Composition of polyphenylene ethers with core-shell rubber-modified polystyrene

There are provided thermoplastic compositions comprising a polyphenylene ether and a rubber modified polystyrene resin having a discontinuous phase comprised largely of particles consisting of a core of polystyrene in a shell of a diene rubber membrane, said particles constituting at least 30 percent of the total volume of the rubber-modified polystyrene. Such compositions provide molded articles with substantial and unexpected properties in impact resistance, transparency and surface gloss, particularly at low mold temperatures, in comparison with known compositions of rubber modified polystyrene alone or those of other polystyrenes combined with polyphenylene ethers.

BACKGROUND OF THE INVENTION 
The polyphenylene ethers are known and described in numerous publications, 
including Hay, U.S. Pat. Nos. 3,306,874 and 3,306,875; and Stamatoff, U.S. 
Pat. Nos. 3,257,357 and 3,257,358, all incorporated herein by reference. 
They are useful for many commercial applications requiring high 
temperature resistance and, because they are thermoplastic, they can be 
formed into films, fibers and molded articles. In spite of these desirable 
properties, parts molded from polyphenylene ethers have low impact 
strength. In addition, the relatively high melt viscosities and softening 
points are considered a disadvantage for many uses. Films and fibers can 
be formed from polyphenylene ethers on a commercial scale using solution 
techniques, but melt processing is commercially unattractive because of 
the required high temperatures needed to soften the polymer and the 
problems associated therewith such as instability and discoloration. Such 
techniques also require specially designed process equipment to operate at 
elevated temperatures. Molded articles can be formed by melt processing 
techniques, but, again, the high temperatures required are undesirable. 
For example, while poly(2,6-dimethyl-1,4-phenylene)oxide is a tough, 
temperature-resistant engineering polymer, it is difficult to process. 
It is known in the art that the properties of the polyphenylene ethers can 
be materially altered by forming compositions with other polymers. For 
example, U.S. Pat. No. 3,379,792 discloses that flow properties of 
polyphenylene ethers are improved by preparing a composition thereof with 
from about 0.1 to 25 parts by weight of a polyamide. In U.S. Pat. No. 
3,361,851, polyphenylene ethers are formed into compositions with 
polyolefins to improve impact strength and resistance to aggressive 
solvents. In U.S. Pat. No. 3,383,435, incorporated herein by reference, 
there is provided a means to simultaneously improve the melt 
processability of the polyphenylene ethers and upgrade many properties of 
polystyrene resins. The latter patent discloses that polyphenylene ethers 
and polystyrene resins, including many modified polystyrenes, are 
combinable in all proportions to provide compositions having many 
properties improved over those of either of the components. 
Preferred embodiments of U.S. Pat. No. 3,383,435 are compositions 
comprising a rubber modified high-impact polystyrene and a 
poly-(2,6-dialkyl-1,4-phenylene)ether. Such compositions are important 
commercially because they provide both an improvement in the melt 
processability of the polyphenylene ether and an improvement in the impact 
resistance of parts molded from the compositions. Furthermore, such 
compositions of the polyphenylene ether and the rubber modified 
high-impact polystyrene may be custom formulated to provide predetermined 
properties by controlling the ratio of the two polymers. 
In preferred embodiments of U.S. Pat. No. 3,383,435, rubber modified 
polystyrenes are used in compositions with polyphenylene ethers because 
they provide an increase in toughness, e.g., resistance to impact 
fracture. However, the use of commercially available graft type rubber 
modified high impact polystyrenes, such as the LUSTREX HT-88 employed in 
Example 7 of U.S. Pat. No. 3,383,435, causes a sacrifice in transparency, 
possibly due to scattering of light by the dispersed elastomeric 
particulate phase in the rubber modified polystyrene. Moreover, the 
average of such rubber particles are greater in diameter than about 1 
micron, because it has been stated often that if smaller particles are 
used, the impact strength of the polystyrene will be lowered. 
In British Pat. No. 1,180,085, it is disclosed that careful attention to 
the morphology, i.e., the size and nature of the dispersed phase, in 
copolymers comprising alkyl acrylates and styrene monomers, rendered 
impact resistant by inclusion of rubber particles, will lead to enhanced 
impact strength, without loss in transparency, even though very small 
particles are used. It is suggested in the British patent that the 
acrylate copolymer should fill the inside of dispersed globular particles, 
and that such particle should have a thin rubbery membrane or shell 
surrounding it. 
The said British patent states, however, that to try the same technique 
with polystyrene alone is unsuccessful--the product will mold into a 
material of low impact strength and, also significantly, the resin will be 
poor in transparency. On page 15 of the British patent, this failure of 
polystyrene to qualify as a suitable, useful composition is laid, at least 
in part, to the magnitude of the difference between the refractive index 
of the rubber component and the resin, i.e., homopolystyrene, component. 
It is stated that such difference must not be in excess of 0.005 
refractive index units. 
Thus the British patent expressly teaches that the only useful compositions 
must always include an alkyl methacrylate in the thermoplastic matrix, and 
further, that there never can be greater than a 0.005 difference in 
refractive index between that of the rubber and that of the thermoplastic. 
Moreover, there is no suggestion that such compositions will be useful to 
modify other thermoplastic resins, and carry their transparency into such 
modified compositions and, particularly, there is no suggestion to use any 
such resins, and especially entirely polystyrene based resins, in 
compositions with polyphenylene ethers. 
More recently, it has unexpectedly been found that a rubber modified 
polystyrene in which particles made up of a core of polystyrene surrounded 
by a diene rubber membrane, having a diameter of about 0.1 to 0.7 microns 
and dispersed throughout a continuous polystyrene phase, will combine with 
polyphenylene ether resins to give compositions which when molded have 
higher impact strength, transparency and higher gloss than known blends. 
The unusual morphology of the rubber modified polystyrene seems to be 
responsible for the observed advantages. Compositions of polyphenylene 
ether with a rubber modified polystyrene containing particles in which 
many polystyrene inclusions are present, are not as tough nor do they have 
as high a surface gloss. This discovery is described by James G. Bennett, 
Jr. and Gim F. Lee, Jr. in copending application Ser. No. 246,383, filed 
Mar. 23, 1981, now U.S. Pat. No. 4,373,064, assigned to the same assignee 
as herein. 
SUMMARY OF THE INVENTION 
It has now been discovered further that compositions of a polyphenylene 
ether and a rubber modified polystyrene, wherein the latter is comprised 
of a continuous polystyrene phase containing dispersed rubbery particles 
of core-shell structure in which the rubbery particles constitute at least 
30 percent by volume of the rubber modified polystyrene, when molded 
possess the same types of improved properties previously thought possible 
by controlling only the rubber particle size.

The particles of BASF 2791 are largely of the core-shell type, with a 
polystyrene core surrounded by a rubber membrane, but other types of 
particles are present as well. Some particles consist simply of a solid 
rubber sphere, some have a rubber sphere at the core, which is surrounded 
by a thick shell of polystyrene, which is in turn surrounded by a rubber 
membrane. A few even more complex structures are present; spheres of 
polystyrene with a rubber shell, another shell of polystyrene, and a final 
shell of rubber. A count of 100 particles in a randomly chosen section of 
the transmission electron microphotograph showed the following 
distribution: 
core-shell: 61 
solid rubber spheres: 28 
clumps of rubber particles: 6 
rubber-polystyrene-rubber: 6 
DETAILED DESCRIPTION OF THE INVENTION 
According to the present invention, in its broadest aspects, there are 
provided thermoplastic compositions with unexpectedly high impact 
strength, greatly improved surface gloss and transparency comprising a 
polyphenylene ether, and a rubber modified polystyrene, the rubber 
modified polystyrene comprising a continuous polystyrene phase or matrix 
in which there is dispersed a discontinuous phase comprised largely of 
particles of a styrene homopolymer surrounded by a diene rubber membrane, 
said particles constituting at least 30 percent of the volume of the 
rubber modified polystyrene, preferably having an average size ranging 
from about 0.2 to about 0.4 microns (average diameter about 0.3 microns). 
The rubber content will range from about 6 to about 15% by weight of the 
rubber modified polystyrene component, with the proviso that in all cases 
the rubbery particles will constitute at least 30 percent by volume of the 
total. 
In general, the compositions according to this invention are prepared by 
combining said polyphenylene ether and a rubber modified polystyrene to 
obtain a composition which also has at least two phases, one of which is 
discontinuous and comprises the rubber-encased polystyrene particles and 
the continuous phase comprising polyphenylene ether and polystyrene. Such 
compositions may be molded to shape using conventional molding procedures. 
According to a preferred aspect of this invention, there are provided high 
impact strength and improved surface gloss thermoplastic compositions 
comprising 
(a) from 10 to 90 parts by weight of a polyphenylene ether resin and 
(b) from 90 to 10 parts by weight of a rubber modified polystyrene resin, 
the preferred range being from 20-80 parts by weight of (a) and 80-20 
parts by weight of (b). The rubber modified polystyrene contains a 
disperse phase of particles composed of polystyrene surrounded by a 
polybutadiene or rubbery copolymer of butadiene with up to about 60% by 
weight of styrene. Most preferably, in the rubber modified polystyrene 
component, the rubber will comprise from about 6 to 15% by weight. 
It has been found that compositions containing about 60-80% of component 
(a) are tough and transparent or substantially transparent. Clarity and 
color are also improved by the addition of (c) a plasticizing 
flame-retardant, such as a triaryl phosphate. The preferred triaryl 
phosphate is triphenyl phosphate. Mixed triaryl phosphate with one or more 
isopropyl groups on some or all of the aryl rings, such as KRONITEX.RTM.50 
supplied by Food Machinery Corp., can also be used. In general, the amount 
of (c) will be about 3-20 parts by weight, per hundred parts (phr) of 
components (a) and (b). 
Methods to determine the morphology of resin systems are well known to 
those skilled in the art. One convenient method comprises examination of 
electron microscope photographs of mounted, sectioned specimens. Three 
such photographs are shown in FIGS. 1, 2 and 3. The techniques are well 
known to those skilled in the art. 
Determination of the rubbery phase volume, that is, the percent of the 
rubber modified polystyrene which is made up of the rubbery particles 
themselves, can also be accomplished by use of established procedures. One 
such procedure, described in the Handbook of Chemical Microscopy, Chamot 
and Mason, is repeated below. 
The compositions of this invention generally consist of a mixture of two 
phases, the continuous phase being a matrix of polyphenylene oxide resin 
and styrene resin in which there is a discontinuous gel phase dispersed 
comprising particles of polystyrene surrounded by a diene rubber membrane 
of the morphology herein-above described. It is important that the 
particles dispersed as shown in FIG. 2, comprise more than 50% and 
preferably to at least about 60% of the total number of rubber particles. 
The present compositions are prepared by combining such a rubber modified 
polystyrene resin with the polyphenylene ether. The rubbery particles are 
provided by polymerizing styrene in the presence of dissolved rubber under 
conditions to be specified, whereby a continuous phase of a solution of 
rubber in styrene becomes dispersed in the form of particles of rubber 
surrounding a shell of polystyrene, in a matrix of the polystyrene. The 
particle size and form in the final composition is kept substantially the 
same by using blending techniques, e.g., extrusion or milling, which avoid 
particle degradation. 
The polyphenylene ethers with which this invention is concerned are fully 
described in the above-mentioned references. The polyphenylene ethers are 
self-condensation products of monohydric monocyclic phenols produced by 
reacting the phenols with oxygen in the presence of complex metal 
catalysts. In general, molecular weight will be controlled by reaction 
time, longer times providing a higher average number of repeating units. 
A preferred family of polyphenylene ethers will have repeating structural 
units of the formula: 
##STR1## 
wherein the oxygen ether atom of one unit is connected to the benzene 
nucleus of the next adjoining unit, n in a positive integer and is at 
least 50, and Q, Q', Q" and Q'" are independently selected from the group 
consisting of hydrogen, halogen, hydrocarbon radicals, halohydrocarbon 
radicals, hydrocarbonoxy radicals, and halohydrocarbonoxy radicals. 
Illustrative members are: poly(2,6-dilauryl-1,4-phenylene)ether; 
poly(2,6-diphenyl-1,4-phenylene)ether; 
poly(2,6-dimethoxy-1,4-phenylene)ether; 
poly(2,6-diethoxy-1,4-phenylene)ether; 
poly(2-methoxy-6-ethoxy-1,4-phenylene)ether; 
poly(2-ethyl-6-stearyloxy-1,4-phenylene)ether; 
poly(2,6-dichloro-1,4-phenylene)ether; 
poly(2-methyl-6-phenyl-1,4-phenylene)ether; 
poly(2,6-dibenzyl-1,4-phenylene)ether; poly(2-ethoxy-1,4-phenylene)ether; 
poly(2-chloro-1,4-phenylene)ether; poly(2,6-dibromo-1,4-phenylene)ether; 
and the like. Examples of polyphenylene ethers corresponding to the above 
formula can be found in the above referenced patents of Hay and Stamatoff. 
Also included are copolymers, such as copolymers of 2,6-dimethylphenol with 
other phenols, for example, with 2,3,6-trimethylphenol or 
2-methyl-6-butylphenol, etc. 
For purposes of the present invention an especially preferred family of 
polyphenylene ethers include those having alkyl substitution in the two 
positions ortho to the oxygen ether atom, i.e., those of the above formula 
wherein Q and Q' are alkyl, most preferably having from 1 to 4 carbon 
atoms. Illustrative members of this class are: 
poly(2,6-dimethyl-1,4-phenylene)ether; 
poly(2,6-diethyl-1,4-phenylene)ether; 
poly(2-methyl-6-ethyl-1,4-phenylene)ether; 
poly(2-methyl-6-propyl-1,4-phenylene)ether; 
poly(2,6-dipropyl-1,4-phenylene)ether; 
poly(2-ethyl-6-propyl-1,4-phenylene)ether; and the like. 
The most preferred polyphenylene ether resin for purposes of the present 
invention is poly(2,6-dimethyl-1,4-phenylene)ether. This resin readily 
forms a compatible and single phase composition with the relevant 
polystyrene resins over the entire range of combining ratios. 
Suitable polystyrene matrix resins are derived from a monovinyl aromatic 
monomer, e.g., one having the formula: 
##STR2## 
wherein R is hydrogen, (lower)alkyl, e.g., of from 1 to 4 carbon atoms or 
halogen; Z is hydrogen, vinyl, halogen or (lower)alkyl; and p is 0 or a 
whole number of from 1 to 5. Illustrative polystyrene matrix resins 
include homopolymers of polystyrene; polychlorostyrene; 
poly-a-methylstyrene; poly(4-methylstyrene); polyvinyl toluene; and the 
like, or mixtures of the foregoing. These resins will also comprise the 
inclusions in the diene rubber membrane envelopes. The most preferred 
polystyrene is homopolystyrene. 
The "rubber" used to envelope the polystyrene resin and provide the 
disperse phase includes polymeric materials, natural and synthetic, which 
are elastomers at room temperatures, e.g., 20.degree. to 25.degree. C. The 
term "rubber" includes, therefore, natural or synthetic rubbers of the 
diene elastomer type generally used in preparing impact polymers. All such 
rubbers will form a two phase system with the polystyrene resin, and will 
comprise the discontinuous phase in the impact resistant polystyrene resin 
composition. Illustrative rubbers for use in this invention are natural 
rubber and polymerized diene rubbers, e.g., polybutadiene, polyisoprene, 
and the like, and copolymers of such dienes with vinyl monomers, e.g., 
vinyl aromatic monomers, such as styrene. Examples of suitable rubbers or 
rubbery copolymers are natural crepe rubber, synthetic SBR type rubber 
containing from 40 to 98% by weight of butadiene and from 60 to 2 percent 
by weight of styrene prepared by either hot or cold emulsion 
polymerization, synthetic GR-N type rubber containing from 65 to 82 
percent by weight of butadiene and from 35 to 18 percent by weight of 
acrylonitrile, and synthetic rubbers prepared from, for example, 
butadiene, butadiene-styrene or isoprene by methods employing 
heterogeneous catalyst systems, such as a trialkylaluminum and a titanium 
halide, for example. Among the synthetic rubbers which may be used in 
preparing the present compositions are elastomeric modified diene 
homopolymers, e.g., hydroxy- and carboxy-terminated polybutadienes; 
polychlorobutadienes, e.g., neoprenes; copolymers of dienes, e.g., 
butadiene and isoprene, with various comonomers, such as alkyl unsaturated 
esters, e.g., methyl methacrylate; unsaturated ketones, e.g., 
methylisopropenyl ketone, vinyl heterocyclics, e.g., vinyl pyridine; and 
the like. The preferred rubbers comprise polybutadiene and rubbery 
copolymers of butadiene with styrene. Such preferred rubbers are widely 
used in forming rubber modified high impact polystyrene resins with a 
broad range of properties. 
A suitable method for preparing the rubber modified polystyrene having 
particles of the type described above, and used in the present 
compositions is derived from the general disclosure described by Echte in 
Angewandte Makromolekulare Chemie 58/59 p. 175 (1977). 
In general, rubber modified polystyrene having particles of the type 
described above, are conveniently prepared by polymerization of solutions 
in styrene of styrene-butadiene block copolymers having suitable molecular 
weights and styrene-butadiene ratios as described in the aforesaid 
Angewandte Makromolekulare Chemie publication. Such a polystyrene is one 
obtained from a diblock copolymer containing 70% butadiene and 30% styrene 
with a polystyrene block length of 49,000. An example of a rubber-modified 
polystyrene having the morphology herein above described which is employed 
in the invention is known as BASF 2791, which has been mentioned 
heretofore. 
As is described in the above-mentioned U.S. Pat. No. 3,383,435, 
polyphenylene ethers and polystyrene resins are combinable with each other 
in all proportions. The present compositions therefore can comprise from 1 
to 99% by weight polyphenylene ether resin and from 99 to 1% by weight 
polystyrene resin, and these are included within the scope of the 
invention. In general, compositions in which the polyphenylene ether resin 
comprises from about 10 to about 90% and the rubber-modified polystyrene 
comprises from about 90 to about 10%, by weight of the total resinous 
components, are preferred because after molding they have the best 
combination of impact strength, and surface gloss. Particularly useful and 
preferred are compositions in which the polyphenylene resin component 
comprises from about 20 to 80% by weight of the combined weight of the 
total resinous components in the composition. Impact strength and surface 
gloss appear to be at a maximum in such preferred compositions, and 
transparency in the range of about 60% or more. 
The method used to form the compositions of the invention is not critical 
provided that it permits efficient dispersion and mixing. The preferred 
method is one in which the polyphenylene ether is mixed with the rubber 
modified polystyrene using any conventional mixing method and the 
composition so formed is molded to any desired shape such as by extrusion, 
compression molding, injection molding, and the like. 
It should, of course, be obvious to those skilled in the art that other 
additives may be included in the present compositions such as 
plasticizers, pigments, flame retardant additives, reinforcing agents, 
such as glass filaments or fibers, stabilizers, and the like. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS AND COMISON WITH PRIOR ART 
The advantages obtained by providing compositions of a polyphenylene ether 
resin and a rubber modified polystyrene of the specified morphology are 
set forth in the following examples which further illustrate the invention 
but are not to be construed as limiting the invention. Parts are by 
weight. 
The physical tests set forth in the tables are carried out by the following 
procedures: 1/8" notched Izod Impact Strength, ASTM D-256; elongation 
(Elong) at break, ASTM D-639, [Tensile yield strength (T.Y.), ASTM D-638; 
Heat-Deflection-Temperature (HDT), ASTM D-648; Gardner Falling Dart 
Impact, and Gloss.] For comparison purposes, control specimens are also 
prepared. 
Example 1, below, comprises a comparison of a blend in accordance with the 
invention, containing BASF 2791, with three other blends containing high 
impact rubber modified polystyrene resins of the core shell type. The 
three comparison materials were: (1) BASF 2790, (2) DXP-9 and (3) Sample 
"A". 
BASF 2790, BASF 2791 and DXP-9 were all obtained from commercial sources. 
The material designated "Sample A" was made as follows: 
SAMPLE A--PREATION 
A solution of 100 grams of a rubbery block copolymer of styrene and 
butadiene (Solprene 308, Phillips Petroleum) in 900 grams of styrene was 
transferred to a one gallon reactor vessel, to which 1.2 grams of dicumyl 
peroxide and 1.0 gram of tert-dodecyl mercaptan were also added. The 
reactor was purged with gaseous nitrogen, the mixture was stirred and 
heated for three hours at 115.degree. C. and then it was transferred by 
means of a gear pump to a second reactor containing 6 grams of poly(vinyl 
alcohol) and 4.5 grams of gelatin in 2 liters of water. The polymer was 
suspended and polymerization was completed by heating the mixture for five 
hours at 20.degree. C., then for 6 hours at 140.degree. C. The product was 
obtained in the form of large chunks, which were then chopped and extruded 
in a single-screw extruder. Examination by transmission electron 
microscopy showed that most of the dispersed rubbery particles were of the 
core-shell structure, with a few more complex particles. 
Prior to their use in blends with a polyphenylene ether resin, each of the 
four rubber modified polystyrenes was examined to determine the rubbery 
phase volume and the average rubber particle diameter by use of the 
following procedures. 
MEASUREMENT OF RUBBER PHASE VOLUME AND AVERAGE TICLE DIAMETER 
The average particle diameter was estimated by dropping a transparent 
plastic ruler at random on a transmission electron miscroscopy (TEM) 
photograph of the sample, measuring the size of the first twenty particles 
contacted by the ruler, and computing an average. 
To compensate for the fact that not all of the particles are cut at their 
maximum diameter, the average diameter of the cross-section of the 
particles in the TEM photograph was multiplied by 1.27 to approximate the 
true average particle diameter. See Handbook of Chemical Microscopy, 
infra, page 466. 
The rubbery phase volume of each sample (i.e., the fraction of the total 
volume made up the rubbery particles) was measured by the method of linear 
intercepts, in accordance with the description in the Handbook of Chemical 
Microscopy, Chamot and Mason, Volume I, 3d Edition, page 486 (1966), as 
summarized below: 
On each of two TEM photographs at a magnification of 25,000 times, five 
straight lines were laid off with a ruler, horizontally, at five different 
places along the vertical axis. On each line, for each rubber particle 
intersected, the length of the segment of the ruler passing through was 
noted in millimeters. The lengths of the ruler segments passing through 
rubber particles were added and the total was recorded. The total length 
of the ten lines (five from each of two TEM photographs) was also 
recorded. The rubbery phase volume (stated another way: the volume 
fraction of the rubber phase) for each sample was computed by dividing the 
former number by the latter number. The results are listed below. 
______________________________________ 
Ave. Particle Diam. 
Rubbery Phase 
Core-shell HIPS 
(Microns) Volume (%) 
______________________________________ 
BASF 2791 0.31 35 
(BASF CO.) 
BASF-2790 0.54 26 
(BASF CO.) 
DXP-9 (Experimental 
0.20 20 
product supplied by 
Dow Chemical Co.) 
Sample A 0.56 27 
(See above) 
______________________________________ 
The four samples of rubber modified polystyrene shown above were employed 
in a blend with polyphenylene ether resin as described in Example 1 below. 
EXAMPLE 1 
A mixture of 80 parts by weight of poly(2,6-dimethyl-1,4-phenylene)oxide 
(General Electric's PPO.RTM. resin), 20 parts by weight of rubber modified 
high impact polystyrene having core-shell rubber particle morphology, and 
5 parts by weight of triphenyl phosphate were extruded in a single screw 
extruder, the extruded strands were chopped into molding pellets, and the 
pellets were molded into standard test pieces using a screw-injection 
molding machine. The properties of the molded pieces are given below: 
______________________________________ 
Polystyrene 
BASF BASF 
Used 2791* 2790** DXP-9** A** 
______________________________________ 
Elongation, 
102 54 35 78 
Tensile Yield 
12,000 12,000 11,600 11,500 
Strength, psi 
Notched Izod 
3.2 2.6 1.1 2.6 
Impact 
strength, 
ft. lbs./in. n 
Gardner 125 20 30 35 
Impact 
strength, in. 
lbs. 
______________________________________ 
*according to invention 
**comparison experiment 
It was observed that the blends had good surface gloss, transparency in the 
unpigmented condition, and satisfactory properties generally, but the 
impact strength, and especially the Gardner impact strength, was sensitive 
to the volume fraction of the rubbery phase of the core-shell HIPS 
employed. As can be seen, there is at least a two-fold increase in Gardner 
impact strength between the blend containing BASF 2790 (having a 26% 
volume fraction) and the blend containing BASF 2791 (having a 35% volume 
fraction, in accordance with the invention). Notably, there is not much 
change in the Gardner impact strength in going from a rubbery phase volume 
of 20% to 27% (i.e., the blend containing DXP-9 versus the blend 
containing Sample A), but there is almost a four-fold increase in Gardner 
impact between a rubbery phase volume of 27% and 35% (blend containing 
Sample A versus blend containing BASF 2791). Moreover, the increase in 
impact strength achieved with a rubbery phase volume above 30% does not 
appear to be dependent upon the particle size: even though DXP-9 has a 
smaller particle size, BASF 2791 confers higher impact strength. 
Blends in accordance with the invention are illustrated further in the 
following additional examples. In these examples, comparison has also been 
made with Foster Grant's FG834 and Monsanto's HT-91, each of which is a 
rubber modified polystyrene that does not have the specified core-shell 
morphology. 
EXAMPLE 2 
A mixture of 50 parts of poly(2,6-dimethyl-1,4-phenylene)ether and 50 parts 
of BASF 2791 polystyrene, (a rubber modified polystyrene resin comprising 
a continuous polystyrene phase containing dispersed particles consisting 
largely of a core of polystyrene in a shell of diene rubber membrane, the 
particles having an average diameter of about 0.3 microns and constituting 
35 percent of the total volume of the rubber modified polyphenylene), 1.5 
parts of polyethylene, 1 part of diphenyldecyl phosphite, 3 parts of 
triphenyl phosphate, 0.15 parts of zinc sulfide and 0.15 parts of zinc 
oxide was extruded at 560.degree. F. in a 28 mm. twin-screw extruder. The 
extruded pellets were molded into standard test pieces at 520.degree. F. 
in a 3 oz. screw injection molding machine. For comparison, blends were 
similarly prepared from BASF-2790 polystyrene and Foster-Grant 834 
polystyrene, described herein above. The blends with BASF-2791 had higher 
Izod and Gardner impact strength and greater surface gloss. The results of 
testing of the compositions are set forth in the following table: 
______________________________________ 
Izod 
Impact 
(ft. Gardner 
Elong. T.Y. lbs./ Impact HDT Gloss 
Polystyrene 
% (psi) in.) (in. lbs.) 
(.degree.F.) 
(45.degree.) 
______________________________________ 
BASF 2791 
50 9,800 4.0 250 237 65.7 
BASF 2790 
40 10,000 2.8 50 238 52.9 
FG-834 51 9,800 3.5 100 244 50.8 
______________________________________ 
EXAMPLE 3 
A mixture of 60 parts of polyphenylene ether (PPO) described in Example 2, 
40 parts of BASF 2791 polystyrene (PS), 0.15 parts of zinc sulfide, 0.15 
parts of zinc oxide, and 1 part of diphenyldecyl phosphite was extruded in 
a single screw extruder and then molded as described in Example 2, along 
with control blends of the same composition with BASF-2790 or FG-834 in 
place of BASF-2791. 
Mixtures of 80 parts of PPO and 20 parts of the above mentioned 
polystyrenes (BASF-2791, BASF-2790 and FG-834) were extruded and molded in 
the same way. Impact strength and gloss were highest in the blend 
containing BASF-2791 in both compositions, as compared with the blends 
containing the other polystyrenes as shown in the table below. 
A mixture of 90 parts of PPO and 10 parts of BASF 2791 polystyrene was 
extruded and molded in the same way. The properties are also included in 
the table. 
______________________________________ 
Polystyrene 
PPO:PS Izod Gardner 
HDT Gloss (Units) 
______________________________________ 
BASF 2791 
60:40 4.1 225 271 66.4 
BASF 2790 
60:40 3.0 125 271 54.5 
FG-834 60:40 3.5 125 273 51.7 
BASF 2791 
80:20 3.5 225 313 63.5 
BASF 2790 
80:20 2.6 40 304 50.2 
FG-834 80:20 2.9 75 304 50.7 
BASF 2791 
90:10 2.5 125 322 60.0 
______________________________________ 
EXAMPLE 4 
Example 2 was repeated with the addition of 3 phr of TiO.sub.2 to each 
blend. The test results are as follows: 
______________________________________ 
Gloss 
Polystyrene 
Elong. T.Y. Izod Gardner 
HDT (Units) 
______________________________________ 
BASF 2791 
75 10,000 3.6 175 233 63.3 
BASF 2790 
57 10,000 2.8 50 236 58.7 
FG-834 65 9,600 3.6 125 241 54.1 
______________________________________ 
EXAMPLE 5 
A mixture of 60 parts of BASF 2791 polystyrene, 40 parts of PPO and 3 parts 
of titanium dioxide was extruded in a twin-screw extruder and molded as 
described in Example 2. Blends of this same composition, with BASF 2791 
replaced by BASF-2790 polystyrene, Foster Grant 834 polystyrene, or 
Monsanto HT-91 polystyrene were similarly prepared. Monsanto HT-91 is a 
high impact polystyrene containing about 6% by weight of polybutadiene, 
with about 95 percent of the particles being greater than 0.5 microns in 
size. It is sold by the Monsanto Co. 
The test results are as follows: 
______________________________________ 
Polystyrene 
Izod Gardner HDT Gloss (Units) 
______________________________________ 
BASF 2791 2.9 125 238 64.1 
BASF 2790 2.1 15 240 61.9 
FG-834 3.2 50 237 55.0 
HT-91 1.3 10 250 58.2 
______________________________________ 
EXAMPLE 6 
A mixture of 60 parts BASF 2791 polystyrene, 40 parts PPO, 1.5 parts 
polyethylene, 8 parts triphenyl phosphate, 0.5 parts diphenyl decyl 
phosphite, 3 parts titanium dioxide, 0.15 parts of zinc sulfide and 0.15 
parts of zinc oxide was extruded and molded as described in Example 2, 
along with a control bend made with Amoco 6H6, a high-gloss polystyrene.* 
The composition containing BASF 2791 had higher impact strength than the 
control. The surface gloss of plaques molded with a mold temperature of 
130.degree. F. was as good as that obtained with the control at 
175.degree. F. The test results are set forth in the following table: 
______________________________________ 
Property Amoco 6H6 BASF 2791 
______________________________________ 
Elongation 68% 78% 
T.Y. 7200 8000 
T.S. 6600 7100 
Izod (73.degree.) 
2.8 4.0 
Izod (-40.degree.) 
1.3 1.4 
Gardner 150 225 
HDT 202 201 
Gloss (130.degree. mold) 
54.8 60.8 
Gloss (175.degree. mold) 
60.9 62.8 
______________________________________ 
FNT *available from Amoco Chemical Co. 
EXAMPLE 7 
PPO was mixed with BASF 2791 rubber-modified polystyrene and extruded in a 
twin screw extruder as described in Example 2 to produce blends containing 
10%, 15% and 20% PPO. To assure uniformity each blend was then re-extruded 
in the same machine. The extruded pellets were molded in an injection 
molding machine as described in Example 2 and properties were compared to 
those of BASF 2791 alone without addition of PPO. As little as 10% PPO 
produces a significant increase in HDT and tensile strength, but Gardner 
impact strength is reduced. With 20% PPO Gardner impact strength is not 
reduced and all other properties are improved. The test results are set 
forth in the following table: 
______________________________________ 
Tensile Izod Gardner 
% PPO HDT Strength Elong. Impact Impact 
______________________________________ 
0 185 5800 30 1.9 50 
10 191 6700 37 2.4 &lt;5 
15 203 7500 24 1.8 &lt;5 
20 212 8000 61 3.0 50 
______________________________________ 
EXAMPLE 8 
Blends of PPO and BASF 2791 rubber-modified polystyrene (PS) were prepared 
as described in Example 3 at PPO:PS ratios of 60:40, 70:30, and 80:20. No 
zinc salts were included; each blend contained 1 phr of diphenyldecyl 
phosphite and 12 phr of triphenyl phosphate. A 60:40 blend with Foster 
Grant 834 polystyrene was also prepared in the same way. The blends 
containing BASF 2791 were transparent, while the blend containing Foster 
Grant 834 was almost completely opaque. Properties are listed in the 
following table. 
______________________________________ 
PPO:PS PS Izod Gardner Appearance 
______________________________________ 
60:40 BASF 2791 5.0 200 Transparent 
60:40 FG 834 3.0 150 Opaque 
70:30 BASF 2791 4.6 225 Transparent 
80:20 BASF 2791 3.7 250 Transparent 
______________________________________ 
It is thus seen that compositions according to this invention have a 
greater impact strength, transparency and gloss than that of any of the 
controls. 
Other modifications can be made, based on the teachings of the foregoing 
specific examples. 
For example, if the procedure of the Examples is repeated and the following 
polyphenylene ethers are substituted for 
poly(2,6-dimethyl-1,4-phenylene)ether in the formulation: 
poly(2,6-diethyl-1,4-phenylene)ether; 
poly(2-methyl-6-ethyl-1,4-phenylene)ether; 
poly(2-methyl-6-propyl-1,4-phenylene)ether; 
poly(2,6-dipropyl-1,4-phenylene)ether, 
poly(2-ethyl-6-propyl-1,4-phenylene)ether, 
poly(2,6-dimethyl-co-2,3,6-trimethyl-1,4-phenylene)ether, 
poly(2,6-dimethyl-co-2-methyl-6-butyl-1,4-phenylene)ether, 
compositions according to this invention will be obtained. 
The compositions of the subject invention can be formed into films, fibers 
and molded articles. They can be used to make molded products, such as 
housing, cabinets, frames for appliances, business machines, etc. pump 
housings, impellers, filters, and the like. They may be mixed with various 
fillers and modifying agents, such as dyes, pigments, stabilizers and 
plasticizers, and the like. 
All of the foregoing patents and/or publications are incorporated herein by 
reference. Obviously, other modifications and variations of the present 
invention are possible in the light of the above teachings. It is, 
therefore, to be understood that changes may be made in the particular 
embodiments of the invention described which are within the full intended 
scope of the invention as defined by the appended claims.