GB2140798A - Catalytic process for the preparation of epoxy resins - Google Patents

Abstract

A process for the preparation of low molecular weight epoxy resins essentially constituted by the diglycidyl ethers of bisphenol A, or bisphenol F, comprises the reaction of an epihalogenohydrin with bisphenol A, or bisphenol F, in the presence of catalysts based on organic sulphur-containing compounds selected from the group consisting of sulphones, sulphonamides, esters of sulphuric acid, heterocyclic thio-compounds, thioacids, thiodiphenols, dithio-heterocyclic compounds, and subsequently with the addition of an alkali, until the reaction is complete.

Description

SPECIFICATION Catalytic process for the preparation of epoxy resins The present invention relates to the preparation of low molecular weight epoxy resins by the reaction of epihalohydrin with bisphenol A or bisphenol F in two reaction stages: a first stage catalysed by organic sulphur-containing compounds and a second stage in which the reaction is completed in the presence of an alkali.

More particularly, the invention relates to the preparation of low molecular weight epoxy resins, by the reaction of propylenic epihalohydrin with bisphenol A, containing from 0 to 1 mole of polycondensed polymers:

where n is between 1 and 7 per 100 moles of

and the preparation of low molecular weight epoxy resins, by the reaction of propylenic epichlorohydrin with bisphenol F, containing from 0 to 1 moles of polycondensed polymers:

where n is between 1 and 30, per 100 moles of

low molecular weight epoxy resins are valued products for which there are numerous applications in the art. For example, they are used in the field of paints and coatings generally, in the field of binders (concrete and bitumen flooring and paving) as well as in numerous other sectors.These resins are also used in the electronics field (casting, printed circuits, sealing and encapsulation of electrical parts).

It is known in the art that epoxy resins can be manufactured by feeding a concentrated, aqueous, alkaline solution in to a solution of bisphenol in an excess of epichlorohydrin.

Examples of catalysts and methods of operation used in the art for the synthesis of epoxy resins are: addition of a benzyltrimethylammonium chloride catalyst (U.S. Patent No. 3,221,032) at a temperature of 150to and at 50 psig, giving a liquid epoxy resin with an epoxy equivalent of more than 1 90 which is too high, addition of alkalis such as lithium hydroxide (U.S.A.

2,943,095) with over-long reaction times (50 hours); in addition of Na2S204 (U.S.A.

2,879,259) giving a solid polymer with an epoxy equivalent of more than 900. In U.S. Patent 3,336,342 the use of organic sulphur-containing compounds has already been described but these are limited to compounds capable of forming sulphonium salts with epichlorohydrin. The catalytic activity of these compounds is, moreover, unsatisfactory, giving products with viscosities and epoxy equivalents which are too high and reaction times which are too long: in the synthesis of the diglycidyl ether of bisphenol A, the viscosity is more than 20,000 cps, the epoxy equivalent is more than 190, the reaction times are 1 5 to 40 hours. In the synthesis of epoxy resins starting from bisphenol A and propylenic epihalohydrin there is difficulty in obtaining products with low molecular weights, corresponding to those of the formula (Ap) where n is zero or very close to zero.Indeed, by known processes, epoxy resins are obtained with values of n of from 1 5 to about 30, corresponding to an epoxy equivalent of from 1 90 to 210 (grams of resin containing one epoxy group). Furthermore the viscosity of the resin is from 20,000 to 40,000 cps at 25"C, which is too high and necessitates the use of special, expensive machinery for working the resin. It has therefore been attempted in the art to reduce the said value of n by various devices, for example, by increasing the molar ratio between the epichlorohydrin and the bisphenol loaded into the reaction environment. Completely satisfactory results have not however been obtained with regard to the molecular weight and viscosity of the resin produced.The high viscosity is disadvantageous in that it create difficulties in various applications, for example, in casting and in the use of inert fillers. Also, in the case of epoxy resins obtained from bisphenol F and propylenic epichlorohydrin, products are obtained with high epoxy equivalents, from 1 90 to 200, and high viscosities, from 50,000 to 60,000 cps.

Furthermore the epoxy resins obtained by the previous processes contain relatively high quantities of hydrolysable chlorine which causes that resins catalysed by amino-hardeners have short pot lives. Short pot lives involve highly exothermic hardening which may create internal strains in the manufactured articles, these being particularly harmful in applications in the electronics field (flaw formation and fracturing) and in paints which become readily attacked by corrosive agents.

The known processes for the preparation of epoxy resins give relatively poor reaction yields and the resins obtained contain rather large quantities of by-products. These latter do not participate in the hardening of the resin and remain as inert substances in the manufactured articles, adversely affecting the mechanical, therme, and electrical characteristics thereof. For example, in the electronics field, bubble formation with the consequent discontinuities in the manufactured article, is particularly harmful while, in the paints field, the formation of pits, cissing and other imperfections is harmful.

It has now been found possible to eliminate, or at least greatly to reduce, the disadvantages of the prior art and to prepare low molecular weight epoxy resins with low values of the epoxy equivalent and of the viscosity, with a very low hydrolysable-chlorine content and with long pot lives in association with amino-type hardeners, with a good reaction yield.

It has now been found, and this is the main object of the present invention, that it is possible to prepare low molecular weight epoxy resins from bisphenol A or bisphenol F and epihalohydric which do not have, or have to a lesser extent, the defects normally found in known resins, if the reaction is carried out in the presence of a catalyst based on sulphur-containing organic compounds chosen from the group consisting of sulphones, sulphonamides, esters of sulphuric acid, heterocyclic thio-compounds, thioacids, thiodiphenols, dithio-heterocyclic compounds, such as:

where R and R, may be -H, -Cl, -Br, -CH20H, -OH, -phenyl, -CH3, -CH2CH3 and higher linear or branched homologues.

The catalyst of the group defined above must be added in quantities of between 0.005 per cent and 0.1 per cent by weight of the reation mass. Larger quantities do not give advantages with regard to the characteristics of the product or the reation rate, and may pollute the products. In the preferred embodiments of the invention, the catalyst's quantities are from 0.01 per cent to 0.08 per cent by weight of the reaction mass. With the use of the said amounts of sulphur-containing organic catalyst from the group defined above, a product is obtained which contains quantities of sulphur which are small enough to be tolerated, also in the case they are not completely removed during the purification washing. The operative methods are essentially those known for this type of reaction. According to one preferred method of carrying out the present invention, the reaction of the epihalohydrin and bisphenol A or bisphenol F is carried out with a molar ratio of from 2:1 to 8:1 in the presence of the organic-sulphur catalysts described above, at temperatures of between 30 and 80"C., at atmospheric pressure and in an inert gas environment over a period of 1 5 to 1 80 minutes. As epihalyhydrins are considered those compounds which contain a halogen atom in a position adjacent the epoxy group. Typical compounds are: 1 ,2-epoxy-3-chlorobutane and 2,3-epoxy-1-chlorobutane. Preferably propylenic epichlorohydrin is used.

After the reaction between epihalohydrin and bisphenol is completed, sodium or potassium hydroxide solution, at concentration of from 10 to 50 percent, is added to the reaction mixture at a temperature of between 40 and 70"C over a period of time preferably between 2 and 4 hours.

The quantity of alkali introduced varies from 2 to 2.1 moles per mole of bisphenol.

The organic phase is then separated from the aqueous phase in the mixture at a temperature of between 30 C and 90"C by decanting and/or centrifuging.

Any excess epihalohydrin is then distilled from the organic phase under vacuum or at atmospheric pressure. The residue is dissolved in an inert solvent, such as toluene, methyl ethyl ketone, methyl isobutyl ketone. The organic solution is washed with a dilute solution of mineral acid or organic acid until it is neutral; the solvent is removed by distillation to obtain the desired diglycidyl ether of the bisphenol with a high purity.

In the preferred embodiments, the alkali treatment is ruined in two stages: the first one before the separation of excess of the epihalohydrin and the second one after the dilution of the reaction mass in the organic solvent.

Typically the second alkali treatment is effected at temperature of from 70 to 90"C and for a period of time of from 15 to 90 minutes with a 0.1 to 0.3 moles of sodium or potassium hydroxide in aq. solution having concentrations of from 10 to 50% by weight per each mole of bisphenol.

The,total amount of alkali used in the two stages does not exceed any way the molar ratio of 2.4:1 in respect of the originary bisphenol.

Example 1 (comparison) 700 g (3.07 moles) of bisphenol A are dissolved in 2266 g (24.5 moles) of epichlorohydrin and heated to 60"C for 30 minutes in a current of inert gas. 1250 g (6.25 moles) of 20% sodium hydroxide are then added at 70"C over a period of 2 hours and 30 minutes. In order to keep the temperature at 70"C, the reaction mass is cooled. After the addition of the alkali, the mass is left under agitation at 70"C for 30 minutes to complete the reaction. The two phases are separated while hot and the excess epichlorohydrin is separated from the organic phase by vacuum distillation. The residue is diluted with 1 000 g of toluene.The reaction product contained in the resulting solution, has the following characteristics: epoxy equivalent: 226 -hydrolysable chlorine: 2.2% by weight In order to remove further hydrogen halide, the solution is heated to 80 to 85"C and reacted with 1 24 g of 20% sodium hydroxide for a period of 60 to 90 minutes. The aqueous layer containing the sodium chloride formed is separated; the organic layer is neutralised with acetic acid, distilled under vacuum to eliminate the solvent and subsequently filtered while hot.Thus a low molecular weight epoxy resin consisting of the diglycidyl ether of bisphenol A is obtained with the following characteristics: epoxy equivalent: 1 96 viscosity at 25 C cps: 26800 --chlorine: 0.1 5% by weight.

Example 2 700 g of bisphenol A (3.07 moles) are dissolved in 2266 g (24.5 moles) of epichlorohydrin and heated in a current of inert gas to 60"C. 0.8 g (0.0053 moles) of 2.2'-thiodiacetic acid (thiodiglycolic acid) are added and'the mixture is agitated for 30 minutes at 60"C.

1 250 g (6.25 moles) of 20% sodium hydroxide are then added at a temperature of 70"C over a period of 2.5 hours. Once the sodium hydroxide has been added the mass is left under agitation at 70"C for 30 minutes to complete the reaction; the two phases are then separated and the excess epicholohydrin is removed from the organic phase by vacuum distillation.

The residue is diluted with inert solvent: 1000 g of toluene.

The characteristics of the reaction product obtained are: epoxy equivalent: 210 -hydrolysable chlorine: 2.52% by weight.

In order to remove further hydrogen halide, the solution is heated to 80 to 85"C and reacted with 125 g of 20% sodium hydroxide for a period of 60 minutes. The sodium chloride formed is separated; the organic layer is neutralised, the solvent distilled under vacuum and subsequently the product is filtered while hot. Thus a low molecular weight epoxy resin consisting of the diglycidyl ether of bisphenol A is obtained with the following characteristics: epoxy equivalent: 1 85 viscosity at 25"C: 10500 cps -hydrolysable chlorine: 0.04% by weight.

Example 3 700 g of bisphenol A (3.07 moles) are dissolved in 2266 g (24.5 moles) of epichlorohydrin and heated in a current of inert gas to 60 C; 0.7 g (0.0032 moles) of bis-4,4'-hydroxyphenyl sulphide (4,4'-thiodiphenol) are added and agitation is continued for 30 minutes at 60"C.

1 250 g (6.25 moles) of 20% sodium hydroxide are then added at a temperature of 70"C over a period of 2.5 hours. After the addition of the alkali, the mass is left under agitation at 70"C for 30 minutes to complete the reaction. The two phases are then separated and the excess epichlorohydrin is removed from the organic phase by vacuum distillation. The residue is diluted with intert solvent: 1000 g of toluene.

The characteristics of the reaction product obtained are: epoxy equivalent: 21 8 -hydrolysable chlorine: 3% by weight.

In order to remove further hydrogen halide, the solution is heated to 80 to 85"C and reacted with 1 60 g of 20% sodium hydroxide over a period of 90 minutes. The sodium chloride formed is separated; the organic layer is neutralised, the solvent distilled under vacuum and the product subsequently filtered while hot.

A low molecular weight epoxy resin, consisting of the diglycidyl ether of bisphenol A is thus obtained with the following characteristics: epoxy equivalent: 180 viscosity at 25"C: 10300 cps hydrolysable chlorine: 0.05% by weight.

Example 4 700 g (3.07 moles) of bisphenol A are dissolved in 2266 9 (24.5 moles) of epichlorohydrin and heated in a current of inert gas to 60"C.0.5 9 (0.0032 moles) of diethyl sulphate are added and agitation is continued for 30 minutes at 60"C. 12509(6.25 moles) of 20% sodium hydroxide are then added at 70"C over a period of 2 hours and 30 minutes.

After the addition of the alkali, the mass is left under agitation at 70"C for 30 minutes to complete the reaction. The two phases are separated and the excess epichlorohydrin is separated from the organic phase by vacuum distillation. The residue is diluted with inert solvent: 1000 g of toluene. The characteristics of the reaction product are: epoxy equivalent: 208 --hydrolysable chlorine: 2.6% by weight In order to remove further hydrogen halide, the solution is heated to 80 to 85"C and reacted with 1 28 g of 20% sodium hydroxide for a period of 60 to 90 minutes. The sodium chloride formed is separated, the organic layer is neutralised and distilled under vacuum and subsequently filtered while hot.Thus a low molecular weight epoxy resin consisting of the diglycidyl ether of bisphenol A is obtained with the following characteristics: epoxy equivalent: 1 82 viscosity at 25"C cps: 10600 --hydrolysable chlorine: 0.03% by weight.

Example 5 700 g of bisphenol A (3.07 moles) are dissolved in 2266 g (24.5 moles) of epichlorohydrin and heated in a current of inert gas to 60"C.

One gram (0.004 moles) of bis-4,4'-hydroxyphenyl sulphone are added and agitation is maintained for 30 minutes at 60"C. 12509(6.25 moles) of 20% sodium hydroxide are then added at a temperature of 70"C over a period of 2 hours and 30 minutes.

After the addition of the alkali, the mass is left under agitation at 70"C for 30 minutes to complete the reaction. The two phases are then separated and the excess epichlorohydrin is removed from the organic phase by vacuum distillation. The residue is diluted with inert solvent: 1000 g of toluene. The characteristics of the reaction product obtained are: epoxy equivalent: 21 5 -hydrolysable chlorine: 2.8% by weight.

In order to remove further hydrogen halide, the solution is heated to 80 to 85"C and reacted with 1 35 9 of 20% sodium hydroxide for a period of 60 to 90 minutes. The sodium chloride formed is separated and the organic layer is neutralised, vacuum distilled and subsequently filtered while hot. Thus a low molecular weight epoxy resin consisting of the diglycidyl ether of the bisphenol A is obtained which has the following characteristics: epoxy equivalent: 185 viscosity at 25"C cps: 10680 -hydrolysable chlorine: 0.08% by weight.

Example 6 (comparison) 620 9 of bisphenol F (3.9 moles) are dissolved in 2280 g (24.64 moles) of epichlorohydrin and heated in a current of inert gas to 60"C for 60 minutes. 11 75 9 (5.87 moles) of 20% sodium hydroxide are then added over a period of 3 hours at 70"C. In order to keep the temperature at 70"C the reaction mass is cooled.

After the addition of the akali, the mass is left under agitation at 70"C for 30 minutes to complete the reaction. The two phases are separated while hot and the excess epichlorohydrin is removed from the organic phase by vacuum distillation. The residue is diluted with 900 9 of methyl isobutyl ketone. The reaction product, has a hydrolysable chlorine content of 4% by weight.

In order to remove further hydrogen halide, the solution is heated to 80 to 85"C and reacted with 1 95 g of 20% sodium hydroxide over a period of 60 to 90 minutes. The aqueous layer containing the sodium chloride formed is separated; the organic layer is neutralised, vacuum distilled to eliminate the solvent and subsequently filtered while hot. Thus a low molecular weight epoxy resin consisting of the polyglycidyl ether of bisphenol F is obtained with the following characteristics: epoxy equivalent: 1 90 viscosity at 25"C cps: 50800 -hydrolysable chlorine: 0.7% by weight.

Example 7 620 g of bisphenol F (3.1 moles) are dissolved in 2280 9 of epichlorohydrin (24.64 moles) and heated in a current of inert gas to 60"C 0.5 9 of N-phenol benzenesulphonamide are added and the mass is kept under agitation of 60 minutes at 60"C 11 70 g (5.85 moles) of 20% sodium hydroxide are then added over a period of 3 hours. After the addition of the basic hydroxide, the mass is heated to 75 to 80"C and left at this temperature for 30 minutes to complete the reaction. The two phases are separated and the excess epichlorohydrin is removed from the organic phase by vacuum distillation.

The residue is diluted with 900 g of methyl isobutyl ketone. The reaction product, has a hydrolysable chlorine content of 3.5 % by weight. In order to remove fruther hydrogen halide, the solution is heated to 80 to 85"C and reacted with 195 g of 20% sodium hydroxide for a period of from 60 to 90 minutes. The aqueous layer, containing the sodium chloride formed in the reaction, is separated; the organic layer is neutralised and distilled under vacuum to eliminate the solvent and subsequently filtered while hot.

Thus a low molecular weight epoxy resin consisting of the polyglycidyl ether of bisphenol F is obtained with the following characteristics: ---epoxy equivalent: 1 75 viscosity at 25"C cps: 16800 -hydrolysable chlorine: 0.4% by weight

Claims (10)

1. Process for the preparation of low molecular weight epoxy resins by reaction between a molar excess of an epihalohydrin and bisphenol A or bisphenol F characterised in that (a) epihalohydrin and bisphenol A or bisphenol F, in a molar ratio of from 2:1 to 8:1, are reacted at a temperature of from 30 to 80"C for a period of time of from 1 5 to 180 minutes in the presence of from 0.005 to 0.1 % by weight of the reaction mass of a catalyst selected from the group consisting of sulphones, sulphonamides, esthers of sulphuric acid, heterocyclic thiocompounds, thio-acids, thio-diphenols and dithio-heterocyclic compounds;; (b) the reaction mass is then added with an aqueous solution of alkali having a concentration of from 10% to 50% by weight over a period of time of from 2, to 4 hours at a temperature of from 40 to 70"C, the amount of alkali employed being from 2 to 2.1 moles for mole of bisphenol; (c) the aqueous layer of the reaction mass is then separated and the epihalohydrin's excess distilled off from organic layer; (d) the distillation residue is dissolved in an inert organic solvent and the obtained solution is again treated with the aq. solution of alkali at a temperature of from 70 to 90"C for 1 5 to 90 minutes, the amount of alkali used being from 0.1 to 0.3 moles for mole of originary bisphenol; then the organic layer is separated, neutralised with a dilute solution of a mineral acid and the solvent is distilled off to recover the low molecular weight epoxy resin as residue.

2. Process as claimed in claim 1 characterised in that the catalyst is bis-4,4'hydroxyphenyl sulphide.

3. Process as claimed in claim 1 characterised in that the catalyst is Nphenol benzenesulphonamide.

4. Process as claimed in claim 1 characterised in that the catalyst is diethyl sulphate.

5. Process as claimed in claim 1 characterised in that the catalyst is thiophene.

6. Process as claimed in claim 1 characterised in that the catalyst is thioantrene.

7. Process as claimed in claim 1 characterised in that the catalyst is 2,2'-thiodiacetic acid.

8. Process as claimed in claim 1 characterised in that the catalyst is bis-4,4'-hydroxyphenyl sulphone.

9. Process as claimed in claim 1 substantially as described in any one of the foregoing Examples 2 to 5 and 7.

10. A low molecular weight epoxy resin whenever prepared by a process as claimed in any one of the preceding claims.