CA1038526A

CA1038526A - Stable polyurethane solutions

Info

Publication number: CA1038526A
Application number: CA224,545A
Authority: CA
Inventors: Charles S. Schollenberger; Kornelius Dinbergs
Original assignee: BF Goodrich Corp
Current assignee: Goodrich Corp
Priority date: 1974-07-01
Filing date: 1975-04-14
Publication date: 1978-09-12
Also published as: NL7505540A; BE830669A; FR2277123A1; US3939111A; DE2527991A1; IT1036398B

Abstract

ABSTRACT

Viscosity stable polyurethane solutions in polar solvents such as N,N-dimethylformamide are obtained when such solutions contain small amounts of ammonium salts of strong acids, such salts include ammonium chloride and nitrate;
the stabilized solutions may be heated without fear of de-gradation and may be used to coat and impregnate fabrics, for example, upholstery, outer garments and shoe fabrics.

Description

~0~;~6 The invention relates to stabilized polyurethane solutions. ~ ; -Solid polyurethanes dissolved in solvents have many applications. For example, such polyurethane solutions are ~: .
used in the manufacture of films, coatings as on fabric, metal and the like, and as adhesives. Unfortunately, in many of these polyurethane'solutions the polyurethane begins to degrade in a relatively short time after preparation in the strongly polar soIvents often required. Degradation of polyesterure-thanes in solutions of O ~.
~Rl R-C-N

; wherein the R, Rl and R2 are each selected from hydrogen and alkyl groups is particularly bad. ~herefore, it is desirable to be able to provide stabilized polyurethane solutions .
which have good storage life even under relatively high temperature conditions.
According to the invention there is provided a ;~
solution of polyurethane in a polar solvent containing a viscosity stabilizing amount of an ammonium salt of a strong ;;
inorganic acid.

Viscosity stable polyurethane solutions are thus provided which contain small amounts of ammonium salts of `~
strong acids.
.; , ~The ammonium salts include the salts of the strong inorganic acids including hydrochloric acid, sulfuric acid, nitric acid and the like in amounts of from about 0.01 to 2 or more, preferably 0.05 t~ 1 percent.
Ammonium salts of weak organic acids such as !~
acetic ~cid are unsatisfactory as stabilizers for the solutions.

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Preferred materials are ammonium chloride, ammonium 1sulfate and ammonium nitrate. Ammonium chloride and ammonium ~; ;
nitrate are particularly effective stabilizers for solutions of polyesterurethane in DMF at elevated temperatures such as 65C. Ammonium acétate is ineffective in this system. ~?
The polyurethanes are readily prepared from a variety of compounds having terminal functional groups reactive ~`~
with -. -'` ~.~.' , ,~
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organic diisocyanates. Normally used are hydroxyl-terminated , compounds. The hydroxyl-terminated compounds or macroglycols usually have molecular weights greater than about 300 to 400. ~;
A great variety of such macroglycols have been prepared and pro-posed for commercial applications. The mo~t commonly used macroglycols are hy~roxyl-terminated polyesters, polyethers~
polylactones and polybutadienes. In the preparation of one type o~ elastomeric ~ilm and sheet materia:L such macroglycols, alone or in admixture, having molecular weights greater than about 400, and difunctional chain èxtenders as glycols, are '~ ~' reacted with the organic diisocyanate. Useful matérials are ;
obtained by reacting the organic diisocyanate`with a mixture of a macroglycol and a small difunctional chain extender such as an alkylene glycol or~ther glycol, a cycloaliphatic glycol, '~
or an aromatic-aliphatic glycol; or the so-called prepolymer technique may be used where an excess of organic dilsocyanate ' ~;
is first reacted with the macroglycol and then the small di~
~unctional chain extender added, normally in amounts equivalent to react with substantially all o~ the free isocyanate groups. '~
The hydroxyl polyester macroglycols are linear hy-droxyl-terminated polyesters having molecular weights between about 500 and 4000 and acid numbers usually less than about 10 The polyesters utilized include those prepared by the poly-esterification o~ allphatic dicarboxylic acids including ~or ',~
example, adipic, succinic, pimelic, suberic, azelalc, sebacic and the llke or their anhydrides. Aromatic dicarboxylic aclds ~ -may also be used, or mixtures of a,liphatic and aromatic dicar-~ .
boxylic acids. Useful acids include aliphatic dicarboxylic '' , acids of the ~ormula HOOC-R-COOH where R is an alkylene radical ; ,, containing 2 to 8 carbon atoms. The phthalic acids are also use~ul. The glycols used in the preparation of the polyesters ~ ~' by reaction with the dicarboxylic acids are al:Lphatic glycols ~ containing between 2 and 10 carbon atoms such as ethylerle gly~
,, -3-col, propanediol, butanediol, hexamethylene glycol, octamethyl~
ene glycol, 2-ethylhexanediol-1,6, neopentyl glycol and the like.
Preparation o~ specific polyesterurethanes from polyesters are ~ ;
described in U.S. Patent 2,871,218 ~or example. PolyesteramideS
also are contemplated, usually by substitution o~ a dlamine or amino alcohol ~or at least part of the glycol.
Poly(epsilon-caprolactone)diol macroglycols are the polyester reaction products o~ epsilon-caprolactones whose polymerization has been initiated by bifunctional compounds having ~WQ active hydrogen sites which are capable o~ opening the lactone ring and initiating polymerization of the lactone.
These bi~unctional materials may be represented by the formula HX-R-XH whereln R is an organic radical which c~n be aliphatic, cycloaliphatic, aromatic or he terocycl~c and X i8 0, NH and NR
where R is a hydrocarbon radical which can be alkyl, aryl, ar~
alkyl and cycloalkyl. Such materials include diols, diamines . ,,. , ~
and aminoalcohols preferably. Use~ul diols include alkylene ~ ;~
glycols wherein the alkylene group contains 2 to 10 carbon atoms ;~
for e~ample, ethylene glycol, 1~2-propane diol, butanediol-1,4, hexamethylene glycol and the like. Ethylene glycol provides . ~ . . .
excellent polyesters.
The lactones preferred for preparing the polyesters ~;
are epsilon-caprolactones having the general ~ormula ~ ;
R R R R R
, H-C-C-C-C-C-C=0 wherein at least 6 o~ the R' B are hydrogen and the remainder are hydrogen or alkyl groups containing 1 to 10 carbon atoms, pre~erably methyl. Mixtures o~ lactones ma~ be employed to ~orm the polyesters as epsilon-caprols.ctone and trime~hyl-epsilon-caprolacton~,-r-methyl-epsi}on-caprolactone, ~-methyl-,.

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epsilon-caprolactone, dimethyl-epsilon-caprolactone and the like.
The lactones are polymerized readily by heating wLth the bi functional reactant to a temperature of about 100 to about 200C.
Catalysts may be ernployed if desired. Particularly preferred are poly(epsilon-caprolactone)diols having molecular weights in the range of about 500 to about 5000.
The hydroxyl(polyalkylene oxide), or polyether, macro-glycols preferably are essentially linear hydroxyl-terminated compounds having ether linkages as the ma3or lin~age ~oining carbon atoms The molecular weights may vary between &bout 500 and 4000. The hydroxyl(polyalkylene oxide)s found useful ~ ;~
include hydroxyl poly(methylene oxide)s as hydroxyl poly(tetra-methylene oxide), hydroxyl poly(trimethylene oxide), hydrox~l i poly(hexamethylene oxide), hydroxyl poly(ethylene oxide) and the like o~ the formula HO(CH2)nOxH wherein n is a number ~rom 2 to 6 and x is an integer, and alkyl substituted types such as hydroxyl poly(l,2-propylene oxide). Prep~ration of polyurethanes from these polyethers is described in U.S. Patent :.:

2,899,411 for example. `
If small glycols are used as chain extender with the macroglycol~ and the organic diLsocyanate, these normally are aliphatic glycols or ~her glycols containing 2 to 10 carbon atoms. Typical glycols which have been employed include etnyl- ;
ene glycol, propylene glycol, butanediol-1,4, hexanediol, 2 ethylhexanediol-1,6, neopentyl glycol and the like. Cycloali~
phatic glycols such as cyclohexanedimethanol, and aromatic-aliphatlc glycols such as bis-1,4(~-hydroxyethoxy)benzene, may also be employed. `~
The amount of glycol chain extender used with the macroglycol and the diisocyanate may vary ~rom abou~ 0.1 to 12 mols per mol o~ macroglycol. Excellent polyurethanes are obtained with a molar ratio of one mol of macroglycol and 1 to , 5 .
n ~

1(~;3 8SZ6 ~
5 mols o~ t~e small chain extender ~lycol. Sub~tituted glycols also may be used.
. :
The organic dilsocyanates which are reacted with the macroglycols will include, for example, both aliphatic and aromatic diisocyanates. Such aliphat~c di:lsocyanates include for example, hex~methylene diisocyanate, methylene-bis(4-cyclo-hexyl isocyanate), lsophorone diisocyanate, etc. The aromatic ;~
diisocyanates include naphthalene-1,5-diisocyanate, diphenyl .: :
methane-4,4'-diisocyanate, tolylene diisocyanate, p~phenylene ~ ~ ;
diisocyanate, dichlorodiphenyl methane d~isocyanate, dimethyl . ~
diphenyl methane diisocyanate, bibenzyl diisocyanate, diphenyl `~ `
ether diisocyanates, bitolylene diisocyanates and the like, I
for example, diisocyanates of the formula ~ `

OCN ~ X ~ NCO

wherein X may be a valence bond, an alkylene radical containing 1 to 5 carbon atoms, NR where R is an alkyl radicaI, oxygen, ;`
sulfur, sulfoxide, sulfone and the like. Also usefill are acy- ~;
clic or alicyclic diisocyanates containing greater than 6 car- ;
bon atoms as 4,4'-methylenebis-(cyclohexyl diisocyanate).
About equimolar ratios of diisocyana-te and diols may be used. When a ~mall glycol ch~in extender is also used, the ratio o~ reactants employed may be varied ~rom about 1.5 to 13 ;
mols of organic diisocyanate per mol of macroglycol with 0.5 to 12 mols of the glycol. The amount of organic dii:socyanate used is dependent on t`he total amount of glycol chain extender and macroglycol and normally is a molar amount essentially eguiva~
lent to the total o~ these latter two reactants so that there are essentially no ~ree unreacted isocyanate groups remaining - ~ -in the polymer. Excellent polyurethanes have been obtained 3o when a molar ratio of one mol of macroglycol of molecular weight : . . , . , . . ,: , . . . .. . .. .. .. . . ..... .
.. : .. .. .. . . . , . . - , ~038~i21~
about 800 to 2500, 1 to 3 mols of glycol, and 2 to 4 mols of the aromatic diisocyanate are caused to react. While essen-tially equimolar amounts of isocyanate and active hydrogen groups are preferred, it will be understood that an excess of any re~
actant, preferably less than 10%, as 5~, of excess organic di-isocyanate can be used, although larger amounts of diisocyanate can, of course, be used in forming prepol,~mers. These, of course, have to be kept free of moisture until further reaction with the chain extender component is desired.
Other polyurethane materials that are well known and prepared in a variety of ways as is described in the patent literature may be used. For example, hydroxyl-terminated poly-esters, polyester~mides, polyalkylene ether glycols and the like of molecular weights from about 800 to 3000 or higher are reacted with organic isocyanates, generally with an excess of the diisocyanate. The resulting polyurethane elastomers may be cured or vulcanized by ~dding additional organic diisocyanate -whereas only a slight excess of isocyanate iB ueed to make the polyurethane; or if a substantial excess of organic diisocyan-.
ate is used in making the polyurethane, then the lsocyanate~
te~ninated polyurethane is mixed or treated or exposed to such ~ -amounts of polyfunctional additives such as water, diamines, : ;
glycols, and t~e like that will result in its curing or vul- ~ ;
canization. The excess dlisocyanate present or added is in ;;
amounts from about 1 to 25~, preferably 3 to 15 weight parts per 100 weight parts of polyurethane. Regardless of the source of the polyurethane, the process of this invention may be used for solutions.
Solvents used are any of those known to those skilled . 30 in the art ~or dissolving polyurethanes, which normally are polar solvents including substituted amides such as N,N-dimethyl- ~-formamide and N,N-dimethyl acetamide. The invention is, in 1~ ~--7~

., ~eneral, useful where solvents having the general formula ~ ~
O '~
R-C~

where R is hydrogen or alkyl, are used. ~ ~;
EXAMPLES
A 30~ polyure~hane solution was prepared by dissolv-ing a polyurethane in dimethylformamide. The polyurethane is ;~
a polyesterurethane prepared ~rom l mol of a poly(tetramethyl~
. , ~ . .
eneadipate) polyester o~ 1050 molecular weight, 2 0 mols of : ~
.. . .
butanediol with an equal molar proportion o~ diphenyl methane diisocyanate. In two portions o~ this solution there are separately dissolved 0.1 weight percent of ammonium sulfate and !;~
0.1 weight percent o~ ammonium nitrate. The Brook~ield viscos~
ity o~ these two solutions, and a control containing no ammonium ~;
salt, was determlned at room temper~ture using spindle 5 at i~ ;
5 rpm and found to be 43,400 cps ~or the control, 42,600 cps for ammonium sulfate and 44,800 cps ~or ammonium nitrate. The samples were heated at a temperature of 69C. for 72 hours, -~
... . ~ ., ~
cooled to room temperature and the Brookfield YiSCQSity deter~
mined again. The control was 23,900 cps, only 55% o~ the ori~
ginal viscosity, that of the ammonium sulfate was 30,800 cps, 72% o~ the original viscosity, and for the ammonium nitrate, `~
41,000 cpS, 92% of the original visoosity value. The behavior o~ ;
the control clearly shows that the polymer was degraded during this aging period by the~substantial decrease ln the molecular ~ weight o~ the polyesterurethane containing no ammonium salt.
A 30~ solutlon Or the polyeste~urethane o~ Example I~
was prepared into which there was dis~olved (l) 0.1 we~ght per~
cent ammonium chloride and (2) another 0.2 weight percent am-monlum chloride. Using spindle 5 at 5 rpm, Brook~ield Visco-meter, the viscosity at room temperature of the 0.1 weight ~ ~ ;

:~

~LQ3~5~6 percent of the ammonium chloride solutions was 49,120 cps and ~ ;
that o~ the 0.2% was 48,560 cps. After aging in a 70C. oven ~or 3 days and cooled to room temperature for testing, it was ~ound that the viscosity of 0.1 weight percent solution was ;
41,600 cps and that o~ the 0.2 weigh~ percent solution was ;~
40,400 cps, retaining 84.5~ and 82.2~ o~ the origlnal unaged ;~
viscosity of the solutions.
Among the advantages o~ this invention is that solu~
,: .
tions may be made more readily by heating the mixture of poly~
.
10 urethane and solvent without fear of degradation which would be " . .
o~ concern in the absence o~ the ammonium salt. Further, in processes where warm solutions are re~uired the stabilized solu~
t~ons o~ this invention may be heated for longer periods of time without degradation than solutionq not containing the ammonium 15 salt. These stabilized solutions find particular utility in coatlng and impregnatlng fabrics useful, ~or example, in up-holstery, outer garments as in coats and shoe ~abrics.

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Claims

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

1. A solution of polyurethane in a polar solvent containing a viscosity stabilizing amount of an ammonium salt of a strong inorganic acid.

2. A solution of claim 1 wherein the solution contains an organic polar solvent and about 0.01 to about 2% by weight of said ammonium salt.

3. A solution of claim 2 wherein the ammonium salt is selected from the group consisting of ammonium chloride, ammonium nitrate and ammonium sulfate.

4. A solution according to claim 3, wherein said solvent is of formula wherein R, R1 and R2 are each selected from hydrogen and lower alkyl.

5. A solution of claim 1, 3 or 4 wherein the polyurethane is a polyetherurethane.

6. A solution of claim 1, 3 or 4 wherein the polyurethane is a polyesterurethane.

7. The solution of claim 1, 3 or 4 wherein the ammonium salt is ammonium chloride or ammonium nitrate present in an amount of about 0.05 to 1%, and said polyurethane is a poly-etherurethane.

8. The solution of claim 1, 3 or 4 wherein the ammonium salt is ammonium chloride or ammonium nitrate present in an amount of about 0.05 to 1%, and said polyurethane is a polyester-urethane.

9. The solution of claim 1 or 3 wherein the solvent is dimethylformamide, the ammonium salt is ammonium chloride or ammonium nitrate present in an amount of about 0.05 to 1%
and said polyurethane is a polyetherurethane.

10. The solution of claim 1 or 3 wherein the solvent is dimethylformamide, the ammonium salt is ammonium chloride or ammonium nitrate present in an amount of 0.05 to 1% and said polyurethane is a polyesterurethane.