Umted States Patent [19] [111 4,303,779 Stenzenberger [45] Dec. 1, 1981

[54] THERMOSETTING IMIDE RESINS FROM Primary Examiner-—-Harold D. Anderson DIHYDRAZIDE Attorney, Agent, or Firm—Schwartz, Jeffery, Schwaab, [75] Inventor: Horst Stenzenberger, Schriesheim, Mack’ Blumemhal & Koch Fed. Rep. of Germany [57] ABSTRACT [73] Assignee: Technochemie Novel imide resins are prepared by reacting a mixture GmbH-Verfahrenstechnik, of a bisimide of an unsaturated and a Dossenheim, Fed. Rep. of Germany monoimide with a dihydrazide of a dicarboxylic acid, [211 App]. NO; 97,657 preferably in an organic solvent or diluent at elevated temperature for a period of time insufficient to yield an [22] Fi1ed= Nov- 27, 1979 insoluble, infusible, fully cured imide resin. Solutions of [51] Int. Cl.3 ...... C08G 73/12 the resulting prepolymerilation PrOduCt are Stable at [52] US. (:1...... 528/312; 428/473.5; room temperature and their viseeeity remains substan 525/422; 528/170; 528/210; 528/211; 528/321; tielly unchanged for a prolonged period of time- Fully 528/322 cured imide resins and articles thereof of a high heat [58] Field of Search ...... 528/322, 170, 312, 315, resistance are obtained by heating said prepolymerized 528/321, 210, 211; 525/422 imide resin or materials such as ?bers, metal wire webs, . and others im re nated therewith, if desired, in the [56] References Cited presence of curringgcatalysts, inhibitors, ?llers and other US PATENT DOCUMENTS materials to curing temperature up to 350° C. 3,562,223 2/1971 Bargain et al...... 528/322 4,211,860 7/1980 Stenzenberger ...... 528/322 17 Claims, N0 Drawings ‘4,303,779 1 2 are mixed with the bisimides and this mixture is reacted with a dicarboxylic acid dihydrazide of the general THERMOSETTINGDIl-IYDRAZIDE IMIDE RESINS , , . . formula III _ 1~

BACKGROUND OF THE INVENTION A‘ 5

1. Field of the Invention , , , The present invention relates to novel ‘and highly advantageous thermosetting imide resin‘s, to a process of The reaction is carried out in such a manner thatthe producing such imide resins, to compositions and meth molar ratio between the imide groups in the mixturejand ods of using same and to articles made therewith. the hydrazide groups in the mixture, , 2. State of the Prior Art _ I i a It is known that the ethylenic double bond of maleic Number of Moles of Unreacted Imide acid imides is readily reacted with basic organic com Number of Moles of Acid I-Iydrazide pounds and especially, with organic arnineswhereby , aspartic acid imides are'foyrmed. This mode of reaction are between 1.1 and 100. The‘ fully unreacted monomer has been used, for instance, forproducing polymeriz mixture contains no free hydrazide groups and poly able imide resins. US. Pat. No. 3,562,223 describes said merizes under heating conditions, for example, between reaction and the reaction products. According to said 100° to 350° C. to a highly crosslinked polyimide resin patent, the speed of reaction is determined ‘to a far having high thermal stability. Accordingly, the novel reaching extent by the basicity of the amino compound. thermosetting imide resins of the present invention are It is also known that the ethylenically unsaturated obtained by reacting: A. a mixture of an N,N'-bisimide of an unsaturated double bond of bis-maleimides'canbe reacted with di dicarboxylic acid of the general formula I " " > hydrazide to ‘form ‘a thermosetting 25 imide resin. West German Pat. No'. P 27 54 631.2 teaches such a reaction wherein the polyimide can be oII II 01 polymerized upon heating to a highly crosslinked poly- ' c c imide having hightemperature ‘stability. _ _ B N-A-N B 30 \ / \ / SUMMARY OF .THE'INVENTION" I . c c II II It is one object of the presentinvention to provide o novel .and "highly-advantageous thermosetting imide resins having improved flow properties. ‘ i' i A I _ ' Another object of the present invention to provide 35 a ‘simple and effective process of producing such ther mosetting imide resin_s._ H I _ - _ r . . 0: Still another object of the present-invention is to provide a simple and effective method of polymerizing and hardening the prepolymerization products obtained according to thepresent invention. - ' r i A further object of the present invention is- to provid articles such as molded articles or coated ?ber materi wherein A represents a divalent organic-radical with at als, ‘webs, ?laments, rovings and the like. 45 least two carbon atoms, E _ represents a monovalent Other objects of the present invention and advanta radical with at least one carbon atom and B represents 'geous features thereof will become apparent as the de a divalent organic radical selected from the group con scription proceeds. ' ' ' i sisting of the following radicals .. The present vinvention relates to novel thermosetting imide resins obtained by the reaction of two compo H CH CH CH nent's, component A, a mixture of N,N’-bisimide of an ’ -\ / \3 / \3 ‘/ ~€ _/ C C C ‘C unsaturated dicarboxylic acid of a speci?c formula and "-1 ll " II’ I a monoimide of a speci?c formula and component B, c . c , c », H20 / \ / \ / \ ,\ the dihydrazide of an organic dicarboxylic acid of a H CH3 H ‘ _ speci?c formula, The' invention also relates to the pro

cess for producing'the thermpsettingjmide resinsf _ with ' ' It has, therefore, been discovered that new thermo B. the dihydrazide of an organic dicarboxylic acid of setting imide resins with ‘optimal flowt'properties can be the general formula III ' ‘ -' obtained when vmonoiinides of the generalv forrnula_.II V 60

,. O . . .|l,,-_ C / \ " ‘ .B ' N-E. wherein‘ D-represents a divalent organic radical. \ :/ is. 65 The group, designated by, A ‘in__,_l_?orrnula I can be an . C , alkylene group with 2 to 12 carbon atoms, a cycloal ll ' I 0 kylene group with 5 or 6 carbon atoms, a heterocy clic group with 4 or 5 carbon atoms, and at least one 14,303,779 3 nitrogen, oxygen‘, ‘or sulfur atom ih'the heterocyclic N-dodecylmaleimide,_ , ,_ ring, . _ ‘ ._,> ,i 1,, .‘ ‘Y N-is‘obutylm‘aleimide, -“'- I a mono- or dicarbocylic group, or ‘ I N-isopropylmaleimide, " at least two mono- or dicarbocylic aromatic or cycloal N-phenylmaleimide, kylene groups which may be linked to each other by LII N-ph'enylc'itroconimide, a carbon to carbonbond or‘ N-phenylitaconimide, by a divalent group such as wN_-toluylmaleimide, oxygen, N-rnono-chlorophenylmaleimide, sulfur, N-biphenylmaleimide ‘ ' ' alkylene with l to 3 carbon atoms, or one of ‘the fol N-napthylmaleimide lowing groups: ' N-vinylrnaleimide ' N-allylmaleimide, and N-cycl'ohexylmaleimide. ' ' The divalent unsaturated group B of the general for 15 mula II is identical ‘as that in" general formula I. ' In general‘ formula III, B represents a divalent or ganic group such as an alkylene group, a cycloalkylene group and arylene group and the like. Suitable dicarboxylic acid dihydrazides‘ are, for in 20 stance, the following compounds: . ' ' ‘ oxalic acid dihydrazide, 'malonic acid dihydrazide, succinic acid dihydrazide, - glutaric acid dihydrazide, adipic acid dihydrazide,: pimelic acid dihydrazide, suberic. acid dihydrazide, .. seba'cic acid dihydrazide, . . cyclohexane dicarboxylic and dihydrazide, 30 dihydrazide, - isophthalic acid dihydrazide, 2,6-naphthalene dicarboxylic acid dihydrazide, 2,7-'naphthalene dicarboxylic acid dihydrazide, v and others. Mixtures of ‘two or more of the above-men tioned dicarboxylic acid'dihydrazides can also be‘used. The production of new, thermosetting, imide resins In said groups, the substituents R1, R2, R3, R4, and having excellent ?ow characteristics is effected, for R5, are alkyl with l to 5 carbon atoms. example,‘ by intimately mixing the'initial materials by Bisimides which have proven to be of special value using conventional methods of the mixing and grinding for preparing the novel imide resins are: of powders and heating them subsequently to tempera 1,2-bismaleimido ethane, tures between 80° and 180° C. until a product that is still 1,4-bismaleimido butane, plastic or possibly still soluble, is formed. The progress 1,6-bismaleimido hexane, of the prepolymerization has the effect that the initially l, l2-bismaleimido dodecane, low viscosity melt of the monomer mixture becomes l,6-bismaleimido-(2,2,4~trimethyl)hexane, '45 steadily thicker and ?nally solidi?es. Such a solidi?ed 1,3-bismaleimido benzene, " ' 7 or highly viscous melt may still be dissolved in high l,4-bismaleimido benzene, boiling solvents such as N-methylpyrrolidone, dimeth 4,4’-bismaleimido diphenyl methane, ylacetamide, dimethylformamide, or 4,4’-bismaleimido diphenyl ether, their mixtures and used in the preparation of glass fabric 4,4’-bismaleimido diphenyl sul?de, 50 preimpregnates (referred to hereinafter as prepregs). 4,4’-bismaleimido diphenyl sulfone, ’ _ The extent to whichthe prepolymerization is taken 4,4-bismaleimido dicyclohexyl‘methane, depends essentially on the intended application of the 2,4-bismaleimido toluene, thermosetting polyimide prepolymer. For ‘processing 2,6-bismaleimido toluene, byv lmeans ofv ‘injection molding, melt viscosities of N,N’-m-xylylene bismaleimide, 55 500-2500 centipoises are advantageous, while for pro N,N'-p-xylylene bismaleimide, cessing with ‘solvents, highly‘ viscous resinslare also

N,N’-m-phenylene biscitraconic acid imide, suitable. . ' ' ' ‘ N,N‘-4,4'-diphenylmethane citraconimide, 'The new thermosetting imide resins may also be pre N,N’-4,4'-diphenylmethane bisitaconimide, pared in inert organic solvents, for example, dimethyl and others. Mixtures of the above-mentioned bisimides 60 formamide, dimethylacetamide, N-methylpyrrolidone, can also be used for producing the imide resins accord tetramethylurea of mixtures thereof. This is done pref ing to the present invention. ' " ' erably whenever further processing requires the use of In the general formula II, E can represent an alkyl a solution. Low boiling solvents, such as tetrahydrofu group, a cycloalkyl group and an aryl group. Examples ran, dioxane and ethyleneglycol ether may be used in of monoimides include the following compounds: 65 the preparation. It is a special characteristic of the resin N-methylmaleimide, ‘ solutions that their viscosity over a period of months N-ethylmaleimide, increases only slightly to a degree which does not inter N-propylmaleimide, fere with the preparation of prepregs of glass fabric or 4,303,079 5 6 carbon ?bers, thus-remaining practically constant. Pre ?ed by‘the application of a partial vacuum. The result pregs prepared by meanspf such solutionsstable with ing‘ ‘imide- resin‘may be further processed as follows: ' respect to viscosity are stable in storage at room tem (a) -.The melt is poured into ; .casting molds perature without deterioration of the properties neces (ll0X-l00X3 mm) preheated to 150° C. andis therein sary for the pressing to laminates, for example, the ?ow subsequently hardened, by raising the temperature in , behavior of the resins. , steps within 4 hours to 200° C. andthen continued heat The imide resins may also be prepared in inert dilu ing for 3 hours at 200° C. ~ ‘ 1' ~ ents, wherein one or two of the three initial components ‘ (b) Following the cooling of the melt to room- tem are insoluble. This method of operation‘is preferably perature, a 50% . solution in N-methylpyrrolidone is applied when the prepolymers having low melting prepared under agitation. The solution is stable in rela points are desired, i.e. when prepolymerization is‘not to tion to viscosity and is-suitable for the preparation of betakentoofar.» ~ ‘- i i ‘ preimpregnated glass ?berwebs. Glass ?ber webs or In numerous industrial applications‘ of the new imide fabrics of Type G 92lllK 1100 of the, Interglas Co. of resins, it is of advantage to accelerate hardening by the Ulm, West Germany are homogeneously coatedwith addition of catalysts. Effective hardening catalysts are, the resin solution by means of immersion. The impreg for example, organic peroxides, such as di-tert-butyl nated glass ?ber web is then dried in a through circula peroxide, dicumylp'eroxide, t-butylperbenzoate in con tion; drying cabinet for 10 minutes at 140° C. The pre centrations of 0.1-0.5% with respect to the total weight pregs produced in this manner have a resin content of of the’thermos'etting imide resin. When catalysts are 38% in a weight per unit area of 320. g/m2 and Ya residual used, they are'mixedduring the preparation of the pre 20 solvent content of 34%. Several glass fabric prepregs polymers with ‘the initial compounds by 'one of the are stacked in a heated plate pressand the. laminateis above-mentioned methods; ' ‘ hardened under pressure at a temperature of: 160° C. for For other industrial applications of the new imide one hour and at 200° C. for two hours. i , . resins, it is advantageous to delay the hardening pro . ,(c) After cooling the melt to room temperature, the cess, which iseffected by meansvof a vvinyl polymeriza 25 prepolymer is homogeneously ground-with graphite tion. In such cases, the imide resins‘ are prepared in the powder in a ball mill. The resulting mixture is suitable presence of inhibitors of polymerization, for example, for use as a compression molding material. Moldings hydroquinone. The amount of the inhibitor to be used is may be prepared under pressure at temperatures around approximatelybetweemO.l to 120%.‘ I 200° C. in astarnping press. 1 ' The imide: resins are hardened by means of heating to 30 temperatures between 100°~350° C.,v possibly‘ under - I EXAMPLE 2 ‘ , pressure, preferably at temperatures between1160°'—260° 135.84. g (01 mole) 4,4’-bismaleimidodiphenylme C. Insoluble, unmeltable, .crosslinked productsiwith thane, 3.46 (0.02 mole) maleimidobenzene and 5.83 g excellent high temperature properties-are obtained. (0.03 mole). terephthalic acid dihydrazide are dissolved A preferred field of application of the new imide 35 in 65.1 g N-methylpyrrolidone with agitation at 90° C. resins are laminating materials. Processing is effected in Agitation is continued for 30 minutes at 90° C. to form a manner so that the imide resins are dissolvedivin high ‘the prepolymer. The solution of thepolyimide prepoly boiling solvents,such as N-methylpyrrolidone, dimeth mer is run slowly into 1.3 1 cold water under agitation, ylacetamide or dimethylformamide and ‘the, solution while the polyimide resin precipitates as a ?ne, yellow used to coat glass ?bers in the form ofrovings or fabric powder and, is separated by means of ?ltering. , or carbon ?bers orv boron ?bers or synthetic organic ?bers in the formof. fabric, ?laments or rovings, fol EXAMPLE '3 ' lowed by the evaporation of the solvent and pressing 43.28 g (0.25 mole) maleimidobenzene, 89.53 g (0.25 the impregnated ?bers into laminates, using pressure mole) 4,4'w-bismaleimidodiphenylmethane and 19.42 g

and heat. \ I ' _ ‘ . ' (0.1 mole) isophthalic acid dihydrazide are dissolved in The imide resins may also be processed by the known 152.29 g dimethylacetamide to-a 50% solution with methods of the powderpressingprocess for thermoset agitation at 50° C. The solution of the polyimide pre ting masses'into shapes, wherein hardening takes place polymer has a viscosity of 26.2 centistoke and may be under pressure simultaneously with the molding pro used, as described in Example 1b, to impregnate glass cess. Forythese applications, the usuallradditives such as 50 ?ber-webs. The separation of the prepolymer may be ?llers, pigments, plasticizers and ?ame retarders, may eliminated in this instance. The solution of the prepoly be added'to’the ‘resins; Suitable ?llers are, for example, mer obtained is extremely stable with respect to viscos glass ?bers, carbon ?bers, organic ?bers with high mod ity. After storing for 50 days at room temperature, the uli, such as aramides, quartz ?our, kaolin, silicon diox viscosity amounts to only 31 centistokes. ide and metals in the form of ?ne powders. -55 In embodiments of the invention‘ on an""i‘ndustrial EXAMPLE _4 scale, the amounts given hereinb'elow in the examples 5 g maleimidobenzene, 56 g 4,4'-bismaleimidodi may be multiplied as needed and ‘adapted to the indus phenylmethane, 24 g 2,4-bismaleimidotoluene and 10 g trial apparatus in existence or to be provided. ' isophthalic acid dihydrazide are mixed homogeneously and in a round bottom ?ask at 140° C. stirred to a clear EXAMPLE i Q melt and degassi?edpThe meltw of the polyimide pre 50 g (0.140 mole) 4,4’-bismaleimidodiphenylmeth‘ane, polymer may be further processed, as described in Ex 50 g (0.289 mole) maleiniidobenz'ene‘and 5.83 g (0.03 ample l, by molding by way of a solution or as a pow mole) isophthaleic acid dihydrazide are ‘ thoroughly der mixture with ?llers. mixed in a ball mill and subsequently melted in a round 65 bottom ?ask at 140° C. The homogeneousclear vmelt is EXAMPLE 5 maintained for 30 minutes at 140° C; The initially ?uid ‘Similar to Example 4, a mixture of 5 g maleimidoben mass becomes increasingly viscousiThemeltis degassi zene, ~ 5 ,- gv maleimidotoluene, 56 g 4,4’-bismalimidodi 4,303,779 7 8 phenylmethane, 24 g 2,4-bismaleimidotoluene" and 10 g I aryl groups and Ba divalent organic group of the isophthalic acid dihydrazide in a round bottom ?ask ~ formulas indicated hereinbelow under rotation at 125° C. is prepolymerized to homoge neous clear melt. The polyimide prepolymer melt has a H. viscosity of 260 centistoke and may be used without \/ cooling in the molten state to impregnate glass fabric c It. blanks (15X 15 cm). Prepregs produced in this manner C, (3:6 0 contain no solvents‘and may be pressed at l70°~2l0° C. /\ / \ ' / \ ' to high quality glass fabric laminates. H c 3 H ‘ 10 EXAMPLE 6 with l 1 I For the purpose of preparing glass fabric prepregs to (b) the dihydrazide of an organic dicarboxylic acid of be processed into glass fabric laminates, the prepolymer the general formula (III) i ' > is prepared in solution and separation is eliminated. 107.51 g (0.3 M) 4,4’-bismaleimidodiphenylmethane, ' 17.3 g maleimidobenzene (0.1 mole) l0 g 'isophthalic acid dihydrazide and 7.46 g terephthalic acid dihydra zide are dissolved in 142.3 g dimethyl acetamide by heating to 120° C. with agitation. After 10-15 minutes a wherein D represents a divalent organic group, the bright solution of the prepolymer is obtained. The vis molar proportion of the reaction between the un cosity of the solution is 52 centistoke. The‘ solution is saturated; imide groups contained in the mixture stable with respect to viscosity and may be stored at and the ihydrazide groups contained in the mixture room temperature for 3 months, without an appreciable increase in viscosity. The solution of the prepolymer may be used directly to impregnate glass fabrics. ' Number of moles of unsaturated imide Number of moles of acid hydrazide EXAMPLE 7 232 g (0.647 mole) 4,4-bismaleirnidopheriyl ether, being between LI and 100. 92.58 g (0.353 mole) 2,4’-bismalemidotoluene, 34.6 g 2. The imide resin of claim 1 wherein the bisimide is (0.2 mole) maleimidobenzene and 26.4 g (0.2 mole) 30 a bisimide selected from the group consisting of malonic acid dihydrazide are mixed well in a ball mill 1,2-bismaleimido ethane, ‘ and subsequently heated in a round bottom ?ask with 1,4-bismaleimido butane, rotation in an oil bath to a temperature of 150° C., until 1,6-bismaleimido hexane, a homogeneous; blank melt ‘is obtained. The melt may 1,12-bismaleimido dodecane, be maintained for another few hours at" 150° C. to in 35 ~ l,6-bismaleimido-(2,2,4-trimethyl)hexane, crease its viscosity. After cooling to room temperature, 1,3-bismaleimido benzene, _ ; the solidi?ed melt is ground to a ?ne powder. This l',4-bismaleirnido benzene, ' ‘ prepolymer may be mixed with other ?llers in the pow 4,4’-bismaleimido diphenyl methan der form (quartz ?our, graphite powder, molybdenum ' 4,4’-bismaleimido diphenyl ether, sul?de). The molding mass obtained in this manner may 4,4'-bismal'eimido diphenyl sul?de, be molded into shapes of high thermal stability. v4,4’-bismaleimido diphenyl sulfone, What is claimed is: 4,4’-bismaleimido dicyclohexyl methane, 1. A thermosetting imide resin comprising the reac ‘2,4-bismaleimido toluene, ' ’ tion product of ‘ ‘ 2,6-bismaleimido toluene, (a) a mixture of an N,N’-bisimide of an unsaturated N,N’-m-xylylene bismaleimide, dicarboxylic acid of the general formula of N,N’Fp-xylylene bismaleirnide, N,N'-m-phenylene biscitraconic acid imide, 0 . (l) N,N’-4,4'-diphenylmethane citraconimide, and‘, II II N,N-4,4'-diphenylmethane bisitaconimide. 50 3. The imide resin of claim 1 wherein the monoimide is a monoimide selected from the group consisting of c C N-methylmaleimide, ‘ II II N-ethylmaleimide, o o 55 N-propylmaleimide, and a monoimide of the general formula (II) N-dodecylmaleimide, . N-isobutylmaleimide, N-isopropylmaleimide, 0 II N-phenylmaleimide, c N-phenylcitroconimide, / \ B N-E N-phenylitaconimide, " \ / N-toluylmaleimide, C ll N-mono-chlorophenylmaleimide, 0 N-biphenylmaleimide, 65 N-naphthylmaleimide, wherein the residue A signi?es a divalent organic N-vinylmaleimide, group with at least two carbon atoms, E is selected N-allylmaleimide, and from the group consisting of alkyl, cycloalkyl, and N-cyclohexylmaleimide. 9 4,303,779 10 4. The imide resin of claim 1 wherein the dicarboxylic from the group consisting of alkyl, cycloalkyl, and acid dihydrazide is a dihydrazide selected from the aryl groups and B a divalent organic group of the group consisting of: formulas indicated hereinbelow oxalic acid dihydrazide, malonic acid dihydrazide, H CH3 CH3 CH2 succinic acid dihydrazide, \ / \ / \ / \ / C C C C glutaric acid dihydrazide, I! II II I adipic acid dihydrazide, C , C , C , H2C pimelic acid dihydrazide, / \ / \ / \ \ suberic acid dihydrazide, H CH3 H sebacic acid dihydrazide, v cyclohexane dicarboxylic acid dehydrazide, with terephthalic acid dihydrazide, (b) the dihydrazide of an organic dicarboxylic acid of isophthalic acid dihydrazide, the general formula (III) 2,6-naphthalene dicarboxylic acid dihydrazide, 15 2,7-naphthalene dicarboxylic acid dihydrazide and mixtures of said dihydrazides. 5. The imide resin of claim 1, said resin being pre pared by using a mixture of bisimides as the bisimide wherein D represents a divalent organic group, the reactant. 20 molar proportion of the reaction between the un 6. The imide resin of claim 1, said resin being pre saturated imide groups contained in the mixture pared by using a mixture of monoimides as the monoi and the hydrazide groups contained in the mixture mide reactant. 7. The imide resin of claim 1, said resin being pre pared by using a mixture of dicarboxylic acid dihydra 25 zide as the dihydrazide reactant. Number of moles of unsaturated imide 8. The imide resin of claim 1, said resin being pre Number of moles of acid hydrazide pared by reacting 4,4’-bismaleimido diphenylmethane, maleimidobenzene and isophthalic acid dihydrazide. being between 1.1 and 100 in a molar proportion of imide groups to dihydrazide group between about 9. The imide resin of claim 1 containing an organic 30 peroxide as curing catalyst. 1.1 and about 100 in an organic diluent to a temper 10. The imide resin of claim 1 containing a curing ature not substantially exceeding about 180° C. for inhibitor. a period of time to yield a moldable and curable, 11. In a process of producing a thermosetting imide thermosetting prepolymerized imide resin. 12. The process of claim 11, in which the diluent is an resin, the step which comprises heating 35 inert, polar organic solvent. (a) a mixture of an N,N’-bisimide of an unsaturated dicarboxylic acid of the general formula of 13. The process of claim 12, in which the inert, polar organic solvent is a solvent selected from the group consisting of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, and tetramethyl urea. 14. The process of claim 11, comprising the additional step of hardening and curing the prepolymerized imide resin by further heating the same to a temperature be tween about 100° C. and about 350° C. to yield a sub 45 stantially insoluble, infusible, cross-linked polymerized imide resin of high thermal stability. 15. The process of claim 14, in which the additional step is carried out with the addition of a curing acceler ating catalyst. 50 16, The process of claim 11", in which the step of 0:0 producing the prepolymerized imide resin is carried out with the addition of a curing inhibiting agent. 17. The solution of moldable and curable, thermoset ting, prepolymerized imide resin of claim 1 in an inert, 55 polar, organic solvent, said solution being stable on storage for a prolonged period of time without its vis wherein the residue A signi?es a divalent organic cosity substantially increasing during said storage. group with at least two carbon atoms, E is selected * 1‘ * * *

65