Abstract:
Polyimide copolymers were prepared by reacting different ratios of 3,4&#39;-oxydianiline (ODA) and 1,3-bis(3-aminophenoxy)benzene (APB) with 3,3&#39;,4,4&#39;-biphenylcarboxylic dianhydride (BPDA), and terminating with an effective amount of a reactive endcapper. The reactive endcappers employed include 4-phenylethynyl phthalic anhydride (PEPA), 3-aminophenoxy-4&#39;-phenylethynylbenzophenone (3-APEB), maleic anhydride (MA) and nadic anhydride (5-norbornene-2,3-dicarboxylic anhydride) (NA). Within a relatively narrow ratio of diamines, from .sup.˜ 50% ODA/50% APB to .sup.˜ 95% ODA/5% APB, the copolyimides prepared with BPDA and terminated with reactive endgroups have a unique combination of properties that make them very attractive for a number of applications. This unique combination of properties includes low pressure processing (200 psi and below), long term melt stability (several hours at 300° C. for the phenylethynyl terminated polymers), high toughness, improved solvent resistance, improved adhesive properties and improved composite mechanical properties.

Description:
ORIGIN OF THE INVENTION 
     The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to high performance polymers. The present invention relates particularly to polyimide copolymers with reactive endgroups that are useful as adhesives, composite matrices, moldings, films and coatings. 
     2. Description of Related Art 
     Wholly aromatic polyimides are known for their exceptional thermal, thermo-oxidative and chemical resistance, but are generally difficult to process as structural adhesives or composite matrices. Several polyimides such as Kapton® (DuPont), PI-2080 (Dow Chemical, licensed to Lenzing), XU-218 (Ciba-Geigy), Ultem® (General Electric) and LaRC™-TPI (Mitsui Toatsu) are commercially available and used as fibers, films, moldings, adhesives or composite matrices. 
     Currently available equipment to process polyimides into useful parts are limited in their pressure and temperature capability, and certain applications require checkering of adhesives and composites with other structures such as foams or honeycombs. Because of the equipment limitations (especially autoclaves) and concuring requirements, it is extremely important to provide materials that are processable at 250 psi or below and 371° C. or below. Because of the foams and honeycombs that are being proposed for use in some applications, reductions in pressure below 250 psi are also very significant. 
     While improved processing conditions are very important, the polyimides must also display better mechanical and adhesive properties to meet the needs of many future applications. Especially important for these applications are properties measured at temperatures of 177° C. or slightly higher for use over long time periods at those elevated temperatures. 
     Thermoplastic polymers currently available are either difficult to process into high quality parts or have limited mechanical performance at the elevated temperatures for short or long periods of time. The related art that comes closest to meeting the needs of future applications is a thermoplastic polyimide known as LARC™-IA, as described by St. Clair and Progar in U.S. Pat. No. 5,147,966. However, this polyimide requires higher processing conditions than desired and/or provides lower mechanical and adhesive properties than desired, depending on the tests performed. 
     The incorporation of ethynyl groups in polyimides has been reported in the literature, typically as terminal groups to yield acetylene-terminated imide oligomers (ATI). Therimid-600, an oligoimide with acetylene end groups was first developed at the Hughes Aircraft Co. [N. Bilow, A. L. Landis and L. J. Miller, U.S. Pat. No, 3,845,018 (1974); A. L. Landis, N. Bilow, R. H. Boschan, R. E. Lawrence and T. J. Aponyi, Polym. Prepr., 15, 537(1974); N. Bilow and A. L. Landis, Natl. SAMPE Tech. Conf. Ser., 8, 94(1976)]. Several reviews on polyimides or acetylene-terminated prepolymers are published and discuss other acetylene containing polyimides [P. M. Hergenrother, in (H. Mark, ed.) Encyclopedia of Polymer Science and Engineering, 2nd. ed., vol. 1, John Wiley and Sons, Inc., New York, 61(1985); P. M. Hergenrother in (H. Mark, ed.) Encyclopedia of Polymer Science and Engineering, 2nd. ed., vol. 7, John Wiley and Sons, Inc., New York, 639(1987); T. Takekoshi, in (C. G. Overberger, ed.) Advances in Polymer Science, 2(1990)]. Polyimides containing pendent ethynyl groups have been reported but one reference contains an abstract only with no experimental details or polymer properties [F. W. Harris, S. M. Padaki and S. Varaprath, Polym. Prep., 21(1 ), 3(1980)]. Another disclosure on polyimides containing pendent ethynyl groups contains detailed experimental information and polymer properties [B. J. Jensen, P. M. Hergenrother and G. Nwokogu, Polym, Prep., 33(1), 914 (1992) and B. J. Jensen, P. M. Hergenrother and G. Nwokogu, Polymer, 34(3), 630, (1993)]. 
     Maleimide terminated polymers (bismaleimides) have been known for many years [G. F. D. Alelio, U.S. Pat. No. 3,929,713 (1975)]. They are a leading class of thermosetting polyimides because of their excellent processability and balance of thermal and mechanical properties, making them extremely popular in advanced composites and electronics. Many different bismaleimides have been synthesized with a variety of connecting groups between the maleimide rings [D. Wilson, H. D. Stenzenberger and P. M. Hergenrother, Polyimides, Blackie &amp; Son Ltd., Bishopbriggs, Glasgow, United Kingdom, 1990]. 
     Norbornene terminated polyimides have also been known for many years [H. R. Lubowitz, U.S. Pat. No. 3,528,950 (1970)]. The norbornene group reacts to form thermo-oxidatively stable polyimides which have found use as high temperature composite matrix resins [D. Wilson, H. D. Stenzenberger and P. M. Hergenrother, Polyimides, Blackie &amp; Son Ltd., Bishopbriggs, Glasgow, United Kingdom, 1990]. 
     A primary object of this invention is to provide polyimides terminated with reactive groups which can be processed at low pressures to provide polyimides with improved solvent resistance, modulus and elevated use temperatures. 
     Another object of this invention is to provide a polyimide copolymer system that can be processed without the evolution of volatiles, which is melt stable at high temperatures, which has improved adhesive properties, which has improved composite mechanical properties, and which has improved solvent resistance. 
     SUMMARY OF INVENTION 
     According to the present invention, polyimide copolymers were prepared by reacting different ratios of 3,4&#39;-oxydianiline (ODA) and 1,3-bis(3-aminophenoxy)benzene (APB) with 3,3&#39;, 4,4&#39;-biphenylcarboxylic dianhydride (BPDA), and terminating with the appropriate amount of a reactive endcapper. The reactive endcappers employed include but should not be limited to 4-phenylethynyl phthalic anhydride (PEPA), 3-aminophenoxy-4&#39;-phenylethynylbenzophenone (3-APEB), maleic anhydride (MA) and nadic anhydride (5-norbornene-2,3-dicarboxylic anhydride, NA). Within a relatively narrow ratio of diamines, from .sup.˜ 50% ODA/50% APB to  18  95% ODA/5% APB, the copolyimides prepared with BPDA and terminated with reactive endgroups have a unique combination of properties that make them very attractive for a number of applications. This unique combination of properties includes low pressure processing (200 psi and below), long term melt stability (several hours at 300° C. for the phenylethynyl terminated polymers), high toughness, improved solvent resistance, improved adhesive properties and improved composite mechanical properties. The general synthetic procedure for a copolymer with 85% ODA and 15% APB at a theoretical molecular weight of .sup.˜ 5000 g/mole (.sup.˜ 9% stoichiometric offset) terminated with PEPA is shown in the single drawing figure. Polymers are designated by LaRC™ for NASA Langley Research Center followed by a number which relates to the ratio of ODA to APB, followed by the endcapper abbreviation; i.e., LaRC™-8515 PEPA for the example above. Data for theoretical number average molecular weights (M n ), inherent viscosities (η inh ) and glass transition and melting temperatures are included in Table 1. Qualitative measurements of polymer processability and molding and/or molding flash toughness are included in Table 2. Thin film properties are included in Table 3. Fracture toughness and fracture energy are included in Table 4. Data for the titanium to titanium adhesive properties are included in Tables 5-8. Data for composite properties are included in Table 9. Data for polymer melt viscosities are included in Table 10. These copolyimides are eminently suitable as adhesives, composite matrices, moldings, films and coatings. 
     
                                           TABLE 1__________________________________________________________________________Properties of Copolymers.         Theoretical                 Inherent                        Glass TransitionCopolymer Terminated         Molecular                 Viscosity.sup.1,                        Temperature.sup.2, Tgwith Reactive Groups         Weight, Mn                 ηinh, dL/g                        (Tm)(°C.)__________________________________________________________________________90/10 3-APEB  5000    0.31   25289/15 3-APEB  5000    0.31   25180/20 3-APEB  5000    0.30   24370/30 3-APEB  5000    0.28   23660/40 3-APEB  5000    0.30   23150/50 3-APEB  5000    0.28   22995/5 PEPA     5000    0.33   280(378)85/15 PEPA    2500    0.22   25485/15 PEPA    5000    0.29   26385/15 PEPA    10000   0.44   26670/30 PEPA    5000    0.29   25285/15 NA.     9200    0.40   26285/15 MA.     9200    0.42   264__________________________________________________________________________ .sup.1 NMP at 25° C. .sup.2 DSC at a heating rate of 20° C./min. 
    
     
                                           TABLE 2__________________________________________________________________________Processability of Copolymers..sup.1Copolymer     TheoreticalTerminated with         Molecular Weight,                    Pressure                          Processability/Reactive Groups         Mn         (psi) Quality__________________________________________________________________________90/10 3-APEB  5000       200   good/tough85/15 3-APEB  5000       150   excellent/tough80/20 3-APEB  5000       150   excellent/tough70/30 3-APEB  5000       150   excellent/tough60/40 3-APEB  5000       150   excellent/tough50/50 3-APEB  5000       150   excellent/tough95/5 PEPA     5000       200   poor/brittle85/15 PEPA    2500        50   excellent/tough85/15 PEPA    5000       150   excellent/tough85/15 PEPA    10000      250   poor/tough70/30 PEPA    5000       150   excellent/tough85/15 NA.     9200       200   good/tough85/15 MA.     9200       200   good/tough__________________________________________________________________________ .sup.1 See Example 14. 
    
     
                                           TABLE 3__________________________________________________________________________Thin Film Properties of Copolymers.Copolymer     Test   Tensile                      TensileTerminated with         Temperature,                Strength,                      Modulus,                            Elongation,Reactive Groups         °C.                Ksi   Ksi   %__________________________________________________________________________85/15 3-APEB   25    16.8  470   5.3(5000).sup.1  177    11.0  385   7.585/15 PEPA     25    18.8  455   32(5000).sup.1  177    12.2  332   8385/15 PEPA     25    18.6  492   15(10000).sup.1 177    10.2  301   61__________________________________________________________________________ .sup.1 Theoretical Number Average molecular weight in g/mole. 
    
     
                       TABLE 4______________________________________Fracture Toughness and Energy.            FractureCopolymer Terminated with            toughness, Fracture energy,Reactive Groups  psi × in.sup.1/2                       in-lbs/in.sup.2______________________________________85/15 3-APEB     3400       25(5000).sup.185/15 PEPA       3550       28(5000).sup.185/15 PEPA       3900       31(10000).sup.1______________________________________ .sup.1 Theoretical Number Average Molecular weight in g/mole. 
    
     
                       TABLE 5______________________________________85/15ive Properties.sup.1 of LaRC ™3-APEB Bonded 1 h at 350° C. under 100 psi.      Exposure,    Tensile Shear Strength,Test Temp, °C.      hours at 177° C.                   psi______________________________________RT         none         6100177° C.      none         4500204° C.      none         3770177° C.      1000         4675177° C.      3000         4270177° C.      5000         4320177° C.      10000        4370______________________________________ .sup.1 See Example 16. 
    
     
                       TABLE 6______________________________________85/15 PEPAroperties.sup.1 of LaRC ™(5000 g/mole) Bonded 1 h at 350° C. under 75 psi.                        Tensile ShearTest Temp, °C.      Exposure          Strength, psi______________________________________RT         none              7630177° C.      none              5000204° C.      none              3770177° C.      1000 hours @ 177° C.                        4340177° C.      5000 hours @ 177° C.                        4330RT         48 hour in MEK    5470RT         48 hour in Jet Fuel                        6975RT         48 hour in Hydraulic Fluid                        4700RT         48 hour Water Boil                        4590______________________________________ .sup.1 See Example 16. 
    
     
                       TABLE 7______________________________________85/15 PEPA of Different.1 of LaRC ™Molecular Weights at Various Cure Conditions Bonded at 75 psi.2500 g/mole     Tensile Shear Strength, psiCure Condition  RT        177° C.______________________________________1 hr @ 350      5470      45201 hr @ 375      5760      43301/2 hr @ 325, then           6490      47201/2 hr @ 3752 hr @ 316      6460      5100______________________________________5000 g/mole     Tensile Shear Strength, psiCure Condition  RT        177° C.______________________________________1 hr @ 350      7630      50001 hr @ 375      5290      38401/2 hr @ 325, then           6370      37101/2 hr @ 3752 hr @ 316      5130      4970______________________________________10000 g/mole    Tensile Shear Strength, psiCure Condition  RT        177° C.______________________________________1 hr @ 350      4260      28401 hr @ 375      N/A       31601/2 hr @ 325, then           4260      30501/2 hr @ 3752 hr @ 316      4250      3830______________________________________ .sup.1 See Example 16. 
    
     
                       TABLE 8______________________________________Effects of Processing Pressure on Adhesive Properties.sup.1 of85/15 PEPA Bonded at 350° C. for 1 Hour.TheoreticalMolecular Weight,             Tensile Shearg/mole       Processing Pressure, psi                         Strength, psi______________________________________2500         75               5470        25               603010000        75               4260        100              6350        200              6380______________________________________ .sup.1 See Example 16. 
    
     
                                           TABLE 9__________________________________________________________________________Composite Properties of Copolymers terminated With ReactiveGroups..sup.1        Short BeamCopolymer    Test        Shear,              Flex  Flex   Open HoleTerminated with    Temp.,        Strength,.sup.2              Strength,.sup.2                    Modulus,.sup.2                           CompressionReactive Groups    °C.        Ksi   Ksi   Msi    Strength,.sup.3 Ksi__________________________________________________________________________85/15™     25 16.4  268   233-APEB   177 10.2  190   2285/15™     25 15.5  259   21     62PEPA      93 14.2  264   22    150 11.7  225   21    177  9.1  209   19     46__________________________________________________________________________ .sup.1 Composites processed at 250 psi and 371° C. .sup.2 Unidirectional specimen layup. .sup.3 Specimen layup:[±45/90/0/0/±45/0/0/±45/0].sub.s. 
    
     
                       TABLE 10______________________________________85/15 PEPA at Variousof LaRC ™Temperatures.Temperature, °C.         Melt Viscosity, Poise______________________________________300           1.2 × 10.sup.6320           9.7 × 10.sup.5340           4.5 × 10.sup.5360           3.4 × 10.sup.4371           8.3 × 10.sup.3371, after 10 min         1.2 × 10.sup.5371, after 20 min         3.0 × 10.sup.5______________________________________ .sup.1 See Example 19. 
    
     A primary advantage of these copolyimides terminated with reactive groups, as compared to other polyimides terminated with reactive groups, is the unique combination of high mechanical properties and easy processing into useful parts. These copolyimides have excellent solvent resistance, high glass transition temperature and high modulus but are processable under low pressures. This combination of properties is unique and is unexpected for these polyimides. The dianhydride used here contains a very rigid biphenyl structure which typically provides polyimides with poor processability. The addition of the highly flexible APB diamine provides the improved processability while the biphenyl structure provides backbone stiffness, improved solvent resistance and improved mechanical properties. These properties are important for applications as films, coatings, moldings, adhesives and composites. If too little APB is incorporated into the polymer backbone, the resulting material becomes semi-crystalline and highly rigid, providing a material that is not processable under desired processing limitations. If too much APB is incorporated into the polymer backbone, the resulting material becomes highly flexible with a low glass transition temperature, providing a material that has poor mechanical properties at elevated temperatures (&gt;150° C.) and decreased solvent resistance. Therefore, by simply changing the ratio of ODA to APB, a material with a unique combination of solubility, Tg, Tm, melt viscosity, toughness and elevated temperature mechanical properties is prepared. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The sole drawing FIGURE is an equation setting forth the general synthetic procedure for providing a polyimide copolymer according to the present invention having 85% ODA and 15% APB, which is terminated with PEPA. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Imide oligomers terminated with reactive groups with a wide range of molecular weights ( .sup.˜ 1500 to .sup.˜ 15,000 g/mole) are readily prepared by offsetting the ratio of one monomer relative to the other by a calculated amount and adding an appropriate amount of endcapper containing the reactive group. The low molecular weight versions of these materials have better processability than the high molecular weight versions, however, the high molecular weight versions have better film forming capabilities than the low molecular weight versions. Copolymers with higher amounts of APB have better processability but lower Tgs, while copolymers with higher amounts of ODA have higher Tgs but poorer processability. Furthermore, copolymers with higher amounts of APB remain soluble after solution imidizing at 160° C. with toluene used to remove water, while copolymers with higher amounts of ODA become insoluble after solution imidizing and precipitate from the reaction. Furthermore, imidized powders of copolymers with higher amounts of ODA are insoluble in NMP at 25° C. after drying at &gt;100° C. However, unexpectedly (because of the rigid BPDA unit) the imidized powders of copolymers with higher amounts of APB are soluble in NMP at 25° C. after drying at &gt;100° C. In addition, this particular imide backbone also has an advantageous effect on volatile removal. Some other polyimides terminated with reactive groups retained a much higher volatile content after a 1 hour at 225° C. hold than these copolyimides. The temperatures and pressures used to process these materials are limited by the equipment available, while the mechanical properties desired are based on current or future applications. The copolymers discussed herein have a unique combination of properties which allow them to be processed on currently available equipment at very low pressures but meet these desired mechanical properties. Therefore, copolymers according to the present invention can be provided with the proper combination of properties for the desired application by controlling the ratio of the amine monomers, the molecular weight and the type of reactive endgroup used. Since the different endgroups have different reaction onset temperatures and different cure chemistries, a variety of properties can be systematically controlled. Specific examples follow. 
     EXAMPLE 1 
     Synthesis of LaRC™-90/10 3-APEB 
     The following example illustrates the synthesis of a phenylethynyl-terminated imide cooligomer with theoretical number average molecular weight of 6000 g/mole. 3,4&#39;-Oxydianiline (ODA) (24.974 mmole, 5.0010 g), 1,3-bis(3-aminophenoxy)benzene (APB) (2.7749 mmole, 0.8112 g), 3,3&#39;,4,4&#39;-biphenyl tetracarboxylic dianhydride (BPDA) (30.00 mmole, 8.8267 g), 4-(3-aminophenoxy)-4&#39;-phenylethynylbenzophenone (3-APEB) (4.5012 mmole, 1.7529 g), N-methylpyrollidinone (NMP) (65 g) were added to a 250 mL three neck flask equipped with a mechanical stirrer, condenser and nitrogen inlet. The reaction was stirred at 25° C. for 16 hours to form the phenylethynyl-terminated polyamide acid (η inh  =0.31 dL/g, NMP at 25° C.) followed by adding toluene (40 mL) and heating at 160° C. for 24 h. A yellow precipitate formed during the heating. After cooling, the yellow precipitate was poured into water, washed in boiling methanol and dried at 110° C. for 72 hours to afford a yellow solid in &gt;95% yield. The resulting phenylethynyl-terminated polyimide powder was insoluble in NMP at 25° C. The final Tg by DSC was 252° C., measured after curing one hour at 350° C. A film cast from the polyamide acid solution and cured one hour at 350° C. was unaffected by MEK, toluene, jet fuel, and hydraulic fluid. 
     EXAMPLE 2 
     Synthesis of LaRC™-85/15 3-APEB 
     The following example illustrates the synthesis of a phenylethynyl-terminated imide cooligomer with theoretical number average molecular weight of 5000 g/mole. 3,4&#39;-Oxydianiline (ODA) (23.199 mmole, 4.6456 g), 1,3-bis(3-aminophenoxy)benzene (APB) (4.094 mmole, 1.1968 g), 3,3&#39;,4,4&#39;-biphenyl tetracarboxylic dianhydride (BPDA) (30.00 mmole, 8.8267 g), 4-(3-aminophenoxy)-4&#39;-phenylethynylbenzophenone (3-APEB) (5.412 mmole, 2.1077 g), N-methylpyrollidinone (NMP) (67 g) were added to a 250 mL three neck flask equipped with a mechanical stirrer, condenser and nitrogen inlet. The reaction was stirred at 25° C. for 16 hours to form the phenylethynyl-terminated polyamide acid (η inh  =0.31 dL/g, NMP at 25° C.) followed by adding toluene (40 mL) and heating at 160° C. for 24 h. A yellow precipitate formed during the heating. After cooling, the yellow precipitate was poured into water, washed in boiling methanol and dried at 110° C. for 72 hours to afford a yellow solid in &gt;95% yield. The resulting phenylethynyl-terminated polyimide powder was insoluble in NMP at 25° C. The final Tg by DSC was 251 ° C., measured after curing one hour at 350° C. A film cast from the polyamide acid solution and cured one hour at 350° C. was unaffected by MEK, toluene, jet fuel, and hydraulic fluid. 
     EXAMPLE 3 
     Synthesis of LaRC™-80/2.0 3-APEB 
     The following example illustrates the synthesis of a phenylethynyl-terminated imide cooligomer with theoretical number average molecular weight of 5000 g/mole. 3,4&#39;-Oxydianiline (ODA) (21.816 mmole, 4.3686 g), 1,3-bis(3-aminophenoxy)benzene (APB) (5.454 mmole, 1.5944 g), 3,3&#39;, 4,4&#39;-biphenyl tetracarboxylic dianhydride (BPDA) (30.00 mmole, 8.8267 g), 4-(3-aminophenoxy)-4&#39;-phenylethynylbenzophenone (3-APEB) (5.46 mmole, 2.1264 g), N-methylpyrollidinone (NMP) (68 g) were added to a 250 mL three neck flask equipped with a mechanical stirrer, condenser and nitrogen inlet. The reaction was stirred at 25° C. for 16 hours to form the phenylethynyl-terminated polyamide acid (η inh  =0.30 dL/g, NMP at 25° C.) followed by adding toluene (40 mL) and heating at 160° C. for 24 h. A precipitate formed during the cool down. After cooling, the greenish-yellow semi-solid was poured into water, washed in boiling methanol and dried at 110° C. for 72 hours to afford a yellow solid in &gt;95% yield. The resulting phenylethynyl-terminated polyimide powder was insoluble in NMP at 25° C. The final Tg by DSC was 243° C., measured after curing one hour at 350° C. A film cast from the polyamide acid solution and cured one hour at 350° C. was unaffected by MEK, toluene, jet fuel, and hydraulic fluid. 
     EXAMPLE 4 
     Synthesis of LaRC™-70/30 3-APEB 
     The following example illustrates the synthesis of a phenylethynyl-terminated imide cooligomer with theoretical number average molecular weight of 5000 g/mole. 3,4&#39;-Oxydianiline (ODA) (19.053 mmole, 3.8153 g), 1,3-bis(3-aminophenoxy)benzene (APB) (8.1655 mmole, 2.3871 g), 3,3&#39;, 4,4&#39;-biphenyl tetracarboxylic dianhydride (BPDA) (30.00 mmole, 8.8267 g), 4-(3-aminophenoxy)-4&#39;-phenylethynylbenzophenone (3-APEB) (5.5632 mmole, 2.1666 g), N-methylpyrollidinone (NMP) (69 g) were added to a 250 mL three neck flask equipped with a mechanical stirrer, condenser and nitrogen inlet. The reaction was stirred at 25° C. for 16 hours to form the phenylethynyl-terminated polyamide acid (η inh  =0.28 dL/g, NMP at 25° C.) followed by adding toluene (40 mL) and heating at 160° C. for 24 h. After cooling, the still soluble polyimide was poured into water, washed in boiling methanol and dried at 110° C. for 72 hours to afford a yellow solid in &gt;95% yield. The resulting phenylethynyl-terminated polyimide powder was soluble in NMP at 25° C. The final Tg by DSC was 236° C., measured after curing one hour at 350° C. A film cast from the polyamide acid solution and cured one hour at 350° C. was unaffected by MEK, toluene, jet fuel, and hydraulic fluid. 
     EXAMPLE 5 
     Synthesis of LaRC™-60/40 3-APEB 
     The following example illustrates the synthesis of a phenylethynyl-terminated imide cooligomer with theoretical number average molecular weight of 5000 g/mole. 3,4&#39;-Oxydianiline (ODA) (16.301 mmole, 3.2642 g), 1,3-bis(3-aminophenoxy)benzene (APB) (10.867 mmole, 3.1769 g), 3,3&#39;, 4,4&#39;-biphenyl tetracarboxylic dianhydride (BPDA) (30.00 mmole, 8.8267 g), 4-(3-aminophenoxy)-4&#39;-phenylethynylbenzophenone (3-APEB) (5.665 mmole, 2.2062 g), N-methylpyrollidinone (NMP) (67 g) were added to a 250 mL three neck flask equipped with a mechanical stirrer, condenser and nitrogen inlet. The reaction was stirred at 25° C. for 16 hours to form the phenylethynyl-terminated polyamide acid (η inh  =0.30 dL/g, NMP at 25° C.) followed by adding toluene (40 mL) and heating at 160° C. for 24 h. After cooling, the still soluble polyimide was poured into water, washed in boiling methanol and dried at 110° C. for 72 hours to afford a yellow solid in &gt;95% yield. The resulting phenylethynyl-terminated polyimide powder was soluble in NMP at 25° C. The final Tg by DSC was 231° C., measured after curing one hour at 350° C. A film cast from the polyamide acid solution and cured one hour at 350° C. was unaffected by MEK, toluene, jet fuel, and hydraulic fluid. 
     EXAMPLE 6 
     Synthesis of LaRC™-50/50 3-APEB 
     The following example illustrates the synthesis of a phenylethynyl-terminated imide cooligomer with theoretical number average molecular weight of 5000 g/mole. 3,4&#39;-Oxydianiline (ODA) (13.559 mmole, 2.7152 g), 1,3-bis(3-aminophenoxy)benzene (APB) (13.559 mmole, 3.9638 g), 3,3&#39;,4,4&#39;-biphenyl tetracarboxylic dianhydride (BPDA) (30.00 mmole, 8.8267 g), 4-(3-aminophenoxy)-4&#39;-phenylethynylbenzophenone (3-APEB) (5.764 mmole, 2.2448 g), N-methylpyrollidinone (NMP) (67 g) were added to a 250 mL three neck flask equipped with a mechanical stirrer, condenser and nitrogen inlet. The reaction was stirred at 25° C. for 16 hours to form the phenylethynyl-terminated polyamide acid (η inh  =0.28 dL/g, NMP at 25° C.) followed by adding toluene (40 mL) and heating at 160° C. for 24 h. After cooling, the still soluble polyimide was poured into water, washed in boiling methanol and dried at 110° C. for 72 hours to afford a yellow solid in &gt;95% yield. The resulting phenylethynyl-terminated polyimide powder was soluble in NMP at 25° C. The final Tg by DSC was 229° C., measured after curing one hour at 350° C. A film cast from the polyamide acid solution and cured one hour at 350° C. was unaffected by MEK, toluene, jet fuel, and hydraulic fluid. 
     EXAMPLE 7 
     Synthesis of LaRC™-95/5 PEPA 
     The following example illustrates the synthesis of a phenylethynyl-terminated imide cooligomer with theoretical number average molecular weight of 5000 g/mole. 3,4&#39;-Oxydianiline (ODA) (28.50 mmole, 5.7070 g), 1,3-bis(3-aminophenoxy)benzene (APB) (1.500 mmole, 0.4385 g), 3,3&#39;,4,4&#39;-biphenyl tetracarboxylic dianhydride (BPDA) (27.345 mmole, 8.0456 g), 4-phenylethynyl phthalic anhydride (PEPA) (5.310 mmole, 1.3182 g), N-methylpyrollidinone (NMP) (62 g) were added to a 250 mL three neck flask equipped with a mechanical stirrer, condenser and nitrogen inlet. The reaction was stirred at 25° C. for 16 hours to form the phenylethynyl-terminated polyamide acid (η inh  =0.33 dL/g, NMP at 25° C.) followed by adding toluene (40 mL) and heating at 160° C. for 24 hours. A yellow precipitate formed during the heating. After cooling, the yellow precipitate was poured into water, washed in boiling methanol and dried at 110° C. for 72 hours to afford a yellow solid in &gt;95% yield. The resulting phenylethynyl-terminated polyimide powder was insoluble in NMP at 25° C. After one hour at 350° C., the final Tg was 280° C. by DSC and a Tm peak of 378° C. was measured. A film cast from the polyamide acid solution and cured one hour at 350° C. was unaffected by MEK, toluene, jet fuel, and hydraulic fluid. 
     EXAMPLE 8 
     Synthesis of LaRC™-85/15 PEPA 
     The following example illustrates the synthesis of a phenylethynyl-terminated imide cooligomer with theoretical number average molecular weight of 5000 g/mole. 3,4&#39;-Oxydianiline (ODA) (1.700 mole, 340.42 g), 1,3-bis(3-aminophenoxy)benzene (APB) (0.300 mole, 87.70 g), 3,3&#39;,4,4&#39;-biphenyl tetracarboxylic dianhydride (BPDA) (1.8196 mole, 535.37 g), 4-phenylethynyl phthalic anhydride (PEPA) (0.3608 mole, 89.57 g), N-methylpyrollidinone (NMP) (1580 g) were added to a 3 L reaction kettle equipped with a mechanical stirrer, condenser and nitrogen inlet. The reaction was stirred at 25° C. for 16 hours to form the phenylethynyl-terminated polyamide acid (η inh  =0.29 dL/g, NMP at 25° C.) followed by adding toluene (40 mL) and heating at 160° C. for 24 hours. A yellow precipitate formed during the heating. After cooling, the yellow precipitate was poured into water, washed in boiling methanol and dried at 110° C. for 72 hours to afford a yellow solid in &gt;95% yield. The resulting phenylethynyl-terminated polyimide powder was insoluble in NMP at 25° C. The final Tg of 263° C. was measured after one hour at 350° C. A film cast from the polyamide acid solution and cured one hour at 350° C. was unaffected by MEK, toluene, jet fuel, and hydraulic fluid. 
     EXAMPLE 9 
     Synthesis of LaRC™-70/30 PEPA 
     The following example illustrates the synthesis of a phenylethynyl-terminated imide cooligomer with theoretical number average molecular weight of 5000 g/mole. 3,4&#39;-Oxydianiline (ODA) (21.00 mmole, 4.2052 g), 1,3-bis(3-aminophenoxy)benzene (APB) (9.00 mmole, 2.6310 g), 3,3&#39;,4,4&#39;-biphenyl tetracarboxylic dianhydride (BPDA) (27,220 mmole, 8.0085 g), 4-phenylethynyl phthalic anhydride (PEPA) (5.56 mmole, 1.3802 g), N-methylpyrollidinone (NMP) (65 g) were added to a 250 mL three neck flask equipped with a mechanical stirrer, condenser and nitrogen inlet. The reaction was stirred at 25° C. for 16 hours to form the phenylethynyl-terminated polyamide acid (η inh )=0.29 dL/g, NMP at 25° C.) followed by adding toluene (40 mL) and heating at 160° C. for 24 h. After cooling, the still soluble polyimide was poured into water, washed in boiling methanol and dried at 110° C. for 72 hours to afford a yellow solid in &gt;95% yield. The resulting phenylethynyl-terminated polyimide was soluble in NMP at 25° C. The final Tg of 252° C. was measured after one hour at 350° C. A film cast from the polyamide acid solution and cured one hour at 350° C. was unaffected by MEK, toluene, jet fuel, and hydraulic fluid. 
     EXAMPLE 10 
     Synthesis of LaRC™-85/15 PEPA 
     The following example illustrates the synthesis of a phenylethynyl-terminated imide cooligomer with theoretical number average molecular weight of 2500 g/mole. 3,4&#39;-Oxydianiline (ODA) (0.2125 mole, 42.5523 g), 1,3-bis(3-aminophenoxy)benzene (APB) (0.0375 mole, 10.9625 g), 3,3&#39;, 4,4&#39;-biphenyl tetracarboxylic dianhydride (BPDA) (0.2069 mole, 60.8749 g), 4-phenylethynyl phthalic anhydride (PEPA) (0.0862 mole, 21.3983 g), N-methylpyrollidinone (NMP) (252 g) were added to a 1 L three neck flask equipped with a mechanical stirrer, condenser and nitrogen inlet. The reaction was stirred at 25° C. for 16 hours to form the phenylethynyl-terminated polyamide acid (η inh  =0.22 dL/g, NMP at 25° C.) followed by adding toluene (100 mL) and heating at 160° C. for 24 hours. A yellow precipitate formed during the heating. After cooling, the reaction was poured into water, washed in boiling methanol and dried at 110° C. for 72 hours to afford a yellow solid in &gt;95% yield. The resulting phenylethynyl-terminated polyimide powder was insoluble in NMP at 25° C. The final Tg of 254° C. was measured after one at 350° C. A film cast from the polyamide acid solution and cured one hour at 350° C. was unaffected by MEK, toluene, jet fuel, and hydraulic fluid. 
     EXAMPLE 11 
     Synthesis of LaRC™-85/15 PEPA 
     The following example illustrates the synthesis of a phenylethynyl-terminated imide cooligomer with theoretical number average molecular weight of 10,000 g/mole. 3,4&#39;-Oxydianiline (ODA) (0.2125 mole, 42.5523 g), 1,3-bis(3-aminophenoxy)benzene (APB) (0.0375 mole, 10.9625 g), 3,3&#39;, 4,4&#39;-biphenyl tetracarboxylic dianhydride (BPDA) (0.2385 mole, 70.1621 g), 4-phenylethynyl phthalic anhydride (PEPA) (0.02306 mole, 5.7245 g), N-methylpyrollidinone (NMP) (240 g) were added to a 1 L three neck flask equipped with a mechanical stirrer, condenser and nitrogen inlet. The reaction was stirred at 25° C. for 16 hours to form the phenylethynyl-terminated polyamide acid (η inh  =0.44 dL/g, NMP at 25° C.) followed by adding toluene (100 mL) and heating at 160° C. for 24 h. A yellow precipitate formed during the heating. After cooling, the yellow precipitate was poured into water, washed in boiling methanol and dried at 110° C. for 72 hours to afford a yellow solid in &gt;95% yield. The resulting phenylethynyl-terminated polyimide powder was insoluble in NMP at 25° C. The final Tg of 266° C. was measured after one hour at 350° C. A film cast from the polyamide acid solution and cured one hour at 350° C. was unaffected by MEK, toluene, jet fuel, and hydraulic fluid. 
     EXAMPLE 12 
     Synthesis of LaRC™-85/15 NA 
     The following example illustrates the synthesis of a norbornene(nadimide)-terminated imide cooligomer with theoretical number average molecular weight of 9200 g/mole. 3,4&#39;-Oxydianiline (ODA) (8.500 mmole, 1.7021 g), 1,3-bis(3-aminophenoxy)benzene (APB) (1.500 mmole, 0.4385 g), 3,3&#39;, 4,4&#39;-biphenyl tetracarboxylic dianhydride (BPDA) (9.500 mmole, 2.7951 g), nadic anhydride (NA) (1.000 mmole, 0.1642 g), N-methylpyrollidinone (NMP) (20.4 g) were added to a 100 mL three neck flask equipped with a mechanical stirrer, condenser and nitrogen inlet. The reaction was stirred at 25° C. for 16 hours to form the norbornene(nadimide)-terminated polyamide acid (η inh  =0.40 dL/g, NMP at 25° C.) followed by adding toluene (20 mL) and heating at 160° C. for 24 h. A yellow precipitate formed during the heating. After cooling, the yellow precipitate was poured into water, washed in boiling methanol and dried at 110° C. for 72 hours to afford a yellow solid in &gt;95% yield. The resulting norbornene(nadimide)-terminated polyimide was insoluble in NMP. The final Tg of 262° C. was measured after one hour at 316° C. A film cast from the polyamide acid solution and cured one hour at 316° C. was unaffected by MEK, toluene, jet fuel, and hydraulic fluid. 
     EXAMPLE 13 
     Synthesis of LaRC™-85/15MA 
     The following example illustrates the synthesis of a maleimide-terminated imide cooligomer with theoretical number average molecular weight of 9200 g/mole. 3,4&#39;-Oxydianiline (ODA) (8.500 mmole, 1.7021 g), 1,3-bis(3-aminophenoxy)benzene (APB) (1.500 mmole, 0.4385 g), 3,3&#39;, 4,4&#39;-biphenyl tetracarboxylic dianhydride (BPDA) (9.500 mmole, 2.7951 g), maleic anhydride (MA) (1.000 mmole, 0.0981 g), N-methylpyrollidinone (NMP) (20.1 g) were added to a 100 mL three neck flask equipped with a mechanical stirrer, condenser and nitrogen inlet. The reaction was stirred at 25° C. for 16 hours to form the maleimide-terminated polyamide acid (η inh  =0.42 dL/g, NMP at 25° C.) followed by adding toluene (20 mL) and heating at 160° C. for 24 h. A yellow precipitate formed during the heating. After cooling, the yellow precipitate was poured into water, washed in boiling methanol and dried at 110° C. for 72 hours to afford a yellow solid in &gt;95% yield. The resulting maleimide-terminated polyimide was insoluble in NMP. The final Tg of 264° C. was measured after one hour at 316° C. A film cast from the polyamide acid solution and cured one hour at 316° C. was unaffected by MEK, toluene, jet fuel, and hydraulic fluid. 
     EXAMPLE 14 
     Preparation of Moldings 
     The following process was used to test the compression molding of polymeric materials prepared according to the aforementioned examples. Dried powders of the polyimide copolymers (1 gram) were placed in a 1.25 inch square stainless steel mold which was placed in a preheated hydraulic press. For all phenylethynyl terminated copolymers, the molds were heated to 350° C. and pressure was applied. For maleic and nadic anhydride terminated copolymers, the molds were heated to 316° C. and pressure was applied. The pressure and temperature were held constant for 1 hour. The results are presented in Table 2. Poor processability means inadequate flow and an unconsolidated molding, good processability means a consolidated molding but little molding flash and excellent processability means a well consolidated molding with a lot of molding flash indicating lower pressures would probably provide good moldings. Quality indicates toughness of the molding and/or molding flash. 
     EXAMPLE 15 
     Preparation of Adhesive Tape 
     Solutions of several of the compositions in the Examples, i.e. 20-40% solids in NMP, were used to prepare adhesive tapes as follows. The solutions were applied to style 112, A1100 finish E-glass cloth which had been dried for 0.5 hours in a forced air oven. The coated cloths were air dried 1 hour each at 100°, 175° and 225° C. between application of subsequent coats. This procedure was continued until a nominal thickness of 0.012 inch was obtained. The area to be bonded was coated (primed) on each adherend with a dilute solution ( 18  5% solids) of the same composition as the adhesive tape and air dried 1 hour each at 100°, 175° and 225° C. prior to bonding with the adhesive tape. 
     EXAMPLE 16 
     Adhesive Bonding 
     The prepared adhesive tapes from Example 15 were cut into strips sufficient to cover the bond area so as to give a 0.5 inch overlap for surface-treated (Pasa Jell 107) titanium alloy (Ti-6AI-4V) four fingered panel adherends. Each tape was placed between the overlapped panels and the specimens were assembled in a bonding jig in such a manner as to hold the specimens securely while being bonded. The assembly was placed in a hydraulic press and 25 to 200 psi pressure was applied. The temperature, monitored by a thermocouple, was increased from room temperature to 371 ° C. during .sup.˜ 45 minutes and held for 1 hour while pressure was maintained. The heat was turned off and the press was allowed to cool under pressure to &lt;150° C. The bonded panel was removed from the press and jig and the individual specimens were separated with a metal shearer. The lap shear strengths were determined according to the procedure for ASTM-1002. Results are given in Tables 5-8. 
     EXAMPLE 17 
     Preparation of Graphite Fiber with Polymer Coating 
     Solutions of polymer from Examples 2 and 8 were coated onto continuous graphite fiber (Hercules, Inc., IM-7). After coating, the wet fiber was dried in ovens to remove most of the solvent and convert the poly(amide) acid to polyimide. The polymer-solids-to-graphite-fiber ratio was approximately one to two. This prepreg was held for composite fabrication. 
     EXAMPLE 18 
     Preparation of Graphite Fiber Reinforced Composite 
     The prepreg from Example 17 was cut into three inch square pieces and placed in a three inch by three inch matched-metal-die mold with the fiber all aligned in the same direction(unidirectional). Ten plies of the prepreg were stacked in this manner and the mold was placed in a heated hydraulic press. The mold was heated to 225° C. for 1 hour, then heated to 371 ° C. with 250 psi pressure applied after 5 minutes at 371 ° C. and held for 1 hour at 371 ° C. After cooling to ambient conditions, the pressure was released and a well consolidated composite part was removed from the mold. The resin content of the molded composite was calculated to be approximately 33 percent. 
     EXAMPLE 19 
     Measurement of Melt Viscosity and Melt Stability 
     The polyimide copolymers according to the present invention were subjected to melt rheology measurements using the Rheometrics System IV rheometer and a Brabender equipped with a Mixer Measuring Head. Both techniques indicate that these copolymers have low melt viscosities and good melt stabilities when heated to and held at the temperatures necessary to process into useful parts. Data for the polymer described in Example 8 from the rheometer is presented in Table 10. The melt viscosity in poise is shown for a sample held at 250° C. for one then heated from 250° C. to 371° C. at 4° C./min. 
     EXAMPLE 20 
     Preparation of Glass Coating 
     Solutions of the terminated polyamide acids according to the present invention were poured onto glass plates and spread to a uniform thickness using a doctor blade with a preset gap. After drying to a tack free form in a dust free atmosphere, the polymers were heated 1 hour each at 100°, 200° and either 316° or 350° C. to form a polyimide coating with high adhesion to the glass plate. 
     EXAMPLE 21 
     Preparation of Wire Coating 
     Steel and copper wires were dipped into the solutions of terminated polyamide acids and removed to form a polymer/solvent coating on the wires. After drying to a tack free form in a dust free atmosphere, the polymers were heated 1 hour each at 100°, 200° and either 316° or 350° C. to form a tough, flexible, polyimide coating with high adhesion to the steel or copper wire.