Reactive flame retardants for flexible polyurethane foams

Abstract

The invention provides reactive multifunctional dialkyl phosphinic ester compounds useful as highly efficient reactive flame retardants in flexible polyurethane foams. The invention also provides flame-retardant polyurethane compositions comprising the multifunctional dialkyl phosphinic ester compounds and applications comprising the same.

Description

[0001] This application claims priority to U.S. Provisional Application No. 63 / 037,180, filed June 10, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure provides the use of reactive dialkyl phosphorus compounds, namely hydroxyl-functionalized dialkylphosphine esters, as highly effective reactive flame retardants in flexible polyurethane foams when reacted with polyols and isocyanates. The invention further provides flame-retardant flexible polyurethane foams having the aforementioned hydroxyl-functionalized dialkylphosphine esters, which are reacted and incorporated into the polymer matrix of the flexible polyurethane foam. The terms "fire retardant" and "flame retardant" are used interchangeably herein. Background Technology

[0003] Brominated or phosphorus-based flame retardants are known to be highly effective and, in many cases, the only option for reducing the fire risk of synthetic materials such as flexible polyurethane foam. However, over the years, there has been increasing (growing) public and governmental oversight of chemicals, particularly flame retardants. The goal is towards more sustainable, reactive, polymeric, and / or halogen-free new products. Oversight is significantly reduced if flame retardants are reacted into the polymer matrix and cannot be leached out.

[0004] Therefore, there is a demand for reactive phosphorus-containing fire retardants for flexible polyurethanes that possess characteristics such as high phosphorus content, transparent light color, and good compatibility with polyether polyols and polyester polyols used in the polyurethane industry.

[0005] Although monofunctional dialkyl phosphinates have been used in foams, the resulting foam products exhibit poor physical properties, such as poor compression set. Furthermore, monofunctional dialkyl phosphinates typically need to be blended with other phosphate esters for efficient use in polyurethane foams. Additionally, some previously prepared monofunctional dialkyl phosphinates require complex, multi-step, and inefficient processes. Summary of the Invention

[0006] This invention provides reactive dialkyl phosphorus-containing polyhydroxy functional aromatic compounds that exhibit highly satisfactory flame-retardant properties and good compatibility with polyol components in flexible polyurethane foam forming systems. When used in polyurethane foams, the polyfunctional dialkyl phosphonates described herein possess physical properties similar to those of polyurethane foams without flame retardants. Furthermore, the polyfunctional dialkyl phosphonates described herein can be prepared efficiently in a single-step reaction. Finally, the polyfunctional dialkyl phosphonates described herein impart excellent flame-retardant properties similar to those of previously used monofunctional dialkyl phosphonates, and can be prepared simultaneously with the monofunctional dialkyl phosphonates in the reaction mixture, making further blending with such monofunctional components to reduce viscosity unnecessary.

[0007] As used in this article to describe "multifunctional dialkyl hypophosphite compounds", "multifunctional" should be understood as meaning that each molecule includes two or more hydroxyl groups.

[0008] As used herein, the term "system for forming flexible polyurethane foam" should be understood to include polyols, isocyanates, and polyfunctional dialkyl hypophosphite compounds as described herein.

[0009] The terms "polyfunctional dialkyl phosphite compounds" and "polyfunctional aromatic dialkyl phosphite compounds" are used interchangeably in this document.

[0010] Monohydroxyl-functional dialkylphosphinate compounds are fully reactive through their hydroxyl functional groups. Surprisingly, the polyfunctional dialkylphosphinate compounds described herein can react (e.g., by reacting with the isocyanate component of a flexible polyurethane foam forming system) and be incorporated into the polymer structure of the flexible polyurethane foam without compromising its elastic properties. This means that the flame retardants of the present invention are integrated into the flexible foam matrix, preventing their release into the environment and making them unlikely to penetrate living tissue cell membranes, thus posing no health hazard. The present invention further provides the aforementioned flexible polyurethane foam forming system, which includes, but is not limited to, the polyfunctional dialkylphosphinate compounds described herein.

[0011] As used herein, the term "foam" refers to flexible polyurethane foam. Flexible polyurethane foam described herein or claimed herein as comprising, substantially composed of, or composed of reacted polyfunctional dialkylphosphine ester compounds is understood herein to mean a polyfunctional dialkylphosphine ester compound comprising, as a reactive material, a polyfunctional dialkylphosphine ester compound reacting into the structure of the flexible polyurethane material, in which case the polyfunctional dialkylphosphine ester compound may not or will not exist in the same structural formula as described herein, but will exist in the flexible polyurethane material as a reaction product with diols and / or polyols, isocyanates, and the structural formula of the polyfunctional dialkylphosphine ester compound described herein.

[0012] The term “polyol” as used in this article should be understood to mean, and may also be defined as, diols and / or polyols.

[0013] This invention provides polyfunctional dialkylphosphinate compounds of general formula (I):

[0014] (I)

[0015] Among them, each R 1 and R 2 The alkyl group is selected individually from alkyl groups containing 1 to 4 carbon atoms, preferably methyl or ethyl, and more preferably both ethyl.

[0016] R is a divalent straight-chain or branched alkyl group containing up to about 4 carbon atoms, a divalent aralkyl group containing 7 to 13 carbon atoms, or a bond, preferably a divalent straight-chain or branched alkyl group containing 1 to about 3 carbon atoms, more preferably a divalent methylene or divalent isopropyl group.

[0017] X and Y are each independently a divalent aryl group containing 6 to 12 carbon atoms, preferably 6 to 8 carbon atoms, and more preferably a divalent phenyl group.

[0018] Subscripts a and b are either 0 or 1.

[0019] The subscript c is an integer from 1 to 5, and

[0020] The subscript d is an integer from 1 to 26, preferably from 1 to 10, and most preferably from 1 to 3.

[0021] The conditions are:

[0022] a+b=1,

[0023] When a = 1, then b is 0, X is an aryl group as defined, except that the hydrogen atom bonded to the aryl group is not part of the group within the parentheses of subscript c, and subscript c is an integer from 1 to 5 and subscript d is 1, and...

[0024] When b = 1, then a is 0, c is 1, and d is an integer from 1 to 26, preferably from 1 to 10, and most preferably from 1 to 3.

[0025] This article also provides a method for preparing the polyfunctional dialkylphosphonates described herein, comprising reacting dialkylphosphonates with aromatic epoxides.

[0026] In addition, this article provides flame-retardant polyurethane foam comprising the reaction product of a polyol, an isocyanate, and an effective amount of a polyfunctional dialkyl hypophosphite compound of general formula (I).

[0027] All the above and other features and advantages of the present invention will be better understood by the following illustrative and non-limiting detailed description of its preferred embodiments. Detailed Implementation

[0028] In one embodiment, the polyfunctional dialkylphosphinate compound of formula (I) may be those of more specific formulas (II) and / or (III), wherein formula (II) is:

[0029] (II)

[0030] Where R 1 and R 2 The alkyl group is independently selected from alkyl groups containing 1 to 4 carbon atoms, preferably methyl or ethyl, and most preferably both are ethyl.

[0031] R is a divalent straight-chain or branched alkyl group containing up to about 4, preferably 1 to about 3 carbon atoms, or a bond, more preferably a divalent methylene or divalent isopropyl group.

[0032] X and Y are each independently a divalent aryl group containing 6 to 12 carbon atoms, preferably 6 to 8 carbon atoms, and more preferably a divalent phenyl group.

[0033] The subscript c is an integer from 1 to 5, preferably from 1 to 3, and the subscript d is 1; wherein equation (III) is:

[0034] (III)

[0035] Where R 1 R 2 R, X, and Y are as defined above, and

[0036] The subscript c is 1, and the subscript d is an integer from 1 to 26, preferably from 1 to 10, and most preferably from 1 to 3.

[0037] Some specific examples of equations (II) and (III) above may include the following equations (A) and (B):

[0038] (A)

[0039] (B)

[0040] The new compounds of formulas (I), (II), and (III) or (A) and (B) can be prepared by reacting a monohydroxy-functional dialkylphosphine acid of formula (IV) with an aromatic epoxy compound, wherein formula (IV) is:

[0041] (IV)

[0042] Where R 1 and R 2 As defined above.

[0043] The dialkylphosphonic acids (IV) used as starting materials in the methods of this invention are mostly known in the art. Compounds of formula (IV) can be obtained, for example, by reacting sodium hypophosphite with ethylene and then acidifying, or alternatively by reacting hypophosphite with ethylene, or less preferably by hydrolysis of the corresponding dialkylphosphonic halogen.

[0044] The aromatic epoxy compound is preferably an epoxy-terminated aromatic compound. The aromatic portion of the aromatic epoxy compound can be as defined above for X and Y, preferably including the XRY portion of the above general formula (I), and more preferably a derivative of a bisphenol compound, such as bisphenol A, bisphenol AP, bisphenol B, bisphenol BP, bisphenol C, bisphenol E, bisphenol F, bisphenol G, 2,2'-biphenyl, 4,4'-biphenyl, etc. Those skilled in the art will understand that the expression "derivative of a bisphenol compound" refers to the aromatic portion remaining when the hydrogen atoms of the two hydroxyl groups in the bisphenol compound are removed, such that the O atom of the bisphenol compound is bonded to another portion of the aromatic epoxy compound, such as an epoxy group and / or an open-ring epoxy portion within the aromatic epoxy compound. Preferably, the derivative of the bisphenol compound will be a derivative of bisphenol A or bisphenol F.

[0045] The specific aromatic epoxides used in the methods for preparing compounds of formula (I), or more specifically formulas (II) and (III), or (A) or (B) of the present invention are selected from, for example, the group consisting of, but not limited to, the following:

[0046] ,

[0047] and its combinations,

[0048] Wherein R is a divalent straight-chain or branched alkyl group containing up to about 4 carbon atoms, a divalent aralkyl group containing 7 to 13 carbon atoms, or a bond, preferably a divalent straight-chain or branched alkyl group containing 1 to about 3 carbon atoms, more preferably a divalent methylene or divalent isopropyl group.

[0049] X and Y are each independently a divalent aryl group containing 6 to 12 carbon atoms.

[0050] The subscript c is an integer from 1 to 5, and the subscript e is an integer from 0 to 25, preferably from 1 to 10, and more preferably from 1 to 3.

[0051] In a preferred embodiment of the invention, the reaction of monohydroxy functional dialkylphosphonic acid (IV) with an aromatic epoxy compound is carried out in a medium with an excess of monohydroxy functional dialkylphosphonic acid (IV), and the residual monohydroxy functional dialkylphosphonic acid (IV) is consumed by reaction with an epoxy compound such as propylene oxide, although other epoxy compounds such as ethylene oxide and epichlorohydrin may also be considered.

[0052] In this method, the use of propylene oxide should exceed any residual monohydroxy functional dialkylphosphonic acid (IV), preferably by a molar excess of about 1 to about 200%.

[0053] Based on the method used to manufacture these materials and the fact that the reaction must be completed by the final addition of propylene oxide (PO), the polyfunctional dialkylphosphonate compounds of the present invention, containing calculated amounts of monofunctional dialkylphosphonates, can be synthesized by using an excess of diethylphosphonic acid, compared to the polyfunctional epoxy resins used.

[0054] The residual monohydroxyfunctional dialkylphosphonic acid (IV) reacts with an excess of an epoxy compound, such as propylene oxide, to generate monofunctional dialkylphosphonates, such as those described in U.S. Patent No. 10,208,187, the entire contents of which are incorporated herein by reference. Those skilled in the art can determine the amount of monofunctional dialkylphosphonate that can be produced by setting the molar ratio of excess monohydroxyfunctional dialkylphosphonic acid (IV) to an aromatic epoxy compound sufficient to produce an amount of participating monohydroxyfunctional dialkylphosphonic acid (IV) sufficient to react with another epoxy compound, such as propylene oxide, to produce in situ the desired weight percentage amount of monofunctional dialkylphosphonate. This step avoids the need for incorporation of additional monofunctional dialkylphosphonates, which is sometimes required to reduce the overall viscosity of the polyfunctional dialkylphosphonate compounds of the present invention.

[0055] The amount of monofunctional dialkylphosphinates that can be generated in situ and / or added to the reaction product mixture of the present invention as described above is about 5 wt% to about 45 wt%, preferably about 10 wt% to about 40 wt%, and most preferably about 15 wt% to about 35 wt%, based on the total weight of the monofunctional and polyfunctional dialkylphosphinate compounds of the present invention.

[0056] The viscosity of the reaction mixture (blend) of the polyfunctional dialkylphosphonate compound and the monofunctional dialkylphosphonate of the present invention is preferably from about 500 cps to about 3000 cps, more preferably from about 1000 cps to about 2500 cps.

[0057] The amount of monohydroxy functional dialkylphosphine (IV) used in reactions with aromatic epoxides is a molar equivalent, or a molar excess of monohydroxy functional dialkylphosphine is required if a higher amount of monofunctional content is needed, for example, a molar excess of 5-100% monohydroxy dialkylphosphine.

[0058] The temperature range for reacting monohydroxy functionalized dialkylphosphonic acid (IV) with aromatic epoxy compounds is from about 50°C to about 120°C, preferably from about 70°C to about 90°C. This temperature range can be used for subsequent reactions of epoxy compounds such as propylene oxide.

[0059] Depending on the dialkylphosphonic acid and aromatic epoxy compound used in the reaction, the polyfunctional dialkylphosphonic acid ester compound of the present invention has a phosphorus content of about 8-15% by weight and a hydroxyl value of about 150-300 mg KOH / g.

[0060] To prepare a target polyfunctional dialkylphosphonic acid ester compound with the highest possible phosphorus content, it is preferable to react the monohydroxydialkylphosphonic acid (IV) described herein with the monohydroxydialkylphosphonic acid having the highest phosphorus content with an aromatic epoxy compound.

[0061] The reaction was carried out at 40°C. o C to 120 o C. Preferred 70 o C to 90 o The reaction is carried out at a temperature of C. Below 40°C, the reaction becomes unacceptably slow. On the other hand, temperatures above 120°C... o Temperatures of C are not recommended because undesirable decomposition products can form at such temperatures.

[0062] The polyfunctional dialkylphosphinate compounds of the present invention have high phosphorus content, good hydrolytic and thermal stability, good compatibility with diol and / or polyol components in flexible polyurethane foam forming systems, and can be used as highly efficient reactive flame retardants in flexible polyurethane foams.

[0063] The compounds of this invention can be used as reactive flame retardants. The flame retardants can be used as is or as mixtures with halogenated or non-halogenated products. For flexible polyurethane foams, it is preferable to use the halogen-free hydroxyl-functionalized dialkyl hypophosphite of this invention, either pure or used with other non-halogenated products.

[0064] The present invention also provides a flame-retardant flexible polyurethane comprising the reactive residue of the polyfunctional dialkyl hypophosphite after reaction in a flexible polyurethane foam forming system to form a flexible polyurethane foam. The polyfunctional dialkyl hypophosphite compounds described herein may be used in flexible polyurethane foam forming systems alone or in mixtures of each other and / or in mixtures with additional flame retardants, including halogenated and phosphorus-containing flame retardants.

[0065] In one non-limiting embodiment, the polyfunctional dialkyl hypophosphite described herein may be combined with a monohydroxy dialkyl hypophosphite, such as the isomer mixture described below, wherein the alkyl portion may be an alkyl group with 1-4 carbon atoms, to form a composition suitable for preparing polyurethane foams as described herein. The amount of the polyfunctional dialkyl hypophosphite may be 1-40 wt%, preferably 1-30 wt%, based on the combined weight of the monofunctional and polyfunctional dialkyl hypophosphite used.

[0066] The compounds of this invention are highly effective reactive flame retardants when introduced into flexible polyurethane foams. It should be noted that the compounds of this invention can be used within a wide range of isocyanate indices (abbreviated herein as MDI or TDI). This index refers to the percentage of the stoichiometric amount of isocyanate actually used in the formulation relative to the theoretically required isocyanate.

[0067] The flexible polyurethane foams described herein contain a typical flame-retardant effective amount of the compounds of the present invention. Typically, the compositions of the present invention are applied in an amount providing a total phosphorus concentration in the polymer (i.e., the flexible polyurethane foam) in the range of 0.3 to 15 wt% based on the total weight of said polymer. Preferably, the total phosphorus concentration in said polymer is in the range of 0.1 to 5 wt%, and more preferably in the range of 0.1 to 3 wt%, based on the total weight of the flexible polyurethane polymer. Most preferably, the amount of the polyfunctional dialkyl hypophosphite of the present invention is sufficient at least to meet the current requirements of the flammability test method MVSS 302.

[0068] Flexible polyurethane foams, varying in their degree of flexibility, can be manufactured by appropriately selecting components and conditions. Therefore, flexible foams typically use water as the primary blowing agent and are made from polymeric diols or triols with hydroxyl values ​​of 20-80.

[0069] The flexible polyurethane foam of the present invention may contain appropriately selected additives such as catalysts, surfactants, foam stabilizers, etc.

[0070] The flexible polyurethane foam used herein is made using diols and / or polyols having a molecular weight of 3,000 to about 6,000, and / or diols and / or polyols as described herein, such as polyether triols prepared by adding propylene oxide to glycerol. The flexible polyurethane foam used herein is characterized by having a core impact resilience of up to 30% and a glass transition point of -80ºC to -60ºC. Here, the flexible polyurethane foam preferably has a hard segment content of up to 40% by mass. Conventional flexible polyurethane foams have a bulk density of 2.5 lb / cubic foot (PCF) or less and a density of 10-90 lb / 50 in… 2 Foam hardness or IFD within the range (measured according to test method ASTM 3574-Test B1).

[0071] The method for manufacturing flexible polyurethane foam of the present invention may include combining one or more of a diol and / or polyol component and / or isocyanate component or catalyst and a flame retardant material of formula (I)-(III) or (A) or (B) as described herein (which may be metered and pumped into a conventional mixing container), and the resulting mixture may then be readily moved to a polymerization site for use in molds, sheet operations, etc.

[0072] The reactive flame retardant of the present invention may also be mixed with a diol and / or polyol reactant before being combined with the isocyanate reactant. Mixing the reactive flame retardant material with an isocyanate, and then combining such a mixture with a diol and / or polyol reactant, is also within the scope of the invention. However, if the isocyanate and the aforementioned flame retardant material are mixed and allowed to stand at room temperature for a substantial period, a reaction may occur. The term "reaction product" as used in the claims and this specification may, in one embodiment, include reacting the contents of a flexible polyurethane foam forming system in any of the aforementioned methods, and may further include reacting the reactive flame retardant via a prepolymer technique, for example, reacting an excess of isocyanate with a polyol to form an isocyanate-terminated prepolymer, and then further reacting the prepolymer with the reactive flame retardant and phosphate ester compound described herein.

[0073] The flame retardant materials of formulas (I)-(III) or (A) or (B) described herein can be described as isocyanate reactive (NCO reactive) materials, that is, they react with isocyanates via hydroxyl groups.

[0074] The diols and / or polyols used in the manufacture of the flexible polyurethane foams described herein may include any organic polyols (including diols, polyols), and polyether, polyester, and polyesteramide polyols having hydrogen atoms that can react with isocyanates may be used. Typically, these materials have a molecular weight ranging from about 62 to about 5,000 and have 2 to about 10 or more hydroxyl groups per molecule and a hydroxyl content ranging from about 0.5 to about 25% by weight. They typically have a hydroxyl value of about 50 to as high as 500 or even 700.

[0075] In polyester-polyol reactants, the acid value should be less than 10, and generally as close to 0 as possible. These materials are simply referred to as "polyol" reactants. Available diols and / or polyols containing active hydrogen include a large family of addition compounds that are produced by adding (adding) ethylene oxide, propylene oxide, 1,2- and 2,3-epoxybutane, or other epoxides to active hydrogen compounds such as diols, glycols, and polyols (examples include ethylene glycol, propylene glycol, glycerol, methyl glucoside, sucrose, sorbitol, hexanetriol, trimethylolpropane, pentaerythritol), as well as various alkylamines and alkylene diamines and polyalkylene polyamines. Depending on the intended use of the polyurethane, varying amounts of these epoxides may be added to the indicated base diol, polyol, or amine molecule.

[0076] For example, the diols and / or polyols used in the manufacture of flexible foams can also be represented by glycerol, to which sufficient propylene oxide is added to obtain a final hydroxyl content of about 1.7%. Such a material would have a molecular weight of about 3,000 and a glycerol-to-propylene oxide molar ratio of about 1 glycerol to 50 propylene oxides.

[0077] The technique of controlling flexibility by selecting diol and / or polyol molecules and the amount of subsequently added epoxide alkane is well known in the art.

[0078] Besides diols, which can be used as base polyol molecules for the addition of epoxides to produce "polyol" molecules for reaction with isocyanates, initial molecules containing primary and / or secondary amine groups with hydrogen atoms capable of reacting with epoxides can also be used. Similarly, the amount of epoxide added depends on the intended use of the final polyurethane product. In the flexible polyurethane products described herein, epoxides will be used to produce polyols with a low hydroxyl content, for example, from about 0.1% to about 5% or 10%.

[0079] Representative amines that can be used as molecules containing active hydrogen to react with epoxides are those having 1 to 6 or more amino nitrogen atoms, examples of which are ethylamine, ethylenediamine (ethylenediamine), diethylenetriamine, triethylenetetramine, tetrapropylenepentamine and other linear saturated aliphatic alkyleneamines. An important requirement is that at least two, and preferably more, i.e. 3 to 8 or 10 epoxides can be added to their active hydrogen sites.

[0080] It is also known that the active hydrogen compounds used in the preparation of polyurethane systems are molecules with hydroxyl groups prepared by esterification-type reactions of polyfunctional acids or anhydrides and polyfunctional alcohols. These compounds are commonly referred to as polyester polyols. Typical acids used in the manufacture of these polyester polyols are maleic acid, phthalic acid, succinic acid, fumaric acid, tetrahydrophthalic acid, chlorobenzene, and tetrachlorophthalic acid. Typical glycols and / or polyols are ethylene glycol, propylene glycol, butanediol, diethylene glycol, and dipropylene glycol, as well as polyethylene glycol, polypropylene glycol, and glycerol, trimethylolpropane, hexanetriol, pentaerythritol, sorbitol, etc. Where applicable, the above-mentioned acids may be used in the form of anhydrides as needed.

[0081] In the manufacture of polyester polyols, any of various polyfunctional acids or anhydrides or mixtures thereof are reacted with any of diols, glycols, or polyols or mixtures thereof in a stoichiometric excess of hydroxyl groups, such that the final polyol product comprises primarily hydroxyl terminal groups (terminal groups). The degree of hydroxyl functionality and percentage of hydroxyl groups can be readily altered using one or more techniques known to those skilled in the art to provide a desired polyol.

[0082] In the field and technology of manufacturing flexible polyurethane, a technique known as prepolymer technology is also known. This technique involves carrying out a portion of the reaction involved in the manufacture of flexible polyurethane to produce a prepolymer with increased molecular weight, wherein, depending on the stoichiometry used in manufacturing the prepolymer, the resulting end groups are hydroxyl or isocyanate groups. The final flexible polyurethane product is then prepared using this prepolymer by reacting it with an isocyanate or a polyol, depending on whether the end groups of the prepolymer are hydroxyl or isocyanate groups, as described above.

[0083] Broadly speaking, the polyurethanes described herein can be manufactured using any of the following: polyesters having free reactive hydrogen and, in particular, hydroxyl groups, isocyanate-modified polyester prepolymers, polyesteramides, isocyanate-modified polyesteramides, alkylene glycols, isocyanate-modified alkylene glycols, polyoxyalkylene glycols, isocyanate-modified polyoxyalkylene glycols, etc.

[0084] Examples of usable isocyanates include those with two or more isocyanate groups that have been used to date in the manufacture of flexible polyurethane foams. Examples of such isocyanate compounds include aromatic isocyanates, aliphatic isocyanates, and alicyclic isocyanates, and mixtures of two or more such isocyanates, as well as modified isocyanates obtained by modifying such isocyanates. Specific examples of such isocyanates are toluene diisocyanate, diphenylmethane diisocyanate, polymethylene polyphenylene polyisocyanate (crude MDI), xylene diisocyanate, isophorone diisocyanate, and hexamethylene diisocyanate; and modified products of such isocyanates, such as carbodiimide-modified products, biuret-modified products, dimers, and trimers. Prepolymers with terminal isocyanate groups obtained from such isocyanates and compounds containing active hydrogen can also be used.

[0085] In one embodiment, the isocyanate index of the flexible polyurethane foam may range from about 130 to about 80, more preferably from about 120 to about 90, and most preferably from about 115 to about 95.

[0086] As the blowing agent in the flexible polyurethane foam forming composition of the present invention, a known blowing agent used to date in such a composition is appropriately selected according to the desired properties of the foamed product.

[0087] In this invention, a crosslinking agent is also used, if necessary.

[0088] As a crosslinking agent, compounds having at least two functional groups possessing active hydrogen, such as hydroxyl, primary amino, or secondary amino groups, are preferred. However, in cases where a polyol compound is used as a crosslinking agent, the following is taken into consideration: That is, a polyol compound having a hydroxyl value of at least 50 mg KOH / g and more than four functional groups is considered as the crosslinking agent, and polyols that do not meet this requirement are considered as any one of the polyols in the above-mentioned polyol mixture (polyol (1), (2), or other polyols). Furthermore, two or more crosslinking agents may be used together. As specific examples, one may mention, for instance, polyols such as glucose, sorbitol, or sucrose; polyols having an epoxide added to the polyol; amine compounds such as monoethanolamine, diethanolamine, ethylenediamine, 3,5-diethyl-2,4 (or 2,6)-diaminotoluene (DETDA), 2-chloro-p-phenylenediamine (CPA), 3,5-bis(methylmercapto)-2,4 (or 2,6)-diaminotoluene, 1-trifluoromethyl-4-chloro-3,5-diaminobenzene, 2,4-toluenediamine, 2,6-toluenediamine, bis(3,5-dimethyl-4-aminophenyl)methane, 4,4'-diaminodiphenylmethane, m-xylylenediamine, 1,4-diaminohexane, 1,3-bis(aminomethyl)cyclohexane, or isophoronediamine; and compounds obtained by adding an epoxide to them.

[0089] When the above-mentioned crosslinking agents are used, even in cases where a large amount of foaming agent is used to manufacture flexible foams with low density, the foaming stability will be good, and it will be possible to manufacture such flexible foams. In particular, when high molecular weight glycols and / or polyols are used, it is possible to manufacture low-density flexible foams that have historically been considered difficult to foam. Furthermore, when crosslinking agents are used, durability is improved compared to when they are not used. In the case of using high molecular weight glycols and / or polyols in this invention, foaming stability can be easily improved, especially when using compounds with relatively high molecular weights, such as at least 4000.

[0090] Water is a typical example of such a blowing agent; other examples include dichloromethane, acetone, carbon dioxide, etc. Depending on the desired density and other properties of the foamed polyurethane, these and other blowing agents may be used alone or in combination of two or more in a manner known in the art.

[0091] There are no particular restrictions on the amount of foaming agent used, but it is generally in the range of 0.1 to 20 parts by weight per 100 parts by weight of the diol and / or polyol components of the foam-forming composition. Preferably, the amount of foaming agent is such that it provides a foam density of 0.8-2.5 lbs / ft, and more preferably 0.9-2.0 lbs / ft.

[0092] The polyurethane foam forming compositions described herein preferably include any and combinations of catalysts known or used to date in the manufacture of polyurethane foams. Examples of usable catalysts include sodium hydroxide, sodium acetate, tertiary amines or materials that produce tertiary amines, such as trimethylamine, triethylenediamine, N-methylmorpholine, N,N-dimethylcyclohexylamine, and N,N-dimethylaminoethanol. Also suitable are metal compounds such as hydrogentin alkyl carboxylate, dibutyltin diacetate, dibutyltin dioctanoate, dibutyltin dilaurate, and stannous octanoate; and other compounds intended to promote the trimerization of isocyanates, such as 2,4,6-tris(N,N-dimethylamino-methyl)phenol, 1,3,5-tris(N,N-dimethyl-3-aminopropyl)-S-hexahydrotriazine, potassium octanoate, potassium acetate, and catalysts such as DABCO TMR. ® and POLYCAT 43 ® .

[0093] Many other types of catalysts can be used instead of those listed above, as needed. The amount of catalyst used can advantageously be in the range of 0.05-5% by weight or greater, based on the total weight of the diols and / or polyols in the foam-forming mixture.

[0094] The isocyanate (NCO) index used in the manufacture of the flexible foam according to the invention is 95-125, and preferably 100-120. It is generally understood that the NCO index of polyurethane foam is about 80-130.

[0095] The density range of flexible polyurethane foam in this article can be 14-80, preferably 16-55, and most preferably 20-40 kg / m³. 3 .

[0096] Surfactants, including organic surfactants and silicone-based surfactants, can be added to act as cell stabilizers. Some representative materials are sold under the names SF-1109, L-520, L-521, and DC-193 (which are typically polysiloxane polyoxyalkylene block copolymers). Organic surfactants comprising polyoxyethylene-polyoxybutylene block copolymers are also included. It is particularly desirable to use a small amount of surfactant to stabilize the foaming reaction mixture until it cures. Other surfactants that may be used herein are polyethylene glycol ethers of long-chain alcohols, long-chain allyl sulfates, alkyl sulfonates, tertiary amines or alkanolamine salts of alkyl aryl sulfonic acids, and combinations thereof. Such surfactants are used in amounts sufficient to stabilize the foaming reaction against collapse and the formation of large, uneven cells. Typically, a total surfactant amount of about 0.2 to about 3 wt% of the formulation as a whole is sufficient for this purpose. However, including certain surfactants, such as DABCO DC-5598, available from Air Products and Chemicals, Inc., in higher amounts may be desirable in some embodiments. Therefore, in the formulations of the present invention, surfactants may be included in any amount ranging from 0-6 wt.% based on the diol and / or polyol components.

[0097] Finally, the polyurethane foam forming formulations described herein may include other additives such as fillers and pigments. These, in non-limiting embodiments, may include barium sulfate, calcium carbonate, graphite, carbon black, titanium dioxide, iron oxide, microspheres, alumina trihydrate, wollastonite, prepared glass fibers (dropped or continuous), polyester fibers, other polymer fibers, combinations thereof, etc. Those skilled in the art will recognize that typical and suitable means and methods for manufacturing flexible polyurethane foams using the formulations of the present invention are available without further instruction, and that such flexible polyurethane foams, while still falling within the scope of the appended claims, exhibit or benefit from desired properties and / or processing modifications.

[0098] The flexible polyurethane foam described herein can be used in the construction and formation of a wide variety of products, such as furniture, bedding, and car seat cushions, and more particularly furniture, automotive, marine, bus, train, RV, office furniture, aviation, tractor, bicycle, engine rack, compressor, bedding, insulation, sports equipment, footwear, carpet, packaging, textiles, cushioning, HVAC, tents, life rafts, luggage, and handbags.

[0099] Flexible polyurethane foam sheets can be used in furniture such as upholstered furniture (e.g., padding, backrests, and armrests), in the automotive industry such as for cars and trucks, for public transportation seats (e.g., buses and airplanes), and for seat and back padding, headrests, and headrests in tractor units, bicycles, and e-bikes, including but not limited to seat bottom and back pads, armrests, support rings for run-flat tires, and other automotive interior components; bedding such as mattresses, seat sound insulation materials, automotive interior components such as elbow rests, steering wheels and gear shift knobs, shoe soles, and sports equipment.

[0100] Example

[0101] Seven different reaction products of epoxides and diethylphosphonic acid (DEPA) were prepared and evaluated as flame retardant additives for flexible polyurethane foams. Example structures of the prepared molecules are shown below:

[0102] Bisphenol A diglycidyl ether phosphonate reaction products (from DER 331, 332 and 383):

[0103]

[0104] The n-values ​​for epoxy resins DER 331, DER 332, and DER 383 can be calculated based on a given epoxy equivalent (EEW), which is the weight associated with each epoxy group in the molecule. Each molecule of DER 331, DER 332, and DER 383 has two epoxy groups. The EEW of DER 331 ranges from 182 to 192 grams. The EEW of pure diglycidyl ether of bisphenol A is 170.2 grams; therefore, if we take the average of 187 grams for DER 331, the n-value for DER 331 is ~1.10. The EEW of DER 332 is 171-175 grams, so the calculated n = ~1.02, and the EEW of DER 383 is 176-183 grams, so the calculated n-value is ~1.05.

[0105] Epoxy phenolic varnish resin phosphonate reaction products (from DEN431):

[0106]

[0107] For DEN oligomers, the same calculation method used for DER 331, DER 332, and DER 383 described above cannot be used to determine n because almost every phenyl group has an epoxy group, regardless of the oligomer length. The EEW of a pure phenolic varnish resin where every phenyl group has an epoxy group is 150.17 g, while the EEW of DEN 431 is 172-179 g. Therefore, not every phenyl moiety has an epoxy group. The n value for these products cannot be calculated; it is the manufacturer's n value or DEN 431 ~ 1.8.

[0108] Comparative compound 1: Neopentyl glycol diglycidyl ether phosphonate reaction product (from Araldite DY-N):

[0109]

[0110] The n-value of the above products can be calculated using a method similar to that described for DER products. The EEW of DY-N is 125-145 g, and that of pure diglycidyl ether is 108.14 g EEW. Therefore, the n-value of DY-N is ~1.25.

[0111] Comparative compound 2: 1,4-Butanediol diglycidyl ether phosphonate reaction product (from Araldite DY-D)

[0112]

[0113] The EEW of DY-D is 117-125 grams, and the EEW of pure diglycidyl ether is 101.12 grams.

[0114] Therefore, the value of n for DY-D is ~1.20.

[0115] Comparative compound 3: Trimethylolpropane triglycidyl ether phosphonate reaction product (from Araldite DY-T):

[0116]

[0117] DY-T has an EEW of 111-143 grams, and pure triglycidyl ether has an EE of 100.79 grams.

[0118] The value of n in DY-T will be ~1.26.

[0119] The molecule was prepared using the following general synthetic method:

[0120]

[0121] Synthesis Examples

[0122] Synthesis Example 1

[0123]

[0124] Where n is ~1.10

[0125] program:

[0126] DER 383 (139.4 g) was added to a 0.5 L four-necked round-bottom flask equipped with a water condenser, a J-Kem temperature probe, a feeding funnel, and a magnetic stirrer. The batch was heated to 60 °C and then stirred at this temperature. Diethylphosphonic acid (100 g; 0.819 mol) was then added to the batch through the feeding funnel. A slight exothermic reaction was observed up to 66 °C. The batch was stirred at 80 °C and maintained at this temperature for 3.0 h, then maintained at 90 °C for 4.0 h. The batch was then cooled to room temperature overnight without stirring.

[0127] The batch was then heated to 40°C, and propylene oxide (32.0 g; 0.55 mol) was added in portions using a water condenser connected to the flask. After adding PO, the batch was stirred at 80°C for 8.0 hours. A sample was taken as a batch for acid value analysis, yielding an acid value of 0.53 mg KOH / g. The batch was then vacuum stripped at 80°C under full vacuum for 2 hours to obtain a transparent glass compound.

[0128] The analysis results are as follows:

[0129] Acid value = 0.05 mg KOH / g

[0130] Water = 990 ppm

[0131] OH value = 202 mg KOH / g

[0132] Synthesis Example 2

[0133]

[0134] Where n is ~1.02

[0135] program:

[0136] DER 332 (139.4 g) was added to a 0.5 L four-necked round-bottom flask equipped with a water condenser, a J-Kem temperature probe, a feeding funnel, and a magnetic stirrer. The batch was heated to 60 °C and then stirred at this temperature. Diethylphosphonic acid (100 g; 0.819 mol) was then added to the batch through the feeding funnel. A slight exothermic reaction was observed up to 63 °C. The batch was stirred at 80 °C and maintained at this temperature for 3.0 h, then maintained at 90 °C for 7.0 h. The batch was then cooled to room temperature overnight without stirring.

[0137] The batch was then heated to 40°C, and propylene oxide (32.0 g; 0.55 mol) was added in portions using a water condenser connected to the flask. After adding PO, the batch was stirred at 80°C for 8.0 hours. A sample was taken for acid value analysis, yielding an acid value of 0.44 mg KOH / g. The batch was then vacuum stripped at 90°C under full vacuum for 2 hours to obtain a transparent glass compound.

[0138] The analysis results are as follows:

[0139] Acid value = 0.03 mg KOH / g

[0140] Water = 930 ppm

[0141] OH value = 197 mg KOH / g

[0142] Synthesis Example 3

[0143]

[0144] Where n is ~1.05

[0145] program:

[0146] DER 383 (139.4 g) was added to a 0.5 L four-necked round-bottom flask equipped with a water condenser, a J-Kem temperature probe, a feeding funnel, and a magnetic stirrer. The batch was heated to 60 °C and then stirred at this temperature. Diethylphosphonic acid (100 g; 0.819 mol) was then added to the batch through the feeding funnel. A slight exothermic reaction was observed up to 61 °C. The batch was stirred at 80 °C and maintained at this temperature for 3.0 h, and then maintained at 90 °C for 9.0 h. The batch was then cooled to room temperature overnight without stirring.

[0147] The batch was then heated to 40°C, and propylene oxide (16.0 g; 0.275 mol) was added in portions using a water condenser connected to the flask. After adding PO, the batch was stirred at 80°C for 3.0 h and then at 90°C for 4.0 h. A sample was taken for acid value analysis, yielding an acid value of 0.48 mg KOH / g. The batch was then vacuum stripped at 90°C under full vacuum for 2 h to obtain a transparent glass compound.

[0148] The analysis results are as follows:

[0149] Acid value = 0.02 mg KOH / g

[0150] Water = 450 ppm

[0151] OH value = 192 mg KOH / g

[0152] Synthesis Example 4

[0153]

[0154] Where n is ~1.8

[0155] program:

[0156] DEN 431 (139.4 g) was added to a 0.5 L four-necked round-bottom flask equipped with a water condenser, a J-Kem temperature probe, a feeding funnel, and a magnetic stirrer. The batch was heated to 60 °C and then stirred at this temperature. Diethylphosphonic acid (100 g; 0.819 mol) was then added through the feeding funnel. Slight exothermic reaction was observed up to 62 °C. The batch was stirred at 80 °C and maintained at this temperature for 3.0 h, and then maintained at 90 °C for 9.0 h. The batch was then cooled to room temperature.

[0157] The batch was then heated to 40°C, and propylene oxide (16.0 g; 0.275 mol) was added in portions using a water condenser connected to the flask. After adding PO, the batch was stirred at 80°C for 3.0 h and then at 90°C for 4 h. A sample was taken for acid value analysis, yielding an acid value of 0.34 mg KOH / g. The batch was then vacuum stripped at 90°C under full vacuum for 2 h to obtain a transparent glass compound.

[0158] The analysis results are as follows:

[0159] Acid value = 0.03 mg KOH / g

[0160] Water = 2300 ppm

[0161] OH value = 205 mg KOH / g

[0162] Table 1 below summarizes the analytical results of four synthetic embodiments of the present invention and three comparative structures:

[0163] Table 1

[0164]

[0165] The above products were then evaluated as flame-retardant additives in polyester polyol polyurethane flexible foams. Due to the high viscosity of the aromatic epoxy resin products (prepared from aromatic epoxy resins – Synthesis Examples 1-4), these materials were also evaluated below based on similar chemistry listed in Table 3 in blends with monofunctional low-viscosity hypophosphite (MFPE) products, which are mixtures of the following isomers:

[0166] .

[0167] Aliphatic epoxy products (comparative compounds 1-3) were evaluated only in pure (net, neat) form because their lower viscosity makes them easier to use in polyurethane formulations and they do not benefit from dilution with the aforementioned MFPE isomer mixtures. The results of the first round of evaluations as pure products are shown in Table 2 below:

[0168] Table 2

[0169]

[0170]

[0171] Density is determined by ASTM D3574 (2003) Test A, density test.

[0172] Airflow rate is measured according to ASTM D3574 (2003) Test G.

[0173] Compression set was measured using standard ASTM method D 3574-03 Test D and used to determine the foam's ability to recover after compression. The applicant used a 90% compression ratio, as mentioned in line 41.3 of the standard in the evaluation. This test method involves bending the foam specimen to a specified deflection, exposing it to specified time and temperature conditions, and measuring the change in specimen thickness after a specified recovery period.

[0174] DG173RLF is a polyester polyol obtainable from COIMs, p, a–Chimica Organica Industriale as MilaneseDIEXTER G 173 RLF.

[0175] Niax C131 NPF is a bis(2-dimethylaminoethyl) ether; 3-dimethylamino-N,N-dimethylpropionamide (CAS 3033-62-3 17268-47-2) available from Momentive Performance Materials GmbH.

[0176] Niax DMP is an N,N'-dimethylpiperazine (CAS 106-58-1) available from Momentive Performance Materials GmbH.

[0177] Niax Silicone L537LF is a polyalkylene oxymethylsiloxane copolymer available from Momentive Performance Materials.

[0178] TDI 65 is an aromatic isocyanate available from Covestro, LLC as MONDUR TD-65 (CAS 584-84-9 (65%), 91-08-7 (35%)).

[0179] TDI 80 is an aromatic isocyanate, type 1 isocyanate, available from Everchem Specialty Chemicals as TDI 80 (CAS 584-84-9 (80%); 91-08-7 (20%)).

[0180] The pure products (i.e., those from Synthetic Examples 1-4) were glassy materials at room temperature, while the comparative products (Comparative Compounds 1-3) were medium-viscosity liquids (similar to Fyrol FR-2, i.e., tris(1,3-dichloro-2-propyl)phosphate (TDCP)). In this first round of evaluation, the products of Synthetic Examples 1-4 had to be heated to 90°C for casting. The seven phosphonates test compounds were slowly added to the polyol along with other polyurethane formulation components. In the case of the products of Synthetic Examples 1-4, they thickened once they came into contact with the polyol at lower temperatures, making it difficult to incorporate the material into the formulation mixture. The addition of Comparative Compounds 1-3 to the polyol and other formulation chemicals proceeded smoothly without problems. Although some foams using the products of Synthetic Examples 1-4 produced good results, the difficulty in handling the material at room temperature led to the conclusion that using these high-viscosity products in a commercial setting would be a challenge.

[0181] As mentioned above, preparing foam using the pure products of Synthetic Examples 1-4 is challenging, but the flammability and physical properties are advantageous for materials that are indeed incorporated into formulations and produce acceptable foams. In formulations with a loading of 6 pph, the products of Synthetic Examples 2 and 3 yielded SE ratings in MVSS 302 and compression set numbers comparable to non-flame-retardant foams. These results are unexpected, as all phosphinic acid ester products based on diethylphosphinic acid chemicals have previously been found to negatively impact the compression set properties of the prepared flexible foams. The combination of good flame-retardant results and favorable physical properties of the foams prepared using the products of Synthetic Examples 2 and 3 demonstrates the commercial advantages of these products.

[0182] Compared to the aromatic epoxy resin products synthesized in Examples 1-4, foam evaluations using aliphatic products (Comparative Compounds 1-3) did not yield positive results. While foams could be prepared using Comparative Compounds 1-3, they negatively impacted the compression set properties of the foam, similar to monofunctional diethyl phosphite products. A height loss of 70-80% during 90% compression set testing was considered unacceptable for commercial foams. All three products of Comparative Compounds 1-3 catalyzed the foaming reaction, resulting in a very rapid reaction and shortening the rise-end time to varying degrees. Comparative Compounds 2 and 3 were significantly faster than Comparative Compound 1.

[0183] Another problem associated with the product of Comparative Compound 1 is the unpleasant odor imparted to the foam product. Given that the end use of flexible foam is almost always in close contact with customers in confined spaces (e.g., automobiles, furniture), such an odor is unlikely to be acceptable. Finally, the trifunctional (three OH groups) product of Comparative Compound 3 introduces instability during the foaming process and is therefore unsuitable for manufacturing flexible foam. This product destabilizes the foam and causes the foam mixture to boil instead of expanding normally. The high OH functionality of this product, combined with the inherent catalytic effect of these hypophosphites during the foaming process, is likely a contributing factor to its incompetence. In conclusion, none of the aliphatic epoxy-based products of Comparative Compounds 1-3 produce an acceptable flexible foam product.

[0184] Table 3

[0185]

[0186]

[0187] A second round of application testing was conducted using the products from Synthetic Examples 1-4 to produce product versions that were easier to handle and cast at room temperature. The method employed was to blend each product from Synthetic Examples 1-4 with a low-viscosity hypophosphite product, MFPE, at a ratio sufficient to achieve a reasonable product viscosity (but not exceeding the desired level), as MFPE is known to cause degradation of the physical properties of foam products. The following datasets in Table 3 were generated using the added 30% and 40% MFPE.

[0188] General observations of the 30 / 70 blends indicate that the viscosity is acceptable and the blends can be cast and used at room temperature without problems. All blends at this ratio showed strong SE ratings in the MVSSS 302 test at a 5 pph loading in the foam formulation, with minimal impact on the compression set properties of the foam. In terms of final foam quality, the products of Synthetic Example 2 and Synthetic Example 3 showed the best preforming at this ratio and were selected for an additional round of testing with alternative blending ratios to MFPE. To further reduce viscosity, MFPE was blended with Synthetic Example 2 and Synthetic Example 3 at a 40 / 60 ratio (see Blending Examples 5-8). At this new ratio, both products showed strong SE ratings in the MVSS 302 test at 5 pph, and even at only 3 parts, a critical SE rating was given. Therefore, it is concluded that a 4-part loading of each blend would be the ideal loading for reliable SE ratings in MVSS 302 for these blends. However, introducing more MFPE into the blend did show a negative impact on the compression set value of the foam made from the blend. The percentage loss of recovery rate did show an increase compared to the 30 / 70 blend. While not wishing to be bound by theory, the 40% MFPE blend may be the practical limit for how much of this low-viscosity diluent can be added to the products of Synthetic Examples 2 and 3 to obtain acceptable processing properties without sacrificing the physical properties of the foam products.

[0189] In summary, products 2 and 3 of Synthetic Examples are the most desirable candidates for future development when blended with up to 40% MFPE (preferably 30%) to provide a reactive hypophosphite blend with a usable viscosity, which exhibits excellent FR performance, good physical foaming properties, and zero VOC emissions from the foam due to the reactive nature of the polyfunctional aromatic hypophosphite and MFPE products. The aromatic epoxy-based products show superior performance compared to the aliphatic epoxy-based products in terms of foam manufacturing performance and the properties of the final foam produced. The negative properties associated with the viscosity of the products of Synthetic Examples 1-4 can be overcome by blending with additional MFPE (which is already present in the product at 5-6 wt%, generated by the final process finishing step using propylene oxide). Based on the process used to prepare these materials, and the fact that the reaction must be completed by the final addition of propylene oxide (PO), the products of Synthetic Examples 1-4 containing a calculated amount of MFPE can be synthesized by using an excess of diethylphosphinoic acid compared to the diepoxy resin used. The resulting blend provides a relatively low-viscosity, highly efficient flame retardant that is phenol-free, has zero emissions, is fully reactive, and exhibits minimal compression set loss in the final foam product.

[0190] Although the invention has been described with reference to certain embodiments, those skilled in the art will understand that various changes can be made and its elements can be substituted with equivalents without departing from the scope of the invention. Furthermore, many changes can be made without departing from its essential scope to make particular scenarios or materials suitable for the teachings of the invention. Therefore, it is intended that the invention not be limited to the specific embodiments disclosed as the best mode contemplated for carrying out the invention, but rather that the invention cover all embodiments falling within the scope of the appended claims.

Claims

1. Polyfunctional dialkylphosphinate compounds of general formula (I): (I) Among them, each R 1 and R 2 Selected individually from alkyl groups containing 1 to 4 carbon atoms, R is a divalent straight-chain or branched alkyl group containing up to 4 carbon atoms, a divalent aralkyl group containing 7 to 13 carbon atoms, or a bond. X and Y are each independently a divalent aryl group containing 6 to 12 carbon atoms. Subscripts a and b are either 0 or 1. The subscript c is an integer from 1 to 5, and The subscript d is an integer from 1 to 26. The conditions are: a+b=1, When a = 1, then b is 0, X is an aryl group as defined, except that the hydrogen atom bonded to the aryl group is not part of the group within the parentheses of subscript c, and subscript c is an integer from 1 to 5 and subscript d is 1, and... When b = 1, then a is 0, c is 1, and d is an integer from 1 to 26.

2. The polyfunctional dialkylphosphinate compound of claim 1, wherein R 1 and R 2 Each is an ethyl group.

3. The polyfunctional dialkylphosphinate compound of claim 1, wherein X and Y are each divalent phenyl, and R is divalent methyl or divalent isopropyl.

4. The polyfunctional dialkylphosphinate compound of claim 1, having the general formula (II): (II) Where R 1 and R 2 Selected individually from alkyl groups containing 1 to 4 carbon atoms, R is a divalent straight-chain or branched alkyl group containing up to 4 carbon atoms, or a bond. X and Y are each independently a divalent aryl group containing 6 to 12 carbon atoms. The subscript c is an integer from 1 to 5, and the subscript d is 1.

5. The polyfunctional dialkylphosphonate compound of claim 1, having the general formula (III): (III) Where R 1 and R 2 Selected individually from alkyl groups containing 1 to 4 carbon atoms, R is a divalent straight-chain or branched alkyl group containing up to 4 carbon atoms, or a bond. X and Y are each independently a divalent aryl group containing 6 to 12 carbon atoms. The subscript c is 1, and the subscript d is an integer from 1 to 26.

6. A method for preparing a polyfunctional dialkylphosphonate compound as defined in claim 1, comprising reacting a dialkylphosphonic acid with an aromatic epoxide.

7. The method of claim 6, wherein the aromatic epoxide is selected from: ； ; and their combinations, Where R is a divalent straight-chain or branched alkyl group containing up to 4 carbon atoms, or a bond. X and Y are each independently a divalent aryl group containing 6 to 12 carbon atoms. The subscript c is an integer from 1 to 5, and the subscript e is either 0 or an integer from 1 to 25.

8. The method of claim 6, wherein the dialkylphosphonic acid is present in excess relative to the aromatic epoxide, resulting in an excess of dialkylphosphonic acid which is subsequently reacted in situ with the epoxide to produce a blend of polyfunctional dialkylphosphonic ester compounds and monofunctional dialkylphosphonic esters.

9. A flame-retardant polyurethane foam comprising the reaction product of a polyol, an isocyanate, and an effective amount of a polyfunctional dialkyl hypophosphite compound of general formula (I): (I) Among them, each R 1 and R 2 Selected individually from alkyl groups containing 1 to 4 carbon atoms, R is a divalent straight-chain or branched alkyl group containing up to 4 carbon atoms, a divalent aralkyl group containing 7 to 13 carbon atoms, or a bond. X and Y are each independently a divalent aryl group containing 6 to 12 carbon atoms. Subscripts a and b are either 0 or 1. The subscript c is an integer from 1 to 5, and The subscript d is an integer from 1 to 26. The conditions are: a+b=1, When a = 1, then b is 0, X is an aryl group as defined, except that the hydrogen atom bonded to the aryl group is not part of the group within the parentheses of subscript c, and subscript c is an integer from 1 to 5 and subscript d is 1, and... When b = 1, then a is 0, c is 1, and d is an integer from 1 to 26.

10. The flame-retardant polyurethane foam of claim 9, wherein R 1 and R 2 Each of them is an ethyl group, X and Y are each divalent phenyl groups, and R is a divalent methyl group or a divalent isopropyl group.

11. The flame-retardant polyurethane foam of claim 9, wherein the polyfunctional dialkyl hypophosphite compound has the general formula (II): (II) Where R 1 and R 2 Selected individually from alkyl groups containing 1 to 4 carbon atoms, R is a divalent straight-chain or branched alkyl group containing up to 4 carbon atoms, or a bond. X and Y are each independently a divalent aryl group containing 6 to 12 carbon atoms, with subscript c being an integer from 1 to 5 and subscript d being 1.

12. The flame-retardant polyurethane foam of claim 9, wherein the polyfunctional dialkyl hypophosphite compound has the general formula (III): (III) Where R 1 and R 2 Selected individually from alkyl groups containing 1 to 4 carbon atoms, R is a divalent straight-chain or branched alkyl group containing up to 4 carbon atoms, or a bond. X and Y are each independently a divalent aryl group containing 6 to 12 carbon atoms. The subscript c is 1, and the subscript d is an integer from 1 to 26.

13. An article comprising the polyurethane foam of claim 9.

14. An article comprising the polyurethane foam of claim 11.

15. An article comprising the polyurethane foam of claim 12.

16. Articles comprising the articles of claim 13, wherein the articles are selected from furniture articles, automotive articles, marine articles, train seat articles, aviation articles, tractor articles, bicycle articles, compressor articles, isolation articles, sports equipment articles, footwear articles, carpet mat articles, packaging articles, textile articles, cushioning articles, HVAC articles, tent articles, life raft articles, luggage articles and handbag articles, wherein the articles comprise the flexible polyurethane of claim 1.

17. The article of claim 16, wherein the furniture article is an RV seating article, an office furniture seating article, or a bedding article.

18. The article of claim 16, wherein the furniture article is upholstered furniture.

19. The article of claim 16, wherein the automotive article is selected from automotive seat cushions, headrests and headrests, backrests for cars and trucks, bus seats, seat bottom and backrest pads, armrests, support rings for run-flat tires, and other automotive interior components.

20. The article of claim 17, wherein the bedding article is selected from mattresses and mattress covers.

21. The article of claim 16, wherein the insulating article is a sound-insulating material.

22. The article of claim 16, wherein the insulating article is a roof insulating material.

23. The article of claim 16, wherein the article is selected from bus seat articles and engine rack articles.

24. A composition comprising: (a) Polyfunctional dialkylphosphinate compounds of general formula (I): (I) Among them, each R 1 and R 2 Selected individually from alkyl groups containing 1 to 4 carbon atoms, R is a divalent straight-chain or branched alkyl group containing up to 4 carbon atoms, a divalent aralkyl group containing 7 to 13 carbon atoms, or a bond. X and Y are each independently a divalent aryl group containing 6 to 12 carbon atoms. Subscripts a and b are either 0 or 1. The subscript c is an integer from 1 to 5, and The subscript d is an integer from 1 to 26. The conditions are: a+b=1, When a = 1, then b is 0, X is an aryl group as defined, except that the hydrogen atom bonded to the aryl group is not part of the group within the parentheses of subscript c, and subscript c is an integer from 1 to 5 and subscript d is 1, and... When b = 1, then a is 0, c is 1, and d is an integer from 1 to 26; and (b) Monohydroxydialkylphosphinate compounds.

25. A polyurethane foam comprising the composition of claim 24.

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