PROCESS FOR PREPARING ADVANCED EPOXY RESIN COMPOSITIONS

Abstract: A pre-catalyzed epoxy resin composition comprising: a) a polyepoxide, and b) a catalytic amount of a catalyst selected from the group consisting of wherein R is a hydrocarbyl or inertly substituted hydrocarbyl group and X is a compatible anion.

Description: This invention relates to a process for reacting a phenol, carboxylic acid or acid anhydride with an epoxy-containing compound and to the resulting products. More particularly, the invention relates to a process for effecting a specific reaction between compounds possessing a vic-epoxy group and a phenolic hydroxyl group, carboxylic group or anhydride group, and to the products obtained thereby. Epoxy compounds are well known and include many compounds of varying molecular weight and epoxy equivalent weight. To simplify the production of a large number of epoxy compounds that vary mainly in molecular weight, it is common practice to manufacture a single epoxy compound of relatively low molecular weight and react the epoxy compound with a compound containing phenolic hydroxyl groups in the presence of catalyst so as to obtain epoxy of phenolic hydroxy ether compounds of desired higher molecular weight. The conventional catalysts employed are inorganic bases or tertiary amines which are also effective catalysts for competing reactions of epoxides with alcoholic hydroxyl groups, homopolymerization of epoxy groups and the like. As a result, the product obtained is a mixture of polymers and resins with varying degrees of molecular weight, chain branching and end group functionality. Such a composition detracts from the performance and utility of the product. More recent catalysts with improved selectivity include phosphonium halides, 3-(trihydrocarbylphosphoranylidene)-2,5-pyrrolidinediones, alkylammonium halides and tetrahydrocarbyl phosphonium salts. For specific examples reference is made to US Patents Nos. 3,477,990; 3,547,881; 3,843,605; 3,824,212 and 4,438,254. Many of the above catalysts have found commercial utility. However, there is a continuing need for process and product improvements. For example, when many of these catalysts are admixed with the epoxy resins to produce a "pre-catalyzed" epoxy composition, the storage stability at elevated temperatures is not acceptable for many applications because of the reduced activity of the stored resin. It has been proposed to use a precatalyzed polyepoxide containing a synergistic catalyst composition comprising a phosphonium halide and an alkali metal halide or hydroxide (cf. US Patent No. 4,320,222). In other cases the process steps must be controlled under strict conditions so as not to deactivate the catalyst. For example, US 4,438,254 cited above requires that the fusion process be conducted at a temperature under 175 °C and under "essentially anhydrous conditions". In this citation the term "essentially anhydrous" is defined to mean that the reaction medium is absolutely free of water or contains a sufficiently "small quantity of water" not to deactivate the catalyst. Deleterious reactions were found to occur with a catalyst with as little as 0.009 weight per cent water present in the reaction medium (column 6, lines 53-58). What is needed is a new catalyst that does not suffer from deleterious reactions with small quantities of water, thereby enabling much greater freedom of operation. Further, the precatalyzed epoxy resin must be stable at elevated temperature and active at the higher fusion temperatures. The present invention relates to a process for preparing an advanced epoxy resin the process comprising reacting a polyepoxide containing at least one vic-epoxy group with a compound selected from the group consisting of phenols, carboxylic acids and carboxylic acid anhydrides in the presence of a catalyst selected from the group consisting of wherein R is a hydrocarbyl or an inertly substituted hydrocarbyl group and X is a compatible anion, in a reaction mixture having a water content greater than 0.01 percent by weight of the weight of said reaction mixture. In a preferred embodiment the catalyst is methylene bis-(triphenyl)phosphonium) dibromide (or "MBTPPB") or the structure of Formula I. Use of this MBTPPB catalyst in the fusion process has produced extraordinary results, as shown in the examples which follow. In particular, the above catalyst has markedly superior thermal stability and resistance to deactivation by water compared to the catalysts employed in the prior art, e.g., the examples disclosed in US patent 4,438,254 mentioned above. The catalyst of Formula II - e.g., triphenylphosphoranemethylenetriphenylphosphonium bromide ("TPPMTPPB") is also a very stable and active catalyst. As shown in the Examples which follow, the conversion to higher molecular weight compounds with the catalyst of the present invention is not affected by the presence of water. As shown in Example 3, the addition of 0.48 per cent weight water did not reduce the conversion, contrary to the prior art catalysts. Such performance is particularly surprising in view of the disclosures in US Patent No. 4,438,254 where much lower amounts of water resulted in dramatic reductions in conversion. In a preferred, specific application the process of the invention involves the reaction of an epoxy compound and a phenol at a temperature between 110 °C and 200 °C in the presence of a particular catalyst to form the desired phenolic hydroxy ether of the partial formula The liquid polyepoxides employed in the present invention include those compounds possessing more than one vic-epoxy group per molecule, i.e. more than one group per molecule. These polyepoxides are saturated or unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic, and are substituted, if desired, with non-interfering substituents, such as halogen atoms, hydroxy groups, ether radicals, and the like. Preferred liquid polyepoxides include the so-called liquid glycidyl polyethers of polyhydric phenols and polyhydric alcohols. More preferred are the glycidyl polyethers of 2,2-bis(4-hydroxyphenyl)propane having an average molecular weight between 340 and 900 and an epoxide equivalent weight of between 170 and 500. Especially preferred are the glycidyl polyethers of 2,2-bis(4-hydroxyphenyl)propane having an average molecular weight of between 340 and 900, an epoxide equivalent weight of between 170 and 500, and containing from 0.01% to 1.0% by weight or higher of saponifiable chlorine. As used herein the terms "epoxide equivalent weight" and "weight per epoxide" refer to the average molecular weight of the polyepoxide molecule divided by the average number of oxirane groups present in the molecule. Various examples of polyepoxides that may be used in this invention are given in the above mentioned US Patent No. 3,477,990 (e.g., column 2, line 30 to column 4, line 75) and it is to be understood that so much of the disclosures of that patent relative to examples of polyepoxides is incorporated by reference into this specification. The phenols are monohydric or polyhydric and are substituted, if desired, with a great variety of different types of substituents. Examples of the phenols include among others, phenol, resorcinol, o-cresol, m-cresol, p-cresol, chlorophenol, nitrophenol, hydroquinone, 2,2-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyphenyl)pentane, and the like, and polymeric type polyhydric phenols obtained by condensing monohydric or polyhydric phenols with formaldehyde. Preferred phenols to be used are the polyhydric phenols containing from 2 to 6 OH groups and up to 30 carbon atoms. Coming under special consideration are the phenols of the formula wherein Q is a polyvalent element or radical and R¹ independently is a member of the group consisting of hydrogen, halogen and hydrocarbon radicals. The preferred elements or radicals represented by Q are hydrogen, sulphur, --SO--, --SO₂--, divalent hydrocarbon radicals containing up to 10 carbon atoms and oxygen, silicon, sulphur or nitrogen containing hydrocarbon radicals, such as radicals wherein R'' is a divalent hydrocarbon radical. Various examples of phenols that may be used in this invention are also given in US Patent No. 3,477,990 (e.g., column 5, line 1 to column 6, line 10) and it is to be understood that so much of the disclosures of that patent relative to examples of phenols is incorporated by reference into this specification. In a further embodiment of the invention the catalyst and polyepoxide may be reacted with a carboxylic acid and/or carboxylic acid anhydride in place of or in addition to the phenol. The carboxylic acid used may be saturated, unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic. Examples of these acids include succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, oxalic acid, abietic acid, maleic acid, aconitic acid, chlorendic acid and phthalic acid. The acid anhydrides used may be any anhydride which is derived from a carboxylic acid and possesses at least one anhydride group, i.e., a group. The carboxylic acids used in the formation of the anhydrides may be saturated, unsaturated, aliphatic, cycloaliphatic, aromatic or heterocyclic. Examples of these anhydride include phthalic anhydride, isophthalic anhydride, di-, tetra- and hexahydrophthalic anhydride. 3,4,5,6,7,7-Hexachloro-3,6-endomethylene 1,2-tetrahydrophthalic anhydride (chlorendic anhydride), succinic anhdyride, maleic anhydride, chlorosuccinic anhydride, monochloromaleic anhydride, 6-ethyl-4-cyclohexiene-1,2-dicarboxylic acid anhydride, 3,6-dimethyl-4-cyclohexiene-1,2-dicarboxylic acid anhydride, 6-butyl-3,5-cyclohexadiene-1,2-dicarboxylic acid anhydride, octadecylsuccinic acid anhydride, dodecylsuccinic acid anhydride, dioctyl succinic anhydride, nonadecadienylsuccinic anhydride, adducts of maleic anhydride with polyunsaturates, such as methylcyclopentadiene. (Nadic methyl anhydride),3-methoxy-1,2,3,6-tetrahydrophthalic acid anhydride, 3-butoxy-1,2,3,6-tetrahydrophthalic anhydride, trimellitic anhydride, pyromellitic anhydride, di-, tetra- and hexahydromellitic anhydride, polyadipic acid anhydride, polysebacic acid anhdyride, and the like and mixtures thereof. Derivatives of the anhydrides, such as their partial esters, amides, etc., may also be employed. Examples of these include esters of glycols and pyromellitic anhydride and partial esters of trimellitic anhydride. The catalysts used in the present invention are selected from the group consisting of salts of the above formulas I and II. The compatible anion, X ⊖ , can be any anion used in the prior art for such catalysts. Preferred as anions are halides, i.e., Br ⊖ , Cl ⊖ , or I ⊖ ; carboxylates, such as formate, acetate, oxalate or trifluoroacetate; conjugate bases of weak inorganic acids, such as bicarbonate, tetrafluoroborate or biphosphate and conjugate bases of a phenol, such as phenate or an anion derived from bisphenol A. The most preferred anions are halides, with bromide being the most preferred halide. The R groups borne by the phosphonium cations can be aliphatic or aromatic in character. Preferably each phosphonium cation bears at least one R group which is aromatic in character, more preferably at least two such aromatic groups. These aromatic groups preferably are phenyl or inertly substituted phenyl groups. Those R groups which are not aromatic are preferably C₁-C₂₀ alkyl groups. Most preferably, all the R groups are phenyl groups, and the catalyst of formula I is used. Accordingly, a much preferred catalyst is methylene bis(triphenylphosphonium) dibromide. The methylene bis(triphenylphosphonium)dibromide can be conveniently prepared by refluxing under nitrogen for about 2 hours a mixture having a mole ratio of methylene bromide to triphenylphosphine of 2. The excess methylene bromide is removed by distillation and the crude product dissolved in methanol and precipitated by the addition of ethyl acetate. In one sample the purfied salt had a bromine content (AgNO₃ titration) of 22.1%w (theory 22.9%w). Triphenylphosphoranemethylenetriphenylphosphonium bromide can be prepared by treating methylene bis(triphenylphosphonium) dibromide (2.5 millimols) with Na₂CO₃ (about 6 millimols) at about 5 %w in water/methanol (3/1 by weight) at reflux for about 3 to 4 hours and then removing the methanol by distillation. The solids separating from the cooled reaction mixture are collected by filtration and recrystallized from methylene chloride/ethyl acetate. In one example, the purified salt had 12.95%w bromine (theory 13.0%w). The amount of the epoxide and the phenol to be employed in the process may vary over a wide range depending upon the type of reactants and the type of product to be produced. In general, these reactants are used in approximately chemical equivalent amounts, i.e., a chemical equivalent amount of the phenol will be that sufficient to furnish one phenolic hydroxyl for every epoxy group to be reacted. For example, if one is reacting a diepoxide with a monohydric phenol and both epoxy groups are to be reacted, one mole of diepoxide should be reacted with about two moles of the monohydric phenol. On the other hand, if one is reacting a diepoxide with a dihydric phenol and a monomer product is desired by reacting both phenolic groups, one should react about two moles of the diepoxide with one mole of the dihydric phenol. If a polymeric product is desired smaller ratios should be utilized as desired, such as, for example, 5 moles of the diepoxide and 4 moles of the dihydric phenol. Superior results are obtained when the higher molecular weight resins are produced and in this case the ratios of reactants are varied depending upon the molecular weight desired and upon the type of end groups, i.e. whether the product is to be terminated with an epoxide or with a phenol. An especially preferred use of the present invention is in the preparation of a phenolic hydroxy ester resin having an epoxide equivalent weight of between 400 and 4000 wherein the resin is prepared by reacting 2,2-bis(4-hydroxyphenyl)propane with the diglycidyl ether of 2,2-bis(4-hydroxyphenyl)propane having a saponifiable chlorine content of between 0.01% and 1.0% weight and an epoxide equivalent weight of between 170 and 500. The amount of the catalyst employed may vary widely. In general, the amount of catalyst varies from 0.001% to 1% by weight, of the total reactants, more preferably from 0.002% to 0.2% and most preferably from 0.03% to 0.1% by weight of the reactants. The reaction is conducted in the presence or absence of solvents or diluents. In most cases, the reactants are liquid and the reaction is easily effected without the addition of solvents or diluents. However, in some cases, where either or both reactants are solids or viscous liquids it is desirable to add diluents to assist in effecting the reaction. Examples of such materials include the inert liquids, such as inert hydrocarbons as xylene, toluene, cyclohexane and the like. If the solvents are employed in the reaction and the resulting product is to be used for coating purposes, the solvent is typically retained in the reaction mixture. Otherwise, the solvent is removed by any suitable method such as by distillation or the like. Phosphonium salts have been used as catalysts for promoting the reaction between epoxides and acidic materials for quite some time. Up to now the salts employed have been ones that even at fairly low concentrations o f water are in the course of the reaction converted into inactive phosphine oxides; temperatures higher than 175 °C are also reported to contribute to the loss of catalytic activity (US Patent 4,438,254). In contrast the subject salts of this invention are quite tolerant of water contents of up to 0.5%w and reaction temperature of up to 195-200 °C. This tolerance for water provides an economic advantage since the cost entailed in achieving very low water contents is avoided; the tolerance for higher temperature also provides an economic advantage since reaction cycle times can be reduced by reacting at higher temperatures. The products obtained by the above process are the desired phenolic hydroxy ether compounds. Their physical characteristics depend upon the desired reactants and proportions. In general, the products vary from liquids to solids. The polyfunctional reactants also give products terminated in phenolic hydroxyl groups and/or epoxy groups, and these are available for further reaction. A group of products which are particularly outstanding are those resins and polymers obtained by the reaction of the polyepoxides and polyhydric phenols in controlled proportions. Those which use an excess of the polyepoxide are terminated in epoxy groups and can be used as polyepoxides in known reactions of polyepoxides and curing agents. These high molecular weight polyepoxides are particularly useful in preparing surface coatings, adhesives, laminates, filament windings, coating for highways and airfields, structural applications, formation of foams and the like. Those prepared from the halogenated polyhydric phenols are particularly useful as flame proofing resins for forming laminates, coatings. As stated earlier, the present invention is particularly useful for preparing epoxy resins to be used as coatings. The epoxy-containing, phenolic hydroxy ether compounds obtained by use of the present invention are reacted with various conventional curing agents to form hard insoluble, infusible products. Examples of suitable curing agents include, among others, the polybasic acids and their anhydrides such as the di-, tri-and higher carboxylic acids; those acids containing sulphur, nitrogen, phosphorous or halogens; amino-containing compounds such as, for example, diethylene triamine, aminoethylpiperazine, dicyandiamide and triethylenetriamine and pyridine; polyamides containing active amino and/or carboxyl groups. The amount of curing agent varies considerably depending upon the particular agent employed. For the alkalies or phenoxides, 1% to 4% by weight is generally suitable. With phosphoric acid and esters thereof with appropriate crosslinking resin, good results are obtained with 1 to 10% by weight added. The tertiary amine compounds are preferably used in amounts of 1% to 15% by weight. The acids, anhydrides, polyamides, polyamines, polymercaptans, anhydrides, etc. are preferably used in at least 0.8 equivalent amounts, and preferably 0.8 to 1.5 equivalent amounts. An equivalent amount refers to that amount needed to give one active hydrogen (or anhydride group) per epoxy group. Solvents or diluents are sometimes added to make the composition more fluid or sprayable. Preferred solvents or diluents include those which are volatile and escape from the polyepoxide composition before or during cure such as ketones, ethers, chlorinated hydrocarbons. To minimize expense, these active solvents are often used in admixture with aromatic hydrocarbons such as benzene, toluene, xylene, etc. and/or alcohols such as ethyl, isopropyl or n-butyl alcohol. Solvents which remain in the cured compositions are used, such as diethyl phthalate, dibutyl phthalate. It is also convenient to employ normally liquid glycidyl compounds, glycidyl cyclopentyl ether, diglycidyl ether, glycidyl ether of glycerol and the like, and mixtures thereof. Other materials are also added to the composition as desired. This includes other types of polyepoxides such as described in US Patent No. 3,477,990. This also includes fillers, such as sand, rock, resin particles, graphite, asbestos, glass or metal oxide fibres, plasticizers, stabilizers, asphalts, tars, resins, insecticides, fungicides, anti-oxidants, pigments, stains. The temperature employed in the cure varies depending chiefly on the type of curing agent. The amino-containing curing agents generally cure at or near temperature and no heat need be applied. The acids, anhydrides, and melamine derivatives, on the other hand, generally require heat, such as temperatures ranging from 66 °C to 204 °C. Preferred temperatures range from 93 °C to 204 °C, and more preferably from 121 °C to 193 °C. The compositions containing the polyepoxides and curing agents are used for a variety of important applications. They are used, for example, as adhesives for metal, wood, concrete, plaster and the like, and as surface coatings for various types of surfaces. The new compositions are also used in the preparation of laminates or resinous particles reinforced with fibrous textiles. They are also used in the formation of castings and moulding and for the encapsulation of electrical equipment. The invention is further illustrated by means of the following examples. As used in the examples which follow, "WPE" refers to weight per epoxide. Gardner-Holdt viscosity is measured according to ASTM Method D-1545, and the significance of the measurement is discussed in J.J. Mattiello, Protective and Decorative Coatings, Volume V, p. 186 (1946). Example 1 In Example 1 the storage stability of various diphosphonium salts were examined. In all examples, the catalyst concentration was 0.25 meq/100 g of resin (or 0.125 millimoles/100 g of resin). The starting epoxy compound containing the catalyst was a liquid polyepoxide having a WPE of about 185. The starting phenolic compound used in the fusion reaction was 2,2-bis(4-hydroxyphenyl)propane (BPA). The storage times for the precatalyzed resins were as shown in Table 1. A small scale reaction was made to assess the retention of activity of the stored resin. Thus, about 10 grams of resin was admixed near 150-160 °C with sufficient bisphenol-A to give a product with a WPE of about 500 at 100% bisphenol-A conversion, the mixture being held at 160 °C for about 45 minutes. The catalyst employed had the formula where all R are phenyl groups, X is bromide and the Y or Z radical moiety is as shown in Table 1. As shown in Table 1, the best candidates were MBTPPB and TPPMTPPB. Example 2 Example 2 deals with additional storage tests using the following catalysts: MBTPPB - methylene bis(triphenylphosphonium)bromide TPPMTPPB -triphenylphosphoranemethylenetriphenylphosphonium bromide ETPPP - ethyl triphenylphosphonium phosphate ETPPI - ethyl triphenylphosphonium iodide The results are shown in Table 2. The rank order of these systems is clearly evident from the active life period, with MBTPPB and TPPMTPPB being clearly the best. It was of great interest to learn how much active catalyst remained in these aged systems, so ³¹P NMR tests were run on them with the following results: the 21-day old ETPPP had no detectable amount of the ethyl triphenyl phosphonium cation left but showed the presence of ethyldiphenyl phosphine oxide and triphenylphosphine oxide in about a 2/1 ratio; the 21-day old MBTPPB still had about 90% of the active catalyst with about 10% present as pro bably triphenylphosphine oxide. This indicates that the MBTPPB catalyst to be an extremely thermally stable catalyst. Example 3 In Example 3 the effect of water on catalyst deactivation is noted. It is quite evident from the data on the per cent conversion that water increases the rate of inactivation of the ETPP⁺, 0.5 %w added water lowering the per cent conversion to the mid nineties for ETPPP and ETPPI. Note, however, that the same per cent conversion was achieved with MBTPP⁺⁺ with or without added water. From the ³¹P NMR data, however, it is clear that for MBTPP⁺⁺ water does increase the rate of inactivation, there being about 80% active catalyst remaining without added water and 60% with added water. However, note below that essentially no active ETPP⁺ remains in ETPPI even when no water is added. Thus, MBTPP⁺⁺'s inactivation by water is very much slower than that for ETPP⁺. The results are shown in Table 3. Example 4 Users of precatalyzed epoxy resins based on ETPPI, who make their own fusion resin and esterify the resin with acids to make surface coatings must add an esterification catalyst since the phosphonium catalyst is "dead" after the initial fusion reaction; with no added catalyst, the esterification cook reaches quite high viscosities or even gels before a satisfactorily low acid number is reached. Sodium carbonate can be used for this purpose at a level of about 0.6 meq of alkalinity/100 g of total charge. Since the catalyst of the present invention is not wholly inactivated, an ester cook (D-4) with a fusion resin catalyzed with MBTPPB was run following the recommendations for typical fusion products but omitting the added Na₂CO₃. As a control a fusion resin catalyzed with ETPPI but without carbonate addition was used. The results were presented in Table 4 along with typical results for ETPPI-catalyzed resins with addition of Na₂CO₃. Note that ETPPI-catalyzed resins without added carbonate ultimately gave a gel at a fairly high acid number. It is of significant practical interest to note that for the above fusion resin made at 177 °C none of the MBTPP⁺⁺ was converted into a phosphine oxide; in contrast, at 193 °C it was found that about 20% converted into inactive oxide.

Claims: A process for preparing an advanced epoxy resin, the process comprising reacting a polyepoxide containing at least one vic epoxy group with a compound selected from the group consisting of phenols, carboxylic acids and carboxylic acid anhydrides, in the presence of a catalyst selected from the groups consisting of wherein R is a hydrocarbyl or an inertly substituted hydrocarbyl group and X is a compatible anion, in a reaction mixture having a water content greater than 0.01 percent by weight of the weight of said reaction mixture. A process as claimed in claim 1 wherein polyepoxide, phenol and catalyst are reacted at a temperature between 110 °C and 200 °C. A process as claimed in claim 1 or 2 wherein the compound is selected from the group consisting of polycarboxylic acids and polycarboxylic acid anhydrides. A process as claimed in any one of the claims 1 to 3 wherein said polyepoxide is a diglycidylether of 2,2-bis(4-hydroxyphenyl)-propane. A process as claimed in any one of the claims 1 to 4 wherein R is a phenyl group. A process as claimed in any one of the claims 1 to 5 wherein X is a bromine ion. A process as claimed in any one of the claims 1 to 6 wherein the catalyst is methylene bis(triphenyl phosphonium)dibromide. A process as claimed in any one of the claims 1 to 7 wherein the amount of catalyst used is between 0.001 and 1.0 percent by weight based on the amount of polyepoxide. A process as claimed in any one of the claims 1 to 8 wherein the compound employed is 2,2-bis(4-hydroxyphenyl)propane.

Inventors: MARSHALL, CLIFFORD DANIEL
Applicants: SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1986
Main classification: C08G59
IPC codes: C08G59