PROCESS FOR THE PREPARATION OF EPOXY RESINS

Abstract: Epoxy resins are prepared by dehydrohalogenat­ ing the reaction product of a polyhydric phenol with an excess of an epihalohydrin in the presence of a quater­ nary ammonium compound wherein prior to dehydrohalogenation, the excess epihalohydrin is removed and, an organic solvent is added and at least a portion of the dehydro­ halogenation is conducted in the presence of added quantities of a quaternary ammonium compound.

Description: Methods mostly mentioned in the literature concerning the preparation of epoxy resin employ caustic alkali catalyst. The insolubility of the phenolate from the caustic-bisphenol-epichlorohydrin coupling process normally requires a large quantity of water and organic solvent to maintain a single-phase operation. Another preparation method (U.S. patent 3,221,032) proposes to eliminate the solubility problem attributable to phenolate formation by catalyzing the coupling of epichlorohydrin and polyhydric phenol with quaternary ammonium catalyst instead of the conventional caustic catalyst. The dehydrochlorination is then carried out at a relatively high temperature in the presence of epichlorohydrin. To increase epichlorohydrin yield, it has been proposed (U S. patent 2,943,096) that removal of the unreacted epichlorohydrin from the coupled intermediate be performed prior to dehydrochlorination of the resin chlorohydrin which would then be carried out in a mixture of solvents other than epichlorohydrin. The disadvantages of this process are undesirable product viscosities and the need to use a mixture of water-soluble and water-insoluble solvents to achieve dehydrochlorination at a rapid enough rate to be practical. Additionally, product viscosity control in the 9,000-10,000 cps (9-10 Pa·s) range has previously required additional process steps (i.e., addition of seed resin, double charging of reactants to the coupling reaction, and post addition of a polyhydric alcohol following dehydrochlorination). From EP-A 31 435 also a process for the preparation of epoxy resins is known, which comprises reacting a polyhydric phenol with an excess epihalohydrin in the presence of a quaternary ammonium catalyst. The present invention describes a process which significantly eliminates the disadvantages and retains most all of the advantages of a non-caustic catalyzed process. Consistent product viscosity and adjustment without additional process steps is achieved by control of the unreacted phenolic OH content in the coupled intermediate prior to dehydrohalogenation, thus minimizing and controlling viscosity building oligomers and high resin bound chloride species. The remaining required product oligomers contributing to viscosity control are formed during dehydrochlorination without significant additional buildup of bound chloride. The processing method according to the invention allows for flexible viscosity control while maintaining a low chloride product, and low coloration. The present invention pertains to an improved process for preparing epoxy resins by (A) reacting at least one polyhydric phenol with at least one epihalohydrin at a molar ratio of epihalohydrin to polyhydric phenol of 3:1 to 30:1, in the presence of at least one quaternary ammonium catalyst at a temperature below the decompostion temperature of the quaternary ammonium catalyst and for a time sufficient to provide a phenolic hydroxyl group conversion of from 90 to 99.99 percent thereby producing a halohydrin intermediate; (B) removing the excess of epihalohydrin from said intermediate; (C) adding an organic solvent or mixture of solvents to the resultant intermediate; (D) dehydrohalogenating the intermediate in the presence of said solvent or solvent mixture and in the presence of added quantities of quaternary ammonium compound in an amount of from 0.0001 to 0.02 part by weight per one part by weight of organic feed and (E) thereafter recovering the resultant epoxy resin; said process being characterized by reducing the content of said quaternary ammonium catalyst from the reaction mixture to less than 200 ppm prior to step (B). Suitable polyhydric phenols which can be employed herein include, for example, those mononuclear and polynuclear polyhydric phenols represented by the formulas wherein each A is independently a divalent hydrocarbon group having from 1 to 12, preferably from 1 to 6 carbon atoms, or A¹ is a trivalent hydrocarbon group having from 1 to 12, preferably from 1 to 6, carbon atoms; each R is independently hydrogen, a hydrocarbyl group having from 1 to 10, preferably from 1 to 4, carbon atoms, a halogen atom, preferably chlorine or bromine, or a hydroxyl group; p has a value of from 1 to 100, preferably from 2 to 50; m has a value from 1 to 6 and n has a value of zero or 1. Also suitable as polyhydric phenols are those represented by the formulas wherein A² is a divalent hydrocarbyl group having from 1 to 18, preferably from 2 to 12 and most preferably from 2 to 6 carbon atoms, a group represented by the following formulas VII, VIII, IX or X or A² can combine with R¹ so as to form a stable heterocyclic ring with the nitrogen atoms; each A³ is independently a divalent hydrocarbyl group having from 1 to 10, preferably from 1 to 4 carbon atoms, each R¹ 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 9 carbon atoms, said alkyl having from 1 to 4, preferably 1 to 3 carbon atoms; each R² is independently hydrogen or an alkyl group having from 1 to 4, preferably 1 to 3 carbon atoms; each R³ is independently hydrogen or an alkyl group having from 1 to 4 carbon atoms; each R⁴ is independently hydrogen, a hydrocarbyl or halogen substituted hydrocarbyl group having from 1 to 9, preferably from 1 to 2 carbon atoms; each R⁸ is the same groups as R¹ except that R⁸ cannot be a hydrogen; each R⁹ is independently a divalent hydrocarbyl group having from 2 to 4, preferably 2 carbon atoms; each X is independently hydrogen, chlorine, bromine or a hydrocarbyl or a hydrocarbyloxy group having from 1 to 9, preferably 1 to 6 carbon atoms; each m¹ independently has a value of zero or 1; n' has an average value of from 0.01 to 6, preferably 0.1 to 4; p' has an average value of from 1 to 10, preferably from 1 to 3; q has an average value of at least 1, preferably from 1 to 150, most preferably from 1 to 100 and usually from 1 to 10 and each y and z independently has a value of 1 or 2. Preferred polyhydric phenol is a bisphenol or mixture of bisphenols, with bisphenol A being the most preferred. Also suitable are polycyclopentadiene polyphenols represented by the formula wherein each R⁵ is independently hydrogen, a hydrocarbyl group having from 1 to 10, preferably from 1 to 4 carbon atoms, a halogen atom, preferably chlorine or bromine or a hydroxyl group or an amino group; n" has a value from 1 to 5; and n"' has a value of from 1 to 10, preferably from 3 to 6. Suitable such polycyclopentadiene polyphenols and methods for their preparation are described in U.S. 4,390,680 issued to Donald L. Nelson on June 28, 1983. Suitable epihalohydrins which can be employed herein include those represented by the following formula wherein R⁶ is hydrogen or a hydrocarbyl group having from 1 to 4 carbon atoms and X¹ is a halogen, preferably chlorine or bromine. The most preferred is epichorohydrin. The epihalohydrin and the polyhydric phenol compound are employed in a molar ratio of from 3:1 to 30:1, preferably from 6:1 to 12:1, respectively. Suitable dehydrohalogenating agents which can be employed herein include alkali metal hydroxides such as, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide or mixtures thereof. 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 include ketones, aromatic hydrocarbons, halogenated aliphatic compounds such as, for example, methyl isobutyl ketone, methyl ethyl ketone, toluene, xylene, methylene chloride, ethylene dichloride, and mixtures thereof. The preferred solvents are methyl isobutyl ketone, methylethyl ketone, toluene or a mixture thereof. The most preferred solvent is methyl isobutyl ketone. The amount of solvent which is employed will depend on the particular solvent and phenolic hydroxyl compound being employed. The solvent generally ranges from 40 to 80 weight percent, preferably from 55 to 65 weight percent based on the total weight of solvent and intermediate product. Any known quaternary ammonium catalyst employed in the preparation of epoxy resins is suitable catalyst in this invention. Examples of such catalysts can be found in U.S. Patent 3,221,032. Particularly useful as catalysts in the present invention are quarternary ammonium halides. Preferred catalysts are aryl trialkyl ammonium halides. The most preferred catalyst is benzyl trimethyl ammonium chloride. The amount of catalyst employed in the coupling reaction (Step A) is any quantity which will suitably catalyze the reaction between the polyhydric phenol and epihalohydrin. Usually, quantities of from 0.005 to 0.15 moles of catalyst per mole of polyhydric phenol is employed with from 0.01 to 0.02 mole being preferred. The coupling reaction (Step A) is usually conducted at a temperature of from 35° to 110°C, preferably from 40°C to 70°C. Higher temperatures tend to produce undesirable by products and β-chlorohydrin intermediate product instead of the more desirable α-chlorohydrin intermediate product. The excess epihalohydrin and glyceroldihalohydrin should be removed at the lowest temperature, time without causing an adverse increase in residual amounts of epihalohydrin and glycerol dihalide in the intermediate product which is subsequently mixed with solvent and dehydrohalogenated to produce the epoxy resin. It is preferred to keep the temperature below 120°C. In the dehydrohalogenation reaction (Step D), the reaction temperature, residence time, reactor agitation, amount of additional catalyst, concentration of caustic feed, quantity of caustic feed compared with hydrolyzable chloride in organic feed are all important and are all correlated with each other. The reactor temperature is kept below 110°C. The preferred reactor temperature is 40° to 80°C. Reactor temperatures operating above 80°C have the tendency to produce undesirable solid resin polymers and plug the reactor. The additional catalyst is very important to react the 2,1-chlorohydrin (β-chlorohydrin) components and thus is dependent on the 2,1-chlorohydrin contents in the feed. The high limit of catalyst feed to the reactor is from 0.02 to 0.08 part by weight per 1 part by weight of organic feed in a typical continuous reactor and preferred at one-tenth of this range. The caustic concentration can be from 10 percent to 25 percent but is preferred at 18 percent to 24 percent. Too high a concentration will cause salt precipitation and too low a concentration will result in less efficiency in reactor operation. The equivalents of alkali metal hydroxide per equivalent of hydrolyzable chloride in the organic feed is determined by the type of reactor, reaction temperature and residence time. In a continuous reactor, the preferred equivalent ratio is from 1.05:1 to 1.5:1, while in multi-stage batch reactors it is from 1.05:1 to 1.1:1. Too much caustic in the dehydrohalogenation step is economically undesirable and produces undesirable polymers. The resultant epoxy resin can be recovered by any conventional means, but it is usually recovered by water washing and solvent removal. The amounts of water, preferably deionized water, required is determined by the efficiency of the washing device and product specifications. The preferred ranges of organic feed to water are 4:1 to 15:1 by weight. The washing temperature is preferred close to ambient temperature, 20° to 50°C. Too much washing water will dissolve more solvent in the aqueous phase. The high temperature limit of the solvent removal system is 230°C but it is preferred to remove the solvent at a temperature less than 200°C. The following examples are illustrative of the present invention but are not to be construed as to limit the scope thereof in any manner. EXAMPLE A To a reactor equipped with mechanical agitation and a temperature control device was added a mixture of epichlorohydrin, benzyl trimethyl ammonium chloride as a 60 percent aqueous solution by weight and bisphenol A in a molar ratio of 9.85:0.013:1, respectively. The reaction temperature was maintained at 55°C isothermally and the progress of the reaction was monitored by measuring the content of unreacted phenolic OH. The reaction was stopped at 98.2 percent phenolic OH conversion and the unreacted epichlorohydrin and by-product glycerol dichloride were stripped off using a wipe falling film evaporator at a temperature of 115°C and a pressure of 20 mm Hg. The stripped resin chlorohydrin intermediate had 8.5 percent hydrolyzable chloride by the liquid chromatographic method. This stripped intermediate was then dissolved in methyl isobutyl ketone to provide a 40 percent solution by weight. The dehydrochlorination reaction was carried out in 2 consecutive batches at 80°C. In the first batch reaction, 200 grams of the reactant and 60 grams of 18 percent NaOH were reacted with agitation for one hour (3600 s) and the aqueous phase was separated at the end of the reaction. In the second batch, forty-five grams of 18 percent NaOH and 0.15 gram of a 60 percent solution of benzyl trimethyl ammonium chloride were added to the organic phase from the previous batch and reacted for another 30 minutes (1800 s). The resulting organic phase was rinsed with deionised water twice. The MIBK solvent was removed by a rotary film evaporator using an oil bath as a heat source and maintaining a temperature of 115°C. The resin thus recovered had a viscosity of 8526 cps (8.526 Pa·s), hydrolyzable chloride content of 230 ppm, and a color of <1 on the Gardner scale. Additional experiments were carried out similar to the above except the coupling reaction was stopped at different phenolic OH conversions. The results are summarized in Table I. EXAMPLE B The following example illustrates the effect of temperature on the formation of resin-amine compounds (undesirable) and β-chlorohydrin (undesirable) in the removal of excess epichlorohydrin and by-product glycerin dichlorohydrin. The epichlorohydrin-bisphenol coupling reaction was carried out as in Example A. The resultant coupled intermediate showed negligible amounts of hydrolyzable chloride from β-chlorohydrin (<150 ppm) and resin-amine compounds (<3 ppm using benzyl trimethyl ammonium chloride (BTMAC) as a standard). The epichlorohydrin removal was carried out using a rotary film evaporator under full vacuum (<10 mm Hg) while varying the oil bath temperatures and residence time. The stripped coupled intermediate was cooled down to ambient temperature immediately. The analytical results of the hydrolyzable chloride from β-chlorohydrin and the resin-amine contents are shown in Table II. EXAMPLE C This example demonstrates that the coupling reaction catalyst, quaternary ammonium compound, also functions well in catalyzing the dehydrochlorination, especially with regards to the 2,1-chlorohydrin (beta) components. The stripped coupled intermediate was obtained similar to Example A except higher phenolic OH conversion (>99 percent) was achieved in the coupling reaction. The total hydrolyzable chloride content, from 1,2-(alpha) and 2,1-chlorohydrins (beta), was 7.39 percent. The dehydrochlorination reactions were carried out at 80°C in batch with two caustic (18 percent NaOH) charges and 20 minutes (1200 s) for each batch. The ratio of eq. NaOH/eq. hydrolyzable chloride for the first batch charge was 1.158. The resultant organic product was divided into 4 equal parts for the second batch. The product after the first batch contained a total hydrolyzable chloride concentration of 5,153 ppm, where 1,058 ppm from 2,1-chlorohydrin (beta) compared with 1,060 ppm in the feed. The second caustic charge (0.386 eq. NaOH/eq. hydrolyzable chloride) was carried out with and without additional benzyl trimethyl ammonium chloride and the results are summarized in the following Table III. EXAMPLE D This example demonstrates the effect of removing the coupling catalyst prior to removing the excess epichlorohydrin. A sample of coupled epichlorohydrin-Bisphenol A intermediate prepared as in Example A containing 500 ppm catalyst (benzyl trimethyl ammonium chloride, BTMAC) was divided into two aliquots of 500 ml each. The first aliquot was washed 2 times with 100 ml of deionised water for 3 minutes (180 s) at 40°C. The solution was coalesced after the 2nd wash to remove any entrained water. The resulting benzyltrimethylammonium chloride (BTMAC) concentration was typically less than 200 ppm. Both aliquots (washed and unwashed) were subjected to distillation in the presence of carbon steel filings to remove epichlorohydrin and glycerine dichlorohydrin. The conditions for the final stage of this distillation were 130°C and 10 mm Hg vacuum for 30 minutes (1800 s). The aliquots were dissolved in methyl isobutyl ketone (MIBK) to a 30 percent solids basis and then BTMAC was added to achieve a concentration of 7500 ppm in batch solutions. Each solution was epoxidized 3 times with 130 percent stoichiometric 25 percent aqueous sodium hydroxide. The epoxidation conditions were 60°C for 20 minutes (1200 s). BTMAC was added to the third epoxidation to give a concentration of 2500 ppm. Both solutions were washed 3 times using 100 ml of deionized water per wash. Following the final phase separation of the wash water and the MIBK solution, each aliquot was distilled to remove the MIBK and any other volatiles. The last stage of the distillation was in two steps involving holding the temperature at 150°C for 15 minutes (900 s) and then raising the temperature to 180°C and purging for 15 minutes (900 s) with helium. The results are given in Table IV. Unwashed Washed Resin Bound Chloride 0.188% 0.172% Color (APHA) 400 200

Claims: A process for preparing epoxy resins by (A) reacting at least one polyhydric phenol with at least one epihalohydrin at a molar ratio of epihalohydrin to polyhydric phenol of 3:1 to 30:1, in the presence of at least one quaternary ammonium catalyst at a temperature below the decomposition temperature of the quaternary ammonium catalyst and for a time sufficient to provide a phenolic hydroxyl group conversion of from 90 to 99.99 percent thereby producing a halohydrin intermediate; (B) removing the excess of epihalohydrin from said intermediate; (C) adding an organic solvent or mixture of solvents to the resultant intermediate; (D) dehydrohalogenating the intermediate in the presence of said solvent or solvent mixture and in the presence of added quantities of quaternary ammonium compound in an amount of from 0.0001 to 0.02 part by weight per one part by weight of organic feed and (E) thereafter recovering the resultant epoxy resin; said process being characterized by reducing the content of said quaternary ammonium catalyst from the reaction mixture to less than 200 ppm prior to step (B). A process of Claim 1 wherein (i) in step (A), the conversion of phenolic hydroxyl groups is from 95 percent to 99 percent; (ii) the quantity of quaternary ammonium catalyst added in step (D) is from 0.002 to 0.008 part by weight per one part by weight of organic feed; (iii) step (A) is conducted at a temperature of from 35°C to 110°C; (iv) the quantity of catalyst employed in step (A) is from 0.005 to 0.15 mole per mole of polyhydric phenol; (v) step (D) is conducted at a temperature below 110°C; and (vi) sodium hydroxide is employed as the dehydrohalogenation agent in a quantity which provides an equivalent ratio of NaOH to hydrolyzable chloride of from 1.05:1 to 1.5:1 in a continuous reactor and from 1.05:1 to 1.1:1 in a multistage batch reactor. A process of Claim 2 wherein (i) the quantity of quaternary ammonium catalyst added in step (D) is from 0.002 to 0.008 part by weight per one part by weight of organic feed; (ii) step (A) is conducted at a temperature of from 40°C to 70°C; and (iii) step (D) is conducted at a temperature of from 40°C to 80°C. A process of Claim 1 wherein (i) said polyhydric phenol is a bisphenol or mixture of bisphenols; (ii) said epihalohydrin is epichlorohydrin; (iii) said solvent is methyl isobutyl ketone, methyl ethyl ketone, toluene or a mixture thereof; and (iv) said quaternary ammonium compound is a quaternary ammonium halide. A process of Claim 4 wherein (i) said bisphenol is bisphenol A; and (ii) said solvent is methyl isobutyl ketone. A process of Claim 2 wherein (i) said polyhydric phenol is a bisphenol or mixture of bisphenols; (ii) said epihalohydrin is epichlorohydrin; (iii) said solvent is methyl isobutyl ketone, methyl ethyl ketone, toluene or a mixture thereof; and (iv) said quaternary ammonium compound is a quaternary ammonium halide. A process of Claim 6 wherein (i) said bisphenol is bisphenol A; and (ii) said solvent is methyl isobutyl ketone. A process of Claim 3 wherein (i) said polyhydric phenol is a bisphenol or mixture of bisphenols; (ii) said epihalohydrin is epichlorohydrin; (iii) said solvent is methyl isobutyl ketone, methyl ethyl ketone, toluene or a mixture thereof; and (iv) said quaternary ammonium compound is a quaternary ammonium halide. A process of Claim 8 wherein (i) said bisphenol is bisphenol A; and (ii) said solvent is methyl isobutyl ketone.

Inventors: CHANG, FENG-CHIH, HEARN, ROBERT L., J.R, HEATHER, MICHAEL L., SHIRTUM, ROBERT P.
Applicants: THE DOW CHEMICAL COMPANY
Application year: 1986
Main classification: C08G59
IPC codes: C08G59