WO2009035881A2 - Phosphorus-sulfur fr additives and polymer systems containing same - Google Patents

Abstract

Certain phosphorus- sulfur compounds are effective in reducing the LOI of combustible organic polymers and in providing better FR characteristics to the polymers as determined by other standardized tests. The phosphorus-sulfur compounds are sulfur-bridged, metal-bridged or in the form of salts such a ammonium, sulfonium or phosphonium salts.

Description

PHOSPHORUS-SULFUR FR ADDITIVES AND POLYMER SYSTEMS CONTAINING

SAME

This application claims benefit of United States Provisional Application No. 60/993,623, filed 13 September 2007.

The present invention relates to flame retardant additives for organic polymers, and in particular to phosphorus-sulfur flame suppressant additives.

Flame suppressant additives are commonly added to polymer products used in construction and other applications. FR additives increase the limiting oxygen index (LOI) of polymer systems, allowing articles made from those polymer systems to pass standard fire tests. Various low molecular weight (<~1500 g/mol) brominated compounds are used as FR additives for organic polymers. Many of these, such as hexabromocyclododecane, are under regulatory and public pressure that may lead to restrictions on their use. For that reason, there is an incentive to find a replacement for them.

Various phosphorus compounds have been used as FR additives. These include organic phosphates, phosphonates and phosphoramides, some of which are described in

U. S. Patent Nos. 4,070,336 and 4,086,205. Another commercially available FR additive is 2,2'-oxybis[5,5-dimethyl-l,3,2-dioxaphosphorinane] 2,2'-disulfide, which has the structure:

These compounds tend to provide moderate ignition resistance, and are generally not as effective as hexabromocyclododecane or other brominated FR additives.

It is desirable to provide an alternative FR additive for organic polymers, and for expanded polymers in particular. The FR additive should be capable of raising the LOI of the polymer system when incorporated into the polymer at reasonably low levels.

Similarly, the FR additive should be capable of conferring good fire extinguishing properties to the polymer system, again when present at reasonably small levels.

Because in many cases the FR additive is most conveniently added to a melt of the organic polymer, or else (or in addition) is present in subsequent melt processing operations, the FR additive should be thermally stable at the temperature of the molten polymer, which is typically in the range of 15O⁰C or higher, and is often at least 200⁰C or above 22O⁰C. It is preferable that the FR additive have low toxicity.

The present invention is in one aspect a polymer composition comprising a combustible polymer having mixed therein a phosphorus- sulfur additive represented by the structure I:

wherein each X is independently oxygen or sulfur, each m is independently zero or 1, p is 1 or 2, and each R is independently an unsubstituted or inertly substituted hydrocarbyl group or the R groups of any R- (X)_1n-P- (X)m-R structure together form an unsubstituted or inertly substituted divalent organic group.

The present invention is also in some embodiments a polymer composition comprising a combustible polymer having mixed therein a phosphorus-sulfur additive represented by the structure II:

wherein each X is independently oxygen or sulfur, each m is independently zero or 1, M represents a metal atom which may have associated waters of hydration, n is a number from 1 to 4, and each R is independently an unsubstituted or inertly substituted hydrocarbyl group or the R groups of any R- (X)_1n-P- (X)_m-R structure together form an unsubstituted or inertly substituted divalent organic group. In structure II, the bond shown between the metal atom M and the sulfur atoms may have a more or less ionic character, depending mainly on the selection of the metal. In addition, in some cases the metal M atom may be hydrated, in which case water molecules may be interposed between the metal atom and the sulfur atoms. In the idealized structures shown, waters of hydration are omitted for purposes of greater clarity, but the structures are understood for purposes of this invention to include hydrated analogs. The present invention is also in some embodiments a polymer composition comprising a combustible polymer having mixed therein a phosphorus-sulfur additive represented by the structure III:

wherein each X is independently oxygen or sulfur, each m is independently zero or 1, 1 is an integer of 1 or more, q is zero when 1 is 1 and q is 1 when 1 is 2 or more, Z represents a cationic group, each R is independently an unsubstituted or inertly substituted hydrocarbyl group or the R groups of any R- (X)_1n-P- (X)_m-R structure together form an unsubstituted or inertly substituted divalent organic group, and A is an organic linking group.

This invention is also a phosphorus-sulfur compound represented by structure II or by structure III.

The polymer compositions of the invention contain certain phosphorus- sulfur additives. A first type of phosphorus-sulfur additive is a sulfur-bridged compound represented by structure (I):

wherein each X is independently oxygen or sulfur, each m is independently zero or 1, p is 1 or 2, and each R is independently an unsubstituted or inertly substituted hydrocarbyl group or the R groups of any R- (X)_1n-P- (X)_m-R structure together form an unsubstituted or inertly substituted divalent organic group. Certain sulfur-bridged phosphorus-sulfur additives include those represented by structures IV and V:

wherein R and p are as before. In structures I, IV and V, the R groups may be, for example, unsubstituted or inertly substituted aliphatic, cycloaliphatic or aromatic groups.

In this application, an "inert" substituent is one that does not undesirably interfere with the flame retardant properties of the compound. A compound containing only inert substituents is said to be "inertly substituted". The inert substituent may be, for example, an oxygen-containing group such as an ether, ester, carbonyl, hydroxyl, carboxylic acid, oxirane group and the like. The inert substituent may be a nitrogen- containing group such as a primary, secondary or tertiary amine group, an imine group, an amide group or a nitro group. The inert substituent may contain other hetero atoms such as sulfur, phosphorus, silicon (such as silane or siloxane groups) and the like. An inert substituent on a phosphorus-sulfur additive is preferably not a halogen.

A hydrocarbyl group, for purposes of this invention, is a group that, except for inert substituents that are explicitly indicated, contains only hydrogen and carbon atoms. A hydrocarbyl group may be aliphatic, alicyclic, aromatic or some combination of two or more of those types.

The R groups in structures IV and V are preferably unsubstituted or inertly substituted lower alkyl, such as methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, t- butyl, sec-butyl and the like.

In some embodiments, two R groups of any R-(X)_m-P-(X)m-R structure together form a divalent organic radical that completes a ring structure with the — (X)_m — P — (X)m — linkage, as shown for example in structures VI and VII:

wherein each R² is independently hydrogen, alkyl or inertly substituted alkyl, each R³ is independently a covalent bond or a divalent linking group, and p is as before. In structures VI and VII, each R² is preferably hydrogen, and R³ is preferably an alkylene diradical having no hydrogens on the carbon atom(s) bonded directly to the adjacent (R²)2C groups. R³ is more preferably dialkylmethylene and most preferably dimethylmethylene (propylidene). Especially preferred sulfur-bridged phosphorus- sulfur additives include those shown in structures VIII and IX:

VIII IX

wherein p is as before.

Other suitable types of sulfur-bridged phosphorus-sulfur additives are illustrated by structures X and XI:

wherein p is as before.

Another type of phosphorus-sulfur additive is a metal-bridged type represented by structure II:

wherein each X is independently oxygen or sulfur, each m is independently zero or 1, M represents a metal atom which may have associated waters of hydration, n is a number from 1 to 4, and each R is independently an unsubstituted or inertly substituted hydrocarbyl group or the R groups of any R- (X)_1n-P- (X)_m-R structure together form an unsubstituted or inertly substituted divalent organic group.

Certain metal-bridged phosphorus-sulfur additives include those represented by structures XII and XIII:

(XII) (XIII) wherein R, n and M are as defined with respect to structure II. In structures XII and XIII, the R groups are preferably as described before with respect to structures IV and V. In some embodiments, the R groups of any R- (X)_1n-P- (X)_m-R structure together form a divalent organic radical that completes a ring structure with the — (X) m — P — (X)m — linkage, as shown for example in structures XIV and XV:

wherein R² and R³ are as defined with respect to structures VI and VII above, and M and n are as defined with respect to structure II. In structures XIV and XV, each R² is preferably hydrogen, and R³ is preferably an alkylene diradical having no hydrogens on the carbon atom(s) bonded directly to the adjacent (R²)2C groups. R³ is more preferably dialkylmethylene and most preferably dimethylmethylene. Especially preferred metal- bridged phosphorus- sulfur additives include those shown in structures XVI and XVII:

wherein M and n are again as defined with respect to structure II.

Other suitable types of metal-bridged phosphorus-sulfur additives are illustrated by structures XVIII and XIX:

xviii xix wherein M and n are again as defined with respect to structure II.

In structures II and XII-XIX, the metal atom M in each case is one which can form dative (coordination) bonds with the sulfur atoms on each thiophosphorate group. Suitable metals include, for example, alkaline earth metals such as magnesium and calcium, alkali metals such as cesium, group 4 metals such as titanium and zirconium, group 15 metals such as antimony and bismuth, group 12 metals such as zinc and cadmium, group 8, 9 and 10 metals such as iron, cobalt, nickel, ruthenium and palladium, and group 11 metals such as copper or silver. Preferred metals include calcium, magnesium, zinc, antimony and bismuth. In structures II and XII-XIX, the bond shown between the metal atom M and the sulfur atoms may have a more or less ionic character, depending mainly on the selection of the metal. In addition, in some cases the metal M atom may be hydrated, in which case water molecules may be interposed between the metal atom and the sulfur atoms. For example, the bond tends to be highly ionic in character when M is Ca or Mg, and in those cases the structure will also include waters of hydration. In the structures shown, waters of hydration are omitted for purposes of greater clarity, but the structures are understood for purposes of this invention to include hydrated analogs.

In addition, structures II and XII-XIX are empirical structures only and are not intended to specify any particular crystalline structure of the molecule when in the solid state. The organo-phosphorus-sulfur moities may assume various geometric or spatial dispositions relative to the metal in the solid state.

A third type of phosphorus- sulfur additive is an ionic compound represented by structure III:

) wherein each X is independently oxygen or sulfur, each m is independently zero or 1, 1 is an integer of 1 or more, q is zero when 1 is one and 1 when 1 is 2 or more; Z represents a cationic group, each R is independently an unsubstituted or inertly substituted hydrocarbyl group or R groups of any R- (X)_1n-P- (X)m-R structure together form an unsubstituted or inertly substituted divalent organic group, and A is an organic linking group.

Certain ionic phosphorus- sulfur additives include those represented by structures XX and XXI:

wherein R, Z, A, q and 1 are as defined with respect to structure III. In structures XX and XXI, the R groups are preferably as described before with respect to structures IV and V. In some embodiments, the two R groups of any R-(X)_m-P-(X)m-R structure together form a divalent organic radical that completes a ring structure with the —

(X)m — P — (X) m — linkage, as shown for example in structures XXII and XXIII:

wherein R² and R³ are as defined with respect to structures VI and VII above, and Z, A, q and 1 are as defined with respect to structure III. In structures XXII and XXIII, each R² is preferably hydrogen, and R³ is preferably an alkylene diradical having no hydrogens on the carbon atom(s) bonded directly to the adjacent (R²)2C groups. R³ is more preferably dialkylmethylene and most preferably dimethylmethylene. Especially preferred ionic phosphorus-sulfur additives include those shown in structures XIV and XV:

wherein Z, A, q and 1 are again as defined with respect to structure III.

Other suitable types of ionic phosphorus-sulfur additives are illustrated by structures XXVI and XXVII:

xxvi xxvii wherein Z, A, q and 1 are again as defined with respect to structure III.

In any of structures III and XX-XXVII, the value of 1 can range from 1 to a very large number. When the A group is an organic polymer as described below, the value of 1 can reach 1000 or more, and may be from 2 to 500, more typically from 2 to 100. When A is something other than an organic polymer, 1 is typically from 2 to 8, more typically from 2 to 6.

In structures III and XX-XXVII, the Z group may be an ammonium, phosphonium, sulfonium or phosphazenium group. In cases in which 1 is 1 and q is zero, an ammonium Z group can take any of the forms H₄N⁺, H₃(R⁴)N⁺, H₂(R⁴)2N⁺, or H(R⁴)₃N⁺ or (R⁴)4N⁺ wherein each R⁴ is independently a hydrocarbyl or inertly substituted hydrocarbyl group. The R⁴ groups are preferably phenyl, substituted phenyl, benzyl, or lower alkyl (such as Ci 4 alkyl). When 1 > 1 and q is 1, an ammonium group Z can take any of the forms H₃N⁺-A, H₂(R⁴)N⁺— A, H(R⁴)₂N⁺— A, or (R⁴)₃N⁺— A, with R⁴ having the same meaning as before. A sulfonium Z group can take the form (R⁴)₃S⁺ (when 1 is 1) or (R⁴)₂S⁺ — A (when 1 > 1 and q is 1). Similarly, phosphonium groups can take the form (R⁴)4P⁺ when 1 is 1 or the form (R⁴)3P⁺ — A when 1>1 and q is 1, R⁴ again being as defined before. Phosphazenium groups contain one or more

) moieties. Suitable phosphazenium groups include those represented by structures XXIX and XXX:

(XXIX) _(χχχ) wherein each R⁵ is independently in each occurrence (a) an unsubstituted or inertly substituted alkyl or aryl group, (b) an unsubstituted or inertly substituted alkylene or arylene group that, together with another R⁵ group on the same nitrogen atom, forms a ring structure including that nitrogen atom, (c) an unsubstituted or inertly substituted alkylene or arylene group that, together with another R⁵ group bonded to a different nitrogen atom bonded to a common phosphorus atom, forms a ring structure including an -N-P-N- or -N-P=N- moiety, or (d) hydrogen. Each R⁵ is preferably hydrogen, a Ci-io alkyl group (especially methyl, ethyl, n-propyl or isopropyl), or together with another R⁵ forms a C2-5 alkylene group that forms part of a ring structure with a nitrogen atom or an — N— P— N— or -N-P=N- moiety. Each A³ is independently -[N=P(A³)]k-NR2, where R is as before. Each k is independently zero or a positive integer. The values of the various k's are preferably such that the group contains 1-6 phosphorus atoms. It is noted that the charge on any phosphazenium group will be delocalized throughout the group and may not reside on the particular phosphorus atom shown as carrying the charge in formulae XXIX and XXX.

The A group in structures III and XX-XXVII can be any organic linking group having a valence equal to 1 (when 1 is 2 or more). It may be hydrocarbyl, including linear or branched aliphatic, alicyclic, aromatic or mixtures of two or more of such sites. Aliphatic and alicyclic groups A may be saturated or unsaturated. The A group may contain inert substituents as described before. In some preferred embodiments, the A group is an organic polymer.

The phosphorus-sulfur additives in most cases can be prepared straightforwardly using simple chemistry. Starting materials are readily prepared by contacting alcohols or thiols with P4S10, which is readily available as a lubricating agent and a raw material for biocide manufacture. The alcohol and thiol have the structure ROH and RSH, respectively, where R is as defined in structure I above. The reaction product is a thiol compound having the structure:

) wherein X, R and m are as defined before. Dialcohols of the form HO-C(R²)2-R³-C(R²)2θH (where R² and R³ are as defined with regard to structures VI and VII above) will react with P4S10 to form cyclic starting materials having the structure XXXII:

) wherein X, R² and R³ are as defined before. In structure XXXII, each R² is preferably hydrogen and R³ is preferably dialkylmethylene, especially dimethylmethylene (propylidene).

The disulfide-bridged phosphorus-sulfur additives of structures I and IV-XI can be prepared by reaction of a thiol compound according to structure XXXI or XXXII with sodium methoxide in methanolic solution, concentrating the reaction product and reacting it with potassium iodide and iodine in aqueous solution. The monosulfide- bridged phosphorus-sulfur additive can be formed from the disulfide-bridged species by reaction with triphenylphosphine in toluene solution.

Metal-bridged phosphorus- sulfur additives of structures II and XII-XIX can be prepared by contacting the starting compound of structures XXXI or XXXII directly with a hydroxide or salt of the metal. Such a synthesis is described, for example, in C. Glidewell, Inorganic Chimica Acta, 1977 25 159. The reaction is conveniently done in solution, in which case the metal hydroxide or salt is soluble in the solvent. Halide, carbonate, hydroxide, oxide and acetate salts of the metal are generally useful. If desired, the starting compound can be formed into the corresponding ammonium salt by mixing with a primary, secondary or tertiary amine compound, prior to the reaction with the metal salt. The reaction can be schematically represented by reaction schemes XXXIII and XXXIV, as follows:

X¹ )

( XXXIV)

wherein X, R, m, n and M are as defined before, X¹ is an anion, each R⁶ is independently hydrogen, hydrocarbyl or inertly substituted hydrocarbyl (preferably alkyl). In reaction scheme XXXII, Xl should not be O²" or carbonate, and in each of thse reaction schemes, Xl w preferably ill be halide, especially chloride or bromide.

Phosphorus- sulfur additives of structures III and XX-XXIX, in which the Z group is an ammonium moiety, can be formed in at least two ways. In the first way, a starting compound of structure XXXI is reacted with a compound having 1 or more primary, secondary, or tertiary amino groups to form the phosphorus- sulfur additive. In the second way, the starting compound of structure XXXI is reacted with a compound having 1 or more ammonium groups to form the phosphorus-sulfur additive.

Amine-containing compounds that can be reacted with the structure XXXI starting material include, for example, polyamines such as ethylene diamine (H2NCH2CH2NH2), diethylenetriamine (H2NCH2CH2NHCH2CH2NH2) and other alkylene amines and alkylene polyamines; piperazine and other cyclic polyamines, and a variety of organic polymers that contain amino groups. Among those organic polymer are polyethers having terminal amino groups, such as primary amino-terminated poly(propylene oxide) polymers including those available commercially under the tradename Jeffamine®. Polymers of acrylamide are useful. In addition, a variety of amine-containing polymers can be formed by introducing amine groups onto previously- formed polymers in various ways. For example, ammonia, primary or secondary amines can react with halogen groups on a halogenated polymer (such as a polymer or copolymer of vinylbenzylchloride, vinyl chloride or vinylidene chloride) to form amino groups on the polymer.

Ammonium compounds can be formed from the corresponding amino compounds by reaction with a protic acid such as hydrochloric or sulfuric acid (to form the chloride or sulfate ammonium salt), or by quaternizing the amino group.

Phosphorus- sulfur compounds according to structures III and XX-XXIX, in which Z is sulfonium, phosphonium or phosphazenium, can be formed by reacting the starting compound of structure XXXI with a compound having 1 sulfonium, phosphonium or phosphazenium groups. An example of such a process is described by Ruff and Schlientz, Inorg. Synth. 1874, 15, 84.

Organic polymers containing phosphazenium groups can be prepared using methods analogous to those described in WO 01/90220A2, using a linear polymer rather than a crosslinked polymer as described therein. In general, the two main methods for attaching phosphazenium groups to the organic polymer are (1) to attach a previously- formed phosphazenium group to the organic polymer, and (2) to "build" the phosphazenium group onto the organic polymer. Phosphazenium groups can be "built" onto the polymer by reacting an amine- substituted organic polymer with phosphorus pentachloride and then with an excess of a compound having the structure NH=P{[-

The corresponding phosphazenium group (in the chloride form) is formed directly.

The phosphorus-sulfur compound is useful as a flame retardant additive for a variety of combustible polymers. "Combustible" here simply means that the polymer is capable of being burned under conditions of ambient or lower oxygen content. Combustible polymers of interest include polyolefins such as polyethylene (including copolymers of ethylene such as ethylene-α-olefin copolymers, polypropylene and the like; polycarbonates and blends of polycarbonates such as blends of a polycarbonate with a polyester, an acrylonitrile-styrene-butadiene resin or polystyrene; polyamides, polyesters, epoxy resins, polyurethanes, and vinyl aromatic polymers (including vinyl aromatic homopolymers, vinyl aromatic copolymers, or blends of one or more vinyl aromatic homopolymers and/or vinyl aromatic copolymers), as well as other flammable polymers in which the phosphorus-sulfur compound can be dissolved or dispersed. A "vinyl aromatic" polymer is a polymer of an aromatic compound having a polymerizable ethylenically unsaturated group bonded directly to a carbon atom of an aromatic ring. Vinyl aromatic monomers include unsubstituted materials such as styrene, divinylbenzene and vinyl naphthalene, as well as compounds that are substituted on the ethylenically unsaturated group (such as, for example alpha- methylstyrene), and/or are ring- substituted. Ring-substituted vinyl aromatic monomers include those having halogen, alkoxyl, nitro or unsubstituted or substituted alkyl groups bonded directly to a carbon atom of an aromatic ring. Examples of such ring- substituted vinyl aromatic monomers include 2- or 4-bromostyrene, 2- or 4-chlorostyrene, 2- or 4-methoxystyrene, 2- or 4-nitrostyrene, 2- or 4-methylstyrene and 2,4-dimethylstyrene. Preferred vinyl aromatic monomers are styrene, alpha-methyl styrene, 4-methyl styrene, divinylbenzene and mixtures thereof. Expanded polymers of any of these types are of interest.

A combustible polymer of interest is a polymer or copolymer of an vinyl aromatic monomer, such as a styrene polymer or copolymer, a styrene- acrylonitrile polymer, or a styrene-acrylonitrile-butadiene (ABS) resin. Polystyrene is an especially preferred combustible polymer.

Another combustible polymer of interest is a random, block or graft copolymer of butadiene and at least one vinyl aromatic monomer. Expanded combustible polymers of any of the foregoing types are of particular interest, as they find applications in vehicles and construction in which fire characteristics are of concern. An expanded combustible polymer suitably has a foam density of from about 1 to about 30 pounds per cubic foot (pcf) (16-480 kg/m³), especially from about 1.2 to about 10 pcf (19.2 to 160 kg/m³) and most preferably from about 1.2 to about 4 pcf (19.2 to 64 kg/m³). The phosphorus-sulfur flame retardant compounds are suitable for manufacturing extruded polymer foams, because the compounds have sufficient thermal stability, as indicated by the 5% weight loss temperature test described below, to be introduced into the foam extrusion process by which the foam is made. Enough of the phosphorus- sulfur compound is used to improve the performance of the combustible polymer in one or more standard fire tests. A suitable amount is typically at least one weight percent, or at least 2 weight percent or at least 3 weight percent, based on the weight of the polymer and phosphorus-sulfur compound. The amount of the phosphorus-sulfur compound may be as much as 25 weight percent, or as much as 15 weight percent, or as much as 10 weight percent.

One such standard fire test is a limiting oxygen index (LOI) test, which evaluates the minimum oxygen content in the atmosphere that is needed to support combustion of the polymer. LOI is conveniently determined in accordance with ASTM D 2863. The combustible polymer containing the phosphorus-sulfur compound preferably has an LOI of at least 20%, more preferably at least 23% and even more preferably at least 25%. Another fire test is a time-to-extinguish measurement, known as FP-7, which is determined according to the method described by A. R. Ingram in J. Appl. Poly. Sci. 1964, 8, 2485-2495. This test measures the time required for flames to become extinguished when a polymer sample is exposed to an igniting flame under specified conditions, and the ignition source is then removed. For non-cellular polymers, a time to extinguishment of less than 10 seconds, preferably less than 5 seconds, is desired. For cellular polymers (having a density of 10 pcf or less), a time of extinguishment of less than 15 seconds, preferably less than 10 seconds and more preferably less than 5 seconds is desired. Generally, these results can be obtained when the phosphorus-sulfur FR additive constitutes from 1 to about 15, preferably from 1 to about 6 weight percent of the compounded combustible polymer.

It is generally convenient to blend the phosphorus-sulfur FR additive into the molten combustible polymer, either prior to or during another melt processing operation (such as extrusion, foaming, molding, etc.). Because of this, the phosphorus- sulfur FR additive is preferably thermally stable at the temperature at which the molten polymer is processed. This temperature is typically above 15O⁰C, and for many combustible polymers of particular interest is 200⁰C or more, or even 22O⁰C or higher.

A useful indicator of thermal stability is a 5% weight loss temperature, which is measured by thermogravimetric analysis as follows: -10 milligrams of the phosphorus- sulfur FR additive is analyzed using a TA Instruments model Hi-Res TGA 2950 or equivalent device, with a 60 milliliters per minute (niL/min) flow of gaseous nitrogen and a heating rate of 10°C/min over a range of from room temperature (nominally 25°C) to 600⁰C. The mass lost by the sample is monitored during the heating step, and the temperature at which the sample has lost 5% of its initial weight is designated the 5% weight loss temperature (5% WLT). This method provides a temperature at which a sample has undergone a cumulative weight loss of 5 weight%, based on initial sample weight. The phosphorus-sulfur FR additive preferably exhibits a 5% WLT of at least the temperature at which the combustible polymer is melt-processed, either to blend it with the phosphorus-sulfur FR additive or to process the blend into an article such as a foam, extruded part, molded part, or the like. For use with many combustible polymers, the phosphorus-sulfur FR additive should have a 5% WLT of at least 15O⁰C. The 5% WLT is preferably at least 200⁰C, more preferably at least 220⁰C, even more preferably at least 240⁰C, and still more preferably at least 250⁰C. Polymer blends in accordance with the invention may include other additives such as other flame retardant additives, flame retardant adjuvants, thermal stabilizers, ultraviolet light stabilizers, nucleating agents, antioxidants, foaming agents, acid scavengers and coloring agents.

Polymer blends containing phosphorus-sulfur FR additives in accordance with the invention may be melt or solution processed to form a wide variety of products. Expanded (cellular) products are of interest because of their use in various building and automotive applications, in which fire performance is a concern. Expanded polymer products may have a bulk density of 10 pcf or less, more typically from 1.5 to 5 pcf and especially from 1.5 to 3 pcf. Expanded polymers of vinyl aromatic polymers, butadiene polymers and copolymers of vinyl aromatic polymers and/or butadiene polymers, as described before, are of particular interest. Non-cellular polymers can also be made in accordance with the invention.

The following examples are provided to illustrate the invention, but not to limit the scope thereof. All parts and percentages are by weight unless otherwise indicated.

Example 1

Sodium methoxide in methanol (10 mL of 25 weight % solution, 45 mmol) is added to 5,5-dimethyl-2-thioxo-l,3,2-dioxaphosphorinane-2-thiol (9.0 g, 45 mmol) and allowed to stir for 30 minutes. The resulting clear solution is concentrated under reduced pressure and the residue is dissolved in 100 mL of water. The aqueous solution is added to a solution of potassium iodide and iodine, resulting in a yellow-brown solid precipitating out. Filtration and recrystallization from ethanol yields 6.2 g (70% yield) of a light yellow solid, 5,5,5',5'-tetramethyl-2,2'-disulfanediyl-bis-[l,3,2- dioxaphosphorinane] 2,2'-disulfide, having the structure:

The 5% WLT for this material is 227°C.

A portion of the sample is melt blended with a polystyrene resin at a 4.2:95.8 weight ratio. The solidified melt blends are ground using a Wiley lab grinder and a 3 millimeter screen size before molding. 25-27 g aliquots of the ground melt blends are compression molded into plaques measuring 100 mm x 100 mm x 1.5 mm, using a

Pasadena Hydraulic Platen Press (Model # BL444-C-6M2-DX2357) operating at a set point temperature of 180⁰C with a pressure application time of 5 minutes and an applied pressure of 25,000 pounds per square inch (psi) (172 MPa). The molded plaques are cut into strips for Limiting Oxygen Index (LOI) and FP-7 ignitability tests. LOI is evaluated according to ASTM D 2863, and is found to be 25.7%. Time to flame extinguishment on the FP-7 test is evaluated and found to be 0.8 s.

Example 2 To a solution of 5,5,5',5'-tetramethyl-2,2'-disulfanediyl-bis-[l,3,2- dioxaphosphorinane] 2,2'-disulfide (3.94 g, 10 mmol) in 25 mL of toluene is added triphenylphosphine (2.62 g, 10 mmol). The mixture is allowed to stir at room temperature for 4 hours. The resulting cloudy solution is filtered and the precipitate is slurried in chloroform (20 mL). Filtration yields 2.5 g (69%) of a white solid, 5, 5,5', 5'- tetramethyl-2,2'-sulfanediyl-bis-[l,3,2-dioxaphosphorinane] 2,2'-disulfide, having the structure:

The 5% WLT for this material is 237°C. Plaques made from a blend of 2.5% of the product in 97.5% polystyrene (see Example 1) have an LOI of 24.5 and a time to flame extinguishment of 1.5 seconds on the FP-7 test.

A concentrate of 10 wt% of the material in polystyrene is prepared by blending the 5,5,5',5'-tetramethyl-2,2'-sulfanediyl-bis-[l,3,2-dioxaphosphorinane] 2,2'-disulfide, polystyrene and a 2 wt-% of a powdered organotin carboxylate stabilizer (e.g. THERMCHEK™ 832, commercially available from Ferro Corporation) based on the weight of the blend. The blend is melt compounded with the polystyrene using a Haake RHEOCORD™ 90 twin screw extruder equipped with a stranding die. The extruder has three temperature zones operating at set point temperatures of 135°C, 170°C and 180°C and a die set point temperature of 180°C. The extruded strands are cooled in a water bath and cut into pellets approximately 5 mm in length. The pellets are converted into foam using, in sequence, a 25 mm single screw extruder with three heating zones, a foaming agent mixing section, a cooler section and an adjustable 1.5 mm adjustable slit die. The three heating zones operate at set point temperatures of 115⁰C, 15O⁰C and 180°C and the mixing zone operates at a set point temperature of 200⁰C. The die opening is adjusted to maintain a back pressure of at least 1000 psi (6.9 MPa). Carbon dioxide (4.5 parts by weight (pbw) per 100 pbw combined weight of the concentrate and polystyrene pellets) is fed into the foaming agent mixing section using two different RUSKA™ (Chandler Engineering Co.) syringe pumps. Concentrate pellets and pellets of additional polystyrene are dry blended together with 0.05 wt%, based on dry blend weight, of barium stearate as a screw lubricant. The ratio of the concentrate pellets and pellets of additional polystyrene are selected to provide a final concentration of FR additive of 4.2% by weight. The dry blend is added to the extruder's feed hopper and fed at a rate of 2.3 kilograms per hour (kg/hr). Pressure in the mixing section is maintained above 1500 psi (10.4 MPa) to provide a polymer gel having uniform mixing and promote formation of a foam with a uniform cross- section. The coolers lower the foamable gel temperature to 12O⁰C to 13O⁰C. The foamable gel expands to form foam as it exits the die to form an expanded polystyrene foam having a bulk density of 2.48 pcf (39.7 kg/m³). LOI for the foam is 24.5%, and time to extinguishment is 7.5 seconds on the FP-7 test.

Example 3 To a solution of 5,5-dimethyl-2-thioxo-[l,3,2-dioxaphosphinane] 2-thiol (4.0 g, 20 mmol) in 70 mL of toluene is added zinc bromide (2.25 g, 10 mmol) and the mixture is then heated to 85⁰C for 4 hours. The clear reaction mixture turns white and cloudy as the reaction proceeds. The reaction mixture is cooled and filtered to yield 2.93 g of a white solid having the idealized structure (ignoring any waters of hydration) :

This material has a melting temperature of 246⁰C and a 5% WLT of 258⁰C. Proton NMR and ³¹P NMR spectra exhibit the following features: 1H NMR(THF-d₈, δ): 3.98 (d, J = 16Hz, 4H), 1.02 (s, 6H). 3¹P NMR (THF- d₈, δ): 100.67 (s,lP). Plaques made from a blend of 2.8% of the product in 97.2% polystyrene have an

LOI of 20.5 and a time to extinguishment of 13 seconds on the FP-7 test.

Example 4

To a solution of zinc bromide (1.13 g, 5 mmol) in 25 mL of ethanol is added the ammonium salt of O,O-dineopentyl dithiophosphate (2.87 g, 10 mmol). The mixture is allowed to stir overnight. The reaction mixture is then concentrated under reduced pressure and the residue is slurried in toluene (75 mL). Filtration and concentration of the filtrate gives 2.85 g (94%) of white solid. Recrystallization from hexane provides white crystals of bis[O,O-bis(2,2-dimethylpropyl) phosphorodithioato-S,S']-zinc having the idealized structure (ignoring any waters of hydration):

The melting temperature for this material is 220-222⁰C, and its 5% WLF is 237⁰C. Proton NMR and ³¹P NMR spectra exhibit the following features: 1H NMR(CDCl₃, δ): 3.80 (d, J = 6.9Hz, 8H), 0.97 (s, 36H). 3¹P NMR (CDCl₃, δ): 98.30.

Plaques made from a blend of 3.3% of the product in 96.7% polystyrene have an LOI of 20% and a time to extinguishment of 10 seconds on the FP-7 test.

Example 5 To a solution of 5,5-dimethyl-2-mercapto-l,3,2-dioxaphosphorinane 2-sulfide

(15.000 g, 75.67 mmol) in 150 mL of ethanol is added antimony triacetate (7.539 g, 25.22 mmol) to form a yellow precipitate that coats the walls of the flask. After heating overnight, the precipitate forms a free-stirring bright yellow slurry. The reaction mixture is then refluxed for several hours and filtered. The yellow precipitate is washed with two portions of ethanol, two portions of water, another two portions of ethanol, and dried under suction filtration. The yield of orange-yellow powder (antimony tris(5,5- dimethyl-2-mercapto-l,3,2-dioxaphosphorinane 2-sulfide)) is 11.01 g (61.2%). The idealized reaction scheme (ignoring any waters of hydration) is represented as follows:

The 5% WLT for this material is 259°C. Plaques made from a blend of 3% of the product in 97% polystyrene have an LOI of 22.5 and an FP-7 value of 3.8.

Example 6

2-Mercapto-5,5-dimethyl-l,3,2-dioxaphosphorinane 2-sulfide (16.00 g, 80.71 mmol) is slurried in 100 mL of water in a 1-neck 250 mL flask. Calcium carbonate (4.2 g, 42 mmol) is added slowly, and about 5 mL of ethanol is added to break up foam that forms. The resulting white slurry is heated for several days. The water is then removed on a rotary evaporator while heating to about 5O⁰C. The white solid is extracted with acetone and filtered to leave a small amount of white powder on the frit. The volatiles are removed from the acetone solution on a rotary evaporator to give a sticky white solid. Water is added to dissolve most of the solid. The resulting mixture is filtered. The aqueous solution is dried on a rotary evaporator to give 17.42 g of a white solid product having the idealized structure (waters of hydration not being shown):

The crystalline structure of this material is consistent with a highly ionic structure in which up to seven waters of hydration are associated with the Ca ion. The 5% WLT for this material is 270⁰C. Plaques made from a blend of 2.8% of the product in 97.2% polystyrene have an LOI of 21.3% and a time to extinguishment of 4.1 seconds on the FP-7 test.

Example 7

To a slurry of magnesium hydroxide (2.207 g, 37.83 mmol) in 100 mL of water in a 1-neck 250 mL flask is added 2-mercapto-5,5-dimethyl-l,3,2-dioxaphosphorinane 2- sulfide (15 g, 75.67 mmol). The mixture is refluxed for several hours. The reaction mixture is filtered to remove insolubles. The water is removed on a rotary evaporator while heating to about 5O⁰C. The residue is extracted with acetone, filtered and the volatiles are removed to give 19.29 g of a white powder of a material having the idealized structure (waters of hydration not being shown):

The crystalline structure of this material is consistent with a highly ionic structure in which up to six waters of hydration are associated with the Mg ion.

Example 8

2-Mercapto-5,5-dimethyl-l,3,2-dioxaphosphorinane 2-sulfide (16.00 g, 80.71 mmol) is slurried in 100 mL of water in a 1-neck 250 mL flask. Cesium carbonate

(13.281 g, 40.76 mmol) is added slowly, and about 10 mL of methanol are added to control foaming. The resulting slurry is stirred at ambient temperature over a weekend under a nitrogen stream which reduces the volume of liquid to about 50 mL. The resulting slurry is filtered and extracted several times with water. A small amount (< 1 g) of a white solid remains on the frit and is discarded. The water is removed on a rotary evaporator. The resulting white solid is soluble in water, DMSO, MeOH, less soluble in acetone and insoluble in CHCI3, toluene and hexane. The residue is extracted with methanol and filtered. The volatiles are removed on a rotary evaporator. The solid is scraped down, slurried/dissolved in methanol and filtered. The white solid is washed with several small portions of methanol, two portions (60 mL each) of toluene, two portions (60 mL each) of hexane and dried under suction filtration to give 21.05 g

(79.0%) of product as a snow-white powder. The product has the idealized structure:

The 5% WLT for this material is 325°C. Example 9

To a solution of 5,5-dimethyl-2-mercapto-l,3,2-dioxaphosphorinane 2-sulfide (20.7 g, 96.16 mmol) and triethylamine (9.73 g, 13.4 niL, 96.2 mmol) in 150 niL of ethanol is added BiCb (10.1 g, 32.1 mmol) to form a yellow precipitate that coats the walls of the flask. After heating overnight, the precipitate forms a free-stirring bright yellow slurry. The reaction mixture is then refluxed for several hours and filtered. The yellow precipitate is washed with two portions of ethanol, two portions of water, another two portions of ethanol, and dried under suction filtration. The yield is 12.98 g of bismuth tris(5,5-dimethyl-2-mercapto-l,3,2-dioxaphosphorinane 2-sulfide). The idealized reaction scheme (ignoring waters of hydration) is as follows:

The 5% WLT for this material is 264°C. Plaques made from a blend of 3.3% of the product in 96.7% polystyrene have an LOI of 22.3% and a time to extinguishment of 6.4 seconds on the FP-7 test.

Example 10

To a stirred slurry of 5,5-dimethyl-2-thioxo-[l,3,2-dioxaphosphorinane 2-thiol (3.41 g, 17.2 mmol) in toluene (200 mL) is added tetramethylethylenediamine (1 g, 8.6 mmol) dropwise. A white solid forms immediately in the flask. The reaction mixture is allowed to stir overnight at room temperature. The solid is filtered on a medium porosity fritted filter with a cold water vacuum. The white solid is washed with cold toluene (2 x 25 mL) and allowed to dry on the filter for 5 minutes. The solid is dried in a vacuum oven for 3 hours to yield 3.98 g of N, N, N', N'-tetramethylethane-l,2- diammonium bis(5,5-dimethyl-l,3,2-dioxaphosphorinane-2-thiolate 2-sulfide) as a white crystalline solid. This material has the idealized structure:

The melting temperature for this material is 218⁰C and its 5% WLT is 226°C. Plaques made from a blend of 1.6% of the product in 98.4% polystyrene have an LOI of 21.3% and a time to extinguishment of 7.1 seconds on the FP-7 test.

Example 11

To a stirred slurry of 2-mercapto-5,5-dimethyl-l,3,2-dioxaphosphorinane 2- sulfide (0.576 g, 2.91 mmol) in toluene (50 mL) is added diethylenetriamine (0.1 g, 0.97 mmol) dropwise. A white solid forms immediately in the flask. The reaction mixture is warmed to ~40°C and allowed to stir for 20 minutes. The reaction mixture is concentrated under reduced pressure and the residue is then dried in a vacuum oven for 2 hours, to yield 0.69 g of N-(2-ammonioethyl)ethane-l,2-diammonium tris(5,5-dimethyl- l,3,2-dioxaphosphorinane-2-thiolate 2-sulfide as a white crystalline solid. This material has the following idealized structure:

The melting temperature for this material is 218⁰C and its 5% WLT is 224°C.

Example 12

Bis(triphenylphosphine)iminium acetate (15.0 g, 25.10 mmol) is suspended in 500 mL of water, then dissolved by heating with a heat gun. The clear solution is filtered from a very small amount of insoluble black material. A slurry of 2-mercapto-

5,5-dimethyl-l,3,2-dioxaphosphorinane 2-sulfide (4.98 g, 25.10 mmol) in 120 mL of hot water is added, and a large quantity of a white solid precipitates. The mixture is allowed to stir overnight. The reaction mixture is heated nearly to boiling on a heating mantle, allowed to cool somewhat and filtered. The precipitate is washed several times with cold water, then dried under an air flow on the suction filter. 16.56 g of a white powder having the idealized structure

is obtained. The 5% WLT for this material is 329°C. The compound is soluble in methanol, chloroform, acetone and DMSO, but insoluble in water, toluene, and hexane. ES-MS in negative and positive ion modes shows the presence of the thiophosphate anion ([M]- = 196.99) and the PPN cation ([M]⁺ = 538.18) respectively.

Proton, ¹³C and ³¹P NMR spectra show that a highly pure material is obtained. These spectra show the following features: ¹H NMR (299.99 MHz, CDCl₃, vs TMS) δ:. 7.66 - 7.72 (m, 6H), 7.43 - 7.55 (m, 24 H), 4.00 (d, 4H, J = 15.38 Hz), 0.99 (s, 6H). ¹³C NMR (75.44 MHz, CDCl₃, vs CDCl₃) δ: 133.70, 131.78 (m - pentet of 1:3:3:3:1, J = 5.7 Hz inner, 2.7 Hz outer), 129.39 (m - pentet of 1:3:3:3:1, J = 6.7 Hz inner, 2.7 Hz outer), 126.64 (d of d, J = 107.99 Hz, J = 2.01 Hz), 74.17 (d, J = 8.05 Hz), 32.26 (d, J = 5.37 Hz), 22.10. ³¹P NMR (121.44 MHz, CDCl₃, vs H₃PO₄) δ: 112.49, 21.73. Hz, CDCl₃, vs H₃PO₄) δ: 21.75.

Example 13

2-Mercapto-5,5-dimethyl-l,3,2-dioxaphosphorinane 2-sulfide (6.0 g, 30.27 mmol) and NaHCO₃ (3.00 g, 35.7 mmol) are combined in 175 mL of water to give a cloudy solution containing a fine precipitate. Tetraphenylphosphonium chloride (11.35 g, 30.27 mmol) dissolved in 100 mL of water is added. The reaction mixture is heated to boiling, then allowed to cool overnight to give a large quantity of white precipitate. The mixture is filtered, washed several times with cold water, and dried under suction filtration to give the product, tetraphenylphosphonium 5,5-dimethyl-2-mercapto-l,3,2- dioxaphosphorinane-2- sulfide, as a white solid in the form of thin crystalline platelets and powder. This material has the idealized structure:

! s^'-b-

The yield is 14.41 g. The 5% WLT for this material is 303°C. The compound has good solubility in methanol, fair solubility in chloroform, acetone and DMSO, but is insoluble in water, toluene, and hexane. NMR spectra show very high purity material is obtained. The spectra exhibit the following features: ¹H NMR (299.99 MHz, CDCl₃, vs TMS) δ: 7.88 - 7.95 (t of m, 4H, J = 7.6 Hz, J =

2.2 Hz), 7.78 - 7.86 (t of m, 8H, J = 7.3 Hz, J = 3.7 Hz, J = 0.6 Hz), 7.62 - 7.70 (d of d of m, 8H. J = 13.1 Hz, J = 8.4 Hz, J = 1.5 Hz, J = 1.2 Hz), 3.94 (d, 4H, J = 15.38), 0.96 (s,

6H). 13c NMR (75.44 MHz, CDCl₃, vs CDCl₃) δ: 135.61 (d, J = 3.35 Hz), 134.27 (d, J = 10.73 Hz), 130.69 (d, J = 12.74 Hz), 117.25 (d, J = 89.21 Hz), 74.17 (d, J = 7.38 Hz), 32.31 (d, J = 5.37 Hz), 22.16. ³¹P NMR (121.44 MHz, CDCl₃, vs H₃PO₄) δ: 112.20, 23.61.

Example 14

2-Mercapto-5,5-dimethyl-l,3,2-dioxaphosphorinane 2-sulfide (6.0 g, 30.27 mmol) and NaHCθ3 (3.00 g, 35.7 mmol) are combined in 175 mL of water to give a cloudy solution containing fine precipitate. Tetramethylammonium chloride (3.32 g, 30.27 mmol) dissolved in 100 mL of water is added to give a cloudy solution. The reaction mixture is heated for several hours to produce a slurry. The water is removed under reduced pressure and gentle heating on a rotary evaporator. The residue is extracted with 300 mL of hot CHCI3 and filtered. Most of the residue remains un dissolved. The undissolved residue is extracted with MeOH and filtered. The combined extracts are evaporated to dryness on a rotary evaporator to give 9.6 g of a white powder. The powder is extracted with a hot mixture of 50/50 MeOH/CHCh and filtered. The volatiles are removed from the organic fraction on a rotary evaporator to give 8.18 g of tetramethylammonium 5,5-dimethyl-2-mercapto-l,3,2-dioxaphosphorinane-2-sulfide as a white powder. This material has the following idealized structure.

This material begins to decompose at about 22O⁰C and its 5% WLT is 232⁰C. The product has good solubility in DMSO, MeOH and water, some solubility in acetone and CHCI3, and is insoluble in toluene and hexane. Proton, ¹³C and ³¹P NMR spectra show the following features:

¹H NMR (299.99 MHz, CDCl₃, vs TMS) δ: 4.00 (d, 4H, J = 15.38 Hz), 3.50 (s, 12H), 1.03 (s, 6H). ¹³C NMR (75.44 MHz, CDCl₃, vs CDCl₃) δ: 74.57 (d, J = 7.38 Hz), 56.30 (t, J =

3.69), 32.59 (d, J = 5.37 Hz), 22.10. ³¹P NMR (121.44 MHz, CDCl₃, vs H₃PO₄) δ: 110.00

Claims

WHAT IS CLAIMED IS:

1. A polymer composition comprising a combustible polymer having mixed therein a phosphorus- sulfur additive represented by the structure:

wherein each X is independently oxygen or sulfur, each m is independently zero or 1, p is 1 or 2, and each R is independently an unsubstituted or inertly substituted hydrocarbyl group or the R groups of any R- (X)_1n-P- (X)_m-R structure together form an unsubstituted or inertly substituted divalent organic group.

2. The polymer composition of claim 1 wherein the phosphorus-sulfur additive is represented by either of the structures

Wherein p is 1 or 2, and each R is independently an unsubstituted or inertly substituted hydrocarbyl group or the R groups of any R- (X)_1n-P- (X)m-R structure together form an unsubstituted or inertly substituted divalent organic group.

3. The polymer composition of claim 1 wherein the phosphorus-sulfur additive is represented by either of the structures

wherein p is 1 or 2, each R² is independently hydrogen, alkyl or inertly substituted alkyl, and each R³ is independently a covalent bond or a divalent linking group, and p is as before.

4. The polymer composition of claim 3 wherein each R² is hydrogen, and R³ is an alkylene diradical having no hydrogens on the carbon atom(s) bonded directly to the adjacent (R²)2C groups.

5. The polymer composition of claim 1 wherein the phosphorus-sulfur additive is represented by either of the structures

wherein p is 1 or 2.

6. The polymer composition of claim 1 wherein the phosphorus-sulfur additive is represented by either of the structures

wherein p is 1 or 2.

7. A polymer composition comprising a combustible polymer having mixed therein a phosphorus- sulfur additive represented by the structure:

wherein each X is independently oxygen or sulfur, each m is independently zero or 1, M represents a metal atom, which may have associated waters of hydration, n is a number from 1 to 4, and each R is independently an unsubstituted or inertly substituted hydrocarbyl group or the R groups of any R- (X)_1n-P- (X)_m-R structure together form an unsubstituted or inertly substituted divalent organic group.

8. The polymer composition of claim 7 wherein the phosphorus-sulfur additive is represented by either of the structures

wherein M represents a metal atom which may have associated waters of hydration, n is a number from 1 to 4, and each R is independently an unsubstituted or inertly substituted hydrocarbyl group or the R groups of any R-(X)_m-P-(X)m-R structure together form an unsubstituted or inertly substituted divalent organic group.

9. The polymer composition of claim 7 wherein the phosphorus-sulfur additive is represented by either of the structures

wherein M represents a metal atom which may have associated waters of hydration, n is a number from 1 to 4, each R² is independently hydrogen, alkyl or inertly substituted alkyl, each R³ is independently a covalent bond or a divalent linking group, and p is as before.

10. The polymer composition of claim 9 wherein each R² is hydrogen, and R³ is an alkylene diradical having no hydrogens on the carbon atom(s) bonded directly to the adjacent (R²)2C groups.

11. The polymer composition of claim 7 wherein the phosphorus-sulfur additive is represented by either of the structures

wherein M represents a metal atom which may have associated waters of hydration and n is a number from 1 to 4.

12. The polymer composition of claim 7 wherein the phosphorus-sulfur additive is represented by either of the structures

wherein M represents a metal atom which may have associated waters of hydration and n is a number from 1 to 4.

13. A polymer composition comprising a combustible polymer have mixed therein a phosphorus- sulfur additive represented by the structure:

wherein each X is independently oxygen or sulfur, each m is independently zero or 1, 1 is an integer of 1 or more, q is zero when 1 is 1 and q is 1 when 1 is 2 or more, Z represents a cationic group, each R is independently an unsubstituted or inertly substituted hydrocarbyl group or the R groups of any R- (X)_1n-P- (X)m-R structure together form an unsubstituted or inertly substituted divalent organic group, and A is an organic group.

14. The polymer composition of claim 13 wherein the phosphorus-sulfur additive is represented by either of the structures:

wherein 1 is an integer of 1 or more, q is zero when 1 is 1 and q is 1 when 1 is 2 or more, Z represents a cationic group, each R is independently an unsubstituted or inertly substituted hydrocarbyl group or the R groups of any R-(X)_m-P-(X)m-R structure together form an unsubstituted or inertly substituted divalent organic group, and A is an organic group.

15. The polymer composition of claim 13 wherein the phosphorus-sulfur additive is represented by either of the structures:

wherein 1 is an integer of 1 or more, q is zero when 1 is 1 and q is 1 when 1 is 2 or more, Z represents a cationic group, each R² is independently hydrogen, alkyl or inertly substituted alkyl, each R³ is independently a covalent bond or a divalent linking group and A is an organic group.

16. The polymer composition of claim 15 wherein each R² is hydrogen, and R³ is an alkylene diradical having no hydrogens on the carbon atom(s) bonded directly to the adjacent (R²)2C groups.

17. The polymer composition of claim 13 wherein the phosphorus-sulfur additive is represented by either of the structures:

wherein 1 is an integer of 1 or more, q is zero when 1 is 1 and q is 1 when 1 is 2 or more, Z represents a cationic group, and A is an organic group.

18. The polymer composition of claim 13 wherein the phosphorus-sulfur additive is represented by either of the structures:

wherein 1 is an integer of 1 or more, q is zero when 1 is 1 and q is 1 when 1 is 2 or more, Z represents a cationic group, and A is an organic group.

19. The polymer composition of any of claims 1-18 wherein the combustible polymer is polystyrene.

20. The polymer composition of claim 19 wherein the polymer composition is expanded.

21. A phosphorus-sulfur compound represented by the structure:

wherein each X is independently oxygen or sulfur, each m is independently zero or 1, M represents a metal atom which may have associated waters of hydration, n is a number from 1 to 4, and each R is independently an unsubstituted or inertly substituted hydrocarbyl group or the R groups of any R- (X)_1n-P- (X)_m-R structure together form an unsubstituted or inertly substituted divalent organic group.

22. The phosphorus-sulfur compound of claim 21 which is represented by either of the structures

wherein M represents a metal atom which may have associated waters of hydration, n is a number from 1 to 4, and each R is independently an unsubstituted or inertly substituted hydrocarbyl group or the R groups of any R-(X)_m-P-(X)m-R structure together form an unsubstituted or inertly substituted divalent organic group.

23. The phosphorus-sulfur compound of claim 21 which is represented by either of the structures

wherein M represents a metal atom which may have associated waters of hydration, n is a number from 1 to 4, each R² is independently hydrogen, alkyl or inertly substituted alkyl, each R³ is independently a covalent bond or a divalent linking group, and p is as before.

24. The phosphorus-sulfur compound of claim 23 wherein each R² is hydrogen, and R³ is an alkylene diradical having no hydrogens on the carbon atom(s) bonded directly to the adjacent (R²)2C groups.

25. The phosphorus-sulfur compound of claim 21 which is represented by either of the structures

wherein M represents a metal atom which may have associated waters of hydration and n is a number from 1 to 4.

26. The phosphorus-sulfur compound of claim 21 which is represented by either of the structures

wherein M represents a metal atom which may have associated waters of hydration and n is a number from 1 to 4.

27. A phosphorus-sulfur compound represented by the structure:

wherein each X is independently oxygen or sulfur, each m is independently zero or 1, 1 is an integer of 1 or more, q is zero when 1 is 1 and q is 1 when 1 is 2 or more, Z represents a cationic group, each R is independently an unsubstituted or inertly substituted hydrocarbyl group or the R groups of any R- (X)_1n-P- (X)_m-R structure together form an unsubstituted or inertly substituted divalent organic group, and A is an organic group.

28. The phosphorus-sulfur compound of claim 27 which is represented by either of the structures:

wherein 1 is an integer of 1 or more, q is zero when 1 is 1 and q is 1 when 1 is 2 or more, Z represents a cationic group, each R is independently an unsubstituted or inertly substituted hydrocarbyl group or the R groups of any R-(X)_m-P-(X)m-R structure together form an unsubstituted or inertly substituted divalent organic group, and A is an organic group.

29. The phosphorus-sulfur compound of claim 27 which is represented by either of the structures:

wherein 1 is an integer of 1 or more, q is zero when 1 is 1 and q is 1 when 1 is 2 or more, Z represents a cationic group, each R² is independently hydrogen, alkyl or inertly substituted alkyl, each R³ is independently a covalent bond or a divalent linking group and A is an organic group.

30. The phosphorus-sulfur compound of claim 29 wherein each R² is hydrogen, and R³ is an alkylene diradical having no hydrogens on the carbon atom(s) bonded directly to the adjacent (R²)2C groups.

31. The phosphorus-sulfur compound of claim 27 which is represented by either of the structures:

wherein 1 is an integer of 1 or more, q is zero when 1 is 1 and q is 1 when 1 is 2 or more, Z represents a cationic group, and A is an organic group.

32. The phosphorus-sulfur compound of claim 27 which is represented by either of the structures:

wherein 1 is an integer of 1 or more, q is zero when 1 is 1 and q is 1 when 1 is 2 or more, Z represents a cationic group, and A is an organic group.