solvents may include ethanol, isopropyl alcohol, acetone, and toluene.

[0051] The polyimide is typically not chemically altered by the contacting step, and therefore the chemical composition of the treated polyimide is typically the same as the chemical composition of the polyimide to be treated as described above.

[0052] The physical properties of the treated polyimide are typically improved as a result of the contacting step. The BET surface area of ​​the treated polyimide is typically greater than the BET surface area of ​​the polyimide to be treated. The BET surface area of ​​the treated polyimide is typically greater than the BET surface area of ​​polyimides washed with solvents previously known in the art.

[0053] BET specific surface areas referred to herein are typically determined in accordance with ISO 9211:2010 using a multipoint method with N2 Technical X47S as the adsorbent material having a purity of 99.999% and <3 ppm impurities present as HO and <5 ppm impurities present as O2.

[0054] Without wishing to be bound by theory, it is believed that the use of supercritical fluids and / or low surface tension liquids interacts with the pores in the polyimide being treated to increase the BET surface area, which is believed to improve tensile strength when the polyimide is molded into a product. It is believed that the fluids used in the present invention are much more effective at extracting residual liquid media from the pores and nanofluidic channels of the polyimide after the polyimide manufacturing process.

[0055] Preparation of polyimides typically involves polymerizing a diamine and a dianhydride to form a poly(amide-acid), followed by condensing groups of the polyamide-acid to form the polyimide. Although reference is made generally herein to contacting a polyimide with a fluid, disclosed herein are embodiments of the invention in which a polyamide-acid (e.g., a solid polyamide-acid, such as in the form of a precipitate) is contacted with a fluid and then converted to a polyimide. Such embodiments are typically as described herein for embodiments in which a polyimide is contacted with a fluid, except that the contacting step includes contacting a polyamide-acid to be treated (e.g., a solid polyamide-acid, such as in the form of a precipitate) with a fluid to obtain a treated polyamide-acid, and the method further includes converting the treated polyamide acid to a treated polyimide. Thus, in such an embodiment, the invention provides a method of treating a polyimide comprising the steps of: providing a polyamic-acid to be treated; contacting the polyamic-acid to be treated with a fluid to obtain a treated polyamic-acid; and converting the treated polyamic-acid to a treated polyimide, the polyimide comprising first repeat units derived from pyromellitic dianhydride (PMDA) and second repeat units derived from 4,4'-oxodianiline (4,4'-ODA); and the fluid being a supercritical fluid, greater than 10.0 mN m under the conditions of the contacting step. -1 The method includes providing a liquid, or a mixture thereof, having the following surface tension:

[0056] Conversion of the polyamide-acid to a polyimide can be carried out by known methods, such as those disclosed in U.S. Pat. Nos. 3,179,631 and / or 4,755,555, for example by heat treatment at a temperature above 160° C., for example in the range of 160° C. to 200° C.

[0057] The treated polyimide is typically in powder form. The particle size of the treated polyimide is typically as described above for the polyimide to be treated.

[0058] The method of the present invention may include an optional further step of mixing the treated polyimide with an additive to obtain a polyimide mixture. The mixing step may include dry blending with the additive (e.g., drying the treated polyimide and then blending with the additive). Suitable additives include molding additives and lubricants. For example, PTFE may be mixed with the treated polyimide in an amount of 0.1 wt% to 15 wt% based on the weight of the polyimide to be treated. PTFE is typically present as a molding additive and / or lubricant. In another example, MoS2 may be mixed with the treated polyimide powder in an amount of typically 0.1 wt% to 15 wt% based on the weight of the polyimide to be treated. MoS2 is typically present as a lubricant.

[0059] The method of the present invention may include the optional further step of shaping the treated polyimide and / or polyimide blend to obtain a shaped polyimide article.

[0060] Suitable forming techniques may include direct forming, hot isostatic pressing, hot compression molding, and ram extrusion (optionally followed by hot isostatic pressing).

[0061] Direct molding, hot isostatic pressing, hot compression molding, and ram extrusion techniques are known in the art, and one skilled in the art would be able to implement the appropriate techniques to obtain the desired molded article, for example, according to the techniques described in U.S. Pat. Nos. 3,413,394, 4,238,538, and CA 890,515.

[0062] For example, a directly molded product can be obtained by direct molding at a pressure of 10,000-500,000 psi (e.g., 50,000-200,000 psi, 75,000-125,000 psi, or about 100,000 psi), followed by firing at 200-600°C (e.g., 250-550°C, 300-500°C, 350-450°C, or about 400°C).

[0063] The hot compression molded product may be molded by hot compression molding at high temperature and pressure, for example, for 1 hour or more, 2 hours or more, 3 hours or more, 4 hours or more, or 5 hours or more, 24 hours or less, 12 hours or less, 6 hours or less, 4 hours or less, 3 hours or less, 2 hours or less, or any applicable combination of the above upper and lower limits. The pressure of hot compression molding may be in the range of 10,000 to 500,000 psi (e.g., 50,000 to 200,000 psi, 75,000 to 125,000 psi, or about 100,000 psi). The temperature of hot compression molding may be in the range of 200 to 600°C (e.g., 250 to 550°C, 300 to 500°C, 350 to 450°C, or about 400°C). The hot compression molding step may be followed by a machining step (e.g., to obtain a precise size and / or shape). A suitable technique is described in US Pat. No. 3,413,394.

[0064] Ram extrusion (optionally followed by hot isostatic pressing) products may be formed, for example, by ram extrusion in a die having (a) a compression zone followed by (b) a back pressure zone followed by (c) a relaxation zone, in particular by (1) compressing the polyimide in the compression zone at a temperature in the range of 20-600°C (e.g., 250-550°C, 300-500°C, 350-450°C, or about 400°C), simultaneously (2) applying back pressure to the polyimide at the exit of the compression zone by passing the compressed polyimide through the back pressure zone, and then (3) relaxing the pressure on the polyimide in the relaxation zone to control its elastic recovery. When such compressed polyimide passes through the relaxation zone to form a molded article, this process typically results in a radial recovery of about 3-5 percent of the compressed polyimide. A suitable technique is described in U.S. Pat. No. 4,238,538.

[0065] The ram-extruded crystalline polyimide products of the present invention include ram-extruded crystalline polyimide products that have been hot isostatically pressed following ram extrusion, and also include ram-extruded crystalline polyimide products that have not been hot isostatically pressed following ram extrusion.

[0066] Hot isostatically pressed products may be formed, for example, by compressing polyimide into a preform, then isostatically pressing the preform to its desired density in an inert molten metal at high pressure while sintering the preform, with or without heat treatment between the two compression steps. The inert molten metal may be, for example, molten lead. The pressure of the isostatic pressing step may be in the range of 1,000 to 50,000 psi (e.g., 5,000 to 20,000 psi, 7,500 to 12,500 psi, or about 10,000 psi). The temperature of the sintering and optional heat treatment steps may be in the range of 200 to 600°C (e.g., 250 to 550°C, 300 to 500°C, 350 to 450°C, or about 400°C). Suitable techniques are described in CA 890515.

[0067] The treated polyimide may be dried, for example, at a temperature of 100° C. to 200° C., prior to molding into a molded polyimide article. Drying may be performed in air, in an inert atmosphere (e.g., N2), or under vacuum.

[0068] The present invention also provides a polyimide.

[0069] The polyimide of the present invention may be a treated polyimide obtainable by the method of the present invention.

[0070] The polyimide of the present invention has a thickness of 100 m 2 g -1 wherein the polyimide comprises a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA), and the polyimide does not comprise an encapsulated filler or comprises an encapsulated filler in an amount of 20 wt % or less (e.g., 16 wt % or less) based on the weight of the polyimide. It may also be polyimide.

[0071] The polyimide of the present invention is 70m 2 g-1 BET specific surface area exceeding 85m 2 g -1 or more), wherein the polyimide comprises a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA), and the treated polyimide comprises an encapsulated filler in an amount of 20 wt% to 60 wt% (e.g., 16 wt% to 60 wt%) based on the weight of the polyimide.

[0072] The polyimides of the present invention may be in the form of a powder, for example, a dry powder. When in powder form (for example, in the form of a dry powder), for example, in an embodiment in which the polyimide does not contain an encapsulated filler, the polyimide may be in the form of 100 ml 2 g -1 Typically, the polyimides of the present invention, particularly in embodiments in which the polyimide does not contain an encapsulated filler, may have a BET specific surface area of ​​greater than 110 m 2 g -1 More than 120m, preferably 2 g -1 More than 130m, preferably 2 g -1 More than 140m, and even more preferably 2 g -1 Above 150m, most preferably 2 g -1 or more.

[0073] In embodiments where the polyimide includes an encapsulated filler, for example in an amount of 10 wt % to 20 wt % based on the weight of the polyimide, the polyimides of the present invention are typically 2 g -1 More than 105m, preferably 105m 2 g -1 More than 110m, preferably 110m 2 g -1 More than 115m, and even more preferably 2 g -1 or more.

[0074] In embodiments where the polyimide includes an encapsulated filler in an amount of, for example, 20 wt % to 60 wt % based on the weight of the polyimide, the polyimides of the present invention typically have a molecular weight of 70 ml or less. 2 g -1 More than 75m, preferably 75m 2 g -1 More than 80m, preferably 80m 2 g -1 More than 85m, and even more preferably 2 g -1 Above 90m, most preferably 2 g -1 It has a BET specific surface area of ​​more than 1000 nm.

[0075] The presence of encapsulated filler in a polyimide resin typically reduces the BET surface area of ​​the polyimide compared to a polyimide without the encapsulated filler, but the BET surface area of ​​a polyimide according to the present invention containing encapsulated filler is typically greater than that obtained for the same amount of encapsulated filler prior to the present invention.

[0076] Polyimide is 500m 2 g -1 For example, 400m 2 g -1 Below, 300m 2 g -1 Below, 200m 2 g -1 Below, 150m 2 g -1 Less than or equal to 100m 2 g -1 It may have a BET specific surface area of:

[0077] BET specific surface areas referred to herein are typically determined in accordance with ISO 9211:2010 using a multipoint method with N2 Technical X47S as the adsorbent material having a purity of 99.999% and <3 ppm impurities present as HO and <5 ppm impurities present as O2.

[0078] The polyimides of the present invention may be in powder form and typically have a particle size characterized by a volume median diameter (Dv50) of 10 to 80 μm. Preferably, the particle size may be characterized by a Dv50 of 20 to 70 μm. More preferably, the particle size may be characterized by a Dv50 of 25 to 60 μm.

[0079] In embodiments in which the polyimide does not include an encapsulated filler, the polyimide of the present invention may have a particle size (Dv50) of 10 to 80 μm, preferably 20 to 70 μm, more preferably 35 to 60 μm, even more preferably 45 to 50 μm, and most preferably about 47.5 μm.

[0080] In embodiments in which the polyimide comprises an encapsulated filler in an amount of 10 wt % to 20 wt %, based on the weight of the polyimide, the polyimide of the present invention may have a particle size (Dv50) of 10 to 80 μm, preferably 20 to 70 μm, more preferably 25 to 50 μm, even more preferably 35 to 40 μm, and most preferably about 38 μm.

[0081] In embodiments in which the polyimide comprises encapsulated filler in an amount of 20 wt % to 60 wt %, based on the weight of the polyimide, the polyimide of the present invention may have a particle size (Dv50) of 10 to 80 μm, preferably 20 to 50 μm, and more preferably 25 to 45 μm.

[0082] The polyimides of the invention may have a BET specific surface area as described above and a particle size (Dv50) as described above. Any combination of the BET specific surface area and any of the Dv50 particle sizes described above is disclosed. For example, particularly in embodiments where the polyimide does not contain an encapsulated filler, the polyimides of the invention may have a particle size (Dv50) of 10 to 80 μm and a particle size of 100 μm. 2 g -1 BET specific surface area exceeding 100 to 500 m 2 g -1 , 100~400m 2 g -1 , 100~300m 2 g -1 , 100~200m2 g -1 );20-70μm particle size (Dv50) and 110m 2 g -1 BET specific surface area above 110~500m 2 g -1 , 110~400m 2 g -1 , 110~300m 2 g -1 , 110~200m 2 g -1 );35-60μm particle size (Dv50) and 120m 2 g -1 BET specific surface area above 120 to 500 m 2 g -1 , 120~400m 2 g -1 , 120~300m 2 g -1 , 120~200m 2 g -1 ); 45-50μm particle size (Dv50) and 130m 2 g -1 BET specific surface area above 130 to 500 m 2 g -1 , 130~400m 2 g -1 , 130~300m 2 g -1 , 130~200m 2 g -1 ); or a particle size of about 47.5 μm (Dv50) and 130 m 2 g -1 BET specific surface area above 130 to 500 m 2 g -1 , 130~400m 2 g -1 , 130~300m 2 g -1 , 130~200m 2 g -1 ).

[0083] In embodiments in which the polyimide comprises an encapsulated filler in an amount of 10 wt % to 20 wt % based on the weight of the polyimide, the polyimide of the present invention has a particle size (Dv50) of 10 to 80 μm and a particle size (Dv50) of 100 μm.2 g -1 BET specific surface area exceeding 100 to 450 m 2 g -1 , 100~350m 2 g -1 , 100~250m 2 g -1 , 100~150m 2 g -1 );20-70μm particle size (Dv50) and 105m 2 g -1 BET specific surface area above (e.g. 105 to 450 m 2 g -1 , 105~350m 2 g -1 , 105~250m 2 g -1 , 105~150m 2 g -1 );25-50μm particle size (Dv50) and 110m 2 g -1 BET specific surface area above 110~450m 2 g -1 , 110~350m 2 g -1 , 110~250m 2 g -1 , 110~150m 2 g -1 );35-40μm particle size (Dv50) and 115m 2 g -1 BET specific surface area above 115~450m 2 g -1 , 115~350m 2 g -1 , 115~250m 2 g -1 , 115~150m 2 g -1 ); or a particle size of about 38 μm (Dv50) and 115 m 2 g -1 BET specific surface area above 115~450m 2 g -1 , 115~350m 2 g -1 , 115~250m 2 g -1 , 115~150m2 g -1 ).

[0084] In embodiments where the polyimide comprises an encapsulated filler in an amount of 20 wt% to 60 wt% based on the weight of the polyimide, the polyimide of the present invention has a particle size (Dv50) of 10 to 80 μm and a particle size (Dv50) of 70 μm. 2 g -1 BET specific surface area exceeding 70 to 200 m 2 g -1 , 70~150m 2 g -1 , 70~100m 2 g -1 , 85~200m 2 g -1 , 85~150m 2 g -1 , 85~100m 2 g -1 );20-50μm particle size (Dv50) and 75m 2 g -1 BET specific surface area of ​​75 to 200 m or more 2 g -1 , 75~150m 2 g -1 , 75~100m 2 g -1 , 85~200m 2 g -1 , 85~150m 2 g -1 , 85~100m 2 g -1 );25-40μm particle size (Dv50) and 80m 2 g -1 BET specific surface area of ​​80 to 200 m or more 2 g -1 , 80~150m 2 g -1 , 80~100m 2 g -1 );25-40μm particle size (Dv50) and 85m 2 g -1 BET specific surface area of ​​85 to 200 m or more 2 g -1 , 85~150m 2 g -1 , 85~100m2 g -1 ); or 25-40 μm particle size (Dv50) and 90 m 2 g -1 BET specific surface area of ​​90 to 200 m or more 2 g -1 , 90~150m 2 g -1 , 90~100m 2 g -1 ).

[0085] The polyimides of the present invention may include an encapsulated filler. The encapsulated filler in the polyimides of the present invention is typically as described elsewhere herein in connection with the method of the present invention. The typical, preferred, more preferred, even more preferred, and most preferred particle sizes described above apply to embodiments in which the polyimides of the present invention include an encapsulated filler, and to embodiments in which the polyimide to be treated does not include an encapsulated filler. The Dv50 values ​​referred to herein are typically measured by laser diffraction in deionized water according to ISO13320:2009.

[0086] The polyimides of the present invention are typically crystalline polyimides. As used herein, the term crystalline refers to a polyimide having a crystallization index of 15.0 or greater in embodiments in which the polyimide does not contain an encapsulated filler and in embodiments in which the polyimide contains an encapsulated filler in an amount up to 20 wt % by weight of the polyimide (e.g., 10 wt % to 20 wt % by weight of the polyimide), and a polyimide having a crystallization index of 17.0 or greater in embodiments in which the polyimide contains an encapsulated filler in an amount of 20 wt % by weight of the polyimide or greater (e.g., 20 wt % to 60 wt % by weight of the polyimide).

[0087] In embodiments in which the polyimide does not contain an encapsulated filler, and in embodiments in which the polyimide contains an encapsulated filler in an amount between 10 wt % and 20 wt %, based on the weight of the polyimide, the crystallization index of the polyimides of the present invention is typically 15.0 or greater, e.g., 15.5 or greater, 16.0 or greater, 16.5 or greater, 17.0 or greater, 17.5 or greater, 18.0 or greater, 20.0 or greater, 22.0 or greater, 24.0 or greater, 26.0 or greater, 28.0 or greater, or 30.0 or greater.

[0088] In embodiments where the polyimide comprises an encapsulated filler in an amount between 20 wt % and 60 wt %, based on the weight of the polyimide, the crystallization index of the polyimides of the present invention is typically 17.0 or greater, e.g., 17.5 or greater, 18.0 or greater, 18.5 or greater, 19.0 or greater, 19.5 or greater, 20.0 or greater, 22.0 or greater, 24.0 or greater, 26.0 or greater, 28.0 or greater, or 30.0 or greater.

[0089] The crystallization index of the polyimides of the present invention may be 90.0 or less, such as 80.0 or less, 70.0 or less, 60.0 or less, or 50.0 or less.

[0090] The crystallization index of the polyimide of the present invention is typically 17.0 to 90.0, preferably 20.0 to 80.0, more preferably 25.0 to 70.0, and even more preferably 30.0 to 60.0.

[0091] The crystallinity index of the polyimides of the present invention is typically measured by differential scanning calorimetry (DSC). A suitable instrument that can be used is, for example, a DSC 1 (Mettler Toledo) equipped with a 70 μl platinum dish with a perforated lid. The sample can be, for example, a 5 mg sample, and can be heated from 40° C. to 700° C. at a heating rate of 10° C. / min. The crystallinity index α is then calculated as the peak area:

[0092]

number

[0093] The present invention also provides a molded polyimide article.

[0094] The molded polyimide articles of the present invention may be obtained by the process of the present invention which includes the step of molding the treated polyimide or polyimide blend to obtain the molded polyimide article.

[0095] The molded polyimide article of the present invention is a directly molded crystalline polyimide article, wherein the polyimide comprises first repeat units derived from pyromellitic dianhydride (PMDA) and second repeat units derived from 4,4'-oxodianiline (4,4'-ODA), the directly molded crystalline polyimide article being - does not contain an encapsulating filler, contains between 0 wt% and 0.5 wt% additives based on the weight of the polyimide, and has a tensile strength of 80.0 MPa or greater (e.g., 85.0 MPa or greater, 90.0 MPa or greater, 95.0 MPa or greater, or 100.0 MPa or greater); or - comprising 10 wt% to 20 wt% of an encapsulating filler, based on the weight of the polyimide, and comprising 0 wt% to 0.5 wt% of an additive, based on the weight of the polyimide, and having a tensile strength of 63.0 MPa or more (e.g., 69.0 MPa or more, 74.0 MPa or more, 79.0 MPa or more, 84.0 MPa or more, or 89.0 MPa or more); or - comprising 20 wt% to 60 wt% of an encapsulating filler, based on the weight of the polyimide, comprising 0 wt% to 2.0 wt% of an additive, based on the weight of the polyimide, and having a tensile strength of 50.0 MPa or greater (e.g., 55.0 MPa or greater, 60.0 MPa or greater, 65.0 MPa or greater, 70.0 MPa or greater, or 75.0 MPa or greater); or - comprising 10 wt% to 20 wt% of an encapsulating filler, based on the weight of the polyimide, comprising 5 wt% to 15 wt% of an additive, based on the weight of the polyimide, and having a tensile strength of 52.5 MPa or more (e.g., 57.5 MPa or more, 62.5 MPa or more, 67.5 MPa or more, or 72.5 MPa or more); or - comprising 20 wt% to 60 wt% of an encapsulated filler based on the weight of the polyimide, comprising 10 wt% to 20 wt% of an additive based on the weight of the polyimide, and having a tensile strength of 39.5 MPa or more (e.g., 44.5 MPa or more, 49.5 MPa or more, 54.5 MPa or more, or 59.5 MPa or more); It may also be a directly molded crystalline polyimide product.

[0096] The molded polyimide article of the present invention may be a directly molded crystalline polyimide article having a tensile strength of 80.0 MPa or more, where the directly molded polyimide article does not include an encapsulated filler, and the polyimide includes a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA). The directly molded polyimide article may include an additive, such as up to 0.5 wt% PTFE based on the weight of the polyimide, which may aid in demolding during molding operations using the resin.

[0097] The molded polyimide article of the present invention may be a directly molded crystalline polyimide article having a tensile strength of 63.0 MPa or more (e.g., 69 MPa or more), where the directly molded polyimide article includes an encapsulating filler (e.g., 15 wt% ± 1.0 wt% graphite by weight of the polyimide), and the polyimide includes a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA). The embodiment where the directly molded polyimide article includes an encapsulating filler (e.g., 15 wt% ± 1.0 wt% graphite by weight of the polyimide) may include an additive, e.g., 0.5 wt% or less PTFE by weight of the polyimide. Such an additive may aid in demolding during molding operations using the resin.

[0098] The molded polyimide article of the present invention may be a directly molded crystalline polyimide article having a tensile strength of 50.0 MPa or more (e.g., 55 MPa or more), where the directly molded polyimide article includes an encapsulating filler (e.g., 40 wt% ± 5.0 wt% graphite by weight of the polyimide), and the polyimide includes a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA). The directly molded polyimide article includes an encapsulating filler (e.g., 40 wt% ± 5.0 wt% graphite by weight of the polyimide), and may include an additive, e.g., up to 2.0 wt% PTFE by weight of the polyimide. Such additives may aid in demolding during molding operations using the resin.

[0099] The molded polyimide article of the present invention may be a directly molded crystalline polyimide article having a tensile strength of 52.5 MPa or greater, wherein the directly molded polyimide article comprises an encapsulating filler (e.g., 15 wt% ± 3.0 wt% graphite based on the weight of the polyimide) and an additive (e.g., 10 wt% ± 1.0 wt% PTFE based on the weight of the polyimide), and the polyimide comprises first repeat units derived from pyromellitic dianhydride (PMDA) and second repeat units derived from 4,4'-oxodianiline (4,4'-ODA).

[0100] The molded polyimide article of the present invention may be a directly molded crystalline polyimide article having a tensile strength of 39.5 MPa or greater, wherein the directly molded polyimide article comprises an encapsulating filler (e.g., 40 wt% ± 5.0 wt% graphite based on the weight of the polyimide) and an additive (e.g., 15 wt% ± 1.0 wt% PTFE based on the weight of the polyimide), and the polyimide comprises first repeat units derived from pyromellitic dianhydride (PMDA) and second repeat units derived from 4,4'-oxodianiline (4,4'-ODA).

[0101] The molded polyimide product of the present invention is a hot isostatically pressed crystalline polyimide product, a ram extruded (optionally subsequently hot isostatically pressed) crystalline polyimide product, or a hot compression molded crystalline polyimide product, wherein the polyimide comprises a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA), and wherein the hot isostatically pressed crystalline polyimide product, the ram extruded (optionally subsequently hot isostatically pressed) crystalline polyimide product, or the hot compression molded crystalline polyimide product is - does not contain an encapsulating filler, contains 0 wt% to 0.5 wt% additives based on the weight of the polyimide, and has a tensile strength of 87.0 MPa or greater (e.g., 92.0 MPa or greater, 97.0 MPa or greater, 102.0 MPa or greater, or 107.0 MPa or greater); or - comprising 10 wt% to 20 wt% of an encapsulating filler, based on the weight of the polyimide, comprising 0 wt% to 0.5 wt% of an additive, based on the weight of the polyimide, and having a tensile strength of 66.0 MPa or more (e.g., 71.0 MPa or more, 76.0 MPa or more, 81.0 MPa or more, or 86.0 MPa or more); or - comprising 20 wt% to 60 wt% of an encapsulating filler, based on the weight of the polyimide, comprising 0 wt% to 2.0 wt% of an additive, based on the weight of the polyimide, and having a tensile strength of 52.5 MPa or greater (e.g., 57.5 MPa or greater, 62.5 MPa or greater, 67.5 MPa or greater, or 72.5 MPa or greater); or - comprising 10 wt% to 20 wt% of an encapsulating filler, based on the weight of the polyimide, comprising 5 wt% to 15 wt% of an additive, based on the weight of the polyimide, and having a tensile strength of 49.5 MPa or greater (e.g., 54.5 MPa or greater, 59.5 MPa or greater, 64.5 MPa or greater, or 69.5 MPa or greater); or - does not contain an encapsulating filler, contains 10 wt% to 20 wt% additive based on the weight of the polyimide, and has a tensile strength of 59.0 MPa or more (e.g., 64.0 MPa or more, 69.0 MPa or more, 74.0 MPa or more, or 79.0 MPa or more); or - comprising 20 wt% to 60 wt% of an encapsulated filler based on the weight of the polyimide, comprising 10 wt% to 20 wt% of an additive based on the weight of the polyimide, and having a tensile strength of 39.5 MPa or more (e.g., 44.5 MPa or more, 49.5 MPa or more, 54.5 MPa or more, or 59.5 MPa or more); It may be a hot isostatically pressed crystalline polyimide product, a ram extruded (optionally followed by hot isostatic pressing) crystalline polyimide product, or a hot compression molded crystalline polyimide product.

[0102] The molded polyimide product of the present invention may be a hot isostatically pressed crystalline polyimide product, a ram extrusion (optionally followed by hot isostatically pressed) crystalline polyimide product, or a hot compression molded crystalline polyimide product, wherein the molded polyimide product has a tensile strength of 87.0 MPa or more, the molded polyimide product does not contain an encapsulated filler, and the polyimide comprises a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA). The embodiment in which the hot isostatically pressed polyimide product, the ram extrusion (optionally followed by hot isostatically pressed) polyimide product, or the hot compression molded polyimide product does not contain an encapsulated filler may contain an additive, such as 0.5 wt% or less of PTFE based on the weight of the polyimide. Such additives may aid in demolding during molding operations in which the resin is used.

[0103] The molded polyimide product of the present invention may be a hot isostatically pressed crystalline polyimide product, a ram extruded (optionally subsequently hot isostatically pressed) crystalline polyimide product, or a hot compression molded crystalline polyimide product, wherein said molded polyimide product has a tensile strength of 66.0 MPa or greater, said molded polyimide product comprises an encapsulated filler (e.g., 15 wt% ± 1.0 wt% graphite based on the weight of the polyimide), and the polyimide comprises a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA). Embodiments in which the hot isostatically pressed, ram extruded (optionally subsequently hot isostatically pressed) or hot compression molded crystalline polyimide products contain an encapsulated filler (e.g., 15 wt% ±1.0 wt% graphite by weight of the polyimide), may also contain additives, such as up to 0.5 wt% PTFE by weight of the polyimide. Such additives may aid in demolding during molding operations using the resin.

[0104] The molded polyimide product of the present invention may be a hot isostatically pressed crystalline polyimide product, a ram extruded (optionally subsequently hot isostatically pressed) crystalline polyimide product, or a hot compression molded crystalline polyimide product, wherein said molded polyimide product has a tensile strength of 52.5 MPa or greater, said molded polyimide product comprises an encapsulated filler (e.g., 40 wt% ± 5.0 wt% graphite based on the weight of the polyimide), and the polyimide comprises a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA). Embodiments in which the hot isostatically pressed, ram extruded (optionally subsequently hot isostatically pressed) or hot compression molded crystalline polyimide products contain an encapsulated filler (e.g., 40 wt% ±5.0 wt% graphite by weight of the polyimide), may also contain additives, such as up to 2.0 wt% PTFE by weight of the polyimide. Such additives may aid in demolding during molding operations using the resin.

[0105] The molded polyimide product of the present invention may be a hot isostatically pressed crystalline polyimide product, a ram extruded (optionally subsequently hot isostatically pressed) crystalline polyimide product, or a hot compression molded crystalline polyimide product, wherein said molded polyimide product has a tensile strength of 49.5 MPa or greater, said molded polyimide product comprises an encapsulated filler (e.g., 15 wt% ± 3.0 wt% graphite based on the weight of the polyimide) and an additive (e.g., 10 wt% ± 1.5 wt% PTFE based on the weight of the polyimide), and wherein the polyimide comprises a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA).

[0106] The molded polyimide product of the present invention may be a hot isostatically pressed crystalline polyimide product, a ram extruded (optionally subsequently hot isostatically pressed) crystalline polyimide product, or a hot compression molded crystalline polyimide product, wherein said molded polyimide product has a tensile strength of 59.0 MPa or greater, said molded polyimide product is free of encapsulated fillers and contains additives (e.g., 15 wt%±1.5 wt% molybdenum disulfide based on the weight of the polyimide), and the polyimide comprises a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA).

[0107] The molded polyimide product of the present invention may be a hot isostatically pressed crystalline polyimide product, a ram extruded (optionally subsequently hot isostatically pressed) crystalline polyimide product, or a hot compression molded crystalline polyimide product, wherein said molded polyimide product has a tensile strength of 39.5 MPa or greater, said molded polyimide product comprises an encapsulated filler (e.g., 40 wt% ± 5.0 wt% graphite based on the weight of the polyimide) and an additive (e.g., 15 wt% ± 1.0 wt% PTFE based on the weight of the polyimide), and wherein the polyimide comprises a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA).

[0108] As used herein, tensile strength of molded polyimide products is as determined by ASTM D1708 based on 2.5 mm thick specimens at a test speed of 1 mm per minute. Unless otherwise specified, tensile strength is as measured at 23° C.

[0109] The molded polyimide articles of the invention comprise a polyimide comprising a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4'-oxodianiline (4,4'-ODA). The composition of the polyimide contained in the molded polyimide articles of the invention is typically as described above for the polyimide to be treated and / or the treated polyimide of the method of the invention.

[0110] The molded polyimide product of the present invention may include an encapsulated filler. In embodiments where the molded polyimide product includes an encapsulated filler, the encapsulated filler is typically graphite. The particles of the encapsulated filler included in the molded polyimide product typically have a Dv90 of 2.0 to 10.0 μm, preferably 3 to 9 μm, more preferably 4.0 to 8.0 μm, and most preferably 5.0 to 7.0 μm. The amount of encapsulated filler present in the molded polyimide product is typically 5 to 60 wt%, such as 10 to 20 wt% or 35 to 45 wt%, preferably 12 to 18 wt% or 37 to 43 wt%, more preferably 14 to 16 wt% or 39 to 41 wt%, and most preferably about 15 wt% or about 40 wt%, based on the weight of the molded polyimide product.

[0111] The molded polyimide product of the present invention may include additives. Suitable additives include molding additives and lubricants, such as PTFE and MoS2. For example, the molded polyimide product may include PTFE in an amount of 0.1 wt% to 15 wt% based on the weight of the molded polyimide product. PTFE is typically present as a molding additive and / or lubricant. In another embodiment, MoS2 may be mixed with the treated polyimide powder in an amount of typically 0.1 wt% to 15 wt% based on the weight of the molded polyimide product. MoS2 is typically present as a lubricant.

[0112] The directly molded polyimide articles of the present invention may have a tensile strength of 80.0 MPa or greater and a specific gravity of 1.40 or less. Typically, in such embodiments, the molded polyimide articles are filler-free (e.g., graphite-free).

[0113] The directly molded polyimide articles of the invention may have a tensile strength of 70.0 MPa or greater and a specific gravity of 1.50 or less. Typically, in such embodiments, the molded polyimide articles include a filler as described above (e.g., 15 wt% ±1.0 wt% graphite based on the weight of the polyimide).

[0114] The directly molded polyimide products of the present invention may have a tensile strength of 40.0 MPa or greater at 260°C, such as 41.0 MPa or greater at 260°C, 42.0 MPa or greater at 260°C, or 43.0 MPa or greater at 260°C, 44.0 MPa or greater at 260°C, or 45.0 MPa or greater at 260°C.

[0115] The directly molded polyimide articles of the present invention may have a tensile strength of 40.0 MPa or greater and a specific gravity of 1.40 or less at 260° C. Typically, in such embodiments, the molded polyimide articles are filler-free (e.g., graphite-free).

[0116] The directly molded polyimide articles of the invention may have a tensile strength of 40.0 MPa or greater and a specific gravity of 1.50 or less at 260° C. Typically, in such embodiments, the molded polyimide articles include a filler as described above (e.g., 15 wt %±1.0 wt % graphite based on the weight of the polyimide).

[0117] The molded polyimide articles of the invention may have a tensile strength of 110.0 MPa or less, e.g., 105.0 MPa or less, 100.0 MPa or less, 95.0 MPa or less, 90.0 MPa or less, 85.0 MPa or less, 80.0 MPa or less, 75.0 MPa or less, or 70.0 MPa or less.

[0118] The presence of encapsulated fillers and / or additives in a polyimide resin typically reduces the tensile strength of the polyimide compared to a polyimide without the encapsulated fillers and / or additives, but the tensile strength of polyimides according to the present invention that include encapsulated fillers and / or additives is typically greater than that obtained with the same amount of encapsulated and / or blended fillers and / or additives in crystalline polyimide products prior to the present invention.

[0119] As used herein, the specific gravity of a molded polyimide article is typically based on deionized water and may be determined by methods known to those skilled in the art, such as by ASTM D792-20, or by determining the volume of a test object at a specified temperature, typically 20.0° C. (e.g., by measuring the length and diameter of a cylindrical test object with a vernier caliper and calculating the volume of the test object based on the measured length and diameter), measuring the mass of the test object (e.g., on a digital scale having an accuracy of 0.001 g or better), calculating the density of the test object based on the calculated volume and the measured mass, and obtaining a density based on a literature value for the density of deionized water at the specified temperature (e.g., 0.9982 gcm at 20.0° C.). -3 ) may be determined by expressing the density as a function of the

[0120] As used herein, the crystallinity of the molded polyimide articles of the invention is typically as described above for the polyimides of the invention.

[0121] The molded polyimide articles of the present invention can be any type of article, including handling machine parts (e.g., semiconductor handling machine parts, glass handling machine parts), chip test sockets, wafer clamping rings, valve seats, articles for sealing applications, spline joints, bearings (e.g., ball bearings), bushings, locking fasteners (e.g., aerospace), pivot bushings (e.g., for unison rings), and thrust washers.

[0122] The present invention also provides an article comprising the molded polyimide product of the present invention. The nature of the article is not particularly limited and will depend on the application of the molded polyimide product. For example, if the molded polyimide product is a semiconductor handling machine part, the article may be a semiconductor handling machine. EXAMPLES

[0123] [Example 1] Polyimide powder was prepared substantially according to the procedure taught in Example III of U.S. Patent No. 3,249,588, with the preparation procedure being stopped prior to the vacuum drying step reported in Example III of U.S. Patent No. 3,249,588.

[0124] The polyimide powder thus obtained was in the form of a wet filter cake and was contacted with supercritical CO2 in a 25 L supercritical fluid extractor at 80°C and 150 bar. 8 kg of CO2 was used per kg of polyimide filter cake in the extraction. A treated polyimide powder was obtained.

[0125] [Example 2] The same procedure as in Example 1 was followed to obtain treated polyimide powder, except that graphite was present in the polyamic acid solution prior to conversion to polyimide. The graphite used was synthetic graphite with a D90 (laser diffraction) of 5.5-6.8 μm. The amount of graphite added was 15 wt% with respect to the weight of the resulting polyimide.

[0126] [Comparative Example 1] A polyimide powder was obtained according to the same procedure as in Example 1, except that the step of contacting the polyimide powder with supercritical CO2 was not performed, and the polyimide powder was dried under vacuum.

[0127] [Comparative Example 2] A polyimide powder was obtained and vacuum dried according to the same procedure as in Example 2, except that the step of contacting the polyimide powder with supercritical CO2 was not performed.

[0128] evaluation The BET specific surface areas of the polyimide powders obtained in Examples 1 and 2 and Comparative Examples 1 and 2 were measured using a multipoint method with N2Technical X47S as the adsorbent having a purity of 99.999% and <3 ppm impurities present as HO and <5 ppm impurities present as O2 in accordance with ISO 9211:2010.

[0129] Test specimens with a thickness of 2.5 mm were prepared from the polyimide powders obtained in Examples 1 and 2 and Comparative Examples 1 and 2 by heating the polyimide powders to 200° C. and then directly molding them in an unheated press tool at 100,000 psi, followed by baking at 400° C. Tensile strength was measured at 23° C. according to ASTM D1708 at a test speed of 1 mm / min.

[0130] The crystallization index was measured by DSC.

[0131] The results are shown in Table 1 below.

[0132] [Table 1]

[0133] Examples 1 and 2 were also tested to determine tensile strength properties at elevated temperature (260°C) and the results were compared to literature values ​​for Vespel SP1 (no filler added) and Vespel SP21 (15% graphite added) products. Apart from the elevated temperature, tensile strength testing was as described above. The results are shown in Table 2 below.

[0134] [Table 2]

[0135] The above results show that the polyimide powder according to the present invention has a higher BET surface area and improved tensile strength at ambient and elevated temperatures than the corresponding polyimide powder obtained without the supercritical / low surface tension cleaning step.

[0136] The present invention has been described in connection with various non-limiting embodiments and examples. Those skilled in the art will recognize that various modifications can be made to the embodiments and examples without departing from the scope of protection conferred by the patent of the invention, which will be determined by the scope of the claims, fully considering any elements equivalent to those specified in the claims.

[0137] All publications referred to herein (including patent and non-patent publications) are hereby incorporated by reference in their entirety.

Claims

1. 1. A method for treating polyimide, said method comprising: providing a polyimide to be treated; contacting the polyimide to be treated with a fluid to obtain a treated polyimide; Including, the polyimide comprises a first repeat unit derived from pyromellitic dianhydride (PMDA) and a second repeat unit derived from 4,4′-oxodianiline (4,4′-ODA); The fluid is a supercritical fluid, and has a viscosity of 10.0 mN m under the conditions of the contacting step. －１ Liquids, or mixtures thereof, having the following surface tensions: the polyimide to be treated is a plurality of polyimide particles; the plurality of polyimide particles have a particle size characterized by a volume median diameter (Dv50) of 10 to 80 μm as measured by laser diffraction in deionized water according to ISO 13320:2009.

2. The method of claim 1 , wherein the fluid comprises a supercritical fluid.

3. The fluid has a viscosity of 8.5 mN m under the conditions of the contacting step. －１ 10. The method of claim 1, comprising a liquid having a surface tension of:

4. The fluid has a viscosity of 4.5 mN m under the conditions of the contacting step. －１ 4. The method of claim 3, comprising a liquid having a surface tension of:

5. The method of claim 1 , wherein the fluid comprises methane, ethane, ethylene, carbon dioxide, nitrous oxide, or mixtures thereof.

6. The method of claim 1, wherein the polyimide to be treated is poly(PMDA-co-4,4'-ODA).

7. The fluid is supercritical carbon dioxide, and / or 2.0 mN m －１ 10. The method of claim 1, comprising liquid carbon dioxide having a surface tension of:

8. The method of claim 1 wherein an encapsulated filler is present in the polyimide to be treated.

9. The method of claim 8 wherein the encapsulated filler is graphite.

10. The treated polyimide does not contain an encapsulating filler or contains an encapsulating filler in an amount of 20 wt % or less based on the weight of the polyimide, and the treated polyimide is ２ g －１ 2. The method of claim 1, wherein the sintered body has a BET specific surface area of ​​greater than 1000 nm.

11. The treated polyimide comprises an encapsulating filler in an amount of 20 wt % to 60 wt % based on the weight of the polyimide, and the treated polyimide is ２ g －１ and having a BET specific surface area of ​​more than 2. The method of claim 1, wherein the BET specific surface area is determined in accordance with ISO 9211:2010.

12. The method of claim 1 further comprising mixing the treated polyimide with an additive to obtain a polyimide mixture.

13. 12. The method of claim 1, further comprising the step of shaping the treated polyimide obtained by the method of claim 1 or the polyimide blend obtained by the method of claim 11 to obtain a shaped polyimide article.

14. 14. The method of claim 13, wherein said forming is performed by direct molding to obtain a directly molded polyimide product, or said forming is performed by hot compression molding to obtain a hot compression molded polyimide product, or said forming is performed by hot isostatic pressing to obtain a hot isostatic pressed polyimide product, or said forming is performed by ram extrusion to obtain a ram extruded polyimide product.

15. the polyimide product is a direct-molded polyimide product, does not contain an encapsulated filler, and has a tensile strength of 80.0 MPa or more and a specific gravity of 1.40 or less; The specific gravity of the molded polyimide article is relative to deionized water and is determined by ASTM D792-20; 15. The method of claim 14, wherein the tensile strength is determined by ASTM D1708.

16. the polyimide product is a direct-molded polyimide product, contains 10 to 20 wt % of an encapsulated filler, and has a tensile strength of 70.0 MPa or more and a specific gravity of 1.50 or less; The specific gravity of the molded polyimide article is relative to deionized water and is determined by ASTM D792-20; 15. The method of claim 14, wherein the tensile strength is determined by ASTM D1708.

17. the polyimide product is a hot compression molded polyimide product, a hot isostatically pressed polyimide product, or a ram-extruded polyimide product, does not contain an encapsulated filler, and has a tensile strength of 90.0 MPa or more; 15. The method of claim 14, wherein the tensile strength is determined by ASTM D1708.

18. the polyimide product is a hot compression molded polyimide product, a hot isostatically pressed polyimide product, or a ram-extruded polyimide product, contains 10 to 20 wt % of an encapsulated filler, and has a tensile strength of 70.0 MPa or more; 15. The method of claim 14, wherein the tensile strength is determined by ASTM D1708.