Note: Descriptions are shown in the official language in which they were submitted.
CA 02284799 1999-09-21
WO 98/54236 PCT/US98/04676
FILMS MADE FROM LONG CHAiN BRANCHED
SYNDIOTACTIC VINYL AROMATIC POLYMERS
The present invention relates to syndiotactic vinyl aromatic polymers and
films produced therefrom.
Syndiotactic vinyl aromatic polymers such as syndiotactic polystyrene (SPS)
are useful polymers having a high melting point and crystallization rate as
well as
excellent heat and chemical resistance. However, in some applications such as
in
cast-tenter dims and fibers, the melt strength is insufficient at processing
temperatures to obtain desired properties.
Syndiotactic copolymers have also been developed having superior heat and
chemical resistance. U.S. 5,202,402 issued to Funaki et al. utilizes a
difunctional
monomer to form a syndiotactic copolymer with styrene, however, the polymer
fully
crosslinks at high temperatures, forming a thermoset and cannot be melt
processed
to produce films, but instead utilizes a solution casting process which is
slow and
has the added problem of solvent removal.
Films have been produced from linear syndiotactic vinyl aromatic polymers
as described in U.S. 5,166,238, U.S. 5,093,758 and U.S. 5,188,930. However,
films
produced from linear syndiotactic vinyl aromatic polymers are known to have
poor
tear strength during manufacture and in applications.
Therefore, it would be useful to obtain a syndiotactic vinyl aromatic polymer,
having good heat and chemical resistance, which is melt processable at high
temperatures while maintaining good melt strength such that films having good
tear
strength can be obtained therefrom.
The present invention is directed to films prepared from a composition
comprising a long chain branched syndiotactic vinyl aromatic polymer. Long
chain
branches can be produced during polymerization by polymerizing in the presence
of
a small amount of a difunctional monomer.
The films of the present invention have improved melt and tear strength.
In one embodiment, the present invention is a film prepared from a
composition comprising a long chain branched syndiotactic vinyl aromatic (LCB-
SVA) polymer.
As used herein, the term "syndiotactic" refers to polymers having a
stereoregular structure of greater than 90 percent syndiotactic, preferably
greater
than 95 percent syndiotactic, of a racemic triad as determined by 13C nuclear
magnetic resonance spectroscopy.
_1_
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WO 98/54236 PCT/US98/04676
Syndiotactic vinyl aromatic polymers are homopoiymers and copolymers of
vinyl aromatic monomers, that is, monomers whose chemical structure possess
both
an unsaturated moiety and an aromatic moiety. The preferred vinyl aromatic
monomers have the formula:
H2C=CR-Ar;
wherein R is hydrogen or an alkyl group having from 1 to 4 carbon atoms, and
Ar is
an aromatic radical of from 6 to 10 carbon atoms. F~camples of such vinyl
aromatic
monomers are styrene, alpha-methylstyrene, ortho-methylstyrene, meta-
methylstyrene, pare-methylstyrene, vinyl toluene, pare-t-butylstyrene, and
vinyl
naphthalene; bromo- substituted styrenes, especially p-vinyltoluene and ring
brominated or dibrominated styrenes. Brominated siyrenes are particularly
useful in
the preparation of ignition resistant syndiotacctic vinylaromatic polymers.
Alternatively, ignition resistant LCB-SVA polymers can be produced by
brominating
LCB-SVA polymers. Representative syndiotactic copolymers include styrene-p-
methylstyrene, styrene-p-t-butylstyrene and styrene-vinyl toluene copolymers.
Syndiotactic vinyl aromatic polymers and monomers made therefrom are known in
the art having been previously disclosed in, for example, US-A-4,680,353; US-A-
4,959,435; US-A-4,950,724; and US-A-4,774,301, included herein by reference.
Syndiotactic polystyrene is the currently preferred syndiotactic vinyl
aromatic
polymer.
Long chain branching can be achieved by polymerizing a vinyl aromatic
monomer in the presence of a small amount of a multifunctional monomer under
conditions sufficient to produce a syndiotactic vinyl aromatic polymer. A
multifunctional monomer is any compound having more than one olefinic
functionality which can react with a vinyl aromatic monomer under
polymerization
conditions. Typically, the multifunctional monomer will contain 2-4 olefinic
functionalities and is represented by formula (I):
HC~ CH2
~R)n
-2-
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WO 98/54236 PCT/US98/04676
wherein R is a vinyl group or a group containing from 2 to 20 carbon atoms
including
a terminal vinyl group, wherein the groups containing 2 to 20 carbon atoms may
be
alkyl, alkenyl, cycloalkyi, or aromatic, wherein cycloalkyl groups contain at
least 5
carbon atoms and aromatic groups contain at least 6 carbon atoms, n is an
integer
from 1 to 3 wherein the R groups are mete or pare in relation to the vinyl
group of
formula (I), and when n is greater than 1, R may be the same or different.
Preferably R is a vinyl group.
Preferably the muitiftrncctional monomer contains two terminal vinyl groups
wherein n would equal 1. Typically, such monomers include difunctional vinyl
aromatic monomers such as di-vinyl-benzene or di-styryl-ethane.
The amount of multifunctional monomer will depend upon the weight average
molecular weight (Mw) of the polymer to be produced, but typically is from 10,
preferably from 50, more preferably from 75, and most preferably from 100 ppm
to
1000, preferably to 800, more preferably to 500, and most preferably to 650
ppm,
based on the amount of vinyl aromatic monomer.
The multifunctional monomer can be introduced into the polymerization by
any method which will allow the multifunctional monomer to react with the
vinyl
aromatic monomer during polymerization to produce a LCB-SVA polymer. For
example, the multifunctional monomer can be first dissolved in the vinyl
aromatic
monomer prior to polymerization or introduced separately into the
polymerization
reactor before or during the polymerization. Additionally, the multifunctional
monomer can be dissolved in an inert solvent used in the polymerization such
as
toluene or ethyl benzene.
Any polymerization process which produces syndiotactic vinyl aromatic
polymers can be used to produce the LCB-SVA polymers of the present invention
as
long as a multifunctional monomer is additionally present during
polymerization.
Typical polymerization processes for producing syndiotactic vinyl aromatic
polymers
are well known in the art and are described in US-A-4,680,353, 5,066,741,
5,206,197 and 5,294,685.
Typically, the weight average molecular weight (Mw) of the LCB-SVA polymer is
from 50,000, preferably from 100,000, more preferably from 125,000, and most
preferably from 150,000 to 3,000,000, preferably to 1,000,000, more preferably
to
500,000 and most preferably to 350,000.
A branched syndiotactic vinyl aromatic polymer contains extensions of
syndiotactic vinyl aromatic polymer chain attached to the polymer backbone. A
long
chain branched syndiotactic vinyl aromatic polymer typically contains chain
-3-
CA 02284799 1999-09-21
.. ~; .. ..
extensions of at least 10 monomer repeating units, preferably at least 100,
more
preferably at least 300, and most preferably at least 500 monomer repeating
units.
Typically, the films of the present invention are produced from a composition
of a LCB-SVA polymer without the presence of other polymers. However, films
may
be produced from compositions comprising a LCB-SVA polymer and other
components including other polymers. The amount of LCB-SVA polymer contained
within a composition for producing films is dependent upon the final
application
wherein advantages may be obtained with only small amounts in some instances.
Generally, at least 5 percent by weight of a LCB-SVA polymer is used in a
composition for producing films, typically at least 20 percent, preferably at
least 40
percent, more preferably at least 70 percent and most preferably 100 percent.
Other
polymers which may be included in such compositions include but are not
limited to
linear SPS, polystyrene, polyphenylene oxide, polyolefins, such as
polypropylene,
polyethylene, poly(4-methylpentene), ethylene-propylene copolymers, ethyene-
butene-propylene copolymers, nylons, for example nylon-6, nylon-6,6;
polyesters,
such as polyethylene terephthalate), poly(butylene terephthalate); and
copolymers
or blends thereof. Other materials or additives, including antioxidants,
antiblock
agents such as fine particles of alumina, silica, aluminosilicate, calcium
carbonate,
calcium phosphate, and silicon resins; impact modifiers, ignition resistant
agents,
coupling agents, for example maleated polymers, including malefic anhydride
modified polyphenylene oxide, or malefic anhydride modified syndiotactic
vinylaromatic polymers, binders to improve the wet strength of a base fabric,
flame
retardants including brominated polystyrene, brominated syndiotactic
vinylaromatic
polymers, antimony trioxide, and polytetrafluoroethylene may be added to the
LCB-
SVA polymer composition, the films or articles made therefrom.
The films of the present invention can be obtained as a monolayer film or a
multilayer film structure. Typically, the films of the present invention are
from
approximately 1 ~ to 10 mils (250 microns) thick, however, thicknesses of up
to 50
mils (1250 microns) can be obtained. Additionally, a >ilm sheet can be
obtained
which can have thicknesses of up to 125 mils (3125 microns).
The films of the present invention can be made by various processes
including blowing film and cast/tentering. Typically cast/tentering is used
wherein
the LCB-SVA polymer is heated in a melt extruder and transferred to a vertical
die
wherein the molten polymer is deposited in the form of a continuous sheet or
web on
a large cylinder or casting drum, orientated, stretched as is well known in
the art.
4
AMENDED SHEET
CA 02284799 1999-09-21
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. , . . ~ , o . . . .
:' ~ , ~ ~ ~ . . . .
.. ~ . ~ . ~ ~ ~ a o00 00.
~ ~ . i ~ 0 0
... .. .: .... ~0 00
The films of the present invention can also be coated or laminated with other
films or coatings to add additional properties to the film.
The films of the present invention can be used in optical magnetic media,
electrical, packaging, release film, automotive and construction applications.
The following examples are provided to illustrate the present invention. The
y
examples are not intended to limit the scope of the present invention and they
should not be so interpreted. Amounts are in weight parts or weight
percentages
unless otherwise indicated.
EXAMPLES
EXAMPLE 1-PRODUCTION OF LCB-SPS
All reactions are conducted under inert atmosphere in a dry box. The
reagents, toluene and styrene monomer are purified and handled using standard
inert atmosphere techniques. Di-styryl-ethane is prepared following the
procedure
described in J. Polymer Sci., Part A, Polymer Chem., 32 (1994) 2023 by W.H.
Li, et
al.
Polymerization is conducted in a 5" (12.7 centimeters) Teledyne kneader-
mixer which is described in US-A-5,254,647. A solution of 1.3 wt. percent di-
styryl-
ethane in toluene is added to styrene monomer in the amounts listed in Table I
and
fed to the reactor at 17.5 kg/hr giving a mean residence time of 18 minutes.
The
polymerization is conducted at temperatures of 55 to 67.5°C.
Octahydrofluorenyl
titanium trimethoxide catalyst (.007 M) with necessary amounts of
methylalumoxane
and triisobutylaluminum is fed to the reactor at styrene to titanium mole
ratios of
80,000:1 to 100,000:1. The product is a fine, white-powder ranging in
conversion
from 36 to 50 percent. The samples are collected under nitrogen and quenched
by
the addition of an excess of methanol. The samples are then dried in a
nitrogen-
swept, 220°C, 5mm Hg vacuum oven for two hours. The weight average
molecular
weight (Mw) of the polymer is determined by high temperature size exclusion
chromatography. The results are shown in Table I:
Sample ppm DSE Mw Mn Mz Mw/Mn
1 400 294,900 82,100 1,151, 3.59
900
2 400 334,800 86,500 1,377,300 3.87
3 250 420,000 92,300 2,418,300 4.55
4 250 368,900 71,600 1,962,000 5.15
5
AMENDED SHEET
CA 02284799 1999-09-21
~ ~ ~~ ~~ ~~ ~~ ~~
J O J ~ i 7 7 7 ~ ~ ~ ~ 1 ~ ~ 1
') 7 ) 7 7 ~ f ~ 1
7 ~ ~ i ) 7 7 ~ 7 ~ ~ ~ ~
7 7 7 ) 1 7 f
~I ! ~ . . . J 7 0 7 ~ ~ ~ Q ~ ~
The significant increase in Mz with di-styryl-ethane is an indication of long
chain branching. The above samples, in the form of powders, are converted to
pellets using a 0.5" (1.27 centimeters) single-screw extruder. The molecular
weight
of the pellets are summarized below:
Sample Mw Mn Mz Mw/Mn
279,900 75,000 1,137,400 3.73
2 304,900 82,000 1,161,100 3.72
3 313,000 74,900 1,294,900 4.18
4 301,000 65,000 1;204,900 4.63
Melt strength is measured according to the technique described in Plastics
Engineering, 51, (2), 25, 1995 by S. K. Goyal with the test conditions of 1
in.imin.
(2.54 centimetersiminutes) plunger speed, 50 ft./min. (15.24 meters/minute)
winder
rate and 279°C. Melt flow rate is measured according to ASTM method
D1238 with
the test conditions of 1.2 Kg load and 300°C. A 300,000 Mw linear SPS
polymer is
used as the control. The results are summarized below:
Sample Melt strength(g) MFR (g/10 min.)
1 4.0 19.1
2 5.4 14.4
3 5.5 15.5
4 4.5 17.1
Control 1.9 3.6
The LCB-SPS samples have higher melt strengths and higher melt flow rates
than the linear SPS control sample.
EXAMPLE 2 PREPARATION OF LCB-SPS AND FILM SHEET THEREFROM
Polymerization reactions are carried out in a 5" (12.7 centimeters) Teledyne
kneader-mixer, with mean residence time of 18 minutes, followed by a 500 liter
tank
reactor, with mean residence time of 10 hours. Operation of these devices are
described in US-A-5,254,647. Styrene monomer is mixed with 250 ppm of a 3.3
percent solution of di-styryl-ethane in toluene and fed to the reactor at 17.5
kgJhr.
Polymerization is carried out at a temperature of 55°C. A catalyst
solution of
methyaluminoxane, triisobutylaluminum and octahydrofluorenyltitanium
trimethoxide
is also fed to the reactor at styrene to titanium mole ratios of 80,000:1.
After
6
AMENDED SHEET
CA 02284799 1999-09-21
a s s. .a .. s s a.
a a » a s s s . . a . s s a a
a a a a s s s v s s s s s
a a. s a s s v s s s sss aaa
a » a s s s a a
a» a. ss a.as :»a
polymerization, the polymer is devolatilized and pelletized as described
previously.
The molecular weight of the polymer is determined via high temperature size
exclusion chromatography and the results are shown below:
Mw Mn Mz Mz+1 MwIMn
284,000 61,400 1,049,500 2,178,900 4.63
A 300,000 Mw linear SPS polymer is used as a control.
The LCB-SPS and linear SPS polymers are converted to film sheets using
the following process: The resin pellets are fed into a 1 inch (2.54
centimeters)
Killion single-screw extruder at 300°C, extruded through a slit die,
and quenched in a
casting drum at 88°C to produce 10-mil-thick (250 microns) sheets. The
sheets are
simultaneously, biaxially stretched in an Iwamoto BIX-703 stretcher to become
1-mil
(25 microns) films under the following stretching conditions, stretching
temperature
of 110°C, sample preheating time of 2 minutes, stretching rate of 1200
percent/min.
and a stretch ratio of 3.5 by 3.5. Twenty percent of the linear SPS films
break during
film stretching, while none of the LCB-SPS films break under the same
stretching
conditions. The films produced are annealed with film edges adhered on a metal
frame, in an oven at 220°C for 1 minute.
Tear strengths of the films are measured according to ASTM D1938. The
average tear strength of the LCB-SPS film is 2.67 g/mil (.11 grams/mircon),
which is
44 percent higher than the 1.86 g/mil (.07 grams/micron) of the linear SPS
film.
7
AMENDED SHEET
