CA1091399A - Method for preparing urethane-modified isocyanurate foams - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The friability exhibited by urethane-modified isocyanurate foams prepared using alkali metal salts of carboxylic acids as the catalyst is reduced by employing certain organotin compounds or stannous salts of carboxylic acids as a co-catalyst.

Description

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The present invention pertains to an improved method for preparing rigid polyisocyanurate cellular compositions which have been modified by addition of polyurethane-producing monomers. More particularly, the present invention relates to the preparation of rigid cellular urethane-modified isocyanurate polymers catalyzed with a synergistic combination of isocyanur-ate trimerization catalysts.
The trimerization reaction of isocyanates to iso-cyanurates using triethylphosphine as the catalyst was first i:
reported by Hofmann. Since that time, many other catalysts for the trimerization of isocyanates have been described. The use of amines is described in United States Patents 2,993,870 and 2,979,485. Additional basic nitrogen compounds, such as triazines and their derivatives are taught in United States Patent 3,804,782. Salts of weak acids such as calcium acetate have been described by Frentzel, and potassium acetate and ' sodium carbonate by Hofmann. The use of potassium octanoate i~:
;. (2-ethylhexoate) is taught in Japanese Patent 71/42,386.
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The preparation of rigid cellular polyisocyanurate ....
or urethane/isocyanurate polymers is generally achieved by reacting either a polyether or polyester polyol with an organic polyisocyanate in the presence of a surfactant, a blowing agent ~ ", j and a suitable catalyst. In the preparation of these ~ ..
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,., foams, the function of the catalyst is to accelerate formation of the cellular product, thereby making the process eco- ¦
nomical and efficient. While amine catalysts such as

2,4,6,(N,N-dimethylaminomethyl) phenyl and hexahydrotriazines are effective, the use of these catalysts has been limited by the high level required and the toxicity of these compounds.
me commercial utility of the alkali metal salts such as potassium 2-ethylhe~oatc has not been fully realized because foams prepared using these catalysts are often so friable that they exhibit little if any resistance to impact and abrasion. In some lnstances, this effect may be so severe ;- that the foams crumble to a powder when subjected to even routine handling during their fabrication. The friability of these foams has delayed their wide use in applications related to the construction industry, which has a need for ~; 15 these types of foams as insulating materials. It has now been found that this shortcoming can be eliminated by using certain organotin compounds, stannic or stannous salts in combination with certain specified alkali metal salts as cocatalyst for preparing urethane -modifl-d isocyanurate foams.

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. ' .. l Accordingly, the invention provides in an improved method . for preparing urethane-modified isocyanurate foams by reacting a polyfunctional isocyanate with a polyol in the presence of a `` catalytically effective amount of a catalyst for the reaction, ' the improvement comprising employing from 2 to 14 equivalent weights of said polyfunctional isocyanate for each equivalent of . polyol and any water and conducting the reaction in the presence ...:
of from Q.5 to 5%, based on the polyisocyanate, of a catalyst `: composition consisting essentially of (1) an alkali metal salt : 10 exhibiting a general formula selected from the group consisting :~ of ,j~ (MOC ) Rl, ( MO ) Rl, ( MS ) Rl, MOCR2SH~ MOCR SM~ R OCR SM~
- MSR20H and MSR20M, and ~2) between 5 and 50%, based on the : weight of said salt, of a tin compound exhibiting a formula sel-~?~'~ ected from the group consisting of RbSnX(4 b)' R24SnS, R42SnO, .~ . oR50 ~ 0 2Sn / SnR24, ~24SnOCR6)20 and SnX2, wherein M is an .!, OR50 . alkali metal, a is 1 or 2, Rl is alkyl containing from 1 to 20 carbon atoms, alkenyl containing from 2 to 20 carbon atoms, cyclo-alkyl, aryl, alkaryl or aralkyl when a is 1, or R is alkylene, ; 20 arylene or alkylidene and contains from 2 to 20 carbon atoms ~-- when a is 2, R2 and R5 each represent identical or different alkylene radicals containing from 2 to 20 carbon atoms, R3, R4 and R6 are individually selected from the group consisting of alkyl radicals containing from 1 to 20 carbon atoms, cycloalkyl, ~ aryl, alkaryl and aralkyl radicals, b is zero or the integer 1, .~. 2 or 3 and X is selected from the group consisting of halogen atoms and radicals of the formula R7Coo-, R7S- and R700C(CH2)nS-, wherein R7 is selected from the same group as R3 and n is 1 or 2.
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- The 2-component catalysts employed in the method of the invention yield cellular urethane-modified isocyanurate polymers that exhibit significantly higher abrasion resistance than can be achieved using many prior art catalysts, including the alkali metal salts that constitute one component of the present two-component catalysts. In addition, the time required for completion of the polymerization reactions is significantly reduced relative to what can be achieved in the absence of the tin compound. This is considered surprising, since tin compounds 10 are not effective catalysts for the trimerization of isocyanates, as will be demonstrated in the accompanying examples.
The concentration of tin compound in the present catalyst compositions depends upon a number of variables, in-cluding the particular polyisocyanate and polyol employed to prepare the cellular polymer. Conventionally the tin compound constitutes between 5 and 50% by weight of the catalyst compo-. sition, preferably between 10 and 30%.
The total catalyst concentration required to achieve ~: acceptable foam product is between 0.5 and 5%, based on the weight of polyisocyanate present in the formulation employedto prepare the foam. The time required for the foam to completely rise is usually a direct function of the catalyst concentration, and is desirably between 5 and 300 seconds for a commercial process, depending upon the method of application and the thick-ness of the foam.

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s The first component of the present catalyst q compositions is a reaction product of 11thium, sodium or potassium hydroxlde with a carboxylic acid, alcohol, phenol, mercaptoacid, mercaptoacid ester or mercaptoalcohol. In those instances when the anionic portion of the resultant salt is derived from a compound containing both hydroxyl and ¦ mercapto radicals, the reaction with the alkali metal hydroxide ' will usually occur at the hydrogen atom of the mercapto radical, since this atom is usually more labile than the hydrogen atom of the hydroxyl group. The latter can be reacted by using more than an equimolar amount of alkali m-tal , hydroxide. The anionic portion of the resultant salts contains between 1 and 20 carbon atoms.
`~ Carboxylic acids suitable for use in preparing the present salts include acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid or other ¦ acid up to and including C20 carboxylic acids. Unsaturated carboxylic acids derived from tall oils or animal fats such ¦ as oleic acid or linoleic acids are also suitable, as are -¦, mixtures of these acids. Aromatic carboxylic acids such as , I benzoic acid and substituted derivatives thereof, such as .~ p-nitrobenzoic acid, salicylic acid, and the isomeric naph-thenoic acids may also be used. Polycarboxylic acids, such ; as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, brassylic acid, thapsic acid, maleic acid, fumaric acid, glutaconic acid, a-hydroxymuconic acid, ~-hydroxymuconic acid, a-butyl-a-ethylglutaric acld, -diethylsuccinic acid, isophthalic acid, terephthalic acid, . -5-:. ~ . , I
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f hemimellitic acid and 1,4-cyclohexane dicarboxylic acid can be reacted with a stoichiometric amount of an alkali metal ¦ hydroxide to form useful catalysts.
Instead of using a carboxylic acid to form the salt ~ one can employ mercaptocarboxylic acids, esters of mercapto-¦ carboxylic acids, phenols, alcohols, mercaptoalcohols or ~ ~ mercaptans as specified hereinbefore. Among these alter-:, native precursors preferred compounds include mercaptoacetic acid, me.captopropionic acid, isooctyl mercaptoacetate, 2-mercaptoethanol, phenol and substituted phenols wherein the substituents on the phenyl radical include halogen and nitro (-NO2) radicals, methanol, ethanol and higher homologs thereof, ethylene and propylene glycol, lauryl mercaptan, benzyl mercaptan and thiophenol.
; 15 - The aforementioned salt is prepared by neutralizing the carboxylic acid or other precursor with an aqueous solution of the alkali-metal hydroxide. Careful control of the exotherm resulting from the heat of neutralization is i usually required to maintain a colorless product. The water 1 of solution and neutralization i5 then removed ur.der reduced jl pressure with stirring to minimize heating.
¦¦ An optional procedure employs a diluent as a viscosity suppressant and/or solvent for the reactants and ~ products. In this procedure, the carboxylic acid or other I precursor is first dissolved in the diluent, then reacted wlth the aqueous caustic solution. The water formed as a byproduct is then removed. Suitable diluents for reacting carboxylic acids and compounds containing a mercaptan radical include alcohols such as methanol, ethanol, propanol, butanol ' ;:''.' 11 ~ ll !
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propylene glycol and poly(propylene glycols) and the like.
The second compo~ent of the present catalyst is a stannous or stannic salt of one of the aforementioned I compounds employed to prepare the alkali metal salt or certain ; I organotin compounds as specified hereinbefore. The organotin -/ ? compounds include diorganotin oxides, sulfides and mono-, I di- and triorganotin compounds derived from reaction of ;he ,,..
corresponding organotin halide or oxide with a carboxylic acid, mercaptan or mercaptoacid ester. Diorganotin derivatives of glycols containing between 2 and 20 carbon atoms are also useful. Representative methyltin compounds include Methyltin-S,S',S"-tris(isooctyl mercaptoacetate) Dimethyltin-S,S'-bis(isooctyl mercaptoacetate) ` i Trimethyltin-S-isooctyl mercaptoacetate i~ Methyltin-S,S',S"-tris(lauryl mercaptide) Dimethyltin-S,S'-bis(lauryl mercaptide) Dimethyltin distearate ? Methyltin tri-2-ethylhexoate ¦¦ Dlmethyltin dibenzoate Dimethyltin maleate Dimethyltin dilaurate ll Dimethyltin sulfide ?
ll Dimethyltin oxide ?
?' Bls(dimethyl lauryloxytin)oxide OCH2CHzO
¦ Bis(dimethyltin)diethylene glycoxide, (CH3)2SnJ Sn(CH3)z ~OCH2CH20~
Homologs of all the foregoing organotin compounds wherein the hydrocarbon radical bonded to the tin atom is ¦ butyl, cyclohexyl, octyl or phenyl are readily available and are particularly suitable for use in the present catalyst compositions. Methods for preparing all of the present organotin catalysts from the corresponding organotin halide I or oxide are reported in the literature and do not form part of I
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,:'1 l . ' this invention. In place of the foregoing organotin compounds ~¦ I one can employ a stannous or stannic salt of a mono- or dicarboxylic acid, mercaptan, mercaptoacid, mercaptoacid ll ester, alcohol or glycol. Suitable acids are of the formula 1l R COOH, wherein R represents a hydrocarbon radical containing jl between 1 and 20 carbon atoms as previously defined.
¦i Representative acids include acetic, propionic, butyric, I! isobutyric pentanoic caproic 2-ethyl hexoic caprylic ¦~ pelargonic, capric, dodecanoic, st~aric, eicosanoic, oleic, cyclohexanecarboxylic, benzoic and toluic acids. The mixture - of acids derived from tall oil is also suitable.
Tin compounds are not satisfactory catalysts for -- preparing cellular isocyanurate polymers, as will be demon-¦ strated in the accompanying examples. It is therefore I surprising that in addition to decreasing friability of the final product, the tin compounds often decrease the time required to form the cellular polymer relative to the time required using the aforementioned alkali metal salt alone.
!~ me cellular urethane/isocyanurate polymers which 11 are prepared in accordance with this invention using the present catalysts comprise the reaction product of an I isocyanate with itself to form a polyisocyanurate, modified by : I the simultaneous reaction of a fraction of the polyisocyanate with an organic compound containing at least two act~ve hydrogen atoms, such as a hydroxy-terminated polyester, polyesteramide, polyamide or polyether or any other compound j that will copolymerize with a polyisocyanate. Suitable comonomers include difunctional epoxide compounds, such as the I diglycidyl ether of 1,4-butanediol and low molecular weight I diglycidyl ethers or di- or bis- phenols.

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. In general, any organic compound containing at least two active hydrogen atoms may be employed herein for reaction wlth the polyisocyanate to produce the necessary urethane . modification of the isocyanurate polymer. Examples of suitable : 5 types of organic compounds containing at least two active hydrogen atoms are castor oil, hydroxy-containing polyesters, . polyalkylene polyether polyols, hydroxy-terminated polyurethane :1 polymers, polyhydric polythioethers, alkylene oxide adducts l of phosphorus-containing salts, polyacetals, aliphatic polyols, .~. simple, oligomeric and polymeric glycols such as ethylene ,j~................ glycol, propylene glycol, butylene glycol, poly(ethylene ~. . glycol), poly(propylene glycol) and poly(butylene glycol).
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: These polyols generally have an average equivalent weight of :.~ from about 31 for ethylene glycol to 2000 for a polyoxypro-pylene adduct of glycerine. Polyol blends, such as a mixture of high molecular weight polyether polyols with lower molecular weight polyether polyols or monomeric polyols, can also be used to achieve a desired level of viscosity.
The organic polyisocyanates which are advantageously 20 employed either alone or ~s mixtures in the present invention can be represented by the formula: ¦

. . R(NC0)z .- wherein R is a polyvalent organic radical selected from the :~ . group of alkyl, aryl, aralkyl and alkaryl organic radicals : 25 and z is an integer corresponding to the valence number of R
;` . and is at least 2. Representa.tive organic polyisocyanates . contemplated herein include, for example, the aromatic ¦¦ d1lsocyanat , such as 2,4-toluene d lsocyanate, 2,6-toluene . _g_ .''',.' , I¦ !
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diisocyanate, mixtures of 2,4- and 2,6-toluene diisocyanate, crude toluene diisocyanate, methylene diphenyl diisocyanate, crude methylene diphenyl diisocyanate and the like; the aromatic triisocyanates such as tris-(4-isocyanatophenyl)-methane; 2,4,6-toluene trisisocyanates; the aromatic tetra- --isocyanates, such as 4,4'-dimethyldiphenylmethane-2,2', 5',5'-tetraisocyanate, and the like; alkylaryl polyisocyanate, such as xylene diisocyanate; aliphatic polyisocyanates~ such as hexamethylene-1,6-diisocyana e; lysine diisocyanate methylester and the like; and mixtures thereof. Other organic polyisocyanates include polymethylene polyphenylisocyanate, hydrogenated methylene diphenylisocyanate, m-phenylene diisocyanate, naphthylene-1,5-diisocyanate, 1-methoxyphenyl-2, , 4-diisocyanate, diphenylmethane-4,4'-diisocyanate, 4,4 t _ biphenylene diisocyanate, 3,3'-dimethoxy-4,4'-biphenyl di-isocyanate, 3,3'-dimethyl-4,4'biphenyl diisocyanate, and

3,3'-dimethyldiphenylmethane-4,4'-diisocyanate.
These polyisocyanates are prepared by conventional methods known in the art such as phosgenation of the I corresponding organic amine. f Still another class of organic polyisocyanates contemplated by the present invention are the so-called "quasi-prepolymers". These quasi-prepolymers are prepared by reacting an excess of organic polyisocyanate or mixtures thereof with a minor amount of an active hydrogen containing compound as determined by the well-known Zerewitinoff test, as described by Kohler in Journal of American Chemical Society, 49, 3181 (1927). These compounds and their method of preparation are well known in the art. The use of any one . ~' ,' ' -10- , i ,., . I .
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specific active hydrogen compound is not critical, rather, any such compound that can be used to prepare a quasi-prepolymer ; can be employed herein. Generally speaking, the quasi-pre-- polymers are prepared by reacting an organic polyisocyanate . with less than a stoichiometric amount, based on the molecular :
weight and functionality of the polyisocyanate, of the active hydrogen-containing compound. Suitable active hydrogen- -containing groups are those hereinbefore described.
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; In the practice of the present invention, the preferred isocyanate is polymethylene polyphenylisocyanate. The relative amount of this polyisocyanate present in the reaction mixture should be such that the number of isocyanate radicals is between 2 and 10 times, preferably between 3 and 5 times the total number of active hydrogen atoms present in the reaction mixture.
Expressed in another way, the number of equivalents of iso-cyanate should be from 2 to 14 times the number of equivalents ^~r,', of polyol and any water present in the reaction mixture.
' In addition to the previously disclosed reagents useful ,~; . :, ~`~ in the preparation of the foam product, other ingredients such as surfactants, fillers, pigments and blowing agents can also ;~ be included. Conventional surfactants used for preparing poly-urethanes include polysiloxanes and the alkylene oxide adducts of organic compounds containing reactive hydrogen atoms. The surfactant is generally used in an amount ranging from about , 0.01 part to 5 parts by weight per hundred parts of polyiso-. . ,~, ~ cyanate.
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¦ The expansion of the polyisocyanate-polyol mixture to a eellular product is aceomplished by use of a blowing agent, a volatile organic liquid which vaporizes during the ex~thermic polymerization reaction. Suitable blowing agents are conventionally halogen-containing hydrocarbons such as methylene chloride, ethylene chloride, trichlorofluoro-methane, diehlorodifluoromethane, ehlorotrifluoromethane, ¦ tetrachloromethane and difluorotetrachloroethane. The blowing j agent used in the preferred embodiment is trichlorofluoro-methane. Water may be used as a supplemental blowing agent in addition to the halocarbon. The use of water as a blowing agent in urethane chemistry is described in Saunders and . ~risch, Advances in Polyurethane Chemistry, Volume 1, Page 76.
Other ingredients conventionally present in poly-urethanes and urethane-modified isocyanurate polymers include fillers, pigments and the like. Conventional fillers for foams include, for example, aluminum silicate, calcium li silicate, magnesium silicate, ealeium earbonate, barium - ¦¦ sulfate, ealeium sulfate, carbon black and silicon. The I filler is usually present in an amount ranging from about 5 parts to 50 parts by weight per hundred parts of total formulation employed to prepare the foam.
Pigments that have been employed in foam produets inelude titanium dioxide, zinc oxide, oxides of iron, antimony 3 oxide, chrome green, chrome yellow, iron blue siennas, molybdatej oranges, organic pigments such as "para1' reds, benzidine yellow, toluidine red, various toners and phthalocyanine dyes.

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` Many procedures conventionally employed to prepare rigld urethane foams are also applicable to urethane-modified isocyanurate polymers. These procedures usually involve combining the reagents and additives other than the poly-isocyanate with rapid agitation to ensure a homogeneous formulation. The resultant composition is then thoroughly , blended with the polyisocyanate after which it is poured ~¦ into a suitable mold or other container wherein the simul-i taneous polymerization and expansion or "blowing" occurs ~ The proper balance between the rates of polymerization and expansion of the resultant polymer must be achieved to obtain a uniform product that exhibits the desired low density and I small cell size.
The following example discloses preferred embodiments of the present method and catalyst compositions and should not be interpreted as limiting the scope thereof. All values expressed in parts are by weight.
~ ll The friability of foam sarnples prepared using bo h ;, I the present and prior art catalysts was determined using ASTM
l (American Society for Testing of Materials) test procedure ; ! C421-71, entitled "Mechanical Stability of Preformed Thermal Insulation by Tumbling". The friability is expressed in terms of the relative weight loss (in percent), based on the initial weight of the sample measured prior to testing, that occurs '.
throughout a ten minute interval during which the sample is ~, ; in a rotating cubicle containing a number of loose oak cubes measuring 1 inch along each edge. Friable samples crumble readily under these conditions.
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¦! To a homogeneous mixture containing 22.5 g. of a i! polyoxypropylene glycol exhibiting a hydroxyl number of 425 (available as Pluracol~ P-410 from BASF Wyandotte Corporation) ii and 2.5 g. of a polyoxyalkylene polysiloxane surfactant (available as Niax silicone L-5340 from the Union Carbide Corporation) were added trichlorofluoromethane and a catalyst ¦! as disclosed in the accompanying table, followed by 100 g. of polymethylene polyphenylisocyanate. The resultant mixturc was !! stirred rapidly for 10 seconds, then poured into a suitable ¦ cardboard container and allowed to rise. The time intervals between combining of the reagents and 1) the onset of f .~ blowing (as evidenced by an opacifying of the mixture) and ~ -2) the completion of ~ising of the foam were measured and are f ¦ referred to as cream time and rise time, respectively, in the ~¦ accompanying table.
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The data in the preceding table demonstrate that while tin compounds alone are ineffective catalysts for : preparing cellular urethane/isocyanurate polymers, these compounds interact favorably with alkali metal salts of : 5 carboxylic acids to ir.crease the structural strength of the I cellular polymers. The tin compounds also decrease the cream ¦ and rise time of the foam, which is unexpected in view of - ¦ their poor catalytic activity when employed in the absence of I the alk~li metal salt.
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Claims (5)

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

1. In an improved method for preparing urethane-modified iso-cyanurate foams by reacting a polyfunctional isocyanate with a polyol in the presence of a catalytically effective amount of a catalyst for the reaction, the improvement comprising employing from 2 to 14 equivalent weights of said polyfunctional isocyanate for each equivalent of polyol and any water, and conducting the reaction in the presence of from 0.5 to 5%, based on the polyiso-cyanate, of a catalyst composition consisting essentially of (1) an alkali metal salt exhibiting a general formula selected from the group consisting of , , , , , , MSR2OH and MSR2OM, and (2) between 5 and 50%, based on the weight of said salt, of a tin compound exhibiting a formula selected from the group consisting of R?SnX(4-b), R?SnS, R?SnO, , and SnX2, wherein M is an alkali metal, a is 1 or 2, R1 is alkyl containing from 1 to 20 carbon atoms, alkenyl containing from 2 to 20 carbon atoms, cycloalkyl, aryl, alkaryl or aralkyl when a is 1, or R1 is alkylene, arylene or alkylidene and contains from 2 to 20 carbon atoms when a is 2, R2 and R5 each represent identical or different alkylene radicals containing from 2 to 20 carbon atoms, R3, R4 and R6 are individ-ually selected from the group consisting of alkyl radicals con-taining from 1 to 20 carbon atoms, cycloalkyl, aryl, alkaryl and aralkyl radicals, b is zero or the integer 1, 2 or 3 and X is selected from the group consisting of halogen atoms and radicals of the formula R7COO-, R7S- and R7OOC(CH2)nS-, wherein R7 is selected from the same group as R3 and n is 1 or 2.

2. A method according to claim 1 wherein M is potassium and a is 1.

3. A method according to claim 2 wherein the salt exhib-its the formula .

4. A method according to claim 3 wherein R1 represents 2-ethylhexyl.

5. A method according to claim 1 wherein R represents methyl, butyl, octyl or phenyl.