CA1038544A - Products and process for preparation of polyamide-imide and shaped articles therefrom - Google Patents

Abstract

Abstract of The Disclosure Polyamide-imides are prepared by reacting trimellitic anhydride or trimellitic acid with an aromatic or an aliphatic diamine in the molar ratio of about 1:0.7 to 1:0.9 and then reacting this product with at least 0.1 to about 0.3 up to about 0.75 moles of an aromatic or ali-phatic diisocyanate. The products are useful as wire enamels and coatings when they are formulated into wire enamels and coated on electrical conductors. They may also be used as molding resins.

Description

This inven~lon relates to high molecular weight polymers deri~ed from trimellitic anhydride trimellltic acid, aromatic and aliphatic diamines, and tiisocyanates. The products are use~ul ~or wire en2mel in the protection of electrically conductive metallic wire such as ~s ` copper.

The new polymers are also useful for the formatian of a variety af heat-resistant insulating films, coatings and molded articles.
It has been discovered that polyamide-imide polymers which result from the reaction of trimellitic anhydrlde or trlmellitic acid with 20 ~ diamines and diisocyanates exhibit surprisingly good wire enàmel ;~

! properties.
The prepolymers of this lnve~tion may be described as low ~olecular ~ we$ght species which by tesign are not formed in high molecular weight i since they are produced by reaction im~alance leavlng an excess of carboxylic acid groups. Advaneageously in this novel re~ctlon imbalance process great care is taken to keep the molar ratlo of ~rimellitlc anhydride or trimelli~ic acld to the dia~ine in a ratiD o~ 1 to 0.7 up . . : ;
to 1 to 0.9. Thus procuring a low molecular weight polg~er whic~ u?on further polymerization with diisocyanates produces high ~olecular weight ~
polyamide-imides.
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16)3~ 4 It ha.~ been known as shown in United State~ Patent ; .
3,570,230 and French Patent 1,575,835 that diimide dibasic acid monomers may be obtained from trimellitic anhydride and ~iamines ;
when the molar ratio of the trimellitic anhydride to the diamine is ~estricted to 2:1. These monomers are-a-lleged by- ~he..
foregoing references as being capable of further re~ction .;
with aiisocyanates.
In one aspect of this invention there is.provided ..
a process ~or preparing high molecular weight polyamide-imide products having film-forming properties which process com- .
prises condensing trimellitic anhydride or trimellitic acid and a primary diamine in a mole ratio of about 1 to 0.7 to about 1 to 0.8 at a temperature of about 210C to about 250C, to give a low molecular weight polymer having an excess o~
trimellitic anhydride moieties and then further condensing this polymer with about 0.1 to about 0.3 moles up to about ;;~
0.75 moles of a diisocyanate for each trimellitic~anhydride ..
moiety in an inert solvent at a temperature o~ about 25C to .
about 150C.
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The novel polyamide-imide prepolymers are polymeric polymer acid compounds having in their molecules units of `:

_ "~: .
., ~ . O "'''`~ . ~''. ,' .

¦ n ~ ~_~ ~ C~2n .
. H02C- r ~C ~ ~ ~
. 'I O ., .~ .

0 ~herein R is a divalent aro~atic or allphatic organic rad cal. Thi~
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.. . ~ . . . . ... . . , . . ,," , . ... .. ...... . . .

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organic radical consists of R' which is a divalent aromatic or aliphatic hydrocarbon radical or two R' diYalent aromatlc or aliphatic hydrocarbon ~
O ', "
radicals ~oined by stable linkages -O-, -CH2-9 -C-, -S-, as are in the j ; ` :~
O O
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~ group9 -R'-O-R', -R'-CH2-R'-,R'-C-R', -R'-S-R~, and -R'-S~-R-. : ~
' These prepolymer products are reacted with diisocyanates to produce high ~:
molecular weight polyamide-imides having to a substantial extent recur-ring units of .
r 1 ~ ~
lo~

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l . 1038$44 wherein R is a dl~alent aromatlc or aliphatic organic radical in which in addition to hydrogen, nitrogen, sulfur and oxygen atoms can be ateached' to the carbon atoms. This organic radical consists of R', which i5 a . ~. :
dlvalent aromatic o,r aliphatic hydrocarbon or two R' divalent aromatic or ., ¦ aliphatic hydrocarbon radicals joined by stable li~kages '~ I ' O o ' ' ' ,.

. ¦ -O-, -CH2-, -C-, -S-, and -S-, as are in groups -R'-0-R'-, -R'-CH~-R'-, : ;~
. ' I . O ~ ' - .
. ~ I 0' '' O . . - . ~ .
lo ¦ -R'-C-R'-, -R'-S-R'-, and R'-S-R'-. , ~ ~ ;

¦ ; It has now been found that wire enamels and polymers can be obtained .

. ¦ by reacting trimelli.tic anhydride or trimellitic acid with aromatic or . .. ..

¦ aliphatic dia~ines in the molar ratio of 1:0.7 to about 1:0.9 and then . . '. ¦ reacting'this product wi.th about 0.10 to about 0.30 up.to,about 0.75 .. ..

¦ moles:of an aromatic.diisocyanate. Suitably, the molar ratio can be 1 .

. . ¦ mole, trimel~litic anhydride or trlmellitic acid, about 0.7 to'about 0.8 - :' ' ' '.

. . ¦ moles aromatic~or aliphatic diamine and at least about 0.'2 to about 0.3 .

';~ . ¦ moles of an aramatic or aliphatic diisocyanate. ~ .

. ¦ .In the above reaction, .the trimell~tic anhydride or trimellitic aci ~. ~
, , 20 , ¦ and the diamine react to form a polyamide-imide prepolymer. This low . ' " ~ ,.

. ¦ molecular weight,species ha~ing carboxylic acid end groups is reacted ', . ¦ with the diisocyanate. In the preferred embodiment 1 mole of trimellitic . ~-. ¦ anhydride or trimellitic acld is reacted'with 0.,8 mole of diamine. This ~ '.

. ~ j polymer is then reacted with at leas~t 0.2 =oles of the diisocyanate.

. , . ¦ .; The rqaction between the tri,mellitic a~hydride and the diamine is . -.

: ' I carried out at a temperature of abo'ut 210 to about 250'C, preferab~y at i ' ! 'about 220-230C when atmospheric pressure is used. Tv.this product is :

¦~ added the diisocyanate at a temperature ranging between room temperature " ! and 125C. Suitably, the reaction tempera~ure may be 120.to 155C and 30 ~ , . .. . .
,, : ,. , - - . . : ' , . - -.3 ~
- ' - ' ' ' ' ' . '~' ' . I ' ' .

~ .... . . . .. .

. 1~3~3~i44 ¦preFerably thls final reaction is initiated at room temperature and completed at about 135C.
¦ The polyamide-imide prepolymer forming reaction is normally carried ¦ out in the same solvent used to form the wire enamel. Nitrogen or ¦ sulfoxide containing organic polar solvents or substituted phenols are advantageously employed. Useful solvents include the following:
N-methylpyrrolidone, cresylic acid, p-cresol, m-cresol, dimethyl sul-foxide, N-methyl caprolactam, dimethylsulfone cyclohexane, and phenol.

l The preferred solvet is N-methylpyrrolidone. -At the completion of the prepolymer forming step, diluents may be -added. Representative diluents include N-methylpyrrolidone, dimethyl-acetamide (DMAC), dimethylformamide, or mixtures of the above with nromatic hydrocarbon streams (9Uch ~9 ~Qlve88o lO~ and 150), . xylenes and toluenes.
The diamines useful for the reaction may be aromatic or aliphatic.

These diamines have the formula H2N-R'-NH2, H2N-R'-O-R'-NH , O O
H N-R'-CH -R~-NH2, H2N-~-C-R -N~12, H2N-R S R 2 2 2 ~
I . O
wherein R~ is a divalent aromatic or aliphatic hydrocarbon radical.

The aromatlc diamines have from one to about four aromatic rings, advantageously from one to about two aromatic rings. The aromatic diamines having more than one aromatic ring may be further characterized l as polycyclic aromatic compounds having two primary amino groups on an 2s 1 interconnected polycyclic aromatic nucleus. ~he aromatic rings may be ~ ;
interconnected by condensation, as in naphthalene or in phenanthrene-type structures, or may be bridged, elther directly as in benzidine or indirectly as, for example, two R~ groups are joined with stable inert linkages such as oxy, alkenyl, carbonyl, sulfonyl and other relatively l ;
.
inactive groups such as sulfide groups as hereinbefore described.

Suitable nuclei (R' divalent aromatic hydrocarbon radical) include phenyl~
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naphthyL7 anthryl, naphtlIacenyl and the like, diphenyl, terphenyl, Iphenylnaphthyl, quaterphenyl and the like; and aromatic rings separated ¦by oxy, sulfonyl and thlo groups, and aliphatic groups containing from 1-12 carbon atoms. The aliphatic diamines, includin~ alkylene diamines such as hexamethylene diamine, ethylene diamine, pentamethylene diamines and dodecamethylene diamine, are useful.
Useful aromatic diamines include methylene bis(aniline)s (4,4'-diaminodiphenylmethane), oxy bis(aniline), (4,4'-diaminodphenylester~, benæidine, m-phenylenediamine, p-phenylenediamine, 2,4- and 2,6-toluene-lo diamine (and mixtures of such), 3,3'-diam~nodiphenyl, 1,4-diaminonaphtha-lene, 4,4'-diaminodiphenyl ketone, 4,4'-diaminodiphenyl sulfone, bis(4-aminophenyl)-1, l-ethylene.
Useful aromatic diisocyanates include methylene bis (4-phenyliso-cyanate), oxy bis t~-phenylisocyanate), 1,5-naphthalene diisocyana~e, m-phenylene diisocyanate, mesithylene diisocyanate, durylene diisocyanate, toluene diisocyanate, 4,4'-bi-o-tolylene diisocyanate, 4,4'-methylene-di-o-tolyldiisocyanate, 4-methoxy-1,3-phenylene diisocyanate, 4-isopropyl-1,3-phenylene diisocyanate, 4-chloro-1,3-phenylene diisocyanate, 3,3'-I dimethyl-4,4-diisocyanatodiphenyl methane, 3,3'-bitolylene-4,4'-diisocya-I nate, 4,4'-diisocyanato diphenyl sulfone. Useful alkylene diisocyanates ! include hexamethylene diisocyanate, ethylene diisocyanate, dodecamethylen j' diisocyanate, and pentamethylene diisocyanate.
~¦ The polyamide-imides are employed as wire enamels while in solution in a solvent system such as those specified above. It is applied to an electrical conductor, e.g., copper, silver, aluminum, or stainless steel ¦
wire in conventional fashion, e.g., by the "free dip" method or the "die application'I procedure, both of which procedures are described in Meyer, U.S. Pat. 3,201,276. ~ire speeds of 15-40 feet per minute can be I `
used with wire tower temperatures of 400 to 900F, usually with a final temperature above 500F. The build-up of the polyamide-imide enamel ..
S ,;

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~! i 1(1;~8544, 'jon ~he wire can be 0.0013 to 0.0049 lnch, preferably 0.0026 to 0.0034 jlinch using No. 18 wire. The wire is passed through the enamel one or more J~times until the desired build-up is obtained. By build-up is meant the l total increase in diameter over the bare wire diameter.
¦ As noted above, the soluble polyamide-imides can be converted to ¦ tough, infusible and insoluble resins. Advantageously, this is accom-plished in the process of forming films, coatings, f:ibers, impregnated ~ and molded articles. For example, a solution of the product, that is IJ the polyamide-imide, is applied to a wire, or other surface, and heated ¦¦ at a temperature of about 200 to about 420C, usually about 300-400C
(for wire coatings), for a time sufficient to evaporate solvents and f orm the insoluble polyamide-imide. At 400C, about one minute is usually sufficient, while at 300C, about two minutes are required.

In this manner, suraces, sheets, etc., made out of metal like steel, copper, aluminum, nickel, etc., or exa~nple, or various a:Lloys~
can be coated. Similarly, lam:lnated ob~ects having a plurallty of layers 'i bonded together with the polyami~e-imide on the material to be laminated 1~ which has been connected to the polyamide-imide. The lamination is carried out by placing the object to be laminated in the polyamide-imide ' of this invention dissolved in an organic solvent and then curing each , layer at elevated temperatures. As one layer of the polyamide-imide is cured, the objects can again be placed in the polymer solution and the process continued. Glass or asbestos fibers can be coated by depositing , the polyamide-imide in solution on said materials and the heat curing it.
The polyamide-imides of this invention generally have inherent vis-cosities of at least 0.3 dl/g (in DMAC, at 25C). The properties of the ¦
polyamide-imide, when cast as a film, show that it has a tensile strength¦ ;
at 25C of between 13,500 and 15,000 psi and an elongation at 25C from 10 to 25~ in addition to having excellent electrical properties and thermal stability.

1S~38544 ¦ The following examples illustrate some embodiments of this invention.
¦It will be understood that they are for illustrative pu~poses only and ¦do not purport to be wholly deflnitive as to conditions or scope.
¦ EXAMPLE I
5 ¦ In a suitable vessel equipped with a nitrogen purge, stirrer, con- ~ ~ ;
¦ denser with trap is placed 1059.0 parts trimellitic anhydride, 717.0 ;
¦ parts N-methylpyrrolidone and 68.0 parts pseudocumene. The mixture is ¦ brought to 100-110C and 374.0 parts of methylenebis(aniline) are added over a 5-10 minute period. The temperature is then raised to 225C
0 over a 3 hour period. The aqueous layer is continually withdrawn from the trap. The solution is held at 225C for 5 hours, heat is removed, 4851.0 parts of N-methylpyrrolidone is added over 30-ll5 minutes, and the solution allowed to cool. At 48C 286.0 parts of Isonate 125 mf are added and the mixture stirred Por 30 minutes. The solution is brought to 100C and held for one hour, then ralsed to 135C and held for one hour. An additional 71.0 parts o 125 mf is added over a 2 hour period until the Gardner-~olt viscosity is ~6-7. At 25C the Brookfleld viscosity was 238 poise at 32.5% solids.

(a) To 1000 parts of the above solution was added 333.3 parts xylene yielding a solution at 23.5% of 32 poise. The solutlon was coated on 18 gauge copper wire. The test data for this are given in the i~
Table following. Run A is sole coat and Run B i9 top coat. The test ;
descriptions are given in the paragraphs headed "Coated Wire Tests."

(b) To 54.9 parts of the solution prepared in Example I were added 2s 18.3 parts xylene, 9.0 parts TiO2, 3.0 parts nickel titanate yellow and ;; ;

14.8 parts N-methylpyrrolidone. All materials were mixed in a ball mill 'i ovPrnight. A sample of the mixture was spread on a Bonderite 37 steel ; ;-panel and cured at 500F for 15 minutes.
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Tes~ U385~3~L4 ! Cured film thickness ~mils~ 1.0 Pencil Hardness - 5H+
~ Sward Hardness - 27 5 ¦¦ Cross-Hatch Adhesion, % 100 1/8" Conical Mandrel Bend, % Pass lO0 l Direct Impact [in-lbs3 > I60 ! Reverse Impact [in-lbs] > 160 l 1. R-900, DuPont Chem~ Co.
¦ 2. #14, Shepard Chem. Co.
~l (c) To 10 parts of the solution prepared in Example I were added ¦¦ 3.3 parts N-methylpyrrolidone and the solution wet-spun into distilled water. The film was cured for 5 minutes at 600F snd gave a strand which I was flexible and could be knotted.
l5 I (d) Adhesive Appllcation.

I Small samples of the product prepared in Example I were spread on Cold Rolled Steel (bonderite 100 treatment) and cured under vacuum at 80C for 16 hrs. (for T-Peel adhesion), and likewise coated on 0.064" Hot Rolled Steel (chloroethene cleaned) and cured (as above) for :
Lap Shear tests.

~! T-Peel Adhesion - 17.9 psi !' ~
¦~ Lap Shear - 1600 p5i ::
The test specimens were prepared uslng a 15. sec. activation at 20 psi at 660F on a Sentinel heat sealer.
EXAMPLE Il Into a suitable vessel equipped with a nitrogen purge, stirrer, con-denser with trap is placed 384.2 parts crimellitic anhydride, 183.8 parts m-phenglenediamine, 260.0 parts ~-methylpyrrolidone and 36.6 parts !
pseudocumene. The mixture was brought to 220C over a 3 hour period and ' held at that temperature for 5 hours. The aqueous layer was continually .. . ~ .... .. . .. . . . .

withdrawn from the trap. After the 5 hour-220C period, 2000.0 parts ¦ dimethylacetamide was added over a 15 minute period and the solution allowed to cool. At 25C 65.0 parts m-phenylene diisocyanate wafi added I¦ and the mixture stirred for 30 minutes. The temperature is raised to ,¦ 135C over 1.5 hours. After 45 minutes at this tempe~ature 15.0 parts Il of m-phenylene diisocyanate are added and heating is continued for 30 ¦I minutes. At 25C the Brookfield viscosity was 62 poise at 24.3% solids.
I¦ The product had an inherent viscosity of 0.38 dl¦g (DMAC, at 25C).
¦i (a) 500 parts of the above solution was precipitated into 1500 o ¦¦ parts distilled water in a Waring Blender. The product was filtered, ¦~ washed, dryed, and molded. The mold used was 8.1/2" diameter and 1.3/4"
¦ thlck. It had a moldlng cavity 5.1/2" in diameter. The mold was charged with 78 parts pol~mer and heated to 620F. The sample was ~ pressed according to ~he following schedule:
15 ~¦ Time Pressure ~1 min, Tons Ij 400 (contact pressure) i~ 2 2.5 1, 2 5 1 `
2~ , 1 10 , 4 25 i !1 1 50 '~ The mold was cooled to 540F and the disc ejected.
2s i' Tensile Strength - 11,121 psi l Elongation - 4.0%
' EXAMPLE III
; Into a suitable vessel equipped as in Examles I and II is placed 192.1 parts trimellitic anhydride, 100.0 parts hexamethylene diamine, 130.0 parts N-methylpyrrolidone and 36.6 parts pseudocumene. The mixture is brought to 225C over a 3 hour period and held at this eml~ersture for 5 ho~rs. Tùe sqoeo~s 1=yer ls cont1n~s11y wlthdr~wn from the trap. Heat is removed and 800 parts N-methylpyrrolidone are added over a 20 minute period. The solution was allowed to cool. At 25C 40 parts Multrathane M were added and the mixture stirred for 30 minutes. The temperature was raised to 135C. After l hour l8.0 parts of Multrathane M were added and heating was continued far 30 minutes.
The product has a Brookfield viscosity (at 25C) of 149 poise at a solids content of 26.9%. A tough, flexible film could be prepared by casting a portlon of the solution on glass and curing at 600F for 3-5 minutes.
loCoated Wire Tests The wire enamel in the example was coated on a G.E. 15~foot two zone, vertical, forced air enameling oven. Six coating passes were used to apply the proper insulation thickness, The wire ~copper) thickness was 18 AWG. The coated magnet wire was tested according to ASTM D-1676 for film thickness, film flexibility and adherence and unidirectional scrape resistance. Short term thermal stability or burnout was determine according to the overload test procedure given in NEMA MW 1000 (Part 3, ; ~ ~;
Sec. 3-2.6).

The flexibility and adhesion were tested according to ASTM D-1676. ~-To be amenable to automatic winding and normal abuse the wire should take a full snap. This means it should be capable of being drawn rapidly¦ -to break and have the stretched portions of the coating on the wire remai~
¦ integral, i.e., it should have no cracks (brittleness) and it should not ¦

1 I'tube" or separate from the substrate (poor adhesion). In addition to ¦ passing this snap adhesion test, it is desirable that the stretched por-! tion of a wire which has been stretched either 20% of its original length¦¦ (20% ~erk) or to the breaking point (full snap) be capable of being wound , about a mandrel as small as possible. The mandrels used are l, 2, 3, etc. ;
jl Nence, a rating terminology for magnet wire flexural properties is full ' snap - or 20X Jerk + SPM (smallest passing mandrel). Normally the Ij , ' ' ~ ,.

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11~38544 20% jerk test is considered more realistic in regard to com~ercial usage with a value of IX being consldered the top rating. A 20% jerk-SPM of 2 is considered very good, 3 is acceptable, 4 i9 a marginal pass-fail and 5 is fail~lre.
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~' lU3tlS44 - l3XAMPLI IV
Into i~n appropriate vessel equipped with a stirrer, nitrogen purge, thermometer, trap with condenser, is placed 420.2 parts ~rimellitic acid, 317.2 parts methylenebis(aniline), 260.0 parts N-methylpyrrolidone and 38.7 parts (40 ml) pseudocumene. The mixture is brought to 220C over a 2.5 hr. period during which time some aqueous material is withdriwn from the trap. The solution is held at 220-225C for 5 hrs. A very gentle reflux will occur. Heat is removed and 1500 parts ~-methyl-pyrrolidone are added over a 20 min. period. When the temperature has reache~vl30C 800 parts xylene are then added. The solution is allowed ~
to cool with stirring. At 25C 100.0 parts Isonate 125 mf are added ~ -and the mixture brought to 155C over a 2 hr. period. The Gardner-Holdt vi8c08ity after 60 min. at 155C was F. An additionàl 34.5 parts ~;
Iisonate 125 mf were added over a 95 min. period giving a Y(~) viscosity.
1S Inspection of the product a~ 25C gave the following:
Brookfield - 24 poise Solids - 24.1%
Inherent (DMAC) - 0.42 dl/g (0.5 g per 100 mI DMAC) ! A. A sample was wire coated on copper wire using 4 passes of ll undercoat Isonel 200 XWE490, which is polyester modified by tris hydroxyethylisocyanurate (manufactured by Schenectady Chemical Co.) and 2 passes of the solution prepared in ~ ~xample IV hereinabove.

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B. A portion of the ~naterial prepared in Example IV was wet spun into distilled water usin& a syringe. The strand produced was cured at 600F for 5 min. The fiber was flexible and could be knotted. ` - ~;
C. Coating~
The following materials were placed in a ball mill: ~ ;
74.7 parts Example I
8. 0 parts TiO21 ;-2. 5 parts ~14 yellow2 !i. ;,, `,.""."
'..'.` ~' ,. ':'`
14.8 parts NMP

The mixture was rolled overnight and then spread on a Bonderite 37 steel panel. After a 12 min. cure at 500F the panel (coating) gave the following properties:

Cured Film Thickness - I mil Pencil Hardness - 5H
.. :; . ,. i Sward Hardness - 27 ;;
Cross-Hatch Adhesion, % - 100 1/8" Conical Mandrel Bend, % - 100 Direct lmpact (in-lbs) - ~160 Reverse Impact (in-lbs) - ~160 1. DuPont R -900 2, Shepard Chem Co.
D. Adhesive AppliGation~
T-Peel - Samples of the product prepared in Example IV were spread on Cold Rolled Steel (Bonderite~ 1000 treatment) and cured under vacuum at 80C for 16 hours (for T-Peel adhesion) and likewise coated on 0. 064" Hot Rolled Steel (chloroethane ~. .
cleaned~ and cured for Lap Shear ~sts.

T-Peel Adhesion - 15. Z psi Lap Shear - 1380 pSI

:
- 15~

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The test ~pecimens were prepared uslng a l5 sec. activation at 20 psi at 660F on a Sentinel heat sealer.

! E- Film~
A sample from Example IV was spread on glass and cured 2 hrs. at 85C (under vacuum), 30 min. at 300F. :~
15 min. at 500F, and 3 min. at 600~F.
, Tensile Strength - 15,800 psi ;
~) Elongation - 11.5%
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Claims (14)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for preparing high molecular weight polyamide-imide products having film-forming properties which process comprises condensing trimellitic anhydride or trimellitic acid and a primary diamine in a mole ratio of about 1 to 0.7 to about 1 to 0.8 at a temperature of about 210°C to about 250°C, to give a low molecular weight polymer having an excess of trimellitic anhydride moieties and then further condensing this polymer with about 0.1 to about 0.3 moles up to about 0.75 moles of a diisocyanate for each trimellitic anhydride moiety in an inert solvent at a temperature of about 25°C to about 150°C.

2. The process of Claim 1 wherein the molar ratio of the trimellitic anhydride or trimellitic acid to the diamine is about 1 to 0.7 to about 1 to 0.8 and the mole ratio of the trimellitic moiety to the diisocyanate is 1:0.3 to 1:0.2.

3. The process of Claim 1 wherein the condensation of the trimellitic anhydride or trimellitic acid with the diamine is carried out at a temperature of about 220°C to about 230°C
and the further condensation is carried out at about 130°C
to about 140°C.

4. An electrical conductor having a continuous coating of the polyamide-imide products prepared according to the process of Claim 1, 2 or 3.

5. A film of the polyamide-imide products prepared according to the process of Claim 1, 2 or 3.

6. A protective coating of the polyamide-imide products prepared according to the process of Claim 1, 2 or 3.

7. A process according to Claim 1, 2 or 3 wherein the diamine is methylene dianiline.

8. A process according to Claim 1, 2 or 3 wherein the diisocyanate is methylene di-p-phenyldiisocyanate.

9. A fiber prepared from the polyamide-imide products prepared according to the process of Claim 1, 2 or 3.

10. An adhesive of the polyamide-imide products prepared according to the process of Claim 1, 2 or 3.

11. A laminate having a plurality of layers bonded together with the polyamide-imide products prepared according to the process of Claim 1, 2 or 3.

12. A molded article of the polyamide-imide products prepared according to the process of Claim 1, 2 or 3.

13. A process according to Claim 1, 2 or 3 wherein the diamine is aromatic.

14. A process according to Claim 1, 2 or 3 wherein the diisocyanate is aromatic.