Sulfur-modified copolyether glycols, a method for preparing them, and polyurethanes prepared therefrom

Copolyether glycols are modified so that they contain 1-25%, by weight of .beta.,.beta.'-dihydroxyalkyl sulfide moieties. These modified copolyether glycols have enhanced resistance to degradation by heat and oxygen. The invention also relates to a method of making the modified copolyether glycols, to their use as stabilizers against the degradation of the polyether chains, and to polyurethanes made with them.

DESCRIPTION 
Technical Field 
This invention relates to copolyether glycols which have been modified so 
that they contain sulfur-containing moieties in their polymer chains. It 
is more particularly directed to such copolyether glycols modified to 
contain dehydrated .beta.,.beta.'-dihydroxyalkyl sulfide (HAS) moieties in 
their chains. 
The invention also relates to a method of making the modified copolyether 
glycols, to their use as stabilizers against the degradation of the 
polyether chains, 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 which has been used for this purpose is the copolyether glycol 
(CPG) based on tetrahydrofuran (THF) and an alkylene oxide (AO), which is 
well known to be degraded by exposure to oxygen, light and heat. It has 
been the general practice to guard against this degradation by blending 
with the CPG an external stabilizer such as a phenolic, an amine or a 
sulfur compound. 
It has now been found, according to the invention, that the stabilization 
can be more effectively and efficiently achieved if the CPG is modified so 
that it contains in its chain 1-25%, by weight, preferably 3-15%, even 
more preferably 4-10%, of moieties represented by the structure 
##STR1## 
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. 
Preferably the modified CPG 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 CPG to be used 
is physically blended with about 0.4-20%, by weight, of the modified CPG. 
In addition, the method for preparing the modified CPG of the invention can 
be used to increase the molecular weight of the CPG by coupling polymer 
chain segments with HAS moieties. 
It has also been found that a CPG modified according to the invention shows 
significantly better resistance to acid-catalyzed depolymerization and to 
oxidative degradation at high temperatures than an unmodified CPG. 
DETAILED DESCRIPTION OF THE INVENTION 
The modified CPG of the invention is made by catalytically reacting a 
suitable CPG with an HAS. 
The CPG starting material is one based on THF and an AO, and is sometimes 
also referred to as a copolymer of THF and an AO. 
"AO", as used herein, means an alkylene oxide whose ring contains two or 
three carbon atoms. The AO can be unsubstituted or substituted with, for 
example, alkyl groups or halogen atoms. Illustrative alkylene oxides are 
ethylene oxide (EO), 1,2-propylene oxide (PO), 1,3-propylene oxide, 
1,2-butylene oxide, 1,3-butylene oxide, 
2,2'-bis-chloromethyl-1,3-propylene oxide and epichlorohydrin. The 
copolyether glycols preferred for use are those of THF and EO and THF and 
PO. The CPG can also be of THF and two or more alkylene oxides, as for 
example a THF/EO/PO polymer. 
The CPG will have 
(1) 10-80%, by weight, of AO units, preferably 20-60%, even more preferably 
30-55%; and 
(2) hydroxyl functionalities of 2.0-4.0, preferably 2.0-2.5. 
The CPG starting material can be of any practical molecular weight, but 
will preferably have a number average molecular weight of 500-4000, even 
more preferably 800-3000. 
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 
##EQU1## 
where n is the hydroxyl functionality of the sample. 
The CPG can be produced by any of the known methods. Illustrative of such 
methods are those shown in British Pat. No. 854,958 and U.S. Pat. No. 
4,127,513. The disclosures of those documents are incorporated into this 
application to show how such copolymers are prepared. 
The HAS used is represented by the structure 
##STR2## 
where R is hydrogen, an alkyl radical of 1-3 carbon atoms or phenyl. 
The HAS preferred for use is .beta.,.beta.'-dihydroxyethyl sulfide. 
Any such HAS not available in the marketplace can be made by the well-known 
reaction of hydrogen sulfide and an alkylene oxide. 
The preparative reaction is conducted in a mixture of CPG and HAS. The 
relative amounts of HAS and CPG used are dictated by the weight of HAS 
moieties desired in the product. These amounts can be easily calculated 
using the principles of stoichiometry. In general, one uses 0.5-6 moles of 
HAS for each mole of CPG, preferably 1-2 moles. 
The catalyst used can be any heterogeneous or homogeneous acid catalyst 
stronger than H.sub.3 PO.sub.4. It is preferably an alkyl- or aryl 
sulfonic acid, even more preferably one of the strongly acidic cationic 
ion-exchange resins bearing --SO.sub.3 H 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 CPG 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 
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 preferred for this use 
according to the invention, is one sold by the Rohm & Haas Company of 
Philadelphia, PA as Amberlyst.RTM. 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 0.005 micron. 
The catalyst is used at a concentration of 0.1-10%, by weight of the CPG, 
preferably 2-5%. 
The preparation is begun by placing the reactants and catalyst in a vessel 
and bringing the resulting mixture to a temperature of 
130.degree.-170.degree. C., preferably about 150.degree. C., 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 water formed by the reaction can be removed from the reaction mass by 
vacuum distillation or by sweeping the reaction zone with an inert gas 
such as 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 easily be held 
within the desired range by adjusting the concentration of toluene. 
When the CPG-HAS reaction is finished, heating is stopped and the catalyst 
is removed from the reaction 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 about 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 CPG and CPG 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 CPG. 
A polyurethane can be prepared from a modified CPG 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 
polyurethanes. "Polyisocyanate" means any compound having 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 polyurethane 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(.beta.-hydroxyethyl)ether, 
tetrachlorohydroquinone-1,4-bis(.beta.-hydroxyethyl)ether and 
tetrachlorohydroquinone-1,4-bis(.beta.-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 
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 polyurethanes can be prepared in two steps, the first of which is 
conducted under nitrogen at ambient pressure to prevent oxidation of the 
reactants and product, and to prevent exposure of the reaction mass to 
atmospheric moisture. In the first step, the modified CPG-starting 
material is dried by heating it at a temperature of 80.degree.-100.degree. 
C. under vacuum, and is then held at 60.degree.-125.degree. C., preferably 
about 70.degree.-90.degree. C., 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 CPG used, as is well known in the art. The reaction mass is held 
for about 1-4 hours at 60.degree.-125.degree. C., 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. 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 
0.1-1.1 to 1 in the reaction mass, preferably 1-1.05 to 1, is degassed at 
about 30.degree.-120.degree. C. and 1330-5330 Pa (10-50 mm Hg) pressure 
and quickly added to the reaction mass. 
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 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.degree.-130.degree. C. until 
it is homogeneous, which normally takes 1-5 minutes. The mass is then 
poured into molds, preferably preheated to 100.degree.-120.degree. C., and 
then cured at about 100.degree.-120.degree. C. 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 techniques, whereby the starting materials are 
simultaneously injected and mixed in a mold, preferably together with a 
conventional polyurethane catalyst and then subjected to pressures ranging 
from ambient to several million pascals and temperatures ranging from 
ambient to 150.degree. C. Use of a foaming agent such as a fluorocarbon or 
water is optional.

BEST MODE 
In the following example, all parts are by weight. 
The following were added to a reaction vessel fitted with a reflux 
condenser and a Dean Stark trap: 
______________________________________ 
Copolyether glycol of 
THF and EO 63/37 
--M.sub.n - 1000 100 parts 
.beta.,.beta.'-dihydroxyethyl sulfide 
12.2 parts 
Toluene 50 parts 
Amberlyst.RTM. XN-1010 4.0 parts 
______________________________________ 
The resulting mixture was heated to and held at reflux temperature for 
nineteen hours, with stirring, while water was continuously removed from 
the reaction zone as the water/toluene azeotrope. 
The reaction mixture was then filtered to remove the Amberlyst.RTM. and the 
volatiles were removed at a pressure of about 667 Pa (5 mm of Hg) and a 
temperature of 150.degree. C., to give a viscous liquid product containing 
5.6% of --O--CH.sub.2 CH.sub.2 --S--CH.sub.2 CH.sub.2 -- moieties, with a 
number average molecular weight of 3611 and an oxygen sulfur atom ratio of 
31/1.