POLYIMIDES

Abstract: A select group of novel polyimides possessing excellent mechanical properties and thermal stability; the polyimides are also soluble in aprotic solvents and display the unique features of being miscible with aromatic poly(arylether ketones).

Description: Polyimides FIELD OF THE INVENTION This invention is directed to a select group of novel polyimides possessing excellent mechanical properties and thermal stability; the polyimides are also soluble in aprotic solvents and display the unique features of being miscible with aromatic pol (ether ketones). BACKGROUND OF THE INVENTION Aromatic polyimides have been known since the early 1960's. These polyimides are tough, very high temperature resistant polymers which find use in a wide variety of commercial applications. Several reviews on po.lyimides have been published, see for example, Cotter et al, Ring-Forming Polymerizations, Vol. B.2., pp. 1-67, Academic Press, New York, 1972. Polyimides are generally prepared by the condensation of a diamine with a tetracarboxylic acid dianhydride. U.S. Patent Nos. 3,179,633, and 3,179,634 disclose a two-step process for producing polyimides which comprises: first the reaction of a diamine with a dianhydride in a polar solvent to yield a poly(amide-acid) composition; and second, heating the poly(amide-acid) to a high temperature which results in the conversion of the poly(amide-acid) into the corresponding polyimide. The intermediate poly(amide-acid) is formed into a shaped article prior to the second step. An alternative to the above-described thermal cyclization is the chemical imidization as described in for example, U.S. Patent No. 3, .20,795. In the latter case cyclization of the poly(amide-acid) is performed in solution, in a polar solvent, using a dehydrating agent such as, for example, the combination of acetic anhydride/pyridine. Another method of preparing polyimides is the reaction of a diisocyanate with a dianhydride. This reaction can be carried out in the presence of select catalysts as described in U.S. Patent No. 4,421,905, or in the absence of catalysts - see Ghatge et al., Journal of Polymer Science, Polymer Chemistry Edition, Vol. 18, pp. 1905-1909 (1980). In both instances polar organic solvents are preferably utilized in the above condensation. A number of polyimides utilizing a variety of dianhydrides and diamines were prepared over the last two decades. It is remarkable, however, that only a few selected structures, such as those described herein were found to be miscible with poly aryl ether ketones). It is to be noted- hat two closely related polymers, i.e. polyimides (1) and (2) CD ( 2 ) are also miscible with ρoly(aryl ether ketones). Both are disclosed in the prior art - see Koton et al., Vysokomolekulyarnye Soedinienia Vol B25, pp. 248-7 (1983) and U.S. Patent No. 4,111,906. However, the miscibility of the polymers (1) and (2) with ρoly(aryl ether ketones) was not recognized in the above-cited publications. THE INVENTION The present invention is directed to a select group of novel polyimide polymers that display excellent mechanical properties and thermal stability. Moreover, the polymers show unique miscibility properties, in particular, with aromatic ρoly(aryl ether ketones). The polyimides of the instant invention are derived from the following diamine (3) (3) wherein the amino functions can be located independently in both the para or the meta position with respect to the isopropylidene radical, and the dianhydrides (4)-(7). Copolyimides in which two or more of the dianhydrides are employed in conjunction with (3), or where several isomers of (3) are used with either one or several of the dianhydrides are also included herein. (4) 0 CT. 0 0 o (5) IIθr -»-" ■ }cφ II° (6) (7) In addition, up to 50 mole percent of the diamine (3) can be replaced by one or several of the following diamines (8)-(ll). (8) (9) > N (10) H 2 N ~~ — CH 2 NH 2 ( 11 ) The homopolymers derived from either the para or meta disubstituted diamine (3) and the dianhydrides (4)-(7) are preferred. The polyimide containing dianhydride (4) is most preferred. As stated, the novel polyimides possess excellent mechanical and thermal properties. The polyimides are soluble in polar solvents such as N-methylpyrolidone, N,N-dimethylacetamide, and the like. Shaped articles can be fabricated from the polyimides by solution casting techniques and by compression molding. Most importantly, however, the novel polymers display the unique property of being- miscible with poly(aryl ether ketones). The poly(aryl ether ketones) with which the polyimides of the instant invention form miscible blends are crystalline materials which can be generically characterized as containing repeating units of one or more of the following formulae: o .-o- -c- — CX-AO a - °}θ c Ω}; 0 }P- C0 -Φ{ 0 -®} d wherein Ar is independently a divalent aromatic radical selected from phenylene, biphenylene or naphthylene, X is independently 0, C, or a direct bond and n is an integer of from 0 to 3; b, c, d and e are 0 to 1, and a is an integer of 1 to 4, and preferably d is 0 when b is 1. Preferred poly(aryl ketone)s include those having repeating units of the formula: -Q-- Q -0 — • The polyimides of the present invention are preferably prepared by the reaction of the appropriate dianhydride or dianhydrides with the appropriate diamine(s) followed by chemical dehydration of the intermediate ρoly(amide-acid). The sequence is illustrated in equation (I) where Ar 1 is the tetravalent residuum 3 14 ; the pol7(asl_*-aeid) (CH j CO j O jTidiD*; rooa-taap . ( 15) ; rinal Polyimide of any of the dianhydrides (4)-(7) and Ar- is the divalent residuum of any of the diamines (3), (8), (9), (10), and (11). The solvents useful in the solution polymerization process for synthesizing the polyamide-acid compositions are the organic solvents whose functional groups do not react with either of the reactants (the diamines or the dianhydrides) to any appreciable extent. In addition to being inert to the system, and preferably, being a solvent for the polyamide-acid, the organic solvent must be a solvent for at least one of the reactants, preferably for both of the reactants. Stated another way, the organic solvent is an organic liquid other than either reactant or homologs of the reactants that is a solvent for at least 1 reactant, and contains functional groups, the functional groups being groups other than monofunctional primary and secondary amino groups and other than the monofunctional dicarboxyl-anhydro groups. The normally liquid organic solvents of the N,N-dialkylcarboxylamide class are useful as solvents in the process. The preferred solvents are the lower molecular weight members of this class, particularly N,N-dimethylformamide and N,N-dimethylacetamide. Other useful solvents are: N,N-diethylformamide, N,N-diethylacetamide, N,N-dimethylmethoxyacetamide, N-methyl caprolactam, and the like. Other solvents which may be used include dimethylsulfoxide, N-methyl-2-pyrrolidone, tetramethyl urea, pyridine, dimethylsulfone, hexamethylphosphoramide, tetramethylene sulfone, formamide, N-methylformamide and butyrolactone. The solvents can be used alone, in combinations of solvents, or in combination with poorer solvents such as benzene, benzonitrile, dioxane, xylene, toluene and cyclohexane. Furthermore, in determining a specific time and a specific temperature for forming the poly(amide-acid) of a specified diamine and a specified dianhydride, several factors must be considered. The maximum permissible temperature will depend upon the diamine used, the dianhydride used, the particular solvent, the percentage of poly(amide-acid) desired in the final composition and the minimum period of time that is desired for the reaction. For most combinations of diamines. and dianhydrides falling within- the definitions given above, it is possible to form compositions of 100% poly(amide-acid) by conducting the reaction below 100°C. However, temperatures up to 175°C may be tolerated to provide shapeable compositions. The particular temperature below 175°C that must not be exceeded for any particular combination of diamine, dianhydride, solvent and reaction time to provide a reaction product composed of the desired minimum of poly(amide-acid) will vary but can be determined by a simple test by any person of ordinary skill in the art. However, to obtain the maximum inherent viscosity, i.e., maximum degree of polymerization, for any particular combination of diamine, dianhydride, solvent, etc., and thus produce ultimately shaped articles such as films and filaments of optimum toughness, it has been found that the temperature throughout the reaction should be maintained below 60°C, preferably below 50°C. The degree of polymerization of the poly(amide-acid) is subject to deliberate control. The use of equal molar amounts of the reactants under the prescribed conditions provides poly(amide-acids) of very high molecular weight. The use of either reactant in large excess limits the extent of polymerization. In addition to using an excess of one reactant to limit the molecular weight of the poly(amide-acid), a chain terminating agent such as phthalic anhydride may be used to • 'cap" the ends of the polymer chains. Typical useful capping agents are monoanhydrides or monoamines such as phthalic anhydride, aniline, p-methylaniline, and the amine (16) and anhydride (17) shown below: (16) 0 (17) In the preparation of the poly(amide-acid), it is desired that the molecular weight be such that the inherent viscosity of the polymer is at least 0.1, preferably 0.3-1.5. The inherent viscosity is measured at 25°C at a concentration of 0.5% by weight of the polymer in a suitable solvent such as N-methylpyrolidone. The quantity of organic solvent used in the process need only be sufficient to dissolve enough of one reactant, preferably the diamine, to initiate the reaction of the diamine and the dianhydride. It has been found that'the most successful results are obtained when the solvent represents at least 60% of the final solution. That is, the solution should contain 0.05-40% of the polymeric component. The second step of the process described in equation (I) is preformed by treating the poly(amide-acid) (14) with a dehydrating agent alone or in combination with a tertiary amine such as acetic anhydride or an acetic anhydride-pyridine mixture. The ratio of acetic anhydride to pyridine can vary from just above zero to infinite mixtures. In addition to acetic anhydride, lower fatty acid anhydrides and aromatic monobasic acid anhydrides may be used. The lower fatty acid anhydrides include propionic, butyric, valeric, mixed anhydrides of these with one another and with anhydrides of aromatic monocarboxylic acids such as benzoic acid, naphthoic acid, etc., and with anhydrides of carbonic and formic acids, as well as aliphatic ketenes (ketene and dimethyl ketene). The preferred fatty acid anhydrides are acetic anhydride and ketene. Ketenes are regarded as anhydrides of carboxylic acids (ref. Bernthsen-Sudborough, textbook of Organic Chemistry. Van Nostrand 1935, p. 861 and Hackh's Chemical Dictionary, Blakiston 1953, p. 468) derived from drastic dehydration of the acids. The aromatic monobasic acid anhydrides include the anhydride of benzoic acid and those of the following acids: o-, m- and p-toluic acids; m- and p-ethyl benzoic acids; p-propyl benzoic acid; p-isopropyl benzoic acid; anisic acid; o-, m- and p-nitro benzoic acids; o-, m- and p-halo benzoic acids; the various dibro o and dichloro benzoic acids; the tribromo and trichloro benzoic acids; isomeric dimethyl benzoic acids, e.g. hemellitic, 3,4-xylic, isoxylic and mesitylenic acids; veratic acid, trimethoxy benzoic acid; alpha- and beta-naphthoic acids; and biphenylcarboxylic (i.e. p-phenyl benzoic) acid; mixed anhydrides of the foregoing with one another and with anhydrides of aliphatic monocarboxylic acids, e.g. acetic acid, propionic acid, etc., and with anhydrides of carbonic and formic acids. Tertiary amines having approximately the same activity as the preferred pyridine can be used in the process. These include isoquinoline, 3,4-lutidine, 3,5-lutidine, 4-methyl pyridine, 3-methyl pyridine, 4-isopropyl pyridine, N-dimethyl benzyl amine, 4-benzyl pyridine, and N-dimethyl dodecyl amine. These amines are generally used from 0.3 to equimolar amounts with that of the anhydride converting agent. Trime ' thyl amine and triethylene diamines are much more reactive, and therefore are generally used in still smaller amounts. On the other hand, the following operable amines are less reactive than pyridine: 2-ethylpyridine, 2-methyl pyridine, triethyl amine, N-ethyl morpholine, N-methyl morpholine, diethyl cyclohexylamine, N, -dimethyl cyclohexylamine, 4-benzoyl pyridine, 2,4-lutidine, 2,6-lutidine and 2,4-6-collidine, and are generally used in larger amounts. An alternative method for the preparation of the polyimides is the thermal dehydration of the intermediate poly(amide-acid)(14). This transformation is generally performed in bulk, preferably using a shaped article, e.g., film or filament of the polymeric acid. The dehydration is conducted stepwise starting at temperatures of about 100°C and increasing the temperature progressively to about 300°C or even higher, depending on the particular case, towards the end of the imidization step. The reaction is preferably performed under an inert atmosphere; atmospheric or reduced pressures can. be employed. The polyimides can also be prepared by the interaction of the dianhydride with a diisocyanate as shown in equation (II): (II ) (12) wherein Ar and Ar- are as defined above. The polyimide forming reactions are conducted in a nitrogen-containing solvent. The specific solvent will depend on the particular aromatic polyimide used. In most cases the solvent is an aprotic organic compound having a dielectric constant between 35 and 45, preferably one which is water soluble. Representative aprotic compounds are N-N-dimethylformamide, N,N-diethylformamide, N,N dimethylmethoxyacetamide, N-methyl caprolactam, caprolactam, N,N-dimethylacetamide, N,N-diethylacetamide, dimethyl sulfoxide, N-methylpyrrolidone, tetramethylurea, hexamethylphosphoramide, N,N,N' ,N'-tetramethylethyl- malonamide, N,N,N' ,N'-tetramethylglutaramide, N,N,N' ,N'-tetramethylsuccinamide, thiobis(N,N-dimethylcarbamylmethyl) ether, N,N,N' ,N'-tetramethyϊfuraramide, methylsuccinonitrile, N,N-dimethylcyanocetamide, N,N-dimeth l-alpha-cyanopropionamide, N-formylpiperidine and butyrolacetone, etc. Preferred solvents are dimethylformamide, dimethylacetamide, N-methyl-pyrrolidone and caprolactam. The reaction temperature is within the range of about 50°C to about 200°C, and preferably, from about 100°C to about 150°C. The polymerization may be performed in the presence or in the absence of a catalyst. Advantageously, the reaction is carried out in the presence of a catalyst for the reaction of an isocyanate and a carboxylic acid and/or anhydride group. Such catalysts are well known in the art; as described in, for example, U.S. Pat. No. 3,701,756. Illustrative catalysts include the alkali metal salts of lactams such as sodium, potassium and lithium butyrolactamates, sodium, potassium and lithium, valerolactamates, sodium, potassium and lithium caprolactamates, alkali metal alkoxides and aryloxides such as sodium, potassium and lithium methoxides, ethoxides, butoxides, and phenoxides, and the like. The reaction between the diisocyanate and the dianhydride is carried out under substantially anhydrous conditions and the progress of the reaction can be followed by any of the routine analytical techniques such as following the viscosity increase of the reaction solution or the evolution of carbon dioxide. The polyimides produced by the reaction remain in solution and can be used as such or can be precipitated therefrom by addition of an appropriate liquid in which the polyimide is insoluble or has low solubility. Other useful reaction catalysts are the metal acetylacetonates which are described in, for example, U.S. Patent No. 4,421,905. The catalysts have the formula when Me is Al, Co, Fe and Ni , n has a value of 3, and when Me is Zr, n has a value of 4. The acetylacetonate-promoted reaction is advantageously conducted at a temperature in the range of about 70 β to 150°C, preferably in the range of about 100° to 140°C. When the temperature is in the upper portion of these ranges, the imidization reaction is substantially completed in 2 to 4 hours. The metal acetylacetonate is advantageously used in an amount of at least 0.005 gm, preferably at least 0.01 gm per equivalent weight of dianhydride and generally there is no need to exceed 1 gm of metal acetylacetonate to obtain the desired results. Advantageously the metal acetylacetonate is used in an amount of 0.005 to 1 gm of metal acetylacetonate, preferably 0.01 to 0.05 gm per gm of aromatic dianhydride. Better thermal stability is achieved by capping the polyimides with either a monoanhydride or a monoisocyanate. Typical capping reagents are phthalic anhydride, phenyl isocyanate, p-methylpheny isocyanate, the isocyanate (18), and the anhydride (19). (19) The polyimides of this invention are solid materials having number average molecular weight's of at least 5,000 and preferably in the range of 8,000 to 50,000. Reduced viscosities of the polymers as measured in N-methylpyrolidone at concentrations of 0.5% by weight and at 25°C are at least 0.1 dl/g and preferably in the range of 0.3 up to 1.5 dl/gm and higher. The polymers of this invention may include mineral fillers such as carbonates including chalk, calcite and dolomite; silicates including mica, talc, wollastonite; silicon dioxide; glass spheres; glass powders; aluminum; clay; quartz; and the like. Also, reinforcing fibers such as fiberglass, carbon fibers, and the like may be used. The polymers may .also include additives such as titanium dioxide; thermal stabilizers, ultraviolet light stabilizers, plasticizers, and the like. The polymers of this invention may be •fabricated into any desired shape, i.e. moldings, coatings, films, or fibers. They are particularly desirable for use as electrical insulation for electrical conductors. Also, the polymers may be woven into monofilament threads which are then formed into industrial fabrics by methods well known in the art as exemplified by U.S. Patent 4,359,501. Further, the polymers may be used to mold gears, bearings and the like. EXAMPLES The following examples serve to give specific illustrations of the practice of this invention but they are not intended in anyway to limit the scope of this invention: Preparation of Polyimides The poly(imides) were prepared by the following method. To a 500ml round bottom flask, fitted with a thermometer and mechanical stirrer, was added (0.050 moles) of the diamine and lOOg of dimethyl acetamide. The solution was stirred and cxyoled in an icebath to 10-15°C. Following addition of 16.11g (0.050 moles) of benzophenone tetracarboxylic acid dianhydride and 10.Og of dimethyl acetamide, the amber colored solution was s.t:irred for three hours at 20 to 23°C. The solution was then diluted with 200 ml of dimethyl acetamide. Imidization was accomplished by adding 11.85g (0.15 moles) of acetic anhydride to the solution and stirring overnight at room temperature. The following day, the contents of the flask were coagulated in deionized water, rinsed twice- with acetone and dried in a vacuum oven at 80°C. The polyimide from benzophenone tetracarboxylic dianhydride and the diamine (20) (20) was compression molded in a 4 x 4 x 0.020 inch cavity mold at about 380°C in a South Bend hydraulic press. The sample was cooled while in the press by passing water through cooling channels within the platens. Cooling from 380°C to room temperature took about 10 minutes. One-eighth inch strips were shear cut from the molded product. These strips were tested for 1% secant modulus according to a procedure similar to ASTM D-638, tensile strength and elongation at break according to ASTM D-638, and pendulum impact strength. Pendulum impact strength is measured as follows: A steel pendulum is used, cylindrical in shape with a diameter of 0.83 inch and weighing 1.562 pounds; the striking piece, mounted almost at the top of the pendulum, is a cylinder 0.3 inch in diameter; film specimens, 4 inches long, 0.125 inch wide and about 1 to 30 mils thick, are clamped between the jaws of the tester so that the jaws are spaced 1 inch apart; the 0.125 inch width of the film is mounted vertically; the pendulum is raised to a constant height to deliver 1.13 foot pounds at the specimen; when the pendulum is released the cylindrical striking piece hits the specimen with its flat end, breaks the film, and travels to a measured height beyond; the difference in the recovery height (i.e., the difference in the potential energy of the pendulum at the maximum point of the upswing) represents the energy absorbed by the specimen during the rupture; the impact strength, expressed in foot-pounds per cubic inch, is obtained by dividing the pendulum energy loss by the volume of the specimen. In order to measure stress crack resistance, samples were placed under stress and a cotton swab saturated with a stress cracking agent was attached to the center of the specimen. The time for the specimen to rupture was then recorded. The longer this time, the higher the stress-crack resistance. The glass transition temperature (Tg) of the molded plaque was measured by two methods. The modulus resilience method as described by Olabisi, et al., in Polymer-Polymer Miscibility, Academic Press, N.Y. , p. 126, was used to determine the Tg of the as molded plaque at a heating rate of 1.6°C/min. The Tg was also determined by placing the sample in an aluminum DSC pan and heating it to 400°C for one minute in the barrel of a Tinius-Olsen Extrusion Plastometer. The sample was then quenched rapidly to room temperature by bringing it in contact with a large metal block. The quenching . process took 1 to 2 seconds. The sample was then placed in a DuPont 1090 thermal analyzer equipped with a dual DSC sample cell and the Tg determined by methods well known in the field of polymer science, by heating at 10°K/min. Properties of the polyimide from benzophenone tetracarboxylic acid dianhydride and diamine (20) are as follows:. TABLE 1% Secant Modulus 299 (ksi) Tensile Strength 14,500 (psi) Elongation at Break 11 Pendulum Impact Strength • 66 (ft-lb/in3) Tg (mechanical) (°C) 265 Tg (DSC) (°C) 263 Time to Rupture (hr) at 1000 psi Tensile Stress Methylene Chloride 0.48 Trichloroethylene 2.1

Claims: WHAT IS CLAIMED IS: 1. A polyimide of the following formula; wherein Ar., is the tetravalent residium of any of the following dianhydrides: 0 - 23 - and Ar2 is the divalent residium of the following diamine: and optionally, with one or more of the following diamines H i 2 'N~ - CH 2— ~ Q— NH 2 2. A polyimide as defined in claim 1 wherein Arr 22 iiss tthhee divalent residuim of the following diamine: _. CH, _ CH, H 2 N CH 3 CH 3 WΛ 2 3. A polyimide as defined in claim 2 wherein up to 50 mole percent of the diamine is replaced by one or more of the divalent residuim of one or more of the following diamines: *_»~Q-°-Q- 2 H 2 N→ζ -CII 2 — _ NH 2 4. A miscible blend of the polyimide of claim 1 and a poly(aryl ether ketone). 5. A blend as defined in claim 4 wherein the poly(aryl ether ketone) is characterized as containing repeating units of one or more of the following formulae ^o °}of{~o);° β-<- -o(° -® t CO wherein Ar is independently a divalent aromatic radical selected from phenylene, diphenylene or naphthylene, X is independently 0, C, or a direct bond and n is an integer of from 0 to 3, b, c, d and e are 0 to 1 and a is an integer of 1 to 4. 6. A blend as defined in claim 5 wherein the poly(aryl ether ketone) is selected from one or more of the following: e -Qr'O-^ ^r- -©- - '0 ^©- • -©- ■ *0-©- —

Inventors: CLIFFTON MICHAEL DUANE, HARRIS JAMES ELMER, CLIFFTON, MICHAEL, DUANE, HARRIS, JAMES, ELMER
Applicants: AMOCO CORP, AMOCO CORPORATION
Application year: 1986
Main classification: C08G73
IPC codes: C08G73, C08L79