Abstract:
Self bondable polyamides are prepared by reacting an aromatic diisocyanate or diamine with a mixture of terephthalic acids and one or two aliphatic dibasic acid having at least 6 carbon atoms and a monocarboxylic acid. These self bondable amides can also be used as topcoats for wires having basecoats of another polymer, e.g., a polyester, polyester-imide, or polyamide-imide.

Description:
REFERENCE TO RELATED APPLICATIONS 
     The present invention is an improvement on the invention disclosed in Walrath et al application 311,385, filed Oct. 14, 1981, now U.S. Pat. No. 4,420,535, the entire disclosure of which is hereby incorporated by reference and relied upon. For convenience the entire disclosure of the Walrath et al application is reproduced below. 
     BACKGROUND OF THE WALRATH ET AL. INVENTION 
     The present invention relates to a novel self bondable aromatic aliphatic polyamide. 
     An all-aromatic polyamide as made in accordance with Allard U.S. Pat. No. 3,642,715 does not exhibit self-bonding characteristics even when tested via the NEMA Bonding Test No. 57.1.1.2. at temperatures up to 260° C. Tha all-aliphatic polyamides as described by the work of Otis U.S. Pat. No. 4,216,263 and Kawaguchi U.S. Pat. No. 4,163,826 are thermoplastic in nature and exhibit good bonding characteristics but do not offer the excellent humidity resistance and resistance to attack by refrigerants as do the aromatic-aliphatic polyamides of the present invention. 
     Gilman U.S. Pat. No. 2,268,586 has a broad teaching of making polyamides by reacting a dibasic acid with a diisocyanate but does not show self-bondable polyamides. 
     Onder U.S. Pat. No. 4,072,665 discloses a novel copolymer of the formula ##STR1## where R is 60 to 85 percent of an aliphatic dibasic carboxylic acid with (CH 2 ) x  recurring units and x being an integer of 7 to 12 inclusive, the remaining 15 to 40 percent of R being m-phenylene. The proportions are indicated to be critical in Onder. Onder also indicates on column 6, lines 43-52 that a portion of the recurring units up to 10% can have R from a different dicarboxylic acid, e.g. terephthalic acid. Onder uses his products for many things including wire coatings, column 6, lines 11-22. However, Onder makes no mention of a solution cast film which is baked and yet retains self-sealing or adhesive properties. 
     SUMMARY OF THE WALRATH ET AL INVENTION 
     There have now been prepared random aromatic-aliphatic copolyamides having the recurring unit ##STR2## where AL is the divalent hydrocarbon residue of an unsubstituted aliphatic dicarboxylic acid having 6 to 36 carbon atoms or more, usually Al is (CH 2 ) x  where x is 4 to 34, preferably 6 to 12, most preferably 10. However, Al can be the residue of an unsaturated dicarboxylic acid, e.g. dimerized linoleic acid or dimerized oleic acid or dimerized tall oil. R is tolylene, phenyl, ##STR3## where F is O, CH 2  or SO 2 . Less preferably all or a part of R can be cycloaliphatic, e.g. cyclohexylene or methylenedicyclohexyl, Ar is p-phenylene, y is 35 to 80% of the recurring units and z is 65 to 20% of the recurring units. Usually y is 40 to 70% of the recurring units and preferably y is about 60 to 70%, most preferably 65% of the recurring units. If y is above 70% there is a tendency to gel on standing. 
     The copolyamides can be prepared in conventional manner by reacting a mixture of the dicarboxylic acids, e.g. dodecanedioic acid and terephthalic acid with a diisocyanate, e.g. toluene diisocyanate or methylene diphenyldiisocyanate, or with the corresponding diamine, e.g. toluene diamine, 4,4&#39;-methylene diphenyl diamine (methylene dianiline), oxydianiline, phenylene diamine, diaminodiphenyl sulfone, or a mixture of such diisocyanates or of such diamines. As indicated there can also be employed a minor amount of 4,4&#39;-methylene diphenyl diamine or cyclohexyl diamine. In reacting with the diamine rather than the diisocyanate it is of course possible to employ other acylating agents than the acid, e.g. there can be used the acyl halides, e.g. the dichloride or dibromide of dodecanedioic acid or the lower alkyl esters, e.g. dimethyl dodecanedioate, diethyl dodecanedioate, and dibutyl dodecanedioate. 
     Preferably in the formula R has the mole percent ratio of 4-methyl-m-phenylene/2-methyl-m-phenylene/4,4&#39;-methylene diphenylene in the range of 40/10/50 to 80/20/0. The reaction is carried out in an amide solvent such as N-methyl-2-pyrrolidone (NMP). 
     The copolyamides of the invention are useful as a self-bonding coating for magnet wire. This coating is usually applied in an amide based solvent system, e.g., N-methyl pyrrolidone or a mixture of N-methyl pyrrolidone and an aromatic hydrocarbon. The major advantages offered by this novel enamel are: 
     (1) High temperature retention of bond strength. 
     (2) The quality of the base coat is not lessened, and in some cases, the quality of the base coat is improved by the bonding overcoat. 
     (3) The coating is resistant to attack by refrigerants. 
     (4) The coating has improved humidity resistance. 
     (5) The coating has improved chemical resistance. 
     (6) The coating is less costly than commercially available alternatives. 
     (7) The end user&#39;s cost is reduced by elimination of a costly secondary insulation. 
     (8) By eliminating the solvent-borne secondary insulation requirement, the bond coat offers obvious ecological advantages. 
     (9) Good adhesion to self-supporting high-temperature films. 
     Thus, the novel, self-bonding wire coating provides the magnet wire user an economical and ecological alternative with significant improvements in bond strengths, hermetic resistance, and chemical resistance when compared to other self-bond wire coatings. This novel coating also offers the motor manufacturer an option to eliminate secondary insulations as the self-bonding wire coating will produce results equivalent to or better than those achieved with the secondary insulations currently used. 
     It was previously pointed out that the copolyamides of the present invention are superior, in humidity resistance and resistance to attack by refrigerants, to the products of Otis U.S. Pat. No. 4,216,263. Thus when a sample of a polyamide as described in Otis is subjected to a 100 percent humidity at 70° C., it exhibits an initial resistance of about 370,000 megohms. After aging one week, the megohm resistance was about 280,000 megohms; after two weeks, the resistance had dropped to about 160,000 megohms. The aromatic-aliphatic polyamide of the present invention (based on Mondur TD-80, 4,4-methylene diphenylenediisocyanate, terephthalic acid and dodecanedioic acid), when submitted to this test, gave the following results: 
     
         ______________________________________        After         AfterInitial      One Week      Two Weeks______________________________________422,000 megohms        900,000 megohms                      820,000 megohms______________________________________ 
    
     The dielectrics of the all-aliphatic polyamides of Otis were reduced by 50 percent after two weeks at 100 percent relative humidity and 70° C. The aromatic-aliphatic polyamides of this invention, however, did not significantly change after the two-week aging. The all-aliphatic nylons are true thermoplastics, unlike the aromatic-aliphatic polyamides of the invention which, when initially bonded at 200° C., retain good bond strength at 200° C. The aromatic-aliphatic polyamides of the invention, when coated over a polyester of the type described by Meyer in U.S. Pat. Nos. 3,201,276 and 3,211,585, will upgrade the base polyester to a NEMA Class 155° C. or greater magnet wire coating system. The entire disclosure of the Meyer patents are hereby incorporated by reference and relied upon. When coated over other wire enamels or wire enamel systems, the inherent properties of the coated wire are not adversely effected. The aliphatic-aromatic polyamides of this invention will self-bond at temperatures of 170° C. or greater when tested in accordance with NEMA Test Specification 57.1.1.2 with resulting bond strengths of greater than seven pounds when broken at 180° C. 
     When this novel enamel is coated over a self-supporting, high-temperature film, such as a polyimide, polyparabanic acid, polyamide, or polyamide-imide film, then baked to dry, the film may then be self-bonded and will exhibit outstanding inner laminar adhesion. 
     If a polyamide, in 70/30 NMP/xylene, is made from 100% of an alkanedioic acid such as dodecanedioic acid and a mixture of toluene diisocyanate and methylene diphenyl diisocyanate, then the enamel product gels on standing. In fact there is a tendency for gelation to occur if the amount of dodecanedioic acid goes above 70 mole percent and especially above 78 mole percent based on the total of dodecanedioic acid and terephthalic acid. 
     Among the advantages of the copolyamides of the invention, in addition to or in amplification of those set forth above are: 
     (1) The wire coating is bondable at 200° C. and yet retains good bond strength at 180° C. However, once the polymer is &#34;Heat Set&#34; above the apparent glass transition temperature of the aromatic-aliphatic polyamide, the apparent glass transition temperature increases, thus giving some thermoset properties to the coating. 
     (2) The aromatic-aliphatic polyamide system of the invention is the only amide bonding system offered which is not in part a physical blend of an all aliphatic amide such as Nylon 6;6,6; 11 or 12. The aromatic-aliphatic polyamide is, however, an in situ reaction product of an aromatic diacid and an aliphatic diacid, preferably with a blend of aromatic diisocyanates to yield a random aromatic-aliphatic polymer. The preferred reactants are terephthalic acid and dodecanedioic acid with toluene diisocyanate and methylenediphenyl diisocyanate in a 70:30 mole ratio. The reaction is carried out in an amide-type solvent such as N-methyl-2-pyrrolidone. 
     (3) The aromatic-aliphatic polyamide, when coated over ISONEL 200, yields a Class 155° C. magnet wire; and, with the exception of the heat shock, displays Class 180° C. properties. 
     When coated over ISOMID, excellent properties as a Class 180° C. magnet wire are observed. 
     (4) The aromatic-aliphatic polyamide coated over ISONEL 200 passes the A. O. Smith Freon Blister Test; conventional Nylon 6,6 coated over ISONEL 200 fails this test. 
     (5) The moisture resistance of the aromatic-aliphatic polyamide is also superior to the Nylon 11 types. 
     (6) The aromatic-aliphatic polyamides offer a significant cost advantage over the systems based upon Nylon 11 or 12. 
     As indicated above the enamels of the invention exhibit good bond strengths when coated over ISONEL 200 and ISOMID wire enamel. Thus when bonded at 200° C. for 20 minutes they have shown bond strengths of 1 to 6.2 lbs. and even up to 7.4 lbs. at 180° C. without degrading other wire properties by application of the bond coat. 
     The heat-bondable copolyamide film of the invention can be applied by conventional wire coating techniques to give a wire that may be wound into coils, armatures, stators, etc., and heat bonded, thereby eliminating the need for an impregnating varnish, to give a wire-insulation system of unusual thermal resistance. In the process of eliminating the need for a varnish dip, the need for expensive dipping apparatus ovens, lengthy cure cycles, and high energy costs are eliminated. 
     The bondable copolyamide of the invention can be employed, for example, as a top coat over a wire having a base coat or coats of, for example: 
     1. a glycerine or other aliphatic polyhydric alcohol polyester, e.g. glycerine-ethylene glycol terephthalate polymer as in Precopio U.S. Pat. No. 2,936,296, 
     2. tris(2-hydroxyethyl)-isocyanurate polyester, e.g. tris(2-hydroxyethyl) isocyanurate (THEIC)-ethylene glycol-terephthalate polymer as in Meyer U.S. Pat. No. 3,342,780. 
     3. a polyester coated with a amide-imide polymer, e.g. the polyester of Precopio or Meyer U.S. Pat. No. 3,342,780 coated with an amide-imide polymer as shown in Koerner U.S. Pat. No. 3,022,200 and Standard Oil British Pat. No. 1,056,564. 
     4. a polyester-imide which is the reaction product of THEIC, ethylene glycol, terephthalic acid (or isophthalic acid), methylene dianiline (or oxydianiline) and trimellitic anhydride, e.g. as in Meyer U.S. Pat. No. 3,426,098. In place of THEIC, there can be used glycerine, e.g. as in the polyester-imides of Schmidt U.S. Pat. No. 3,697,471. Likewise, there can be used as the base coat the diethylene glycol or triethylene glycol monoether modified polyester-imide resins of Keating U.S. Pat. No. 4,119,608, 
     5. amide-imide coated polyester-imide as in the Keorner and Standard Oil patents, 
     6. monolithic amide-imide as in the Standard Oil patent, 
     7. polyimide such as Pyre ML as in Edwards U.S. Pat. Nos. 3,179,634; 3,179,630; 3,179,631; 3,179,632, and 3,179,633, 
     8. as a coating over an acrylic (acrylic-methacrylic acid ester) top coated polyimide of the type of Lecton (DuPont), 
     9. conventional Formvar (polyvinyl formal), epoxy (e.g. bisphenol A-epichlorohydrin), urethane, and nylon top coated urethane. The entire disclosures of the Meyer U.S. Pat. No. 3,342,780, Precopio, Koerner, Standard Oil, Keating, Meyer U.S. Pat. No. 3,426,098, and the Edwards patents are hereby incorporated by reference and relied upon. 
     The wire enamels can be applied to either bare or base coated copper, aluminum, silver, or other wires using conventional coating procedures and wire speeds, e.g., 30-150 ft/min. and curing the wire is carried out at conventional temperatures. The speed is adjusted according to wire size and enamel to obtain optimum cure as is known in the art. 
     The copolyamides of the invention are also useful as bondable coatings over film wrapped wire, e.g. 
     1. Kapton--a polyimide film of DuPont as in the Edwards patents. 
     2. Nomex--a DuPont aromatic polyamide (isophthalic acid with an aromatic diamine). 
     The copolyamides of the invention can be used as adhesives to apply over self-supporting films, e.g. used in printed circuit boards and capacitors. Typical self-supported films include Kapton polyimide, Mylar (polyethylene terephthalate) polyester, Nomex, polytetrafluoroethylene and perfluoroethylene-perfluoropropylene copolymer. 
     The copolyamides of the invention can be employed as cast films for adhesive use. The film is cast from solution and can then be used as an adhesive. 
     In film, strand or filament form the copolyamide can be used as a substitute for Dacron in wrapped glass cloth. Dacron is not high temperature resistant. Hence replacing the Dacron filaments by filaments of the copolyamide of the invention gives higher temperature resistant products. 
     Nomex is available as cast or sheet insulation. The heat bondable copolyamide of the invention can be used as a wrapping therefore to hold the Nomex together. 
    
    
     BRIEF DESCRIPTION OF THE WALRATH ET AL DRAWINGS 
     FIG. 1 is a graph of bond strength vs. percent of aliphatic dibasic acid (dodecanedioic acid); and 
     FIG. 2 is a graph comparing the bond strength of the copolyamide with that of Nylon 11. 
     The composition can comprise, consist essentially of, or consist of the materials set forth. 
    
    
     EXAMPLE 1 
     This example is a working example of the present invention. 
     
         ______________________________________                   LoadRaw Materials           in Grams______________________________________1 N--methyl-2-pyrrolidone                   41682 Toluene diisocyanate (Mondur TD-80)*                   10333 4,4&#39; Methylene diphenyldiisocyanate                    6374 Terephthalic Acid      4945 Dodecanedioic Acid    12676 Xylene                22437 N--methyl-2-pyrrolidone                   1050______________________________________ *Mondur TD80 is a 80/20 blend of 4methyl-m-phenylene diisocyanate and 2methyl-m-phenylene diisocyanate and is commercially available from Mobay Chemical Company, Pittsburgh, Pennsylvania. 
    
     Parts one through three charged at room temperature into a 12-liter, round-bottom reaction flask, equipped with an agitator, a thermometer, an inert gas purge, and a water-cooled condenser fitted with a flexible tube which was immersed in a flask containing a mixture of water and denatured ethyl alcohol. (The reaction by-products carried through the condenser by the carbon dioxide and nitrogen are trapped in the water-alcohol solution). Parts four and five were added at room temperature with agitation and a blanket of nitrogen was applied over the reaction. The temperature was raised slowly by use of an electric heating mantel to approximately 75° C. when carbon dioxide evolution began. The external heat was then reduced and the temperature of the batch was allowed to rise over a four-hour time period to approximately 170° C. At about 80° C., the batch became clear. After an approximate four-hour hold at 170° to 175° C., the reaction was allowed to cool slowly to room temperature over night. The next morning the reaction mixture was sampled and a 60 percent solution in N-methyl-2-pyrrolidone was determined to have a viscosity at 25° C. on the Gardner-Holdt scale of W 1/2. Parts six and seven were then added. The final viscosity of the solution at 25° C. was Z on the Gardner-Holdt scale, or 2,500 centipoises as measured by a Brookfield RVT Viscometer. 
     The percent non-volatiles of the solution were determined to be 27 percent by baking a two-gram sample for two hours at 200° C. The specific gravity of the solution was determined to be 1.025 at 25° C. This solution was then used to overcoat a commercially available polyester (ISONEL 200)**. The test properties were as shown in Table One. It was also coated over a commercially available polyester-imide (ISOMID)*** and tested as shown in Table One. 
    
    
     The temperature of coating the wires in all of the examples was 370°-480° C. 
     EXAMPLE 2 
     
         ______________________________________                   LoadRaw Materials           in Grams______________________________________1 N--methyl-2-pyrrolidone                   41682 Toluene diisocyanate (Mondur TD-80)                   10333 4,4-Methylene diphenyldiisocyanate                    6374 Terephthalic Acid      4945 Dodecanedioic Acid    12676 Xylene                19827 N--methyl-2-pyrrolidone                    910______________________________________ 
    
     The reaction was carried out much in the same fashion as described in Example one, with the exception of the over night cooling step. The reaction medium was sampled after a three-hour hold at 165° to 180° C. at 60 percent in N-methyl-2-pyrrolidone and found to have a viscosity of V 1/2 at 25° C. on the Gardner-Holdt Scale. The batch was then reduced with six and seven to a final viscosity of Y 1/4 at 25° C. on the Gardner-Holdt Scale at 28.45 percent non-volatiles determined as described in Example One. 
     The material was then coated over a polyester (ISONEL 200), a polyester imide (ISOMID), a polyester coated with a polyamide-imide, (ISONEL 200 overcoated with trimellitic anhydride-methylene dianiline polymer), a polyamide-imide (trimellitic anhydride-methylene dianiline polymer) wire coating and as a monolithic enamel. The results of the testing on the coated conductors are as shown in Table One. 
     EXAMPLES 3 THROUGH 8 
     Examples Three through Eight describe the effects of the mole percent ratio of aliphatic diacid to aromatic diacid. The effects on bond strength are shown on Graph Number One. (Bond strength versus percent aliphatic diacid). Also shown on Graph Number One is the relationship of bond strength to breaking temperature. The other properties of the coated conductors are as displayed in Table One. 
     The general procedure for making these enamels is as described in Example One. 
     
         ______________________________________Example     3       4      5     6    7     8Reactants   Batch Weight______________________________________1   N--methyl-2-           644     611  623   633  655   664    pyrrolidone2   Toluene     159     159  159   159  159   159    diisocyanate3   4,4&#39;-methylene            98      98   98    98   98    98    diphenyl    diisocyanate4   Terephthalic            76     141  118    97   54    32    Acid5   Dodecanedioic           194     104  135   164  224   254    Acid6   Xylene      327     382  346   331  335   3667   N--methyl-2-           119     140  241   140  126   210    pyrrolidoneGardner-Holdt       Y 3/4   X 1/2  Y+    Z+   Y 1/4 YViscosity @ 25° C.Percent Non-       27.8    24.9   25.2  26.8 23.8  25.7VolatilesDetermined2 gm., 2 hr.,200° C.______________________________________ 
    
     EXAMPLE 9 
     This example describes the use of an aliphatic acid as described in the disclosure where X equals four. 
     
         ______________________________________Reactants             Batch Weight______________________________________1 N--methyl-2-pyrrolidone                 6002 Toluene diisocyanate                 1713 4,4&#39; Methylene diphenyldiisocyanate                 1054 Terephthalic Acid    815 Adipic Acid         1336 Xylene              257Gardner-Holdt Viscosity (25° C.)                 W 1/2Determined Percent Non-Volatiles                 32.4(2 grams, 2 hours, 200° C.)______________________________________ 
    
     This example was prepared as described in Example One. 
     The properties of this enamel when used to overcoat ISOMID are as described in Table One. 
     EXAMPLE 10 
     This example demonstrates the use of a diabasic acid where X equals eight. 
     
         ______________________________________Reactants             Batch Weight______________________________________1 N--methyl-2-pyrrolidone                 5602 Toluene diisocyanate                 1453 4,4&#39; Methylene diphenyl diisocyanate                  894 Terephthalic Acid    695 Sebacic Acid        1566 N--methyl-2-pyrrolidone                 2077 Xylene              411Gardner-Holdt Viscosity (@ 25° C.)                 X 1/2Determined percent Non-Volatiles                 24.2(2 grams, 2 hours, 200° C.)______________________________________ 
    
     This example was prepared in accordance with the procedure described in Example One. 
     The test results obtained when this enamel was applied over 18-AWG copper wire coated with ISOMID are shown in Table One. 
     EXAMPLE 11 
     This example indicates that the allowable number of methylene groups between the two carboxyl groups of the aliphatic diacid may not have an upper limit. 
     
         ______________________________________Reactants             Batch Weight______________________________________1 N--methyl-2-pyrrolidone                 5852 Toluene diisocyanate                  943 4,4&#39; methylene diphenyl diisocyanate                  684 Terephthalic Acid    455 Empol 1010*         2836 N--methyl-2-pyrrolidone                 1407 Xylene              310Gardner-Holdt Viscosity (@ 25° C.)                 Y 1/4Determined percent Non-Volatiles                 29.4(2 grams, 2 hours, 200° C.)______________________________________ 
    
     This reaction was cooked in accordance with the procedure outlined in Example One. The test results obtained when this enamel was applied over 18-AWG copper wire coated with ISOMID are shown in Table One. 
     &#34;Empol 1010 is a C 36  dimerized fatty acid available from Emery Industries, Inc., Cincinnati, Ohio. 
     EXAMPLE 12 
     This working example demonstrates the use of a cyclic aliphatic diisocyanate to replace a portion of the aromatic diisocyanate. 
     
         ______________________________________Reactants             Batch Weight______________________________________1 N--methyl-2-pyrrolidone                 6002 Toluene diisocyanate                 1463 Desmondur W*         974 Dodecanedioic Acid  1795 Terephthalic Acid    766 N--methyl-2-pyrrolidone                 1557 Xylene              323Gardner-Holdt Viscosity (@ 25° C.)                 Z 1/4Determined Percent Non-Volatiles                 27.5(2 grams, 2 hours, 200° C.)______________________________________ *Desmondur W is a cycloaliphatic diisocyanate available from Mobay Chemical Company, Pittsburgh, Pennsylvania. 
    
     This enamel was prepared as described in Example One. It was then applied as an overcoat to ISOMID-coated copper wire. The test results obtained from this construction are as shown in Table One. 
     EXAMPLE 13 
     This example shows the use of all toluene diisocyanate to make an acceptable bond coat. 
     
         ______________________________________Reactants            Batch Weight______________________________________1 N--methyl-2-pyrrolidone                6062 Toluene diisocyanate                2263 Dodecanedioic Acid 1944 Terephthalic Acid   765 N--methyl-2-pyrrolidone                2106 Xylene             350Gardner-Holdt Viscosity (@ 25° C.)                X 1/4Determined percent Non-Volatiles                27.2(2 grams, 2 hours, 200° C.)______________________________________ 
    
     This example was prepared using the procedure described in Example One. However, as indicated no 4,4&#39;-methylene diphenyl diisocyanate was employed. 
     When coated over 18-AWG ISOMID coated wire, the bond coat gave the properties as shown in Table One. 
     COMPARATIVE EXAMPLE 1 
     A commercial solution of Nylon 66 was coated over a polyester wire enamel, namely, ISONEL 200. The resulting magnet wire exhibited the properties shown in Table One. 
     COMPARATIVE EXAMPLE 2 
     A solution of Nylon 11 was prepared in accordance with U.S. Pat. No. 4,216,263 by Otis. The viscosity of this solution was approximately Z5 1/2 on the Gardner-Holdt Scale at 25° C. The percent non-volatiles of the solution was determined to be 16.1 percent by baking a two-gram sample for two hours at 200° C. This enamel solution was coated over a polyester-imide of the ISOMID type on AWG-24 copper wire. The electrical and bonding test results are shown in Table One. 
     COMPARATIVE EXAMPLE 3 
     A solution of Nylon 11 was prepared in accordance with U.S. Pat. No. 4,216,263 by Otis. The viscosity of the solution was approximately Z2 3/4 on the Gardner-Holdt Scale at 25° C. at approximately 16.1 percent non-volatiles determined as in Example One. This enamel was coated over a polyesterimide wire coating, namely ISOMID on 18-AWG copper wire. The test results are shown on Table One. A comparison of the bond strength of this example to the preferred composition of this disclosure as described by Example One is shown on Graph Number Two. 
     COMPARATIVE EXAMPLE 4 
     A solution of Nylon 11 was prepared in accordance with U.S. Pat. No. 4,216,263 Otic. The viscosity of this solution was approximately Z3 1/2 on the Gardner-Holdt Scale at 25° C. The percent non-volatiles determined as in Example One were 16.8 percent. This enamel was coated over a polyester wire coating, namely ISONEL 200 on 18-AWG copper wire. The electrical and bonding test results are as shown in Table One. 
     
         ______________________________________Abbreviation Key for Table 1______________________________________F.O.M.      Figure of MeritHrs.        HoursFPM         Feet per MinuteVPM         Volts Per MilBase Coat:PE          Polyester of the ISONEL ® 200 typePEI         Polyester-imide of the ISOMID ® typePAI         Aromatic polyamide-imidePAI/PE      Polyamide imide based upon       4,4&#39; methylene diphenyl diisocyanate       and trimellitic anhydride over-       coated over a polyester of the       ISONEL ® 200 typeNone        Indicates the bond coat was applied       in eight passes to obtain a three-       mil buildBuild       total increase in the wire diameter       as a result of the coating.Wire Size   All AWG sizesSpeed       The rate the wire traveled as it       was coated in multiple passes and       baked in a 15-foot, gas-fired oven.Appearance:G           Indicates good or smooth surface.VSW         Indicates smooth surface with a       very slight wave.SW          Indicates minor flaws in the       coating surfaceHeavy Grain Indicates a rough surface without       blistersRough       Is an indication the coating is       unacceptable as it may contain       blisters, or a very heavy grain,       or an extreme wave.(+)         Indicates slightly better than       given rating(-)         Indicates slightly worse than given       ratingSnap        Measured in accordance with NEMA       Standards Publication Part 3,       paragraph 3.1.1.Mandrel After Snap       Smallest mandrel around which wire       which has been &#34;snapped&#34; as above can       be wound without exhibiting surface       cracks.Abrasion    Measured in accordance with NEMAUnilateral  Standard Publication Part 3,Scrape      paragraph 59.1.1.Windability 1500 volts are passed through a       six foot long wire sample which is       wrapped around a specified mandrel.       The mandrel moves along the wire       at fixed rate elongating and       abrading the wire. Failure is       described when three shorts occur       along the surface of the sample.Cut Through Measured in accordance with NEMA       Standards Publication Part 3,       paragraph 50.1.1.2.Heat Shock  Tested in accordance with NEMA       Standards Publication, Part 3,       paragraph 4.1.1.Burn Out    Tested in accordance with NEMA       Standards Publication, Part 3,       paragraph 53.1.1.4. F.O.M. is       Figure of Merit calculated as       described in NEMA Standards       Publication, Part 3, paragraph       53.1.1.3.A. O. Smith A five-foot sample of wire isFreon Blister       wound into a coil which producesTest        four to six percent stretch, baked for       two hours at 150° C., then cooled       to room temperature. The samples       are then placed in a freon bomb       charged with Freon 22 ® and the       pressure in the bomb is brought up       to 600 pounds per square inch by       heating and held six hours. After       the six-hour hold, the pressure is       immediately released and coils are       placed in an oven at 150° C. for       four hours. The coils are then       removed from the oven and checked       for blistering. One large blister,       or two medium, or five small blister       constitutes a failure. The wire is       then wrapped around a five times       mandrel for ten turns and checked       for cracks or peeling. If the       coating cracks or peels, it is       a failure. Finally, the wire is       made into a twisted pair and       dielectrics are determined in       accordance with NEMA Standards       Publication, Part 3, paragraph       7.1.1.3.Dielectrics:Dry         Determined in accordance with NEMA       Standards Publication, Part 3,       paragraph 7.1.1.3.Wet         After soaking in water for 24 hours,       the samples are tested as described       above.Bonding     Determined following the procedure       described in NEMA Standards Publication       Part 3, paragraph 57.1.1.2 at the       temperature stated under Bonding       Temperature.Dissipation Factor       Tested in accordance with NEMA       Standards Publication, Part 3,       Paragraph 9.1.1.2.Heat Aging  Number of hours up to 168 (at 180° C.)at 180° C.       required for a sample to be baked       to fail a post winding of around a       one times mandrel.______________________________________ 
    
     
                                           TABLE 1__________________________________________________________________________           Example        Example           1              2__________________________________________________________________________Basecoat        PE     PEI     PE      PEI     PEI     PEIBuild (mils) bondcoat/basecoat           1.0/2.0                  1.0/2.0 1.0/2.1 0.9/1.9 1.0/2.0 1.0/2.0Wire Size (AWG) 18     18      18      24      24      24Wire Speed (fpm)           50     50      50      100     120     130Appearance, bondcoat/basecoat           VSW/VSW                  VSW/VSW VSW/VSW+                                  VSW/VSW VSW/VSW VSW-/VSWMECHANICAL PROPERTIESMandrel, before snap           1X     1X      1X      1X      1X      1XSnap (OK or Fail)           OK     OK      OK      OK      OK      OKMandrel, after snap           1X     1X      1X      1X      1X      1XAbrasion (gms.) 2000+  2000+   1933    1000+   1000+   1000+Windability     25     20Helical Coil Bonding:Bond Temp., °C.           200    200             200     200     200Bond Str., lbs. @25° C.   10.63  16.09           6.6     9.7     9.2150° C.  6.40   10.88           4.9     5.2     5.6180° C.  3.52   5.87            1.7     0.9     0.8200° C.  2.09   2.64            0.4     0.4     0.2THERMAL PROPERTIESCut Through Temp., °C.           365    340     355     342     318     316Heat Shock, 1X  50     80      70      80      60      70(1/2 Hr. at test, 2X           80     90      80      90      80      80temp. 20%, 3X   100    100     100     100     100     100pre-stretch), 4X           100    100     100     100     100     100Heat Shock Test Temp., °C.           175    200     175     200     200     200Burnout (F.O.M.)           5.4    6.67Heat Aging (hrs.)           168-OKELECTRICAL PROPERTIESDielectric Strength, dry           14.6   15.6(vpm), wet      11.1   11.1Dissipation Factor           11.5   4.92            3.34    3.16    5.45CHEMICAL PROPERTIESA.O. Smith Freon Test;           Fail   OK/OKappearance/flexibility__________________________________________________________________________                   Example          Example Example                                                   Example                   2                3       4      5__________________________________________________________________________Basecoat        PAI/PE  PAI    None None PEI     PEI    PEIBuild (mils) bondcoat/basecoat           2.3     1.0/2.0          1.0/2.0 1.0/2.0                                                   1.0/2.0Wire Size (AWG) 18      18     18   18   18      18     18Wire Speed (fpm)           50      50     40   50   50      50     50Appearance, bondcoat/basecoat           VSW/VSW/                   VSW/VSW          VSW/VSW VSW/VSW                                                   VSW/VSWMECHANICAL PROPERTIESMandrel, before snap           1X      1X     1X   1X   1X      1X     1XSnap (OK or Fail)           OK      OK     OK   OK   OK      OK     OKMandrel, after snap           1X      1X     1X   1X   1X      1X     1XAbrasion (gms.) 2000+   1816   2000+                               2000+                                    1883    1866   1800Windability     17      14Helical Coil Bonding; -Bond Temp., °C.           200     200    200  200  200     200    200Bond Str., lbs. @25° C.   19.80   18.65  --   --   21.7    0.4    1.0150° C.  --      --     --   --   10.9    0.0    1.0180° C.  4.3     3.43   7.4  3.68 6.2     0.0    0.0200° C.  --      --     --   --   3.2     0.0    0.0THERMAL PROPERTIESCut Through Temp., °C.           385     325    280  260Heat Shock, 1X  80      70     80   80(1/2 Hr. at test, 2X           90      90     90   90temp. 20%, 3X   100     100    100  100pre-stretch), 4X           100     100    100  100Heat Shock Test Temp., °C.           260     260    260  260Burnout (F.O.M.)        8.51   2.46 1.13Heat Aging (hrs.)ELECTRICAL PROPERTIESDielectric Strength, dry           15.9    11.5(vpm), wet      14.5    11.2Dissipation Factor           28.72   22.26  453.0                               1874.0CHEMICAL PROPERTIESA.O. Smith Freon Test; -appearance/flexibility__________________________________________________________________________           Example Example Example Example                                         Example  Example           6       7       8       9     10       11__________________________________________________________________________Basecoat        PEI     PEI     PEI     PEI   PEI      PEIBuild (mils) bondcoat/basecoat           1.0/2.0 1.0/2.0 1.0/2.1 1.0/2.0                                         1.0/2.0  1.0/2.1Wire Size (AWG) 18      18      18      18    18       18Wire Speed (fpm)           50      50      50      50    50       50Appearance, bondcoat/basecoat           VSW/VSW VSW/VSW VSW-/VSW                                   Wavy/ VSW/VSW+ VSW-/VSW                           VSWMECHANICAL PROPERTIESMandrel, before snap           1X      1X      1X            1X       1XSnap (OK or Fail)           OK      OK      OK      Fail  OK       OKMandrel, after snap           1X      1X      1X      --    1X       1XAbrasion (gms.) 1950    2000+   1933    --    1808     1708WindabilityHelical Coil Bonding;Bond Temp., °C.           200     200     200     200   200      200Bond Str., lbs. @25° C.   2.9     16.2    12.5    --    --       --150° C.  2.0     8.0     5.2     --    --       --180° C.  1.4     4.7     1.5     0.4   2.8      1.25200° C.  1.4     2.2     1.1     --    --       --THERMAL PROPERTIESCut Through Temp., °C.Heat Shock, 1X(1/2 Hr. at test, 2Xtemp. 20%, 3Xpre-stretch), 4XHeat Shock Test Temp., °C.Burnout (F.O.M.)Heat Aging (hrs.)ELECTRICAL PROPERTIESDielectric Strength, dry(vpm), wetDissipation FactorCHEMICAL PROPERTIESA.O. Smith Freon Test;appearance/flexibility__________________________________________________________________________                        Compara-        Compara-                                              Compara-                                                    Compara-           Example                 Example                        tive            tive  tive  tive           12    13     Example 1       Example 2                                              Example                                                    Example__________________________________________________________________________                                                    4Basecoat        PEI   PEI    PE      PEI     PEI   PEI   PEBuild (mils) bondcoat/basecoat           1.0/2.1                 1.0/2.1                        1.0/2.0 1.0/2.0 1.0/2.0                                              1.0/2.1                                                    1.0/2.0Wire Size (AWG) 18    18     18      18      24    18    18Wire Speed (fpm)           50    50     50      50      90    50    50Appearance, bondcoat/basecoat           SW/VSW                 Hvy    VSW-/VSW                                VSW-/VSW                                        SW/VSW                                              VSW-/ SW/VSW                 Grain/VSW                    VSWMECHANICAL PROPERTIESMandrel, before snap           1X    1X     1X      1X      1X    1X    1XSnap (OK or Fail)           OK    OK     OK      OK      OK    OK    OKMandrel, after snap           1X    1X     1X      1X      1X    1X    1XAbrasion (gms.) 1950  2000+  2000+   1916    1000+ 1750  1608WindabilityHelical Coil Bonding;Bond Temp., °C.           200   200    200     200     200   200   200Bond Str., lbs. @25° C.   --    --     0.0     0.0     4.7   22.4  21.7150° C.  --    --     --      --      0.8   11.0180° C.  6.3   5.5    0.0     0.0     0.2   2.8200° C.  --    --     --      --      --    0.4THERMAL PROPERTIESCut Through Temp., °C.                        280     285     334   315   395Heat Shock, 1X               80      90      50    90    20(1/2 Hr. at test, 2X         90      100     70    100   30Temp. 20%, 3X                100     100     80    100   40pre-stretch), 4X             100     100     100   100   40Heat Shock Test Temp., °C.                        175     200     200   175   175Burnout (F.O.M.)                                   5.97  5.46Heat Aging (hrs.)ELECTRICAL PROPERTIESDielectric Strength, dry                           11.1(vpm), wetDissipation FactorCHEMICAL PROPERTIESA.O. Smith Freon Test;appearance/flexibility__________________________________________________________________________ 
    
     It is critical to use terephthalic acid in copolyamides of the invention. Thus if in place of terephthalic acid there is used isophthalic acid in whole or in part as taught by Onder U.S. Pat. No. 4,072,665, the bond strength is reduced. 
     Thus there were prepared copolyamides similar to Example 1 replacing the terephthalic acid in whole or in part by isophthalic acid. 
     COMPARATIVE EXAMPLE 5 
     The procedure was similar to Example 1 but there were used as reactants a 70/30 molar ratio mixture of toluene diisocyanate and methylene diisocyanate and there was used a 65/25/10 molar mixture of dodecanedioic acid, isophthalic acid and terephthalic acid. 
     COMPARATIVE EXAMPLE 6 
     The procedure was the same as in Comparative Example 5 except the dibasic acids employed was 65/35 molar mixture of dodecanedioic acid and isophthalic acid. 
     Examples 1 and 3 which are within the present invention both employ a 65/35 molar mixture of dodecanedioic acid and terephthalic acid. The bond strength of Comparative Example 5, Comparative Example 6, Example 1, and Example 3 were tested by coating their resultant enamel solutions on top of ISOMID-coated wire at 50 ft./min., followed by bonding at 200° C. for 20 minutes under 1-kg load. The results were as set forth in Table 2: 
     
                       TABLE 2______________________________________Test              Bond Strength,Specimen          Lbs. at 180° C.______________________________________Comparative Example 5             4.75Comparative Example 6             3.2Example 1         5.9Example 3         6.2______________________________________ 
    
     It can be seen from Table 2 that the greater the replacement of terephthalic acid by isophthalic acid the greater the reduction in bond strength. 
     SUMMARY OF THE PRESENT INVENTION 
     It has now been found that the shelf stability of the self bondable copolyamides as set forth in Walrath et al can be dramatically increased and gelation prevented by using a mixture of aliphatic dicarboxylic acids and a monofunctional carboxylic acid to break up crystallinity, thus improving solubility, and controlling molecular weight. It will become apparent in the following examples that the sole use of either a mixture of aliphatic dicarboxylic acids or a monocarboxylic acid will not improve the shelf stability nor prevent the tendency for gelation. The monobasic acid should have at least 4 carbon atoms and preferably at least 6 carbon atoms. Preferably hydrocarbon carboxylic acids are employed as the monocarboxylic acids. 
     This new bondable coating offers all the advantages set forth in Walrath et al and it is also apparent, in many instances, there are examples exhibiting superior bonding characteristics under the same test conditions. 
     A polyamide of this new invention is prepared by the reaction of a diisocyanate, or mixture of diisocyanates of the general formula 
     
         OCN--R--NCO 
    
     with a dicarboxylic acid, or mixture of dicarboxylic acids, of the general formula 
     
         HOOC--R&#39;--COOH 
    
     and a monocarboxylic acid of the general formula 
     
         R&#34;--COOH 
    
     Where R, R&#39; and R&#34; may be the same or different and are aliphatic, cycloaliphatic, or aromatic hydrocarbon groups, which may or may not have non-reactive substituents. Most preferably R is as defined in Walrath et al and R&#39; is defined as AL and/or Ar in Walrath et al. 
     Examples of diisocyanates are hexamethylene-(1,6)-diisocyanate, tetramethylene-(1,4)-diisocyanate, cyclohexane-(1,4)-diisocyanate, dicyclohexylmethane-(4,4&#39;)-diisocyanate, phenyl-(1,3)-diisocyanate, phenyl-(1,4)-diisocyanate, tolylene-(2,4)-diisocyanate, tolylene-(2,6)-diisocyanate, diphenylmethane-(4,4&#39;)-diisocyanate, etc. 
     More preferred is a mixture of the diisocyanate of tolylene-(2,4)-, tolylene-(2,6)-, and diphenylmethane-(4,4&#39;), in a molar percent ratio ranging from 40:10:50 to 80:20:0. Tolylene-(2,4)- and tolylene-(2,6)-diisocyanate are more commonly supplied and used as an 80:20 isomer mixture. 
     Examples of dicarboxylic acids are adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, 1,12-dodecane-dioic acid, the dimerized tall oil acid, dimerized oleic acid, dimerized linoleic acid, cyclohexane-(1,4)-dicarboxylic acid, isophthalic acid, terephthalic acid, etc. 
     As stated in Walrath et al in place of the diisocyanates there can be employed the corresponding diamines, e.g. those mentioned above and there can be used in reacting with the diamines in place of the acids, the acyl halides or lower alkyl esters, e.g. those mentioned above. 
     Preferred is a mixture of aliphatic acids and terephthalic acid in a molar percent ratio ranging from 100:0 to 60:40, more preferably from 90:10 to 65:35, most preferably 85:15, where the aliphatic acids are 1,12-dodecanedioic acid and azelaic or sebacic acid in a molar percent ratio ranging from 100:0 to 0:100, and more preferably from 80:20 to 20:80. The mixture of aliphatic acids is not necessarily limited to two but may be a combination of two or more dicarboxylic acids in any ratio, where R&#39; is (CH 2 )x, and x is 4 to 34. 
     Examples of monofunctional carboxylic acids are palmitic acid, toluic acid, hexanoic acid, decanoic acid, dodecanoic acid, nonanoic acid, stearic acid, oleic acid, cyclohexane carboxylic acid, benzoic acid, phenylacetic acid, etc. The lower order monocarboxylic acids, such as acetic acid and propionic acid, are not preferred as a chainstopper to control molecular weight and prevent gelation. Other monobasic acids include butyric acid and valeric acid. 
     The amount of monocarboxylic acid may be from 0.5 to 5 equivalent percent and preferably between 1 and 2 equivalent percent of the functional carboxylic acid based on the total equivalents of carboxylic acid groups. 
     The polyamides of this invention are prepared by reacting diisocyanates (or diamines) with carboxylic acids in an amide-type solvent, such as N-methyl-2-pyrrolidone, at reaction temperatures from 150° F. to 400° F. Most preferably the reaction is initiated at 170° F. to 220° F. and held at these temperatures until CO 2  evolution ceases, then further reacted at temperatures between 280° F. and 390° F. More isocyanate may be added, at these temperatures, to increase the molecular weight to a desired viscosity-solids and the finished polymer is reduced in a mixture of N-methyl-2-pyrrolidone and an aromatic hydrocarbon for application as a wire enamel. 
     The following examples help to define this invention, its improvements over Walrath et al, and show what materials are necessary. 
     The composition can comprise, consist essentially of, or consist of the stated materials. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 3 is a graph comparing the bond strength of the copolyamide of Example IV within the present invention and Example A which is within Walrath et al. FIG. 3 is based on the data in Table 3. 
     The copolyamides of the invention can have the formula ##STR4## where y represents 95 to 99.5% of the equivalents of carboxyl groups and x represents 5 to 0.5% of the equivalents of carboxyl groups. 
     More preferably the copolyamides have the formula ##STR5## where AL is the divalent hydrocarbon residues of at least two unsubstituted aliphatic dicarboxylic acids having at least 6 carbon atoms, R is tolylene, phenylene, ##STR6## where F is O, CH 2 , or SO 2  or is a cycloaliphatic hydrocarbon, Ar is p-phenylene, y is 35 to 90% of the recurring units, z is 65 to 10% of the recurring units, R&#34; is the monovalent hydrocarbon radial of a hydrocarbon monocarboxylic acid having at least 3 carbon atoms and x represents 0.5 to 5% of the equivalents of carboxyl groups present. 
     The presently preferred dibasic acid is a mixture of either azelaic or sebacic acid with 1,12-dodecanedioic acid. The 50--50 equivalent ratio being most preferred. 
     The presently most preferred product is that of Example IV. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Example A 
     The working example of Walrath et al is the reaction product of a 70:30 molar ratio of tolylene diisocyanate:diphenylmethane diisocyanate with a 65:35 molar ratio of dodecanedioic acid:terephthalic acid in N-methyl-2-pyrrolidone (NMP). Its shelf stability is limited to no greater than three months and most always becomes insoluble on standing after two months. 
     For the purpose of reference, the basic polymer preparation for Example A is described below, as written in the &#34;Bondable Polyamide&#34; invention of Walrath et al. In general, this procedure is the same for Examples I through XV; however, for some reactions, excess diisocyanate was added during the final reaction stages to increase the molecular weight to a desired viscosity-solids. 
     
         ______________________________________                   LoadRaw Materials           in Grams______________________________________1 N--methyl-2-pyrrolidone                   41682 Toluene diisocyanate (Mondur TD-80)                   10333 4,4&#39; Methylene diphenyldiisocyanate                    6374 Terephthalic Acid      4945 Dodecanedioic Acid    12676 Xylene                22437 N--methyl-2-pyrrolidone                   1050______________________________________ 
    
     Parts one through three were charged at room temperature into a 12-liter, round-bottom reaction flask, equipped with an agitator, a thermometer, an inert gas purge, and a water-cooled condenser fitted with a flexible tube which was immersed in a flask containing a mixture of water and denatured ethyl alcohol. (The reaction by-products carried through the condenser by the carbon dioxide and nitrogen are trapped in the water-alcohol solution.) Parts four and five were then added at room temperature with agitation and a blanket of nitrogen was applied over the reaction. The temperature was raised slowly by use of an electric heating mantel to approximately 75° C. when carbon dioxide evolution began. The external heat was then reduced and the temperature of the batch was allowed to rise over a four-hour time period to approximately 170° C. At about 80° C., the batch became clear. After an approximate four-hour hold at 170° to 175° C., the reaction was allowed to cool slowly to room temperature over night. The next morning the reaction mixture was sampled and a 60 percent solution in N-methyl-2-pyrrolidone was determined to have a viscosity at 25° C. on the Gardner-Holdt Scale of W 1/2. Parts six and seven were then added. The final viscosity of the solution at 25° C. was Z on the Gardner-Holdt Scale, or 2,500 centipoises as measured by a Brookfield RVT viscometer. 
     The percent non-volatiles of the solution were determined to be 27 percent by baking a two-gram sample for two hours at 200° C. The specific gravity of the solution was determined to be 1.025 at 25° C. 
     The test properties for this example and the following examples are listed in Table 3. 
     EXAMPLE I 
     The process of Example A is carried out with 50 equivalent percent of the dodecanedioic acid replaced by azelaic acid. The polyamide, in 70:30 NMP/Xylol, has improved shelf stability; however, there is a decrease in bond strength. 
     EXAMPLE II 
     The aliphatic acid portion is increased to 80 percent of the dicarboxylic acid, 50 percent each of dodecanedioic and azelaic acid, with 20 percent terephthalic acid and the same diisocyanate ratio as in Example A, improving the shelf stability, however, decreasing the bond strength. 
     EXAMPLE III 
     A 70:30 molar ratio of tolylene diisocyanate: diphenylmethane diisocyanate is reacted in NMP with an 85:15 molar ratio of aliphatic dicarboxylic acids to terephthalic acid, where the aliphatic acids are a 50:50 ratio of dodecanedioic acid:azelaic acid. This reaction gelled. 
     EXAMPLE IV 
     Similar to Example III, however, 2.0 equivalent percent of the dicarboxylic acid is replaced by benzoic acid, preventing gelation and making a polyamide wire enamel, in 70:30 NMP/Xylol, with at least six months shelf stability. Bond strengths are equal to or better than Example A over the same basecoats. 
     EXAMPLE V 
     This example illustrates the reaction of 70:30 toluene diisocyanate and diphenylmethane diisocyanate with 100 percent aliphatic dicarboxylic acids, essentially 50 percent each of dodecanedioic acid and azelaic acid, in NMP. Following the procedure set forth in Example A, this reaction gelled. 
     EXAMPLE VI 
     1.0 equivalent percent of the aliphatic acids, in Example V, is replaced by benzoic acid, preventing gelation and improving shelf stability to 5 months. 
     EXAMPLE VII 
     1.5 equivalent percent of the aliphatic acids, in Example V, is replaced by benzoic acid, preventing gelation and improving shelf stability to greater than 6 months. 
     EXAMPLE VIII 
     Referring to Example A, 2.0 equivalent percent of the dicarboxylic acids, consisting of 65:35 dodecanedioic acid and terephthalic acid, is replaced by benzoic acid. In comparison with Example A, wire properties were not affected, however, shelf stability was not improved. 
     The next three examples illustrate the use of sebacic acid in combination with dodecanedioic acid. 
     EXAMPLE IX 
     A 70:30 ratio of toluene diisocyanate and diphenylmethane diisocyanate is reacted in NMP with an 85:15 ratio of aliphatic acids and terephthalic acid where the aliphatic acids are 50:50 dodecanedioic acid and sebacic acid. 2.0 equivalent percent of benzoic acid is added to prevent gelation. 
     EXAMPLE X 
     Similar to Example IX, the percentage of terephthalic acid is increased from 15 to 20, while the aliphatic ratio is retained at 50:50. 
     EXAMPLE XI 
     In this reaction, the amount of sebacic acid is increased to 75 percent of the aliphatic acid, which comprises 80 percent of the total acid, and no mono-carboxylic acid is used. This reaction gelled. 
     EXAMPLE XII 
     A 70:30 ratio of toluene diisocyanate and diphenylmethane diisocyanate is reacted with an 85:15 mixture of aliphatic acids and terephthalic acid, where the aliphatic acid mixture consists of 80 percent azelaic acid and 20 percent dodecanedioic acid, with 2 percent stearic acid to control gelation. The bondable polyamide wire enamel, in 70:30 NMP-Xylol solvents, has a shelf stability greater than six months. 
     EXAMPLE XIII 
     A 70:30 molar ratio of toluene diisocyanate and diphenylmethane-diisocyanate is reacted in NMP with an 80:20 mixture of aliphatic acids and terephthalic acid where the aliphatic acid mixture consists of 65 percent dodecanedioic acid and 35 percent azelaic acid, with 2.0 equivalent percent of the total acid being nonanoic acid. 
     EXAMPLE XIV 
     1.8 equivalent percent of an 80:20 aliphatic acid to terephthalic acid, where the aliphatic acid mixture is 65:35 azelaic acid to dodecanedioic acid, is replaced by acetic acid and reacted according to Example A using the same diisocyanates. There was no increase in viscosity or molecular weight during this reaction. 
     EXAMPLE XV 
     Similar to Example XIV, the acetic acid is replaced by propionic acid; however, again, there is no increase in molecular weight. 
     
         ______________________________________ABBREVIATION KEY FOR TABLE 3______________________________________ReactantsNMP =      N--methyl-2-pyrrolidoneTDI =      80/20 mixture of 2,4 and 2,6 tolylene      diisocyanate (Mondur TD-80)MDI =      diphenylmethane-(4,4&#39;)-diisocyanateTA =       terephthalic acidDDDA =     1,12-dodecanedioic acidAzA =      azelaic acidSeA =      sebacic acidWire Properties      on 18-AWG copper wire at 50 feet per      minute through a 20 ft. vertical oven      with a temperature range of 260-480° C.Basecoat, PE      a polyester wire coating, ISONEL ® 200, PEI      a polyesterimide wire coating, ISOMID ®Freon Resistance      a Freon test developed by A. O. Smith Co.Bond Strength      tested in accordance with NEMA Standards      Publication, Part 3, paragraph 57.1.1.2      at a bonding temperature of 200° C.______________________________________ 
    
     
                                           TABLE 3__________________________________________________________________________       Example A     Example I                            Example II                                   Example 111                                          Example IV__________________________________________________________________________REACTANTSNMP         4168          1900   687    634    1848TDI         1033          487    172    158    461MDI         637           300    106    98     283TA          494           232    47     32     92DDDA        1267          300    131    127    364AzA         0             244    107    104    297SeA         0             0      0      0      0Monobasic Acid       None          None   None   None   Benzoic       0             0      0      0      14.0Excess MDI  0             10     2      0      30NMP         1050          505    228           575Xylol       2243          1011   361           1264Viscosity   Z             Z      Y 1/2  Reaction                                          Z                                   Gelled 24.3% Solids    27.0          27.5   27.0Mos. Shelf Life       Less than 3   Less than 3                            Less Than 3   Greater Than 6WIRE PROPERTIESBasecoat    PE     PEI    PEI    PEI           PE      PEIBuild (mils)-       1.0/2.0              1.0/2.0                     1.0/2.0                            1.0/2.0       1.0/2.0 1.0/2.0Bondcoat/BasecoatAppearance  VSW/VSW              VSW/VSW                     VSW/VSW                            VSW/VSW       VSW/VSW VSW/VSWBondcoat/BasecoatMandrel, A.S.       1×              1×                     1×                            1×      1×                                                  1×Cut Through, °C.       365    340                         315     330Heat Shock1×    50     80                          50      802×    80     90                          60      1003×    100    100                         70      1004×    100    100                         80      100HS Test Temp., °C.       175    200                         175     200Freon Resist.       Fail   OK/OK                       Fail    FailBond Strength-lbs. @ 25° C.       10.6   16.1   4.0    7.2           27.9    28.6150° C.       6.4    10.9                        8.7     7.7180° C.       3.5    5.9    1.7    3.9           2.5     2.2__________________________________________________________________________       Example V              Example VI                     Example VII                            Example VIII                                    Example IX                                           Example                                                  Example__________________________________________________________________________                                                  XIREACTANTSNMP         595    595    595    535     708    640    630TDI         146    146    146    133     158    158    164MDI         90     90     90     81      98     98     97TA          0      0      0      59      32     43     43DDDA        138    137    136    159     124    117    60AzA         113    112    111    0       0      0      0SeA         0      0      0      0       109    102    164Monobasic Acid       None   Benzoic                     Benzoic                            Benzoic Benzoic                                           Benzoic                                                  None       0      2.9    4.4    4.4     6.3    6.3    0Excess MDI  0      6      6      5       15     10     0NMP                198    216    234     140    183Xylol              333    340    329     360    353Viscosity   Reaction              Y 3/4  Y 1/2  Y       Y 1/4  Z      Reaction       gelled                                     Gelled% Solids           25.4   24.6   24.3    26.0   26.0Mos. Shelf Life    5      Gtr. Than 6                            Less Than 3                                    Gtr. Than 6                                           Gtr. Than 6WIRE PROPERTIESBasecoat           PEI    PEI    PEI     PE     PEIBuild (mils)-      1.0/2.0                     1.0/2.0                            1.0/2.0 1.0/2.0                                           1.0/2.0Bondcoat/BasecoatAppearance-        VSW/VSW                     VSW/VSW                            VSW/VSW VSW/VSW                                           VSW/VSWBondcoat/BasecoatMandrel, A.S.      1×                     1×                            1×                                    1×                                           1×Cut Through, °C.Heat Shock1×                         702×                         903×                         904×                         100HS Test Temp., °C.        200Freon Resist.Bond Strength-lbs. @ 25° C.              13.3   7.5    15.3    27.2   35.6150° C.180° C.     1.9    1.8    6.6     2.5    2.6__________________________________________________________________________                           Example XII                                  Example XIII                                          Example XIV                                                  Example__________________________________________________________________________                                                  XV               REACTANTS               NMP         677    643     652     652               TDI         170    159     159     159               MDI         105    98      98      98               TA          34     42      42      42               DDDA        54     152     92      92               AzA         175    67      140     140               SeA         0      0       0       0               Monobasic Acid                           Stearic                                  Nonanoic                                          Acetic  Propionic                           15.9   8.2     3.1     3.8               Excess MDI  10     10      11      20               NMP         230    140               Xylol       413    339               Viscosity   Y      Y 1/2   No Molecular                                                  No Molecular                                          Weight  Weight               % Solids    25.0   26.8               Mos. Shelf Life                           Gtr. Than 6                                  Gtr. Than 6               WIRE PROPERTIES               Basecoat    PE     PE               Build (mils)-                           1.0/2.0                                  1.0/2.0               Bondcoat/Basecoat               Appearance- VSW/VSW                                  VSW/VSW               Bondcoat/Basecoat               Mandrel, A.S.                           1×                                  1×               Cut Through, °C.               Heat Shock               1×    20     20               2×    40     50               3×    60     60               4×    80     70               HS Test Temp., °C.                           175    175               Freon Resist.               Bond Strength-               lbs. @ 25° C.                           28.2   25.8               150° C.               180° C.                           2.6__________________________________________________________________________