Latent Catalysts for Epoxy Reactions

The present inention concerns epoxy resins containing latent catalysts for reacting epoxy resins with polyhydric phenols.

It is desirable to have epoxy resin compositions which contain catalysts which will not become active until heated so as to improve storage life. Tyler, Jr. et al in U.S. Pat. No. 4,366,295, Perry in U.S. Pat. No. 3,948,855 and Dante in U.S. Pat. No. 3,477,990 disclsoe precatalyzed epoxy resin compositions which contain onium compounds as the catalyst. While the epoxy resin compositions containing these catalysts are relatively storage stable, it would be desirable for the precatalyzed epoxy resin composition to be even more stable.

It has now been discovered that when an onium compound or amine compound has been contacted with an acid having a weak-neucleophilic anion that the storage stbility of precatalyzed epoxy resins is improved.

The present invention pertains to a composition which when stored at a temperature of 52.degree. C. for a period of nine weeks exhibits an inrease in viscosity measured in centipoise of not greater than about 22, preferably not greater than about 18, percent a scompared to the viscosity of the composition prior to storing and wherein the viscoisty measurements are taken at room temperature and which composition comprises a material that has an average of more than one vicinal epoxy group per molecule and a catalytic quantity of at least one latent catalyst which results from contacting (1) (a) an onium compound represented by the following formula I. ##STR1## wherein each R, R.sup.1, R.sup.2 and R.sup.3 is independently an aliphatic hydrocarbyl group having from 1 to about 20, preferably from about 1 to about 9, carbon atoms, or an aliphatic group having from 1 to about 20, preferably from 1 to about 9 carbon atoms which group also contains one or more oxygen, sulfur, halogen, or nitrogen atoms; z has a value of zero or 1 depending on the valence of Z; Z is phosphorus, nitrogen, sulfur or arsenic and each X is the anion portion of an acid of an element selected from carbon or a halogen and m has a value equal to the valence of the anion X or (b) an aliphatic or aromatic amine with (2) an acid having a weak-nucleophilic anion selected from the group consisting of fluoboric acid, fluoarsenic acid, fluoantimonic acid, fluophosphric acid, chloroboric acid, chloroarsenic acid, chloro-antimonic acid, chloro-phosphoric acid, perchloric acid, chloric acid, bromic acid, iodic acid and combinations thereof in an amount which provides from about 0.9 to about 1.5, preferably from about 1 to about 1.4 moles of weaknucleophilic anion X per mole of onium or amine compound.

The term hydrocarbyl as employed herein refers to a monovalent aliphatic hydrocarbon group such as alkyl, cycloaklyl, alkenyl and similar hydrocarbon groups.

The term weak-nucleophilic as employed herein means that the material has a nucleophilicity value "n" of greater than about zero and less than about 2.5 as described by C. G. Swain and C. B. Scott in J. Am. Chem. Soc., Vol. 75, p. 141 (1953) which is incorporated herein by reference.

The catalysts of the present invention are prepared by simply mixing the onium compound or the amine compound with the acid having a weak-nucleophilic anion in the desired proportions and stirring to insure intimate contact. The contact can be conducted at temperatures of from about 0.degree. C. to about 100.degree. C., preferably from about 20.degree. C. to about 60.degree. C. for a time sufficient to complete any reaction which occurs. The time depends upon the temperature, but usually from about 1 to about 120, preferably from about 5 to about 60 minutes is sufficient. Other methods for preparing the catalyst of the present invention is to employ an insitu method wherein the onium compound or the amine compund and the acid containing a weak-nucleophilic anion are added separately to the resin formulation or component parts thereof thereby forming the catalyst insitu.

Particularly suitable onium or amine compounds or complexes which can be reacted or complexed with the acids having a weak-nucleophilic anion to form the catalysts of the present invention include, for example, tetrabutylphosphonium acetate.acetic acid complex, tetrabutylphosphonium hydroxide, tetrabutylammonium hydroxide, tetraethylammonium hydroxide, tetramethylammonium hydroxide, N-methylmorpholine, 2-methylimidazole, triethylamine, N,N,N',N'-tetramethylethylenediamine, ethyltri(2-hydroxyethyl)ammonium hydroxide, ethyltri(2-ethoxyethyl)ammonium hydroxide, triethyl(2-thioethylethyl)ammonium hydroxide, mixtures thereof and the like.

The resultant catalyst is believed to be a material represented by the aforementioned formula I wherein X is fluoborate, fluoarsenate, fluoantimonate, fluophosphate, chloroborate, chloroarsenate, chloroantimonate, chlorophosphate, and the like. Suitable epoxy resins with which the catalysts of the present invention can be mixed include, for example, those represented by the following formulas II-V ##STR2## wherein each A is independently a divalent hydrocarbyl group having from 1 to about 9, preferably from 1 to about 4, carbon atoms, --O--, --S--, --S--S, --SO--, SO.sub.2 --, or --CO--; each A' is independently a divalent hydrocarbyl group having from 1 to about 9, preferably from 1 to about 4 carbon atoms; Q is hydrogen or a hydrocarbyl group having from 1 to about 10 carbon atoms; Q' is hydrogen or an alkyl group having from 1 to about 4 carbn atoms; each R is independently hydrogen or an alkyl group having from 1 to about 4 carbon atoms; each X is independently hydrogen, bromine, chlorine, or a hydrocarbyl group having from 1 to about 9, preferably from 1 to about 4 carbon atoms; m has an average value from zero to about 12, preferably from about 0.2 to about 9, most preferably from about 1 to about 6; m' has a value from about 0.01 to about 10, preferably from about 0.2 to about 8, more preferably from about 0.5 to about 6; n has a value of zero or 1; and n' has an average value of from zero to about 10, preferably from zero to about 5, most preferably from about 0.1 to about 3.

Particularly suitable such epoxy resins include, for example, the diglycidyl ethers of resorcinol, catechol, hydroquinone, biphenol, bisphenol A, tetrabromobis-phenol A, phenol-aldehyde novolac resins, alkylsub-stituted phenol-aldehyde resins, bisphenol K, tetra-methylbiphenol, tetramethyltetrabromobiphenol, tetramethyltribromobiphenol, tetrachlorobisphenol A, combinations thereof and the like.

Also suitable as the epoxy resin to which the catalysts of the present invention can be mixed include those partially advanced epoxy resins of allowed copending application Ser. No. 716,279, filed Mar. 25, 1985 by Bertram et al which is incorporated herein by reference.

Suitable aromatic hydroxyl containing materials which can be employed herein include, for example, those represented by the following formulas VI-IX ##STR3## wherein A, A', Q, Q' X, n and m are as defined above in formulas II-V. Particularly suitable aromatic hydroxyl-containing materials include, for example, biphenol, bisphenol A, bisphenol K, tetrabromobisphenol A, tetrabromobisphenol K, resorcinol, phenol-aldehyde novolac resins, cresol-aldehyde novolac resins, tetramethylbiphenol, tetramethyltribromobiphenol, tetramethyltetrabromobiphenol, tetrachorobisphenol A, combinations thereof and the like.

These and other suitable aromatic hydroxylcontaining materials are disclosed in U.S. Pat. No. 4,594,291 issued June 10, 1986 by Bertram et al which is incorporated herein by reference.

The precatalyzed compositions of the present invention can contain, if desired, pigments, fillers, dyes, diluents, solvents, stabilizers, epoxy resin curing agents, combinations thereof and the like.

Suitable stabilizer materials and curing agents which can be employed herein include, for example, those disclosed in the aforementioned U.S. Pat. No. 4,594,291 by Bertram et al which is incorporated herein by reference.

The following examples are illustrative of the invention but are not to be construed as to limiting the scope thereof in any manner.

EPOXY RESIN A was a diglycidyl ether of bisphenol A having an epoxide equivalent weight of 180.8.

EXTENDER COMPOUND A was tetrabromobisphenol A having a phenolic hydroxyl equivalent weight (PHEW) of 272.

CURING AGENT A was sulfanilamide having an active hydrogen equivalent weight of about 43.

CURING AGENT B was 4,4'-diaminodiphenylsulfone having an amine hydrogen equivalent weight of about 62.

STABILIZER A was methyl-p-toluene sulfonate.

STABILIZER B was p-toluene sulfonic acid.monohydrate.

The catalysts employed in the present invention were prepared by the following general procedure. To a methanol solution of the onium or amine compound was added a 60 percent aqueous solution of fluoboric acid. A sufficient quantity of methanol was added such that the resultant product contained 40 percent of the onium or amine compound by weight. Stirring was continued until the reaction was essentially complete. The quantities and reaction conditions are given in the following Table I.

For comparative purposes, the following catalysts were utilized.

Catalyst A was ethyltriphenylphosphonium acetate.acetic acid complex.

Catalyst B was tetrabutylphosphonium acetate.acetic acid complex.

Catalyst C was ethyltriphenylphosphonium acetate.acetic acid complex plus an equimolar amound of phosphoric acid as described by tyler, Jr. in U.S. Pat. No. 4,366,295.

Catalyst D was tetrabutylphosphnium acetate.acetic acid complex plus an equimolar amount of phosphoric acid as described by Tyler, Jr. in U.S. Pat. No. 4,366,295.

Catalyst E was 2-methylimidazole.

Catalyst F was benzyl dimethyl amine.

Catalyst G was ethyltriphenylphosphonium iodide, 30 percent active.

Precatalyzed epoxy resins were prepared by adding to 120 grams (0.638 equiv.) of a diglycidyl ether of bisphenol A having an epoxide equivalent weight of 188 (commercially available from The Dow Chemical Company as D.E.R..TM. 331 epoxy resin) 0.45 milliequivalent of catalyst and stirring. The precatalyzed resins were placed in a vacuum oven under a full vacuum (approximately 0.1 mm Hg) controlled at 50.degree. C. to 55.degree. C. for one hour (3600 s). The samples were then stored in a convection oven controlled at 52.degree. C. and the viscosity of the samples were measured at periodic intervals. The samples were allowed to cool for 4 hours (14400 s) at room temperature before measuring the viscosity. The results are given in the following Table II.

A portion of each of the precatalyzed resins from Table II, after aging for 9 weeks (5,443,200 s) at 52.degree. C., were mixed with 22.5 weight percent bisphenol A at 160.degree. C. until all of the bisphenol A had dissolved. The homogeneous solutions were then held at 160.degree. C. for two additional hours, then cooled and the resultant advanced resins analyzed for percent oxirane (epoxide) content and melt viscosity measured at 150.degree. C. The results are given in Table III.

The procedure of Resin Advancement A was followed using 33.48 weight percent of bisphenol A instead of 22.5 weight percent. A resin/bisphenol A blends were held for 4 hours (14400 s) at 160.degree. C. and then analyzed for oxirane content and melt viscosity measured at 200.degree. C. The result are given in Table IV.

To 181 grams (1 equiv.) of the diglycidyl ether of bisphenol A having an epoxide equivalent weight of 181 (commercially available from The Dow Chemical Company as D.E.R..TM. 383 epoxy resin) as added 136 grams (0.5 equiv.) of tetrabromobisphenol A and an indicated amount of catalyst. In two of the examples or comparative experimetns 1 or 1.125 milliequiv. of methyl toluene sulfonate (MTS) was added as indicated. The mnixture as stirred at 130.degree. C. until the tetrabromobisphenol A was dissolved, then cooled to 80.degree. C. and the indicated catalyst was added. The homogeneous resin was then stored at 52.degree. C. and the viscosity measured at 100.degree. C. was measured periodically. The result are given in Table V.

The procedure of precatalyzed resin formulation B was employed except that 0.125 millequiv. of sulfanilamide was added along with the tetrabromobisphenol A, and the mixture was stirred and heated to 150.degree. C. until homogeneous, then cooled to 80.degree. C. and the following amounts of catalyst as indicated was added. The homogeneous resin was then stored at 52.degree. C. and the viscosity measured at 100.degree. C. was measured periodically. The results are given in Table VI.

To 45.3 grams (0.25 equiv) of D.E.R..TM. 383 epoxy resin as described above, 34 grams (0.125 equiv.) of tetrabromobisphenol A and 5.37 grams (0.125 equiv.) of sulfanilamide were added 1 milliequiv. of the indicated catalyst. A small amount of the resin mixture was then analyzed by a DuPont model 1090 Differential Scanning Calorimeter (DSC) at a rate of 2.degree. C. per minute (0.033.degree. C./s). The temperature at which an exothermic reaction was indicated via baseline, drift, the actual onset of a major exotherm, and the exotherm peak were noted. The results are given in Table VII.

The Resin Formulations D were duplicated. The formulations were stored at 80.degree. C. and the viscosity at 100.degree. C. was measured peridically. The results are given in the following Table VIII.

A portion of the precatalyzed Resin Formulations from Table VIII was heated at 177.degree. C. for 4 hours (14400 s) to cure the samples. The glass transition temeprature (Tg) of the cured resins was determined by a DuPont model 1090 Differential Scanning Calorimeter (DSC). The results are given in Table IX.

Epoxy Resin A, 180.8 grams (1.0 equiv.), Extender Compound A, 136.0 grams (0.50 equiv) and 4.3 grams (0.1 equiv.) of curing agent A were heated with stirring under a nitrogen atmosphere at 120.degree. C. until the melt viscosity measured at 100.degree. C. had increased from about 80 cps to 200 cps, an increase in melt viscosity of 150 percent. Then 0.19 ml of Stabilizer A was added. After 5 minutes (300 s) stirring, the homogeneous mixture was cooled to 70.degree. C., 2.16 ml of Catalyst 2 added and the resin cooled to ambient temperature.

A portion (714.8 grams) of the resin from Example 22 was mixed at 130.degree. C. with 47.0 grams (0.76 equiv.) of Curing Agent B until homogeneous, then cured for 4 hours (14400 s) at 150.degree. C. followed by 3 hours (10800 s) at 200.degree. C. The cured casting had a glass transition temperature of 134.9.degree. C. and a GIC value of 0.61 kJ/m2.

Epoxy Resin A (1012.5 grams, 5.6 equiv.), 761.6 grams (2.8 equiv.) of Extender A and 24.08 grams (0.56 equiv.) of Curing Agent A were heated with stirring under a nitrogen atmosphere at 120.degree. C. until the melt viscosity measured at 100.degree. C. had inreased from about 80 cps to 200 cps, an increase in melt viscosity of 150 percent. Then 1.06 grams (5.6 mequiv.) of Stabilizer B was added. After 5 minutes (300 s) at 120.degree. C., the homogeneous mixture was cooled to 70.degree. C., 12.1 ml (11.2 mequiv.) of catalyst 2 added and the resin cooled to ambient temperature.

A portion (731.9 grams) of the resin from Example 24 was mixed at 130.degree. C. with 48.06 grams (0.78 equiv.) of Curing Agent B until homogeneous, then cured for 4 hours (14400 s) at 150.degree. C. followed by 3 hours (10800 s) at 200.degree. C. The cured casting had a glass transition temperature of 137.3.degree. C. and a GIC value of 0.72 kJ/m2.