Copolymer blend of improved impact resistance

A vinylarene-olefinically unsaturated nitrile copolymer, such as a styrene-acrylonitrile copolymer, is blended with a resinous conjugated diene-vinylarene copolymer, such as a butadiene-styrene copolymer, to improve the impact resistance of the latter.

This invention relates to a novel composition of matter comprising a blend 
of (a) a resinous, essentially non-elastomeric copolymer of conjugated 
diene and vinylarene and (b) a copolymer of vinylarene and olefinically 
unsaturated nitrile. This invention also relates to a method for improving 
the impact resistance of (a) by blending (a) with a small amount of (b). 
The currently preferred blend of this invention comprises a 
butadiene-styrene copolymer and a small amount of a styrene-acrylonitrile 
copolymer. It has been discovered that the addition of a 
styrene-acrylonitrile copolymer to a resinous butadiene-styrene copolymer 
improves the impact resistance of the latter. 
It is known in the prior art to improve the impact resistance of a 
styrene-acrylonitrile copolymer by adding a lesser amount of a 
butadiene-styrene copolymer. U.S. Pat. No. 3,584,081, for example, 
discloses a composition comprising 83-97 parts by weight of a 
styrene-acrylonitrile copolymer and 17-3 parts by weight of a 
butadiene-styrene copolymer. 
The novelty of our invention resides in the unexpected discovery that a 
small amount of a styrene-acrylonitrile copolymer can be used to improve 
the impact resistance of a resinous butadiene-styrene copolymer. More 
specifically it has been discovered that the addition of up to 30 weight 
percent of a styrene-acrylonitrile copolymer can improve the impact 
resistance of a resinous butadiene-styrene copolymer. Broadly this 
invention contemplates the use of up to 30 weight percent of a copolymer 
of vinylarene and olefinically unsaturated nitrile to improve the impact 
resistance of a resinuous, essentially non-elastomeric copolymer of 
conjugated diene and vinylarene. 
Accordingly it is an object of this invention to provide a polymer blend of 
improved impact resistance. 
A further object of this invention is to provide a method for improving the 
impact resistance of a resinous conjugated diene-vinylarene copolymer. 
These and other objects and advantages of this invention will be made 
apparent from a study of this disclosure and the appended claims. 
The resinous, non-elastomeric conjugated diene-vinylarene copolymers useful 
in the practice of this invention include the polymodal, radially branched 
block copolymers described in U.S. Pat. No. 3,639,517 and U.S. Pat. No. 
4,091,053 and the linear block copolymers described in U.S. Pat. No. 
4,080,407. The conjugated diene-vinylarene copolymers can also be mixtures 
of two or more solution polymerized copolymers such as those described in 
U.S. Pat. No. 4,051,197 or they can contain more than one diene comonomer 
as described in U.S. Pat. No. 4,120,915. All of the above patents are 
incorporated by reference. 
It is generally preferred to use conjugated diene-monovinylarene copolymers 
prepared by employing an alkali metal-based initiator to copolymerize the 
monomers in a hydrocarbon diluent. The conjugated dienes generally 
preferred in the copolymerization are those of 4 to 12 carbon atoms per 
molecule with those of 4-8 carbon atoms per molecule being more preferred. 
Examples of these monomers include 1,3-butadiene, isoprene, 
2,3-dimethyl-1,3-butadiene, piperylene, 3-butyl-1,3-octadiene and 
2-phenyl-1,3-butadiene. The generally preferred monovinylarenes contain 
8-20, and more preferably 8-12, carbon atoms per molecule. Examples 
include styrene, alpha-methylstyrene, 1-vinylnaphthalene, 
2-vinylnaphthalene and alkyl, cycloalkyl, aryl, alkaryl and aralkyl 
derivatives thereof. Examples of substituted mononers include 
3-methylstyrene, 4-n-propylstyrene, 4-cyclohexylstyrene, 4-dodecylstyrene, 
3-ethyl-4-benzylstyrene, 4-p-tolylstyrene and 4-(4-phenyl-n-butyl)styrene. 
The weight ratio of conjugated diene: monovinylarene is such that the 
copolymer is resinous and usually will be in the range of about 45:55 to 
1:99. 
The most preferred conjugated diene-monovinylarene copolymers of my 
invention are the substantially radially branched butadiene-styrene 
copolymers marketed by Phillips Petroleum Company under the trademark 
K-Resin having a bound styrene content varying from about 60 percent by 
weight to about 90 percent by weight. Currently, the most preferred of 
these copolymers have a bound styrene content varying from 66 to 76 weight 
percent. 
The vinylarene-olefinically unsaturated nitrile copolymers encompassed 
within the scope of this invention can be prepared by copolymerizing at 
least one vinylarene with at least one olefinically unsaturated nitrile. 
Examples of suitable vinylarene monomers include styrene, 
alpha-methylstyrene, o-, m-, and p-vinyltoluene, 2,4-dimethylstyrene, 
2,4-diethylstyrene, 2-chlorostyrene, 2-chloro-5-methylstyrene, 
vinylnaphthalene and the like and mixtures thereof. The olefinically 
unsaturated nitrile should have the following structure 
##STR1## 
wherein R is hydrogen, an alkyl group having from 1-6 carbon atoms or a 
halogen. Examples of suitable nitriles include acrylonitrile, 
alpha-chloroacrylonitrile, alpha-fluoroacrylonitrile, methacrylonitrile, 
ethyacrylonitrile and the like and mixtures thereof. 
The currently preferred vinylarene-olefinically unsaturated nitrile 
copolymers are the styrene-acrylonitrile copolymers having a bound styrene 
content of 50-90 weight percent. The most preferred copolymer is 
manufactured by Dow Chemical Company under the trademark Tyril 860 and has 
a bound styrene content of 75 weight percent and a bound acrylonitrile 
content of 25 weight percent. 
The weight ratio of conjugated diene-vinylarene copolymer to 
vinylarene-olefinically unsaturated nitrile copolymer in the inventive 
blend generally will vary from about 99:1 to about 70:30. A finite lower 
limit is not placed on the amount of vinylarene-olefinically unsaturated 
nitrile copolymer present in the blend, the only requirement being that at 
least an impact resistance improving amount be employed. 
The inventive blends can be prepared by any suitable mixing means, such as 
dry-blending, melt-blending or solution-blending. The preferred, least 
expensive mode of operation is dry-blending of the components, e.g., in a 
drum tumbler. Molding of the inventive blends can be carried out by any of 
the well known molding techniques, such as injection molding. 
The inventive blend can optionally contain processing aids, antiblocking 
agents, thermal stabilizers, antioxidants and other known additives or 
fillers. These additional materials may be present in either of the 
copolymers before blending or may be added during or after the blending of 
the copolymers. The practitioner should be alert to possible adverse 
effects of additional material on the impact resistance of the blend but 
such adverse effects are not generally contemplated.

The following examples are intended to further illustrate the invention. 
Particular materials, ratios and procedures should be considered exemplary 
and not interpreted to limit the scope of this invention. 
EXAMPLE I 
In this example, the preparation of a resinous polymodal radially branched 
butadiene-styrene copolymer is described. This copolymer was prepared in a 
pilot K-Resin (Trademark) plant of Phillips Petroleum Company and later 
used for preparing the inventive blends. 
After charging 400 lb. of cyclohexane and 0.05 lb of tetrahydrofuran to an 
agitated reactor 0.06 lb of n-butyllithium initiator was added and 
followed by a first styrene charge of 59 lb. The temperature was raised 
from about 50.degree. C. to about 80.degree. C. over a time interval of 
about 4 minutes after the styrene charge. About 21 minutes after the first 
styrene charge a second styrene charge of 33 lb. was added after briefly 
cooling the reactor down about 20.degree. C. A third styrene charge (40 
lb) and a second n-butyllithium charge (0.32 lb) followed after a brief 
cooling down period. A third peak temperature of about 87.degree. C. was 
reached 32 minutes after the first styrene charge. The reactor pressure 
during these reaction stages was about 21-24 psig. About 50 minutes after 
the start of the polymerization reaction 68 lb of butadiene were added. 
The temperature and pressure were raised to about 100.degree. C. and about 
45 psig, respectively, over a period of about 5 minutes and then 1.0 lb of 
Admex.RTM. 711, an epoxidized soybean oil coupling agent marketed by 
Sherex Chemical Company, was added. 
The copolymer solution was transferred to a blowdown vessel to which 0.8 lb 
of water plus 0.8 lb of CO.sub.2 were charged as terminating agents. 1.9 
lb of BHT (2,6-di-t-butyl-p-cresol) and 1.3 lb of TNPP 
(tris-nonyltriphenyl phosphite) were added as antioxidants and 0.5 lb of a 
microcrystalline paraffin wax was added as an anti-blocking agent. 
Finally, the copolymer was recovered by solvent removal in a film 
evaporator and a devolatilizing extruder. The polymer melt flow of the 
prepared resinous polymodal branched copolymer was 7.0 g/10 min. at 
200.degree. C. (ASTM D 1238, Condition G). The copolymer had a 
butadiene:styrene weight ratio of 34:66. 
EXAMPLE II 
Pellets of the resinous polymodal butadiene-styrene copolymer of Example I 
having a bound styrene content of 66 weight percent were dry-blended by 
tumbling in a plastic bag for 60 seconds with various amounts of 
pelletized Tyril.RTM. 860, a styrene-acrylonitrile copolymer having a 
bound styrene content of about 25 percent by weight, a melt flow of 9.5 
g/10 min. (ASTM D 1238, Condition I), a specific gravity of 1.08 and a 
Vicat softening temperature of 227.degree. F. (ASTM D 1525). Tyril.RTM. 
860 is marketed by Dow Chemical Company, Midland, Mich. 
Dry-mixed blends were molded in an Arburg 221 E/150, 11/2 ounce molding 
machine at a barrel temperature of about 200.degree. C., a mold 
temperature of about 50.degree. C., a screw speed of about 120 r.p.m., an 
injection pressure ranging from 43 to 82 MPa and a total cycle time of 35 
seconds. 
Molded disks having a thickness of about 56-60 mils (1.43-1.52 mm) made of 
inventive and control blends containing resinous butadiene-styrene 
copolymer and styrene-acrylonitrile copolymer were tested in a Gardner 
IG-1120 heavy-duty impact tester according to a modified ASTM D2440-70 
procedure described in the IG-1120 manual of Gardner Laboratories, 
Bethesda, Md. All tests were carried out with a 4-lb weight and a 40-inch 
guide tube slot at room temperature for determining impact energy, which 
is divided by the specimen thickness in millimeters to give impact values 
in units of cm-Kg/mm. Imact data are listed in Table I. 
TABLE I 
______________________________________ 
Gardner 
Weight-% of 
Impact.sup.4 
Weight-% of 
Weight-% of 
Butadiene 
(cm. 
Run K-Resin.RTM..sup.1 
Tyril.RTM. 860.sup.2 
in Blend.sup.3 
Kg/mm) 
______________________________________ 
(Control) 
100 0 34 56 
2 
(Inven- 
tion) 88.8 11.2 30.2 67 
3 
(Inven- 
tion 75.0 25.0 25.5 68 
4 
(Inven- 
tion) 70.6 29.4 24.0 58 
5 
(Control) 
58.8 41.2 20.0 36 
6 
(Control) 
50.0 50.0 17.0 10 
7 less than 
(Control) 
25.0 75.0 8.5 1 
8 less than 
(Control) 
0 100.0 0 1 
______________________________________ 
.sup.1 A resinous polymodal radial butadienestyrene copolymer having a 
bound butadiene content of 34 percent by weight. 
.sup.2 A styrene acrylonitrile copolymer having a bound styrene content 
of 25 percent by weight. 
##STR2## 
.sup.4 Determined according to the modified ASTM D244470 procedure 
described in Gardner Laboratories IG1120 manual, using a 4lb weight. 
Data in Table I surprisingly show that the addition of up to nearly 30 
weight percent of a low-impact resin (Tyril.RTM. 860) to a high-impact 
resin (K-Resin.RTM.) improves the impact resistance of the latter. This 
novel use of a small amount of a vinylarene-olefinically unsaturated 
nitrile copolymer to improve impact resistance represents a contribution 
to the art. 
We have attempted herein to fully and accurately describe our invention and 
to set forth the presently contemplated best mode of operation. Reasonable 
variations from and modifications of this disclosure, not departing from 
the essence of our invention, are also contemplated to be within the scope 
of patent protection desired and sought.