Flame-retardant compositions having an excellent balance of properties are obtained by flame-retarding rubber-modified polystyrenes with a mixture of about 55-95% by weight of a first flame retardant corresponding to the formula: ##STR1## AND ABOUT 45-5% BY WEIGHT OF A SECOND FLAME RETARDANT CORRESPONDING TO THE FORMULA: ##STR2## wherein X is bromo or chloro, Y is halo, hydrogen, or an alkyl, haloalkyl, alkoxy, or haloalkoxy group, and Z is a tetravalent hydrocarbon group containing 4-20 carbon atoms.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to flame-retardant compositions and more 
particularly relates to such compositions comprising a rubber-modified 
polystyrene. 
2. Description of the Prior Art 
It is known that normally flammable polymers can be rendered 
flame-retardant by the incorporation of the flame retardants of British 
Pat. No. 1,377,282 or the flame retardants of U.S. Pat. Nos. 3,382,204 and 
3,403,036, the former being brominated monoadducts of 
polyhalocyclopentadienes and multi-unsaturated hydrocarbons, and the 
latter being diadducts of polyhalocyclopentadienes and multi-unsaturated 
hydrocarbons. However, neither type of flame retardant has proved to be 
satisfactory for incorporation into rubber-modified polystyrene 
compositions. The monoadducts flame-retard the compositions efficiently 
but lower the heat distortion and softening temperatures more than is 
sometimes acceptable; the diadducts, which have less deleterious an effect 
on heat distortion and softening temperatures, have poor efficiency as 
flame retardants. It would be desirable to find a flame retardant or flame 
retardant system capable of functioning efficiently but providing 
compositions having a good balance of properties. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide novel flame-retardant 
rubber-modified polystyrene compositions. 
Another object is to provide such compositions having a good balance of 
properties. 
These and other objects are attained by intimately mixing a rubber-modified 
polystyrene with a flame-retarding amount of a mixture of about 55-95% by 
weight of a first flame retardant corresponding to the formula: 
##STR3## 
AND ABOUT 45-5% BY WEIGHT OF A SECOND FLAME RETARDANT CORRESPONDING TO THE 
FORMULA: 
##STR4## 
wherein X is bromo or chloro, Y is halo, hydrogen, or n alkyl, holoalkyl, 
alkoxy, or haloalkoxy group, and Z is a tetravalent hydrocarbon group 
containing 4-20 carbon atoms. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The rubber-modified polystyrene that is flame-retarded in accordance with 
the present invention can be any of the compositions that are 
conventionally known as impact polystyrenes, impact-resistant 
polystyrenes, or toughened polystyrenes. As is well known, such 
compositions essentially consist of polystyrene that has been physically 
and/or chemically combined with a minor proportion, usually about 1-25% by 
weight, of one or more natural or synthetic rubbers, usually a diene 
rubber. The rubber component of such compositions is ordinarily a 
substantially linear or branched polymer of a conjugated diene, such as 
butadiene, isoprene, etc., optionally containing up to about 50% by weight 
of one or more randomly copolymerized monomers, such as styrene, 
acrylonitrile, methyl methacrylate, etc. However, it is sometimes a 
rubbery diene block polymer, such as a polystyrene-polybutadiene 
polystyrene block copolymer. All such rubber-modified polystyrenes are 
utilizable in the practice of the invention. 
As indicated above, the rubber-modified polystyrene is flame-retarded with 
a mixture of two flame retardants, one of which is a dibrominated adduct 
of hexachlorocyclopentadiene and cyclooctadiene, i.e., a compound 
corresponding to the formula: 
##STR5## 
and the other of which is a diadduct of a polyhalocyclopentadiene and a 
multi-unsaturated hydrocarbon, i.e., a compound corresponding to the 
formula: 
##STR6## 
The first flame retardant, i.e., the monoadduct, constitutes about 55-95%, 
preferably about 60-80%, and most preferably about 70% by weight of the 
flame retardant mixture. The second flame retardant, i.e., the diadduct, 
constitutes, respectively, about 45-5%, preferably about 40-20%, and most 
preferably about 30% by weight of the flame retardant mixture. 
Both flame retardants, of course, are well known, the first being one of 
the flame retardants of British Pat. No. 1,377,282, and the second being 
the type of flame retardant taught in U.S. Pat. Nos. 3,382,204 and 
3,403,036. As is also known, the second flame retardant is essentially a 
diadduct of: 
1. a polyhalocyclopentadiene, such as hexachlorocyclopentadiene; 
hexabromocyclopentadiene; 5,5-difluorotetrachlorocyclopentadiene; 
5,5-dibromotetrachlorocyclopentadiene; 
5,5-dihydrotetrachlorocyclopentadiene; 5-methylpentachlorocyclopentadiene; 
5-methyl-5-hexyltetrabromocyclopentadiene; 
5,5-didecyltetrachlorocyclopentadiene; 
5,5-bis(chloromethyl)tetrachlorocyclopentadiene; 
5-bromoethylpentabromocyclopentadiene; 
5,5-dimethoxytetrachlorocyclopentadiene; 
5-decoxypentachlorocyclopentadiene; 
5,5-bis(chloromethoxy)tetrachlorocyclopentadiene, etc., with 
2. a multi-unsaturated acyclic or cyclic hydrocarbon, such as 
butadiene-1,3; dimethylbutadiene; hexadiene-1,5; octadiene-1,7; 
dodecadiene-1,11; cyclopentadiene; methylcyclopentadiene; 
dicyclopentadiene; cyclohexadiene; cyclooctadiene-1,5; cyclodecadiene; 
cyclododecadiene, etc. 
In these diadducts the two polyhalocyclopentadiene moieties may be the same 
or different but are usually the same, and any organic group represented 
by a Y of the formula usually contains 1-10 carbon atoms. 
Any such diadduct corresponding to the above formula may be used as the 
second flame retardant in the practice of the present invention, but the 
preferred second flame retardants are those having melting points above 
250.degree. C. The most preferred second flame retardant is the diadduct 
of hexachlorocyclopentadiene and cyclooctadiene-1,5 i.e., a compound 
corresponding to the formula: 
##STR7## 
To prepare the compositions of the invention, the rubber-modified 
polystyrene is intimately mixed with the flame retardant system and any 
optional additives, such as fillers, pigments, plasticizers, stabilizers, 
lubricants, synergists, etc., in any suitable manner, e.g., by the use of 
an extruder, a two-roll mill, or a Banbury mixer, so as to prepare a 
composition containing a flame-retarding amount of the flame retardant 
mixture. Ordinarily the concentration of flame retardant mixture in the 
composition is about 1-25%, based on the combined weights of 
rubber-modified polystyrene and flame retardant mixture. However, larger 
amounts may be employed if desired. The compositions of the invention 
preferably contain about 9-15%, most preferably about 11-13%, of the flame 
retardant mixture, based on the combined weights of rubber-modified 
polystyrene and flame retardant mixture. 
Although the flame retardant mixture of the invention is fairly efficient, 
it is frequently desirable to enhance its effectiveness by including one 
or more synergists, such as the synergists conventionally used with 
halogenated flame retardants. These synergists include, e.g., zinc borate, 
sodium tetraborate, lead arsenate, etc., but are more commonly compounds, 
such as oxides, sulfides, or organic acid salts, of antimony, arsenic, or 
bismuth. The preferred synergist for use in the compositions of the 
invention is antimony trioxide. When a synergist is employed, it is 
usually used in an amount such as to provide a flame retardant/synergist 
weight ratio of about 1-4.5/1, preferably about 2/1. 
The flame retardant mixtures of the invention are particularly advantageous 
in that they provide rubber-modified polystyrene compositions having an 
excellent balance of flame retardancy and other properties, such as impact 
strength, heat distortion temperature, softening temperature, UV 
stability, and thermal stability. A particularly unexpected advantage of 
the mixture is that they provide a higher degree of flame retardancy than 
would be predicted from the levels of flame retardancy obtained with 
comparable amounts of the individual components of the flame retardant 
mixtures.

The following examples are given to illustrate the invention and are not 
intended as a limitation thereof. Unless otherwise specified, quantities 
mentioned are quantities by weight. 
EXAMPLE I -- CONTROL 
Blend 89 parts of a commercial polybutadiene rubber-modified polystyrene 
with 11 parts of the dibrominated monoadduct of hexachlorocyclopentadiene 
and cyclooctadiene-1,5 (hereinafter designated as the monoadduct), 5.5 
parts of antimony trioxide, 0.25 part of dibutyl tin maleate, 0.25 part of 
calcium stearate, 0.25 part of dilauryl thiodipropionate, and 0.12 part of 
a hindered phenol stabilizer. Test the composition for oxygene index. The 
composition has an oxygene index of 24.5. 
EXAMPLE II -- CONTROL 
Repeat Example I except for replacing the 11 parts of the monoadduct with 
11 parts of the diadduct of hexachlorocyclopentadiene and 
cyclooctadiene-1,5 (hereinafter designated as the diadduct). The 
composition has an oxygen index of only 23.5. 
EXAMPLE III 
Prepare five compositions by repeating Example I except for replacing the 
11 parts of the monoadduct with, respectively, (a) a mixture of 10 parts 
of the monoadduct and one part of the diadduct, (b) a mixture of 9.5 parts 
of the monoadduct and 1.5 parts of the diadduct, (c) a mixture of 9 parts 
of the monoadduct and 2 parts of the diadduct, (d) a mixture of 7 parts of 
the monoadduct and 4 parts of the diadduct, and (e) a mixture of 6 parts 
of the monoadduct and 5 parts of the diadduct. Project the expected oxygen 
indices of the compositions from the values obtained in Examples I and II, 
and test for actual oxygen indices. A comparison of the projected and 
actual oxygen indices of the compositions is shown below. 
______________________________________ 
Monoadduct/Diadduct 
Projected O.I. 
Actual O.I. 
______________________________________ 
10/1 24.4 25.2 
9.5/1.5 24.35 25.5 
9/2 24.3 25.2 
7/4 24.15 24.5 
6/5 24.05 24.2 
______________________________________ 
EXAMPLE IV 
Blend 88 parts of the commercial polybutadiene rubber-modified polystyrene 
of Example I with 9.6 parts of the monoadduct, 2.4 parts of the diadduct, 
6 parts of antimony trioxide, 0.25 part of dibutyl tin maleate, 0.25 part 
of calcium stearate, 0.25 part of dilauryl thiodipropionate, and 0.12 part 
of a hindered phenol stabilizer. Test the composition for physical 
properties. The composition has an Izod impact strength of 6 kg. cm./cm., 
a heat distortion temperature of 78.degree. C. at 18.6 kg./sq.cm., and a 
Vicat softening temperature of 94.degree. C. 
EXAMPLE V 
Repeat Example IV except for replacing the flame retardant mixture with a 
mixture of 8.4 parts of the monoadduct and 3.6 parts of the diadduct. The 
composition has an Izod impact strength of 6.5 kg.cm./cm., a heat 
distortion temperature of 80.degree. C. at 18.6 kg./sq.cm., and a Vicat 
softening temperature of 97.degree. C. 
EXAMPLE VI 
Repeat Example IV except for replacing the flame retardant mixture with a 
mixture of 7.2 parts of a monoadduct and 4.8 parts of the diadduct. The 
composition has an Izod impact strength of 6 kg.cm./cm., a heat distortion 
temperature of 82.degree. C. at 18.6 kg./sq.cm., and a Vicat softening 
temperature of 98.degree. C. 
As demonstrated above, compositions of the invention exhibit better flame 
retardancy than would be expected but still have good physical properties. 
Similar results are observed when the examples are repeated except for 
replacing the ingredients with materials taught to be their equivalents in 
the specification. 
It is obvious that many variations may be made in the products and 
processes set forth above without departing from the spirit and scope of 
this invention.