CA1050699A - Hydrolytically stable urethane foam precursors - Google Patents

Abstract

Abstract of the Disclosure - Flexible and rigid polyurethane foams are obtained using as the gel catalyst specified di- and triorganotin compounds wherein the hydro-carbon radicals bonded to the tin atom are methyl or methoxy-methyl radicals. These catalysts are at least comparable in performance to prior art catalysts and offer the additional advantage of forming stable aqueous solutions.

Description

~ 69~
BACKCROUN~

This invention relates to the preparation of cellular polyurethanes. This lnvention further relates to the preparation of' rigid and flexible cellular polyurethanes using a class of gel catalysts that are water soluble and hydrolytically stable.
It is well known to prepare cellular polyurethanes by reacting polyfunctional isocyanates with polyalkylene polyols in the presence of water as a foaming or blowing agent. The water reacts with some of the isocyanate present to generate bubbles of carbon dioxide that are entrapped as , the remainder of the isocyanate copolymerizes with the polyol to form the polyurethane. A silicone type of surfactant is often included to obtain a uniform structure of small cells within the polymer. Both a gel catalyst and a blowing catalyst are usually required to obtain a proper balance between the rates of the polymerization and foaming reactions.
The balance is required to obtain a commercially acceptable product.
Cellular polyurethanes are often prepared using a prec~rsor or master batch containing all of the lngredients, - other than the polyfunctional isocyanate 3 required to prepare ~ the polymer. Such a precursor could be made up in large -~ quantities and used as required. In addition to simplifying preparation of the polyurethane, employing a master batch could improve product uniformity, since it ensures that all of the reagents except the isocyanate are present in the same proportions in all polymers obtained from the same master .~ batGh .
Organic and inorganic tin compounds are preferred gel catalysts ~or cellular polyurethanes. Many o~ these tin compounds decompose relatively rapidly in the presence of ~' -1 ~a :: .- . . . ..

69gl water, which may contain a tertiary amine co-catalyst, to yield stannous or stannic oxide. These tin com-pounds therefore cannot be employeci in any precursor or master batch containing significant amo~mts of wat~r -. and ter~iary amine.
An objective of this invention is to provide water soluble, hydrolytically stable tin-containing gel catalysts for cellular polyurethanes.
Unexpectedly it has now been found that cer-tain methyltin compounds and methoxymethyltin compounds - are unique among tin compounds in that they are both sol-uble in and not significantly affected by water, and can therefore be incorporated into precursors for cellular polyurethanes that con~ain water as a blowing agent.
` This invention provides hydrolytically stable precursors for preparing flexible or rigid cellular polyurethanes, said precursors comprising 100 parts by ~ ;
weight of a polyol, from about 0.5 to 5 parts of `i water, from about 0.05 to 1.0 part of a foaming ~' 20 catalyst, from about 0.5 to 2 par~s of a silicone surfactant, and from about 0.05 to about 1.0 part ,'J'. of a gel catalyst, wherein the gel catalyst is an ... ~ , organo~in compound of the formula RaSnX4 a~ R2SnO
or ~R3Sn)20 wherein R is CH3- or CH3OCH2-, a ~
- is the integer 2 or 3 and X represents a chlorine, ~`
bromine or iodine atom or the radical -OOCCH or 3 ~-~.! -OOCCH2CH3- ~
'!; The hydrolytically stable organotin gel cata~
-~ lysts used in this invention are methyltin and methoxy-,i ~
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methyltin halides (chlorides, bromides and iodides), oxides and derivatives of either acetic or propionic acid. The compounds contain ;2 or 3 methyl or methoxy-methyl radicads bonded to the tin atom, and are of the form~la Ra5nX4 a ~2SnO or (R3Sn)20 wherein R, a and X
are as previously deined. Depending upon conditions, tlle oxides may exis~ as the corresponding hydroxides.
Thiis equilibriwn is well known in the art.
The concentra~ion of the present gel cata-lysts in polyurethane formulations is similar to that of other organotin co~.po~nds conventionally employed as gel catalysts. From about 0.05 to 1.0 part of cata- ~
lyst per 100 parts by weight of polyol is usually ef- ~ -fective.
-` Cellular polyurethanes are prepared by reac-ting a polyol with an organic polyisocyanate in the presence of a polymerization or gel catalyst and a ~. ~
foaming agent.
A silicone type surfactan~ and a foaming cat- `
alyst are also present to obtain the desired cell struc-- ture within the poly~er. Suitable foaming catalysts in-clude both linear and heterocyclic amines and specified mixtures of antimony oarboxylates with salts of nitrogen containing compounds as disclosed in U.S. Patent 3,620,985.
- Any available organic polyisocyanate can be ;

used to prepare cellular polyuret]lanes by reaction wi~h the precursors of the invention. The criteria that go-vern selection of a particular isocyanate are suffi-ciently well known to one skilled in the art that a detailed discussion of the subject is not required in this specification.

~ne of the most widely employed polyisocyanates is a commercially available type of mixed tolylene di-isocyanates containing about ~0~ by weight of

2,4-tolylene diisocyanate and 20% of the 2,6-isomer.
Representative members from other classes of suitable poly-isocyanates include, hut are not limited to methylene-bis-- (4-phenyl isocyanate), 3,3'-dimethoxy-~,4'-biphenylene diisocyanate, naphthalene-1,5-diisocyanate, hexamethylene diisocyanate, 1~4-phenylene diisocyanate and polyphenylene polymethylene diisocyanate. For a flexible foam, the concentration of polyisocyanate in the polyurethane reaction mixture should be equivalent to between 1 and 7 isocyanate groups for each active hydrogen (as determined by the . Zerewitinoff method) present in the polyol component.
The polyalkylene polyol component of the poly-urethane reaction mixture typically exhibits a molecular weight greater than 200. The molecule may contain one or more ester, ether, amide, thio(-S-) or amino radicals.
Preferred types of polyols include hydroxyl terminated ; 20 polyethers and polyesters, and may contain one or more pendant hydroxyl groups on the polymer chain. ~ibasic carboxylic acids suitable for preparing hydroxyl terminated polyesters include aromatic and aliphatic acids such as ` adipic, furmarlc, sebacic and the isomeric phthalic acids.
The acids are reacted with a glycol or polyol such as ethylene glycol, diethylene glycol, propylene glycol or `
trimethyol propane. If the polyol component contains 3 or more hydroxyl groups, the stoichiometry should be such as ; to avoid formation of highly cross-linked products.
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1050~g9 Polyether polyols are derived from a controlled polymerization of olerin oxides~ and include polyethylene glycols, polypropylene glycols and copolymers of ethylene oxide and propylene oxide wherein the molecular weight of the poly~er is at least 200. Most desirably these polyols are liquids exhibiting a molecular weight of between 500 and 5,000. ~requently an olefin oxide such as propylene oxide is reacted with a linear diol or triol such as glycerine to form the final polyol, which is subsequently reacted with a poly-functional isocyanate to obtain the polyurethane.
The reaction of a stoichiometric excess of di-- isocyanate with a polyol produces a modified polyether having : terminal isocyanate groups. When it is desired to form a cellular polyurethane, the isocyanate-modified polyether reacts through the isocyanate groups with a chain-extending agent containing active hydrogen, such as water. This involves several different reactions that proceed simultaneously, including a reaction between the isocyanate groups and water to form urylene links (-NHCOHN-) and carbon dioxide. The resultant urylene links will react further with free isocyanate groups to form biuret cross links. Depending upon the desired density and degree of crosslinking, the relative concentrations of isocyanate and active hydrogen (including both water and polyol) should be such as to provide a ratio of o.8 to 1.2 equivalents of isocyanate per equivalent of active hydrogeng and preferably a ratio of 0.9 to 1.1.
The amount of water present in the polyurethane reaction mixture should be sufficient to produce the required amount of carbon dioxlde for a foam of the desired density.

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As previously disclosed, carbon dioxide is generated by the reaction of water with some of the polyfunctional isocyanate.
Auxiliary foaming or "blowing" agents, SUCII as liquid fluorocarbons that boil between 30 ~md 60C. can be includetl in the formulation, t~gether with the foaming catalyst, which is believed to catalyze the reaction between the water and polyisocyana~e, thereby ensuring a proper balance betweerl the rates of polymer formation and gas evolution. Suitable foam-ing catalysts include tertiary amines such as N-ethyl mor-- 10 pholine, triethylene diamine and dimethylethanolamine, Cellular polyurethanes are often prepared using the 'one-shot" method whereby controlled amoun~s of all reagents, - catalysts and a cell modifier are continuously ed into a suita-~: .
- ble mixing device such as a mixing head. The resultant foam is removed as it is formed by conveyor or other suitable transport means. While this technique is suitable for large scale production of a given type of polyurethane foam, for smaller quantities it may be desirable to employ a batch processing using a precursor or "master batch" containing all com-ponents except the polyisocyanate. The batch process is particularly desirable when different types of foams are to be prepared Using the same polymerization vessel. It is in this application that the present llydrolytically stable organotin compounds are markedly superior to other organotin compounds conventionally employed as gel catalysts. Percursors containing water and the present methyltin or methoxymethyltin compounds can be stored for extended periods of time with substantially no loss in catalyst activity.

:. :. . . . ~ : :, .: : . . . -In add~tlon to bei.ng hydrolytically stable, the present gel catalysts are soluble ln water. Thls solubility is advantageous, since the tin compounds are present in relatively small amounts (0.05 to 1.0 parts per 100 parts by wei~ht of polyol~ in the polyurethane formulation. By dissolving the tin compound in a large amount of water and addlng an aliquot of the resulting solution to a given formulation, it is possible to exercise greater control over catalyst concen.ration in the formulation, thereby improving uniformity between successive batches of foam.
The prior art relating to so called "one-shot"
methods for preparing polyurethane foams teaches that the organotin type of gel catalyst should usually be added to the reaction mixture as a separate component because the catalyst is usually insoluble in the other components of the formulation.
Since the amount of catalyst added is relatively small compared to the amount of polyol, effective process control may be difficult to achieve. By comparison, an aqueous solution containing one o~ the present hydrolytically stable catalysts can be prepared and stored until needed with no significant loss in catalyst activity.
Stannous compounds such as stannous octoate are often preferred over tetravalent organotin compounds in J flexible foam formulations because the organotin compounds, as a rule~ do not yield a foam exhibiting good heat stability.
Dibutyltin derivatives of carboxylic acids, such as dibutyltin dilaurate, are conventionally employed as gel -~7-., , :. ' : . . ' . ,. , ; -: , , catalysts ln rigid polyurethane foam formulations, however these catalysts exhiblt poor hydrolytic stabil1ty, and therefore cannot be in contact wi~h water until just prior to addition of both the polyol and isocyanate.
In addition to being hydrolytically stable, the present organotin gel catalysts do not adversely affect the heat stability of the final foam, and are therefore useful for preparing both flexible and rigid foams that meet the severe criteria required ~or a commercial scale process. The catalysts of this invention are therefore more versakile than either the stannous or tetravalent organotin compounds formerly employed as gel catalysts.
The following examples illustrate preferred embodiments of the present invention and should not be interpreted as limiting the scope thereof except as defined in the accompanying claims.

Bis(methoxymethyl)tin dichloride was prepared by heating a mixture containing powdered tin metal ~120 g.) and chloromethyl methyl ether (300 cc.) to reflux kemperature for two hours. A flow of nitrogen and agitation were continued throughout the course of the reaction. The resultant mixture was filtered while hot. A solid precipitated as the filtrate cooled to ambient temperature. The solid material was : isolated, washed with 100-200 cc. of diethyl ether and dried to yield 82.1 g. o~ a solid melting between 95-97C. Thls solid was washed twlce with cold ether, recrystallized from benzene and finally washed with pentane to yield 51.8 g. of a tan solid melting between 99 and 102C. An additional ; .-: . . . . .

::, : .. . . .

63.5 g. of a white solld meltln~ between 99 and 102C. was obtained following recrystal:Lization from benzene of the gray solid present in the initial reaction mixture. This recrystallized material was washed with pentane and dried prior to being weighed. Upon analysis, the combinedisolids were found to contain 42.64% tin and 25.43% chlorine. The calculated concentrations of tin and chlorine in bis (methoxymethyl)tin dichloride are 42.43% and 25.35%, respectively.
Bis(methoxymethyl)tin oxide was prepared by reacting bis(methoxymethyl)tin dichloride (14.0 g.) dissolved in 50 cc. o~ methanol with a solution containing 4.0 g. of sodium hydroxide and 75 cc. of methanol containing a few drops of water. The solution of sodium hydroxide was added over a 15 minute period during which the temperature of the reaction mixture was maintained below 10C. A white solid began to precipitate when the addition of sodium hydroxide was about half completed. Following completion of the addition the resultant mixture was allowed to remain at ambient temperature for 1/2 hour, after whic~ the white solid in the reaction vessel was recovered, washed with cold (0C.) methanol and dried under reduced pressure to yield

3.7 g. of material that did not melt below 300C. The liquid phase of the initial reaction mixture was evaporated to dryness under reduced pressure, and the resultant solid washed with cold (0C.) methanol and dried to yield 6.9 g.
of a white solid that did not melt below 300C. The solid was washed with deonized water to remove soluble chlorides, then dried under reduced pressure. Upon analysls the combined . , _g_ .~
.

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produ~ts were found to contain 51.61% by weight of tin. ~he calculated tin content for bis(methoxymethyl)tin oxide is 52.80%.
Bistmethoxymethyl)tin diacetate was prepared by reac-ting bis(methoxymethyl)tin dichloride (7.0 g.) with 10.8 g.
of silver acetate using 100 cc. of chloroform as a diluent.
The resultant mixture was heated to the boiling point (63C.) under a nitrogen atmosphere for one hour in a reaction vessel equipped with a stirrer and a reflux condenser. After it had cooled to ambient temperature, the mixture ~as filtered and the solid phase washed wi~h 400 cc. of chloroform. The - combined filtrates were evaporated to dryness to give a brown - oil weighing 7.3 g, which solidified to a crystalline mass at room temperature. The product was found to contain 38.27%

by weight of tin and 35.96% of aceta~e radical ' ,~ ~
~C~ ~ The calculated values of tin and acetate content for bis(methoxyme~hyl)tin diacetate are 36.31% and 36.12%, res-pectively.
~' 20 The methyltin compounds evaluated as gel catalysts are either commercially available or were prepared from trimethyl-- tin chloride or dimethyltin dichloride using knol~n symthetic '~ procedures.
EXAMPL~ 2 - Thi.s example demonstrates the use of the bis(methoxy-methyl)tin compounds disclosed in Example 1 as gel catalysts for preparing flexible polyurethane foams. Each gel cata-lyst was added to the formulation as an aqueous solution containing 10% by weight of catalyst. A 10% aqueous solution ~ 30 of bis(methoxymethyl)tin di~hloride showed no evidence of ! hydrolysis, as indicated by the absence of solid ~ --10--, `

.- .. - . : .. . . .

:10~06~9 material, af~er remaining undisturbed for one week under -ambient conditions.
The foams were prepared by combining 2.0 parts by weight o~ the aforementioned ~el catalyst solution, 22.5 parts of a mixture containing 80% by weight of 2,ll-tolylene diisocyanate and 20% by weight of 2,6-tolylene diisocyanate ~` and 50.8 parts of a precursor or master batch containing 50 part of a glYcerine-based polyoxypropylene triol having a molecular weight of 3000, 0.5 part of a polysiloxane type of surfactant, 0.15 part of N-ethyl morpholine and 0.15 part of a 33%
solution of triethylene diamine in dipropylene glycol. The gel catalysts evaluated were bis(methoxymethyl)tin dichloride, bis(methoxymethyl)tin oxide and bis(methoxymethyl)tin ~ diacetate. The time interval between combining of the - reagents and completion of foam formation, conventionally referred to as the rise time, was between 90 and about 200 seconds for each of the formulations tested. The size~
density and color of the foams were similar to those of a ~oam prepared by replacing the aforementioned aqueous gel catalyst solution with 0.15 part dioctyl phthalate, 0.15 part stannous octoate and 1.75 parts of water. The water and stannous octoate were added as separate components to the formulation, since stannous octoate is known to decompose rapidly in the presence of even trace amounts of water.
All of the foams passed the "Dry Heat Test" as described in the American Society for Testing of Materials procedure D-1654-64-A, which is hereby incorporated by ¦~ re~erence .` ~ ' ~` .
.: ; . . :

10~0699 ~ lexlble polyurethane foams were prepared as described ln the preceeding Example 2. The precursor contained 100 parts o~ the same polyoxypropylene triol, 3.5 parts of water, 1.0 part of a polysiloxane surfactant, 0.3 part N-ethyl morpholine and 0.3 part of a 33% solution of triethylene diamine in dipropylene glycol. To 52.5 par~s of this precursor was added 20 parts of the tolylene diisocyanate mixture described in Example 2 together with 0.15 g. o~ dimethyltin dichloride. The resultant mixture was stirred rapidly for 10 seconds to obtain a homogeneous ~ system and was then allowed to rise. The rise time was 113 .- seconds. The resultant foam passed the Dry Heat Test referred to in Example 2.
;` EX~MPLE 4 Rigid foams were prepared using the following 1~ formulation:

Parts Polyoxypropylene tetrol 100.0 ~sucrose based, hydroxyl no. = 435) ; Trichlorofluoroethane 37.0 Polysiloxane surfactant 1.5 Dimethylethanolamine 1.0 Water 1.0 Polymethy1ene polyphenylene isocyanate 37.0 Each o~ the foregoing ingredients was separately added to a reaction vessel together with 1.0 part Or dimethyl-tin dichloride as a solution in 1.0 part of water. The rise time was 62.9 seconds. A foam prepared froril the same formulati~n using 1.0 part of dibutyltin dilaurate, a con-ventional gel catalyst for rigid polyurethane foams, required 71 seconds to rise.
~he foregoing examples demonstrate that the present methyltin and methoxymethyltin compounds are at least equivalent in perro~mance to prior art catalysts, while providlng the additlonal advantage of water solubility and hydrolytic stabillty. -12-.
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Claims (3)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A hydrolytically stable precursor for preparing a flexible or rigid cellular polyurethane, said precursor comprising 100 parts by weight of a polyalkylene polyol, from about 0.5 to 5 parts of water, from about 0.05 to about 1.0 part of a foaming catalyst, from about 0.5 to 2 parts of a silicone surfactant and from about 0.05 to about 1.0 part of a gel catalyst, wherein the gel catalyst is an organotin compound of the formula RaSnX4-a, R2SnO or (R3Sn)2O wherein R is the radical CH3- or CH3OCH2-, X is selected from the group consisting of chlorine, bromine and iodine atoms and radicals of the formula -OOCCH3 or -OOCCH2CH3 and a is the integer 2 or 3.

2. A hydrolytically stable precursor as defined in claim 1 wherein X
is chlorine or -OOCCH3.

3. A hydrolytically stable precursor as defined in claim 2 wherein R
is methyl.