Process for the preparation of rubber-modified thermoplastic resins

A process for the impact modification of a plastic with a rubber polymer to form a thermoplastic resin in a reactor extruder is provided. The process includes the steps of dissolving a rubber polymer in a solvent selected from the group consisting of ethylenically unsaturated monomers and non-polymerizable organic compounds to form a feed solution, introducing the feed solution into the feed section of a twin screw reactor extruder, introducing a separate feed stream containing a material in sufficient amount to precipitate the rubber polymer, heating the feed solution and feed stream under pressure to a temperature sufficient for polymerization to begin, polymerizing the monomers with the rubber polymer in the reactor extruder to form a thermoplastic resin and extruding the thermoplastic resin through a die. A novel ABS thermoplastic resin is also provided having a uniform distribution of rubber particles dispersed within the plastic phase of the resin, the rubber particles ranging in size of from about 0.01 to 0.25 microns. The thermoplastic portion of resin has an acrylonitrile content of more than about 26 weight percent and can have as much as 60 weight percent.

TECHNICAL FIELD 
The present invention provides a process for the preparation of 
rubber-modified thermoplastic copolymers in order to improve properties 
such as impact strength and tensile properties. One such resin of proven 
utility is the terpolymer of acrylonitrile, butadiene and styrene (ABS) 
and the process provided herein can produce superior ABS as compared with 
the products from known bulk and/or emulsion processes. ABS resins are 
useful in injection and compression molding applications where high impact 
thermoplastics are desired. The process of the present invention is 
conducted in a single vessel, preferably a twin screw reactor extruder. 
The process is applicable to the preparation of ABS resins having a high 
acrylonitrile content as well as a host of other rubber-modified 
thermoplastic resins. 
BACKGROUND ART 
Bulk polymerization processes are employed to prepare copolymers of rubber 
and plastic forming monomers, however, they require a second stage 
shearing step or the particle size of the rubber formed is very large and 
non-uniform. Emulsion processes produce a more favorable particle size and 
better gloss product but have the disadvantage that water is included in 
the process. 
One way in which particle size of the rubber can be controlled without 
resort to an emulsion system is by employing a reactor extruder as the 
polymerization vessel. Reactor extruders of the twin screw design provide 
sufficient shearing action during polymerization of the monomers within 
that smaller rubber particle sizes can result. 
The continuous production of copolymers from 1,3-dienes and monovinyl 
aromatics in an extruder is described in U.S. Pat. No. 3,780,139. The 
patent does not disclose, however, the formation of resin copolymers of 
monomers such as styrene, acrylonitrile, methylacrylate and the like 
grafted onto a preformed rubber. 
Work with preformed rubbers in the presence of various plastic monomers 
which are polymerized in a reactor extruder has been set forth in a 
copending patent application, U.S. Ser. No. 309,718, now U.S. Pat. No. 
4,410,659 commonly owned by the Assignee of record herein. A feature of 
that application includes dissolving a rubber in the plastic monomers 
prior to feeding into the extruder, coupled with the shearing action 
within the extruder to produce a uniform dispersion of the rubber 
throughout the plastic phase yielding high impact strength materials. 
A process which also discloses dissolving a preformed rubber in a solution 
of one or more plastic forming monomers is set forth in U.S. Pat. No. 
3,511,895. The patent calls for a three stage mass polymerization 
conducted in separate reactors having agitators for shear and mixing. The 
resulting polymer product has a broad and uniform distribution of 
molecular weight including a "tail" of a very low molecular weight 
material comprising 10 to 25 percent by weight. 
The process provides that a solution comprising 2.5 to 19 weight percent 
polybutadiene in a mixture of acrylonitrile and styrene monomers be added 
to the first stage reactor which already contains a styrene homopolymer or 
acrylonitrile/styrene copolymer. Combining the two solutions causes the 
rubber to precipitate while the agitation within the vessel disperses the 
rubber before significant crosslinking can occur. Viscosity is 
continuously reduced and polymerization increases in each of the three 
reactors. The patent states that particle size of the rubber in the 
product is generally fixed in the second stage reactor and comprises at 
least about 80 percent of the particles falling within the range of 0.5 to 
2.0 microns and less than about one percent being larger than six microns. 
The patent further states that by controlling the microgel particle size 
of the rubber and by providing the low molecular weight tail, physical 
properties and surface appearance of the product are improved. 
Thus, the patents discussed herein have not disclosed a simple one stage 
polymerization, as can be conducted in a reactor extruder, where 
rubber-modified plastics can be prepared having a uniformly distributed 
rubber of uniform small particle size, on the order of less than 0.25 
micron, in the plastic phase. While this object can be met to an extent 
according to the process set forth in the aforementioned Ser. No. 309,718, 
the present invention differs in that higher strength thermoplastics can 
be obtained resulting from the feeding and chemical precipitating 
techniques disclosed herein. 
DISCLOSURE OF THE INVENTION 
It is therefore an object of the present invention to provide a process for 
the preparation of rubber-modified thermoplastic resins in a reactor 
extruder, which resins have improved impact strength and tensile 
properties over existing resins. 
It is another object of the present invention to provide a process for the 
preparation of rubber-modified thermoplastic resins in a reactor extruder, 
which resins have a smaller rubber particle and more uniform distribution 
thereof throughout the thermoplastic resin than resins of comparable 
composition produced via other techniques. 
It is yet another object of the present invention to provide a process for 
the preparation of rubber-modified thermoplastic resins in a reactor 
extruder which resins can comprise a higher content of certain 
ethylenically unsaturated monomers than has been possible with existing 
emulsion or bulk processes. 
It is still another object of the present invention to provide a process as 
set forth hereinabove wherein a preformed rubber polymer is dissolved in 
one or more ethylenically unsaturated monomers which solution is then 
polymerized within a reactor extruder along with a separate liquid feed 
stream containing a material to precipitate the rubber polymer. 
It is yet another object of the present invention to provide a process 
wherein a preformed rubber polymer can be dissolved in a non-polymerizable 
organic solvent or non-monomer which solution is fed to a reactor extruder 
with one or more ethylenically unsaturated monomers which cause 
precipitation of the rubber polymer and subsequently polymerize. 
It is yet another object of the present invention to provide a process for 
the preparation of high acrylonitrile ABS type resins in a reactor 
extruder, which resins have improved impact strength and improved tensile 
properties over existing resins. 
It is yet another object of the present invention to provide 
rubber-modified thermoplastic resins having a uniform, small particle size 
of rubber uniformly dispersed within the plastic phase of the resin and a 
high content of specific ethylenically unsaturated monomers. 
These and other objects, together with the advantages thereof over the 
prior art, which shall become apparent from the specification which 
follows, are accomplished by our invention as hereinafter described and 
claimed. 
In general, the process of the present invention includes the steps of 
dissolving a rubber polymer in a solvent selected from the group 
consisting of ethylenically unsaturated monomers and non-polymerizable 
organic compounds to form a feed solution, introducing the feed solution 
into the feed section of a twin screw reactor extruder, introducing into 
the feed section a separate liquid feed stream containing a material in 
sufficient amount to precipitate the rubber polymer, heating the feed 
solution and feed stream under pressure to a temperature sufficient for 
polymerization to begin, polymerizing the monomers around the precipitated 
rubber polymer in the reactor extruder to form a thermoplastic resin and 
extruding the thermoplastic resin through a die. 
Another process for the preparation of rubber-modified thermoplastic resins 
in a reactor extruder has been provided and includes the steps of 
dissolving a rubber polymer in a solvent selected from the group 
consisting of ethylenically unsaturated monomers and non-polymerizable 
organic compounds to form a feed solution, introducing the feed solution 
into the feed section of a twin screw reactor extruder, introducing into 
the feed section a separate liquid feed stream containing a material in 
sufficient amount to precipitate the rubber polymer and form a dispersion 
thereof in the feed solution and separate feed stream, heating the feed 
solution, feed stream and precipitated rubber under pressure to a 
temperature sufficient for polymerization of the monomers to begin, 
shearing the feed solution and feed stream to maintain the dispersion of 
precipitated rubber, thereafter reacting the dispersion of precipitated 
rubber, feed solution and feed stream until at least about 70 weight 
percent of the monomers have been converted to a thermoplastic resin, and 
extruding the thermoplastic resin through a die. 
The rubber-modified thermoplastic resins formed according to the process of 
the present invention are also deemed to be novel and are characterized by 
having a uniform, small particle size of rubber uniformly dispersed within 
the plastic phase of the resin and, in some instances, a composition 
comprising greater percentages of a plastic such as acrylonitrile than has 
been possible heretofore utilizing emulsion or bulk polymerization 
techniques. Exemplary novel resins include ABS thermoplastics having an 
acrylonitrile content greater than 26 weight percent and as high as about 
60 weight percent. Rubber particle size of the resins of this invention is 
on the order of from about 0.01 to 0.25 microns.

PREFERRED MODE FOR CARRYING OUT THE INVENTION 
Polymers prepared according to the process of the present invention are 
polymerized within a twin screw extruder as will be discussed hereinbelow. 
The polymer product or resin is prepared by polymerizing a feed solution, 
which comprises a solution of a rubber polymer in a solvent selected from 
the group consisting of ethylenically unsaturated monomers and 
non-polymerizable organic compounds, along with a separate feed which 
contains a material that will precipitate the rubber polymer which 
material can also be an ethylenically unsaturated monomer and/or 
non-polymerizable organic compound. 
The rubber-modified thermoplastic copolymers that can be prepared according 
to the process of the invention include those which are produced by 
polymerizing a mono-unsaturated or olefinically unsaturated nitrile, e.g., 
acrylonitrile, and another monovinyl monomer component copolymerizable 
therewith such as styrene. 
More specifically, the olefinically unsaturated nitriles that can be 
employed in the present invention are the alpha, beta-olefinically 
unsaturated mononitriles having the structure: 
##STR1## 
wherein R is hydrogen, a lower alkyl group having from one to four carbon 
atoms or a halogen. Such compounds include acrylonitrile, 
alpha-chloroacrylonitrile, alpha-fluoroacrylonitrile, methacrylonitrile, 
ethacrylonitrile and the like. The most preferred olefinically unsaturated 
nitriles useful in the present invention are acrylonitrile and 
methacrylonitrile and mixtures thereof. 
The monovinyl aromatic monomers are those having from about eight to 20 
carbon atoms including styrene, alpha-methyl styrene, halogen substituted 
styrene, such as chlorostyrene and bromostyrene, the vinyl toluenes, the 
vinyl xylenes and the like with styrene being preferred. 
As stated hereinabove, the feed solution being polymerized contains a 
preformed rubber polymer, preferably having a high elongation, low modulus 
and low glass transition temperature. Such polymers can be a homopolymer 
or copolymer of a conjugated diene monomer having from about four to 
twelve carbon atoms selected from the group consisting of butadiene-1,3, 
isoprene, chloroprene, bromoprene, cyanoprene, 2,3-dimethyl butadiene-1,3, 
2-ethyl butadiene-1,3, 2,3-diethyl butadiene-1,3 and the like, with 
butadiene-1,3 and isoprene being preferred. Additionally, other rubbers 
can be employed such as atactic polypropylene, epichlorohydrin polyethers 
and ethylene-propylene-diene rubber. 
The conjugated diene monomer selected for preparation of the rubber may 
itself be copolymerized with a comonomer selected from the group 
consisting of the monovinyl aromatic monomers described hereinabove such 
as styrene giving styrene butadiene rubber or SBR, the olefinic nitrile 
monomers having the structure: 
##STR2## 
such as acrylonitrile wherein R has the foregoing designation giving 
butadiene acrylonitrile copolymer or nitrile rubber and, an ester having 
the structure: 
##STR3## 
wherein R.sub.1 is hydrogen, an alkyl group having from one to 30 carbon 
atoms, or a halogen, and R.sub.2 is an alkyl group having from one to six 
carbon atoms. Compounds of this type include methyl acrylate, ethyl 
acrylate, the propyl acrylates, the butyl acrylates, the amyl acrylates, 
the hexyl acrylates, methyl methacrylate, ethyl methacrylate, the propyl 
methacrylates, the butyl methacrylates, the amyl methacrylates and the 
hexyl methacrylates, methyl alpha-chloroacrylates, ethyl 
alpha-chloroacrylates and the like with methyl acrylate, ethyl acrylate, 
methyl methacrylate and ethyl methacrylate being preferred. The rubber 
polymer contains from 50 to 100 percent by weight of polymerized 
conjugated diene monomer and from zero to 50 percent by weight of a 
comonomer. 
Where the rubber selected is not soluble in any ethylenically unsaturated 
monomer or at least one that is desired for the polymerization, an organic 
solvent for the rubber should be employed. Thus, in the instance of 
atactic polypropylene which is not soluble in any of the monomers 
disclosed herein, an inert solvent such as heptane is employed. By inert 
is meant the solvent does not contain unsaturation and will not 
polymerize. Other such solvents would include compounds such as aliphatic 
and aromatic ketones, oxygen and nitrogen-containing heterocyclic 
compounds, formamides and carbonates. 
By proper selection of the monomers or inert solvents, an initially 
homogeneous feed solution is obtained which will provide a uniform 
distribution of the rubber throughout the plastic. Upon the subsequent 
addition of the separate feed stream which contains a material selected to 
precipitate the rubber from the feed solution, small and uniform rubber 
particles are formed which greatly benefits the properties of the 
thermoplastic resin product. While the polymerization in a reactor 
extruder of the foregoing feed solution of rubber dissolved in monomers 
improves properties of the thermoplastics, the present invention employs 
at least one additional step which permits greater concentrations of 
particular monomers to be employed. 
As an example, ABS copolymers can be obtained by polymerizing a solution of 
butadiene rubber in styrene and acrylonitrile monomers. However, in order 
to maintain any useful amount of rubber dissolved in the monomers, the 
acrylonitrile content cannot exceed 35 percent. Any attempt to increase 
the content of acrylonitrile in the feed solution will cause the 
precipitation of the rubber. If precipitation in the feed solution were to 
occur, it could not properly be pumped to and into the reactor extruder 
and the distribution of rubber in the subsequently formed plastic would 
not be uniform. In order to avoid this occurrence, a separate feed stream 
of acrylonitrile is added to the reactor extruder after the feed solution 
has been introduced. Once inside the extruder, precipitation of the rubber 
is desirable so that the particles can become encapsulated within the 
plastic polymer being formed. Also, within the extruder intensive 
controlled shear provides a good suspension of the rubber. 
Although a solution of the rubber in the monomers is thus desirable for 
practice of the present invention, there are some rubbers that are not 
soluble in the monomer or monomers selected or any monomers. In such an 
instance, the feed solution should comprise the rubber in an inert solvent 
and the monomers should be introduced in a separate feed stream. Thus, the 
step of introducing a separate feed stream of a material to precipitate 
the rubber polymer inside the reactor extruder provides a means for 
distributing the rubber throughout the plastic uniformly. 
The addition of a separate feed stream of rubber precipitating compound 
provides several benefits. First, where a monomer is employed, the 
separate feed stream allows the monomer to become part of the resin 
composition. In some instances, even a small amount of a given monomer 
would cause precipitation of the rubber and hence it cannot be present in 
the initial feed solution. In other instances, the initial feed solution 
can tolerate the presence of some of a given monomer but not in amounts 
sufficient to provide the desired composition. Thus, a high acrylonitrile 
containing ABS resin can be prepared according to the present invention by 
use of an initial feed solution wherein butadiene rubber is dissolved in 
styrene and a small amount of acrylonitrile. In order to increase the 
content of acrylonitrile, a separate feed stream of 100 percent 
acrylonitrile is fed to the reactor extruder with the initial feed 
solution. Without the separate feed stream, acrylonitrile content of the 
ABS resin product will not exceed about 25 percent by weight. By employing 
the independent feed stream, the content of acrylonitrile in the product 
can easily exceed about 26 percent and can be extended to as much as about 
60 percent. 
With more specific reference to the preferred rubber-modified thermoplastic 
resins of the present invention, the composition, discussed throughout the 
specification, is based upon 100 parts of thermoplastic polymer or 
copolymer. Thus, 100 parts of the desired thermoplastic copolymer can 
comprise from about 40 to 74 parts of a monovinyl aromatic such as styrene 
and from about 26 to 60 parts of an olefinically unsaturated nitrile such 
as acrylonitrile. The rubber content is next given as an amount based upon 
the weight of the thermoplastic portion of the resin and for the preferred 
resin, the rubber is present in an amount of from about five to about 35 
parts per 100 parts of the aforementioned thermoplastic copolymer. Of 
course, the rubber content can exceed 35 parts where it is desired to 
increase it beyond the preferred amount. 
Any references in the specification or claims to the composition of the 
resin product should be considered in light of this explanation and thus, 
a resin product having up to about 60 weight percent of acrylonitrile 
comprises a thermoplastic copolymer having 60 percent acrylonitrile and 40 
percent of a copolymer. This copolymer can then contain between about five 
to 35 parts of rubber based upon 100 parts of copolymer. 
A second benefit of the separate feed stream is that of the rubber 
precipitation which provides the small, uniformly distributed rubber 
particles throughout the plastic matrix that improve properties of the 
resin. In order to cause precipitation, a compound that is incompatible 
with the solubility of the rubber in the feed solution is selected. This 
can be either a monomer or a non-monomer which functions as a rubber 
precipitator. An example of the latter would be an alcohol such as 
methanol which will cause butadiene rubber to precipitate from styrene. 
Thus, in order to prepare a high impact polystyrene, butadiene rubber can 
be distributed throughout by initial precipitation of the rubber once 
inside the reactor extruder. The separate feed stream may contain all 
alcohol for precipitation, or a mixture of alcohol with monomer, e.g., 
styrene. 
In brief summary, the first step requires that a homogeneous, 
precipitate-free solution of dissolved rubber be formed which is fed to 
the reactor extruder. The next step requires that the dissolved rubber be 
precipitated in the reactor extruder which is accomplished by adding a 
compound which is inherently a precipitator for the rubber employed or, 
which is added in such an amount that precipitation occurs. 
The amount of the rubber and thermoplastic monomers will be in part 
controlled by the solubility of the rubber and partially by the ultimate 
physical properties desired. In order to impart improved properties such 
as greater impact strength and adequate tensile strength, it is necessary 
that the rubber-modified thermoplastic resins have at least about five 
parts of rubber. An upper limit of about 50 parts is a maximum otherwise 
the product will be more characteristically a rubber rather than a 
plastic. It is to be understood that 50 parts is only an upper limit 
insofar as improving physical properties of the plastics are concerned and 
that the process of the present invention can be employed to incorporate 
even greater amounts of rubber. 
The initial feed solution contains all of the rubber that is desired or can 
be dissolved in the inert solvent or thermoplastic monomer or monomers. 
Generally this amount will range from about five to 25 percent by weight 
based upon the weight of the feed solution, the remaining 75 to 95 percent 
comprising the rubber solvent. It is important that the feed solution be 
homogeneous and contain no precipitate of rubber. This condition can be 
physically observed to exist where the feed solution does not appear 
cloudy or turbid when examined. 
With respect to the amount of the separate liquid feed material, this 
should be at least enough to cause precipitation of the rubber in the feed 
solution to commence. Such an amount can be determined empirically by 
adding a gradually increasing volume of the precipitating monomer or other 
compound to a known volume of the feed solution. At the point where 
turbidity in the feed solution is detected, precipitation of the rubber 
has commenced and the minimum volume is known. Greater amounts can be 
employed to concentrate the rubber and, in the case of a monomer, such 
amounts will also depend upon the amount desired in the specific 
rubber-modified thermoplastic resin being prepared. It is believed that 
for some feed solutions a quantity of separate liquid monomer or rubber 
precipitating monomer equal to five weight percent can be sufficient for 
precipitation while other rubber solutions may accommodate as much as 60 
to 80 weight percent of separate liquid monomer or rubber precipitating 
material. 
A simple method for determining the amount of precipitating separate liquid 
feed material is depicted in FIG. 1 to which reference should be made. 
First, a series of suitable glass containers such as beakers, graduated 
cyclinders, vials, or the like should be about half filled with a measured 
amount of the rubber solution initial feed. The number of containers 
necessary will be a function of the volume of separate material added 
incrementally to cause precipitation of the rubber. An actual experiment 
was conducted for the preparation of a high acrylonitrile containing ABS 
resin in nine containers as follows: 
To each of nine 500 ml containers, 10-18, was added 250 ml of rubber 
solution feed stream comprising 15 weight percent of butadiene rubber in a 
75/25 styrene/acrylonitrile comonomer solvent. Next, 10 to 20 ml aliquots 
of pure acrylonitrile monomer were added. Conditions were at room 
temperature and after each addition of monomer the solution was stirred 
and then examined for precipitation of rubber. Once precipitation 
commenced, two phases were observed and further examined. 
It can be seen that container 10 had one phase, the clear phase 20 which 
depicts the rubber dissolved in the monomers. To container 11 was added 10 
ml of acrylonitrile, bringing the total volume to 260 ml; only a clear 
phase 20 was observed. Similarly, containers 12, 13 and 14 received 20, 30 
and 40 ml of acrylonitrile, respectively, and a clear, single phase 20 
remained. However, in container 15, to which was added 50 ml of 
acrylonitrile, bringing the total volume to 300 ml, a precipitate of 
rubber was observed in the lower layer 22, above which was a small clear 
upper layer 21. 
While a range exists between 40 and 50 ml of acrylonitrile wherein 
precipitation first occurs, the actual amount is usually not critical. The 
minimum amount of acrylonitrile in this instance that should be fed to the 
reactor extruder is about 50 ml. It is to be understood that in container 
15 not all of the rubber has been depleted from the clear upper layer 21, 
nor has all of the solvent been driven from the lower precipitate layer 
22. 
In container 16, 60 ml of acrylonitrile were added and it can be seen that 
the clear upper layer 21 increased in volume. Meanwhile the lower 
precipitate layer 22 of rubber lost volume as it became more concentrated. 
To container 17, 80 ml of acrylonitrile were added and it can be seen that 
the clear upper layer 21 has a greater volume than the lower layer 22. 
Finally, to container 18, 100 ml of acrylonitrile were added, bringing the 
total volume to 350 ml. At this stage, the lower layer 22 occupies only 
one-half the starting volume of 250 ml, indicating that a 100 percent 
enhancement of rubber concentration has occurred. 
We have found from this data that at least 50 ml of acrylonitrile should be 
present in the feed zone of the reactor extruder to contact 250 ml of the 
rubber solution, i.e., a 1:5 ratio for precipitation to occur. The 
preferred amount of acrylonitrile that should be added is that amount that 
would cause the volumes of layers 21 and 22 to be equal. From FIG. 1, it 
appears that approximately 70 ml of acrylonitrile would be sufficient. 
While greater concentration of acrylonitrile would be helpful an upper 
limit is approached at the stage where the volume of precipitate layer 22 
has been halved. It is to be understood that the explanation of FIG. 1 is 
directly applicable to the use of the solution and monomers exemplified. 
For other rubber solutions and separate, precipitating liquid feed 
streams, a different ratio of liquids can be expected, and, of course, the 
number of containers employed and volume of aliquots added is not critical 
so long as observations of precipitation commencement, equal layer volumes 
21 and 22 and 50 percent reduction in rubber precipitate layer 22 can be 
made. 
Not all of the monomers become polymerized in the extruder and therefore 
residual amounts of unreacted compounds are removed. Conversions generally 
run as high as about 70 percent and yield a product comprising from five 
to 50 percent by weight rubber. Average molecular weights of the product 
can range from about 60,000 to 200,000 with 120,000 being preferred. 
The polymerization of the monomers is via a bulk polymerization system for 
which an initiator may be employed. Suitable initiators include the azo 
and organic peroxide types, which are well known to those skilled in the 
art. These may readily be dissolved in an organic solvent and fed to the 
reactor extruder with the feed solution and separate feed stream. 
In producing the resins from these components, other items can be added 
such as chain transfer agents, dyes and stabilizers. The use and amount of 
such items, along with the amount of initiators and crosslinking agents 
are all known in the art and not the subject of the present invention. 
For purposes of exemplification, the process of the present invention is 
particularly suitable for the preparation of high acrylonitrile content 
ABS copolymers. High acrylonitrile ABS copolymers contain at least 26 
weight percent acrylonitrile and can contain as much as about 60 weight 
percent. The feed solution for the preparation of the high acrylonitrile 
copolymer should comprise from about five to 25 percent by weight of 
rubber polymer, based upon the total weight of the feed solution. 
Polybutadiene rubber having a cis content of at least 98 percent is 
preferred although a range of 8.0 to 100 percent is entirely operable. 
Average molecular weight of the rubber polymer is from about 100,000 to 
about 500,000 with 300,000 being preferred. As stated hereinabove, the 
feed monomers make up the balance of the feed solution, ranging in amount 
of from about 75 to 95 percent, with 90 percent being preferred. 
The monomers in the feed solution include acrylonitrile and styrene, the 
amount of the former being from about 10 to 30 percent and the amount of 
the latter being from about 70 to 90 percent with a 1:3 ratio being about 
the preferred maximum. Such amounts will provide for an acrylonitrile 
content of up to about 25 percent by weight. The addition of a separate 
feed stream of precipitating monomer, in this instance acrylonitrile, will 
raise the level of acrylonitrile in the product to that discussed 
hereinabove. 
Regarding the reactor extruder itself, a twin screw extruder is preferred. 
Such extruders are known and provide mating twin screws which rotate in 
the same direction. Different bushings are placed on the screw shafts, 
which provide helical screw sections for conveying, and kneading blocks 
for shearing, wherein controlled polymerization is allowed to occur. The 
specific configuration and arrangement of conveying and kneading sections 
selected will depend upon a plurality of factors which relate to the 
product being sought. Thus, screw rotation and the pitch of the conveying 
sections will provide control over backpressure, throughput time and to 
some extent temperature. The kneading sections similarly are designed to 
effect control over polymerization time and temperature. 
Generally speaking, the arrangement must provide for conveyance and mixing 
to begin at the feeding port. After a suitable temperature is reached, one 
or more kneading blocks are located to provide high shearing forces. When 
a plurality of kneading blocks are employed, which is preferred, they will 
be separated by conveying sections in order to move the material through 
the extruder. A conventional die or pelletizer head is positioned at the 
exit of the extruder to shape the resin for subsequent use. 
Twin screw extruders of the type useful for the practice of the present 
invention are set forth in U.S. Pat. Nos. 3,536,680 and 3,799,234. For 
practice of the present invention, all of the feeds to the extruder should 
be liquid. Pressure in the feed section is developed by pumps which 
deliver the feed solution thereto. As the solution passes through the 
extruder and polymerization occurs, the material becomes solid. Viscous 
drag forces from the rotating screw create additional pressure. As is 
known, heat is normally added as needed by incorporating heating elements 
around the extruder. Similarly, heat can be controlled by suitable heating 
or cooling means positioned along the extruder to provide the temperatures 
necessary for polymerization and optimization of physical properties. As 
heat is generated in the reaction zones, where shearing and polymerization 
occur, it is usually necessary to provide suitable cooling means. 
The extruder is also provided with appropriate vents for the removal of 
volatile, unreacted monomers or side products prior to extrusion. In 
systems where the reactivity ratio is low, removal and recycling of 
unreacted components is advantageous. A flow control valve can also be 
incorporated to regulate the overall pressure within the extruder. Just 
prior to extrusion through the pelletizer die, the heat can be adjusted to 
the approximate melt temperature of the resin to facilitate the formation 
of a smooth extrudate. 
Apart from the fact that the process claimed herein employs a reactor 
extruder as the polymerization vessel, novelty of the present invention is 
not premised solely on the use of such extruders per se. The process being 
claimed is directed more particularly to the components being fed; the use 
of a liquid feed solution comprising a rubber polymer dissolved in one or 
more thermoplastic monomers or solvents; a separate feed stream containing 
a precipitating material; and, the various polymerization conditions 
disclosed herein. Thus, while the twin screw reactor extruder that has 
been employed for practice of the present invention is available from 
Werner and Pfleiderer, other comparable equipment could readily be 
substituted. 
Resins such as high acrylonitrile ABS, produced in the reactor extruder are 
slightly different in chemical and physical properties from their emulsion 
produced analogs because greater amounts of acrylonitrile can be present 
with good generation of rubber particle size and distribution. Higher 
acrylonitrile content does stiffen the resin; however, much better tensile 
properties and impact strength also result. The resin from the reactor 
extruder offers better control over elastomer crosslink density and 
occluded phase volume than resin produced via conventional emulsion or 
bulk systems. 
To aid discussion of the polymerization conducted in the reactor extruder, 
reference can be made to FIG. 2 which provides a schematic representation 
of the extruder, indicated generally by the numeral 30. The extruder 30 
includes the outer barrel 31, which can be heated and cooled via means not 
shown, a drive motor 32 and a pelletizer head or other suitable extrusion 
die 33. A feeding zone 34 is provided for the rubber containing feed 
solution, separate precipitating liquid material feed and initiator from 
independent tanks 35, 36 and 37, respectively, connected by supply lines 
38, 39 and 40. Within the extruder 30 are twin screws driven by shafts 41 
and 42. The screws, not shown, provide a combination of conveying and 
kneading action, as discussed hereinabove. Polymerization zones 1 to 5 are 
depicted which can be heated or cooled independently to control 
temperature, as indicated for the examples. Vents, not shown, can be 
provided as necessary to remove volatile gases or residual unreacted 
monomers flashed off at the die head by the hot polymer. 
Polymerization zones 1 to 5 contain different arrangements of conveying 
sections and kneading or shearing sections as stated hereinabove. 
Conveying sections are usually provided in zones 1 and 5 while kneading 
sections will be provided in zones 2 to 4. Individual zones 2 to 4 can 
also contain some short conveying sections to maintain a flow of polymer 
as it is formed. The design or arrangement of the extruder screws does not 
form a part of the subject invention, inasmuch as such technology is 
within the skill of the art and is determined or controlled by factors 
such as the polymer being formed and the temperature, pressure, residence 
time and shear rate desired. 
As stated hereinabove, the process of the present invention is practiced by 
dissolving a rubber polymer in one or more plastic forming monomers or 
inert solvents to form a solution which is thereafter fed to the reactor 
extruder for polymerization. In order for polymerization to begin, an 
initiation temperature ranging from about 20.degree. to 100.degree. C. 
should be reached in the feeding zone 34. While the desired temperature 
could also be obtained in zone 1 or subsequently, it is desirable that 
polymerization commence as soon as possible first, to form a viscous 
product that can be conveyed through the extruder and second, so that the 
polymer can be subjected to the shearing action of the kneading blocks. As 
will be appreciated by those skilled in the art, the use of a known 
initiator can result in lower initiation temperatures and/or the earlier 
commencement of polymerization. Also, specific initiators can be selected 
that will selectively migrate to the rubber phase being precipitated 
within the feed port of the reaction extruder. 
The step of shearing occurs within the reactor extruder, specifically as 
the combined feed streams are subjected to the kneading blocks. It is 
necessary for the shearing to occur and continue to such an extent that 
the solids content i.e., the resin product, formed is equal to about twice 
the elastomer content in the feed solution so that phase inversion caused 
by chemical precipitation will be maintained. The occurrence of phase 
inversion is necessary for the formation of the resins of the present 
invention and it is initially triggered by the impingement of the feed 
solution with the separate feed stream which causes precipitation of the 
rubber. Initially the plastic forming monomer, or monomers, are dispersed 
throughout the homogeneous rubber polymer in the feed solution. As 
acrylonitrile or other material is fed, the solubility limit of the rubber 
is surpassed and a point is reached where there are present more units of 
plastic polymer and/or solvent of a character different from the rubber 
and the rubber becomes dispersed in the plastic and other solvent that may 
be present. 
Causing the phase inversion to occur within the reactor extruder feed port 
by the use of a separate stream of acrylonitrile or any other liquid that 
will precipitate the rubber, a feature of the process herein disclosed, 
results in a very small and uniform rubber particle size as well as 
uniform dispersion within the thermoplastic matrix. 
We believe that in order for the most uniform particle size and 
distribution of rubber particle, the shearing within the reactor extruder, 
to which the feed solution and polymer is subjected, must be controlled 
until the amount of solids present is equal to at least twice the amount 
of the elastomer content present in the feed solution. Thus, if the rubber 
content of the feed solution is equal to X, for instance 10 weight 
percent, then the solids content must be equal to at least 2X or 20 weight 
percent before shearing is complete. 
The amount of shearing action can be controlled by many factors such as 
screw rotation, positioning of the kneading sections and residence time 
within the reactor extruder. Another factor is the rubber polymer content 
of the feed solution. If the content is high, that is, greater than 15 
percent, then the shearing zone may extend beyond zone 3 in order to 
produce the two-fold increase in solids content. On the other hand, a 
lower rubber content feed solution may not require as long a shearing zone 
in order to avoid over shearing of the resin. Of course, control over the 
amount of shear in a longer shearing section can still be facilitated to 
an extent by adjusting temperature, pressure and throughput rate. 
The extruder can operate at pressures of from about 0.69 to 6.9 MPa so long 
as the feed solution is forced into the feed section at a pressure at 
least equal to the vapor pressure of the monomers at the maximum zone 
temperature being employed. If the pressure is lower, monomer gases will 
form which do not polymerize. Above this minimum pressure value, there is 
an optimum pressure range that exists but only when all other variables 
are held constant. 
In general, reaction rate increases as pressure increases. Reaction rate 
increases with higher pressure because the higher pressure insures that 
liquid monomers are forced into the voids created by previously reacted 
monomers, so additional reaction can take place. Best operation can be 
achieved when the overall machine pressure is maintained above the vapor 
pressure of the monomers, preventing the formation of internal vapor 
spaces. In general, the monomers employed herein react to polymers with a 
higher density than the starting monomers. There also exists an upper 
limit for process feed pressure. If the feed pressure is above the plastic 
viscous drag forces, the plastic will be pushed or forced out of the 
reaction/shear zone before the optimum plastic has formed, that is, one 
having optimum viscosity, elastomer level and elastomer crosslinking 
level. 
With respect to temperature, the rate of reaction increases with increasing 
temperature. When all other variables are held constant, in particular the 
length and location of the shear zone, an optimum temperature range exists 
that reacts feed solution to a plastic in the shear zone at an optimum 
elastomer level. If the temperature is too high, elastomer crosslinking 
level may be too high causing the molecular weight of the rubber and resin 
product to suffer as well as a lowering of resin impact strength. If the 
temperature is too low, the plastic may have passed through the shear zone 
without having reacted to the optimum solids level for shear forces to 
form the proper elastomer particle size. Temperatures can generally range 
from about 80.degree. C. to as high as the melt temperature of the resin 
formed e.g., 177.degree. to about 191.degree. C. 
Residence time within the reactor is a factor particularly applicable to 
the reaction/shear zones. It is approximately equal to the total 
volumetric void space of the reaction/shear zones, divided by the 
volumetric feed solution rate to the reactor extruder. With all other 
variables held constant, it is indirectly proportional to the feed 
solution rate. There is an optimum residence time range for any given set 
of variables. Too high of a feed rate could result in too short of a 
residence time to allow for the optimum plastic reaction to have been 
reached in the shear zone. Too low of a feed rate could result in too long 
of a residence time such that the plastic became "over reacted" or "over 
sheared" in the shear zone. 
With respect to shear, even though a plastic is being formed in the shear 
zone with the optimum viscosity and elastomer level, if the optimum shear 
forces are not applied, the elastomer particles will not be maintained at 
the proper size. Shear forces are generally varied by varying screw 
configuration and/or screw RPM. If all variables are held constant, 
including screw configuration, shear is directly proportional to screw 
RPM. Too little or too much shear can result in an undesirable too large 
or too small elastomer particle size. It is believed that a Shear Rate 
ranging between about 50 to 300 sec.sup.-1 will provide the necessary 
shearing action to maintain the suspension of precipitated rubber. 
Similarly, the desired size of the elastomer particles for the resins set 
forth herein should range from about 0.01 to 0.25 microns. 
Lastly, although not a novel step per se, properties of the resins prepared 
by the process of the present invention can be modified by the selection 
of proper crosslinking catalysts in the initiator feed stream. If, for 
example, the system is constrained to a certain temperature such as due to 
concern for thermal stability of the plastic components, peroxides can be 
used to insure that the elastomer becomes sufficiently cured while 
polymerization is taking place. 
In the work which is reported hereinbelow, three reactor extruder resins 
have been produced and characterized. Properties measured and reported for 
two of the resins include molecular weight, rubber content, impact 
strength, tensile measurements, melt flow rheological properties, heat 
distortion temperature (HDT) and hardness. In each instance of 
preparation, the feed solution, comprising the rubber polymer 
polybutadiene dissolved in the plastic forming monomers is fed to the feed 
zone of the reactor extruder. Respective amounts of each component are 
specified for Resins 1 and 2 with reaction times, temperatures, monomer 
feed rates and RPM of the extruder screws. Initiator/crosslinker stream 
composition and flow rate are also indicated. 
Preparation of Rubber-Modified Resins 
The first two resins reported hereinbelow are high acrylonitrile content 
ABS resins which were prepared using styrene (S), acrylonitrile (An), and 
polybutadiene rubber (BR). Polybutadiene utilized was Taktene 502, the 
properties of which, as well as Taktene 1202, are set forth in Table I 
hereinbelow. All parts are presented on a weight percent basis. The 
polymerizations were initiated in part with peroxides and thermally aided 
with heat. A third resin was also prepared wherein the rubber feed 
solution comprised Taktene 502 dissolved in styrene and the independent 
feed stream comprised a mixture of styrene and methanol, the latter being 
employed to precipitate the rubber. 
The resins discussed hereinbelow were analyzed and are reported in Tables 
II to IV which follow. Table II provides composition and molecular weights 
of the three resins and Tables III and IV provide resin properties for 
Resins 1 and 2. 
TABLE I 
______________________________________ 
Characterizing Properties of the 
Taktene 1202 and Taktene 502 Samples 
Taktene Taktene Taktene 
Rubber 1202 1202 502 
Identification 
Lot 14 Lot 863 Lot 13 
______________________________________ 
Bulk Polymer 
Properties 
Mooney Viscosity 
41.0 39.0 28.0 
(ML.sub.1+4 at 100.degree. C.) 
Ash (Wt %) 0.08 0.10 0.08 
Volatiles (wt %) 
0.24 0.26 0.20 
Stabilizer.sup. a 
0.6 0.6 0.6 
(wt % by addition) 
Solution Properties 
(as a 5 w/w % solution 
in styrene monomer) 
Fluid Viscosity 
78.9 60.0 35.5 
(mPa.s.) 
APHA Color 7.5 7.5 7.5 
______________________________________ 
.sup.a Stabilizer System comprises Irganox 1076 0.15 wt % Polygard HR 
0.45 wt % 
______________________________________ 
Resins 1-2 
Rubber feed solution: 
74.06% S, 25.94% An, 10.85% 
Taktene 502 
Independent feed solution: 
100% An 
Temperature: 163.degree. C. zones 1 to 5, die 177.degree. C. 
No. 1: 
Feed rate: Rubber feed solution 
25 cc/min 
Pure Acrylonitrile 10 cc/min 
Initiator 0.5 cc/min com- 
posed of 25 wt % Di Cup plus 
50 wt % Polygard 
Operating Pressure: 
1.38 to 1.55 MPa at 
the feed port 
Product rate: 17.5 grams/min 
No. 2: 
Feed rate: Rubber feed solution 
22 cc/min 
Pure Acrylonitrile 10 cc/min 
Initiator 0.7 cc/min com- 
posed of 25 wt % Di Cup plus 
50 wt % Polygard 
Operating Pressure: 
1.24 to 1.38 MPa at 
the feed port 
Product rate: 17.5 grams/min 
Resin 3 
Rubber feed solution: 
100% S with 15.0 wt % Taktene 502 
Independent feed solution: 
50/50 wt % mixture of methanol 
and S 
Temperature: 187.8.degree. C. Zones 1 to 5, die 
187.8.degree. C. 
No. 3: 
Feed rate: Rubber feed solution 
27 cc/min 
Methanol/Styrene feed 
11 cc/min 
Initiator 0.6 cc/min com- 
posed of 10 wt % Di Cup in 
toluene 
Operating Pressure: 
2.07 MPa at the feed port 
Product rate: 21.7 grams/min 
______________________________________ 
TABLE II 
______________________________________ 
Resin Characteristics 
Residual Molecular 
Composition Monomers Weight 
Resin S.sup.a An.sup.a 
BR.sup.b 
S An Mn Mw 
No. (wt %) (wt %) (wt %) 
(ppm) (ppm) 10.sup.3 
10.sup.3 
______________________________________ 
1 61.63 38.37 20.77 8665 3310 32.10 
103.0 
2 60.87 39.14 19.55 9690 3490 41.80 
128.4 
3 100.0 -- 25.6 N/A N/A 15.8 42.1 
______________________________________ 
.sup.a Composition of the thermoplastic matrix 
.sup.b Total weight percent of rubber contained within the resin product 
TABLE III 
______________________________________ 
Resin Properties 
Heat Melt Flow 
Notched Hard- Distortion 
Brabender 
Index 
Resin Izod ness Temp. Torque (grams/ 
No. kJ/m (RWR) (.degree.C.) 
(M-grams) 
10 min) 
______________________________________ 
1 0.335 105 85 970 1.03 
2 0.304 101.5 87 1210 1.63 
______________________________________ 
TABLE IV 
__________________________________________________________________________ 
Resin Tensile Properties 
Flex Flex Tensile 
Yield 
Break 
Resin 
Strength 
Modulus 
Elong. at 
Elong. at 
Modulus 
Strength 
Strength 
No. MPa GPa Yield % 
Break % 
GPa MPa MPa 
__________________________________________________________________________ 
1 61.75 
1.91 3.2 48.0 1.93 35.88 
24.52 
2 64.17 
1.94 4.1 31.0 1.80 36.57 
37.12 
__________________________________________________________________________ 
As can noted from studying Tables III and IV, the physical properties of 
Resins 1 and 2 are very good, particularly impact strength. The 
transmission electron photomicrographs of Resins 1 and 2 produced 
according to the process of the present invention are quite similar, one 
of which appears in FIG. 3. The dark regions in the photograph are the 
rubber phase which have a uniform average size of about 0.01 to 0.25 
microns and it can be noted that the distribution thereof is highly 
uniform. 
Preparation of Resin 3 was an attempt to demonstrate phase precipitation in 
a system containing only one polymerizable component. Unfortunately, the 
slower kinetics of the polystyrene formation necessitated the use of 
elevated process temperatures in order to yield a product rate equivalent 
to those obtained with Resins 1 and 2. A consequence of the higher 
temperatures and residence times employed was an extremely low product 
molecular weight. Although the low molecular weight precluded obtaining 
realistic physical properties, the microstructure shown in FIG. 4 
illustrates that the same type of rubber particles are produced as with 
the addition of pure acrylonitrile as a precipitating material for Resins 
1 and 2. A photomicrograph of a commercially available bulk produced 
rubber-modified polystyrene appears in FIG. 5 and although the 
magnification is significantly lower, it can readily be noted that the 
sizes of rubber particle are larger and greatly varied and that the 
distribution thereof is random and uneven. It is therefore evident that 
rubber precipitation occurring within the reactor extruder is a physical 
process for fixing rubber particle size and distribution independent of 
subsequent polymerization chemistry that may take place. 
The tensile properties, HDT and Brabender Torque of the high acrylonitrile 
containing resins, 1 and 2, are somewhat higher than normal ABS (75 wt % 
S/25 wt % An) while the melt index is lower than most typical ABS resins. 
These trends are expected as the acrylonitrile level is raised and the 
resin takes on the properties normally found in other high acrylonitrile 
type plastics. Perhaps the most significant feature of the high 
acrylonitrile containing ABS is the strong Notched Izod at a relatively 
low rubber content, i.e., about 20 wt % polybutadiene. From this it is 
evident that the less expensive acrylonitrile can be substituted for the 
more expensive elastomer component while still maintaining a high Notched 
Izod and improved tensile properties. 
In conclusion, it is to be understood that practice of the process of the 
present invention should not be limited to a particular reactor extruder 
so long as the necessary shear is provided while the polymer resin is 
forming. Likewise, so long as a feed solution is employed comprising a 
rubber polymer in a non-polymerizable solvent or ethylenically unsaturated 
monomer or mixture thereof and, an independent liquid feed of a material 
that will precipitate the rubber from the solution is fed to the reactor 
extruder, selection of the various solvent and precipitating materials and 
rubber polymers can be made based upon the type of thermoplastic resin 
sought. Moreover, it is believed that the use of particular components as 
well as the amounts thereof can be made depending upon the resin 
properties desired. Similarly, control over the process regarding 
temperature, pressure, throughput rate, residence time, Shear Rate and the 
like can be varied as desired depending upon the reactor extruder employed 
and the resin to be prepared. 
Thus, it can be seen that the disclosed invention carries out the objects 
set forth hereinabove. It is believed that the variables disclosed herein 
can readily be determined and controlled without departing from the spirit 
of the invention herein disclosed and described. Moreover, the scope of 
the invention shall include all modifications and variations that fall 
within the scope of the attached claims.