CA1219598A

CA1219598A - Process for the preparation of polyoxybutylene- polyoxyalkylene glycol carboxylic acid diester

Info

Publication number: CA1219598A
Application number: CA000438136A
Authority: CA
Inventors: Herbert Mueller
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1982-10-01
Filing date: 1983-09-30
Publication date: 1987-03-24
Also published as: DE3236432A1; EP0104609B1; EP0104609A1; DE3368066D1; JPS5981332A; JPH0623245B2

Abstract

PROCESS FOR THE PREPARATION OF POLYOXYBUTYLENE-POLYOXYALKYLENE GLYCOL CARBOXYLIC ACID DIESTER

Abstract of the Disclosure The invention relates to a process for the preparation of polyoxybutylene-polyoxyalkylene glycol carboxylic acid diesters through the reaction of tetrahydro-furan with at least one 1,2-alkylene oxide and a carboxylic anhydride in the presence of bleaching earth having a water content of less than 3 percent by weight as the catalyst.

Description

Case 1403 PROCESS FOR THE PREPARATION OF POLYOXYBUTYLENE-POLYOXYALKYLENE GLYCOL CARBOXYLIC_ACID DIESTER
Back~ound of the Invention 1. Field of the Invention Thi~ invention relates to polyoxyalkylene glycol derivatives. More specifically, it relates to the car-boxylic acid diesters of copolymers of tetrahydrofuran and 1,2-alkylene oxideq.

2. Description of the Prior Art The use of bleaching earths for the pretreatment and polymerization of tetrahydrofuran is known. According to EP published application 3112 (U. S. 4,189,566), polyoxy-butylene glycol carboxylic acid diesterq are prepared with good yields through the catalytic polymerization of pre-treated tetrahydrofuran in the presence of carboxylic anhydride and essentially anhydrous bleaching earth as a catalyst. The only disadvantage of this process is that the reaction rate is relatively slow.
U. S. Patents 4,127,513 and 4,228,272 further teach that alkylene oxide and tetrahydrofuran can be copolymerized using a special acid-activated montmorillonite clay having a pore volume of from 0.4 to 0.8 m3/g, a surface area of from 220 to 260 m2/g, and an average pore diameter of from 0.1 to 0.3 ~m in the presence of, for example, water as a regulating substdnce. The use of these special - montmorillonite clays can reduce the amount of cyclic 123L9S~

oligomer by-products formed during copolymerization to from 4 to 8 percent by weight compared with from 10 to 15 percent by weight commonly encountered previou~ly. However, this content iq still too high to permit the resulting glycols to be used for highly demanding polyurethane applications. The cyclic oligomers are an inert material which does not pos~ess hydroxyl groups which react with isocyanate groups. Since the cyclic oligomers are very soluble in all standard qolvents, they can cause processing difficulties or adversely affect the mechanical properties of the finished products.
Summary of the Invention The purpose of the invention is to prepare copolymers of tetrahydrofuran and 1,2-alkylene oxides which essentially contained no linear low molecular weight oligomers, and preferably no cyclic oligomer~, and which, therefore, could not cause the problems noted above.
Thi~ goal was achieved unexpectedly with a process for the preparation of polyoxybutylene-polyoxyalkylene glycol carboxylic acid diesters comprising reacting a mixture of: (a) tetrahydrofuran with (b) at least one 1,2-alkylene in a mole ratio of 1:1 to 1:20 with the tetrahydrofuran, and (c) a carboxylic anhydride in an amount of 0.1 to 20 mole percent of the total reactant charge, in the presence of bleaching earth as a catalyst, said s~

bleaching earth having a water content of less than 3 percent by weight.
Description of the Preferred Embodiments _ _ _ _ _ _ _ _ . . _ _ _ _ _ _ _ _ The polyoxybutylene-polyoxyalkylene glycol carboxylic acid diesters prepared in accordance with the invention can easily be converted to the corresponding glycol3 through transesterification or saponification of the terminal ester groups.
It was surprising and, based on the prior art, in no way expected that copolymerization would proceed so effectively with the process of the invention. It is known, for example, from Houben-Weyl, Methoden der or~anischen Chemie, Vol. 6/3, p 482, (Georg-Thieme-Verlag, Stuttgart 1965), that 1,2-alkylene oxide and carboxylic anhydrides react very easily and quickly, in particular in the presence of catalysts, to form dicarboxylic acid esters of 1,2-diols. As already noted, though, the polymerization of tetrahydrofuran in the pre~ence of bleaching earth and carboxylic anhydrides to form polyoxybutylene glycol carboxylic acid diesters occurs at a relatively slow rate.
Thereore, it had to be assumed that both reactions, namely, the formation of 1,2-dicarboxylic acid diesters from 1,2-alkylene oxide and carboxylic anhydrides as well as the tetrahydrofuran polymerization, would take place simulta-neously and that no copolymerization would occur.

Since the cited U. S. Patents and GB Patent 854,958 also teach that the copolymerization of alkylene oxides and tetrahydrofuran with bleaching earth as the catalyst can only be performed in the presence of compounds with reactive hydrogen atoms, a qignificant predisposition had to be overcome in order to perform the process of the invention.
The process of the invention has the advantage of producing nearly no by-products of the copolymerization, in particular no cyclic oligomers, and the process also has the advantage of completely converting the l,2-alkylene oxide.
The resulting copolymerq have an extremely low color index, which has a very desirable effect on further proce ~qing.
The bleaching earths used as catalyst~ have an extremely long service life, and they can be separated from the polyoxybutylene-polyoxyalkylene glycol carboxylic acid diesters without great difficulty.
The following must be noted relative to the initial components which can be used in the proces~ of the invention:
1,2-Alkylene oxides and tetrahydrofuran are used as the monomers, most advantageously in water-free form or, at least, with a water content less than 0.2 percent by weight, preferably less than 0.1 percent by weight.

-Unsubstituted or substituted 1,2-alkylene oxide~
are used, for example, those ~ub~tituted with linear or branched alkyl groups having from 1 to 6 carbon atom~, preferably from 1 to 2, with a phenyl radical, unsubstituted or substituted with alkyl and/or alkoxy groupq with from 1 to 2 carbon atoms or halogen atoms, or with halogen atom~, preferably chlorine atoms. Typical examples are: 1,2-butylene oxide, 2,3-butylene oxide, styrene oxide, epi-chlorohydrin, and, preferably, ethylene oxide and 1,2-propylene oxide. The 1,2--alkylene oxideq can be used individually or as mixtures, for example, ethylene oxide/1,2-propylene oxide mixtures. The tetrahydrofuran used for the copolymerization i9 appropriately treated prior to polymerization with strong mineral acids, organic sulfonic acids, silica gel, and, preferably, bleaching earths using the proces~ described in EP publiYhed applica-tion 3112.
In the process of the invention, copolymerization takeq place in the pre~ence of organic carboxylic anhydrides as promoters. Carboxylic anhydrides derived from aliphatic or aromatic poly- and/or, preferably, monocarboxylic acids with from 2 to 12, preferably from 2 to 8, carbon atoms are used to advantage. Typical example~ are anhydrides of aliphatic carboxylic acids having from 2 to 12 carbon atom~, which can also sometimes contain olefinically un~aturated S~8 bonds: for example, butyriLc anhydride, valeric anhydride, caproic anhydride, caprylic anhydride, pelargonic anhydride, acrylic anhydride, and, preferably, propionic anhydride and acetic anhydride, anhydrides of aromatic and aliphatic polycarboxylic acids, in particular, dicarboxylic acids, such aq phthalic anhydride, naphthalenedioic anhydride, and, preferably, succinic and maleic anhydride. Since the polyoxybutylene-polyoxyalkylene glycol carboxylic acid diesters prepared in accordance with the invention can be transformed into the corresponding glycols for most applica-tions, in actual practice it is preferable to use carboxylic anhydride~ with a low number of carbon atoms. For price and accessibility reasons, acetic anhydridle is preferred. Of course, mixed anhydrides and mixtures of the above anhy-drides can be used.
Bleaching earths are describ,ed, for example, in Ullmann'~ Enzyklopadie der technischen Chemie, 3rd ed., Vol. IV, pp. 541-545. Natural or synthetic bleaching earths suitable as catalysts are, in particular, aluminum hydro-silicates or aluminum-magnesium hydrosilicates of the montmorillonite type, which can be actiivated by acid and are available commercially, for example, under the trade mark "~onsil. n Synthetic bleaching earths are described, for example, in GB Patent 854,958. In order to prepare the bleaching earths that can be utilized in accordance with the invention and which are largely free of water, ~tandard commercially available bleaching earths containing water are dehydrated at temperatures from lOO~C to ~00C, preferably from 110C to 150~C, for from 1 to 8 hours, preferably 2 to 4 hours, at standard pressure or, preferably, at a reduced pressure. The bleaching earths which can be used as catalysts in accordance with the invention and are largely free of water, have water contents of less than 3 percent by weight, preferably from 0.001 to 1.5 percent by weight, more preferably from 0.1 to 1.0 percent by weight. Only very slight amounts of the essentially water-free bleaching earths are needed for the copolymerization of the tetra-hydrofuran and the 1,2-alkylene oxides. The copolymeriza-tion can be performed with water-free bleaching earth suspended in the polymerization mixture. Desirable results are obtained if they are used in amounts ranging from 1 to 20 percent by weight, preferably from 5 to 10 percent by weight, ba~ed on the total polymerization mixture. Of course, larger and smaller amounts may be used.
The suspended bleaching earths can be ~eparated from the polymerization mixture by conventional physical separation methods, e g., filtration or centrifugation.
They can then be reused for any number of further polymeri-zation reactions. This separation, however, requires expensive engineering operations and sometimes produces ~lZ~L95~3 colored copolymers when the atmosphere cannot be completely sealed out during the separation and return of the catalyst. Moreover, the catalyst can be deactivated by the effects of atmospheric moisture.
In a preferred embodiment, the essentially water-free bleaching earth is, therefore, pressed into a molded object and is po~itioned in a catalyst bed and is made to come in contact with the copolymerization mixture or is located in a fixed position in a tubular reactor through which the copolymerization mixture flows.
In order to prepare the molded pieces of catalyst, standard commercial bleaching earths containing water are kneaded with binders, in particular water, and compressed into molded pieces. Then these molded pieces containing water are dehydrated to the water contents noted above at temperatures in excess of 100C, preferably at temperatures from 150C to 700C, at standard pressure or at a reduced pressure, in some cases in the presence of inert gases, e.g., noble gases such as helium or argon, or, in partic-ular, nitrogen.
The compressed bleaching earths can be in the shape of spheres, rings, cylinders, or tablets. When using spherical bleaching earth molded pieces, the spheres generally have diameters from 2 to 15 mm, preferably from 3 to 6 mm. The cylindrical molded pieces generally are from 2 ~23~9~ 8 to 15 mm long and have a diameter of from 2 to 6 mm. Non-spherical or cylindrical molded pieces generally exhibit a volum~ corre~ponding to that of the cylindrical molded pieces.
The dry bleaching ear~h molded pieces are loaded into a reaction vessel, preferably a tubular or shaft-type oven. The ~ize of the catalyst charge i3 preferably deter-mined by its ability to remove the heat of polymerization.
The reaction vessel~, which are generally column-shaped, can have any desired cross-sectional configuration, for example, they can be square or elliptical. However, long, cylinderical reaction vessels are preferred. The ratio of inside diameter-to-lenyth for the reaction vessel iq generally from 1:2 to 1:100, preferably from 1:10 to 1:40. The reaction vessels can be positioned vertically or horizontally and can also have in-between positions.
However, vertical tubular ovens with a tube diameter from approximately 10 to 100 mm are preferred. If accurate temperature contol during polymerization i9 not so impor-tant, simple ~haft-type ovens can also be used as reaction vessels, with or without product return systems. It was unexpectedly observed that bleaching earths compressed into molded pieces and dried at temperatures in e~cess of 100C
which were installed in a stationery, non-mobile catalyst bed are not destroyed by the polymerization mixture of _ g _ s~

tetrahydrofuran, 1,2-alkylene oxide, and carboxylic anhy-dride, but rather maintained their original solid ~hape and exhibited no phy~ical wear for more than one year, for example. Moreover, the final product leaving the cataly~t bed i~ free of inorganic impurities. This simplifie~
continual processing, so that accurately reproducible polyoxybutylene-polyoxyalkylene glycol carboxylic acid diesterq can be prepared, in particular relative to color and degree of polymerization. In addition, since catalyqt loss iq 90 low as to be negligible, the process is partic-ularly sound from the environmental standpoint.
With the aid of the copolymerization in accordance with the invention, carboxylic acid diesters of polyoxy-butylene-polyoxyalkylene glycols can be prepared with any desired degree of polymerization, for example, from 2 to 200, preferably from 10 to 70. Such polymerization indice~
result in polyoxybutylene-polyoxyalkylene glycols which have mean molecular weights of approximately 130 to 15,000, preferably from 500 to 3500, after hydrolysis. The degree of polymerization i~ primarily determined by the carboxylic anhydride concentration in the polymerization mixture. As lower and lower carboxylic anhydride concentrations are selected, the molecular weights become higher and higher and vice versa. Since the polymerization indices are also determined by the characteristics of the largely water-free ~2~L9S~

bleaching earths, it is generally necessary to determine the acid anhydride concentration which produces the desired molecular weight for a given bleaching earth and at a desired temperature. The tetrahydrofuran-to-1,2-alkylene oxide monomer ratio also influences molecular weight.
Since, however, the type of essentially water-free bleaching earth ha~ less effect on molecular weight than does the mole ratio of tetrahydrofuran-to-1,2-alkylene oxide, which i~
pre~ent in a copolymerizable monomer mixture preferably at from 1:1 to 20:1, more preferably from 2:1 to 10:1, and than the carboxylic anhydride concentration, the following values, for example, are provided here for orientation purposes: a solution of 14 molar percent ethylene oxide, 83 molar percent tetrahydrofuran, and 3 molar percent acetic anhydride produces at a polymerization temperature of 35C a copolymer with a molecular weight of 1500. If the anhydride concentration is doubled and the monomer ratio is held constant, a polymer with a molecular weight of approximately 1000 is obtained at the same reaction temperature. The carboxylic anhydride i9 normally used in an amount of 0.1 to 20, preferably 2 to 10 mole percent of the total reactant charge.
In order to perform the copolymerization in a fixed catalyst bed, largely water-free bleachin~ earth molded piece~ contained in the reaction vessel are contacted with a mixture of ~etrahydrofuran, 1,2-alkylene oxide or a mixture of 1,2-alkylene oxides, and carboxylic anhydride using familiar reaction methods, for example, cascade or liquid phase processes. The liquid phase process is one in which the entire catalyst volume has the polymerization mixture of the three components flowing through it with the absence of a gas phase. The heat of polymerization can then be removed by suitably installed cooling units in the polymerization tower or by means of an external cooler connected in parallel.
The copolymeri2ation i~ efficaciously performed in a ixed catalyst bed at temperature~ from 20C to 70C, preferably from 35C to 64C at standard pres~ure. If additional pressure is applied, the copolymerization temperature can also be higher. Copolymerization mixtures with a high ethylene oxide content are best copolymerized at elevated pres~ure. The residence times are generally from 5 to 50 hours, preferably from 8 to 30 hours.
The reaction mixture leaving the reaction vessel contains, in addition to the carboxylic acid diesters of the polyoxybutylene-polyoxyalkylene glycols in accordance with the invention, from 30 to 60 percent by weight non-converted tetrahydrofuran and a maximum of 10 percent by weight, preferably le~s than 3 percent by weight, non-converted carboxylic anhydride, depending on the reaction conditions ~L~t~

utilized, for example, depending on the catalyst activity, the residence time on the catalyst, and the reaction temperatureO These non-reacted components can ~hen be separated by simple distillation, in some cases under reduced pressure, and can then be recycled if desired. On the other hand, the 1,2-alkylene oxide which is used initially is completely polymerized into the polyoxybuty-lene-polyoxyalkylene glycol carboxylic acid diester.
The polyoxybutylene-polyoxyalkylene glycol carboxylic acid diesters prepared in accordance with the invention process can be converted to the corresponding glycol~ using familiar methods: saponification, for example, with calcium oxide and/or hydroxide as a catalyst, or, preferably, by transesterification, for example, with methanol similar to the specifications of U. S. Patent 2,499,725 or in accordance with the Journal of the American Chemical Society, vol. 70, p. 1842.
The resulting polyoxybutylene-polyoxyalkylene glycols, in particular those with molecular weights of from 500 to 3000, are ideally suited for the preparation of polyurethanes or polyesters. For example, they give the polyurethanes very high mechanical properties. In compar-ison with polytetramethylene ether glycols, they have a low freezing point and can, therefore, be primarily used in a liquid form without the need for prior expensive liquifica-tion or melting processes.

5~3~

The following examples serve to elucidate ~he process in accordan~e with the invention, but do not limit it in any way. The specified parts are parts by weight, such parts correlate with parts by volume in the same manner that kilograms correlate with liters.

5~

Exame~e 1 A commercially available technical-grade tetra-hydrofuran was purified in accordance with the specifica-tions of EP Published Application 3112 by treatment with a commercial bleaching earth (Tonsil~ Optimum FF, Sud-Chemie AG, Munich) and wa~ used for the copolymerization.
Pellet~ with a diameter of from 2 to 3 mm and an average length of 4 mm were prepared from the commericial bleaching earth (Tonsil~ Optimum FF, Sud-Chemie ~G, Munich) and were dried for four hours at 200C.
A reaction tube equipped with a thermostatically controlled cooling jacket and possessing a volume of 1000 volume units and a diameter-to-length ratio of approximately 5:7 was filled with the dried pellets described above. A
mixture comprising 2000 parts by weight (27.75 mole~) tetrahydrofuran, 126 parts by weight acetic anhydride, and 223 part~ by weight (5 moles) ethylene oxide was pumped through the reaction tube at 35C in the absence of a gaseous phase. The pump speed was 1000 volumetric parts per hour in such a way that the mixture leaving the reaction vessel was supplied to the front side of the rotary pump.
This test setup remained in operation for 60 hours. The residence time in the catalyst was approximately 24 hours.
When the volatile components (34 percent by weight) were separated from the reaction mixture by means of distillation

3~9~

in a vacuum, a liquid polyoxybutylene-polyoxyethylene glycol diacetate wa3 obtained with an ester number of 71 mg KOH/g. The molecular weight wa~ then calculated to be 1580. By transesterification with methanol in the presence of 0.01 percent by weight sodium methylate, a polyoxy-butylene-polyoxyethylene glycol having a molecular weight of 1500 was obtained. An analytical analysis of the volatile components of the resulting reaction mixture showed that the ethylene oxide was completely polymerized into the polyoxy-butylene-polyoxyethylene glycol diacetate. The distillate was comprised of 99 percent by weight tetrahydrofuran and 1 percent by weight acetic anhydride.
Example 2 Four millimeter catalyst beads of bentonite (KA 3 catalyst beads from Sud-Chemie AG, Munich) were dried similar to the manner described in Example 1 and were filled into the reaction tube cited above. The reaction tube was then charged with a mixture of 2000 parts by weight tetra-hydrofuran, 223 parts by weight ethylene oxide, and 126 parts by weight acetic anhydride under the conditions cited in Example 1. The residence time at the catalyst was 20 hour~. Under these conditions, the ethylene oxide polymer-ized completely into the polyoxybutylene-polyoxyethylene glycol diacetate, whose molecular weight was 1480. Thirty-five percent by weight of the tetrahydrofuran charged wa3 ~9~

recovered into the reaction mixture by means of distilla-tion.
Example 3 When the procedure described in Example 1 was followed, but a polymerization mixture comprising a3 mole percent tetrahydrofuran, 13 mole percent 1,2-propylene oxide, and 3 mole percent acetic anhydride was used, a polyoxybutylene-polyoxypropylene glycol diacetate was obtained with a molecular weight of 1555, and the 1,2-propylene oxide wa~ fully polymerized therein as wa~ 65percent by weight of the initially used tetrahydrofuran.

Claims

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. A process for the preparation of polyoxy-butylene-polyoxyalkylene glycol carboxylic acid diesters comprising reacting a mixture of:
(a) tetrahydrofuran, (b) at least one 1,2-alkylene oxide in a mole ral:io of 1:1 to 1:20 with the tetrahydro-furan, and (c) a carboxylic anhydride in an amount of 0.1 to 20 mole percent of the total reactant charge, in the presence of a catalytic amount of a bleaching earth which has a water content of 0.001 to 1.5 percent by weight.

2. The process of claim 1 wherein the 1,2-alkylene oxide used is selected from the group consisting of ethylene oxide and 1,2-propylene oxide.

3. The process of claim 1 wherein the mole ratio of tetrahydrofuran to 1,2-alkylene oxide in the copolymeri-zable mixture is 2:1 to 10:1.

4. The process of claim 1 wherein acetic anhy-dride is used as the carboxylic anhydride.

5. The process of claim 1, wherein the bleaching earth as catalyst is placed in a fixed bed and is brought into contact with a mixture of tetrahydrofuran, 1,2-alkylene oxide and carboxylic anhydride.

6. The process of claim 1, wherein the bleaching earth is located in a stationary position in a tube reactor and wherein a mixture of tetrahydrofuran, 1,2-alkylene oxide and carboxylic anhydride flows through the catalyst.

7. The process of claim 1, wherein the bleaching earth with a water content of 0.001 to 1.5 percent by weight is located in a tube reactor in a stationary position and wherein a mixture of tetrahydrofuran, ethylene oxide and/or 1,2-propylene oxide and acetic anhydride flows through the catalyst.

8. The process of claim 1, 2 or 3, wherein the co-polymerization is carried out at a reaction temperature of 20 to 70°C under normal pressure.

9. The process of claim 1, 2 or 3, wherein the water content of the mixture of tetrahydrofuran and 1,2-alkylene oxide is less than 0.2 percent by weight.

10. The process of claim 1, 2 or 3, wherein the water content of the mixture of tetrahydrofuran and 1,2-alkylene oxide is less than 0.1 percent by weight.

11. The process of claim 1, wherein the tetrahydro-furan used for the copolymerization is treated prior to poly-merization with a strong mineral acid, an organic sulfonic acid, silica gel or a bleaching earth, or a mixture thereof.

12. The process of claim 11, wherein the water content of the mixture of tetrahydrofuran and 1,2-alkylene oxide is less than 0.2 percent by weight.