OLIGOMERIC FORMAL DIOLS OF COPOLYMER GLYCOLS

Abstract: Oligomeric formal diols are prepared by coupling seg­ ments of copolyether glycols with formaldehyde. The formal diols are useful in preparing polyurethanes.

Description: TITLE Oligomeric Formal Diols of Copolymer Glycols DESCRIPTION Technical Field This invention relates to oligomeric formal diols of copolyether glycols. It is more particularly directed to such formal diols made by coupling copolyether glycol segments with formaldehyde. The invention also relates to polyurethanes made with these oligomeric formal diols. Background and Summary of the Invention Polyurethanes have been known and used for many years, and the basic general chemistry for their preparation, the reaction of a polyol, a polyisocyanate and a chain extender, is well documented. A type of polyol sometimes used for this purpose is the copolyether glycol based on tetrahydrofuran (THF) and an aik-lene-'oxide (AO). In some applications, especially where a polyurethane of high modulus and hardness is needed, it is desirable to use a copolyether glycol wit a molecular weight of over about 2000. Unfortunately, a copolyether glycol of such high molecular weight is difficult to make and use because its high viscosity hinders handling' and subsequent reaction. It has now been found that this difficulty can be eliminated by using a product made by coupling segments of the copolyether glycol with formaldehyde. This gives an oligomeric formal diol with a viscosity much lower than that of the conventional copolyether glycol of equivalent molecular weight. 'Moreover, when such a formal diol is used to prepare a polyurethane, the product shows no significant degradation of properties when compared to one made with a conventional copolyether glycol of equivalent molecular weight. Detailed Description of the Invention The oligomeric formal diols of the invention are ade b catalytically reacting a suitable copolyether glycol with formaldehyde. The copolyether glycol starting material is cne based on THF and an AO, and is sometimes also reerred to as a copolymer of THF and an AO. "AO" as -sed herein, means an alkylene oxide whose ring contails two or three carbon atoms. The AO can be unsubsuited or substituted with, for example, alkyl groups or halogen atoms. Illustrative alkylene oxides are ethylene oxide (EO), 1,2-propylene oxide (PO), 1,3propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide, ,2'-bischloromethyl-1,3-propylene oxide and epichloro :--.d-'n. The copolymers preferred for use are those of = and EO and THF and PO. The copolymer can also be of THF and two or more alkylene oxides, as for example a THF/EO/PO polymer. The copolymer will have (1) 10-80t, by weight, of AO units, prefer ably 20-60k, even more preferably 30-55i; and (2) hydroxyl functionalities of 2:0-4.0, preferably 2.0-2.5. The copolyether glycol starting material can be of any practical molecular weight, but will preferably have a number average molecular weight of 600 30C, even more preferably 1000-3000. Number average molecular weight is determined by first determining the '-ydroxyl number of the sample by titrating it with acetic anhydride according to ASTM-D-1638 and then converting this number to number average molecular weight according to the formula Molecular weight = 56,000 X n hydroxyl weight = hydroxyl number where n is the hydroxyl functionality of the sample. The copolyether glycol can be produced by any of the known methods. Illustrative of such methods are those shown in British Patent 854,958 and U.S. Patent 4,l2,5l3. The disclosures of those documents are incorporated into this application to show how such copolymers are prepared. The formaldehyde can be used as a gas, as an aqueous solution, or in the form of paraformaldehyde. As used herein, "forma,ldehyde" means any of'these forms. If an aqueous solution is used, the water thus introduced must later be removed from the-reaction mass, and the use of paraformaldehyde is therefore preferred. The amounts of copolyether glycol and formaldehyde used are of course governed by the molecular weight desired in the product and concomitantly, the number of glycol segments that are to be coupled. It is preferred to use an excess of paraformaldehyde when it is used because it has a tendency to sublime under reaction conditions; it is desirable that this loss be compensated for. The coupling reaction can be carried out in an aromatic hydrocarbon like toluene or xylene, or it can be carried out in bulk, using the copolyether glycol itself as the reaction medium. The catalyst can be- any strongly acidic cationic ion-exchange resin bearing -SO3H groups, insoluble in the copolyether glycol. "Insoluble" means that the amount of resin which dissolves in the glycol under process conditions will give the formal diol product an acid numberc'o':f no greater than 0.05 mg of KOH per gram. For purposes of the invention, the nature of the "backbone" of the ion-exchange resin is unimportant. The most common of the commercially available resins of this type have backbones which are of the polystyrene type, but resins having other backbones can be used. Preferred among the polystyrene-type resins, and pre- ferred for use, is one sold by the Rohm & Haas Company of Philadelphia, PA, as Amberlysts XN-1010. This macroreticular resin has a cation exchange capacity of 3.1 milliequivalents per gram, a surface area of 450 square meters per gram, a porosity of 41%, and a mean pore diameter of 50 Angstrom units. The catalyst is used at a concentration of 1-10%, by weight of the co?D*éther glycol, preferably 5-10%. The reaction is carried- out at a temperature of 60-ll00C, preferably 70-90 C. If the reaction is conducted in an aromatic hvdrocarbon medium, the water of condensation formed can DC removed by azeotropic distillation. If it is co¯l-;c.ed in bulk, the water can be removed under vacuum cr by sweeping the reaction zone with nitrogen. When an oligomeric formal diol having the desired molecular weight has been obtained, as determined by periodic sampling and analysis, the reaction mass is cooled to ambient temperature and. the catalyst and unreacted paraformaldehyde (if it is used) are removed by filtration. If formaldehyde is used, any which remains unreacted can be removed under vacuum. Any number of copolyether ether segments can be coupled in this manner. The simplest oligomeric formal diol is of course trat formed by coupling two glycol segments. The upper limit of the number of segments which can be couple is a practical one: beyond a certain range, the viscosity of the product makes preparation self-limiting. Most commercial and industrial applications will require a formal diol with a number average molecular weight in the range 120012,000, more preferably 4000-9000. The formal diol will be a liquid at room temperature and will have a viscosity within the range 0.5-10.0 pascal seconds, as determined at 600C with a glass capillary viscometer, according to ASTM-D-445 and ASTM-D-2515. A polyurethane can be prepared from such an oligomeric formal diol by reacting it with an organic polyisocyanate and an aliphatic polyol or polyamine chain extender, as is well known in the art. The polyisocyanates used in preparing the polyurethanes can be any of the aliphatic or aromatic polyisocyanates ordinarily used to prepare polyurethanes. Illustrative are 2, 4-toluene diisocyanate 2, 6-toluene diisocyanate hexamethylene-1,6-diisocyanate tetramethylene-1,4-diisocyanate cyclohexane- 1, 4-diisocyanate naphthalene-l, 5-diisocyanate diphenylnethane-4,4'-diisocyanate xylylene diisocyanate hexahydro xylylene diisocyanate dicyclohexylmethane-4 , 4 '-diisocyanate 1, 4-benzene diisocyanate 3,3'-dimethoxy-4,4'-diphenyl diisocyanate m-phenylene diisocyanate isophorone diisocyanate polymethyl ene polyphenyl i socyanate 4 , 4 1 -biphenylene diisocyanate 4-isocyanatocyclohexyl-41-isocyanatophenyl methane p-isocyanatomethyl phenol isocyanate. Mixtes of isocyanates can also be used. The isocyanates preferred for use because of the desirable properties they confer on the polure than: products are diphenylmethane-4,4'-diisocyanate ana t:ie toluene diisocyanates. The chain extenders used in preparing the polyurethanes can be any of the aliphatic polyols or any of the aliphatic or aromatic polyamines ordinarily used to prepare polyurethanes. Illustrative of the aliphatic polyols which can be used as chain extenders are 1,4-butanediol ethylene glycol 1,6-hexanediol glycerine trimethylolpropane pentaerythritol 1,4-cyclohexane dimethanol phenol diethanolamine. Dials like hydroquinone bis(betahydroxyethyl)ether, tetrachlorohydroquinone-1,4-bis(betahydroxyethyl)ether and tetrachlorohydroquinone-1,4-bis(betahydroxyethyl) sulfide, even though te contain aromatic rings, are consdered to be aliphatic polyols for purposes of the invention. Aliphatic diols of 2-10 carbon atoms are preferred. Especially preferred is 1,4-butanediol. Mixtures of diols can also be used. Illustrative of the polyamines which can be used as chain extenders are p,p'-methx,-lene dianiline and complexes thereof with alkali metal chlorides, bromides, iodides, nitrites and nitrates. 4,4'-methylene bis (2-chloroaniline) dichlorobenzidine piperazine 2-methylpiperazine oxydianiline-' hydrazine ethylenediamine hexamethylenediamine xylylenediamine bis(p-aminocyclohexyl)methane dimethyl ester of 4,4'-methylenedi anthranilic acid ' p-phenylenediamine m-phenylenediamine 4,4 '-methylene bis(2-methoxyaniline) 4,4'-methylene bis(N-methylaniline) 2,4-toluenediamine 2,6-toluenediamine benzidine 3,4'-dimethylbenzidine 3,3'-dimethoxybenzidine dianisidine 1,3-propanediol bis(p-aminobenzoate) isophorone diamine 1,2-bis(2'-aminophenylthio)ethane. The amines preferred for use are 4,4'methylene bis(2-chloroaniline), 1,3-propanediol bis (p- aminobenzoate), and p,p'-methylenedianiline and complexes thereof with alkali metal chlorides, bromides, iodides, nitrites and nitrates. Mixtures of amines can also be used. The polurethanes can be prepared in two steps, the first of which is conducted under nitrogen at ambient pressure to prexTent oxidation of the reactants and product, and to prevent exposure of the reaction mass to atmospheric moisture. In the first step, the oligomeric formal diol starting material is dried by heating it at a temperature of 80-1000C under vacuum, and is then held at 60-1250C, preferably about 70-900C, while a stoichiometric excess, preferably twofold to tenfold, of organic diisocyanate is added1 with stirring. The actual amount of isocyanate used depends on the molecular weight of the oligomeric formal diol, as is well known in the art. The reaction mass is held for about 1-4 hours at 60-1250C, with stirring, and the free isocyanate content of the mass is then determined by titrating it with di-n-butylamine, as described in Analytic Chemistry of the Polyurethanes, Volume XVI, Part III, D. J. David and H. B. Stale, Wiley-Interscience, 1969, pages 357-359. In the second step, an amount of polyamine or polyol chain extender calculated to give an isocyanate/hydroxyl or amine mole ratio of about 0.91.1/1 in the reaction mass, preferably 1-1.05/1, is degassed at about 30-1200C and 1330-5330 Pa (10-50 mm Hg) pressure and quickly added to the reaction mass. k conventional curing catalyst can be added at this point if desired. Illustrative of catalysts which can be used are dibutyltin dilaurate and stannous octoate. The catalyst can be added to the reaction mass to give a concentration of about 0.001-0.1%, by weight, preferably about 0.01%. The reaction mass is held with stirring at 60-1300C until it is homogeneous, which normally takes 1-5 minutes The mass is then poured into molds, preferably preheated to 100-1200C, and then cured at about 100-1200C at a pressure of 1700-2500 kPa for from 5 minutes to several hours. The casting is then cooled, removed from the mold, aged for about one week at ambient temperature, and is then ready for use. The polyurethanes can also be made by reaction-ir.ection and liquid-injection molding tec- niques, whereby the starting materials are simultan- eously injected and mixed in a mold, preferably together wit a conventional polyurethane catalyst, and then subjected to pressures ranging from ambient to several million pascals and temperatures ranging from ambient to 150 C. Use of a foaming agent such as a fluorocarbon or water is optional. The polyurethanes thus prepared are characterized by their high modulus and hardness, which suits them. for use in fabricating automobile bumpers, cast tires and the like. BEST MODE In the following description, all parts are by weight. A reactor was charged with ThFYEC copolymer (63/37) 550 parts Mn 1029 (0.53 mol) Paraformaldehyde 35.2 parts (1.17 mols) Amberlyst@ XN-1010 27.5 parts This mixture was heated to and held at 100 C and a pressure of 5330 Pa for four hours, with stirring, while volatiles, mainly water and THF, were continuously withdrawn. The mixture was then cooled to about 60 C, the vacuum released and the catalyst resin removed by filtration, to give a clear oligomeric formal diol with a number average molecular weight of 3336 and a viscosity of 1.11 pascal seconds at 600C. 131 Parts of the diol were dried for one hour at 850C under a vacuum of 1333-5330 Pa. The diol was then coole to 6G-70 C and to it were then added, with stirring, 52.9 parts cf diphenylmethane-4,4'-diiso- cyanate. A nitrogen sweep of the reaction zone was begun. Stirring was continued for 5 minutes, and the mixture was then again brought to and held at 850C, with stirring, for 2' hours, to give a product having a free isocyanate content of 7.73E, as determined by the di-n-butylamine titration technique. 176.2 Parts of the resulting prepolymer were then heated at 850C for one hour under a vacuum of 1333-5330 Pa to remove entrapped air. Heating was then stopped and to the mixture were added, with stirring, 13.9 parts of 1,4-butanediol, preheated to 600C. This mixture was stirred for 5 minutes and then poured into molds preheated to 110 C, which were then pressed in a platen press at 1100C and a platen pressure of 2155 kPa for 17 hours. The resulting elastomeric material was held for one week at ambient temperature and was then ready for use

Claims: CLAIMS 1. An oligoreric formal diol made by coupling copolyether glycol segments with formaldehyde. 2. The diol of claim 1 in which the copolyether glycol is a copolymer of tetrahydrofuran and ethylene oxide or a propylene oxide. 3. The diol of claim 1 or claim 2 having a number average molecular weight of 1200-12,000. 4. A polyurethane which is the reaction product of (a) an oligomeric formal diol of claim 1, (b) an organic polyisocyanate, and (c) a chain extender. 5. A polyurethane which is the reaction product of (a) an oligomeric formal diol of claim 2, (b) an organic polyisocyanate, and (c) a chain extender. 6. A polyuretrane which is the reaction product of (a) an oligomeric formal diol of claim 3, (b) an organic polyisocyanate, and (c) a chain extender. 7. The polyurethane of claim 6 wherein the polyisocyanate is diphenylmethane-4,4'-diisocyanate or a toluene diisocyanate. 8. The polyrethane of claim 6 wherein the chain extender is an aliphatic polyol, an aliphatic polyamine or an aromatic polyamine. 9. The polyurethane of claim 8 wherein the chain extender is an aliphatic diol of 2-10 carbon atoms. 10. The polyurethane of claim 9 wherein the aliphatic diol is 1,4-butanediol.

Inventors: PECHHOLD, ENGELBERT
Applicants: E.I. DU PONT DE NEMOURS AND COMPANY
Application year: 1981
Main classification: C07C43
IPC codes: C07C43, C08G65, C08G18, C08G4