KR20260015905A - Flame-retardant polyurethane and its uses - Google Patents

Abstract

Flame-retardant polyurethane obtained by reacting a polyol and an isocyanate in the presence of a flame retardant comprising a phosphinate of the following chemical formula (I):
(I)
In the above formula, R1 is a hydrocarbon radical selected from C ₁ -C ₁₂ alkyl and C ₆ -C ₂₀ aryl groups; R2 and R3 are the same or different and independently represent H or C ₁ -C ₁₂ C1-C12 alkyl.

Description

Flame-retardant polyurethane and its uses

The present invention relates to flame retardant polyurethanes containing a specific type of phosphinate flame retardant, a process for producing the same and their use in industry.

To achieve the desired flame retardancy for industrial applications, combustion-modified polyurethanes typically include at least one type of flame retardant. In these application scenarios, liquid flame retardants are often preferred over solid flame retardants. This preference stems from several advantageous properties: Compared to solid flame retardants, liquid flame retardants can be more easily and uniformly dispersed, or even dissolved, within the polymer during the blending process, providing consistent flame retardant efficacy throughout the polymer. Furthermore, liquid flame retardants can often be processed at lower temperatures than solids, mitigating potential polymer degradation issues associated with high temperatures. Because these liquid additives have a larger surface area for interaction, they can be incorporated into the resin mixture more quickly than solids. Furthermore, liquid flame retardants are generally easier to handle during the blending process with the polyol, allowing for precise dosage control and seamless integration into the polymer formulation.

One common liquid flame retardant widely used in industry is tris(1-chloro-2-propyl) phosphate (TCPP), which is often incorporated into polyurethane foams for consumer products and home insulation, as well as electronics. However, despite providing effective flame retardancy, TCPP has been shown to leach into the environment over time due to its halogenated nature, causing negative toxicological and ecotoxicological effects. Furthermore, the leaching of TCPP flame retardants reduces their overall flame retardant effectiveness over time.

US 9,631,144 B2 describes a different liquid flame retardant composition comprising at least one halogenated flame retardant, which is a brominated epoxide obtained by reacting tetrabromobisphenol A with epichlorohydrin. This particular liquid flame retardant is said to provide stable incorporation into rigid polyurethane foams and to exhibit excellent flame retardancy. However, it is noteworthy that in the working examples provided in US 9,631,144B2, the brominated epoxide is obtained in the form of a resin having a high softening point, which requires further processing at high temperatures. Furthermore, the resulting liquid flame retardant composition is particularly characterized by a high bromine content of at least 30 wt.-%.

As environmental concerns about the use of halogenated flame retardants grow, efforts have been made to find alternative non-halogenated liquid flame retardants for polymers and polymer foams.

US 4 458 035 A describes an oligomeric phosphate flame retardant for polyurethane foams, wherein the phosphate has the following chemical formula (1):

(1)

In the above formula,

n is 0 to 10,

R is a C ₁ -C ₁₀ (halo)alkyl radical,

R ₁ and R ₂ are hydrogen atoms or C ₁ -C ₁₀ (halo)alkyl radicals.

US 7 288 577 B1 describes a blend of two different phosphate flame retardants for polyurethanes, said blend consisting essentially of:

(a) 50 wt% of butylated triphenyl phosphate of the blend, and

(b) 50 wt% of poly(ethylethyleneoxy) phosphate of the blend.

While the above patent disclosures describe several effective liquid phosphorus-based flame retardants, some of these have been found to be susceptible to hydrolysis under humid conditions, which can ultimately negatively impact the polymerization process or the final polymer properties. Specifically, the acids generated by hydrolysis are known to deactivate polymerization catalysts during the foaming process and can further cleave covalent bonds within the polymer foam product, destroying the intended three-dimensional foam network.

Several liquid phosphorus-based flame retardant products are commercially available, including Antiblaze® 1045 (Albemarle), a cyclic phosphonate compound commonly used in polymers such as PET and PBT. The chemical structure of this cyclic phosphinate is illustrated by the following formula (2):

.

Antiblaze® 1045 exhibits a high viscosity, typically exceeding 500,000 mPa·s at 25°C. Consequently, its effective use may involve careful impregnation onto a carrier material or meticulous application as an aqueous solution onto the polymer fiber surface. In the latter case, subsequent heating is required to soften the fiber and dissolve the cyclic phosphonate to achieve the desired results.

The object of the present invention is to provide a novel non-halogenated flame retardant for use in polyurethane, particularly polyurethane foam. The non-halogenated flame retardant takes a liquid form at room temperature and under conventional polyurethane manufacturing conditions, has a suitably low viscosity to facilitate processing and handling, demonstrates excellent hydrolytic stability even under humid conditions, and provides equivalent or improved flame retardancy to polyurethane materials compared to existing commercial standards.

The present invention aims to provide a flame-retardant polyurethane, specifically a polyurethane foam, which achieves excellent flame-retardant efficiency by incorporating the above-mentioned non-halogenated flame retardant.

The present invention provides the use of a phosphinate of the following formula (I) as a flame retardant for polyurethane:

In the above formula, R1 is a hydrocarbon radical selected from C ₁ -C ₁₂ alkyl and C ₆ -C ₂₀ aryl groups;

R2 and R3 are the same or different and independently represent H or C ₁ -C ₁₂ alkyl.

The present invention further provides a flame-retardant polyurethane obtained by reacting a polyol and an isocyanate in the presence of a flame retardant comprising a phosphinate of the formula (I).

Unless otherwise indicated, the term "hydrocarbon radical" as used herein refers to an aliphatic radical, aromatic radical or alicyclic radical which may be saturated or unsaturated, straight or branched chain and optionally substituted with a heteroatom (e.g., O, N, S).

Preferably, R1 is selected from C1-C6 alkyl, more preferably from C2-C4 alkyl.

Also preferably, R2 and R3 are not H at the same time.

In a preferred embodiment of the present invention, one of R2 and R3 is H or ethyl and the other is C1-C6 alkyl.

In another preferred embodiment of the present invention, one of R2 and R3 is methyl and the other is H or C1-C4 alkyl.

In a particularly preferred embodiment, R1 is ethyl, one of R2 and R3 is methyl, and the other is ethyl.

In another particularly preferred embodiment, R1 is butyl, one of R2 and R3 is methyl, and the other is H.

In another particularly preferred embodiment, R1 is butyl, one of R2 and R3 is methyl, and the other is butyl.

The phosphinate flame retardant according to the present invention, due to its chemical properties, takes the form of a liquid at room temperature and under conventional polyurethane production conditions. Advantageously, the liquid phosphinate flame retardant is characterized by a low viscosity of less than 100 mPa·s, preferably less than 50 mPa·s, more preferably less than 10 mPa·s at a temperature of 25°C. The viscosity can be measured according to DIN 51398. As described above, the advantageous property of low viscosity can play an important role in the practical application of liquid flame retardants for the production of flame-retardant polyurethanes. The use of viscous liquid flame retardants is typically difficult because it requires heating of containers, supply lines, and discharge lines involved in the storage or transportation of the liquid. Furthermore, obtaining a homogeneous incorporation of a high-viscosity flame retardant liquid into a polymer composition often requires additional efforts, especially in large-scale industrial processes for the production of bulk chemicals.

Phosphinates of the following formula (I) can be prepared by various methods. One approach is to react an α-monoolefin with an (alkyl)phosphinate in the presence of a free radical generator, as described in US 39 14 345 A, EP 23 73 666 A1, US 87 35 477 B2, and EP 23 67 834 A1:

.

Phosphinates of formula (I) can also be prepared from their corresponding phosphites by a catalytic rearrangement reaction. For example, one corresponding phosphite has the following structural formula (II):

.

As illustrated in Synthetic Example 1, this manufacturing process can be realized by a two-step method. In the first step, a phosphite corresponding to the desired phosphinate product is prepared as an intermediate, and in the second step, this intermediate is subjected to a catalytic rearrangement reaction to obtain the phosphinate of formula (I). Alternatively, if the corresponding phosphite is readily available from the chemical market, the manufacturing process can be simplified to a single-step reaction.

The rearrangement catalyst in this manufacturing process may be an iodine-containing catalyst and a Lewis acid catalyst, such as iodine, alkyl iodides and alkali metal iodide salts (particularly potassium iodide) as described in CN 104693238A. Alternatively, the rearrangement catalyst may be sodium iodide as described in CN 109400643A.

Advantageously, the rearrangement catalyst may be a small molecule organic sulfonate, more advantageously selected from the group consisting of diethyl sulfate, ethyl ethanesulfonate, p-toluenesulfonic acid methyl ester, p-toluenesulfonic acid ethyl ester, p-chlorobenzenesulfonic acid methyl ester and p-chlorobenzenesulfonic acid ethyl ester. Advantages of using small molecule organic sulfonate rearrangement catalysts in such manufacturing processes include, inter alia, cost effectiveness and simplified catalyst recovery.

When R2 or R3 is H, the phosphinate of formula (I) can be prepared by reacting an alkyldichlorophosphine with an alcohol at a moderate temperature, as illustrated in Synthesis Example 2. This reaction, known as alcoholysis, results in partial oxidation of the phosphine to form the corresponding alkyl phosphinate ester, generating one P-H bond.

An illustrative example of this chemical reaction is presented in CN 113493478A, wherein methyldichlorophosphine is reacted with n-butanol at room temperature. The reaction produces n-butyl methyl phosphinate as the desired product, with hydrogen chloride and n-butyl chloride as byproducts.

The present invention also provides a flame retardant polymer obtained by reacting a monomer in the presence of a flame retardant comprising a phosphinate of the formula (I) under polymerization conditions.

The flame retardant polyurethane (PUR) of the present invention is a polyurethane composition comprising a phosphinate of formula (I) as a flame retardant. In one embodiment of the polyurethane composition, the phosphinate of formula (I) is present in an amount ranging from 0.5 wt% to 30 wt% based on the weight of the polyurethane. Preferably, the phosphinate of formula (I) is present in an amount ranging from 0.5 wt% to 20 wt% based on the weight of the polyurethane.

The flame-retardant polyurethane of the present invention is preferably obtained by reacting a polyol and an isocyanate in the presence of a flame retardant comprising a phosphinate of the formula (I), optionally in the presence of a polymerization catalyst. Suitable polymerization catalysts for the production of flame-retardant polyurethanes may be selected from aliphatic tertiary amines (e.g. triethylamine, tetramethylbutanediamine), cycloaliphatic tertiary amines (e.g. 1,4-diaza(2,2,2)bicyclooctane), aliphatic aminoethers (e.g. dimethylaminoethyl ether and N,N,N-trimethyl-N-hydroxyethyl-bisaminoethyl ether), cycloaliphatic aminoethers (e.g. N-ethylmorpholine), aliphatic amidines, cycloaliphatic amidines, ureas, urea derivatives (e.g. aminoalkyl ureas, cf. for example EP-A 0 176 013; in particular (3-dimethylaminopropylamine) urea) and tin catalysts (e.g. dibutyltin oxide, dibutyltin dilaurate, tin octoate).

One notable advantage of using the phosphinate of formula (I) as a flame retardant for polyurethanes is its high compatibility with polyols, an essential starting material for polyurethanes. The phosphinate of formula (I) readily dissolves in the polyol, forming a homogeneous solution that remains stable over extended periods of storage or transportation. This homogeneous solution serves as a beneficial starting material for polymerization, ensuring that the resulting polyurethane product exhibits consistently distributed flame retardancy throughout the entire polymer.

The present invention provides a method for producing a flame-retardant polyurethane, the method comprising the steps of: producing a mixture comprising a polyol and a flame retardant comprising a phosphinate of formula (I); and adding an isocyanate compound into the mixture.

For the purposes of the present invention, the term "polyol" refers to a compound having at least two hydrogen atoms capable of reacting with an isocyanate. These are compounds having amino, thio or carboxyl groups, preferably compounds having hydroxyl groups, especially compounds having from 2 to 8 hydroxyl groups.

Polyols suitable for the purposes of the present invention include polyols having a molecular weight (Mw) of from 400 to 10,000, in particular polyols having a molecular weight of from 1,000 to 6,000, preferably from 2,000 to 6,000, and are generally di- to octa-hydric, preferably di- to hexa-hydric polyethers or polyesters, or else polycarbonates or polyesteramides, which are known per se for the production of homogeneous or cellular polyurethanes and are described, for example, in DE-A 28 32 253.

Preferred polyester polyols are obtained by polycondensation of polyalcohols such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, methylpentanediol, 1,6-hexanediol, trimethylolpropane, glycerol, pentaerythritol, diglycerol, glucose and/or sorbitol with dibasic acids such as oxalic acid, malonic acid, succinic acid, tartaric acid, adipic acid, sebacic acid, maleic acid, fumaric acid, phthalic acid and/or terephthalic acid. These polyester polyols may be used alone or in combination.

For the production of thermosetting flame retardant polyurethanes, additional preferred groups of polyester polyols are those having two, three or four hydroxyl groups, including ethylene glycol, propylene glycol, trimethylolpropane and pentaerythritol.

Preferred polyether polyols include, but are not limited to, triols such as glycerol, trimethylolethane (i.e., 1,1,1-tris(hydroxymethyl)ethane) and trimethylolpropane (i.e., 1,1,1-tris(hydroxymethyl)propane); tetraols such as pentaerythritol; pentaols such as glucose; hexaols such as dipentaerythritol and sorbitol; or alkoxylated derivatives of all the above polyalcohols, including, but not limited to, ethoxylated and propoxylated derivatives thereof, preferably.

A particularly preferred polyether polyol is polyoxypropylene triol.

Other polyols suitable for the purposes of the present invention include polyols having a molecular weight of 30 to 400, which are preferably compounds having hydroxyl groups and/or amino groups and acting as chain extenders or cross-linking agents. Such compounds generally have 2 to 8, preferably 2 to 4, hydrogen atoms capable of reacting with isocyanates.

Suitable isocyanates used in the preparation of the flame-retardant polyurethane of the present invention may be selected, for example, from aliphatic, cycloaliphatic, araliphatic, aromatic or heterocyclic polyisocyanates (see, for example, W. Siefken in Justus Liebigs Annalen der Chemie, 562, pp. 75-136), for example from those of the formula Q(NCO) _r , wherein r is 2 to 4, preferably 2 or 3, and Q is an aliphatic hydrocarbon radical having 2 to 18 carbon atoms, preferably 6 to 10 carbon atoms, an alicyclic hydrocarbon radical having 4 to 15 carbon atoms, preferably 5 to 10 carbon atoms, an aromatic hydrocarbon radical having 6 to 15 carbon atoms, preferably 6 to 13 carbon atoms, or an aromatic hydrocarbon radical having 8 to 15 carbon atoms, preferably It is an araliphatic hydrocarbon radical having 8 to 13 carbon atoms.

Polyisocyanates suitable for the purposes of the present invention are aromatic, cycloaliphatic and/or aliphatic polyisocyanates having at least two isocyanate groups and mixtures thereof. Aromatic polyisocyanates such as tolyl diisocyanate, methylene diphenyl diisocyanate, naphthylene diisocyanate, xylylene diisocyanate, tris(4-isocyanatophenyl)methane and polymethylene-polyphenylene diisocyanate; Aliphatic polyisocyanates such as methylenediphenyl diisocyanate and tolyl diisocyanate; Aliphatic polyisocyanates and hexamethylene diisocyanate, isophorone diisocyanate, dimeryl diisocyanate, 1,1-methylenebis(4-isocyanatocyclohexane-4,4'-diisocyanatodicyclohexylmethyl and isomer mixtures, 1,4-cyclohexyl diisocyanate and lysine diisocyanate and mixtures thereof are preferred.

In general, polyisocyanates readily available in the industry, such as 2,4- and 2,6-toluene diisocyanate, and methylene diphenyl isocyanate (MDI) or its polymer form (pMDI) are particularly preferred.

For the purposes of the present invention, the flame-retardant polyurethane may be, for example, a linear PUR prepared by a diol and a diisocyanate, or a crosslinked PUR prepared by, for example, converting a triisocyanate-diisocyanate mixture using a triol-diol mixture. The properties of the flame-retardant polyurethane can vary widely. Depending on the degree of crosslinking and/or the isocyanate or OH component used, a thermoset, a thermoplastic, or an elastomer is obtained.

The flame-retardant polyurethane of the present invention may be a flame-retardant polyurethane foam used as a flexible or rigid foam or alternatively as a molding compound for molding, a casting resin (isocyanate resin), (textile) elastic fiber, a polyurethane coating and a polyurethane adhesive.

The present invention also provides a flame-retardant polyurethane foam obtained by reacting a polyol and an isocyanate in the presence of a flame retardant comprising a phosphinate of the formula (I), and further in the presence of a blowing agent, a foaming catalyst, a foam stabilizer, and optionally other additives.

In a preferred embodiment of the present invention, the flame retardant polyurethane foam of the present invention is a flexible foam.

In another preferred embodiment of the present invention, the flame retardant polyurethane foam of the present invention is a rigid foam.

For the purposes of the present invention, the term "blowing agent" refers to a substance capable of providing gas in a polyol-isocyanate reaction and producing a foam with a cellular structure. Any conventional blowing agent for the production of polyurethane foams, including physical blowing agents and chemical blowing agents, is suitable for use herein. Examples of physical blowing agents include butane and carbon dioxide, which expand at reduced pressure, as well as short-chain (C ₅ -C ₆ ) aliphatic molecules such as pentane or cyclopentane, and various hydrofluoroolefins such as 1,3,3,3-tetrafluoropropene, which are low-boiling liquids. Examples of chemical blowing agents include water and carboxylic acids, which release gas upon reaction with an isocyanate. A particularly preferred blowing agent is water.

For the purposes of the present invention, suitable blowing catalysts for the production of the flame-retardant polyurethane foam of the present invention are preferably selected from amine catalysts (e.g., tertiary amines) and organometallics (e.g., stannous octoate, stannous acetate, dibutyltin diacetate, etc.).

For the purposes of the present invention, a suitable foam stabilizer for producing flame-retardant polyurethane foam may be any conventional stabilizer for controlling and stabilizing polyurethane foam. As a preferred example, the stabilizer may be selected from silicone surfactants.

For the production of the flame-retardant polyurethane foam according to the present invention, other additives including fillers, pigments, light stabilizers and processing aids may be added to the reactant mixture.

The present invention also relates to the use of the above-mentioned flame-retardant polyurethane or flame-retardant polyurethane foam for the manufacture of doorliners, headliners, seat covers, high-resilience foam seating, high-resilience foam mattresses, rigid foam insulation panels, viscoelastic foam mattresses, potting foam for battery applications, microcellular foam seals and gaskets, durable elastomeric wheels or tires, automotive suspension bushings, electrical potting compounds, high-performance adhesives, surface coatings and sealants, synthetic fibers, carpet underlay, hard-plastic parts and hoses.

The present invention also relates to the use of flame retardant polyurethane or flame retardant polyurethane foam for the manufacture of electrical switch components, components in automobile construction, electrical engineering or electronics, printed circuit boards, prepregs, potting compounds for electronic components, boat and rotor blade construction, outdoor GFRP applications, household and sanitary applications and engineering materials.

Example

Hereinafter, the present invention will be described in more detail and specifically with reference to examples, but these are not intended to limit the present invention.

1. Ingredients used:

Flame retardant :

FR-1 : Ethyl ethyl (methyl) phosphinate (MEPE) product of Synthesis Example 1

FR-2 : Butyl methylphosphinate product of Synthesis Example 2

FR-3 : Butyl butyl (methyl) phosphinate (MUPU) product of Synthesis Example 3

Ref-1 : Fyrol® PCF, TCPP (tris(1-chloro-2-propyl)phosphate), halogenated phosphate ester from ICL Industrial Products

Ref-2 : Exolit® OP 55 from Clariant International Ltd, a non-halogenated, polymeric phosphorus polyol specifically designed for flexible polyurethane foams, a phosphate ester with hydroxyalkyl groups.

Polyol :

Polyether polyol ( P1 ): Arcol® 1104 or 1108 from Covestro AG, medium molecular weight polyoxypropylene triol with an OH number of 56 mg KOH/g

Polyester polyol ( P2 ): Terate® HT 5510, an aromatic polyester polyol from Stepan Company with a hydroxyl number of 257 mg KOH/g

Polymerization catalyst :

Cat 1: Kosmos® EF, a tin(II) (stannous) catalyst from Evonik Industries

Cat 2: Kosmos® 29 from Evonik Industries, tin(II) octoate catalyst

Cat 3: Niax® A1, an amine catalyst based on bis(2-dimethylaminoethyl)ether from Momentive Performance Materials Inc.

Category 4: Tegoamin® 33 from Evonik Industries, an amine catalyst based on triethylenediamine

Cat 5: JEFFCAT® ZF-10 from Huntsman, an amine catalyst based on N,N,N'-trimethyl-N'-hydroxyethylbisaminoethyl ether

Cat 6: Polycat 5 from Evonik Industries, an amine catalyst based on bis(2-dimethylaminoethyl)methylamine

Category 7: Kosmos 75 MEG from Evonik Industries, a foam catalyst based on low-viscosity potassium octoate.

Foam stabilizer :

S1: Tegostab® B 8232, silicone surfactant from Evonik Industries

S2: Tegostab® B 8522, silicone surfactant from Evonik Industries

TDI (tolyl diisocyanate) :

T80: Desmodur® T80, 2,4- and 2,6-toluene diisocyanate from Covestro AG, 80/20 mixture of isomers

MDI (methylene diphenyl diisocyanate) :

MDI1: Desmodur® 44 V 70 L from Covestro AG is a mixture of diphenylmethane-4,4'-diisocyanate (MDI) with isomers and higher functional homologues (PMDI).

2. Synthesis examples for flame retardants FR-1, FR-2 and FR-3 of the present invention

2.1. Synthesis Example 1: Preparation of FR-1

Step 1: Preparation of diethyl methylphosphonite

A mixture of 5280 g of petroleum ether, 413 g of absolute ethanol, and 1100 g of triethylamine was added to a 25 L autoclave equipped with a thermometer and a condenser. The reaction system was purged with nitrogen three times, and a solution of 501 g of methyldichlorophosphane was added dropwise at 25°C. After the addition was complete, the temperature was maintained at 25°C for 30 minutes.

The resulting reaction mixture was then subjected to pressure filtration to remove the resulting NEt ₃ ·HCl. The resulting filter cake was washed with 1000 mL of petroleum ether. The filtrate, weighing 6590 g, was then subjected to distillation to recover the petroleum ether and obtain the crude product of diethyl methylphosphonite.

Finally, 557.8 g of diethyl methylphosphonite was obtained through rectification. The purity detected by gas chromatography (GC) was 98.5%, and the yield was 96.1%.

Step 2: Preparation of ethyl ethyl(methyl)phosphinate (FR-1)

A mixture of 557.0 g of diethyl methylphosphonite and 27.50 g of p-toluenesulfonate was added to a 1 L three-necked flask equipped with a thermometer and condenser. The flask was then purged with N ₂ . The temperature was gradually increased, and the reaction mixture was stirred vigorously and refluxed. The oil temperature before insulation slowly increased from 120°C to 170°C. After 9 hours, no significant reflux was observed (less than 0.5% of the raw material was detected by GC), indicating the completion of the reaction.

Finally, 535.0 g of FR-1 product having a viscosity of 3.5 mPa·s was obtained by vacuum distillation (2 to 3 kPa, 101°C). The purity of the product was 98% as determined by GC, and the yield was 98%.

2.2. Synthesis Example 2: Preparation of FR-2

Methyldichlorophosphane was continuously fed into a vaporizer at a flow rate of 119.39 g/h. The vaporized methyldichlorophosphane was then transferred to a tower continuous reactor using a nitrogen flow at a rate of 80 ml/min.

Simultaneously, 99.5% n-butanol was introduced into another evaporator at a rate of 243 g/h. The vaporized butanol was purged into the tower reactor using a nitrogen flow at a rate of 80 ml/min. Subsequently, the vaporized methyldichlorophosphane and n-butanol were rapidly reacted in the tower reactor.

The light fraction of chloro-butane produced by the rapid reaction was condensed and collected in a low-boiling material receiving bottle. The heavy fraction of crude butyl methylphosphinate produced during the reaction process was collected in a separate receiving bottle and subsequently neutralized using triethylamine.

After neutralization, n-butanol was removed by vacuum distillation. The process produced 96.0% butyl methylphosphinate with a viscosity of 3.4 mPa·s and a purity of 98.5%, which was obtained through rectification.

2.3. Synthesis Example 3: Preparation of FR-3

Step 1: Preparation of dibutyl methylphosphonite

A mixture of 6,200 g of petroleum ether, 674 g of anhydrous n-butanol, and 910 g of triethylamine was added to a 25 L autoclave equipped with a thermometer and condenser. The reaction system was purged with nitrogen three times, and then a solution of 507 g of methyldichlorophosphane was added dropwise at a temperature of -10°C. After the addition was complete, the temperature was maintained at 0°C for 30 minutes.

The resulting reaction mixture was then subjected to pressure filtration to remove the resulting NEt ₃ ·HCl. The resulting filter cake was washed with 1000 mL of petroleum ether. The filtrate, weighing 7506 g, was then subjected to distillation to recover the petroleum ether, yielding the crude product of dibutyl methylphosphonite.

Finally, 756.7 g of dibutyl methylphosphonite was obtained through rectification. The purity detected by gas chromatography (GC) was 95%, and the yield was 88%.

Step 2: Preparation of butyl butyl (methyl) phosphinate (FR-3)

A mixture of 600 g of dibutyl methylphosphonite and 30 g of p-toluenesulfonate was added to a 1 L three-necked flask equipped with a thermometer and condenser. The flask was then purged with N ₂ . The temperature was gradually increased, and the reaction mixture was stirred vigorously and refluxed slightly. The oil temperature before insulation was slowly increased from 150°C to 180°C. After 6 hours, less than 0.5% of the raw material was detected by GC, indicating the completion of the reaction.

Finally, 571 g of FR-3 product having a viscosity of 6.4 mPa·s was obtained by vacuum distillation (0.2 to 0.3 kPa, 86°C). The purity of the product was 98% as determined by GC, and the yield was 98.0%.

3. Hydrolysis stability comparison test

The hydrolytic stability provided by different flame retardants was compared by measuring the acid value of polyol blends containing flame retardants and water over time during storage at elevated temperature. For this purpose, 90 g of polyol, 9 g of flame retardant, and 4.5 g of water were homogenized by stirring at 1500 rpm for 2 minutes. The acid value was then determined using a 3:1 (v/v) isopropanol/water mixture as the solvent and a 0.1 N NaOH (aq.) solution as the titration agent. The samples were then stored at 40°C, and the acid value was determined after 11, 17, and 28 days. Prior to analysis, the samples were homogenized by stirring at 1500 rpm for 2 minutes. The acid value evolution of polyol-water blends without flame retardants was also determined after 11 and 28 days, respectively, as shown in Table 1 below.

[Table 1]

Comparison of hydrolytic stability: Evaluation of acid value of polyol blends containing flame retardants and water over time during storage at 40°C.

Compared to the flame retardant-free reference, Example FR-1 of the present invention did not cause a noticeable increase in the acid value of their polyol blends during and after a total of 28 days of storage at 40°C. This indicates the high hydrolytic stability of FR-1 during storage within the polyol blend, i.e., no or negligible hydrolysis of FR-1. In comparison, the acid value of the polyol blend containing Ref-2 increased significantly after only 11 days under the same storage conditions, which can only be explained by the hydrolysis of Ref-2.

4. Comparison of viscosity of polyol-flame retardant mixtures

As mentioned above, the viscosity of the liquid flame retardants of the present invention is advantageously low, which facilitates processing and handling in industrial applications. In the synthetic examples provided, both FR-1 and FR-2 have viscosities of less than 5 mPa·s, FR-3 has a viscosity of less than 7 mPa·s, whereas TCPP (Ref-1) typically has a viscosity ten times higher (60 to 70 mPa·s) at room temperature as measured by DIN 51398.

In Table 2 below, the viscosity is compared between neat polyol (P2) and mixtures of polyol (P2) with flame retardants (FR-1, FR-2, FR-3, or Ref-1). The polyol-flame retardant mixtures were prepared by combining polyol P2 with the specified flame retardant (FR-1, FR-2, FR-3, or Ref-1) in a weight ratio of 89.5:10.5 at room temperature. The mixtures were thoroughly mixed using a mechanical stirrer at 1000 rpm for 1 minute to ensure homogeneity. The dynamic viscosity of the neat polyol and the polyol-flame retardant mixtures was then measured according to DIN 51398.

[Table 2]

Viscosity at room temperature for pure polyols and polyol-flame retardant blends

From the data in Table 2, it was observed that the liquid flame retardant of the present invention has additional advantages over conventional liquid flame retardants, such as TCPP (Ref-1), in effectively reducing the viscosity of polyol-flame retardant mixtures during the blending process. Utilizing these advantageous properties in polymer manufacturing can further improve overall processability.

5. Flexible polyurethane (PUR) foam formulation and performance testing

The tin(II) catalyst, polyol, flame retardant, water, foam stabilizer, and amine catalyst were weighed and placed in a dry beaker in the above order, and premixed at 500 rpm (for polyether polyol blends) or 1000 rpm (for polyester polyol blends) for 60 seconds, respectively. After the addition of TDI, the mixture was stirred at 2500 rpm for 7 seconds. The resulting mass was quickly poured into a paper-lined box mold (25*26*26 cm). The rise time and further observations were recorded during the foaming process. The foams were cured at room temperature for about 16 hours before cutting and collected from each of the comparative examples (C1 to C3) or the inventive examples (I1 to I2) for further evaluation.

The selection of polymerization catalyst, foam stabilizer and TDI for each foam example was based on existing empirical guidelines for optimal foamability in each case, details of which are listed in Table 3 below.

[Table 3]

Polyol, flame retardant, catalyst, foam stabilizer and TDI for each PUR foam example

Evaluation of Flame Retardancy for Flexible Foams (FMVSS 302)

The effectiveness of flame retardants was evaluated by testing the combustion behavior of flexible polyurethane foam samples containing flame retardants and having a target density of 30 kg/m ³ in a horizontal burn test as described in Federal Motor Vehicle Safety Standard 302 (FMVSS 302). The foam density in the examples was measured according to DIN 53420. According to this standard, a sample is assigned the highest rating (SE, "self-extinguishing") if the flame does not travel beyond a 38 mm mark on the specimen and is extinguished within this distance. Subratings include SE/NBR (no self-extinguishing/burn rate), SE/B (self-extinguishing/burn rate), and B (burn rate). Five sample specimens were cut from each foam and submitted to the test. The specimen with the lowest rating determined the overall rating for the foam.

The flame retardancy of the tested flexible foam examples is compared in Table 4 below.

[Table 4]

Performance data for flexible polyurethane polyether (P1) foam formulations

*All ingredient quantities are given in parts (php) per hundred parts of polyol by weight.

As shown in the performance data listed in Table 4, Comparative Example C1 (polyether polyurethane foam without flame retardant additive) does not meet the required flame retardancy standards. Using a halogenated reference flame retardant TCPP (Ref-1) 12 php, Comparative Example C2 provides a polyether polyurethane foam that meets the required flame retardancy. As shown in Comparative Example C3, when the amount of flame retardant was reduced to 8 php TCPP, it was found that the amount of flame retardant was insufficient and the resulting foam did not achieve optimal flame retardancy (SE).

Example I1 of the present invention demonstrates the efficacy of the non-halogenated flame retardant (FR-1) of the present invention in achieving optimal flame retardancy standards for polyether polyurethane foams even at low loadings of only 4 php.

Example I2 of the present invention, which is a polyether polyurethane foam containing the non-halogenated flame retardant (FR-2) 4 php of the present invention, exhibits a flame retardancy grade that is equally excellent as I1.

6. Rigid polyisocyanurate (PIR) foam formulation and performance testing

The octoate catalyst, polyol, flame retardant, water, foam stabilizer, and amine catalyst were weighed and placed in a dry beaker in the above order and premixed at 1000 rpm for 50 seconds. After adding n-pentane, the mixture was stirred at 1000 rpm for 10 seconds to incorporate it into the mixture. MDI was then added to the mixture, and the liquid was mixed at 2500 rpm for 7 seconds. The resulting mass was quickly poured into a paper-lined box mold (25*26*26cm). The rise time and further observations were recorded during the foaming process. The foam was cured at room temperature for approximately 16 hours before cutting and collected from each of the comparative examples (C4 to C6) or the inventive examples (I3 to I4) for further evaluation.

The selection of polymerization catalyst, foam stabilizer and MDI for each rigid foam embodiment was based on existing empirical guidelines for optimal foamability in each case, details of which are listed in Table 5 below.

[Table 5]

Polyol, flame retardant, catalyst, foam stabilizer and MDI used in PIR foam examples

Method for evaluating the flame retardancy of rigid foams (DIN4102-1)

DIN 4102-1 classifies building materials according to their flammability. The valid standard distinguishes between two fire protection classes: 'A' for non-combustible materials and 'B' for combustible materials. Class B is suitable for polyurethane foams such as PIR insulation panels. It is further subdivided into the following levels: B1 = low flammability; B2 = moderate flammability; B3 = high flammability. For reference, most spray-can construction foam systems sold in Germany fall into building material class B2. The primary criterion for classifying B2 flammability is the flame height in a vertical burning test, which must remain below 150 mm. This is an ideal guideline for benchmarking the flame resistance of building materials.

The flame retardancy of different stiffness PIR foam samples was evaluated using DIN4102-1 and is listed in Table 6 below.

[Table 6]

Performance data for rigid polyisocyanurate polyester (P2) foam formulations

*All ingredient quantities are given in parts per hundred parts polyol (php) by weight.

As shown in the performance data listed in Table 6, Comparative Example C4 (PIR foam without flame retardant additive) does not meet the desired flame retardancy standard grade B2. By incorporating 15 php of the halogenated reference flame retardant TCPP (Ref-1), Comparative Example C5 exhibits a rigid PIR foam with the desired flame retardancy grade. However, as demonstrated in Comparative Example C6, when attempting to reduce the amount of this halogenated flame retardant to 12 php TCPP, it was observed that this reduced level of flame retardant was insufficient and the foam did not achieve the desired flame retardancy grade.

Example I3 of the present invention demonstrates excellent flame retardancy achieved by incorporating the same level of 12 php of the non-halogenated flame retardant FR-1 of the present invention into a rigid PIR foam, meeting optimal flame retardancy standards.

Similarly, Examples I4 and I5 of the present invention achieve equally excellent flame retardancy ratings by replacing FR-1 with FR-2 or FR-3, respectively, at the same level as in I3. This further emphasizes the effectiveness of the non-halogenated flame retardant of the present invention in achieving the desired flame retardancy level in rigid foams.

Claims (15)

A flame-retardant polyurethane obtained by reacting a polyol and an isocyanate in the presence of a flame retardant comprising a phosphinate of the following chemical formula (I):

In the above formula, R1 is a hydrocarbon radical selected from C ₁ -C ₁₂ alkyl and C ₆ -C ₂₀ aryl groups;
R2 and R3 are the same or different and independently represent H or C ₁ -C ₁₂ alkyl. A flame retardant polyurethane in claim 1, wherein R1 is selected from C1-C6 alkyl, preferably C2-C4 alkyl. A flame-retardant polyurethane according to claim 1 or 2, wherein R2 and R3 are not H at the same time. A flame retardant polyurethane in claim 3, wherein one of R2 and R3 is H or ethyl, and the other is C1-C6 alkyl. A flame retardant polyurethane in claim 3, wherein one of R2 and R3 is methyl and the other is H or C1-C4 alkyl. A flame retardant polyurethane in claim 1, wherein R1 is ethyl, one of R2 and R3 is methyl, and the other is ethyl. A flame retardant polyurethane in claim 1, wherein R1 is butyl, one of R2 and R3 is methyl, and the other is H. A flame retardant polyurethane in claim 1, wherein R1 is butyl, one of R2 and R3 is methyl, and the other is butyl. A flame-retardant polyurethane foam, wherein the flame-retardant polyurethane foam is obtained by reacting a polyol and an isocyanate in the presence of a flame retardant as defined in any one of claims 1 to 8, and further in the presence of a blowing agent, a foaming catalyst, and a foam stabilizer. A flame-retardant polyurethane foam according to claim 9, wherein the flame-retardant polyurethane foam is a flexible foam. A flame-retardant polyurethane foam according to claim 9, wherein the polyurethane foam is a rigid foam. A flame-retardant polyurethane according to any one of claims 1 to 8 or a flame-retardant polyurethane according to any one of claims 9 to 11 for the manufacture of doorliners, headliners, seat covers, high-resilience foam seating, high-resilience foam mattresses, rigid foam insulation panels, viscoelastic foam mattresses, potting foam for battery applications, microcellular foam seals or gaskets, durable elastomeric wheels or tires, automotive suspension bushings, electrical potting compounds, high-performance adhesives, surface coatings or sealants, synthetic fibers, carpet underlays or hard-plastic parts or hoses. Uses of polyurethane foam. A method for producing a flame-retardant polyurethane according to any one of claims 1 to 8, wherein the method comprises:
A manufacturing method comprising: a step of manufacturing a mixture containing a polyol and a flame retardant; and a step of adding an isocyanate compound into the mixture. Use of phosphinates of the following formula (I) as flame retardants for polyurethanes:

In the above formula, R1 is a hydrocarbon radical selected from C ₁ -C ₁₂ alkyl and C ₆ -C ₂₀ aryl groups;
R2 and R3 are the same or different and independently represent H or C ₁ -C ₁₂ alkyl. A flame retardant polyurethane composition comprising a phosphinate of the following chemical formula (I) as a flame retardant:

In the above formula, R1 is a hydrocarbon radical selected from C ₁ -C ₁₂ alkyl and C ₆ -C ₂₀ aryl groups;
R2 and R3 are the same or different and independently represent H or C ₁ -C ₁₂ alkyl.