Title of Invention	TWO-STAGE CURE POLYIMIDE OLIGOMERS
Abstract	A method of making high temperature, low void volume, fiber-reinforced composite materials from prepregs using a two-stage cure schedule; characterized in that: in a first stage, a prepreg, which comprises a solution of citraconic anhydride-endcapped polyamic acid and/or polyimide oligomers in a fibrous reinforcing material, is cured to remove volatiles, the viscosity of the oligomers during the first stage being less than or equal to 250 pascal-seconds (2500 poise); and in a second stage, full cure is effected by crosslinking via a nonvolatile-producing reaction.

Title of Invention

TWO-STAGE CURE POLYIMIDE OLIGOMERS

Abstract

A method of making high temperature, low void volume, fiber-reinforced composite materials from prepregs using a two-stage cure schedule; characterized in that: in a first stage, a prepreg, which comprises a solution of citraconic anhydride-endcapped polyamic acid and/or polyimide oligomers in a fibrous reinforcing material, is cured to remove volatiles, the viscosity of the oligomers during the first stage being less than or equal to 250 pascal-seconds (2500 poise); and in a second stage, full cure is effected by crosslinking via a nonvolatile-producing reaction.

Full Text	RELATED APPLICATIONS [0001] This application is a continuation-in-part of U.S. Patent Application Serial No. 10/931,070, ftied August 30, 2004, which claims priority from U.S. Provisional Patent Application Serial No. 60/499,849, filed September 2, 2003. TECHNICAL FIELD [0002] The present invention generally relates to a method for using citraconic anhydride and itaconic anhydride as addition cure end caps in reactions for forming polyamic acid oligomers and polyimide oligomers. The present invention also generally relates to prepregs and high temperature adhesives made from Hie resulting oligomers,' as well as, high temperature, low void volume, fiber-reinforced composites made from the prepregs. BACKGROUND ART [0003] Fiber-reinforced composite materials, which are made up of reinforcing fibers and matrix resins, are lightweight and have excellent mechanical properties. As such, these composite materials nave been widely used in a variety of structural and non- structural applications such as aerospace, automotive, infra-structure repair, marine, military, and sporting goods or other consumer products that must have sufficient toughness and impact resistance to endure many years of harsh service. [0004] Epoxy resins, and to a lesser extent, unsaturated polyester resins, vinyl ester resins, phenol resins, and polyimide resins, have been employed as matrix resins in fiber-reinforced composite materials. The use of composite materials having polyimide resin matrices is increasing, however, where these materials are now recognized as preferred structural materials in aerospace applications, because of their lightweight and load-bearing characteristics and their oxidative stability at elevated temperatures. [0005] Various methods or techniques such as prepreg, hand lay-up, filament winding, pull-trusion, resin transfer molding (RTM) and resin infusion (Rl), have been used to produce fiber-reinforced composite materials. [0006] Current technologies for making prepreg and composites from polyimides utilize solutions from the poly(amide) acids of these resins. Poiy(amide) add solutions are processed into prepreg with various reinforcing fibers. These poiy(amide) acid solutions are of low solids contents and high viscosity. Therefore, the processing of these types of solutions requires overcoming significant problems such as solvent management and good fiber wet out from the high viscosity solutions. The resultant prepreg typically requires residual solvent contents of 20 to 25% by weight (approximately 2-3% water from thermal imidization reaction) for adequate tack and drape. This residual solvent must then be removed during the composite cure cycle. This material is hand-laid into composites which makes working with this type of material very labor intensive and costly. [0007] One example of a prior art prepreg solution that when processed into prepreg with suitable reinforcing fibers yielded a high temperature resistant composite, was first marketed in the 1960s under the trade designation SKYBOND by Monsanto Corporation, 800 N. Lindbergh Blvd., St. Louis, Missouri 63167: The SKYBOND prepreg solution was prepared by prereacting 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA) with ethanol using NMP as the solvent. Then, either m-phenylenediamine (MPD) or 4,4'-methylenedianiline (MDA) was added to the solution. No endcapping agent was employed. It was (and continues to be) difficult to fabricate low void composites using this type of chemistry. One of the reasons offered for this difficulty has been that during the cure process branching can occur by the reaction of amine end-groups with the bridging carbonyl group of the BTDA moiety leading to branching and intractability of the matrix resin. [0008] The processability (and thus end-use applications) of these polyimides has been improved by lowering molecular weight and by using reactive endcapping agents to produce thermosetting polyimides. [0009] Originally developed in the 1970s for military aircraft applications, these thermosetting polyimides are produced by dissolving an aromatic diamine, a dialkyl ester of tetracarboxylic acid and a monofunctional nadic ester endcapping agent in a solvent (e.g., alcohol). [0010] The best known of these early thermosetting polyimides is PMR-15, which is shorthand for in-situ polymerization of monomer reactants. These thermosetting polyimides (/.e.t benzophenone dianhydride//methylenedianiline//nadic anhydride) were originally developed at NASA Lewis for military aircraft engines and airframes, undergo crosslinking at 250 °C to 300 °C (482 °F to 572 °F), and demonstrate good thermal and mechanical properties. PMR-15 thermosetting polyimides, however, contain the hazardous compound methylenedianiline (MDA), which raises health and safety concerns. [0011] PMR-15 cures with a condensation reaction, which means that water and alcohol are evolved and given off from the polymer chain during cure. PMR-15 does not give a clean two-stage cure. In particular, PMR-15 crosslinks while volatiles are being removed and decomposes during cure to evolve cyclopentadiene. Moreover, the volume of solvent removed such as water, methanol and cyclopentadiene, produces voids in the final composite in an amount equal to greater than 2 percent (%) of the volume of the composite. [0012] A direct PMR-15 replacement with very similar chemistry but using less toxic monomers is the nadic end-capped polyimides RP-46. These thermosetting polyimides (i.e., benzophenone dianhydride//3,4-oxydianiline//nadic anhydride), like PMR- 15, cure with a condensation reaction. The two-stage cure is not a clean two-stage cure. Moreover, the resulting composite contains voids in an amount of greater than 2 % of the volume of the composite. [0013] Other non-MDA containing polyimides include PETI {i.e., phenylethynyl terminated imide) resins, which represent a different polyimide chemistry. These resins were developed to address the need for structural matrix resins that could provide higher temperature performance and longer-term thermoxidative stability. While more expensive than PMR-type materials, these high temperature resins, which cure in an addition reaction without volatile evolution, can be used to produce substantially void-free composites. Unfortunately, these resins require extremely high cure temperatures of around 375 °C/707 °F. which are very close to the degradation temperature of these resins. In addition, such high cure temperatures may necessitate specialized autoclave or press equipment for some manufacturers. [0014] A need therefore exists for polyamic acid and polyimide oligomers for use in making adhesives and prepreg, where the polyimide oligomers provide a clean two- stage cure at temperatures of less than or equal to about 370 °C. [0015] It is therefore an object of the present invention to provide such polyamic acid and polyimide oligomers. [0016] It is another object to provide solutions suitable for use as prepreg solutions or as high temperature adhesives, which contain one or more of the above- described oligomers and an organic solvent. [0017] It is yet another object of the present invention to provide high temperature, low void volume, fiber-reinforced composites prepared from prepregs made using the inventive prepreg solutions. SUMMARY OF THE INVENTION [0018] The present invention therefore provides a method for using citraconic anhydride and itaconic anhydride, the method comprising using these materials as addition cure end caps in reactions for forming polyamic acid oligomers and polyimide oligomers. [0019] The present invention also provides a polyamic acid oligomer, which is obtained by reacting one or more aromatic dianhydrides, one or more aromatic diamines, and one or more addition cure end caps selected from the group of citraconic anhydride and itaconic anhydride. [0020] Also provided by way of the present invention is a two-stage cure polyimide oligomer, which is obtained by condensing the polyamic acid oligomer described above. [0021] The present invention also provides a solution suitable for use as a prepreg solution or as a high temperature adhesive, which contains the above-described . polyamic acid oligomer and/or polyimide oligomer, and an organic solvent. [0022] The invention further provides a high temperature, low void volume, fiber- reinforced composite material which may be obtained by curing a prepreg in which a fibrous reinforcing material is impregnated with the above-described prepreg solution. [0023] Other features and advantages of the invention will be apparent to one of ordinary skill from the following detailed description. [0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Ail publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. BEST MODE FOR CARRYING OUT THE INVENTION [0025] By way of the present invention, novel addition cure end caps for two- stage cure polyimides have been identified. The novel end caps, namely, citraconic anhydride (CA) and itaconic anhydride (IA), allow for the manufacture of very low void volume composites from polyimide impregnated prepreg using a simple cure schedule. As noted above, the evolution of cure volatiles from condensation cure polyimide resins is well known as a limiting factor in the use of polyimides in structural composites. The present invention solves this problem by providing novel addition cure end caps that possess the correct reactivity to allow volatiles to be removed during composite manufacture. The novel end caps also control molecular weight and act as cr'osslinkers at higher temperatures. [0026] The polyamic acid oligomer of the present invention is obtained by reacting one or more aromatic dianhydrides, one or more aromatic diamines, and one or more addition cure end caps selected from the group of citraconic anhydride and itaconic anhydride. [0027] Aromatic dianhydrides deemed suitable for use in preparing the inventive polyamic acid oligomer are dianhydrides that generally have more than one aromatic ring in the structure, such as those dianhydrides represented by the following formula (I) or by the following general formula (II) where Z represents -CO-, -O-, -SOr, or a direct bond. The aromatic dianhydride having the structure (I) is 1,2,4,5-benzenetetracarboxylic dianhydride (pyromellitic dianhydride or PMDA), while aromatic dianhydrides having the structure (II) include 3,3',4,4'- biphenyltetracarboxylic dianhydride (BPDA), 2,2'-bis[4-(3,4- dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), 1,1',2,2'-benzophenone tetracarboxylic dianhydride (BTDA), 4,4-oxydiphthalic anhydride (OPDA), and 3,3',4,4'- diphenylsulfone tetracarboxylic diandydride (DSDA). [0028] One or more dianhydrides are used to prepare the inventive polyamic acid oligomer. When two dianhydrides are used, the first dianhydride (e.g., BTDA) is preferably present in an amount ranging from about 5 to about 40 % by wt (more preferably, from about 10 to about 25 % by wt., and most preferably, from about 20 to about 25 % by wt.). based on the total weight of the dianhydrides, while the second dianhydride (e.g., BPDA) is preferably present in an amount ranging from about 95 to about 60 % by wt. (more preferably, from about 90 to about 75 % by wt., most preferably, from about 80 to about 75 % by wt.), based on the total weight of the dianhydrides. [0029] Aromatic diamines deemed suitable for use in the present invention are diamines that generally have at least one ether linkage in the structure, such as 3,4'- oxydianiline (3,4'-ODA), 4,4'-oxydianiline (4,4'-ODA), m-phenylenediamine (m-PDA), 2,2'- bis[4-(4-aminophenoxy)phenyi]propane (BAPP), bis[4-(3-aminophenoxy)phenyl]suffone (BAPS-M), 1,3-bis(3-aminophenoxy)benzene (APB), and 1,3-bis(4- aminophenoxy)benzene (TPE-R). [0030] One or more diamines are used to prepare the inventive polyamic acid oligomer. When two diamines are used, it is preferred that at least one diamine have one or more oxygen linkages and that this diamine be present in an amount of at least about 50 % by wt., based on the total weight of the diamines. [0031] In select embodiments, the aromatic diamine(s) is used in combination with a rubber component. Suitable rubber components include, but are not limited to, amine terminated rubbers. In a preferred embodiment, an amine-terminated silicone rubber (SR) is used to prepare the inventive oligomers. In this preferred embodiment, the rubber is present in an amount of less than about 30 % by wt, and more preferably in an amount of less than about 20 % by wt., based on the total weight of the aromatic diamine(s) and rubber component. [0032] Addition cure end caps suitable for use in preparing the inventive polyamic acid oligomer are selected from the group of methyl maleic anhydride (citraconic anhydride) and 2-methylenesuccinic anhydride (itaconic anhydride). As will be described in more detail below, these addition cure end caps serve to control volatiles during cure. [0033] The preparation of the polyamic acid oligomer, in accordance with the teachings of the present invention, basically comprises: (1) charging at least one dianhydride {e.g., BPDA) and at least one diamine (e.g., BAPP) to separate reaction vessels; (2) adding quantities of a suitable solvent (e.g., 1-methyl-2-pyrrolidinone (NMP)) to each reaction vessel to form a slurry or solution of dianhydride(s) in one vessel, and a slurry or solution of diamine(s) in the other vessel, (3) heating the slurry or solution contained in each reaction vessel to a temperature ranging from about 50 to about 120 °C to dissolve the dianhydride(s) and the diamine(s); (4) cooling the solutions contained in each reaction vessel to ambient or room temperature; (5) slowly adding the dianhydride solution to the diamine solution over a period of time ranging from about 10 to about 60 minutes; (6) adding a solution of addition cure end cap(s) (e.g., citraconic anhydride (CA) in NMP) to the reaction vessel; and (7) stirring the solution for a period of time ranging from about 15 to about 120 minutes to form an amic acid solution, wherein, the molar ratio of dianhydride(s) to diamine(s) to addition cure end cap(s) in the amic acid solution ranges from about 1.0/1.95/2.10 to about 1.0/2.1/2.0. [0034] By way of the present invention, it has been discovered that by slowly adding the dissolved dianhydride reactant to the dissolved diamine reactant, while controlling the reaction temperature, the molecular weight of the resulting resin is reduced causing an advantageous reduction in its melting point and melt viscosity. [0035] Solvents suitable for use in the present inventive method include amide- based solvents such as NMP, N,N-dimethylacetamide, N,N-demethylformamide and N- methylcaprolactam, among which NMP and N.N-dimethylacetamide are preferred. [0036] The molar ratio of dianhydride to diamine to addition cure end cap is such that stirring the solution forms low molecular weight prepolymers having at least one end cap radical and suitable for chain extension and crosslinking to form polyimides that have a melting point of less than about 250 °C, and a melt viscosity at 250 °C of less than about 25000 cps. Typically the prepolymers have a weight average molecular weight of less than about 10000 grams per mole (g/mol), and generally less than about 5000 g/mol. [0037] In a preferred embodiment, the molar ratio of dianhydride(s):diamine(s):addition cure end cap(s) is 1.0/2.0/2.01, and more preferably the molar ratio is n/n+1/2. [0038] The polyimide oligomer or resin of the present invention is obtained by imidizing the polyamic acid oligomer by chemical or thermal means to cause dehydration and cyclization to occur. In one embodiment, the synthesis of the polyimide oligomer in the form of an imide powder is carried out via chemical imidization in which a strong acid and an azeotropic agent are used to promote ring closure and to remove azeotropic water, respectively. In a preferred embodiment, a strong acid such as methane sulfonic add is employed as a catalyst arid azeotropic water removed by use of a tertiary amine co-solvent such as toluene. More specifically, the imide powder is prepared by: (1) placing from about 20 to about 40 % by wt. (preferably from about 25 to about 35 % by wt.) of the amic acid solution and from about 80 to about 60 % by wt. (preferably from about 75 to about 65 % by wt.) of an azeotropic agent (e.g., toluene) in a reaction vessel; (2) charging from about 0.05 to about 0.5 % by wt. (preferably from about 0.1 to about 0.2 % by wt) of a strong acid catalyst (e.g., methane sulfonic acid) to the reaction vessel to form a mixture; (3) heating the mixture in the reaction vessel to a temperature of from about 100 to about 130 °C (preferably, from about 120 to about 125 °C) for from about 2 to about 6 hours; (4) cooling the mixture to ambient or room temperature; (5) removing the azeotropic agent from the reaction vessel; and (6) isolating and recovering the solids or imide powder from the remaining solution contained in the reaction vessel. [0039] By way of the present invention, it has been further discovered that the strong acid and the azeotropic agent, when used in the amounts noted above, serve to effectively control ring closure temperature. More- specifically, the strong acid causes more water to be generated, while the azeotropic agent decreases the reflux point of the system. [0040] Particularly advantageous polyimide oligomers or resins are provided when the oligomer is prepared by reacting BPDA or BTDA with a diamine selected from the group of 3,4'-ODA, 4,4'-ODA, BAPP and APB. and end-capping any remaining amine groups with either CA or IA. For example, the following oligomers (among others) are contemplated by the present invention: (i) BPDA//3,4'-ODA/BAPP//CA; (ii) BPDA//4,4'-ODA/BAPP//CA; (iii) BTDA//3,4'-ODA/BAPP//CA; (iv) BPDA//3,4,-ODA/m-APB//CA; and (v) BPDA//3,4,-ODA/BAPP//IA. [0041] Solutions contemplated by the present invention which are suitable for use as a prepreg solution or as an adhesive contain the above-described polyamic acid oligomer and/or polyimide oligomer, and an organic solvent. In a preferred embodiment, the concentration of oligomers in the solution is greater than or equal to about 25 wt. % (preferably, from about 25 to about 40 wt. %), and the viscosity of the solution ranges from about 10 to about 140 poise (preferably, from about 25 to about 70 poise). [0042] Prepregs for composites may be made by the conventional method of impregnating a suitable fabric or other reinforcement with the above-described prepreg solution. [0043] Prepregs for composites may also be made by interleaving layers of fabric with layers of a resin film comprising the inventive oligomers, and then subjecting the resultant stack of interleaved materials to a simple cure schedule or cycle, as detailed below. [0044] According to a further alternative, the inventive oligomers can be spun into fibers, and woven with fibers of reinforcing material to produce a prepreg. This prepreg is cured in a manner comparable to the method of forming a composite from interleaved oligomer film and fabric layers. [0045] Polymer powder impregnation methods or techniques may also be used to prepare the prepregs. In one such solventless method or technique, dry powder is impregnated into a fiber bundle by causing the fiber bundle to spread, thereby allowing the powder to disperse within the fiber bundle, and then allowing the fiber bundle to contract to hold the powder in place. The impregnated fiber bundle may then be passed through an oven to prepare a prepreg. [0046] The low void volume composites of the present invention may be manufactured from the polyimide impregnated prepreg using conventional methods or techniques (e.g., hot pressing techniques) and a simple cure schedule. [0047] As noted above, the polyimide oligomers or resins of the present invention cure at temperatures of less than or equal to about 370 °C (preferably, less than or equal to about 350 °C) by an addition reaction rather than a condensation reaction, thus controlling volatiles during cure. The cure temperature of the inventive polyimide oligomers or resins is lower than that noted above for PETI resins. [0048] The cure schedule or cycle for the composites of the present invention is composed of two stages: a first stage for volatile removal followed by consolidation; and a second stage for full cure. Preferably, in the first stage, the temperature of the prepreg would be increased to about 250 °C by, for example, a hot-pressing machine and kept at this temperature for from about 1 to about 4 hours to effect volatile removal. Pressure would then be applied to the prepreg by the hot-pressing machine to effect consolidation and thus to remove voids, the pressure increasing from about 4.2 to about 6.0 megapascals (MPa). Simultaneously, the temperature of the prepreg would be increased to about 350 oC. In the second stage, the temperature of the consolidated prepreg would be maintained at 350 °C for from about 1 to about 4 hours, to effect crosslinking via a nonvolatile producing reaction. [0049] The polyimide oligomers or resins with novel addition cure end caps of the present invention maintain a low enough viscosity (i.e., less than or equal to 2500 poise) during the first stage of the two-stage cure cycle thereby allowing for effective removal of volatiles followed by consolidation of the composite to remove voids. During the second stage of the two-stage cure cycle, crosslinking takes place by way of a nonvolatile producing reaction. In other words, the polyimide oligomers or resins of the present invention give a "clean" two stage cure. [0050] The resulting high temperature composites of the present invention demonstrate a combination of desirable properties after cure that render them suitable for use in a wide variety of applications such as aerospace, military, and infra-structure repair applications. More specifically, these high temperature composites exhibit a use temperature of greater than about 200 °C, and further exhibit a Ta ranging from about 210 °C to about 300 °C (preferably from about 210 °C to about 275 °C), flexural strength (ASTM D-790) ranging from about 400 to about 1200 MPa, toughness, microcrack resistance, solvent and moisture resistance, damage tolerance, and good retention.of mechanical properties under hot/wet conditions. [0051] The inventive composites also have a low void volume. By "low void volume" it is meant that the composite has a void volume, i.e. the volume of the composite which is air space, of from about 1 to about 2 (preferably, from about 0.5 to about 1.5, more preferably, from about 0.5 to about 1.0) percent (%) of the volume of the composite. The void volume of the inventive composites is lower than that noted above for the PMR-15 and RP-46 composites. [0052] Reinforcing fibers suitable for use in the inventive composite include carbon fibers, glass fibers, and quartz fibers. [0053] The solution of the present invention may also be used as an adhesive allowing for substantially void-free bonding of large areas and thus the production of substantially void-free laminates. By way of example, materials such as carbon or glass fabrics may be laminated together by applying the inventive solution to the fabric surfaces, assembling the fabric layers, and then subjecting the assembled layers to the two-stage cure schedule or cycle described above. As will be readily appreciated by those skilled in the art, debonding problems attributed to volatile evolution during cure of prior art polyimide laminates are solved by the present invention. EXAMPLES [0054] The subject invention will now be described by reference to the following illustrative examples. The examples are not. however, intended to limit the generally broad scope of the present invention. [0055] Each example was tested for flexural strength and glass transition . temperature in accordance with the following test methods. Flexural Strength (MPa) - Flexural strength was measured according to ASTM D-790. Glass Transition Temperature (Tg) - The glass transition temperature was measured at a temperature rising rate of 2 PC/minute in a nitrogen atmosphere using a dynamic mechanical analyzer (DMA). [0056] Unless otherwise stated, procedures, conditions, etc. detailed below for the preparation of the BPDA/CA//3,4'-ODA/BAPP prepreg solution and composites were also used to prepare the remaining prepreg solutions and composites of Examples 9 to 17 in this EXAMPLES section. Examples 1 to 8 BPDA/CA(83/34)//3,4'-ODA/BAPP(85/15) [0057] In Examples 1 to 8, components 3,4-ODA (34.000 g, 0.170 mol), BAPP (12.300 g, 0.030 mol) and NMP (104.15g) were added to a 500 milliliter (ml) three-neck flask equipped with a mechanical stirrer and a heater. The resulting mixture was completely dissolved to from a solution. BPDA (48.804 g, 0.166 mol) was dispersed in NMP (104.15g) and the resulting dispersion was added to the solution in the three-neck flask. The resulting mixture was then stirred at a rate of 80 revolutions per minute (rpm) at 60 °C for 8 hours to provide a solution. Finally, a solution of CA (7.616 g, 0.068 mol) in NMP (10.0g) was added to the solution in the three-neck flask and the resulting mixture stirred at 60 °C for 2 hours. A prepreg solution having a solids content of 30 wt. % and a viscosity of 31 poise was obtained. [0058] Eight sheets of woven carbon fabric obtained from Cytec Engineered Materials. Inc., 1440 N. Kraemer Blvd., Anaheim, CA 92806 ("Cytec Engineered Materials") were then impregnated with the prepreg solution urider the following conditions: Each sheet was wetted with the prepreg solution and then dried at 80 °C for 20 minutes. Each sheet was then re-wetted with the prepreg solution and dried again at 80 °C for 20 minutes. The dried sheets were then imidized according to the following schedule: 120 °C for 1 hour; 150 °C for 0.5 hour, 200 °C for 1 hour, and 250 °C for 1 hour. Eight imidized sheets were then arranged In an 11 x 18 centimeter (cm) hot- pressing machine manufactured by Toyo Seiki Seisaku-sho, Ltd. (model no. MP-SCH) and subjected to an initial pressure of 4.2 megapascals (MPa) and a cure regimen as described in Table 1 below. The initial pressure increased to 5 to 6 MPa over time as the cure temperature increased. This process was repeated seven times. The weight percent of cured resin to the sum of cured resin and carbon fabric ([cured resin]/{[cured resin] + [carbon fabric]}) of the resulting composites ranged from 30 to 35 wt.%. Once prepared, the composites were tested for flexural strength and glass transition temperature, with the results reported in Table 1. [0059] Examples 1 to 8 showed high levels of flexural strength (flexural strength avg = 826). The surface of each composite (with the exception of the Example 7 composite) was smooth, indicating good resin flow and a good processing window. Also, the glass transition temperatures of these composites (Tg avg = 227 °C) were tow, and in fact lower than that obtained for films cast from the same prepreg solution. Example 9 BPDA/CA(83/34)//4,4'-ODA/BAPP(85/15) [0060] In this Example, aromatic diamine 4,4'-ODA was used instead of aromatic diamine 3,4'-ODA. The prepreg solution had a solids content of 30 wt % and a viscosity of 64 poise. The composite test results are shown in Table 2. [0061] Example 9 showed an acceptable level of flexural strength, but had a somewhat rough surface indicating less than optimal resin flow. The glass transition temperature of this composite was higher than the average of the above Examples 1 to 8. Examples 10 to 13 BPDA/CA(80/40)//4,4'-ODA/BAPP(50/50) [0062] In these Examples, the ratios of aromatic dianhydride to end cap and aromatic diamine 4,4'-ODA to aromatic diamine BAPP were changed to 80/40 and 50/50, respectively. The prepreg solution had a solids content of 30 wt. % and a viscosity of 28 poise. The composite test results are shown in Table 3. [0063] Examples 10 to 13 showed high levels of flexural strength (flexural strength avg = 765). The surface of each composite was smooth, indicating good resin flow and a good processing window. Also, the glass transition temperatures of these composites (Tg avg = 219 °C) were slightly lower than the previous Examples as well as lower than that obtained for films cast from the same prepreg solution. Examples 14 and 15 BTDA/CA(83/34)//3,4'-ODA/BAPP(85/15) [0064] Instead of the aromatic dianhydride BPDA used in Examples 1 to 8, these Examples used aromatic dianhydride BTDA. The prepreg solution had a solids content of 30 wt. % and a viscosity of 32 poise. The composite test results are shown in Table 4. [0065] Examples 14 and 15 also showed high levels of flexural strength (flexural strength avg= 718), but had somewhat rough surfaces indicating less than optimal resin flow. The glass transition temperatures of these composites (Tg avg = 248 °C) were slightly higher than the average of the above Examples 1 to 8. Example 16 BPDA/CA(83/34)//3,4'-ODA/m-APB(85/15) [0066] Instead of the aromatic diamine BAPP used in Examples 1 to 8, this Example used aromatic diamine m-APB. The prepreg solution had a solids content of 30 wt. % and a viscosity of 33 poise. The composite test results are shown in Table 5. [0067] Example 16 showed high levels of flexural strength. The surface of this composite was smooth, indicating good resin flow and a good processing window. Also, the glass transition temperature of this composite was lower than the average glass transition temperatures obtained for previous Examples as well as lower than that obtained for films cast from the same prepreg solution. Example 17 BPDA/IA(83/34)//3,4'-ODA/BAPP(85/15) [0068] Instead of the end cap CA used in Examples 1 to 8, this Example used end cap IA. The prepreg solution had a solids content of 30 wt % and a viscosity of 31 poise. The composite test results are shown in Table 6. [0069] Example 17 also showed high levels of flexural strength. The surface of this composite was smooth, indicating good resin flow and a good processing window. Also, the glass transition temperature of this composite was the same as Example 16 as well as lower than that obtained for films cast from the same prepreg solution. [0070] The above-referenced Examples demonstrate that the polyamic acid oligomers and polyimtde oligomers prepared in accordance with the teachings of the present invention have low Tgs and good processing windows, while the inventive composites exhibit good flexural properties in the form of high flexural strength. Comparative Examples C-1 to C-3 SKYBOND 1000 [0071] In these Comparative Examples, eight sheets of woven carbon fabric obtained from Cytec Engineered Materials were Impregnated with a solution of polyimide precursors obtained from Industrial Summit Technology Corporation, 500 Cheesequake Road, Parlin, NJ 08859, under the product designation SKYBOND 1000, under the following conditions: Each sheet was wetted with the SKYBOND 1000 prepreg solution and then dried at 80 °C for 20 minutes. The dried sheets were then imidized according to the following schedule: 120 °C for 1 hour, 150 °C for 0.5 hour; 200 °C for 1 hour, and 225 °C for 1 hour. The dried, imidized sheets were then arranged in an 11 x 18 cm hot- pressing machine manufactured by Toyo Seiki Seisaku-sho, Ltd. (model no. MP-SCH) and subjected to an initial pressure of 4.2 MPa and a cure regimen as described in Table 7 below. The initial pressure increased to 5 to 6 MPa over time as the cure temperature increased. This process was repeated two times. The weight percent of cured'resin to the sum of cured resin and carbon fabric ([cured resin]/{[cured resin] + [carbon fabric]}) of the resulting composites ranged from 35 to 40 wt.%. Once prepared, the composites were tested for flexural strength and glass transition temperature, with the results reported in Table 7. [0072] Comparative Examples C-1 to C-3 showed lower levels of flexural strength (flexural strength avg= 543). The surfaces of these composites were rough, indicating less than optimal resin flow. Moreover, the glass transition temperatures of these composites (Tg avg = 308 °C) were considerably higher than the average of the above Examples 1 to 17. Comparative Examples C-4 to C-8 SKYBOND 2000 [0073] Instead of SKYBOND 1000 prepreg solution. Comparative Examples C-4 to C-8 were prepared using SKYBOND 2000 prepreg solution in accordance with the procedures, conditions, etc. detailed above for Comparative Examples C-1 to C-3. The composite test results are shown in Table 8. [0074] Comparative Examples C-4 to C-8 also showed lower levels of flexural strength (flexural strength avg = 660). The surface of Comparative Example C-4 was rough. The glass transition temperatures of these composites (Tg avg = 266 °C) were also higher than the average of the above Examples 1 to 17. [0075] While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any of the exemplary embodiments. [0076] Having thus described the invention, what is claimed is: WE CLAIM: 1. A method of making high temperature, low void volume, fiber- reinforced composite materials from prepregs using a two-stage cure schedule; characterized in that: in a first stage, a prepreg, which comprises a solution of citraconic anhydride- endcapped polyamic acid and/or polyimide oligomers in a fibrous reinforcing material, is cured to remove volatiles, the viscosity of the oligomers during the first stage being less than or equal to 250 pascal-seconds (2500 poise); and in a second stage, full cure is effected by crosslinking via a nonvolatile- producing reaction. 2. A high temperature, low void volume, fiber-reinforced composite made from a prepreg comprising a solution of a polyimide oligomer in a fibrous reinforcing material, using a two-stage cure schedule, wherein the polyimide oligomer is a condensation product of a polyamic acid oligomer, which is obtained by reacting one or more aromatic dianhydrides, one or more aromatic diamines, and one or more addition cure end caps of citraconic anhydride. 3. The composite as claimed in claim 2, wherein the aromatic dianhydrides(s) has more than one aromatic ring in its chemical structure. 4. The composite as claimed in claim 2, wherein the aromatic dianhydride(s) is represented by the following formula (I) or by the following general formula (II) wherein, Z represents -CO-, -O-, -SO2-, or a direct bond. 5. The composite as claimed in claim 4, wherein the aromatic dianhydride(s) is represented by formula (I) and comprises 1,2,4,5- benzenetetracarboxylic dianhydride. 6. The composite as claimed in claim 4, wherein the aromatic dianhydride(s) is represented by formula (II) and is selected from the group including 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2'-bis[4-(3,4- dicarboxyphenoxy)phenyl]propane dianhydride, 1,1',2,2'-benzophenone tetracarboxylic dianhydride, 4,4-oxydiphthalic anhydride, 3,3,'4,4'-diphenylsulfone tetracarboxylic diandydride, and mixtures thereof. 7. The composite as claimed in claim 2, wherein the polyamic acid oligomer is a reaction product of two aromatic dianhydrides, one or more aromatic diamines, and one or more addition cure end caps of citraconic anhydride, wherein a first dianhydride is present in an amount ranging from 5 to 40 % by wt., based on the total weight of the dianhydrides, and wherein a second dianhydride is present in an amount ranging from 95 to 60 % by wt., based on the total weight of the dianhydrides. 8. The composite as claimed in claim 2, wherein the aromatic diamine(s) has at least one ether linkage in its chemical structure. 9. The composite as claimed in claim 8, wherein the aromatic diamine(s) is selected from the group of 3,4'-oxydianiline, 4,4'-oxydianiline, m- phenylenediamine, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, bis[4-(3- aminophenoxy)phenyl]sulfone, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4- aminophenoxy)benzene, and mixtures thereof. 10. The composite as claimed in claim 2, wherein the polyamic acid oligomer is a reaction product of one or more aromatic dianhydrides, two aromatic diamines, and one or more addition cure end caps of citraconic anhydride, and wherein at least one diamine has one or more oxygen linkages in its chemical structure and is present in an amount of at least 50 % by wt., based on the total weight of the diamines. 11. The composite as claimed in claim 2, wherein the aromatic diamine(s) is mixed with a rubber component. 12. The composite as claimed in claim 11, wherein the rubber component is an amine terminated rubber. 13. The composite as claimed in claim 12, wherein the amine terminated rubber is an amine terminated silicone rubber. 14. The composite as claimed in claim 13, wherein the amine terminated silicone rubber is present in an amount of less than 30 % by wt., based on the total weight of the aromatic diamine(s) and silicone rubber. 15. The composite as claimed in claim 2, wherein the polyimide oligomer cures at temperatures of less than or equal to 370 °C. 16. A solution suitable for use in making high temperature, low void volume, fiber-reinforced composite materials, the solution comprising: (a) a polyimide oligomer; and (b) one or more organic solvents, wherein the polyamic acid oligomer is obtained by reacting one or more aromatic dianhydrides, one or more aromatic diamines, and one or more addition cure end caps selected from the group of citraconic anhydride, and wherein the polyimide oligomer is a condensation product of the polyamic acid oligomer. 17. The solution as claimed in claim 16, wherein the oligomer is present in the solution at a concentration of greater than or equal to 25 wt. %, and wherein the solution has a viscosity ranging from 1 to 14 pascal-seconds (10 to 140 poise). 18. A high temperature, low void volume, fiber-reinforced composite material obtained by consolidating and curing a prepreg in which a fibrous reinforcing material is impregnated with the solution as claimed in claim 16 using a two-stage cure schedule; characterized in that: in a first stage, the prepreg is cured to remove volatiles, the viscosity of the oligomers during the first stage being less than or equal to 250 pascal-seconds (2500 poise); and in a second stage, full cure is effected by crosslinking via a nonvolatile- producing reaction. 19. The high temperature, low void volume, fiber-reinforced composite as claimed in claim 18, which has a void volume ranging from 1 to 2 percent of the volume of the composite. 20. The high temperature, low void volume, fiber-reinforced composite as claimed in claim 19, which has a void volume ranging from 0.5 to 1.5 percent of the volume of the composite. 21. An adhesive, which is prepared from the solution as claimed in claim ABSTRACT TWO-STAGE CURE POLYIMIDE OLIGOMERS A method of making high temperature, low void volume, fiber-reinforced composite materials from prepregs using a two-stage cure schedule; characterized in that: in a first stage, a prepreg, which comprises a solution of citraconic anhydride-endcapped polyamic acid and/or polyimide oligomers in a fibrous reinforcing material, is cured to remove volatiles, the viscosity of the oligomers during the first stage being less than or equal to 250 pascal-seconds (2500 poise); and in a second stage, full cure is effected by crosslinking via a nonvolatile-producing reaction.

Full Text

RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. Patent Application Serial
No. 10/931,070, ftied August 30, 2004, which claims priority from U.S. Provisional Patent
Application Serial No. 60/499,849, filed September 2, 2003.
TECHNICAL FIELD
[0002] The present invention generally relates to a method for using citraconic
anhydride and itaconic anhydride as addition cure end caps in reactions for forming
polyamic acid oligomers and polyimide oligomers. The present invention also generally
relates to prepregs and high temperature adhesives made from Hie resulting oligomers,'
as well as, high temperature, low void volume, fiber-reinforced composites made from the
prepregs.
BACKGROUND ART
[0003] Fiber-reinforced composite materials, which are made up of reinforcing
fibers and matrix resins, are lightweight and have excellent mechanical properties. As
such, these composite materials nave been widely used in a variety of structural and non-
structural applications such as aerospace, automotive, infra-structure repair, marine,
military, and sporting goods or other consumer products that must have sufficient
toughness and impact resistance to endure many years of harsh service.
[0004] Epoxy resins, and to a lesser extent, unsaturated polyester resins, vinyl
ester resins, phenol resins, and polyimide resins, have been employed as matrix resins in
fiber-reinforced composite materials. The use of composite materials having polyimide
resin matrices is increasing, however, where these materials are now recognized as
preferred structural materials in aerospace applications, because of their lightweight and
load-bearing characteristics and their oxidative stability at elevated temperatures.
[0005] Various methods or techniques such as prepreg, hand lay-up, filament
winding, pull-trusion, resin transfer molding (RTM) and resin infusion (Rl), have been
used to produce fiber-reinforced composite materials.
[0006] Current technologies for making prepreg and composites from polyimides
utilize solutions from the poly(amide) acids of these resins. Poiy(amide) add solutions
are processed into prepreg with various reinforcing fibers. These poiy(amide) acid
solutions are of low solids contents and high viscosity. Therefore, the processing of these

types of solutions requires overcoming significant problems such as solvent management
and good fiber wet out from the high viscosity solutions. The resultant prepreg typically
requires residual solvent contents of 20 to 25% by weight (approximately 2-3% water
from thermal imidization reaction) for adequate tack and drape. This residual solvent must
then be removed during the composite cure cycle. This material is hand-laid into
composites which makes working with this type of material very labor intensive and
costly.
[0007] One example of a prior art prepreg solution that when processed into
prepreg with suitable reinforcing fibers yielded a high temperature resistant composite,
was first marketed in the 1960s under the trade designation SKYBOND by Monsanto
Corporation, 800 N. Lindbergh Blvd., St. Louis, Missouri 63167: The SKYBOND prepreg
solution was prepared by prereacting 3,3',4,4'-benzophenonetetracarboxylic dianhydride
(BTDA) with ethanol using NMP as the solvent. Then, either m-phenylenediamine (MPD)
or 4,4'-methylenedianiline (MDA) was added to the solution. No endcapping agent was
employed. It was (and continues to be) difficult to fabricate low void composites using
this type of chemistry. One of the reasons offered for this difficulty has been that during
the cure process branching can occur by the reaction of amine end-groups with the
bridging carbonyl group of the BTDA moiety leading to branching and intractability of the
matrix resin.
[0008] The processability (and thus end-use applications) of these polyimides has
been improved by lowering molecular weight and by using reactive endcapping agents to
produce thermosetting polyimides.
[0009] Originally developed in the 1970s for military aircraft applications, these
thermosetting polyimides are produced by dissolving an aromatic diamine, a dialkyl ester
of tetracarboxylic acid and a monofunctional nadic ester endcapping agent in a solvent
(e.g., alcohol).
[0010] The best known of these early thermosetting polyimides is PMR-15, which
is shorthand for in-situ polymerization of monomer reactants. These thermosetting
polyimides (/.e.t benzophenone dianhydride//methylenedianiline//nadic anhydride) were
originally developed at NASA Lewis for military aircraft engines and airframes, undergo
crosslinking at 250 °C to 300 °C (482 °F to 572 °F), and demonstrate good thermal and
mechanical properties. PMR-15 thermosetting polyimides, however, contain the
hazardous compound methylenedianiline (MDA), which raises health and safety
concerns.

[0011] PMR-15 cures with a condensation reaction, which means that water and
alcohol are evolved and given off from the polymer chain during cure. PMR-15 does not
give a clean two-stage cure. In particular, PMR-15 crosslinks while volatiles are being
removed and decomposes during cure to evolve cyclopentadiene. Moreover, the volume
of solvent removed such as water, methanol and cyclopentadiene, produces voids in the
final composite in an amount equal to greater than 2 percent (%) of the volume of the
composite.
[0012] A direct PMR-15 replacement with very similar chemistry but using less
toxic monomers is the nadic end-capped polyimides RP-46. These thermosetting
polyimides (i.e., benzophenone dianhydride//3,4-oxydianiline//nadic anhydride), like PMR-
15, cure with a condensation reaction. The two-stage cure is not a clean two-stage cure.
Moreover, the resulting composite contains voids in an amount of greater than 2 % of the
volume of the composite.
[0013] Other non-MDA containing polyimides include PETI {i.e., phenylethynyl
terminated imide) resins, which represent a different polyimide chemistry. These resins
were developed to address the need for structural matrix resins that could provide higher
temperature performance and longer-term thermoxidative stability. While more expensive
than PMR-type materials, these high temperature resins, which cure in an addition
reaction without volatile evolution, can be used to produce substantially void-free
composites. Unfortunately, these resins require extremely high cure temperatures of
around 375 °C/707 °F. which are very close to the degradation temperature of these
resins. In addition, such high cure temperatures may necessitate specialized autoclave
or press equipment for some manufacturers.
[0014] A need therefore exists for polyamic acid and polyimide oligomers for use
in making adhesives and prepreg, where the polyimide oligomers provide a clean two-
stage cure at temperatures of less than or equal to about 370 °C.
[0015] It is therefore an object of the present invention to provide such polyamic
acid and polyimide oligomers.
[0016] It is another object to provide solutions suitable for use as prepreg
solutions or as high temperature adhesives, which contain one or more of the above-
described oligomers and an organic solvent.
[0017] It is yet another object of the present invention to provide high
temperature, low void volume, fiber-reinforced composites prepared from prepregs made
using the inventive prepreg solutions.

SUMMARY OF THE INVENTION
[0018] The present invention therefore provides a method for using citraconic
anhydride and itaconic anhydride, the method comprising using these materials as
addition cure end caps in reactions for forming polyamic acid oligomers and polyimide
oligomers.
[0019] The present invention also provides a polyamic acid oligomer, which is
obtained by reacting one or more aromatic dianhydrides, one or more aromatic diamines,
and one or more addition cure end caps selected from the group of citraconic anhydride
and itaconic anhydride.
[0020] Also provided by way of the present invention is a two-stage cure
polyimide oligomer, which is obtained by condensing the polyamic acid oligomer
described above.
[0021] The present invention also provides a solution suitable for use as a
prepreg solution or as a high temperature adhesive, which contains the above-described .
polyamic acid oligomer and/or polyimide oligomer, and an organic solvent.
[0022] The invention further provides a high temperature, low void volume, fiber-
reinforced composite material which may be obtained by curing a prepreg in which a
fibrous reinforcing material is impregnated with the above-described prepreg solution.
[0023] Other features and advantages of the invention will be apparent to one of
ordinary skill from the following detailed description.
[0024] Unless otherwise defined, all technical and scientific terms used herein
have the same meaning as commonly understood by one of ordinary skill in the art to
which this invention belongs. Ail publications, patent applications, patents and other
references mentioned herein are incorporated by reference in their entirety. In case of
conflict, the present specification, including definitions, will control. In addition, the
materials, methods, and examples are illustrative only and not intended to be limiting.
BEST MODE FOR CARRYING OUT THE INVENTION
[0025] By way of the present invention, novel addition cure end caps for two-
stage cure polyimides have been identified. The novel end caps, namely, citraconic
anhydride (CA) and itaconic anhydride (IA), allow for the manufacture of very low void
volume composites from polyimide impregnated prepreg using a simple cure schedule.
As noted above, the evolution of cure volatiles from condensation cure polyimide resins is
well known as a limiting factor in the use of polyimides in structural composites. The
present invention solves this problem by providing novel addition cure end caps that

possess the correct reactivity to allow volatiles to be removed during composite
manufacture. The novel end caps also control molecular weight and act as cr'osslinkers at
higher temperatures.
[0026] The polyamic acid oligomer of the present invention is obtained by reacting
one or more aromatic dianhydrides, one or more aromatic diamines, and one or more
addition cure end caps selected from the group of citraconic anhydride and itaconic
anhydride.
[0027] Aromatic dianhydrides deemed suitable for use in preparing the inventive
polyamic acid oligomer are dianhydrides that generally have more than one aromatic ring
in the structure, such as those dianhydrides represented by the following formula (I)

or by the following general formula (II)

where Z represents -CO-, -O-, -SOr, or a direct bond. The aromatic dianhydride having
the structure (I) is 1,2,4,5-benzenetetracarboxylic dianhydride (pyromellitic dianhydride or
PMDA), while aromatic dianhydrides having the structure (II) include 3,3',4,4'-
biphenyltetracarboxylic dianhydride (BPDA), 2,2'-bis[4-(3,4-
dicarboxyphenoxy)phenyl]propane dianhydride (BPADA), 1,1',2,2'-benzophenone
tetracarboxylic dianhydride (BTDA), 4,4-oxydiphthalic anhydride (OPDA), and 3,3',4,4'-
diphenylsulfone tetracarboxylic diandydride (DSDA).
[0028] One or more dianhydrides are used to prepare the inventive polyamic acid
oligomer. When two dianhydrides are used, the first dianhydride (e.g., BTDA) is
preferably present in an amount ranging from about 5 to about 40 % by wt (more

preferably, from about 10 to about 25 % by wt., and most preferably, from about 20 to
about 25 % by wt.). based on the total weight of the dianhydrides, while the second
dianhydride (e.g., BPDA) is preferably present in an amount ranging from about 95 to
about 60 % by wt. (more preferably, from about 90 to about 75 % by wt., most preferably,
from about 80 to about 75 % by wt.), based on the total weight of the dianhydrides.
[0029] Aromatic diamines deemed suitable for use in the present invention are
diamines that generally have at least one ether linkage in the structure, such as 3,4'-
oxydianiline (3,4'-ODA), 4,4'-oxydianiline (4,4'-ODA), m-phenylenediamine (m-PDA), 2,2'-
bis[4-(4-aminophenoxy)phenyi]propane (BAPP), bis[4-(3-aminophenoxy)phenyl]suffone
(BAPS-M), 1,3-bis(3-aminophenoxy)benzene (APB), and 1,3-bis(4-
aminophenoxy)benzene (TPE-R).
[0030] One or more diamines are used to prepare the inventive polyamic acid
oligomer. When two diamines are used, it is preferred that at least one diamine have one
or more oxygen linkages and that this diamine be present in an amount of at least about
50 % by wt., based on the total weight of the diamines.
[0031] In select embodiments, the aromatic diamine(s) is used in combination
with a rubber component. Suitable rubber components include, but are not limited to,
amine terminated rubbers. In a preferred embodiment, an amine-terminated silicone
rubber (SR) is used to prepare the inventive oligomers. In this preferred embodiment, the
rubber is present in an amount of less than about 30 % by wt, and more preferably in an
amount of less than about 20 % by wt., based on the total weight of the aromatic
diamine(s) and rubber component.
[0032] Addition cure end caps suitable for use in preparing the inventive polyamic
acid oligomer are selected from the group of methyl maleic anhydride (citraconic
anhydride) and 2-methylenesuccinic anhydride (itaconic anhydride). As will be described
in more detail below, these addition cure end caps serve to control volatiles during cure.
[0033] The preparation of the polyamic acid oligomer, in accordance with the
teachings of the present invention, basically comprises:
(1) charging at least one dianhydride {e.g., BPDA) and at least one diamine
(e.g., BAPP) to separate reaction vessels;
(2) adding quantities of a suitable solvent (e.g., 1-methyl-2-pyrrolidinone
(NMP)) to each reaction vessel to form a slurry or solution of dianhydride(s)
in one vessel, and a slurry or solution of diamine(s) in the other vessel,

(3) heating the slurry or solution contained in each reaction vessel to a
temperature ranging from about 50 to about 120 °C to dissolve the
dianhydride(s) and the diamine(s);
(4) cooling the solutions contained in each reaction vessel to ambient or room
temperature;
(5) slowly adding the dianhydride solution to the diamine solution over a period
of time ranging from about 10 to about 60 minutes;
(6) adding a solution of addition cure end cap(s) (e.g., citraconic anhydride
(CA) in NMP) to the reaction vessel; and
(7) stirring the solution for a period of time ranging from about 15 to about 120
minutes to form an amic acid solution, wherein, the molar ratio of
dianhydride(s) to diamine(s) to addition cure end cap(s) in the amic acid
solution ranges from about 1.0/1.95/2.10 to about 1.0/2.1/2.0.
[0034] By way of the present invention, it has been discovered that by slowly
adding the dissolved dianhydride reactant to the dissolved diamine reactant, while
controlling the reaction temperature, the molecular weight of the resulting resin is reduced
causing an advantageous reduction in its melting point and melt viscosity.
[0035] Solvents suitable for use in the present inventive method include amide-
based solvents such as NMP, N,N-dimethylacetamide, N,N-demethylformamide and N-
methylcaprolactam, among which NMP and N.N-dimethylacetamide are preferred.
[0036] The molar ratio of dianhydride to diamine to addition cure end cap is such
that stirring the solution forms low molecular weight prepolymers having at least one end
cap radical and suitable for chain extension and crosslinking to form polyimides that have
a melting point of less than about 250 °C, and a melt viscosity at 250 °C of less than
about 25000 cps. Typically the prepolymers have a weight average molecular weight of
less than about 10000 grams per mole (g/mol), and generally less than about 5000 g/mol.
[0037] In a preferred embodiment, the molar ratio of
dianhydride(s):diamine(s):addition cure end cap(s) is 1.0/2.0/2.01, and more preferably
the molar ratio is n/n+1/2.
[0038] The polyimide oligomer or resin of the present invention is obtained by
imidizing the polyamic acid oligomer by chemical or thermal means to cause dehydration
and cyclization to occur. In one embodiment, the synthesis of the polyimide oligomer in
the form of an imide powder is carried out via chemical imidization in which a strong acid
and an azeotropic agent are used to promote ring closure and to remove azeotropic
water, respectively. In a preferred embodiment, a strong acid such as methane sulfonic

add is employed as a catalyst arid azeotropic water removed by use of a tertiary amine
co-solvent such as toluene. More specifically, the imide powder is prepared by:
(1) placing from about 20 to about 40 % by wt. (preferably from about
25 to about 35 % by wt.) of the amic acid solution and from about 80
to about 60 % by wt. (preferably from about 75 to about 65 % by
wt.) of an azeotropic agent (e.g., toluene) in a reaction vessel;
(2) charging from about 0.05 to about 0.5 % by wt. (preferably from
about 0.1 to about 0.2 % by wt) of a strong acid catalyst (e.g.,
methane sulfonic acid) to the reaction vessel to form a mixture;
(3) heating the mixture in the reaction vessel to a temperature of from
about 100 to about 130 °C (preferably, from about 120 to about 125
°C) for from about 2 to about 6 hours;
(4) cooling the mixture to ambient or room temperature;
(5) removing the azeotropic agent from the reaction vessel; and
(6) isolating and recovering the solids or imide powder from the
remaining solution contained in the reaction vessel.
[0039] By way of the present invention, it has been further discovered that the
strong acid and the azeotropic agent, when used in the amounts noted above, serve to
effectively control ring closure temperature. More- specifically, the strong acid causes
more water to be generated, while the azeotropic agent decreases the reflux point of the
system.
[0040] Particularly advantageous polyimide oligomers or resins are provided
when the oligomer is prepared by reacting BPDA or BTDA with a diamine selected from
the group of 3,4'-ODA, 4,4'-ODA, BAPP and APB. and end-capping any remaining amine
groups with either CA or IA. For example, the following oligomers (among others) are
contemplated by the present invention:
(i) BPDA//3,4'-ODA/BAPP//CA;
(ii) BPDA//4,4'-ODA/BAPP//CA;
(iii) BTDA//3,4'-ODA/BAPP//CA;
(iv) BPDA//3,4,-ODA/m-APB//CA; and
(v) BPDA//3,4,-ODA/BAPP//IA.
[0041] Solutions contemplated by the present invention which are suitable for use
as a prepreg solution or as an adhesive contain the above-described polyamic acid
oligomer and/or polyimide oligomer, and an organic solvent. In a preferred embodiment,
the concentration of oligomers in the solution is greater than or equal to about 25 wt. %

(preferably, from about 25 to about 40 wt. %), and the viscosity of the solution ranges
from about 10 to about 140 poise (preferably, from about 25 to about 70 poise).
[0042] Prepregs for composites may be made by the conventional method of
impregnating a suitable fabric or other reinforcement with the above-described prepreg
solution.
[0043] Prepregs for composites may also be made by interleaving layers of fabric
with layers of a resin film comprising the inventive oligomers, and then subjecting the
resultant stack of interleaved materials to a simple cure schedule or cycle, as detailed
below.
[0044] According to a further alternative, the inventive oligomers can be spun into
fibers, and woven with fibers of reinforcing material to produce a prepreg. This prepreg is
cured in a manner comparable to the method of forming a composite from interleaved
oligomer film and fabric layers.
[0045] Polymer powder impregnation methods or techniques may also be used to
prepare the prepregs. In one such solventless method or technique, dry powder is
impregnated into a fiber bundle by causing the fiber bundle to spread, thereby allowing
the powder to disperse within the fiber bundle, and then allowing the fiber bundle to
contract to hold the powder in place. The impregnated fiber bundle may then be passed
through an oven to prepare a prepreg.
[0046] The low void volume composites of the present invention may be
manufactured from the polyimide impregnated prepreg using conventional methods or
techniques (e.g., hot pressing techniques) and a simple cure schedule.
[0047] As noted above, the polyimide oligomers or resins of the present invention
cure at temperatures of less than or equal to about 370 °C (preferably, less than or equal
to about 350 °C) by an addition reaction rather than a condensation reaction, thus
controlling volatiles during cure. The cure temperature of the inventive polyimide
oligomers or resins is lower than that noted above for PETI resins.
[0048] The cure schedule or cycle for the composites of the present invention is
composed of two stages: a first stage for volatile removal followed by consolidation; and
a second stage for full cure. Preferably, in the first stage, the temperature of the prepreg
would be increased to about 250 °C by, for example, a hot-pressing machine and kept at
this temperature for from about 1 to about 4 hours to effect volatile removal. Pressure
would then be applied to the prepreg by the hot-pressing machine to effect consolidation
and thus to remove voids, the pressure increasing from about 4.2 to about 6.0
megapascals (MPa). Simultaneously, the temperature of the prepreg would be increased

to about 350 oC. In the second stage, the temperature of the consolidated prepreg would
be maintained at 350 °C for from about 1 to about 4 hours, to effect crosslinking via a
nonvolatile producing reaction.
[0049] The polyimide oligomers or resins with novel addition cure end caps of the
present invention maintain a low enough viscosity (i.e., less than or equal to 2500 poise)
during the first stage of the two-stage cure cycle thereby allowing for effective removal of
volatiles followed by consolidation of the composite to remove voids. During the second
stage of the two-stage cure cycle, crosslinking takes place by way of a nonvolatile
producing reaction. In other words, the polyimide oligomers or resins of the present
invention give a "clean" two stage cure.
[0050] The resulting high temperature composites of the present invention
demonstrate a combination of desirable properties after cure that render them suitable for
use in a wide variety of applications such as aerospace, military, and infra-structure repair
applications. More specifically, these high temperature composites exhibit a use
temperature of greater than about 200 °C, and further exhibit a Ta ranging from about 210
°C to about 300 °C (preferably from about 210 °C to about 275 °C), flexural strength
(ASTM D-790) ranging from about 400 to about 1200 MPa, toughness, microcrack
resistance, solvent and moisture resistance, damage tolerance, and good retention.of
mechanical properties under hot/wet conditions.
[0051] The inventive composites also have a low void volume. By "low void
volume" it is meant that the composite has a void volume, i.e. the volume of the
composite which is air space, of from about 1 to about 2 (preferably, from about 0.5 to
about 1.5, more preferably, from about 0.5 to about 1.0) percent (%) of the volume of the
composite. The void volume of the inventive composites is lower than that noted above
for the PMR-15 and RP-46 composites.
[0052] Reinforcing fibers suitable for use in the inventive composite include
carbon fibers, glass fibers, and quartz fibers.
[0053] The solution of the present invention may also be used as an adhesive
allowing for substantially void-free bonding of large areas and thus the production of
substantially void-free laminates. By way of example, materials such as carbon or glass
fabrics may be laminated together by applying the inventive solution to the fabric
surfaces, assembling the fabric layers, and then subjecting the assembled layers to the
two-stage cure schedule or cycle described above. As will be readily appreciated by
those skilled in the art, debonding problems attributed to volatile evolution during cure of
prior art polyimide laminates are solved by the present invention.

EXAMPLES
[0054] The subject invention will now be described by reference to the following
illustrative examples. The examples are not. however, intended to limit the generally
broad scope of the present invention.
[0055] Each example was tested for flexural strength and glass transition
. temperature in accordance with the following test methods.
Flexural Strength (MPa) -
Flexural strength was measured according to ASTM D-790.
Glass Transition Temperature (Tg) -
The glass transition temperature was measured at a temperature rising rate of 2
PC/minute in a nitrogen atmosphere using a dynamic mechanical analyzer (DMA).
[0056] Unless otherwise stated, procedures, conditions, etc. detailed below for the
preparation of the BPDA/CA//3,4'-ODA/BAPP prepreg solution and composites were also
used to prepare the remaining prepreg solutions and composites of Examples 9 to 17 in
this EXAMPLES section.
Examples 1 to 8
BPDA/CA(83/34)//3,4'-ODA/BAPP(85/15)
[0057] In Examples 1 to 8, components 3,4-ODA (34.000 g, 0.170 mol), BAPP
(12.300 g, 0.030 mol) and NMP (104.15g) were added to a 500 milliliter (ml) three-neck
flask equipped with a mechanical stirrer and a heater. The resulting mixture was
completely dissolved to from a solution. BPDA (48.804 g, 0.166 mol) was dispersed in
NMP (104.15g) and the resulting dispersion was added to the solution in the three-neck
flask. The resulting mixture was then stirred at a rate of 80 revolutions per minute (rpm)
at 60 °C for 8 hours to provide a solution. Finally, a solution of CA (7.616 g, 0.068 mol) in
NMP (10.0g) was added to the solution in the three-neck flask and the resulting mixture
stirred at 60 °C for 2 hours. A prepreg solution having a solids content of 30 wt. % and a
viscosity of 31 poise was obtained.
[0058] Eight sheets of woven carbon fabric obtained from Cytec Engineered
Materials. Inc., 1440 N. Kraemer Blvd., Anaheim, CA 92806 ("Cytec Engineered
Materials") were then impregnated with the prepreg solution urider the following
conditions: Each sheet was wetted with the prepreg solution and then dried at 80 °C for
20 minutes. Each sheet was then re-wetted with the prepreg solution and dried again at
80 °C for 20 minutes. The dried sheets were then imidized according to the following
schedule: 120 °C for 1 hour; 150 °C for 0.5 hour, 200 °C for 1 hour, and 250 °C for 1

hour. Eight imidized sheets were then arranged In an 11 x 18 centimeter (cm) hot-
pressing machine manufactured by Toyo Seiki Seisaku-sho, Ltd. (model no. MP-SCH)
and subjected to an initial pressure of 4.2 megapascals (MPa) and a cure regimen as
described in Table 1 below. The initial pressure increased to 5 to 6 MPa over time as the
cure temperature increased. This process was repeated seven times. The weight
percent of cured resin to the sum of cured resin and carbon fabric ([cured resin]/{[cured
resin] + [carbon fabric]}) of the resulting composites ranged from 30 to 35 wt.%. Once
prepared, the composites were tested for flexural strength and glass transition
temperature, with the results reported in Table 1.

[0059] Examples 1 to 8 showed high levels of flexural strength (flexural strength
avg = 826). The surface of each composite (with the exception of the Example 7
composite) was smooth, indicating good resin flow and a good processing window. Also,
the glass transition temperatures of these composites (Tg avg = 227 °C) were tow, and in
fact lower than that obtained for films cast from the same prepreg solution.
Example 9
BPDA/CA(83/34)//4,4'-ODA/BAPP(85/15)
[0060] In this Example, aromatic diamine 4,4'-ODA was used instead of aromatic
diamine 3,4'-ODA. The prepreg solution had a solids content of 30 wt % and a viscosity
of 64 poise. The composite test results are shown in Table 2.

[0061] Example 9 showed an acceptable level of flexural strength, but had a
somewhat rough surface indicating less than optimal resin flow. The glass transition
temperature of this composite was higher than the average of the above Examples 1 to 8.
Examples 10 to 13
BPDA/CA(80/40)//4,4'-ODA/BAPP(50/50)
[0062] In these Examples, the ratios of aromatic dianhydride to end cap and
aromatic diamine 4,4'-ODA to aromatic diamine BAPP were changed to 80/40 and 50/50,
respectively. The prepreg solution had a solids content of 30 wt. % and a viscosity of 28
poise. The composite test results are shown in Table 3.

[0063] Examples 10 to 13 showed high levels of flexural strength (flexural strength
avg = 765). The surface of each composite was smooth, indicating good resin flow and a
good processing window. Also, the glass transition temperatures of these composites
(Tg avg = 219 °C) were slightly lower than the previous Examples as well as lower than
that obtained for films cast from the same prepreg solution.

Examples 14 and 15
BTDA/CA(83/34)//3,4'-ODA/BAPP(85/15)
[0064] Instead of the aromatic dianhydride BPDA used in Examples 1 to 8, these
Examples used aromatic dianhydride BTDA. The prepreg solution had a solids content of
30 wt. % and a viscosity of 32 poise. The composite test results are shown in Table 4.

[0065] Examples 14 and 15 also showed high levels of flexural strength (flexural
strength avg= 718), but had somewhat rough surfaces indicating less than optimal resin
flow. The glass transition temperatures of these composites (Tg avg = 248 °C) were
slightly higher than the average of the above Examples 1 to 8.
Example 16
BPDA/CA(83/34)//3,4'-ODA/m-APB(85/15)
[0066] Instead of the aromatic diamine BAPP used in Examples 1 to 8, this
Example used aromatic diamine m-APB. The prepreg solution had a solids content of 30
wt. % and a viscosity of 33 poise. The composite test results are shown in Table 5.

[0067] Example 16 showed high levels of flexural strength. The surface of this
composite was smooth, indicating good resin flow and a good processing window. Also,
the glass transition temperature of this composite was lower than the average glass
transition temperatures obtained for previous Examples as well as lower than that
obtained for films cast from the same prepreg solution.

Example 17
BPDA/IA(83/34)//3,4'-ODA/BAPP(85/15)
[0068] Instead of the end cap CA used in Examples 1 to 8, this Example used end
cap IA. The prepreg solution had a solids content of 30 wt % and a viscosity of 31 poise.
The composite test results are shown in Table 6.

[0069] Example 17 also showed high levels of flexural strength. The surface of
this composite was smooth, indicating good resin flow and a good processing window.
Also, the glass transition temperature of this composite was the same as Example 16 as
well as lower than that obtained for films cast from the same prepreg solution.
[0070] The above-referenced Examples demonstrate that the polyamic acid
oligomers and polyimtde oligomers prepared in accordance with the teachings of the
present invention have low Tgs and good processing windows, while the inventive
composites exhibit good flexural properties in the form of high flexural strength.
Comparative Examples C-1 to C-3
SKYBOND 1000
[0071] In these Comparative Examples, eight sheets of woven carbon fabric
obtained from Cytec Engineered Materials were Impregnated with a solution of polyimide
precursors obtained from Industrial Summit Technology Corporation, 500 Cheesequake
Road, Parlin, NJ 08859, under the product designation SKYBOND 1000, under the
following conditions: Each sheet was wetted with the SKYBOND 1000 prepreg solution
and then dried at 80 °C for 20 minutes. The dried sheets were then imidized according to
the following schedule: 120 °C for 1 hour, 150 °C for 0.5 hour; 200 °C for 1 hour, and 225
°C for 1 hour. The dried, imidized sheets were then arranged in an 11 x 18 cm hot-
pressing machine manufactured by Toyo Seiki Seisaku-sho, Ltd. (model no. MP-SCH)
and subjected to an initial pressure of 4.2 MPa and a cure regimen as described in Table
7 below. The initial pressure increased to 5 to 6 MPa over time as the cure temperature
increased. This process was repeated two times. The weight percent of cured'resin to
the sum of cured resin and carbon fabric ([cured resin]/{[cured resin] + [carbon fabric]}) of

the resulting composites ranged from 35 to 40 wt.%. Once prepared, the composites
were tested for flexural strength and glass transition temperature, with the results
reported in Table 7.

[0072] Comparative Examples C-1 to C-3 showed lower levels of flexural strength
(flexural strength avg= 543). The surfaces of these composites were rough, indicating less
than optimal resin flow. Moreover, the glass transition temperatures of these composites
(Tg avg = 308 °C) were considerably higher than the average of the above Examples 1 to
17.
Comparative Examples C-4 to C-8
SKYBOND 2000
[0073] Instead of SKYBOND 1000 prepreg solution. Comparative Examples C-4
to C-8 were prepared using SKYBOND 2000 prepreg solution in accordance with the
procedures, conditions, etc. detailed above for Comparative Examples C-1 to C-3. The
composite test results are shown in Table 8.

[0074] Comparative Examples C-4 to C-8 also showed lower levels of flexural
strength (flexural strength avg = 660). The surface of Comparative Example C-4 was
rough. The glass transition temperatures of these composites (Tg avg = 266 °C) were also
higher than the average of the above Examples 1 to 17.
[0075] While various embodiments of the present invention have been described
above, it should be understood that they have been presented by way of example only,
and not limitation. Thus, the breadth and scope of the present invention should not be
limited by any of the exemplary embodiments.
[0076] Having thus described the invention, what is claimed is:

WE CLAIM:
1. A method of making high temperature, low void volume, fiber-
reinforced composite materials from prepregs using a two-stage cure schedule;
characterized in that:
in a first stage, a prepreg, which comprises a solution of citraconic anhydride-
endcapped polyamic acid and/or polyimide oligomers in a fibrous reinforcing material,
is cured to remove volatiles, the viscosity of the oligomers during the first stage being
less than or equal to 250 pascal-seconds (2500 poise); and
in a second stage, full cure is effected by crosslinking via a nonvolatile-
producing reaction.
2. A high temperature, low void volume, fiber-reinforced composite made
from a prepreg comprising a solution of a polyimide oligomer in a fibrous reinforcing
material, using a two-stage cure schedule, wherein the polyimide oligomer is a
condensation product of a polyamic acid oligomer, which is obtained by reacting one
or more aromatic dianhydrides, one or more aromatic diamines, and one or more
addition cure end caps of citraconic anhydride.
3. The composite as claimed in claim 2, wherein the aromatic
dianhydrides(s) has more than one aromatic ring in its chemical structure.
4. The composite as claimed in claim 2, wherein the aromatic
dianhydride(s) is represented by the following formula (I)

or by the following general formula (II)

wherein, Z represents -CO-, -O-, -SO2-, or a direct bond.
5. The composite as claimed in claim 4, wherein the aromatic
dianhydride(s) is represented by formula (I) and comprises 1,2,4,5-
benzenetetracarboxylic dianhydride.
6. The composite as claimed in claim 4, wherein the aromatic
dianhydride(s) is represented by formula (II) and is selected from the group including
3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,2'-bis[4-(3,4-
dicarboxyphenoxy)phenyl]propane dianhydride, 1,1',2,2'-benzophenone
tetracarboxylic dianhydride, 4,4-oxydiphthalic anhydride, 3,3,'4,4'-diphenylsulfone
tetracarboxylic diandydride, and mixtures thereof.
7. The composite as claimed in claim 2, wherein the polyamic acid
oligomer is a reaction product of two aromatic dianhydrides, one or more aromatic
diamines, and one or more addition cure end caps of citraconic anhydride, wherein a
first dianhydride is present in an amount ranging from 5 to 40 % by wt., based on the
total weight of the dianhydrides, and wherein a second dianhydride is present in an
amount ranging from 95 to 60 % by wt., based on the total weight of the
dianhydrides.
8. The composite as claimed in claim 2, wherein the aromatic
diamine(s) has at least one ether linkage in its chemical structure.

9. The composite as claimed in claim 8, wherein the aromatic
diamine(s) is selected from the group of 3,4'-oxydianiline, 4,4'-oxydianiline, m-
phenylenediamine, 2,2'-bis[4-(4-aminophenoxy)phenyl]propane, bis[4-(3-
aminophenoxy)phenyl]sulfone, 1,3-bis(3-aminophenoxy)benzene, 1,3-bis(4-
aminophenoxy)benzene, and mixtures thereof.
10. The composite as claimed in claim 2, wherein the polyamic acid
oligomer is a reaction product of one or more aromatic dianhydrides, two aromatic
diamines, and one or more addition cure end caps of citraconic anhydride, and
wherein at least one diamine has one or more oxygen linkages in its chemical
structure and is present in an amount of at least 50 % by wt., based on the total
weight of the diamines.
11. The composite as claimed in claim 2, wherein the aromatic
diamine(s) is mixed with a rubber component.
12. The composite as claimed in claim 11, wherein the rubber
component is an amine terminated rubber.
13. The composite as claimed in claim 12, wherein the amine
terminated rubber is an amine terminated silicone rubber.
14. The composite as claimed in claim 13, wherein the amine
terminated silicone rubber is present in an amount of less than 30 % by wt., based on
the total weight of the aromatic diamine(s) and silicone rubber.
15. The composite as claimed in claim 2, wherein the polyimide
oligomer cures at temperatures of less than or equal to 370 °C.
16. A solution suitable for use in making high temperature, low void
volume, fiber-reinforced composite materials, the solution comprising: (a) a polyimide
oligomer; and (b) one or more organic solvents, wherein the polyamic acid oligomer
is obtained by reacting one or more aromatic dianhydrides, one or more aromatic

diamines, and one or more addition cure end caps selected from the group of
citraconic anhydride, and wherein the polyimide oligomer is a condensation product
of the polyamic acid oligomer.
17. The solution as claimed in claim 16, wherein the oligomer is present in
the solution at a concentration of greater than or equal to 25 wt. %, and wherein the
solution has a viscosity ranging from 1 to 14 pascal-seconds (10 to 140 poise).
18. A high temperature, low void volume, fiber-reinforced composite
material obtained by consolidating and curing a prepreg in which a fibrous reinforcing
material is impregnated with the solution as claimed in claim 16 using a two-stage
cure schedule; characterized in that:
in a first stage, the prepreg is cured to remove volatiles, the viscosity of the
oligomers during the first stage being less than or equal to 250 pascal-seconds (2500
poise); and
in a second stage, full cure is effected by crosslinking via a nonvolatile-
producing reaction.
19. The high temperature, low void volume, fiber-reinforced composite as
claimed in claim 18, which has a void volume ranging from 1 to 2 percent of the
volume of the composite.
20. The high temperature, low void volume, fiber-reinforced composite as
claimed in claim 19, which has a void volume ranging from 0.5 to 1.5 percent of the
volume of the composite.
21. An adhesive, which is prepared from the solution as claimed in claim

ABSTRACT

TWO-STAGE CURE POLYIMIDE OLIGOMERS
A method of making high temperature, low void volume, fiber-reinforced
composite materials from prepregs using a two-stage cure schedule;
characterized in that: in a first stage, a prepreg, which comprises a solution of
citraconic anhydride-endcapped polyamic acid and/or polyimide oligomers in a
fibrous reinforcing material, is cured to remove volatiles, the viscosity of the
oligomers during the first stage being less than or equal to 250 pascal-seconds
(2500 poise); and in a second stage, full cure is effected by crosslinking via a
nonvolatile-producing reaction.

Documents:

02641-kolnp-2008-abstract.pdf

02641-kolnp-2008-claims.pdf

02641-kolnp-2008-correspondence others.pdf

02641-kolnp-2008-description complete.pdf

02641-kolnp-2008-form 1.pdf

02641-kolnp-2008-form 3.pdf

02641-kolnp-2008-form 5.pdf

02641-kolnp-2008-international publication.pdf

02641-kolnp-2008-international search report.pdf

02641-kolnp-2008-pct priority document notification.pdf

02641-kolnp-2008-pct request form.pdf

2641-KOL NP-2008-OTHERS PATENT DOCUMENTS.pdf

2641-KOLNP-2008-(07-12-2011)-CORRESPONDENCE.pdf

2641-KOLNP-2008-(11-07-2013)-CORRESPONDENCE.pdf

2641-KOLNP-2008-(13-02-2012)-CORRESPONDENCE.pdf

2641-KOLNP-2008-(28-11-2013)-CORRESPONDENCE.pdf

2641-KOLNP-2008-(28-11-2013)-FORM-3.pdf

2641-KOLNP-2008-(28-11-2013)-OTHERS.pdf

2641-kolnp-2008-ASSIGNMENT.pdf

2641-KOLNP-2008-CORRESPONDENCE 1.2.pdf

2641-kolnp-2008-CORRESPONDENCE-1.1.pdf

2641-KOLNP-2008-EXAMINATION REPORT.pdf

2641-KOLNP-2008-FORM 18.pdf

2641-KOLNP-2008-FORM 3 1.2.pdf

2641-kolnp-2008-FORM 3-1.1.pdf

2641-KOLNP-2008-FORM 5.pdf

2641-kolnp-2008-GPA.pdf

2641-KOLNP-2008-GRANTED-ABSTRACT.pdf

2641-KOLNP-2008-GRANTED-CLAIMS.pdf

2641-KOLNP-2008-GRANTED-DESCRIPTION (COMPLETE).pdf

2641-KOLNP-2008-GRANTED-FORM 1.pdf

2641-KOLNP-2008-GRANTED-FORM 2.pdf

2641-KOLNP-2008-GRANTED-SPECIFICATION.pdf

2641-KOLNP-2008-INTERNATIONAL PUBLICATION.pdf

2641-KOLNP-2008-INTERNATIONAL SEARCH REPORT.pdf

2641-KOLNP-2008-OTHERS.pdf

2641-KOLNP-2008-PCT REQUEST FORM.pdf

2641-KOLNP-2008-REPLY TO EXAMINATION REPORT.pdf

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Patent Number

258799

Indian Patent Application Number

2641/KOLNP/2008

PG Journal Number

07/2014

Publication Date

14-Feb-2014

Grant Date

07-Feb-2014

Date of Filing

30-Jun-2008

Name of Patentee

I. S. T. (MA) CORPORATION

Applicant Address

730 WORCESTER STREET, P.O. BOX 51029 INDIAN ORCHARD, MA

Inventors:

#	Inventor's Name	Inventor's Address
1	DEETS, GARY L.	745 MERROW ROAD, #155, CONVENTRY, CT 06238
2	XIONG, JIANMING	15B PARDUN ROAD, NORTH BRUNSWICK, NJ 08902

PCT International Classification Number

C08G 73/10

PCT International Application Number

PCT/US2006/048279

PCT International Filing date

2006-12-18

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	11/318138	2005-12-23	U.S.A.