CA1057299A - Biuret polyisocyanates - Google Patents

Abstract

Abstract of the Disclosure Biuret polyisocyanate is prepared by reacting a hin-dered polyamine and a polyisocyanate at elevated tempera-tures, in the presence of an excess of polyisocyanate. The resulting product may be utilized to prepare an outstanding foam composition.

Description

~C3 57Z~
B~CKGROUND OF T~ INVENTION
Thifi Invention relate6 to a method for preparlng bluret polylsocyanates, and ln particular relates to a method ~or preparing biuret polyl~ocyanate~ from hindered dlamlnes and dlisocyanates.
It has been known, in the past, to form polyure-thanes by reacting polyols and polyisocyanates. Foam~ may ~;'`'r be produced by this reactlon lf it is conducted in the presence of a blowing agent.
The foams which have been formed in-this manner, have in general, been satisfactory but a need for improvement in certain areas still exists. For instance9 foams often are shipped in railroad box cars and because of their volumin-ous nature a great deal of space is needed to transport them.
A foam which could be compressed during shipment and de-.
compressed at ite distination to its original s~ze and shape would of course be an improvement since it would require less space in transit and enaple one to ship greater quantities .
i~ the same txansporting vehlcle.
Further~ quality control when preparing polyure-. .
; thane ~oamsg h~s been d~icult because the ultimate physical ~
.
properties have been slow to develop after requirlng periods `-~
up to a ~ew days for completion. Consequently~ prompt re- ;
cognition and rectification of problems could not be made æince approximately several days were xequired on occa610n to determine i~ there wa in fact a problem to be solved.
Thusg a need exists for polyurethane foam which may readily be compressed for shipplng and also develop ultimate -;~
properties rapidly so tllat quallty controls procedures may be .. . .. .
: 30 applied promptly when they are needed; the foam must not be ~ deficient with respect to any other properties.
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SUr~MARY 0~ THE INVFNTION
According to this invention a biuret polyisocyante has been discovered which when reacted with an organic com pound containing active hydrogen will ~orm the desired polyurethane foams. It is also intended to be within the ;~
~ - scope of the instant invention to ~orm elastomers, coatings -~ and adhesives by means of reactions wlth the same biuret ,- . . . .
polyisocyanate.
The biuret polyisocyanate, which is preferably a polybiuret polyisocyanate~ is formed by reacting a hindered `~ polyamine and an excess of a polyisocyanate, e.g. diiso~
cyanate.
The diisocyanate which is utilized may be aromatic, aliphatic or cycloaIiphatic diisocyanate. The preferred organic polyisocyanates are Cg-C25 aromatics, C2-Cl~ ali-phatics and C~-C25 cycloaliphatics.
In particular, an aromatic diisocyanate~ e.g., `
....
toluene diisocyanate is much preferred. This would include toluene-2,4 diisocyanate, toluene-2,6-diisocyanate, and , ~ . . . .
~20 mixtures thereof.
, . , ~ ~ -.
Regarding the reaction itself, at least two moles of di:isocyanate are present for each equivalent of ~he amine :
group. The temperature for the reaction is elevated and should range between about 80-200C., preferably 130-180C. ~`~
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Pressure is preferably arnbient but superatmospheric may also be utilir~ed. The reaction ~ill generally take place in a : . .:

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max:imum period of about 24 hours deper~cl:Lng on the :ingredi ents, their concentration, the temperat;ure and the equlpment available.
The resulting biuret, if it is to be formed into a foam, is then reacted with a suitable organic compound containing active hydrogen groups as determined by the Zerewitinoff method in the presence o~ a blowing agent such as water or trichlorofluoromethane. Flexible foams having the desired proper-ties which are enumerated above can be prepared in this manner.
- DETAILED DESCRIPTION
' This invention relates to novel biuret polyiso-cyanates, a method for their preparation and their use in producing superior polyurethanes, especially flexible foams.
The biurets are produced by reacting a hindered polyamine and a diisocyanate. The polyamine component must have at least 50% of its amine groups substituted to an aromatic nucleus and is hindered by having positioned ; ~ ortho thereto a fluorine, chlorine7 bromine, CF3, NO2 or COOR (where R is Cl-C4 alkyl) subskituent.
Polyamines prepared by condensation of properly substituted aniline derivatives with formaldehyde in the presence of strong acids are preferred. The crude conden-sates obtained by this reaction can be used directly after -:. :
any excess aniline derivatives have been removed. In carrying out the condensation from about 1.0 to 10 moles of substituted aniline per mole of formaldehyde can be used.
If less than about 3 moles of aniline are used per mole of ,: :
formaldehyde, significant amounts of polyamines having 3 functionalities of three or more are obtained in addition : :.. '~

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~ ;i72~9 to the dlamine. ~uch prodllcls are use:f'ul in the present invention. Suitab:le anilirle derivatives include o-chlorO-aniline, o-nitroaniline, o-trif`luoromethylanilirle and o-carbomethoxyaniline. Condensation products in which a portion of the ortho-substituted aniline is replaced by aniline itself or an unhindered aniline derivative such as meta-toluidine can be used ln the present invention as long as at least 50~ of the amine groups in the condensation product are hindered by fluorine, chlorine, bromine, -CF3, -N02 or COOR wherein R is Cl-CIl alkyl. A preferred product of' this type is prepared by condensing a mixture of-o-chloro-aniline and aniline (about 2 to 4 moles of o-chloroaniline per mole of aniline) with formaldehyde using 1.3 to 2.0 ~ -moles of tota] amines per mole of'formaldehyde. This con-densate is an improvement over other condensates prepared ~' from the reaction of a single aniline with ~ormaldehyde in ;~ ' that it is lower melting and crystallizes slowly, which ' facilitates its handling during the preparation of the ~
' biuret polyisocyanate. ' -~20 Other substituents may be present on the aromatic . . .
nucleus or nuclei as long as they are inert toward isocyanate and amino groups. Representative of` additional substituents ~', which may be present are alkyl~ aryl, alkoxy, aryloxy and ;`
alkenyl groups. More than one hindering substituent may also be present as long as at least one of them is ortho to the amino group.
Polyisocyanates are reacted with the polyamine component to f'orm the biuret po].yisocyanate. Again, the description will be made in terms of' diisocyanates; however~
it is to be emphasized that they are merely illustrative of _5_ 572~

polyisocyanates and polyisocyana~es conta-lning 3 or more :~ .
; isocyanate groups arç intended to be included as well as ~ the diisocyanates. Broadly, the organic diisocyanates whlch ~ ;
: are to be utllized may be defined as aromatic diisocyanates : containing 8-?5 carbons, aliphati.c diisocyanates containing ` 2-18 carbons and cycloaliphatics containing 5-25 carbon : akoms. Specifically, aliphatic diisocyanates and cyclo- :
aliphatic diisocyanates which are'preferred include 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, ' 1,3- and 1,4.-cyclohexyl diisocyanates, methylene-bis-(4-cyclo- :
hexyl diisocyanate), 1,3- and 1,4-xylene diisocyanates. Of :' ~: these, 1,6-hexamethylene diisocyanate and methylene-bis-cyclohexyl diisocyanate) are preferred. ~ ;
. ~ .
~ rrhe aromatic diisocyanates are preferred.
.~ Representative of these diisocyanates are tolylene-2,4-: diisocyanate, tolylene-2,'6-diisocyanate and mixtures thereof ,, . . ~
:l such as those mixtures containing at least 50% of the ~ ~ ~
, ' ' 2,4-isomer. Other representatlve aromatic diisocyanates ~:
.~-include 4,4'-methylene-bis-(phenyl isocyanate), 1,3- and . ~i .
~ : 1,4-phenylene diisocyanate, 2,4-bis-(4-isocyanatobenzyl)-'. phenyl isocyanate and related polyaryl polyisocyanates, ' 1,5-naphthalene diisocyanate and mixtures thereof. The .
~ : diisocyanates may be substituted with alkyl, alkoxy, halogen, `I nitro, or carboalkoxy groups. Thè 2,4- a~d 2,6-tolylene .
~ diisocyanates are especially prefe~red. 4,4~-Methylene-bis-.` (phenyl isocyanate) is also preferred.
. . .
.All of the above isocyanates can be employed in either refined or crude (undistilled) form.
. .. .
Concerning the rati.o of the reactants, at least .:
.'- two moles of polyisocyanate are utilized per equivalent of ~.~ , ,; :"~: ' -6- .. ~

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am.ine group, preferably between 3-20 moles of diisocyanake ; are utilized per equivalent of amine group.
The react:Lon may take place at a temperakure bel;ween about ~0-200C., perferably between about 130-180C.
The reaction is normally run at ambient pressure but pressure ca.n be employed if required because of the presence of low boiling intermediates or solvents. Ambient pressure is much preferred. The use of elevated temperature is, however, critical since it appears that in this manner the insoluble urea which is initially formed is converted to the soluble polybiuret. I'c shouId be emphasized thak this is theoretical and there is no intention to be bound by any theory.
It is difficult to be precise regarding the time required for completing khe reaction since the reaction speed will vary with the type of equipment being employed .1 , ~and the temperature utilized as well as the parkicular starting materials and their concentration. In batch reactions, usually 1-24 hours are required. Reaction times of less than an hour can be achieved in continuous reactors.
The progress o~ the reaction can be rollowed by measuring the isocyanate group content of the reaction mass. Two .: ................... . . .
~ ~ equivalents of isocyanate group react with an equivalent of ,.. ~ , .
.~ amine. ;~
Solvents can be employed if desired in carrying ~ out the reaction. The solvents must of course be inert ;, toward isocyanate and amine groups. In addition, if low boiling solvents are used it may bé necessary to use pressure ., . .~ .
reactors at the temperatures required to complete the ~ ~
. . . . .
- reaction. Suikable solvents include benzene, xylene, . . . .
~3 o-dichloro benzene, 1,2,5-trichlorobenzene, diethylene .;, . ...
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~]ycol~ d:imet,hyl ether and d:lb-lt~ hthalate to name a ~ew.
The buiret polyisocyanates are normally obtained as solutions or slurries in the excess diisocyanate which was used in their preparation. They may be used as such' ;~ or may be isolated by filtratioll. They may be precipitated ~ from kheir solu~ions by addition of aliphatic hydrocarbons ,, such as hexane and obtained by filtration. It is par- ' ticularly convenient to prepare the biuret polyisocyanates in the presence of a sufficient excess of diisocyanate ,~
LO such that a solution of biuret polyisocyanate which is '` stable at room temperature is obtained. Such solutions are ' particularly useful for preparing foams and elastomers. "' The biuret polyisocyanates are low molecular ` weight makerials'.whic,h yeld solutions having low viscosity , and no visible solids. This 1s surprising in view of , ,-~
,~ prior art indicating that polyamines in general when reacted '~' 1 . ~
', with diisocyanates yield unsatisfactory products.
The resulting biuret polyisocyanate mày be used ~ ,~to form polyurethanes and other isocyanate reaction products by reacting it with organic compounds containing active `~'~
', hydrogen as determined by the Zerewitinoff method. Any suitable organic compound containing at least two active '' hydrogen containing groups may be used. Generally speaking, compounds containing alcoholic groups are strongly preferred ' because they are readily available and yield stronger ' , , ' , urethane linkages than do phenolic type hydroxyl groups, In ~,~ addition, compounds containing NH2,,NH, GOOH, SH groups '~ and the like may be utilized to form the various known ' , types of isocyanate reaction products. Examples of suitable ','~
types of organic compounds containi,ng at least two actlve '~

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hydrogen containing groups which are reactive with an lso-cyanate group ~re polye~ters, polyols, polyhydric poly alk~lene ethers, polyhydric polythioethers, polyacetal~, aliphatic polyols including alkane, alkene and alk:Lne diols 5 trlols, tetrols and the.like~ aliphatic thiols including ::
alkane, alkene and alkine thiols having two or more -SH
group~; polyamines containing both aromatic~ aliphatic .. and hetrocyclic diamines, triamines, tetramines and the : like; a~ well aæ mixtures thereof. Listings o~ com~ounds which fall wlthin these v~rious categories may be found in U.S~ Patent 3 201 372~
A preferred reaction of the biuret polyiso- :;
cyanates3 particularly in the form o~ their solutions in additional isocyanate, ls that with polyeth~r polyols or ..
polyester polyols containing 2-8 hydrox~l groups and having equivalent weLghts of about 100 to 3000 ln the presence of an expanding agent to ~orm rigid, 3emi-rigid .~ and rlexible foams. Prepolymer, semL-prepolymer and one- .
shot procedure~ can be used for foam preparation. Generally, the one-shot procedure is pre~erred. .~-An especiall~ pre~erred reaction of the bluret polyisocyanates in the instant invention i~ that with a ~ ;. .
high molecular weight po~ether polyol in the presence o~
a blowing agent to form a ~lexlble polyurethane foam. The polyols preferably have number ~verage molecular welghts of from about 3,000~jO00, most pre~erably from about 4~000-6,500. The pre~erred polymeric polyols are polyalkylene ~ `
ether glycols or triols or mixtures thereo~. Polyether polyols of this type can be obtained by xeaction o.~ an .. .:
_g_ . : .
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; alkylene oxide, f~or example, ethylene oxide, propylene oxide, etc., wit}l a polyhydric alcohol such as ethylene glycol, propylene glycol, dlpropylene glycol, glycerol, trimethylolpropane or mlxtures ther~of. Activated or balanced polyols can also be used. ~ctivated polyols are ; prepared from a mixture o~ allcylene oxides such as ethylene oxide and propylene oxide, and balanced polyols are pre-pared by separately reacting different alkylene oxides so that a block copolymer containing two or more different ;~10 poly(oxyalkylene) blocks is obtained. Balanced polyols in . ' ,, which the termlnal blocks are derived from ethylene oxide ~-~
are especially preferred as are polyols capped with limited amounts of ethylene oxide. Such polyols contain at least -some primary hydroxyl groups which increase the reactivity , of the polyol.
The blowing agent which is to.be employed to expand these preferred formulations of this invention to a oam during the reactlon of the polyol and the biuret poly- `~
isocyanate is utilized by techniques well known in khe art.
Suitable blo~ing agents are water and halogenated hydro-carbons such as trichlorofluoromethane and methylenechloride.
The density of the foam can be varied by using different . I , . . .
proportions of the blowing agent. The preferred blowing agent is water because of its convenience and availability. ~

In general, about 2-5 parts by weight of water per 100 parts ~ -~;; of polyol are used. However, greater or lesser amounts can : -~

-~ be employed depending upon the density of the foam desired. ~ i ~ ~ Catalysts are normally used to promote the . j .
isocyanate-polyol reaction and the water-isocyanate reaction ~30 when water is the blowing agent. Conventional type catalysts ,''~ ' . ' ~ .
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can be used such as ter~iary anlines and the usual organo-t:in catalysts such as dibut~ltin dilaurate and stann-ls octoate. The catalyst is generally used in the amount of about 0.01-2.0 parts per 100 parts of polymeric polyol.
Other materials which can be employed in the production of the' foams of this invention at the discretion of one skilled in the art include stabilizers, pigments, fillers, flame retardants and extenders.
A typical stabilizer would be, for example, sulfonated castor oil and silicones such as polydimethyl-~, siloxanes. On occasion it may be desirable to employ ,' silicones of the block copolymer in minor amounts.
Outstanding HR (high resilience) foams can be prepared from the capped polyols of 3, ooo-8, ooo molecular '' weight described hereinbefore using a solution in excess toluene diisocyanate of the biuret polyisocyanate derived ;~ from the condensation products of aniline and o-chloroaniline with formaldehyde and toluene diisocyanate, with water as a blowing agent. No added cross-linking agent such as a ~ 20 low molecula~ weight polyamine or polyol is required to `I ~chieve hardness and rapid demolding using this system.
The flexible polyurethane foams of this invention can be produced either in slab stock or in a specifically molded configuration; thus they can be used as a seating - material in f'urniture or automobiles. Other automotive applications such as head rests, instrument panels and elastomeric bumpers form an important outlet for these ~ -, . .
foams, If' i~ is desired to prepare rigid foams from the biuret polyisocyanate compositions of this invent-lon ,, , ~.

ll~57~
polyether polyols havlng high functionalJty obtained by ; oxypropylating polyols should be utilLzed. Such polyols include sucross, sorbitol, glycerin, trimethylol propane, 1,2,6-hexanetriol, pentaer~thritol, or mixtures thereo~.
Such polyols usually have equivalent welghts of about 100-140. When rigid ~oams are prepared the blowing agent which is most preferred is Freon~. Optionally, one may utilize the carbon dioxide gas ~ormed in situ by the ;~
reaction o~ water and isocyanate. A detailed discussion of the materials and techniques which can be used in the preparation of polyurethane rigid foams using the isocyanates of this invention can be found in "High Polymers", Saunders and Frisch, Vol. XVI, Polyurethanes: _emistry and Tech- -nology, Interscience Publishers, New York, Ch~pter VIII, .~:
entitled "Rigid Foams".
~ Important uses of the rigid ~oams o~ this inven~
; -tion include re~rigeration insulation and flotation in ~-.:. . . .
marine applications.
The biuret polyisocyanates of this invention are also use~ul in pxeparing polyurethane elastomer~. Iso~
cyanate-t~xmi~ated prepo~ymers can be readily prepared from polyether or polyester glycols h~ving molecular weights of :!i,'~
about 300-3,000 and solutions o~ biruet polyisocyanates in diisocyanates. I~e resulting prepolymers can be cured to use~ul ela~tomers with curing agents such as low molecular weight polyols or polyamines. D lustrative curing agents include 1,4-butanediol t~imethylol propane, methylenebis-~, (2-chloroaniline) and methylene dianiline. A detailed ;~
,~ discussion o~ materlals and techniques ~or polyure-thane ~ , .
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elastomers can be found in ~'HiXh Polymers"~ S~unders and Frisch, Vol~ XVI, Polyurethanes~ Chemistry and ~echnolo~y, Part II, Interscience Publishers, New Yorky Chapter IX, entitled "Elae-tomers"~ The above-men-tioned chapter is hereln incorporated by reference.
Coatlngs can also be prepared from the biuret polyisocyanates, either in the ~orm of its Rolution in excess isocyanate or a solution in an organic solvent, or as the isolated solid, the latter being o~ course free of any free dlisocyanate. Both one-part moisture cure coatin~s and two-part coatings can be prepared by conventlonal techniques. Xandling o~ the pure biuret can be simplified by dissolving it in an inert solvent. Ch~pter X
of Saudners and Frisch which was ci-ted hereinbefore contains detailed procedures ~or coating prep~ration. ;~
me invention is ~urther illustrated by the ~ollowing exampleæ wherein part and percentages are by we~ght unless otherwise indicated. -~
;"' A polyamine i~ prepared by adding 18695 parts of 37% ~ueouæ ~ormaldehyde to a slurr~ o~ 382.5 parts ortho~
chloro~niline, 93 parts o~ aniline, ~45 parts o~ 97~
sulfuric acid and 650 parts o~ water at 50C. With~n 30 minuteæ, the temperature ls raised to 85C where it is maintained for 1 hour. The mass iæ ~hen neutralized with 52.6% sodium hydroxide solution. me ~r~an~c phase is -separated and washed wi-th hot water. The resulting poly- -amine is dried b~ distillation at reduced pressure. `~
To 2940 grams o~ an 80/20 mixture o~ `

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. . .

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2,4-/2,6-tolylene dli~ocyan~te he~ted to 110C.~ 238 gr~m~
of the above polyarnine is added over a period o~ 30 seconds, with agit~tion. A precipitate is observed to ~orm with~n about 10 seconds after the addition ~f the polyamine is commenced. This disappears as the resulting exotherm -elevates the reaction medium to 140-150C.
After all of the solid ma~erial has disappeared, in about 30 minutes~ the reaction mass ls cooled to ambient , temperature. me resulting product has an NC0 assay o~
40.1~ by weight. mis produc~ is used to prepare a high - resilience foam by the following procedure.
- The following streams are mixed contlnuously in a commercially available foa~ machine. ;~
Stream 1 (Temperature ~ 27C) Polyisocyanate prepared in 4~.6 parts this example Stream 2 (Temperature~~ 27C) :; . . .
Polyoxypropylene triol based 80 parts on trimethylol propane, capped 20 ~ with ethylene oxide, ratio o~ `
ethylene oxide to propylene :
oxide 12/88 to 15/85, number -;
average molecular weight `
about 4700 Graft polymer/polyol (hydroxyl 20 parts number about 28) containing about 20~ by weight graft polymer and 80~ by weight polyol3 prepared by copolymerizing acrylonitrile and styrene in a ~-polyether triol having a molecular weight of about 50~0 Polydimethylsiloxane oil - 0~01 part 5 centistoke grade Dibutyltin dllaurate 0.005 part Water 2.8 parts Triethylene diamine dissolved in 0.4 part 2 parts o~ dipropylene glycol Bis(N,N-dimethylarninoethyl) ether o.4 part ~14-3L~57Z9~

MaterLal leaving the foam mixing machine ls introduced lnto a 15 x 15 x 4 1/~ inch aluminurn mold and the mold is closed so that foaming takes place under the !~
pressure developed during foaming. The foam is removed from the mold after 8-10 minutes and passed through rolls to break any closed cells. The foam is then cured for 30 minutes at 120~C and conditioned for 3 days at about 25C prior to testing.
Typical properties obtained from this foam b~
ASTM D-1564 methods are as follows:

Overall Density, lb /cu.ft. 2.8 Core Density, lb./cu.ft. 2.4 Tensile at break, psi - 15 ~
Elongation at break, ~ 120 - ~-Split tear, pli 1.2 -~

50% comp. set after humid age 5 hrs., 121C~ 100% R.H. 28 90% comp. set, ~ 6 ILD at 65% defl., lbs. 103 ; ~ ,.. .
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Claims (7)

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

1. In a process for preparing a biuret polyisocyanate by reacting a hindered polyamine and an excess of a polyisocyanate at a temperature of about 80-200°C, the improvment wherein said hindered polyamine is a condensation product of aniline, a substituted aniline, and formaldehyde, at least 50% of the amino groups in said condensation product being hindered by ortho substituents selected from the group consisting of F, Cl and Br.
2. The process of Claim 1 wherein said poly-amine is a condensation product of a mixture of aniline, o-chloroaniline, and formaldehyde, the mole ratio of o-chloroaniline to aniline being 2 to 4 and the total moles of amine per mole of formaldehyde being 1.3 to 2.0 3. The process of Claim 1 wherein said diiso-cyanate is a member selected from the group consisting of a C8-C25 aromatic, a C2-C18 aliphatic, and a C5-C25 cycloaliphatic diisocyanate.
4. The process of Claim 1 wherein said diiso-cyanate is a mixture of 2,4-tolylene diisocyanate and a maximum of 50% 2,6-tolylene diisocyanate.
5. In a process wherein a resilient foam is prepared by reacting a biuret polyisocyanate with an organic compound containing at least two active hydrogens as determined by the Zerewitinoff method and in the presence of a blowing agent, the improvement comprising employing as the biuret polyisocyanate one which is prepared by the reaction of a hindered polyamine and an excess of a polyisocyanate, said hindered polyamine being a condensation product of an aniline, a substituted aniline, and formaldehyde; at least 50% of the amino groups in said condensation product being hindered by ortho substituents selected from the group consisting of F, Cl and Br.
6. The process of Claim 5 wherein said hindered polyamine is a condesation product of a mixture of aniline, o-chloroaniline, and formaldehyde, the mole ratio of o-chloroaniline to aniline being 2 to 4 and the total moles of amine per mole of formaldehyde being 1.3 to 2Ø
7. The process of Claim 5 wherein said biuret polyisocyanate is reacted with a polyether or polyester polyol containing 2-8 hydroxyl groups and having an equivalent weight of about 100 to 3,000.
8. The product prepared by the process of
1. Claim 1.
   9. The product prepared by the process of
2. Claim 2.
   10. The product prepared by the process of
3. Claim 3.
   11. The product prepared by the process of
4. Claim 4.
   12. The product prepared by the process of
5. Claim 5.
   13. The product prepared by the process of
6. Claim 6.
   14. The product prepared by the process of
7. Claim 7.