POLYURETHANE PREPOLYMER COMPOSITIONS, FOAMS MADE THEREFROM AND METHODS OF MAKING EACH THEREOF

Abstract: A polyisocyanate prepolymer composition is comprised of the reaction product of (a) a polyisocyanate having an average functionality of at least 2 and containing at least 20 percent by weight of a diisocyanate monomer, (b) a monohydric alcohol and (c) a polyol having an average hydroxyl functionality of at least 1.8 to at most 3.2, wherein the prepolymer composition has (i) an amount of isocyanate groups by weight sufficient to react with water in the absence of a supplemental blowing agent to make a foam, (ii) at most 10.0 percent by weight of the diisocyanate monomer and (iii) an amount of the polyisocyanate that is capped by the monohydric alcohol sufficient to prevent gelling of the prepolymer composition. The prepolymer composition may be formed by contacting (i) an organic polyisocyanate having an average isocyanate functionality of at least 2.0 and an amount of diisocyanate monomer of at least 20 percent by weight, (ii) a monohydric alcohol and (iii) a polyol having an average hydroxyl functionality of at least 1.8 to at most 3.2 for a time and temperature sufficient to form the prepolymer composition, wherein the organic polyisocyanate, monohydric alcohol and polyol are contacted at a ratio of NCO to hydroxyl of at least 2, to at most 5, and the monohydric alcohol and polyol are provided in a ratio of monohydric alcohol to polyol of at least 0.1, to at most 2, based upon the hydroxyl equivalence of the monohydric alcohol and polyol. The prepolymer composition may be reacted with water to form a polyurethane foam.

Description: POLYURETHANE PREPOLYMER COMPOSITIONS, FOAMS MADE THEREFROM AND METHODS OF MAKING EACH THEREOF Polyurethanes are formed by the reaction of a polyisocyanate compound, such as toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI) with a polyhydroxyl compound, such as a polyol. Generally, streams of approximately equal volume of the polyol and polyisocyanate are intermixed in a mixing head and then dispensed into a cavity or mold. In the mold or cavity, the hydroxyls of the polyol and isocyanates of the polyisocyanate react to form the polyurethane, while simultaneously water added to the polyol reacts with the isocyanates to provide CO 2 in situ that causes the polyurethane to foam. Since isocyanates readily react with water, they are generally known to be an irritant and can be toxic when inhaled. Prepolymers have been used in place of polyisocyanates to decrease the amount of vaporous isocyanate when making polyurethane foams. Prepolymers generally are made by reacting a diol with a diisocyanate monomer (for example, MDI or TDI) at a great excess of NCO (that is, isocyanate) to OH (that is, hydroxyl). Commonly, the NCO to OH equivalence ratio is well in excess of 5. The ratio is large to keep the prepolymer from gelling while still providing enough NCO to produce a foam. As a consequence of the large NCO to OH ratio, a significant amount of diisocyanate monomer (for example, MDI), typically, is still present in the prepolymer. Generally, when making foams from these prepolymers, a gas blowing agent, such as a chlorofluorocarbon, is used to froth the prepolymer and ambient moisture reacts with the prepolymer to form polyurethane. Since ambient moisture causes the urethane reaction to proceed (that is, formation of urea linkages and amines), foams of this sort suffer from inconsistencies depending on ambient humidity. Thick foams made by this method also tend to collapse as they cure. The foam collapses because an insufficient amount of water penetrates through the outer portion of the foam into the interior of the mass to adequately cure (that is, cross-link) the interior of the foam. More recently, International Patent Application No. 96/06124 has described prepolymers that have attempted to decrease the amount of diisocyanate monomer when making a foam. The 96/06124 application describes forming a prepolymer by reacting a - polyisocyanate having an isocyanate functionality of 2.3 to 3.7 and having a diisocyanate monomer content of less than 20 percent by weight of the polyisocyanate with a polyol at -1- high NCO to OH ratios (for example, 4.6). The 96/06124 application also describes, when making a foam from these prepolymers, a blowing agent, such as a di ethylether, is used. Thus, this reference describes a technique of making a prepolymer with a low diisocyanate monomer concentration by starting with a polyisocyanate having a low concentration of diisocyanate monomer initially. This technique suffers from the need to use a polyisocyanate that must have a low diisocyanate monomer content initially, which may require, for example, expensive distillation or reaction processes to form said polyisocyanate. These prepolymers also require a gaseous blowing agent (for example, CFCs) when making a foam. Thus, it would be desirable to provide a prepolymer composition, method to form the prepolymer composition, foam made from the prepolymer composition and method to make the foam that avoids one or more of the deficiencies of the prior art, such as one of those described above. A first aspect of the present invention is a polyisocyanate prepolymer composition comprising the reaction product of (a) an organic polyisocyanate having an average isocyanate functionality of at least 2 and containing at least 20 percent by weight of a diisocyanate monomer, (b) a monohydric alcohol and (c) a polyol having an average hydroxyl functionality of at least 1.8 to at most 3.2, wherein the prepolymer composition has (i) an amount of isocyanate groups by weight sufficient to react with water in the absence of a supplemental blowing agent to make a foam, (ii) at most 10.0 percent by weight of the diisocyanate monomer and (iii) an amount of the polyisocyanate that is capped by the monohydric alcohol sufficient to prevent gelling of the prepolymer composition. A second aspect of the invention is a method of forming a prepolymer polyisocyanate composition for preparing polyurethane foams, the method comprises: contacting (i) an organic polyisocyanate having an average isocyanate functionality of at least 2 and an amount of diisocyanate monomer of at least 20 percent by weight, (ii) a monohydric alcohol and (iii) a polyol having an average hydroxyl functionality of at least 1.8 to at most 3.2 for a time and temperature sufficient to form the prepolymer composition, wherein the organic polyisocyanate, monohydric alcohol and polyol are contacted at a ratio of NCO to hydroxyl, of at least 2 to at most 5, and the monohydric alcohol and polyol are provided in a ratio of monohydric alcohol to polyol, of at least 0.1 to at most 2, based upon the hydroxyl equivalents of the monohydric alcohol and polyol. -2- The prepolymer polyisocyanate composition surprisingly may be made with a low NCO:OH ratio (that is, 2 to 5) due to the discovery of the beneficial effect of the monohydric alcohol added in a specific ratio with the polyol. Consequently, a prepolymer composition may be formed that avoids gelation and has a low diisocyanate monomer content while still providing sufficient amounts of NCO (that is, isocyanate groups) to form a foam in situ (that is, from the reaction of water with NCO of the prepolymer composition). The amount of diisocyanate monomer still remaining (that is, residual) in the prepolymer composition after forming may be so small that little or no special ventilation (for example, ventilation hoods) or protective breathing apparatus (for example, half mask chemical respirators) may be required when making a foam therefrom. In addition, a third aspect of the invention is a method of forming a polyurethane foam comprising contacting the prepolymer composition of the first aspect with a foaming reactant comprised of water for a time and temperature sufficient to form the polyurethane foam. In particular, a foam may be formed wherein essentially the only blowing agent is CO 2 produced by the reaction of the NCO groups of the prepolymer composition and the water of the foaming reactant. Finally, a fourth aspect of the invention is a foam comprising a continuous cellular matrix reaction product of water and the polyisocyanate prepolymer composition of the first aspect. The prepolymer composition may be used to make, among other things, polyurethane foams useful as adhesives, sealants, coatings, insulative coatings, membranes and acoustical baffles for use in the automotive industry. The Prepolymer Composition The polyisocyanate prepolymer composition comprises the reaction product of (a) an organic polyisocyanate having an average functionality of at least 2 and containing at least 20 percent by weight of a diisocyanate monomer, (b) a monohydric alcohol and (c) a polyol having an average hydroxyl functionality of at least 1.8 to at most 3.2. The prepolymer composition (that is, reaction product) has an amount of isocyanate groups by weight sufficient to react with water in the absence of a supplemental blowing agent to make a foam. A supplemental blowing agent, herein, is a blowing agent other than CO 2 generated in situ during the formation of the foam. Supplemental blowing -3- agents include, for example, gases that are used to create a froth (for example, nitrogen), liquids that volatilize during foam formation (for example, methylene chloride, methyl chloride, and FREON™ 113) and solids that release a gas during foam formation (for example, azo compounds, such as barium azodicarboxylate). Generally, the amount of NCO present is 2 percent to 20 percent by weight of the prepolymer composition. Preferably the amount of NCO is at least 5 percent, and more preferably at least 6 percent to preferably at most 15 percent, more preferably at most 13 percent, even more preferably at most 12 percent, and most preferably at most 10 percent by weight of the prepolymer composition. Even though the prepolymer composition may form a foam without a supplemental blowing agent, one may still be present in the composition to give a desired foam characteristic, such as greater thermal insulation for a foam of a specific thickness. Small quantities of a supplemental blowing agent may be present in the prepolymer composition, such as a low boiling hydrocarbon (for example, pentane, hexane, heptane, pentene and heptene) directly added carbon dioxide, an azo compound (for example, azohexahydrobenzodinitrile) or a halogenated hydrocarbon (for example, dichlorodifluoroethane, vinylidene chloride and methylene chloride). However, the amount of supplemental blowing agent is preferably at most a trace amount and more preferably none at all. The prepolymer composition contains an amount of diisocyanate monomer of at most 10 percent by weight of the prepolymer. Preferably the amount of diisocyanate monomer is at most 6 percent, more preferably at most 3 percent, even more preferably at most 2.5, and most preferably at most 2 percent by weight of the prepolymer composition. Also, the amount of diisocyanate monomer present in the prepolymer composition generally results in very low concentrations of vaporous isocyanate compounds in the surrounding air space when making a foam therefrom. Very low concentrations of isocyanate correspond to levels generally deemed safe to handle without special equipment, such as hoods, when making a foam. For example, the amount of vaporous isocyanate compounds found in the air space is, typically, at most 5 parts per billion (ppb), preferably at most 3 ppb, more preferably at most 2 ppb, even more preferably at most 1 ppb and most preferably at most 0 ppb, the parts being parts by weight. -4- It has been found that the prepolymer composition, when made, and particularly when made with a low NCO to OH ratio of 2 to 5, requires an amount of the polyisocyanate that is capped by a monohydric alcohol sufficient to prevent gelling of the prepolymer composition. Herein, capped means the hydroxyl of the monohydric alcohol has reacted with an NCO of the polyisocyanate to form a urethane linkage. Gelling, herein, is when the prepolymer gels or increases in viscosity, such that the prepolymer composition is impractical to process into a foam. Typically, it is impractical to use a prepolymer composition having a viscosity greater than 100,000 centipoise. Generally, the monohydric alcohol is provided in a ratio of monohydric alcohol to polyol of at least 0.1 to at most 2, based upon the hydroxyl equivalents of the monohydric alcohol and polyol. Too much monohydric alcohol is generally undesirable because foam properties, such as compressive strength, uniformity of cell size and chemical resistance, may be degraded to a point where the foam fails to be useful in applications. Preferably the ratio of monohydric alcohol to polyol is at least 0.5, more preferably at least 0.6, most preferably at least 0.7 to preferably at most 1.5, more preferably at most 1 , and most preferably at most 0.7 The prepolymer composition surprisingly is stable (that is, fails to gel) when stored, for example, for 6 months or more under standard conditions in the industry (for example, under a dry atmosphere, "that is dew point less than -40°C"). The prepolymer composition is stable even when the composition is made at a low NCO to OH ratio described previously. Preferably the prepolymer composition is stable for at least a year and more preferably at least 2 years. Method of Making the Prepolymer Composition Reactants Because the prepolymer composition may be made with an organic polyisocyanate containing at least 20 percent by weight of diisocyanate monomer (for example, MDI in a polymeric MDI or TDI in polymeric TDI), the organic polyisocyanate may be, for example, an aromatic polyisocyanate, aliphatic polyisocyanate, polymeric isocyanate, aromatic diisocyanate, aliphatic diisocyanate or mixtures thereof. Exemplary polyisocyanates include m-phenylene diisocyanate, tolylene-2-4-diisocyanate, tolylene-2-6- diisocyanate, hexarnethylene-1 ,6-diisocyanate, tetramethylene-1 ,4-diisocyanate, cyclohexane-1 ,4-diisocyanate, hexahydrotolyiene diisocyanate, naphthylene-1 ,5- diisocyanate, methoxyphenyl-2,4-diisocyanate, diphenylmethane-4,4'-diisocyanate, 4,4'biphenylene diisocyanate, 3,3'dimethoxy-4,4'-biphenyl diisocyanate, 3,3'-dimethyl-4-4'- biphenyl diisocyanate, 3,3'-dimethyldiphenylmethane-4,4'-diisocyanate, 4,4',4"-triphenyl methane triisocyanate, polymethylene polyphenylisocyanate and tolylene-2,4,6- triisocyanate, 4,4'-dimethyldiphenylmethane-2,2'5,5'-tetraisocyanate. Preferably the polyisocyanate is diphenylmethane-4,4'-diisocyanate (MDI), tolylene-2-4-diisocyanate, tolylene-2-6-diisocyanate or mixtures thereof. Tolylene-2-4-diisocyanate, tolylene-2-6- diisocyanate and mixtures thereof are generally referred to as TDI. More preferably, the polyisocyanate is a polymeric polyisocyanate formed from MDI, such as those available from The Dow Chemical Company under the trademark PAPI™. The polymeric polyisocyanate "PAPI 20" is particularly preferred. Generally, the average measured isocyanate functionality of the polyisocyanate is at least 2 to at most 6. Preferably the average functionality of the polyisocyanate is at least 2.5, and more preferably at least 2.7 to preferably at most 3.5, and more preferably at most 3.2. As understood in the art, functionality is the average number of isocyanate groups per molecule in the polyisocyanate. The polyol used to make the prepolymer composition has an average hydroxyl functionality of at least 1.8 to at most 3.2. Preferably the average functionality of the polyol is at most 2.8, more preferably at most 2.5, and most preferably at most 2.0. A suitable polyol may be known polyols, such as those described by U.S. Patent Nos. 3,383,351 ; 3,823,201 ; 4,119,586 and 4,148,840. Exemplary polyols include polyhydroxyalkane polyols, polyoxyalkylene polyols, alkylene oxide adducts of polyhydroxyalkanes, alkylene oxide adducts of non-reducing sugars and sugar derivatives, alkylene oxide adducts of phosphorus and polyphosphorus acids, alkylene oxide adducts of polyphenols and polyols derived from natural oils, such as caster oil. Preferably the polyols are diols (for example, propylene glycol), triols or mixtures of these. More preferably, the polyol is a diol (that is, glycol). The polyol is also preferably a diol, triol or mixture thereof of poly(oxyethylene), poly(oxypropylene), poly(oxypropylene-oxyethylene), such as those available under the trademark VORANOL™ from The Dow Chemical Co., Midland, Ml. The polyols employed may have hydroxyl numbers which vary over a large range. The particular polyol or polyols are selected based upon the desired polyurethane foam properties. In general, the polyols have a hydroxyl number that ranges from 20 to - 1500. Preferably the hydroxyl number is at least 25, and more preferably at least 30 to preferably at most 600, and more preferably at most 450. The hydroxyl number (OH -6- number) is defined as the number of milligrams of potassium hydroxide required for the complete hydrolysis of the fully acetylated derivative prepared from 1 gram of polyol. The hydroxyl number may also be given by the following equation: (56.1) (1000) OH number = Equivalent Weight wherein (56.1 ) is the atomic weight of potassium hydroxide, (1000) is the number of milligrams in 1 gram of a polyol sample and equivalent weight is the molecular weight of the polyol divided by the hydroxyl functionality of the polyol (hydroxyls/polyol molecule) The monohydric alcohol is an alcohol that has one hydroxyl per molecule. The monohydric alcohol may be any having, for example, from 1 to 50 carbons (that is, a C,- C 50 monohydric alcohol) and preferably from 2 to 20 carbons (that is, a C 2 -C 20 monohydric alcohol). The monohydric alcohol may be substituted with other groups that essentially fail to react with the isocyanate under the conditions to make the prepolymer or foam. Particularly preferred monohydric alcohols include C,-C 20 unsaturated aliphatic monohydric alcohols. More preferably, the monohydric alcohol is selected from ethanol, methanol, butanol (for example, 1-butanol, 2-butanol or isobutyl alcohol), propanol( for example, isopropyl alcohol or n-propyl alcohol), EXXAL 12™ (C 11 -C aliphatic alcohols, available from Exxon Chemical America, Houston TX) or mixtures thereof. Most preferably the monohydric alcohol is butanol. Optional Additives The prepolymer composition may be made by using a catalyst. Consequently, the prepolymer composition may contain a catalyst. The catalyst may also be added after forming the prepolymer composition, for example, to aid in forming a foam made therefrom. A suitable catalyst includes known catalysts, such as those described by U.S. Patent No. 4,390,645, at col. 10, lines 14 to 27. More specifically, representative catalysts include: (a) tertiary amines, such as trimethylamine, triethylamine, N-n- methylmorpholine, N-ethylmorpholine, N,N-dimethylbenzylamine, N,N- dimethylethanolamine, N,N,N',N'-tetramethyl-1 ,4-butanediamine, N,N-dimethylpiperazine,. 1 ,4-diazobicyclo[2,2,2]octane, bis(dimethylaminoethyl)ether, bis(2-dimethylaminoethyl) ether, morpholine,4,4'-(oxydi-2,1-ethanediyl)bis and triethylenediamine; -7- (b) tertiary phosphines, such as trialkylphosphines and dialkylbenzylphosphines; (c) chelates of various metals, such as those which can be obtained from acetylacetone, benzoylacetone, trifluoroacetyl acetone, or ethyl acetoacetate with metals, such as Be, Mg, Zn, Cd, Pd, Ti, Zr, Sn, As, Bi, Cr, Mo, Mn, Fe, Co and Ni; (d) acidic metal salts of strong acids, such as ferric chloride, stannic chloride, stannous chloride, antimony trichloride, bismuth nitrate and bismuth chloride; (e) strong bases, such as alkali and alkaline earth metal hydroxides, alkoxides and phenoxides; (f) alcoholates and phenolates of various metals, such as Ti(OR) 4 , Sn(OR) 4 and AI(OR) 3 , wherein R is alkyl or aryl and the reaction products of the alcoholates with carboxylic acids, beta-diketones and 2-(N,N-dialkylamino)alcohols; (g) salts of organic acids with a variety of metals, such as alkali metals, alkaline earth metals, Al, Sn, Pb, Mn, Co, Ni and Cu including, for example, sodium acetate, stannous octoate, stannous oleate, lead octoate, metallic driers, such as manganese and cobalt naphthenate; (h) organometallic derivatives of tetravalent tin, trivalent and pentavalent As, Sb and Bi and metal carbonyls of iron and cobalt and (i) mixtures thereof. Catalysts are typically used in small amounts. For example, the total amount of catalyst present in the prepolymer composition may be 0.0015 to 5 percent by weight. The catalyst present may be added after the prepolymer composition is formed or may be used to reduce the time to form the prepolymer composition. Catalysts, when used to form the prepolymer composition, are generally employed in small amounts, such as from 0.01 percent to 1 percent by weight of the prepolymer composition. When a catalyst is used to form the prepolymer composition, generally only small amounts of catalyst remain, which are insufficient alone to adequately catalyze the reaction to form a foam. The prepolymer composition may be made in the presence of a plasticizer and, consequently, contain a plasticizer. The plasticizer may also be added after the -8- prepolymer composition is made. The plasticizer may be, for example, present in the prepolymer composition to alter the properties of the foam made from the prepolymer composition or reduce the viscosity of the composition, making it easier to process and handle. Suitable plasticizers may include those known in the art. Examples of plasticizers include phthalates (for example, dioctyl phthalate, diisooctyl phthalate, dimethyl phthalate, dibutyl phthalate and mixtures of phthalates, such as those sold under the trademark PALATINOL™, available from BASF Corporation, Mt. Olive, NJ), phosphates (for example, tributyl phosphate, triphenyl phosphate and cresyl diphenyl phosphate), chlorinated biphenyls and aromatic oils. Preferably the plasticizer is one available under the trademark PALITINOL™ and more preferably PALATINOL™ 711 P from BASF Corporation, Mt. Olive, NJ. The amount of plasticizer, when employed, may range over a wide range, for example, depending on the foam properties desired. Generally, the plasticizer, when present, ranges from 1 percent to at most 50 percent by weight of the prepolymer composition. When making a rigid foam, the prepolymer composition preferably contains a plasticizer. The prepolymer composition may also be made in the presence of a surface active agent, such as those described by U.S. Patent No. 4,390,645, at col. 10, lines 28 to 43. The surface active agent may also be added after the prepolymer composition is formed and said agent, for example, may be useful in cell formation and cell stabilization when the prepolymer is used to form a foam. Examples of surface active agents include nonionic surfactants and wetting agents, such as those prepared by the sequential addition of propylene oxide and then ethylene oxide to propylene glycol, the solid or liquid organosilicones, polyethylene glycol ethers of long chain alcohols, tertiary amine or alkylolamine salt of long-chain alkyl acid sulfate esters, alkyl sulfonic ester and alkyl arylsulfonic acids. The surface active agents prepared by the sequential addition of propylene oxide and then ethylene oxide to propylene glycol and the solid or liquid organosilicones are preferred. Liquid organosilicones, which are not hydrolyzable, are more preferred. Examples of non-hydrolyzable organosilicones include those available under the trademarks "DABCO™ DC 5043," "DABCO™ DC 5169," "DABCO™ DC 5244" and "DABCO™ DC198," available from Dow Corning Corp., Freeiand, Ml and "Y-10515," available from Union Carbide Corp., Danbury CT. Surface active agents are typically used in small amounts when making a foam. Consequently, the surface active agent, when present in the prepolymer composition, is typically present in an amount of 0.0015 to 1 percent by weight of the prepolymer composition. -9- The prepolymer composition may also be made in the presence of an additive, such as those known in the art, including, for example, an odor mask, a flame retardant, fungicide, UV stabilizer, antistatic agent, filler, pigment and cell opener. Examples of a flame retardant include phosphorous compounds, halogen containing compounds and melamine. These additives may also be added to the prepolymer composition after it has been formed. Examples of fillers and pigments include calcium carbonate, titanium dioxide, iron oxide, chromium oxide, azo/diazo dyes, phthalocyanines, dioxazines and carbon black. Examples of UV stabilizers include hydroxybenzotriazoles, zinc dibutyl thiocarbamate, 2,6- ditertiary butylcatechol, hydroxybenzophenones, hindered amines and phosphites. Examples of a cell opener include silicon-based antifoamers, waxes, finely divided solids, liquid perfluorocarbons, paraffin oils and long chain fatty acids. Generally, these additives, when present, are employed in small amounts, such as from 0.01 percent to 1 percent by weight of the prepolymer composition. Forming the Prepolymer Composition The prepolymer composition may be formed by contacting the organic polyisocyanate, monohydric alcohol and polyol at a ratio of NCO to hydroxyl of at least 2 to at most 5, where the monohydric alcohol and polyol are provided in a ratio of monohydric alcohol to polyol of at least 0.1 to at most 2, based upon the hydroxyl equivalents of the monohydric alcohol and polyol. Preferably the organic polyisocyanate, monohydric alcohol and polyol provide a NCO to OH ratio of at least 2.5 to preferably at most 4.0 and more preferably less than 3. The ratio of monohydric alcohol to polyol is preferably at least 0.5, and more preferably at least 0.6 to preferably at most 1.5, more preferably at most 1 , and most preferably at most 0.9. The organic polyisocyanate, monohydric alcohol, polyol and any optional additive may be contacted for any time and temperature sufficient to form the prepolymer composition. The polyisocyanate, monohydric alcohol, polyol and optional additive or additives may be contacted by any convenient method, such as those known in the art, provided that the reactants and additives are sufficiently mixed to make a substantially homogeneous reactant mixture. The time the reactants and additives may be contacted to form the prepolymer composition may vary over a large range due to, for example, the presence of a catalyst. Generally, the reaction time is at least 1 minute to at most 48 hours. The temperature the reactants are contacted at may also vary over a large range, but generally are limited to where one or more of the reactants decompose or the reaction is so -10- slow that the process is rendered impracticable. Preferably the temperature is at least 0°C to 250°C. The reactants are generally contacted under a dry atmosphere, such as those known in the art (for example, dry air or dry nitrogen, "that is gas having a dew point of less than -40°C"). Method of Forming a Foam from the Prepolymer Composition A foam prepared from the prepolymer composition may be made by any suitable method, such as those known in the art. Examples of methods include those described in U.S. Patent Nos. 4,390,645; 2,866,744; 3,755,212; 3,849,156 and 3,821 ,130. Suitable techniques include, for example, stirring the prepolymer composition, adding a foaming reactant comprised of water, mixing these for a short time, pouring the mixture into a mold and allowing the foam to form. Preferably the foaming reactant is pumped, for example, to a mixing head where it is mixed with the prepolymer composition in a very short time, such as at most 5 seconds, more preferably at most 2 seconds, and most preferably at most 1 second, and subsequently dispensed, for example, into a cavity or mold. The foaming reactant may contain other compounds besides water, such as the optional additives and the polyol previously described. Preferably the foaming reactant is comprised of water, a viscosity thickener (for example, methyl cellulose, guar gum, cellulose ethers, clay, treated fillers, surface treated clay, fumed silica, starch, monomix, polyols and corn syrup) and a catalyst, such as one previously described. The water of the foaming reactant is preferably distilled water. Most preferably the water is distilled and deionized water having essentially no impurities. When making a foam, the foaming reactant may be reacted with the prepolymer composition at any volume ratio sufficient to make the foam. Generally, the volume ratio of the foaming reactant to prepolymer composition is set by the stoichiometry of NCO to OH desired and ease of processing. Because the NCO content of the prepolymer composition is typically less than, for example, MDI or TDI, the volume of the foaming reactant is typically at most 10 percent by volume of the entire foam mixture (that is, the volume of the foaming reactant and prepolymer composition). Preferably the foaming reactant is at most 7.5 percent by volume of the foam mixture, and more preferably at most 5 percent by volume of the foam mixture. Even though the viscosity of the foaming reactant may vary over a wide range, it is desirable for the foaming reactant viscosity to be similar to the viscosity of the -11- prepolymer composition, for example, to enhance mixing. Preferably the viscosity of the foaming reactant has a viscosity of at least 50 percent to at most 500 percent of the viscosity of the prepolymer composition. The viscosity of the prepolymer composition may be modified, for example, by the plasticizers and thickeners previously described. The amount of these should not be so great that the properties of the resultant foam are degraded substantially. When forming a foam from the prepolymer composition, where the foaming reactant is at most 10 percent by volume of the total foaming mixture, it is preferred that the prepolymer composition and foaming reactant are two separate streams that are contacted and uniformly mixed and dispensed from a mixing head. Suitable mixing heads include those commercially available for making polyurethane foams, such as the one incorporated in MODEL N-4400 foaming apparatus, available from Jesco Products Company, Sterling Heights, Ml. Generally, the time to form the foam is as short as practicable and may be from 1 second to 48 hours. Preferably the time to form the foam is from 1 to 60 seconds. The temperature of the reaction, generally, is great enough for the foam to be formed but not so great that the polyurethane foam or components of the foam, for example, decompose. Generally, the temperature ranges from room temperature up to 300°C. When forming the foam, the only blowing agent is generally the CO 2 produced by the water isocyanate reaction. A supplemental blowing agent may be present, such as a low boiling hydrocarbon (for example, pentane, hexane, heptane, pentene and heptene), directly added carbon dioxide, an azo compound (for example, azohexahydrobenzodinitrile or a halogenated hydrocarbon (for example, dichlorodifluoroethane, vinylidene chloride and methylene chloride). However, preferably the amount of these supplemental blowing agents, other than the CO 2 produced by the water-isocyanate reaction, is at most a trace amount, and more preferably none at all. The polyurethane foam that is formed by the above method may have a large range of properties depending on the particular components used (for example, polyol). For example, the foam may have a bulk density of 1 to 50 pounds per cubic foot but is preferably 1 to 5 pounds per cubic foot. The foam may also have a wide range of compressive strengths. For example, the foam may have a compressive strength of 1 to 5000 pounds -12- per square inch (psi). Preferably the compressive strength is 5 to 20 psi as determined by ASTM D1621 A. Below are specific examples within the scope of the invention and comparative examples. The specific examples are for illustrative purposes only and in no way limit the invention described herein. EXAMPLES Example 1 (Formation of the Prepolymer) The prepolymer was prepared as follows. In a jacketed 1000 mL glass reaction flask, 352 parts by weight of polymeric MDI, available from The Dow Chemical Company under the trademark PAPI™ 20, are agitated and heated to 70°C under a constant blanket of nitrogen. The PAPI 20 had an average molecular weight of 400, functionality of 3.2, isocyanate equivalent weight of 141 and NCO percent by weight of 30. During heating, the PAPI 20 was stirred with a paddle (two 2.5 inch paddles) stirrer rotated at 500 rpm (revolutions per minute). The reactor and its content were heated by flowing water heated to 70°C through the jacket of the reactor. Once the reactor and its contents reached 70°C, agitation was stopped and the following were added to the reaction flask: 336 parts by weight PALATINOL™ 71 1 P. 84 parts by weight VORANOL™ 220-260, 20 parts by weight 1 -Butanol, 4 parts by weight DMDEE Catalyst, where PALATINOL 711 P is a mixture of phthalate esters, available from BASF Corp.; VORANOL 220-260 is a polyether polyol, available from The Dow Chemical Company and the DMDEE is a morpholine,4,4'-(oxydi-2,1 -ethanediyl)bis catalyst, available from Huntsman Corporation, Austin, TX. The VORANOL 220-260 is a polyether polyol initiated by polypropylene that had an average molecular weight of 425, average functionality of 2 and hydroxyl number of 260. After adding these 4 ingredients, the contents of the reaction flask were agitated at 70°C, as previously described. Periodically (every 30 minutes), the amount of NCO of the reaction mixture was determined by dissolving a sample of prepolymer in 20 -13- mL of tetrahydrofuran, then adding 25 mL of a 1.5 weight percent dibutylamine in toluene solution and stirring this titration mixture for 15 minutes. Once this was completed, 50 mL of 2-propanol was added to the titration mixture and was stirred for 5 more minutes. Using a 682 Titroprocessor, available from Brinkmann Instruments, Westbury, NY, the percent by weight of NCO of the titration mixture was determined by titrating with a 0.5N (Normal) hydrochloric acid solution. Once the theoretical amount of NCO (that is, 9.62 percent by weight) is reached (that is, in this Example 60 minutes), agitation was stopped and the prepolymer formed was put into a metal can under a nitrogen blanket. The measured NCO was 9.40 percent and the viscosity at 25°C was 3500 centipoise, as measured by a Brookfield viscometer using a #5 Spindle at 10 RPM. Example 2 (Foam Formed from Prepolymer of Example 1) 100 Grams of the prepolymer of Example 1 was heated to and maintained at 80°C in a plastic container. To the heated prepolymer, 0.5 mL of DC198 silicone surfactant was added by a disposable syringe and stirred with a wooden tongue depressor until the surfactant was well dispersed. Then 0.5 mL of bis(2-dimethylaminoethyl) ether catalyst (DABCO™ BL-19, available from Air Products and Chemicals Inc., Allentown, PA) was added by disposable syringe and stirred with a wooden tongue depressor until the catalyst was well dispersed. Finally, 2.1 mL of water was added by disposable syringe and the contents of the container were quickly mixed for 3 seconds at 2500 rpm with a paddle stirrer described previously. The resultant foaming mixture was quickly poured into a 16 ounce paper container. The following describes the characteristics of the foam. Cream Time: 2 seconds Gel Time: 8 seconds Tack-Free Time: 15 seconds Free Rise Density: 2.2 pounds per cubic foot (pcf) (35.24 grams per liter) -14- Foam Quality: The foam had no wet spots or regional richness of foam components and a homogeneous uniform fine ceil structure without any apparent mixing striations Water Absorption: The foam had an integral skin and essentially failed to absorb water after being immersed in water for 24 hours, as determined by standard SAE J315 Dimensional Stability: The foam, 20 minutes after foam manufacture, had a maximum percent volume change of 5 percent following a 15 minute heat treatment at 120°C Compressive Strength: 10 pounds per square inch (psi ) (.68 atmospheres) as per ASTM D1621 A Lap Shear/Panel Adhesion: The foam displayed excellent adhesion to electro-coated steel under conditions known in the art for painting automobiles. Example 3 (Foam Formed from Prepolymer of Example 1) First, a foaming reactant was formed by the following method. 394 Parts by weight(pbw) of deionized water at 90°C was added to 6 pbw of METHOCEL™ K100M Food Grade, available from The Dow Chemical Company, Midland, Ml, in a jacketed 1000 mL glass reaction flask previously described. The water and METHOCEL was mixed at 90°C and 500 rpm, as described in Example 1 , until the METHOCEL was completely dispersed (approximately 1 hour). After the METHOCEL was completely dispersed, the reactor was cooled to 10°C. After cooling to 10°C, 400 pbw of DABCO™ BL-19 catalyst was added and subsequently mixed for 60 minutes. The resultant foaming reactant was removed and stored in a metal quart container. The prepolymer of Example 1 and the foaming reactant were then mixed and dispensed using a Jesco Model N4400 foaming apparatus. The operating conditions of the apparatus were as follows. The prepolymer composition at 80°C and the foaming reactant at 40°C were pumped to the mixing head at a prepolymer composition to foaming reactant volume ratio of 24 to 1 and at 75 cc per second. The mixing head also called "heated foam impingement applicator with trigger handle" was heated and maintained at 60°C. -15- The foam characteristics are the same as those of Example 2, except as follows: Cream time: Instantaneous Gel Time: 2 to 4 seconds Tack Free Time: 6 seconds Comparative Example 1 A prepolymer composition was made using the materials shown below. The procedure used was the same as described in Example 1. The theoretical percent by weight NCO is 13.01 percent. The measured NCO content was 12.51 percent by weight. Material Wt % PAPI 20 56.2 PALATINOL 711 P 23.0 VORANOL 220-260 18.8 DMDEE 2.0 The resulting prepolymer was unstable as shown by the below viscosity data measured at 25°C, as described previously. 24 hours after production: 34,000 centipoise 48 hours after production: 48,000 centipoise 72 hours after production: 54,300 centipoise 96 hours after production: 62,700 centipoise -16-

Claims: CLAIMS: 1. A polyisocyanate prepolymer composition comprising the reaction product of (a) an organic polyisocyanate having an average isocyanate functionality of at least 2 and containing at least 20 percent by weight of a diisocyanate monomer, (b) a monohydric alcohol and (c) a polyol having an average hydroxyl functionality of at least 1.8 to at most 3.2, wherein the prepolymer composition has (i) an amount of isocyanate groups by weight sufficient to react with water in the absence of a supplemental blowing agent to make a foam, (ii) at most 10.0 percent by weight of the diisocyanate monomer and (iii) an amount of the polyisocyanate that is capped by the monohydric alcohol sufficient to prevent gelling of the prepolymer composition. 2. The prepolymer composition of Claim 1 , wherein the monohydric alcohol is a C, to C 50 alcohol. 3. The prepolymer composition of Claim 2, wherein the monohydric alcohol is a C 2 to C 20 alcohol. 4. The prepolymer composition of Claim 3, wherein the monohydric alcohol is selected from the group consisting of 1 -butanol, 2-butanol, isobutyl alcohol and mixtures of C π -C 14 aliphatic alcohols. 5. The prepolymer composition of Claim 1 , wherein the NCO content is at least 2 to at most 20 percent by weight of the prepolymer composition. 6. The prepolymer composition of Claim 5, wherein the NCO content is at most 10 percent by weight of the prepolymer composition. 7. The prepolymer composition of Claim 6 further comprising a plasticizer. 8. The prepolymer composition of Claim 1 further comprising a plasticizer. 9. The prepolymer composition of Claim 8, wherein the plasticizer is a dialkyl phthalate or mixture of dialkyl phthalates. -17- 10. The prepolymer composition of Claim 8, wherein the plasticizer is selected from the group consisting of dioctyl phthalate, diisooctyl phthalate, dimethyl phthalate, dibutyl phthalate and mixtures thereof. 11. The prepolymer composition of Claim 1 , wherein the average hydroxyl functionality of the polyol is at most 2.5. 12. The prepolymer composition of Claim 11 , wherein the average hydroxyl functionality of the polyol is at most 2.2. 13. The prepolymer composition of Claim 12, wherein the polyol has a hydroxyl number 20 to 1000. 14. The prepolymer composition of Claim 13, wherein the polyol has an average hydroxyl functionality of at least 1.8 to at most 2.2 and a hydroxyl number of at least 20 to at most 1500. 15. The prepolymer composition of Claim 1 , wherein the amount of the diisocyanate monomer is at most 5 percent by weight of the prepolymer composition. 16. The prepolymer composition of Claim 15, wherein the amount of the diisocyanate monomer is at most 4 percent by weight of the prepolymer composition. 17. The prepolymer composition of Claim 1 , wherein the prepolymer composition is formed from a polymeric MDI having an isocyanate functionality of at least 2.5 to at most 3.2 and having at least 20 percent to at most 40 percent by weight MDI. 18. The prepolymer composition of Claim 17, wherein the isocyanate functionality of the polymeric MDI is greater than or equal to 2.8 to at most 3.2. 19. The prepolymer composition of Claim 1 , wherein the polyisocyanate, monohydric alcohol and polyol provide an NCO to OH ratio of at least 2 to at most 5. 20. The prepolymer composition of Claim 19, wherein the ratio of NCO to OH is at least 2 to at most 4. 21. The prepolymer composition of Claim 19, wherein the ratio of NCO to OH is at least 2.5 to less than 3. -18- 22. The prepolymer composition of Claim 1 , wherein the monohydric alcohol and polyol are provided in a ratio of monohydric alcohol to polyol of at least 0.1 to at most 2, based upon the hydroxyl equivalents of the monohydric alcohol and polyol. 23. The prepolymer composition of Claim 22, wherein the ratio of monohydric alcohol to polyol is at least 0.5 to at most 1.5. 24. The prepolymer composition of Claim 23, wherein the ratio of monohydric alcohol to polyol is at most 1. 25. The prepolymer composition of Claim 24, wherein the the ratio of monohydric alcohol to polyol is at least 0.6 to at most 0.9. 26. A method of forming a polyurethane foam comprising contacting a polyisocyanate prepolymer composition comprising the reaction product of (a) an organic polyisocyanate having an average isocyanate functionality of at least 2 and containing at least 20 percent by weight of a diisocyanate monomer, (b) a monohydric alcohol and (c) a polyol having an average hydroxyl functionality of at least 1.8 to at most 3.2, wherein the prepolymer composition has (i) an amount of isocyanate groups by weight sufficient to react with water in the absence of a supplemental blowing agent to make a foam, (ii) at most 10.0 percent by weight of the diisocyanate monomer and (iii) an amount of the polyisocyanate that is capped by the monohydric alcohol sufficient to prevent gelling of the prepolymer composition with a foaming reactant comprised of water for a time and temperature sufficient to form the polyurethane foam. 27. The method of Claim 26, wherein the blowing agent is essentially CO 2 produced by the reaction of the NCO groups of the prepolymer composition and the water of the foaming reactant. 28. The method of Claim 26, wherein air surrounding the foam during formation contains at most 5 parts per billion of the diisocyanate monomer. 29. The method of Claim 27, wherein the foaming reactant is further comprised of a catalyst and a viscosity thickener. -19- 30. The method of Claim 29, wherein the foaming reactant and prepolymer composition are two separate streams that are contacted, uniformly mixed and dispensed as one stream. 31. The method of Claim 30, wherein the two streams are contacted, uniformly mixed and dispensed in less than, or equal to, about 1 second. 32. A polyurethane foam produced by the method of Claim 26. 33. A foam comprising a continuous cellular matrix reaction product of water and a polyisocyanate prepolymer composition comprising the reaction product of (a) an organic polyisocyanate having an average isocyanate functionality of at least 2 and containing at least 20 percent by weight of a diisocyanate monomer, (b) a monohydric alcohol and (c) a polyol having an average hydroxyl functionality of at least 1.8 to at most 3.2, wherein the prepolymer composition has (i) an amount of isocyanate groups by weight sufficient to react with water in the absence of a supplemental blowing agent to make a foam, (ii) at most 10.0 percent by weight of the diisocyanate monomer and (iii) an amount of the polyisocyanate that is capped by the monohydric alcohol sufficient to prevent gelling of the prepolymer composition. 34. The foam of Claim 33, wherein the monohydric alcohol is selected from the group consisting of 1 -butanol, 2-butanol, isobutyl alcohol and mixtures of 0,,-C,,, aliphatic alcohols. 35. The foam of Claim 33, wherein the prepolymer composition is further comprised of a plasticizer. 36. The foam of Claim 35, wherein the plasticizer is selected from the group consisting of dioctyl phthalate, diisooctyl phthalate, dimethyl phthalate, dibutyl phthalate and mixtures thereof. 37. The foam of Claim 33, wherein the amount of the diisocyanate monomer is at most 5 percent by weight of the prepolymer composition. 38. The foam of Claim 37, wherein the amount of the diisocyanate monomer is at most 4 percent by weight of the prepolymer composition. -20- 39. The foam of Claim 33, wherein the prepolymer composition is formed from a polymeric MDI having an isocyanate functionality of at least 2.5 to at most 3.2 and having at least 20 percent to at most 40 percent by weight MDI. 40. The foam of Claim 39, wherein the isocyanate functionality of the polymeric MDI is greater than or equal to 2.8 to at most 3.2. 41. The foam of Claim 33, wherein the polyisocyanate, monohydric alcohol and polyol provide an NCO to OH ratio of at least 2 to at most 5. 42. The foam of Claim 41 , wherein the ratio of NCO to OH is at least 2.5 to less than 3. 43. The foam of Claim 33, wherein the monohydric alcohol and polyol are provided in a ratio of monohydric alcohol to polyol of at least 0.1 to at most 2, based upon the hydroxyl equivalents of the monohydric alcohol and polyol. 44. The foam of Claim 43, wherein the ratio of monohydric alcohol to polyol is at about 1. 45. The foam of Claim 44, wherein the ratio of monohydric alcohol to polyol is at least 0.6 to at most 0.9. -21-

Inventors: PEARSON BRAD A, RIZK SIDKY D, SPRADLING JERRY L, PEARSON, BRAD, A., RIZK, SIDKY, D., SPRADLING, JERRY, L.
Applicants: ESSEX SPECIALTY PROD, ESSEX SPECIALTY PRODUCTS, INC.
Application year: 1999
Main classification: C08G18
IPC codes: C08G18, C08G101