CA1241024A - Sulfur-modified polypropylene ether glycols, a method for preparing them, and polyurethanes prepared therefrom - Google Patents

Abstract

TITLE
Sulfur-Modified Polypropylene Ether Glycols, A Method for Preparing Them, and Polyurethanes Prepared Therefrom ABSTRACT OF THE DISCLOSURE
Polypropylene ether glycol is modified so that it contains 1-25%, by weight of .beta.,.beta.'-dihydroxyalkyl sulfide moieties.
These modified polypropylene ether glycols have enhanced resistance to degradation by heat and oxygen.

Description

124~024 1 TITLE
Sulfur-Modified Polypropylene Ether Glycols, A Method for Preparing Them, and Polyurethanes Prepared Therefrom DESCRIPTION
Technical Field -This invention relates to polypropylene ether glycol ~PPG), which has been modified so that it con-tains sulfur-containing moieties in its polymer chain.
It is more particularly directed to such a PPG modified to contain dehydrated ~,~'-dihydroxyalkyl sulfide (HAS) moieties in its chain.
The invention also relates to a method of making the modified PPG's, to their use as stabilizers against the degradation of the polyether chain, and to polyurethanes made with them.
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 fully documented.
A polyol frequently used for this purpose is PPG, which is well known to be degraded by exposure to oxygen, light and heat. It has been the general prac-tice to guard against such degradation by blending withthe PPG an external stabilizer such as a phenolic, an amine or a sulfur compound.
It has now been found, according to the in-vention, that the stabilization can be more effectively and efficiently achieved if the PPG is modified so that it contains in its chain 1-25%, by weight, pref-erably 3-15%, of moieties represented by the structure R R

lZ41024 where R is hydrogen, an alkyl radi-cal of 1-3 carbon atoms or phenyl, and the oxygen atom is linked to a hydrogen atom or a carbon atom.
Preferably, the modified PPG has an oxygen~sulfur atom ratio of 3/1 or greater, even more preferably 5-60/1.
It has been found, according to the invention, that the stabilization against degradation can also be achieved if the unmodified PPG to be used is physically blended with about 0.4-20~, by weight, of the modified PPG .
In addition, the method for preparing the modified PPG of the invention can be used to increase the molecular weight of the PPG by coupling polymer chain segments with HAS moieties.
It has also been found that PPG ~odified according to the invention shows significantly better resistance to acid-catalyzed depolymerization and to oxidative degradation at high temperatures than un-modified PPG .~etailed Description of the Invention The modified PPG of the invention is made by catalytically reacting a PPG with an HAS.
The PPG used can be any of those commer-cially available, or can be prepared by the well-known method of polymerizing propylene oxide, using an alkaline catalyst and a glycol or polyol initiator.
Preferably, the PPG has a number average molecular weight of 400-6000, more preferably 650-3000.
Number average molecular weight is determined by first determining the hydroxyl 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 -- ~1241024 Molecular weight = 56,000 X n hydroxyl number where n is the hydroxyl functi~nality of the sample.
The HAS used is represented by the structure R R

where R is hydrogen, an alkyl radi-cal of 1-3 carbon atoms, or phenyl.
The HAS preferred for use is ~,~'-dihydroxy-ethyl sulfide.
Any such HAS not available in the marketplace can be made by the well-known reaction of hydrogen sul-fide and an alkylene oxide.
The preparative reaction is conducted in a mixture of PPG and HAS. The relative amounts of HAS
and PPG used are dictated by the weight of HAS moieties desired in the product PPG. These amounts can be easily calculated using the principles of stoichio-metry. In general, one uses 0.5-6 moles of HAS for each mole of PPG, preferably 1-2 moles.
The catalyst used can be any heterogeneous or homogeneous acid catalyst stronger than H3PO4. It is preferably an alkyl- or aryl sulfonic acid such as methanesulfonic acid, or one of the strongly acidic cationic ion-exchange resins bearing -SO3H groups, insoluble in the reaction medium. "Insoluble" means that the amount of resin which dissolves in the medium under reaction conditions will give the modified PPG
product an acid number of no greater than 0.05 mg of KOH per gram. The nature of the "backbone" of the resin is unimportant. The most common of the 12~10~

commercially available resins of this type have back-bones which are of the polystyrene type, but resins having other backbones can be used.
Preferred among the polystyrene type resins, and preferred for use according to the invention, is one sold by the Rohm ~ Haas Company of Philadelphia, PA as Amberlyst* XN-lOlO. This macroreticular resin has a cation exchange capacity of 3.1 milliequivalents per gram, a surface area of 4~0 s~uare meters per gram, a porosity of 41%, and a mean pore diameter of 0.005 micron.
The catalyst is used at a concentration of 0.1-10%, by weight of the PPG, preferably 2-5%.
The preparation is begun by placing the PPG, about 10% by weight of the total HAS to be used, and the catalyst in a vessel and bringing the resulting mixture to a temperature of 130-170C, preferably about 150C, and holding it at that temperature, with stirring, until the HAS has been consumed, as shown by periodic sampling and analysis by gas chromatography.
The rest of the HAS to be used is slowly added to the reaction mass during this period, continuously or in small increments.
The water formed by the reaction can be re-

2~ moved from the reaction mass by vacuum distillation orby sweeping the reaction zone with an inert gas e.g nitrogen. Preferably, the water is removed as a water/hydrocarbon azeotrope, even more preferably as a water/toluene azeotrope. The hydrocarbon can then be separated from the azeotrope by condensation in a suitable trap and can be recycled to the reaction mass.
When this procedure is used, the temperature of the reaction mass can be easily held within the desired range by adjusting the concentration of toluene.
* denotes trade mark " ~Z*~02A`

When the PPG-HAS reaction is finished, heating is stopped and the catalyst is removed from the re-action mass, by precipitation with calcium hydroxide in the case of a homogeneous catalyst, or by filtration in the case of a heterogeneous catalyst. The remaining material is then stripped of residual volatiles.
The resulting product is a viscous liquid having a number average molecular weight of 500-10,000, preferably 800-5000, and an oxygen/sulfur atom ratio of 3/1 or greater, preferably 5-60/1. Molecular weight can be varied by simply allowing the reaction to proceed until the desired molecular weight is reached.
The blends of unmodified PPG and PPG modified according to the invention can be made by simply mixing them in amounts which will give a mixture containing 0.4-20%, by weight, of the modified PPG.
A polyurethane can be prepared from a modified PPG of the invention, or from a modified-unmodified blend, 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 polyure-thanes. "Polyisocyanate" means any compound bearing two or more -NCO radicals. Illustrative are 2,4-toluene diisocyanate 2,6-toluene diisocyanate hexamethylene-1,6-diisocyanate tetramethylene-1,4-diisocyanate cyclohexane-1,4-diisocyanate naphthalene-1,5-diisocyanate diphenylmethane-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 polymethylene polyphenyl isocyanate

4,4'-biphenylene diisocyanate 4-isocyanatocyclohexyl-4'-isocyanatophenyl methane p-isocyanatomethyl phenyl isocyanate.
Mixtures of isocyanates can also be used.
The isocyanates preferred for use because of the desirable properties they confer on the polyure-thane products are diphenylmethane-4,4'-diisocyanate and the 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 phenyl diethanolamine Diols like hydroquinone bis(~-hydroxyethyl)ether, tetra-chlorohydroquinone-1,4-bis(~-hydroxyethyl)ether and i241024 7 tetrachlorohydroquinone-1,4-bis(~-hydroxyethyl)sulfide, even though they contain aromatic rings, are considered 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'-methylene 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'-methylenedianthranilic 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 ~z4~0Z4 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 com-plexes thereof with alkali metal chlorides, bromides, iodides, nitrites and nitrates. Mixtures of amines can also be used.
The polyurethanes can be prepared in two steps, the first of which is conducted under nitrogen at ambient pressure to prevent oxidation of the re-actants and product, and to prevent exposure of the reaction mass to atmospheric moisture. In the first step, the modified PPG starting material is dried by heating it at a temperature of 80-100C under vacuum, and is then held at 60-125C, preferably about 70-90C, while a stoichiometric excess, preferably twofold to tenfold, of organic polyisocyanate is added, with stirring. The actual amount of isocyanate used depends on the molecular weight of the modified PPG used, as is well known in the art. The reaction mass is held for about 1-4 hours at 60-125C, with stirring, and the free isocyanate content of the mass is then deter-mined by titrating it with di-n-butylamine, as des-cribed in Analytic Chemistry of the Polyurethanes, Volume XVI, Part III, D. J. David and H. B. Staley, 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 0.9-l.l to 1 in the reaction mass, preferably 1-1.05/1, is degassed at about 30-120C and 1330-5330 Pa (10-50 mm Hg) pressure and quickly added to the reaction mass~

~24102~ 9 A 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 S 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 60-130~C until it is homogeneous, which normally takes 1-5 minutes. The mass is then poured into molds, pref-erably preheated to 100-120C, and then cured at about 100-120C 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-injection and liquid-injection molding tech-niques, whereby the starting materials are simultan-eously injected and mixed in a mold, preferably to-gether with a conventional polyurethane catalyst and then subjected to pressures ranging from ambient to several million pascals and temperatures ranging from ambient to 150DC. Use of a foaming agent e.g. a fluorocarbon or water is optional.
BEST MODE
In the following example, all parts are by weight.
The following were added to a reaction ves-sel fitted with a reflux condenser and a Dean Stark trap:
Polypropylene glycol Mn 1225 122.5 parts Toluene 50 parts ~,~'-dihydroxyethyl sulfide 5 parts Methanesulfonic acid0.4 part ~241024 lo The resulting mixture was heated to and held at reflux temperature for 7.5 hours, with stirring, while water was continuously removed from the reaction zone as the water/toluene azeotrope. During this interval, an additional 42.9 parts of ~ dihydroxyethyl sulfide were slowly added to the reaction mass over a six hour period. Samples removed at intervals during this pro-cess contained 8.6-14.3% of -O-CH2-CH2-S-CH2-CH2-moieties.
The catalyst was then neutralized with cal-cium hydroxide, filtered, and the volatiles removed from the remaining material at a pressure of about 667 Pa (5 mm of Hg) and a temperature of about 150C, to give a viscous liquid product containing 22% of -O-CH2-CH2-S-CH2-CH2- moieties, with a number average molecular weight of 4500 and an oxygen/sulfur atom ratio of 7/1.

Claims (15)

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

1. Polypropylene ether glycol modified so that it contains in its chain 1-25%, by weight, of moieties represented by the structure where R is hydrogen, an alkyl radical of 1-3 carbon atoms or phenyl, and the oxygen atom is linked to a hydrogen atom or a carbon atom.

2. The polypropylene ether glycol of Claim 1 having an oxygen/sulfur atom ratio of 3/1 or greater.

3. The polypropylene ether glycol of Claim 1 in which the moieties are represented by the structure -O-CH2CH2-S-CH2CH2-.

4. The copolyether glycol of Claim 1 which has a number average molecular weight of 500-10,000.

5. A mixture of unmodified polypropylene ether glycol and 0.4-20%, by weight of the mixture, of the polypropylene ether glycol of Claim 1.

6. A mixture of unmodified polypropylene ether glycol and 0.4-20%, by weight of the mixture, of the polypropylene ether glycol of Claim 2.

7. A mixture of unmodified polypropylene ether glycol and 0.4-20%, by weight of the mixture, of the polypropylene ether glycol of Claim 3.

8. A mixture of unmodified polypropylene ether glycol and 0.4-20%, by weight of the mixture, of the polypropylene ether glycol of Claim 4.

9. A method for preparing a thio-modified polypropylene ether glycol, the method comprising bringing together, under conditions suitable for reaction (a) polypropylene ether glycol;
(b) .beta.,.beta.'-dihydroxyalkyl sulfide represented by the structure where R is hydrogen, an alkyl radical of 1-3 carbon atoms or phenyl;
and (c) an acid catalyst.

10. The method of Claim 9 in which the catalyst is methanesulfonic acid.

11. The method of Claim 10 in which water is removed from the reaction mass by azeotropic distillation.

12. The method of Claim 11 in which the azeotrope is water/toluene.

13. A polyurethane which is the reaction product of (a) the polypropylene ether glycol of Claim 1;
(b) an organic polyisocyanate;
and (c) a chain extender.

14. A polyurethane which is the reaction product of (a) the mixture of Claim 5.

(b) an organic polyisocyanate;
and (c) a chain extender.

15. The method of Claim 9 in which the catalyst is Amberlyst (trade mark) XN-1010 resin.