CA1069237A - Faster preparation of polyurethane coating solutions - Google Patents

Abstract

METHOD OF PREPARING SOLVENT-BASED
COATING SOLUTIONS

Abstract of the Disclosure Disclosed is a novel procedure for making solvent-based polyurethane or polyurethane-polyurea compositions which makes it possible to avoid the production of compo-sitions that are undesirably underpolymerized or over polymerized. Moreover, the invention shortens the over-all time required to produce the composition. In essence, the invention involves a reversal in the order of steps usually \
used for making compositions of this sort: after a desired quasi-prepolymer of polyisocyanate and polyol is formed, a relatively small amount of secondary amine is added. The main polymerization with polyols and/or polyamines and the like is then permitted to take place. Desirably, as a last step, a suitable quantity of monoisocyanate is added to react with any unreacted amine groups and yield a final solution that has no reactive groups and has consequently an excellent pot life.

Description

sackground Of The Invention l. Field Of The Invention .
This invention relates to the making of solvent-based urethane coating solutions and in particular to a method whereby said solutions may be made reliably so that they have a desired degree of viscosity and so that this may be done in a time relatively shorter than that hitherto required for the making of compositions of this sort.

2. Description Of The Prior Art In accordance with the procedures hitherto known ..
for the making of solvent-based polyurethane coating solu~
tions, the isocyanate-terminated prepolymer has been per-mitted to react with a polyol and/or a polyamine compound -until a desired.degree of viscosity has been reached, at which point there is added to the reaction mixture a quan-tity of secondary amine. Secondary amines have the property of reacting with isocyanate groups to placeJ in effect, a limit upon the length of chain that can be achieved~with a~
given ratio of diisocyanate or polyisocyanate to active-: . .
hydrogen compound.
The~problem has been that it has been diffLcult ~ to determine when the monofunctional secondary amine should I; be added to the reaction mixture. If it is added too soon, 1~ a mixture o:E undesLrably low molecular weight results. If ¦ it i9 added too late, polymerization to an undesir~bly high ~ -;
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~L06923~
average molecular weight (gelling) tends to take place. In many instances, the interval between "too early" and "too late" is on the order of two minutes or somewhat less, taken in a total reaction time on the order of three to eight hours.
The failure to attain the desired degree of poly-merization results in unsatisfclctory compositions. If the reaction mixture is underpolymerized, it usually lacks the viscosity required for the intended application and needs to be diverted to another use~ often one less economically val- .
uable. When overpolymerization occurs, the results are ;
; usually far more serious; not only is the material fed to the batch substantially lost, but often the equipment in which the overpolymerized batch was made must be cleaned by time-consuming and arduous methods.
., - ,.:, .
In accordance with prior-art practices~ it has ~ -, been especially difficult to avoid gelling when working with~
; new and untried polyurethane compositions, even when using conditions such that the reactions should take place rather ~ ;
slowly. It has, moreover, been usual, in the making of -polyurethane coating compositions on a commercial scale, to ~ ~
.. ..
cause the reactions to proceed slowly, for example, over a period of three to eight hours as mentioned above. Though it has been apparent that it would be desirable to shorten !
' ~i- ,' ' .

'~ ' , -~C~6~7 the reaction time, it has not been apparent to those skilled in the art how this could be done, without making the time interval for adding the reaction-stopping amine so very short that it would be very difficult or impossible -to control the process adequately. According to the prior art, reaction times as short as 50 to 9O minutes in reactions of this kind have been unknown.
It has been found that by adding a relatively small proportion of secondary amine to a quasi-prepolymer derived from a polyisocyanate and a polyol, it is possible to obtain rapidly and with regularity polyurethane or polyurethane-polyurea compositions of desired molecular weight character-istics. In the remainder of the process, the polyurethane quasi-prepolymer to which a secondary amine has been added as mentioned above, is then reacted with an appropriate equivalent of polyol or polyamine to obtain a desired product. Then, usually, àny remaining amino groups are destroyed with a mono-functional isocyanate or the like.
Accordingly, the present invention provides an improved method of preparing a solvent-based polyurethane coating solution wherein a polyisocyanate is reacted with a polyol selected from the group consisting of hydroxy-terminated polyethers, polyesters and polyester-polyethers of an average molecular weight of about 350 to 5,000, which contain at least two terminal hydroxy groups, to form an NCO-terminated quasi-prepolymer and then the NCO-terminated quasi-prepolymer is ;
reacted with a composition having active ingredients selected from the group consisting of polyols, polyamines, and mixtures thereof to obtain a desired polymer having a room temperature viscosity of 5,800 to 16,000 centipoises. The improvement com-prises heating the polyol and the polyisocyanate at 70 to 100C
to produce a quasi-prepolymer having an NCO/OH ratio o~ 1.5 to 6.5, dissolving the quasi-prepolymer in a solvent to obtain -- ~a -- .
a`

`- ~069237 a solution having a solids content of 10 to 60% by weight, reacting with the quasi-prepolymer 0.010 to 0.3 equivalents of a monofunctional secondary-amine compound per equivalent of available NCO groups in the quasi-prepolymer to obtain a treated quasi-prepolymer, then reacting the treated quasi-prepolymer with substantially one equivalent of material having as an active ingredient a polyol, a polyamine, or mixtures thereof to obtain a product polymeric material.
The first step in the practice of the instant invention is the preparation of an isocyanate-terminated quasi-prepolymer having an NCO/OH ratio of 1.5 to 6.5. The quasi-prepolymer is not a true prepolymer, but rather a mixture or solution of prepolymer with some unreacted di-isocyanate. This is done by heating a diol and an organic diisocyanate at 70 to 100 degrees Centigrade for one to three ; hours, or until the theoretical percentage of available isocyanate is achieved.
The reaction is preferably conducted in the presence of a catalyst, such as stannous octoate or dibutyltin dilaurate.
The selection of a proper catalyst depends upon the particular diisocyanate and diol to be reacted. Other catalysts that are sometimes useful include cobalt naphthenate, lead benzoate, lead oleate, zinc naphthenate, zinc 2-ethylhexoate, and antimony pentachloride. For a discussion of the merits of various -~
; catalysts, see pages 64 to 69 of E.N. Doyle, The Development and Use of Polyurethane Products (McGraw-Hill, New York, 1971). -In monitoring a reaction of this kind, the avail-able isocyanate is readily determined in the usual manner, i.e., by reaclting a small sample with a suitable (excess) quantity of a suitable amine, such as dibutylamine, and then back-titrating.

Illustrative organic polyisocyanates which may be employed in accordance with the present invention include aromatic, aliphatic, and cycloaliphatic polyisGcyanates and combinations thereof. Representative of these types _ : : .

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are the diisocyanates such as m-phenylene diisocyanate, tolylene-2,,4-dii~socyanate, tolylene-2,6-diisocyanate, mixtures of 2J4- and 2,6-tolylene diisocyanate, hexamethylene-1,6-diisocyanate~
tetramethylene-1,4-diisocyanate, cyclohexane-1,4-diisocyanate~
naphthylene-1,5-diisocyanate, : 10 1-methoxyphenyl-2,4-diisocyanate, ~,3'-dimethoxy-4,4'-biphenyl diisocyanate,

3,3'-dimethyl-4,4'-biphenyl diisocyanate, and 3,3'-dimethyldiphenylmethane-4~4'-diisocyanate;
the triisocyanates such as

4,4',4"-triphenylmethane triisocyanate, and tolylene 2,4,6-triisocyanate, :
and the tetraisocyanates such as 4,4'-dimethyldiphenylmethane 2,2',5,5'-tetraisocyanate. ~:~
Others that may be useful include , 20 polymethylene polyphenylisocyanate 3 : ~ 4,4'-methylene-bis-(cyclohexylisocyanate)~;
1,5-pentamethylene:~diisocyanate;
4,4'-dicyclohexyldiisocyanate;
1 .
p-menthane-1,8^diisocyanate;
~ :-.

.' .

: . . . :

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isophorone diisocyanate; and trimethyl. hexamethylene diisocyanate. ...
Especially useful du~e to their availability andproperties are tolylene diisocyanate, diphenylmethane~4,4'-diisocyanateJ
polymethylene polyphenylisocyanate, and 4,4'-methylene-bis(cyclohexylisocyanate).
The polyols employed in the present Lnvention are hydroxy-terminated polyethers, polyesters or polyester-polyethers of an average molecular weight of about ~50 to

5,000, which contain two or more terminal hydroxy groups.
. Typical hydroxy-terminated polyethers include the following representative examples: .-.
polyoxytetramethylene diols, polyoxytrimethylene diols, .. .. .
hydroxy-terminated adducts of glycerol; trimethylolpropane; propylene glycol; ethylene glycol; neopentyl glycol; 1,4-butanediol; trimethylene~
glycol; 2,2-bis(4-hydroxyphenyl) propane; hydroquinone;
2,4-bis-hydroxymet~hyl cyclohexane; 2,2-b (~-hydroxycyclo- ..
hexyl) propane and the like with propylene oxide; 1,2-buty-lene oxide or mixtures thereof, and adducts of the above hydroxy compounds with propylene oxlde and ethylene oxide in ;` which the two oxides are added as a mixture or in sequence.

TyE)ical suitable hydroxy-terminated polyesters include the i.~ollowing representative examples: ~;.... .

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hydroxy-termina~ed poly(epsilon-caprolactone);
hydroxy-terminated copolymers of:
glycerine and adipic acid;
propylene glycol and succinic acid; :
trimethylene glycol and succinic acid;
diethylene glycol and phthalic acid;
l,4-butanediol and dime-thyl maleic acid;
2,2-diethyl-1,3-propanediol and isophthalic acid;
ethylene glycol and 2-methyl terephthallc acid; -` lO diethylene glycol and isophthalic acid;
trimethylene glycol and tetrachlorophthalic acid;
`; ethylene glycol and adipic acid: - :
neopentyl glycol and adipic acid;
`. 1J 4-butanediol and adipic acid;
, neopentyl glycol and isophthalic acid;
: l,6-hexanediol and adipic acid; :
diethylene glycol and adipic acid, ~ -~. and mixtures of any of the above glycols with any~
:.~ of the above acids or mixtures thereof.
Typical suitable hydroxy-terminated polyester~
`~ polyethers are represented by hydroxy-terminated copolymers of any of the foregoing or equivaLent polycarboxylic acids : and the previously listed polyether polyols. : : :~
Preferably the polyol employed is a diO1J and ~ ~.
especiaIly a polyester diol or mixture thereof with a : - . . . .. .
~ polyether diol.

~06~237 After ~here has been obtained, using polyols and polyisocyanates as indica~ed above, a quasi-prepolymer having an NCO/OH ratio as defined above, such quasi-pre-polymer is dissolved in a solvent or solvents to obtain a material having an appropriate solids content, taking lnto account the materials used and the intended purpose. ~ -Usually, this means the use of a material having a solids content on the order of 10% to 60% by weight.
In making the above-mentioned quasi-prepolymerJ
there will be used a relatively high NCO/OH ratio, on the order of 2.75 to 6.5 if a final product of relatively greater rigidity or strength is desired3 and there will be used an NCoioH ratio on the order of 1.5 to 2.75 if a relatively more flexibls material is desired. Of course, other things being equal, the nature of the final product can be influenced importantly by the chemical identity of the diisocyanate or polyisocyanate and the diol or polyol used. Those skilled~in the art are familiar with the con~

cept of using materials of greater '1functionality"
. .
(alcohols, isocyanates, or amines with three or more func~
tional groups per molecule) to obtain greater cross-linking . .
and correspondingly more nearly rigid polymerized materials.

Thus, in a desired case, trimethylolpropane or pentaerythri-~

~ ~ tol or sorbitol may be substituted for ethylene glycol, in ,~ ,. .. . .

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whole or in part~ or a triisocyanate or tetraisocyanate may be substituted, in whole or in partJ for the usual diiso-cyanate. As is usual, the molecular weights of the mono-meric materials use~, the time and temperature of reaction used to make a quasi-prepolymer or polymeric material of a given average molecular weight, the identity and effective-; ness of the catalyst presentJ if any, and the opportunity for cross-linking all need to be taken into account in establishing the nature of the polymeric material formed~
and those skilled in the art are well aware how one or more of these various factors can, in a given case, be suitably adjusted.
The next step in the practice of the invention is the addition of secondary amine. An important point is that the secondary amine is added in a relatively small quantity, compared with the amount of quasi-prepolymer i~ . . .
present. We use at this point 0.010 to 0.3 equivalent of ;
secondary amine per equivalent of available isocyanate in the quasi-prepolymer. The proportion that is used is de-.. . ..
.
pendent upon the state of viscosity at which it is desired j to stop the over-all polymerization reaction. If a rela-tively viscous final material or relatively high average molecular wleight is desired, the numbar of equivalents of , secondary amine added at this stage will be kept low, '~ : : ,' - ~' :, . : . ,' :.

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whereas if a material of relatively lower molecular weight and lower viscosi~y is desiredJ relatively more equivalents of secondary amine may be used.
Among the secondary amines that may be used are the following: dimethylamine~ diethylamineJ methyl-n- '" '' propylamineJ methylisopropylamine, ethyl-n-propylamineJ
di-n-propylamine, di-isopropylamine J n-propyl-n-butylamine, di-n-butylamine J di-isobutylamine J di-sec-butylamine J
ethylpentylamine J dipentylamine J di-isopentylamine, ethyl-hexylamineJ and dihe,xylamine.
IfJ as is usual in accordance with the prior artJ
no secondary amine is added at this stage, there exists the possibility that in the next step of the process, when the , polyisocyanate is treated with polyols and/or polyaminesJ
the reaction will proceed (with relatively little or no ..... .
,, chain-terminated material present) to the production of polymers of exceedingly high molecular weightJ a phenomenon ' ' that occurs readiIy as the ratio NCO/OH approaches unity.
What is accomplished by the addition of the secondary amine at this stage is to ensure that there is present at least ' .
some small fraction of polymeric material of relatively low , molecular weight. ~ ~

~' Having thus assured the presence of a certain : ,' proportion of chain-terminated polymeric moleculesJ we . ' : :'. , .
:

~069~

proceed with the reaction of the quasi-prepolymer with a substantially equivalent quantity of polyol and/or poly-amine. In this step of the reaction, it now becomes pos-sible to proceed more rapidly, in most instances, than has been possible in accordance with the prior art. In the prior-art practice, it has not been uncommon to devote a relatively long time, such as three to eight hours, to the process of adding the polyol and/or polyamine to the quasi-prepolymer. The final polymerization reaction is exothermic.
It has been desirable to proceed with it cautiously, adding relatively small amounts of polyol, polyamine or polyol-polyamine mixture, with the intention of adding chain-terminating secondary amine as soon as the viscosity reaches a desired level. It was frequently the case that the tim~g ~ the addition of the chain-terminating secondary amine needed to be gauged accurately, i.e., within some-; thing on the order of one to three minutes; otherwise, a product of undesirably higher or lower viscosity would result. With the instant invention, however, such accuracy is not required, and it becomes possible to add substan-tially one equivalent of polyol, polyamine, or polyol~
polyamine mixture per equivalent of available -NC0 groups and to adopt reaction conditions that cause a relatively rapid reaction of substantially all of the functional ~ ~
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~)69237 groups~ with the reaction being comple~ed within a period of time on the order of 45 minutes to 120 minutes. The reaction may be conducted at a suitable temperature, such as 25 to 70C. The shortening of the reactlon time is an important advantage, since it increases considerably the productivity o~ the reactor within which the chain-extending reaction is conducted and leads to correspond-ingly lower production costs.
- As chain-extending polyols used for reaction with the secondary-amine-~reated quasi-prepolymer in this step of the process, there may be used any suitable aliphatic or aromatic polyhydric alcohol, such as ethylene glycol, 1,3-propylene glycol, 1,2-propylene glycol, 1,4-butylene glycol, 1,3-butylene glycol, 1, 2-butylene glycol, :
l,5-pentanediol, 1,4-pentanediol, 1,3-pentanediol, ~
1,6-hexanediol, 1,7-heptanediol, glycerol, l,l,l-trimeth- ~ -ylolpropane, l,l,l-trimethylolethane, hexane-1,2,6-triol, ~-methyl glucoside, pentaerythritol, or sorbitol. Also - included with the term "polyhydric alcohol" are compounds ~-derived from phenol such as 2,2-(4,4'-hydroxyphenyl)propane, ;~-j ~ ~ commonly known as 'iBisphenol A".
. .
The chain extender primary diamines that can be used in this step of the process include ~

,` : ~ '-~

. - : .
.
: . .

~ 2 ~ 7 (a) ~3-bis(aminomethyl)oxacyclobutane, (b) ~ ~ -polyoxyalkylene primary diamines, (c) 1,4-cyclohexyl bis(methyl amine), (d) diaminodicyclohexylmethane, (e) isophorone diamine, (f) 1,6-hexanediamine, (g) ethylene diamine, (h) 2,3-diamino toluene, (i) 1,3-propylene diamine, (j) 1,4-butylene diamine, and (k) 1,3-butylene diamine.
Among these diamines, asymmet~c ones are pre-ferred to symmetrical ones.
Although in a usual case, there are used at this step in the reaction as many equivalents of polyol, poly- -amine or polyol-polyamine as there were of available iso-cyanate in the quasi-prepolymer, slight variations can, of course, be made, to suit particular requirements. For `~ exampleJ if there are used exactly as many equivalents of 20` polyol, polyamine or~polyol-polyamine mixture as there were of available isocyanate in the quasi-prepolymer initially ~`
(befoxe addition of the secondary amine), there will be as many excess hydr~oxyl or amine groups a9 there were equiv~
alents of 9econdary amine added to control the reaction.
.:

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~ Z ~ 7 Permi~ting these excess functional groups to remain in the composition is undesirable, since it tends to shorten the pot life or storage life of the final material; the un-reacted functional groups form sites for possible additional reactions. This is par~icuLIrly a problem when polyester-polyols are used. Accordingly, it is sometimes theoreti-cally desirable to diminish the amount of polyol, polyamine or polyol-polyamine present in the mixture by an appropriate amount, or if this is not done, to add to the reaction mixture, exactly an amount of monoisocyanate compound needed to react with the leftover -OH or -NH2 groups and `
- thus leave a product having substantially no reactive groups therein and having consequently a good pot life. In `
some instances, it may be appropriate to omit the taking of measures to eliminate reactive groups in the final product; -for example, if a composition is being prepared for imme- ~ `
diate use, obtaining a good pot life is not necessary.
The subsequent use of solvent-based polyurëthane coating compositions prepared according to the process explained above may be conducted in accordance with usual, conventional practices for coating substrates ~ith the similar compositions made by prior-art practices. This includes the use of such coatings on paper, textiles, leather, wood, and metal. Such coatings often have val-.

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~.. ~:~., -~6~Z37 uable pro~erties such as high adhesiveness, high gloss,good resistance to water and solvents and chemicals of various kinds, excellent electrical proper~ies, low perme-ability to gases, and good resistance to weather. They may find use in applications in which impact resistance and abrasion resistance are important. Thus, one may coat paper to make garments resistant to mustard gas, or textiles to make raincoats. One may coat wood to make bowling pins or spill-resistant table tops. One may coat the leading edge of an aluminum aircraft wing to improve its smoothness -~
and/or its resistance to weath~r. One may coat various -parts of chemical equipment to render them corrosion-resistant. One may coat wire eo provide it with electrical insulation and abra`sion resistance. The mode of applying the coating may be varied to suit requirements of the particular desired use. In a given case, dipping or ;
spraying or brushing may be used. Where it is convenient to do so, the coated part may some~imes be subsequently heated to assist~in the removal of the solvent and possibly to effect a curing reaction3 but some`coatings dry ade-i quately in air in several hours or days.
j .
,~ An unde`rstanding of the instant invention will be aided by reference to the following specific examples.

. , . .:

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.: : -t :1~6~23'7 An isocyanate-terminated quasi-prepolymer mate-rial is prepared by heating 100 parts by weight of a poly-ester diol having a hydroxyl number of 55.5 and an acid number of 0.3, obtained by esterification of equimolar proportions of ethylene glycol and l,4-butanediol with adipic acid, and 42 parts by weight of 4,4'-methylene-bis (cyclohexylisocyanate) in the presence of dibutyltin di-laurate as catalyst. The reaction is conducted at 70 to 80 degrees Centigrade for two hours, and there is thus ob-tained a polymer having an amine equivalent weight of 663.
Then~ 100 grams of this quasi-prepolymer are dissolved in 260 grams of dimethylformamide, and to this solution 2 grams of dibutylamine are added. This amounts to 0.1026 ~' equivalents of secondary amine per equivalent o~ available isocyanate in the quasi-prepolymer.
1: . , ~ . .
I Then, 12.9 grams of isophoronediamine are dis-,~ ; solved in 38.6 grams of dimethylformamide, and this i~
added to the quasi-prepolymer solution slowly, maintaining the temperature between 40 and 60 degrees Centigrade. The , ~ addition is completed within one hour.
After this, 3.1 grams of phenyl isocyanate are added to the solution;to react with any unreacted amine I~ ~ groups, and finally, 40 grams of isopropyl alcohol are f ` ~ .

.~
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, .,,. , . . . .. .. ~ .: . - . ` .

~237 added to the sol-ltion, to react with any unreacted iso-cyanate groups. The viscosity of the final solution is 7200 centipoises at 22 degrees Centigrade, and the solids content is 25.8~. After fifteen days of storage, the solution shows the same viscos:ity, i.e., 7200 centipoises at 22 degrees Centigrade.
The final solution is used to form a coa~ing in accordance with conventional practices.

A quasi-prepolymer is prepared by heating I00 parts by weight of hydroxy-terminated poly(epsilon-capro-lactone), having a hydroxyl number of 135 and an acid number of 0.04, and 61.6 parts by weight of 4,4'-methylene-bis -(cyclohexylisocyanate) at ~0 to 80 degrees Centigrade for two hours in the presence of stannous octoate as catalyst.
The amine equivalent weight of this quasi-prepolymer is ` 773. Then, 600 grams of this quasi-prepolymer are dis- ~
solved in 700 grams of toluene, and 7.5 grams of dibutyl- ~ -amine (0.0747 equivalents per equivalent of quasi-prepoly-mer are added to the solution. In 800 grams of isopropyl alcohol9 70 grams of isophoronediamine are dissolved, and this is added slowly (but within sixty minutes) to the quasi-prepolymer solution, while maintaining the temperature at ~0 to 50 degrees Centigrade. Phenyl isocyanate (9.
grams)is disoolved i~ to~uene (2a gr~ms) and this is -. : .
'~.,:

, ' ~ ' ' :
': ' ' ~ '' ' ~al69Z3~7 ; added to the above solution. Finally, isopropyl alcohol (40 grams) is add~d to this solution. The viscosity of the resultant solution is 5800 centipoises at 28 degrees CentigradeJ and the solids content is 25~ by weight. After fifteen days of storage, the viscosity of the solution is the same. The solution is used to produce a polyurethane coating in accordance with conventional practices.

A quasi-prepolymer is prepared by heating hydroxy-terminated polyepsiloncaprolactone (100 parts by weight) of nominal equivalent weight 1000 with 4,4'-methylene bis-(phenyl isocyanate) (32 parts by weight) at 40-50 degrees Centigrade for 2-3 hours. This quasi-prepolymer of amine equivalent weight 500 is dissolved in dimethylformamide ~ -(~50 parts by weight~ and heated to 45 degrees Centigrade.
Diethylamine (o.66 parts by weight; 0.03 equivalent per equivalent of prepolymer) is added to this solution. Extend-, . .. ..
er 1,4-butanediol (17.8 parts by weight) is gradually added `~ to above solution. Addition is completed within 60-go 20 minutes, and phenyl isocyanate (o.8 parts by weight) is finally added. Isopropanol (50 parts by weight) is added to ~
this solution to obtain a coating solution having 30% solid~ ~-by weight. The coating solution has a viscosity of 12,000 ;-. ~
centipoises at 25 degrees Centigrade. No change in vis-cosity is observed during storage.

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~69237 A quasi-prepolymer is prepared by heating poly~tet-ramethylene)glycol (100 parts by weight) of nominal equiva~
lent weight 1000 with 4,4'-methylene-bis-(phenyl isocyanate) (32 parts by weight) at 50-60 degrees Centigrade for 2-3 hours in toluene (238 parts by weight) as a solvent. The ; resultant solution has 30~ solids and an amine equivalent weight of 29~7~ This solution is cooled to ~0 degrees Centigrade, and diisopropylamine (0.45 parts by weight; 0.03 equivalent per equivalent of prepolymer) is added to it.
Chain extender 1,4-cyclohexane-bis(methylamine) (10.63 parts -by weight) is dissolved in isopropanol (130 parts by weight), and this is gradually added to the above solution. Addition is completed within 45-60 minutes. At this stage phenyl ;
isocyanate (0.5 part by weight) is added to the solution.
The viscosity of the resultant solution is 16,000 centipoises ;
at 25 degrees Centigrade, and the solid content is 28~ by weight. No change in viscosity is observed during storage.

To prepare a tie-coat type coating solution ini~
tially a prepolymer is prepared by reacting poly(oxypropylene) .,: .
glycol (100 parts by weight) of nominal equivalent weight : looo with tolylene diisocyanate (80/20) (15.2 par~s by weight) at 70-~0 degrees Centigrade for 2-3 hours. This , ', ~
1~ ~ ~..... ' :' -: , '.~ ' .
~. .

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prepolymer has an~ine equivalent weight of 1550. This is dis-solved in toluene (200 parts by weight), and methyl n-propyl-amine (0.16 parts by weight, 0.03 equivalent per equivalent of prepolymer) is added to it. Hexamethylene diamine (4.3 parts by weight) is dissolved in isopropanol (160 parts by weight), and this is gradually added to above solution at 40-45 degrees Centigrade. Addition is completed within 60-go minutes. Finally phenyl isocyanate (0.2 part by weight) is added to the solution. The resultant solution has 25% solids by weight and has a viscosity of 9000 centi-poises at 25 degrees Centigrade. No change in viscosity is - observed during storage. -~ `

.
A prepolymer o~ nominal equivalent weight 2260 is prepared by heating poly(diethylene glycol adipate) of .: ~ :
nominal equivalent weight 1250 (100 parts by weight) with ~ -tolylene diisocyanate (80/20) (13 parts by weight) for 2-3 ¦
hours at 70-80 degrees Centigrade. This prepolymer is dis~
solved in dimethyl formamide (140 parts by weight) and di-ethylamine (0.15, 0.04 equivalent per equivalent of pre~
polymer) is added to it. Methylene dianiline (4.96 parts by weight) is dissolved in 2-nitropropanol (11 parts by f weight) and methylethylketone (15 parts by weight). This ~s ¦~
'~ ~ gradually added to prepolymer solution. Addition is ~ completed within 60-go minutes. At this stage, phenyl ~ ;

t' ' i , j:' "

`: ~: r ;
-: . : ' l : ' ' . 10~;923'7 isocyanate (0.2 part by weight) is added to the solution.
Finally isopropanol (~ parts by weight) is added to the solution to obtain a coating solution having 40% solids by weight and a viscosity of 12,0lD0 centipoises at 25 degrees Centigrade. No change in viscosity is observed during storage.
There has thus been shown and described above a novel and unobvious procedure whereby solvent-based poly- ;
-urethane coating solutions or similar polyurethane composi-tions may be made in less time and~or with better control of the viscosity of the product solution.
While we have shown and described herein certain embodiments of our invention~ we intend to cover as well any change or modification therein which may be made without ~
; departing from its spirit and scope. u ~; :

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Claims (5)

1. The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:
   
   l. In making a solvent-based polyurethane coating solution wherein a polyisocyanate is reacted with a polyol selected from the group consisting of hydroxy-terminated polyethers, polyesters and polyester-polyethers of an average molecular weight of about 350 to 5,000, which contain at least two terminal hydroxy groups, to form an NCO-terminated quasi-prepolymer and then said NCO-terminated quasi-prepolymer is reacted with a composition having active ingredients selected from the group consisting of polyols, polyamines, and mixtures thereof to obtain a desired polymer having a room temperature viscosity of 5,800 to 16,000 centipoises, the improvement comprising heating the polyol and the polyisocyanate at 70 to 100°C to produce a quasi-prepolymer having an NCO/OH ratio of 1.5 to 6.5, dissolving said quasi-prepolymer in a solvent to obtain a solution having a solids content of 10 to 60% by weight, reacting with said quasi-prepolymer 0.010 to 0.3 equivalents of a monofunctional secondary-amine compound per equivalent of available NCO groups in said quasi-prepolymer -to obtain a treated quasi-prepolymer, then reacting said treated quasi-prepolymer with substantially one equivalent of material having as an active ingredient a polyol, a polyamine, or mixtures thereof to obtain a product polymeric material.
2. 2. An improvement as defined in claim 1, further characterized by the additional final step of reacting said product polymeric material with an amount of a monofunctional compound effective to destroy reactive groups therein and yield a product having good storage life.
3. 3. An improvement as defined in claim 1, characterized in that the step of reacting said treated quasi-prepolymer with substantially one equivalent of material having as an active ingredient a polyol, a polyamine or mixture thereof is done by addition of said material to said treated quasi-prepolymer over a period of time substantially less than three hours.
4. 4. An improvement as defined in claim 3, characterized in that the step of reacting said treated quasi-prepolymer with substantially one equivalent of material having as an active ingredient a polyol, a polyamine or mixture thereof is done by addition of said material to said treated quasi-prepolymer over a period of time on the order of 45 to 120 minutes.
5. 5. An improvement as defined in claim 4, further characterized by the additional final step of reacting said product polymeric material with an amount of a monofunctional compound effective to destroy reactive groups therein and yield a product having good storage life.