MXPA97002869A - A process for the preparation of polyurethane foam in the presence of a hydrocarb blowing agent - Google Patents

Abstract

The present invention relates to a process for the preparation of a rigid polyurethane foam, blown with hydrocarbon, by the reaction of a polyisocyanate with a polyurethane precursor composition comprising a polyol and a compatibilizing agent containing a compatibilizing radical of the formula - (CnH2n + 1), where n is a number greater than or equal to 5, and wherein the compatibilizing agent contains at least one active hydrogen atom, since there is not more than one aromatic group per molecule, and also where the compatibilizing agent is a fat, oil, monoglyceride, diglyceride, fatty acid, fatty alcohol, fatty amide, fatty amine, fatty acid ester, alkoxylated adduct of any of the foregoing, alkyl phenol or propoxylated adduct thereof, alkyl phenol or adduct thereof propylene oxide, phenol alkyl or adduct thereof with less than the average of four molecules of ethylene oxide per phenol alkyl molecule Ixil, or a mixture thereof. A preferred compatibilizing agent is castor oil. The compatibilizing agent improves the miscibility of the hydrocarbon blowing agent. Conveniently, polyurethane precursor compositions improve storage stability

Description

A PROCESS FOR THE PREPARATION OF POLYURETHANE FOAM IN THE PRESENCE OF A HYDROCARBON BLOWING AGENT The present invention relates to a process for the preparation of a rigid polyurethane foam, blown with hydrocarbon, by the reaction of a polyisocyanate with a polyol composition comprising a material that compatibilizes the hydrocarbon in the polyurethane formulation. A recent trend in the manufacture of polyurethane foam, especially rigid polyurethane foam, is the use of hydrocarbon blowing agents as a substitute or replacement for the traditionally employed blowing agents, including trichlorofluoromethane. This trend has been motivated by the desire to eliminate the use of certain fully halogenated alkanes, in an effort to protect the environment, including the ozone content of the atmosphere. The general use of hydrocarbons as a blowing agent for polyurethane foam is widely reported in the literature. For example, United States Patent Number 5,096,933 describes the use of cyclopentane, cyclohexane or mixtures thereof. United States Patent Number 5,182,309 describes the use of pentane. U.S. Patent No. 5,001,164 describes the use of pentane in combination with trichloroethane. U.S. Patent No. 5,286,759 discloses combinations of hydrocarbons containing at least 4 four carbon atoms with perfluoroalkanes as a blowing agent for the manufacture of polyurethane foam. U.S. Patent No. 4,263,412 describes the preparation of polyurethane foam in the presence of butane. Of the aforementioned hydrocarbons, the use of cyclopentane and pentane is currently favored due to the availability and general benefit for the physical properties of the foam. However, to prepare polyurethane foam exhibiting attractive physical properties, all reagents should conveniently be easily miscible with each other and / or high efficiency mixing procedures should be employed to ensure uniform distribution of all starting materials. In the presence of poor miscibility or poor mixing, the resulting foam may exhibit inferior, unattractive physical properties. Hydrocarbon blowing agents, especially when used in significant amounts as might be required to produce a low density foam, are generally not noted as having an attractive miscibility with most polyester or polyether polyols commonly used to prepare foam. polyurethane. Frequently, the separation results in poor mixing and / or poor foam quality. In the art, when problems of miscibility are encountered, using the traditional type of blowing agents, they can often be solved by varying the amount of cell stabilizing agent or surfactant present in the foaming process. In many instances, the problem has been solved by the use of a surfactant in an amount of 0.1 to 2 parts per 100 parts of polyol. The use of higher amounts of surfactants, usually a mineral oil of the polysiloxane type, can lead to a significant decline in the physical properties of the resulting foam. For rigid closed cell polyurethane foam, this may be a reduction in compressive strength, a loss of potential for technical insulation as a consequence of an acquired open cell content, or poor mold filling characteristics (from flow). When preparing low density polyurethane foam in the presence of a hydrocarbon blowing agent with high loads of conventional surfactants, the problem of poor miscibility is not solved in a satisfactory manner. In accordance with the above, it would be desirable to provide an alternative foaming process that allows the manufacture of polyurethane foam, especially low density foam, in the presence of a hydrocarbon blowing agent that does not suffer from the deficiencies mentioned above. For this purpose, the use of compatibilizing agents has been investigated. In a first aspect, the present invention relates to a process for the preparation of a closed cell polyurethane foam, which includes reacting, in the presence of a hydrocarbon blowing agent, a polyisocyanate with a polyol composition, wherein the polyol composition comprises: i) a polyether or polyester polyol having a hydroxyl number value of 100 to 1,200; and ii) from 5 to 25 parts, per 100 parts by total weight of the polyol composition, of a compatibilizing agent containing a compatibilizing radical of the formula: wherein n is a number greater than or equal to 5, and wherein the compatibilizing agent contains at least one active hydrogen atom, since there is not more than one aromatic group per molecule, and also where the compatibilizing agent is a fat, oil, monoglyceride, diglyceride, fatty acid, fatty acid ester, alkoxylated adduct of any of the foregoing, alkyl phenol or propoxylated adduct thereof, alkyl phenol or adduct thereof with ethylene oxide or propylene oxide, alkyl phenol or adduct of the same with less than an average of four ethylene oxide molecules per alkyl phenol molecule, or a mixture thereof. In a second aspect, the present invention is a process for the preparation of a closed cell polyurethane foam, which comprises reacting, in the presence of a hydrocarbon blowing agent, a polyisocyanate with a polyol composition, wherein The polyol composition comprises: i) a polyether or polyester polyol having a hydroxyl number value of 100 to 1,200; and includes: ii) from 5 to 25 parts, per 100 parts by total weight of the polyol composition, of a compatibilizing agent comprising a fat or an oil having a hydroxyl number of from 100 to 550. In a third aspect, The present invention relates to a closed cell polyurethane foam obtained in accordance with the aforementioned process. In a fourth aspect, the present invention relates to a mixture, suitable for use in the process of the invention as a polyurethane precursor composition, which comprises the aforementioned polyol composition containing compatibilizing agent as defined herein , and in addition a blowing agent which is present in an amount of 1 to 20 parts per 100 parts by total weight of the composition, and which is a hydrocarbon of 1 to 8 carbon atoms, and is preferably butane, normal pentane, isopentane, hexane, cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, isomers thereof or a mixture of two or more thereof. Surprisingly, it has been found that the use of a compatibilizing agent as defined improves the miscibility of the hydrocarbon blowing agent, and minimizes the susceptibility to separation of the formulation. The presence of the compatibilizing agent allows having a higher charge of the hydrocarbon blowing agent, thus allowing the manufacture of foam having a lower density, while retaining the overall attractive physical properties. The present invention relates to a process for the preparation of a rigid, closed-cell polyurethane foam, by reacting, in the presence of a hydrocarbon blowing agent, a polyisocyanate with a polyol composition comprising a certain compatibilizing agent . Conveniently, the resulting foam is of a low free elevation density of 10 to 50, preferably 15 to 40, and more preferably 15 to 35 kg / m3. The polyurethane precursor polyol composition, comprises: (a) an isocyanate-reactive component, typically a polyether or polyester polyol, having a hydroxyl number value of 100 to 1,200, preferably 100 to 800, more preferably 200 to 800, and still more preferably 200 to 600, and which is preferably a polyester or polyether polyol; and (b) a compatibilizing agent. The compatibilizing agent allows having an attractive miscibility of the hydrocarbon blowing agent with the polyol, and is present in an amount of 5 to 25, preferably 6, more preferably 7, and preferably up to 18, more preferably up to 15 parts. in total weight of the polyol composition, which includes the polyol and the compatibilizing agent. The compatibilizing agent is defined herein as containing a compatibilizing radical of the formula: - (CnH2n + 1) wherein n is a number greater than or equal to 5;, and wherein the compatibilizing agent contains at least one active hydrogen atom, since there is not more than one aromatic group per molecule, wherein the compatibilizing agent is a fat, oil, monoglyceride, diglyceride, fatty acid, fatty acid ester alkoxylated adduct of any of the foregoing, alkyl phenol or propoxylated adduct thereof, alkyl phenol or adduct thereof with ethylene oxide or propylene oxide, alkyl phenol or adduct thereof with less than an average of four molecules of ethylene oxide per alkyl phenol molecule, or a mixture thereof. In the preferred embodiments, each molecule contains only one active hydrogen atom. The active hydrogen atoms contained in these compatibilizing agents are those associated with the functionality of hydroxyl, thiol, amine, and carboxylic acid. The presence of the isocyanate-reactive hydrogen atom is desired to allow reaction with the polyisocyanate, thereby incorporating, with advantage of the physical properties of the polymer, the compatibilizing agent into the polyurethane polymer. Conveniently, the compatibilizing agent is a grease, oil, or alkoxylated adduct thereof, with hydroxyl functionality, and having a hydroxyl number value from 100, preferably from 130, more preferably from 140, and up to 550 , more preferably up to 300, still more preferably up to 200, and still more preferably up to 180. When fats or oils are selected, they preferably comprise a fatty acid constituent substituted by hydroxyl. Detailed descriptions of these materials and their fatty acid constituents are well known. See, for example, the introduction of "Fats and Fatty Oils" in Ullmann's Encyclopedia of Industrial Chemistry, ISBN 0-89573-160-6, or alternatively, Kirk-Othmer Encyclopedia of Chemical Technology, ISBN 0-471-02062 -1. For the present invention, suitable compatibilizing agents contain, as a fatty acid constituent, for example, ricinoleic acid, dihydroxystearic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, eicosanoic acid, or mixtures of two or more of the same. In one embodiment of the present invention, ricinoleic acid is preferred, which exhibits the peculiarity of excellent miscibility with polar substances, such as alcohols, including polyols, and a limited miscibility with non-polar substances, such as hydrocarbons. A convenient and readily available natural fatty acid source comprising a hydroxyl-substituted fatty acid constituent is castor oil, which is understood to comprise, on average, 90 weight percent of a ricinoleic acid glyceride, and 4 weight percent of a glyceride of linoleic acid, the remainder being up to 100 percent glycerides of dihydroxystearic acid, palmitic acid, stearic acid, oleic acid, linolenic acid and eicosanoic acid. Castor oil, essentially independent of the source, has a hydroxyl number of 160 to 168. Suitable polyols include polyester or polyether polyols, such as are conventionally used in the preparation of rigid polyurethane foam, and which have a value of hydroxyl number within the aforementioned scale. Additionally, these polyols will generally contain from 2 to 8, preferably from 3 to 8, and more preferably from 3 to 6 hydroxyl groups per molecule. Examples of suitable and preferred polyols are polyether polyols, as described more fully in U.S. Patent No. 4,394,491. Examples of these polyether polyols include those commercially available under the registered trademark VORANOL, and include VORANOL 202, VORANOL 360, VORANOL 370, VORANOL 446, VORANOL 490, VORANOL 575, VORANOL 640, VORANOL 800, VORANOL CP1000, VORANOL CP260, VORANOL CP450 and VORANOL RN482, all available from The Dow Chemical Company. Other preferred polyols include alkylene oxide derivatives of annich condensate, as described, for example, in U.S. Patent Numbers 3,297,597; 4,137,265 and 4,383,102; and polyether polyols initiated by aminoalkylpiperazine, as described in U.S. Patent Nos. 4,704,410 and 4,704,411. As mentioned, the polyurethane foaming process of the present invention requires the presence of a hydrocarbon blowing agent suitably comprising an aliphatic or cycloaliphatic hydrocarbon of 1 to 8 carbon atoms, preferably 4 to 8 carbon atoms , which is an alkane, alkene or alkyne. These hydrocarbons are selected as the blowing agent, because they have a boiling point lower than the exotherm of the reaction, generally higher than 120 ° C, and usually from 150 ° C to 200 ° C, which is found when prepare a polyurethane foam. Suitable hydrocarbons include those having a boiling point less than 120 ° C, preferably less than 100 ° C, and more preferably less than 50 ° C, such as, for example, butane, normal pentane, isopentane, cyclopentane, methylcyclopentane , hexane, cyclohexane, methylcyclohexane, isomers thereof, or mixtures of two or more thereof. Preferred hydrocarbons, due to their ability to impart attractive thermal insulation properties to the polyurethane foam, are normal pentane, isopentane and cyclopentane. Especially preferred is a mixture of isomers of normal pentane and isopentane, wherein the ratio of normal pentane to isopentane is from 5:95 to 50:50, preferably from 10:90 to 35:65. It is found that this isopentane fraction is suitable for optimum flow properties when preparing a polyurethane foam, and for imparting attractive thermal insulation properties to the resulting foam. Typically, the hydrocarbon will be present in an amount of 1 to 20, preferably 5 to 20, and more preferably 7 to 18 parts per 100 parts by total weight of the composition comprising polyol and compatibilizing agent. In addition to the hydrocarbon blowing agent, a complementary blowing medium can optionally be provided by the presence of water. The water reacts with the polyisocyanate, leading to the production of carbon dioxide, which can confer a reduced density to the polyurethane polymer. When present, the amount of water is conveniently 0.5 to 10, preferably 1.5 to 8, and more preferably 2 to 6 parts per 100 parts by weight of the polyol composition, including the fatty oil. In a highly preferred embodiment of the present invention, the polyurethane foam is prepared in the presence of water and hydrocarbon blowing agent, wherein, per 100 parts by weight of the polyol composition, including the compatibilizing agent, the water is present in an amount of 2 to 6 parts, and the hydrocarbon blowing agent which is normal pentane, isopentane, cyclopentane, or mixtures of at least two thereof, is present in an amount of 1 to 20 parts. In a less preferred embodiment, it is also possible to use conventional fluorocarbons or chlorofluorocarbons containing hydrogen, as a complementary physical blowing agent, including difluorochloromethane, difluoroethane, difluorochloroethane, tetrafluoroethane, dichlorotrifluoroethane and others, such as those described, for example, in the Patent of the United States of America Number 4,945,119. Suitable polyisocyanates include aromatic, aliphatic and cycloaliphatic polyisocyanates, and combinations thereof. A crude polyisocyanate can also be used in the practice of the present invention, such as the crude toluene diisocyanate obtained by the phosgenation of a mixture of toluene diamines, or the crude diphenylmethane diisocyanate obtained by the phosgenation of crude methylenediphenylamine. Preferred are aromatic polyisocyanates comprising a methylene diphenylisocyanate, polymethylene polyphenylisocyanate, or mixtures thereof. Suitable mixtures include those containing, based on the total weight of the polyisocyanate, from 10 to 50 weight percent of methylene diphenylisocyanate; and from 90 to 50 weight percent of polymethylene polyphenylisocyanate. For the purpose of providing crosslinks in the final polymer, conveniently this aromatic polyisocyanate has an average isocyanate functionality of at least 2.3, preferably 2.5 to 3.5, and more preferably 2.7 to 3.1. Exemplary commercially available aromatic polyisocyanates suitable for use in the present invention include crude methylene diphenyl isocyanate mixtures supplied by The Dow Chemical Company under the registered trademark VORANATE, and designated as M220, M229, M269, 595 and M580.

The amount of polyisocyanate present when the polyurethane foam is prepared is such that it provides an isocyanate reaction rate typically of 60 to 550, preferably from 70, more preferably from 80, and preferably up to 300, more preferably up to 200, still more preferably up to 160, and still more preferably up to 140. An isocyanate reaction number of 100 corresponds to an isocyanate group per isocyanate reactive hydrogen atom present, including those of the polyol composition containing compatibilizing agent and, if present , Water. Optionally, other ingredients may be present when the polyurethane foam is prepared. Among these other ingredients are catalysts, surfactants, colorants, antioxidants, reinforcing agents, fillers, antistatic agents and fire retardants. Suitable fire retardants include phosphorus-containing substances, such as tris (chloroalkyl) phosphate and t-phrisalkyl phosphates, for example, triethyl phosphate; and substances that contain nitrogen, such as melamine. Conveniently one or more catalysts are present for the reaction of the active hydrogen-containing compound with the polyisocyanate. Suitable catalysts include tertiary amine compounds and organometallic compounds. Exemplary tertiary amine catalysts include triethylene diamine, pentamethyl diethylene triamine, N-ethylmorpholine, N-co-morpholine, N-methylmorpholine, tetramethylethylenediamine, dimethylbenzylamine, l-methyl-4-dimethylaminoethylpiperazine, 3-methoxy-N-dimethylpropylamine, diethylethanolamine, N, N-dimethyl-N1, N '-dimethylisopropyl-propylenediamine, or N, N-diethyl-3-diethylaminopropylamine. Exemplary organometallic catalysts include organomercury, organolead, organoferric and organotin catalysts, organotin catalysts being preferred therebetween. Suitable tin catalysts include stannous chloride, stannic salts of carboxylic acids, such as dibutyltin di-2-ethylhexanoate, as well as other organometallic compounds, such as those described in U.S. Patent No. 2,846,408. A . catalyst for the trimerization of polyisocyanates and for the formation of polyisocyanurate polymers, such as an alkali metal alkoxide, alkali metal carboxylate, or an amine quaternary compound, may also be optionally employed herein. When used, the amount of catalyst used is sufficient to increase the speed of the polymerization reaction. The precise amounts must be determined experimentally, but in general they will be from 0.01 to 3.0 parts by weight per 100 parts of polyol, depending on the type and activity of the catalyst.

In general it is highly preferred to employ a minor amount of a surfactant to stabilize the foaming reaction mixture until it is cured. These surfactants, distinguished from the compatibilizing agent, are in general manufactured mineral oils, including liquid or solid organosilicone surfactants. Other less preferred surfactants include amine salts of long chain alkyl acid sulfate esters, alkyl sulfonate esters and alkyl arylsulfonic acids. These surfactants are used in sufficient amounts to stabilize the foaming reaction mixture against collapse and the formation of large, irregular cells. Typically, 0.1 to 3 parts of the surfactant per 100 parts by weight of the polyol are sufficient for this purpose. In the manufacture of a polyurethane foam, the polyol (s), the polyisocyanate and other components, are contacted, mixed thoroughly, and allowed to expand and cure to a cellular polymer. The particular mixing apparatus is not critical, and various types of mixing head and spray apparatus are conveniently used. It is often convenient, but not necessary, pre-mix some of the raw material before reacting the polyisocyanate and the components containing active hydrogen. For example, it is often useful to mix the polyol (s), the blowing agent, the surfactants, the catalysts and other components, except for the polyisocyanates, and then to contact this mixture with the polyisocyanate. Alternatively, all the components can be introduced individually into the mixing zone where the polyisocyanate and the polyol (s) are contacted. It is also possible to pre-react all or a part of the polyols with the polyisocyanate to form a prepolymer, although it is not preferred. For optimal processing, it is found convenient to prepare the polyurethane by mixing, at room temperature, the reagents which themselves have a temperature of 10 ° C to 35 ° C, and preferably 15 ° C to 25 ° C. The polyurethane foam obtained in accordance with the present invention is valuable for the apparatus and construction industry where its attractive compressive strength, dimensional stability and thermal insulation are highly desirable. The present invention can also be used to provide polyurethane foam for semi-rigid applications, such as, for example, sealant foam applications. The invention is illustrated in the manner of the examples given below. Unless indicated otherwise, all amounts given are parts by weight.

Example 1 In Table I, the storage stability of different hydrocarbon / polyol mixtures optionally containing castor oil is reported. The substances and the relative amounts which form the hydrocarbon and polyol mixtures are also given in Table I. The storage stability is determined according to the following general procedure, wherein the hydrocarbon is mixed in a polyol mixture, representative of a formulation typically used for the manufacture of rigid polyurethane foam, and the resulting mixture is allowed to stand at room temperature for 7 days. After this period, the stability of the resulting mixture is visually evaluated according to the following scheme: "Separated" - the mixture is separated into multiple layers. "Turbid" - the cloudy mixture does not separate into multiple layers and does not become transparent when shaken. "Limit" - the cloudy mixture does not separate into multiple layers and when agitated it becomes transparent. "Transparent" - the mixture is transparent and does not separate into multiple layers.

Mixtures 1, 2 and 5, which are separated, are undesirable for the purposes of preparing a polyurethane foam; it is noted that Mixtures 3 and 4 have a "transparent" or "boundary" state, and are preferred, since they are handled more easily in a consistent manner for the benefit of the foaming process.

TABLE I It is not an example of the present invention Polyol 1: An oxypropylene polyether polyol initiated with sorbitol having a hydroxyl number of 480. Polyol 2: An oxypropylene polyether polyol initiated with ethylenediamine having a hydroxyl number of 640. Polyol 3: A polyether polyol of oxypropylene initiated with glycerin having a hydroxyl number of 160. Surfactant 1: TEGOSTAB B8462, a silicon-based surfactant of Th Goldschmidt AG. Catalyst: A mixture of urethane promoter catalysts containing 1.2 parts by weight of dimethylcyclohexylamine, 0.4 parts by weight of pentamethyl diethylenetriamine; and 0.6 parts by weight of CURITHANE 206, a proprietary urethane promoter catalyst available from The Dow Chemical Company. EXAMPLE 2 The rigid polyurethane foam is prepared by machine in the presence of a hydrocarbon blowing agent and castor oil, using the formulation given in Table II. High-pressure mixing conditions are used, the reagents being introduced to the mixing head at a temperature of about 20 ° C. The results indicate that a better stability of the mixture is obtained, while still maintaining an acceptable overall physical performance of the foam. TABLE II It is not an example of the present invention (1) As given for Example 1 (2) VORATEC SD100, a polymeric methylene diphenylisocyanate with an NCO functionality of 2.7, available from The Dow Chemical Company.

Example 3 In Table III the storage stability of different hydrocarbon / polyol mixtures containing compatibilizing agents different from castor oil is reported. Alternative compatibilizing agents and the relative amounts that form the hydrocarbon and polyol mixtures are also given in Table III. The storage stability reported is determined according to the general procedure described for Example 1.

TABLE III It is not an example of the present invention Polyol 1: A sucrose / oxypropylene glycerin polyol having a hydroxyl number of 490. Compatibilizing Agent 1: C12H25- (OCH2CH2) 4-OH Compatibilizing Agent 2: p (C9H19) -C6H4- (OCH2CH2) 2-OH Agent Compatibilizer 3: Adduct of monoglyceride of oleic acid.

Claims (13)

1. A process for the preparation of a closed cell polyurethane foam, which comprises reacting, in the presence of a hydrocarbon blowing agent, a polyisocyanate with a polyol composition, wherein the polyol composition comprises: i) a polyether or polyester polyol having a hydroxyl number value of 100 to 1,200; and ii) from 5 to 25 parts, per 100 parts by total weight of the polyol composition, of a compatibilizing agent containing a compatibilizing radical of the formula: - (CnH2n + 1) wherein n is a number greater than or equal to 5, and wherein the compatibilizing agent contains at least one active hydrogen atom, since there is not more than one aromatic group per molecule, and also wherein the compatibilizing agent is a fat, oil, monoglyceride, diglyceride, fatty acid, ester of fatty acid, alkoxylated adduct of any of the foregoing, alkyl phenol or propoxylated adduct thereof, alkyl phenol or adduct thereof with ethylene oxide or propylene oxide, alkyl phenol or adduct thereof with less than an average of four molecules of ethylene oxide per alkyl phenol molecule, or a mixture thereof.

2. A process for the preparation of a closed cell polyurethane foam, which comprises reacting, in the presence of a hydrocarbon blowing agent, a polyisocyanate with a polyol composition, wherein the polyol composition comprises: ) a polyether or polyester polyol having a hydroxyl number value of 100 to 1,200; and ii) from 5 to 25 parts, per 100 parts by total weight of the polyol composition, of a compatibilizing agent, a fat, or an oil, or an alkoxylated adduct thereof, having a hydroxyl number of 100 to 550.

3. A process according to claim 1 or 2, chaerized in that the hydrocarbon blowing agent comprises an aliphatic or cycloaliphatic hydrocarbon of 1 to 8 carbon atoms, which is an alkane, alkene, or I rent 4.

A process according to claim 2, chaerized in that the compatibilizing agent has a hydroxyl number of 130 to 180.

A process according to claim 1 or 2, chaerized in that the agent compatibilizer is a fat or an oil comprising a fatty acid constituent.

6. A process according to claim 5, chaerized in that the fatty oil constituent is ricinoleic acid, dihydroxystearic acid, palmitic acid, stearic acid, oleic acid, linoleic acid, eicosanoic acid, or a mixture of two or more of the same.

7. A process according to claim 6, chaerized in that the fatty acid constituent is ricinoleic acid.

8. A process according to claim 1 or 2, chaerized in that the compatibilizing agent is castor oil.

9. A process according to claim 1 in any of claims 1 to 8, chaerized in that it also comprises water in an amount of 0.5 to 10 parts per 100 parts by total weight of the polyol composition.

10. A process for the preparation of a closed cell polyurethane foam having a density of 10 to 50 kg / cm 3, by the reaction, in the presence of a hydrocarbon blowing agent, of a polyisocyanate with a polyol composition , wherein the polyol composition comprises: i) a polyol composition containing a polyether polyol having a hydroxyl number value of from 100 to 1,200, and including from 7 to 15 parts, per 100 parts by weight total of the polyol composition of castor oil; in the presence of: ii) from 2 to 6 parts of water per 100 parts by weight of the polyol composition; and iii) a hydrocarbon blowing agent, which is normal pentane, isopentane, hexane, cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, or mixtures thereof, and wherein the polyisocyanate is present in an amount to provide a reaction index of isocyanate from 60 to 550.

11. A mixture, suitable as a polyurethane precursor, containing a hydrocarbon and a polyol composition, wherein the composition comprises: i) a polyether or polyester polyol having a hydroxyl number value from 100 to 1,200; and ii) from 5 to 25 parts, per 100 parts by total weight of the composition, of a compatibilizing agent which is a fat, an oil, or an alkoxylated adduct thereof, having a hydroxyl number of from 100 to 550, and wherein the hydrocarbon, present in an amount of 1 to 20 parts per 100 parts by total weight of the composition, is butane, normal pentane, isopentane, hexane, cyclopentane, methylcyclopentane, cyclohexane, methylcyclohexane, isomers thereof, or mixtures of two or more of them.

12. A mixture, suitable as a polyurethane precursor, containing a hydrocarbon and a polyol composition, wherein the composition comprises: i) a polyether or polyester polyol having a hydroxyl number value of 100 to 1200; and ii) from 5 to 25 parts, per 100 parts by total weight of the composition, of a compatibilizing agent containing a compatibilizing radical of the formula: "(Cníí2n + 1) where n is a number greater than or equal to 5, and wherein the compatibilizing agent contains at least one active hydrogen atom, since there is not more than one aromatic group per molecule, wherein the compatibilizing agent is a fat, oil, monoglyceride, diglyceride, fatty acid, fatty acid ester, alkoxylated adduct of any of the foregoing, alkyl phenol or propoxylated adduct thereof, alkyl phenol or adduct thereof with ethylene oxide or propylene oxide, alkyl phenol or adduct thereof with less than an average of four molecules of ethylene oxide per alkyl phenol molecule, or a mixture thereof

13. A polyurethane foam obtained in accordance with the process claimed in claims 1 to 10.