GB2038855A - Scavengers for Reducing Aromatic Amine Content in Polyurethane Foams - Google Patents

Abstract

Certain hindered aliphatic monoisocyanates have been found to be effective scavengers for aromatic amine produced during polyurethane foam production either by the one shot or the prepolymer process. These monoisocyanates have the general formula: <IMAGE> wherein R1 to R7 are each independently H, alkyl of 1 to 18 carbon atoms, cycloalkyl of 4 to 8 carbon atoms, aryl of 6 to 14 carbon atoms, alkaryl or aralkyl with the proviso that where R3 is not H, R1, R2, R4 and R5 can be H and with the further proviso that where R3 is H at least two of R1, R2, R4 and R5 are not H and x is 1 to 7. Some of these monisocyanates and their amine precursors are novel.

Description

SPECIFICATION Scavengers for Reducing Aromatic Amine Content in Polyurethane Foams This invention relates to urethane forming compositions and a method of forming polyurethanes having low residual potentially carcinogenic aromatic amines.

Recently it has been discovered that polyurethane foams contain aromatic amines and that certain aromatic amines may represent a potential health hazard. Although the theory of formation of the aromatic amines is not clearly understood, it appears that aromatic isocyanates and possibly their reaction products containing urea and urethane linkages are hydrolyzed to produce free aromatic amines which can be leached from the polyurethane foam.

It has been discovered according to the present invention that at least a stoichiometric amount, sufficient to react with any aromatic amines present, of an amine scavenger which is a hindered cycloaliphatic monoisocyanate of the general formula:

wherein R1-R7 are each independently H, C1-C18 alkyl, C4C8 cycloalkyl, C6-C14 aryl, alkaryl or aralkyl with the proviso that where R3 is not H, R1, R2, R4, and R5 can be H and with the further proviso that where R3 is H at least two of R1, R2, R4 and R5 are not H, and xis 1 to 7 (hereafter referred to as aromatic amine scavengers") when added to a urethane prepolymer or the components of a one shot foam system results in polyurethane foams having a low residue of aromatic amines.

The amount of aromatic amine scavengers added to the system is generally from 0.01 to 1 5 parts by weight based on the weight of the total reactants used to form the polyurethane other than water. The lower limit is not critical and is determined by the degree of scavenging activity desired.

Thus the present invention provides a method for preparing a polyurethane foam having a reduced aromatic amine content which comprises incorporating into either (i) a urethane-containing prepolymer comprising polyether or polyester units end-capped with an aromatic isocyanate and water, or (ii) an aromatic polyisocyanate, a polyether or polyester, polyol and water, up to 15% by weight based on the weight of (i) or (ii) of a hindered cycloaliphatic monoisocyanate of the general formula give above.

Exemplary hindered aliphatic monoisocyanates include 1 -methylcyclohexylisocyanate; 1 ,2,6- trimethyl-cyclohexylisocyanate; 2,2,6-trimethylcyclohexylisocya nate; 1 ,2dimethylcyclohexylisocyanate; 2,6-dimethylcyclohexylisocyanate; 2,6-diethylcyclohexylisocyanate; 2,2,6,6-tetramethylcyclohexylisocyanate; 1 ,2,2 ,6,6-penta methylcyclohexylisocyanate; 2,3,6- triphenylcyclohexylisocyanate, 6-methyl-2-benzylcyclohexylisocyanate, 2,4,6-trimethylcyclohexylisocyanate, 2,6-dipropylcyclohexylisocyanate, 6-methyl-2-ethylcyclohexylisocyanate and 2,5-dimethyl-cyclopentylisocyanate. Mixtures of the isocyanates may also be used.

As used herein, the term "aromatic amine" refers to amine formed from any of various well known aromatic isocyanates used to form polyurethanes, including PAPI (a polyaryl polymethylenepolyisocyanate, triphenylmethane-4,4',4"-triisocyanate, benzene-1 ,3,5-triisocyanate, toluene-2,4,6-triisocyanate, diphenyl-2,4,4'-triisocyanate, xylenediisocyanate, m-phenylene diisocyanate, cumene-2,4-diisocyanate, chlorophenylene diisocyanate, diphenylmethane-4,4'diisocyanate, naphthalene-1 ,5-diisocyanate, xylene-alpha, 3,3'-dimethyl-4,4'-biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenylene diisocyanate, 2,2',5,5'-tetramethyl-4,4'-biphenylene diisocyanate, 4,4'-methylenebis (phenylisocyanate), 4,4'-sulfonylbis(phenylisocyanate), 4,4'-methylene diorthotolylisocyanate and 2,4-diisocyanatodiphenylether and mixtures thereof.Toluene diisocyanate is used for illustration. The low residue foams produced according to the present invention can be rigid, semi-rigid or flexible.

It will be apparent to one skilled in the art that not all isocyanates are operable as scavengers.

Thus when one adds an aliphatic isocyanate as a scavenger, to prepolymer or reactants to form a polyurethane, obviously the water will, if possible, react with the aliphatic isocyanate as well as the aromatic isocyanate to form the polyurethane.

To ensure that the scavenger has a slower reaction rate with water than aromatic isocyanates, the aliphatic monoisocyanates used herein are sterically hindered.

Other factors which are important in reducing the level of aromatic amines and optimizing the effect of the aromatic amine scavengers include the following. Polyurethane foams which are stored while still wet tend to exhibit a higher level of aromatic amines than corresponding foams stored following drying. Thus, higher percentages of aromatic amine scavengers should be added to these materials to reduce aromatic amine content to an acceptable level. Additionally, the use of certain catalysts in the foaming reaction have been found to be detrimental; it is preferred that any catalyst employed be a "mild" catalyst which promotes reaction between the aromatic isocyanate and hydroxyl groups of the polyol and permits the foaming reaction to proceed at a reasonable rate but does not cause undesirable side reactions consuming the aromatic amine scavenger.If conventional strong catalysts (e.g., tin salts) are employed, the amount thereof should be reduced.

The aromatic amine scavenger system is operable with all presently known polyurethane foaming systems including the one shot method and hydrophobic prepolymer method. Additionally, it is operable in the more recent method for forming hydrophilic polyurethane foam from hydrophilic prepolymers.

The methods of forming polyurethanes are conventional. The one shot (see, for example, U.S.

Patents 3,790,508, 3801687, 3748288, 3709843 and 3681273 and British Specification 1,368,625) and hydrophobic prepolymer (including semiprepolymer) methods are well documented (e.g., see Kirk-Othmer, Encyclopedia of Chemical Technology, 2nd Ed., Vol. 12, pp. 45-50 and Voi 9, pp. 853-855). The method of forming polyurethane foams from hydrophilic prepolymers is disclosed in, for example, U.S. Patent 41 37200. In the one-shot process all the necessary ingredients for producing the foam are mixed together and then discharged from the mixer onto a suitable surface. The reactions begin immediately and proceed at such a rate that expansion generally starts in about 10 sec; the entire expansion is generally completed in 1 or 2 min.The completion of the curing may take several days.

In the hydrophobic prepolymer process the polyhydroxy component is reacted with enough polyisocyanate to produce a prepolymer with isocyanate end groups plus excess isocyanate: (where R is typically a polyether structure containing less than 40 mole % oxyethylene units but can also be a polyester).

prepolymer The prepolymer mixture is then reacted with water to simultaneously release carbon dioxide for expansion and link the chains together into a crosslinked matrix. This method is most often used for flexible foams.

In a "semiprepolymer process which has become more extensively used for forming rigid foams, a prepoiymer containing excess isocyanate is mixed with more polyhydroxy resin and a separate blowing agent such as a halocarbon. In this case the prepolymer may contain only a few percent of the total polyhydroxy resin. A more detailed explanation of these conventional methods follows.

A preferred method comprises foaming (under conventional conditions) a mixture comprising: (a) the aromatic amine scavenger and (b) a urethane prepolymer having polyether or polyester backbone segments capped with an aromatic isocyanate e.g. TDI and wherein said aromatic amine scavenger is present in an amount less than or equal to about 15 parts by weight of said prepolymer. Preferably, the amount of scavenger is less than or equal to about 10 parts by weight of said prepolymer. The lower limit is not critical but generally, a level of not less than 0.01 parts should be employed.

In preparing foams by the prepolymer technique, the prepolymer is generally admixed with a suitable blowing agent (e.g., water), a catalyst (optional) and other additives (e.g., fire retardants) depending on the ultimate properties desired in the foam. See, for example, U.S. Patent 3,748,288 and Saunders and Frisch, Polyurethanes Chemistry and Technology, Interscience Publishers, New York, 1964. The amount of water employed as blowing agent is from about 0.4 moles to about 1,000 moles of H20/mole of NCO groups. The term "mole of NCO groups" refers to the NCO groups in the aromatic isocyanate remaining after reaction of the theoretical amount of the NCO groups in the aromatic isocyanate necessary to react with all the hydroxyl groups of the polyol have been used up.Suitable polyether prepolymers used for the polyurethane prepolymer include the polyalkylene oxide ethers, such as the reaction products of ethylene oxide, propylene oxide, butylene oxide, styrene oxide, picoline oxide or methyl glycoside, with a compound containing two or more reactive hydrogens, such as water, resorcinol, glycerol, trimethylol propane, pentaerythritol, ethylene glycol, diethylene glycol, triethylene glycol and the like, as well as compounds such as polyoxypropylene glycol, polyoxyethylene glycol, polyoxyethyleneoxypropylene glycol, polyoxyethyleneoxybutylene glycol, polyoxybutylene glycol and polyoxypropyleneoxybutylene glycol. To obtain hydrophilic urethane foams by the prepolymer method, the polyether urethane prepolymers employed are hydrophilic; this means, in effect, that at least 40 mole % of the oxyalkylene units in the prepolymer backbone are oxyethylene units with the balance being oxypropylene, oxybutylene or other oxyalkylene units. In the resulting polyurethane foams the branch-points of the polymer chains are connected by essentially linear polyoxyalkylene chains containing at least 40 mole % of oxyethylene units (excluding initiators at branch-points) as described above. Preferably, the oxyethylene content is from about 60 to 75 mole %. At oxyethylene levels of 40 to 60 mole %, it may be desirable to use a surfactant known in the art to promote dispersion of the prepolymer in water prior to foaming.

Suitable hydrophilic prepolymers can be prepared by capping a polyoxyalkylene polyol with an excess of polyisocyanate. Prior to capping, the polyol should generally have a molecular weight of from 200 to 20,000 and preferably from 600 to 6,000. The hydroxy functionality of the polyol and the corresponding isocyanate functionality following capping is generally from 2 to about 8. If foams are formed from prepolymers with an isocyanate functionality of about 2, the resulting foam is essentially linear and does not have as much tensile strength as crosslinked foams. Accordingly, if the isocyanate functionality is about 2, a crosslinker can be employed if desired. To minimize adverse reactions involving the scavenger, any crosslinkers employed should preferably be aliphatic polyols (e.g., TMOP, glycerol or pentaerythritol) rather than amines.

Examples of suitable polyols (to be capped with polyisocyanates) include: (A) essentially linear polyols formed, for example, by reaction of ethylene oxide (optionally with other alkylene oxides) with water, ethylene glycol or higher molecular weight glycols as an initiator. Where the linear polyethers are mixtures of ethylene oxide with, e.g., propylene oxide, the polymer can be either random or a block copolymer and the terminal units can be either oxyethylene or oxypropylene. A second class of polyol (B) includes those with a hydroxy functionality of 3 or more, commonly formed by reacting alkylene oxides e.g., ethylene oxide optionally with other alkylene oxides, with a polyfunctional initiator such as trimethylolpropane, pentaerythritol, etc.Further polyols include (C) a mixture of linear and branched polyfunctional polyols as exemplified in A and B above together with an initiator or crosslinker. A specific example of C is a mixture of polyethylene glycol (m.w. about 1,000) with trimethylolpropane, trimethylolethane or glycerine. This mixture can be subsequently reacted with excess polyisocyanate to provide a prepolymer. Alternatively, the linear polyols (e.g. polyethylene glycol) can be reacted separately with excess polyisocyanate. The initiator e.g., trimethylolpropane, can also be separately reacted with polyisocyanate. Subsequently, the two capped materials can be combined to form the prepolymer.

Thus, by using a hydrophilic prepolymer as disclosed in U.S. Patent 4137200, a crosslinked hydrophilic foam having a three-dimensional network can be formed from the reaction product of A.

isocyanate capped prepolymers consisting of a mixture of (1) an isocyanate capped hydrophilic polyoxyethylene diol having an ethylene oxide content of at least 40 mole percent; and (2) an isocyanate capped polyol having a hydroxyl functionality of 3 to 8 prior to capping said isocyanate capped polyol being present in an amount from 2.9 to 50% by weight of (1) and (2); B. 0.5 to 10.0% by weight of A and B of a polyisocyanate having an isocyanate functionality of 2.0 to 3.0; and C. 6.5 to 390 moles of water for each mole of unreacted isocyanate.

The process of forming said crosslinked hydrophilic urethane foam typically comprises mixing the hydrophilic polyoxyethylene diol with the polyol, said polyol being present in the mixture in an amount from 1.0 to 20% by weight, reacting with the mixture at a temperature of 0 to 1 200C an amount of the polyisocyanate equal to 1.8 to 1.9 NCO to OH equivalents for a time sufficient to cap substantially all the hydroxyl groups of the mixture, adding more of the polyisocyanate to provide 0.1 to 0.3 equivalents of NCO per initial equivalent of OH in excess of the theoretical amount necessary to react with the hydroxyl groups and thereafter adding 6.9 to 390 moles of water for each mole of unreacted isocyanate in the admixture.

Useful hydrophobic prepolymers are based on polyether polyols containing less than 40 mole percent polyoxyethylene units as well as polyester polyols. The polyester polyols are based on the reaction product of polyfunctional organic carboxylic acids (or anhydrides) and polyhydric alcohols.

Typical such acids include dicarboxylic, aliphatic acids such as succinic, adipic, sebacic, azelaic, glutaric, pimelic acids, dicarboxylic aromatic acids such as phthalic acid, terephthalic acid and isophthalic acid as well as the "dimer acids" such as the dimer of linoleic acid. Hydroxyl-containing monocarboxylic acids such as ricinoleic acid may also be employed. Typical polyhydric alcohols include monomeric polyhydric alcohols such as glycerol, 1,2,6-hexane triol, ethylene glycol, trimethylol propane, trimethylol ethane, pentaerythritol, propylene glycol, 1 ,3-butylene glycol and 1,4-butylene glycol.

A second preferred embodiment of the invention is a method for preparing polyurethane foams by the one-shot process. The method involves foaming (using conventional techniques) a mixture comprising: (a) the aromatic amine scavenger, (b) aromatic isocyanate, (c) a polymeric polyol and (d) a catalyst system. The aromatic isocyanate index is generally from 110 to 96.

The expression "index" is an art recognized term indicating the ratio of the actual amount of aromatic isocyanate in the reaction mixture to the theoretical amount of aromatic isocyanate needed for reaction with all active hydrogen compounds present in the reaction mixture multiplied by 100.

Conventional catalyst systems can be employed in a conventional manner. However, it has been found that many catalysts increase the amount of aromatic amines in the foams and accordingly the amount of catalyst employed should be kept to a minimum consistent with obtaining a desirable rate in the foaming reaction as well as desirable properties in the finished foam. Suitable catalysts should promote reaction between the polyol and the NCO groups of the aromatic isocyanate and should be employed under conditions such that detrimental side reactions (e.g., trimerization, dimerization and biuret formation) are minimized. A listing of such conventional catalysts is set forth at Table LXX (page 212) of Saunders and Frisch, Polyurethanes Chemistry and Technology (Part 1), 1962 by John Wiley 8 Sons.

Conventional catalysts and suitable amounts thereof (in parts of catalyst/100 parts by weight of the polyol) are set forth below. Frequently mixtures of catalysts can be used and thus, the actual amounts employed may vary considerably. Whether employed singly or in combination, the total amount of catalyst should be as little as possible, consistent with obtaining desired results.

Catalysts TertiaryAmines Tin Salts Fe Salts Miscellaneous Catalysts N-ethyl- morpholine Stannous octoate Ferric 2-ethylhexanoate Cobaltnaphthenate (0.2-1.0) (0.01-0.5) (0.05-1.0) (0.01-1.0) Diethylenetriamine Dibutyltindiacetate Ferric chloride Tetrabutyl titanate (0.2-1.5) (0.01-0.5) (0.03-1.0) (0.01-1.2) Triethylenediamine Dibutyltindilaurate Ferric acetylacetonate Lead oleate (0.3-1.5) (0.01-0.5) (0.03-1.5) (0.01-1.0) Triethylamine Dibutyltindioctoate (0.3-1.5) (0.01-0.5) N,N-dimethyl,N'N'- dimethyl-1,3 diaminobutane (0.2-1.0) In the one-shot method all of the ingredients, e.g., the polyether or polyester polyol, the aromatic isocyanate, the aromatic amine scavenger, the blowing agent, catalyst and any additional components such as UV absorber, surfactant, fire retardant additive, fillers, etc., should be vigorously mixed together and poured onto a surface or into a mold where foaming takes place.

In both the one shot and the hydrophobic prepolymer process for forming polyurethane foams the amount of water employed is substantially stoichiometric to react with the NCO groups remaining after theoretically all of the OH groups on the polyol have been reacted with isocyanate. Thus, the amount of water is generally from 0.4 to 0.6 moles of H2O per mole of NCO groups remaining after the polyisocyanate reacts with all of the OH groups in the polyol.

In the one shot process the scavenger should be incorporated simultaneously with the other ingredients. In all types of prepolymer process the scavenger is preferably added to the prepolymer and then water is added to the prepolymer mixture. Alternatively the scavenger can be added to the water but this is generally less desirable since it increases the likelihood of reaction between the scavenger and the water.

The present invention also provides aliphatic monoisocyanates of the general formula given above wherein R, to R7 are each independently H, alkyl, cycloalkyl, aryl, alkaryl or aralkyl wherein the alkyl groups contain 2 to 1 8 carbon atoms, the cycloalkyl groups contain 4 to 8 carbon atoms and the aryl groups contain 6 to 14 carbon atoms with the proviso that at least two of Rr, R2, R4and R5 are other than H or methyl and x is 1 to 7. In one embodiment R3 is other than hydrogen; in another embodiment at least two of Ra, R2, R4 and R5 are ethyl. x is preferably 3. A specific isocyanate of the present invention is 2,6-diethylcyclohexylisocyanate.

As used herein, a "hindered" cycloaliphatic monoisocyanate means the a-position contains an alkyl, aryl, cycloalkyl, alkylaryl or arylalkyl substituent and "di- or polyhindered" cycloaliphatic isocyanate means the a and ss carbons have a minimum of two substituents.

These monoisocyanates can be used not only as amine scavengers in the preparation of polyurethanes, but also in epoxy resins, polyamides and other polymeric compositions.

The monoisocyanates can be prepared from the corresponding monoamines. Some of these monoamines are known. Those of the formula:

wherein R,, R2 and R4 to R7 are each independently H, alkyl, cycloalkyl, or alkaryl wherein the alkyl groups contain 2-1 8 carbon atoms, the cycloalkyl groups contain 4-8 carbon atoms and the alkaryl groups contain 7-14 carbon atoms with the proviso that at least two of R1, R2, R4 and R5 are group members other than H or methyl and with the further proviso that, when only two of Rt, R2, R4 and Ra are alkyl, at least one of the alkyl groups contains at least 4 carbon atoms, and x is 1 to 7 form another aspect of the present invention.Examples include 2,6-dibutylcyclohexylamine and 2-butyl, 6ethylcyclohexylamine.

There are two general synthetic routes for preparing the dihindered monoamines. The first route is by nitration of the substituted aromatic compound, reduction of the aromatic nitro compound to the aromatic amine and reduction of the aromatic amine. Alternatively, the aromatic amine can be formed and alkylated to give the dihindered aromatic amine.

The first route includes nitration in the 2-position of an appropriately substituted, for example, a 1,3-disubstituted, aromatic compound using nitric acid alone or with sulphuric acid, generally at a temperature of 00--1 500C. See Kobe and Brennecke, Industrial 8 Engineering Chemistry, Viol. 46. No.

4, pages 728-732. Reduction of the nitro compound to the amine using a reduction catalyst such as Raney nickel is then carried out under hydrogen pressure of, say, 1-100 atmospheres and temperatures from, say, 0 to 1 500C for example in dioxane as solvent. Alternatively, nitrobenzene can be hydrogenated to aniline and the aniline alkylated using the desired olefin or alkyl halide. For example, aniline in the presence of ethylene can be converted to the 2,6-diethylaniline by the Ethyl process using aluminium anilide as catalyst at 3250C and 800 psi. Alkylation can also be conducted or ortho-substituted anilines to give mixed alkyl derivatives in the 2,6 position.Reduction from the aromatic nitro to the aromatic amine can be accomplished by standard methods described in Coll. Vol.

I-V Index of Organic Synthesis, p. 211. Reduction of the aromatic amine to an aliphatic amine is then accomplished in the presence of a hydrogenation catalyst such as Raney nickel or cobalt or rhodium/A12O3 at hydrogen pressures of, say, 2-200 atmospheres and a temperature from, say, 0 250"C (see Coll. Vol I-V Index of Organic Synthesis, pp 208 and 209).

A specific example of the overall process starts from m-xylene:

N02 CH3 -CH3 HN03 CH3 < 2 CH3 CH3 by [H2so4J + products

dioxane (solvent) 250C/70 atm.

150 atm.

NH2 excess NCO CH3CH3 cOCl2 CH3 CH3 S S solvent (i) 20 - +200C (ii) 1100-1800C 1-15 atm.

The solvent is typically chlorobenzene or dichlorobenzene.

The alternative steps in the first route may be written as follows:

NO 2 NH2 2 cCaI.t2SCH2 NH2 C NH2 CII2CH2 Ni < catalyst 3250C, 800 psi and the dihindered aromatic amine then reduced.

A second general route for forming the dihindered aliphatic monoamine is to treat a cyclic ketone (or the cyclic alcohol oxidized to the ketone) with hydroxylamine to form the corresponding oxime which is then reduced either using H2 and catalyst or H2 generating couples (Na-alcohol) for example at 0 to 800C and 1-5 atmospheres. Typically the oxime is prepared using hydroxylamine hydrochloride and Na2CO3 at a temperature of 0 to 500C and 1-10 atmospheres.

Alternatively, the same compound can be prepared through 2-methylcyclohexanone. 2,6 Dimethylcyclohexanone has been prepared by formylation of 2-methylcyclohexanone in the 6-position, methylation at the 6-position and removal of the formyl group. The ketone may then be aminated and phosgenated to give the 2,6-dimethylcyclohexylisocyanate.

Cycloaliphatic amines with a substituent for example phenyl, in the 1-position, such as 1 -phenyl- 1 -cyclohexlamine, can be prepared from 1 -phenylcyclohexanol which is available commercially. This can be converted to the corresponding iodide using potassium iodide and polyphosphoric acid. The phenylcyclohexyliodide can then be converted to the amine through the reaction with potassium phthalimide and subsequent hydrolysis with hydrochloric acid to give the amine hydrochloride.The amine hydrochloride can be converted to the amine by use of sodium hydroxide or may be used directly for phosgenation to the corresponding isocyanate:

{1I o1lvphospboric + C=o ~~~ )NK 0 acid NH2HC1 NH2 S NaOII 2 S COCL2 solvent COCl2 solvent piiyco The monoamine can be converted into the monoisocyanate by phosgenation.The amine may be phosgenated as the free amine, the amine hydrochloride, the amine-carbon dioxide adduct or any other suitable amine salt without or with a solvent such as o-dichlorobenzene, in the presence of excess phosgene, either in one or two temperature stages, for example either at 80--1800C or first at minus 20 to plus 200C and second at 200C to 2000C at pressures from atmospheric to 50 e.g. 1 to 15, atmospheres.

The following Examples further illustrate the present invention. Unless otherwise noted, all parts and percentages are by weight.

Example 1 50 g of known 2,6-diethylcyclohexylamine was dissolved in 230 g of chlorobenzene in an addition funnel. In a separate multiple neck, round bottom flask equipped with stirrer, phosgene and nitrogen inlets and outlets, reflux condenser and thermometer, 200 g of COCI was condensed in 230 g of chlorobenzene while maintaining the flask at about -50C in a bath of acetone cooled with dry ice.

The amine solution was added dropwise to the flask over 10 minutes with stirring at 600 rpm while maintaining the reaction temperature at --5 to -30C. After addition, stirring was continued at 300 rpm allowing the contents to warm to 130-1 350C and excess phosgene was distilled. The reaction was continued for 1 3/4 hrs. with stirring while additional COCK, was passed through the reaction mixture.

Nitrogen was then sparged through the flask to flush out excess phosgene and hydrogen chloride. The product was freed of chlorobenzene solvent by stripping on a rotary evaporator at 730C. The residue was distilled under vacuum (0.1 mm Hg) and the fraction boiling between 58-61 OC was collected.

The yield was 45.6 g (78% theoretical). IR showed a strong NCO absorption. NMR revealed the product to be free of contaminants and to have the desired structure, i.e.,

Elemental analysis found C=70.97, H=1 0.30, 0=9.33, N=7.95 whereas theoretical is C=72.93, H=1 0.50, 0=8.84 and N=7.73.

Example 2 A prepolymer was prepared by mixing 2 molar equivalents of polyethylene glycol of average molecular weight 1,000 with one molar equivalent of trimethylolpropane. The mixture was dried at 100-11 1 00C 5-1 5 Torr to remove water and slowly added over about one hour to a vessel containing 6.65 molar equivalents of toluene diisocyanate (TDI) while stirring the TDI and polyol mixture. The temperature was maintained at 600C during the addition and for a further three hours.

Then an additional 1.05 molar equivalent of TDI was added with stirring over about one hour while maintaining the temperature at 600C. The final reaction mixture contained a 10% molar excess of TDI.

All hydroxyl groups were capped with isocyanate and some chain extension occurred because of crosslinking of the polyols with TDI. The prepolymer contained 5.6% by weight of free TDI.

1 00 g of the prepolymer reaction mixture were mixed with 4 g of 2,6-diethylcyclohexyl isocyanate in a beaker. In a separate beaker 2 g of a non-ionic polyether based surfactant sold under the tradename "Pluronic L-62" by BASF-Wyandotte and 100 g of water were mixed. The two mixtures were combined in a Waring blender and agitated. The resultant foam, after oven-drying for 1/2 hour at 650C, was analyzed in accord with the method described in J. L. Guthrie and R. W. McKinney, Analytical Chemistry, September 1977 pp. 1 676-1 680. The amine content was less than 1.0 ppm. In a control run wherein no 2,6-diethylcyclohexyl isocyanate was added to the system, the foam contained 14.3 ppm of toluene diamine.

Claims (15)

Claims

1. A method for preparing a polyurethane foam having a reduced aromatic amine content which comprises incorporating into either (i) a urethane-containing prepolymer comprising polyether or polyester units end-capped with an aromatic isocyanate and water, or (ii) an aromatic polyisocyanate, a polyether or polyester polyol and water, up to 15% by weight, based on the weight of (i) or (ii) of a hindered cycloaliphatic monoisocyanate of the general formula

wherein R1 to R7 are each independently H, alkyl of 1 to 1 8 carbon atoms, cycloalkyl of 4 to 8 carbon atoms, aryl of 6 to 14 carbon atoms, alkaryl or aralkyl with the proviso that where R3 is not H, R1, R2, R4 3 1' 2' 4 dR5arenot and R5 can be H and with the further proviso that where R is H at least two of R R R and H and x is 1 to 7, as scavenger, 0.4 to 1,000 moles of water being present for each mole of NCO groups, and allowing the resulting mixture to react.

2. A method according to claim 1 wherein the hindered isocyanate is added in an amount from 0.01 to 15% by weight based on the weight of (i) or (ii).

3. A method according to claim 1 or 2 wherein the hindered isocyanate is added to the prepolymer and water is added to the resulting mixture.

4. A method according to any one of claims 1 to 3 wherein at least two of Rr, R2, R4 and R5 are other than H or methyl.

5. A method according to claim 4 wherein the scavenger is 2,6-diethylcyclohexyl isocyanate.

6. A method according to any one of the preceding claims wherein the prepolymer is a reaction product of aromatic isocyanate-capped prepolymers consisting of a mixture of (a) an aromatic isocyanate-capped hydrophilic polyoxyethylene diol, said diol having an ethylene oxide content of at least 40 mole percent; (b) an aromatic isocyanate-capped polyol having a hydroxyl functionality from 3 to 8 prior to capping; said isocyanate capped polyol being present in an amount from 2.9 to 50% by weight of (a) and (b); and (c) 0.5 to 10.0% by weight of (a) and (b) of an aromatic polyisocyanate having an isocyanate functionality from 2.0 to 3.0.

7. A method according to claim 1 substantially as described in Example 2.

8. A polyurethane foam whenever prepared by a process as claimed in any one of the preceding claims.

9. A mixture suitable for preparing a polyurethane foam having a reduced aromatic amine content which comprises a mixture of (a) (i) or (ii) as defined in claim 1, (b) up to 1 5% by weight based on the weight of (i) or (ii) of a hindered cycloaliphatic monoisocyanate as defined in claim 1 and (c) 0.4 to 1000 moles of water for each mole of NCO groups.

10. A cycloaliphatic monoisocyanate of the general formula:

wherein R, to R7 are each independently H, alkyl of 1 to 18 carbon atoms, cycloalkyl of 4 to 8 carbon atoms, aryl of 6 to 14 carbon atoms, alkaryl or aralkyl with the proviso that at least two of R,, R2, R4 and R5 are other than H or methyl, and x is 1 to 7.

11. A monoisocyanate according to claim 10, wherein R3 is other than H.

12. A monoisocyanate according to claim 10 or 11, wherein at least two of Rt, R2, R4 and R5 are ethyl.

13. A monoisocyanate according to any one of claims 10 to 1 2 wherein x is 3.

14. 2,6-diethylcyclohexylisocyanate.

15. A cycloaliphatic monoamine of the general formula:

wherein Rt, R2, and R4 to R, are each independently H, alkyl of 1 to 1 8 carbon atoms, cycloalkyl of 4 to 8 carbon atoms or alkaryl of 7 to 14 carbon atoms with the proviso that at least two of R1, R2, R4and R5 are other than H or methyl and with the further proviso that, when only two of R1, R2, R4 and R5 are alkyl, at least one of the alkyl groups contains at least 4 carbon atoms, and x is 1 to 7.