This invention relates to a process for forming a mixture of an epoxidized poly(phenylene ether) and an epoxy resin.

Epoxy resins are consumed globally in large quantities. They are widely used in adhesives, to form the resin phase of composites, in making electronic laminates, and for other purposes.

Cured epoxy resins tend to be hard, brittle materials, particularly when made using diglycidyl ethers of aromatic compounds such as bisphenols or novolac resins. Brittle materials tend to fracture easily, and for this reason epoxy resins are excluded from many applications unless modified to reduce their friability. A common type of modification is to include a rubbery material in the epoxy resin formulation. Examples of such rubbery materials include polyethers (which may be capped with epoxy groups and/or epoxy-reactive groups), epoxy-, amine- or carboxyl-terminated butadiene polymers or copolymers, and core-shell rubbers.

Polyether tougheners tend to reduce the glass transition temperature of the cured epoxy resin, and so their use is disfavored when a high transition temperature cured epoxy resin is wanted. Core-shell rubbers only inefficiently reduce friability in highly cross-linked, high glass transition temperature epoxy resin systems.

Poly(phenylene ether) (PPE) has been proposed as an additive to reduce friability. PPE is somewhat miscible with epoxy resins such as diglycidyl ether of bisphenol A. However, when a PPE/epoxy resin mixture is cured, the PPE often phase segregates, forming discrete domains that may be of the order of 50-200 μπι in diameter. Because of this, PPE is not very effective in reducing friability. Fracture resistance is increased when a PPE is present, but not very significantly.

Mo et al., J. Appl. Polym. Sci. 2013 pp. 4879-88, describe a method by which PPE is reacted with epichlorohydrin using sodium hydroxide as the catalyst. Chao et al. J. Appl. Polym. Sci. Vol. 59, pp. 473-481 (1966), describe a process in which PPE, bisphenol A and an epoxy novolac resin are reacted in toluene solution to form an "upstaged" epoxy-terminated resin. This process requires the use of solvents and adds synthetic steps, each of which introduces additional costs and complexity. As such, this process is not industrially viable. Cured epoxy resins made using blends of the epoxy-terminated resin form highly phase-segregated cured materials. An inexpensive and effective method of producing epoxy-functional PPE resins is desired. In addition, a method by which by which a high glass transition temperature cured epoxy with low friability can be made is desired.

This invention is a process for preparing an epoxy-terminated poly(phenylene ether), comprising

a) forming a liquid mixture containing a poly(phenylene ether) having at least one terminal phenolic group, 0.9 to 1.25 equivalents of a cyclic anhydride compound per equivalent of hydroxyl groups of the poly(phenylene ether) and at least 2 equivalents of an epoxy resin per equivalent of hydroxyl groups of the poly(phenylene ether), wherein the poly(phenylene ether) having at least one terminal phenolic group constitutes 5 to 50% of the combined weight of the poly(phenylene ether), cyclic anhydride compound and epoxy resin; and

b) heating the liquid mixture formed in step a) to a temperature of 80 to 180°C to produce a mixture of i) an epoxy-terminated reaction product of the poly(phenylene ether), the cyclic anhydride and a portion of the epoxy resin and ii) unreacted epoxy resin.

Because the three reactants all can react with each other, the reaction in step b) potentially could form a complex mixture. Surprisingly, this is not the case. The cyclic anhydride appears to react preferentially, and monofunctionally, with the phenolic groups of the PPE. Likewise, the epoxy resin appears to react preferentially and monofunctionally with carboxyl groups formed when the cyclic anhydride reacts with the PPE. The result of this sequence of reactions is a well-defined mixture of unreacted epoxy resin and the epoxy-terminated reaction product of the poly(phenylene ether), the cyclic anhydride and epoxy resin. For convenience below, this reaction product is referred to as the "epoxy-terminated PPE" .

The resulting mixture can be used directly as the epoxy resin component (or portion thereof) of a curable epoxy system. The epoxy resin system also includes at least one epoxy hardener, and optionally contains an epoxy curing catalyst, one or more other epoxy resins, and other suitable components as described below. The resulting cured epoxy resin typically has a glass transition temperature at least as high as that of an otherwise like system that lacks any PPE component, and in addition is significantly less friable.

Surprisingly, a core-shell rubber is an efficient toughening additive in such an epoxy resin system. Although core-shell rubbers tend to perform poorly in other high glass transition temperature cured epoxies, it has been found to provide excellent toughening when used with the invention, leading to a cured epoxy resin that has both a high glass transition temperature and low friability.

Therefore, in additional aspects, the invention is a) a mixture of i) an epoxy - terminated reaction product of the poly(phenylene ether), the cyclic anhydride and a portion of the epoxy resin and ii) unreacted epoxy resin formed in the process of the first aspect of the invention, b) a curable epoxy resin system including the mixture and further including at least one epoxy hardener and preferably at least one core-shell rubber, and c) a cured epoxy resin obtained by curing the curable epoxy resin system.

The PPE is a polyether in which aryl groups are linked into a polymer chain through ether linkages. The aryl groups may be phenyl, other aryl groups such as naphthyl, and may contain alkyl or other hydrocarbyl substitution. The PPE has at least one terminal phenolic group and preferably contains at least two phenolic groups. The PPE may be linear or branched. The PPE may have a weight per hydroxyl group of 400 to 5000 g/equivalent, preferably 500 to 2000 g/equivalent and more preferably 600 to 1200 g/equivalent, as determined by titration methods.

In some embodiments, he PPE has a structure corresponding to structure I:

where each Ar group independently represents an aryl group, which may be substituted with alkyl or other hydrocarbyl substitution, Y represents a covalent bond or the residue of an initiator compound, each m is independently zero or a positive number and x is at least one. Preferably m, x and Y are selected together so the PPE has a weight per hydroxyl group as indicated above, x is preferably 2 to 4 and more preferably 2. Each m may be, for example, 2 to 20, preferably 3 to 15, more preferably 4 to 10. Y preferably has a weight of 200 g/mole or less and may be, for example, oxygen or the residue (after removal of phenolic hydrogens) of a phenolic compound having x phenolic hydroxyl groups. Each Ar is preferably phenyl or dimethylphenyl, with the methyl groups each being preferably in the ortho position with respect to an ether oxygen.

A particularly preferred PPE corresponds to structure II:

wherein Y and m are as defined above. As before, Y preferably has a weight of 200 g/mole or less and may be, for example, oxygen or the residue (after removal of phenolic hydrogens) of a phenolic compound having 2 phenolic hydroxyl groups.

The PPE constitutes 5 to 50% of the combined weight of the poly(phenylene ether), cyclic anhydride compound and epoxy resin. A preferred amount is 5 to 20% and a more preferred amount is 5 to 15% or 8 to 12%, on the same basis.

The cyclic anhydride is a compound having a cyclic carboxylic anhydride group, or a mixture of two or more such compounds. The cyclic carboxylic anhydride group is a ring structure that contains a:

o o

-c-o-c- linkage as part of the ring structure. The anhydride may have a molecular weight of up to 500, preferably up to 350 and more preferably up to 200. It may be aromatic and/or aliphatic. Examples of useful anhydrides include methyltetrahydrophthalic anhydride, tetrahydrophthalic anhydride, phthalic anhydride, trimellitic anhydride, maleic anhydride, tetrachlorophthalic anhydride, pyromellitic anhydride, succinic anhydride, dodecenylcsuccinic anhydride and tetrabromophthalic anhydride.

Methyltetrahydrophthalic anhydride is a preferred anhydride compound.

The cyclic anhydride is provided in approximately a stoichiometric amount, relative to the phenolic groups provided by the PPE. A small deficiency or small excess may be provided. A preferred amount is at least 0.95 equivalent or at least 0.98 equivalent of cyclic anhydride per equivalent of phenolic groups, up to about 1.2 equivalents or up to 1.15 equivalents per equivalent of phenolic groups.

The epoxy resin is one or more materials having a number average of at least 1.5, preferably at least 1.8, epoxide groups per molecule, and an epoxy equivalent weight of up to 1000. The number average epoxy equivalent weight preferably is up to 500, more preferably is up to 250 and still more preferably is up to 225. The epoxy resin preferably has up to eight epoxide groups and more preferably has 1.8 to 4, especially 1.8 to 3, epoxide groups per molecule. The epoxy resin (or mixture of epoxy resins, if a mixture is used) is preferably a liquid at room temperature, to facilitate easy mixing with other components.

Among the useful epoxy resins include, for example, polyglycidyl ethers of polyphenolic compounds. One type of polyphenolic compound is a diphenol (i.e., has exactly two aromatic hydroxyl groups) such as, for example, resorcinol, catechol, hydroquinone, biphenol, bisphenol A, bisphenol AP (1, l-bis(4-hydroxylphenyl)-l-phenyl ethane), bisphenol F, bisphenol K, tetramethylbiphenol, or mixtures of two or more thereof. The polyglycidyl ether of such a diphenol may be advanced, provided that the epoxy equivalent weight is about 1000 or less, preferably about 500 or less, more preferably about 250 or less and still more preferably about 225 or less.

Other useful polyglycidyl ethers of polyphenols include epoxy novolac resins. The epoxy novolac resin may contain, for example, 2 to 10, preferably 3 to 6, more preferably 3 to 5 epoxide groups per molecule. Among the suitable epoxy novolac resins are those having the eneral structure III:

in which 1 is 0 to 8, preferably 1 to 4, more preferably 1 to 3, each R' is independently alkyl or inertly substituted alkyl, and each x is independently 0 to 4, preferably 0 to 2 and more preferably 0 to 1. R' is preferably methyl if present.

Other useful polyglycidyl ethers of polyphenol compounds include, for example, tris(glycidyloxyphenyl)methane, tetrakis(glycidyloxyphenyl)ethane and the like.

Still other useful epoxy resins include polyglycidyl ethers of aliphatic polyols, in which the epoxy equivalent weight is up to 1000, preferably up to 500, more preferably up to 250, and especially up to 200. These may contain 2 to 6 epoxy groups per molecule. The polyols may be, for example, alkylene glycols and polyalkylene glycols such as ethylene glycol, diethylene glycol, tripropylene glycol, 1,2-propane diol, dipropylene glycol, tripropylene glycol and the like as well as higher functionality polyols such as glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, sorbitol and the like. These preferably are used together with an aromatic epoxy resin such as a diglycidyl ether of a biphenol or an epoxy novolac resin.

Still other useful epoxy resins include tetraglycidyl diaminodiphenylmethane; oxazolidone-containing compounds as described in U. S. Patent No. 5, 112,932; cycloaliphatic epoxides; and advanced epoxy-isocyanate copolymers such as those sold commercially as D.E.R.™ 592, D.E.R.™ 6508 and D.E.R™ 6510 (Olin Corporation) as well as those epoxy resins described in WO 2008/140906.

The epoxy resin is provided to the reaction mixture in an amount sufficient to provide at least 2 equivalents of epoxide groups per equivalent of anhydride group provided by the cyclic anhydride compound(s). The epoxy resin may constitute, for example at least 40%, at least 50%, at least 60%, at least 70% at least 80% or at least 85% to the combined weight of the PPE, cyclic anhydride compound, and epoxy resin(s).

The reaction mixture may include a catalyst for the reaction of a phenolic group with an anhydride group, and/or a catalyst for the reaction of a carboxyl group with an epoxide. In some cases, a single catalyst may serve to catalyze all of these reactions. Examples of suitable catalysts include inorganic salts of a strong base and a weak acid, such as potassium carbonate and potassium carboxylates, various amine compounds; and various phosphines. Suitable amine catalysts include various tertiary amine compounds such as dimethylbenzylamine, cyclic or bicyclic amidine compounds such as l,8-diazabicyclo-5.4.0-undecene-7, tertiary aminophenol compounds, benzyl tertiary amine compounds, imidazole compounds, or mixtures of any two or more thereof.

The basic catalyst is present in a catalytically effective amount. A suitable amount is typically from about 0.005 to about 1 weight percent, based on the combined weight of the PPE, cyclic anhydride compound and epoxy resin(s).

The reaction may be performed in the presence of a solvent if desired, but this is generally unnecessary, particularly if the epoxy resin or epoxy resin mixture is a room temperature liquid.

It is generally preferred to omit from the reaction mixture any epoxide-reactive materials other than the PPE and the cyclic anhydride, and to omit any materials that react with phenolic groups and/or cyclic carboxylic anhydride groups other than the epoxy resin(s). Non-reactive materials may be included, such as colorants, fillers, reinforcing agents, biocides, preservatives, antioxidants, and the like. The reaction mixture can be prepared by mixing the ingredients in any order, although it is preferred to avoid subjecting a mixture of the cyclic anhydride compound and epoxy resin to reaction conditions in the absence of the PPE.

In some embodiments, the PPE and epoxy resin are combined in the absence of the cyclic anhydride compound. Because the PPE is often a solid or viscous liquid at room temperature, a suitable way of doing this is to mix the PPE and epoxy resin and then stir the mixture at a temperature of, for example, 80°C to 200°C in the absence of catalyst until a visually homogeneous blend is obtained. The cyclic anhydride compound and catalyst(s) (if any) are then added to the resulting blend to form the reaction mixture.

The reaction is suitably performed at a temperature of 80 to 180°C, preferably 100 to 150°C and more preferably 110 to 130°C. Ambient, superatmospheric or subatmospheric pressures all are suitable. The reaction time may be 10 minutes to 10 hours, more preferably 1 to 5 hours.

The reaction is believed to proceed step-wise, with the cyclic anhydride reacting first with the PPE to form a capped PPE having one or more carboxylic acid end groups (which are formed in the ring-opening reaction of a cyclic anhydride group with a phenolic group). A portion of the epoxy resin is then believed to react with the carboxylic acid end groups to form the epoxy-terminated reaction product. This epoxy- terminated reaction product is dispersed or dissolved in the excess epoxy resin(s).

The progress of the reaction can be followed, for example, by infrared spectroscopy, by which the disappearance of the anhydride groups and consequent formation of ester groups can be monitored. Alternatively or in addition, the reaction progress can be followed by measuring the epoxy equivalent weight of the reaction mixture, with the reaction being completed when the measured epoxy equivalent weight reaches the theoretical equivalent weight of the product, plus or minus 2%. The theoretical equivalent weight is calculated as:

where EW is the theoretic equivalent weight, Eq _ep oxy is the starting number of equivalents of epoxy resin, Eq _a nh _y dride is the starting number of equivalents of the cyclic anhydride compound, and Wt is the weight of the reaction mixture. The formation of a product mixture having an equivalent weight very close to the theoretical equivalent weight EW indicates the formation of a well-defined reaction mixture in which the anhydride, PPE react and a portion of the epoxy resin react to form the desired epoxy- terminated reaction product. The reaction mixture typically contains few if any products of binary reactions between the PPE and the epoxy resin, or between the cyclic anhydride compound and the epoxy resin.

The product mixture obtained from the foregoing process is useful as the epoxy resin component of a curable epoxy resin system. Such a curable epoxy resin system also includes at least one epoxy hardener. It optionally contains an epoxy curing catalyst, other epoxy resins, and other suitable components.

The epoxy hardener is a compound or mixture of compounds having epoxy- reactive groups. The hardener may be, for example, a compound having two or more amine hydrogens, an anhydride compound, a di- or polycarboxylic acid, a thiol compound having two or more thiol groups, a phenolic compound having two or more phenolic groups, and the like. If desired, the epoxy hardener may be a latent or thermally activated type that melts or otherwise becomes reactive only when heated to a elevated temperature such as at least 80°C. Such latent or thermally activated hardeners are preferred for formulating a one-component curable epoxy resin composition.

Examples of suitable hardeners include phenolic hardeners such as D.E.H. 80, D.E.H. 81, D.E.H. 82, D.E.H. 84, D.E.H. 85 and D.E.H. 87 hardeners, from Olin Corporation; amine-epoxy adducts such as D.E.H. 4043, D.E.H. 4129, D.E.H. 4353, D.E.H. 4354, D.E.H, 444, D.E.H.445, D.E.H. 4702, D.E.H. 4712, D.E.H. 4723, D.E.H. 487, D.E.H. 488, D.E.H. 489, D.E.H. 52, D.E.H. 530, D.E.H. 534, D.E.H. 536, D.E.H. 554, D.E.H. 581, D.E.H. 595 and D.E.H 4060, from Olin Corporation; modified polyamide curing agents such as D.E.H. 1504, D.E.H. 545 and D.E.H. 1450, from Olin Corporation; Mannich bases and modified amines such as D.E.H. 613, D.E.H. 614, D.E.H. 615, D.E.H. 616, D.E.H. 619, D.E.H. 622, and D.E.H. 630, from Olin Corporation; guanidines and substituted guanidines including dicyandiamine; melamine resins, aromatic amines such aniline, toluene diamine, diphenylmethanediamine, diethyltoluenediamine; urea compounds such as p-chlorophenyl-N,N-dimethylurea, 3- phenyl- 1, 1-dimethylurea, 3,4-dichlorophenyl-N,N-dimethylurea; imidazole compounds such as 2-ethyl-2-methylimidazole, benzimidazole and N-butylimidazole; polythiol curing agents such as mercaptoacetate and mercaptopropionate esters of low molecular weight polyols having 2 to 8, preferably 2 to 4 hydroxyl groups and an equivalent weight of up to about 75, in which all of the hydroxyl groups are esterified with the mercaptoacetate and alkylene dithiols such as 1,2-ethane dithiol, 1,2-propane dithiol, 1,3-propanedithiol, 1,4-butane dithiol, 1,6-hexane dithiol and the like, trithiols such as 1,2,3-trimercaptopropane, l,2,3-tri(mercaptomethyl)propane, 1,2,3- tri(mercaptoethyl)etliane, (2,3-bis(2-mercaptoethyl)thio)l-propanetliiol; aminocyclohexanealkylamines such as cyclohexanemethanamine, 1,8-diamino-p- menthane and 5-amino-l,3,3-trimethylcyclohexanemethylamine (isophorone diamine); linear or branched polyalkylene polyamines such as, for example, diethylene triamine, triethylene diamine, tetraethylenepentamine, higher polyethylene polyamines, Ν',Ν'- bis(2-aminoethyl)ethane-l,2-diamine, 2-methylpentane-l,5-diamine; other amine curing agents include gem-di-(cyclohexanylamino)-substituted alkanes, diaminocyclohexane, aminoethylpiperazine and bis((2-piperazine-l-yl)ethyl)amine; and aminoalcohols include, for example, ethanolamine, diethanolamine, l-amino-2-propanol, diisopropanolamine, and the like.

The amount of the hardener used can vary considerably, depending on the properties that are wanted in the cured product, and in some cases depending on the type of curing reactions that are desired. The amount of hardener typically provides at least 0.7, at least 0.8 or at least 0.9 equivalents, up to 1.25 equivalents, preferably up to 1.15 equivalents and in some cases up to 1.05 equivalents of hardener, per equivalent of epoxy groups in the curable epoxy resin composition.

In addition to the foregoing ingredients, the curable epoxy resin composition may contain various other materials such as one or more additional epoxy resins, one or more additional impact modifiers such as polyethers (which may be capped with epoxy groups and/or epoxy-reactive groups), epoxy-, amine- or carboxyl-terminated butadiene polymers and copolymers, one or more colorants, one or more epoxy curing catalysts, one or more solvents or reactive diluents, one or more antioxidants, one or more preservatives, one or more fibers, one or more non-fibrous particulate fillers (including micron- and nano-particles), wetting agents and the like.

A core-shell rubber is a preferred additional ingredient in the curable epoxy resin composition. Core-shell rubber particles may constitute, for example, 1 to 30 weight percent, 5 to 25 weight percent or 5 to 15 weight percent of the total weight of the curable epoxy resin composition. The core-shell rubber particles may have a rubbery polymeric core having a glass transition temperature (by DSC) of 0°C or lower, and at at least one polymeric shell having a glass transition temperature of at least 50°C. The core polymer may be, for example, an acrylate polymer or copolymer, a polymer or copolymer of a conjugated diene, a polyether, or a polysiloxane. The polymeric shell may be, for example, a polymer or copolymer of methyl methacrylate. Examples of useful core-shell rubbers include those sold by the Dow Chemical Company under the Paraloid™ brand name, including Paraloid™ KM 355 and Paraloid™ BPM 500 core-shell rubbers, as well as those sold by Kaneka under the KaneAce™ brand name, such as KaneAce ECO- 100 and MX- 153 core-shell rubbers. Some commercially available products such as the KaneAce products are sold as a dispersion of the core- shell rubber particles in a liquid phase which may be an epoxy resin. In such cases, the liquid phase is not counted toward the weight of the core-shell rubber particles. If the liquid phase includes an epoxy resin, the weight of the epoxy resin in the liquid phase is counted toward the total weight of epoxy resins in the curable epoxy resin composition.

The curable epoxy resin composition can be formulated as a one-part or two-part system. In a one-part system, all ingredients, including hardener(s) and catalyst(s) are formulated into a single component. In such a case, the hardener(s) and/or catalyst(s) preferably are latent types that become activated at an elevated temperature of at least 60°C, preferably at least 80°C. A one-component curable epoxy resin composition is then heated to above the activation temperature to effect the cure.

In a two-part system, the epoxy resin (including a reaction mixture prepared in accordance with this invention) is formulated into a first component, and the hardener(s) are formulated into a second component. The components are mixed at the time the cured adhesive is to be prepared. A two-part system can be cured at room temperature or an elevated temperature, as desired.

The epoxy-terminated PPE has been found to have little or adverse effect on the glass transition temperature of the cured epoxy resin system. Often the glass transition temperature of the cured epoxy resin remains unchanged or is even increased when the epoxy-terminated PPE is present in the epoxy resin system. Preferably, the cured epoxy resin has a glass transition temperature, as measured by DSC as described in the following examples, of at least 130°C, more preferably at least 135°C and still more preferably at least 140°C or at least 145°C.

The presence of the epoxy terminated PPE in the curable resin system provides a significant toughening effect when the system is cured, as indicated by Kic fracture resistance of the cured epoxy resin, measured according to ASTM E 399. Kic fracture resistance values may increase, for example to 150% to 500% or more of the values of an otherwise like cured epoxy resin that lacks the epoxy-terminated PPE. The Kic fracture resistance value may be, for example, at least 1.0, at least 1.5, at least 1.75, at least 2.0 or at least 2.25 MPa/m ² . Surprisingly, this advantage often is achieved without significant adverse effect on other properties such as tensile strength, elongation, e- modulus and glass transition temperature. The presence of the epoxy-terminated PPE has been seen to increase tensile strength by 50 to 100% or more, together with an increase in elongation. A small decrease in elastic modulus is sometimes seen, as is typical when a toughener is incorporated into an epoxy resin composition. Preferably, the elastic modulus of the cured epoxy resin of the invention is at least 2500 MPa, measured according to ATSM D-638.

The cured epoxy resin of the invention in some embodiments has a glass transition temperature of at least 130°C, a Kic fracture resistance of at least 1.5 MPa/m ² , and an elastic modulus of at least 2500 MPa. The cured epoxy resin of the invention in some embodiments has a glass transition temperature of at least 135°C, a Kic fracture resistance of at least 1.75 MPa/m ² , and an elastic modulus of at least 2500 MPa. The cured epoxy resin of the invention in some embodiments has a glass transition temperature of at least 135°C, a Kic fracture resistance of at least 2.25 MPa/m ² , and an elastic modulus of at least 2500 MPa.

The following examples are provided to illustrate the invention, but not limit the scope thereof. All parts and percentages are by weight unless otherwise indicated.

Example 1 - Reaction of PPE, Cyclic Anhydride Compound and Epoxy Resin

A 4-neck round bottom flask equipped with a mechanical stirrer and thermocouple is charged with 450 g of a diglycidyl ether of bisphenol A (D.E. R. 383, from Olin Corporation) and placed under a nitrogen atmosphere. The resin is warmed to 60°C, and 118.3 g of a finely ground, solid 850 equivalent weight, difunctional PPE having a structure corresponding to structure II above (Noryl™ SA90 from Saudi Basic Industries Corporation) is added while stirring. The resulting mixture is then warmed to 150°C for about an hour until homogeneous in appearance. The homogeneous mixture is cooled to 80°C. 23.13 g of methyltetrahydrophthalic anhydride and 0.055 g of benzyldimethylamine are added together. The reaction mixture is then heated at 120°C for 4 hours.

The theoretical equivalent weight of the product of this reaction, assuming that each phenolic group of the PPE reacts with an anhydride group to produce an adduct with a terminal carboxyl group that then reacts with an epoxide group, is 267. If the PPE were to react instead with the epoxy resin directly, the equivalent weight of the product would be expected to be 255. If the PPE instead were to react first with an epoxide group, then the anhydride compound and then another epoxide group, the product would be expected to have an equivalent weight of 285.

Samples are taken periodically during the course of the reaction for measurement of epoxy equivalent weight and infrared analysis. The epoxy equivalent weight reaches 264 after one hour of reaction, and slowly increases to 267 over the remaining course of the reaction. This clearly indicates the formation of the desired epoxy- terminated reaction product of the PPE, the cyclic anhydride and epoxy resin in 1 1:2:2 molar ratio, with little if any by-product formation. Infrared analysis indicates the consumption of anhydride groups (at 1778 cm ¹ ) and the formation of ester groups (at 1736 cm ¹ ), consistent with the formation of the desired product.

Examples 2-8 and Comparative Samples A-E

Examples 2-8 and Comparative Samples A-E are made by mixing the ingredients listed in Table 1. "D.E.R. 383" is the epoxy resin described in Example 1. "PPE" is unmodified Noryl™ SA90. "Ex. 1" is the reaction product of Example 1. "CSR Dispersion" refers to Kane-Ace MX- 153 core-shell rubber dispersion sold by Kaneka Corporation. This material contains 33% by weight core-shell rubber particles and 67% by weight of an epoxy resin; its overall epoxy equivalent weight is 270. "DDA5" refers to Omnicure™ DDA5 dicyandiamine (Emerald Materials), and "U-52M" refers to Omnicure™ U-52M Noryl™ 4,4-methylene bis (phenyl dimethyl urea) (Emerald Materials).

Table 1

In each case, the various ingredients are combined, heated to 70°C in a highspeed laboratory mixture and degassed in a vacuum oven at 60-70°C. Plaques for tensile testing are formed by curing the composition at 170°C in a 178" X 178" X 3 mm mold. Plaques for fracture toughness testing are made in the same way using a 178" X 178" X 6 mm mold.

Glass transition temperature of the cured samples is measured by DSC using a TA Instruments DSC Q 10, using nitrogen as the purge gas. The temperature is increased from -90°C to 250°C at the rate of 10°C/minute.

Tensile properties are measured according to ASTM D-638.

Fracture toughness (Kic) is measured according to ASTM D5045.

Results of the various testing are as indicated in Table 2. Table 2 further indicates the PPE content, whether the PPE is present before curing in its unreacted form ("Neat PPE") or in the form of an epoxy-terminated adduct ("ETPPE"), and the amount of core-shell rubber ("CSR") particles in the various samples. Table 2

Comparative Sample A is a baseline case, showing the properties of a model system that does not contain any toughener. The fracture toughness is only 0.8 MPa/m ² . The addition of a polyurethane toughener increases the fracture toughness to about 2.3 MPa/m ² , but reduces the glass transition temperature to about 110°C.

Adding the PPE into the epoxy formulation at the 10% level as a neat material, as in Comparative Sample B, leads to a 25% increase in fracture toughness. Moderate increases in tensile strength and elongation are seen, and an expected decrease in elastic modulus is seen. The glass transition temperature of the cured material is essentially the same as Comparative Sample A.

Examples 2-4 show the effect of adding 2.5, 5% and 10% of an ETPPE made by reacting the PPE with a cyclic anhydride in the excess of an epoxy resin, in accordance with the invention. The fracture toughness increases more (in Example 2 and 4) than when neat PPE is added (Comparative Sample 2), and greater increases in tensile strength and elongation are seen. There is also a positive effect on glass transition temperature, which is increased by 5- 15°C compared to Comparative Sample A. Examples 2-4 in comparison with Comparative Sample B shows the enhanced effect of adding the PPE by forming an epoxy-terminated reaction product in accordance with this invention. Examples 2-4 exhibit a higher glass transition temperature at equal or better fracture toughness, compared to Comparative Sample B. Comparative Sample C shows the effect of adding core- shell rubber particles at the 10% level to increase fracture resistance. Fracture resistance is increased similarly to Examples 2 and 4, and glass transition temperature is increased, but with a large loss in tensile strength and elastic modulus compared to Examples 2-4.

Examples 5-7 show the effect of adding the epoxy-terminated PPE to a system that also contains the core-shell rubber. Further increases in fracture resistance are seen, compared to Comparative Sample D. Increases in tensile strength and elongation are seen as well, with no further loss of elastic modulus despite the high toughener levels. Example 7 is particularly noteworthy, as the fracture resistance is very high, the glass transition temperature is above that of Comparative Samples A and B, and the elastic modulus remains above 2500 despite the very high fracture resistance.

Comparative Samples D and E and Examples 7 and 8 all contain 20% of a toughener. In Comparative Sample D, equal quantities of the neat PPE and core-shell rubber particles form the toughener. In Comparative Sample E, the core-shell rubber is the only toughener. In Example 8, the epoxy-terminated PPE is the only toughener, and in Example 7, the toughener is a mixture of equal quantities of the epoxy-terminated PPE and the core-shell rubber.

Example 8 shows a decrease in fracture resistance compared to Comparative Samples D and E. Taken together with Examples 2-4, this data suggests that the optimal level of the epoxy-terminated PPE by itself is from 2.5 to something less than 20 weight-percent. Example 7, on the other hand, exhibits the best fracture resistance of all the samples tested, and has a significantly higher elastic modulus than Comparative Sample E (which exhibits the next highest fracture toughness). The large depression in elastic modulus of Comparative Sample E is notable, and is representative of epoxy systems toughened with a core-shell rubber.

Comparative Sample D, when compared with Example 7 and Comparative Sample E, again shows that neat PPE provides poorer results than the epoxy- terminated PPE, including a large loss of fracture resistance and tensile strength.