Process for Making Polyglycidyl Esters

Vandenberg U.S. Pat. No. 3,446,757 discloses a process for making polymers of glycidol by (1) polymerizing silicon esters of glycidol, alone or with other alkylene oxides, and then removing the silicon groups by hydrolysis.

Vanlerberghe, British Pat. No. 1,267,259, discloses the dealkylation of polymers of tert.-butyl glycidyl ether by heating the polymer with water and a sulfonic acid catalyst. The resulting polyglycidol may then be esterified.

Homopolymers and copolymers of glycidyl esters are made by reacting the acids corresponding to the desired esters with the corresponding tert.-alkyl glycidyl ethers. In the reaction the tert.-alkyl moieties of the ethers are displaced and, to the desired degree, replaced with the acyl moieties of the acid, thus producing glycidyl ester moieties. Those tert.-alkyl groups not converted to ester groups are predominantly converted to primary hydroxyl groups. These reactions may be illustrated as follows: ##STR1## wherein R is tert.-alkyl, R'COOH is a carboxylic acid and the wavy lines represent the polyoxyalkylene backbone of the polymer. The proportion of the tert.-alkyl ether groups that are converted to ester or to hydroxyl groups, respectively, is determined by the proportion of esterifying acid used and/or the amount of water produced in the reaction.

The tert.-alkyl glycidyl ether polymers useful in practicing the invention are those having tert.-alkyl groups such that the corresponding alkene is volatile at the reaction temperature so that it may be removed during the reaction. As a practical matter, the tert.-butyl ethers are of primary interest, though others, such as the tert.-amyl ethers, can be used.

The process of the invention is conducted in the presence of a strong acid catalyst. Suitable catalysts include boron trifluorides, phosphoric acid, sulfuric acid, alkanesulfonic acids and arylsulfonic acids. Examples of the latter types include octanesulfonic acid, hexadecanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid and naphthalenesulfonic acid. The arylsulfonic acids are preferred. Only a catalytic amount of such acids is needed.

The tert.-alkyl glycidyl ether polymers that are used as starting materials in the process of the invention may be substantially any polymer comprising tert.-alkyl glycidyl ether moieties. They constitute a known class of materials, useful examples of which are shown in our above-cited copending applications, in British Pat. No. 1,267,159 and in U.S. Pat. Nos. 3,519,559 and 3,509,074. Other useful examples are shown by Okada et al., Kogyo Kagaku Zasshi, 66, 115 (1963) (C.A., 59, 4046 (1963)), Il'chenko et al., Dokl. Akad. Navk SSSR 1970, 192 (C.A. 73, 88253 (1970)) and Koinuma et al., Makromol. Chem., 136, 65 (1970). Any of the tert.-alkyl glycidyl ether polymers disclosed in the foregoing references are useful in the present invention and other similar ones can be made by the methods there disclosed. The term "polymers" as used herein is intended to include homopolymers, copolymers, terpolymers, etc., including heteric (random) as well as block copolymers wherein the comonomers may be present in any significant proportion and arrangement.

The acids useful to make esters according to the invention include substantially any carboxylic acid. The monocarboxylic acids produce esters having the same polymer backbone as the tert.-alkyl ether starting material, the difference being that most or all of the tert.-alkyl groups have been removed and, to the desired extent, replaced with the acyl group of the reactant acid. Those not so replaced are converted to hydroxyl groups. Dicarboxylic acids extend the chain length of the backbone of the polymer and may also initiate branching and, ultimately, cross-linking of the polymer. Polycarboxylic acids of functionality greater than two, even when used in small amounts, quickly cross-link and gel the polymer; hence, they are ordinarily used in very small amounts if at all.

The preferred monocarboxylic acids are the saturated fatty acids, such as acetic butyric, lauric and stearic acids; the olefinic fatty acids, such as acrylic, methacrylic, undecylenic, oleic and linoleic acids; the aromatic acids, such an benzoic, alkylbenzoic and naphthoic acids, and the chloro- and bromo-analogs of the foregoing. It is, of course, possible to use the anhydrides of the acids rather than the acids themselves. They are particularly useful where partial esters of polycarboxylic acids are desired as the final product, in which case a mole of the anhydride is used for each carboxyl group desired in the product and the esterification is run under mild conditions so as to minimize the formation of diesters of the acid derived from the anhydride. Suitable polycarboxylic acids and anhydrides include the alkanedicarboxylics, such as succinic, adipic and sebacic; the alkenedicarboxylics, such as maleic, itaconic, citraconic and glutaconic; and the aromatics, such as phthalic, isophthalic and terephthalic.

In practicing the invention, a polyoxyalkylene compound containing tert.-alkyl glycidyl ether moieties, i.e., groups of the formula ##STR2## wherein R is a tert.-alkyl group, is prepared by known means. This is conveniently done by the homopolymerization of a tert.-alkyl glycidyl ether or the copolymerization of such an ether with one or more other cyclic ethers, such as ethylene oxide, propylene oxide, butylene oxide, trimethylene oxide, tetrahydrofuran, epichlorohydrin, 2,2-bis(halomethyl)oxetane, or the like. Such polymerizations may be conducted with various catalysts, such as alkali metal hydroxides, Friedel-Crafts catalysts, aluminum alkyls, zinc alkyls or other known catalysts for the polymerization of alkylene oxides. If conducted in the presence of an initiator compound having one or more active hydrogen atoms, polymer chains are initiated at the sites of these atoms, as is well known in the art. Such polymers have terminal hydroxyl groups which may, if desired, be esterified prior to or simultaneously with the sites of the tert.-alkyl ether groups.

The essential step of the process of the invention, i.e., the simultaneous dealkylation and esterification reaction, is carried out by heating the polymer having tert.-alkyl ether groups with the acid or anhydride that is to be esterified in the presence of a strong acid catalyst and simultaneously removing the alkene corresponding to the tert.-alkyl group and any water formed in the reaction. The reaction may be conducted by simply mixing the reactants and the catalyst and heating to reaction temperature. Removal of the by-product alkene may be facilitated by operating under reduced pressure and/or sparging a stream of inert gas through the reaction mixture. These techniques likewise aid in removal of any water produced in the reaction. Removal of water is further facilitated by using as a reaction solvent a water-immiscible organic solvent, such as a hydrocarbon or halohydrocarbon of suitable boiling point such that at reflux its azeotrope with water is distilled and the water removed. Upon completion of the reaction, as indicated by the evolution of olefin and/or water, the product is obtained by removal of the catalyst, solvent and unreacted acid if any.

Since the polyether reactant is more or less polymeric in nature, the esterification reaction with a carboxylic acid becomes slow toward the end and tends to be incomplete unless vigorously pushed. Where it is important to accomplish complete esterification it is often expedient to add the anhydride of the acid near the end of the reaction, since it is much more reactive than the acid itself. Use of a stoichiometric excess of the acid or anhydride also favors complete esterification.

The following examples illustrate the practice of the invention.

Monomeric tert.-butyl glycidyl ether (TBGE) was homopolymerized or copolymerized in various proportions with other cyclic ethers in known manner, the products and their preparation being summarized in Table I. The indicated initiators were the active hydrogen compounds used to initiate the polymer chains. In all runs, the reaction was continued until all TBGE and other alkylene oxides fed to the reactor had reacted, thus assuring that the molar proportions in the product were the same as in the reactor feed. Molecular weights of the products were estimated by the acetic anhydride method, based on the expected number of hydroxyl groups per molecule.

The polymers of Table I have n terminal hydroxyl groups, where n is the functionality of the initiator RH.sub.n. These hydroxyl groups can be esterified without disturbing the tert.-butoxy groups by reaction with an acid anhydride or, in the presence of a base, by use of an acyl halide. Attempts to esterify them with carboxylic acids in the presence of strong acid catalysts result in dealkylation (loss of isobutylene) together with esterification of the resultant primary hydroxyl groups. Thus, a particular feature of this invention is the discovery that the tert.-butyl glycidyl ether polymers and copolymers can be terminally esterified independently of the tert.-butoxy groups and that the latter groups can be simultaneously and in a single step dealkylated and, to any desired extent, esterified by reaction with a carboxylic acid. The latter reactions are catalyzed by strong acid catalysts, especially the arylsulfonic acids.

Esterification of the terminal hydroxyl groups of the tert.-butyl ether polymers and copolymers by use of acyl halides or half-esterification of acid anhydrides can be accomplished under mild conditions, such as 30.degree.-90.degree. C., whereas dealkylation and/or esterification of carboxylic acids requires acid catalysis and temperatures of about 90.degree. or more for a convenient rate of reaction. When esterifying saturated acids, temperatures of about 125.degree.-150.degree. are preferred. When using highly polymerizable acids, such as acrylic or methacrylic acid, it is necessary to use a polymerization inhibitor, such as Cu.sub.2 O or a hydroquinone. Lower temperatures, such as about 90.degree.-110.degree. may be used, however, because of their higher reactivity.

The following typical example illustrates the dealkylation-esterification process.

A reactor was charged with 50 g. (0.05 m.) of a homopolymer of tert.-butyl glycidyl ether of molecular weight of 1000, 27.4 g. (0.19 m) of octanoic acid and 0.8 g. of p.-toluenesulfonic acid. The charge was heated at 137.degree. C. for 6 hours, water being distilled out as formed (3.4 g.).

The crude product was dissolved in methanol and passed through a mixed ion exchange column. The solvent and other volatile materials were distilled to a final temperature of 100.degree. at 1 mm. pressure, thus leaving the purified product as an oily liquid. Yield, 48 g. (93%). Analysis by NMR confirmed that essentially all of the tert.-butyl groups had been removed and that one-half of them had been replaced with octanoyl groups, the other half being replaced by hydrogen, thus generating primary alcoholic groups (glycidol moieties).

Because of the desirability of some primary hydroxyl in the products, the above examples show only partial esterification of the polymers. However, essentially complete esterification is readily accomplished by use of at least the stoichiometric amount of acylating agent and continuing the reaction until essentially complete. Thus, the reaction of Run No. 65 or 66 was repeated except that 46 moles of stearic acid were used, the product was essentially full esterified and contained essentially no primary hydroxyl.

Table II summarizes the results of a series of experiments wherein the polymers listed in Table I were dealkylated and partially esterified as described above. The starting material is identified by the Run No. as shown in Table I. The amounts of acids used in the esterification reactions are shown as moles/mole of starting material. It may be noted that in some instances excess acid was used. When the esterification was conducted stepwise with two different acids, the acid used in the first step was completely reacted, then the second acid was added and reacted either partially or entirely (e.g., Runs 43, 47 and 54. In Run 49 the acetate esters were made by use of the acetic anhydride after the dealkylation-acrylic acid ester step was completed. In all runs in which both acrylic acid and maleic anhydride were used, the two were mixed and, hence, reacted simultaneously.

In Table II the products are characterized by the number of acyl groups and the number of primary hydroxyl groups (glycidol units) per molecule of the product. The ester groups were determined by NMR and the hydroxyl groups were calculated by difference, all calculations being based on the molecular weights shown in Table I.

In a manner similar to that for producing the products of Table II, a 50:50 (mole) TBGE/EO copolymer of about 1300 molecular weight, very similar to that of Run No. 11, was dealkylated and esterified. About 655 g (0.5 mole) copolymer, 250 g toluene, 144 g (1 mole) octanoic acid and 25 g BF.sub.3 etherate (48% BF.sub.3) were charged to a flask and the mixture slowly raised to about 125.degree. C. The reaction was complete in about 2 hours as determined by separation of water and evolution of isobutylene. Titration indicated the octanoic acid was completely consumed. The products primary hydroxyls were therefor about 27% esterified.