U.S. patent application number 09/943540 was filed with the patent office on 2002-03-07 for processing olefin copolymers.
Invention is credited to Fetters, Lewis J., Garcia-Franco, Cesar A., Hadjichristidis, Nikos, Lohse, David J., Mead, David W., Mendelson, Robert A., Milner, Scott T..
Application Number | 20020028896 09/943540 |
Document ID | / |
Family ID | 26693239 |
Filed Date | 2002-03-07 |
United States Patent
Application |
20020028896 |
Kind Code |
A1 |
Garcia-Franco, Cesar A. ; et
al. |
March 7, 2002 |
Processing olefin copolymers
Abstract
The invention is directed to essentially saturated hydrocarbon
polymer composition comprising essentially saturated hydrocarbon
polymers having A) a backbone chain; B) a plurality of essentially
hydrocarbyl sidechains connected to A), said sidechains each having
a number-average molecular weight of from 2500 Daltons to 125,000
Daltons and a MWD by SEC of 1.0-3.5; and having A) a Newtonian
kimiting viscosity (.eta..sub.0) at 190.degree. C. at least 50%
greater than that of a linear olefinic polymer of the same chemical
composition and weight average molecular weight, preferably at
least twice as great as that of said linear polymer, B) a ratio of
the rubbery plateau modulus at 190.degree. C. to that of a linear
polymer of the same chemical composition less than 0.5, preferably
<0.3, C) a ratio of the Newtonian limiting viscosity
(.eta..sub.0) to the absolute value of the complex viscosity in
oscillatory shear (.eta.*)at 100 rad/sec at 190.degree. C. of at
least 5, and D) a ratio of the extensional viscosity measured at a
strain rate of 1 sec.sup.-1, 190.degree. C., and time 3 sec (i.e.,
a strain of 3) to that predicted by linear viscoelasticity at the
same temperature and time of 2 or greater. Ethylene-butene prepared
by anionic polymerization and hydrogenation illustrate and
ethylene-hexene copolymers prepared by coordination polymerization
illustrate the invention. The invention polymers exhibit improved
processing characteristics in that the shear thinning behavior
closely approaches that of ideal polymers and exhibit improved
strain thickening.
Inventors: |
Garcia-Franco, Cesar A.;
(Houston, TX) ; Lohse, David J.; (Bridgewater,
NJ) ; Mendelson, Robert A.; (Houston, TX) ;
Fetters, Lewis J.; (Annandale, NJ) ; Milner, Scott
T.; (Clinton, NJ) ; Hadjichristidis, Nikos;
(Athens, GR) ; Mead, David W.; (Anne Harbor,
MI) |
Correspondence
Address: |
ExxonMobil Chemical Company
P.O. Box 2149
Baytown
TX
77522
US
|
Family ID: |
26693239 |
Appl. No.: |
09/943540 |
Filed: |
August 30, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09943540 |
Aug 30, 2001 |
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09020270 |
Feb 6, 1998 |
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60037149 |
Feb 14, 1997 |
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Current U.S.
Class: |
526/282 ;
526/346; 526/348.2; 526/348.3; 526/348.4; 526/348.5; 526/348.6 |
Current CPC
Class: |
C08L 55/005 20130101;
C08F 255/02 20130101; C08F 290/044 20130101; C08F 290/06 20130101;
C08F 110/02 20130101; C08L 51/06 20130101; C08L 55/005 20130101;
C08F 2500/09 20130101; C08F 290/042 20130101; C08L 2666/02
20130101; C08F 2500/03 20130101; C08L 2666/02 20130101; C08L
2666/04 20130101; C08L 55/00 20130101; C08F 2500/12 20130101; C08F
279/02 20130101; C08L 51/06 20130101; C08L 23/02 20130101; C08L
23/0815 20130101; C08L 23/0815 20130101; C08F 255/00 20130101; C08L
55/005 20130101; C08L 23/02 20130101; C08L 2666/02 20130101; C08L
2666/24 20130101; C08F 110/02 20130101; C08F 257/02 20130101; C08F
297/08 20130101 |
Class at
Publication: |
526/282 ;
526/346; 526/348.2; 526/348.3; 526/348.4; 526/348.5; 526/348.6 |
International
Class: |
C08F 112/02 |
Claims
We claim:
1. A polymer composition comprising essentially saturated
hydrocarbon polymers having: A) a backbone chain; B) a plurality of
essentially hydrocarbon sidechains connected to A), said sidechains
each having a number-average molecular weight of from 2,500 Daltons
to 125,000 Daltons and a MWD by SEC of 1.0-3.5; and, C) and a mass
ratio of sidechains molecular mass to backbone molecular mass of
from 0.01:1 to 100:1.
2. The hydrocarbon polymer composition of claim 1 wherein said mass
ratio is 0.1:1 to 10:1.
3. The hydrocarbon polymer composition of claim 1 wherein said mass
ratio is 0.3:1 to 3:1.
4. The hydrocarbon polymer composition of claim 1 wherein said mass
ratio is 0.5:1 to 2:1.
5. The hydrocarbon polymer composition of claim 1 wherein said
backbone chain and said sidechains are derived from one or more of
ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene,
1-decene, 1-dodecene, 4-methyl-pentene-1, styrene, alkyl styrenes,
norbornene, and alky-substituted norbornenes.
6. The hydrocarbon polymer composition of claim 1 wherein said
backbone chain and said sidechains are essentially of an
ethylene-butene copolymer structure.
7. The hydrocarbon polymer composition of claim 1 wherein said
backbone chain and said sidechains are essentially of an
ethylene-propylene copolymer structure.
8. The hydrocarbon polymer composition of claim 1 wherein said
backbone chain and said sidechains are essentially of an
ethylene-hexene copolymer structure.
9. The hydrocarbon polymer composition of claim 1 wherein said
backbone chain and said sidechains are essentially of an
ethylene-octene copolymer structure.
10. The polymer composition of claim 1 comprising 0.1-99.9 wt. %,
said essentially saturated hydrocarbon polymers and 99.9-0.1 wt %
essentially linear ethylene copolymers of weight-average molecular
weight from about 25,000 Daltons to about 500,000 Daltons, and
having an MWD of from about 1.75-30 and density of 0.85 to
0.96.
11. A polymer composition comprising essentially saturated
hydrocarbon polymers having: A) a Newtonian limiting viscosity
(.eta..sub.0) at 190.degree. C. at least 50% greater than that of a
linear olefinic polymer of the same chemical composition and weight
average molecular weight, preferably at least twice as great as
that of said linear polymer, B) a ratio of the rubbery plateau
modulus at 190.degree. C. to that of a linear polymer of the same
chemical composition less than 0.5, preferably <0.3, C) a ratio
of the Newtonian limiting viscosity (.eta..sub.0) to the absolute
value of the complex viscosity in oscillatory shear (.eta.*)at 100
rad/sec at 190.degree. C. of at least 5.
12. The composition of claim 11 additionally having D) a ratio of
the extensional viscosity measured at a strain rate of 1
sec.sup.-1, 190.degree. C., and time=3 sec (i.e., a strain of 3) to
that predicted by linear viscoelasticity at the same temperature
and time of 2 or greater.
13. The composition of claim 12 comprising 0.1-99.9 wt. %, said
essentially saturated hydrocarbon polymers and 99.9-0.1 wt %
essentially linear ethylene copolymers of weight-average molecular
weight from about 25,000 Daltons to about 500,000 Daltons, and
having an MWD of from about 1.75-30 and density of 0.85 to
0.96.
14. The composition of claim 12 comprising 0.3-50 wt %, said
essentially saturated hydrocarbon polymers and 50.-99.7 wt %
essentially linear ethylene copolymers of weight-average molecular
weight from about 25,000 Daltons to about 500,000 Daltons, and
having an MWD of from about 1.75-8 and density of 0.85-0.93.
15. The composition of claim 12 comprising 0.3-50 wt %, said
essentially saturated hydrocarbon polymers and 50.-99.7 wt %
essentially linear ethylene copolymers of weight-average molecular
weight from about 25,000 Daltons to about 500,000 Daltons, and
having an MWD of from about 1.75-30 and density of 0.93-0.96.
16. The composition of claim 12 comprising 1.0-5 wt. %, said
essentially saturated hydrocarbon polymers and 95-99 wt %
essentially linear ethylene copolymers of weight-average molecular
weight from about 25,000 Daltons to about 500,000 Daltons, and
having an MWD of from about 1.75-8 and density of 0.85-0.93.
17. The composition of claim 12 comprising 1.0-5 wt. %, said
essentially saturated hydrocarbon polymers and 95-99 wt %
essentially linear ethylene copolymers of weight- average molecular
weight from about 25,000 Daltons to about 500,000 Daltons, and
having an MWD of from about 1.75-30 and density of 0.93-0.96.
18. The composition of claim 12 wherein said saturated hydrocarbon
polymers consist of a backbone chain and sidechains derived from
ethylene alone or ethylene and one or more of propylene, 1-butene,
1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene,
4-methyl-pentene-1, styrene, alkyl styrenes, norbomene, and
alky-substituted norbornenes.
19. The composition of claim 18 wherein said backbone chain and
said sidechains are essentially of an ethylene-butene copolymer
structure.
20. The composition of claim 18 wherein said backbone chain and
said sidechains are essentially of an ethylene-hexene copolymer
structure.
21. The composition of claim 18 wherein said backbone chain and
said sidechains are essentially of an ethylene-propylene copolymer
structure.
Description
TECHNICAL FIELD
[0001] The invention relates to improved processing olefin
copolymers having a plurality of substantially linear branches and
to compositions comprising them.
BACKGROUND OF THE INVENTION
[0002] Ethylene copolymers are a well-known class of olefin
copolymers from which various plastic products are now produced.
Such products include films, fibers, and such thermomolded articles
as containers and coatings. The polymers used to prepare these
articles are prepared from ethylene, optionally with one or more
additional copolymerizable monomers. Low density polyethylene
("LDPF") as produced by free radical polymerization consists of
highly branched polymers where the branches occur randomly
throughout the polymer, that is on any number of formed segments or
branches. The structure exhibited easy processing, that is polymers
with it could be melt processed in high volumes at low energy
input. Machinery for conducting this melt processing, for example
extruders and film dies of various configurations, was designed
into product finishing manufacturing processes with optimal design
features based on the processing characteristics of the LDPE.
[0003] However, with the advent of effective coordination catalysis
of ethylene copolymers, the degree of branching was significantly
decreased, both for the now traditional Ziegler-Natta ethylene
copolymers and those from the newer metallocene catalyzed ethylene
copolymers. Both, particularly the metallocene copolymers, are
essentially linear polymers, which are more difficult to melt
process when the molecular weight distribution
(MWD=M.sub.w/M.sub.n, where M.sub.w is weight-average molecular
weight and M.sub.n is number-average molecular weight) is narrower
than about 3.5. Thus broad MWD copolymers are more easily processed
but can lack desirable solid state attributes otherwise available
from the metallocene copolymers. Thus it has become desirable to
develop effective and efficient methods of improving the melt
processing of olefin copolymers while retaining desirable melt
properties and end use characteristics.
[0004] The introduction of long chain branches into substantially
linear olefin copolymers has been observed to improve processing
characteristics of the polymers. Such has been done using
metallocene polymers where significant numbers of olefinically
unsaturated chain ends are produced during the polymerization
reaction. See, e.g., U.S. Pat. No. 5,324,800. The olefinically
unsaturated polymer chains can become "macromonomers" or
"macromers" and, apparently, can be re-inserted with other
copolymerizable monomers to form the branched copolymers.
International publication WO 94/07930 addresses advantages of
including long chain branches in polyethylene from incorporating
vinyl-terminated macromers into polyethylene chains where the
macromers have critical molecular weights greater than 3,800, or,
in other words contain 250 or more carbon atoms. Conditions said to
favor the formation of vinyl terminated polymers are high
temperatures, no comonomer, no transfer agents, and a non-solution
process or a dispersion using an alkane diluent. Increase of
temperature during polymerization is also said to yield 0-hydride
eliminated product, for example while adding ethylene so as to form
an ethylene "end cap". This document goes on to describe a large
class of both monocyclopentadienyl and biscyclopentadienyl
metallocenes as suitable in accordance with the invention when
activated by either alumoxanes or ionizing compounds providing
stabilizing, noncoordinating anions.
[0005] U.S. Pat. Nos. 5,272,236 and 5,278,272 describe
"substantially linear" ethylene polymers which are said to have up
to about 3 long chain branches per 1000 carbon atoms. These
polymers are described as being prepared with certain
monocyclopentadienyl transition metal olefin polymerization
catalysts, such as those described in U.S. Pat. No. 5,026,798. The
copolymer is said to be useful for a variety of fabricated articles
and as a component in blends with other polymers. EP-A-0 659 773 A1
describes a gas phase process using metallocene catalysts said to
be suitable for producing polyethylene with up to 3 long chain
branches per 1000 carbon atoms in the main chain, the branches
having greater than 18 carbon atoms.
[0006] Reduced melt viscosity polymers are addressed in U.S. Pat.
Nos. 5,206,303 and 5,294,678. "Brush" polymer architecture is
described where the branched copolymers have side chains that are
of molecular weights that inhibit entanglement of the backbone
chain. These branch weight-average molecular weights are described
to be from 0.02-2.0 M.sub.e.sup.B, where M.sub.e.sup.B is the
entanglement molecular weight of the side branches. Though the
polymers illustrated are isobutylene-styrene copolymers, calculated
entanglement molecular weights for ethylene polymers and
ethylene-propylene copolymers of 1,250 and 1,660 are provided.
Comb-like polymers of ethylene and longer alpha-olefins, having
from 10 to 100 carbon atoms, are described in U.S. Pat. No.
5,475,075. The polymers are prepared by copolymerizing ethylene and
the longer alpha-olefins which form the side branches. Improvements
in end-use properties, such as for films and adhesive compositions
are taught.
DISCLOSURE OF THE INVENTION
[0007] The invention is directed to a polymer composition
comprising essentially saturated hydrocarbon polymers having: A) a
backbone chain; B) a plurality of essentially hydrocarbon
sidechains connected to A), said sidechains each having a
number-average molecular weight of from 2,500 Daltons to 125,000
Daltons and an MWD by SEC of 1.0- 3.5; and, C) a mass ratio of
sidechains molecular mass to backbone molecular mass of from 0.01:1
to 100:1. These invention compositions comprise essentially
saturated hydrocarbon polymers having: A) a Newtonian limiting
viscosity (,no) at 190.degree. C. at least 50% greater than that of
a linear olefinic polymer of the same chemical composition and
weight average molecular weight, preferably at least twice as great
as that of said linear polymer, B) a ratio of the rubbery plateau
modulus at 190.degree. C. to that of a linear polymer of the same
chemical composition less than 0.5, preferably <0.3, C) a ratio
of the Newtonian limiting viscosity (.eta..sub.0) to the absolute
value of the complex viscosity in oscillatory shear (.eta.*) at 100
rad/sec at 190.degree. C. of at least 5, and D) a ratio of the
extensional viscosity measured at a strain rate of 1 sec.sup.-1,
190.degree. C., and time=3 sec (i.e., a strain of 3) to that
predicted by linear viscoelasticity at the same temperature and
time of 2 or greater. The invention polymers exhibit highly
improved processing properties, improved shear thinning properties
and melt strength.
BRIEF DESCRIPTION OF DRAWINGS
[0008] FIGS. I-IV illustrate viscometric data of an ethylene-butene
copolymer of the invention in comparison with similarly obtained
data for traditional low density polyethylene (LDPE) and
metallocene low density polyethylenes (LLDPE). FIG. I illustrates
the complex viscosity vs. the frequency of oscillatory deformation
at 190.degree. C. FIG. II illustrates the normalized viscosity vs.
the frequency times the zero shear viscosity at 190.degree. C. FIG.
III illustrates the storage modulus vs. the frequency at
190.degree. C. FIG. IV illustrates the storage modulus vs. the
frequency times the zero shear viscosity at 190.degree. C. FIG. V
illustrates the relation between the extensional viscosity
(.eta..sub.ext (linear)) and that measured (.eta..sub.ext (meas))
for a polymer that shows significant strain hardening.
DETAILED DESCRIPTION OF THE INVENTION
[0009] The branched hydrocarbon copolymers according to the
invention can be described as those having a main, or backbone
chain, of ethylene and other insertion copolymerizable monomers,
containing randomly distributed side chains of ethylene and other
insertion copolymerizable monomers. The backbone chain has a
weight-average molecular weight from about 5,000 to about 1,000,000
Daltons, preferably from about 10,000 to about 500,000 Daltons,
most preferably from about 20,000 to about 200,000 Daltons. The
side chains have weight-average molecular weights from about 2,500
to about 125,000 Daltons, preferably from about 3,000 to about
80,000 Daltons, most preferably from about 4,000 to about 60,000
Daltons. As expressed in M.sub.e.sup.B, side chains have
weight-average molecular weights ranging from above 2 to 100 times
the entanglement weight of copolymer, preferably 3-70 times the
entanglement weight of copolymer, and most preferably 4-50 times
the entanglement weight of copolymer. The number of side chains per
backbone chain is determined by the average spacing between the
branches, the backbone segment between each branch averaging a
weight average of at least twice the entanglement molecular weight
of polyethylene, preferably 3 to 25 times the entanglement
molecular weight of polyethylene. In practice this establishes a
number of arms of from 2-100, preferably 2-70, most preferably
3-50.
[0010] The MWD, defined as the ratio of weight-average molecular
weight to number-average molecular weight, for both the backbone
chain and the sidechains, independently, can be from 1.0-6,
preferably 1-5, and most preferably 1-3.5.
Rheological Properties
[0011] Definition of linear viscoelastic behavior of polymeric
materials is complex, but utilizes well known concepts. Thus, the
invention may be described in terms of melt rheological parameters
including the Newtonian limiting viscosity, the rubbery plateau
modulus, and in terms of "shear thinning" characteristics readily
quantified in terms of the ratio of the Newtonian limiting
viscosity (.eta..sub.0) to the absolute value of the complex
viscosity in oscillatory shear (.eta.*) at 100 rad/sec at
190.degree. C. Shear thinning may be characterized by the ratio of
the Newtonian viscosity (.eta..sub.0) to viscosity the complex
viscosity at an arbitrarily chosen frequency of 100 rad/sec
(.eta.*.sub.100). This .eta..sub.0 may be measured in various ways
well known to those skilled in the art. Included among these are
rotational oscillatory shear rheometry and totaional steady shear
rheometry, including shear creep. The value of .eta..sub.0 may be
obtained from these methods by direct observation of the frequency
independent or shear rate independent value of viscosity, or it may
be determined from an appropriate fitting equation such as the
Cross equation when the data extend into the Newtonian region.
Alternative data handling methods included evaluating the limiting
value of the ratio of the loss modulus to frequency, G"/.omega., at
low frequency:
.eta..sub.0=lim G"/.omega..vertline..sub..omega..fwdarw.0,
[0012] or by linearly extrapolating the reciprocal of viscosity vs.
shear stress to zero shear stress (e.g., G. V. Vmogradov, A- Ya.
Maikin, Rheology of Polymers, Mir Publications Moscow,
Springer-Verlag, p.153 (1980)). Direct observation of the frequency
independent value of the complex viscosity, .eta.*, from rotational
oscillatory shear and/or the fitting of the Cross equation to the
same data were the methods used for this description.
[0013] At low frequencies the melt viscosity expressed as the
absolute value of the complex viscosity (.eta.*) of high polymers
is independent of the frequency, i.e., it is constant with
frequency and is called the Newtonian limiting viscosity,
.eta..sub.0. At increasing frequencies .eta.* decreases with
increasing frequency in a manner determined by its relaxation
spectrum and this decrease in viscosity is called shear thining
(or, pseudoplasticity in earlier nomenclature). The plateau modulus
may be defined in several interrelated ways, e.g., the value of the
storage modulus (real part of the complex modulus), G', in a region
of G' constant with frequency, or the value of G' at the frequency
of a minimum in the loss modulus (imaginary part of the complex
modulus), G", or the value of G' at the minimum in tan .delta.,
where tan .delta.=G"/ G', or other definitions which lead to
similar answers. For purposes of the description we chose to use
the ratio of the Newtonian viscosity to the complex viscosity as
discussed above.
[0014] Definitions and description of these and other parameters
discussed here may be found, e.g., in Ferry (J. D. Ferry,
Viscoelastic Properties of Polymers, 3rd Ed., John Wiley &
Sons, N.Y., 1980) and in Dealy and Wissbrun (J. M. Dealy, K F.
Wissbrun, Melt Rheology and Its Role in Plastics Processing. Theory
and Applications, Van Nostrand Reinhold, N.Y., 1990). The methods
of measurement, e.g., rotational oscillatory shear between parallel
circular plates in an instrument such as a Rheometrics Scientific
Mechanical Spectrometer, and data treatment, e.g., interconversion
of complex variable Theological parameters and time-temperature
superposition, are also well known and frequently used by those of
ordinary skill in the art. Again, these are largely described in
the above references and in numerous other texts and peer-reviewed
publications in the field.
[0015] The ability of a polymer to exhibit strain hardening under
extension (i.e., or increase of the extensional viscosity with
strain rate) has been shown to correlate with the melt strength of
that polymer and the ease of forming a bubble from it as in blown
film operations in industry. A measure of the strain hardening can
be given as follows. One can predict what the extensional viscosity
would be if the polymer obeyed linear viscoelasticity through the
model of Chang and Lodge (Chang, H.; and Lodge, A- S.; Rheologica
Acta, 11, pp. 127-129 (1972)). This is shown in the FIG. V as
.eta..sub.ext,(linear). This can be compared to the experimentally
measured viscosity, called .eta..sub.ext (measured) in the figure.
The sharp rise of next (measured) over the predicted value
.eta..sub.ext (linear) is the result of strain hardening. To
extract a number from the data that expresses the degree of this
strain hardening, we selected the value of .eta..sub.ext (measured)
at conditions characteristic of film blowing--a strain rate of 1
secd.sup.-1, temperature of 190.degree. C., and time of 3 sec. The
ratio then becomes the measured value divided by that predicted by
the Chang and Lodge model at the same temperature and time. This
ratio must be greater than 2 for clear evidence of strain
hardening, so it can be represented as the following:
.eta..sub.ext
(measured)/.eta..sub.ext(linear).ident..eta..sub.extratio.gt-
oreq.2.
[0016] Polymer melt elongation (or extension) is another important
deformation in polymer processing. It is the dominant deformation
in film blowing, blow molding, melt spinning, and in the biaxial
stretching of extruded sheets. Often, an extensional deformation
producing molecular orientations takes place immediately before
solidification resulting in anisotropy of the end-use properties.
Extensional rheometry data are very sensitive to the molecular
structure of a polymer system therefore, these data is a valuable
tool for polymer characterization.
[0017] The time dependent uniaxial extensional viscosity was
measured with a Rheometrics Scientific Melt Elongational Rheometer
(Row). The RME is an elongational rheometer for high elongations of
polymer melts. The sample is supported by an inert gas, heated to
the test temperature by electrical heaters mounted in the side
plates of the rheometer. The temperature is controlled from ambient
to 350.degree. C. The polymer melt sample is extended homogeneously
by two metal belt clamps, each consisting of two metal belts with
its fixtures. The metal belts control a range of extensional strain
rates from 0.0001 to 1.0 s.sup.-1. The forces generated by the
sample are measured by a spring type transducer with a range from
0.001 to 2.0 N. The maximum Hencky strain achievable by this
instrument is 7 ( stretch ratio=1100). This instrument is based
upon a published design, see Meissner, J., and J. Hostettler,
Rheological Acta, 33, 1-21 (1994), and is available from
Rheometrics Scientific, Inc.
[0018] The rheological behavior of these polymers with controlled
branching shows surprising and useful features. These polymers have
a zero-shear viscosity that is larger than a linear polymer of the
same molecular weight. They show a rapid drop in viscosity with
shear rate (large degree of shear thinning); and a plateau modulus
that is at least two times lower than that of prior art linear and
branched polymers. This latter characteristic is especially
surprising, since ethylene polymers of various types exhibit
essentially the same plateau modulus. This was thought to be
intrinsic to the monomer type and not dependent on polymer
architecture. The lower plateau modulus means that the comb
polymers likely are much less entangled than the linears, thus
giving it such low viscosity for their molecular weight. The
utility of these properties of the invention polymers is that they
have a very low viscosity for its molecular weights under melt
processing conditions and so will process much more easily than the
prior art polymers while exhibiting increased extensional viscosity
indicative of increased melt strength.
Polymer Preparation
[0019] Initial studies conducted to determine optimum polymer
structures suitable for the improved properties sought were based
on knowledge as to production of hydrocarbon polymers with
precisely controlled structures through the saturation of
anionically synthesized polydienes. Various polydienes can be
saturated to give structures that are identical to polyolefins as
was reported by Rachapudy, H.; Smith, G. G.; Raju, V. R.;
Graessley, W. W.; J. Polym. Sci.--Phys. 1979, 17, 1211. The
techniques completely saturate the polydiene without any side
reactions that might degrade or crosslink the molecules. The
controlled molecular weight and structure available from anionic
polymerization of conjugated dienes are thus preserved. A unit of
butadiene that has been incorporated 1, 4 into the polybutadiene
chain will have the structure of two ethylenes (four methylenes)
after saturation, and those that go in as 1, 2 will be like one
butene unit. So the saturated versions of polybutadienes of a range
of microstructures are identical in structure to a series of
ethylene-butene copolymers. Similarly saturated polyisoprenes
resemble an alternating ethylene-propylene copolymer, and other
polydienes can give the structures of polypropylene and other
polyolefins upon saturation. A wide variety of saturated
hydrocarbon polymers can be made in this way.
[0020] Thus linear ethylene-butene copolymers can be made by the
saturation of linear polybutadienes and linear ethylene-propylene
copolymers of the invention can be made by the saturation of linear
polyisoprenes. The linear polymers can be prepared by anionic
synthesis on a vacuum line in accordance with the teachings of
Morton, M.; Fetters, L. J.; Rubber Chem. & Technol. 1975, 48,
359. The polymers of the invention made in this manner were
prepared in cyclohexane at -0.degree. C., with butyllithium as
initiator. The polydiene polymers were then saturated under H.sub.2
pressure using a Pd/CaCO.sub.3 catalyst of J. Polym. Sci.--Phys.
1979, 17, 1211, above. This technique can be used to make polymers
over a wide range of molecular weights, e.g. polymers with
molecular weights from 3,500 to 800,000.
[0021] The branched polymers of the invention can be made by
attaching one or more linear polymers, prepared as above, as
branches to another of the linear polymers serving as a backbone or
main chain polymer. The general method is to produce branch or arm
linear polymers by the procedure above, using the butyllithium
initiator; this produces a polybutadiene with a lithium ion at the
terminal end. A linear backbone is made in the manner described
above, some number of the pendant vinyl double bonds on the
backbone polymers are then reacted with (CH.sub.3).sub.2SiClH using
a platinum divinyl tetramethyl disiloxane catalyst. The lithium
ends of the arm polybutadiene polymers then are reacted with the
remaining chiorines on the backbone polybutadiene vinyls, attaching
the arms. Because both the placement of the vinyl groups in the
backbone and the hydrosilylation reaction are random, so is the
distribution of arms along and among the backbone molecules. These
polybutadiene combs can be saturated as shown above to form
ethylene-butene copolymer combs with nearly monodisperse branches
randomly placed on a nearly monodisperse backbone. Polymers having
two branches can be made by a similar synthetic procedure. Four
anionically synthesized polymers (arms) are attached to the ends of
a separately synthesized polymer ("connector"), two at each end.
This results in an H-shaped structure, i.e., a symmetric placement
of the arms and non-random distribution of the of arms of the
molecule.
[0022] An alternate method of preparing the branched olefin
copolymers of the invention, particularly ethylene copolymers, is
by preparing olefinically unsaturated macromers having molecular
weight attributes within that described for the branch or arm
polymers or copolymers and incorporating those into a branched
polymer by copolymerization. Such can be done, for example, by
preparing branch macromers from olefins such that there is vinyl or
vinylidene unsaturation at or near the macromer chain end. Such is
known in the art and the teachings of the background art as to the
use of metallocenes to prepare these macromers, and then to insert
or incorporate the macromers into a forming polymer as long chain
branches, are applicable in this regard. Each of U.S. Pat. No.
5,324,800 and international publication WO 94/07930 are
incorporated by reference for purposes of U.S. patent practice.
Such can be accomplished by the use of series reactions or in situ
single processes where the selection of catalyst or catalyst mix
allows for the preparation of olefinically unsaturated macromers
and subsequent incorporation of them into forming polymeric
chains.
[0023] In order to assure the quality and number of branches
sought, it is suitable to use a multistep reaction process wherein
one or more branch macromers are prepared and subsequently
introduced into a reaction medium with a catalyst capable of
coordination copolymerization of both the macromer and other
coordination polymerizable monomers. The macromer preparation
preferably is conducted so as to prepare narrow MWD macromers,
e.g., 2.0-3.5, or even lower when polymerization conditions and
catalyst selection permit. The comonomer distribution can be either
narrow or broad, or the macromer can be a homopolymeric macromer.
The use of essentially single site catalysts, such as metallocene
catalysts, permits of the sought narrow MWD. Branch separation, or
stated alternatively, branch numbers by molecular weight of the
backbone chain, is typically controlled by assuring that the
reactivity ratios of the macromers to the copolymerizable monomers
is in a ratio that allows the preferred ranges for the branch
structure as described above. Such can be determined empirically
within the skill in the art. Factors to be adjusted include:
catalyst selection, temperature, pressure, and time of reaction,
and reactant concentrations, all as is well-known in the art.
[0024] In this manner, branched copolymers are made directly
without hydrogenation and the selection of comonomers is extended
to the full extent allowed by insertion or coordination
polymerization. Useful comonomers include ethylene, propylene,
1-butene, isobutylene, 1-hexene, 1-octene, and higher
alpha-olefins; styrene, cyclopentene, norbornene, and higher carbon
number cyclic olefins; alkyl-substituted styrene or ;
alkyl-substituted norbornene; ethylidene norbornene, vinyl
norbornene, 1,4-hexadiene, and other non-conjugated diolefins. Such
monomers can be homopolymerized or copolymerized, with two or more
copolymerizable monomers, into either or both of the branch
macromers or backbone chains along with the macromers. The
teachings of co-pending U.S. provisional patent application Ser.
No.60/037323 (Attorney Docket No. 96B006) filed Feb. 7, 1997, is
incorporated by reference for purposes of U.S. patent practice. See
also the examples below where a mixed zirconocene catalyst was used
in a fluidzed gas phase polymerization of an ethylene-hexene
copolymer product which contained component copolymer fractions
meeting the limiting elements of the invention described
herein.
Industrial Applicability
[0025] The branched polyethylene copolymers according to the
invention will have utility both as neat polymers and as a portion
or fraction of ethylene copolymer blend compositions. As neat
polymers, the polymers have utility as film polymers or as adhesive
components, the discussion of WO 94/07930 being illustrative. The
fabricated articles of U.S. Pat. Nos. 5,272,236 and 5,278,272 are
additionally illustrative.
[0026] The copolymers of the invention will also have utility in
blends, those blends comprising the branched copolymer of the
invention at from 0.1-99.9 wt. %, preferably from 0.3-50 wt. %,
more preferably 0.5-25 wt. %, and even more preferably 1.0-5 wt %,
the remainder comprising an essentially linear ethylene copolymer
of weight-average molecular weight from about 25,000 Daltons to
about 500,000 Daltons, typically those having an MWD of from about
1.75-30, preferably 1.75-8.0, and more preferably 1.9-4.0, with
densities form 0.85 to 0.96, preferably 0.85 to 0.93, as
exemplified by the commercial polymers used for comparison in this
application. The blends in accordance with the invention may
additionally comprise conventional additives or adjuvants in
conventional amounts for conventional purposes. The blends
according to the invention exhibit improved processing, largely due
to the inclusion of the branched ethylene copolymer according to
the invention, and can be more easily processed in conventional
equipment.
EXAMPLES
Example 1--Preparation of C1
[0027] A comb polybutadiene polymer (PBd) was prepared by coupling
hydrosilylated polybutadiene backbone chains with
polybutadienyllithium sidechains, or branches. The polybutadiene
which was used as backbone for the hydrosilylation reaction was
prepared by anionic polymerization using high vacuum techniques,
with sec-BuLi in benzene at room temperature.
(Characterization=M.sub.n106,500 by size exclusion chromatography
(SEC) based upon a polybutadiene standard; 10% 1,2 units). 10 grams
of this backbone polymer chain were dissolved in 120 ml
tetrahydrofuran (THF) in an one-liter round bottom flask equipped
with a good condenser, to which 3 drops of platinum divinyl
tetramethyl disiloxane complex in xylene (catalyst, Petrarch PC072)
were added. The solution was dried overnight with 1.5 ml
trimethylchworosilane, followed by the addition of 7.55 mmole
dimethylchworosilane. The mixture's temperature was raised slowly
to 70.degree. C. Changing of the color, vigorous boiling and
refluxing indicated the start of the reaction which was continued
for 24 hours at 70.degree. C. THF and chlorosilane compounds were
removed in the vacuum line by heating the polymer at 45.degree. C
for 5 days. The hydrosilylated polymer was freeze dried under high
vacuum for 2 days.
[0028] Living polybutadiene branch polymers (PBdLi, M.sub.n=6,400
by SEC; T3) used for the coupling reaction was prepared in the same
manner as the backbone. The synthesis of PBdLi was performed by
reacting 12.75 grams of butadiene monomer with 2.550 mmoles of
initiator. Prior to the coupling reaction 1 gram of PBdLi was
removed, terminated with methanol and used for characterization.
40% excess of PBdLi was used for the coupling reaction, which was
monitored by SEC and allowed to proceed for 2 weeks. Excess PBdLi
was terminated with methanol. The comb polymer was protected
against oxidation by 2,6-di-tert-butyl-p-cresol and was
fractionated in a toluene-methanol system. Fractionation was
performed until no arm or undesirable products were shown to be
present by SEC. The comb was finally precipitated in methanol
containing antioxidant, dried and stored under vacuum in the dark.
Characterization, which was carried out by SEC, membrane osmometry
(MO), vapor pressure osmometry (VPO), low-angle laser light
scattering (LALLS), and laser differential refractometry, indicated
the high degree of molecular and compositional homogeneity.
Molecular characterization results are shown in Table I. Using the
M.sub.n (MO, VPO) and M.sub.w (LALLS) of Table I the number of arms
experimentally obtained is calculated, which is smaller than the
theoretically expected, indicating a small yield in the
hydrosilylation reaction. Fractionation and characterization
results are shown in Table I and II.
[0029] The number of branches, or sidechains, was determined by
both .sup.13C-NMR and .sup.1H-NMR. Resonances characteristic of
methyl groups adjacent to a Si atom (at the point of connection to
the backbone) was found from both methods: similarly, resonances
characteristic of the methyl adjacent of the methine in a sec-butyl
group (at the terminus of the arm from the initiator used to
polymerize it) was measured. From the combination of these methods,
the number of arms per 10,000 carbons was found to be 15+5, which
is consistent with 34 arms for this example.
[0030] The resulting comb (branched polybutadiene polymer) ("C1")
was saturated catalytically. 3 grams of the comb polymer were
dissolved in cyclohexane and reacted with H.sub.2 gas at 90.degree.
C. and 700 psi in the presence of 3 g of a catalyst made by
supporting Pd on CaCO3. The reaction was allowed to proceed until
the H.sub.2 pressure stopped dropping, or about 24 h. The polymer
solution was then filtered to remove the catalyst residues. The
saturation of the polymer was seen to be greater than 99.5% by
proton NMR. The polymer was thus converted by hydrogenation to an
ethylene-butene branched copolymer. See Tables I and II, below.
Example 2--Preparation of C2
[0031] 8 grams of PBd (M.sub.n=87,000 by MO, prepared as described
in Example 1; BB.sub.3) dissolved in 150 ml THF were hydrosilylated
in the same manner as described in Example 1, using 0.5 ml of
trimethylchiorosilane and 2.43 mmoles of dimethylchlorosilane. The
hydrosilylated polymer was freeze dried under high vacuum for 5
days. PBdLi (M, =4,500 by VPO; T.sub.5) was prepared as described
in Example 1 by reacting 11.5 grams of butadiene with 2.550 mmoles
of initiator. 1 gram of T.sub.5 was removed in order to be used for
characterization purposes. The coupling reaction was accomplished
as described in Example 1. Fractionation and characterization
results are shown in Table I and Table II.
[0032] The resulting comb PBd (C2) was saturated catalytically as
in Example 3. The saturation of the polymer was seen to be greater
than 99.5% by proton NMR. The resulting saturated polymer had an
M.sub.w of 97,000 by LALLS.
Example 3--Preparation of C3
[0033] 2 grams of PBd (M.sub.n=108,000 by SEC, prepared as
described in Example 1; BB4) dissolved in 50 ml THF were
hydrosilylated in the same manner as described in Example 1, using
0.5 ml of trimethylchlorosilane and 0.77 mmoles of
dimethylchiorosilane. The hydrosilylated polymer was freeze dried
under high vacuum for 2 days. PBdLi (M.sub.n=23,000 by SEC; T6) was
prepared as described in Example 1 by reacting 22 grams of
butadiene with 0.936 mmoles of initiator. 1 gram of T6 was removed
in order to be used for characterization purposes. The coupling
reaction was accomplished as described in Example 2. Fractionation
and characterization results are shown in Table I and Table II.
[0034] The resulting comb PBd (C3) was saturated catalytically as
in Example 3. The saturation of the polymer was seen to be greater
than 99.5% by proton NMR. The resulting saturated polymer had an
M.sub.w of 598,000 by LALLS.
Example 4--Preparation of C4
[0035] 6 grams of PBd (M.sub.n=100,000 by SEC, prepared as
described in Example 1; BB5) dissolved in 60 ml THF were
hydrosilylated in the same manner as described in Example 1, using
1.0 ml of trimethylchlorosilane and 3.83 mmoles of
dimethylchlorosilane. The hydrosilylated polymer was freeze dried
under high vacuum for 2 days. PBdLi (M.sub.n=5,100 by SEC; T7) was
prepared as described in Example 1 by reacting 27 grams of
butadiene with 5.370 mmoles of initiator. 1 gram of T7 was removed
in order to be used for characterization purposes. The coupling
reaction was accomplished as described in Example 2. Fractionation
and characterization results are shown in Table I and Table II. The
resulting comb PBd (C4) was saturated catalytically as in Example
3. The saturation of the polymer was seen to be greater than 99.5%
by proton NMR.
1TABLE I Molecular characteristics of precursors and final
polymers. 10.sup.-3 M.sub.n 10.sup.-3 M.sub.n 10.sup.-3 M.sub.w
10.sup.-3 M.sub.w Part Sample (SEC).sup.a (MO).sup.b (LALLS).sup.c
(VpO).sup.d M.sub.w/M.sub.n Backbone BB.sub.2 106.5 101 103 -- 1.05
Arm T.sub.3 6.4 -- -- 6.5 1.03 Comb Cl 274 -- -- 1.07 Backbone
BB.sub.3 99.0 87 90.0 -- 1.04 Arm T.sub.5 4.8 -- -- 4.5 1.05 Comb
C2 -- 105.5 107 1.08 Backbone BB.sub.4 108 97 104 1.05 Arm T.sub.6
23 23.5 1.04 Comb C3 -- 612 1.07 Backbone BB.sub.5 100 100.5 -- --
1.04 Arm T.sub.7 51 -- -- 4.75 1.04 Comb C4 -- 194 198 -- 1.04
.sup.aTHF at 30.degree. C., Phenomenex columns (Type P Phenogel 5
linear, pore size: 50 to 10.sup.6.ANG.). .sup.bToluene at
35.degree. C., Model 231, Wescan. .sup.cCyclohexane at 30.degree.
C., KMX-6, Chromatix. .sup.dToluene at 50.degree. C., Model 833,
Jupiter Instrument Company.
[0036]
2TABLE II Number of arms Comb Maximum possible.sup.a
Calculated.sup.b Measured.sup.d Yield (%) C1 100 29.sup.c 34 29-34
C2 -- 3.9.sup. 2.4 -- C3 -- 22.sup.c -- -- C4 -- 19.sup.c -- --
.sup.aFrom total number of pendant vinyl groups. .sup.bCalculated
from M.sub.n by MO and VPO. .sup.cCalculated from M.sub.w by LALLS.
.sup.dMeasured by .sup.13C-NMR.
Example 5--Preparation of Blend 1
[0037] Blend 1:6.8685 g of EXCEED(.RTM. 103 ("ECD103"), a
commercially available ethylene-l-hexene linear low density
polyethylene of Exxon Chemical Co. having a density of 0.917 and MI
of 1.0, and 0.1405 g of C1 (above) were dissolved in 100 ml of
xylene at 130.degree. C. 0.0249 g of a stabilizer package (a 1:2
mixture of Irganox.RTM. 1076 and Irgafos.RTM.168 from Ciba-Geigy,
Inc.) was also added. The solution was allowed to mix for 2 hours
at 130 .degree. C., and then the polymer blend was precipitated by
adding the xylene solution to 1800 ml of methanol chilled to 2
.degree. C. The precipitate was washed with more methanol, and the
remaining xylene was removed by drying in a vacuum oven at 88
.degree. C for two days.
Example 6--Preparation of Blend 2
[0038] Blend 2 : 6.8607 g of the EXCEED.RTM. 103 (ECD103), 0.1402 g
of C3 (above) and 0.0248 of the stabilizer package were mixed in
the same manner as Blend 1.
H-shaped Polymer Examples
Example 7--Preparation of HI
Preparation of Arms
[0039] 6.3 ml (5.0 g) 1,3-butadiene was diluted in 75 ml benzene
(6.1% w/v). To this solution was added 16.3 ml sec-BuLi 0.062M in
n-hexane (1.01.times.10.sup.-3 mol sec-BuLi). After 24 h at room
temperature the reaction was complete. 1.0 g of the product
polybutadiene (Y; M.sub.n=5,500 by SEC) in 18 ml solution was
removed for the characterization procedure and the rest of Y was
mixed with 8.3 ml CH.sub.3SiCl.sub.3 0.046 M in benzene
(0.38.times.10.sup.-4 mol CH.sub.3SiCl.sub.3). After 7 days at room
temperature the reaction was complete and the Y.sub.2Si(CH.sub.3)Cl
was formed.
Preparation of Connector
[0040] A difunctional initiator was prepared by the addition of
sec-butyl lithium to 1,3-bis(1-phenyl ethenyl) benzene, resulting
in 1,3-bis(1-phenyl -3 methyl pentyl lithium) benzene, called here
DLI. 15.4 ml (11.4 g) 1,3-butadiene was diluted in 355 ml benzene
(2.3% w/v). To this solution was added 33.8 ml of DLI 0.0225M in
benzene (7.3.times.10.sup.-4 mol DLI) and 8.4 ml of sec-BuLi 0.10M
in benzene (8.36.times.10.sup.-4 mol sec-BuLi). After 4 days at
room temperature the reaction was complete. 1.0 g of the product
difunctional polybutadiene (X; M.sub.n=27,100 by SEC;
M.sub.w=24,500 by LALLS) in 35 ml solution was removed for the
characterization procedure. 4.8 g of X in 175 ml solution was
removed for the formation of the
Y.sub.2Si(CH.sub.3)X(CH.sub.3)SiY.su- b.2.
Formation of H1
[0041] 4.0 g of Y.sub.2Si(CH3)Cl and 34.8 g of X were mixed. To the
solution was added 1.0 ml THF. After 7 days at room temperature the
formation of the Hi was complete. H1 comprised a structure having a
backbone of about 38,000 M.sub.n plus tow Y arms and two brancheds
each of about 5,500 Mn (Y arms).
Fractionation
[0042] The product of the previous reaction was precipitated in
1000 ml methanol and was redissolved in 900 ml toluene (1% w/v).
450 ml methanol was added and the solution was stirred at room
temperature to reach the cloud-point. After that 20 more ml of
methanol were added and the temperature was increased slowly, until
the solution became clear. Then it was left to cool down and next
day the separated part of the H1 was collected, as the lower phase
in a two-phase system. To the upper phase was added 25 ml methanol,
to reach again the cloud-point and then 20 ml more methanol. The
temperature was increased slowly and after the clearance of the
solution, it was left to cool down. The newly separated part of the
Hi was mixed with the previous part from the first fractionation
and it composed the final pure H1. By LALLS the H1 had an M.sub.w
of 50,000.
Saturation
[0043] The H1 was saturated in the same manner as in Example 3,
except that 0.2 g of triphenyl phosphate and 0.0366 g of
tris(triphenyl phosphine)rhodium(I)chloride were added to the
reaction for every gram of polymer. Essentially complete saturation
was achieved. The resulting saturated polymer had an Mw of 48,000
by LALLS.
Example 8--Preparation of H2
Preparation of Arms
[0044] 9.0 ml (6.7 g) 1,3-butadiene was diluted in 65 ml benzene
(10.3% w/v). To this solution was added 10.7 ml sec-BuLi 0.062M in
n-hexane (6.66.times.10.sup.-4 mol sec-BuLi). After 24 h at room
temperature the reaction was complete. 1.0 g of the product
polybutadiene (Z; M.sub.n=11,000 by SEC; M.sub.w=10,800 by LALLS)
in 13 ml solution was removed for the characterization procedure
and the rest of Z was mixed with 5.8 ml of CH3SiCl.sub.3 0.046M in
benzene (0.27.times.10.sup.-3 mol CH.sub.3SiCl.sub.3). After 7 days
at room temperature the reaction was complete and the
Z.sub.2Si(CH.sub.3)Cl was formed.
Preparation of Connector
[0045] 3.4 g of X in 125 ml solution was removed for the formation
of the Z.sub.2Si(CH.sub.3)X(CH.sub.3)SiZ.sub.2 (H2) in the manner
of Example 7.
Formation of H2
[0046] 5.7 g of Z2Si(CH.sub.3)Cl and 3.4 g of X were mixed. To the
solution was added 1.0 ml ThF. After 7 days at room temperature the
formation of the H2 was complete. H2 had a resulting H-shaped
structure like H1.
Fractionation
[0047] The procedure followed was the same as in Example 7. The
resulting polymer had an M.sub.w of 67,000 by LALLS.
Hydrogenation
[0048] The procedure followed was the same as in Example 7. The
resulting saturated polymer had an M.sub.w of 64,700 by LALLS.
Rheological Properties of Examples
[0049] The melt shear rheological behavior of the various resulting
copolymer examples was measured by well known methodology, i.e.,
rotational sinusoidal oscillatory shear between parallel plates in
a Rheometrics Scientific RMS-800 Mechanical Spectrometer. Frequency
ranges of from 0.1 to 100 rad/sec or from 0.1 to ca. 250 rad/sec or
from 0.1 to ca. 400 rad/sec or from 0.01 to 100 rad/sec or from 100
to 0.01 rad/sec were covered at a sequence of temperatures ranging
from 120.degree. C. to 250.degree. C. and in some cases to as high
as 330.degree. C. Typically, the examples were tested at isothermal
conditions from 0.1 to 100 rad/sec or to ca. 250 rad/sec at
120.degree. C., 150.degree. C., 170.degree. C., 190.degree. C., and
220.degree. C., successively, and then from 0.01 to 100 rad/sec at
250.degree. C., 280.degree. C. or higher as necessary to access the
terminal linear viscoelastic regime. Repeat testing was
periodically performed on the same specimens at 150.degree. C.
(sometimes at 220.degree. C.) to check reproducibility. All
measurements were performed at strains within the linear
viscoelastic regime, and either one or two specimens were used to
cover all temperatures tested. The parallel plates were 25mm in
diameter and the gap between the plates (sample thickness) was
precisely set at values from ca. 1.6 mm to 2.3 mm for different
test specimens and temperatures. Use of successive temperature
testing on single specimens requires compensation for tooling
expansion with increasing set temperature in order to maintain
constant gap distance at all temperatures. This was accomplished in
all cases by raising the upper platen (plate) at each new increased
temperature by the amount 0.0029 mm/.degree. C. Additionally, in
some cases sample expansion evidenced by normal stress increase was
compensated by maintaining a constant (low) normal stress in the
sample at the various temperatures. The above methods are all well
known to practicing rheologists. All samples were stabilized by
addition of 1%(wt) of a 1:2 mixture of Irganox.RTM.
1076/Irgafos.RTM.D 168 (Ciba-Geigy, Inc.) prior to compression
molding test specimens in a Carver Laboratory Press.
[0050] The resultant linear viscoelastic data, which may be
expressed in numerous ways, but here were expressed as complex
viscosity, .eta.*, elastic storage modulus, G', loss modulus, G",
and complex modulus, G*, were then superimposed to the 190.degree.
C. reference temperature by well known time-temperature
superposition methodology, yielding master curves of the above
parameters vs. frequency over up to seven orders of magnitude of
frequency from the terminal regime through the rubbery plateau
region (where possible). Superposition specifically was performed
by vertical shifting of the log.sub.10 complex modulus according to
the equation
b.sub.T=.rho..sub.oT.sub.o/.rho.T
[0051] where b.sub.T is the vertical shift factor, .rho. is the
melt density at temperature, T's are absolute temperatures in OK,
and the subscript, o, refers to the 190.degree. C. reference
temperature. Vertical shifting was followed by arbitrary horizontal
shifting of log.sub.10 complex modulus along the log.sub.10
frequency axis to yield the horizontal shift factors, a.sub.T,
which were then fitted to an Arrhenius form equation to yield the
energy of activation for viscous flow, E.sub.a, where E.sub.a is
derived from
a.sub.Texp[(E.sub.a/R)(1/T-1/T.sub.o)]
[0052] and where R=1.987.times.10.sup.-3 in kcal/mol .degree.
K.
[0053] The following critical melt shear Theological attributes at
190.degree. C., derived from the master curve data, describing
aspects of the invention are given in Tables III and VI for each of
the examples:
[0054] Newtonian viscosity, .eta..sub.o, in Pa-s
[0055] Plateau modulus, G.sub.N.sup.o, in Pa (evaluated at the
frequency of G"minimum)
[0056] Ratio of Newtonian value to viscosity at 100 rad/sec,
.eta..sub.o/.eta.*.sub.(100s.sup.-1),
[0057] Ratio of the extensional viscosity measured at a strain rate
of 1 sec.sup.-7, 190.degree. C., and time=3 sec (i.e., a strain of
3) to that predicted by linear viscoelasticity at the same
temperature and time, and
[0058] Energy of activation, E.sub.a.
[0059] The high Newtonian viscosities of the invention indicate
advantageously high extensional viscosities (at low strain rate).
The low plateau moduli of the invention, as well as the measures of
shear thinning, are indicative of low viscosity at, e.g.,
extrusion, blow molding, and injection molding shear rates.
EXAMPLE 1-1 (C1)
[0060] C1 was ground into coarse powder and dry mixed with 1%(wt)
of a 1:2 mixture of Irganox.RTM. 1076/Irgafos.RTM. 168 (Ciba-Geigy,
Inc.). This material was then compression molded into 1 inch (25.4
mm) diameter.times.2 mm thickness disks in a Carver Laboratory
Press (Fred S. Carver, Inc.) using a cavity of these dimensions and
Teflon.RTM. coated aluminum sheet liners. Molding was performed at
ca. 190.degree. C. and 10,000 psi. The melt linear viscoelastic
testing as a function of frequency was performed at the various
temperatures given below on two such specimens in a Rheometrics
Scientific RMS-800 Mechanical Spectrometer in parallel plate
sinusoidal oscillatory shear mode. Plate diameters and specimen
diameters at test conditions were 25 mm and gap setting (sample
thickness) at the initial 150.degree. C was 1.865 mm. Measurements
were made on a single specimen at 150.degree. C. (0.1-251 rad/sec,
1.865 mm gap), 120.degree. C. (0.1-251 rad/sec, 1.865 mm gap),
170.degree. C. (0.1-251 radi/sec, 1.908 mm gap), 190.degree. C.
(0.1-158 rad/sec, 1.993 mm gap), and 220.degree. C. (0.1-251
rad/sec, 2.071 mm gap). On a second specimen, measurements were
then performed at 220.degree. C. (0.1-251 rad/sec, 2.081 mm gap),
250.degree. C. (0.01-100 rad/sec, 2.111 mm gap), and 220.degree. C.
(100-0.01 rad/sec, 2.081 mm gap). Maintaining the gap setting
constant with increasing temperature at the lower temperatures was
accomplished compensating for tooling thermal expansion/contraction
as described in the general section above. The increased gap
setting at higher temperatures compensated both for tooling
dimension change and for sample expansion, where the latter was
accomplished by maintaining a constant (low) normal stress on the
sample.
[0061] The resultant melt rheological parametric data were
expressed as described in the general section above and were
superimposed to 190.degree. C. reference temperature master curves
covering seven decades of reduced frequency in the well known
manner described above using IRIS computer software (HIS version
2.5, IRIS Development, Amherst, Mass.). Specific values of the
parameters, Newtonian viscosity, plateau modulus, ratio of the
Newtonian viscosity to the viscosity at 100 rad/sec, and energy of
activation for viscous flow, are given in Table III.
[0062] FIGS. I-IV illustrate the surprising features of the C1 as
compared to those of commercial low density and linear low density
polyethylene polymers. G28
[0063] FIG. I shows that the invention C1 exhibited a
stronger-frequency dependence of the viscosity than any of the
comparative examples A, B, C, and D. This translates into lower
energy input per throughput unit for the invention polymer. Note,
this plot is dependent on the temperature and molecular weight of
the example polymers, in addition to MWD and molecular
architecture.
[0064] FIG. II is a plot of these variables in a reduced variable
manner that renders viscosity curves which are independent of the
temperature and the magnitude of the molecular weight, hence the
comparison was made on equal footing. The differences were only due
to the MWD and the branching characteristics. Note that the reduced
viscosities of the two LDPE examples (A & B) were on top of
each other. As for FIG. I, this plot clearly shows that for high
throughputs, as desired in melt processing, the invention Example I
exhibited lower values of the viscosity than any of the comparative
examples (A, B, C, & D). This translates into lower energy
requirements per throughput unit.
[0065] FIG. H1 shows that C1 exhibited a region over which G' was
essentially frequency independent, which can be taken as the
plateau modulus. The behavior of the storage modulus of the
comparative examples showed each to increase with the frequency,
even after the frequency at which the invention reached a plateau.
As with FIG. I the effects of the molecular weight and temperature
have not been removed.
[0066] FIG. IV shows the storage modulus of the example polymers
against the product of the zero shear viscosity and frequency, thus
removing the effects of temperature and molecular weight.
Accordingly this plot reflects only the influence of the MWD and
branching characteristics on the behavior of the storage modulus.
This plot unquestionably shows that the storage modulus of Example
I reached the rubbery plateau region whereas the storage moduli of
the comparative examples were still increasing with frequency.
EXAMPLE 2-1 (C2)
[0067] A single test specimen of C2 was prepared with stabilization
and compression molding as described in the general discussion
above and tested at the sequence of temperatures, 150.degree. C.
(0.1-100 rad/sec, 1.221 mm gap) 1200C (0.1-100 rad/sec, 1.221 mm
gap), 170.degree. C. (0.1-100 rad/sec, 1.221 mm gap), 1900C
(100-0.01 rad/sec, 1.221 mm gap), 220.degree. C. (100-0.01 rad/sec,
1.221 mm gap), and 150.degree. C. (0.1-100 rad/sec, 1.221 mm gap).
The resultant melt Theological parametric data were expressed as
described in the general section above and were superimposed to
190.degree. C. reference temperature master curves covering six to
seven decades of reduced frequency in the well known manner
described above using IRIS computer software (IRIS version 2.5,
IRIS Development, Amherst, Mass.). Specific values of the
parameters, Newtonian viscosity, plateau modulus, ratio of the
Newtonian viscosity to the viscosity at 100 rad/sec, and energy of
activation for viscous flow, are given in Table III.
EXAMPLE 3-1 (C3)
[0068] A single test specimen of C3 prepared as in Example 2-1 was
tested at a sequence of temperatures ranging from 120.degree. C. to
330.degree. C. with repeat tests at 1500C performed after the
250.degree. C. and the 300.degree. C. tests. The frequency ranges
at the individual temperatures were as described in the general
description of methodology above. The resultant melt rheological
parametric data were expressed as described in the general section
above and were superimposed to 190.degree. C. reference temperature
master curves covering seven to eight decades of reduced frequency
by the methods described in Examples 1-1 and 2.-1 Specific values
of the parameters, Newtonian viscosity, plateau modulus, ratio of
the Newtonian viscosity to the viscosity at 100 rad/sec, and energy
of activation for viscous flow, are given in Table III.
EXAMPLES 4-1 through 8-1 (C4, BLEND 1, BLEND 2, H1, H2)
[0069] Examples 4-1 through 8-1 were prepared and tested variously
within the general methodology described in the above sections. The
data from the various temperatures for each example were
superimposed to 1900C master curves as described in Example 1-1.
Specific values of the parameters, Newtonian viscosity, plateau
modulus, ratio of the Newtonian viscosity to the viscosity at 100
rad/sec, and energy of activation for viscous flow, are given in
Table III. Where specific values are omitted, they could not be
determined with reasonable certainty from the data.
EXAMPLE 9-1 (ECD103) (Comparative)
[0070] Example 9-1 was linear polyethylene used in the blends,
Examples 5-1 and 6-1. It was stabilized as described in the general
method description and compression molded into a
2.5in..times.2.5in..times.2 mm plaque from which three 25 mm
diameter.times.2 mm thickness disks were cut. Melt viscoelastic
testing was performed on the first specimen from 0.1 to 400 rad/sec
at the succession of temperatures, 130.degree. C., 120.degree. C.,
1150C, 150.degree. C. Subsequently tests were performed on separate
specimens from 0.1 to 100 rad/sec at 170.degree. C. and at
190.degree. C. Data superposition to 190.degree. C. master curves
was performed as described in previous examples, and specific
values of the parameters, Newtonian viscosity, plateau modulus,
ratio of the Newtonian viscosity to the viscosity at 100 rad/sec,
and energy of activation for viscous flow, are given in Table III.
Where specific values are omitted, they could not be determined
with reasonable certainty from the data.
Sample Preparation For Extensional Rheology
[0071] Samples identified in Tables III and VI were tested in a
Rheometrics Polymer Melt Elongational Rheometer (RME) for the value
of the .eta..sub.ext ratio. They prepared as rectangular
parallelepipeds whose length, width and thickness are approximately
60, 8, and 1.5 mm, respectively. These samples were prepared by
compression molding the polymer of interest within a brass
mask.
[0072] The first step in the procedure used to mold these samples
was to weigh out approximately 0.9 g of polymer, which was
sufficient to completely fill the mask. When the bulk material was
in pellet or powder form, the weighing process was straightforward.
However, when the material to be tested was received in hard
chunks, an Exacto knife was used to cut small pieces of polymer
from the bulk until the aforementioned mass had been collected. The
next step was to stabilize the polymer, which was only necessary
for those materials that were not in pelletized form. This was
accomplished by adding one weight percent IRGAFOS.RTM. 168
stabilizer (Ciba-Geigy, Inc.) to the weighed out polymer. The brass
extrusion die was then filled with the stabilized polymer, and
sandwiched between heated platens at 190.degree. C. that are
mounted on a hydraulic press (Carver Inc.) The purpose of the die
is to mix the melted polymer so that the resulting test specimens
are free of air bubbles and weld lines. The presence of either can
cause the test specimen to break at lower total strains versus the
case in which the polymer chains of the test specimen are fully
entangled. Note that 1".times.1".times.{fraction (1/16)}" sheets of
mylar were used to cap the die in order to keep the polymer within
the die from contacting and sticking to the platens.
[0073] Once the polymer had melted within the die, the bottom sheet
of mylar was removed, and the plunger was placed into the hole of
the die. The brass mask was then mounted onto the bottom platen,
with a sheet of mylar (3".times.2".times.{fraction (1/16)}") being
placed between the mask and the platen. The die and plunger were
then placed onto the brass mask, so that the hole of the die
coincided with the geometric center of the mask slit. The polymer
was then extruded into the mask by closing the platens of the
press, which drove the plunger into the die. The mask and die were
then removed from the press and allowed to cool to approximately
100.degree. C. at which point the mask was separated from the die.
Because the sample held within the mask is not dimensionally
homogeneous after extrusion, it was remolded within the press at
190.degree. C. and 2000 psi between two 4".times.2".times.{fraction
(1/16)}" mylar sheets. After applying heat to the sample and mask
for approximately ten minutes, the power to the platen heaters was
turned off, and the sample and mask were allowed to cool to room
temperature (approximately 2 hours). It was necessary to slowly
cool the polymer specimen in this way so that the molded sample was
free of residual stresses. Finally, the specimen was carefully
removed from the mask. its dimensions were measured, and it was
tested within the RME. Sample Testing in the Rheometrics Polymer
Melt Elongational Rheometer (RME) After allowing for the oven of
the RME to heat up to the desired testing temperature, calibration
of the force transducer was performed. This was accomplished with
the rotary clamps (with stainless steel belts) installed, and the
top clamp on the transducer side (right-hand side) of the oven in
the lowered position. With no mass hanging from the transducer
shaft and pulley located at the back of the oven, the force
calibration window was brought up in the data acquisition software.
After choosing the desired force scale, the force gain was set to
unity, and offset values were input until the average force readout
on the screen was zero. A mass corresponding to that chosen for the
force scale was then attached to the transducer shaft and hung over
the pulley. The gain in the calibration window was then adjusted
until the average measured force was equal to the mass attached to
the transducer. Once this was accomplished, the mass was removed
from the shaft/pulley and the offset in the force calibration
window was adjusted until me average measured force. was again
zero. The mass was then re-attached and the gain was readjusted
until the proper force readout was achieved. This procedure of
zeroing and scaling the transducer readout was repeated iteratively
until values for the offset and gain in the calibration window of
the data acquisition software were obtained that simultaneously
yielded a zero force when the transducer shaft was load free and
the proper force for the attached mass.
[0074] After calibrating the force transducer and measuring the
dimensions of the parallelepiped test specimen, the temperature
within the oven was checked to ensure that the oven was at the
appropriate test temperature. The valve on the gas flow regulator
was then turned 180.degree. so that 99.6% pure nitrogen was
delivered to the oven for temperature control. After waiting for
the oven to be flooded with nitrogen gas (2-3 minutes), the
specimen was loaded between the rotary clamps using the RME loading
block (i.e. the top clamps are in locked or upper position).
Typically, 16 (cm.sup.3/min) of gas were delivered to the air
table, while 14 (cm.sup.3/min) were used to heat the rotary clamps.
During loading it was important for the specimen not to touch the
top of the air table, because this can cause the specimen to stick
and an extra force will be measured during elongational
testing.
[0075] Immediately after releasing the specimen above the air
table, the right-hand clamp was lowered to hold the specimen in
place The sample was then allowed to melt, while being levitated
over the table for approximately 5-6 minutes. The left-hand rotary
clamp was then closed, and the specimen was checked to insure that
it did not stick to the air table. Generally, the melted specimen
had sagged somewhat between the table and the clamps, which can
cause some sticking to the air table and erroneous force data at
low strains. To overcome this problem, the slack was drawn up by
jogging the clamps at an angular velocity of 1 rev/min. Sample
testing was then initiated by setting the VCR to record mode,
initiating the video timer, and choosing start test in the data
acquisition software, respectively. Subsequent to the sample being
elongated, the valve on the gas flow regulator was returned to the
air side, and the required test parameters were entered into the
data acquisition software. The rotary clamps and oven door were
then opened, and the clamps were removed. Finally, the tested
polymer was extracted from the stainless steel belts, and recycled
for additional elongational tests.
3TABLE III 190.degree. C. SHEAR RHEOLOGY and EXTENSIONAL RHEOLOGY
EXAMPLES .eta..sub.0 (190.degree. C.) Linear .eta..sub.0 Equivalent
G.sub.N.sup.0 .eta..sub.0/.eta.* E.sub.a EXAMPLE (Pa .multidot. s)
(Pa .multidot. s) (Pa) .eta..sub.ext ratio (100s.sup.-1) (kcal/mol)
MULTIPLY BRANCHED (>2) STRUCTURES 1 (C1) 1.0 .times. 10.sup.6
1.0 .times. 10.sup.5 1.3 .times. 10.sup.5 -- 710 18.4 2 (C2) 9
.times. 10.sup.5 4.5 .times. 10.sup.3 .about.6 .times. 10.sup.5 --
130 15.0 3 (C3) >5 .times. 10.sup.7 1.6 .times. 10.sup.6
.about.3 .times. 10.sup.4 -- >1200 17.6 4 (C4) >1 .times.
10.sup.7 3.5 .times. 10.sup.4 .about.3 .times. 10.sup.5 -- >2500
17.0 (No terminal region) 5 (BLEND 1) 7.5 .times. 10.sup.3 -- --
2.25 3.2 7.88 (2% C1/98%ECD103) (Rubbery plateau not accessed) 6
(BLEND 2) 8 .times. 10.sup.3 -- -- 3.18 3.3 8.54 (2% C3/98%EDC103)
(Rubbery plateau not accessed) H-STRUCTURES 7 (H1) 6.4 .times.
10.sup.3 3.0 .times. 10.sup.2 5 .times. 10.sup.5 -- 2.4 12.2 8 (H2)
6.4 .times. 10.sup.4 8.2 .times. 10.sup.2 .about.3 .times. 10.sup.5
-- 26 15.8 LINEAR 9 (ECD103) (Comparative) 6.7 .times. 10.sup.3 8.3
.times. 10.sup.3 -- 1.48 2.7 7.86 NOTES: G.sub.N.sup.0 was
evaluated as the value of G' at the frequency of G" minimum. For
comparison, the .eta..sub.0 for a linear equivalent (same M.sub.w)
polymer is shown in col. 2 using the equation .eta..sub.0
(190.degree. C.) = 5.62 .times. 10.sup.-14 M.sub.w.sup.336(Pa
.multidot. s) derived from Eq. 16, Mendelson, et al, J. Poly. Sci.,
Part A, 8, 105-126. (1970).
Example 10--In situ Mixed Zirconocene Catalyst Example
[0076] This example illustrates the preparation of branched
copolymers via an in situ coordination polymerization method using
a mixed zirconocene catalyst as described in U.S. Pat. No
5,470,811.
[0077] 1) Preparation of mixture of isomers of
(MeEtCp).sub.2ZrCl.sub.2 [bis(1,2-MeEtCp)ZrCl.sub.2,
bis(1,3-MeEtCp)ZrCl.sub.2, and (1,2-MeEtCp) (1,3-MeEtCp)ZrCl.sub.2,
where Me =methyl, Et=ethyl, Cp=cyclopentadienyl], hereinafter
called (1,2/1,3-MeEtCp).sub.2ZrCl.sub.2:
[0078] Methylcyclopentadiene dimer was cracked to the monomeric
units over high viscosity silicone oil. A sample of the freshly
prepared methylcyclopentadiene (100.5 g, 1.26 mol) was diluted in
500 cm.sup.3 tetrahydrofuran in a 3-liter flask. The flask was
cooled in an ice-bath to 0.degree. C. and 900 cm.sup.3 of 1.4 M
solution of methyllithium in hexane was added slowly. After
complete addition of the MeLi the ice-bath was removed and stirring
continued for 3 hours at room temperature. Then the flask was
cooled again to 0.degree. C. and bromoethane (139.2 g, 1.28 mol)
was added slowly as solution in THF. The mixture was then stirred
for 15 hours. The resulting product was washed with distilled water
and the organic layer was dried over sodium sulfate.
[0079] This was then filtered and concentrated under vacuum and the
concentrate was dissolved with a gentle N.sub.2 sparge. The
fraction boiling between 118-120.degree. C. was saved.
[0080] Freshly distilled methylethyl-cyclopentadiene isomers (41.9
g, 0.388 mol) as above was dissolved in 30 cm.sup.3 THF. 242
cm.sup.3 of 1.6 M solution of n-BuLi in hexane was slowly added to
this and stirring was continued for 3 hours after all the n-BuLi
had been added. This solution was then added slowly to a slurry of
ZrCI4 (45.2 g; 0.194 mol.) in 200 cm.sup.3 THF at -80.degree. C.
Stirring continued for 15 hours as the temperature slowly warmed up
to 20.degree. C. The solvent was removed under vacuum and the solid
recovered was extracted with toluene. The toluene extract was
concentrated and pentane was added to aid precipitation of the pure
compound at -30.degree. C.
[0081] 2.) Preparation of Mixed Zirconocene Catalyst:
[0082] 2300 g of Davison 948 silica dried at 200.degree. C. was
slurried in 6000 cm.sup.3 heptane in a reaction flask. The flask
was maintained at 24.degree. C. and 2500 cm.sup.3 of 30 wt %
methylalumoxane in toluene was added. After 0.5 hours, the
temperature was raised to 68.degree. C., and maintained for 4
hours. Then a toluene solution of 24.88 g
(1,3-MeBuCp).sub.2ZrCI.sub.2 (where Bu is butyl), mixed with 21.64
g of the isomeric mix (1,2/1,3-MeEtCp).sub.2ZrCl.sub.2, prepared
above, was added slowly followed by a 1 hour hold of the reaction
conditions. Then the resultant catalyst was washed with hexane 4
times and then dried to a free-flowing powder with a gentle N.sub.2
flow.
Fluidized-Bed Polymerization
[0083] The polymerization was conducted in a continuous gas phase
fluidized bed reactor. The fluidized bed was made up of polymer
granules. The gaseous feed streams of ethylene and hydrogen
together with liquid comonomer were mixed together in a mixing tee
arrangement and introduced below the reactor bed into the recycle
gas line. Hexene was used as comonomer. Triethyl aluminum (TEAL)
was mixed with this stream as a 1% by weight solution in isopentane
carrier solvent. The individual flow rates of ethylene, hydrogen
and comonomer were controlled to maintain fixed composition
targets. The ethylene concentration was controlled to maintain a
constant ethylene partial pressure. The hydrogen was controlled to
maintain a constant hydrogen to ethylene mole ratio. The
concentration of all the gases were measured by an on-line gas
chromatograph to ensure relatively constant composition in the
recycle gas stream.
[0084] The solid catalyst (above) was injected directly into the
fluidized bed using purified nitrogen as a carrier. Its rate was
adjusted to maintain a constant production rate. The reacting bed
of growing polymer particles was maintained in a fluidized state by
the continuous flow of the make up feed and recycle gas through the
reaction zone. A superficial gas velocity of 1-2 ft/sec was used to
achieve this. The reactor was operated at a total pressure of 300
psig. To maintain a constant reactor temperature, the temperature
of the recycle gas was continuously adjusted up or down to
accommodate any changes in the rate of heat generation due to the
polymerization.
[0085] The fluidized bed was maintained at a constant height by
withdrawing a portion of the bed at a rate equal to the rate of
formation of particulate product. The product was removed
semi-continuously via a series of vanes into a fixed volume
chamber, which was simultaneously vented back to the reactor. This
allowed for highly efficient removal of the product, while at the
same time recycling a large portion of the unreacted gases back to
the reactor. This product was purged to remove entrained
hydrocarbons and treated with a small stream of humidified nitrogen
to deactivate any trace quantities of residual catalyst.
4TABLE IV Polymerization Run Conditions Metallocene Catalyst.sup.1
mixed Zr Bed Weight (kg) 110 Zr (wt %) 0.58 TEAL Bed Concentration
(ppm) 49 Al (wt %) 14.92 Catalyst Productivity (kg/kg) 3900 Al/Zr
(mole/mole) 87 Bulk Density (g/cc) 0.456 Temperature (.degree. C.)
78.9 Average Particle Size (microns) 777 Pressure (bar) 21.7 Melt
Index (dg/min) 0.83 Ethylene (mole pct) 50.2 Melt Index Ratio 21.5
Hydrogen (mole ppm) 147 Density (g/cc) 0.9166 Hexene (mole pct)
1.13 Production rate (kg/br) 33 .sup.1See, Example 1-1.) and 1-2.)
catalyst preparation above. Mixed Zirconocene Catalyst Copolymer
("EXP 10")
[0086] This experimental copolymer was an ethylene-hexene copolymer
produced with the mixed zirconocene catalyst described above. This
example had the following properties: 0.9187 g/cc density, 0.91
dg/min I.sub.2, 6.53 dg/min I.sub.10, 21.1 dg/min I.sub.21, 7.18
I.sub.10/I.sub.2, 23.2I.sub.21/I.sub.2, 31,900 M.sub.n, 98,600
M.sub.w, 23,1700 M.sub.z, 3.08 M.sub.w/M.sub.n, 2.35
M.sub.z/M.sub.w, and 10.9 cN melt strength.
Commercial Resins
[0087] Comparative Ex. A is ESCORENE.RTM. LD-702 from Exxon
Chemical Co., a commercial ethylene-vinyl acetate copolymer (LDPE
film resin) having a Melt Index of 0.3 g/10 min a density of 0.943
and a vinyl acetate content of 13.3 wt. %. Comparative Ex. B is
ESCORENE.RTM. LD-1 13 from Exxon Chemical Co., a commercial
homopolyethylene polymer (LDPE packaging resin) having a Melt Index
of 2.3 g/10 min. and a density of 0.921. Comparative Ex. C is
EXCEED.RTM. 399L60 from Exxon Chemical Co., a commercial
ethylene-hexene copolymer (LLDPE blown film resin) having a Melt
Index of 0.75 g/10 min. and a density of 0.925. Comparative Ex. D
is AFFNITY.RTM. PL-1840 from The Dow Chemical Company, a commercial
ethylene-octene copolymer (LLDPE blown film resin) having a Melt
Index of 1.0 g/10 min. a density of 0.908 and an octene content of
9.5 wt. %.Comparative Ex. E is ELVAX.RTM. 3135 from DuPont Co., a
commercial ethylene-vinylacetate copolymer (EVA resin for blown
film/flexible packaging applicatioins ) having Melt Index of
0.3g/10 min. and a vinyl acetate content of 12 wt %.
Test Methods
[0088] Melt Index (12) of the resin samples was determined
according to ASTM-D-1238, Condition E. Melt Flow Rate with a 10 kg
top load (I.sub.10 was determined according to ASTM-D-1239,
Condition N. Melt Flow Rate with a 21.6 kg top load (I21) was
determined according to ASTM-D1238, condition F. Density of the
resin samples was determined according to ASTM-D-1505. Bulk
Density: The resin was poured via a 7/8" diameter funnel into a
fixed volume cylinder of 400 cc. The bulk density is measured as
the weight of resin divided by 400 cc to give a value in g/cc.
Particle Size: The particle size was measured by determining the
weight of material collected on a series of U.S. Standard sieves
and determining the weight average particle size based on the sieve
series used.
Description of Supercritical Fractionation
[0089] The use of supercritical fluids as solvents allows for the
fractionation of polymers by either molecular weight or
composition. For example, supercritical propane is a good solvent
for polyethylene and other polyolefins (homo- and copolymers) at
high enough pressure and temperature. If the temperature is kept
constant and is high enough so that the polymer is totally
non-crystalline, then one can fractionate the sample by molecular
weight by varying the pressure. The critical pressure for
solubility (that is, the pressure below which the polymer is no
longer soluble in the supercritical propane) increases with
molecular weight, so that as the pressure is dropped from some
large values the higher molecular weight fractions will drop out of
solution first, followed by progressively smaller molecular weight
fractions as the pressure is lowered (Watkins, J. J.; Krukonis, V.
J.; Condo, P. D.; Pradhan, D.; Ehrlich, P.; J. Supercritical Fluids
1991, 4, 24-31). On the other hand, if the pressure is held
constant and the temperature is lowered, then the most
crystallizable portions of the polymer will come out first. Since
for ethylene-a-olefin copolymers the crystallizability is generally
controlled by the amount of ethylene in the chain, such an isobaric
temperature profiling will fractionate the sample by composition
(Watkins, J. J.; Krukonis, V. J.; Condo, P. D.; Pradhan, D.;
Ehrlich, P.; i J. Supercritical Fluids 1991, 4, 24-31; Smith, S.
D.; Satkowski, M. M.; Ehrlich, P.; Watkins, J. J.; Krukonis, V. J.;
Polymer Preprints 1991, 32(3), 291-292). Thus, one has the option
of fractionating by either molecular weight or composition from the
same supercritical solution, by varying either pressure or
temperature, respectively. In the samples used herein, we chose to
obtain fractions of various molecular weights by isothermal
pressure variation.
Supercritical Fractionation Example
[0090] 100 grams of EXPIO resin was fractionated using a
supercritical propane solution in the manner described above. This
was carried out by Phasex Corp., 360 Merrimack St., Lawrence, Mass.
01843. This resulted in 14 fractions with the following molecular
weights:
5TABLE V Amount M.sub.n M.sub.w Fraction (g) (1000 g/mol) (1000
g/mol) M.sub.w/M.sub.n EXP 10-1 18.50 18.8 88.8 4.72 EXP 10-2 24.62
31.5 87.9 2.79 EXP 10-3 15.76 23.6 85.0 3.60 EXP 10-4 10.24 17.0
80.9 4.76 EXP 10-5 6.36 14.6 44.1 3.01 EXP 10-6 6.51 30.1 62.7 2.08
EXP 10-7 5.93 37.3 72.9 1.96 EXP 10-8 6.65 48.0 91.9 1.91 EXP 10-9
2.12 63.7 110. 1.73 EXP 10-10 3.30 78.9 128. 1.63 EXP 10-11 3.38
88.1 138. 1.56 EXP 10-12 1.83 88.0 146. 1.65 EXP 10-13 1.98 131.
220. 1.68 EXP 10-14 1.96 145. 268. 1.85 note: Molecular weights
(weight average molecular weight (M.sub.w) and number average
molecular weight (M.sub.n) were measured by Gel Permeation
Chromatography, unless other wise noted, using a Waters 150 Gel
Permeation Chromatograph equipped with a differential refractive
index detector (DRI) and calibrated using polystyrene standards.
Samples were run in 1,2,4-trichlorobenzene (145.degree. C.) using
three Shodex GPC AT-80 M/S columns in series. This general
#technique is discussed in "Liquid Chromatography of Polymers and
Related Materials III" J. Cazes Ed., Marcel Decker, 1981, page 207,
which is incorporated by reference for purposes of U.S. Pat.
practice herein. No corrections for column spreading were employed;
however, data on generally accepted standards, e.g. National Bureau
of Standards Polyethylene 1475, demonstrated a precision of 0.1
units for M.sub.w/M.sub.n which was calculated from elution times.
The numerical analyses #were performed using Expert Ease software
available from Waters Corporation.
Comparison of Commercial Polymers with Fractionated Polymer
Samples
[0091]
6TABLE VI .eta..sub.0 Linear T .eta..sub.0 Equiv. G.sub.N.sup.0
.eta..sub.ext Polymer (.degree. C.) (Pa .multidot. s) (Pa
.multidot. s) .eta..sub.0/.eta.*.sub.- 100 (Pa) ratio A--LD-702 190
81740 71 2.3 .times. 10.sup.6 B--LD-113 190 10000 19 2.3 .times.
10.sup.6 C--ECD-399L60 190 10500 3.3 2.3 .times. 10.sup.6
D--PL-1840 190 20570 12.7 2.3 .times. 10.sup.6 E--ELVAX3135 190
45000 45 2.3 .times. 10.sup.6 4.12 EXP10-Bulk 190 6800 6.7 .times.
10.sup.3 3.6 2.8 EXP10-9 190 12000 4.9 .times. 10.sup.3 5 1.45
.times. 10.sup.6 1.43 EXP10-10 190 30000 8.1 .times. 10.sup.3 9.1
1.7 .times. 10.sup.6 2.5 EXP10-11 190 >4.1 .times. 10.sup.4 1.0
.times. 10.sup.4 >9.5 1.9 .times. 10.sup.6 2.22 EXP10-12 190
>8.94 .times. 10.sup.4 1.3 .times. 10.sup.4 >21 1.74 .times.
10.sup.6 3.15 EXP10-13 190 >1.95 .times. 10.sup.5 5.0 .times.
10.sup.4 >33 1.45 .times. 10.sup.6 EXP10-14 190 >1.45 .times.
10.sup.6 9.7 .times. 10.sup.4 >181 1.3 .times. 10.sup.6 note The
values of the plateau modulus G.sub.N.sup.0 were calculated
according to the equation G.sub.N.sup.0 = 4.83 G"(.omega.).sub.max,
where G"(.omega.).sub.max stands for the value of G" at the
frequency at which G" is maximum, see R.S. Marvin and H. Oser,
J.Res. Nat. Bur. Std., 66B, 171 (1962); and, H. Oser and R.S.
Marvin, ibid., 67B, 87 (1963). For comparison, the rio for a linear
# equivalent (same M.sub.w) polymer is shown in col. 2 using the
equation .eta..sub.0(190.degree. C.) = 5.62 .times. 10.sup.-14
M.sub.w.sup.336 (Pa .multidot. s) derived from Eq. 16, Mendelson,
et al, J. Poly. Sci., Part A, 8, 105-126. (1970).
Discussion
[0092] Therefore we expect that the multiply branched coomb and
H-shaped polymers of the invention and comb/linear copolymer blends
are expected to exhibit high levels of melt strength at low MIR in
view of their strain thickening in uniaxial extension. The comb
copolymers and their blends with linear copolymers show strain
hardening (even at low levels of incorporation). Low levels of comb
copolymers in a blends with linear polymer will exhibit little
effect on shear thinning (or MIR), but can cause a significant
enhancement in strain thickening and melt strength. This gives one
the opportunity to design for that combination of properties for
those applications where it is desirable. The neat comb samples
also exhibit the suppression of plateau modulus, as distinguished
from linear copolymers alone, and should be beneficial for
extrudability.
* * * * *