U.S. patent application number 09/849203 was filed with the patent office on 2002-02-07 for ethylene/alpha-olefin polymer blends comprising components with differing ethylene contents.
Invention is credited to Daniel, Christian, Edmondson, M. Stephen, Laughner, Michael K., Parikh, Deepak R..
Application Number | 20020016415 09/849203 |
Document ID | / |
Family ID | 26898489 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020016415 |
Kind Code |
A1 |
Laughner, Michael K. ; et
al. |
February 7, 2002 |
Ethylene/alpha-olefin polymer blends comprising components with
differing ethylene contents
Abstract
An ethylene/.alpha.-olefin polymer blend is described comprising
first and second ethylene/.alpha.-olefin polymer components in
which the ethylene content of the first component is at least 10
weight percent different than the ethylene content of the second
component. These blends exhibit an improved combination of low
temperature, pellet flow, compression set, melt strength and/or
shape retention properties as compared to either component, or an
ethylene/.alpha.-olefin polymer blend of similar composition but in
which the ethylene content of each component is substantially the
same.
Inventors: |
Laughner, Michael K.; (Lake
Jackson, TX) ; Parikh, Deepak R.; (Lake Jackson,
TX) ; Daniel, Christian; (Thoiry, FR) ;
Edmondson, M. Stephen; (Alvin, TX) |
Correspondence
Address: |
WHYTE HIRSCHBOECK DUDEK S C
111 EAST WISCONSIN AVENUE
SUITE 2100
MILWAUKEE
WI
53202
|
Family ID: |
26898489 |
Appl. No.: |
09/849203 |
Filed: |
May 4, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60203298 |
May 11, 2000 |
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Current U.S.
Class: |
525/240 |
Current CPC
Class: |
C08L 2205/025 20130101;
C08L 23/16 20130101; C08F 210/18 20130101; C08L 2308/00 20130101;
C08L 2205/02 20130101; C08L 23/16 20130101; C08L 2666/04 20130101;
C08F 210/18 20130101; C08F 210/06 20130101; C08F 2500/25 20130101;
C08F 2500/03 20130101 |
Class at
Publication: |
525/240 |
International
Class: |
C08L 023/00 |
Claims
What is claimed is:
1. An ethylene/.alpha.-olefin polymer blend comprising first and
second ethylene/.alpha.-olefin polymer components in which the
ethylene content of the first component differs by at least about
10 weight percent from the ethylene content of the second
component.
2. The blend of claim 1 in which the ethylene content of the first
component differs by at least about 15 weight percent from the
ethylene content of the second component.
3. The blend of claim 1 in which the .alpha.-olefin in each
component contains from 3 to about 8 carbon atoms.
4. The blend of claim 3 in which the .alpha.-olefin in each
component is propylene.
5. The blend of claim 4 in which the first and second
ethylene/.alpha.-olefin polymer components further comprise a
polyene.
6. The blend of claim 5 in which the polyene is
5-ethylidene-2-norbornene.
7. The blend of claim 3 in which the .alpha.-olefin in the first
component is propylene and the .alpha.-olefin in the second
component contains from 4 to 8 carbon atoms.
8. The blend of claim 7 in which at least one of the first and
second ethylene/.alpha.-olefin polymer components further comprises
a polyene.
9. An ethylene/(.alpha.-olefin polymer blend comprising first and
second ethylene/.alpha.-olefin polymer components, the blend
prepared by (i) contacting ethylene, an .alpha.-olefin, an
activated constrained geometry catalyst and, optionally, a polyene,
under polymerization conditions, in a first reactor to produce the
first ethylene/.alpha.-olefin polymer component, (ii) transferring
the first ethylene/.alpha.-olefin polymer component to a second
reactor and in the presence of the first ethylene/.alpha.-olefin
polymer component, (iii) contacting fresh ethylene, an
.alpha.-olefin, an activated constrained geometry catalyst and,
optionally, a polyene, under polymerization conditions to produce
the second ethylene/.alpha.-olefin polymer component, the
polymerizations of the first and second reactors conduct in such a
manner that the ethylene content of the first
ethylene/.alpha.-olefin polymer component is at least 10 weight
percent different than the ethylene content of the second
ethylene/.alpha.-olefin polymer component.
10. The blend of claim 9 in which the polymerization conducted in
each reactor is a solution phase polymerization.
Description
FIELD OF THE INVENTION
[0001] This invention relates to ethylene/.alpha.-olefin polymer
blends. In one aspect, this invention relates to polymer blends
comprising two or more ethylene/.alpha.-olefin components while in
another aspect, this invention relates to blends in which one or
more of the components comprises an ethylene/.alpha.-olefin/polyene
polymer. In yet another aspect, this invention relates to polymer
blends of ethylene/.alpha.-olefin components in which the ethylene
content of one component differs from the ethylene content of at
least one other component by at least about 10 weight percent.
BACKGROUND OF THE INVENTION
[0002] Ethylene/.alpha.-olefin polymer blends are well known in the
art. The blends taught in U.S. Pat Nos. 4,438,238; 4,722,971;
4,874,820; 4,902,738; 4,937,299; 4,939,217; 5,013,801; 5,236,998;
5,292,845; 5,382,631; 5,494,965; 5,539,076; 5,691,413; 5,728,766;
4,429,079; 4,530,914; 5,605,969; 5,338,589; 5,260,384; 5,478,890;
5,438,100; 5,476,903; 5,703,180; 5,464,905; 5,744,551; 5,747,620
and 5,798,427 are representative, and each of these patents are
incorporated herein by reference.
[0003] Blends are useful because they provide properties not
available from the individual components from which the blend is
made. For example, an ethylene/.alpha.-olefin polymer with a
relatively narrow molecular weight distribution (MWD), e.g., 2 or
less, will usually produce a film with good transparency but it
will usually process less efficiently than an
ethylene/.alpha.-olefin polymer alike in all aspects except with a
MWD of 3 or more. However, an ethylene/.alpha.-olefin polymer with
a MWD of 3 or more usually produces a film that is less transparent
than a like ethylene/.alpha.-olefin polymer with a MWD of 2 or
less. Blending the two polymers will usually produce a composition
that will produce a film with both desirable transparency and
processability. Moreover, depending upon the particular
ethylene/.alpha.-olefin polymers, the relative proportions of each,
the manner in which the polymers are made and/or blended, the
properties of interest and a host of other variables, one or more
properties of the blend may be more than a simple average of its
component parts.
[0004] While ethylene/.alpha.-olefin polymer blends can be prepared
by any one of a number of different processes, generally these
processes fall into one of two categories, i.e., post-reactor
blending and in-reactor blending. Illustrative of the former are
melt extruders into which two or more solid ethylene/.alpha.-olefin
polymers are fed and physically mixed into a substantially
homogeneous composition, and multiple solution, slurry or gas-phase
reactors arranged in a parallel array the output from each blended
with one another to form a substantially homogeneous composition
which is ultimately recovered in solid form. Illustrative of the
latter are multiple reactors connected in series, and single
reactors charged with two or more catalysts. While each general
process category has its own advantages and disadvantages,
in-reactor blending is a favored technique for making blends in
which component compatibility, i.e., the ability to make a
substantially homogeneous blend from the components, is a factor.
Generally, forming a substantially homogeneous blend from
ethylene/.alpha.-olefin polymer components that are less than fully
compatible is easier and more successful and cost effective using
an in-reactor technique than a post-reactor technique, particularly
melt extrusion.
[0005] Ethylene/.alpha.-olefin polymers and blends of these
materials are commercially important because they exhibit and/or
impart desirable properties to various products, e.g., films and
molded and extruded articles. Properties of frequent interest are
low temperature impact strength, compression set, melt strength,
shape retention, pellet flow, mechanical strengths and modulus.
Depending upon the end use, often one or more of these properties
will be more important than the others. Enhancement of these more
important properties often requires the use of a blend of
ethylene/.alpha.-olefin polymers. The industry interest, of course,
is in blends in which the properties of primary importance are
enhanced without significant diminution of the other
properties.
SUMMARY OF THE INVENTION
[0006] According to this invention, ethylene/.alpha.-olefin polymer
blends with improved low temperature, pellet flow, compression set,
melt strength and/or shape retention properties are prepared by
blending a first ethylene/.alpha.-olefin polymer component with a
second ethylene/.alpha.-olefin polymer component, with the proviso
that the ethylene content of the first and second
ethylene/.alpha.-olefin polymer components differ from one another
by at least about 10 weight percent. The blends can be made by
either post-reactor or in-reactor blending, and the weight ratio of
first component to second component can vary widely, typically from
between 80:20 to 20:80. One hallmark of this invention is that the
enhanced properties of the blend are achieved without significant
diminution of other desirable properties of the blend
components.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a graph reporting the residual crystallinity of
exemplary elastomer blends of this invention as compared to a
control elastomer.
[0008] FIG. 2 is a graph reporting the modulus G' of exemplary
elastomer blends of this invention as compared to a control
elastomer and two commercially available elastomers.
DETAILED DESCRIPTION OF THE INVENTION
[0009] The ethylene/.alpha.-olefin blend components of this
invention are polymers, i.e., interpolymers, of ethylene with at
least one C.sub.3-C.sub.20 .alpha.-olefin (preferably an aliphatic
.alpha.-olefin) comonomer, and/or a polyene comonomer, e.g., a
conjugated diene, a nonconjugated diene, a triene, etc. The term
interpolymer includes copolymers, e.g. ethylene/propylene (EP), and
terpolymers, e.g. EPDM, but it is not limited to polymers made with
only ethylene and one or two monomers. Examples of the
C.sub.3-C.sub.20 .alpha.-olefins include propene, 1-butene,
4-methyl-1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene,
1-tetradecene, 1-hexadecene, 1-octadecene and 1-eicosene. The
.alpha.-olefin can also contain a cyclic structure such as
cyclohexane or cyclopentane, resulting in an .alpha.-olefin such as
3-cyclohexyl-1-propene (allyl-cyclohexane) and vinyl-cyclohexane.
Although not .alpha.-olefins in the classical sense of the term,
for purposes of this invention certain cyclic olefins, such as
norbornene and related olefins, are .alpha.-olefins and can be used
in place of some or all of the .alpha.-olefins described above.
Similarly, styrene and its related olefins (e.g.,
.alpha.-methylstyrene, etc.) are .alpha.-olefins for purposes of
this invention.
[0010] Polyenes are unsaturated aliphatic or alicyclic compounds
containing more than four carbon atoms in a molecular chain and
having at least two double and/or triple bonds, e.g., conjugated
and nonconjugated dienes and trienes. Examples of nonconjugated
dienes include aliphatic dienes such as 1,4-pentadiene,
1,4-hexadiene, 1,5-hexadiene, 2-methyl-1,5-hexadiene,
1,6-heptadiene, 6-methyl-1,5-heptadiene, 1,6-octadiene,
1,7-octadiene, 7-methyl-1,6-octadiene, 1,13-tetradecadiene,
1,19-eicosadiene, and the like; cyclic dienes such as
1,4-cyclohexadiene, bicyclo[2.2.1]hept-2,5-diene,
5-ethylidene-2-norbornene, 5-methylene-2-norbornene,
5-vinyl-2-norbornene, bicyclo[2.2.2]oct-2,5-diene,
4-vinylcyclohex-1-ene, bicyclo[2.2.2]oct-2,6-diene,
1,7,7-trimethylbicyclo-[2.2.1]hept-2,5-diene- , dicyclopentadiene,
methyltetrahydroindene, 5-allylbicyclo[2.2.1]hept-2-e- ne,
1,5-cyclooctadiene, and the like; aromatic dienes such as
1,4-diallylbenzene, 4-allyl-1H-indene; and trienes such as
2,3-diisopropenylidiene-5-norbornene,
2-ethylidene-3-isopropylidene-5-nor- bornene,
2-propenyl-2,5-norbornadiene, 1,3,7-octatriene, 1,4,9-decatriene,
and the like; with 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene
and 7-methyl-1,6-octadiene preferred nonconjugated dienes.
[0011] Examples of conjugated dienes include butadiene, isoprene,
2,3-dimethylbutadiene-1,3,1,2-dimethylbutadiene-1,3,1,4-dimethylbutadiene-
-1,3,1-ethylbutadiene-1,3,2-phenylbutadiene-1,3,
hexadiene-1,3,4-methylpen- tadiene-1,3,1,3-pentadiene
(CH.sub.3CH.dbd.CH--CH.dbd.CH.sub.2; commonly called piperylene),
3-methyl-1,3-pentadiene, 2,4-dimethyl-1,3-pentadiene,
3-ethyl-1,3-pentadiene, and the like; with 1,3-pentadiene a
preferred conjugated diene.
[0012] Examples of trienes include 1,3,5-hexatriene,
2-methyl-1,3,5-hexatriene, 1,3,6-heptatriene,
1,3,6-cycloheptatriene, 5-methyl-1,3,6-heptatriene,
5-methyl-1,4,6-heptatriene, 1,3,5-octatriene, 1,3,7-octatriene,
1,5,7-octatriene, 1,4,6-octatriene, 5-methyl-1,5,7-octatriene,
6-methyl-1,5,7-octatriene, 7-methyl-1,5,7-octatriene,
1,4,9-decatriene and 1,5,9-cyclodecatriene.
[0013] Exemplary copolymers include ethylene/propylene,
ethylene/butene, ethylene/1-octene,
ethylene/5-ethylidene-2-norbornene, ethylene/5-vinyl-2-norbornene,
ethylene/-1,7-octadiene, ethylene/7-methyl-1,6-octadiene and
ethylene/1,3,5-hexatriene. Exemplary terpolymers include
ethylene/propylene/1-octene, ethylene/butene/1-octene- ,
ethylene/propylene/5-ethylidene-2-norbornene,
ethylene/butene/5-ethylide- ne-2-norbornene,
ethylene/butene/styrene, ethylene/1-octene/5-ethylidene-2-
-norbornene, ethylene/propylene/1,3-pentadiene,
ethylene/propylene/7-methy- l-1,6-octadiene,
ethylene/butene/7-methyl-1,6-octadiene,
ethylene/1-octene/1,3-pentadiene and
ethylene/propylene/1,3,5-hexatriene. Exemplary tetrapolymers
include ethylene/propylene/1-octene/diene (e.g. ENB),
ethylene/butene/1-octene/diene and ethylene/propylene/mixed dienes,
e.g. ethylene/propylene/5-ethylidene-2-norbornene/piperylene. In
addition, the blend components can include minor amounts, e.g.
0.05-0.5 percent by weight, of long chain branch enhancers, such as
2,5-norbornadiene (aka bicyclo[2,2,1]hepta-2,5-diene), as
diallylbenzene, 1,7-octadiene
(H.sub.2C.dbd.CH(CH.sub.2).sub.4CH.dbd.CH.sub.2), and 1,9-decadiene
(H.sub.2C.dbd.CH(CH.sub.2).sub.6CH.dbd.CH.sub.2).
[0014] Typically, the blend components of this invention comprise
at least about 20, preferably at least about 30 and more preferably
at least about 40, weight percent ethylene; at least about 1,
preferably at least about 5 and more preferably at least about 10,
weight percent of at least one .alpha.-olefin; and, if a
polyene-containing terpolymer, greater than 0, preferably at least
about 0.1 and more preferably at least about 0.5, weight percent of
at least one conjugated or nonconjugated polyene. As a general
maximum, the blend components of this invention comprise not more
than about 95, preferably not more than about 85 and more
preferably not more than about 75, weight percent ethylene; not
more than about 80, preferably not more than about 70 and more
preferably not more than about 60, weight percent of at least one
.alpha.-olefin; and, if a terpolymer, not more than about 20,
preferably not more than about 15 and more preferably not more than
about 12, weight percent of at least one of a conjugated or
nonconjugated diene. All weight percentages are based on weight of
the blend.
[0015] Important to this invention is that the difference in
ethylene content between the first and second components of the
blend is at least about 10 weight percent, preferably at least
about 15 and more preferably at least about 20, weight percent. The
maximum difference in ethylene content between the first and second
components of the blend can vary widely although as a practical
matter, the maximum difference does not exceed about 30, preferably
about 25, weight percent.
[0016] The ethylene/.alpha.-olefin polymer components of this
invention can be produced using conventional
ethylene/.alpha.-olefin polymerization technology. Preferably, the
ethylene/.alpha.-olefin polymer components of this invention are
made using a mono- or bis-cyclopentadienyl, indenyl, or fluorenyl
transition metal (preferably Group 4) catalysts or constrained
geometry catalysts (CGC) in combination with an activator, in a
solution, slurry, or gas phase polymerization process. The catalyst
is preferably mono-cyclopentadienyl, mono-indenyl or mono-fluorenyl
CGCs. The solution process is preferred. U.S. Pat. No. 5,064,802;
WO93/19104 (U.S. Ser. No. 8,003, filed Jan. 21, 1993), and
WO95/00526 disclose constrained geometry metal complexes and
methods for their preparation. Variously substituted indenyl
containing metal complexes are taught in WO95/14024 and WO98/49212.
The relevant teachings of all of the foregoing patents or their
corresponding U.S. patents or allowed applications are hereby
incorporated by reference for purposes of U.S. patent practice.
[0017] In general, polymerization may be accomplished at conditions
well known in the art for Ziegler-Natta or Kaminsky-Sinn type
polymerization reactions, that is, temperatures from 0-250.degree.
C., preferably 30-200.degree. C., and pressures from atmospheric to
10,000 atmospheres (1013 megapascals (MPa)). Suspension, solution,
slurry, gas phase, solid state powder polymerization or other
process conditions may be employed if desired. A support,
especially silica, alumina, or a polymer (especially
poly(tetrafluoroethylene) or a polyolefin) may be employed, and
desirably is employed when the catalyst is used in a gas phase
polymerization process. The support is preferably employed in an
amount sufficient to provide a weight ratio of catalyst (based on
metal):support within a range of from 1:100,000 to 1:10, more
preferably from 1:50,000 to 1:20, and most preferably from 1:10,000
to 1:30. In most polymerization reactions, the molar ratio of
catalyst:polymerizable compounds employed is from 10.sup.12:1 to
10.sup.1:1, more preferably from 10.sup.-9:1 to 10.sup.5:1.
[0018] Inert liquids serve as suitable solvents for polymerization.
Examples include straight and branched-chain hydrocarbons such as
isobutane, butane, pentane, hexane, heptane, octane, and mixtures
thereof, cyclic and alicyclic hydrocarbons such as cyclohexane,
cycloheptane, methylcyclohexane, methylcycloheptane, and mixtures
thereof, perfluorinated hydrocarbons such as perfluorinated
C.sub.4-10 alkanes; and aromatic and alkyl-substituted aromatic
compounds such as benzene, toluene, xylene, and ethylbenzene.
Suitable solvents also include liquid olefins that may act as
monomers or comonomers including butadiene, cyclopentene, 1-hexene,
1-hexane, 4-vinylcyclohexene, vinylcyclohexane, 3-methyl-1-pentene,
4-methyl-1-pentene, 1,4-hexadiene, 1-octene, 1-decene, styrene,
divinylbenzene, allylbenzene, and vinyltoluene (including all
isomers alone or in admixture). Mixtures of the foregoing are also
suitable. If desired, normally gaseous olefins can be converted to
liquids by application of pressure and used herein.
[0019] The ethylene/.alpha.-olefin polymer components of this
invention can be blended by any in-reactor or post-reactor process.
The in-reactor blending processes are preferred to the post-reactor
blending processes, and the processes using multiple reactors
connected in series are the preferred in-reactor blending
processes. These reactors can be charged with the same catalyst but
operated at different conditions, e.g., different reactant
concentrations, temperatures, pressures, etc, or operated at the
same conditions but charged with different catalysts.
[0020] Examples of processes that can be use to form the blends of
this invention include the use of an ethylene/.alpha.-olefin
polymerization catalyst utilized in combination with at least one
additional homogeneous or heterogeneous polymerization catalyst in
the same reactor or in separate reactors that are connected in
series or in parallel to prepare polymer blends having desirable
properties. An example of such a process is disclosed in WO
94/00500 at page 29 line 4 to page 33 line 17. The process uses a
continuously stirred tank reactor (CSTR) connected in series or
parallel to at least one other CSTR or tank reactor. WO 93/13143
(at page 2 lines 19-31) teaches polymerizing monomers in a first
reactor using a first CGC having a first reactivity and
polymerizing monomers in a second reactor using a second CGC having
a second reactivity and combining the products from the two
reactors. Page 3, lines 25-32 of WO 93/13143 provides teachings
about the use of two CGCs having different reactivities in one
reactor. WO 97/36942 (page 4 line 30 through page 6 line 7) teaches
the use of a two-loop reactor system. The relevant teachings of
such applications or their corresponding U.S. patents and allowed
applications are incorporated herein by reference for purposes of
U.S. patent practice.
[0021] The polydispersity (molecular weight distribution or Mw/Mn
or MWD) of the polymer blend generally ranges from at least about
2, preferably at least about 2.1, and especially at least about 2.2
to about 10, preferably about 6, and especially about 4.
[0022] The polydispersity index is typically measured by gel
permeation chromatography (GPC) on a Waters 150.degree. C. high
temperature chromatographic unit equipped with three linear mixed
bed columns (Polymer Laboratories (10 micron particle size))
operating at a system temperature of 140.degree. C. The solvent is
1,2,4-trichlorobenzene from which about 0.5% by weight solutions of
the samples are prepared for injection. The flow rate is 1.0
milliliter/minute, and the injection size is 100 microliters.
[0023] The molecular weight determination is deduced by using
narrow molecular weight distribution polystyrene standards (from
Polymer Laboratories) in conjunction with their elusion volumes.
The equivalent polyethylene molecular weights are determined by
using appropriate Mark-Houwink coefficients for polyethylene and
polystyrene (as described by Williams and Ward in Journal of
Polymer Science, Polymer Letters, Vol. 6, (621) 1968) to derive the
equation:
M.sub.polyethylene=(a)(M.sub.polystyrene).sup.b
[0024] In this equation, a=0.4316 and b=1.0. Weight average
molecular weight, Mw, is calculated in the usual manner according
to the formula:
Mw=.SIGMA.(w.sub.i)(M.sub.i)
[0025] where w.sub.i and M.sub.i are the weight fraction and
molecular weight respectively of the ith fraction eluting from the
GPC column. Generally, the Mw of the polymer blend ranges from
about 10,000, preferably about 20,000, more preferably about
40,000, and especially about 60,000, to about 1,000,000, preferably
about 800,000, more preferably about 600,000, and especially about
500,000.
[0026] The polymer blends of this invention cover a range of
viscosities, depending upon the molecular weight of the blend and
optional post-polymerization rheological modification. In general,
the blend viscosity is characterized by a Mooney viscosity which is
measured according to ASTM D 1646-89 using a shear rheometer at
125.degree. C. The polymer blend Mooney viscosity generally ranges
from a minimum of less than 0.01, preferably 0.1, more preferably
about 1, and especially about 15 to a maximum of about 150,
preferably about 125, more preferably about 100, and especially
about 70.
[0027] The rheological or shear thinning behavior of the ethylene
interpolymer is determined by measuring the ratio of interpolymer
viscosity at 0.1 rad/sec to viscosity at 100 rad/sec. This ratio is
known as the Rheology Ratio (RR), V0.1/V100, or more simply,
0.1/100. The RR is an extension of I.sub.10/I.sub.2 and as such, in
those instances in which the measurement of I.sub.2 and I.sub.10
are difficult, e.g., the I.sub.2 is less than 0.5, or the molecular
weight of the interpolymer is relatively high, or the Mooney
viscosity of the interpolymer is greater than about 35, the RR of
the interpolymer can be measured using a parallel plate
rheometer.
[0028] The density of the polymer blends is measured according to
ASTM D-792, and this density ranges from a minimum of about 0.850
grams/cubic centimeter (g/cm.sup.3), preferably about 0.853
g/cm.sup.3, and especially about 0.855 g/cm.sup.3, to a maximum of
about 0.970 g/cm.sup.3, preferably about 0.940 g/cm.sup.3, and
especially about 0.930 g/cm.sup.3. For those polymer blends that
are elastomers, i.e., with a crystallinity less than about 45%, the
maximum density is about 0.895, preferably about 0.885 and more
preferably 0.875, g/cm.sup.3.
[0029] For polymer blends intended for use as elastomers, the
crystallinity is preferably less than about 40, more preferably
less than about 30, percent, preferably in combination with a
melting point of less than about 115, preferably less than about
105, C, respectively. Elastomeric polymer blends with a
crystallinity of zero to 25 percent are even more preferred. The
percent crystallinity is determined by dividing the heat of fusion
as determined by differential scanning calorimetry (DSC) a of
polymer blend sample by the total heat of fusion for that polymer
blend sample. The total heat of fusion for high-density homopolymer
polyethylene (100% crystalline) is 292 joule/gram (J/g).
[0030] One hallmark of this invention is that a desirable property
of one component of the blend can be enhanced without a significant
diminution of one or more desirable properties of another
component. For example, certain blends of this invention exhibit an
enhanced low temperature impact property relative to one component
of the blend without any significant diminution of the glass
transition temperature (Tg) of the other component of the blend.
Other blends of this invention exhibit the same phenomena (i.e., no
significant diminution of Tg) with respect to pellet flow (i.e.,
the ability of pellets made from the blend to move pass one another
without sticking or blocking), compression set for a given
crystallinity, melt strength and shape retention.
[0031] Another hallmark of this invention is that these blends
exhibit an improved combination of low temperature, pellet flow,
compression set, melt strength and/or shape retention properties as
compared to an ethylene/.alpha.-olefin polymer blend of similar
composition but in which the ethylene content of each component is
substantially the same.
[0032] The following examples are provided as a further
illustration of the invention. Unless stated to the contrary, all
parts and percentages are by weight.
Specific Embodiment
[0033] Four elastomers were prepared using a dual loop reactor such
as that described in WO 98/49212. Each elastomers was prepared
under the same conditions with the same reactants and catalyst and
to the same total ethylene content (66 weight percent based upon
the weight of the polymer component) as the other elastomers. The
control elastomer was a blend of two essentially identical
components, i.e., the component made in the first loop reactor was
essentially the same in composition and properties as the component
made in the second loop reactor. The remaining three elastomers,
i.e., Elastomers 1, 2 and 3, are embodiments of this invention.
Each is essentially the same as the other and the control except
that the ethylene content of the component made in the first loop
reactor is different than the ethylene content of the component
made in the second loop reactor. The composition, Mooney viscosity,
weight average molecular weight (Mw), molecular weight distribution
(MWD), temperature of crystallinity (Tc, both onset and peak), and
glass transition temperature (Tg) for each elastomer and two
commercially available elastomers (Dutral.TM. 4038 manufactured and
sold by Enichem, and Nordel.TM. IP 4770 manufactured and sold by
Dupont Dow Elastomers) are reported in the following table.
1 Physical Properties of Two Commercial Elastomers, One Control
Elastomer, and Three Elastomers with a Split Ethylene Composition
Nordel .TM. Dutral .TM. Control Elastomer 1 Elastomer 2 Elastomer 3
Description IP 4770 4038 66/66 74/60 54/74 48/78 Mooney 70 62 63.2
58 59 64 Ethylene 70.0 70.6 66.9 67.3 66.8 67.4 Propylene 25.1 24.4
28.2 28.1 28.4 27.7 ENB 4.9 5.0 4.91 4.66 4.82 4.9 Mw 196,700
180,000 179,700 177,800 184,000 185,800 MWD 2.8 2.71 2.92 2.9 2.34
2.93 Tc Onset 29.36 24.40 16.78 38.46 22.95 30.94 Tc Peak 23.23
16.70 10.46 27.06 13.54 21.20 Tg -37.00 -40.96 -42.93 -43.1 -43.10
-44.98
[0034] As is evident from the data in the above table, Elastomers
1, 2 and 3 not only have a lower Tg than the control elastomer, but
also a lower Tg than the two commercially available elastomers
(both of similar composition). Lower Tg usually means better low
temperature flexibility in such products as seals, belts and
automotive hoses.
[0035] The residual crystallinity at elevated temperatures of
Elastomers 1, 2 and 3 are compared with the Control Elastomer in
FIG. 1. As can be seen from this graph, as the ethylene split
between the elastomer components increases, the so does the
residual crystallinity. Usually, the larger the residual
crystallinity at higher temperatures, the better the shape
retention of the elastomer (neat or deployed in its intended
end-use).
[0036] FIG. 2 reports the modulus G'0 of the Control Elastomer,
Elastomers 1, 2 and 3, Nordel IP 4770 and Dutral 4038. Modulus G3',
or storage modulus, is another measure of the shape retention of
the elastomer. Here too, Elastomers 1, 2 and 3 outperform the
Control Elastomer even with a slightly higher overall ethylene
content.
[0037] Finally, Elastomers 1 and 2 were compared with the Control
Elastomer for pellet flow. Elastomers 1 and 2 demonstrated superior
temperature resiliency and lower blocking than the Control
Elastomer.
[0038] Although the invention has been described in considerable
detail through the specification and examples, one skilled in the
art can make many variations and modifications without departing
from the spirit and scope of the invention as described in the
following claims.
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