Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
;;~ 3~
BACKGROUND OF THE INVENTION
It is known to make rubber-modified styrene/
maleic anhydride copolymers by dissolving a rubbery addi-
tive in the monomer mixture and copolymerizing. Generally,
the rubbery additives are soluble in the vinyl aromatic
monomer or in the mixture of monomers. ~owever, in the
past the addition of as much as about 16 or 17% by weight
of the total copolyTner of rubber is all that can be tolerated
in a commercial-type reactor due to the high viscosity of
the monomers when adrnixed with a rubbery additive.
The blending of rubbery additives to a styrene/
maleic anhydride copolymer or to a rubbery modified co-
polymer is also known.~SPatents such as 4,097,5~0, 4,097,551,
3,641,212 and 2,914,505 all relate to the irnprovement of
thermoplastic compositions by rubbery additive admixtures
but all of these patents teach the blending of the rubbery
additives with the copolymer.
Patent 3,919,354, issued November 11, 1975, shows
the making of a rubber-modified styrene/maleic anhydride
copolymer having impact resistance and that is prepa~ed by
providing a solution of the rubber in styrene, initiating
free radical polymerization and then adding maleic anhydride
at a rate substantially less than the rate of polymerization
of the styrene. However, this patent does not teach or
achieve the greater product or improvement obtained by the
present invention, nor -the improvements in the process of
making such improved product. E`urther, the patent states
that the non-equimolar random copolymers are obtainable,
preferably by the steps described in the patent as set forth
above. In fact, the patent states that a polymer prepared
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7~939
from 75 mole percent styrene and 25 mole percent maleic
anhydride by admixing the monomers with suitable diluent
and catalyst, heating until polymerization is about com-
plete, will yield a polymer or polymer mixture which is
not suitable for the practice of the invention.
. _
It has been discovered by the present invention
that when two different rubbery additives are used and are
present during the polymerization of the copolymer that a
striking phenomenon occurs. As the copolymerization occurs,
a lower viscosity of the complete mixture is evident, the
process may thus be more readily carried out with a marked
decrease in the energy requirements. Secondly, an improved
product is made in that not only is heat resistance improved,
but, in addition, impact is significantly improved and the
product is upgraded to the quality of the so-called engineer-
ing materials which are considered specialty products with
a correspondingly high price.
The surprising discovery of using at least t~o
rubbery additives and having the same present during the
polymerization of the copolymer permits the permissible
amount of rubber additives to be greatly increased and this
in turn correspondingly improves the impact properties of
the resulting product. As an additional feature, it has been
found that the processability of the resultant product, as
well as its glossy surface appearance, is greatly improved.
SUMMARY OF T~IE PRESENT INVENTION
An improved copolymer composition suitable for
fabrication by many methods, such as, injection molding, ex-
trusion, thermoforming and the like and the process for mak-
ing the same is an essential object of -the present invention.
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The composition comprises a copolymer base resin,
preferably a vinyl aromatic compound and an alpha, beta-un-
saturated cyclic anhydride, modified by at least two differ-
ent rubbery additives, wherein at least one, but not all, of
said rubbery additives consists of a copolymer of from 40 to
95% by weight of a vinyl aromatic monomer and 5 to 60% by
weight of a conjugated diene monomer.
It is essential to the present invention that the
rubbery additives are present at the time of polymerization
of the base copolymer resin. It is believed that (1) greater
dispersion of the rubbery additives is thereby achieved and
(2) an interaction of the rubbery additives reduces the par-
ticle size of the resultant rubber particles precipitated
during polymerization of the base resin copolymer or matrix
to provide the improved results. It is known that the result-
ant product of the present process possesses high heat resist-
ance, considerably increased impact strength and irnproved pro-
cessability during fabrication. For example, in thermoforming,
higher draw depths at increased temperatures are permissible.
The final product exhibited higher clraw depths (elongation)
before detecting a minimal five pound force on the test in-
strument and at the break point, especially at elevated temper-
atures and in comparison to a non-modified styrene copolymer.
The end product also has a glossier finish, believed attribut-
able to the finer size rubbery additive particles.
DETAILED DESCRIPTION OF THE INV~NTION
The compositions of the present invention comprise
(a) from 60 to 90% by weight of a base resin or copolymer of
70 to 98% by weight based on copolymer of a more vinyl
aromatic compound and Erom 2 -to 30% by weight based on
3~
copolymer of an ethylenically unsaturated dicarboxylic
acid moiety that have been copolymerized in the presence of
(b) from 7 to 40% by weight of at least two differing
rubbery additives. The rubbery additives comprise 5 to 20
by weight based on total composition of at least one high
diene rubbery additive and from 2 to 20~ by weight based
on total composition of at least one high vinyl aromatic
rubbery additive. These rubbery additives are generally
soluble in the vinyl aromatic compound. It is essential
to achieve the results of the present invention that the
rubbery additives are present during polymerization of the
base resin copolymer or matrix. As will be further explained
later, blends of the same ingredients even as intimately
blended as melt blends do not provide the results obtainable
by the practice oE the present invention.
THE DICARBOXYLIC ACID MOIETY
The ethylenically unsaturated dicarboxylic acid
moiety may be an acid itself, its anhydride, its imide or
substituted imides or a half acid derivative of such a
dicarboxylic acid or mixtures thereof. Suitable acids and
their derivatives useful in the present invention are
maleic acid, fumaric acid, itaconic acid, citraconic acid,
mesaconic acid, ethylmaleic acid, methyl itaconic acid,
chloromaleic acid, dichloromaleic acid, bromomaleic acid,
dibromomaleic acid, and phenylmaleic acid, the anhydrides
of these acids, the imides and N-substituted imides of these
acids, or the half esters of these acids with suitable alcohols.
The alcohol used may be the primary and secondary alkanols
containing up to 6 carbon atoms, such as, methyl alcohol,
ethyl alcohol, n-propyl alcohol, sec-butyl and n-pentyl
alcohol; halogenated alcohols having up to ~ carbon atoms
such as 2,3-dichloro-1-propanol, and 2-bromo-1-propanol;
arylalkyl alcohol, such as benzyl alcohol; cyclic alcohols
having up to 6 carbon atoms, such as, cyclopentanol, cyclo-
hexanol, and tetrahydrofurfuryl alcohol; ether alcohols,
such as 2-butoxyethanol and the ethyl ether of diethylene-
glycol r and the like.
The imide derivatives may be prepared by reacting
the starting anhydride or diacid copolymers with aqueous
ammonia or amines. Suitable amines are the alkyl amines
having 1 to 4 carbon atoms, such as, methylamine, ethyl-
amine, propylamine, isopropylamine and butylamine; ethanol-
amine; aniline, benzylamine, allylamine and the like.
Also suitable are the water soluble ~ alkylenediamines
having 2 to 6 carbon atoms in the alkylene group, such as
ethylenediamine, and hexamethylenediamine. Arylene dia-
mines such as phenylene diamines and benzidines may also
be used. The diamines are useful ~or preparing copolymers
having varying degrees o~ crosslinking. These diamines
may be used alone or in combination with other monoamines
to give varying degrees o~ crosslinking.
THE VINYL AROMATIC COMPOUNDS
Suitable vinyl aromatic comonomers include styrene,
alpha-methylstyrene, nuclear methylstyrenes, ethylstyrene,
isopropylstyrene, tert-butylstyrene, chlorostyrenes, di-
chlorostyrenes, vinylnaphthalene and mixtures o~ these.
HIGH DIENE RUBBERY ADDITIVES
Suitable rubbery additives or elastomers include
diene rubbers which contain at least 50% by weight of a con-
jugated 1,3-diene These include conjugated 1,3-diene rub-
bers, styrene-diene copolymer rubbers, acrylonitrile-diene
~3793~33
copolymer rubbers, ethylene-propylene-diene terpolymer rub-
bers, acrylate-diene copolymer rubbers and mixtures thereof.
Preferred rubbers are diene rubbers such as homopolymers of
conjugated dienes such as butadiene, isoprene, chloroprene,
and piperylene and copolymers of such dienes with up to 50
mole percent of one or more copolymerizable mono-ethylenically
unsaturated monomers, such as styrene, substituted styrenes,
acrylonitrile, methacrylonitrile and isobutylene. Also suit-
able are the graded block copolymer rubbers and A-B block
copolymer rubbers containing 70 to 95% by weiyht of butadiene
and 5 to 30% by weight of styrene.
The diene block copolymer rubbers suitable for the
present invention are block copolymers of vinyl aromatic
compounds and conjugated dienes wherein the blocks of conju-
gated dienes will have average molecular weights greater than
the molecular weight of the combined blocks of vinyl aromatic
compounds.
These block copolymers will generally be 2 to 50%
by weight vinyl aromatic compound and 50 to 98% by weight
conjugated diene Preferably, the vinyl content will be 10
to 40~ with the diene content o~ 60 to 90%. The vinyl aro-
matic compounds may be styrene, alpha methylstyrene, nuclear
methylstyrenes, ethylstyrene, isopropylstyrene, tert-butyl-
s-tyrene, chlorostyrenes, dichlorostyrenes and vinyl naphtha-
lene and the like. The preferred compound is styrene.
The conjugated diene may be butadiene, isoprene,
chloroprene and piperylene. The preferred dienes are buta-
diene and isoprene.
Suitable block copolymer rubbers are the graded
block, A-B diblock, the radial or star block, A-B-A triblock
1~'7~3~
and the A-B-A hydrogenated triblock rubbers.
All of the block copolymer rubbers can be made by
known processes involving anionic initiators such as butyl
lithium.
Graded diblock rubbers are those A-B type block
copolymers in which each A block is essentially polymerized
vinyl aromatic monomer with a minor amount of a conjugated
diene, and each B block is essentially a conjugated diene
polymer with a minor amount of vinyl aromatic monomer.
Such graded block rubbers may be prepared by polymerizing a
mixture of the vinyl aromatic monomer and the diene in a
neutral solvent, such as n-hexane, using a sec-butyl lithium
catalyst. In this type of system, the initial polymer
chains are predominantly polydiene, but as the diene is
depleted, the later polymer formed is predominantly poly-
vinyl aromatic monomer. Such copolymer rubbers are also
available commercially, as for instance Stereon 720, a
Firestone Synthetic Rubber & Latex Co. product having 90%
by weight butadiene and 10~ by weight styrene with 55~
by ~eight of the styrene appearing as polystyrene blocks.
Diblock copolymer rubbers are copolymers of A-B
type ~herein A represents a block of poly(vinyl aromatic
monomer) and B represents a blocX of poly(conjugated diene).
True diblock copolymer rubbers are made by polymerizing one
of the monomers to essential completion and then adding the
second monomer. Thus, butadiene may be anionically polymer-
ized using sec-butyl lithium catalyst. Then, prior to term-
ination of the polymer chains, the styrene is added and poly-
merization allowed to continue. Diblock copolymers may also
be prepared by separately polymerizing each monomer in the
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* Trade Mark
7939
presence of a lithium catalyst and then combining the sepa-
rate blocks by reacting the lithium terminated blocks together
in the presence of a difunctional coupling agent. Such di-
block rubbers are also available commercially, as for instance
*
Solprene 1205, a Phillips Petroleum Company product having 75%
by weight polybutadiene and 25~ by weight polystyrene.
Radial or star block copolymer rubbers are branched
copolymers having at least three A-B diblock chains connected
to a central nucleus. Thus, chains of block copolymers
prepared by polymerizing vinyl aromatic monomers and conju-
gated diene monomers in inert solvents using organo-lithium
catalysts can be added, while still lithium terminated, to
compounds having at least three functional sites capable of
reacting with the lithium to carbon bond and adding to the
carbon possessing this bond in the copolymer. Such polyfunc-
tional compounds are, for example, polyepoxides, polyisocya-
nates, polyimines, polyaldehydes, polyketones, polyanhydrides,
polyesters, etc. Such radial block rubbers are also available
commercially, as for instance Solprene 406 and Solprene 414
products of Phillips Petroleum Co. having 60% by weight poly-
butadiene and 40% by weight polystyrene. Another example is
Solprene S411P, containing 70% butadiene, 30% styrene and a
coupling ayent.
Triblock copolymer rubbers are linear copolymers of
the A-B-A or B-A-B type, wherein~ again, A represents a block
of poly(vinyl aromatic monomer) and B represents a block of
poly(conjugated diene~. Such triblock copolymers can be pre-
pared by sequential addition of the desired monomers into a
lithium alkyl initiated polymerization. Another effective
method would be to polymerize the diene monomer, for example
* Trade Mark
93S~
in the presence of a difunctional catalyst, such as dilithio-
stilbene, and then adding the vinyl aryl monomer to form the
end blocks. Such triblock copolymer rubbers are also availa-
ble commercially as, for example, Kraton 1101, a product of
Shell Chemical Co. being a polystyrene-polybutadiene-poly
styrene triblock rubber having 70% by weight polybutadiene and
30% by weight polystyrene.
Also s~itable are the hydrogenated triblock copoly-
mer rubbers formed by, for example, selective hydrogenation
of A-B-A triblock type copolymers. Especially suitable are
the hydrogenated triblock copolymer rubbers wherein the hydro-
genation has been primarily in the polydiene blocks, B. Thus,
~.S. Patent No. 3,595,942 describes the polymers and suitable
methods for their hydrogenation such that at least 80% of the
aliphatic unsaturation has been reduced by hydrogenation and
less than 25~ of the aromatic unsaturation of the vinyl aromat-
ic monomer blocks, A, have been hydrogenated. Such copolymers
*
are available commercially as, for example, Kraton G, a product
of Shell Chemical Co., being a polystyrene-polyisoprene-poly-
styrene triblock rubber wherein the polyisoprene portion has
been hydrogenated to a poly(ethylene/propylene) copolymer
bl ock .
Another preferred rubbery additive is a high cis
content 1,4, polybutadiene with 98% cis content, sold under
the trademark Taktene 1202.
HIGH VINYL AROMATIC RUBBERY ADDITIVES
Although the high monovinyl aromatic copolymers
are not strictly "rubbery", they are designated as rubbery
additives herein because of the-effect their addition to
the present system has on the impact and thermal properties.
* Trade Mark 10
79;3~
Any of the types of block copolymers described
above under High Diene Rubbery Additives can be prepared
using greater amounts of vinyl aromatic monomer than conju-
gated diene in the described procedures. Those prepared
having from 40 to 95% by weight of vinyl aromatic monomers
and 5 to 60% by weight of conjugated diene monomers are
suitable for use in the present invention as high vinyl
aromatic additives.
Thus, Stereon 840 is a graded diblock copolymer
of about 57% by weight butadiene and 43% by weight styrene
and is sold by Firestone Synthetic Rubber & Latex Co.
Another suitable high vinyl aromatic rubbery
additive is a radial block copolymer of 75% by weight styrene
and 25% by weight butadiene, sold by Shell Chemical Co. under
the tradename KR03.
Branched, radial block copolymers, which are also
suitable for the present invention~ can be prepared using
the methods taught in U.S. patent 4,180,530.
The polymerization of the base resin copolymer
may be accomplished by any of the several available methods
for ~ile preparation of the non-equimolar copolymers of
vinyl aromatic compounds and dicarboxylic acid moieties.
They may be prepared in accordance ~ith the principles of
the continuous recycle polymerization process such as
described in U.S~ patents nos. 2,769,804 and ~,989,517;
or by the suspension polymerization process described in
U.S. patent no. 3,509,110. A continuous polymerization
process is preferred (even though recycling is only done
after purification of the materials), because it appears to
lend itself to the advantages of the present invention, such
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~'7~3g
as, the possibility of the increase of greater rubber con-
tent and the energy conservation potential discovered in
carrying out the present invention.
For example, in continuous polymerization process
there are inherent limitations in that if more than about
15 to 17% by weight of finished product of a rubbery additive
is used, the viscosity of the total mix or syrup becomes
so high that agitation and continued polymerization cannot
be accomplished.
According to the present invention, when a total
of 20% of at least two different rubbery additives are present
during polymerization, it is found that when polymerization
reaches a point where the syrup contains about 45% or so
solids, the viscosity, which at the start of polymerization
was 195 cps is only 4,~70 cps compared to a syrup containing
only 15% of one rubber additive which starts with a viscosity
of about 95 cps and progresses to where, at the level of 45%
or so solids, the viscosity is about 17,430 cps.
This remarkable decrease in viscosity cannot be
fully explained but may be accounted for by the fact that
the rubber particles precipitating out of the syrup as poly-
merization proceeds have a much finer particle size than
when a single rubbery additive is used.
Similarly, in producing compositions in accordance
with the present invention, the amperage required at a point
near the end of polymerization to drive the agitators decreased
from 64 to 66 amperes for a copolymer containing enough of
a rubbery additive to provide 15% by weight of the final
product to about 60 to 62 amperes for a final product
containing 17% of one rubbery additive and 5% of a different
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rubbery additive for a total 22% rubbery additive.
In another instance a composition containing 15%
of one rubber and 10% of another rubber or a total of 25%
rubber only required 59 to 62 amperes at a point near the
end o~ polymerization in contrast to the 64 to 66 amps for
a compositio~ containing 15% of a single rubbery additive.
On another production line, the composition containing 15%
of a single rubber required 70 to 72 amperes to drive the
agitator at the time of final polymerization in contrast
to a composition containing 17% of one rubber and 5% of
another rubber ~or a total of 22~ rubber) which required
only 61~1/2 to 62 amperes. When produ~tion planning requires
consideration of energy conservationr it is highly advanta-
geous to make a better product while using considerably
less energy.
To illustrate the advantages of the present inven-
tion over melt blended compositions of the same ingredients,
that is, a copolymer of a vinyl aromatic compound and an
ethylenically unsaturated dicarboxylic acid moiety with a
rubbery additive, the following Example I is provided.
Example I
Sample A comprises a composition containing styrene
in an amount of about 77%~ maleic anhydride in an amount of
about 8%, a Stereon 720, a rubbery additive, in an amount of
about 15% but which has been polymerized together with the
styrene and maleic anhydride.
Sample B comprises Sample A to which has been melt
blended 5% by weight of the total composition of the rubbery
additive sold under the trademark KR03.
Sample C comprises Sample A to which has been melt
~ ~793~
blended 10% by weight of the total composition of the rubbery
additive KR03.
Sample D is the same as Sample A except that it
has 20% of the rubbery additive KR03 melt blended therewith.
Table I shows the physical properties of Samples
A through D. The use of two rubbery additives does add some
slight improvement to the impact properties.
Table I
Sample A B C D
Izod Impact, notched 3.2 3.4 3.5 3.7
ft.-lbs./inc~.
(ASTM D-256)
Falling Weight Impact, 302 362 356 442
inch lbs.
Gardner Impact,9~ 128 129 112
inch lbs.
Vicat Softening Pt.
(ASTM D-1525)
C 119 118 117 116
F 246 244 243 241
Tens. Strength, psi4,700 4,500 4,200 4,300
(ASTM D-638)
Flex. Strength, psi9,100 8,200 7,700 7,500
(ASTM D-790)
Flex Modulus 326 327 309 294
ps i x10-3
(ASTM D-790)
The following Example II shows the advantages of
polymerization of the copolymer base resin in the presence
of the rubbery additives and the improvement in properties
achieved in contrast -to intimate mixing of the rubbery addi-
tives by blending as shown in Example I.
Example II
Sample A duplicates Sample A as shown in Example I
and comprises a base copolymer which has been polymerized in
~'793~
the presence of a rubbery additive (Stereon 720) in sufficient
~uan-tity to provide an end product with 15% by weight of
rubbery additive. This represents a control sample.
Sample E is a sample with the same composition as
Sample A made from a different run, and also represents
another control sample.
Sample F is a sample in which two different rubbery
additives were present during polymerization of the base
copolymer resin in amounts sufficient to provide an end
product having 15% Stereon 720 and 5% KR03.
Sample G is a product having 15% by weight of Stereon
720 and 5% by weight of Stereon 840 as the rubbery additives,
which were present duriny polymerization of the base copolymer
resinO
Sample H is similar to Sample G but contains 15%
Stereon 720 and 10~ Stereon 840.
Table II sets forth the physical property data of
the Samples A, E, F, G and H. It can be seen that the
samples having at least two rubbery additives present during
polymeri2ation gives significantly be-tter properties than the
samples which were melt blended in Table I.
- \
~7~39
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3~3
In Tables I and II the Falling Weight Impact Test
is one devised by ARCO Polymers, Inc. It involves falling
weights of from one to ten pounds each having a 3/4" radius
on the nose and a 1.5" diameter body. Test specimens are
flat sheets having a thickness of 0.0625" to .250" and are
a minimum area of 36 square inches (6" x 6" plaques). The
specimens are injection molded, compression molded or
extruded sheets, and are tested at an ambient temperature of
about 73F. The test procedure comprises selecting an
appropriate weight and height at which 50~6 failure of the
-test specimens should occur. This will depend on the
thickness and type of material being tested. The selected
weight is raised to the desired height and allowed to fall
freely onto the testing area. The testing area comprises a
4" hole in the base of the test apparatus over which a test
specimen plaque has been disposed and clamped. Care should
be taken to avoid multiple impacts; that is, if the striking
weight should bounce off the test specimen, the operator
should catch it to prevent it from striking the test specimen
a second time. The previous steps are repeated for the
remaining plurality test specimens in conformance with a
dropping procedure known as the Bruceton Staircase Method
in which the drop height is raised one inch after a non-
failure and lowered one inch after a failure. This gives
results which have a large number of failures of data
points near the Fso or mean value. The mean height of
the specimens that fail and those that do not fail is cal-
culated using the following Eormula:
mean = ~ I NI ~ in which
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~7~33~
N = the total number of specimens that failed
or did not Eail,
I = drop height, and
NI = the number of specimens -that failed or did
not fail at height I.
The two means (failure and non-failure~ are then
averaged -to produce the Fso or mean failure height
which multiplied by the striker weight used gives
the falling weight impact in inch-pounds. An
adequate number of test specimens, such as, 30 or
more, should be used to provide accurate, meaning-
ful results.
Exa_ple III
In this Example varying amounts of rubbery addi-
tive KR03 with a constant amount of rubbery additive Stereon
7~0 were prepared and tested as Sarnples I through M. The
rubbery additive content and physical properties of the
resultant products are shown in the following Table III.
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~ ~ $7939
Ln1~ ~ r- +1 ~ ~DO O O
r~ ~r O O
rl r~ O
Ln
~1 ~ ~
LnLn o ~ + I ~ ~9
--l r~ ~) r~l ~ O O O
~ ~\ r~ 0 0
Ln~Y ~ o + ¦ ~9 r-l O O O
:~ r-l r~ ~ r` r-l ~r O O O
~ 9 r-l ~1~ Ln O
~r a) ~
H Ln ~I-- + I Ln ~ O O
~) r-l r-l [~ r~ O O O
~1) ~ o r~ ~1 r-l Ln O
r-l
~ ~ t~ I_
E~
Ln o Ln~r + I ~ ~ o o o
H r-l rl O r~ O O
r~3 ~r ~) O
~r CO r
~n
Q
U~ ~
~ V
rl
rl rl
\ ~ U~ ,,
Q ~ Ln
~ ~1 ~-
0~ ~ Ln `
C) H ~1 ~1 ,~ ~ U~
~ Q L~ ~) e a ~ ~ ~
a) ~ ~
0 ~1 ~ ~ O
~o ~ u a) P~
~ o~oQ, o ~~ ~1
~ ~ o
a) 0 3 H S P~
Q ~ a 3~ ~ ~ o ~n x X
1~ ~J o ~ O
1~1 ~ P:;O N
u~ U~ K
--lq--
939
From Table III it may be seen that in con-trast to
Sample I, the progressive presence of amounts of 2, 4, 5 and
7% of rubbery additive KR03 gave higher impact strengths with-
out significantly affec-ting the temperature resistance or other
physical properties of the products. The use of total rubbery
additive contents of 20% and 22% using two different rubbers
showed falling weight impact improvements oE 64% and 72% re-
spectively over the product containing 15% of a single rubbery
additive. This is especially significant when it is realized
that rubbery additive KR03 by itself has a relatively low
impact strength.
Example IV
Samples N, O and P were prepared to show effects
similar to Example III but using Stereon 840 rather -than
KR03 as the high vinyl aromatic rubbery additive along with
Stereon 720. The rubbery additive amounts and physical
properties are shown in the following Table IV.
Table IV
Sample N O P
Stereon 720 wt. % 15 15 15
Stereon 840 wto % 0 5 10
Total of 2 Rubbery15 20 25
Additives wt. ~
Izod Impact, ft. lbs./in. 3.4 4.4 4.6
Falling Weight Impact, 300+8 404+13 638+7
inch lbs.
(ARCO Polymers' test)
Vicat, (ASTM ~-1525)
C 119 122 120
F 246 252 248
Tens. Strength, psi 4,400 4,400 4,000
Flex. Strength, psi 8,300 7,600 7,000
Flex. Modulus, psi x10-3 340 310 286
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'7~39
Table IV shows the use of two different rubbery
additives in total amounts of 20% and 25% (samples O and P),
which prior to the present invention was not feasible, follow-
ing the same commercial methods in use prior to this invention.
The doubling of the Falling Weight Impact Test for a product
using 25% total of two different rubbery additives in contrast
to the impact strength of a product having 15% oE a single
rubbery additive is an outstanding result to provide a high
heat resistance, very high impact strength product. The
fact that the product has increased ease of formability is
an additional important beneficial factor for its commercial
use.
Preliminary testing shows tha-t products embodying
the present invention that include the use of more than two
rubbery additives, such as, 3 or 4, or more may further
dramatically contribute to better products, especially when
the additives are carefully selected to provide special
properties for predetermined applications. Erom the experi-
mental testing~ it is concluded that the total rubbery
additive content by weight of the base resin matrix may be
as much as 40%, and still provide the impact strength
improvements illustrated by the Examples set forth herein.
Electron micrographs of the finished product shows that the
si~e of the rubbery additive particles precipitated from the
base resin during its polymerization are materially smaller
when at least -two rubbery additives are used. I-t is postu-
lated that there is an interaction that occurs when at leas-t
two rubbery additives are used that accounts for the preci-
pitation of the significantly smaller rubber particles, their
greater dispersemen-t through the matrix, and the greatly
3~
improved lmpact resistance of the resultant product. It is
also believed that this same phenomenon accounts for the
higher gloss of the surface of articles fabricated from the
resultant product.
Products made in accordance with the present in-
vention are also compatible with reinforcement additives,
such as, glass fibers or other additives for this purpose
that are well known in the art. In one instance, the use
of 10% glass fibers raised the tensile strength from a
range of about 4,000 to 5,000 psi to about 8,000 psi, flex-
ural strength was raised from the range of about 7,000 to
9,000 psi to about 13,000 to 14,000 psi, and flexural
modulus was improved from the range of about 300,000 to
350,000 psi to about 492,000 psi. When glass fibers in
the amount of 20% were added, the tensile strengths reached
about 10,000 or ll,000 psil flexural strengths attained
about 18,000 psi, and flexural modulus attained about
714~000 psi.
As previously described~ the preferred base resin
or copolymer composition comprises an aromatic vinyl monomer
and an ethylenically unsaturated dicarboxylic acid moiety.
The proportions of these two ingredients may be varied,
according to the degree of heat resistance desired. Thus,
the proportion of the dicarboxylic acid moiety may be varied
from a minimum amount sufficient to provide a significant
amount of increased heat resistance to a maximum of 25% or
more. At amounts of about 25% or 30% or even slightly less,
the impact increasing propensity of the multiple rubbery
additives during polymerization is believed -to decrease.
In other words, the beneficial effec-ts on improvement of
-2~-
3~
the impac-t strenyth are proportionally decreased. This
brings into play the economics of the final product and
whether the cost of such a final product will be compatible
or competitive with other available diEferent materials.
At some point the final product with high dicarboxylic acid
moiety content and high total rubbery additive content may
be deficient in one or more specific physical properties
desired for certain end use applications.
It is also contemplated by the present invention
that in addition to reinforcing agents, the products may
also contain colorants, fire retardant agents, plasticizers,
extenders, lubricants, oxidation inhibitors, stabilizers,
and the like, provided they are compatible with the ingredi-
ents being used and do not distort the usefulness of such
final products to an unsatisfactory degree.
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