Preparation of Epoxy Resins

The present invention pertains to the preparation of glycidyl ethers.

The preparation of glycidyl ethers by the reaction of an aromatic hydroxyl-containing compound with epihalohydrin in the presence of a base is well known as disclosed by Lee and Neville in HANDBOOK OF EPOXY RESINS, McGraw-Hill, 1967. Because of increased material costs and since in most instances, the reaction is conducted in excess epihalohydrin, any increase in epihalohydrin yields provide for a considerable economy in manufacturing costs. Also, particularly when the epoxy resin is to be employed in electrical applications, it is desired that the epoxy resin have low hydrolyzable halide levels. The present invention provides a process for maximizing epihalohydrin yields and also produces epoxy resins low in hydrolyzable halide.

The present invention pertains to an improvement in a method for preparing glycidyl derivatives of compounds having at least one aromatic hydroxyl group or aromatic amine group per molecule by reacting at least one compound having at least one aromatic hydroxyl group or aromatic amine group per molecule with an excess of at least one epihalohydrin in the presence of an alkali metal hydroxide and subsequently recovering the glycidyl derivatives; wherein the improvement resides in

(1) conducting the reaction in the presence of an organic solvent which codistills with water and said epihalohydrin at a boiling point below the boiling point of the lowest boiling compound among the components in the reaction mixture;

(2) conducting the reaction under a reduced pressure sufficient to provide a distillate with a boiling point of from about 45.degree. C. to about 80.degree. C., preferably from about 55.degree. to about 70.degree. C.;

(3) employing said alkali metal hydroxide as an aqueous solution and adding said aqueous alkali metal hydroxide in a continuous or intermittent manner over a period of from about 0.5 to about 10, preferably from about 1 to about 5 hours;

(4) continuously removing water by means of codistillation at a rate such that the water content in the reaction mixture is less than about 6%, preferably from about 1.5 to about 4 percent by weight;

(5) separating the water from the distillate and returning the solvent and epihalohydrin to the reaction mixture.

Suitable compounds having at least one aromatic hydroxyl group which can be employed herein include, for example, phenols, bisphenols, novolac resins, polyvinyl phenols, the corresponding amine compounds and the like, such as those represented by the following formulas: ##STR1## wherein each A is independently a divalent hydrocarbon group having from 1 to about 12, preferably from 1 to about 6 carbon atoms, --O--, --S--, --S--S--, ##STR2## A' is a trivalent hydrocarbon group having from 1 to about 12, preferably from 1 to about 6, carbon atoms; each R is independently hydrogen, a hydrocarbyl group having from 1 to about 10, preferably from 1 to about 4, carbon atoms, a halogen atom, preferably chlorine or bromine or a hydroxyl group or an amino group; each Z is independently --OH or NH.sub.2 ; p has a value of from about 1 to about 100, preferably from about 2 to about 50; m has a value from about 1.00 to about 6 and n has a value of zero or 1.

Also suitable as compounds having at least one aromatic hydroxyl or aromatic amine group per molecule are those represented by the formulas ##STR3## wherein each R is a divalent hydrocarbyl group having from 1 to about 18, preferably from about 2 to about 12 and most preferably from about 2 to about 6 carbon atoms, a group represented by the following formulas IX, X, XI or XII ##STR4## or R can combine with R.sup.1 so as to form a stable heterocyclic ring with the nitrogen atoms; each A is independently a divalent hydrocarbyl group having from 1 to about 10, preferably from 1 to about four carbon atoms, --O--, --S--, --S--S--, ##STR5## each R.sup.1 is independently hydrogen, a 2,3,-epoxypropyl group, a 2-alkyl-2,3-epoxypropyl group, a monovalent hydrocarbyl group or a hydroxyl substituted monovalent hydrocarbyl group, said hydrocarbyl groups having from 1 to about 9 carbon atoms, said alkyl having from 1 to about 4, preferably 1 to about 3 carbon atoms; each R.sup.2 is independently hydrogen or an alkyl group having from 1 to about 4, preferably 1 to about 3 carbon atoms; each R.sup.3 is independently hydrogen or an alkyl group having from 1 to about 4 carbon atoms; each R.sup.4 is independently hydrogen, a hydrocarbyl or halogen substituted hydrocarbyl group having from 1 to about 9, preferably from 1 to about 2 carbon atoms; each R.sup.8 is independently selected from the group represented by formula XIV or the same groups as R.sup.1 except that R.sup.8 cannot be a hydrogen; each R.sup.9 is independently a divalent hydrocarbyl group having from 2 to about 4, preferably 2 carbon atoms; each Z is independently --OH or --NH.sub.2 ; each X is independently hydrogen, chlorine, bromine or a hydrocarbyl or a hydrocarbyloxy group having from 1 to about 9, preferably 1 to about 6 carbon atoms; each m independently has a value of zero or 1; n has an average value of from about 0.01 to about 6, preferably 0.1 to about 4; p has an average value of from 1 to about 10, preferably from 1 to about 3; q has an average value of at least 1, preferably from 1 to about 150, most preferably from 1 to about 100 and usually from 1 to about 10 and each y and z independently has a value of 1 or 2.

Also suitable are polycyclopentadiene polyphenols or aromatic polyamines represented by the formula ##STR6## wherein Z is --OH or --NH.sub.2 and n has a value from 1 to about 5; n' has a value of from about 1 to about 10, preferably from 3 to about 6; each R is independently hydrogen, a hydrocarbyl group having from 1 to about 10, preferably from 1 to about 4 carbon atoms, a halogen atom, preferably chlorine or bromine or a hydroxyl group or an amino group.

Suitable such polycyclopentadiene polyphenols and methods for their preparation can be found in U.S. Pat. No. 4,390,680 issued to Donald L. Nelson on June 28, 1983 which is incorporated herein by reference. The polycyclopentadiene aromatic polyamines can be prepared in a similar manner by substituting an aromatic amine for the phenolic compound.

Also suitable are compounds containing both at least one aromatic hydroxyl group and at least one aromatic amine group such as, for example, hydroxy aniline, aminoxylenol and the like.

Suitable epihalohydrins which can be employed herein include those represented by the following formula ##STR7## wherein R is hydrogen or a hydrocarbyl group having from 1 to about 4 carbon atoms and X is a halogen, preferably chlorine or bromine.

The epihalohydrin and the aromatic hydroxyl or aromatic amine compound are employed in a molar ratio of from about 2:1 to about 10:1, preferably from about 2:1 to about 6:1, respectively.

Suitable alkali metal hydroxides which can be employed herein include, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide or mixtures thereof. The alkali metal hydroxide is employed as an aqueous solution, usually at a concentration of from about 20 to about 50, preferably from about 40 to about 50 percent by weight.

The amount of alkali metal hydroxide which is employed in the process of the present invention is from about 0.80 mole to about 1.2 mole of alkali metal hydroxide, preferably from about 0.90 mole to 1.0 mole per each aromatic hydroxyl group and aromatic amine hydrogen.

The alkali metal hydroxide can be added either continuously or incrementally, but never is all of the alkali metal hydroxide added in one increment.

Suitable solvents which can be employed herein include any solvent which does not react with any component in the reaction mixture, is partially or wholly miscible with water, forms a codistillate with the epihalohydrin and water and the distillate has a boiling point below that of the lowest boiling component of the reaction mixture at the pressure employed. Suitable such solvents include primary and secondary alcohols such as, for example, 1-methoxy-2-hydroxy propane, 1-butoxy-2-hydroxy ethane, cyclohexanol. The secondary alcohols are preferred.

The amount of solvent which is employed will depend on the particular solvent and hydroxyl or amino compound being employed. The solvent generally ranges from about 5 to about 50 weight percent, preferably from about 10 to about 40 weight percent based on the total weight of reactants.

Suitable pressures which are employed in the process of the present invention is that which will provide the codistillate with a boiling point of from about 45.degree. C. to about 80.degree. C., preferably from about 55.degree. C. to about 70.degree. C.

The reaction is conducted for a length of time such that the quantity of phenolic hydroxyl groups remaining in the reaction mixture is not greater than about 0.5, preferably not greater than about 0.2 percent by weight.

Upon completion of the reaction, the resultant epoxy resin is finished in any of the methods normally employed. The excess epihalohydrin is usually removed by distillation and the salt removed by filtration, centrifugation and/or water washing.

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

The following components were employed in the examples and comparative experiments.

PHENOLIC COMPOUND A was a phenol-formaldehyde novolac resin having an average hydroxyl equivalent weight of about 104.5 and an average phenolic hydroxyl functionality of about 5.7.

PHENOLIC COMPOUND B was a phenol-formaldehyde novolac resin having an average hydroxyl equivalent weight of about 101 and an average phenolic hydroxyl functionality of about 3.6.

PHENOLIC COMPOUND C was bisphenol A.

PHENOLIC COMPOUND D was 4,4'-dihydroxybiphenyl.

PHENOLIC COMPOUND E was a cresol-formaldehyde novolac resin having an average hydroxyl equivalent weight of about 118.5 and an average phenolic hydroxyl functionality of about 5.7.

PHENOLIC COMPOUND F was a composition containing about 60 to 70 weight percent of tri(hydroxyphenyl) methane, the remaining 30-40% being higher homologs thereof.

PHENOLIC COMPOUND G was a polycyclopentadiene polyphenol resin having an average hydroxyl equivalent weight of about 180 and an average phenolic hydroxyl functionality of about 3.2

PHENOLIC COMPOUND H was polycyclopentadiene polyresorcinol resin having an average hydroxyl equivalent weight of about 93 and an average phenolic hydroxyl functionality of about 5.5.

Into a one liter reaction vessel equipped with temperature and pressure control and indicating means, a means for the continuous or intermittent addition of aqueous sodium hydroxide, a means for condensing and separating water from a codistillate mixture of water, solvent and epichlorohydrin and a means for returning the solvent and epihalohydrin to the reaction vessell was added 104.5 grams (1 equivalent) of phenolic compound A, 370 grams (4 equivalents) of epichlorohydrin and 247 grams of the methylether of propylene glycol (1-methoxy-2-hydroxy propane) as a solvent. After stirring at room temperature and atmospheric pressure to thoroughly mix the contents, the temperature was raised to 65.degree. C. and the pressure was reduced to 160 mm Hg absolute. To the resultant solution was continuously added 76 grams, 0.95 equivalent of a 50% aqueous sodium hydroxide solution at a constant rate over a period of 1 hour (3600 s). During the addition of the sodium hydroxide, the water was removed by codistilling with epichlorohydrin and solvent. The distillate was condensed thereby forming two distinct phases, an aqueous phase (top) and an organic epichlorohydrin-solvent phase (bottom). The organic phase was continuously returned to the reactor. After completion of the sodium hydroxide addition, the reaction mixture was maintained at a temperature of 65.degree. C. and a pressure of about 160 mm Hg absolute for an additional 30 minutes (1800 s). A sample of the reaction mixture was washed to remove salt and subsequently distilled resulting in an epoxidized novolac resin having a hydrolyzable chloride content of 0.02% and an epoxide content of 23.5% which corresponds to an epoxide equivalent weight of about 183. The epichlorohydrin yield was 99% based on an analysis of the reaction mixture for formation of by-products such as glycidol, glycerine monochlorohydrin and glycerine diglycidylether.

In a manner similar to Example 1, the following components and reaction conditions were employed.

104.5 grams (1 equiv.) of phenolic compound A

462.5 grams (5 equiv.) of epichlorohydrin

76 grams (0.95 equiv.) of 50% aqueous sodium hydroxide

The reaction temperature was 65.degree. C. and the reaction pressure was 160 mm Hg absolute. The sodium hydroxide was added over a period of 1 hour (3600 s) and the reaction continued thereafter for a period of 5 hours (18,000 s). During the addition of the sodium hydroxide, the water and epichlorohydrin formed a binary azeotrope which was condensed to form two distinct phases. The organic, epichlorohydrin, (bottom) phase was continuously returned to the reaction mixture.

Even after the 5 hours of additional reaction, only 80% of the phenol-formaldehyde novolac had reacted and the epichlorohydrin yield was only about 80%.

In a manner similar to Example 1, the following components and reaction conditions were employed.

104.5 g (1 equiv.) phenolic compound A

370 g (4 equiv.) epichlorohydrin

247 g propylene glycol methylether (1-methoxy-2-hydroxy propane)

76 g (0.95 equiv.) 50% aqueous sodium hydroxide

The reaction temperature was 105.degree. C., the reaction pressure was atmospheric; and the sodium hydroxide was added continuously over a period of 1 hour (3600 s). During the addition of sodium hydroxide, the water, epichlorohydrin and propylene glycol methylether formed a codistillate which was condensed. The epichlorohydrin and propylene glycol methylether from overhead was recycled to the reaction mixture while the aqueous phase was discarded. After the completion of sodium hydroxide addition, the reaction mixture was further stirred at 105.degree. until all of the caustic has been used up (10-15 minutes, 600-900 s). A sample was taken and analyzed for by-product formation (glycidol, glycerine monochlorohydrin, glycerine and glycerine diglycidyl ether . . . ). Besides .about.5% epichlorohydrin hydrolysis product, approximately 6% of epichlorohydrin polymers were observed which indicated a yield on epichlorohydrin of .about.89%. A sample of the reaction mixture was washed to remove salt and then distilled to give an epoxy novolac with a hydrolyzable chloride content of 0.2% (10 times higher than the one under a reduced pressure) and an epoxide content of 21.6%.

The procedure of Comparative Experiment B was followed except that the reaction was carried out at 65.degree. C., but no water was removed by codistillation. The water from the sodium hydroxide addition and the water of reaction remained in the reaction mixture. The yield of epichlorohydrin was 92%. A sample of the reaction mixture was washed to remove salt and then distilled thereby resulting in an epoxidized novolac having a hydrolyzable chloride content of 0.1% (5 times that produced in Example 1).

In a manner similar to Example 1, the following components and conditions were employed.

51 grams (0.5 equiv.) of phenolic hydroxyl compound B 231.5 grams (2.5 equiv.) of epichlorohydrin

75 grams cyclohexanol

38 grams (0.475 equiv.) of 50% aqueous sodium hydroxide

The reaction temperature was 60.degree. C. and the reaction pressure was about 155 mm Hg. The sodium hydroxide was added over a period of 1 hour (3600 s) and the reaction continued for an additional 15 minutes (900 s). The product had an epoxide content of 24.51 percent which corresponds to an equivalent weight of about 175 and a hydrolyzable chloride content of about 0.02%. The epichlorohydrin yield was 98%.

In a manner similar to Example 1, the following components and conditions were employed.

114 grams (1 equiv.) of phenolic compound C

370 grams (4 equiv.) of epichlorohydrin

247 grams of propylene glycol methylether (1-methoxy-2-hydroxy propane)

80 grams (1 equiv.) of 50% aqueous sodium hydroxide

The reaction temperature was 65.degree. C. and the reaction pressure was about 160 mm Hg absolute. The sodium hydroxide was added over a period of one hour (3600 s) and the reaction was continued for an additional 15 minutes (900 s).

The product had an epoxide content of 24% corresponding to an epoxide equivalent weight of about 179 and a hydrolyzable chloride content of 0.02%. The epichlorohydrin yield was 99%.

In a manner similar to Example 1, except where noted, the following components and conditions were employed.

93 grams (1 equiv.) of phenolic compound D

370 grams (4 equiv.) of epichlorohydrin

330 grams of propylene glycol methylether (1-methoxy-2-hydroxy propane)

80 grams (1 equiv.) 50% aqueous sodium hydroxide

The reaction temperature was 70.degree. C. and the reaction pressure was 190 mm Hg absolute. The sodium hydroxide was added over a period of 1 hour (3600 s). The reaction was continued for an additional 15 minutes (900 s). The product was insoluble, and precipitated from the reaction mixture; therefore, 330 grams of water was added to the reaction mixture to facilitate the precipitation thereof and the mixture was cooled to 30.degree. C. The solid was suction filtered, washed on the filter with water and methanol and then dried in a vacuum oven thereby producing a white solid having a softening point of 155.degree. C., an epoxide content of 26.4% corresponding to an epoxide equivalent weight of about 163. The hydrolyzable chloride content was 0.02%. The epichlorohydrin yield was 98%.

4,4'-methylenedianiline (99.2 g, 0.5 mole), epichlorohydrin (370 g, 4 eq.) and 1-methoxy-2-hydroxypropane (92.5 g) were stirred under atmospheric pressure to achieve a complete solution. The solution was heated to 80.degree. and maintained at that temperature for 3 hours (10800 s). The reaction was then cooled to 65.degree. and under a reduced pressure of 160 mm Hg absolute. Aqueous sodium hydroxide (50% concentration, 176 g, 1.1 eq.) was added to the reaction mixture at a constant rate over a period of 1 hour (3600 s). During the addition of caustic, the water was removed by codistilling with epichlorohydrin and 1-methoxy-2-hydroxypropane. The distillate was condensed and the organic phase was continuously returned to the reaction mixture. After the addition of caustic was completed, the reaction mixture was further stirred at 65.degree., 160 mm Hg for another 15 minutes. Work-up of product as in Example 1 gave a product with 34.8% epoxide.

In a manner similar to Example 1, the following components and conditions were employed.

59.3 grams (0.5 equiv.) of cresol-formaldehyde novolac (phenolic compound E)

185 grams (2.0 equiv.) of epichlorohydrin

46 grams 1-methoxy-2-hydroxypropane

38 grams (0.475 equiv.) of 50% aqueous sodium hydroxide

The reaction temperature was 65.degree. C. and the reaction pressure was about 180 mm Hg. The sodium hydroxide was added over a period of 1 hour (3600 s) and the reaction continued for an additional 15 minutes (900 s). The water content in the reaction mixture was found to be 1.3%.

The product had an epoxide content of 20.5% corresponding to an epoxide equivalent weight of about 210 and a hydrolyzable chloride content of 0.02%. The epichlorohydrin yield was 98%.

In a manner similar to Example 1, the following components and conditions were employed.

97.3 grams (1.0 equiv.) of tri(hydroxyphenyl)methane (phenolic compound F)

555 grams (6.0 equiv.) of epichlorohydrin

139 grams 1-methoxy-2-hydroxypropane

76 grams (0.95 equiv.) of 50% aqueous sodium hydroxide.

The reaction temperature was 65.degree. C. and the reaction pressure was 195 mm Hg. The sodium hydroxide was added over a period of 1 hour (3600 s) and the reaction continued for an additional 30 minutes (1800 s). The water content in the reaction mixture was found to be 1.9%.

The product had an epoxide content of 26.5% corresponding to an epoxide equivalent weight of about 162 and a hydrolyzable chloride content of 0.02%. The epichlorohydrin yield was 98%.

In a manner similar to Example 1, except where noted, the following components and conditions were employed.

90 grams (0.5 equiv.) of polycyclopentadiene polyphenol (phenolic compound G)

185 grams (2.0 equiv.) of epichlorohydrin

46 grams propylene glycol methylether

38 grams (0.475 equiv.) of 50% aqueous sodium hydroxide

The reaction temperature was 65.degree. C. and the reaction pressure was about 180 mm Hg. The sodium hydroxide was added over a period of 1 hour (3600 s) and the reaction continued for an additional 30 minutes (1800 s). The product had a softening point of about 85.degree. C. with an epoxide content of 15.8 percent and a hydrolyzable chloride content of about 0.02%. The epichlorohydrin yield was 98%.

In a manner similar to Example 1, except where noted, the following components and conditions were employed.

93 grams (1.0 equiv.) of polycyclopentadiene polyresorcinol (phenolic compound H)

370 grams (4.0 equiv.) of epichlorohydrin

92 grams propylene glycol methyl ether

76 grams (0.95 equiv.) of 50% aqueous sodium hydroxide

The reaction temperature was 65.degree. C. and the reaction pressure was about 180 mm Hg. The sodium hydroxide was added over a period of 1 hour (3600 s) and the reaction continued for an additional 30 minutes (1800 s). The product had a softening point of about 89.degree. with an epoxide content of 24.7 percent and a hydrolyzable chloride content of about 0.02%. The epichlorohydrin yield was 98%.

A series of experiments were conducted in a manner similar to Example 1 except that the amount of water in the reaction vessel was varied. The following components and reaction conditions were employed.

104.5 grams (1 equiv.) of phenolic compound A

370 grams (4 equiv.) of epichlorohydrin

92.5 grams of the methylether of propylene glycol (1-methoxy-2-hydroxy propane) as a solvent

After stirring at room temperature and atmospheric pressure to thoroughly mix the components, the temperature was raised to 65.degree. and the pressure was reduced to a predetermined value. To the resultant solution was continuously added 76 grams, 0.95 equivalent, of a 50% aqueous sodium hydroxide solution at a constant rate over a period of two hours (7200 s). During the addition of the sodium hydroxide, the water was removed by codistilling with epichlorohydrin and solvent. The distillate was condensed thereby forming two distinct phases. The organic phase (bottom) was continuously returned to the reactor. After completion of the sodium hydroxide addition, the reaction mixture was maintained at a temperature of 65.degree. for an additional 30 minutes (1800 s). A sample was taken for analysis of by-products to determine the epichlorohydrin yield and the rest of reaction mixture was washed to remove salt and subsequently distilled resulting in an epoxidized novolac resin. Results of experiments were as follows:

At too low a water content, epichlorohydrin yield is high but insoluble polymer formation requires filtration in order to remove the polymer. At water contents of between 1.5-4.0%, the epichlorohydrin yields are 98% or above and insoluble polymer formation is less than 1%. A water content of 6% and above in the reaction mixture resulted in reduced epichlorohydrin yield and also increased the hydrolyzable chloride content of the resultant product.