Patent Publication Number: US-2017355820-A1

Title: Aromatic polyimides suitable for aerospace parts via 3d printing processes

Description:
CLAIM OF PRIORITY 
     This application claims priority from U.S. Provisional Patent Application Ser. No. 62/348,453 bearing Attorney Docket Number 12016021 and filed on Jun. 10, 2016, which is incorporated by reference. 
    
    
     GOVERNMENT LICENSE RIGHTS 
     This invention was made with government support under Contract No. P1401943 (RSC13006) awarded by the United States Air Force. The government has certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     This invention concerns the production of new aromatic polyimides suitable for use in the manufacture of aerospace parts using thermoplastic polymer articles via 3D printing, also known as “additive manufacturing” or “fused deposition modeling”. 
     BACKGROUND OF THE INVENTION 
     High performance imide polymers are characterized by excellent thermal stability, solvent resistance and high glass transition temperatures (Tg). U.S. Pat. No. 7,015,304 and RE43,880 (both Chuang), the disclosures of which are incorporated by reference, disclose the preparation by a batch process of solvent-free, low-melt imide oligomers and thermosetting polyimides, and to the process of preparing such oligomers and polyimides. 
     U.S. Pat. No. 6,066,710 (Becker et al.) discloses an extrusion process for making aromatic polyimides from symmetrical dianhydrides. 
     Also U.S. Pat. No. 8,093,348 (Chuang), the disclosure of which is incorporated by reference, discloses a variety of starting asymmetric dianhydride monomers, diamine monomers, and endcap monomers useful for making aromatic polyimide polymers. 
     PCT Patent Application Publication No. WO 2015/048,071 (Hu and Avakian) discloses four new thermoplastic aromatic polyimides suitable for 3D printing. None of them uses a symmetrical dianhydride. 
     None of these prior efforts has addressed the particular and peculiar requirements for polymerizing monomers to yield thermosettable aromatic polyimides which are processed like thermoplastic prior to being cured to form thermoset polyimides and also are suitable for aerospace parts using 3D printing. 
     3D printing (also known by the other phrases identified above) is being hailed in the polymer industry as a new means of forming shaped polymeric articles, literally from the ground up. Like soldering, a space is filled by a material coming from a filamentary form and being heated for delivery precisely to the x-y-z coordinates of that space. A lattice or scaffold of supporting material is also often delivered to adjoining spaces in the same precise manner to fortify the polymeric material of the shaped, printed article until that polymeric material sufficiently cools to provide a final rigid structure in the desired shape, which can be separated from the supporting material. 
     The polymeric material considered for use in 3D printing has included customary amorphous thermoplastic polymers but has recently also focused on thermoplastic resins and blends of polymer resins which have high temperature performance properties. Both thermoplastic and thermoset aromatic polyimides have been considered candidates for use in 3D printing. 
     SUMMARY OF THE INVENTION 
     What the art needs is a thermosettable aromatic polyimide having a Tg greater than about 170° C. after curing which has high enough molecular weight to be sufficiently ductile that it can be formed into a filament or self-supporting spaghetti form having a diameter ranging from about 1.6 to about 2.1 mm and preferably from about 1.74 to about 1.86 mm for spooling or other delivery mechanism to a 3D printer. 
     Thus, aromatic polyimides having high Tg values in excess of 220° C. and preferably in excess of 270° C. after curing can be included in the cadre of resins available for the emerging industry of 3D printing of articles using polymers. 
     The present invention has made 3D printing for high Tg resins possible by synthesizing new thermosettable aromatic polyimides which are both strong enough to be made into a 3D printing filament or self-supporting spaghetti of the diameter described above and also ductile enough to be useful as a filament for delivery to a 3D printing head. 
     None of the prior art identified above arose in the time when the particularities of 3D printing were truly understood, particularly for high temperature polymers which have melting temperatures hotter than a pizza oven. 
     The present invention utilizes a particular combination of monomers: (a) a symmetric dianhydride in reaction with (b) an asymmetric aromatic diamines while being subjected to a competing reaction with (c) either a mono-anhydride capable of capping the end(s) of the growing polyimide polymer chains but having retained functionality for crosslinking of the polyimide or other subsequent reaction or an endcapping mono-anhydride without retained functionality. 
     Unfortunately, preparation of high performance imide polymers involve difficult reactions and can benefit from reactive extrusion, a continuous process with timed introduction of the ingredients to form the imide oligomer taught in U.S. Pat. Nos. 7,015,304 and RE43,880 (both Chuang). 
     But neither Chuang (who utilized asymmetric dianhydrides and asymmetric diamines) nor Becker et al. (who utilized symmetric dianhydrides and symmetric diamines) recognized the particular properties necessary for making the high Tg polymer into filaments to be deliverable in ductile form for 3D printing. Hence, this invention involves synthesis of new polymers. 
     One aspect of the invention is a new aromatic polyimide comprising: 
     Thermosettable Poly (2-(4-{3-[1,3-dioxo-5-(2-phenylethynyl)-2,3-dihydro-1H-isoindol-2-yl]phenoxy}phenyl)-5-{[2-(3-{4-[1,3-dioxo-5-(2-phenylethynyl)-2,3-dihydro-1H-isoindol-2-yl]phenoxy}phenyl)-1,3-dioxo-2,3-dihydro-1H-isoindol-5-yl]oxy}-2,3-dihydro-1H-isoindole-1,3-dione)) 
     or 
     Thermoplastic Poly (2-{4-[3-(1,3-dioxo-2,3-dihydro-1H-isoindol-2-yl)phenoxy]phenyl}-5-[(2-{3-[4-(1,3-dioxo-2,3-dihydro-1H-isoindol-2-yl)phenoxy]phenyl}-1,3-dioxo-2,3-dihydro-1H-isoindol-5-yl)oxy]-2,3-dihydro-1H-isoindole-1,3-dione)) 
     Another aspect of the present invention is an aromatic polyimide comprising the reaction product of (1) 3, 4′-oxydianiline (3,4′ ODA); (2) 4, 4′-Oxydiphthalic anhydride (ODPA); and (3) a crosslinking agent selected from the group consisting of 4-phenylethynyl phthalic anhydride (4-PEPA) and phthalic anhydride (PA); wherein the 3, 4′ ODA, the ODPA, and the crosslinking agent are in a molar ratio of about 1:0.80:0.4 to about 1:0.98:0.03, respectively. 
     Embodiments of the invention are explained with reference to the drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a schematic view of the reactive extrusion process of the invention. 
     
    
    
     EMBODIMENTS OF THE INVENTION 
     Ingredients for Preparing the High Temperature Polyamides 
     Table 1 shows the ingredients used to prepare the novel polyimides. The amount of endcap determines the molecular weight of the resulting aromatic polyimide because the endcap competes with the symmetric dianhydride for reaction sites at the asymmetric diamine(s). It has been found that to synthesize filament-quality polyimide, the amount of endcap such as 4-phenylethynyl phthalic anhydride or phthalic anhydride should be less than about 0.4 mole percent of reactant. 
     The choice of endcap can be based on the desire to produce either a thermoplastic aromatic polyimide of 3, 4′ ODA and ODPA or a thermosettable aromatic polyimide of the same asymmetric diamine and symmetric dianhydride. For the former, a non-functional mono-anhydride such as phthalic anhydride can be used, in which the anhydride opens for endcapping but has no further functionality for crosslinking or other later reaction. For the latter, 4-phenylethynyl phthalic anhydride can be used, whereby the anhydride opens for endcapping but the phenylethynyl moiety remains functional for crosslinking or other later reaction. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 Brand Name 
                 Ingredient 
                 Formula 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Asymmetric Diamine 
               
            
           
           
               
               
               
            
               
                 3,4′ ODA 
                 3,4′-oxydianiline, CAS No. 2657-87-6; Mw = 200.24, Tm = 74~75° C., 
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
            
           
           
               
            
               
                 Symmetric Dianhydride 
               
            
           
           
               
               
               
            
               
                 4,4′ODPA 
                 4,4′-oxydiphthalic anhydride, CAS#: 1823-59-2; Mw = 310.21, Tm = 225~229° C. 
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
            
           
           
               
            
               
                 Endcaps 
               
            
           
           
               
               
               
            
               
                 4-PEPA 
                 4-phenylethynylphthalic anhydride, CAS No. 119389-05-8, Mw = 248.24, Tm = 152.0° C. 
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
               
                 PA 
                 Phthalic anhydride, MW = 148.12 (Tm = 131~134° C., and Tb = 284° C.) (CAS:85-44-9) 
                 
                   
                     
                     
                         
                         
                     
                   
                 
               
               
                   
               
            
           
         
       
     
     The use of a symmetrical dianhydride with an asymmetrical diamine is novel to the collection of known aromatic polyimides. The choice of endcap is made based on the desire for a thermoplastic aromatic polyimide or a thermosettable aromatic polyimide in which the endcap remains functional at the phenylethynyl moiety for cross-linking to form a thermoset aromatic polyimide or to form another reaction. 
     As explained in PCT Patent Application Publication No. WO 2015/048,071, it was described that the use of a symmetrical diamine: 1,3,-Bis(3-aminophenoxy)benzene (1,3,3′ APB) failed while the use of a very related symmetrical diamine: 1,3-Bis(4-aminophenoxy)benzene (1,3,4′ APB) succeeded in the synthesis of those aromatic polyimides from an asymmetric dianhydride and a combination of asymmetric and symmetric diamines. In other words, with all other factors constant, the difference in performance between 1,3,3′ APB and 1,3,4′ APB used in combination with an asymmetric diamine was unexplainable. 
     For this reason, it is not presently possible for one having ordinary skill in the art to predict which combination of symmetric dianhydride, asymmetric diamine(s), and endcaps will result in a new polyimide resin with sufficient ductile and flexible strength to be formed into a filament and wound upon a spool of conventional size for use in 3D printing. 
     Concurrent or Sequential Reactive Extrusion 
     One method of reaction is the contact of the endcap with the diamine concurrent with the contact of the dianhydride with the diamine, in order to establish a competition for diamine reaction sites as soon as melting has commenced in the upstream zones of an extruder. The melt-mixing of the dianhydride and the diamine can result in suitable reaction, even while the endcap is also competing for reaction with the diamine(s) in the extruder. 
       FIG. 1  provides a schematic view of the reactive extrusion method useful for the polyimide. 
     Alternatively, as explained in PCT Patent Publication WO 2013/006621 (Golba et al.), a second method of reaction can be the delayed addition of endcap in a later zone, such as the fourth zone, allowing the dianhydride and the diamine(s) to melt and commence reaction before introduction of the endcap commences competition for the diamine reaction sites. 
     The process can be based on the use of an extruder  100  having a source of power  120  and a series of heated zones  130  through which ingredients travel in a molten state. The extruder can be a twin screw extruder, either co-rotating or counter-rotating and have a screw diameter ranging from 16 mm to 45 mm. 
     The series of heated zones  130  can number more than six and usually eight or nine, allowing the establishment of different temperatures associated with different segments of screws (not shown) propelling the molten ingredients through the extruder and encountering other ingredients in conditions ripe for planned reaction.  FIG. 1  shows twelve zones  130  for extruder  100 . 
     Among the series of zones is a first unheated or cooled zone or throat  140  of the extruder, into which all of the ingredients are added. In the alternative approach, sequential reactive extrusion, a subsequent or downstream zone  150  contains a port for injection of at least one other ingredient. After the last ingredient(s) is(are) added at zone  150 , regardless of concurrent or sequential technique, further melt-mixing and planned reaction occur, until an evacuation zone  160  is reached further downstream. Zone  160  can be connected to a source of vacuum power  170  to vent any volatiles, such as water or steam. The melted, mixed, and reacted product of the extruder  100  is extruded through a die  180 , for further processing such as pelletizing for later melt-mixing or reaction. 
     Alternatively, directly for 3D printing, the die  180  can be of a diameter to yield filaments of a diameter of from about 1.6 to about 2.1 mm and preferably from about 1.7 mm to about 1.9 mm, and the extrudate can be wound directly upon the spool for later use in the 3D printing in any shape conceivable in three dimensional space. 
     In the present invention, the reactive extruder  100  can be configured to have a first feeder  200 , a second feeder  220 , and a third feeder  230  to introduce the dianhydride, the diamine, and the endcap, respectively, into the throat  140 , commencing the journey through the extruder in which the early or upstream zones are heated to melt all three or more ingredients and to facilitate a reaction among them. 
     At the throat, shown as  140  in  FIG. 1 , the endcap can be introduced via third feeder  230  even before the dianhydride and the diamine to have begun reacting. The endcap can be a solid or a liquid, preferably, the latter to assist in the competition of reacting with the diamine while the dianhydride also is reacting with the diamine. In the alternative, sequential technique, the feeder  230  delivers the endcap at a downstream zone  150 . 
     The reaction temperature, as reported by Chuang for a batch process, can range from about 232° to about 280° C. 
     However, in this invention, it has been found that each of the zones of the reactive extruder should be heated to a temperature within the range of 320° C. to 400° C. Conventionally, the temperature remains the same or increases for the sequential zones, until the die zone  180 , at which the same or slightly lower or higher temperature prepares the extrudate for exit from the extruder and cooling into strands, pellets, etc. 
     Those persons having ordinary skill in the art of reactive extrusion, without undue experimentation, can select the appropriate temperatures for the zones within the 320° C. to 400° C. range identified above, as a result of review of the Examples below. Also, those same persons, without undue experimentation, can establish screw rotation revolutions per minute to establish the time of transit through each zone of the extruder  100 , which can be a factor in the kinetics of the reactive extrusion planned for the dianhydride and diamine in the concurrent or sequential presence of the mono-anhydride endcap, with or without phenylethynyl functionality to determine thermoplastic or thermosettable performance properties. 
     Usefulness of the Invention 
     The thermoplastic aromatic polyimide formed by the concurrent reactive extrusion process of this invention using PA can be blend by melt-mixing with a variety of other ingredients. 
     The thermosettable aromatic polyimide formed by the concurrent reactive extrusion process of this invention using 4-PEPA can be further reacted or crosslinked at temperatures ranging from about 340° to 360° C. to obtain a thermosetting polyimide matrix having a Tg ranging from about 300°-370° C. 
     In one usage, either of the specific polyimides synthesized according to this invention are engineered for use in the 3D printing technique of plastic article shaping. Simple or complex shapes can be printed digitally relying upon the x-y-z coordinates of space and computer software to drive the printer using filaments of the polyimides of this invention to melt, deposit, and cool layer-by-layer in the z axis above the x-y plane to build any conceivable three-dimensional polyimide object. 
     Combining the emerging technique of 3D printing with the high temperature performance of polyimide is a tremendous combination of manufacturing processing and end-use performance not previously achieved. 3D printed polymer articles can be of any form or shape conceivable, even a Möbius strip. 
     Composites of either of the aromatic polyimides of this invention with other ingredients added for functional purposes can be used in a number of high performance articles, such as lightweight polymer composites (e.g., airframe and engine components); military and commercial aircraft; missiles, radomes, and rockets, etc.; high temperature laminates; electrical transformers; bushings/bearings for engines; oil drilling equipment; oil drilling risers; automotive chassis bearings; and films for use in electronics, fuel cells and batteries. 
     The new production of composites begins with the solvent-less reactive extrusion process described above, which has resulted in polyimide in the form of dry powders, pellets, filaments, films, etc. The production utilizes powder or pellets of the polyimide to be fed as solid articles into a single screw extruder with an appropriate film or sheet extrusion die and operating at temperatures above the melting point of the polyimide. The extruder would rapidly melt the dry polymer to produce a thin film emerging from the die. 
     It is also possible to include carbon, glass, or synthetic fibers as additives in the reactive extrusion to form the aromatic polyimide. 
     It is also possible for the polyimide being reactively extruded to be extruded using a sheet or film die in the melt form directly onto fibers (woven or nonwoven) for cooling and subsequent use. 
     One embodiment of forming a composite from a thermosettable aromatic polyimide of the invention solves problems with the production of polyimide pre-pregs or preforms. The means of curing can be a resin-transfer molding process or selective laser sintering or other means in which the functional phenylethynyl moiety can further react. 
     This conventional production currently relies on the melting of solid resins in heated feed tanks, transfer of the melt to a three-roll mill type feeding system, production of a thin film on a roller, and then transfer of the film to a uni-dimensional tape or a fabric which can be made of carbon fibers, fiberglass, and polymers, such as Kevlar™ brand polymer, or combinations of them. This conventional production requires that these imide oligomeric thermoset resins be stored at elevated temperatures for long periods of time in the heated feed tanks, which can allow those resins to begin their cross-linking chemical reactions before being rolled into films for laminated composite construction. 
     At best, it is estimated that the current production method allows only for a short “pot life” of one to two hours for those resins in the heated tanks before they need to be discarded as no longer reliable or viable reactive polymer systems. 
     The new production of composites begins with the solvent-less reactive extrusion process described above, which has resulted in polyimide oligomers in the form of dry powders, pellets, filaments, films, etc. The production utilizes powder or pellets of the imide oligomer to be fed as solid articles into a single screw extruder with an appropriate film or sheet extrusion die and operating at temperatures above the melting point of the imide oligomer. The extruder would rapidly melt the dry oligomer to produce a thin film emerging from the die, which would then be fed directly into the prepreg or preform machine for impregnation into the tape or fabric, such machine as described in U.S. Pat. No. 7,297,740 (Dyksterhouse). 
     The use of an extruder to re-melt the powder or pellets of aromatic polyimide still having an endcap functionality dramatically reduces the time during which the aromatic polyimide is exposed to elevated temperatures. It is probable that the total time from feeding of powder or pellets into the extruder to impregnation into the uni-dimensional tape or fabric will be only a few minutes, during which time the aromatic polyimide will have a very limited chance to react inadvertently until the time is proper in the prepreg machine. 
     It is also possible for the aromatic polyimide to be extruded using a sheet or film die in the melt form directly onto fibers (woven or nonwoven) for cooling and subsequent curing. 
     Examples further explain the invention. 
     Examples 
     Table 2 shows the acceptable, desirable, and preferable molar ratio ranges of the monomers useful for synthesizing the polyimides. The polyimide can comprise, consist essentially of, or consist of these monomers. The monomers can be introduced separately into the throat of the extruder as seen in  FIG. 1  or pre-blended before addition via a single feeder. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Molar Ratios 
                 Acceptable 
                 Desirable 
                 Preferable 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 Asymmetric Diamine 
                 1.0 
                 1.0 
                 1.0 
               
               
                 Symmetric Dianhydride 
                 0.80-0.98 
                 0.90-0.98 
                 0.95 
               
               
                 Endcap 
                 0.03-0.4  
                 0.04-0.2  
                 0.1 
               
               
                   
               
            
           
         
       
     
     Table 3 shows the ingredients used for the Examples and the Comparative Examples. Tables 4-6 show the molar ratios of the ingredients, the extrusion reaction conditions, and the results. 
     For thermosettable Examples 1-5 and Comparative Examples A-C, 10 grams of each was cured at 360° C. in an ash oven for 5 hours, followed by cooling to room temperature to be ready for DSC characterization. 
     Differential scanning calorimetry (DSC) was utilized to determine glass transition temperature and thermal stability. Each of Examples 1-12 and Comparative Examples A-C was analyzed using a TA Instruments model DSC Q20. The samples were exposed to a heat-cool-heat cycle in the analysis. The temperature range of each segment was from 20° C. to 350° C. at heating/cooling rates of 10° C./minute. A nitrogen gas purge of 50 ml/minute was used. The glass transition temperature (Tg) of the sample was determined using the half-height from the data recorded in the second heating segment of the analysis. 
     
       
         
           
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                   
                   
                 Commercial 
               
               
                 Brand Name 
                 Ingredient and Purpose 
                 Source 
               
               
                   
               
             
            
               
                 3,4′ ODA 
                 3,4′-oxydianiline, Mw = 
                 Miki Sanyo (USA) 
               
               
                   
                 200.24, Tm = 74~75° C. 
                 Inc. 
               
               
                 ODPA 
                 4,4′-oxydiphthalic anhydride, 
                 Evonik Industries 
               
               
                   
                 CAS#: 1823-59-2; Mw = 
                 (USA) 
               
               
                   
                 310.21, Tm = 225~229° C. 
               
               
                 4-PEPA 
                 4-phenylethynylphthalic 
                 Nexam (USA) 
               
               
                   
                 anhydride, CAS No.119389-05-8, 
               
               
                   
                 Mw = 248.24, Tm = 152.0° C. 
               
               
                 PA 
                 Phthalic anhydride, 
                 Sigma Aldrich 
               
               
                   
                 MW = 148.12 (Tm = 131~134° C., 
               
               
                   
                 and Tb = 284° C.) (CAS: 85-44-9) 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
               
               
             
               
                   
                 TABLE 4 
               
               
                   
                   
               
               
                   
                 Comp. A 
                 Comp. B 
                 Comp. C 
                 1 
                 2 
                 3 
                 4 
                 5 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Mole Ratio of 3,4′-ODA:4, 
                 1:0.5:1 
                 1:0.6:0.8 
                 1:0.7:0.6 
                 1:0.8:0.4 
                 1:0.85:0.3 
                 1:0.9:0.2 
                 1:0.925:0.15 
                 1:0.95:0.1 
               
               
                 4′-ODPA:4-PEPA 
               
            
           
           
               
            
               
                 Monomers 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 3,4′-ODA 
                 40.00 
                 41.67 
                 43.48 
                 45.45 
                 46.51 
                 47.62 
                 48.19 
                 48.78 
               
               
                 4,4′ ODPA 
                 20.00 
                 25.00 
                 30.43 
                 36.36 
                 39.53 
                 42.86 
                 44.58 
                 46.34 
               
               
                 4-PEPA 
                 40.00 
                 33.33 
                 26.09 
                 18.18 
                 13.95 
                 9.52 
                 7.23 
                 4.88 
               
            
           
           
               
               
            
               
                 Extruder 
                 Prism 16 millimeter Twin Screw Extruder (L/D: 40) 
               
               
                 Order of addition 
                 All ingredients were mixed by blender and then added at throat 
               
            
           
           
               
            
               
                 Temperature at different Zone, ° C. 
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                 Zone 1 
                 n/a 
                 n/a 
                 n/a 
                 n/a 
                 280 
                 280 
                 280 
                 280 
               
               
                 Zone 2 
                 100 
                 100 
                 210 
                 250 
                 280 
                 280 
                 280 
                 280 
               
               
                 Zone 3 
                 230 
                 230 
                 270 
                 270 
                 320 
                 280 
                 320 
                 320 
               
               
                 Zone 4 
                 230 
                 230 
                 270 
                 270 
                 320 
                 280 
                 320 
                 320 
               
               
                 Zone 5 
                 230 
                 230 
                 270 
                 270 
                 350 
                 320 
                 320 
                 320 
               
               
                 Zone 6 
                 230 
                 230 
                 270 
                 270 
                 350 
                 320 
                 340 
                 340 
               
               
                 Zone 7 
                 230 
                 230 
                 270 
                 270 
                 350 
                 320 
                 340 
                 340 
               
               
                 Zone 8 (vacuum port) 
                 230 
                 230 
                 270 
                 270 
                 350 
                 320 
                 340 
                 340 
               
               
                 Zone 9 
                 230 
                 230 
                 270 
                 270 
                 350 
                 320 
                 340 
                 340 
               
               
                 Die 
                 210 
                 210 
                 250 
                 250 
                 340 
                 300 
                 320 
                 320 
               
               
                 Mole Ratio of 3,4′-ODA:4, 
                 1:0.5:1 
                 1:0.6:0.8 
                 1:0.7:0.6 
                 1:0.8:0.4 
                 1:0.85:0.3 
                 1:0.9:0.2 
                 1:0.925:0.15 
                 1:0.95:0.1 
               
               
                 4′-ODPA:4-PEPA 
               
               
                 Screw RPM 
                 150 
                 150 
                 150 
                 200 
                 250 
                 250 
                 250 
                 250 
               
               
                 Results 
                 Very Low 
                 Yellow 
                 Yellow 
                 Yellow 
                 Yellow 
                 Yellow 
                 Clear 
                 Clear 
               
               
                   
                 Viscosity 
                 Molten 
                 Molten 
                 Molten 
                 Molten 
                 Molten 
                 Brown 
                 Brown 
               
               
                   
                 Yellow 
                 Material 
                 Material 
                 Material 
                 Material 
                 Material 
                 Molten 
                 Molten 
               
               
                   
                 Molten 
                   
                   
                   
                   
                   
                 Material 
                 Material 
               
               
                   
                 Material 
               
               
                 Tg Of Uncured Resin 
                 135.5 
                 143.4 
                 158.1 
                 171.6 
                 184.6 
                 207.6 
                 210.9 
                 212.7 
               
               
                 Measured By DSC, ° C. 
               
               
                 (Room Temp To 350 C.) 
               
               
                 Tg Of The Cured Resin 
                 301.4 
                 291.1 
                 280.3 
                 272.6 
                 262.3 
                 255.9 
                 252.1 
                 246.6 
               
               
                 By DSC (Room Temp To 
               
               
                 400 C.) 
               
               
                 Possibility To Make 
                 No 
                 No 
                 No 
                 Yes, 
                 Yes 
                 Yes 
                 Yes 
                 Yes 
               
               
                 Spaghetti Form Which 
                   
                   
                   
                 barely 
               
               
                 Can Support By Itself 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 5 
               
             
            
               
                   
                   
               
               
                   
                 6 
                 7 
                 8 
                 9 
                 10 
               
            
           
           
               
               
            
               
                   
                 Mole Ratio of 3,4′-ODA:4,4′-ODPA:4-PEPA 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                 1:0.925:0.15 
                 1:0.925:0.15 
                 1:0.8:0.4 
                 1:0.85:0.3 
                 1:0.95:0.1 
               
               
                   
                   
               
            
           
           
               
            
               
                 Monomers 
               
            
           
           
               
               
               
               
               
               
            
               
                 3,4′-ODA 
                 48.19 
                 48.19 
                 45.45 
                 46.51 
                 48.78 
               
               
                 4,4′ ODPA 
                 44.58 
                 44.58 
                 36.36 
                 39.53 
                 46.34 
               
               
                 4-PEPA 
                 7.23 
                 7.23 
                 18.18 
                 13.95 
                 4.88 
               
            
           
           
               
               
            
               
                 Extruder 
                 Prism 16 millimeter Twin Screw Extruder (L/D: 40) 
               
               
                 Order of addition 
                 All ingredients were mixed by blender and then added at 
               
               
                   
                 throat 
               
            
           
           
               
            
               
                 Temperature at different Zone, ° C. 
               
            
           
           
               
               
               
               
               
               
            
               
                 Zone 1 
                 280 
                 280 
                 250 
                 280 
                 340 
               
               
                 Zone 2 
                 280 
                 280 
                 270 
                 280 
                 340 
               
               
                 Zone 3 
                 320 
                 320 
                 270 
                 280 
                 340 
               
               
                 Zone 4 
                 320 
                 320 
                 270 
                 280 
                 340 
               
               
                 Zone 5 
                 320 
                 320 
                 300 
                 320 
                 340 
               
               
                 Zone 6 
                 320 
                 340 
                 300 
                 320 
                 340 
               
               
                 Zone 7 
                 320 
                 340 
                 300 
                 320 
                 340 
               
               
                 Zone 8 (vacuum port) 
                 320 
                 340 
                 300 
                 320 
                 340 
               
               
                 Zone 9 
                 320 
                 340 
                 300 
                 320 
                 340 
               
               
                 Die 
                 320 
                 340 
                 280 
                 320 
                 350 
               
               
                 Screw RPM 
                 250 
                 250 
                 200 
                 200 
                 250 
               
               
                 Results 
                 Clear 
                 Clear 
                 Yellow 
                 Yellow 
                 Nice 
               
               
                   
                 Brown 
                 Brown 
                 Opaque 
                 Opaque 
                 Ductile 
               
               
                   
                 Molten 
                 Molten 
                 Strand 
                 Strand 
                 Clear 
               
               
                   
                 Material 
                 Material 
                   
                   
                 Strand 
               
               
                 Tg Of Uncured Resin 
                 212.8 
                 214.7 
                 180.9 
                 195.6 
                 223~224 
               
               
                 Measured By DSC, ° C. 
               
               
                 (Room Temp To 350° C.) 
               
               
                 Tg Of The Cured Resin 
                 Not 
                 Not 
                 Not 
                 Not 
                 Not 
               
               
                 By DSC (Room Temp To 
                 Tested 
                 Tested 
                 Tested 
                 Tested 
                 Tested 
               
               
                 400° C.) 
               
               
                 Possibility To Make 
                 Yes 
                 Yes 
                 Yes, 
                 Yes 
                 Yes 
               
               
                 Spaghetti Form Which 
                   
                   
                 barely 
               
               
                 Can Support By Itself 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
               
             
               
                   
                 TABLE 6 
               
             
            
               
                   
                   
               
               
                   
                 Example 
               
            
           
           
               
               
               
            
               
                   
                 11 
                 12 
               
            
           
           
               
               
            
               
                   
                 Mole Ratio of Mole Ratio of 
               
               
                   
                 3,4′-ODA:4,4′-ODPA:PA 
               
            
           
           
               
               
               
            
               
                   
                 1:0.0.95:0.1 
                 1:0.0.98:0.04 
               
               
                   
                   
               
            
           
           
               
            
               
                 Monomers (Mole %) 
               
            
           
           
               
               
               
            
               
                 3,4′-ODA 
                 48.78 
                 49.50 
               
               
                 4,4′ ODPA 
                 46.34 
                 48.51 
               
               
                 PA 
                 4.88 
                 1.98 
               
            
           
           
               
               
            
               
                 Extruder 
                 Prism 16 millimeter Twin Screw Extruder 
               
               
                   
                 (L/D = 40) 
               
               
                 Order of addition 
                 All Ingredients Mixed via Blender and 
               
               
                   
                 Added at Throat 
               
            
           
           
               
            
               
                 Temperature at different zones, ° C. 
               
            
           
           
               
               
               
            
               
                 Zone 1 
                 340 
                 280 
               
               
                 Zone 2 
                 340 
                 370 
               
               
                 Zone 3 
                 340 
                 370 
               
               
                 Zone 4 
                 360 
                 370 
               
               
                 Zone 5 
                 360 
                 370 
               
               
                 Zone 6 
                 360 
                 370 
               
               
                 Zone 7 
                 360 
                 370 
               
               
                 Zone 8 (vacuum port) 
                 360 
                 370 
               
               
                 Zone 9 
                 360 
                 380 
               
               
                 Die 
                 380 
                 380 
               
               
                 Screw RPM 
                 250 
                 150 
               
               
                 Observation at Die 
                 Semi-Transparent 
                 Yellow Opaque 
               
               
                   
                 Brown Strand Came 
                 Ductile Strand Came 
               
               
                   
                 Out Of Die 
                 Out Of Die 
               
               
                 Tg Measured By DSC, ° C. 
                 217~223 
                 234 
               
               
                 Tg Of Uncrosslinked 
               
               
                 Aromatic Polyimide 
               
               
                 Measured By DSC, (Room 
               
               
                 Temp To 350° C.) 
               
               
                 Filament Possibility 
                 Yes 
                 Yes 
               
               
                   
               
            
           
         
       
     
     Examples 1-10 demonstrated that a clear, ductile strand capable of being used as a 3D printing filament can be formed from the asymmetric 3,4′ ODA, the symmetric ODPA, and the 4-PEPA endcap in the molar ratio shown. It is significant to note that the molar ratio of 1:0.8:0.4 was the maximum amount of 4,4′-ODPA and 4-PEPA possible. 
     The IUPAC name for this new thermosettable aromatic polyimide of Examples 1-10 is: Poly (2-(4-{3-[1,3-dioxo-5-(2-phenylethynyl)-2,3-dihydro-1H-isoindol-2-yl]phenoxy}phenyl)-5-{[2-(3-{4-[1,3-dioxo-5-(2-phenylethynyl)-2,3-dihydro-1H-isoindol-2-yl]phenoxy}phenyl)-1,3-dioxo-2,3-dihydro-1H-isoindol-5-yl]oxy}-2,3-dihydro-1H-isoindole-1,3-dione). 
     Examples 11-12 also demonstrated that an acceptable, ductile strand capable of being used as a 3D printing filament can be formed from the asymmetric 3,4′ODA, the symmetric ODPA, and the PA endcap in the molar ratios shown. 
     The IUPAC name for the second new thermoplastic polyimide of Examples 11 and 12 is: Poly (2-{4-[3-(1,3-dioxo-2,3-dihydro-1H-isoindol-2-yl)phenoxy]phenyl}-5-[(2-{3-[4-(1,3-dioxo-2,3-dihydro-1H-isoindol-2-yl)phenoxy]phenyl}-1,3-dioxo-2,3-dihydro-1H-isoindol-5-yl)oxy]-2,3-dihydro-1H-isoindole-1,3-dione). 
     The formula for the new thermosettable polyimide of is: 
     
       
         
         
             
             
         
       
     
     where n is a number from about 6 to about 50 and preferably from about 6 to about 20. 
     The formula for the new thermoplastic aromatic polyimide is: 
     
       
         
         
             
             
         
       
     
     where n is a number greater than 20. 
     Separately, the thermosettable aromatic polyimide of the ingredients of Example 10 was replicated as Example 13 in a reactive extrusion using an 18 mm Leistritz Twin Screw Extruder (L/D: 60) using the reaction conditions of Table 7. 
     
       
         
           
               
               
             
               
                   
                 TABLE 7 
               
               
                   
                   
               
               
                   
                 Example 
               
               
                   
                 13 
               
               
                   
                 Mole ratio of 
               
               
                   
                 3,4′ODA:4,4′ODPA:4-PEPA 
               
               
                   
                 1:0.95:0.1 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
            
               
                 Monomers (Mole %) 
               
            
           
           
               
               
            
               
                 3,4′-ODA 
                 48.78 
               
               
                 ODPA 
                 46.34 
               
               
                 4-PEPA 
                 4.88 
               
               
                 Extruder 
                 18 mm Leistritz Twin Screw 
               
               
                   
                 Extruder (L/D: 60) 
               
               
                 Order of addition 
                 All Ingredients Added At 
               
               
                   
                 Throat 
               
            
           
           
               
            
               
                 Temperature at different zones, ° C. 
               
            
           
           
               
               
            
               
                 Zone 1 
                 340 
               
               
                 Zone 2 
                 340 
               
               
                 Zone 3 
                 340 
               
               
                 Zone 4 
                 340 
               
               
                 Zone 5 
                 340 
               
               
                 Zone 6 
                 340 
               
               
                 Zone 7 
                 340 
               
               
                 Zone 8 (vacuum port) 
                 340 
               
               
                 Zone 9 
                 340 
               
               
                 Die 
                 350 
               
               
                 Screw rpm 
                 250 
               
               
                 Observation at Die 
                 Nice Ductile Clear Strand 
               
               
                 Tg Measured By DSC, ° C. Tg Of 
                 224 
               
               
                 Uncrosslinked Aromatic 
               
               
                 Polyimide Measured By DSC, 
               
               
                 (Room Temp To 350° C.) 
               
               
                 Filament Possibility 
                 Yes 
               
               
                   
               
            
           
         
       
     
     The aromatic polyimide of Example 13 was further tested by melt-mixing in the presence of carbon fiber at three weight percent levels: 1, 10, and 15 weight percent. The carbon fiber was “immediate modulus” in form and made by SGL of Strongsville, Ohio. USA. Each of those three experiments showed good dispersion of the carbon fiber in the aromatic polyimide, good adhesion of the carbon fiber to the aromatic polyimide, and no perceptible voids, which would otherwise make the filament deficient for 3D printing. 
     Each of the carbon-filled composites was then cured at 320° C. for 5 hours. It was noted that viscosity increased as carbon fiber loading increased except 1 wt. % carbon fiber filled composite. 
     There was no significant increase in viscosity after 2-hour testing. The gel time was greater than 120 minutes. However, for all the three carbon fiber filled composites, there was a faster increase in viscosity in the first 20 minutes which might be due to carbon fiber recovery from sample loading but not due to curing. 
     Another experiment determined that the thermosettable aromatic polyimide with functional endcap ready for crosslinking could be ground into a fine powder ranging from about 120 μm to about 670 μm. Powder is useful for selective laser sintering, showing the versatility of the aromatic polyimide to be further processed in a variety of ways. 
     The invention is not limited to above embodiments. The claims follow.