FLEXIBILIZED EPOXY RESINS

Abstract: Epoxy resin systems having good flexibility and impact resistance are modified to provide improved resistance to solvents. Incorporation of a polyalkyleneoxide segment of a molecular weight less than 500 provides improved chemical resistance without sacrifice of mechanical properties. To achieve this an alkoxylated polyol with low molecular weight is reacted with a polycarboxylic acid anhydride to produce the half ester, which is then used to synthesize the flexibilized epoxy resin by forming adducts with polyglycidyl ethers. The flexibilized epoxy resins as well as the acid functionalized oligooxyalkylenes are claimed.

Description: FLEXIBILIZED EPOXY RESINS As polymeric resins, epoxy resins are cross-linked The cross-linking that gives epoxy resins many of their favorable physical and chemical properties also limits the application of epoxy resins to uses where the brittle properties of cross-linked resins are not a handicap Several means have been used to impart flexibility to epoxy resins This 10 invention provides a reactive external flexibilizer for epoxy resins, and epoxy resins which incorporate the reactive external flexibi zer In General, three approaches have been taken to provide flexibility to epoxy resin systems non-reactive external flexibilizers, reactive external flexibilizers, and modifications to the chemical backbone of the epoxy resin Non-reactive external flexibilizers for epoxy resin systems are frequently considered as plasticizers including natural or synthetic rubbers, such as styrene-butadiene, acrylonitrile-butadiene polymers, or dibutylphthalate High boiling point solvents such as benzyl alcohol are sometimes used as plasticizers Reactive external flexibilizers for epoxy resin systems include products such as DESMOCAP™ marketed by BAYER AG Such external flexibilizers may be prepared from polyalkylene oxides bound to a common backbone such as tπmetholpropane A similar reactive external stabilizer is reported in German Patent DE 3202300 There a polyalkylene oxide component having a molecular weight of from 500 to 3500 is described To the hydroxyl groups of the polyalkylene oxide, a cyclic carboxylic acid anhydride is added to generate a carboxyl group The polyalkylene oxide component is derived from the addition reaction of an alkyl oxide such as ethylene oxide or propylene oxide to an active hydrogen compound such as a mono- or polyalcohol Efforts to impart flexibility to cross-linked epoxy resins by chemical modification of the epoxy backbone (internal flexibilization) include incorporation of aliphatic components in generally aromatic epoxy resins by reaction of aromatic epoxy resins with aliphatic acids A different means of internally flexibiiizing epoxy resins is the incorporation of diglycidyl ether of a polyol according to EP 0 253 404 Of the forgoing systems for imparting flexibility, each faces limitations in application While contributing flexibility and impact resistance to the cured epoxy resin system, the foregoing approaches impair the cured resin's resistance to chemical attack and to solvents, increase the coefficient of thermal expansion, and reduce the heat distortion temperature. Lee and Neville, Handbook of Epoxy Resins, McGraw Hill, New York, 1967, p 16-5 In contrast to prior teachings, the Applicant has determined that polyalkylene oxide blocks of less than 500 molecular weight provide good flexibility to epoxy resin systems and provide additional properties including surprising resistance to hydrocarbon solvents The external reactive flexibilizers of the instant invention may be prepared starring from polyoxyalkylene oxide blocks having molecular weights less than 500. Examples of suitable starting materials are polyether polyols such as the series marketed under the trademark VORANOL by The Dow Chemical Company. Examples of three functional glycerine based polypropylene glycol are VORANOL™ CP3055 and VORANOL™ CP255. The polyether polyol may be prepared by the addition of an alkylene oxide to a polyalcohol such as glycerine. The resulting polyoxyalkylene oxide may advantageously then be reacted with a cyclic carboxylic acid anhydride to yield a half-ester of the cyclic carboxylic acid. The invention provides a compound of the Formula I: Formula I wherein the segment has a molecular weight of less than 500, A is the residue of an alcohol having a hydroxyl functionality from 1 to 5, W is a divalent residue derived from a difunctional anhydride, L is a leaving group, for example OH or halogen, X is hydrogen, a branched or linear alkyl group of from 1 to 10 carbon atoms, or an alkyl group of from 1 to 10 carbon atoms substituted by a halogen, n is from 1 to 10, a is from 0 to 4, and b is from 1 to 5, provided that a + b is from 1 to 5. Component A may be derived from a mono or a polyfunctional alcohol. A may have from 1 to 30 carbon atoms, and preferably A is derived from a polyalcohol or a polyphenol. In addition to alcohols as sources for A, other possible sources are compounds containing acid hydrogen, such as compounds containing carboxyl or hydroxyl groups or CH groups which are activated by adjacent carbonyl groups. Residues of polyphenols such as bisphenol A, bisphenol F, or phenol novolac are also suitable as component A in Formula I. Monohydric to pentahydric aliphatic alcohols of from 1 to 5 carbon atoms are preferred. Examples of such preferred alcohols include dihydric alcohols, such as ethylene glycol, propylene or butylene glycol, trihydric alcohols such as glycerol, 1,1,1 -tris- (hydroxymethyl)-propane, 1 ,3,5-tris- (2-hydroxyethyl)-isocyanuric acid tetrahydric alcohols such as pentaerythritol, or pentahydric alcohols, such as arabitol. X may be hydrogen, a branched or linear alkyl group having from 1 to 10 carbon atoms, or an alkyl group of from 1 to 10 carbon atoms substituted by a halogen. n is from 1 to 10, preferably from 2 to 4. Further, the combination of the variable X, and the number n in segment are chosen so that the molecular weight of the segment is less than 500. W is a divalent-radical derived from a cyclic anhydride such as C 2 -C 20 alkane-diyl or alkylene-diyl, a C 4 -C 10 1 ,2-cycloalkylene or cycloalken-1 ,2-ylene, a C 6 -C, 0 cycloalkadien-1 ,2-ylene, and is derived from a dicarboxylic acid cyclic anhydride or its chemical equivalent, such as an acid halide. The cyclic ring may or may not be substituted with one or more C,-C 6 hydrocarbon residues. W is alternatively an ortho-arylene derived from a 1 ,2-aromatic dicarboxylic acid anhydride. Preferred sources for component W include known anhydrides reactive with epoxy groups as are summarized by Lee and Neville at pages 12-3, to 12-7. Preferred anhydrides include the alkyl, alkylene, and aromatic anhydrides succinic anhydride, maleic anhydride, phthalic anhydride, dichloromaleic anhydride, dodecenylsuccinic anhydride, glutaric anhydride, tetrahydrophthalic anhydride, 3,6-dimethyltetrahydrophthalic anhydride, methyltetrahydrophthalic anhydride, methylhexahydro-phthalic anhydride pyromellitic dianhydride, cis-cyclopentanetetra carboxylic acid dianhydride, hemimellitic anhydride, trimellitic anhydride, and naphthalene-1 ,8-dicarboxylic acid anhydride. Formula I provides an available carboxylic acid group for the reaction of an oxirane ring of an epoxide and a carboxylic acid to generate a second ester linkage from the anhydride. When one of many commercially available aliphatic or aromatic di-epoxy functional compounds are used as reactants with the half-ester, a second oxirane ring is available to react with the external flexibiiizing compound into the epoxy resin system. The flexibilized epoxy resin compounds of the invention may be represented by the following Formula II: Formula II (H O Jj; A j-04-CH 2 — CH Component B is generally derived from an epoxy resin having more than one epoxy group. B may correspond to one of Formulas IX to XII Formula IX Formula X Formula XI wherein R 1 is separately in each occurrence C,. 10 alkane-diyl, C, . , 0 haloalkylene, C 410 cycloalkylene, carbonyl, sulfonyl, sulfinyl, oxygen, sulfur, or a direct bond. R' is preferably C, 3 alkylene, C 1 3 haloalkylene, carbonyl, sulfur, or a direct bond; more preferably a direct bond, isopropylidene, or fluorinated isopropylidene (-C(CF 3 ) 2 -); and most preferably isopropylidene. R 2 is separately in each occurrence C, 3 alkyl or a halogen; R 2 is preferably methyl, bromo or chloro; and most preferably methyl or bromo. R 3 is separately in each occurrence C,. 10 alkylene or C^ cycloalkylene; R 3 is preferably C 1 3 alkylene or polycyclic moiety corresponding to Formula VIII Formula VIII wherein a is independently at each occurrence 0 to 4; and m is independently at each occurrence from 0 to 4. Preferably, m is from 0 to 2. The variable m' is independently at each occurrence from 0 to 3. The variable n is as previously defined, that is, from 1 to 10. The variable s is from 0 to 8; and more preferably from 0 to 4. The variable r is from 0 to 40. Preferably, r is from 0 to 10, and most preferably 0 to 5. The symbols: a, b, m, m', n, r, and s may represent an average number, as the compounds to which they refer are generally found as a mixture of compounds with a distribution of the units to which they refer. X is as previously defined. The external reactive flexibilizer described, when combined with polyepoxides, forms a flexibilized epoxy resin system. The chosen amount of flexibilizer may be added to the total epoxy resin of the system to be so flexibilized, or it may be combined with a fraction of the total epoxy resin of an epoxy resin system to be flexibilized. In the total resin system, the portion comprising the flexibilizer, according to Formula II, will comprise from 5 to 70 per 100 parts by weight of the epoxy resin of the system. A lesser amount of flexibilizer generally yields insufficient flexibilization to be useful in the resin properties. When more than 75 parts flexibilizer is incorporated into the resin system it is found that chemical resistance becomes unacceptable. The epoxy resin as modified with the flexibilizer may be cured to form a hardened useful resin by means of any of the known curing agents such as: dicyandiamide and its derivatives; polycarboxylic acid anhydrides, such as those previously mentioned; aromatic polyamines such as m- phenylenediamine or cycloaliphatic polyamines. At room temperature, the epoxy resin systems may be cured by polyamiπoamides, polyaminoimidazoline, aliphatic polyamines or polyether-polyamines. Useful curing agents are taught by Lee and Neville at Chapters, 7-12. The epoxy resin systems described, and acrylation or methacrylation reaction products thereof are useful for the purposes for which epoxide resins have found utility generally. Specifically, the epoxide resin systems are particularly useful where impact resistance is required such as fiber reinforced composite articles such as boats, recreational vehicle body parts, automotive body parts, helmets and sport rackets. The flexibilized epoxy resins described also find use as coatings where the substrate is subject to deflection. The following examples are illustrative of the art of epoxy resin systems and of the invention. Examples 1 to 4 The polyalkylene oxide half-ester flexibiiizing agent may be prepared according to the following procedure. Measurements are in parts by weight, unless otherwise stated. A polypropylene glycol prepared from the reaction of glycerin and propylene oxide to form a three-functional polypropylene glycol in the quantity indicated is introduced into an appropriately sized reaction vessel. The indicated quantity of the designated dicarboxylic acid anhydride is added to the reaction vessel. The gas volume of the reactor was purged with Nitrogen gas. The reaction mixture was heated to 130°C to 140°C with stirring for 2 to 3 hours. At time intervals, the reaction mixture was tested to determine the acid number of the reaction mixture. When the acid number approached the theoretical acid number calculated for the expected reaction product, the reaction vessel was cooled. The acid number was defined for this purpose as the mg KOH per gram of resin necessary to neutralize the resin in a simple titration using phenolphthaleme as a color indicator KOH was conveniently 0 1 N in water The resin aliquot was dissolved in a solvent such as acetone TABLE I Example 1 2 3 4 polypropylene oxide 53 4 49.6 0 0 mol Wt 3000 (pbw) polypropylene oxide 0 0 17 8 16 2 mol Wt 255 (pbw) anhydride methylhexa hydrophtha c anhydride 6 02 7 92 23.62 21 51 (pbw) catalyst ethyl-tπphenyl-phosphonium acetate 70% in methanol (pbw) 0 15 0 15 0.15 0 1 polyepoxide resin dipropylene glycol diglycidylether aliphatic resin (pbw) 40.6 42 5 58 6 62 3 EEW = 175-205 EEW of resulting resin 536 549 592 493 Examples 5 11 The flexibilized epoxy resin systems of the invention incorporating the polyalkylene oxide components prepared according to Examples 1 to 4 may be prepared as follows. To an appropriately sized reaction vessel there was charged a measured quantity of a polyepoxide A measured quantity of polyalkylene oxide flexibiiizing agent was added to the reactor. Sufficient known catalyst was added to catalyze the reaction of the epoxide groups of the polyepoxide with the carboxylic acid groups of the polyalkylene oxide-anhydride adduct. Typically, tetramethylammonium chloride was suitable at 0 3 weight percent Ethyl-tnphenylphosphonium acetate was used in these examples At a temperature of 120°C to 125°C polyacid and epoxy resin were reacted for 1 5 to 2 hours Epoxidized flexibilizer is incorporated into an epoxy resin system by room temperature blending according to the ratios in Table II As a hardener for resins of Examples 5 to 11 , there was used a reaction product of isophorone diamine and a liquid epoxy resin which was a 50 50 blend of diglycidyl ether of bisphenol A and diglycidyl ether of bisphenol F, having an amine hydrogen equivalent weight [AHEW] of 96, 10.7 parts; benzylalcohol 36.6 parts; isophorondiamine 356 parts; m- xylenediamine 9.0 parts; salicylic acid 5.4 parts and nonylphenol 2.7 parts. After room temperature curing for 7 days, the samples are tested for chemical resistance by immersion in the indicated solvent/acid for 7 days at room temperature Mechanical properties are measured according to ASTM D-638M. TABLE II *cracked From the foregoing examples it is apparent that epoxide resin compositions having segments of polyalkylene oxide of molecular weight less than 500 provide flexibility comparable to epoxide resin compositions having molecular weight in excess of 500. Moreover, the epoxide resin compositions having polyalkylene oxide segments of molecular weight less than 500, Examples 9, 10, and 11 , provide superior resistance to organic solvents, and without sacrifice of resistance to acids or mechanical properties.

Claims: CLAIMS; A compound of the Formula I Formula I (HO) . A wherein A is the residue of glycerine, 1 ,1 ,1-tris-(hydroxymethyl)-propane, 1,3,5-tris(2-hydroxyethyl)- isocyanuric acid, pentaerythritol, or arabitol, W is a divalent residue derived from a difunctional anhydride, L is a leaving group, X is hydrogen, a branched or linear alkyl group of from 1 to 10 carbon atoms, or an alkyl group of from 1 to 10 carbon atoms substituted by a halogen, n is from 1 to 10, a is from 0 to 4, and b is from 1 to 5, provided that a + b is from 1 to 5, and wherein the segment has a molecular weight of less than 500. 2. The compound of Claim 1 wherein n is from 2 to 4. 3. The compound of Claim 1 or Claim 2, wherein W is a C 2 -C 20 alkane-diyl, a C 6 -C 10 alkylene-diyl, C , -C 10 1 ,2-cycloalkylene, cycloalken-1,2-ylene, C e -C 10 cycloalkadien-1 ,2-ylene, or C 6 -C 10 cycloalkadien-1 ,2-ylene. 4. The compound of any one of the preceding Claims, wherein a is from 1 to 2 and b is from 1 to 2. 5. The compound of Claim 3 where n is from 2 to 4, a is from 1 to 2, b is from 1 to 2, a + b is from 2 to 4, and X is methyl. 6. The compound of Claim 1 wherein W is derived from succinic anhydride, maleic anhydride, phthalic anhydride, dichloromaleic anhydride, dodecenylsuccinic anhydride, glutaric anhydride, tetrahydrophthalic anhydride, 3,6-dimethyltetrahydrophthalic anhydride, methy -tetrahydrophthalic anhydride, methylhexahydrophthalic anhydride pyromellitic dianhydride, cis- cyclopentanetetracarboxylic acid dianhydride, hemimellitic anhydride, trimellitic anhydride, or naphthalene-1 ,8-dicarboxylic acid anhydride. 7. A polyepoxide resin composition incorporating the flexibilizer of Claim 1 wherein the polyepoxide resin composition comprises molecules according to Formula II Formula II wherein a, X, n, W and b are each as defined in claim 1 and B is derived from an epoxy resin having more than one epoxy group. 8. A polyepoxide resin composition as claimed in Claim 7, wherein B is a group of the Formula IX, X, XI or XII Formula IX Formula X Formula XI wherein each R 1 independently is C,. 10 alkanediyl, C,. 10 haloalkylene, C 4 . 10 cycloalkylene, carbonyl, sulfonyl, sulfinyl, oxygen, sulfur, or a direct bond, each R 2 independently is C 1 3 alkyl or a halogen; each R 3 independently is C,., 0 alkylene or C 550 cycloalkylene; each m independently is from 0 to 4; each m' independently is from 0 to 3; each s independently is from 0 to 8; and r is from 0 to 40. 9. The polyepoxide resin composition of Claim 8 wherein R' is C, .3 alkylene, C, .3 haloalkylene, carbonyl, sulfur, or a direct bond; R 2 is methyl, bromo or chloro; R 3 is C 1 3 alkylene or polycyclic moiety corresponding to Formula VIII Formula VIII m is from 0 to 2, s is from 0 to 4, and r is from 0 to 10. 10. The polyepoxide resin composition of Claim 9 wherein R 1 is a direct bond, isopropylidene, or fluorinated isopropylidene (-C(CF 3 ) 2 -); R 2 is methyl or bromo, and r is from 1 to 5. 11. The polyepoxide resin composition of any one of Claims 8 to 10, wherein n is from 2 to 4. 12. The polyepoxide resin composition of any one of Claims 8 to 11 , wherein B corresponds to Formula X wherein m is 0 and R' is isopropylidene. 13. The polyepoxide resin composition of any one of Claims 8 to 11 , wherein B corresponds to Formula IX. 14. The polyepoxide resin composition of Claim 13 wherein a is from 1 to 2, b is from 1 to 2, and a + b is from 3 to 4.

Inventors: GAN JOSEPH, MEEUS FERDINAND, GAN, JOSEPH, MEEUS, FERDINAND
Applicants: DOW CHEMICAL CO, GAN JOSEPH, MEEUS FERDINAND, GAN, JOSEPH, MEEUS, FERDINAND, THE DOW CHEMICAL COMPANY
Application year: 1997
Main classification: C08G65
IPC codes: C08G59, C08G65, C08L63, C08L71