Polyamide-imide polymers having fluorine-containing linking groups
BACKGROUND OF THE INVENTION 
     This application is related to copending applications Ser. Nos. 316,254; 316,342; and 316,380, all filed on even date herewith. 
     1. Field of the Invention 
     The present invention relates to aromatic polyamide-imide polymers containing the hexafluoroisopropylidine or the 1-phenyl-2,2,2-trifluoroethane linking group having improved physical and chemical properties, and to a method for preparing such polymers. 
     2. Description of Related Art 
     Polyamide-imide polymers and copolymers are known in the art. These materials are generally prepared by the condensation polymerization of trifunctional acid monomers such as the 4-acid chloride of trimellitic anhydride and one or more aromatic diamines. Examples of such polyamide-imide polymers are disclosed in U.S. Pat. Nos. 3,347,828, 3,494,890, 3,661,832 and 3,920,612. These polymers may be characterized by extremely good high temperature properties (Tg of about 275° C. or higher), good high temperature stability, good tensile strength at high temperatures, good mechanical properties and good chemical resistance. These polyamide-imides are useful as wire enamel coatings, laminates, molded products, films, fibers impregnating varnishes and in other applications where high thermal stability is required. 
     One of the problems associated with such polymers is that they exhibit generally poor flow properties which render them difficult to process, particularly to injection mold or to spin into fibers. These polymers are also relatively hydrophilic and tend to absorb moisture which can effect their clarity, heat stability, processability, mechanical and electrical properties. 
     Attempts have been made in the art to improve the flow properties of polyamide-imide polymers. For example, U.S. Pat. No. 4,448,925 discloses including from about 1 to about 10 percent phthalic anhydride into the polymerization recipe to provide polyamide-imide copolymers having improved flow properties. However, this technique for improving flow properties is made at the expense of the heat stability and chemical resistance of the polymer. Yet another method for improving the flow properties of such polymers is to form blends thereof with up to about 10% by weight of a polyamide such as nylon 6 or nylon 66, as disclosed in U.S. Pat. No. 4,575,924. Once again however, such an approach to solving the flow problem is made at the expense of the thermal stability and optical clarity of the resultant polymer blend. 
     SUMMARY OF THE INVENTION 
     The present invention provides novel heat stable polyamide-imide polymers having excellent flow properties which render them more readily processible into fibers, films, sheets and other molded articles. The polymers are prepared by forming the polycondensation product of one or more aromatic diamines, one more trifunctional acid anhydride monomers, and one or more tetrafunctional aromatic dianhydrides, at least one of said monomers containing the groups ##STR2## linking two aromatic moieties, wherein R is CF 3  or phenyl. In addition to improved flow properties, the polyamide-imide polymers of this invention also exhibit improved solubility properties in most organic solvents, improved resistance to attack by chlorinated solvents such as trichloroethylene as compared with polyimides, improved hydrophobic properties as well as excellent thermal properties, including resistance to thermooxidative degradation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The polyamide-imide polymers of the present invention may be characterized as having structural units of the formula: ##STR3## wherein the terms (a) and (b) are equal to the mole fraction of each recurring unit in the polymer chain and (a) ranges from about 0.05 to about 0.95, (b) ranges from about 0.05 to about 0.95, with the proviso that the sum of (a) and (b) is equal to 1.00, n is a number sufficient to give rise to a polyamide-imide inherent viscosity of at least about 0.1 as measured from a solution of the polymer in dimethyl acetamide at 25° C. at a polymer concentration of 0.5 weight percent, A is a divalent aromatic moiety, and B is a tetravalent aromatic moiety of the residuum formula: ##STR4## With respect to polyamide-imides of formula 1, B may be the tetravalent residuum of either 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride, 1,3-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl] hexafluoropropane dianhydride, 1,1-bis(3,4-dicarboxyphenyl)-1-phenyl- 2,2,2-trifluoroethane dianhydride, 1,1-bis[4-(3,4-dicarboxyphenyl) phenyl]-1-phenyl-2,2,2-trifluoroethane dianhydride, and 4,4-bis[2-(3,4-dicarboxyphenyl) hexafluoroisopropyl] diphenyl ether dianhydride. 
     In the polyamide-imides of formula 1, A may be the divalent residuum of one or a combination of aromatic diamines having the formula: 
     
         NH.sub.2 --R--NH.sub.2                                     (4) 
    
     wherein R is the aromatic moiety of a phenylene, naphthalene, bis or polyphenylene type compound. R is preferably selected from: ##STR5## wherein R&#39; is a divalent moiety independently selected from a covalent carbon to carbon bond, methylene, ethylene, propylene, isopropylene, hexafluoroisopropylidene, 1-phenyl-2,2,2-trifluoroethylidene, dichloro and difluoroalkylenes up to 3 carbons, oxy, thio, sulfinyl, sulfonyl, sulfonamido, carbonyl, oxydicarbonyl, oxydimethylene, sulfonyldioxy, carbonyldioxy, disilanylene, polysilanylene up to 8 Si atoms disiloxanylene, and a polysiloxanylene up to 8 Si atoms. Preferably, the linking group R&#39; is selected from oxy, hexafluoroisopropylidene, 1-phenyl-2,2,2-trifluoroethylidene, carbonyl, methylene, a covalent carbon to carbon bond, disiloxanylene and polysiloxanylenes. Most preferably, R&#39; is a carbon to carbon bond methylene, hexafluoroisopropylidene, 1-phenyl-2,2,2-trifluoroethylidene and oxy. 
     The hydrogen atoms of the aromatic groups A and/or B may be substituted by one or more non-interfering monovalent substituents such as chloro, fluoro, lower alkyl or alkoxy having up to 6 carbon atoms, and phenyl. Also, the term &#34;aromatic&#34; as used herein is meant to include heteroaromatics wherein one or more of the ring atoms is replaced with --O--, --S-- or --N-- atoms. 
     Divalent diamine monomers which may be used in preparing the polyamide-imide copolymers of the present invention include: 
     m-phenylene diamine; 
     p-phenylene diamine; 
     1,3-bis(4-aminophenyl) propane; 
     2,2-bis(4-aminophenyl) propane; 
     4,4&#39;-diamino-diphenyl methane; 
     1,2-bis(4-aminophenyl) ethane; 
     1,1-bis(4-aminophenyl) ethane; 
     2,2&#39;-diamino-diethyl sulfide; 
     bis(4-aminophenyl) sulfide; 
     2,4&#39;-diamino-diphenyl sulfide; 
     bis(3-aminophenyl)sulfone; 
     bis(4-aminophenyl) sulfone; 
     4,4&#39;-diamino-dibenzyl sulfoxide; 
     bis(4-aminophenyl) ether; 
     bis(3-aminophenyl) ether; 
     bis(4-aminophenyl)diethyl silane; 
     bis(4-aminophenyl) diphenyl silane; 
     bis(4-aminophenyl) ethyl phosphine oxide; 
     bis(4-aminophenyl) phenyl phosphine oxide; 
     bis(4-aminophenyl)-N-phenylamine; 
     bis(4-aminophenyl)-N-methylamine; 
     1,2-diamino-naphthalene; 
     1,4-diamino-naphthalene; 
     1,5-diamino-naphthalene: 
     1,6-diamino-naphthalene; 
     1,7-diamino-naphthalene; 
     1,8-diamino-naphthalene; 
     2,3-diamino-naphthalene; 
     2,6-diamino-naphthalene; 
     1,4-diamino-2-methyl-naphthalene; 
     1,5-diamino-2-methyl-naphthalene; 
     1,3-diamino-2-phenyl-naphthalene; 
     4,4&#39;-diamino-biphenyl; 
     3,3&#39;-diamino-biphenyl; 
     3,3&#39;-dichloro-4,4&#39;-diamino-biphenyl; 
     3,3&#39;-dimethyl-4,4&#39;-diamino-biphenyl; 
     3,4&#39;-dimethyl-4,4&#39;-diamino-biphenyl; 
     3,3&#39;-dimethoxy-4,4&#39;-diamino-biphenyl; 
     4,4&#39;-bis(4-aminophenoxy)-biphenyl; 
     2,4-diamino-toluene; 
     2,5-diamino-toluene; 
     2,6-diamino-toluene; 
     3,5-diamino-toluene; 
     1,3-diamino-2,5-dichloro-benzene; 
     1,4-diamino-2,5-dichloro-benzene; 
     1-methoxy-2,4-diamino-benzene; 
     1,4-diamino-2-methoxy-5-methyl-benzene; 
     1,4-diamino-2,3,5,6-tetramethyl-benzene; 
     1,4-bis(2-methyl-4-amino-pentyl)-benzene; 
     1,4-bis(1,1-dimethyl-5-amino-pentyl)-benzene; 
     1,4-bis(4-aminophenoxy)-benzene; 
     oxylylene diamine; 
     m-xylylene diamine; 
     p-xylylene diamine; 
     3,3&#39;-diamino-benzophenone; 
     4,4&#39;-diamino-benzophenone; 
     2,6-diamino-pyridine; 
     3,5-diamino-pyridine; 
     1,3-diamino-adamantane; 
     3,3&#39;-diamino-1,1,1&#39;-diadamantane; 
     N-(3-aminophenyl)-4-aminobenzamide; 
     4-aminophenyl-3-aminobenzoate: 
     2,2-bis(4-aminophenyl) hexafluoropropane; 
     2,2-bis(3-aminophenyl) hexafluoropropane; 
     2-(3-aminophenyl)-2-(4-aminophenyl) hexafluoropropane; 
     2,2-bis[4-(4-aminophenoxy)phenyl] hexafluoropropane; 
     2,2-bis[4-(2-chloro-4-aminophenoxy)phenyl] hexafluoropropane; 
     1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane; 
     1,1-bis[4-(4-aminophenoxy)phenyl]-1-phenyl-2,2,2-trifluoroethane; 
     1,4-bis(3-aminophenyl)buta-1-ene-3-yne; 
     1,3-bis(3-aminophenyl) hexafluoropropane; 
     1,5-bis(3-aminophenyl) decafluoropentane; and mixtures thereof. 
     In the preferred embodiments of the present invention, polyamide-imides of formula 1 above are prepared by forming the polymer condensation product of a mixture of a mono-acid anhydride such as 4-trimellitoyl anhydride chloride (4-TMAC) having the structure: ##STR6## and 2,2-bis(3,4 dicarboxyphenyl) hexafluoropropane dianhydride (6F-Dianhydride) having the structure: ##STR7## with one or more aromatic diamines of the structure of formula 4 above. 
     Polyamide-imides of formula 1 above may also be prepared wherein the aromatic diamine monomer is 6F-Diamine or a mixture of 6F-Diamine and a non-fluorine containing aromatic diamine. 
     The polyamide-imide polymers of this invention may be based 100 mole % on fluorine-containing monomers as in the case of polymers of formula 1 wherein both the A and B moieties are based on fluorine-containing residuums of formula 2 or formula 3. More preferably, however, the polymers contain from about 1 to about 100 mole percent of fluorine containing monomers and more particularly from about 2 to about 50 mole percent of fluorine containing monomers, based on the total weight of acid/anhydride or dianhydride and amino monomers present in the polymer. 
     The acid/anhydride, dianhydride and diamine reactants, particularly those containing fluorine, are preferably substantially electronically pure and are referred to as electronic grade monomers. They generally should be at least about 98.5% pure, and more preferably at least about 99.5% pure. 
     The polyamide-imides of the present invention are preferably prepared by a solution polymerization process, i.e., by reacting the acid anhydride, dianhydride and diamine monomers in an appropriate solvent, optionally in the presence of a catalyst or an added inorganic salt such as lithium chloride or calcium chloride, and in a nitrogen atmosphere. Polymerization is conducted under anhydrous, isothermal polymerization conditions and preferably at a temperature of less than 35° C. The intermediate polyamide-polyamic acid reaction product is then cyclized to form the polyamide-imide either by chemical dehydration or by an appropriate heat treatment. The polymer may be recovered by precipitation in water or an alcohol such as methanol, and washed. 
     The solvents useful in the solution polymerization process for synthesizing the polyamide-imide compositions are the organic solvents whose functional groups do not react with the reactants to any appreciable extent. In addition to being inert to the system, and preferably, being a solvent for the polyamide-imide, the organic solvent must be a solvent for at least one of the reactants, preferably for all of the reactants. The normally liquid organic solvents of the N,N,dialkylcarboxylamide class are useful as solvents in the process. The preferred solvents are the lower molecular weight members of this class, particularly N,N-dimethylformamide and N,N-dimethylacetamide. Other useful solvents are N,N-diethylformamide, N,N-diethylacetamide, N,N-dimethylmethoxyacetamide, N-methyl caprolactam, and the like. Other solvents which may be used include dimethylsulfoxide. N-methyl-2-pyrrolidone, tetramethyl urea, pyridine, dimethylsulfone, hexamethylphosphoramide, tetramethylene sulfone, formamide, N-methylformamide, butyrolactone and phenols such as m-cresol. The solvents can be used alone or in combinations. 
     To obtain the maximum inherent viscosity, i.e., maximum degree of polymerization, for any particular combination of monomers, solvent, etc., and thus produce shaped articles such as films and filaments of optimum toughness, it has been found that the temperature throughout the reaction should be maintained at 50° C., preferably below about 35° C. The degree of polymerization of the polyamide-imides is subject to deliberate control. The use of equimolar amounts of the reactants under the prescribed conditions provides polyamide-imides of very high molecular weight. The use of either reactant in large excess limits the extent of polymerization. In addition to using an excess of one reactant to limit the molecular weight of the polyamide-imides, a chain terminating agent such as phthalic anhydride may be used to &#34;cap&#34; the ends of the polymer chains. Typical useful capping agents are monoanhydrides or monoamines such as phthalic anhydride, aniline or p-methylaniline. 
     In the preparation of the polyamide-imides, it is desired that the molecular weight be such that the inherent viscosity of the polymer is at least about 0.1, more preferably from about 0.2 to about 1.0. The inherent viscosity is measured at 25° C. at a concentration of 0.5% by weight of the polymer in a suitable solvent such as dimethylacetamide. 
     The quantity of organic solvent used in the process need only be sufficient to dissolve enough of one reactant, preferably the diamine, to initiate the reaction of the diamine and the other monomers. It has been found that the most successful results are obtained when the solvent represents at least 60% of the final solution, that is, the solution should contain 0.05-40% of the polymeric component, more preferably 15 to 25%. 
     The second step of the process (dehydration) is performed by treating the polyamide-polyamic acid with a dehydrating agent alone or in combination with a tertiary amine such as acetic anhydride or an acetic anhydride-pyridine mixture. The ratio of acetic anhydride to pyridine can vary from just above zero to infinite mixtures. 
     Tertiary amines having approximately the same activity as the preferred pyridine can be used in the process. These include isoquinoline, 3,4-lutidine, 3,5-lutidine, 4-methyl pyridine, 3-methyl pyridine, 4-isopropyl pyridine, N,N-dimethyl benzyl amine, 4-benzyl pyridine, and N,N-dimethyl dodecyl amine. These amines are generally used from 0.3 to equimolar amounts with that of the anhydride converting agent. Trimethyl amine and triethlene diamines are much more reactive, and therefore are generally used in still smaller amounts. On the other hand, the following operable amines are less reactive than pyridine: 2-ethylpyridine, 2-methyl pyridine, triethyl amine, N-ethyl morpholine, N-methyl morpholine, diethyl cyclohexylamine, N,N-dimethyl cyclohexylamine, 4-benzoyl pyridine, 2,4-lutidine, 2,6-lutidine and 2,4,6-collidine, and are generally used in larger amounts. 
     An alternative method for the preparation of the polyamide-imides is the thermal dehydration of the intermediate polyamide-polyamic acid. This transformation is generally performed in bulk, preferably in the form of a shaped article, e.g., film or filament of the polymamic acid. The dehydration is conducted stepwise starting at temperatures of about 100° C. and increasing the temperature progressively to about 300° C. or even higher, depending on the particular case, towards the end of the imidization step. The reaction is preferably performed under an inert atmosphere, and atmospheric or reduced pressures can be employed. 
     The polyamide-imides of the present invention generally have a weight average molecular weight (M w ) within the range of from about 5,000 to about 200,000 or more. The following examples are illustrative of the invention: 
     EXAMPLE 1 
     This example details the preparation of a polyamide-imide having the structure of formula 1 above and based on the reaction product of 0.10 mole of methylene dianiline (MDA), 0.08 moles of 4-trimellitoyl anhydride chloride (4-TMAC) and 0.02 moles of 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6F-Dianhydride) to yield a polyamide-imide containing about 20 mole percent 6F-Dianhydride, based on the total acid/anhydride monomer content, or about 10 mole percent based on the total acid/anhydride/diamine monomer content of the polymer. 
     A 1000 ml 4 neck flask, fitted with a stirrer, condenser, Y tube, powder addition funnel, thermometer, dry ice-acetone cooling bath and nitrogen blanket was charged under nitrogen atmosphere with 19.8 grams (0.10 moles) of MDA along with 208.0 grams of reagent grade dimethyl acetamide (DMAC). The mixture was stirred to dissolve the MDA and cooled down to a temperature of about -10° C. The 4-TMAC and 6F-Dianhydride were separately blended in a ratio of 16.84 g of 4-TMAC (0.08 moles) and 8.88 grams of 6F-Dianhydride (0.02 moles) and 1/2 of this blend (12.86 grams) was gradually added to the solution of MDA in DMAC over a period of about 20 minutes time while continuing agitation and maintaining a temperature of about -5° C. under nitrogen atmosphere. The remainder of the 4-TMAC/6F-Dianhydride blend (12.86 grams) was then gradually added over about 30 minutes time while continuing agitation at about -5° C. under nitrogen atmosphere. The beaker containing the blend was rinsed with 25 grams of additional DMAC and this was also added to the polymerization solution. The temperature of the solution was allowed to rise to 5° C. and 11.0 grams (0.10 mole) of triethylamine was charged dropwise over about 30 minutes time under nitrogen atmosphere while continuing agitation. Thereafter, 25 grams of DMAC was charged under nitrogen and the reaction mass was agitated at a temperature within the range of 6°-10° C. for three hours. Thereafter, 37.8 grams of pyrridine and 54.2 grams of acetic anhydride was charged under nitrogen atmosphere and the reaction mass was then allowed to agitate for about 12 hours at room temperature to complete cyclization. The reaction mass was then filtered to remove pyrridine hydrochloride. The polymer formed above was precipitated from solution in methanol by the addition of methanol to the reaction liquor, that is by reverse precipitation, using about 2000 ml of methanol for every 500 grams of polymeric solution. The resulting polymer was then washed with water and methanol, and chopped to a fine powder as an aqueous suspension in a mechanical blender. The powder was dried overnight in a vacuum oven at 60° C. 
     This polymer has the structural statistical formula: ##STR8## 
     EXAMPLE 2 
     This example sets forth the preparation of a polyamide-imide having the structure of formula 1 above based on the reaction product of 0.1 moles MDA, 0.05 moles of 4-TMAC and 0.05 moles of 6F-Dianhydride to yield a polyamide-imide containing about 50 mole percent 6F-Dianhydride based on the total acid/anhydride monomer content, or about 25 mole percent based on the total acid/anhydride/diamine monomer content of the polymer. 
     The procedure of Example 1 was repeated but the following materials and quantities were employed: 
     MDA--19.8 grams 
     4-TMAC--10.5 grams 
     6F-Dianhydride--22.2 grams 
     DMAC--258.0 grams 
     pyridine--37.8 grams 
     Triethylamine--11.0 grams 
     Acetic Anhydride--54.2 grams 
     Polymerization was conducted and sequential addition of the above reactants and materials and polymer recovery was as set forth in Example 1. 55.0 grams of a light yellow polymer in powdered form was obtained. 
     EXAMPLE 3 
     This example sets forth the preparation of a polyamide-imide having the structure of formula 1 above based on the reaction product of 0.2 moles MDA, 0.18 moles of 4-TMAC and 0.02 moles of 6F-Dianahydride to yield a polyamide-imide containing about 10 mole percent of 6F-Dianhydride based on the total acid/anhydride monomer content, or about 5 mole percent based on the total acid/anhydride/diamine monomer content of the polymer. 
     The procedure of Example 1 was repeated but the following materials and quantities were employed: 
     MDA--39.6 grams 
     4-TMAC--37.9 grams 
     6F-Dianhydride--8.9 grams 
     DMAC--351.0 grams 
     Pyridine--75.6 grams 
     Triethylamine--22.0 grams 
     Acetic anhydride--108.4 grams 
     Polymerization was conducted and sequential addition of the above reactants and materials and polymer recovery was as set forth in Example 1. 
     73.2 grams of a light yellow polymer in powdered form was obtained. 
     EXAMPLE 4 
     This example sets forth the preparation of a polyamide-imide having the structure of formula 1 above based on the reaction product of 0.25 moles of bis(4-aminophenyl) ether (ODA), 0.2 moles of 4-TMAC and 0.05 moles of 6F-Dianhydride to yield a polyamide-imide polymer containing about 20 mol percent of 6F-Dianhydride based on the total acid/anhydride monomer content, or about 10 mole percent based on the total acid/anhydride/diamine monomer content of the polymer. 
     The procedure of Example 1 was repeated, but the following materials and quantities were employed: 
     ODA--50.0 grams 
     4-TMAC--41.1 grams 
     6F-Dianhydride--22.2 grams 
     DMAC--1544.0 grams 
     Pyrridine--95.0 grams 
     Triethylamine--27.5 grams 
     Acetic anhydride--140.0 grams 
     Polymerization and sequential additions were conducted as set forth in Example 1 except that the amount of DMAC added to the reaction mixture up to the point just after the addition of triethylamine was such as to yield a 10% by weight polymerization solution. 400 grams of the total 1544 grams of DMAC was then added prior to the 3 hour polymerization step. The polymer was recovered as set forth in Example 1, yielding 96.5 grams of bright yellow fluffy solids. 
     COMPARATIVE EXAMPLE 5 
     This example sets forth the preparation of a control polyamide-imide of the prior art which does not contain the fluorine-containing monomers. The control polymer is based on the reaction product of 0.12 moles of MDA and 0.12 moles of 4-TMAC to yield a polyamide-imide of the prior art having the structure: ##STR9## 
     The procedure of Example 1 was repeated but the following materials and quantities were employed: 
     MDA--24.0 grams 
     4-TMAC--25.2 grams 
     DMAC--278.0 grams 
     Pyrridine--45.4 grams 
     Triethylamine--13.2 grams 
     Acetic anhydride--65.0 grams 
     Polymerization was conducted and sequential additions of the above reactants and materials and polymer recovery was as set forth in Example 1. 42.5 grams of a light yellow polymer in powdered form was obtained. 
     Properties of the polyamide-imide polymers prepared in accordance with Examples 1-5 appear in Table 1. 
     
                                           TABLE 1                                 
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4-TMAC     6F-Dianhydride                                                 
                         Inherent                                         
                              GPC           DSC TGA                       
     mole %                                                               
           mole %  Diamines                                               
                          Viscosity                                       
                              Mw   Mn  Mw/Mn                              
                                            Tg  5% wt. loss               
Example                                                                   
     (acid side)                                                          
           (acid side)                                                    
                   mol % dl/gm                                            
                              Mw   Mn  Mw/Mn                              
                                            deg. C.                       
                                                deg. C.                   
__________________________________________________________________________
1    80    20      100 (MDA)                                              
                         0.49 40500                                       
                                   21400                                  
                                       1.9  276 520                       
2    50    50      100 (MDA)                                              
                         0.68 64000                                       
                                   34900                                  
                                       1.8  298 500                       
3    90    10      100 (MDA)                                              
                         0.33 40000                                       
                                   21000                                  
                                       1.9  270 500                       
4    80    20      100 (ODA)                                              
                         1.37 167000                                      
                                   75800                                  
                                       2.2  300 490                       
5 Control                                                                 
     100   0       100 (MDA)                                              
                         0.33 41300                                       
                                   20700                                  
                                       2.0  271 510                       
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     The weight average molecular weight (M w ) and number average molecular weight (M n ) of the polymers described above were measured by gel permeation chromatography (GPC) performed on dilute solutions of the polymer in dimethylacetamide (DMAC). The actual apparatus employed consisted of a Waters (Millipore Corp.) programmable automatic sampler, vacuum pump, chromatography columns with heater, and a differential refractometer connected to a Shimadzu CR 30A data reduction system with accompanying software (version 1.1, Shimadzu part No. T/N 22301309-91). The refractometer used was a Waters model 410 and four chromatography columns, 500 Angstron, 1000 Angstron, 10,000 Angstron and 100,000 Angstron (available from Waters) were connected in series. The system was calibrated using multiple available polystyrene standards ranging in molecular weight as follows: 
     
         ______________________________________                                    
GPC CALIBRATlON                                                           
Calibration Standard                                                      
(Polystyrene)          Mol. Wt.                                           
______________________________________                                    
1                      470,000                                            
2                      170,000                                            
3                      68,000                                             
4                      34,500                                             
5                      9,200                                              
6                      3,200                                              
7                      1,250                                              
______________________________________                                    
 
    
     The standards are essentially monodisperse, consisting substantially of a single molecular weight. With the system thus calibrated the relative (relative to polystyrene standards) weight average molecular weight M w , the relative number average molecular weight M n , and polydispersity (d), M w  /M n  were obtained for polymers produced in accordance with the Examples given hereinabove. 
     Glass transition temperatures (Tg) were determined by differential scanning calorimetry using a Perkin Elmer DSC-4 calorimeter operating at 20° C./min., nitrogen atmosphere at 60 cc/min. Glass transition temperature by this method is generally defined as the point of intersection of tangent lines about the point of first inflection of the heating curve of the polymer. Thermogravimetric analysis (TGA) was performed with a Perkin Elmer 65-2 analyzer at 20° C./min. with an air rate of 80 cc/min. TGA values given herein are for five percent weight loss; in other words, the temperature at which 5% weight loss is observed is reported. 
     As is evident from the data in Table 1, the polyamide-imides of the present invention have Tg values essentially equivalent or higher than the control polyamide-imide of the prior art while at the same time exhibiting improved flow properties and injection molding properties. Thus, the flow properties of the polymers of this invention are markedly improved without significant alteration of the glass transition temperature (Tg). 
     EXAMPLE 6 
     The flow properties of the polyamide-imides of this invention, the control of Example 5, and a commercially available polyamide-imide sold by Amoco under its Trade Name Torlon® 4203L may be compared by forming compression molded discs of each polymer type. Discs of approximately 1 inch diameter were prepared using a hot press and piston cylinder mold to form the molded discs. Approximately 1/2 inch of polymer in powder form was sprinkled into the bottom of a mold piston and the piston was inserted between the pallets of a hot press and heated to 300° C. After coming to temperature, a pressure of 2000 psi was applied to the piston for 3 minutes. The pressure was then released, the mold cooled and the molded polymer disc having a thickness of about 20 mil was removed from the mold. Each of the polymers of Examples 1-4 produced a clear, transparent, yellow disc having good flexural properties. The control disc of Example 5 was a non-transparent, compressed, fused yellow powder which was sintered in nature, indicative of poor flow and poor molding properties. The disc made from Torlon was in the form of compressed, fused yellow green pellets. 
     EXAMPLE 7 
     A calendered film of the polyamide-imide polymer prepared in Example 1 was made by the following method. Two grams of the powdered polymer of Example 1 was evenly spread on the surface of a dried 3 mil sheet of Kapton® polyimide polymer, available from the DuPont Company, and another sheet of pre dried Kapton was placed over this to form a sandwich. This sandwich structure was heated on a hot plate at 200° C., and a metal plate heated to 250° C. was then placed on top of the sandwich structure. The structure was heated for 2 minutes under mild (50-100 psi) pressure to thoroughly dry the sample. The dried/heated structure was then passed between two rotating heated calender rolls having a gap of 5 mils, the top roll being at a temperature of 348° C. and the bottom roll at 314° C. The roll pressure was 1500 psi. The calendered sample was cooled and peeled from the upper and lower sheets of Kapton to yield a film having a thickness of 3.5 mil. This process was repeated two more times. 
     The average tensile, modulus and % elongation of the three samples were evaluated with the following results: 
     Tensile (K-PSI)--14.76 
     Modulus (M-PSI)--0.39 
     Elongation (%)--7.86 
     EXAMPLE 8 
     Melt spun fibers of the polyamide-imide polymer of Example 1 were made by the following method. Approximately 10 grams of dried powdered polymer prepared as in Example 1 was placed into the barrel of a one piece cylindrical die and subjected to a cold-form pressure of 3000 psi using a hydraulic press and a plunger. The resultant cold-formed compressed rod was fed under pressure into a hot melt spinning machine wherein the polymer was subjected to temperatures in the range of about 350° to 370° C., and extrusion pressures in the range of about 900 to 4000 psi. The melt was passed through a filter and a spinnerette die and the extruded fiber was taken up by a take up roller at speeds of 230 RPM and 690 RPM respectively. Four different fibers were prepared by this technique. The fiber properties and extrusion conditions are listed in Table 2. 
     
                       TABLE 2                                                     
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Spinnerette Conditions                                                    
             Pres-         Tensile                                        
Sam- Temp.   sure    Speed (GM/  Modulus                                  
                                        Elong.                            
                                              Den-                        
ple  (C)     (PSI)   (RPM) D)    (GM/D) (%)   ier                         
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A    350     1,530   230   0.98  25.73  34.06 9.85                        
B    360       900   230   0.87  25.74  38.91 7.17                        
C    360     4,000   690   1.55  27.41  36.45 9.00                        
D    370     1,100   690   0.62  23.25  31.10 7.97                        
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 *Speed (RPM): Take up speed of the meltspun fiber via a metal roller. (23
 &amp; 690 RPM equal 0.15 &amp; 0.4 gm/min sample respectively.                   
 
    
     The polyamide-imides of the present invention may be used in their preimidized form (polyamide-polyamic acid) as solutions in organic solvent to produce films, coatings, composites and the like which may be cured in-situ to form the polyamide-imide by the application of heat. 
     The polyamide-imides may be molded using techniques such as compression molding or injection molding to produce melt fabricated articles such as fibers, films, safety masks, windshields, electronic circuit substrates, airplane windows or the like. Shaping may be accomplished by subjecting the polymer to temperatures of at least about 300° C. and pressure of at least about 500 psi. They may be compounded with graphite, graphite fiber, molybdenum disulphide or PTFE for the production of self-lubricating wear surfaces useful for piston rings, valve seats, bearings and seals. They may also be compounded with fibers such as glass, graphite or boron fibers to produce molding compounds for high strength structural components such as jet engine components. The polyamide-imides may also be compounded with friction materials to produce molding compounds for high temperature braking components or with abrasive materials such as diamonds for high speed grinding wheels. 
     The polyamide-imides may be cast as films useful as wire and cable wraps, motor slot liners or flexible printed circuit substrates. They may be used as coatings on substrates such as aluminum or silicone dioxide. They are also useful to produce high temperature coatings for magnetic wire, dip coatings for various electronic components, protective coatings over glass, metal and plastic substrates, wear coatings, and photoresist coatings useful in microelectronic processing. 
     The polyamide-imides may also be used to produce high temperature adhesives for bonding aerospace structures or electrical circuitry, conductive adhesives when mixed with conductive fillers such as silver or gold for microelectronic applications, or adhesives for glass, metal or plastic substrates. 
     The polyamide-imides may also be used as varnish compositions or matrix resins to produce composites and laminates. The varnish compositions and matrix resins may be used to impregnate glass or quartz cloth, or graphite or boron fibers, for the production of radomes, printed circuit boards, radioactive waste containers, turbine blades, aerospace structural components or other structural components requiring high temperature performance, non-flammability and excellent electrical properties. 
     In general, the polyamide-imides and polyamic-acid precursors of this invention may be used in all applications as disclosed in copending application Ser. No. 124,704, filed in the U.S. Patent and Trademark Office on Nov. 24, 1987, the disclosure of which application is incorporated herein by reference. 
     It is to be understood that the above described embodiments of the invention are illustrative only and that modifications throughout may occur to those skilled in the art. Accordingly, this invention is not to be regarded as limited to the embodiments disclosed herein, but is to be limited as defined by the appended claims.