EP0690890A1

EP0690890A1 - Phosphorus-containing flame retardants

Info

Publication number: EP0690890A1
Application number: EP94910460A
Authority: EP
Inventors: Jonathan Stuart Leake; Paul William Law
Original assignee: Courtaulds PLC
Current assignee: Akzo Nobel UK PLC
Priority date: 1993-03-23
Filing date: 1994-03-23
Publication date: 1996-01-10
Also published as: GB9305969D0; WO1994021724A1

Abstract

A phosphonocarboxylate ester of formula (I) in which the groups R are alkyl groups having 1 to 4 carbon atoms; R1 represents an alkyl group having 1 to 8 carbon atoms, an aryl group having 6 to 8 carbon atoms or a group of formula (a), where Y is an alkylene group having 1 to 4 carbon atoms and R14 is an alkyl group having 1 to 4 carbon atoms; X represents a methylene group, a substituted methylene group or a vinylidine or substituted vinylidene group; and n is 0 or 1; or a diphosphonate ester of formula (b) is used as a flame retardant. It is particularly suitable for polyurethane or polyisocyanurate foam and can for example be added to the polyol from which polyurethane foam is formed.

Description

Phosphorus-Containing Flame Retardants

Field of the invention

This invention relates to phosphorus-containing compounds and to their use as flame retardants, particularly in the production of polyurethane foam and also in other plastics materials. The flame retardants currently most widely used in polyurethane foam contain halogen in addition to phosphorus; but halogenated compounds are becoming regarded as environmentally undesirable for some uses. The present invention provides halogen-free flame retardants which are at least as effective in most uses as the known halogenated compounds.

Background art

US-A-4576971 discloses a polyacrylimide or polymethacrylimide resin foam containing at least 1% by weight of phosphorus present in the form of an organophosphorus compound of the formula:

0 //

X - CH- - P(OR)₂, wherein each R is methyl, ethyl or chloro- methyl and X is hydrogen, halogen, hydroxyl or RO-CO-.

US-A-3694430 and US-A-3764570 disclose a polyurethane foam made by reacting a polyisocyanate in the presence of a blowing agent with the ester-interchange reaction product obtained by heating 1 mole of an oxyalkylated sugar with 1-6 moles of a phosphorus ester of the formula: 0 0

N n (R0)₂P(CH_)_nC0R' , wherein R and R' are alkyl groups having

1 to 4 carbon atoms and n is 1 or 2. US-A-4254018 and US-A-

4483970 describe the use of a phosphorus ester of this formula respectively as a heat stabiliser for polyesters and as a deactivator for polyester-urethane thermoplastic elastomers. JP-A-60-185821 discloses the treatment of freshly spun polyester fibres with a mixture of a polyalkylene glycol, for example triethylene glycol, and a phosphorus compound which is phosphoric acid, phosphorous acid, a phosphonic acid or a phosphinic acid or an ester of any of these acids, for example:

0 0

(C-H₅0)-PCH-CH-COC₂H₅ .

Disclosure of the invention

According to one aspect of the present invention a polyurethane foam or polyisocyanurate foam contains a phosphorus-containing flame retardant, and is characterised in that the flame retardant is a phosphonocarboxylate ester of the formula:- 0 0

(RO).P - (X)_n - C - OR¹ (I)

in which the groups R, which can be the same or different, each represent an alkyl group having 1 to 4 carbon atoms; R represents an alkyl group having 1 to 8 carbon atoms, an aryl group having 6 to 8 carbon atoms or a group of the formula:-

0

" ₁₄ - Y - P(0R )₂, where Y is an alkylene group having 1 to 4 carbon atoms and R¹* is an alkyl group having 1 to 4 carbon atoms;

X represents a methylene group, a substituted methylene group of the formula CR²R³ or a vinylidene or substituted vinylidene group of the formula:-

and n is 0 or 1; wherein R² represents an alkyl group having 1 to 4 carbon atoms, an aryl group having 6 to 8 carbon atoms or a group of the formula:-

R⁷ 0 R¹⁰ 0

I ₆ W ₉ I II ₉ - COOR , - P OR , - - P(OR⁹).

in which R⁶ represents an alkyl group having 1 to 4 carbon atoms; R⁷ and R⁸, which can be the same or different, each represent hydrogen or an alkyl group having 1 to 4 carbon atoms; the groups R⁹, which can be the same or different, each represent an alkyl group having 1 to 4 carbon atoms; R¹⁰ represents hydrogen, an alkyl group having 1 to 4 carbon atoms or a group of the formula -COOR¹² where R¹² is an alkyl group having 1 to 4 carbon atoms; and R¹¹ represents hydrogen or an alkyl group having 1 to 4 carbon atoms; R represents hydrogen, an alkyl group having 1 to 4 carbon atoms or a group of the formula COOR⁶ where R⁶ is defined as above; and R⁴ and R^s, which can be the same or different, each represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an aryl group.

A polyol composition according to the invention comprises a polyol selected from polyether and polyester polyols suitable for preparing polyurethane foam, said polyol composition containing a phosphorus-containing flame retardant, and is characterised in that the flame retardant is a phosphonocarboxylate ester of the formula (I) defined as above.

The invention also includes the use as a flame retardant of a compound of the formula:-

or an addition polymer thereof, or a compound of the formula

0 R² 0 n \\ .

(R0)₂ P - C - C - OR (III)

R³

where R, R¹, R², R³, R⁴ and R⁵ are defined as above. R² and R³ are preferably methyl or ethyl groups. If R⁴ or R⁵ is an aryl group it preferably contains 6 to 8 carbon atoms.

According to another aspect of the invention a plastics material contains a phosphorus compound as flame retardant and is characterised in that the flame retardant is a compound of the formula (II) or an addition polymer thereof or a compound of the formula (III).

The phosphonocarboxylate esters of formula (I) are generally effective flame retardants for organic polymers. They readily lose C0₂ on moderate heating; the C0₂ suppresses vapour-phase flame spread. As heating proceeds, the phosphonate moiety is converted to polyphosphoric acid, which promotes char formation.

The compounds of formula (I) can be prepared with a wide range of physical properties by varying the groups R, R¹ and X. The compounds of formula (I) can for example be liquids or can be solids of high or low melting point. The compounds of formula (I) generally have a high solubility in most organic solvents; some have high solubility in water and some are substantially insoluble in water.

One class of compounds of formula (I) is the trialkyl phosphonoformates of the formula: 0 0

" " i

( RO ) ₂P - C - OR ;

examples are trimethyl phosphonoformate where R = R¹ = CH₃, triethyl phosphonoformate where R = R¹ = C-H-, and methyl (diethyl phosphono)formate where R = C-H. and R¹ = CH₃. The phosphonoformates can be prepared by reacting a chloroformate ester with a trialkyl phosphite according to the equation:

0 0 i II II ₁ C1COOR + (R0)₃P > (RO)₂ P - C - OR + RC1

The phosphonoformates are effective flame retardants, but they are generally soluble in water unless the two groups R and the group R¹ contain a total of at least 9 carbon atoms; for some flame retardant uses water-insoluble flame retardants are preferred.

Another class of compounds of formula (I) is the trialkyl phosphonoacetates of the formula:

0 0 \\ II

(RO)₂P - CH₂ - C - OR¹;

examples are trimethyl phosphonoacetate, triethyl phosphonoacetate, isopropyl (dimethyl phosphono)acetate where R = CH. and R¹ = -CH(CH.)₂, isopropyl (diethyl phosphono)acetate and isopropyl (di(n-butyl) phosphono)acetate. The phosphonoacetates can be prepared by reacting a chloroacetate ester with a trialkyl phosphite according to the equation:

0 0 // // . CICH.COOR' + (R0)₃P -> (RO)-P -CH- - COR¹ + RC1

The reaction is preferably carried out at elevated temperature, more preferably at at least 100°C, for example at a temperature in the range 130-200°C, with removal of the alkyl chloride RC1 evolved. The reagents are generally liquid and the reaction is preferably carried out under solventless conditions; a high-boiling organic solvent can be used if desired. The phosphonoacetates are effective flame retardants, but they are generally soluble in water unless the two groups R and the group R¹ contain a total of at least 8 carbon atoms. Examples of water-insoluble phosphonoacetate flame retardants are:-

isopropyl (di(n-butyl) phosphono)acetate (R= C₄H_g, R¹ = -CH(CH₃)₂), n-butyl (diethyl phosphono)acetate (R= C_H_, R¹ = C₄H_g) , 4-methyl-2-pentyl (dimethyl phosphono)acetate (R= CH₃, R¹ = -CH(CH₃)CH₂CH(^"CH₃)₂), 4-methyl-2-pentyl (diethyl phosphono)acetate, and 2-octyl (dimethyl phosphono)acetate.

Chloroacetate esters in which R¹ is a group of the formula: O

- Y - P^tt(OR14)₂ can be prepared by the reaction of an unsaturated phosphonate with chloroacetate anion; for example a dialkyl vinyl phosphonate:

0 ^tt 14

CH₂ = CH - P(OR )₂ can be reacted with an alkali metal chloroacetate to produce a chloroacetate ester of the formula: 0

CICH-COOCH-CH.P(OR").

Compounds of formula (I) in which X represents a substituted methylene group can be prepared by the reaction of an alpha-halocarboxylate ester with a trialkyl phosphite according to the equation:

Y 0 R² 0

2 ' i II i » .

R - CH - COOR¹ + (R0)₃P —► (RO).P - C - C - OR +RY

R³ R³ (III) where R² is an alkyl or aryl group and Y is a halogen, preferably bromine or chlorine. The preferred temperature and reaction conditions are generally those described above for preparation of the phosphonoacetates. For example, an alkyl alpha-chloropropionate can be reacted with a trialkyl phosphite to produce a compound of formula (III) where R² represents CH₃ and R³ represents H.

Compounds of the formula (III) in which R² and optionally R³ are alkyl groups can alternatively be prepared by alkylating a phosphonoacetate, for example by reacting the phosphonoacetate with an alkoxide such as potassium t- butoxide and an alkyl halide such as iodomethane in a solvent in which the corresponding alkali metal halide is insoluble. The compounds of formula (III) in which R² and R³ are both alkyl groups, preferably methyl groups, have the advantage of greater stability because of the absence of an activated methylene group.

Compounds of formula (III) in which R² represents a carboxymethyl group of the formula;

R⁷

- COOR⁶

R⁸

can be prepared by the reaction of an unsaturated dicarboxylic acid diester with a dialkyl phosphite in the presence of a base. For example, a dialkyl maleate or fumarate can be reacted with a dialkyl phosphite to produce a phosphonosuccinate according to the equation:

0 ι i ^w 1 R OOC - CH = CH - COOR¹ + ( RO) ₂PHO ( RO) ₂P - CH - COOR

CH_jCOOR¹

The reaction is base catalysed and is generally carried out in the presence of a base such as an alkali metal alkoxide, for example sodium methoxide or ethoxide. The reaction temperature is preferably 55 to 100°C. The reaction is usually carried out in an alcohol solvent, but it can be carried out solventless or in an inert solvent. Examples of this reaction are the reaction of dimethyl maleate with dimethyl phosphite to produce tetramethyl phosphonosuccinate, the reaction of diethyl maleate with diethyl phosphite to produce tetraethyl phosphonosuccinate, and the reaction of dimethyl fumarate with diethyl phosphite to produce dimethyl diethyl phosphonosuccinate. The phosphonosuccinate esters are effective flame retardants, are soluble in most organic solvents and are substantially water-insoluble if the two groups R and the two groups R¹ contain a total of at least 6 carbon atoms; for example tetraethyl phosphonosuccinate is a valuable water-insoluble flame retardant.

Compounds of the formula (III) in which R² represents a group of the formula:

R¹⁰ 0

\ w ₉

- C - P(OR⁹)₂ R¹¹

in which R¹⁰ represents a group of the formula -COOR¹², can be prepared by the reaction of acetylene dicarboxylic acid with a trialkyl phosphite, for example trimethyl or triethyl phosphite, according to the equation:

0 0

// //

2P(OR)₃ + HO - C - C s C - C - OH-

The reaction can be carried out in a polar organic solvent such as acetonitrile at ambient temperature. The presence of two phosphonate groups in the phosphonocarboxylate ester can give enhanced flame retardancy due to increased phosphorus content and/or can give lower volatility at the same phosphorus content.

Further valuable flame retardants having two phosphonate groups are those of the formula (III) in which R² represents a phosphonate group of the formula: 0

- P(OR⁹)₂. These di(phosphono)-carboxylate esters can be prepared by the reaction of a tetraalkyl methylene diphosphonate with an alkyl chloroformate in the presence of sodium hydride in an anhydrous aprotic polar organic solvent. Reaction with a substantially equimolar amount of chloroformate produces a pentaalkyl diphosphonoacetate according to the equation:

where R¹⁵ is hydrogen or alkyl of 1 to 4 carbon atoms.

When R¹⁵ is hydrogen reaction with excess chloroformate produces a hexaalkyl diphosphonomalonate according to the equation:-

The tetraalkyl methylene diphosphonate can be prepared by reacting a dialkyl phosphite with a 1,1-dihaloalkane such as dichloromethane or ethylidene dichloride in the presence of a strong base, for example an alkoxide, as described in Synthetic Communications, Vol. 20., pp 1865-1867 (1990). We have found that the tetraalkyl methylene diphosphonate is itself an effective flame retardant, as well as being an intermediate in the preparation of the di(phosphono)- carboxylate ester flame retardant, and it can be incorporated in polyurethane foam or polyisocyanurate foam, for example by mixing it with a polyol such as a polyether or polyester polyol suitable for preparing polyurethane foam.

The tetraalkyl methylene diphosphonate can be used as an intermediate to prepare a further class of phosphonocarboxylate esters useful as flame retardants by reaction with a dialkyl ester of an unsaturated dicarboxylic acid. The tetraalkyl methylene diphosphonate is first reacted with sodium hydride and then with the dialkyl dicarboxylate, for example with a dialkyl maleate or fumarate according to the equation: -

or with a dialkyl ester of acetylene dicarboxylic acid to produce a phosphonocarboxylate ester of the formula:-

6 - li ¬ as described in J. Org. Chem. , vol 45, pp 2698-2703 (1980).

A further class of valuable compounds of formula (I) is those in which the group X is a group of the formula:

that is to say alpha-phosphonoacrylates (where R⁴ and R⁵ represent hydrogen) and other alpha-phosphonoalkenoates. These can be made by the Knoevenagel reaction of a phosphonoacetate with an aldehyde or ketone according to the equation:

0 w

(RO) OR^A - C -

The Knoevenagel reaction is catalysed by a base, preferably a heterocyclic base such as pyrrolidine, morpholine or piperidine, or an N-methyl derivative thereof, or pyridine, optionally in the presence of a Lewis acid, for example titanium tetrachloride. Examples of aldehydes and ketones which can be reacted with a trialkyl phosphonoacetate are acetaldehyde, acetone, formaldehyde, methyl ethyl ketone, benzaldehyde, acetophenone and benzophenone. Examples of compounds of formula (II) useful as flame retardants are:- trimethyl alpha-phoβphonocinn-unatβ C 6-H5.CH = iC - P(0)(OCH3,),2

COOCH- isopropyl (dimethyl alpha-phoβphono) βenecioate (CH, ) , C = C - P (0) (OCH ) COOCH (CH₃ ) ₂ triethyl alpha-phosphonocrotonate CH CH = C - P (0) (OC H )

COOC 2H 5 iaopropyl (diethyl alpha-phosphono)acrylate CH2, = CI -P(O) (OC2 H5 )2

COOCH(CH ), isopropyl (diethyl alρha-ρhosphono)crotonate CH CH = C_* - P(O) (OC2H5)2

COOCH(CH₃)₂ trimethyl alpha-phoaphonocrotonate CH CH = C - P(0)(OCH )

³ I ^{3 2}

COOCH tπ-tW ,__, 3)',2 C - C - >(0) <CCH 3₎,'2

COOCH methyl (diethyl alpha-phosphono)senecioate (CH ) C = C - P(O) (OC H ) COOCH₃

The phosphonoalkenoates of formula (II) are effective flame retardants, and those in which the groups R, R¹, R⁴ and R⁵ contain a total of at least 7 carbon atoms are substantially insoluble in water.

When the carbonyl compound R 4 - - R5 is an aldehyde having at least 2 carbon atoms the product of the reaction may comprise a mixture of isomeric phosphonoalkenoates differing in double bond position. For example, when: 0

. II _s . .

R - C - R is butanal (R = C.H₇, R = H) , the product is a mixture of isomers consisting mainly of the expected compound

but with a significant amount of the isomer

0

0 The mixture of isomers can be used as a flame retardant with no loss of effectiveness.

The phosphonoalkenoates of formula (II) have a double bond sufficiently reactive to undergo nucleophilic addition. This can be used to produce flame-retardant compounds containing a further phosphonate group. The phosphonoalkenoate of formula (II) can for example be reacted with a dialkyl phosphite such as dimethyl phosphite under basic conditions according to the equation:

o o O O H O

II // « I

( RO ) _P - C - c - OR (R⁹0 ) .PH -* ( RO) ₂P - C c - OR^A w c 5

R⁴ - C - R

₉ <

( R⁹0) P = O

The product is a phosphonocarboxylate ester of formula ( III ) in which the group s :

10 0

- ^W P (OR 9 ) .

11

R¹⁰ and R¹¹ being the groups R⁴ and R⁵ of the phosphonoalkenoate (II).

As a further example, the phosphonoalkenoate of formula (II) can be reacted with a phosphonoacetate under basic conditions in a Michael-type nucleophilic addition reaction according to the equation:

o o o

(RO)-P * - C - C" - OR1¹ + (R90),P" - CH, ² l\ ^{2 2}

C

The product is a phosphonocarboxylate ester of formula (III) in which the group R² is:

R¹⁰ H 0 —C - C - P(OR⁹)₂ R¹¹ COOR⁶

R¹⁰ and R¹¹ being the groups R⁴ and R⁵ of the phosphonoalkenoate (II).

The phosphonoalkenoates of formula (II) contain a polymerisable double bond and can be polymerised by free radical addition polymerisation using an initiator such as dibenzoyl peroxide or azobisisobutyronitrile. They may also be polymerised by anionic polymerisation in the presence of a weak base. Polymers of the phosphonoalkenoates of formula (II) can be used as flame retardants. Polymers of molecular weight below 10,000 are usually preferred, and for such molecular weights the homopolymers generally have a similar solubility in organic solvents, including polyols for polyurethane production and water, to the corresponding monomers. Polymers of higher molecular weight which are water-insoluble may be preferred if the monomer is water- soluble. For use as a flame retardant, the polymer is preferably a homopolymer of the phosphonoalkenoate of formula (II) or is a copolymer containing at least 50%, preferably at least 80%, by weight of units of the phosphonoalkenoate of formula (II) and the balance of units of at least one olefinically unsaturated comonomer. The phosphonoalkenoate can for example be copolymerised with acrylonitrile, styrene, an acrylate or methacrylate ester or vinyl acetate. Phosphonoacrylates are generally less readily polymerisable by free radical polymerisation than acrylates or styrene but polymerise at a similar rate to vinyl acetate. Other phosphonoalkenoates of formula (II) polymerise somewhat less readily than phosphonoacrylates.

Polyurethane foams are generally produced by reacting a polyol composition with a polyisocyanate in the presence of a foaming agent. The polyol is generally a polyether polyol or polyester polyol. For production of a flexible foam the polyol is usually a polyether polyol of average functionality 2.5 to 3.5 and molecular weight 3000 to 6000, for example a polyether triol of molecular weight 3000 to 6000 prepared by the addition of propylene oxide and optionally ethylene oxide to a polyalcohol such as glycerol or to an aminoalcohol or polyamine. The polyether triol can optionally contain a dispersion of another polymer, for example a polyurea or a styrene/acrylonitrile copolymer, to produce a high-resilience flexible foam. For production of a rigid foam a more highly functional polyol, for example of average functionality 4 to 5, of lower hydroxy equivalent weight, for example 100 to 150, is generally used. The polyisocyanate is usually toluene diisocyanate (TDI) for production of flexible foam, and it may for example be a TDI prepolymer or diphenylmethane-4,4'-diisocyanate or an oligomer thereof for rigid foam production. The foaming agent can be a volatile compound such as a halocarbon, but for flexible foam it is usually water, which reacts with isocyanate groups to release C0₂. The foam-forming composition also generally contains a surfactant and catalysts and may contain other additives; all these are generally premixed with the polyol.

The flame retardant is preferably dissolved in the polyol. The flame retardants of formula (I) are all soluble in the polyether polyols and polyester polyols used to prepare polyurethane, for example they are soluble in a polyoxypropylene triol of molecular weight 3500. Polymers of the phosphonoalkenoates of formula (II) are also soluble in such polyols.

Although many of the flame retardants of the invention are especially suitable for use in polyurethane foam, they are highly effective flame retardants in substantially all polymers which contain oxygen or nitrogen, for example polyesters, polyamides, acrylic ester polymers, vinyl ester polymers, nitrile polymers such as polyacrylonitrile and unfoamed polyurethanes, and they can also be used as flame retardants in other polymers such as polyolefins or polystyrene. The flame retardants of the invention can be used at 0.1 to 50% by weight based on the plastics materials. In general, at least 0.5% and preferably at least 1% by weight is used to obtain a significant effect. The amount of flame retardant is preferably less than 20%, most preferably less than 10%, by weight based on the plastics material. When the flame retardant is incorporated in a polyol composition for producing polyurethane foam, it preferably forms 1.5 to 15% by weight of the polyol composition.

The flame-retardant compounds of formula (I), and in particular the polymers of phosphonoalkenoates of formula (II), can be incorporated in artificial fibres to impart flame resistance. The flame-retardant compound or polymer can for example be melt-blended with a polyamide, polyester or polyolefin in the formation of melt-spun synthetic fibres. Alternatively, the flame-retardant compound or polymer can be mixed into a spinning dope which is a solution of cellulose in a tertiary amine N-oxide such as N- methylmorpholine N-oxide and extruded into an aqueous bath to form flame-resistant solvent-spun cellulose filaments. When thus incorporated into artificial fibres, the polymers of phosphonoalkenoates of formula (II) are highly resistant to washing out and impart durable flame resistance. The proportion of flame retardant in the fibres is preferably at least 2%, for example 5-25%, by weight.

A phosphonoalkenoate of formula (II) can alternatively be copolymerised by free radical polymerisation with at least one olefinically unsaturated comonomer to form an inherently flame-retardant addition copolymer. Such a copolymer can for example contain 1-50% by weight of units of the phosphonoalkenoate of formula (II). Examples of olefinically unsaturated comonomers are vinyl compounds such as styrene or vinyl acetate, acrylic compounds such as acrylate or methacrylate esters or acrylonitrile, olefins such as ethylene or propylene and diolefins such as butadiene. For many uses, the proportion of the phosphonoalkenoate used is preferably 2-20%, most preferably 5-10%, by weight to produce a polymer having enhanced flame retardancy but substantially retaining the physical properties imparted by the comonomer(s) . For example, the phosphonoalkenoate can be copolymerised with styrene to produce flame-retardant thermoplastic moulding compositions, with one or more acrylate or methacrylate esters to produce flame-retardant moulding compositions, coatings or adhesives, depending on the acrylate or methacrylate esters chosen, or with acrylonitrile to produce compositions which can be spun to form acrylic fibres.

The invention is illustrated by the following Examples:-

Examples 1 to 4

Combustion Tests of Polyurethane Foam containing Phosphonocarboxylate Esters

The flame-retardant performances of several phosphonocarboxylate esters were compared with those of commercial chloroalkyl phosphate flame retardants, tris-(2- chloroethyl) phosphate [TCEP] and tris-(l-chloro-2-propyl) phosphate [TCPP], in rigid polyurethane foam. The phosphonocarboxylate esters tested were trimethyl phosphonoacetate [TMPA], triethyl phosphonoacetate [TEPA], trimethyl phosphonoformate [TMPF] and triethyl phosphonoformate [TEPF] . The foam, of density 35-45 kg m^"3 and containing 4.1% by weight of phosphonocarboxylate ester or chloroalkyl phosphate, was made from ICI "PBA 6919" high- functionality polyether polyol containing the appropriate phosphorus ester (10% by weight based on polyol), plus ICI "Suprasec 5005" p,p'-methylenediphenyl diisocyanate. Assessment of the horizontal burning characteristics of foam strips of dimensions 150 mm x 50 mm x 13 mm was carried out in accordance with the BS 4735 combustion test. For each phosphorus ester, the mean extent of combustion of 10 foam strips containing 4.1% by weight of the phosphorus ester was determined. The rate of burn was also measured. Where flame became extinguished without total burn-out of specimens, the extent of combustion quoted refers to the average of percentage distance burnt and percentage weight lost. The extent of combustion and rate of burn for the phosphonocarboxylate esters and for TCPP are expressed relative to the corresponding figures for TCEP in the following Table 1. Results for 10 foam strips of similar density, containing no flame retardant (No FR) but otherwise the same, are also included.

Table 1

BS 4735 Combustion Tests of Polyurethane Foam containing Phosphorus Esters.

TCEP TCPP TMPA TEPA TMPF TEPF No FR Relative Extent of 1.00 1.22 0.44 1.09 0.31 0.47 1.25 Combusion

Relative Rate of Burn 1.00 1.55 0.92 1.09 0.75 0.88 3.25

Foam Density (kg m^"3) 41 38 36 34 44 44 36

Examples 5 to 7

The flame-retardant performances of TMPA, TEPA and

TEPF were tested by the procedure used in Examples 1 to 4, but using ICI "PBA 6917" polyether polyol containing a chlorofluorocarbon auxiliary blowing agent to give a lower density foam (about 27 kg m^"3). Each phosphorus ester was used at 10% by weight based on the proprietary polyol, and the foams produced contained 4.2% by weight of the phosphorus ester. The mean extent of combustion of each foam was measured and compared to the foam containing TCEP as described in Examples 1 to 4. Results are shown in Table 2 below, which also shows the results for a foam of density 25 kg m^"3 containing no flame retardant, but otherwise the same.

Table 2

BS 4735 Combustion Tests of Polyurethane Foam containing Phosphorus Esters.

Relative Extent of Combustion

The polyurethane foams of Examples 5 to 7 show reduced combustion (improved flame-retardant performance) compared to the known halogen-containing phosphate ester flame retardants under the test conditions used.

Example 8

Isopropyl (dimethyl phosphono)acetate

To isopropyl chloroacetate (81.9g, 0.60 mol) at 55°C was added trimethyl phosphite (74.4g, 0.60 mol) dropwise over 30 minutes, during which time the reaction mixture was heated to 90°C with stirring. The temperature was then raised to 127°C (reflux) over 15 minutes, and evolution of methyl chloride commenced. The reaction mixture was heated under reflux, with collection of methyl chloride (25 ml liquid), to a maximum of 201°C over a further 4 hours. A quantitative yield of isopropyl (dimethyl phosphono)acetate

(129.45g) was obtained as a clear yellow liquid, identified by ^- MR and FT-IR. The product was soluble in water and organic solvents. When used in preparing a polyurethane foam, it had a similar flame retardant performance to the phosphonocarboxylate esters of Examples 1 to 4. Example 9

Isopropyl (di-n-butyl phosphono)acetate

To isopropyl chloroacetate (13.69g, 0.100 mol) at 20°C was added tri-n-butyl phosphite (25.06g, 0.100 mol) over 1 hour, during which time the reaction mixture was heated to 163°C with stirring, and the temperature was then increased to 204°C over a further 2 hours. After cooling to 20°C, a quantitative yield of isopropyl (di-n-butyl phosphono)acetate (31.39g) was obtained as a clear yellow liquid, identified by ^-NMR and FT-IR. The product was soluble in organic solvents and immiscible with water. It was an effective flame retardant in polyurethane foams, although slightly less effective than the phosphonocarboxylate esters of Examples 1 to 4, and it had the added advantage that it was not removed from the foam if the foam became soaked with water.

Example 10

Trimethyl 2-methyl-2-phosphonopropionate (TMPP)

To a stirred solution of potassium tert-butoxide (246.9g, 2.2 mol) in anhydrous tetrahydrofuran (THF) (800 mis), cooled at -5°C and protected from atmospheric moisture, was added dropwise over 20 minutes trimethyl phosphonoacetate (182.1g, 1.0 mol). The resulting solution was allowed to stir for 1 hour at ambient temperature. The solution was then cooled to 5°C and iodomethane (312g, 2.2 mol) added dropwise with stirring.

Removal of solvent and drying at 60°C/2 mbar gave an off-white slurry. Dichloromethane (200 ml) was added and the resulting solution was washed with water (4 x 75 mis) and dried (Na-SO . Removal of solvent and drying at 62°C/2 mbar gave trimethyl 2-methyl-2-phosphonopropionate (92.35g, 45.91%), identified by ^-N R and FT-IR. Example 11

Triethyl 2-methyl-2-phosphonopropionate (TEPP)

The procedure of Example 10 was followed using 224.2 g

(1.0 mol) triethyl phosphonoacetate in place of the trimethyl phosphonoacetate. 182.Og triethyl 2-methyl-2- phosphonopropionate, identified by ^Η-NMR and FT-IR, was produced (72% yield).

Example 12

Hexamethyl 2,3-diphosphonosuccinate (HMDS)

To a stirred solution of acetylene dicarboxylic acid

(29g, 0.25 mol) in acetonitrile (120 ml) at -2°C trimethyl phosphite (70 ml, 0.51 mol) was added dropwise. During addition the reaction temperature was kept below 35°C by controlling the addition of trimethyl phosphite.

Rotary evaporation was carried out to remove acetonitrile and any excess trimethylphosphite present to give crude product (60g), which was washed with ether to give the desired product hexamethyl 2,3-diphosphonosuccinate (64%, coffee-brown solid, mp 71-78°C) .

Example 13

Tetraethyl methylenediphosphonate (TMDP)

To a stirred solution of sodium ethoxide (54g, O.βmol) in ethanol (250 ml) diethylphosphite (110 ml, 0.8 mol) was added dropwise. After all the phosphite was added, the solution was allowed to stir for 1 hour at ambient temperature. The solution was then concentrated on a rotary evaporator, giving a yellow residue (thick liquid which begins to solidify) . This residue was dissolved in dichloromethane (280 ml) giving a clear yellow solution. This was stirred for 2 weeks and then washed with water (3 x 125 ml). The methylene chloride phase was dried with anhydrous sodium sulphate, filtered and then concentrated on a rotary evaporator.

The resulting residue (105 ml) was fractionally distilled at 5-6 millibars using a Fischer fractional distillation apparatus, the product being collected at 160- 165°C. Yield 44g: 38% yield

Examples 10 to 13

The compounds of Examples 10 to 13 were incorporated into polyurethane foam at 4.1% by weight using the formulation and procedure of Example 1. The horizontal burning characteristics of strips of the foam (10 samples) were tested in accordance with BS 4735, using as comparisons a foam containing no flame retardant and a foam containing 4.1% by weight TCPP. The results are shown in the following Table 3:-

density (kgπf ) Example 14

Triethyl alpha-phosphonohex-2-enoate (TEPH)

The above compound was prepared by the Knoevenagel reaction between triethyl phosphonoacetate (TEPA) and n- butanal.

To stirred anhydrous THF (800 ml) at 0°C, TiCl₄ (88 ml, 0.8 mol) in CC1₄ (200 ml) was added under a nitrogen atmosphere. To this, n-butanal (36 ml, 0.4 mol) was added dropwise, followed by dropwise addition of triethylphos- phonoacetate (80 ml, 0.4 mol). The solution was stirred for 1 hour, after which triethylamine (224 ml, 1.6 mol) in THF (280 ml) was added at 0°C. The reaction mixture was stirred at 0°C for 6 hours and then allowed to warm up to ambient temperature over 12 hours.

The reaction mixture was then cooled (ice/salt bath) and diethylether (400 ml) was added dropwise. The ether layer was separated and dried (Na_S0₄) and the solvent removed under vacuum to give a dark brown liquid. This was then distilled in a Fischer apparatus (0.67-0.8 mbar) to give a product (75g) having an elemental analysis corresponding to TEPH. ^ NMR and FT-IR analysis indicated that this product was a mixture of isomers consisting predominantly of TEPH

- ⁵

with a minor amount of the isomer triethyl 2-phosphonohex-3- enoate 0

^C_^H5 P ( OC₂H- ) ₂

C = C CH t

H H C - OC,H, 0

The product (mixture of isomers) was incorporated as flame retardant into polyurethane foam using the formulation and procedure of Example 1.

The product (mixture of isomers) could be polymerised using azobisisobutyronitrile as free radical initiator in organic solvent solution at 60-100°C.

Example 15

Pentaethyl Diphosphonoacetate

O H O r i if ( C₂H₅0) ₂P - C - C - OC₂H

(C₂H₅0) ₂P = 0

Tetraethyl methylene diphosphonate (12.4g, 0.041 mol) and ethyl chloroformate (4ml, 0.041 mol) were dissolved together in toluene (10 ml). The resulting solution was added dropwise to a stirred suspension of sodium hydride (3.28g, 0.082 mol, 60% dispersed in mineral oil) in toluene (50 ml) held at 0°C. After complete addition, the reaction mixture was stirred for a further 3 hours at 0°C and then allowed to warm up to ambient temperature and stirred for a further 24 hours.

Ethanol (2 ml) was then added to react with any excess sodium hydride. The solid in the reaction mixture was filtered off and solvent was removed under vacuum to give a pale yellow oily residue. The oil was then dissolved in dichloromethane (150 ml) and washed with water (4 x 50 ml). The dichloromethane layer was dried (Na₂S0₄) and filtered. and the solvent was removed under vacuum to give a product consisting mainly of the desired pentaethyl diphosphonoacetate with a minor proportion of hexaethyl diphosphonomalonate.

The product produced was incorporated as flame retardant into polyurethane foam using the formulation and procedure of Example 1.

Example 16

Hexaethyl diphosponomalonate

The reaction procedure of Example 15 was followed using twice the amount of ethyl chloroformate (8ml, 0.082 mol).

After treatment with ethanol and filtering, toluene was evaporated by rotary evaporator. The oily residue was dissolved in 70 ml distilled water and washed with diethyl ether (80 ml). The aqueous layer was rotary evaporated to give a cloudy yellow liquid, which was dissolved in dichloromethane (80 ml), filtered to remove white solid, dried and evaporated to give a yellow viscous liquid. The product obtained consisted of hexaethyl diphosphonomalonate of the following formula:

as shown by ^XH NMR and ¹³C NMR analysis, in 50% yield.

Claims

1. A polyurethane foam or polyisocyanurate foam containing a phosphorus-containing flame retardant, characterised in that the flame retardant is a phosphonocarboxylate ester of the formula:-

in which the groups R, which can be the same or different, each represent an alkyl group having 1 to 4 carbon atoms; R¹ represents an alkyl group having 1 to 8 carbon atoms, an aryl group having 6 to 8 carbon atoms or a group of the formula:- 0

- Y - P "(OR14)₂, where Y is an alkylene group having 1 to 4 carbon atoms and R¹⁴ is an alkyl group having 1 to 4 carbon atoms;

X represents a methylene group, a substituted methylene group of the formula CRR³ or a vinylidene or substituted vinylidene group of the formula:-

R⁴

C = C

R I

R⁷ 0 R¹⁰ 0

- C ¹ - COOR6, - P<(0R9)₂ , - C' - "P(0R9)₂

R^β R¹¹

in which R⁶ represents an alkyl group having 1 to 4 carbon atoms; R⁷ and R⁸, which can be the same or different, each represent hydrogen or an alkyl group having 1 to 4 carbon atoms; the groups R⁹, which can be the same or different, each represent an alkyl group having 1 to 4 carbon atoms; R¹⁰ represents hydrogen, an alkyl group having 1 to 4 carbon atoms or a group of the formula -COOR¹² where R¹² is an alkyl group having 1 to 4 carbon atoms; and R¹¹ represents hydrogen or an alkyl group having 1 to 4 carbon atoms; R³ represents hydrogen, an alkyl group having 1 to 4 carbon atoms or a group of the formula COOR⁶ where R⁶ is defined as above; and R and R⁵, which can be the same or different, each represent a hydrogen atom, an alkyl group having 1 to 4 carbon atoms or an aryl group.

2. A polyol composition comprising a polyol selected from polyether and polyester polyols suitable for preparing polyurethane foam, said polyol composition also containing a phosphorus-containing flame retardant, characterised in that the flame retardant is a phosphonocarboxylate ester of the formula (I) defined as in claim 1.

3. A polyol composition according to claim 2, characterised in that the polyol is a polyether polyol of average functionality 2.5 to 3.5 and molecular weight 3000 to 6000.

4. A polyol composition according to claim 2, characterised in that the polyol has an average functionality of 4 to 5 and a hydroxy equivalent weight of 100 to 150.

5. A process for the preparation of a flexible polyurethane foam by reacting a polyol composition with a polyisocyanate, characterised in that the polyol composition is as claimed in claim 3.

6. A process for the preparation of a rigid polyurethane foam by reacting a polyol composition with a polyisocyanate, characterised in that the polyol composition is as claimed in claim 4.

7. The use as a flame retardant of a phosphonocarboxylate ester of the formula:-

R⁴

0 C 0 (II)

II II II ,

(R0)₂P - C - C - OR

or an addition polymer thereof, where R, R¹, R⁴ and R are defined as in claim 1.

8. A plastics material containing a phosphorus compound as flame retardant, characterised in that the flame retardant is a phosphonocarboxylate ester of the formula (II) defined as in claim 7 or an addition polymer thereof.

9. The use as a flame retardant of a phosphonocarboxylate ester of the formula:-

0 R² 0 ιι i u .

(R0)₂P - C - C - OR (HI) R³

in which the groups R, R¹, R² and R³ are defined as in claim 1.

10. The use according to claim 9, characterised in that the gjrroouuppss RR²² aanndd RR³³ ooff tthhee pphhoosspphhoonnooccaarrbboojxylate ester are each selected from methyl and ethyl groups.

11. The use according to claim 9, characterised in that the phosphonocarboxylate ester has the formula:-

0 R 0 n I II . (RO)₂P - C - C - OR 0 = P(OR⁹), in which R, R¹ and R³ are defined as in claim 9 and the groups R⁹, which can be the same or different, each represent an alkyl group having 1 to 4 carbon atoms.

12. The use according to claim 9, characterised in that the phosphonocarboxylate ester has the formula:-

0 R³ 0

II I \\ .

(RO)₂P - C - C - OR R¹⁰ - C - R¹¹ g

0 = P(OR )₂

in which R, R¹ and R³ are defined as in claim 9, R¹⁰ and R¹¹, which can be the same or different, each represent hydrogen or an alkyl group having 1 to 4 carbon atoms, and the groups R R⁹⁹,, wwhhiicchh ccaann bbee tthhee ssaammee oorr ddiiffffeerreennlt, each represent an alkyl group having 1 to 4 carbon atoms,

13. The use according to claim 9, characterised in that the phosphonocarboxylate ester has the formula:-

in which R is defined as in claim 9 and R¹² represents alkyl of 1 to 4 carbon atoms.

14. A plastics material containing a phosphorus compound as flame retardant, characterised in that the flame retardant is a phosphonocarboxylate ester of the formula (III) defined as in claim 9.

15. A plastics material containing a phosphorus compound as flame retardant, characterised in that the phosphorus compound is a diphosphonate ester of the formula:- 0 R^1S 0 II I w

( RO ) ₂P - CH - P ( OR ) ₂

in which the groups R, which can be the same or different, each represent an alkyl group having 1 to 4 carbon atoms, and the group R¹⁵ represents hydrogen, an alkyl group having 1 to 4 carbon atoms or a group of the formula:-

H O H O

' " 16 ' " 16

— C — CH, - C - OR or ^.C - C - OR

I ² — c C - OR¹⁶ ^- C — OR¹⁶

II H 0 0

where the groups R¹⁶, which can be the same or different, are alkyl groups having 1 to 4 carbon atoms.

16. A plastics material according to claim 15, characterised in that the polymer material is a polyurethane foam, a polyisocyanurate foam or a polyol selected from polyether and polyester polyols suitable for preparing polyurethane foam.