EP4780891A1 - Method of preparing phosphorus-containing flame retardants having improved powder properties - Google Patents

Abstract

A phosphorus-containing flame retardant is produced by preparing metal phosphonic acid solution, and reacting a reaction mixture of unsubstituted or alkyl or aryl substituted pyrophosphonic acid with the metal phosphonic acid solution at a reaction temperature from 130 °C to 240 °C for an amount of time sufficient to produce the phosphorus-containing flame retardant in crystalline form. The resulting flame retardant is stable and has improved powder properties for formulating in polymer compositions, particularly thermoplastics processed at high temperatures, over a wide range of applications.

Description

METHOD OF PREPARING PHOSPHORUS-CONTAINING FLAME RETARDANTS HAVING IMPROVED POWDER PROPERTIES

A highly effective, thermally-stable, phosphorus-containing flame retardant is produced by a process comprising reacting a phosphonic acid and a metal or suitable metal compound in a solvent to provide a metal phosphonic acid solution, and adding pyrophosphonic acid to the solution under conditions as described herein. The chemical composition of the resulting flame retardant product, in many embodiments, is produced as one or predominantly one compound having good flowability and powder properties, leads to excellent flame retardancy and exhibits high thermal stability. The presently disclosed flame retardants are useful, for example, in polymer compositions, particularly thermoplastics processed at high temperatures, over a wide range of applications.

BACKGROUND

Phosphonic acid salts, i.e. , compounds of the formula directly below, are known flame retardants in many polymer compositions: wherein R is an optionally substituted alkyl, aryl, alkylaryl or arylalkyl group, p is typically a number of from 1 to 4, M is a metal, and y is typically a number of from 1 to 4, so that M^{( +)y} is a metal cation where (+)y represents the charge formally assigned to the cation.

As disclosed in US 2007/0029532, decomposition of phosphonic acid salts is known at temperatures encountered during processing of polyesters and polyamides, damaging the polymers in the process, e.g., temperatures above 260 or 270 °C.

US Pat 5,053,148 discloses that brittle, heat resistant foams can be obtained by heating phosphonic acid salts at elevated temperatures.

In Comparative Examples 1 and 2 of US Pat. 9,745,449, glass filled polyamide compositions comprising 10 to 25 wt% of methylphosphonic acid aluminum salt were processed at elevated temperatures. A decrease in torque was observed during compounding, consistent with polymer degradation, producing a final product material that was friable upon cooling, dusty after grinding, and which could not be molded. Analysis of the compounded material by gel permeation chromatography (GPC) and differential scanning calorimetry (DSC) provided additional evidence of degradation. The loss of desired polymer properties observed is consistent with the degradation of polymers suggested in US 2007/0029532 and the brittle foam formed in US Pat 5,053,148.

Thus, simple phosphonic acid salts are not suitable for use in many polymers that are processed at, or subsequently exposed to, high temperatures, such as 250 °C, 260 °C, 270 °C or higher, as they undergo chemical transformation at such temperatures via processes that harm the polymer. This may happen during compounding, e.g., in an extruder, or while the salt is present in a polymer in a high temperature application.

On the other hand, US Pat. 9,745,449 discloses that heating a phosphonic acid salt at high enough temperatures generally in the absence of other materials thermally transforms the salt into a different, more thermally stable material exhibiting excellent flame retardant activity when incorporated into polymeric substrates. The thermally transformed materials do not degrade at high temperatures, nor do they cause degradation of a polymer, when processed in polymer compositions at elevated temperatures, e.g., 240°C, 250°C, 260°C, 270°C or higher, which is an important advantage over previously known phosphonate salts, which exhibit flame retardant activity but often degrade the polymer during processing. The thermally transformed materials are described as comprising one or more compounds represented by empirical formula (IV): wherein R is alkyl or aryl, M is a metal, q is a number of from 1 to 7, e.g., 1, 2 or 3, r is a number from 0 to 5, e.g., 0, 1 or 2, y is a number of from 1 to 7, e.g., from 1 to 4, and n is 1 or 2, provided that 2(q)+r = n(y).

Challenges, however, are encountered with the process and materials of US Pat. 9,745,449, such as the production of product generally in the form of a solid mass requiring grinding, milling, or other such physical processing before use; formation of product mixtures containing water soluble or thermally unstable compounds; and difficulty in controlling the phosphorus to metal ratio of the resulting product. In addition, the Examples of US Pat. 9,745,449 describe producing a phosphorus-containing flame retardant in several steps wherein an intermediate metal salt of a phosphonic acid is produced and the dried salt is then heated at temperatures over 200° C. WO 2020/132095 describes an improved process that is able to directly produce flame retardant material as a powder or in small particle form by heating a phosphonic acid metal salt in a high boiling, water miscible, acid stable solvent, such as a sulfone.

Applicant’s WO 2020/132075, WO 2021/257749, WO 2021/076169, WO 2021/257755, WO 2021/257756, WO 2023/096795, and co-pending application No. US 63/441 ,482 disclose processes for producing a new class of crystalline flame retardant having formula (III), and its inclusion in additive compositions for thermoplastic polymers. wherein R is H, an alkyl, aryl, alkylaryl, or arylalkyl group, M is a metal and y is 2 or 3, such that M^(+)y is a metal cation where (+)y represents the charge formally assigned to the cation, a, b, and c represent the ratio of the components to which they correspond relative to one another in the compound, and satisfy the charge-balance equation 2(a)+c=b(y), and c is not zero. The crystalline powder produced by such processes typically yields average particle size of about 20-40 pm (D90) and long crystals with a high aspect ratio, such about 12.5, that can be difficult to formulate in certain circumstances.

It was desired to have an alternative, energy efficient process for preparing crystalline phosphorous flame retardant of empirical formula (III) as described above, and particularly compounds of empirical formula (Illa)

It was further desired to have a process for manufacturing phosphorous material of formulas (III) and (Illa) having a smaller aspect ratio and narrower particle size distribution than the powder produced according to Applicant’s previously disclosed processes. The present disclosure addresses the above-identified objectives, while also producing a phosphorus-containing flame retardant without requiring the production or use of an intermediate salt as described in US Pat. 9,745,449.

SUMMARY

In accordance with the present disclosure, a phosphorus-containing flame retardant is prepared by a process comprising preparing a metal phosphonic acid solution; and reacting a reaction mixture of unsubstituted or alkyl or aryl substituted pyrophosphonic acid with the metal phosphonic acid solution at a reaction temperature from 130 °C to 240 °C for an amount of time sufficient to produce the phosphorus-containing flame retardant.

In certain embodiments, the alkyl or aryl substituted pyrophosphonic acid is prepared by adding a catalytic amount of a catalyst to unsubstituted or substituted alkyl or aryl phosphonic acid, and heating at a temperature of about 105 °C or higher, such as 130 °C to 240 °C, preferably 180 °C to 210 °C, for an amount of time sufficient to produce the unsubstituted or substituted pyrophosphonic acid.

Preferably, prior to the step of reacting the reaction mixture, the process comprises removing all or substantially all of any water generated when preparing the metal phosphonic acid solution and/or the unsubstituted or substituted pyrophosphonic acid.

Often, the reaction product forms as a slurry as the resulting flame retardant product of the present invention precipitates from the reaction mixture. Phosphonic acid, pyrophosphonic acid, and/or solvent remaining after the reaction can be removed along with any possible byproducts by filtration and/or washing, e.g., with water. In many embodiments, a substantially pure flame retardant material is produced, e.g., a flame retardant comprising essentially a single compound with flame retardant activity or essentially a mixture of active compounds having good powder properties for formulating with polymers. Conversion based on the metal or metal compound is typically high, and the product can be readily isolated and optionally further purified if desired.

The present process overcomes difficulties observed in processes such as found in US Pat. 9,745,449, because, e.g., production of water soluble or thermally unstable compounds are reduced or avoided, and the flame retardant product, which crystallizes as a powder or small particles, can be produced directly in a readily processable form, i.e., without requiring or necessitating grinding, granulating, or other such physical processing. Surprisingly, the presently described process was able to produce crystalline product of formulas (III) and (Illa) with improved powder properties over Applicant’s previous disclosures. The products of formulas (III) and (Illa) made by the process herein have an reduced aspect ratio, such as Aspd90 less than 10, preferably Aspd90 less than 8, more preferably Aspd90 less than 7, or Aspd50 that is less than 7, preferably less than 5, more preferably less than 4 as determined by SEM imaging, and a narrower particle size distribution. This allows for easier formulation and manufacturing of flame retardant polymer compositions.

Other embodiments of the present disclosure include, but are not limited to, a phosphorus- containing flame retardant produced according to a process described herein, such as a compound of formula (III) or (Illa); a flame retardant polymer composition comprising (i) a polymer and (ii) a phosphorus-containing flame retardant of the present disclosure; a process for improving the flame retardancy of a polymer by incorporating therein a flame retardant of the present disclosure; and a process for incorporating into a polymer a flame retardant composition comprising a flame retardant of the present disclosure.

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.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a scanning electron microscope image of flame retardant material produced according to WO 2021/076169.

FIG. 2 shows a scanning electron microscope image of flame retardant material produced according to Example 4.

FIG. 3 shows a scanning electron microscope images of flame retardant material produced according to Example 6.

FIG. 4 is a particle size distribution of flame retardant material made according to WO 2021/076169. FIG. 5 is a particle size distribution of flame retardant material made according to Example 5.

FIG. 6 shows a scanning electron microscope image of flame retardant material produced according to Example 4.

FIG. 7 is a particle size distribution of flame retardant material produced according to Example 4.

FIG. 8 is graph showing covernsion rate of methylphosphonic acid into pyrophosphonic acid in accordance with Example 10.

DETAILED DESCRIPTION

Unless otherwise specified, the word “a” or “an” in this application means “one or more than one”.

The term “alkyl” in this application includes “arylalkyl,” unless the context dictates otherwise.

The term “aryl” in this application includes “alkylaryl,” unless the context dictates otherwise.

The term “phosphonic acid” as used herein refers to unsubstituted or alkyl or aryl substituted phosphonic acid, unless the context dictates otherwise.

The term “pyrophosphonic acid” as used herein refers to unsubstituted or alkyl or aryl substituted pyrophosphonic acid, unless the context dictates otherwise.

The term “aspect ratio” describes the extent to which the overall three-dimensional shape of a particle is generally deviating from a compact three-dimensional shape (eg, a spherical or cubic shape). The aspect ratio of a given particle or population of particles is expressed as a length: width ratio. Particles with large aspect ratios are generally long and narrow, while particles with an aspect ratio near 1 are generally dense. By definition, particles cannot have an aspect ratio of less than 1.

The term “Aspd” as used herein refers to an aspect ratio of a fraction of a particle size distribution, such as a D10, D50 or D90. As used herein, a D10 or d10 value represents the 10^th percentile, a D50 or d50 value represents the 50^th percentile, and a D90 or d90 value represents the 90^th percentile. 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.).

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 metal phosphonic acid solution and an unsubstituted or alkyl or aryl substituted pyrophosphonic acid are reacted to form a phosphorus-containing flame retardant. The reaction temperature can range from 130 °C to 240 °C, preferably 190 °C to 210 °C, more preferably 195 °C to 205 °C. Due to limited commercial availability of pyrophosphonic acid and a desire to avoid having any water in it that will cause degradation and decrease reaction yield, the process will typically include preparing the unsubstituted or alkyl or aryl substituted pyrophosphonic acid before adding it to the reaction mixture with the metal phosphonic acid solution.

The pyrophosphonic acid prepared and/or used in the present process may be represented by formula (II) wherein R is H, alkyl, aryl, alkylaryl, or arylalkyl. In many embodiments, R is H, C1-12 alkyl, C6-10 aryl, C7-18 alkylaryl, or C7-18 arylalkyl, wherein said alkyl, aryl, alkylaryl, or arylalkyl are unsubstituted or are substituted by halogen, hydroxyl, amino, CM alkylamino, di-Ci-4 alkylamino, CM alkoxy, carboxy or C2-5 alkoxycarbonyl. In some embodiments, said alkyl, aryl, alkylaryl, or arylalkyl are unsubstituted C1-12 alkyl, Ce aryl, C7-10 alkylaryl, or C7-10 arylalkyl, for example, C1-6 alkyl, phenyl, or C7-9 alkylaryl. In some embodiments, R is substituted or unsubstituted C1-6 alkyl, Ce aryl, C7-10 alkylaryl, or C7-12 arylalkyl, e.g., C1-4 alkyl, Ce aryl, C7-9 alkylaryl, or C7-10 arylalkyl. In many embodiments, R is unsubstituted C1-12 alkyl, e.g., C1-6 alkyl. In many embodiments, lower alkyl phosphonic acids are used, e.g., methyl-, ethyl-, propyl-, isopropyl-, butyl-, t-butyl- and the like.

R as alkyl may be a straight or branched chain alkyl group having the specified number of carbons and includes e.g., unbranched alkyls such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, and branched alkyl such as isopropyl, isobutyl, sec-butyl, t-butyl, ethyl hexyl, t-octyl and the like. For example, R as alkyl may be chosen from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-buty, and t-butyl. In many embodiments, R is methyl, ethyl, propyl or isopropyl, for example methyl or ethyl.

Often, when R is aryl it is phenyl. Examples of R as alkylaryl include phenyl substituted by one or more alkyl groups, for example groups selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-buty, t-butyl, and the like. Examples of R as arylalkyl, include for example, benzyl, phenethyl, styryl, cumyl, phenpropyl and the like.

In many embodiments, R is chosen from methyl, ethyl, propyl, isopropyl, butyl, phenyl and benzyl.

The process of preparing the the unsubstituted or alkyl or aryl substituted pyrophosphonic acid may comprise adding a catalyst to to unsubstituted or substituted phosphonic acid, and heating for an amount of time sufficient to produce the unsubstituted or substituted pyrophosphonic acid.

A heating temperature of 105 °C or higher is used. In many embodiments, the catalyst and the phosphonic acid are reacted at temperatures higher than 105 °C, such as about 115 °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, about 220 °C or higher, about 240 °C or higher, about 260 °C or higher, about 280 °C or higher, or any range therebetween. The heating temperature may be higher than those described above, such as up to about 350 °C, up to about 400 °C, or higher, but it typically does not meet or exceed the boiling temperature of the phosphonic acid. In many embodiments, the heating temperature ranges from about 110 °C to about 350 °C, from about 115 °C to about 300 °C, from about 125 °C to about 280 °C, or from about 130 °C to about 290°C. In certain preferred embodiments, the heating temperature is about 180 °C to 240 °C, more preferably about 200 °C. Through the dehydration reaction(s), water is formed, which can potentially lead to the undesirable reverse (hydrolysis) reaction. Thus, in some embodiments, the reaction system is designed to facilitate removal, such as the continuous removal, of water from the reaction mixture. For example, the reaction temperature may be chosen above the boiling temperature of the water to the extent necessary to boil off at least a portion or desired amount (e.g., a majority, substantially all, or all) of the water from the reaction. Additional means, such as a gas purge, vacuum, and/or other known means, may be used to facilitate removal of water from the reaction system.

In certain embodiments, where the temperature to heat the unsubstituted or substituted phosphonic acid is about 240°C or higher, and a vacuum or nitrogen purge is utilized, a catalyst may not be necessary to produce pyrophosphonic acid. The nitrogen flow rate is typically about 2L/min to about 6L/min, most preferably about 5L/min.

Alternatively, a catalyst may not be necessary where vacuum is pulled below 10 Torr.

The phosphonic acid used to form pyrophosphonic acid may be represented by formula (I) wherein R is H, alkyl, aryl, alkylaryl, or arylalkyl. In many embodiments, R is H, C1-12 alkyl, C6-10 aryl, C7-18 alkylaryl, or C7-18 arylalkyl, wherein said alkyl, aryl, alkylaryl, or arylalkyl are unsubstituted or are substituted by halogen, hydroxyl, amino, CM alkylamino, di-Ci-4 alkylamino, CM alkoxy, carboxy or C2-5 alkoxycarbonyl. In some embodiments, said alkyl, aryl, alkylaryl, or arylalkyl are unsubstituted C1-12 alkyl, Ce aryl, C7-10 alkylaryl, or C7-10 arylalkyl, for example, C1-6 alkyl, phenyl, or C7-9 alkylaryl. In some embodiments, R is substituted or unsubstituted C1-6 alkyl, Ce aryl, C7-10 alkylaryl, or C7-12 arylalkyl, e.g., C1-4 alkyl, Ce aryl, C7-9 alkylaryl, or C7-10 arylalkyl. In many embodiments, R is unsubstituted C1-12 alkyl, e.g., C1-6 alkyl. In many embodiments, lower alkyl phosphonic acids are used, e.g., methyl-, ethyl-, propyl-, isopropyl-, butyl-, t-butyl- and the like.

R as alkyl may be a straight or branched chain alkyl group having the specified number of carbons and includes e.g., unbranched alkyls such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, and branched alkyl such as isopropyl, isobutyl, sec-butyl, t-butyl, ethyl hexyl, t-octyl and the like. For example, R as alkyl may be chosen from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-buty, and t-butyl. In many embodiments, R is methyl, ethyl, propyl or isopropyl, for example methyl or ethyl.

Often, when R is aryl it is phenyl. Examples of R as alkylaryl include phenyl substituted by one or more alkyl groups, for example groups selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-buty, t-butyl, and the like. Examples of R as arylalkyl, include for example, benzyl, phenethyl, styryl, cumyl, phenpropyl and the like.

In many embodiments, R is chosen from methyl, ethyl, propyl, isopropyl, butyl, phenyl and benzyl.

The catalyst used to prepare pyrophosphonic acid may be any Lewis Acid that facilitates dehydration. Suitable Lewis acid catalysts include, but are not limited to iron halide (FeX_n), titanium halide (TiX_n), titanium alkoxide (Ti(OR)4), titanium oxide (TiCh), aluminum halide (AIX3), aluminum alkoxide (AI(OR)a), tin halide (SnX_n), boron trihalide (BX3), magnesium halide (MgX2), calcium halide (CaX2), and zinc halide (ZnX2). Alternatively, aluminum oxide may be used as a catalyst. Other suitable catalysts include thionyl chloride (SOCI2), phosphorous pentoxide, concentrated sulfuric acid, and acetic anhydride. The catalyst can be present in the reaction in a catalytic amount ranging from about 0.001 to about 0.5 mol %, and preferably from about 0.01 to 0.1 mol%. In certain embodiments, the catalyst is present at greater than 0.005 to less than 0.5 mol%, or from about 0.01 mol%, or from about 0.025 mol%, or from about 0.05 mol% to about 0.4 mol %, or to about 0.25 mol% , or to about 0.1 mol%, or any range therebetween.

In preparation of the metal phosphonic acid solution, the phosphonic acid used may also be represented by formula (I) wherein R is H, alkyl, aryl, alkylaryl, or arylalkyl. In many embodiments, R is H, C1-12 alkyl, C6-10 aryl, C7-18 alkylaryl, or C7-18 arylalkyl, wherein said alkyl, aryl, alkylaryl, or arylalkyl are unsubstituted or are substituted by halogen, hydroxyl, amino, CM alkylamino, di-Ci-4 alkylamino, CM alkoxy, carboxy or C2-5 alkoxycarbonyl. In some embodiments, said alkyl, aryl, alkylaryl, or arylalkyl are unsubstituted C1-12 alkyl, Ce aryl, C7-10 alkylaryl, or C7-10 arylalkyl, for example, C1-6 alkyl, phenyl, or C7-9 alkylaryl. In some embodiments, R is substituted or unsubstituted C1-6 alkyl, Ce aryl, C7-10 alkylaryl, or C7-12 arylalkyl, e.g., C1-4 alkyl, Ce aryl, C7-9 alkylaryl, or C7-10 arylalkyl. In many embodiments, R is unsubstituted C1-12 alkyl, e.g., C1-6 alkyl. In many embodiments, lower alkyl phosphonic acids are used, e.g., methyl-, ethyl-, propyl-, isopropyl-, butyl-, t-butyl- and the like.

R as alkyl may be a straight or branched chain alkyl group having the specified number of carbons and includes e.g., unbranched alkyls such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, and branched alkyl such as isopropyl, isobutyl, sec-butyl, t-butyl, ethyl hexyl, t-octyl and the like. For example, R as alkyl may be chosen from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-buty, and t-butyl. In many embodiments, R is methyl, ethyl, propyl or isopropyl, for example methyl or ethyl.

Often, when R is aryl it is phenyl. Examples of R as alkylaryl include phenyl substituted by one or more alkyl groups, for example groups selected from methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-buty, t-butyl, and the like. Examples of R as arylalkyl, include for example, benzyl, phenethyl, styryl, cumyl, phenpropyl and the like.

In many embodiments, R is chosen from methyl, ethyl, propyl, isopropyl, butyl, phenyl and benzyl.

The metal phosphonic acid solution may be prepared from a mixture comprising (a) the unsubstituted or alkyl or aryl substituted phosphonic acid, (b) a solvent for the phosphonic acid, and (c) a metal or suitable metal compound, which are reacted at a temperature above the melting point of the phosphonic acid but below the boiling point of the phosphonic acid to ensure that a solution is maintained and no metal phosphonic acid salt is formed. That is, the metal phosphonic acid should be free of precipitate. Typically, the components (a), (b), and (c) will be mixed at temperature ranging from 100 °C to 280 °C for a time sufficient to ensure that a solution is maintained that is free of precipitate.

The solvent (i.e. , component (b)) may be any solvent capable of dissolving the phosphonic acid component (a), should be inert or substantially inert to the reaction between the phosphonic acid (a) and the metal or suitable metal compound (c), and may further be chosen taking into account other reaction parameters, e.g., the preparation and/or reaction temperature or the type of metal or suitable metal compound, such as to prepare a homogenous or substantially homogenous reaction mixture. In some embodiments, the solvent (b) may be a combination of solvents for the phosphonic acid to allow the phosphonic acid (a) to substantially or completely dissolve in the solvent (b) and form a solution. The type of solvent, the amount of solvent relative to the phosphonic acid, and the mixing conditions can be chosen to achieve dissolution of the phosphonic acid, such as to obtain a high concentration of phosphonic acid in the mixture while maintaining the phosphonic acid in solution. Often, the ratio by weight of the phosphonic acid (a) to the solvent (b) ranges from about 1:3 to 1:50, more preferably about 1 :2.5 to 1:25, most preferably about 1:2.75. In some embodiments where the phosphonic acid (a) is partially dissolved and partially suspended or dispersed in the solvent (b), the preparation temperature may be selected at or higher than the melting temperature of the phosphonic acid to liquefy the phosphonic acid which is suspended or dispersed in the solvent.

The metal of the metal phosphonic acid solution should be capable of being oxidized and may be represented in its corresponding cationic form by the formula M^(+)y where M is a metal, (+)y represents the charge of the metal cation, and y is 3. A suitable metal compound may be represented by the formula Mp^+)yX_q, where M is a metal, (+)y represents the charge of the metal cation, y is 3, X is an anion, and the values for p and q provide a charge balanced metal compound.

As described above, depending on the boiling temperature of the solvent for the phosphonic acid (i.e. , component b), at least a portion of the solvent may boil off from the mixture while heating. In some embodiments, all, substantially all, or at least a majority of the solvent (b) boils off during heating. The solvent (b) may be high-boiling (e.g., sulfolane or dimethyl sulfoxide (DMSO)) or low-boiling (e.g., chloroform or tetrahydrofuran (THF)). For example, in some embodiments, the solvent boils at a temperature at or below the heating temperature such that at least a portion of the solvent boils off during heating of the mixture, e.g., where all, substantially all, or a majority of the solvent boils off. The temperature may be selected at or higher than the melting temperature of the phosphonic acid to ensure that the same remains in liquid form as the solvent boils off.

Suitable solvents may be organic or inorganic. Examples of suitable solvents for the phosphonic acid include, but are not limited to, water, sulfones, sulfoxides, halogenated (e.g., chlorinated) hydrocarbons, aromatic hydrocarbons, and ethers. For example, in some embodiments, the solvent may be chosen from water, sulfolane, dimethylsulfone, tetrahydrofuran (THF), dimethoxyethane (DME), 1,4-dioxane, dimethyl sulfoxide (DMSO), 1 ,2-dichlorobenzene, chloroform, carbon tetrachloride, xylene and mesitylene. In some embodiments, the solvent comprises water. In some embodiments, the solvent comprises an aqueous solution. In some embodiments, the solvent (b) is a protic solvent (e.g., water) and the mixture system is designed to facilitate removal, such as the continuous removal, of the protic solvent during heating of the mixture. For example, a mixing temperature may be chosen at or higher than the boiling temperature of the protic solvent to the extent necessary to boil off at least a portion or desired amount (e.g., a majority, substantially all, or all) of the protic solvent during mixing. In certain embodiments, the solvent is water and the temperature is about 110 °C or higher, about 115 °C or higher, about 120 °C or higher, about 130 °C or higher, about 140 °C or higher, about 150 °C or higher, or about 160 °C or higher. Additional means, such as a gas purge, vacuum, and/or other known means, may be used to facilitate removal of water from the system. The mixing temperature may also be chosen at or higher than the melting temperature of the phosphonic acid but should be below the boiling point of the phosphonic acid so as to avoid formation of metal salt.

As used herein, “suitable metal compound” and the like refer to a compound of the formula M^^+)yX_q, where M is a metal capable of forming a polycation, e.g., a metal that forms a cation of 3+, and X is any anion that provides a charge balanced compound with metal M. Suitable examples for X include, but are not limited to, anions that, together with the metal M, form oxides, halides, alkoxides, hydroxides, carbonates, carboxylates, and phosphonates. The values for p and q provide a charge balanced metal compound, for example, alumina, AI2O3. In some embodiments, an unsubstituted metal, M, is used as described herein. Examples of suitable metals (M) include, but are not limited to B, Al, Ga, In, Tl, Zr, Ti, Cu, Fe, Co, Ga, Bi, Mn, Cr, Sb, Rh, Y. In certain embodiments, M is chosen from Al, Ga, Sb, Fe, Co, B, and Bi. In some preferred embodiments, M is Al or Fe, most preferably Al.

Suitable metal compounds include, but are not limited to, compounds having a metal-oxygen bond, metal-nitrogen bond, metal-halogen bond, metal-hydrogen bond, metal-phosphorus bond, metal sulfur bond, metal boron bond, etc., for example, oxides, halides, alkoxides, hydroxides, carboxylates, carbonates, phosphonates, phosphinates, phosphonites, phosphates, phosphites, nitrates, nitrites, borates, hydrides, sulfonates, sulfates, sulfides, etc.

In some embodiments, the metal, M, of the metal or suitable metal compound is aluminum or iron. In some embodiments, the suitable metal compound is chosen from halides, oxides, hydroxides, alkoxides, carbonates, carboxylates and phosphonates of aluminum. In some embodiments, the suitable metal compound is chosen from halides, oxides, hydroxides, and alkoxides of aluminum. In some embodiments, the suitable metal compound is chosen from alumina, aluminum trichloride, aluminum trihydroxide, aluminum isopropoxide, aluminum carbonate, and aluminum acetate. In other embodiments, the suitable metal compound is chosen from halides, oxides, alkoxides, carbonates, and acetates of iron. In some embodiments, the suitable metal compound is chosen from iron(lll) oxide, iron(lll) chloride, iron(lll) isopropoxide, and iron(lll) acetate.

The mixture of (a), (b), and (c) can be prepared in any manner suitable for combining or mixing (a) the unsubstituted or alkyl or aryl substituted phosphonic acid, (b) the solvent for the phosphonic acid, and (c) the metal or suitable metal compound. For example, the components may be combined simultaneously or at different times and at different temperatures. In some embodiments, the metal or suitable metal compound (c) is added to a mixture, such as a solution, of the phosphonic acid (a) and solvent (b). The metal or suitable metal compound (c) can be added to the mixture all at once or in portions. Similarly, the phosphonic acid (a), solvent (b), or mixture, such as a solution, of the phosphonic acid (a) and solvent (b), can be added to the mixture all at once or in portions.

In a similar manner, the reaction mixture of the metal phosphonic acid and pyrophosphonic acid can be prepared in any manner suitable for combining or mixing the unsubstituted or alkyl or aryl substituted pyrophoshonic acid and the metal phosphonic acid solution. For example, the components may be combined simultaneously or at different times. The pyrophosphonic acid can be added to the reaction mixture all at once or in portions.

Similarly, phosphonic acid metal solution can be added to the reaction mixture all at once or in portions.

The process of the present disclosure may employ more than one phosphonic acid, more than one pyrophosphonic acid, or a combination of phosphonic and pyrophosphonic acids.

The reaction temperature of 130 °C to 240 °C for producing a phosphorus-containing flame retardant according to the present disclosure facilitates the formation of monoanionic and/or dianionic pyrophosphonic acid ligands in the reaction product in a more energy efficient manner than previous methods. In many embodiments, the metal phosphonic acid solution and the pyrophosphonic acid are reacted at temperatures below 240 °C, such as below 230 °C, below 220 °C, below 210 °C, below 205 °C and does not require a system designed to facilitate removal of water and solvent.

As described above, the reaction mixture is heated or reacted at the reaction temperature for an amount of time sufficient to produce the phosphorus-containing flame retardant. 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 flame retardant product, based on the metal or suitable metal compound in the reaction mixture, will depend on the reaction temperature, with higher temperatures in the range generally resulting in shorter reaction times. Advantageously, heating or reacting occurs at the reaction temperature only for from about 0.1 to about 1 hour, such as about 20 minutes, about 10 minutes, about 15 minutes, or about 5 minutes, although other durations may be used.

In many embodiments, the molar ratio of the pyrophosphonic acid to the metal in the reaction mixture is higher than 2:1 , such as about 3: 1 or higher, about 4: 1 or higher, about 5:1 or higher. In many embodiments, the molar ratio ranges from about 2:1, from about 2.5:1 to about 3:1.

The reaction mixture may be prepared at a temperature that is lower than the reaction temperature, such as room temperature or, alternatively, be prepared at the reaction temperature. That is, the reaction mixture is prepared by combining the phosphonic acid metal solution with pyrophosphonic acid at the reaction temperature. For example, in some embodiments, preparing the reaction mixture comprises preheating the pyrophosphonic acid to the reaction temperature and combining with the metal phosphonic acid solution.

After reacting, the product reaction mixture is cooled ensuring that the pyrophosphonic acid remains in liquid form. The excess pyrophosphonic acid and the solvent if present in the product reaction mixture can be removed by filtration/washing and optionally recovered. The recovered excess pyrophosphonic acid and/or solvent may be recycled, e.g., back into the reactor in which a metal phosphonic acid solution reacts with the pyrophosphonic acid. The flame retardant product is often isolated by filtration, optionally followed by additional work up (e.g., washing, drying, sieving, etc.). The resulting crystalline flame retardant product, which is generally in the form of a powder or small particles, is readily processable, i.e. , without requiring or necessitating grinding, milling, or other such physical processing before use. It should be understood that producing the flame retardant material “directly” as a powder or small particles in accordance with the presently disclosed process permits workup of the reaction product, such as isolating the flame retardant product (e.g., separating the flame retardant product from remaining solvent), which may include, e.g., processing the reaction product by filtering, sieving, washing, drying, and the like.

The process of the present disclosure predominantly yields a crystalline flame retardant comprising one or more metals and two bi-dentate pyrophosphonic acid ligands. In some embodiments, compounds that additionally comprise phosphonate ligands may be produced, but in all embodiments compounds comprising a pyrophosphonic acid monoanionic ligand and/or a pyrophosphonic acid di-anionic ligand, or a mixture a mono-anionic and di-anionic ligand are obtained.

A crystalline product made by the process herein has a reduced aspect ratio, such as Aspd90 less than 10, preferably Aspd90 less than 8, more preferably Aspd90 less than 7, or Aspd50 that is less than 7, preferably less than 5, more preferably less than 4 as determined by SEM imaging, and a narrower particle size distribution as compared to the product according to Applicant’s WO 2020/132075, WO 2021/257749, WO 2021/076169, WO 2021/257755, 2021/257756, and co-pending application Nos. PCT/US2022/050062 and US 63/441 ,482. The reduced aspect ratio and narrower particle size distribution provides adavantages with respect to formulation and manufacturing of flame retardant polymer compositions. Moreover, the process described herein results in less fines, which may also provide formulation and manufacturing advantages.

The process may yield mixtures of flame retardant compounds, but in many embodiments the process produces a flame retardant material as one, or predominantly one, compound of formula (III), with high conversion based on the metal or metal compound, such as at least 70%, 80%, 85%, 90%, 95%, 98% or higher conversion, or any range therebetween, as opposed to the mixtures of compounds that are obtained with certain prior art processes involving heat treatment of metal phosphonate salts. In a general embodiment, the reaction proceeds generally as shown: wherein M is a metal cation and (+)y represents the charge of the cation, e.g., M is a tricationic metal; X is an anionic ligand or ligands attached to the metal and the stoichiometry of M and X (i.e. , p and q) provides a charge balanced metal compound; R is H, an alkyl, aryl, alkylaryl or arylalkyl; a, b and c represent the ratio of the components to which they correspond relative to one another in the reaction product, and y, a, b, and c are values that provide a charge balanced product, with the proviso that none of a or c can be 0. In certain preferred embodiments, where the pyrophosphonic acid is prepared, the process includes multiple steps as follows: ° ii MpX_q, solvent M in phosphonic acid solution

^R'^P®^H 130 °C, 100 RPM, Vac

O O M in phosphonic acid solution Flame Retardant HO" i O" i OH POWDER

R R 200 °C, 300 RPM

In a further aspect, a flame retardant product produced according to the present disclosure, in the form of a powder or small particles, comprises a compound or mixture of different compounds of empirical formula (III) wherein R is H, an alkyl, aryl, alkylaryl or arylalkyl group, a, b, and c represent the ratio of the components to which they correspond relative to one another in the compound, and a is generally a number of from 0 to 8, e.g., from 0 to 6, from 0 to 4, or from 0 to 2, c is generally a number of from 1 to 10, e.g., from 1 to 8, from 1 to 6, from 1 to 4 or from 1 to 2, M is a metal, y is 3, and M^(+)y is a metal cation where (+)y represents the charge formally assigned to the cation. The values of a, b, and c may vary, but will satisfy the charge-balance equation 2(a)+c=b(y). The value for b is limited only in that it must satisfy the preceding equations, but in many embodiments b is a number of from 1 to 4, e.g., 1 or 2. In some embodiments, a is 1 , or 2, c is 1 or 2, and the product is charge balanced.

In some embodiments, M^(+)y is a tri-cationic metal, such as described herein, a is 1 , b is 1 , and c is 1. In certain embodiments, the tri-cationic metal M is chosen from Al, Ga, Sb, Fe, Co, B, and Bi. In certain embodiments, the tri-cationic metal M is Al, Fe, Ga, Sb, or B.

As demonstrated in the Examples disclosed herein, when employing the process of the present disclosure the ratio of phosphorus to aluminum, or the ratio of phosphorus to iron, in the resulting flame retardant product was 4:1. Such a phosphorus to metal ratio leads to high efficiency and can allow for reduced loadings when compounded into thermoplastic polymers.

As is common with inorganic coordination compounds, the reaction product in the above described reaction and the compounds of empirical formulas (III) are idealized such that the reaction product or compounds may be coordination polymers, complex salts, salts where certain atomic valences are shared, etc.

For example, in many embodiments, empirical formula (III), as described herein, represents a monomer unit (i.e., coordination entity) of a coordination polymer, the extended coordination polymer structure thereby forming the flame retardant compound of the present disclosure.

Preferably, where M is Al and y is 3, a compound of empirical formula (III) is produced according to the following empirical formula (Illa):

As shown herein, the absence of subscripts a, b and c in empirical formulas indicates that the subscripts are each 1, signifying a 1:1 :1 ratio of the components (which, in the case of empirical formula (Illa), a 1:1:1 ratio of di-anionic pyrophosphonic acid ligand, metal atom, and mono-anionic pyrophosphonic acid ligand). In this example, empirical formula (Illa) represents a repeating monomer unit (i.e. , coordination entity) of a coordination polymer, the extended coordination polymer structure thereby forming the flame retardant compound of the present disclosure.

Often, a compound of empirical formula (III) (e.g., (Illa)), which in many embodiments is an extended coordination polymer as described herein, makes up all, substantially all, or at least a majority of the flame retardant product, such as at least 75%, 85%, 90%, 95%, 98%, or higher, or any range therebetween, by weight of the flame retardant product.

A compound of empirical formula (III) (e.g., (Illa)) may be produced with high conversion based on the metal or metal compound, such as at least 70%, 80%, 85%, 90%, 95%, 98% or higher conversion, e.g., at least 70 to 95% or higher conversion. In certain embodiments, M is aluminum (i.e. , the reaction product is produced using aluminum or one or more aluminum compounds, such as those described herein) or iron (i.e., the reaction product is produced using iron or one or more iron compounds, such as those described herein).

In certain embodiments, R as shown herein is methyl, ethyl, propyl, isopropyl or butyl and M is Al or Fe. In further embodiments, X is an oxygen, hydroxy, alkoxy or halogen.

The reaction as described herein may, but need not, be run under reduced pressure or vacuum.

The product reaction mixture formed from the reaction described herein, often presenting as a slurry, may be combined with an additional solvent, which may be the same or a different solvent than the solvent used in preparing the metal phosphonic acid solution. The additional solvent may, for example, be chosen from those described herein for the solvent component (b). The additional solvent I slurry mixture may be agitated as desired to break up any clumps that may have formed. 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.

Advantageously, the solid product produced prior to any sieving is a crystalline material having a larger average particle size, an aspect ratio that is smaller than material produced according to prior disclosed processes, and also has a particle size distribution that is narrower with less fines than material produced according to prior disclosed processes.

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 (d). Often, the seeding material is added to the reaction mixture upon or after heating to the reaction temperature. In many embodiments, the seeding material is added before conversion to and/or precipitation of the flame retardant product occurs. In some embodiments, the seeding material comprises a flame retardant material produced according to the process of the present disclosure, such as a flame retardant compound of empirical formula (III), or (Illa) as described herein. The seeding material may be selected or refined to have a desired particle size. In certain embodiments, the process provides a material of formula (Illa) having a median particle size D50 of about 30 to 35 pm as determined using a laser scattering analyzer.

In some embodiments, the process provides a material of formula (Illa) that has a median aspect ratio Aspd50 that is less than 7, preferably less than 5, more preferably less than 4 as determined by SEM imaging. In certain of those embodiments the Aspd90 is less than 10, preferably less than 8, more preferably less than 7.

In some embodiments, the suitable metal compound is alumina, and the flame retardant material is produced as follows: °

In one example, a reaction mixture comprising a pyrophosphonic acid, such as a C1-C12 alkyl pyrophosphonic acid (e.g., methyl, ethyl, propyl, iso-propyl, butyl or t-butyl phosphonic acid), and a solution of an oxide, hydroxide, halide, alkoxide, carbonate or carboxylate of Al, such as alumina, aluminum trichloride, aluminum trihydroxide, aluminum isopropoxide, aluminum carbonate or aluminum acetate in phosphonic acid, such as a C1-C12 alkyl phosphonic acid (e.g., methyl, ethyl, propyl, iso-propyl, butyl or t-butyl phosphonic acid), is heated to a reaction temperature as described herein, such as about 130 °C to 240 °C, about 190 °C to about 210 °C, about 195 °C to about 205 °C, or about 200 °C. Typically, a slurry forms as the reaction proceeds, and the solid flame retardant product may be isolated by filtration to yield a crystalline product. Additional workup on the product reaction mixture may be performed prior to isolating the solid product, such as cooling the product reaction mixture above or no less than the melting point of excess phosphonic acid and combining with an additional solvent as described herein, e.g., water. The additional solvent I slurry mixture may be optionally agitated as described above. The solid flame retardant product may be isolated by filtration, optionally washed with additional solvent and dried, to yield the crystalline product. The flame retardant product contains phosphorus and aluminum in a 4:1 ratio of phosphorus to aluminum according to the following empirical formula:

The example described directly above can be performed with iron or a suitable iron compound, such as halides, oxides, alkoxides, carbonates, or acetates of iron, e.g., iron(lll) oxide, iron(lll) chloride, iron(lll) isopropoxide, or iron(lll) acetate. The resulting flame retardant product contains phosphorus and iron in a 4:1 ratio according to the following empirical formula:

Often, the compound of the empirical formulas above (which in many embodiments is an extended coordination polymer as described herein) makes up all, substantially all, or at least a majority of the flame retardant product, such as at least 75%, 85%, 90%, 95%, 98%, or higher, or any range therebetween, by weight of the flame retardant product.

The flame retardant of the invention may be used with a variety of other flame retardants and/or synergists or flame retardant adjuvants as known in the art. For example, the flame retardant of the invention may be formulated with one or more materials selected from: carbon black, graphite, carbon nanotubes, siloxanes, polysiloxanes; polyphenylene ether (PPE), phosphine oxides and polyphosphine oxides, e.g., benzylic phosphine oxides, poly benzylic phosphine oxides and the like; melamine, melamine derivatives and melamine condensation products, melamine salts such as, but not limited to, melamine cyanurate, melamine borate, melamine phosphates, melamine metal phosphates, melam, melem, melon, and the like; inorganic compounds including clays, metal salts such as hydroxides, oxides, oxide hydrates, borates, carbonates, sulfates, phosphates, phosphites, hypophosphites, silicates, mixed metal salts, etc., e.g., talc and other magnesium silicates, calcium silicate, aluminosilicate, aluminosilicate as hollow tubes (DRAGONITE), calcium carbonate, magnesium carbonate, barium sulfate, calcium sulfate, HALLOYSITE or boron phosphate, calcium molybdate, exfoliated vermiculite, zinc stannate, zinc hydroxystannate, zinc sulfide and zinc borate, zinc molybdate (or complexes thereof, e.g., Kemgard 911B), zinc molybdate/magnesium hydroxide complex (e.g., Kemgard MZM), zinc molybdate/magnesium silicate complex (Kemgard 911C), calcium molybdate/zinc complex (e.g., Kemgard 911 A), zinc phosphate (or complexes thereof, e.g., Kemgard 981), magnesium oxide or hydroxide, aluminum oxide, aluminum oxide hydroxide (Boehmite), aluminum trihydrate, silica, tin oxide, antimony oxide (III and V) and oxide hydrate, titanium oxide, and zinc oxide or oxide hydrate, zirconium oxide and/or zirconium hydroxide and the like.

Unless otherwise specified, in the context of the present application, the term "phosphate" when used as a component in a "phosphate salt", such as in metal phosphate, melamine phosphate, melamine metal phosphate, etc., refers to a phosphate, hydrogen phosphate, dihydrogen phosphate, pyrophosphate, polyphosphate, or a phosphoric acid condensation products anion or polyanion.

Likewise, unless otherwise specified, in the context of the present application, the term "phosphite" when used as a component in a "phosphite salt", such as in metal phosphite, etc., refers to a phosphite or hydrogen phosphite.

The flame retardant of the invention may also be formulated with other flame retardants such as halogenated flame retardants, alkyl or aryl phosphine oxide flame retardants, alkyl or aryl phosphate flame retardants, alkyl or aryl phosphonates, alkyl or aryl phosphinates, and salts of alkyl or aryl phosphinic acid. In some embodiments, the flame retardant comprises a mixture of the flame retardant according to the instant disclosure and a phosphinic salt of the following formula (e.g., an aluminum tris(dialkylphosphinate),

Ri and R2 each independently may be a group according to R as described herein, M is a metal as described herein (e.g., Al or Ca), and n is a number of from 2 to 7, e.g., from 2 to 4, often 2 or 3.

In many embodiments, a flame retardant polymer composition according to the present disclosure comprises (i) a polymer, (ii) a flame retardant material of the present disclosure, and (iii) one or more additional flame retardants and/or one or more synergists or flame retardant adjuvants.

For example, in some embodiments the flame retardant polymer composition comprises one or more additional flame retardants, e.g., halogenated flame retardants, phosphine oxide flame retardants, alkyl or aryl phosphonates, or salts of alkyl or aryl phosphinates, e.g., an aluminum tris(dialkylphosphinate) such as aluminum tris(diethylphosphinate).

In some embodiments the flame retardant polymer composition comprises one or more synergists or flame retardant adjuvants, e.g., melamine, melamine derivatives and melamine condensation products (e.g., melam, melem, melon), melamine salts, phosphine oxides and polyphosphine oxides, metal salts such as hydroxides, oxides, oxide hydrates, borates, phosphates, phosphonates, phosphites, silicates and the like, e.g. aluminum hydrogen phosphite, melem or a melamine metal phosphate, e.g., a melamine metal phosphate wherein the metal comprises aluminum, magnesium or zinc. In particular embodiments the one or more additional flame retardant, synergist or flame retardant adjuvant comprises an aluminum tris(dialkylphosphinate), aluminum hydrogen phosphite, methylenediphenylphosphine oxide-substituted polyaryl ether, xylylenebis(diphenylphosphine oxide), 4, 4’-bis(diphenylphosphinylmethyl)-1 ,1 ’-biphenyl, ethylene bis-1 ,2-bis-(9,10-dihydro-9-oxy- 10-phosphaphenanthrene-10-oxide)ethane, melem, melam, melon, or dimelamine zinc pyrophosphate. In other embodiments the syngergist is at least one metal hypophosphite of the chemical formula:

Me⁽⁺⁾ⁿ(H₂PO₂)n, where Me is a metal cation, (+)n represents the oxidation state of the metal cation and n is 2 or 3, such as calcium hypophosphite or aluminum hypophosphite.

Certain embodiments provide a halogen free polymer composition. In such embodiments, halogen containing flame retardants or synergists would be excluded as much as possible.

The flame retardant material of the present disclosure may be combined with an additional flame retardant, synergist or adjuvant in a range of 100:1 to 1:100 by weight of the inventive flame retardant to the total weight of additional flame retardant, synergist and/or adjuvant. In some embodiments, the flame retardant material of the present disclosure is present in a range of 10:1 to 1:10 by weight of the inventive flame retardant to the total weight of additional flame retardant, synergist and/or adjuvant, for example, weight ratios ranging from 7:1 to 1:7, 6:1 to 1 :6, 4:1 to 1:4, 3:1 to 1 :3 and 2:1 to 1:2. The inventive flame retardant is often the majority component in such a combination, e.g., a 10:1 to 1.2:1 ratio or a 7:1 to 2:1 ratio by weight of the inventive flame retardant material to the total weight of additional flame retardant, synergist and/or adjuvant, but the inventive material can also be the minor component of the mixture, e.g., a 1 :10 to 1 :1.2 ratio or a 1 :7 to 1 :2 ratio.

The thermally stable flame retardant 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.

The polymer of the flame retardant composition of the present invention may be any polymer known in the art, such as polyolefin homopolymers and copolymers, rubbers, polyesters including polyalkylene terephthalates, epoxy resins, polyurethanes, polysulfones, polyimides, polyphenylene ethers, styrenic polymers and copolymers, polycarbonates, acrylic polymers, polyamides, polyacetals, and biodegradable polymers. Mixtures of different polymers, such as polyphenylene ether/styrenic resin blends, polyvinyl chloride/acrylonitrile butadiene styrene (ABS) or other impact modified polymers, such as methacrylonitrile and a- methylstyrene containing ABS, and polyester/ABS or polycarbonate/ABS and polyester or polystyrene plus some other impact modifier may also be used. Such polymers are available commercially or made by means well known in the art.

The flame retardant of the invention is particularly useful in thermoplastic polymers that are processed and/or used at high temperatures, for example, styrenic polymers including high impact polystyrene (HIPS), polyolefins, polyesters, polycarbonates, polyamides, polyurethanes, polyphenylene ethers and the like.

For example, the polymer may be a polyester-series resin, a styrenic resin, a polyamide- series resin, a polycarbonate-series resin, a polyphenylene oxide-series resin, a vinyl-series resin, an olefinic resin, an acrylic resin, epoxy resin, or a polyurethane. The polymer can be a thermoplastic or a thermoset resin and may be reinforced, e.g., glass reinforced. In some embodiments, the polymer is a thermoplastic polyurethane. In some embodiments, the polymer is a thermosetting epoxy resin. More than one polymer resin may be present. In particular embodiments the polymer is an engineering polymer, e.g., a thermoplastic or reinforced thermoplastic polymer, e.g., glass reinforced thermoplastic polymer, such as an optionally glass filled polyester, epoxy resin or polyamide, for example, a glass-filled polyester such as a glass filled polyalkylene terephthalate, or a glass filled polyamide. Polyester-series resins include homopolyesters and copolyesters obtained by, for example, polycondensation of a dicarboxylic acid component and a diol component, and polycondensation of a hydroxycarboxylic acid or a lactone component, for example, aromatic saturated polyester-series resin, such as polybutylene terephthalate or polyethylene terephthalate.

Polyamide (PA)-series resins include polyamides derived from a diamine and a dicarboxylic acid; polyamides obtained from an aminocarboxylic acid, if necessary in combination with a diamine and/or a dicarboxylic acid; and polyamides derived from a lactam, if necessary in combination with a diamine and/or a dicarboxylic acid. The polyamide also includes a copolyamide derived from at least two different kinds of polyamide constituent components. Examples of polyamide-series resins include aliphatic polyamides such as PA 46, PA 6, PA 66, PA 610, PA 612, PA 11 and PA 12, polyamides obtained from an aromatic dicarboxylic acid, e.g., terephthalic acid and/or isophthalic acid, and an aliphatic diamine, e.g., hexamethylenediamine or nonamethylenediamine, and polyamides obtained from both aromatic and aliphatic dicarboxylic acids, e.g., both terephthalic acid and adipic acid, and an aliphatic diamine, e.g., hexamethylenediamine, and others. These polyamides may be used singly or in combination. In some embodiments, the polymer comprises PA 6. In some embodiments, the polymer comprises PA 66. In some embodiments, the polymer comprises a polyphthalamide.

Polyamides with melting points of at least 280°C are used extensively for producing molding compositions which make possible the production of molded articles, e.g. for the electrical and electronics industry, with excellent dimensional stability at high temperatures and with very good flame-retardant properties. Molding compositions of this type are demanded for example in the electronics industry for producing components which are mounted on printed circuit boards according to the so-called surface mounting technology, SMT. In this application, these components must withstand temperatures of up to 270°C for short periods of time without dimensional change.

Such high temperature polyamides include certain polyamides produced from alkyl diamines and diacids as polyamide 4,6, however many high temperature polyamides are aromatic and semi-aromatic polyamides, i.e., homopolymers, copolymers, terpolymers, or higher polymers that are derived from monomers containing aromatic groups. A single aromatic or semiaromatic polyamide may be employed or blends of aromatic and/or semi-aromatic polyamides are used. It is also possible that the preceding polyamide and polyamide blends are blended with other polymers, including aliphatic polyamides. Examples of these high temperature aromatic or semi-aromatic polyamides include polyamide 4T, poly(m-xylylene adipamide) (polyamide MXD,6), poly(dodecamethylene terephthalamide) (polyamide 12, T), poly(decamethylene terephthalamide) (polyamide 10, T), poly(nonamethylene terephthalamide) (polyamide 9,T), hexamethylene adipamide/hexamethylene terephthalamide copolyamide (polyamide 6,T/6,6), hexamethylene terephthalamide/2-methylpentamethylene terephthalamide copolyamide (polyamide 6,T/D,T); hexamethylene adipamide/hexamethylene terephthalamide/hexamethylene isophthalamide copolyamide (polyamide 6,6/6,T/6, 1); poly(caprolactam-hexamethylene terephthalamide) (polyamide 6/6, T); hexamethylene terephthalamide/hexamethylene isophthalamide (6,T/6, 1) copolymer; and the like.

Certain embodiments of the invention are thus to compositions comprising a polyamide that melts at high temperatures, e.g., 280° C or higher, 300°C, or higher, in some embodiments 320°C or higher, e.g. from 280 to 340°C, such as polyamide 4,6 and the aromatic and semiaromatic polyamide described above, articles comprising high temperature polyamides and the flame retardant material of the invention, methods for preparing the compositions and methods for shaping the articles.

As described herein, in many embodiments of the present disclosure, the flame retardant polymer composition comprises (i) a polymer, (ii) the flame retardant of the present disclosure, and (iii) one or more additional flame retardants and/or one or more synergists or flame retardant adjuvants. Thus, while the flame retardant (ii) alone exhibits excellent activity in polymer systems, it may be used in combination with (iii) one or more compounds chosen from other flame retardants, synergists and adjuvants. Exemplary compounds (iii) include halogenated flame retardants, alkyl or aryl phosphine oxides, alkyl or aryl polyphosphine oxides, alkyl or aryl phosphates, alkyl or aryl phosphonates, alkyl or aryl phosphinates, salts of alkyl or aryl phosphinic acid, carbon black, graphite, carbon nanotubes, siloxanes, polysiloxanes, polyphenylene ether, melamine, melamine derivatives, melamine condensation products, melamine salts, metal hydroxides, metal oxides, metal oxide hydrates, metal borates, metal carbonates, metal sulfates, metal phosphates, metal phosphonates, metal phosphites, metal hypophosphites, metal silicates, and mixed metal salts. For example, the one or more compounds (iii) may be chosen from aluminum tris(dialkylphosphinate), aluminum hydrogen phosphite, benzylic phosphine oxides, poly benzylic phosphine oxides, melam, melem, melon, melamine phosphates, melamine metal phosphates, melamine cyanurate, melamine borate, talc, clays, calcium silicate, aluminosilicate, aluminosilicate as hollow tubes, calcium carbonate, magnesium carbonate, barium sulfate, calcium sulfate, boron phosphate, calcium molybdate, exfoliated vermiculite, zinc stannate, zinc hydroxystannate, zinc sulfide, zinc borate, zinc molybdate, zinc phosphate, magnesium oxide, magnesium hydroxide, aluminum oxide, aluminum oxide hydroxide, aluminum trihydrate, silica, tin oxide, antimony oxide (III and V), antimony (III and V) oxide hydrate, titanium oxide, zinc oxide, zinc oxide hydrate, zirconium oxide, and zirconium hydroxide. For example, the one or more compounds (iii) may be chosen from aluminum tris(dimethylphosphinate), aluminum tris(diethylphosphinate), aluminum tris(dipropylphosphinate), aluminum tris(dibutylphosphinate), methylene-diphenylphosphine oxide-substituted polyaryl ether, xylylenebis(diphenylphosphine oxide), 1 ,2-bis-(9, 10- dihydro-9-oxy-10-phosphaphenanthrene-10-oxide)ethane, 4,4'- bis(diphenylphosphinylmethyl)-1,1 '-biphenyl, melam, melem, melon, and dimelamine zinc pyrophosphate.

In some embodiments, the flame retardant synergist comprises a material chosen from melam, melem, melon, melamine cyanurate, melamine polyphosphate, and melamine- poly(metal phosphate) (e.g., melamine-poly(zinc phosphate) (Safire 400)). In some embodiments, the synergist comprises a triazine-based compound, such as a reaction product of trichlorotriazine, piperazine and morpholine, e.g., poly-[2,4-(piperazine-1 ,4-yl)-6- (morpholine-4-yl)-1 ,3,5-triazine]/piperazin (MCA® PPM Triazine HF). In some embodiments, the synergist comprises a metal hypophosphite, such as aluminum hypophosphite (e.g., Italmatch Phoslite® IP-A) or calcium hypophosphite (e.g., Phoslite® B85CX). In some embodiments, the synergist comprises an organic phosphinate, such as aluminum dialkylphosphinate, e.g., aluminum diethylphosphinate (Exolit OP).

In some embodiments, the flame retardant polymer composition comprises one or more compounds chosen from hydrotalcite clays, metal borates, metal oxides, and metal hydroxides, such as metal borates, metal oxides, or metal hydroxides wherein the metal is zinc or calcium.

The concentration of the inventive flame retardant in the polymer composition is of course dependent on the exact chemical composition of the flame retardant, the polymer and other components found in the final polymer composition. For example, when used as the sole flame retarding component of a polymer formulation the inventive flame retardant may be present in a concentration of from 1 to 35%, e.g., 1 to 30%, by weight of the total weight of the final composition. Typically, when used as the sole flame retardant there will be at least 2% of the inventive material present, for example 3% or more, 5% or more, 10% or more, 15% or more, 20% or more or 25% or more. In many embodiments, the inventive flame

T1 retardant is present in amounts up to 45%, while in other embodiments, the amount of inventive flame retardant is 40% of the polymer composition or less, e.g., 35% or less. When used in combination with other flame retardants or flame retardant synergists, less of the inventive material may be needed.

Any known compounding techniques may be used to prepare the flame retardant polymer composition of the present disclosure, 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 flame retardant polymer composition of the invention will often contain one or more of the common stabilizers or other additives frequently encountered in the art, such as phenolic antioxidants, hindered amine light stabilizers (HALS), the ultraviolet light absorbers, phosphites, phosphonites, alkaline metal salts of fatty acids, hydrotalcites, metal oxides, borates, epoxidized soybean oils, hydroxylamines, tertiary amine oxides, lactones, thermal reaction products of tertiary amine oxides, thiosynergists, basic co-stabilizers, for example, melamine, melem, etc., polyvinylpyrrolidone, dicyandiamide, triallyl cyanurate, urea derivatives, hydrazine derivatives, amines, polyamides, polyurethanes, hydrotalcites, alkali metal salts and alkaline earth metal salts of higher fatty acids, for example, Ca stearate, calcium stearoyl lactate, calcium lactate, Zn stearate, Zn octoate, Mg stearate, Na ricinoleate and K palmitate, antimony pyrocatecholate or zinc pyrocatecholate, nucleating agents, clarifying agents, etc.

In certain embodiments, the stabilizer is at least one carbodiimide, and the at least one carbodiimide is preferably of the formula (V), (VI) or (VII): where R¹ and R² are independently hydrogen or Ci-Cio-alkyl, Ce-Ci2-aryl, C7-C13- aralkyl, or C?-Ci3-alkylaryl, a and b are mutually independently a whole number from 1 to 5 and c and d are mutually independently a whole number from 0 to 10; where R⁴ is NCO,

R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹² are independently hydrogen or Ci-C -alkyl, C6-C12- aryl, C?-Ci3-aralkyl, or C?-Ci3-alkylaryl, g is a whole number from 0 to 5, and h is a whole number from 1 to 100; where m is a whole number from 1 to 5000,

R³ is arylene, alkyl-substituted arylene, alkylaryl-substituted arylene, or aralkylsubstituted arylene,

R' is aryl, alkylaryl, aralkyl or R³-NCO, and

R" is -N=C=N-aryl, -N=C=N-alkylaryl, -N=C=N-aralkyl or -NCO.

In certain of those embodiments, the carbodiimide is of the formula (V) and R³ is chosen from arylene, Ci-Ci2-alkyl-substituted arylene, CyCis-alkylaryl-substituted arylene, C7-C18- aralkyl-substituted arylene, and Ci-Ci2-alkyl-substituted Ci-Cs-alkylene-bridged arylene comprising a total of 7 to 30 carbon atoms, such as where R³ is are independently C1-C3 alkyl. In other embodiments, the carbodiimide is of the formula (VI): where R¹³, R¹⁴ and R¹⁵ are independently C1-C3 alkyl, R¹⁶ is -NCO, and n is from 0 to 200, such as where R¹³, R¹⁴ and R¹⁵ are each independently methyl, ethyl or isopropyl or R¹³, R¹⁴ and R¹⁵ are each independently methyl, ethyl or isopropyl. In yet other embodiments, carbodiimide is of the formula (IX) or (X): where R in formula (VII) is -NCO, and n is a whole number from 1 to 200.

In some embodiments, the stabilizer may be at least one epoxide compound, such as an epoxide having at least two epoxide groups. The epoxide may be a polyglycidyl or poly(beta-methylglycidyl) ether or derived from a phenolic novolac.

Other additives may also be present, for example, plasticizers, lubricants, emulsifiers, pigments, dyes, optical brighteners, other flame proofing agents, anti-static agents, blowing agents, anti-drip agents, e.g., PTFE, and the like. In certain of those embodiments, the phenolic novolac is chosen from cresol novolacs, bisphenol A novolacs, and bisphenol F novolacs. In other embodiments, the epoxide compound is a phenolic novolac polyglycidyl ether, such as phenolic novolac polyglycidyl ether is of the formula (XI): where R in formula (III) is independently chosen from the group consisting of hydrogen, halogen, alkyl, alkoxy, aryl, alkylaryl and aralkyl, and n is 0 to 1000. In certain embodiments, R in formula (III) is C1-C4 alkyl. The epoxide compound can also be a polyglycidyl ether of cresol novolac of the formula (XII): where n is from 0 to 100 and represents the average number; or an oligomeric reaction product of bisphenol A with epichlorohydrin of formula (XIII): where a is from 0 to 100 and represents the average number.

Optionally the polymer may include fillers and reinforcing agents, for example, calcium carbonate, silicates, glass fibers, talc, kaolin, mica, barium sulfate, metal oxides and hydroxides, carbon black and graphite. Such fillers and reinforcing agents may often be present at relatively high concentrations, including formulations where the filler or reinforcement is present in concentrations of over 50 wt% based on the weight of the final composition. More typically, fillers and reinforcing agents are present from about 5 to about 50 wt%, e.g., about 10 to about 40 wt% or about 15 to about 30 wt% based on the weight of the total polymer composition.

In some embodiments, the flame retardant polymer composition of the present disclosure is formulated with any one or more materials selected from carbon black, graphite, carbon nanotubes, siloxanes, polysiloxanes, talc, calcium carbonate, magnesium carbonate, barium sulfate, calcium sulfate, calcium silicate, magnesium silicate, aluminosilicate hollow tubes (Dragonite), Halloysite, boron phosphate, calcium molybdate, exfoliated vermiculite, zinc stannate, zinc hydroxystannate, zinc sulfide, zinc borate, zinc molybdate (or complexes thereof, e.g., Kemgard 911 B), zinc molybdate/magnesium hydroxide complex (e.g., Kemgard MZM), zinc molybdate/magnesium silicate complex (Kemgard 911 C), calcium molybdate/zinc complex (e.g., Kemgard 911 A), zinc phosphate (or complexes thereof, e.g., Kemgard 981) and the like; hydroxides, oxides, and oxide hydrates of group 2, 4, 12, 13, 14, 15 (semi)metals, e.g., magnesium oxide or hydroxide, aluminum oxide, aluminum oxide hydroxide (Boehmite), aluminum trihydrate, silica, silicates, tin oxide, antimony oxide (III and V) and oxide hydrate, titanium oxide, and zinc oxide or oxide hydrate, zirconium oxide and/or zirconium hydroxide and the like; melamine and urea based resins such as melamine cyanurate, melamine borate, melamine polyphosphate, melamine pyrophosphate, polyphenylene ether (PPE) and the like; and clays, including e.g., hydrotalcite, boehmite, kaolin, mica, montmorillonite, wollastonite, nanoclays or organically modified nanoclays and the like.

In some embodiments, the flame retardant polymer composition of the present disclosure is formulated with any one or more materials selected from zinc borate, zinc stannate, polysiloxanes, kaolin, silica, magnesium hydroxide, zinc molybdate complex (e.g., Kemgard 911 B), zinc molybdate/magnesium hydroxide complex (e.g., Kemgard MZM), zinc molybdate/magnesium silicate complex (Kemgard 911C), calcium molybdate/zinc complex (e.g., Kemgard 911 A), zinc phosphate complex (e.g., Kemgard 981), and melamine- poly(metal phosphate) (e.g., melamine-poly(zinc phosphate) (Safire 400)).

In some embodiments, in addition to a polymer (such as described herein) and the flame retardant of the present disclosure, the flame retardant polymer composition comprises melam and any one or more materials selected from zinc borate, zinc stannate, zinc molybdate complex, zinc molybdate/magnesium hydroxide complex, zinc molybdate/magnesium silicate complex, calcium molybdate/zinc complex, zinc phosphate complex, and zinc oxide, optionally with additional additives, such as described herein.

In some embodiments, in addition to a polymer (such as described herein) and the flame retardant of the present disclosure, the flame retardant polymer composition comprises melon and any one or more materials selected from zinc borate, zinc stannate, zinc molybdate complex, zinc molybdate/magnesium hydroxide complex, zinc molybdate/magnesium silicate complex, calcium molybdate/zinc complex, zinc phosphate complex, and zinc oxide, optionally with additional additives, such as described herein.

Further non-limiting disclosure is provided in the Examples that follow.

EXAMPLES

Example 1- Comparative Process

O AI₂O₃, H₂O, 3.0% seed

- *• Flame Retardant oft^H 240 °C, 300 RPM MPA (1441g, 30eq, aq sol, fresh, use DK-FR12075, 74.7% MPA solution, filtered through size D frit funnel) and AI2O3 (51.0g, 0.50mol, 1.0eq) were mixed at room temperature. The pot temperature was ramped from rt to 130 degree C over 2h, at 200 RPM without nitrogen purge. It was kept at 130 degree C for 3 hours and the white slurry turned into a clear solution. It was then elevated to 240 degree C over 16 hours. Then 3.0 %wt seed (100 meshed needles, 11.2 g) was added as soon as the pot temperature arrived at 240 degree C @ 300 RPM, and the slurry stayed. The reaction mixture was kept at 240 degree C for 3 hour. The reaction mixture was then cooled to about 150 degree C and then poured slowly and carefully into 2.8L water in a 4L beaker at room temperature and stirred at 250 RPM for 10 min. The white slurry was then filtered off and dried over house vacuum for 4 hours. The solid was then transferred to a beaker and stirred with 700 mL water for 10 min and suction dried with house vacuum overnight. The crude yield was 87.6%. The product was further dried in 50°C oven overnight, which provided decent sifting yields (76.7% @ 99 min; 99.2% @ 198 min).

Example 2 - Preparation of Methylpyrophosphonic acid

O pot @ 200°C p P " _ 0.05 mol% AI0O3 ^J > oft*"* vacuum

Methylposphonic acid (MPA) (1920g, 15eq, fresh aq. sol. 75%) and AI2O3 (0.8g, 7.5 mmol, 0.05 mol% base on total MPA) were put in a 2 L RBF at room temperature with magnetic stir bar. It was heated carefully to remove the solvent water (pot set to 200 °C), and then carefully pulling vacuum to remove the water generated from the reaction. The target end point is 33% conversion.

Hour 1, pot set @ 200 °C, vacuum started @ 19.4 Torr, end @ 14.2 Torr, conversion 34.1%

Example 3 - Aluminum in Methylphosphonic acid Solution AI₂O₃. H₂0, 75% MPA _{A| |n MpA} 130 °C, 100 RPM, Vac solution

MPA (1024g, 8eq, fresh aq. sol. 75%) and AI2O3 (50.2 g, total 0.50mol, 1.0eq, combining with catalytical amount from Example 2) were mixed at room temperature in a 3L reactor. The pot temperature was set to 130 °C at 100 RPM without nitrogen purge. The pot temperature was stable around 110 degree C for about 1 hour, while the white slurry turned into opaque and then a clear pale yellow solution. After the pot temperature became stable at 130 °C, kept the reaction mixture at 130 °C overnight. The second morning, carefully pulled vacuum to remove water while set up the pot temperature to 200 °C, and the house vacuum was stable at 57 Torr in the end till no distillate coming out.

Example 4- Flame Retardant

M ethyl pyrophosphonic acid product of Example 2 was preheated to 205 °C and a seeding material (1.9 g, 0.5 wt% of the theoretical amount of the flame retardant) was added to it. The preheated methylpyrophosphonic acid was then poured into the 200 °C solution of Example 3 at 300 RPM. After mixing, the reaction was kept at 200 °C for 5 min. The reaction mixture was then cooled to 130 °C and poured slowly and carefully into 2.8L water in a 4L beaker at room temperature and stirred at 250 RPM for 10 min. The white slurry was filtered off and dried over house vacuum for 4 hours. The solid was then transferred to a beaker and stirred with 700 mL water for 10 min and suction dried with the house vacuum overnight. The crude yield was 83.0%, 100 mesh at 99 min sifting yield was 94.0%.

The resulting material had Acid # < 0.1 mg KOH/g sample and 4:1 P to Al ratio (ICP Elemental Analysis).

An image of the resulting crystals at x500 magnification obtained with a scanning electron microscope is shown in FIG. 2.

Particle size was determined using a Sympatec HELOS/KR RODOS laser diffraction sensor with VIBRI/L dry dispersion plate. The particle size distribution of the material is shown in FIG. 6

Example 5 - Flame Retardant

MPA (1553g, 12eq, sol. 75%aq) was put in a 3L resin reactor. It was heated carefully to remove water (pot set to 200 °C, 150 RPM), carefully pulling vacuum when there was not distillate coming out. Target end point of conversion is 71% (31 P NMR measurement, set MPA 100 %). Day 2, pot set @ 200 °C, vacuum @ 150 Torr, 37.2% conversion; Day 3, pot set @ 200 °C, vacuum @ 200 Torr, 54.4% conversion; Day 4, pot set @ 200 °C, vacuum @ 120 Torr, 69.1% conversion to pyrophosphonic acid.

Separately, MPA (768g, 6eq, fresh aq. sol. 75%) and AI2O3 (51.0g, 0.50mol, 1.0eq) were mixed at room temperature. The pot temperature was set to 130 °C first, at 250 RPM without nitrogen purge. The pot temperature stabled around 110 degree C for about 1 hour, while the white slurry turned into opaque and then the clear pale yellow solution. The pot temperature then set to 200 °C. Carefully pulling vacuum to remove water with vacuum stable at 140 Torr in the end till no distillate coming out.

O AI₂O₃, H₂O, 75% MPA Al in MPA solution

^{/ P}S?^H 200 °C, 250 RPM, 140 Torr

The pyrophosphonic acid was preheated to 200 °C and then mixed at 200 °C and 250 RPM with the Al in MPA solution. No seeding material was used and the slurry stayed. The reaction mixture was kept at 200 °C for 3 hour. The reaction mixture was then poured slowly and carefully into 2.8L water in a 4L beaker at room temperature and stirred at 250 RPM for 10 min. The white slurry was filtered off and dried over house vacuum for 4 hours. The solid was then transferred to a beaker and stirred with 700 mL water for 10 min and suction dried with house vacuum overnight. The crude yield was 88.7%. The SEM showed that the product was in needle form. The material was further dried in 60 °C oven and sift through 100 Mesh sieves (67.5% @ 99 min; 97.2% @ 198 min).

The particle size of the resulting material was determined using a Sympatec HELOS/KR RODOS laser diffraction sensor with VIBRI/L dry dispersion plate. The particle size distribution of the material is shown in FIG. 7 Example 6 - Effect of Precipitation Temperature on Crystal Morphology

The process of Example 5 was repeated but at different precipitation temperatures ranging from 130°C to 210°C. Images of the resulting crystalline product obtained with a HITCHI TM3030Plus Tabletop Microscope at x500 are shown in FIG. 3.

The particle size of some of the resulting material was determined using a Sympatec HELOS/KR RODOS laser diffraction sensor with VIBRI/L dry dispersion plate.

Example 7 - Aspect Ratio Of Flame Retardant Material

A. SEM Sample Preparation

~50 mg of flame retardant and 5 mg of hexadecyltributylammonium bromide were combined in a 60 mL jar. Diluted with 60 mL hexane. Shaken 2 x 10s and pipetted 1-2 drops onto an SEM sample stage.

B. SEM Image Collection

Collected 6 images at 100x magnification on a HITCHI TM3030Plus Tabletop Microscope avoiding repeat measurements of the same crystal.

C. Results

Length, width and aspect ratio Example 8 - Flame Retardant Polymer Compositions

Polymer compositions were prepared and evaluated for flame retardant activity under UL-94 testing. UL-94 V-0 ratings at 0.8 mm thicknesses were measured for 30% by weight glass filled polymer compositions of polyamide 6,6 containing 14% by weight of flame retardant of

Example 6 and 10% by weight melam.

Example 9 - Preparation of Pyrophosphonic Acid

MPA (1920g, 15eq, sol. 75%aq) was put in a 2 L round bottom flaks with a magnetic stir bar, heated carefully to remove the solvent water (pot set to 200 °C), and then carefully pulling vacuum to remove the water generated from the reaction. Three trials were conducted; trials 2 and 3 were loaded with certain amount of AI2O3 as a catalyst for pyro formation.

Trial 1. vacuum @ 9.31 Torr, conversion 40.5%, 1 d

Trial 2. vacuum @ 19.4 Torr, 0.05 mol% AI2O3, conversion 34.1% @ 1 h

Trial 3. vacuum @ 14.6 Torr, 0.5 mol% AI2O3, conversion 34.8% @ 1 h

Example 10 - Preparation of Pyrophosphonic Aid

MPA (1920g, 15eq, sol. 75%aq) was put in a 2 L round bottom flask with magnetic stir bar. It was heated carefully to remove the solvent water (pot set to 240 °C). When the pot temperature arrived at 240 °C, started purging N2 through a diffusion tube under the surface at 5 L/min. The pot temperature would drop temporarily and then come back to 240 °C. Started timing the reaction at 240 °C and taking aliquots every 0.5 h until the end of 5 h mark, and using 31 P NMR to measure the conversion. The loading of the catalyst AI2O3 was shown as, series 1, 0 mol% catalyst; series 2, 0.005 mol%; series 3, 0.05 mol%; series 4, 0.5 mol%. o pot @ 240°C fl fl - ► Px

"^P8f?^H N₂ purge 5 L/min HO | 0 | OH

The conversion rate over time is shown below and in FIG. 8.

A lower conversion rate was observed when the nitrogen flow rate was lowered to 2-4L/min.

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 process for producing a phosphorus-containing flame retardant, comprising preparing a metal phosphonic acid solution; and reacting a reaction mixture of unsubstituted or alkyl or aryl substituted pyrophosphonic acid with the metal phosphonic acid solution at a reaction temperature from 130 °C to 240 °C for an amount of time sufficient to produce the phosphorus-containing flame retardant.

2. The process according to claim 1 , further comprising a step of preparing the unsubstituted or alkyl or aryl substituted pyrophosphonic acid by adding a catalytic amount of a catalyst to unsubstituted or substituted alkyl or aryl phosphonic acid, and heating at a temperature of about 105°C or higher for an amount of time sufficient to produce the unsubstituted or substituted pyrophosphonic acid.

3. The process according to claim 2, wherein the temperature of the heating step is about 130 °C to about 290 °C.

4. The process according to claim 3, wherein the temperature of the heating step is about 180 °C to 240 °C.

5. The process according to claim 2, wherein the catalyst is a Lewis Acid.

6. The process according to claim 5, wherein the Lewis Acid is selected from the group consisting of iron halides (FeX_n), titanium halides (TiX_n), titanium alkoxides (Ti(OR)4), titanium oxides (TiCh), aluminum halides (AIX3), aluminum alkoxides (AI(OR)s), tin halides (SnX_n), boron trihalides (BX3), magnesium halides (MgX2), calcium halides (CaX2), and zinc halides (ZnX2).

7. The process according to claim 1 , further comprising a step of preparing the unsubstituted or alkyl or aryl substituted pyrophosphonic acid by heating unsubstituted or substituted alkyl or aryl phosphonic acid at a temperature ranging from 230°C to 250°C, preferably about 240°C, in the presence of nitrogen, wherein the nitrogen is provided at a flow rate of 4L/min to 6 L/min, preferably about 5L/min.

8. The process according to any of claims 1-7, further comprising, prior to the step of reacting the reaction mixture, removing all or substantially all of any water generated when preparing the metal phosphonic acid solution and/or the unsubstituted or substituted pyrophosphonic acid.

9. The process according to claim 8, wherein the step of removing comprises use of vacuum.

10. The process according to any of claims 1-9, wherein the reaction mixture is prepared at a preparation temperature below the reaction temperature.

11. The process according to claim 10, wherein the preparation temperature ranges from about 15 °C to about 40 °C.

12. The process according to any of claims 1-11, wherein the reaction temperature ranges from about 190 °C to about 210 °C.

13. The process according to claim 12, wherein the reaction temperature ranges from about 195 °C to about 205 °C.

14. The process according to any of claims 1-13, wherein the metal phosphonic acid solution is prepared from a mixture of

(a) an unsubstituted or alkyl or aryl phosphonic acid,

(b) a solvent for the phosphonic acid, and

(c) a metal which is capable of forming a polycation, or a suitable metal compound which is represented by the formula Mp^+)yX_q where M is a metal, (+)y represents the charge of the metal cation, y is 3, X is an anion, and the values for p and q provide a charge balanced metal compound.

15. The process according to claim 14, wherein the components (a) and (b) of the mixture are in the form of a solution, and preparing the mixture comprises mixing the component (c) with the solution.

16. The process according to claim 14, wherein the molar ratio of component (a) to component (c) in the reaction mixture ranges from about 4:1 to about 50:1.

17. The process according to claim 14, wherein the solvent is chosen from water, sulfones, sulfoxides, halogenated hydrocarbons, aromatic hydrocarbons, and ethers.

18. The process according to claim 17, wherein the solvent comprises water.

19. The process according to claim 14, wherein M is chosen from Al, Ga, Sb, Fe, Co, B, and Bi.

20. The process according to claim 19, wherein M is Al.

21. The process according to claim 14, wherein component (c) of the reaction mixture comprises the suitable metal compound, and the suitable metal compound is chosen from a metal oxide, halide, alkoxide, hydroxide, carbonate, carboxylate, or phosphonate.

22. The process according to claim 21 , wherein the suitable metal compound is chosen from alumina, aluminum trichloride, aluminum trihydroxide, aluminum isopropoxide, aluminum carbonate, aluminum acetate, iron(lll) oxide, iron(lll) chloride, iron(lll) isopropoxide, and iron(lll) acetate.

23. The process according to claim 14, wherein the unsubstituted or alkyl or aryl substituted phosphonic acid is represented by formula (I) wherein R is H, C1-12 alkyl, Ce- aryl, C7-18 alkylaryl, or C7-18 arylalkyl, wherein the alkyl, aryl, alkylaryl, or arylalkyl are unsubstituted or are substituted by halogen, hydroxyl, amino, CM alkylamino, di-Ci-4 alkylamino, C1-4 alkoxy, carboxy or C2-5 alkoxycarbonyl.

24. The process according to claim 23, wherein R is unsubstituted C1-12 alkyl, Ge aryl, C7-10 alkylaryl, or C7-10 arylalkyl.

25. The process according to claim 24, wherein R is unsubstituted C1-6 alkyl.

26. The process according to claim 254, wherein R is methyl, ethyl, propyl, isopropyl, butyl, or t-butyl.

27. The process according to any of claims 1-26, wherein the unsubstituted or alkyl or aryl substituted pyrophosphonic acid is free of or substantially free of water.

28. The process according to any of claims 1-27, wherein the metal phosphonic acid solution is free of precipitate prior to the step of reacting.

29. The process according to claim 1 , further comprising a step of seeding the reaction mixture with a compound of of empirical formula (III): wherein R is H, an alkyl, aryl, alkylaryl, or arylalkyl group;

M is a metal and y is 3, such that M^(+)y is a metal cation where (+)y represents the charge formally assigned to the cation; a, b, and c represent the ratio of the components to which they correspond relative to one another in the compound and satisfy the charge-balance equation 2(a)+c=b(y); and c is not zero.

30. The process according to any of claims 1-29, wherein the unsubstituted or alkyl or aryl substituted pyrophosphonic acid is represented by formula (II) wherein R is H, C1-12 alkyl, Ce- aryl, C7-18 alkylaryl, or C7-18 arylalkyl, wherein the alkyl, aryl, alkylaryl, or arylalkyl are unsubstituted or are substituted by halogen, hydroxyl, amino, CM alkylamino, di-Ci-4 alkylamino, C1-4 alkoxy, carboxy or C2-5 alkoxycarbonyl.

31. The process according to claim 30, wherein R of formula (II) is unsubstituted C1-12 alkyl, Ce aryl, C7-10 alkylaryl, or C7- arylalkyl.

32. The process according to claim 30, wherein R of formula (II) is unsubstituted C1-6 alkyl.

33. The process according to claim 30, wherein R of formula (II) is methyl, ethyl, propyl, isopropyl, butyl, or t-butyl.

34. A phosphorus-containing flame retardant produced according to the process of any one of claims 1 through 26, wherein the phosphorus-containing flame retardant comprises a

M is a metal and y is 3, such that M^(+)y is a metal cation where (+)y represents the charge formally assigned to the cation; a, b, and c represent the ratio of the components to which they correspond relative to one another in the compound and satisfy the charge-balance equation 2(a)+c=b(y); and c is not zero wherein the phosphorus-containing flame retardant is a crystalline material having Aspd90 less than 10 as determined using SEM imaging system.

35. The phosphorus-containing flame retardant according to claim 34, wherein M is Al, a is 1 , b is 1 , and c is 1.

36. A flame retardant polymer composition comprising (i) a polymer and (ii) the phosphorus- containing flame retardant according to claim 34 or 35.

37. A flame retardant material comprising a compound of empirical formula (III)

M is a metal and y is 3, such that M^(+)y is a metal cation where (+)y represents the charge formally assigned to the cation; a, b, and c represent the ratio of the components to which they correspond relative to one another in the compound, and satisfy the charge-balance equation 2(a)+c=b(y); and c is not zero; wherein the phosphorus-containing flame retardant is a crystalline material having aspect ratio (Aspd90) less than 10 as determined by SEM imaging.

38. The flame retardant material according to claim 37, wherein M is Al, a is 1 , b is 1, and c is 1.

39. The flame retardant material according to claims 37 or 38, wherein R is H or alkyl.

40. The flame retardant material according to claim 39, wherein R is C1-6 alkyl.

41. The flame retardant material according to claim 40, wherein R is methyl or ethyl.

42. A flame retardant polymer composition comprising (i) a polymer and (ii) the flame retardant material according to any one of claims 38 through 41.