Resinous compositions containing aromatic bisphosphoramidates as flame retardants

Bisphosphoramidates such as N,N'-bis[di-(2,6-xylenoxy)phosphinyl]piperazine are effective flame retardant agents for thermoplastic polymers and blends thereof. In addition, the blends containing such bisphosphoramidates have excellent high temperature properties, as demonstrated by high heat deflection temperatures and a low tendency to decrease glass transition temperature.

BACKGROUND OF THE INVENTION 
This invention relates to flame retardation, and more particularly to the 
use of a specific class of compounds as flame retardants for polymers. 
Improvement of the fire resistant properties of polymers has long been a 
goal of polymer compounders. Fire resistance is typically evaluated by the 
UL-94 test of Underwriters Laboratories (ASTM procedure D3801). In this 
test, the desirable V-0 rating is given to polymers of which specimens do 
not burn with flaming combustion for more than 10 seconds after 
application of a test flame, and specimens do not burn with flaming 
combustion for a time exceeding 50 seconds upon 2 flame applications to 
each of 5 specimens; i.e., the total "flame-out time" (FOT) for said 
samples is not greater than 50 seconds. 
Various types of chemical compounds may be employed as flame retardancy 
additives. They include halogenated and especially brominated compounds 
and phosphate-based compounds. Such additives are often employed in 
combination with anti-drip agents such as fluorocarbon polymers, and 
synergists such as antimony halides. 
It is desirable in some instances to employ exclusively phosphate-based 
compounds. Among the compounds known to be useful for this purpose are the 
bis(diaryl phosphate) esters of dihydroxyaromatic compounds, as 
illustrated by resorcinol bis(diphenyl phosphate), hydroquinone 
bis(diphenyl phosphate) and bisphenol A bis(diphenyl phosphate). These 
compounds, however, frequently also have undesirable effects on the high 
temperature properties of the polymer substrates, as demonstrated by a 
pronounced decrease in heat deflection temperature (HDT) and/or glass 
transition temperature (Tg). 
It is of interest, therefore, to develop resinous blends containing 
phosphate-based flame retardant additives having a minimum effect on the 
high temperature properties of the blends. 
SUMMARY OF THE INVENTION 
The present invention is based on the discovery of a class of 
phosphate-based additives which afford the desired degree of flame 
retardancy to thermoplastic polymers, accompanied by an effect on high 
temperature properties which is significantly less than that observed with 
other additives having related molecular structures. 
The invention includes resinous compositions comprising a major amount of 
at least one thermoplastic polymer and a minor flame retarding amount of 
at least one aromatic bisphosphoramidate of the formula 
##STR1## 
wherein A is a monocyclic aromatic radical and R.sup.1 is a C.sub.1-4 
primary or secondary alkyl radical or both R.sup.1 radicals taken together 
are ethylene.

DETAILED DESCRIPTION PREFERRED EMBODIMENTS 
It has not been determined and is immaterial to the invention whether the 
components of the compositions of the invention undergo chemical 
interaction to form other materials. Therefore, the invention is directed 
to said compositions whether or not any chemical interaction has taken 
place. That is, the invention includes both compositions comprising said 
components and compositions comprising reaction products thereof. 
The major constituent of the compositions of the invention is at least one 
thermoplastic polymer. Both addition and condensation polymers are 
included. Illustrative thermoplastic materials are olefin polymers such as 
polyethylene and polypropylene; polymers of ethylenically unsaturated 
carboxylic acids and their functional derivatives, including acrylic 
polymers such as poly(alkyl acrylates), poly(alkyl methacrylates), 
polyacrylamides, polyacrylonitrile and polyacrylic acid; alkenylaromatic 
polymers such as polystyrene; diene polymers such as polybutadiene and 
polyisoprene; polyamides such as nylon-6 and nylon-66; polyesters such as 
poly(ethylene terephthalate) and poly(1,4-butylene terephthalate); 
polycarbonates; and polyarylene ethers. Both homopolymers and copolymers 
are included, and the latter may be of the random, block or graft type. 
Thus, for example, suitable polystyrenes include homopolymers and 
copolymers. The latter embraces high impact polystyrene (HIPS), a genus of 
rubber-modified polystyrenes comprising blends and grafts wherein the 
rubber is a polybutadiene or a rubbery copolymer of about 70-98% styrene 
and 2-30% diene monomer. Also included are ABS copolymers, which are 
typically grafts of styrene and acrylonitrile on a previously formed diene 
polymer backbone (e.g., polybutadiene or polyisoprene). 
Polycarbonates useful in the compositions of the invention include those 
comprising structural units of the formula 
##STR2## 
wherein at least about 60 percent of the total number of R.sup.2 groups 
are aromatic organic radicals and the balance thereof are aliphatic, 
alicyclic, or aromatic radicals. More preferably, R.sup.2 is an aromatic 
organic radical and still more preferably a radical of the formula 
EQU --A.sup.1 --Y--A.sup.2 --, (IV) 
wherein each A.sup.1 and A.sup.2 is a monocyclic divalent aryl radical and 
Y is a bridging radical in which one or two carbon atoms separate A.sup.1 
and A.sup.2. For example, A.sup.1 and A.sup.2 typically represent 
unsubstituted phenylene or substituted derivatives thereof. The bridging 
radical Y is most often a hydrocarbon group and particularly a saturated 
group such as methylene, cyclohexylidene or isopropylidene. The most 
preferred polycarbonates are bisphenol A polycarbonates, in which each of 
A.sup.1 and A.sup.2 is p-phenylene and Y is isopropylidene. Preferably, 
the weight average molecular weight of the initial polycarbonate 
composition ranges from about 5,000 to about 100,000; more preferably, 
from about 25,000 to about 65,000. 
The polyphenylene ethers are known polymers having structural units of the 
formula 
##STR3## 
wherein each Q.sup.1 is independently halogen, primary or secondary lower 
alkyl, phenyl, haloalkyl, aminoalkyl, hydrocarbonoxy, or 
halohydrocarbonoxy wherein at least two carbon atoms separate the halogen 
and oxygen atoms, and each Q.sup.2 is independently hydrogen, halogen, 
primary or secondary lower alkyl, phenyl, haloalkyl, hydrocarbonoxy or 
halohydrocarbonoxy as defined for Q.sup.1. 
Both homopolymer and copolymer polyphenylene ethers are included. The 
preferred homopolymers are those containing 2,6-dimethyl-1,4-phenylene 
ether units. Suitable copolymers include random copolymers containing such 
units in combination with (for example) 2,3,6-trimethyl-1,4-phenylene 
ether units. Also included are polyphenylene ethers containing moieties 
prepared by grafting onto the polyphenylene ether in known manner such 
materials as vinyl monomers or polymers such as polystyrenes and 
elastomers, as well as coupled polyphenylene ethers in which coupling 
agents such as low molecular weight polycarbonates, quinones, heterocycles 
and formals undergo reaction in known manner with the hydroxy groups of 
two polyphenylene ether chains to produce a higher molecular weight 
polymer, provided a substantial proportion of free OH groups remains. 
The polyphenylene ethers generally have an intrinsic viscosity greater than 
about 0.1, most often in the range of about 0.25-0.6 and especially 
0.4-0.6 dl./g., as measured in chloroform at 25.degree. C. 
The polyphenylene ethers are typically prepared by the oxidative coupling 
of at least one monohydroxyaromatic compound such as 2,6-xylenol or 
2,3,6-trimethylphenol. Catalyst systems are generally employed for such 
coupling; they typically contain at least one heavy metal compound such as 
a copper, manganese or cobalt compound, usually in combination with 
various other materials. 
Particularly useful polyphenylene ethers for many purposes are those which 
comprise molecules having at least one aminoalkyl-containing end group. 
The aminoalkyl radical is covalently bound to a carbon atom located in an 
ortho position to the hydroxy group. Products containing such end groups 
may be obtained by incorporating an appropriate primary or secondary 
monoamine such as di-n-butylamine or dimethylamine as one of the 
constituents of the oxidative coupling reaction mixture. Also frequently 
present are 4-hydroxybiphenyl end groups and/or biphenyl structural units, 
typically obtained from reaction mixtures in which a by-product 
diphenoquinone is present, especially in a copper-halide-secondary or 
tertiary amine system. A substantial proportion of the polymer molecules, 
typically constituting as much as about 90% by weight of the polymer, may 
contain at least one of said aminoalkyl-containing and 4-hydroxybiphenyl 
end groups. 
It will be apparent to those skilled in the art from the foregoing that the 
polyphenylene ethers contemplated for use in the invention include all 
those presently known, irrespective of variations in structural units or 
ancillary chemical features. 
The preferred thermoplastic polymers for many purposes are polycarbonates, 
polyesters, polyphenylene ethers, HIPS and styrene-acrylonitrile 
copolymers (SAN), including ABS copolymers. These may be employed 
individually or as blends. Especially preferred are polyphenylene 
ether-HIPS blends, polycarbonate-SAN blends and polycarbonate-polyester 
blends. 
The flame retardant additive is an aromatic bisphosphoramidate having 
formula I in which A may be any monocyclic aromatic radical. Included are 
aromatic hydrocarbon radicals and substituted radicals wherein the 
substituents may be, for example, alkyl, alkoxy, nitro or carbalkoxy 
groups. The preferred aromatic radicals are phenyl, 2,6-dialkylphenyl 
(especially 2,6-xylyl) and 2,4-6-trialkylphenyl (especially 
2,4,6-trimethylphenyl). Each R.sup.1 radical is primary or secondary 
C.sub.1-4 alkyl, preferably methyl, or both of said radicals taken 
together are ethylene. 
Bisphosphoramidates of the desired molecular structure may be prepared by 
the reaction of a corresponding tertiary diamine such as piperazine or 
N,N'-dimethylethylenediamine with a diaryl chlorophosphate of the formula 
(AO).sub.2 POCl in the presence of a tertiary amine. This method of 
preparation is described in Talley, J. Chem. Eng. Data, 33, 221-222 
(1988), the disclosure of which is incorporated by reference herein. 
The resinous compositions of this invention contain a flame retarding 
amount of the bisphosphoramidate. This amount is typically in the range of 
about 0.25-2.5 parts of phosphorus per 100 parts of resinous materials 
(phr), all percentages herein being by weight. Total amounts of 
bisphosphoramidate are most often in the range of about 5-35 phr. 
Said compositions may also contain other conventional additives including 
inhibitors, plasticizers, fillers, mold release agents and anti-drip 
agents. The latter are illustrated by tetrafluoroethylene polymers, 
including copolymers with such other monomers as styrene and 
acrylonitrile. 
A principal characteristic of the compositions of the invention is their 
improved high temperature properties. These are demonstrated by the fact 
that the decrease in glass transition temperature (Tg) exhibited as a 
result of the incorporation of the aromatic bisphosphoramidate in the 
composition is substantially less than the corresponding decrease 
exhibited in blends containing, for example, bis(diaryl phosphates) of 
dihydroxyaromatic compounds as flame retardants. This is true when each 
flame retardant is employed in an amount suitable to provide a V-0 rating 
in the UL-94 test procedure. In the case of phase-separated blends such as 
polycarbonate-ABS blends, the decrease in Tg is noted in the polycarbonate 
phase. 
Experience has shown that the flame retarding properties of a 
phosphate-based compound as an additive in a resinous composition are 
generally proportional to the amount of phosphorus in the composition 
rather than to the amount of the compound itself. Thus, equal weights of 
two additives having different molecular weights but the same flame 
retarding properties may produce different UL-94 results, but amounts of 
the two additives which contribute the same proportion of phosphorus to 
the resinous composition will produce the same UL-94 results. On the other 
hand, other physical properties such as high temperature resistance are 
dependent on the amount of the compound itself and relatively independent 
of the phosphorus proportion therein. For this reason, the dependence of 
flame retarding and high temperature resistance of compositions containing 
two phosphorus-based compounds may not follow the same pattern. 
It has been shown, however, with respect to the aromatic biphosphoramidate 
employed according to the present invention that their superior properties 
of flame retardance and high temperature resistance are consistent. Thus, 
for example, proportions of the prior art additive resorcinol 
bis(di-2,6-xylyl phosphate) effective to confer a suitable flame-out time 
on certain resinous compositions are similar to those produced by a 
typical bis(2,6-xylyl)phosphoramidate at an essentially equivalent level 
of phosphorus, but the bisphosphoramidate has a substantially lower 
tendency to decrease HDT despite the slightly greater amount of the bulk 
additive. 
The invention is illustrated by the following examples. All parts and 
percentages are by weight. Intrinsic viscosity was determined in 
chloroform at 25.degree. C. HDT values were determined at 264 psi (1820 
kPa) according to ASTM procedure D648. 
Example 1 
Blends of various amounts of a bisphenol A homopolycarbonate, 6.5 parts of 
a commercially available high rubber graft ABS copolymer and 9 parts of a 
commercially available SAN copolymer were prepared under identical 
conditions by blending in a Henschel mixer followed by extrusion on a twin 
screw extruder and were molded into test specimens. The blends also 
contained conventional additives including 0.4 part of a 
tetrafluoroethylene-styrene-acrylonitrile copolymer as an anti-drip agent, 
which were not considered in determining proportions, and various amounts 
of the following phosphate-based flame retardant additives: 
N,N'-bis-[di-(2,6-xylenoxy)phosphinyl]piperazine (XPP), a compound 
according to formula I wherein A is 2,6-xylyl and whose use is part of the 
present invention; N,N'-bis(neopentylenedioxy)phosphinyl)piperazine (NPP), 
a compound of similar structure but not within the scope of the invention; 
and resorcinol bis(di-2,6-xylyl) phosphate (RDP) and bisphenol A 
bis(di-2,6-xylyI) phosphate (BPADP), two conventional phosphate-based 
flame retardants. The FOT and Tg of the polycarbonate phase of each test 
specimen was determined and the results are given in Table I. 
TABLE I 
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Sample 1 2 3 4 
______________________________________ 
Polycarbonate, 
72.2 76.9 73.6 71.6 
parts 
FR, identity 
XPP NPP RDP BPADP 
FR, phr 12.4 6.9 10.7 13.2 
FR, phr P 1.16 1.11 0.97 1.02 
FOT, sec 19.4 84 20.3 27.3 
Tg, .degree. C. 
131 149 111 112 
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It is apparent that the composition of this invention (Sample 1) had an 
acceptable FOT and a Tg that differed from that of neat polycarbonate 
(147.degree. C.) by an acceptable increment. Sample 2 had a Tg essentially 
equal to that of neat polycarbonate but the FOT was unacceptably high. 
Samples 3 and 4, employing conventional FR's, had unacceptably low Tg's. 
The variations in FR content in terms of phr of total FR and of phosphorus 
are not considered significant from the standpoint of properties. 
Example 2 
Blends of 62 parts of a commercially available 
poly(2,6-dimethyl-1,4-phenylene ether) and 38 parts of a commercially 
available HIPS were prepared and molded under identical conditions similar 
to those of Example 1. The blends also contained conventional additives 
including 0.21 part of a tetrafluoroethylene-styrene-acrylonitrile 
copolymer as an anti-drip agent, which were not considered in determining 
proportions, and 20.5 phr of XPP, RDP and BPADP as phosphate-based flame 
retardant additives. The FOT and heat deflection temperature (HDT) of each 
test specimen was determined and the results are given in Table II. 
TABLE II 
______________________________________ 
Sample 5 6 7 
______________________________________ 
FR, identity 
XPP RDP BPADP 
FR, phr P 1.92 1.85 1.58 
FOT, sec 2.4 2.1 3.7 
HDT, .degree. C. 
223.9 177.9 190.5 
______________________________________ 
Again, it is apparent that the composition of the invention (Sample 5) had 
acceptable FR properties and a significantly higher HDT than the 
compositions containing conventional FR additives, indicating superior 
high temperature properties. 
Example 3 
A blend of 40 parts of a commercially available 
poly(2,6-dimethyl-1,4-phenylene ether) and 60 parts of a commercially 
available HIPS were prepared and molded under conditions similar to those 
of Example 2, using N,N'-bis[di-(2,6-xylenoxy)phosphinyl]ethylenediamine 
as the flame retardant material in essentially the same proportion. The 
observed FOT was 3.4 seconds.