The present invention relates to a flame retardant prepolymer composition which is in tended primarily for the use in a flame retardant polymer. Further, the present invention re lates to a flame retardant polyurethane composition, methods to prepare the flame retar dant polymer and the flame retardant polyurethane composition, and a use of said flame re tardant polyurethane composition.

In industry, polyurethane coatings are used to improve the hydrostatic resistance, life en durance, breathability of textiles and flame resistance of the coated objects. Usually solvent- based polyurethanes are applied due to fast drying of the polyurethane coating. Nowadays, it is commonly known that the used organic solvents in the polyurethane coatings are harm ful to health and the environment especially during manufacture and drying of the polyurethane coating. Additionally, solvent-based polyurethane coatings are often flammable. Therefore, it is an aim to replace the organic solvents by a less harmful solvent. Current applications show that aqueous polyurethane dispersions may overcome these dis advantages.

In order to meet fire protection requirements, the polyurethane dispersions are further equipped with flame retardants. The flame retardants are used to inhibit or completely pre vent combustion. The processing and service properties of flame retardant coatings can dif fer significantly from those without flame retardants. Not only the flammability of the used solvent is important during manufacturing, but also the resulting polyurethane coating after evaporation of the solvent must be flame retardant due to the flammability of polyurethane itself.

A distinction is made between halogenated, phosphorus-containing and inorganic flame re tardants in terms of chemistry and mode of action. Halogenated flame retardants act in the gas phase by chemically interrupting the combustion process. Chlorine or bromine contain ing halogenated flame retardants show a decreased flammability but as side effect toxic degradation products are created during the combustion of the flame retardant. Inorganic flame retardants such as aluminum hydroxide or magnesium hydroxide decompose in the event of a fire, splitting off water, diluting the fire gas and cooling the fire. These mineral flame retardants are inexpensive and generally harmless from an environmental point of view. Due to the high quantities added, however, the properties of the materials are fre quently impaired by the addition of inorganic flame retardants.

Phosphor-containing flame retardants can also act in the gas phase, but this is not preferred. In the condensed phase, oxygen-rich phosphorus compounds react preferentially, for exam ple phosphates, phosphonates, while the gas phase mechanism is influenced by hydrogen- and carbon-rich phosphorus compounds. Phosphor-containing flame retardants form a pro tective layer on the burning surface by charring. This layer has an insulating effect and insu lates the oxygen supply to the source of the fire. The phosphor-containing flame retardants act by forming a "polyphosphoric acid" protective layer in the condensed phase. At the same time, water is formed by charring, which has a cooling effect. Phosphor-containing flame re tardants are largely environmentally neutral and relatively effective in relation to the amount of phosphor used. Typical phosphorus compounds that can be added as flame retar dant additives are ammonium polyphosphate, melamine polyphosphate, red phosphorus, metal phosphinates, phosphorus and phosphonic acid esters, and phosphazenes. The disad vantage of all these flame-retardant additives is that these inorganic compounds are incom patible with the binder of the coating and can also be distributed insufficiently evenly in the coating.

The object of the present invention is to provide a flame retardant prepolymer composition as well as a flame retardant polyurethane composition which overcomes the aforemen tioned disadvantages. They should have a superior flame resistance, should be environmen tal unobjectionable and should exhibit good coating abilities.

Said object of the present invention is solved by a flame retardant prepolymer composition comprising at least one isocyanate-terminated polyurethane prepolymer, wherein the at least one isocyanate-terminated polyurethane prepolymer contains at least one phospho- nate oligomer, phosphonate monomer or a mixture thereof in an amount of from 5 to 75 parts by weight, referring to the total amount of the at least one isocyanate-terminated polyurethane prepolymer, wherein the at least one phosphonate oligomer, phosphonate monomer or a mixture thereof contains units according to the following structural formula I: in which n is an integer from 1 to 20, R is a Ci_ ₀ alkyl, C _2-20 alkene, C _2-20 alkyne, C _3-20 cy cloalkyl, or C _6-20 aryl, and R ₂ is an aliphatic and/or aromatic group, wherein R and R ₂ may comprise heteroatoms; wherein a NCO value is in a range between approximately 2% to approximately 10 %, and preferred approximately 4.1 % to approximately 6.4 % obtained by titration against a dibuty- lamine/tolulene solution as per ISO 14896: 2009-07 Method A.

The term "alkyl" or "alkyl group" refers to an unbranched or branched hydrocarbon or group of 1 to 20 carbon atoms, such as but not limited to methyl, ethyl, n-propyl, isopropyl, n- butyl, isobutyl, t-butyl, octyl, decyl, tetradecyl, hexadecyl, elcosyl, tetracosyl and the like. "Cycloalkyl" or "cycloalkyl groups" are unbranched or branched hydrocarbons in which all or some of the carbons are arranged in a ring such as but not limited to cyclopentyl, cyclohexyl, methylcyclohexyl, and the like. The term "aryl" or "aryl group" refers to monovalent aro matic hydrocarbon radicals or groups of one or more fused rings in which at least one ring is aromatic in nature. Aryls may include but not limited to phenyl, naphthyl, biphenyl ring sys tems and the like. The aryl group may be unsubstituted or substituted with a variety of sub stituents including but not limited to alkyl, alkenyl, halide, benzylic, alkyl or aromatic ether, nitro, cyano and the like and combinations thereof. Substituent refers to a molecular group that replaces a hydrogen in a compound and may include but is not limited to trifluo- romethyl, nitro, cyano, C^ _Q alkyl, aromatic or aryl, halide (F, Cl, Br, I), C^ _Q alkyl ether, C _5-20 alkyl ester, benzyl halide, benzyl ether, aromatic or aryl ether, hydroxy, amino, alkylamino (- NHR'), diaklylamino (-NR'R) or other groups which do not interfere with the formation of the diaryl alkylphosphonate. The term "heteroatom" refers to an atom which replaces a carbon in the backbone of the molecular structure in a compound and may include but is not limited to halide (F, Cl, Br, I), nitrogen, sulfur, silicon, boron, phosphor, selenium or metals such as lithium and magnesium.

The terms "flame retardant" or "flame resistance" as used herein, means that the composi tion exhibits a limiting oxygen index (LOI) of at least 27. "Flame retardant" or "flame resis tance" may also be tested by measuring the after-burning time in accordance with the UL-94 VTM test.

The term "NCO value" defines the percentage of free isocyanate groups of the at least one isocyanate-terminated polyurethane prepolymer in the inventive flame retardant prepoly mer composition. The term "NCO value"in the sense of the present invention and as used in claim 1 refers to the experimental NCO value. Said experimental NCO value is measured in accordance with ISO 14896: 2009-07 Method A by titration against a dibutylamine/tolulene solution. The experimental NCO value is calculated on the basis of the so-called theoretical NCO value, also determined in accordance with ISO 14896: 2009-07 Method A. The theoreti cal NCO value is calculated by the following formula:

(n I,socyanate - } n pol ,yol ,)·' MW N _r C _n O - group

NCO theoretical [%] = 100% m reaction wherein n is the amount of substance, MW is the molecular weight and m _reaction defines the overall mass of the reaction compounds. This theoretical NCO value gives the range of the non reacting isocyanate groups of the reaction mixture and is needed for the calculation of the actual free isocyanate groups after reaction to obtain the inventive flame retardant pre polymer composition.

The purpose of the experimental NCO value is that it gives a measure for the finishing of the reaction. A blank sample and a sample of the inventive flame retardant prepolymer compo sition prepared in accordance to ISO 14896: 2009-07 Method A are titrated with hydrochlo ric acid (HCI). The experimental NCO value is calculated by the following formula: wherein V _b|ank defines the hydrochloric acid (HCI) required for titration of the blank in ml, V _sampie defines the (HCI) required for titration of the sample in ml, N is the normality of the used HCI in meq/ ml and 4.202 is a constant as follows: wherein 42.02 is the equivalent of the NCO in mg/ meq and conversion of g in 1000 mg. The non-volatile content gives the wt-% of the at least one isocyanate-terminated polyurethane prepolymer in the inventive flame retardant prepolymer composition. The non-volative con tent is calculated as follows: non wherein m _wet is the weight before and m _dry is the weight after heating the sample of the the inventive flame retardant prepolymer composition. The experimental NCO value of the in ventive flame retardant prepolymer composition is in a range between approximately 2% to approximately 10 %, and preferrably approximately 4.1 % to approximately 6.4 %.

The inventive flame retardant prepolymer composition comprises at least one isocyanate- terminated polyurethane prepolymer, which is prepared in-situ by a polyaddition reaction of at least two building blocks. An at least one diol and an at least one isocyanate are required for the polyaddition to obtain polyurethane. The polyurethane can be adapted to the re quired fields of application by modifying its properties. The properties of the polyurethane may be adapted by using different building blocks as flame retardant components, branched or unbranched diols, diols with multiple functionalizations to create linear or branched polyurethanes and further functionalization by incorporating ionic or water-soluble com pounds. By implementing an at least one phosphonate oligomer, phosphonate monomer or a mixture thereof according to formula (I) into the least one isocyanate-terminated polyurethane prepolymer under reaction with an at least one diol and an at least one iso cyanate, the flame retardant capability is incorporated into the backbone of the least one isocyanate-terminated polyurethane prepolymer. The at least one isocyanate-terminated polyurethane prepolymer is comprised in the flame retardant prepolymer composition in an amount of approximately 80 wt-% to approximately 95 wt-%, in each case referring to the total amount of the flame retardant prepolymer composition. The different building blocks of the at least one isocyanate-terminated polyurethane pre polymer as the at least one phosphonate oligomer, phosphonate monomer or a mixture thereof, the at least one diol and the at least one isocyanate are described in the following.

According to the present invention the at least one phosphonate oligomer, phosphonate monomer or a mixture thereof is used as a first building block. The at least one phosphonate oligomer, phosphonate monomer or a mixture thereof is further referred to as at least one phosphonate oligomer without being limited to the phosphonate oligomer. The at least one phosphonate oligomer used in the preparation of the at least one isocyanate-terminated polyurethane prepolymer is preferably a phosphonate diol selected from the group consist ing of a random co-oligo(phosphonate carbonate), a block co-oligo(phosphonate carbonate), a random co-oligo(phosphonate ester), a block co-oligo(phosphonate ester) or any mixture thereof. Described herein are reactive phosphonate oligomers, random or block co- oligo(phosphonate ester)s, and random or block co-oligo(phosphonate carbonate)s as the at least one phosphonate oligomer. In various embodiments, the at least one phosphonate oligomer may include reactive substituents such as, for example, hydroxyl groups, epoxy groups, isocyanate groups, vinyl groups, vinyl ester groups, isopropenyl groups, and the like and combinations thereof. The reactive substituents may allow the at least one phosphonate oligomer to react chemically with other monomers, oligomers, or polymers in polymer com positions leading to crosslinking or chain extension or a combination thereof. For example, reactive substituents such as hydroxyl groups, epoxy groups, vinyl groups, vinyl ester groups, isopropenyl groups, or isocyanate groups are capable of reacting with functional groups such as, but not limited to, alcohols, carboxylic acids and salts thereof, anhydrides, acyl chlorides, epoxides, aldehydes, ketones, amines, thiols, Grignard reagents, vinyl groups, acetylene groups and sodium hydroxide acids and salts thereof. When monomers, oligomers, or poly mers including these functional groups are combined with the at least one phosphonate oligomer having hydroxyl groups, epoxy groups, vinyl groups, vinyl ester groups, isopropenyl groups, or isocyanate groups crosslinking or chain extension or a combination of both may occur. The reactive phosphonate oligomer may thereby impart flame resistance while not detracting from the mechanical properties of the base polymer of the polymer composition. The at least one phosphonate oligomer of the claimed invention may be linear or branched. Further, the at least one phosphonate oligomer according to formula (I), wherein n is prefer ably from 1 to 10, and R ² is preferably an aromatic group. Further preferred, R and R ² may comprise heteroatoms. Even more preferred, the phosphonate oligomer used in the prepa ration of the at least one isocyanate-terminated polyurethane prepolymer is a copolymer of bisphenol-A and diphenyl methyl phosphonate. In an especially embodiment R of the at least one phosphonate oligomer is preferably a methyl group. In a further preferred embodiment the phosphonate oligomer building block has a structure according to one of the following formulae: in which R ¹ and R ² are aliphatic or aromatic hydrocarbons, and n is an integer from 1 to 20. The phosphonate oligomer chain according to formula II may include alternating phospho- nate and carbonate or ester monomers or short segments in which several phosphonate or carbonate or ester monomers are linked by an aromatic dihydroxide. The length of such seg ments may vary within individual random co-oligo(phosphonate carbonate)s or co- oligo(phosphonate ester). The at least one phosphonate oligomer may be comprised as a liq uid or a solid. If the at least one phosphonate oligomer is a liquid a dynamic viscosity at 25 °C of approximately 150 mPa*s to approximately 4.500 mPa*s and preferred of approximately 190 mPa*s to approximately 4.200 mPa*s is required. The molecular weight M _n of the at least one phosphonate oligomer is in a range of approximately 900 g/ mol to approxymately 5000 g/ mol and further preferred in a range from approximately 1000 g/ mol to approxi mately 4000 g/ mol, in each case referring to the average molar mass of the at least one phosphonate oligomer. The least one phosphonate oligomer is preferably comprised in an amount of approximately 5 wt to approximately 75 wt-% and further preferred in an amount of approximately 10 wt-% to approximately 55 wt-%, in each case referred to the total amount of the flame retardant prepolymer composition.

The inventive flame retardant prepolymer composition comprises at least one isocyanate- terminated polyurethane prepolymer, which is obtained by using at least one diol and/or at least one polyol, whereby the diol and the polyol are selected from a group comprising polyetherglycols, polyester diols, polycarbonates, polytetrahydrofurans, dimer diols, fatty acids, dimerized fatty acid based diols and/ or polyester based diols preferred biobased polyester diols in the manufacturing process of the at least one isocyanate-terminated polyurethane prepolymer. The at least one diol and/or at least one polyol is preferably used as a second building block. Preferably, the at least one diol and/or at least one polyol is ob tained by a reaction of at least one lactone and at least one diol. The at least one lactone is preferred e-caprolactone. The lactone used in the at least one isocyanate-terminated polyurethane prepolymer remarkably increases the amount of oxygen in the backbone of the at least one isocyanate-terminated polyurethane prepolymer. In addition, the resulting coating by using lactones in the at least one isocyanate-terminated polyurethane prepoly mer gives a more flexible and clearer film compared to other polyols such as polycarbonate polyols. The at least one diol and/or at least one polyol is preferably a polyester polyol and more preferred a biobased polyester polyol selected from a group comprising biobased polyesters, dimer fatty acid based polyester diol having molecular weight (M _n ) in a range of approximately 1000 g/mol to approximately 2000 g/mol, dehydrated castor oil and/ or fatty acid thereof. The at least one diol and/or at least one polyol is preferably a solid. The hy droxy number (OH number) of the at least one diol and/or at least one polyol is preferred in a range of approximately 90 mg KOH/ g to approximately 150 mg KOH/ g and more pre ferred in a range of approximately 100 mg KOH/ g to approximately 140 mg KOH/ g, in each case referring to the total amount of the at least one diol and/or at least one polyol. The molecular weight (Mn) of the at least one diol and/or at least one polyol is preferably in a range between approximately 900 g/ mol and approximately 3000 g/ mol and more pre ferred between approximately 1000 g/ mol and approximately 2000 g/ mol, in each case re ferring to the total average molecular weight of the at least one diol and/or at least one polyol. The at least one diol and/or at least one polyol is preferably comprised in a range of approximately 5 wt-% to approximately 50 wt-%, further preferred in a range of approxi mately 10 wt-% to approximately 50 wt-%, and even more preferred in a range from approx imately 35 wt-% to approximately 45 wt-%, in each case referring to the total amount of the inventive flame retardant prepolymer composition.

Preferably, the at least one diol and/or at least one polyol is at least one multifunctional diol selected from the group comprising at least one trifunctional diol, branched diol with an at least one hydroxyl group and an at least one carboxyl group, linear non-ionic polyethylene glycol ether diol or a mixture thereof. The multifunctional diol is selected from glycerol, dimethylol popionic acid (DMPA), trimethylol propane, polyether gycol and/or silicone diols. Further preferred, two at least one diol and/or at least one polyol are comprised from the at least one isocyanate-terminated polyurethane prepolymer, wherein one at least one diol and/or at least one polyol is obtained by a reaction of at least one lactone and at least one diol and another is an at least one multifunctional diol. Therefore, the at least one multifunc tional diol is preferably a third building block. The at least multifunctional diol is introduced into the at least one isocyanate-terminated polyurethane prepolymer to enhance the dis persibility of the at least one isocyanate-terminated polyurethane prepolymer in polar sol vents and/ or to obtain free functional groups for at least one cross- linking step. A branched diol with an at least one hydroxyl group and an at least one carboxyl group introduces an ionic functionality into the backbone of the at least one isocyanate-terminated polyurethane prepolymer. The anionic functionality of the backbone creates adequate polarity to enhance the dispersibility in polar solvents especially water. A linear non-ionic polyethylene glycol ether diol creates partial higher solubility in polar solvents, especially, water of the at least one isocyanate-terminated polyurethane prepolymer backbone. The at least one multifunc tional diol comprises at least three functional groups. To apply an at least one cross-linking step later on, free functional groups in the backbone are needed like but not limited to un saturated double bonds, amino, hydroxy, carboxy, thiol, nitro or a combination thereof. These free functional groups may be incorporated into the at least one isocyanate-termi nated polyurethane prepolymer by the at least one multifunctional diol. The at least one multifunctional diol is preferably comprised in an amount of approximately 0,2 wt-% to ap proximately 7 wt-% and further preferred in an amount of approximately 0,2 wt-% to ap- proximnately 5 wt-%, in each case referring to the total amount of the flame retardant pre polymer composition.

At least one isocyanate is comprised from the at least one isocyanate-terminated polyurethane prepolymer. The at least one isocyanate is preferably a fourth building block. The active hydrogen in the at least one phosphonate oligomer, the at least one diol and/ or at least one polyol and at least one trifunctional diol reacts with the at least one isocyanate, so that the at least one isocyanate is chemically bonded via covalent bonds to the first, sec ond and third building block. The at least one isocyanate is preferably a diisocyanate. The at least one isocyanate is preferred a diisocyanate selected from the group comprising aro matic diisocyanate, aliphatic diisocyanates and cycloaliphatic diisocyanates, such as toluene diisocyanate (TDI), p-phenylene diisocyanate (PPDI), 4,4'-diphenylmethane diisocyanate (MDI), p,p'-bisphenyl diisocyanate(BPDI), isophorone diisocyanate (IPDI), 1,6-hexamethylene diisocyanate (HDI), dicyclohexylmethane, hydrogenate diphenylmethane-4,4'-diisoyanate (HI MDI), meta-tetramethylxylene diisocyanate (TMXDI) and a mixture thereof. Additionally, the at least one isocyanate may comprise substituents of halo, nitro, cyano, alkyl, alkoxy, haloalkyl, hydroxyl, carboxy, amido, amino, or combinations thereof. The at least one iso cyanate has a viscosity at 25°C measured by DIN EN ISO 3219/A.3 in a range of approxi mately 1 mPa*s to approxymately 15 mPa*s and preferred in a range of approximately 2 mPa*s to approximately 13 mPa*s. The density of the at least one isocyanate at 20°C mea sured by DIN EN ISO 2811 is in a range of approximately 1,00 g/ cm ³ to approximately 1,10 g/ cm ³ and preferred in a range of approximately 1,01 g/ cm ³ to approximately 1,09 g/ cm ³ . The used excess of the at least one isocyanate depends on the calculated free isocyanate-value calculated via the theoretical NCO value as set forth above.The theoretical NCO value of the at least one isocyanate is in a range of approximately 25 wt-% to approximately 55 wt-%, and preferably in a range of approximately 30 wt-% to approximately 50 wt-%, in each case re ferred to the total amount of the at least one isocyanate molecule. The at least one iso cyanate is preferably comprised in an amount of approximately 10 wt-% to approximately 50 wt-%, further preferred in an amount of 15 wt-% to approximately 45 wt-%, in each case re ferred to the total amount of the flame retardant prepolymer composition. Preferably, the flame retardant prepolymer composition comprises at least one non-aque- ous solvent. The at least one non-aqueous solvent is preferably selected from a group com prising acetone, diethylamine, methanol, isopropanol, dichloromethane or a mixture thereof. To obtain the flame retardant prepolymer composition the reaction is carried out in an at least one non-aqueous solvent, the non-aqueous solvent preferably having a low boil ing point. A low boiling point is advisable to evaporate the non-aqueous solvent under re duced pressure after the preparation of the isocyanate-terminated polyurethane polymer. Non-aqueous solvents which are recyclable are preferably used due to lower production costs, lower industrial waste and resulting better environmental sustainability. Therefore high boiling solvents such as N-methyl pyrrolidone (NMP) are not in the sense of the inven tion. Further on, the at least one non-aqueous solvent is used to lower the viscosity of the gained inventive at least one isocyanate-terminated polyurethane prepolymer. The at least one non-aqueous solvent is used in range of approximately 5 wt-% to approximately 20 wt-% and preferred in a range from approximately 8 wt-% to approximately 17 wt-%, in each case referred to the total amount of the flame retardant prepolymer composition.

The present invention further relates to a flame retardant polyurethane composition ob tained from the flame retardant prepolymer composition as extensive described above by reacting the flame retardant prepolymer composition in at least one cross-linking step with at least one crosslinking agent selected from a group comprising diamines, triamines, or ganic aminosilanes and/or carbodiimides. Preferably, the at least one diamine and/ or tri amine is selected from a group comprising alkyldiamines and alkyltriamines. Examples for cross-linking agents are diamines such as ethylendiamine, hydrazine, hydrazine hydrate, di ethanol amine, 2-hydroxy amine; triamines such as diethylene triamine; amino silanes such as y-aminopropyltriethoxysilane and siloxanes. The at least one crosslinking agent may be act as an chain extender as well. The at least one crosslinking agent provides several func tional groups so that the individual strands of the at least one isocyanate- terminated polyurethane prepolymer can be cross-linked to create a polymeric network. Aforesaid at least one crosslinking agent is forming the mentioned polymeric network by forming ure thane urea linkages. Therefore, the obtained inventive isocyanate-terminated polyurethane may also be described as an isocyanate-terminated polyurethane urea. The purity of the at least one crosslinking agent is preferably above 97 %. The density of the at least one crosslinking agent at 25 °C measured according to DIN 51757 is in a range of approximately 0,80 g/ cm ³ to approximately 1,10 g/ cm ³ , and preferably in a range of approximately 0,92 g/ cm ³ to approximately 1,05 g/ cm ³ . The at least one crosslinking agent is used in a range of approximately 0,5 wt-% to approximately 8 wt-%, which depends on the experimental mea sured isocyanate-value, further referred to as NCO-value of the flame retardant prepolymer composition, in each case referring to the total amount of the flame retardant polyurethane composition.

Preferably, in the at least one crosslinking step, before the at least one crosslinking step, or after the at least one crosslinking steps, water is added in order to obtain a polyurethane composition dispersion. Further preferred a chain extension step should be carried out be fore adding water.

Preferably, at least one neutralization step is carried out before the at least one crosslinking step. The at least one neutralization step is carried out by using at least one neutralizing agent selected of a group comprising tertiary amines, amino alcohols, metal hydroxides, am monia or a mixture thereof. Examples of neutralizing agents are trialkyl amines such as trimethylamine, triethyl amine and tributyl amine; amino alcohols such as dimethyl ethanolamine; tertiary amine compounds such as N-alkyl-N,N-dialkanol amines and tri ethanol amine; basic compounds such as ammonia, trimethyl ammonium hydroxide, sodium hydroxide, potassium hydroxide and lithium hydroxide. This at least one neutralizing agent neutralizes cationic groups. Cationic groups were implemented by the aforesaid at least one multifunctional diol as third building block in the preparation of the flame retardant polyurethane composition. The at least one neutralizing agent is preferably used in a molar ratio of approximately 0,5 to approximately 1 to the total amount of the at least one multi functional diol . The at least one neutralizing agent is used in a range of approximately 1 wt- % to approximately 3 wt-%, in each case referring to the total amount of the flame retardant polyurethane composition.

The inventive flame retardant polyurethane composition is an aqueous isocyanate-termi nated polyurethane urea dispersion. Due to the incorporated ionic or water-soluble at least one multifunctional diol as third building block the aqueous isocyanate-terminated polyurethane urea dispersion is stable at normal storage, handling and transport. The inven tive flame retardant polyurethane composition obtained after the at least one cross-linking step comprises a non-volatile content of the flame retardant polyurethane composition in a range of approximately 25 wt-% to approximately 50 wt-% and preferably in a range of ap proximately 30 wt-% to approximately 45 wt-%, in each case referring to the total amount of the flame retardant polyurethane composition. Further on, the pH value of the inventive flame retardant polyurethane composition at 25 °C is preferred in a range of approximately 8.0 to approximately 10.0. The viscosity of the inventive flame retardant polyurethane com position is preferably in a range of approximately 50 mPa*s to approximately 2000 mPa*s at 20°C with a rotational frequency of 20 rpm. Due to the incorporated at least one phospho- nate oligomer as a first building block in the isocyanate-terminated polyurethane of the in ventive flame retardant polyurethane composition the flame retardant effect is evenly dis tributed throughout the whole isocyanate-terminated polyurethane. Therefore, the inven tive flame retardant polyurethane composition contains good flame resistance by itself and no further flame retardant additives have to be added to the inventive composition. This is proven by the flammability of the inventive flame retardant polyurethane composition, which is measured by the UL 94 VTM assay.

The present invention further relates to a method for manufacturing the flame retardant prepolymer composition as described above, whereby

- mixing of at least one phosphonate oligomer, at least one polyether glycol, at least one diol and/or at least one polyol with at least one non-aqueous solvent, and heating said solution to a temperature in a range from approximately 30°C to approximately 100°C, and preferred from approximately 50°C to approximately 85 °C;

- adding at least one isocyanate in excess to relation to the total amount of the at least one polyetherglycol, at least one diol and/or at least one polyol;

- heating the obtained solution to a temperature in a range from approximately 65°C to ap proximately 96°C until a NCO value is in a range between approximately 2,0 % to approx imately 10 %, obtained by titration against a dibutylamine/tolulene solution.

Preferably, the method for manufacturing the flame retardant polyurethane composition comprises further - providing a flame retardant prepolymer composition manufactured as described above;

- adding water to obtain a polyurethane dispersion; and

- adding at least one crosslinking agent.

Further preferred, the non-aqueous solvent is evaporated in order to obtain an aqueous iso cyanate-terminated polyurethane composition. The at least one non-aqueous solvent is preferably selected from a group comprising acetone, diethylamine, methanol, isopropanol, dichloromethane or a mixture thereof. To obtain the flame retardant prepolymer composi tion the reaction is carried out in an at least one non-aqueous solvent, the non-aqueous sol vent preferably having a low boiling point. A low boiling point is advisable to evaporate the non-aqueous solvent under reduced pressure after the preparation of the isocyanate-termi nated polyurethane polymer. Non-aqueous solvents which are recyclable are preferably used due to lower production costs, lower industrial waste and resulting better environmen tal sustainability. Therefore high boiling solvents such as N-methyl pyrrolidone (NMP) are not in the sense of the invention. Further on, the at least one non-aqueous solvent is used to lower the viscosity of the gained inventive at least one isocyanate-terminated polyurethane prepolymer.

The present invention further relates to the use of the flame retardant polyurethane compo sition as described above and obtained by the manufacturing method also described above as a flame retardant component in paints, lacquers, intumescent coatings, wood, leather and paper. The inventive flame retardant polyurethane composition for the use as flame retar dant component in paints, lacquers, intumescent coatings, wood and paper of the present invention is remarkably useful for industry, since it can provide articles having excellent flame resistance as well as it has no bleeding on the coated surfaces of flame retardant addi tives. In addition, no harmful substances such as dioxin are produced during combustion and no environmental hormones are used, since the phosphonate oligomer building block is used as a polymeric building block in the flame retardant polyurethane composition to achieve the flame retardant effect.

As far as the term weight percent or % by weight is used with respect to the components be ing comprised from the claimed grease composition, the term weight percent is referred to the amount of one or more components relative to the total amount of the composition throughout this specification, except where expressively stated otherwise. The expression "wt-%" is used throughout the present invention as an abbreviation for weight percent if not indicated otherwise.

In the context of the invention, the expressions "about" and "approximately" in connection with numerical values or ranges are to be understood as a tolerance range, which a person skilled in the art would consider as common or reasonable based on his or her general knowledge and in view of the invention as a whole. In particular, the expressions "about" and "approximately" refer to a tolerance range of ±20 %, preferred ±10 % and further pre ferred ±5 % with respect to the designated value. The lower end values and the upper end values of the various ranges, especially the weight percent ranges, but not restricted thereto, claimed in the present invention may be combined with each other in order to de fine new ranges.

Further, in the context of the present invention, all references to standards, norms, or stan dardization protocols, e.g. ISO, ASTM etc., in connection with properties, numerical values or ranges referred to are to be understood as the latest updated version of said standard, norm, or standardization protocol being in force at the date of filling of the invention.

In an especially preferred embodiment of the present invention, a flame retardant prepoly mer composition is defined comprising approximately 80 wt-% to approximately 95 wt-% of at least one isocyanate-terminated polyurethane prepolymer and approximately 5 wt-% to approximately 20 wt-% of at least one non-aqueous solvent, wherein the at least one iso cyanate-terminated polyurethane prepolymer contains approximately 5 wt-% to approxi mately 75 wt-% of at least one phosphonate oligomer, phosphonate monomer or a mixture thereof as a first building block, referring to the total amount of the at least one isocyanate- terminated polyurethane prepolymer.

In a further preferred embodiment of the present invention, a flame retardant prepolymer composition is defined comprising approximately 80 wt-% to approximately 95 wt-% of at least one isocyanate-terminated polyurethane prepolymer and approximately 5 wt-% to ap- proximately 20 wt-% of at least one non-aqueous solvent, wherein the at least one iso cyanate-terminated polyurethane prepolymer contains approximately 5 wt-% to approxi mately 75 wt-% of at least one phosphonate oligomer, phosphonate monomer or a mixture thereof as a first building block, referring to the total amount of the at least one isocyanate- terminated polyurethane prepolymer, wherein the at least one phosphonate oligomer may be comprised as a liquid or a solid , wherein the molecular weight M _n of the at least one phosphonate oligomer is in a range of approximately 900 g/ mol to approximately 5000 g/mol, in each case referring to the average molecular weight of the at least one phospho nate oligomer.

In a further preferred embodiment of the present invention, a flame retardant prepolymer composition is defined comprising approximately 80 wt-% to approximately 95 wt-% of at least one isocyanate-terminated polyurethane prepolymer and approximately 5 wt-% to ap proximately 20 wt-% of at least one non-aqueous solvent, wherein the at least one iso cyanate-terminated polyurethane prepolymer contains approximately 5 wt-% to approxi mately 75 wt-% of at least one phosphonate oligomer, phosphonate monomer or a mixture thereof as a first building block, referring to the total amount of the at least one isocyanate- terminated polyurethane prepolymer, wherein the at least one diol and/or at least one polyol is preferably a solid, wherein the hydroxyl number (OH number) of the at least one diol and/or at least one polyol is preferred in a range of approximately 90 to approximately 150 mg KOH/ g, in each case referring to the total amount of the at least one diol and/or at least one polyol, wherein the molecular weight (Mn) of the at least one diol and/or at least one polyol is preferably in a range between approximately 900 g/ mol and approximately 3000 g/mol, in each case referring to the total average molecular weight of the at least one diol and/or at least one polyol, wherein the at least one diol and/or at least one polyol is preferably comprised in a range of approximately 5 wt-% to approximately 50 wt-%, in each case referring to the total amount of the flame retardant prepolymer composition.

In a further preferred embodiment of the present invention, a flame retardant prepolymer composition is defined comprising approximately 80 wt-% to approximately 95 wt-% of at least one isocyanate-terminated polyurethane prepolymer and approximately 5 wt-% to ap proximately 20 wt-% of at least one non-aqueous solvent, wherein the at least one iso- cyanate-terminated polyurethane prepolymer contains approximately 5 wt-% to approxi mately 75 wt-% of at least one phosphonate oligomer, phosphonate monomer or a mixture thereof as a first building block, referring to the total amount of the at least one isocyanate- terminated polyurethane prepolymer, wherein preferably a third building block selected from the group comprising at least one trifunctional diols, branched diols with an at least one hydroxyl group and an at least one carboxyl group, linear non-ionic polyethylene glycol ether diols or a mixture thereof is comprised, wherein the third building block is preferably comprised in an amount of approximately 0,2 wt-% to approximately 7 wt-%, in each case referring to the total amount of the flame retardant prepolymer composition.

In a further preferred embodiment of the present invention, a flame retardant prepolymer composition is defined comprising approximately 80 wt-% to approximately 95 wt-% of at least one isocyanate-terminated polyurethane prepolymer and approximately 5 wt-% to ap proximately 20 wt-% of at least one non-aqueous solvent, wherein the at least one iso cyanate-terminated polyurethane prepolymer contains approximately 5 wt-% to approxi mately 75 wt-% of at least one phosphonate oligomer, phosphonate monomer or a mixture thereof as a first building block, referring to the total amount of the at least one isocyanate- terminated polyurethane prepolymer, wherein preferably a fourth building block is an at least one isocyanate, wherein the NCO-value, which is calculated from GC, of the at least one isocyanate is in a range of approximately 25 wt-% to approximately 55 wt-%, in each case referred to the total amount of the isocyanate molecule, wherein the at least one iso cyanate is preferably comprised in an amount of approximately 10 wt-% to approximately 50 wt-%, in each case referred to the total amount of the flame retardant prepolymer composi tion.

In a further preferred embodiment of the present invention, a flame retardant prepolymer composition is defined comprising approximately 80 wt-% to approximately 95 wt-% of at least one isocyanate-terminated polyurethane prepolymer and approximately 5 wt-% to ap proximately 20 wt-% of at least one non-aqueous solvent, wherein the at least one iso cyanate-terminated polyurethane prepolymer contains approximately 5 wt-% to approxi mately 75 wt-% of at least one phosphonate oligomer, phosphonate monomer or a mixture thereof as a first building block, referring to the total amount of the isocyanate-terminated polyurethane prepolymer, the at least one non-aqueous solvent is preferably selected from a group comprising acetone, diethylamine, methanol, isopropanol, dichloromethane or a mixture thereof.

In a further preferred embodiment of the present invention, a flame retardant prepolymer composition is defined comprising approximately 80 wt-% to approximately 95 wt-% of at least one isocyanate-terminated polyurethane prepolymer and approximately 5 wt-% to ap proximately 20 wt-% of at least one non-aqueous solvent, wherein the at least one iso cyanate-terminated polyurethane prepolymer contains approximately 10 wt-% to approxi mately 75 wt-% of at least one phosphonate oligomer, phosphonate monomer or a mixture thereof as a first building block, referring to the total amount of the at least one isocyanate- terminated polyurethane prepolymer.

In an especially preferred embodiment of the present invention, a flame retardant prepoly mer composition is defined comprising approximately 80 wt-% to approximately 95 wt-% of at least one isocyanate-terminated polyurethane prepolymer and approximately 5 wt-% to approximately 20 wt-% of at least one non-aqueous solvent, wherein the at least one iso cyanate-terminated polyurethane prepolymer contains approximately 5 wt-% to approxi mately 55 wt-% of at least one phosphonate oligomer, phosphonate monomer or a mixture thereof as a first building block, referring to the total amount of the at least one isocyanate- terminated polyurethane prepolymer.

In an especially preferred embodiment of the present invention, a flame retardant polyurethane composition obtained from the flame retardant prepolymer composition by reacting the flame retardant prepolymer composition in at least one cross-linking step with approximately 0,5 wt-% to approximately 8 wt-% of at least one crosslinking agent.

In a further preferred embodiment of the present invention, a flame retardant polyurethane composition obtained from the flame retardant prepolymer composition by reacting the flame retardant prepolymer composition in at least one cross-linking step with approxi mately 0,5 wt-% to approximately 8 wt-% of at least one crosslinking agent, wherein the flame retardant prepolymer composition comprises approximately 80 wt-% to approxi- mately 95 wt-% of at least one isocyanate-terminated polyurethane prepolymer and approx imately 5 wt-% to approximately 20 wt-% of at least one non-aqueous solvent, wherein the at least one isocyanate-terminated polyurethane prepolymer contains approximately 5 wt-% to approximately 55 wt-% of at least one phosphonate oligomer, phosphonate monomer or a mixture thereof as a first building block, referring to the total amount of the at least one isocyanate-terminated polyurethane prepolymer.

In a further preferred embodiment of the present invention, a flame retardant polyurethane composition obtained from the flame retardant prepolymer composition by reacting the flame retardant prepolymer composition in at least one cross-linking step with approxi mately 0,5 wt-% to approximately 8 wt-% of at least one crosslinking agent, wherein the least one crosslinking agent is selected from a group comprising diamines, triamines, organic aminosilanes and/or carbodiimides.

In a further preferred embodiment of the present invention, a flame retardant polyurethane composition obtained from the flame retardant prepolymer composition by reacting the flame retardant prepolymer composition in at least one cross-linking step with approxi mately 0,5 wt-% to approximately 8 wt-% of at least one crosslinking agent, wherein an at least one neutralizing agent is preferably selected of a group comprising tertiary amines, amino alcohols, metal hydroxides, ammonia or a mixture thereof, wherein the at least one neutralizing agent is preferably used in a molar ratio of approximately 0,5 to approximately 1 to the total amount of the at least one multifunctional diol . The at least one neutralizing agent is used in a range of approximately 1 wt-% to approximately 3 wt-%, in each case re ferring to the total amount of the flame retardant polyurethane composition.

In a further preferred embodiment of the present invention, a flame retardant polyurethane composition obtained from the flame retardant prepolymer composition by reacting the flame retardant prepolymer composition in at least one cross-linking step with approxi mately 0,5 wt-% to approximately 8 wt-% of at least one crosslinking agent, wherein the flame retardant prepolymer composition comprises approximately 80 wt-% to approxi mately 95 wt-% of at least one isocyanate-terminated polyurethane prepolymer and approx imately 5 wt-% to approximately 20 wt-% of at least one non-aqueous solvent, wherein the at least one isocyanate-terminated polyurethane prepolymer contains approximately 5 wt-% to approximately 55 wt-% of at least one phosphonate oligomer, phosphonate monomer or a mixture thereof as a first building block, referring to the total amount of the at least one isocyanate-terminated polyurethane prepolymer, wherein the least one crosslinking agent is selected from a group comprising diamines, triamines, organic aminosilanes and/or carbodi- imides, and wherein an at least one neutralizing agent is preferably selected of a group com prising tertiary amines, amino alcohols, metal hydroxides, ammonia or a mixture thereof, wherein the at least one neutralizing agent is preferably used in a molar ratio of approxi mately 0,5 to approximately 1 to the total amount of the at least one isocyanate-terminated polyurethane prepolymer, wherein the non-volatile content of the flame retardant polyurethane composition is preferably in a range of approximately 25 wt-% to approxi mately 50 wt-%, in each case referring to the total amount of the flame retardant polyurethane composition.

The present invention will be hereunder described in more detail with reference to the fol lowing non-limitating examples in accordance with the present invention of the flame retar dant prepolymer composition and the flame retardant polyurethane composition.

The pH value is detected with a pH meter set model pH50+DHS - COND51+ - PC52+DHS at 50°C. The products are measured with a dilution of 1:9 in water. The Calibration standards were a pH buffer solution with a pH of 4.01 ± 0.02 at 25°C and a pH buffer solution with a pH of 7.00 ± 0.02 at 25°C.

The viscosity was measured with a Brookfield DV2T EXTRA™ Viscometer. The viscosity was measured at 20°C with rotational frequency of 20 rpm and a spindle 2 of the RV EZ-Lock Spindle Set.

The non-volatile content, also known as active content, was measured with a Sartorius bal ance. 0.5 to 2.0 g of the inventive flame retardant polyurethane composition was poured on a filter paper made of Fiber Glass Filter and a diameter of 90mm in an disposable aluminum Sample Pan with an diameter of 90 mm and an height of 7 mm and heated to 120°C for SO min. The weight before m _wet and the weight after heating m _dry was detected. By calculating as set forth below, the weight percent of the non-volatile content could be determined by: m d.ry non - volatile content [ wt - %] = 100%. m wet The theoretical NCO value and the experimental NCO value were calculated as described above according to ISO 14896: 2009-07 Method A.

The fire performance measurements were carried out on the basis of the results obtained with the five test specimens each on paper and cellulose cloth comparable to the UL 94 VTM (Vertical flame test of thin materials: ASTM D4804). In this test, the tested materials are given test results comparable to the classifications of UL-94 VTM-0, UL-94 VTM-1 and UL-94 VTM-2. Briefly, the criteria for each of these UL-94-VTM-classifications are as follows:

Table 1: Inflammability classification according to UL 94 VTM

Testing criteria VTM-0 VTM-1 VTM-2

After-burning time of each sample [s]

< 10 < 30 < 30 (after the 1st and 2nd flame treatment)

Total of all after-burning times [s]

< 50 < 250 < 250

(10 flame treatments)

Afterburning time plus afterglow time after 2nd flame treatment

< 30 < 60 < 60 [s]

Burning dripping (inflammation of the cotton wool)

Burn to the retaining clip (complete destruction of the sample) no no no

To judge the flame retardant effect of inventive flame retardant polyurethane composition coated fabrics were manufactured by using a paper or cellulose cloth which was impreg nated with the inventive flame retardant polyurethane composition and dried at room tem perature for 24h. In order to assess the flammability of the flame retardant polyurethane composition itself, a thin film of dried flame retardant polyurethane composition was pre- pared for the flammability test comparable to UL 94 by drying the flame retardant polyurethane composition a shell at room temperature. The samples were treated with a flame having a height of about 20 mm for 3 seconds, after a 10 sec break the flame treat ment was repeated for again 3 sec.

The following compounds were used in the preparation of the composition of Example 1, Ex ample 2, Comparative example 3 and Table 2.

Polyol derived from e-caprolactone as a white paste with a viscosity at 60°C of 150 mPA*s and a molecular weight of 1000 g/ mol obtainable as CAPA 2101 from Ingevity was used. Dimethylol propionic acid powder having a purity of 95-100% from Perstorp was used. Trimethylol propane flakes with a hydroxy number of 1238 - 1260 mg KOH/g from Perstrop was used. Phosphonate oligomer powder with an ignition temperature of 590 to 600 °C ob tainable as Nofia OL 1001 from FRX Polymers was used. Acetone with a purity of 98,5 % from Panreac was used. Isophorone diisocyante obtainable as Vestanat IPDI from Evonik was used. Triethylamine with a purity of 99 % from Alfa Aesar was used. As crosslinking agent y- aminopropyl triethoxysilane with purity above 97 % obtainable as Genosil GF 93 silane from Wacker Silicones was used. Ethylene diamine with a purity of 99 % from Alfa Aesar was used.

Example 1: Preparation of flame retardant prepolymer composition

The following raw materials 401,7 g of polyol, 47,1 g of dimethylol propionic acid (Bis-MPA), 21 g of trimethylol propane (TMP) and 164, 6g of phosphonate oligomer were charged into a round bottom flask equipped with a thermometer, an agitator and a condenser. Add 60 g of acetone to the polyol mixture. Heat the polyol mixture to 85-90 °C under good agitation. Be fore adding 365,5 g of isophorone diisocyante under stirring the polyol mixture was cooled down to 55°C. When the exothermic reaction has subsided the reaction mixture was heated to 75-80°C for 2 hours. When the reaction mixture reached the theoretical NCO value of 4.55 %, cool the reaction mixture down to 60-65°C. The NCO value is determined by the di-n- butylamine titration method A. After reaching the temperature of 60-65°C, 28 g of triethyl amine for neutralization of the reaction mixture was added and the temperature was main tained for 20-30 min. 140 g of acetone was poured to the reaction mixture to reduce the vis cosity of the gained flame retardant prepolymer composition. Example 2: Preparation of the flame retardant polyurethane composition The flame retardant prepolymer composition was transferred into a plastic container con taining 1300 g cold water under high-speed mixing. The addition of flame retardant prepoly mer composition into the cold water was completed within 15 min. Once the addition was complete, 11,8 g of crosslinking agent diluted with 100 g deionized water was added. After 5 min subsequently a solution of 32 g ethylene diamine with 100 g deionized water was poured into the reaction mixture within 5-10 min. The reaction mixture was stirred with a stirring rate of 500 to 800 rpm for about 2-3 h. When the reaction time was over, the reac tion mixture was filtered through a 70-100 micron filter and acetone was distilled off under reduced pressure to obtain an organic solvent free flame retardant polyurethane composi tion. Filtering the flame retardant polyurethane composition by using a 100-micron polyester filter bag gave the desired flame retardant polyurethane composition.

Comparative example 3: Preparation of a comparative polyurethane composition without fire performance:

The following raw materials 978,2 g of polyol based on polyester and 79,9 g of dimethylol propionic acid (Bis-MPA) were charged into a round bottom flask equipped with a ther mometer, an agitator and a condenser. 120 g of acetone was added to the polyol mixture. The polyol mixture was heated to 75-80 °C under agitation. The polyol mixture was cooled down to 55°C then 544,2 g of isophorone diisocyante was added under stirring. When the exothermic reaction subsided the reaction mixture was heated to 75-80°C for 2 hours. When the reaction mixture reached the theoretical NCO value of 4.55 %, cool the reaction mixture down to 60-65°C. The NCO value is determined by the di-n-butylamine titration method A. After reaching the temperature of 60-65°C, 48,2 g of triethylamine for neutralization of the reaction mixture was added and the temperature was maintained for 20-30 min. 120 g of acetone was poured to the reaction mixture to reduce the viscosity of the gained prepoly mer composition. The prepolymer composition was transferred into a plastic container con taining 1519 g cold water under high-speed mixing. The addition of prepolymer composition into the cold water was completed within 15 min. Subsequently a solution of 48.1 g ethylene diamine with 747 g deionized water was poured into the reaction mixture within 5-10 min. The reaction mixture was stirred with a stirring rate of 500 to 800 rpm for about 2-3 h. When the reaction time was over, the reaction mixture was filtered through a 70-100 micron filter and acetone was distilled off under reduced pressure to obtain an organic solvent free polyurethane composition. Filtering the polyurethane composition by using a 100-micron polyester filter bag gave the desired comparative polyurethane composition.

The experimental results of the flame retardant polyurethane composition were shown in the following Table 2.

Table 2: Comparison of the inventive example 2 and the comparative example 3

Parameters Example 2 Comparative example 3 pH value 8.21 pH 8.63 pH Viscosity, 20 °C 190 mPa*s 164 mPa*s Non-volatile content 40 wt-% 40 wt-%

Fire Performance: Paper: Burn to the retain

Paper: After-burning time of each sam ing clip holding the sam ple <10 sec after the 1st flame treat ple; burning dripping (in ment; after the 2nd flame treatment flammation of the cotton one out of five samples started burning wool) (Total of all after-burning times <50 sec); no burning dripping

Cellulose Cloth: Burn to the retaining clip holding

Cellulose Cloth: After-burning time of the sample; burning drip each sample <10 sec; no burning drip ping (inflammation of the ping cotton wool)

From the above results, it was shown that the flame retardant polyurethane composition achieved flame retardancy comparable to the class UL-94 VTM-0 respectively UL-94 VTM-1 of the UL 94 flammability testing standards.