Title of Invention	A NOVEL EPOXY RESIN COMPOSITION AND A PROCESS FOR PREPARING THE EPOXY RESIN COMPOSITION
Abstract	The subject invention relates to a toughened epoxy resin composition, wherein the incorporation of 5 to 25% of a polycyano arylene ether thermoplastic containing pendant alkyl groups having a molecular weight of from about 2000 to about 50,000 and Tg of at least about 190°C into heat curable epoxy resin systems significantly increases the toughness of such systems without loss of other desirable properties. The invention also relates to a process for preparing a toughened epoxy resin composition.

Title of Invention

A NOVEL EPOXY RESIN COMPOSITION AND A PROCESS FOR PREPARING THE EPOXY RESIN COMPOSITION

Abstract

The subject invention relates to a toughened epoxy resin composition, wherein the incorporation of 5 to 25% of a polycyano arylene ether thermoplastic containing pendant alkyl groups having a molecular weight of from about 2000 to about 50,000 and Tg of at least about 190°C into heat curable epoxy resin systems significantly increases the toughness of such systems without loss of other desirable properties. The invention also relates to a process for preparing a toughened epoxy resin composition.

Full Text	The present invention relates to novel epoxy resin composition and a process for preparing the epoxy resin composition. More specifically, the invention relates to the improvement of the properties of epoxy resin composition by adding thereto a thermoplastic component with pendent alkyl groups. The epoxy resin material is used in many applications, such as in aerospace field, as matrix resins for fibre reinforced pre-pregs and the composites prepared from fibre reinforced prepregs and as structural adhesives. The use of fibre-reinforced thermoset composites continues to grow. Epoxy resins are one of the most important thermosetting polymers, and they have outstanding mechanical and thermal properties. Epoxy resins have gained widespread use as matrix resins for advanced composites in the field of aerospace, electronic and automobile industries. However, a major drawback of these resins is that they are brittle and thus easily subject to impact-induced damage. On the other hand many thermoplastics are tough and ductile however, their use in structural materials has been minimized for several reasons. Many of the thermoplastics do not have the required solvent resistance, thermal stability and high softening points required in demanding aerospace applications. The high temperature engineering thermoplastics are difficult to process, often requiring both high temperature and pressure to produce acceptable fibre reinforced parts. Blending of engineering thermoplastics with thermosetting resins has gained commercial importance due to ease of processability and tremendous improvement in solvent resistance and toughness. Of the thermosets available, by far the most common are the epoxies, the bismaleimides and the cyanates. Various resins are blend together to obtain the best properties of each of the resin used to improve properties. But the best properties of each resin are rarely achieved. Elastomers have been used with good success in toughening a number of thermosetting resins, particularly epoxy resins. Examples of such systems are given in Bauer, Epoxy resin Chemistry II, chapter 1-5, ACS symposium series 221, American Chemical Society, Washington DC 1983. Both soluble and infusible elastomers have been utilized, the former generally increasing flexibility at the expense of physical properties such as tensile modulus, while the latter generally increase toughness without substantially affecting bulk properties. Both types of modification generally lead to lower thermal properties. US patent Nos. 3715252, 3737352,3784433,3796624,4073670 and 4131502 disclose the possible combination of epoxy resins and non heat-curable thermoplastic components including poly(vinyl acetal), nylon, neoprene rubber, acrylonitrile rubber, phenoxy resins, polysulfones and alpha olefin copolymer. US patent 3641195 discloses curable composition comprising an epoxide resin dispersed in a thermoplastic copolymer of an olefin hydrocarbon with an alpha olefin, which is an ether, or ester of a carboxylic acid. US patent 4117038 discloses epoxy resin adhesives containing a polyglycidyl compound, an acrylonitrile-butadiene-styrene graft polymer and a copolymer of ethylene, acrylic acid and acrylate. Despite the general thermoplastic nature of these materials, they have not provided a broad pattern of increase performance characteristics. Engineering thermoplastics are frequently have been used as toughness modifiers for epoxy resins. The optimum performance properties are obtained for systems, which are miscible before curing. High molecular weight engineering thermoplastics with desired properties are often immiscible with epoxy resins. Low molecular weight reactive oligomers have been successfully used as toughness modifiers for epoxy resins. The solution of thermoplastic in the epoxy is normally accomplished by either dissolving the two components in a common solvent and removing the solvent, or by heating the thermoplastic and the epoxy to a temperature above the Tg of the thermoplastic and melting the two components together. The high viscosity, as well as poor tack, drape and stiffness, make the matrix unacceptable for hot melt processing or for prepregging. Using less than 10% thermoplastic solution allows the user to control the viscosity of the matrix, however, the resultant composite will not achieve the desired toughness. Toughening of epoxy resins with polyether sulfone was disclosed by Bucknall and Partridge in the British Polymer Journal, V.15, Mar 1983 pages 71-75. The systems demonstrating the greatest toughness developed a multiphase morphology upon cure. U.S. Patent No 4,656,208 discloses a similar multiphase system wherein a reactive polyether sulfone oligomer and an aromatic diamine curing agent react to form complex multiphase domains. However, the systems of Bucknall have very high viscosities due to requiring excessive amounts of dissolved thermoplastic, and yet still do not meet the desired toughness standards. Blends of polyimides and epoxy resins are also known to those skilled in the art. EP-A99,338 discloses the incorporation of a thermoplastic polyimide into an epoxy resin system which provides a substantially discontinuous phase with in the continuous phase of the epoxy resin. As a result, toughness, mechanical and thermal properties are enhanced without significant adverse effect on their performance characteristics. U.S Patent 4,608,404 discloses epoxy resin toughened with an oligomeric amine terminated polyether sulfone provides composites having compression after impact values of greater than 30 Ksi, particularly when DDS was used as a co-curative. U.S patent No 4,567,216 discloses an epoxy composition modified with a polyetherimide or polyaryl ether thermoplastic to improve tensile properties. U.S patent 2001034430 discloses carboxy-functionalised poly phenylene ether and its blends with epoxy resins. U.S patent 2003224177 discloses an epoxy resin composition comprising a phosphorous containing epoxy resin and an aromatic polysulfone resin. The cured product has not only excellent toughness but also high flame retardancy and high heat resistance, and is advantageous as an insulation material for a multi-layer printed wiring board, particularly as an insulation material for a build up substrate. EP0583224 and US5434226 disclose thermosetting resins of epoxy or bismaleimides toughened with polyaryl sulfide sulfone and polyether sulfone. US patent 5242748 and CA 1339496 discloses toughened thermosetting structural materials wherein the incorporation of 2 to 25 Jim particles of a limited class of poly imides having appreciable non-aromatic character into heat curable epoxy resin systems significantly increases the toughness of such systems with out loss of other desirable properties. Reactive terminated oligomers preferably amine terminated PEEK oligomers based on bisphenol A, tert-butyl hydroquinone, methyl hydroquinone and hydroquinone increased the fracture toughness of bisphenol A and resorcinol based epoxy resin as reported by G.S.Bennet, RJ.Farris, S.A.Thomson, Polymer, 32, 1633,1991. The fracture toughness of diglycidyl ether of bisphenol A-poly phthaloyl diphenyl ether blend increased without reduction in the mechanical properties of the resin as reported by T.Iijima, T.Tochimoto, M.Tomoi, J.Appl.Polym.Sci, 43, 1685, 1991. US patent 4,999,238 discloses a multiphase epoxy resin composition prepared by polymerising an epoxy resin, a diamine curing agent, a reactive polyether sulfone oligomer, and a solution of an elastomer such as B.F.Goodrich Hycar RTM 1472. However, such multiphase systems are difficult to process and leads to unpredictable changes in morphology due to variations in resin processing, cure temperature and cure cycle. US patent 4118535 describes the invention of polyetheramide-imide epoxy resin blends with melt viscosities suitable for solventless dry powder coating and curing of PEI insulating material on various substrates. US5162450 discloses a curable composition containing low molecular weight polyphenylene ether and a polyepoxide composition containing brominated and non-brominated bisphenol polyglycidyl ethers, in combination with further components including specific catalysts for manufacture of multiplayer printed circuit assemblies having excellent physical and electrical properties. US5929151 discloses a blend of ketone polymer and epoxy resin prepared by heating the ketone polymer and epoxy into a homogeneous melt processable blend. This composition can be mixed with a curing agent to give a curable composition. On curing phase separation occurred and ketone polymer formed continuous phase and crosslinked epoxy formed dispersed phase. The preferred ketone polymers are copolymers of carbon monoxide, ethylene and a second ethylenically unsaturated hydrocarbon of at least three carbon atoms, particularly an a-olefin such as polypropylene. However, none of the prior art teaches or discloses polycyanoarylene ether with an epoxy resin and a catalyst for curing the epoxy polycyanoarylene ether blend. Polyarylene ethers are well known class of engineering thermoplastics. The aromatic portion of the polyarylene ether imparts thermal stability and good mechanical properties of the polymer and the ether linkages facilitates the processing of the polymer while maintaining oxidative and thermal stability. Polyarylene ethers having an aryl moiety substituted with an electron-withdrawing nitrile group are illustrated by the known class of poly cyano aiyl ethers. Polycyano aryl ether is an engineering plastic with superior heat resistance and has been widely used as a material for electric and electronic equipments or mechanical components. The cyano group on an aromatic ring imparts adhesion of the polymer to many substrates, through polar interaction with other functional groups, and it serves as a potential site for polymer cross linking. The glass transition temperatures of many polycyano aryl ethers are relatively high with values in the range of from about 150°C to about 230°C depending upon the particular aryl group present. Although polycyano aryl ethers possess excellent heat resistance, solvent resistance, flame retardancy and thermo-mechanical properties, they are difficult to process, often requiring both high pressure and temperatures to produce acceptable fibre reinforced parts. The primary object of the invention is to provide a novel epoxy resin composition for use in the advanced composite field, which imparts increased toughness and good processability and handleability, while maintaining good thermal characteristics. Another object of the invention is to provide a process for producing a toughened epoxy composition, which displays good handleability as well as excellent performance characteristics. The present invention provides a toughened epoxy resin composition comprising at least one epoxy resin, an amine hardener, 5% to about 25% of a hydroxy terminated polycyano arylene/aryl ether oligomer with pendant alkyl groups having a molecular weight from about 2000 to about 50,000 and Tg of at least about 190°C. The present invention also a process for preparing a toughened epoxy resin composition comprising the steps of blending hydroxy-terminated polycyanoarylene/aryl ether oligomers with pendant alkyl groups and epoxy resin, at a temperature of 120°C to 180°C, adding to the epoxy and thermoplastic oiligomer blend and amine hardener and mixing at 120°C to 180°C until a low mix viscosity of epoxy resin composition is obtained. The present invention concerns the addition of poly cyano aryl ether oligomers/polymers containing pendant alkyl groups with molecular weight of about 2000 to about 50,000 to a heat curable epoxy system to impart toughness without decreasing other desirable properties. The thermoplastic polycyano arylene ethers are added to the epoxy resin preferably by means of melt mixing. By the term toughness is meant resistance to impact induced damage. Toughness in cured neat resin samples may be assessed by the critical stress intensity factor, Kic, among others. The epoxy resins used in the process of the present invention preferably contain an average more than one epoxide group per molecule and preferably at least 2 epoxide groups per molecule. Such epoxy resins are well known to those skilled in the art and numerous examples may be found in the Handbook of epoxy resins, Lee and Neville, McGraw-Hill, Publishers 1967; Epoxy resins, Chemistry and Technology, 2nd Edition; Clayton May. Ed., Marcel Dekker, 1988, & U.S Pat 4,608,404; 4,604,319 & 4,656,207 which are herein incorporated by reference. The glycidyl ethers of various phenolic compounds having between 2 and about 4 epoxide groups per molecule and a glass transition temperature below 20°C are particularly preferred. Particularly preferred epoxy resins include the epoxy resins which are the diglycidyl ether of bisphenol A (or 2,2-bis[p-(2,3-epoxy propoxy) phenyl] propane), diglycidyl ether of bisphenol F (or 2,2-bis[p-2,3-epoxy propoxy)phenyl] methane, diglycidyl ether of bisphenol S and diglycidyl ether of bisphenol K, diglycidyl ether of the cresol & phenol based novalacs, resorcinol diglycidyl ether (or 1,3-bis(2-3-epoxy propoxy)benzene, triglycidyl p-amino phenol (or 4-(2,3-epoxy propoxy) N,N-bis(2,3-epoxy propyl)aniline and tetraglycidyl methylene dianiline (or N,N,N,N-tetra(2,3-epoxy propyl) 4,4'-diamino diphenyl methane) The aromatic oligomer contains functional groups, which are reactive with the polyepoxide component and /or the amine hardener of the composition. The reactive aromatic oligomer preferably contains divalent aromatic groups such as phenylene or diphenylene groups linked by the same or different divalent non-aromatic linking groups like oxy(-O-), sulfonyl (-SO2-), carbonyl (-CO-) or oxyalkylene . The aromatic units can be substituted with non interfering substituents such as chlorine, lower alkyl, phenyl etc. Generally, at least twenty-five percent of the total number of carbon atoms in the reactive aromatic oligomer will be in aromatic structures, and preferably at least about 50% of the total carbon atoms are in aromatic structures. Aromatic oligomers are polyethers, polysulfones or polyethersulfones , polyether ketone or poly ether ether ketone are particularly prefered. Prefered reactive oligomers have reactive groups that are terminal groups on the oligomer backbone and more preferably are reactive groups at the ends of oligomeric backbones which have little or no branching. The preferred reactive groups of the reactive aromatic oligomer are primary amine (--NH2), hydroxyl (--OH), carboxyl (--COOA, where A is hydrogen or an alkali metal), anhydride, thiol, secondary amine and epoxide groups. The functionally terminated thermoplastic comprises recurring units of the following formula wherein XisOH, Ri and R2 is H, methyl, ethyl, propyl, pentyl, hexyl, tert-butyl or ditert-butyl, R is derived from hydroquinone or resorcinol, Z is selected from 2,6-dichlorobenzonitrile, 2,6-difluorobenzonitrile, 2,4- dichlorobenzonitrile, 2,5-dichlorobenzonitrile, 3,5-dichlorobenzonitrile, 2,4- difluorobenzonitrile, 2,5-difluorobenzonitrile, 3,5-difluorobenzonitrile or 2,6- dinitrobenzonitrile and n is from 5 to 166. The reactive aromatic oligomers are preferable produced by reacting a dihydroxy compound like hydroquinone or alkyl substituted hydroquinone with alkali metal carbonate. The alkali metal salt of the dihydroxy compound is reacted with an aromatic nitrile compound with halogen groups. The temperature of the reaction mixture is maintained at least about 160°C to ensure reaction to completion in a reasonable period of time. The preferred temperature range is about 160°C to 200°C. The glass transition temperature of the preferred reactive aromatic oligomers is preferably in range between 130°C and 170°C. The molecular weight of the reactive aromatic oligomers is preferably in the range of between 2000 and 50000. The reactive aromatic oligomers preferably have a polydispersity between 2 and 4. The amine hardener for the thermosetting composition is preferably an aromatic diamine having a molecular weight below 750. The preferred aromatic diamines are 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl methane, 3,3'-diaminodiphenyl methane, 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone or 3,3'-diaminobenzophenone. The hardener is present in the composition in an amount sufficient to crosslink or cure the composition into a thermoset and preferably is present in an amount which provides from 0.8 to 1.5 equivalents and more preferably 0.8 to 1.2 equivalents of active hydrogen atoms per one equivalent of epoxide groups in the composition. Catalysts may sometimes be necessary when formulating epoxy resin composition. Such catalysts are well known to those skilled in the art. When amine functional curing agents are utilized, catalysts are generally optional, and preferably catalysts are selected from tertiary amines and complexes of amines such as monoethylamine with borontrifluoride may be useful. However when phenolic functional curing agents or toughening oligomers are used, the epoxy-phenol reaction are catalyzed. Suitable catalysts are the phosphines, for example triphenylphosphine and hexyldiphenylphosphine. The thermoplastic polymer and the epoxy resin is blended preferably by hot melt processing. The polyepoxide and reactive aromatic oligomer, when mixed together, form a low viscosity mixture. The preferred mixing temperature is from about 120°C to about 180°C. Preferably about 5% to about 25% reactive oligomer is used for making the blends and most preferably 5 to 15% reactive aromatic oligomer is used. The amine hardener is added to the blend after complete dissolution of the reactive aromatic oligomer at about 120°C to 180°C with constant stirring. Preferably, for casting purposes this blend is degassed in a vacuum oven while maintaining the temperature at about 120°C to 180°C. After degassing the blend is cast into an open heated mould. The blend is cured at 180°C for three hours and post cured at 200°C for two hours. The above-mentioned curing cycle is only an example. Many variations in curing cycle are possible, all of which will be readily apparent to those who are skilled in the art. The preferred crosslinked resins are characterised by a Tg of 220°C and a fracture toughness of at least 1.46MNm"3/2 as per ASTM STP410. The most preferred crosslinked resins have a fracture toughness of 3.42MNm"3/2. The following examples illustrate the synthesis of thermoplastic, blend formulation with epoxy, curing and property evaluation of the toughened epoxy matrices. EXAMPLE 1 Part A Hydroxy terminated tertiary butyl polyether nitrile oligomers (Mn, 4000g/mol) were prepared according to a method described in the literature, J. E. McGrath, T. C. Word, E. Schehori and A. J. Wnuk, Polym. Eng. Sci, 17,647,1977. The following example illustrates the preparation of a hydroxy terminated tert-butyl polyether nitrile oligomer with a calculated molecular weight (Mn) of 4000g/mol, based on a stoichiometric imbalance (r = 0.8757) using excess hydroxy containing monomers. This example further illustrates the use of this material to toughen bisphenol-A based diglycidyl ether, which was cured by using a diamine tert-butyl hydroquinone (54.5g, 0.3278mol), 2,6-dichlorobenzonitrile (DCBN) (49.3899g, 0.2871mol), powdered anhydrous potassium carbonate (54.3793g, 0.3934mol), N-methyl pyrrolidone (346ml) and toluene (150ml) were added to a 1 litre four necked flask equipped with a thermocouple, nitrogen inlet, mechanical stirrer and a Dean-Stark trap. When heating, provided by a heating mantle the stirred mixture was slowly heated to approximately 160°C under an atmosphere of flowing nitrogen. Water was removed over a period of several hours, then the toluene was removed through the Dean-stark trap and the temperature of the reaction mixture was allowed to reach 200°C and maintained at 200°C for 3hours, cooled to approximately 100°C and filtered through a fritted glass funnel. The filtrate was acidified by the addition of glacial acetic acid (57ml, 1 mol) mixed with 200ml NMP and precipitated into a total of 4 to Slitre of water in a blender. The precipitated polymer was collected by filtration, washed with water and dried in air at 105°C and under vacuum at 130°C. Yield of hydroxy terminated tert-butyl PEN oligomer was 98%. Glass transition temperature determined by DSC was 191°C and inherent viscosity was 0.134dl/g for 0.2% concentration in p-chlorophenol at 60°C. Part B Several epoxy compositions with increasing amounts of hydroxy terminated PEN oligomer were made. The amount of oligomer varied from 0% to 15%. The hydroxy terminated tert-butyl PEN oligomer was added to diglycidyl ether of bisphenol A and then mechanically stirred the mixture, heated at 140°C to 180°C until the PEN oligomer dissolved completely (1 to 2hrs) and the catalyst triphenyl phosphine was added. DDS was added to the stirred mixture and kept at this temperature till DDS dissolved fully. The mixture was degassed under vacuum at approximately 180°C, poured hot into a hot SS mould and the specimens were cured at 180°C for three hours and post cured at 200°C for two hours. The cured epoxy system is having Tg of at least about 214°C. Table 1 illustrates the composition and properties of the blends. EXAMPLE 2 Part A Tert-butyl polyether nitrile oligomer Procedure of Example 1 Part A was followed with stoichiometric imbalance (r = 1). Tert-butyl hydroquinone (50.1796g, 0.3018mol), 2,6-dichlorobenzonitrile (DCBN) (51.9275g, 0.3018mol), powdered anhydrous potassium carbonate (50.0685g, 0.3622mol), N-methyl pyrrolidone (340ml) and toluene (150ml) were used. Glass transition temperature determined by DSC was 203 °C and inherent viscosity was 1.26dl/g for 0.2% concentration in p-chlorophenol at 60°C. Part B Procedure of Example 1 Part B was repeated with tert-butyl PEN oligomer from Example 2 Part A. Table-2 illustrates the composition and properties of the blends. The cured epoxy system is having Tg of at least about 220°C. EXAMPLE 3 Hydroxy-terminated tertiary butyl polyether nitrite oligomer (Mm 12000g/mol) Part A Procedure of Example 1 Part A was followed with stoichiometric imbalance (r = 0.9567) using excess hydroxy containing monomers. 2,6-dichlorobenzonitrile (DCBN) (51.4860g, 0.2993mol) and N-methyl pyrrolidone (345ml) were used. Glass transition temperature determined by DSC was 197°C and inherent viscosity was 0.33dl/g for 0.2% concentration in p-chlorophenol at 60°C. Part B The procedure of Example 1 Part B was repeated with hydroxy-terminated PEN oligomer from Example 3 Part A. The cured epoxy system is having Tg of at least about 215°. Table 3 illustrates the composition and properties of the blends. EXAMPLE 4 Part A Hydroxy-terminated tert-butyl polyether nitrite oligomer (Mn, 8000g/mol) Procedure of Example 1 Part A was followed with stoichiometric imbalance (r = 0.9358) using excess hydroxy containing monomers. 2,6-dichlorobenzonitrile (DCBN) (51.3291g, 0.2984mol) and N-methyl pyrrolidone (348ml) were used. Glass transition temperature determined by DSC was 194°C and inherent viscosity was 0.22dl/g for 0.2% concentration in p-chlorophenol at 60°C. Part B The procedure of Example 4 Part B was repeated with hydroxy-terminated PEN oligomer from Example 4 Part A. The cured epoxy resin system is having Tg of atleast 217°C. Table 5 illustrates the composition and properties of the blends. The toughened epoxy resin composition of the present invention is used in fibre-reinforced composites in rocket motor cases, for LH2 cryo tank and in damage tolerant aerospace structural applications. The said material is also used as an insulation material for high performance wiring in electrical and electronics industries and in printed circuit boards and as structural adhesives for low and high temperature aerospace applications. We Claim: 1. A toughened epoxy resin composition comprising at least one epoxy resin, an amine hardener, 5% to 25% of a hydroxy terminated polycyanoarylen/aryl ether oligomer with pendant alkyl groups having a molecular weight from 2000 to 50,000 and Tg of at least about 190°C. 2. The formulation as in claim 1, wherein said epoxy resin is with a functionality of 2 or more. 3. The composition as claimed in 2, wherein said epoxy resin is selected from bisphenol A diglycidyl ether, bisphenol AF (4,4'-hexafluoro isopropylidene) diphenol diglycidyl ether, bisphenol F (4,4'-dihydroxydiphenyl methane) diglycidyl ether, bisphenol S (4,4'-dihydroxydiphenyl sulfone) diglycidyl ether, tris hydroxy phenyl methane based tri-epoxy, tris hydroxy phenyl ethane based tri-epoxy, diamino diphenyl methane based tetra-epoxy, diamino diphenyl ether based tetra-epoxy, diamino diphenyl sulfone based tetra-epoxy and diamino benzophenone based tetra-epoxy or mixtures thereof. 4. The composition as claimed in 1, wherein the functionally terminated thermoplastic comprises recurring units of the following formula Z is selected from 2,6-dichlorobenzonitrile, 2,6-difluorobenzonitrile, 2,4-dichlorobenzonitrile, 2,5-dichlorobenzonitrile, 3,5-dichlorobenzonitrile, 2,4-difluorobenzonitrile, 2,5-difluorobenzonitrile, 3,5-difluorobenzonitrile or 2,6-dinitrobenzonitrile and n is from 5 to 166. 5. The composition as clamed in 1, wherein said amine hardener is an aromatic diamine. 6. The composition as claimed in 5, wherein said aromatic diamine is 4,4'diamino diphenyl sulfone or 3,3'-diamino diphenyl sulfone, 4,4'-diamino diphenyl methane, 3,3'-diamino diphenyl methane, 4,4'-diaminodiphenyl ether, or 3,3'-diaminobenzophenone or mixtures thereof. 7. The composition as claimed in 1, comprises a triphenyl phosphine catalyst. 8. The composition as claimed in 1, wherein said triphenyl phosphine catalyst is 0.1 to 3% by weight. 9. A process for preparing a toughened epoxy resin composition comprising the steps of blending hydroxy-terminated polycyanoarylene/aryl ether oligomers with pendant alkyl groups and epoxy resin such as herein described, at a temperature of 120°C to 180°C, adding to the epoxy and thermoplastic oligomer blend an amine hardener and mixing at 120°C to 180°C until a low mix viscosity of epoxy resin composition is obtained. 10. The process as claimed in claim 9, wherein a catalyst triphenylphosphine is added to the epoxy and thermoplastic blend. 11. The process as claimed in claim 9, wherein the blend mixing temperature does not exceed 180°C. 12. A toughened epoxy resin composition substantially as herein described and exemplified. 13. A process for preparing a toughened epoxy resin composition substantially as herein described and exemplified.

Full Text

The present invention relates to novel epoxy resin composition and a process for preparing the epoxy resin composition. More specifically, the invention relates to the improvement of the properties of epoxy resin composition by adding thereto a thermoplastic component with pendent alkyl groups. The epoxy resin material is used in many applications, such as in aerospace field, as matrix resins for fibre reinforced pre-pregs and the composites prepared from fibre reinforced prepregs and as structural adhesives.
The use of fibre-reinforced thermoset composites continues to grow. Epoxy resins are one of the most important thermosetting polymers, and they have outstanding mechanical and thermal properties. Epoxy resins have gained widespread use as matrix resins for advanced composites in the field of aerospace, electronic and automobile industries. However, a major drawback of these resins is that they are brittle and thus easily subject to impact-induced damage. On the other hand many thermoplastics are tough and ductile however, their use in structural materials has been minimized for several reasons. Many of the thermoplastics do not have the required solvent resistance, thermal stability and high softening points required in demanding aerospace applications. The high temperature engineering thermoplastics are difficult to process, often requiring both high temperature and pressure to produce acceptable fibre reinforced parts.
Blending of engineering thermoplastics with thermosetting resins has gained commercial importance due to ease of processability and tremendous improvement in solvent resistance and toughness. Of the thermosets available, by far the most common are the epoxies, the bismaleimides and the cyanates. Various resins are blend together to obtain the best properties of each of the resin used to improve properties. But the best properties of each resin are rarely achieved.
Elastomers have been used with good success in toughening a number of thermosetting resins, particularly epoxy resins. Examples of such systems are given in Bauer, Epoxy resin Chemistry II, chapter 1-5, ACS symposium series 221, American Chemical Society, Washington DC 1983. Both soluble and infusible elastomers have been

utilized, the former generally increasing flexibility at the expense of physical properties such as tensile modulus, while the latter generally increase toughness without substantially affecting bulk properties. Both types of modification generally lead to lower thermal properties.
US patent Nos. 3715252, 3737352,3784433,3796624,4073670 and 4131502 disclose the possible combination of epoxy resins and non heat-curable thermoplastic components including poly(vinyl acetal), nylon, neoprene rubber, acrylonitrile rubber, phenoxy resins, polysulfones and alpha olefin copolymer. US patent 3641195 discloses curable composition comprising an epoxide resin dispersed in a thermoplastic copolymer of an olefin hydrocarbon with an alpha olefin, which is an ether, or ester of a carboxylic acid. US patent 4117038 discloses epoxy resin adhesives containing a polyglycidyl compound, an acrylonitrile-butadiene-styrene graft polymer and a copolymer of ethylene, acrylic acid and acrylate. Despite the general thermoplastic nature of these materials, they have not provided a broad pattern of increase performance characteristics.
Engineering thermoplastics are frequently have been used as toughness modifiers for epoxy resins. The optimum performance properties are obtained for systems, which are miscible before curing. High molecular weight engineering thermoplastics with desired properties are often immiscible with epoxy resins. Low molecular weight reactive oligomers have been successfully used as toughness modifiers for epoxy resins.
The solution of thermoplastic in the epoxy is normally accomplished by either dissolving the two components in a common solvent and removing the solvent, or by heating the thermoplastic and the epoxy to a temperature above the Tg of the thermoplastic and melting the two components together. The high viscosity, as well as poor tack, drape and stiffness, make the matrix unacceptable for hot melt processing or for prepregging. Using less than 10% thermoplastic solution allows the user to control the viscosity of the matrix, however, the resultant composite will not achieve the desired toughness.

Toughening of epoxy resins with polyether sulfone was disclosed by Bucknall and Partridge in the British Polymer Journal, V.15, Mar 1983 pages 71-75. The systems demonstrating the greatest toughness developed a multiphase morphology upon cure. U.S. Patent No 4,656,208 discloses a similar multiphase system wherein a reactive polyether sulfone oligomer and an aromatic diamine curing agent react to form complex multiphase domains. However, the systems of Bucknall have very high viscosities due to requiring excessive amounts of dissolved thermoplastic, and yet still do not meet the desired toughness standards. Blends of polyimides and epoxy resins are also known to those skilled in the art. EP-A99,338 discloses the incorporation of a thermoplastic polyimide into an epoxy resin system which provides a substantially discontinuous phase with in the continuous phase of the epoxy resin. As a result, toughness, mechanical and thermal properties are enhanced without significant adverse effect on their performance characteristics. U.S Patent 4,608,404 discloses epoxy resin toughened with an oligomeric amine terminated polyether sulfone provides composites having compression after impact values of greater than 30 Ksi, particularly when DDS was used as a co-curative. U.S patent No 4,567,216 discloses an epoxy composition modified with a polyetherimide or polyaryl ether thermoplastic to improve tensile properties. U.S patent 2001034430 discloses carboxy-functionalised poly phenylene ether and its blends with epoxy resins. U.S patent 2003224177 discloses an epoxy resin composition comprising a phosphorous containing epoxy resin and an aromatic polysulfone resin. The cured product has not only excellent toughness but also high flame retardancy and high heat resistance, and is advantageous as an insulation material for a multi-layer printed wiring board, particularly as an insulation material for a build up substrate. EP0583224 and US5434226 disclose thermosetting resins of epoxy or bismaleimides toughened with polyaryl sulfide sulfone and polyether sulfone. US patent 5242748 and CA 1339496 discloses toughened thermosetting structural materials wherein the incorporation of 2 to 25 Jim particles of a limited class of poly imides having appreciable non-aromatic character into heat curable epoxy resin systems significantly increases the toughness of such systems with out loss of other desirable properties. Reactive terminated oligomers preferably amine terminated PEEK oligomers based on bisphenol A, tert-butyl hydroquinone, methyl hydroquinone and hydroquinone increased the fracture toughness of bisphenol A and resorcinol based

epoxy resin as reported by G.S.Bennet, RJ.Farris, S.A.Thomson, Polymer, 32, 1633,1991. The fracture toughness of diglycidyl ether of bisphenol A-poly phthaloyl diphenyl ether blend increased without reduction in the mechanical properties of the resin as reported by T.Iijima, T.Tochimoto, M.Tomoi, J.Appl.Polym.Sci, 43, 1685, 1991. US patent 4,999,238 discloses a multiphase epoxy resin composition prepared by polymerising an epoxy resin, a diamine curing agent, a reactive polyether sulfone oligomer, and a solution of an elastomer such as B.F.Goodrich Hycar RTM 1472. However, such multiphase systems are difficult to process and leads to unpredictable changes in morphology due to variations in resin processing, cure temperature and cure cycle. US patent 4118535 describes the invention of polyetheramide-imide epoxy resin blends with melt viscosities suitable for solventless dry powder coating and curing of PEI insulating material on various substrates.
US5162450 discloses a curable composition containing low molecular weight polyphenylene ether and a polyepoxide composition containing brominated and non-brominated bisphenol polyglycidyl ethers, in combination with further components including specific catalysts for manufacture of multiplayer printed circuit assemblies having excellent physical and electrical properties. US5929151 discloses a blend of ketone polymer and epoxy resin prepared by heating the ketone polymer and epoxy into a homogeneous melt processable blend. This composition can be mixed with a curing agent to give a curable composition. On curing phase separation occurred and ketone polymer formed continuous phase and crosslinked epoxy formed dispersed phase. The preferred ketone polymers are copolymers of carbon monoxide, ethylene and a second ethylenically unsaturated hydrocarbon of at least three carbon atoms, particularly an a-olefin such as polypropylene. However, none of the prior art teaches or discloses polycyanoarylene ether with an epoxy resin and a catalyst for curing the epoxy polycyanoarylene ether blend.
Polyarylene ethers are well known class of engineering thermoplastics. The aromatic portion of the polyarylene ether imparts thermal stability and good mechanical properties of the polymer and the ether linkages facilitates the processing of the polymer while maintaining oxidative and thermal stability. Polyarylene ethers having

an aryl moiety substituted with an electron-withdrawing nitrile group are illustrated by the known class of poly cyano aiyl ethers. Polycyano aryl ether is an engineering plastic with superior heat resistance and has been widely used as a material for electric and electronic equipments or mechanical components. The cyano group on an aromatic ring imparts adhesion of the polymer to many substrates, through polar interaction with other functional groups, and it serves as a potential site for polymer cross linking. The glass transition temperatures of many polycyano aryl ethers are relatively high with values in the range of from about 150°C to about 230°C depending upon the particular aryl group present. Although polycyano aryl ethers possess excellent heat resistance, solvent resistance, flame retardancy and thermo-mechanical properties, they are difficult to process, often requiring both high pressure and temperatures to produce acceptable fibre reinforced parts.
The primary object of the invention is to provide a novel epoxy resin composition for use in the advanced composite field, which imparts increased toughness and good processability and handleability, while maintaining good thermal characteristics.
Another object of the invention is to provide a process for producing a toughened epoxy composition, which displays good handleability as well as excellent performance characteristics.
The present invention provides a toughened epoxy resin composition comprising at least one epoxy resin, an amine hardener, 5% to about 25% of a hydroxy terminated polycyano arylene/aryl ether oligomer with pendant alkyl groups having a molecular weight from about 2000 to about 50,000 and Tg of at least about 190°C.
The present invention also a process for preparing a toughened epoxy resin composition comprising the steps of blending hydroxy-terminated polycyanoarylene/aryl ether oligomers with pendant alkyl groups and epoxy resin, at a temperature of 120°C to

180°C, adding to the epoxy and thermoplastic oiligomer blend and amine hardener and mixing at 120°C to 180°C until a low mix viscosity of epoxy resin composition is obtained.
The present invention concerns the addition of poly cyano aryl ether oligomers/polymers containing pendant alkyl groups with molecular weight of about 2000 to about 50,000 to a heat curable epoxy system to impart toughness without decreasing other desirable properties. The thermoplastic polycyano arylene ethers are added to the epoxy resin preferably by means of melt mixing. By the term toughness is meant resistance to impact induced damage. Toughness in cured neat resin samples may be assessed by the critical stress intensity factor, Kic, among others.
The epoxy resins used in the process of the present invention preferably contain an average more than one epoxide group per molecule and preferably at least 2 epoxide groups per molecule. Such epoxy resins are well known to those skilled in the art and numerous examples may be found in the Handbook of epoxy resins, Lee and Neville, McGraw-Hill, Publishers 1967; Epoxy resins, Chemistry and Technology, 2nd Edition; Clayton May. Ed., Marcel Dekker, 1988, & U.S Pat 4,608,404; 4,604,319 & 4,656,207 which are herein incorporated by reference. The glycidyl ethers of various phenolic compounds having between 2 and about 4 epoxide groups per molecule and a glass transition temperature below 20°C are particularly preferred. Particularly preferred epoxy resins include the epoxy resins which are the diglycidyl ether of bisphenol A (or 2,2-bis[p-(2,3-epoxy propoxy) phenyl] propane), diglycidyl ether of bisphenol F (or 2,2-bis[p-2,3-epoxy propoxy)phenyl] methane, diglycidyl ether of bisphenol S and diglycidyl ether of bisphenol K, diglycidyl ether of the cresol & phenol based novalacs, resorcinol diglycidyl ether (or 1,3-bis(2-3-epoxy propoxy)benzene, triglycidyl p-amino phenol (or 4-(2,3-epoxy propoxy) N,N-bis(2,3-epoxy propyl)aniline and tetraglycidyl methylene dianiline (or N,N,N,N-tetra(2,3-epoxy propyl) 4,4'-diamino diphenyl methane)

The aromatic oligomer contains functional groups, which are reactive with the polyepoxide component and /or the amine hardener of the composition. The reactive aromatic oligomer preferably contains divalent aromatic groups such as phenylene or diphenylene groups linked by the same or different divalent non-aromatic linking groups like oxy(-O-), sulfonyl (-SO2-), carbonyl (-CO-) or oxyalkylene . The aromatic units can be substituted with non interfering substituents such as chlorine, lower alkyl, phenyl etc. Generally, at least twenty-five percent of the total number of carbon atoms in the reactive aromatic oligomer will be in aromatic structures, and preferably at least about 50% of the total carbon atoms are in aromatic structures. Aromatic oligomers are polyethers, polysulfones or polyethersulfones , polyether ketone or poly ether ether ketone are particularly prefered. Prefered reactive oligomers have reactive groups that are terminal groups on the oligomer backbone and more preferably are reactive groups at the ends of oligomeric backbones which have little or no branching. The preferred reactive groups of the reactive aromatic oligomer are primary amine (--NH2), hydroxyl (--OH), carboxyl (--COOA, where A is hydrogen or an alkali metal), anhydride, thiol, secondary amine and epoxide groups.
The functionally terminated thermoplastic comprises recurring units of the following formula
wherein XisOH,
Ri and R2 is H, methyl, ethyl, propyl, pentyl, hexyl, tert-butyl or ditert-butyl,
R is derived from hydroquinone or resorcinol,
Z is selected from 2,6-dichlorobenzonitrile, 2,6-difluorobenzonitrile, 2,4-
dichlorobenzonitrile, 2,5-dichlorobenzonitrile, 3,5-dichlorobenzonitrile, 2,4-
difluorobenzonitrile, 2,5-difluorobenzonitrile, 3,5-difluorobenzonitrile or 2,6-
dinitrobenzonitrile and n is from 5 to 166.

The reactive aromatic oligomers are preferable produced by reacting a dihydroxy compound like hydroquinone or alkyl substituted hydroquinone with alkali metal carbonate. The alkali metal salt of the dihydroxy compound is reacted with an aromatic nitrile compound with halogen groups. The temperature of the reaction mixture is maintained at least about 160°C to ensure reaction to completion in a reasonable period of time. The preferred temperature range is about 160°C to 200°C.
The glass transition temperature of the preferred reactive aromatic oligomers is preferably in range between 130°C and 170°C. The molecular weight of the reactive aromatic oligomers is preferably in the range of between 2000 and 50000. The reactive aromatic oligomers preferably have a polydispersity between 2 and 4.
The amine hardener for the thermosetting composition is preferably an aromatic diamine having a molecular weight below 750. The preferred aromatic diamines are 4,4'-diaminodiphenyl sulfone, 3,3'-diaminodiphenyl sulfone, 4,4'-diaminodiphenyl methane, 3,3'-diaminodiphenyl methane, 4,4'-diaminodiphenyl ether, 4,4'-diaminobenzophenone or 3,3'-diaminobenzophenone. The hardener is present in the composition in an amount sufficient to crosslink or cure the composition into a thermoset and preferably is present in an amount which provides from 0.8 to 1.5 equivalents and more preferably 0.8 to 1.2 equivalents of active hydrogen atoms per one equivalent of epoxide groups in the composition.
Catalysts may sometimes be necessary when formulating epoxy resin composition. Such catalysts are well known to those skilled in the art. When amine functional curing agents are utilized, catalysts are generally optional, and preferably catalysts are selected from tertiary amines and complexes of amines such as monoethylamine with borontrifluoride may be useful. However when phenolic functional curing agents or toughening oligomers are used, the epoxy-phenol reaction are catalyzed. Suitable catalysts are the phosphines, for example triphenylphosphine and hexyldiphenylphosphine.

The thermoplastic polymer and the epoxy resin is blended preferably by hot melt processing. The polyepoxide and reactive aromatic oligomer, when mixed together, form a low viscosity mixture. The preferred mixing temperature is from about 120°C to about 180°C. Preferably about 5% to about 25% reactive oligomer is used for making the blends and most preferably 5 to 15% reactive aromatic oligomer is used. The amine hardener is added to the blend after complete dissolution of the reactive aromatic oligomer at about 120°C to 180°C with constant stirring. Preferably, for casting purposes this blend is degassed in a vacuum oven while maintaining the temperature at about 120°C to 180°C. After degassing the blend is cast into an open heated mould. The blend is cured at 180°C for three hours and post cured at 200°C for two hours. The above-mentioned curing cycle is only an example. Many variations in curing cycle are possible, all of which will be readily apparent to those who are skilled in the art.
The preferred crosslinked resins are characterised by a Tg of 220°C and a fracture toughness of at least 1.46MNm"3/2 as per ASTM STP410. The most preferred crosslinked resins have a fracture toughness of 3.42MNm"3/2.
The following examples illustrate the synthesis of thermoplastic, blend formulation with epoxy, curing and property evaluation of the toughened epoxy matrices.
EXAMPLE 1 Part A
Hydroxy terminated tertiary butyl polyether nitrile oligomers (Mn, 4000g/mol) were prepared according to a method described in the literature, J. E. McGrath, T. C. Word, E. Schehori and A. J. Wnuk, Polym. Eng. Sci, 17,647,1977. The following example illustrates the preparation of a hydroxy terminated tert-butyl polyether nitrile oligomer with a calculated molecular weight (Mn) of 4000g/mol, based on a stoichiometric imbalance (r = 0.8757) using excess hydroxy containing monomers. This example further illustrates the use of this material to toughen bisphenol-A based diglycidyl ether, which was cured by using a diamine tert-butyl hydroquinone (54.5g, 0.3278mol), 2,6-dichlorobenzonitrile (DCBN) (49.3899g, 0.2871mol), powdered anhydrous

potassium carbonate (54.3793g, 0.3934mol), N-methyl pyrrolidone (346ml) and toluene (150ml) were added to a 1 litre four necked flask equipped with a thermocouple, nitrogen inlet, mechanical stirrer and a Dean-Stark trap. When heating, provided by a heating mantle the stirred mixture was slowly heated to approximately 160°C under an atmosphere of flowing nitrogen. Water was removed over a period of several hours, then the toluene was removed through the Dean-stark trap and the temperature of the reaction mixture was allowed to reach 200°C and maintained at 200°C for 3hours, cooled to approximately 100°C and filtered through a fritted glass funnel. The filtrate was acidified by the addition of glacial acetic acid (57ml, 1 mol) mixed with 200ml NMP and precipitated into a total of 4 to Slitre of water in a blender. The precipitated polymer was collected by filtration, washed with water and dried in air at 105°C and under vacuum at 130°C. Yield of hydroxy terminated tert-butyl PEN oligomer was 98%. Glass transition temperature determined by DSC was 191°C and inherent viscosity was 0.134dl/g for 0.2% concentration in p-chlorophenol at 60°C. Part B
Several epoxy compositions with increasing amounts of hydroxy terminated PEN oligomer were made. The amount of oligomer varied from 0% to 15%. The hydroxy terminated tert-butyl PEN oligomer was added to diglycidyl ether of bisphenol A and then mechanically stirred the mixture, heated at 140°C to 180°C until the PEN oligomer dissolved completely (1 to 2hrs) and the catalyst triphenyl phosphine was added. DDS was added to the stirred mixture and kept at this temperature till DDS dissolved fully. The mixture was degassed under vacuum at approximately 180°C, poured hot into a hot SS mould and the specimens were cured at 180°C for three hours and post cured at 200°C for two hours. The cured epoxy system is having Tg of at least about 214°C. Table 1 illustrates the composition and properties of the blends.

EXAMPLE 2
Part A
Tert-butyl polyether nitrile oligomer
Procedure of Example 1 Part A was followed with stoichiometric imbalance (r = 1).
Tert-butyl hydroquinone (50.1796g, 0.3018mol), 2,6-dichlorobenzonitrile (DCBN)
(51.9275g, 0.3018mol), powdered anhydrous potassium carbonate (50.0685g,
0.3622mol), N-methyl pyrrolidone (340ml) and toluene (150ml) were used. Glass
transition temperature determined by DSC was 203 °C and inherent viscosity was
1.26dl/g for 0.2% concentration in p-chlorophenol at 60°C.
Part B
Procedure of Example 1 Part B was repeated with tert-butyl PEN oligomer from Example 2 Part A. Table-2 illustrates the composition and properties of the blends. The cured epoxy system is having Tg of at least about 220°C.

EXAMPLE 3
Hydroxy-terminated tertiary butyl polyether nitrite oligomer (Mm 12000g/mol)
Part A
Procedure of Example 1 Part A was followed with stoichiometric imbalance (r = 0.9567) using excess hydroxy containing monomers. 2,6-dichlorobenzonitrile (DCBN) (51.4860g, 0.2993mol) and N-methyl pyrrolidone (345ml) were used. Glass transition temperature determined by DSC was 197°C and inherent viscosity was 0.33dl/g for 0.2% concentration in p-chlorophenol at 60°C.
Part B
The procedure of Example 1 Part B was repeated with hydroxy-terminated PEN oligomer from Example 3 Part A. The cured epoxy system is having Tg of at least about 215°. Table 3 illustrates the composition and properties of the blends.

EXAMPLE 4
Part A
Hydroxy-terminated tert-butyl polyether nitrite oligomer (Mn, 8000g/mol)
Procedure of Example 1 Part A was followed with stoichiometric imbalance (r =
0.9358) using excess hydroxy containing monomers. 2,6-dichlorobenzonitrile (DCBN)
(51.3291g, 0.2984mol) and N-methyl pyrrolidone (348ml) were used. Glass transition
temperature determined by DSC was 194°C and inherent viscosity was 0.22dl/g for
0.2% concentration in p-chlorophenol at 60°C.

Part B
The procedure of Example 4 Part B was repeated with hydroxy-terminated PEN oligomer from Example 4 Part A. The cured epoxy resin system is having Tg of atleast 217°C. Table 5 illustrates the composition and properties of the blends.

The toughened epoxy resin composition of the present invention is used in fibre-reinforced composites in rocket motor cases, for LH2 cryo tank and in damage tolerant aerospace structural applications. The said material is also used as an insulation material for high performance wiring in electrical and electronics industries and in printed circuit boards and as structural adhesives for low and high temperature aerospace applications.

We Claim:
1. A toughened epoxy resin composition comprising at least one epoxy resin,
an amine hardener, 5% to 25% of a hydroxy terminated
polycyanoarylen/aryl ether oligomer with pendant alkyl groups having a
molecular weight from 2000 to 50,000 and Tg of at least about 190°C.
2. The formulation as in claim 1, wherein said epoxy resin is with a
functionality of 2 or more.
3. The composition as claimed in 2, wherein said epoxy resin is selected from
bisphenol A diglycidyl ether, bisphenol AF (4,4'-hexafluoro isopropylidene)
diphenol diglycidyl ether, bisphenol F (4,4'-dihydroxydiphenyl methane)
diglycidyl ether, bisphenol S (4,4'-dihydroxydiphenyl sulfone) diglycidyl
ether, tris hydroxy phenyl methane based tri-epoxy, tris hydroxy phenyl
ethane based tri-epoxy, diamino diphenyl methane based tetra-epoxy,
diamino diphenyl ether based tetra-epoxy, diamino diphenyl sulfone based
tetra-epoxy and diamino benzophenone based tetra-epoxy or mixtures
thereof.
4. The composition as claimed in 1, wherein the functionally terminated
thermoplastic comprises recurring units of the following formula

Z is selected from 2,6-dichlorobenzonitrile, 2,6-difluorobenzonitrile, 2,4-dichlorobenzonitrile, 2,5-dichlorobenzonitrile, 3,5-dichlorobenzonitrile, 2,4-difluorobenzonitrile, 2,5-difluorobenzonitrile, 3,5-difluorobenzonitrile or 2,6-dinitrobenzonitrile and n is from 5 to 166.
5. The composition as clamed in 1, wherein said amine hardener is an aromatic diamine.
6. The composition as claimed in 5, wherein said aromatic diamine is 4,4'diamino diphenyl sulfone or 3,3'-diamino diphenyl sulfone, 4,4'-diamino diphenyl methane, 3,3'-diamino diphenyl methane, 4,4'-diaminodiphenyl ether, or 3,3'-diaminobenzophenone or mixtures thereof.
7. The composition as claimed in 1, comprises a triphenyl phosphine catalyst.
8. The composition as claimed in 1, wherein said triphenyl phosphine catalyst is 0.1 to 3% by weight.
9. A process for preparing a toughened epoxy resin composition comprising the steps of blending hydroxy-terminated polycyanoarylene/aryl ether oligomers with pendant alkyl groups and epoxy resin such as herein described, at a temperature of 120°C to 180°C, adding to the epoxy and thermoplastic oligomer blend an amine hardener and mixing at 120°C to 180°C until a low mix viscosity of epoxy resin composition is obtained.
10. The process as claimed in claim 9, wherein a catalyst triphenylphosphine is added to the epoxy and thermoplastic blend.
11. The process as claimed in claim 9, wherein the blend mixing temperature does not exceed 180°C.

12. A toughened epoxy resin composition substantially as herein described and
exemplified.
13. A process for preparing a toughened epoxy resin composition substantially
as herein described and exemplified.

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Patent Number

279923

Indian Patent Application Number

1180/CHE/2004

PG Journal Number

06/2017

Publication Date

10-Feb-2017

Grant Date

03-Feb-2017

Date of Filing

09-Nov-2004

Name of Patentee

INDIAN SPACE RESEARCH ORGANISATION

Applicant Address

ISRO HEADQUATERS DEPARTMENT OF SPACE ANTARIKSH BHAVAN NEW BEL ROAD BANGALORE 560094

Inventors:

#	Inventor's Name	Inventor's Address
1	VATTIKUTI LAKSHMANA RAO	VIKRAM SARABHAI SPACE CENTRE THIRUVANANATHAPURAM KERALA 695 022
2	AKANKSHA SAXENA	VIKRAM SARABHAI SPACE CENTRE THIRUVANANATHAPURAM KERALA 695 022
3	BEJOY FRANCIS	VIKRAM SARABHAI SPACE CENTRE THIRUVANANATHAPURAM KERALA 695 022
4	KORAH BINA CATHERINE	VIKRAM SARABHAI SPACE CENTRE THIRUVANANATHAPURAM KERALA 695 022
5	PANKAJAKSHAN RADHAKRISHNAN NAIR	VIKRAM SARABHAI SPACE CENTRE THIRUVANANATHAPURAM KERALA 695 022
6	VILLOONNIL CHACKO JOSEPH	VIKRAM SARABHAI SPACE CENTRE THIRUVANANATHAPURAM KERALA 695 022
7	KOVOOR NINAN NINAN	VIKRAM SARABHAI SPACE CENTRE THIRUVANANATHAPURAM KERALA 695 022
8	KUCHIBHATLA SITARAMA SASTRI	VIKRAM SARABHAI SPACE CENTRE THIRUVANANATHAPURAM KERALA 695 022

PCT International Classification Number

C08L 63/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA