TW202506866A - Flame-retardant polyurethane and uses thereof - Google Patents

Abstract

A flame-retardant polyurethane obtained by reacting a polyol and an isocyanate in the presence of a flame retardant comprising a phosphinate of formula (I): wherein R1 is a hydrocarbyl radical selected from C1-C12 alkyl and C6-C20 aryl groups; and wherein R2 and R3, which are the same or different, independently denote H or a C1-C12 alkyl.

Description

Flame retardant polyurethane and its use

The present invention relates to a flame retardant polyurethane containing a specific type of phosphinate flame retardant, a preparation method thereof and industrial use thereof.

To achieve the desired flame retardancy for industrial use, combustion-modified polyurethanes are often blended with at least one type of flame retardant. In these applications, liquid flame retardants are often preferred over their solid counterparts. This preference stems from several favorable properties: Compared to solid flame retardants, liquid flame retardants can be more easily and evenly dispersed or even dissolved in the polymer during the blending process, thereby providing a consistent flame retardant effect throughout the process. In addition, liquid flame retardants can often be processed at lower temperatures than solids, alleviating potential polymer degradation issues associated with high temperatures. Due to their larger interactive surface area, these liquid additives can be mixed into the resin mixture faster than solids. Additionally, liquid flame retardants are generally easier to handle during blending with polyols, allowing precise dosage control and seamless integration into polymer formulations.

TCPP (tris(1-chloro-2-propyl) phosphate) is a popular liquid flame retardant widely used in the industry and is often mixed into polyurethane foams in consumer products, home insulation materials, and electronic products. However, although TCPP provides effective flame retardancy, it has been found that TCPP will escape into the environment over time, causing negative toxicological and ecotoxicological effects due to its halogenated nature. In addition, the leaching of TCPP flame retardant will cause the overall flame retardant effect to weaken over time.

US 9 631 144 B2 describes a different liquid flame retardant composition comprising one or more halogenated flame retardants, which are brominated epoxides obtained by reacting tetrabromobisphenol A with epichlorohydrin. This particular liquid flame retardant is said to provide stable mixing into rigid polyurethane foams and exhibit good flame retardancy. However, it is worth noting that in the examples provided in US 9 631 144 B2, the brominated epoxide is obtained in the form of a resin with a high softening point, requiring further processing at high temperatures. In addition, the resulting liquid flame retardant composition is characterized by a high bromine content of at least 30% by weight.

In view of the increasing concern about halogenated flame retardants for environmental protection, efforts are constantly being 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, and the phosphate is of the following formula (1), wherein: n is 0 to 10, R is a C ₁ -C ₁₀ (halogen) alkyl group, and R ₁ and R ₂ are hydrogen atoms or C ₁ -C ₁₀ (halogen) alkyl groups.

US 7 288 577 B1 describes a blend of two different phosphate flame retardants for polyurethanes, which consists essentially of: (a) 50% by weight of the blend of butylated triphenyl phosphate and (b) 50% by weight of the blend of poly(ethylethyleneoxy)phosphate.

Although the aforementioned patent disclosures may have mentioned some effective liquid phosphorus-based flame retardants, it has been found that some of them are susceptible to hydrolysis under humid conditions, which in turn leads to adverse effects on the polymerization process or the final polymer properties. In particular, it is known that the acid formed by hydrolysis can inactivate the polymerization catalyst during the foaming process and further cleave the covalent bonds in the polymer foam product, thereby destroying the expected 3-D foam network.

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

Antiblaze® 1045 has a high viscosity, typically 500,000 mPa·s or more at 25°C. Therefore, its effective use may involve careful impregnation onto a carrier material or delicate application onto the surface of a polymer fiber as an aqueous solution. In the latter case, subsequent heating is required to achieve softening of the fiber and dissolution of the cyclic phosphonate to obtain the desired result.

The object of the present invention is to provide a novel non-halogenated flame retardant for polyurethane, and in particular polyurethane foam, which is in liquid form at room temperature and under conventional polyurethane manufacturing conditions, has a suitably low viscosity for easy processing and handling, exhibits excellent hydrolytic stability even under humid conditions, and produces the same or enhanced degree of flame retardancy in polyurethane materials compared to existing commercial standards.

The object of the present invention is to provide a flame retardant polyurethane, in particular a polyurethane foam, which achieves excellent flame retardant efficiency by combining the above-mentioned non-halogenated flame retardant.

The present invention provides a use of a phosphinate of formula (I) as a polyurethane flame retardant. wherein R1 is a alkyl group selected from C ₁ -C ₁₂ alkyl and C ₆ -C ₂₀ aryl; and wherein 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 composition, which is obtained by reacting a polyol and an isocyanate in the presence of a flame retardant comprising a phosphinate of formula (I).

Unless otherwise specified, the term "alkyl group" used herein refers to an aliphatic group, an aromatic group, or an alicyclic group, which may be saturated or unsaturated, straight chain or branched, and optionally substituted with heteroatoms (eg, O, N, S).

Preferably, R1 is selected from C ₁ -C ₆ alkyl, more preferably selected from C ₂ -C ₄ 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 C ₁ -C ₆ alkyl.

In another preferred embodiment of the present invention, one of R2 and R3 is methyl and the other is H or C ₁ -C ₄ 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.

Due to its chemical nature, the phosphinate flame retardant of the present invention is in liquid form at room temperature and under conventional polyurethane manufacturing conditions. Advantageously, the liquid form of the phosphinate flame retardant is further characterized by a low viscosity of less than 100 mPa·s, preferably less than 50 mPa·s, and more preferably less than 10 mPa·s at a temperature of 25°C. Viscosity can be measured by DIN51398. As mentioned previously in the above text, the advantageous property of low viscosity can play an important role in the practical application of liquid flame retardants in the manufacture of flame retardant polyurethanes. There are challenges in utilizing viscous liquid flame retardants because they typically require heating of containers, feed pipes, and discharge pipes involved in liquid storage or transportation. Furthermore, additional efforts are often required to obtain uniform mixing of high-viscosity flame retardant liquids into polymer compositions, especially in scaled-up industrial processes for large-volume chemical production.

The phosphinates of formula (I) can be prepared by various methods. One method is to react an α-monoolefin with an alkyl phosphinate in the presence of a free radical generator, as described in US Pat. No. 3,914,345 A, EP Pat. No. 2,373,666 A1, US Pat. No. 8,735,477 B2 and EP Pat. No. 2,367,834 A1.

The phosphite of formula (I) can also be prepared from its corresponding phosphite by catalytic rearrangement reaction. For example, the corresponding phosphite is the structure of the following formula (II):

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

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

Advantageously, the rearrangement catalyst can be a small organic molecule sulfonate, and more advantageously is selected from the group consisting of diethyl sulfate, ethyl ethanesulfonate, methyl p-toluenesulfonate, ethyl p-toluenesulfonate, methyl p-chlorobenzenesulfonate and ethyl p-chlorobenzenesulfonate. In addition, the benefits of using a small organic molecule sulfonate rearrangement catalyst in this preparation process include cost effectiveness and simplified catalyst recovery.

When either R2 or R3 is hydrogen, the phosphinate of formula (I) can be prepared by reacting an alkyl dichlorophosphine with an alcohol at moderate temperature, as shown in Synthesis Example 2. This reaction, known as alcoholysis, results in partial oxidation of the phosphine, resulting in the formation of the corresponding alkyl phosphinate, while generating a P-H bond.

CN 113493478A presents an illustrative example of this chemical reaction, in which methyl dichlorophosphine is reacted with n-butanol at room temperature. This reaction produces n-butyl methylphosphinate as the desired product, with hydrogen chloride and n-butyl chloride formed as byproducts.

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

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 of 0.5 wt % to 30 wt % relative to the weight of the polyurethane. Preferably, the phosphinate of formula (I) is present in an amount of 0.5 wt % to 20 wt % relative to 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 formula (I) and optionally in the presence of a polymerization catalyst. Suitable polymerization catalysts for the preparation of flame retardant polyurethanes can be selected from aliphatic tertiary amines (e.g. triethylamine, tetramethylbutanediamine), alicyclic tertiary amines (e.g. 1,4-diaza(2,2,2)biscyclooctane), aliphatic amino ethers (e.g. dimethylaminoethyl ether and N,N,N-trimethyl-N-hydroxyethyl-bisaminoethyl ether), alicyclic amino ethers (e.g. N-ethylmorpholine), aliphatic amidines, alicyclic amidines, urea, urea derivatives (e.g. aminoalkyl urea, see e.g. EP-A 0 176 013, in particular (3-dimethylaminopropylamine) urea), and tin catalysts (e.g. dibutyltin oxide, dibutyltin dilaurate, tin octoate).

One significant advantage of using the phosphinate of formula (I) as a polyurethane flame retardant is its high compatibility with polyols, an essential starting material for polyurethanes. The phosphinate of formula (I) can be easily dissolved in polyols to form a homogeneous solution that remains stable over a long period of time during storage or transportation. This homogeneous solution can serve as a useful starting material for polymerization, ensuring that the resulting polyurethane product always has a uniform distribution of flame retardancy.

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

For the purposes of the present invention, the term "polyol" refers to compounds having at least two hydrogen atoms capable of reacting with isocyanates. These are compounds having amino, thio or carboxyl groups and preferably having hydroxyl groups, in particular 2 to 8 hydroxyl groups.

Suitable polyols for the purposes of the present invention include those having a molecular weight (Mw) of 400 to 10,000, in particular those having a molecular weight of 1000 to 6000, preferably 2000 to 6000, and generally di- to octa-, preferably di- to hexa-hydric polyethers or polyesters, or other polycarbonates or polyesteramides as are known per se for the preparation of homogeneous polyurethanes or cellular polyurethanes (and described, for example, in DE-A 28 32 253).

Preferred polyester polyols are obtained by condensing polyols such as ethylene glycol, diethylene glycol, propylene glycol, 1,4-butanediol, 1,5-pentanediol, methylpentanediol, 1,6-hexanediol, trihydroxymethylpropane, 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 can be used alone or in combination.

For the production of thermosetting flame retardant polyurethanes, other preferred groups of polyester polyols are those with two, three or four hydroxyl groups, including ethylene glycol, propylene glycol, trihydroxymethylpropane and pentaerythritol. Preferred polyether polyols include but are not limited to triols, such as glycerol, trihydroxymethylethane (i.e., 1,1,1-tri(hydroxymethyl)ethane), and trihydroxymethylpropane (i.e., 1,1,1-tri(hydroxymethyl)propane); tetraols, such as pentaerythritol; pentaols, such as glucose; hexaols, such as dipentaerythritol and sorbitol; or alkoxylated derivatives of all the above polyols, such as preferably ethoxylated derivatives and propoxylated derivatives thereof.

A particularly preferred polyether polyol is polyoxypropylene triol.

Other suitable polyols for the purposes of the present invention include low molecular weight polyols of 30 to 400, preferably compounds having hydroxyl and/or amine groups and acting as chain extenders or crosslinkers. These compounds generally have 2 to 8, preferably 2 to 4 hydrogen atoms capable of reacting with isocyanates.

Suitable isocyanates for preparing the flame retardant polyurethanes of the present invention can 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, of the formula Q(NCO) _r , wherein r is 2 to 4 (preferably 2 to 3), and Q is an aliphatic hydrocarbon group having 2 to 18 carbon atoms (preferably 6 to 10 carbon atoms), an alicyclic hydrocarbon group having 4 to 15 carbon atoms (preferably 5 to 10 carbon atoms), an aromatic hydrocarbon group having 6 to 15 carbon atoms (preferably 6 to 13 carbon atoms), or an aromatic aliphatic hydrocarbon group having 8 to 15 carbon atoms (preferably 8 to 13 carbon atoms).

Suitable polyisocyanates for the purposes of the present invention are aromatic, cycloaliphatic and/or aliphatic polyisocyanates having at least two isocyanate groups and mixtures thereof. Preferred are aromatic polyisocyanates such as tolyl diisocyanate, methylene diphenyl diisocyanate, naphthalene diisocyanate, xylyl diisocyanate, tris(4-isocyanatophenyl)methane and polymethylene-polyphenylene diisocyanate; cycloaliphatic polyisocyanates such as methylene diphenyl diisocyanate and tolyl diisocyanate; aliphatic polyisocyanates and hexamethylene diisocyanate, isophorone diisocyanate, dimer diisocyanate, 1,1-methylenebis(4-isocyanatocyclohexane-4,4'-diisocyanatodicyclohexyl methyl ether) and isomer mixtures, 1,4-cyclohexyl isocyanate, and lysine diisocyanate and mixtures thereof.

Industrially readily available polyisocyanates such as 2,4-tolyl diisocyanate and 2,6-tolyl diisocyanate, and methylene diphenyl isocyanate (MDI) or its polymeric form (pMDI) are particularly preferred.

For the purposes of the present invention, the flame-retardant polyurethanes can be linear PURs (produced, for example, from diols and diisocyanates) or crosslinked PURs (produced, for example, by converting triisocyanate-diisocyanate mixtures using triol-diol mixtures). The properties of the flame-retardant polyurethanes can be varied within a wide range. Depending on the degree of crosslinking and/or the isocyanate or OH component used, thermosetting plastics, thermoplastics or elastomers are obtained.

The flame retardant polyurethane of the present invention can be a flame retardant polyurethane foam as a soft foam or a hard foam, or alternatively as a molding compound for molding, as a casting resin (isocyanate resin), as a (textile) elastic fiber, a polyurethane coating and as 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 formula (I) (and further in the presence of a blowing agent, a blowing catalyst, a foam stabilizer and optionally other additives).

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

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

For the purpose of the present invention, the term "blowing agent" refers to a substance that can provide gas in the polyol-isocyanate reaction and produce a foam with a porous structure. Any known blowing agent used to make polyurethane foams is suitable for use herein, including physical blowing agents and chemical blowing agents. Examples of physical blowing agents include butane and carbon dioxide that expand under reduced pressure, as well as short-chain ( _C5 - _C6 ) aliphatic molecules such as pentane or cyclopentane and various hydrofluoroolefins such as 1,3,3,3-tetrafluoropropylene, which are low-boiling liquids. Examples of chemical blowing agents include water and carboxylic acids, which release gas when reacting with isocyanates. A particularly preferred blowing agent is water.

For the purpose of the present invention, suitable foaming catalysts for preparing the flame-retardant polyurethane foams of the present invention are preferably selected from amine catalysts (e.g., tertiary amines) and organometallic compounds (e.g., stannous octoate, stannous acetate, dibutyltin diacetate, etc.).

For the purpose of the present invention, suitable foam stabilizers for making flame retardant polyurethane foams can be any known stabilizers for controlling and stabilizing polyurethane foams. As a preferred example, the stabilizer can be selected from polysilicone surfactants.

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

In addition, the present invention also relates to the use of the above-mentioned flame retardant polyurethane or flame retardant polyurethane foam to manufacture door frame linings, roof linings, seat covers, high-resilience foam seats, high-resilience foam mattresses, rigid foam insulation boards, viscoelastic foam mattresses, potting foams for battery applications, microcellular foam seals and gaskets, durable elastic wheels and tires, automotive suspension linings, electrical potting compounds, high-performance adhesives, surface coatings and sealants, synthetic fibers, carpet linings, hard plastic parts and hoses.

The invention also relates to the use of flame retardant polyurethane or flame retardant polyurethane foam to manufacture electrical switch components; components in automobiles, electrical engineering or electronics; printed circuit boards; prepregs; potting compounds for electronic components; marine and rotor blade structures; outdoor GFRP applications; household and sanitary products and engineering materials. [ Specific Examples ]

Hereinafter, the present invention will be described in more detail with reference to embodiments, but the present invention is not limited to these embodiments.

1. Components used:

Flame retardants: FR-1 : Ethyl ethyl (methyl) phosphinate (MEPE) product of Synthesis Example 1. FR-2 : Butyl methyl phosphinate product of Synthesis Example 2. FR-3 : Butyl butyl (methyl) phosphinate (MUPU) product of Synthesis Example 3. Ref-1 : Fyrol® PCF from ICL Industrial Products, TCPP (tris (1-chloro-2-propyl) phosphate), is a halogen phosphate. Ref-2 : Exolit® OP 550 from Clariant International Ltd, is a non-halogenated polyphosphorus polyol designed for flexible polyurethane foams, which is a phosphate ester with a hydroxyl group.

Polyols: Polyether polyol ( P1 ): Arcol® 1104 or 1108 from Covestro AG, a 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 with a hydroxyl number of 257 mg KOH/g.

Polymerization Catalysts: Cat 1: Kosmos® EF from Evonik Industries, a stannous catalyst. Cat 2: Kosmos® 29 from Evonik Industries, a stannous octoate catalyst. Cat 3: Niax® A1 from Momentive Performance Materials Inc., a bis(2-dimethylaminoethyl)ether-based amine catalyst. Cat 4: Tegoamin® 33 from Evonik Industries, a triethylenediamine-based amine catalyst. Cat 5: JEFFCAT® ZF-10 from Huntsman, an N,N,N'-trimethyl-N'-hydroxyethyldiaminoethyl ether-based amine catalyst. Cat 6: Polycat 5 from Evonik Industries is a bis(2-dimethylaminoethyl)methylamine-based amine catalyst. Cat 7: Kosmos 75 MEG from Evonik Industries is a low-viscosity potassium octanoate-based foam catalyst.

Foam Stabilizers: S1: Tegostab® B 8232 from Evonik Industries, a silicone surfactant. S2: Tegostab® B 8522 from Evonik Industries, a silicone surfactant.

TDI (Tolyl diisocyanate): T80: Desmodur® T80 from Covestro AG is an isomeric mixture of 2,4-tolyl diisocyanate and 2,6-tolyl diisocyanate in a ratio of 80/20

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

2. Synthesis Examples of 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 In a 25 L autoclave equipped with a thermometer and a condenser, a mixture of 5280 g of petroleum ether, 413 g of anhydrous ethanol and 1100 g of triethylamine was added. The reaction system was purged with nitrogen three times, and then 501 g of methyldichlorophosphane solution was added dropwise at 25° C. Once the addition was completed, the temperature was maintained at 25° C. for 30 minutes.

The reaction mixture was then filtered under pressure to remove the generated NEt ₃ ·HCl. The filter cake was washed with 1000 mL of petroleum ether. Subsequently, 6590 g of the filtrate was distilled to recover petroleum ether and obtain a crude product of diethyl methylphosphite.

Finally, 557.8 g of diethyl methylphosphite was obtained by distillation. The purity was 98.5% as determined by gas chromatograph (GC), and the yield was 96.1%.

Step 2 : Preparation of ethyl ( methyl ) phosphinate (FR-1) In a 1L three-neck flask equipped with a thermometer and a condenser, a mixture of 557.0 g of diethyl methylphosphinate and 27.50 g of p-toluenesulfonate was added. The flask was then purged with _N2 . The temperature was gradually increased, and the reaction mixture was stirred and refluxed vigorously. Before insulation, the oil temperature was slowly increased from 120°C to 170°C. After 9 hours, no obvious reflux was observed (less than 0.5% of the starting material by GC), indicating that the reaction was complete.

Finally, 535.0 g of FR-1 product with 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

Methyl dichlorophosphine was continuously fed into the evaporator at a flow rate of 119.39 g/h. The evaporated methyl dichlorophosphine was then transferred to the tower continuous reactor using a nitrogen flow at a rate of 80 ml/min.

At the same time, 99.5% n-butanol is introduced into another evaporator at a rate of 243 g/h. The evaporated butanol is swept into the tower reactor using a nitrogen flow, also at a flow rate of 80 ml/min. Subsequently, the evaporated methyl dichlorophosphine and n-butanol react rapidly in the tower reactor. The light dilution fraction of chlorobutane produced by the rapid reaction is condensed and collected in a low-boiling-point substance receiving bottle. The heavy dilution fraction of crude methyl butyl phosphinate produced during the reaction is collected in a separate receiving bottle and then neutralized with triethylamine.

After neutralization, n-butanol was removed by vacuum distillation. This process yielded 96.0% butyl methylphosphinate, which had a viscosity of 3.4 mPa·s and a purity of 98.5% after purification.

2.3 Synthesis Example 3: Preparation of FR-3 Step 1 : Preparation of dibutyl methylphosphite In a 25 L autoclave equipped with a thermometer and a condenser, a mixture of 6200 g of petroleum ether, 674 g of anhydrous n-butanol and 910 g of triethylamine was added. The reaction system was purged with nitrogen three times, and then 507 g of a solution of methyldichlorophosphine was added dropwise at -10°C. Once the addition was completed, the temperature was maintained at 0°C for 30 minutes.

The reaction mixture was then filtered under pressure to remove the generated NEt ₃ ·HCl. The filter cake was washed with 1000 mL of petroleum ether. Subsequently, 7506 g of the filtrate was distilled to recover the petroleum ether and obtain a crude product of dibutyl methylphosphite.

Finally, 756.7 g of dibutyl methylphosphite was obtained by distillation. The purity was 95% and the yield was 88% as determined by gas chromatograph (GC).

Step 2 : Preparation of butyl ( methyl ) phosphinate (FR-3) In a 1 L three-neck flask equipped with a thermometer and a condenser, add a mixture of 600 g of dibutyl methylphosphinate and 30 g of p-toluenesulfonate. Then purge the flask with _N2 . Gradually increase the temperature, and stir the reaction mixture vigorously and reflux gently. Before keeping warm, the oil temperature is slowly increased from 150°C to 180°C. After 6 hours, the starting material detected by GC is less than 0.5%, indicating that the reaction is complete.

Finally, 571 g of FR-3 product with 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%.

Comparative hydrolytic stability test The hydrolytic stability provided by different flame retardants was compared by measuring the acid value of polyol admixtures containing flame retardants and water as a function of time during storage at high temperature. For this purpose, 90 g of polyol, 9 g of flame retardant and 4.5 g of water were homogenized at 1500 rpm for 2 minutes. The acid value was then determined using a 3:1 (v/v) mixture of isopropanol/water as solvent and 0.1 N NaOH (aq.) as titrant. The samples were then stored at 40 °C and the acid value was determined after 11, 17 and 28 days. The samples were homogenized at 1500 rpm for 2 minutes before analysis. The acid value changes of the polyol-water blend without added flame retardant were also measured after 11 days and 28 days, as shown in Table 1.

Compared to the reference example without flame retardant, the present example FR-1 did not cause a significant increase in acid value in its polyol blend during and after storage at 40°C for the entire 28 days. This shows that FR-1 has a high hydrolysis stability in the polyol blend during storage, i.e., the hydrolysis of FR-1 is zero to negligible. In contrast, under the same storage conditions, the polyol blend containing Ref-2 has a significant increase in acid value after only 11 days, which can only be explained by the hydrolysis of Ref-2.

4. Comparison of Viscosities of Polyol-Flame Retardant Mixtures As mentioned above, the viscosity of the liquid flame retardant of the present invention is advantageously low, which facilitates easy processing and handling in industrial applications. In the synthetic examples, FR-1 and FR-2 both have a viscosity below 5 mPa·s, FR-3 has a viscosity below 7 mPa·s, and TCPP (Ref-1) has a viscosity ten times higher (60 to 70 mPa·s) at room temperature, measured according to DIN 51398.

In Table 2 below, the viscosity of pure polyol (P2) and mixtures of polyol (P2) with flame retardant (FR-1, FR-2, FR-3 or Ref-1) are compared. The polyol-flame retardant mixtures were prepared by mixing polyol P2 with the specified flame retardant (FR-1, FR-2, FR-3 or Ref-1) at a weight ratio of 89.5:10.5 at room temperature. The mixture was thoroughly mixed for 1 minute at a speed of 1000 rpm using a mechanical stirrer to ensure homogeneity. The dynamic viscosity of the pure polyol and the polyol-flame retardant mixtures was then measured according to DIN51398.

From the data in Table 2, it can be observed that the liquid flame retardant of the present invention has an additional advantage over conventional liquid flame retardants (such as TCPP (Ref-1)) in that it can effectively reduce the viscosity of the polyol-flame retardant mixture during the blending process. When used in polymer manufacturing, this advantageous feature can further enhance the overall processability.

5.5 Flexible polyurethane (PUR) foam formulation and performance testing

Stannous catalyst, polyol, flame retardant, water, foam stabilizer and amine catalyst were weighed in order into a drying beaker and premixed for 60 seconds at 500 rpm (for polyether polyol formulation) or 1000 rpm (for polyester polyol formulation). After adding TDI, the mixture was stirred at 2500 rpm for 7 seconds. The resulting material was quickly poured into a box mold (25*26*26cm) lined with paper. The rise time and further observation were recorded during the foaming process. For each comparative example (C1-C3) or embodiment of the present invention (I1-I2), the foam was cured at room temperature for about 16 hours, then cut and collected for further evaluation.

The polymerization catalyst, foam stabilizer and TDI for each foam example were selected based on existing empirical guidance for optimal foamability in each case, as detailed in Table 3 below.

Evaluation of the flame retardancy of flexible foams (FMVSS302) The efficiency of the flame retardant is evaluated by testing the burning behavior of flexible polyurethane foam specimens containing the flame retardant and having a target density of 30 kg/m ³ in a horizontal burning test as described in Federal Motor Vehicle Safety Standard 302 (FMVSS 302). The foam density in the examples is measured according to DIN 53420. According to this standard, a specimen is classified as having the highest level (SE, "self-extinguishing") if the flame does not extend beyond the 38 mm mark on the specimen and is extinguished within this distance. Lower grades include SE/NBR (self-extinguishing/no burning rate), SE/B (self-extinguishing/burning rate) and B (burning rate). Five specimens are cut from each foam and tested. The lowest-rated specimen determines the overall grade of the foam.

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

As shown in the performance data in Table 4, Comparative Example C1 (polyether polyurethane foam without flame retardant additive) did not meet the required flame retardancy standards. Comparative Example C2 used 12 php of halogenated reference flame retardant TCPP (Ref-1) to provide a polyether polyurethane foam that met the required flame retardancy. When an attempt was made to reduce the amount of flame retardant to 8 php of TCPP, as shown in Comparative Example C3, it was found that the amount of flame retardant was insufficient and the resulting foam did not achieve the optimal flame retardancy (SE).

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

Example I2 of the present invention is a polyether polyurethane foam having a non-halogenated flame retardant (FR-2) of the present invention of 4 php, having the same excellent flame retardancy rating as I1.

6. Rigid polyisocyanurate (PIR) foam formulation and performance test Octanoate catalyst, polyol, flame retardant, water, foam stabilizer and amine catalyst were weighed in order into a drying beaker and premixed at 1000 rpm for 50 seconds. After adding n-pentane, the mixture was stirred at 1000 rpm for 10 seconds to mix 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 observation were recorded during the foaming period. For each comparative example (C4-C6) or inventive example (I3-I4), the foam was cured at room temperature for about 16 hours and then cut and collected for further evaluation.

The selection of polymerization catalyst, foam stabilizer and MDI for each rigid foam example is based on the existing experience guidance of the best foaming properties in various situations, and is listed in detail in Table 5 below.

Method for evaluating the flame retardancy of rigid foam plastics (DIN4102-1) DIN4102-1 classifies building materials according to their flammability. The valid standard is divided into two fire classes. "A" stands for non-flammable materials and "B" for flammable materials. Class B is associated with polyurethane foams, such as PIR insulation boards. It is then subdivided into the following classes: B1 = low flammability; B2 = normal flammability; B3 = high flammability. As a reference, most building foam systems sold in spray cans in Germany correspond to class B2 building materials. The main criterion for the classification of flammability class B2 is the flame height in the vertical burning test, which needs to remain below a maximum of 150 mm, which is an ideal guide to the benchmark of the flame retardancy of building materials.

The flame retardancy of different rigid PIR foam samples was evaluated using DIN4102-1, as listed in Table 6 below.

As shown in the performance data listed in Table 6, Comparative Example C4 (PIR foam without flame retardant additives) did not achieve the desired flame retardant standard rating of B2. Comparative Example C5 showed a rigid PIR foam with the desired flame retardant rating by mixing in 15 php of the halogenated reference flame retardant TCPP (Ref-1). However, when attempting to reduce the amount of this halogenated flame retardant to 12 php of TCPP, as shown in Comparative Example C6, it was observed that this reduction in flame retardant was insufficient, resulting in the foam failing to achieve the desired flame retardant rating.

Example 13 of the present invention shows that excellent flame retardancy is achieved by mixing the same level of 12 php of the non-halogenated flame retardant FR-1 of the present invention into the rigid PIR foam, achieving the best flame retardancy standard.

Similarly, Examples I4 and I5 of the present invention achieve the same excellent flame retardancy rating as I3 by replacing FR-1 with FR-2 or FR-3. This further highlights the effectiveness of the non-halogenated flame retardant of the present invention in obtaining the desired flame retardancy in rigid foams.

Claims (15)

A flame retardant polyurethane is obtained by reacting a polyol and an isocyanate in the presence of a flame retardant comprising a phosphinate of formula (I): wherein R1 is a alkyl group selected from C ₁ -C ₁₂ alkyl and C ₆ -C ₂₀ aryl; and wherein R2 and R3 are the same or different and independently represent H or C ₁ -C ₁₂ alkyl. The flame retardant polyurethane of claim 1, wherein R1 is selected from C ₁ -C ₆ alkyl groups, preferably C ₂ -C ₄ alkyl groups. The flame retardant polyurethane of claim 1 or 2, wherein R2 and R3 are not H at the same time. The flame retardant polyurethane of claim 3, wherein one of R2 and R3 is H or ethyl and the other is C ₁ -C ₆ alkyl. The flame retardant polyurethane of claim 3, wherein one of R2 and R3 is methyl and the other is H or C ₁ -C ₄ alkyl. The flame retardant polyurethane of claim 1, wherein R1 is ethyl, one of R2 and R3 is methyl and the other is ethyl. The flame retardant polyurethane of claim 1, wherein R1 is butyl, one of R2 and R3 is methyl and the other is H. The flame retardant polyurethane of claim 1, wherein R1 is a butyl group, one of R2 and R3 is a methyl group and the other is a butyl group. A 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 blowing catalyst and a foam stabilizer. The flame retardant polyurethane foam of claim 9, wherein the polyurethane foam is a flexible foam. The flame retardant polyurethane foam of claim 9, wherein the polyurethane foam is a rigid foam. A flame retardant polyurethane as described in any one of claims 1 to 8 or a flame retardant polyurethane foam as described in any one of claims 9 to 11 is used to manufacture the following applications: door frame linings, roof linings, seat covers, high-resilience foam seats, high-resilience foam mattresses, rigid foam insulation panels, viscoelastic foam mattresses, potting foams for battery applications, microcellular foam seals or gaskets, durable elastic wheels or tires, automotive suspension linings, electrical potting compounds, high-performance adhesives, surface coatings or sealants, synthetic fibers, carpet padding, or hard plastic parts or hoses. A method for producing a flame retardant polyurethane as claimed in any one of claims 1 to 8, comprising: Preparing a mixture comprising a polyol and a flame retardant; and adding an isocyanate compound to the mixture. A use of a phosphinate of formula (I) as a polyurethane flame retardant, wherein R1 is a alkyl group selected from C ₁ -C ₁₂ alkyl and C ₆ -C ₂₀ aryl; and wherein 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 formula (I) as a flame retardant, wherein R1 is a alkyl group selected from C ₁ -C ₁₂ alkyl and C ₆ -C ₂₀ aryl; and wherein R2 and R3 are the same or different and independently represent H or C ₁ -C ₁₂ alkyl.