Process for preparing high purity aluminum methyl methylphosphonate flame retardant and its use

Abstract

A method of preparing an aluminum methyl methylphosphonate (AMMP) flame retardant by reacting at a reaction temperature of about 110 °C or higher for an amount of time sufficient to produce the AMMP, a reaction mixture containing an aqueous aluminum- containing methylphosphonic acid solution; and dimethyl methylphosphonate. The resulting product is intumescent.

Description

[0001] PROCESS FOR PREPARING HIGH PURITY ALUMINUM METHYL METHYLPHOSPHONATE FLAME RETARDANT AND ITS USE

[0002] TECHNICAL FIELD

[0003] The disclosure relates to a preparation method for and application of aluminum methyl methylphosphonate (AMMP) flame retardant.

[0004] BACKGROUND

[0005] Phosphorus flame retardants are widely used in polymer compositions. AMMP is a solid material that was first reported by Ciba-Geigy to show flame retardancy in Obeche wood shingles. Early reports, such as in EP 0299922 A2, EP327496 A2, DE 3833977 A1 , EP 451101 A2, and WO 9820012 A1 , disclosed that the material was made from aluminum trioxide (ATH) and showed no clear evidence that the pure compound was produced. ATH is a solid, as is AMMP. The solid to solid transformation following these methods would generate solid AMMP product coated over the solid ATH starting material, thus preventing completion of the reaction. Residual un-reacted starting ATH in the core caused issues in the application stage.

[0006] WO 2013077989 A1 ; WO 2011 163207 A2; US 8889773 B2; and US 20170130030 A1 disclose improved methods to make AMMP from ATH with higher purity, which requires a pressurized reactor to achieve the desired purity.

[0007] CN 102086401 teaches a method of making AMMP from a solution of sodium or potassium methyl methylphosphonate. However, completely removing sodium or potassium is difficult and ppm levels of the residual sodium or potassium can catalyze the decomposition of plastics, like PA66.

[0008] Therefore, it is an objective of the present disclosure to provide improved methods of preparing AMMP, preferably in which the reactants are in a solution and only one metal ion is utilized in order to reduce residual impurities. The high purity AMMP produced therefrom can be utilized as a flame retardant in a wide variety of thermoplastic compositions.

[0009] SUMMARY OF THE INVENTION

[0010] The foregoing is achieved by a method of preparing an aluminum methyl methylphosphonate (AMMP) flame retardant comprising reacting at a reaction temperature of about 110 °C or higher for an amount of time sufficient to produce the AMMP flame retardant

[0011] (a) an aqueous aluminum-containing methylphosphonic acid (MPA) solution; and (b) dimethyl methylphosphonate (DMMP).

[0012] The reaction proceeds generally as shown: The reaction temperature will typically range from about 120 to about 180 °C, preferably about 120 to 140 °C, most preferably about 125 to 135 °C. The reaction temperature is held for about 0.5 to about 5 hours, preferably about 1 to about 4 hours, most preferably about 1.5 to about 3.5 hours.

[0013] In certain embodiments, the (a) aqueous aluminum-containing MPA solution is prepared by heating an aluminum compound and an aqueous solution of MPA until a clear solution forms.

[0014] The aluminum compound and the MPA can be agitated at about 25 to about 400 rpm, preferably about 50 to about 200 rpm. The aluminum compound may be selected from the group consisting of alumina, aluminum trichloride, aluminum trihydroxide, aluminum isopropoxide, aluminum carbonate, and aluminum acetate, preferably alumina, aluminum trihydroxide, aluminum isopropoxide, and aluminum carbonate, most preferably alumina. In some of those embodiments, the heating temperature ranges from about 104 to about 260°C, preferably from about 120 to about 140°C, most preferably 125 to about 135 °C.

[0015] In some embodiments, a molar ratio of the aluminum compound to the MPA is about 1 :10 to 1 :4, preferably about 1 :4.5 to about 1 :4. The DMMP can be added to the aqueous aluminum- containing MPA solution, e.g., at a rate of about 50 mL / min or higher to form the reaction mixture.

[0016] In certain embodiments, the method can include seeding the reaction mixture with previously prepared AMMP.

[0017] In some embodiments, the method further comprises agitating the reaction mixture, preferably from about 200 to about 600 rpm, more preferably from about 250 to about 500 rpm, most preferably about 350 to about 450 rpm.

[0018] The product of the reaction can be washed and filtered with a solvent selected from water, acetone, isopropanol, methanol, ethanol, and mixtures thereof. Advantageously, preparing AMMP in such a manner from a clear aluminum MPA solution eliminates problems associated with a solid to solid transformation and can provide intumescent material. Performing the reaction without any metal element present other than aluminium eliminates issues relating to low level detrimental residual impurities and produces a product that is free of sodium and potassium impurities. Moreover, the reaction can be performed with high yield at a fairly low temperature under atmospheric pressure, which brings down the cost of the process significantly as compared to prior art processes.

[0019] Other embodiments of the present disclosure include, but are not limited to, AMMP produced according to a process described herein; a flame retardant polymer composition comprising (i) a polymer and (ii) the AMMP flame retardant of the present disclosure; a process for improving the flame retardancy of a polymer by incorporating therein the AMMP flame retardant prepared according to the present disclosure; and a process for incorporating into a polymer the AMMP flame retardant prepared according to the present disclosure.

[0020] The preceding summary is not intended to restrict in any way the scope of the claimed invention. In addition, it is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

[0021] BRIEF DESCRIPTION OF THE DRAWING

[0022] FIG. 1 shows the result of a thermogravimetric analysis (TGA) of material prepared according to Example 1 of the present disclosure.

[0023] FIG. 2 shows particle size distribution of material prepared according to Example 1 of the present disclosure.

[0024] FIG. 3 is an SEM image of material prepared according to Example 1 of the present disclosure.

[0025] FIG. 4 is a particle size distribution of material prepared according to Example 2.

[0026] FIG. 5 a solid state H1 NMR spectra of the material prepared according to Example 2.

[0027] FIG. 6 is a solid state C13 NMR spectra of the material prepared according to Example 2.

[0028] FIG. 7 is a solid state P31 NMR spectra of the material prepared according to Example 2.

[0029] FIG. 8 is a solid state AI27 NMR spectra of the material prepared according to Example 2.

[0030] FIG. 9 is a particle size distribution of material made according to Example 3.

[0031] FIG. 10 is a particle size distribution of material made according to Example 4.

[0032] FIG. 1 1 is a particle size distribution of material made according to Example 5. DETAILED DESCRIPTION

[0033] Unless otherwise specified, the word “a” or “an” in this application means “one or more than one.” The term “averaged,” when referring to a value, is intended to mean an average, a geometric mean, or a median value.

[0034] As used herein, a D10 or d10 value represents the 10thpercentile, a D50 or d50 value represents the 50thpercentile, and a D90 or d90 value represents the 90thpercentile. Thus, D50 corresponds to the median value. The recitation of numerical ranges by endpoints includes all numbers subsumed within that range (e.g., 1 to 5 includes 1 , 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.) Further, disclosure of ranges includes all subranges included within the broader range (e.g., 1 to 5 discloses 1-4, 1.5-4.5, 1-2, etc.).

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples are illustrative only and not intended to be limiting. To the extent not described herein, many details regarding specific materials and processing acts are conventional and may be found in textbooks and other sources within the flame retardants field. According to one aspect of the present disclosure, a method of preparing AMMP comprises reacting at a reaction temperature of about 110 °C or higher for an amount of time sufficient to produce the AMMP flame retardant a reaction mixture containing

[0036] (a) an aqueous aluminum-containing methylphosphonic acid solution; and

[0037] (b) dimethyl methylphosphonate (DMMP). The reaction proceeds generally as shown: wherein Al is aluminum, “sol” means solution and “MPA” is methylphosphonic acid. The preparation of AMMP is simple and the efficiency is high. The reaction does not require alkaline conditions or formation of a sodium or potassium salt of DMMP. The AMMP prepared by this method can be used as a V-0 flame retardant for thermoplastic resins.

[0038] To prepare the (a) aqueous aluminum-containing methylphosphonic acid solution, the aluminum metal or suitable aluminum compound can be added to an aqueous MPA mixture all at once or in portions. Similarly, the phosphonic acid can be added to a mixture of water and aluminum or aluminum-containing compound all at once or in portions. The components are heated until a clear solution forms. Generally, the components will be heated to greater than 104 °C, such as about 1 15 °C or higher, about 120 °C or higher, about 130 °C or higher, about 140 °C or higher, about 150 °C or higher, about 160 °C or higher, about 170 °C or higher, about 180 °C or higher, about 200 °C or higher, or any range therebetween. In general, the amount of time required to achieve a clear solution will depend on the heating temperature, with higher temperatures generally resulting in shorter times. Often, heating occurs for from about 0.1 to about 48 hours, such as from about 0.2 to about 24 hours, from about 0.5 to about 12 hours, or from about 1 hour to about 6 hours.

[0039] For example, methylphosphonic acid and a solvent (e.g., water) may be stirred to form a homogeneous solution. The solution may be cooled, e.g., from about 0 to about 20 °C, and an aluminum compound, such as an oxide, halide, alkoxide, or hydroxide, may be added to react with the phosphonic acid at an elevated temperature with stirring. The aluminum compound may be selected from the group consisting of alumina, aluminum trichloride, aluminum trihydroxide, aluminum isopropoxide, aluminum carbonate, and aluminum acetate, preferably alumina, aluminum trihydroxide, aluminum isopropoxide, and aluminum carbonate, most preferably alumina.

[0040] According to the presently disclosed process, the reaction mixture containing the aqueous aluminum-containing methylphosphonic acid solution (a) is reacted with DMMP at 1 10°C or higher for an amount of time sufficient to produce the flame retardant product. As used herein, the step of “reacted at a reaction temperature for an amount of time sufficient to produce the phosphorus-containing flame retardant” and the like include, but are not limited to, embodiments where all or substantially all the solvent for the phosphonic or acid boils off from the reaction mixture during the course of heating the reaction mixture to or at the reaction temperature. It is therefore understood that the “reaction mixture” described herein is still said to be heated at the reaction temperature even where all or substantially all of the solvent boils off during the course of heating the reaction mixture to or at the reaction temperature.

[0041] The reaction mixture is reacted at temperatures higher than 1 10 °C, such as about 115 °C up to about 300 °C, or about 1 15 °C up to about 288 °C, or about 120 °C to about 265 °C. Typically, the reaction temperature does not meet or exceed the boiling temperature of the MPA.

[0042] As described above, the reaction mixture is heated or reacted at the reaction temperature for an amount of time sufficient to produce the AMMP. Often, the flame retardant product will precipitate from the reaction mixture such that the reaction is run for a time sufficient to achieve such precipitation. In general, the amount of time required to achieve at least substantial conversion to the AMMP product, depends on the reaction temperature, with higher temperatures generally resulting in shorter reaction times. Often, heating or reacting occurs at the reaction temperature for from about 0.1 to about 48 hours, such as from about 0.2 to about 36 hours, from about 0.5 to about 30 hours, from about 1 hour to about 24 hours, e.g., from about 0.5 hour to about 12 hours, from about 1 hour to about 8 hours, or from about 0.5 hour to about 4 hours, although other durations may be used.

[0043] The reaction mixture can be prepared in any manner suitable for combining or mixing the (a) aqueous aluminum-containing MPA solution, and (b) DMMP. For example, the components may be combined simultaneously or at different times. In some embodiments, the DMMP is added to a solution, of aluminum or aluminum compound, phosphonic acid, water and optionally another solvent. The DMMP can be added to the reaction mixture all at once or in portions. Alternatively, the (a) aqueous aluminum-containing MPA solution can be added into DMMP all at once or in portions.

[0044] In preparing the reaction mixture, the (a) aqueous aluminum-containing MPA solution and the DMMP may be combined at a preparation temperature below the reaction temperature. The reaction mixture is subsequently heated to the reaction temperature. A preparation temperature may be chosen, for example, to facilitate hydrolysis of the DMMP. At the preparation temperature, the reaction mixture may form a suspension or slurry, such as a well- dispersed suspension or slurry. In many embodiments, the preparation temperature is about 0 °C or higher, but often below 150 °C, such as below 125 °C, below 1 15 °C, below 100 °C, below 85 °C, or below 65 °C. For example, the preparation temperature may range from about 0 °C to about 65 °C or from about 15 °C to about 40 °C. In some embodiments, the reaction mixture is prepared at room temperature (e.g., from about 15 °C to about 25 °C). In some embodiments, the AI-MPA solution (a) is preheated to the preparation temperature and is combined with the DMMP.

[0045] The reaction mixture may alternatively be prepared at the reaction temperature. That is, the reaction mixture is prepared by combining the AI-MPA solution (a) and DMMP at the reaction temperature. For example, in some embodiments, preparing the reaction mixture comprises preheating solution (a) to the reaction temperature and combining with DMMP. The particle size of the AMPP can be controlled purely by the rate of agitation of the reaction mixture, with a higher rate of agitation resulting in smaller particle size. The rate of agitation will generally range from 50 to 1 ,000 rpm, such as about 200 to about 600 rpm, preferably about 250 to about 500 rpm, more preferably about 350 to about 450 rpm. Agitation within these ranges can produce AMMP having particle size less than 500 pm, and preferably having D90 of less than 250 pm, more preferably D90 less than 100 pm, as determined using a laser scattering analyzer.

[0046] The solid product may be isolated by filtration, optionally washed and dried, to yield the product in the form of a powder or small particles. In some cases, the product may be sieved to refine the particle size.

[0047] The reaction as described herein may optionally be facilitated with a seeding material. For example, use of a seeding material may reduce the time to achieve conversion to the flame retardant product and may lead to increased consistency in the product’s physical characteristics. Thus, in some embodiments, the reaction mixture further comprises a seeding material (c). Often, the seeding material is added to the reaction mixture upon or after mixing DMMP with a preheated Al MPA solution. In some embodiments, the seeding material comprises a flame retardant material produced according to the process of the present disclosure. The seeding material may be selected or refined to have a desired particle size.

[0048] The AMMP produced as described herein may be used with a variety of other flame retardants and / or synergists or flame retardant adjuvants as known in the art. In many embodiments, a flame retardant polymer composition according to the present disclosure comprises (i) a polymer, (ii) AMMP of the present disclosure, and (iii) one or more additional flame retardants and / or one or more synergists or flame retardant adjuvants.

[0049] The thermally stable AMMP of the invention can be compounded into thermoplastic polymers at high temperatures, such as high temperature polyamides and polyterephthalate esters, without decomposing or negatively impacting the physical properties of the polymer, and the flame retardant activity is excellent. The flame retardant of the invention may be used in other polymers, with other synergists and with conventional polymer additives. Any known compounding techniques may be used to prepare the flame retardant polymer composition, for example, the flame retardant may be introduced into molten polymer by blending, extrusion, fiber or film formation etc. In some cases the flame retardant is introduced into the polymer at the time of polymer formation or curing, for example, the flame retardant of the invention may be added to a polyurethane prepolymer prior to crosslinking or it may be added to a polyamine or alkyl-polycarboxyl compound prior to polyamide formation or to an epoxy mixture prior to cure. The following examples are helpful for further understanding of the present invention, but the content of the present invention is not limited thereby.

[0050] EXAMPLES Example 1

[0051] To a 1 L cylinder reactor, equipped with thermocouple, mechanical agitator, and distillation setup, was added alumina (20.0 g, 0.196 mol, 1.0 eq Al) and 75% aqueous solution of methyl phosphonic acid (155.7 g, 1.22 mol, 3.1 eq) at room temperature. The heating mantle temperature was set to 190 °C with the agitator at 100 RPM. The white slurry did not change after 4 hours (the pot temperature 104.6 degree C). More MPA (146.1 g, 1.14 mol, total 6.0 eq) was added and the mantle temperature was set to 220 °C. The white slurry turned into a clear solution upon heating for 1 hour (pot temperature 102.9 degree C).

[0052] After the reaction mixture turned into clear solution, dimethyl methylphosphonate (DMMP, 212.6 ml, 243.4 g, 1 .96 mol, 5.0 eq) was added into 104.2 °C clear solution drop by drop from an addition funnel over 25 minutes with agitation at 250 RPM. No obvious temperature change was observed for the reaction pot. The reaction mixture stayed a clear solution for 3 hours upon heating (pot temperature at 104 °C). Set the pot temperature to 130 °C. The reaction mixture started to turn cloudy when the pot temperature arrived at 1 18 °C. The reaction mixture was then kept at 130 °C (pot) overnight and then cooled to room temperature. 500 ml DI water was added and then the slurry was filtered off. The white solid was washed with DI water (200 mL x 2) and suction dried for 4 hours. The solid cake was transferred into a 1 L beaker with 500 mL DI water, stirred at 250 RPM for 20 min, and then filtered off and washed with DI water (200 mL x 2). The cake was suction dried overnight and then dried in a 60 °C oven for 4 hours resulting in a white solid. Elemental analysis results comparing to the theoretical numbers (Theoretical: C% 20.35, H% 5.12, Al% 7.62, P% 26.24; Measurement: C% 20.50, H% 5.53,

[0053] Al% 7.71 , P% 27.40). The crude yield was 53.9%.

[0054] Al in MPA clear solution

[0055] A thermal weight loss curve is shown in FIG. 1 and a particle size distribution based on duplicate measurements in FIG. 2 (D90 (average) 247.27 pm). An image showing morphology of the resulting solid material by SEM at 500 magnitude is shown in FIG. 3.

[0056] Example 2 - Al as limiting agent

[0057] To a 1 L cylinder reactor, equipped with thermocouple, mechanical agitator, and distillation setup, was added alumina (20.0 g, 0.196 mol) and 75% aqueous solution of methyl phosphonic acid (200.9 g, 1.57 mol) at room temperature. The pot temperature was set to 130 °C with an agitator at 100 RPM. The white slurry turned into clear solution in about 2 hours after the pot temperature arrived at 130 °C.

[0058] After the reaction mixture turned into clear solution, dimethyl methylphosphonate (DMMP, 212.6 ml, 243.4 g, 1.96 mol) was added dropwise into 130 °C clear solution from an addition funnel over 3 hours with agitation at 350 RPM. Obvious exotherm was observed at the beginning of the addition of DMMP (pot temperature increased from 130 °C to 140 °C within 30 min and then gradually dropped to 130 °C). The clear solution turned cloudy within 10 min of addition. After finishing addition of DMMP, the white slurry was kept at 130 °C, 350 RPM for 1 hour, and then cooled to room temperature. 500 ml DI water was added and then the slurry was filtered off. The white solid was washed with DI water (200 ml_ x 2) and suction dried for 4 hours. The solid cake was transferred into a 1 L beaker with 500 mL DI water, stirred at 350 RPM for 20 min, and then filtered off and washed with DI water (200 mL x 2). The cake was suction dried overnight and then dried in a 60 °C oven for 4 hours to obtain a white solid with crude yield of 89.3%. Elemental analysis (Theoretical: C% 20.35, H% 5.12, Al% 7.62, P% 26.24; Measurement: C% 20.50, H% 5.53, Al% 7.71 , P% 27.40).

[0059] Particle size distribution for duplicate measurements of the resulting material is shown in FIG. 4 (D90 (average) 96.25 pm). Solid state NMR shown in FIGs. 5-8 was consistent with the composition of the material and certified that the material with high purity as well. Example 3 - DMMP as limiting agent

[0060] To a 3 L cylinder reactor, equipped with thermocouple, mechanical agitator, and distillation setup, was added alumina (80.0 g, 0.785 mol, 1 .0 eq Al) and 75% aqueous solution of methyl phosphonic acid (903.4 g, 75% aq, 7.06 mol, 9.0 eq) at room temperature. The pot temperature was set to 130 °C with the agitator at 100 RPM. The white slurry turned into clear solution in about 2 hours after the pot temperature arrived at 130 °C.

[0061] After the reaction mixture turned into clear solution, dimethyl methylphosphonate (DMMP, 492.8 ml, 564.3 g, 4.55 mol, 2.9 eq) was added into 130 °C clear solution from an addition funnel in 3 minutes with agitation at 400 RPM. The pot temperature dropped to 1 12 °C and came back to 130 °C within 15 minutes. 20 minutes after the pot temperature came back to 130 °C, 10 g seed of previously made AMMP was added into the clear solution, and the reaction mixture started to foam up to about double volume and then subsided back to the original volume within 1 hour. The slurry stayed. The white slurry was kept at 130 °C, 400 RPM for 3 hour, and then cooled to room temperature. 2000 ml DI water was added and then the slurry was filtered off. The white solid was washed with DI water (500 mL x 2) and suction dried for 4 hours. The solid cake was transferred into a 1 L beaker with 1000 mL DI water, stirred at 250 RPM for 20 min, and then filtered off and washed with DI water (500 mL x 2). The cake was suction dried overnight and then dried in a 60 °C oven for 4 hours, resulting in a white solid. Elemental analysis (Theoretical: C% 20.35, H% 5.12, Al% 7.62, P% 26.24; Measurement: C% 21.02, H% 5.59, Al% 7.39, P% 25.80). The crude yield was 75.2%. MPA H Q

[0062] Particle size distribution of duplicate measurements of the resulting material is shown in FIG.

[0063] 9 (D90 (average) 74.57 pm).

[0064] This procedure is economical to scale up and with less concerns with environmentally hazardous DMMP, as it will be completely consumed during the reaction.

[0065] Example 4

[0066] The procedure of Example 2 was followed but the scale was doubled, and reaction mixture was stirred at 400 rpm. Yield was 82%. Particle size distribution of resulting material is shown in FIG. 10 (D90 74.39 pm).

[0067] Example 5

[0068] The procedure of Example 3 was followed with same 3 hour hold time, but the scale was doubled. Yield was 70 to 75%. Particle size distribution of duplicate measurements of the resulting material is shown in FIG. 11 (D90 (average) 107.95 pm).

[0069] Although particular embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art from consideration of the specification and practice of the present disclosure that various modifications and variations can be made without departing from the scope of the invention, as claimed. Thus, it is intended that the specification and examples be considered as exemplary only, with a true scope of the present invention being indicated by the following claims and their equivalents.

Claims

What is claimed is:

1. A method of preparing an aluminum methyl methylphosphonate (AMMP) flame retardant comprising reacting at a reaction temperature of about 1 10 °C or higher for an amount of time sufficient to produce AMMP a reaction mixture containing(a) an aqueous aluminum-containing methylphosphonic acid solution; and(b) dimethyl methylphosphonate (DMMP).

2. The method according to claim 1 , wherein the reaction temperature is from about 120 to about 180 °C, preferably about 120 to 140 °C, most preferably about 125 to 135 °C.

3. The method according to claims 1 or 2, wherein the (a) aqueous aluminum-containing methylphosphonic acid solution is prepared by combining an aluminum compound and an aqueous solution of methylphosphonic acid to form an aqueous methylphosphonic acid slurry and heating the slurry until a clear solution forms.

4. The method according to claim 3, wherein the heating temperature ranges from about 104°C to about 260 °C.

5. The method according to claim 3, further comprising agitating the slurry, preferably at about 25 to about 400 rpm, more preferably about 50 to about 200 rpm.

6. The method according to claim 3, wherein the aluminum compound is selected from the group consisting of alumina, aluminum trichloride, aluminum trihydroxide, aluminum isopropoxide, aluminum carbonate, and aluminum acetate, preferably alumina, aluminum trihydroxide, aluminum isopropoxide, and aluminum carbonate, most preferably alumina.

7. The method according to claim 5, wherein molar ratio of the aluminum compound to the methylphosphonic acid is about 1 :10 to 1 :4, preferably about 1 :4.5 to about 1 :4.

8. The method according to any of the preceding claims, further comprising adding the DMMP to the aqueous aluminum-containing methylphosphonic acid solution at a rate of about 50 mL / min or higher to form the mixture.

9. The method according to any of the preceding claims, further comprising seeding the reaction with previously prepared AMMP.

10. The method according to claim 8, wherein the seeding occurs after mixing the DMMP with the aqueous aluminum-containing methylphosphonic acid solution at the reaction temperature.1 1 . The method according to any of the preceding claims, further comprising agitating the reaction mixture, preferably from about 200 to about 600 rpm, more preferably from about 250 to about 500 rpm, most preferably about 350 to about 450 rpm12. The method according to any of the preceding claims, wherein the reaction temperature is held for about 0.5 to about 5 hours, preferably about 1 to about 4 hours, most preferably about 1 .5 to about 3.5 hours.

13. The method according to any of the preceding claims, further comprising washing and filtering the produced AMMP with a solvent selected from water, acetone, isopropanol, methanol, ethanol, and mixtures thereof.

14. AMMP produced by a method according to any of the foregoing claims.

15. The AMMP according to claim 14, wherein the AMMP is intumescent.

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