Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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IMPROVED IMPACT STYRENE POLYMER
Impact resistant alkenyl aromatic resins
such as polystyrene containing reinforcing rubber
therein are highly desirable items of commerce and
are used for r.lany end use applications. Oftentimes
such impact resistant styrene polymer is employed
~o~ housings, liners, molded articles, vacuum formed.
articles and the like which are expose~ to oily
contaminants. For example, a refrigerator liner
may be vacuum formed from an impact resistant poly-
styrene and give excellent service until the sur-
face of the liner has ~een contaminated with a
material such as butter. In general, it is rather
difficult to prevent the occasional conta~t of an
oily foodstuff with a refrigerator liner when the
refriserator is used in the normal household manner.
Impact polystyrene in general is easily and quickly
formed into such liners and has satisfactory resis-
tance to physical abuse. In some instances, refrigerator liners have been prepared from a two-layer
sheet where the principal component of the sheet
is impact polystyrene and a thinner surface layer
of a polymér which is more resistant to oils and
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solvent is provided on the side which ultimately
would be exposed to possible food or oil contami-
nation.
It would be desirable if there were avail-
able an improved impact resistant styrene polymer.
It would be desirable if there were avail-
able an impact resistant styrene polymer having
improved stress crack resistance.
It would also be desirable if there were
an improved impact resistant styrene polymer which
showed a reduced tendency toward cracking under
~tress when in the presence of an oily material.
These benefits ~nd advantages in accox-
dance ~ith the present invention are achieved in a
process for the preparation of an impact resistant
al~enyl aromatic polymer wherein a stream is pro-
vided, the stream containing a polymerizing alkenyl
aromatic monomer, a reinforcing rubber dissolved
therein, initiating polymerization of the alkenyl
aromatic monomer in the presence of dissolved rubber
to cause the rubber to form a plurality of rubber
par~icles, therein subse~uently polymerizing an
additional amount of the alkenyl aromatic mono~ler
to form alkenyl aromatic resinous polymer having
a desired amount of rubber dispersed therethrouyh
as a plurality of particles, and subseguently re-
moving from the stream at least a major portion
of the unreacted al~enyl aromatic monomer and organic
solvent, the improvement which comprises employing
as the solvent an aliphatic hydroc~rbon composition
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selected from the C-6 to C-10 aliphatic hydrocarbons
and mixtures thereof.
By the term "alkenyl aromatic monomer" i-
meant an alkenyl aromatic compound having the general
formu]a
R
Ar-C-CH
wherein Ar represents an aromatic hydrocarbon radical,
or an aromatic hydrocarbon radical of the benzene
series, and R is hydrogen or the methyl radical
and containing up to 12 carbon atoms. Examples of
such alkenyl aromatic monomers are styrene, a-methyl-
~tyrene, o-methylstyrene, m-methylstyrene, p-methyl-
styrene, ar-ethylstyrene, ar-vinylxylene, ar-chloro-
~tyrene or ar-bromostyrene, and the like. Such
polymerizations may be catalyæed or uncatalyzed
and conducted under conventional temperatures and
conditions and are readily controlled as to the
particle size of the rubber in accordance with the
present invention. Comonomers polymerizable with the
alkenyl arolnatic monomer and anhydride are methyl-
methacrylate, methylacrylate, ethylmethacrylate,
ethylacrylate, acrylonitrile, methacrylonitrile
acrylic acid and the like. Beneficially, such
monomers are employed in a proportion of from about
1 to 40 weight percent of the polymer composition,
and advantageously from about 20 to 35 wei~ht per-
cent of the polymer composition.
Suitable ruhbers for the practice of the
present invention are diene rubbers or mixtures of
diene rubbers; i.e., any rubbery polymers (a polymer
having a glass temperature not higher than 0C., and
preferably not higher than -20C., as determined by
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ASTM Test D-746-52T~ of one or more conjugated
1,3 dienes; e.g., butadiene, isoprene, piperylene,
chloroprene, etc. Such rubbers include homopolymers,
interpol~ners and block copolymers of conjugated
1,3 dienes with up to an equal amount by weight of
one or more copolymerizable monoethylenically un-
saturated monomers, such as monovinylidene aromatic
hydrocarbons (e.g., styrene; an aralkylstyrene,
cuch as the o-, m- and p-methylstyrenes, 2,4-di-
methylstyrene, the ar-ethylstyrenes, p-tertbutyl-
styrene, etc.; an ~-alkylstyrene, such as ~-methyl-
styr~ne, ~-ethylstyrene, a-methyl-p-methylstyrene,
etc.; vinyl naphthalene, etc.); ar-halo monovinylidene
aromatic hydrocarbons (e.g., the o-, m- and p-chloro-
styrenes, 2,4-di-bromostyrene, 2-methyl-4-chloro-
styrene, etc.); acrylonitrile; methacrylonitrile;
alkylacrylates (e.g., methylacrylate, butyl acrylate,
2-ethylhexyl acrylate, etc.); the corresponding
alkyl methacrylates; acrylamides (e.g., acrylamide,
methacrylamide, N-butyl acrylamide, etc.); unsat-
urated ketones (e.g., vinyl methyl ketone, methyl
i80pxopenyl ~.etone, etc.); a-olefins (e.g., ethylene,
propylene, etc.); pyridines; vinyl esters (e.g.,
vinyl acctate, vinyl stearate, etc.); vinyl and
~5 vinylidene halides (e.g., the vinyl and vinylidene
chlorides and bromides, etc.); and the like.
Although the rubber may contain up to about
2 percent of a cross-linking agent, based on the
weight of ~he rubber forming monomer or monomers,
cross-linking snay presellt problems in dissolving
the rubber in the monosners for the graft polymeri-
zation reaction, particularly for a mass or bulk
polymerization reaction. In addition, excessive
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cross-linXing can result in loss of the rubbery
~haracteristics. The cross-linking agent can be
any of the agents conventionally employed for cross-
-linking diene r~bers; e.g., divinylbenzene, di-
allyl malleate, diallyl fumarate, diallyl adipate,allyl acrylate, allyl methacrylate, diacrylates and
dimethacrylates of polyhydric alcohols; e.g., ethylene
glycol dimethacrylate, etc.
A preferred group of rubbers are those
consisting essentially of 65 to 100 percent by weight
of butadiene and/or isoprene and up to 35 percent
by weight of a monomer selected from the group con-
~isting of alkenyl aromatic hydrocarbons (e.g.,
~tyrene) and unsaturated nitriles (e.g., acrylo-
nitrile), or mixtures thereof. Particularly advan-
tageous substrates are butadiene homopolymer or an
interpolymer or A-B block copolymers of from 70 to
95 percent by weight butadiene and from 5 to 30
percent by weight of styrene.
~0 The rubbers or rubbery reinforcing agents
employed in the present invention must also meet
the following requirements: an inherent viscosity
from about 0.9 to 2.5 and preferably 0.9 to 1.7
grams per deciliter (as determined at 25C employing
2S 0.3 grams of rubber per deciliter of toluene).
Advantageously, the amount of such rubbery reinforcing
agent can be from 5 to 35 weight percen~ of the final
product, and beneficially from 10 to 25 percent,
and most advantageously from 15 to 25 percent.
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~ lS079 1
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Suitable solvents for use in the practice
of the present invention are aliphatic hydrocarbon
~olvents which are ~enerally nonreactive in th~
polymerizing system and have a solubility parameter
of from about 6.0 to 7.7 and beneficially the solu-
bility parameter is from about 7.0 to 7.6. Such
solvents are generally used in a quantity such that
in the polymerizing stream the solvent is present
at a level of fxom about 2 to 20 weight percent
based on the total weight of the stream, and pre-
ferably from about 5 ~o 15 weight percent of the
total weight of the stream. Such solvent may be
a single compound or be a mixture of many compounds;
for example, V.M. & P naphtha, white gasoline normal
octane, and various C-6 to C-10 mixtures such as
B are sold under the trade designation of Isopar ~ and
- I80par C by Exxon Corporation. Practical limitations
in selecting a suitable aliphatic solvent are the
~apor pressure it will generate in the polyrnerizing
8ystem, and the ease with which it can be removed
during the de-~olitilization of the polymerizing
8tream. When 10 weight percent ethyl ~enz~ne is
employed as a solvent in a stream containing 8.75
weight percent of rubber commercially designated
as Diene 55 and 81~25 weight percent styrene, phase
inversion occurs at about 22.4 percent solids. When
the ethyl benzene is replaced with 10 weight percent
of Isopar C, the phase inversion point is 24.8 per-
cent. The resultant rubber particles obtained with
Isopar C which has a solubility parameter of 7.1
8how less occluded polystyrene than the particles
obtained when ethyl benzene is employed as solvent.
It is believed that as the amount of occluded poly-
styrene in the rubber particles is dec~eased for a
~ trad~ ~k
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fixed rubber content of the styrene polymer, environ-
mental stress crack resistance is improved.
Polymerization of the polymerizable mix-
ture may be accomplished by thermal polymerization
generally between temperatures of 60~C to 170 and
preferably from 70 to 140C, or alternately any
free radical generating catalyst may be used in the
practice of the invention, including actinic radiation.
It is preferable to incorporate a suitable catalyst
system for polymerizing the monomer, such as ~e
conventional monomer-soluble peroxy and perzao com-
pounds. Exemplary catalysts are di-tert-butyl peroxide,
benzoyl peroxide, lauroyl peroxide, oleyl peroxide,
toluyl peroxide, di-tert-butyl diperphthalate, tert-
-butyl peracetate, tert-butyl perbenzoate, dicumyl
peroxide, tert-butyl peroxide, isopropyl carbonate,
2,5-dimethyl-2,5-di(tert-butylperoxy3hexane, 2,5-
-dimethyl-2,5 di(tert-butylperoxy) hexyne-3,
tert~-butyl hydroperoxide, cumene hydroperoxide,
p-methane hydroperoxide, cyclopentane hydroperoxide,
dii~opropylbenzene hydroperoxide, p-tert-butyl-cumene
hydropexoxide pinane hydroperoxide, 2,5-dimethyl-
hexane-2,5-dihydroperoxide, 2,2'-azobisisobutyro-
nitrile, e~c., and mixtures thereof.
2S The catalyst is generally included within
the range of 0.001 to 1.0 percent by weight, and
preferably on the order of O.OOS to 0.5 percent by
weight of the polymerizable material depending upon
the monomers and the desired polymerization cycle.
If desired, small amounts of antio~idants
are included in the feed stream, such as alkylated
phenols; e.g., 2,6-di-tert-butyl-p-cresol, phosphites
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~uch as trinonyl phenyl phosphite and mixtures con-
taining tri (mono and dinonyl phenyl) phosphites. Such
materials in general may be added at any stage during
polymerization.
Plastifiers or lubricants such as butyl
stearate, polyethylene glycol, polybutenes and mineral
~il may also be added if desired. Polymers prepared in
accordance with the present invention are well suited
for extrusion into sheet or film. Such sheet is bene-
ficially employed and thermally formed into containers,
packages, refrigerator liners, housings and the like.
Alternatively the polymer is employed with benefit of
injection molding of a wide variety of components such
as containers, ducts, racks and the like.
The figure schematically depicts apparatus
su;table for continuing polymerization in accordance
with the present invention. In the Figure there is an
apparatus generally designated by the numeral 10. The
apparatus 10 comprises in cooperative combination a
~0 feed tank 11, connected to a first reactor 12 of a line
or conduit 14 having a metering pump 15 therein. The
reactor 12 has an agitator not shown driven by a motor 16.
The reactor 12 has an upper end adjacent motor 16 and a
lower end remote from motor 16, a recirculation line or
conduit 17 having a pump 18 therein is connected between
the upper end and lower end of the reactor 12. A line
or conduit 19 is connected to the lower end of reactor
12 and to an upper end of a generally like reactor 12A.
Reactor 12A has an agitator, not shown, driven by a
motor 16A. The lower end of reactor 12A is connected
by means of line 21 to an upper end of a third re-
actor 12B, the reactor 12B which has an agitator is
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driven by motor 16B. A discharge line 22 is connected
to the bottom of reactor 12B and with a heat exchanger 23.
The heat exchanger 23B discharges to a devolatizer or
chamber 24, the devolatizer has a lower outlet line 25
having a pump 26 therein and an overhead discharge line
27 having pump 28 therein. Flow direction polymerization
apparatus is indicated by the arrowheads. The numerals
1 through 7 indicate individual temperature control
zones thereof. The first reactor 12 has two temperature
control zcnes thereof. The first reactor 12 has t~o
temperature control zones 1 and 2, the second reactor
has 3 and the third reactor two zones.
In operation of the apparatus for the
practice of the method of the present invention, the
polymerizable monomer, for example styrene, a desired
quantity of reinforcing rubber diluent, the free radical
initiator, and other optional additives are added to-
the feed tank 11 to provide a homogeneous solution.
The ~eed pump 15 forwards the feed material tank 11
20 into the upper portion of the reactor 12 to fill the
reactor 12. The pump 18 removes material from ~he
bottom of the reactor 12 and returns it to the top of
the reactor 12, making the reactor 12 a back-mixed
reactor. The effluent from ~he reactor 12 passes
through the line 19 into the reactor 12A in which
generally plug flow is maintained. The effluent from
the reactor 12A passes to the reactor 12B which is also
of plug flow variety. Effluent from the reactor 12B
passes through the line 22 into a heat exchanger 23
where the polyrnerizing stream is heated to devolatilizing
temperature and the stream discharges into devola-
tilizing chamber 24. The pump 28 is a vacuum pump
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which carries away all or almost all of the volatile
materials remaining in the stream. Molten polymer
is discharged therethrough the line 25 and the pump
26. In practice of the method of the present inven-
tion employing apparatus such as illustrated in thefigure, generally it is desirable to maintain a
solids level of from about 20 to 40 precent in the
first or recirculated reactor. Discharge from the
second reactor is from about 40 to 55 percPnt, and
the discharge into the hea* exchanger 23 being at
a level of from about 60 to 95 percent solids. In
the first reactor a relatively high rate of agitation
is maintained. The second reactor is operating at
about one-half the shear rate of the first reactor
lS and minimum agitation employed in the third reactor.
The method of the invention can also be readily
practiced batch wise wherein a partial addition of
the feed mixture is added with agitation at about
the rate of the al]senyl aromatic monomer polymeri-
zation. The rate of addition of the polymerizablefeed mixture containing rubber and the desired
801vent should be such that only gradual phase
inversion occurs; that is, separation of the rubber
particles in the polymerizing mass. It is desirable
that after the addition of all of the feed mixture
to the reactor, the solids be from about 25 to 35
percent.
The invention is further illustrated but
not limited by the following examples:
Exam~le 1
A plurality of impact resistant poly- -
styrenes were prepared employing various solven~s.
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The feed consisted of 7.2 parts by weight of a poly-
butydiene rubber, sold under the trade designation of
Diene-55, 63.2 parts styrene and 9.6 parts by weight
of solvent. An apparatus generally as depicted in
the figure was employed for the polymerization. The
reactors each were elongated cylinders having a bar
agitator extending almost full length; each of the
cylindrical reactors had a volume of 72 cubic inches.
About 75 weight percent of the feed was introduced
through the equivalent of line 14 and the remainder in-
troduced into the equivalent of zone 4 of reactor 12a.
Effluent from the first stage was 35 weight percent
~olids and the agitator of the first stage rotated at
about 110 revolutions per min~te. Effluent from the
second stage was about 45 weight percent solids and the
second stage agitator corresponding to the motor 16a
rotated at about 65 revolutions per minute.
All parts are parts by weight unless other-
wise specified.
The agitator in the third vessel corres-
ponding to the vessel lOB rotated at 4 revolutions
per minute, and the effluent entering line 22 was
70 percent solids. Temperatures in zones 1 through
7 were about 102, 117, 119, 118, 124, 133, 153C,
respectively. The pump 18 provided a recirculation
rate of about 225 percent per hour based on the
volume of reactor 12. The feed mixture was fed at
a rate of about 5~0 grams per hour. The heat ex-
changer raised the temperature of the stream being
processed to about 246C and the polymer stream
was discharged into the devolatilizer 24 as a strand
and the pressure within the devolatilizer was about
23 mm of mercury absolute. ~n each pol~nerization,
it was attempted to obtain a rubber particle si~e
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as determined by phase contrast microscopy of between
about 2 and 5 microns and a rubber level of about 10
percent. The polymer was cooled, pelletized and sub-
~eguently molded into test specimens. The weight
avexage molecular weight of the polymers was determined
by gel permeation chromatography. Particle size was
determined by phase contrast microscopy. The environ-
mental stress crack resistance was determined by coating
a molded specimen with a 1 to 1 by weight mixture of
cottonseed oil and oleic acid thickened with about 20
weight percent fumed silica based on the weight of oil
plus acid. The test specimens were stressed to 1,000
pounds per square inch and the approximate time of
breaking recorded. The results are set forth in the
Table I.
C-27,0~8
1 ~0793
-- 13 --
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C-27, 048
1 16079~
-14-
Footnote followinq Table I: Isopar-C is an isoparaf-
finic hydrocarbon fraction with a narrow boiling range
of about 97 to 105C; Aromatics, Vol. % 0.02; Satu-
rates, Wt. % 2,3-dimethylpentane 3.5; 3-methylhexane
0.5; 2,2,4-trimethylpentane 84.4; 2,2,3-trimethylpen-
tane 2.2; 2,3,4-trimethylpentane 1.6; 2,3,4-trimethyl-
pentane 1.6; 2,3,3-trimethylpentane 1.0; 2,2,3-tri-
methylbutane 2.3; methylcyclopentane 0.1; 2-methyl-
hexane 0.6; 2-methylheptane 2.2.; 4-methylheptane 1.6;
total sulfur 1 ppm; peroxides 0 ppm; chlorides 1 ppm.
Isopar-E is an isoparaffinic fraction having a boiling
range of about 115~ to 142~C.
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In a manner similar to the foregoing
example, other resins of improved environmental
~tress crack resistance may be prepared employing
principally aliphatic solvents boiling at a tem-
perature from about 90C to about 260C.
As is apparent from the foxegoing speci-
fication, the present invention is susceptible of
being embodied with various alterations and modi-
fications which may differ particularly from those
that have been described in the preceding speci-
fication and description. Fcr this reason, it is
to be fully understood that all of the foregoing
is intended to be merely illustrative and is not
to be construed or interpreted as being restrictive
or otherwise limiting of the present invention,
excepting as it is set forth and defined in the
hereto-appended claims.
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