Note: Descriptions are shown in the official language in which they were submitted.
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BLENDS_F POLYP:HENYLENE ETHER RESINS AND:STYRENE-
TERT-B;UT~LSTYRENE COPOLYMERS
_
BACKGROUND OF THE INVENTION
~ .
The polyphenylene ether ~also known as
polyphenylene oxide) resins are well known family
of engineering plastics capable of being extruded,
molded or otherwise shaped into articles of various
shapes and sizes. A number of these resins and methods
for their preparation are disclosed by Hay in U.S.
Patent Nos. 4,306/874, issued February 28, 1967 and
3,306,875, issued February 28, 1967, and by
Gelu Stammatoff in U.S. Patent Nos. 3,257,357 and
3~257~358/ issued June 21, 1966.
It is known from Cizek, U.SO Patent No~
3,383,435, issued May 14~ 1968, and elsewhere~ that
polyphenylene ethers are admixable with polystyrene to
form blends having good properties.
Blends of polyphenylene ether and poly(4-tert-
butylstyrene) in particular, after molding, have been
found to be too brittle, with low tensile strength.
INTRODUCTION TO THE IN~ENTION
The discovery has now been made that certain
copolymers of 4-tert-butylstyrene and styrene, unmodified
or modified with rubber, can be blended with polyphenylene
ether resin to produce a homogeneous (single phase)
thermoplastic composition which can be molded into a
ductile material having good tensile strength and good
impact strength. Moreover, the composition has a higher
heat distortion temperature (~DT) than the corresponding
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composite made with polyphenylene ether and polystyrene.
The copolymers useful in the present kinds of
compositions are those in which the tert-butylstyrene
content is in the range between 5~ and 65% by weight
based on the total weight of the copolymer without the
rubber modifier. Copolymers containing less than 5~ of
tert-butylstyrene do not significantly improve the heat
distortion temperature of the blend, while copolymers
having greater than 65% of tert-butylstyrene result in
blends which after molding are brittle, with very low
impact strength. The sharp drop in properties which
occurs with use of a tert-butylstyrene content of greater
than 65~ is believed due to the incompatibility of such
copolymers with polyphenylene ether resin; the blends
are not homogeneous~ but rather comprise two distinct
phases. The styrene-t-butylstyrene copolymers can be
modified with rubber to improve the ductility and impact
strength of the composi-tion.
The specified styrene-tert-butylstyrene
copolymers are not compatible with polystyrene alone,
and blends of these copolymers with conventional rubber
modified high impact polystyrene (hereinafter also
"HIPS") have lower impact strength in the moldings than
blends of the same HIPS with polystyrene homopolymer.
However, the further discovery has been made that
addition of polyphenylene ether resin produces a homo
geneous matrix, i.e., a single phase, and properties of
the resultant blends o~ polyphenylene ether resin, styrene-
tert-butylstyrene copolymer and HIPS are equal to those of
blends with the same rubber and polyphenylene ether
concentration made with polystyrene hbmopolymer in place
of the styrene-t-butylstyrene copolymer.
DESCRIPTION OF THE INVENTION
The polyphenylene ether resins useful in
accordance with the present compositions are well known
and readily available.
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The preferred polyphenylene ethers are
homo-- and copolymers oE the formula:
Q"' Q'
~ O ~
Q" Q
wherein Q, Q', Q' and Q"', are independently selected
from the group consisting of hydrogen, hydrocarbon
radicals, halohydrocarbon radicals having at least two
carbon atoms between the halogen atom and the phenol
nucleus, hydrocarbonoxY radicals and halohydrocarbonoxy
radicals having at least two carbon atoms between the
halogen atoms and the phenol nucleus, and Q'~ Q" and
Q"' in addition may be halogen with the proviso that Q
and Q' are preferably free of a tertiary carbon atom;
and n represents the total number of monomer residues
and is an integer of at least 50
Especially pxeferred is poly(2,6-dimethyl-1,4-
phenylene) ether.
The compositions can also contain, as an
optional ingredient, a rubber modified high impact
polystyrene. The terminology "rubber modified high
impact polystyrene" is used in this d~clogur~ in its
conventional sense to refer to a wel`l known class of
materials, methods for the preparation of which are known.
Examples are Foster Grant's FG 834 HIPS and Amoco's 6H~
grade of HIPS.
This invention thus provides thermoplastic
compositions suitable for molding which comprise
polyphenylene ether resin with or withbut rubber modified
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high impact polystyrene, and a rubber modified copolymer
of styrene and tert-butylstyrene; or composition which
comprises polyphenylene ether resin and styrene-t-
butylstyrene copolymer, with or without rubber modified
high impact polystyrene.
The rubber modified styrene-tert-butylstyrene
copolymers which are useful in the present kinds of
compositions can be made by the procedures known for
preparing conventional rubber modified high impact
polystyrene (HIPS).
By way of illustration, in one procedure
styrene and tert-butylstyrene in the relative amounts
desired for the finished copolymer are co-polymerized
by heating in the presence of a radical forming catalyst,
e.g., a peroxide, and a rubber, to form a pre-polymer,
Polymerization is then continued in suspension in water.
The resultant polymer will comprise a copolymer of
styrene and tert-butylstyrene in approximately the
original relatively proportions and an amount of the rubber.
The resinous ingredients are combinable in
virtually all proportions in the compositions. In the
preferred forms, however, the weight percent of poly-
phenylene ether resin to total resin weight varies from
10 to 90 percent.
The compositions can optionally also include
additional resins to further modify physical and chemlcal
properties. Such modifying resins as are described in
Cizek, above, are useful, including linear, block or
random copolymers of styrene and elastomeric materials,
e.g., isoprene or butadiene. The additional resins
include, by was of illusrtation, styrene containing co-
polymers such as styrene-acrylonitrile copolymers (SAN~,
styrene-butadiene copolymers, styrene-maleic anhydride
copolymers, styrene-acrylonitrile-butadiene terpolymers
(ABS), block copolymers of the A-B-A and A-B type where
A is, for instance, polystyrene and B is, for instance,
~8~B~
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polybutadiene or polyisoprene, radial teleblock copolymers
of -these two materials, as well as hydrogenated forms of
the block or radial teleblock copolymers in which the
aliphatic unsaturation has been reduced, and acrylic
resin modified styrene-butadiene copolymers.
The molding compositions of the invention
can and advantageously do contain one or more of the
supplementary non-resinous agents which have heretofore
been customarily present in polyphenylene ether resin
molding compositions to improve certain other physical
and ~hemic~l properties of the moldings. The agents include
flame retardants~ plasticizers~ anti-oxidants, strengthening
fibers (for example, glass fibers and graphite whiskers),
mineral fillers/reinforcements, abrasion resistant
components, dyes, and pigments. Many of such agents
are disclosed in U.S. Patent No. 4,172,929, issued
October 30, 1979 to Cooper, et al.
The supplementary non-resinous agents are
present in total amount of between about 1% and 50% on a
weight basis, so as to provide the benefits which these
materials have conferred in the past on shaped molded
articles made from thermoplastic resins.
For applications where flammability is important,
the optimum copolymer composition is from 5 to about 40%
by weight of tert-butylstyrene. Copolymers containing
25% of tert-butylstyrene yield blends with polyphenylene
ether resin which have a flammability equal to or slightly
better than blends of the polyphenylene ether with poly-
styrene, but at 50% or more of tert-butylstyrene the blends
have poorer flammability than blends with polystyrene.
Blends of polyphenylene ether and copolymers of 25%
tert-butylstyr~ne and 75% styrenel for ins-tance, have gGod
flammability and physical properties and increase the
heat dis-tortion temperature by about 20F.
The compositions can be prepared by any of a
number of procedures. In one such procedure the
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components are dry blended, fed through a single screw
Brabender or twin screw Werner-Pfleiderer extruder,
Cllt or ground into particles and fed to an injection
molding device.
The invention is further illustrated in the
examples which follow. These examples are not to be
construed as limiting the invention to the particular
forms shown there, but rather are intended as preferred
or best embodiments. Parts are by weight unless stated
otherwise.
EXAMPLE 1
Preparation of a Rubber-Modified Copolymer of
Styrene and tert-Butylstyrene.
A solution of 90g of Taktene 1202 poly(butadiene)
15 rubber in 455g of styrene and 455g of tert-butylstyrene
(Dow Chemical Company Monomer No. CX2290; 95% para, 5%
meta~ was transferred to a one-gallon stainless steel
reactor along with 0.6g of benzoyl peroxide and 0.6g of dic-
umyl peroxide. The reactor was purged with nitrogen and
the contents were heated, whlle being stirred at 700 rpm
by a turbine blade agitator, for 4-1/2 hours at 90C.
(styrene conversion 28%). The prepolymer was transferred
by a gear pump to a second reactor and suspended in
2000 ml of water containing 4.8g of poly(vinyl alcohol)
and 3.6 of gelatin. Polymerization was completed by
heating the suspension for 5 hours at 100 , 5 hours at
120 , and 6 hours at 140C. The mixture was cooled
and the product, beads of a 50:50 copolymers of styrene
and tert-butylstyrene containing 9% rubber, was filtered
off, washed with water and dried.
This procedure was repeated with proportions of
styrene and tert-butylstyrene varied to obtain a 25:75
copolymer and a 75:25 copolymer.
EXAMPLE 2
A mixture of 55 parts of poly(2,6-d~methyl-lr4-
phenylene ether) resin (General Electric's PP , 45 parts
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of tert-butylstyrene copolymer prepared as described
in Example 1, ~.5 parts of polyethylene, 3.5 parts of
txiphenyl phosphate, 1 part of diphenyl decyl phosphite,
0.15 part of zinc sulfide and 0.15 part of zinc oxide
was extruded in a 2g mm twin-screw extruder and extruded
pellets were molded into standard test pieces by means of
a screw injection molding machine. Properties are listed
in Table 1.
TABLE 1
Tert-Butylstyrene Izod (ft. Gardner IIDT Ave. Burn
in Copolymer Elong.% lbs./in.) tin.lbs.) ( F.~ UL 94 (sec.
0* 50 3.6 110 250 V-l 16.0
~S 60 3.1 100 270 V-l 13.4
32 2.9 125 283 drip 37
7 0.6 ~ 5 279 drip 80
* Amoco 6H6 HIPS; control experiment
The blends have good tensile strength, impact strength and
ductility up to a copolymer composition of 50% tert-butyl-
styrene, with heat distortion temperatures substantially
higher than that of a blend containing ordinary rubber-
modified poly tyrene. Physical properties dropped sharply
when the tert-butylstyrene content of the copolymer was
increased to 75%. Flammability of the blend made with the
copolymer containing 25% tert-bu-tylstyrene was as good
as th~t of the control blend, but flammability was sub-
stantially worse than the control for blends made with
copolymer containing 50% or more oE tert-butylstyrene.
EXAMPLE 3
A mixture of 40 parts poly(2,6-dimethyl-1,4-
phenylene ether~, PPO, 60 parts of rubber-modified copolymer
prepared as described in Example 1, 1.5 parts of polyethylene,
8 parts of triphenyl phosphate, 1 part of diphenyl decyl
phosphite, 0.15 part of zinc sul:Eide and 0.15 part of zinc
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oxide was extruded and molded as described in Example 2.
Properties are listed in Table 20
TABLE 2
%Tert-Butyl~tyrene Izod (ft. Gardner ~IDT Ave.Burn
in Copol~nerElong.% lbs./in.) (in.lbs.)( F.) ~lL-9a~ (sec.1
__
0 41 ~.2 110 211 drip 24
31 3.5 100 228 drip 17
2~ 2.9 75 239 drip 72
7 0.6 ~ 5 241 drip 90
EXAMPLE 4
Copolymers of styrene and 4-tert-butylstyrene were
prepared by the procedure described in Example l, but
with no rubber present. E~ual weights of poly(2,6-dimethyl-
1,4-phenylene ether) (PPO) and the tert-butylstyrene
copolymer were dissolved in toluene, and the polymers
were co-precipitated by adding the toluene solution
rapidly to a large volume of rapidly stirred methanol.
The co-precipitated polymer was filtered off, dried
in vacuum, and compression molded into film at ~ 500 F.
A film was also prepared from a co-precipitated l:l
mixture of ordinary polystyrene with a 50:50 copolymer of
styrene and tert-butylstyrene. The films were tested
in a Perkin Elmer DSC-II differential scanning
calorimeter, at a heating rate of 40C./minute, with the
results listed in Table 3 below; a single transistion
indicates a homogeneous blend, while two transitions
show the presence of two distinct phases.
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TABLE 3
Glass Transition Temperatures of 50:50 Blends of Tert-
Butylstyrene with other Polymers.
Copolymer Composition
5 (%Ter-t-Butylstyrenel Second Polymer Tg( C.)
O PPO 1~1
PPo 158
PP0 169
PP0 173 & 194
0100 PP0 160 & 210
Polystyrene 98 & 121
EXAMPLE 5
A mixture of 40 parts of a conventional high
impact polystyrene containing 19.7% of rubber, 60 parts of
styrene-4-tert-butylstyrene copolymer and 0.2 part of
Irganox 1076 hindered phenolic antioxidant was blended in a
twin-screw extruder. ~lends were prepared from copolymers
containing 25%, 50% and 75% tert-butylstyrene. A control
blend was prepared from 40 parts of the high impact
polystyrene and 60 parts of ordinary polystyrene. A portion
of the extruded pellets from each blend was molded into test
bars in a screw injection molding machine.
%Tert Butylstyrene Izod impact strength
Blendin Copolymer(ft.lbs./in.n.) _ ( F~
A 0 1.9 177
B 25 1.1 178
C 50 0.7 181
D 75 0.5 186
EXAMPLE 6
A mixture of 50 parts of poly(2,6-dimethyl-1,4-
phenylene ether~ resin (PPO), 50 parts of the blend
described in Example 5 and 3 parts of triphenyl pho~phate
was extruded and molded as described in Example 2
Properties of the blends are summarized in Table 4.
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~lthough impact strength of the blends of HIPS with tert-
butylstyrene copolymers decreased steadily with increasing
tert-butylstyrene content, the blends containing PPO in
addition to the HIPS and tert-butylstyrene copolymer
retained impac~ strength, tensile strength and ductility
up to 50~ tert-butylstyrene, and had higher HDT than blends
containing only polystyrene. Ductility, tensile strength,
Izod impact strength, and Gardner impact strength all
decreased sharply in blends made with the copolymer of
75% tert-butylstyrene and 25~ styrene.
TABI,~ 4
%Tert-Butylstyrene Tensile Yld. Izod (ft. Gardner ~DT
Blendln Copolymer Elong.% (psi) lbs./in.~ (in.lbs.) ( F)
E 0 41 10,400 3.1 50 244
F 25 30 10,000 3.0 75 252
G 50 30 10,000 3.0 75 261
7 8,500 l.O ~5 261
Obviously, other modifications and variations of
the present in~ention are possible, in light of the above
disclosure. For instance, instead of poly(2,6-dimethyl-
1,4-phenylene ether), copolymers such as poly(2,6-dimethyl-
co~2,3,6-trimethyl-1~4-phenylene ether) can be used. It is
therefore, to be understood that changes may be made in the
specific embodiments described without departing from the
scope of the invention as defined by the appended claims.
