U.S. patent application number 11/133685 was filed with the patent office on 2005-09-22 for ziegler-natta catalyst for polyolefins.
This patent application is currently assigned to Fina Technology, Inc.. Invention is credited to Coffy, Tim J., Enriquez, Henry, Gray, Steven D., Knoeppel, David W..
Application Number | 20050209094 11/133685 |
Document ID | / |
Family ID | 34987095 |
Filed Date | 2005-09-22 |
United States Patent
Application |
20050209094 |
Kind Code |
A1 |
Knoeppel, David W. ; et
al. |
September 22, 2005 |
Ziegler-natta catalyst for polyolefins
Abstract
A Ziegler-Natta type catalyst component can be produced by a
process comprising contacting a magnesium dialkoxide compound with
a halogenating agent to form a reaction product A, and contacting
reaction product A with a first, second and third
halogenating/titanating agents. Catalyst components, catalysts,
catalyst systems, polyolefin, products made therewith, and methods
of forming each are disclosed. The reaction products can be washed
with a hydrocarbon solvent to reduce titanium species [Ti] content
to less than about 100 mmol/L.
Inventors: |
Knoeppel, David W.; (League
City, TX) ; Coffy, Tim J.; (Houston, TX) ;
Enriquez, Henry; (Pearland, TX) ; Gray, Steven
D.; (Houston, TX) |
Correspondence
Address: |
FINA TECHNOLOGY INC
PO BOX 674412
HOUSTON
TX
77267-4412
US
|
Assignee: |
Fina Technology, Inc.
|
Family ID: |
34987095 |
Appl. No.: |
11/133685 |
Filed: |
May 20, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11133685 |
May 20, 2005 |
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10667578 |
Sep 22, 2003 |
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10667578 |
Sep 22, 2003 |
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09687560 |
Oct 13, 2000 |
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6693058 |
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09687560 |
Oct 13, 2000 |
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08789862 |
Jan 28, 1997 |
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6174971 |
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Current U.S.
Class: |
502/103 ;
502/102; 502/115; 502/118; 526/124.3 |
Current CPC
Class: |
C08F 110/02 20130101;
B01J 2231/122 20130101; C08F 110/02 20130101; C08F 110/02 20130101;
C08F 110/02 20130101; C08F 10/00 20130101; C08F 10/00 20130101;
C08F 10/00 20130101; C08F 10/00 20130101; C08F 2500/12 20130101;
C08F 4/6567 20130101; C08F 2500/18 20130101; C08F 2500/02 20130101;
C08F 2500/12 20130101; C08F 2500/04 20130101; C08F 2500/12
20130101; C08F 4/6546 20130101; C08F 2500/07 20130101; C08F 4/651
20130101; C08F 4/6557 20130101; B01J 2531/46 20130101; B01J 2531/31
20130101; C08F 2500/04 20130101; C08F 2500/07 20130101; C08F
2500/23 20130101; C08F 2500/02 20130101; C08F 2500/23 20130101;
B01J 31/0212 20130101; C08F 10/00 20130101 |
Class at
Publication: |
502/103 ;
502/102; 502/118; 502/115; 526/124.3 |
International
Class: |
B01J 031/00; C08F
004/44 |
Claims
We claim:
1. A catalyst produced by a process comprising: a) contacting a
catalyst component with an organometallic preactivating agent,
wherein the catalyst component is produced by a process comprising,
i) contacting a magnesium dialkoxide compound with a halogenating
agent to form a reaction product A; ii) contacting reaction product
A with a first halogenating/titanating agent to form reaction
product B; iii) contacting reaction product B with a second
halogenating/titanating agent to form reaction product C; and iv)
contacting reaction product C with a third halogenating/titanating
agent to form a catalyst component.
2. The catalyst of claim 1 wherein the organometallic preactivating
agent is an aluminum alkyl of the formula AIR.sub.3 wherein at
least one R is an alkyl having 1-8 carbon atoms or a halide, and
wherein each R may be the same or different.
3. The catalyst of claim 2 wherein the organometallic preactivating
agent is a trialkyl aluminum.
4. The catalyst of claim 3 wherein the second and third
halogenating/titanating agents comprise titanium tetrachloride.
5. The catalyst of claim 4 wherein the ratio of aluminum to
titanium is in the range from 0.1:1 to 2:1.
6. The process of claim 1 wherein reaction products A, B, and C are
washed with a hydrocarbon solvent prior to subsequent
halogenating/titanating steps.
7. The process of claim 1 wherein the catalyst component is washed
with a hydrocarbon solvent until titanium species [Ti] content is
less than about 20 mmol/L.
8. A polymer produced by a process comprising: a) contacting one or
more olefin monomers together in the presence of a catalyst under
polymerization conditions, wherein the catalyst is produced by a
process comprising i) contacting a magnesium dialkoxide compound
with a halogenating agent to form a reaction product A; ii)
contacting reaction product A with a first halogenating/titanating
agent to form reaction product B; iii) contacting reaction product
B with a second halogenating/titanating agent to form reaction
product C; iv) contacting reaction product C with a third
halogenating/titanating agent to form a catalyst component; and b)
extracting polyolefin polymer.
9. The polymer of claim 8 wherein the catalyst is produced by a
process further comprising: v) contacting the catalyst component
with an organoaluminum agent.
10. The polymer of claim 8 wherein the second and third
halogenating/titanating agents comprise titanium tetrachloride.
11. The polymer of claim 8 wherein reaction products A, B, and C
are washed with a hydrocarbon solvent prior to subsequent
halogenating/titanating steps.
12. Film, fiber, pipe, textile material, or an article of
manufacture comprising the polymer of claim 8.
13. A process for olefin polymerization, comprising: a) contacting
one or more olefin monomers together in the presence of a catalyst
under polymerization conditions, wherein the catalyst was produced
by a process comprising: i) contacting a magnesium dialkoxide
compound with a halogenating agent to form a reaction product A;
ii) contacting reaction product A with a first
halogenating/titanating agent to form reaction product B; iii)
contacting reaction product B with a second halogenating/titanating
agent to form reaction product C; iv) contacting reaction product C
with a third halogenating/titanating agent to form a catalyst
component to form reaction product D; b) extracting a polyolefin
polymer; wherein at least one reaction product A, B, and C are
washed with a hydrocarbon solvent prior to subsequent
halogenating/titanating steps; and wherein the reaction product D
is washed with a hydrocarbon solvent until titanium species [Ti]
content is less than about 100 mmol/L.
14. The process of claim 13 wherein the polymer has a molecular
weight distribution of at least 4.0.
15. The process of claim 13 wherein the polymer has a bulk density
of at least 0.31 g/cc.
16. An article comprising polymer produced by the process of claim
13.
Description
REFERENCE TO RELATED APPLICATION
[0001] The present application is a Continuation-in-part of U.S.
patent application Ser. No. 09/687,560, entitled, Ziegler-Natta
Catalyst For Narrow to Broad MWD of Polyolefins, Method of Making,
Method of Using, And Polyolefins Made Therewith, filed Oct. 13,
2000, incorporated herein by reference, which is a
Continuation-in-part of U.S. patent application Ser. No.
08/789,862, entitled, Ziegler-Natta Catalysts for Olefin
Polymerization, filed Jan. 28, 1997, which issued as U.S. Pat. No.
6,174,971 on Jan. 16, 2001, also incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to catalysts, to
methods of making catalysts, to methods of using catalysts, to
methods of polymerizing, and to polymers made with such catalysts.
More particularly, the present invention relates to polyolefin
catalysts and to Ziegler-Natta catalysts, to methods of making such
catalysts, to methods of using such catalysts, to polyolefin
polymerization, and to polyolefins.
[0004] 2. Description of the Related Art
[0005] Olefins, also called alkenes, are unsaturated hydrocarbons
whose molecules contain one or more pairs of carbon atoms linked
together by a double bond. When subjected to a polymerization
process, olefins can be converted to polyolefins, such as
polyethylene and polypropylene. One commonly used polymerization
process involves contacting an olefin monomer with a Ziegler-Natta
type catalyst system. Many Ziegler-Natta type polyolefin catalysts,
their general methods of making, and subsequent use, are well known
in the polymerization art. Typically, these systems include a
Ziegler-Natta type polymerization catalyst component; a
co-catalyst; and an electron donor compound. A Ziegler-Natta type
polymerization catalyst component can be a complex derived from a
halide of a transition metal, for example, titanium, chromium or
vanadium, with a metal hydride and/or a metal alkyl that is
typically an organoaluminum compound. The catalyst component is
usually comprised of a titanium halide supported on a magnesium
compound complexed with an alkylaluminum. There are many issued
patents relating to catalysts and catalyst systems designed
primarily for the polymerization of propylene and ethylene that are
known to those skilled in the art. Examples of such catalyst
systems are provided in U.S. Pat. Nos. 4,107,413; 4,294,721;
4,439,540; 4,114,319; 4,220,554; 4,460,701; 4,562,173; 5,066,738,
and 6,174,971 which are incorporated by reference herein.
[0006] Conventional Ziegler-Natta catalysts comprise a transition
metal compound generally represented by the formula: MR.sub.x where
M is a transition metal compound, R is a halogen or a
hydrocarboxyl, and x is the valence of the transition metal.
Typically, M is selected from a group IV to VII metal such as
titanium, chromium, or vanadium, and R is chlorine, bromine, or an
alkoxy group. Common transition metal compounds are TiCl.sub.4,
TiBr.sub.4, Ti(OC.sub.2H.sub.5).sub.3Cl,
Ti(OC.sub.3H.sub.7).sub.2Cl.sub.2,
Ti(OC.sub.6H.sub.13).sub.2Cl.sub.2,
Ti(OC.sub.2H.sub.5).sub.2Br.sub.2, and
Ti(OC.sub.12H.sub.25)Cl.sub.3. The transition metal compound is
typically supported on an inert solid, e.g., magnesium
chloride.
[0007] Ziegler-Natta catalysts generally are provided on a support,
i.e. deposited on a solid crystalline support. The support can be
an inert solid, which is chemically unreactive with any of the
components of the conventional Ziegler-Natta catalyst. The support
is often a magnesium compound. Examples of the magnesium compounds
which can be used to provide a support source for the catalyst
component are magnesium halides, dialkoxymagnesiums,
alkoxymagnesium halides, magnesium oxyhalides, dialkylmagnesiums,
magnesium oxide, magnesium hydroxide, and carboxylates of
magnesium.
[0008] The properties of the polymerization catalyst can affect the
properties of the polymer formed using the catalyst. For example,
polymer morphology typically depends upon catalyst morphology. Good
polymer morphology includes uniformity of particle size and shape
and an acceptable bulk density. Furthermore, it is desirable to
minimize the number of very small polymer particles (i.e., fines)
for various reasons, such as for example, to avoid plugging
transfer or recycle lines. Very large particles also must be
minimized to avoid formation of lumps and strings in the
polymerization reactor.
[0009] Another polymer property affected by the type of catalyst
used is the molecular weight distribution (MWD), which refers to
the breadth of variation in the length of molecules in a given
polymer resin. In polyethylene for example, narrowing the MWD may
improve toughness, i.e., puncture, tensile, and impact performance.
On the other hand, a broad MWD can favor ease of processing and
melt strength.
[0010] While much is known about Ziegler-type catalysts, there is a
constant search for improvements in their polymer yield, catalyst
life, catalyst activity, and in their ability to produce
polyolefins having certain properties.
SUMMARY OF THE INVENTION
[0011] One embodiment of the present invention provides a process
for making a catalyst comprising: a) contacting a magnesium
dialkoxide compound with a halogenating agent to form a reaction
product A; b) contacting reaction product A with a first
halogenating/titanating agent to form reaction product B; c)
contacting reaction product B with a second halogenating/titanating
agent to form reaction product C; and d) contacting reaction
product C with a third halogenating/titanating agent to form
reaction product D. The second and third halogenating/titanating
agents can comprise titanium tetrachloride. The second and third
halogenating/titanating steps can each comprise a titanium to
magnesium ratio in the range of about 0.1 to 5. The reaction
products A, B and C can each be washed with a hydrocarbon solvent
prior to subsequent halogenating/titanating steps. The reaction
product D can be washed with a hydrocarbon solvent until titanium
species [Ti] content is less than about 100 mmol/L.
[0012] Another embodiment of the present invention provides a
polyolefin catalyst produced by a process generally comprising
contacting a catalyst component of the invention together with an
organometallic agent. The catalyst component is produced by a
process as described above. The catalysts of the invention can have
a fluff morphology amenable to polymerization production processes,
and may provide a polyethylene having a molecular weight
distribution of at least 5.0 and may provide uniform particle size
distributions with low levels of particles of less than about 125
microns. The activity of the catalyst is dependent upon the
polymerization conditions. Generally the catalyst will have an
activity of at least 5,000 gPE/g catalyst, but the activity can
also be greater than 50,000 gPE/g catalyst or greater than 100,000
gPE/g catalyst.
[0013] Even another embodiment of the present invention provides a
polyolefin polymer produced by a process comprising: a) contacting
one or more olefin monomers together in the presence of a catalyst
of the invention, under polymerization conditions; and b)
extracting polyolefin polymer. Generally the monomers are ethylene
monomers and the polymer is polyethylene.
[0014] Yet another embodiment of the present invention provides a
film, fiber, pipe, textile material or article of manufacture
comprising polymer produced by the present invention. The article
of manufacture can be a film comprising at least one layer
comprising a polymer produced by a process comprising a catalyst of
the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 illustrates the settling efficiency curves for
polymer made using a catalyst of the invention (Example 1), and
polymer made using a conventional catalyst (Comparative Example
4).
DETAILED DESCRIPTION OF THE INVENTION
[0016] According to one embodiment of the invention, a method for
making a catalyst component generally includes the steps of forming
a metal dialkoxide from a metal dialkyl and an alcohol,
halogenating the metal dialkoxide to form a reaction product,
contacting the reaction product with one or more
halogenating/titanating agent in three or more steps to form a
catalyst component, and then treating the catalyst component with a
preactivation agent such as an organoaluminum.
[0017] One embodiment of the present invention can be generally as
follows:
MRR'+2R-OH.fwdarw.M(OR").sub.2 1.
M(OR").sub.2+ClAR'".sub.x.fwdarw."A" 2.
"A"+TiCl.sub.4/Ti(OR"").sub.4.fwdarw."B" 3.
"B"+TiCl.sub.4.fwdarw."C"; 4.
"C"+TiCl.sub.4.fwdarw."D" 5.
"D"+preactivating agent.fwdarw.catalyst
[0018] In the above formulas, M can be any suitable metal, usually
a Group IIA metal, typically Mg. In the above formulas, R, R', R",
R'", and R"" are each independently hydrocarbyl or substituted
hydrocarbyl moieties, with R and R' having from 1 to 20 carbon
atoms, generally from 1 to 10 carbon atoms, typically from 2 to 6
carbon atoms, and can have from 2 to 4 carbon atoms. R" generally
comprises from 3 to 20 carbon atoms, R'" generally comprises from
2-6 carbon atoms, and R"" generally comprises from 2-6 carbon atoms
and is typically butyl. Any combination of two or more of R, R',
R", R'", and R"" can be used, may be the same, or the combination
of the R groups may be different from one another.
[0019] In the above embodiment comprising formula ClAR'".sub.x, A
is a nonreducing oxyphilic compound which is capable of exchanging
one chloride for an alkoxide, R'" is a hydrocarbyl or substituted
hydrocarbyl, and x is the valence of A minus 1. Examples of A
include titanium, silicon, aluminum, carbon, tin and germanium,
typically is titanium or silicon wherein x is 3. Examples of R'"
include methyl, ethyl, propyl, isopropyl and the like having 2-6
carbon atoms. Nonlimiting examples of a chlorinating agent that can
be used in the present invention are ClTi(O.sup.iPr).sub.3 and
ClSi(Me).sub.3.
[0020] The metal dialkoxide of the above embodiment is chlorinated
to form a reaction product "A". While the exact composition of
product "A" is unknown, it is believed that it contains a partially
chlorinated metal compound, one example of which may be
ClMg(OR").
[0021] Reaction product "A" is then contacted with one or more
halogenating/titanating agent, such as for example a combination of
TiCl.sub.4 and Ti (OBu).sub.4, to form reaction product "B".
Reaction product "B" which is probably a complex of chlorinated and
partially chlorinated metal and titanium compounds. Reaction
product "B" can comprise a titanium impregnated MgCl.sub.2 support
and for example, may possibly be represented by a compound such as
(MCl.sub.2).sub.y(TiClx(OR)- .sub.4-x).sub.z. Reaction product "B"
can be precipitated as a solid from the catalyst slurry.
[0022] The second halogenation/titanation step produces reaction
product, or catalyst component, "C" which is also probably a
complex of halogenated and partially halogenated metal and titanium
compounds but different from "B" and may possibly be represented by
(MCl.sub.2).sub.y(TiCl.sub.X'(OR).sub.4-x').sub.z'. It is expected
that the level of halogenation of "C" would be greater than that of
product "B". This greater level of halogenation can produce a
different complex of compounds.
[0023] The third halogenation/titanation step produces a reaction
product, or catalyst component, "D" which is also probably a
complex of halogenated and partially halogenated metal and titanium
compounds but different from "B" and "C", and may possibly be
represented by (MCl.sub.2).sub.y(TiCl.sub.X"(OR).sub.4-x").sub.z".
It is expected that the level of halogenation of "D" would be
greater than that of product "C". This greater level of
halogenation would produce a different complex of compounds. While
this description of the reaction products offers the most probable
explanation of the chemistry at this time, the invention as
described in the claims is not limited by this theoretical
mechanism.
[0024] Metal dialkyls and the resultant metal dialkoxides suitable
for use in the present invention can include any that can be
utilized in the present invention to yield a suitable polyolefin
catalyst. These metal dialkoxides and dialkyls can include Group
IIA metal dialkoxides and dialkyls. The metal dialkoxide or dialkyl
can be a magnesium dialkoxide or dialkyl. Non-limiting examples of
suitable magnesium dialkyls include diethyl magnesium, dipropyl
magnesium, dibutyl magnesium, butylethylmagnesium, etc.
Butylethylmagnesium (BEM) is one suitable magnesium dialkyl.
[0025] In the practice of the present invention, the metal
dialkoxide can be a magnesium compound of the general formula
Mg(OR").sub.2 where R" is a hydrocarbyl or substituted hydrocarbyl
of 1 to 20 carbon atoms.
[0026] The metal dialkoxide can be soluble and is typically
non-reducing. A non-reducing compound has the advantage of forming
MgCl.sub.2 instead of insoluble species that can be formed by the
reduction of compounds such as MgRR', which can result in the
formation of catalysts having a broad particle size distribution.
In addition, Mg(OR").sub.2, which is less reactive than MgRR', when
used in a reaction involving chlorination with a mild chlorinating
agent, followed by subsequent halogenation/titanation steps, can
result in a more uniform product, e.g., better catalyst particle
size control and distribution.
[0027] Non-limiting examples of species of metal dialkoxides which
can be used include magnesium butoxide, magnesium pentoxide,
magnesium hexoxide, magnesium di(2-ethylhexoxide), and any alkoxide
suitable for making the system soluble.
[0028] As a non-limiting example, magnesium dialkoxide, such as
magnesium di (2-ethylhexoxide), may be produced by reacting an
alkyl magnesium compound (MgRR') with an alcohol (ROH), as shown
below.
MgRR'+2R-OH.fwdarw.Mg(OR").sub.2+RH+R'H
[0029] The reaction can take place at room temperature and the
reactants form a solution. R and R' may each be any alkyl group of
1-10 carbon atoms, and may be the same or different. Suitable MgRR'
compounds include, for example, diethyl magnesium, dipropyl
magnesium, dibutyl magnesium and butyl ethyl magnesium. The MgRR'
compound can be BEM, wherein RH and R'H are butane and ethane,
respectively.
[0030] In the practice of the present invention, any alcohol
yielding the desired metal dialkoxide may be utilized. Generally,
the alcohol utilized may be any alcohol of the general formula R"OH
where R" is an alkyl group of 2-20 carbon atoms, the carbon atoms
can be at least 3, at least 4, at least 5, or at least 6 carbon
atoms. Non-limiting examples of suitable alcohols include ethanol,
propanol, isopropanol, butanol, isobutanol, 2-methyl-pentanol,
2-ethylhexanol, etc. While it is believed that almost any alcohol
may be utilized, linear or branched, a higher order branched
alcohol, for example, 2-ethyl-1-hexanol, can be utilized.
[0031] The amount of alcohol added can vary, such as within a
non-exclusive range of 0 to 10 equivalents, is generally in the
range of about 0.5 equivalents to about 6 equivalents (equivalents
are relative to the magnesium or metal compound throughout), and
can be in the range of about 1 to about 3 equivalents.
[0032] Alkyl metal compounds can result in a high molecular weight
species that is very viscous in solution. This high viscosity may
be reduced by adding to the reaction an aluminum alkyl such as, for
example, triethylaluminum (TEAl), which can disrupt the association
between the individual alkyl metal molecules. The typical ratio of
alkyl aluminum to metal can range from 0.001:1 to 1:1, can be 0.01
to 0.5:1 and also can range from 0.03:1 to 0.2:1. In addition, an
electron donor such as an ether, for example, diisoamyl ether
(DIAE), may be used to further reduce the viscosity of the alkyl
metal. The typical ratio of electron donor to metal ranges from 0:1
to 10:1 and can range from 0.1:1 to 1:1.
[0033] Agents useful in the step of halogenating the metal alkoxide
include any halogenating agent which when utilized in the present
invention will yield a suitable polyolefin catalyst. The
halogenating step can be a chlorinating step where the halogenating
agent contains a chloride (i.e, is a chlorinating agent).
[0034] Halogenating of the metal alkoxide compound is generally
conducted in a hydrocarbon solvent under an inert atmosphere.
Non-limiting examples of suitable solvents include toluene,
heptane, hexane, octane and the like. In this halogenating step,
the mole ratio of metal alkoxide to halogenating agent is generally
in the range of about 6:1 to about 1:3, can be in the range of
about 3:1 to about 1:2, can be in the range of about 2:1 to about
1:2, and can also be about 1:1.
[0035] The halogenating step is generally carried out at a
temperature in the range of about 0.degree. C., to about
100.degree. C. and for a reaction time in the range of about 0.5 to
about 24 hours. The halogenating step can be carried out at a
temperature in the range of about 20.degree. C. to about 90.degree.
C. and for a reaction time in the range of about 1 hour to about 4
hours.
[0036] Once the halogenating step is carried out and the metal
alkoxide is halogenated, the halide product "A" can be subjected to
two or more halogenating/titanating treatments.
[0037] The halogenation/titanation agents utilized can be blends of
two tetra-substituted titanium compounds with all four substituents
being the same and the substituents being a halide or an alkoxide
or phenoxide with 2 to 10 carbon atoms, such as TiCl.sub.4 or
Ti(OR"").sub.4. The halogenation/titanation agent utilized can be a
chlorination/titanation agent.
[0038] The halogenation/titanation agent may be a single compound
or a combination of compounds. The method of the present invention
provides an active catalyst after the first
halogenation/titanation; however, there are desirably a total of at
least three halogenation/titanation steps.
[0039] The first halogenation/titanation agent is typically a mild
titanation agent, which can be a blend of a titanium halide and an
organic titanate. The first halogenation/titanation agent can be a
blend of TiCl.sub.4 and Ti(OBu).sub.4 in a range from 0.5:1 to 6:1
TiCl.sub.4/Ti(OBu).sub.4, the ratio can be from 2:1 to 3:1. It is
believed that the blend of titanium halide and organic titanate
react to form a titanium alkoxyhalide, Ti(OR).sub.aX.sub.b, where
OR and X are alkoxide and halide, respectively and a+b is the
valence of titanium, which is typically 4.
[0040] In the alternative, the first halogenation/titanation agent
may be a single compound. Examples of a first
halogenation/titanation agent are Ti(OC.sub.2H.sub.5).sub.3Cl,
Ti(OC.sub.2H.sub.5).sub.2Cl.sub.2,
Ti(OC.sub.3H.sub.7).sub.2Cl.sub.2, Ti(OC.sub.3H.sub.7).sub.3Cl,
Ti(OC.sub.4H.sub.9)Cl.sub.3, Ti(OC.sub.6H.sub.13).sub.2Cl.sub.2,
Ti(OC.sub.2H.sub.5).sub.2Br.sub.2, and
Ti(OC.sub.12H.sub.5)Cl.sub.3.
[0041] The first halogenation/titanation step is generally carried
out by first slurrying the halogenation product "A" in a
hydrocarbon solvent at room temperature/ambient temperature.
Nonlimiting examples of suitable hydrocarbons solvent include
heptane, hexane, toluene, octane and the like. The product "A" can
be at least partially soluble in the hydrocarbon solvent.
[0042] A solid product "B" is precipitated at room temperature
following the addition of the halogenation/titanation agent to the
soluble product "A". The amount of halogenation/titanation agent
utilized must be sufficient to precipitate a solid product from the
solution. In general, the amount of halogenation/titanation agent
utilized, based on the ratio of titanium to metal, will generally
be in the range of about 0.5 to about 5, typically in the range of
about 1 to about 4, and can be in the range about 1.5 to about
2.5.
[0043] The solid product "B" precipitated in this first
halogenation/titanation step is then recovered by any suitable
recovery technique, and then washed at room/ambient temperature
with a solvent, such as hexane. Generally, the solid product "B" is
washed until the [Ti] is less than about 100mmol/L. Within the
present invention [Ti] represents any titanium species capable of
acting as a second generation Ziegler catalyst, which would
comprise titanium species that are not part of the reaction
products as described herein. The resulting product "B" is then
subjected to a second and third halogenating/titanating steps to
produce products "C" and "D". After each halogenating/titanating
step the solid product can be washed until the [Ti] is less than a
desired amount. For example, less than about 100 mmol/L, less than
about 50 mmol/L, or less than about 10 mmol/L. After the final
halogenating/titanating step, the product can be washed until the
[Ti] is less than a desired amount, for example, less than about 20
mmol/L, less than about 10 mmol/L, or less than about 1.0 mmol/L.
It is believed that a lower [Ti] can produce improved catalyst
results by reducing the amount of titanium that can act as a second
generation Ziegler species. It is believed that a that a lower [Ti]
can be a factor in producing improved catalyst results such as a
narrower MWD.
[0044] The second halogenation/titanation step is generally carried
out by slurrying the solid product recovered from the first
titanation step, solid product "B", in a hydrocarbon solvent.
Hydrocarbon solvents listed as suitable for the first
halogenation/titanation step may be utilized. The second and third
halogenation/titanation steps can utilize a different compound or
combination of compounds from the first halogenation/titanation
step. The second and third halogenation/titanation steps can
utilize the same agent at a concentration that is stronger than
that used in the first halogenation/titanation agent, but this is
not a necessity. The second and third halogenating/titanating
agents can be a titanium halide, such as titanium tetrachloride
(TiCl.sub.4). The halogenation/titanation agent is added to the
slurry. The addition can be carried out at ambient/room
temperature, but can also be carried out at temperatures and
pressures other than ambient.
[0045] Generally, the second and third halogenation/titanation
agents comprise titanium tetrachloride. Typically the second and
third halogenation/titanation steps each comprise a titanium to
magnesium ratio in a range of about 0.1 to 5, a ratio of about 2.0
can also be used, and a ratio of about 1.0 can be used. The third
halogenation/titanation step is generally carried out at room
temperature and in a slurry, but can also be carried out at
temperatures and pressures other than ambient.
[0046] The amount of titanium tetrachloride utilized, or alternate
halogenation/titanation agent, may also be expressed in terms of
equivalents, an equivalent herein is amount of titanium relative to
the magnesium or metal compound. The amount of titanium of each of
the second and third halogenating/titanating steps will generally
be in the range of about 0.1 to about 5.0 equivalents, can be in
the range of about 0.25 to about 4 equivalents, typically is in the
range of about 0.3 to about 3 equivalents, and it can be desirable
to be in the range of about 0.4 to about 2.0 equivalents. In one
particular embodiment, the amount of titanium tetrachloride
utilized in each of the second and third halogenation/titanation
steps is in the range of about 0.45 to about 1.5 equivalent.
[0047] The catalyst component "D" made by the above described
process may be combined with an organometallic catalyst component
(a "preactivating agent") to form a preactivated catalyst system
suitable for the polymerization of olefins. Typically, the
preactivating agents which are used together with the transition
metal containing catalyst component "D" are organometallic
compounds such as aluminum alkyls, aluminum alkyl hydrides, lithium
aluminum alkyls, zinc alkyls, magnesium alkyls and the like.
[0048] The preactivating agent is generally an organoaluminum
compound. The organoaluminum preactivating agent is typically an
aluminum alkyl of the formula AIR.sub.3 wherein at least one R is
an alkyl having 1-8 carbon atoms or a halide, and wherein each of
the R may be the same or different. The organoaluminum
preactivating agent can be a trialkyl aluminum such as, for
example, trimethyl aluminum (TMA), triethyl aluminum (TEAI) and
triisobutyl aluminum (TiBAl). The ratio of Al to titanium can be in
the range from 0.1:1 to 2:1 and typically is 0.25:1 to 1.2:1.
[0049] Optionally, the Ziegler-Natta catalyst may be
pre-polymerized. Generally, a prepolymerization process is affected
by contacting a small amount of monomer with the catalyst after the
catalyst has been contacted with the co-catalyst. A
pre-polymerization process is described in U.S. Pat. Nos.
5,106,804; 5,153,158; and 5,594,071, hereby incorporated by
reference.
[0050] The catalyst of the present invention may be used in any
process for the homopolymerization or copolymerization of any type
of .alpha.-olefins. For example, the present catalyst can be useful
for catalyzing ethylene, propylene, butylene, pentene, hexene,
4-methylpentene and other .alpha.-alkenes having at least 2 carbon
atoms, and also for mixtures thereof. Copolymers of the above can
produce desirable results such as broader MWD and multi-modal
distributions such as bimodal and trimodal properties. The
catalysts of the present invention can be utilized for the
polymerization of ethylene to produce polyethylene.
[0051] Various polymerization processes can be employed with the
present invention, such as for example, single and/or multiple loop
processes, batch processes or continous processes not involving a
loop-type reactor. An example of a multiple loop process that can
employ the present invention is a double loop system in which the
first loop produces a polymerization reaction in which the
resulting polyolefin has a lower MW than the polyolefin produced
from the polymerization reaction of the -second loop, thereby
producing a resultant resin having broad molecular weight
distribution and/or bimodal characteristics. In the alternative,
another example of a multiple loop process that can employ the
present invention is a double loop system in which the first loop
produces a polymerization reaction in which the resulting
polyolefin has a greater MW than the polyolefin produced from the
polymerization reaction of the second loop, thereby producing a
resultant resin having broad molecular weight distribution and/or
bimodal characteristics.
[0052] The polymerization process may be, for example, bulk, slurry
or gas phase. A catalyst of the invention can be used in slurry
phase polymerization. Polymerization conditions (e.g., temperature
and pressure) are dependent upon the type of equipment utilized in
the polymerization process, as well as the type of polymerization
process utilized, and are known in the art. Generally, the
temperature will be in a range of about 50-110.degree. C., and the
pressure in a range of about 10-800 psi.
[0053] The activity of the resulting catalyst of embodiments of the
present invention is at least partially dependent upon the
polymerization process and conditions, such as, for example,
equipment utilized and temperature of reaction. For example in the
embodiment of polymerization of ethylene to produce polyethylene,
generally the catalyst will have an activity of at least 5,000 g
PE/g catalyst but can have an activity of greater than 50,000 g
PE/g catalyst, and the activity may be greater than 100,000 g PE/g
catalyst.
[0054] Additionally, the resulting catalyst of the present
invention can provide a polymer with improved fluff morphology.
Thus, the catalyst of the present invention can provide for large
polymer particles with a uniform distribution of sizes, wherein
fine particles (less than about 125 microns) are only present in
low concentrations, such as for example, less than 2% or less than
1%. The catalysts of the present invention, which include large,
readily transferred powders with high powder bulk densities, are
amenable to polymerization production processes. Generally the
catalysts of the invention provide polymer with fewer fines and
higher bulk densities (B.D.) wherein the B.D. value can be greater
than about 0.31 g/cc, can be greater than about 0.33 g/cc, and can
even be greater than about 0.35 g/cc.
[0055] The olefin monomer may be introduced into the polymerization
reaction zone in a diluent that is a nonreactive heat transfer
agent that is a liquid at the reaction conditions. Examples of such
a diluent are hexane and isobutane. For the copolymerization of
ethylene with another alpha-olefin, such as, for example, butene or
hexene, the second alpha-olefin may be present at 0.01-20 mole
percent, and can be present at between about 0.02-10 mole
percent.
[0056] Optionally, an electron donor may be added with the
halogenation agent, the first halogenation/titanation agent, or the
subsequent halogenation/titanation agent or agents. It may be
desirable to have an electron donor utilized in the second
halogenation/titanation step. Electron donors for use in the
preparation of polyolefin catalysts are well known, and any
suitable electron donor may be utilized in the present invention
that will provide a suitable catalyst. Electron donors, also known
as Lewis bases, are organic compounds of oxygen, nitrogen,
phosphorous, or sulfur which can donate an electron pair to the
catalyst.
[0057] The electron donor may be a monofunctional or polyfunctional
compound, can be selected from among the aliphatic or aromatic
carboxylic acids and their alkyl esters, the aliphatic or cyclic
ethers, ketones, vinyl esters, acryl derivatives, particularly
alkyl acrylates or methacrylates and silanes. An example of a
suitable electron donor is di-n-butyl phthalate. A generic example
of a suitable electron donor is an alkylsilylalkoxide of the
general formula RSi(OR').sub.3, e.g., methylsilyltriethoxide
[MeSi(OEt.sub.3)], where R and R' are alkyls with 1-5 carbon atoms
and may be the same or different.
[0058] For the polymerization process, an internal electron donor
can be used in the synthesis of the catalyst and an external
electron donor or stereoselectivity control agent (SCA) to activate
the catalyst at polymerization. An internal electron donor may be
used in the formation reaction of the catalyst during the
halogenation or halogenation /titanation steps. Compounds suitable
as internal electron donors for preparing conventional supported
Ziegler-Natta catalyst components include ethers, diethers,
ketones, lactones, electron donors compounds with N, P and/or S
atoms and specific classes of esters. Particularly suitable are the
esters of phthalic acid, such as diisobutyl, dioctyl, diphenyl and
benzylbutylphthalate; esters of malonic acid, such as diisobutyl
and diethylmalonate; alkyl and arylpivalates; alkyl, cycloalkyl and
arylmaleates; alkyl and aryl carbonates such as diisobutyl,
ethyl-phenyl and diphenylcarbonate; succinic acid esters, such as
mono and diethyl succinate.
[0059] External donors which may be utilized in the preparation of
a catalyst according to the present invention include organosilane
compounds such as alkoxysilanes of general formula
SiR.sub.m(OR').sub.4-m where R is selected from the group
consisting of an alkyl group, a cycloalkyl group, an aryl group and
a vinyl group; R' is an alkyl group; and m is 0-3, wherein R may be
identical with R'; when m is 0, 1 or 2, the R' groups may be
identical or different; and when m is 2 or 3, the R groups may be
identical or different.
[0060] The external donor of the present invention can be selected
from a silane compound of the following formula: 1
[0061] wherein R.sub.1 and R.sub.4 are both an alkyl or cycloalkyl
group containing a primary, secondary or tertiary carbon atom
attached to the silicon, R.sub.1 and R.sub.4 being the same or
different; R.sub.2 and R.sub.3are alkyl or aryl groups. R.sub.1 may
be methyl, isopropyl, cyclopentyl, cyclohexyl or t-butyl;
R.sub.2and R.sub.3may be methyl, ethyl, propyl, or butyl groups and
not necessarily the same; and R.sub.4 may also methyl, isopropyl,
cyclopentyl, cyclohexyl or t-butyl. Specific external donors are
cyclohexylmethydimethoxy silane (CMDS), diisopropyldimethoxysilane
(DIDS) cyclohexylisopropyl dimethoxysilane (CIDS),
dicyclopentyldimethoxysilane (CPDS) or di-t-butyl dimethoxysilane
(DTDS).
[0062] Polyethylene produced using the above described catalyst can
have an MWD of at least 5.0, and can be greater than about 6.0.
[0063] The polyolefins of the present invention are suitable for
use in a variety of applications such as, for example, an extrusion
process, to yield a wide range of products. These extrusion
processes include, for example, blown film extrusion, cast film
extrusion, slit tape extrusion, blow molding, pipe extrusion, and
foam sheet extrusion. These processes may comprise mono-layer
extrusion or multi-layer coextrusion.
[0064] End use applications that can be made utilizing the present
invention can include, for example, films, fibers, pipe, textile
material, articles of manufacture, diaper components, feminine
hygiene products, automobile components and medical materials.
[0065] All references cited herein, including research articles,
all U.S. and foreign patents and patent applications, are
specifically and entirely incorporated by reference.
EXAMPLES
[0066] The invention having been generally described, the following
examples are provided merely to illustrate certain embodiments of
the invention, and to demonstrate the practice and advantages
thereof. It is understood that the examples are given by way of
illustration and are not intended to limit the scope of the
specification or the claims in any manner.
[0067] The synthetic scheme employed for this family of catalysts
is as follows (all ratios are relative to BEM):
(BEM+0.03 TEA1+0.6 DIAE)+2.09
2-Ethylhexanol.fwdarw.Mg(OR).sub.2
Mg(OR).sub.2+ClTi(OPr).sub.3.fwdarw.Solution A
Solution A+(2TiCl.sub.4/Ti(OBu).sub.4.fwdarw.Catalyst B (MgCl.sub.2
based support)
Catalyst B+X TiCl.sub.4.fwdarw.Catalyst C
Catalyst C+0.156TEAl.fwdarw.Final Catalyst
[0068] The optimal formulation was regarded as X=0.5 to 2, with
zero to two washes prior to preactivation of catalyst C with TEAl.
The following modifications were made to the catalyst preparation
for a more effective titanation:
Catalyst B+X TiCl.sub.4.fwdarw.Catalyst C
Catalyst C+Y TiCl.sub.4.fwdarw.Catalyst D
Catalyst D+0.156 TEAl.fwdarw.Final Catalyst
[0069] As shown, TiCl.sub.4 addition is completed in two steps
where X and Y=0.5 to 1.0. Catalyst C is generally washed one to two
times, while two washes are completed after Y to remove soluble
titanium species that act as second generation Ziegler species.
Example 1
[0070] In the nitrogen purge box, 1412.25 g (2.00 moles) of BEM-1,
27.60 g (0.060 moles) of TEAl (24.8% in heptane), and 189.70 g
(1.20 moles) of DLAE were added to a 3 L round bottom flask. The
contents were then transferred to the 20 L Buchi reactor via
cannula under a nitrogen flow. The flask was then rinsed with
approximately 400 ml of hexane which was transferred to the
reactor. The stirrer was set to 350 rpm.
[0071] The 2-ethylhexanol (543.60 g, 4.21 moles) was added to a 1 L
bottle and capped. It was then diluted to a total volume of 1 L
with hexane prior to addition to the reactor. This solution was
transferred to the reactor via cannula using the mass flow
controller. The initial head temperature was 25.3.degree. C. and
reached a maximum temperature of 29.6.degree. C. Following the
addition (approximately 2 hours), the bottle was rinsed with 400 ml
of hexane which was transferred to the reactor. The reaction
mixture was left stirring at 350 rpm overnight under a nitrogen
pressure of 0.5 bar and the heat exchanger was turned off.
[0072] The heat exchanger was turned on and set to 25.degree. C.
The chlorotitanium triisopropoxide was added to two 1 L bottles
(774.99 and 775.01 g, 2.00 total moles) to give a total of two
liters. The contents of each bottle were transferred to the reactor
via cannula using the mass flow controller. The initial head space
temperature was 24.6.degree. C. and reached a maximum temperature
of 25.9.degree. C. during the addition of the second bottle. The
addition times were 145 and 125 minutes for bottles 1 and 2,
respectively. After the addition, each bottle was rinsed with 200
ml of hexane which was transferred to the reactor. The reaction
mixture was left stirring at 350 rpm overnight under nitrogen
pressure of 0.5 bar. The heat exchanger was turned off.
[0073] Preparation of TiCl.sub.4/Ti(OBu).sub.4 The titanium
tetrachloride/titanium tetrabutoxide mixtures were prepared in a 5
liter round bottom flask using standard schlenk line techniques. In
a 1 L pressure bottle, 680.00 g (1.99 moles) of Ti(OBu)4 was
diluted to 1 L total volume with hexane. This solution was then
cannula transferred to the reactor. The bottle was rinsed with 200
ml of hexane and transferred to the reactor. In a 1 L measuring
cylinder, 440 ml (.about.760 g, 4.00 moles) of TiCl.sub.4 was
diluted to a total volume of 1 L with hexane. The solution in the 5
liter flask was stirred and the TiCl.sub.4 solution was added to
the reactor dropwise under N.sub.2 pressure via cannula. After the
addition was complete, the 1 L cylinder was rinsed with 200 ml of
hexane which was transferred to the reactor. After 1 hour, the
reaction mixture was diluted to 4 L total volume with hexane and
stored in the flask prior to use.
[0074] The heat exchanger was turned on and set to 25.degree. C.
The TiCl.sub.4/Ti(OBu).sub.4 mixture was transferred to the 20
liter reactor via cannual and mass flow controller. The initial
head space temperature was 24.7.degree. C. and reached a maximum
temperature of 26.0.degree. C. during the 225 minute addition.
Following the additions, the vessel was rinsed with one liter of
hexane and allowed to stir for 1 hour.
[0075] The stirrer was turned off and the solution allowed to
settle for 30 minutes. The solution was decanted by pressuring the
reactor to 1 bar, lowering the dip tube, and making sure no solid
catalyst came through the attached clear plastic hose. The catalyst
was then washed three times using the following procedure. Using a
pressure vessel on a balance, 2.7 kg of hexane was weighed into the
vessel and then transferred to the reactor. The stirrer was turned
on and the catalyst mixture was agitated for 15 minutes. The
stirrer was then turned off and the mixture was allowed to settle
for 30 minutes. This procedure was repeated. After the third
addition of hexane, the slurry was allowed to settle overnight and
the heat exchanger was turned off.
[0076] The supernatant was decanted, and 2.0 kg of hexane added to
the reactor. Stirring was resumed at 350 rpm and the heat exchanger
was turned on and set to 25.degree. C. In a one liter graduated
cylinder, 440 milliliters (760 g, 4.00 moles) of titanium
tetrachloride were added. The TiCl.sub.4 was diluted to one liter
with hexane, and half of the solution was transferred to the
reactor via cannula and mass flow controller. The initial head
temperature of 24.7.degree. C. increased 0.5.degree. C. during the
addition. The total addition time was 45 minutes. After one hour,
the stirrer was turned off and the solids were allowed to settle
for 30 minutes. The supernatant was decanted, and the catalyst was
washed once with hexane following the procedures described above.
After the wash was complete, 2.0 kg of hexane was transferred to
the reactor and the agitation was resumed. The second TiCl.sub.4
drop was completed in a similar manner to that described above
using the remaining 500 milliliters of solution. Following the
addition, the cylinder was rinsed with 400 milliliters of hexane,
which was added to the Buchi. After one hour of reaction, the
stirrer was turned off and the solids were allowed to settle for 30
minutes. The supernatant was then decanted, and the catalyst washed
three times with hexane. 2.0 kg of hexane was then transferred to
the reactor.
[0077] In a one liter pressure bottle, 144.8 g (312 mmol) of TEAl
(25.2% in hexane) were added. The bottle was capped and diluted to
one liter with hexane. This solution was then transferred to the
reaction mixture via cannula using the mass flow controller. During
the 120 minute addition, the color of the slurry turned dark brown.
The initial head temperature was 24.5.degree. C. and reached a
maximum temperature of 25.3.degree. C. Following the addition, the
bottle was rinsed with 400 milliliters of hexane, which was
transferred to the reactor. After 1 hour of reaction, the stirrer
was shut off and the catalyst was allowed to settle for 30 minutes.
The supernatant was decanted and the catalyst was washed once
following the procedures previously described. Following the wash,
2.7 kg of hexane was added to the reactor. The contents were then
transferred to a three gallon pressure vessel. The Buchi was rinsed
with 1.0 kg and 0.5 kg of hexane, which were added to the pressure
vessel. Estimated catalyst yield was 322 g.
[0078] In one embodiment the composition in weight percent was: Cl
53.4%; Al 2.3%; Mg 11.8% and Ti at 7.9%. Observed ranges for each
element were; Cl at 48.6-55.1%; Al at 2.3-2.5%; Mg at 11.8-14.1%;
and Ti of 6.9-8.7%. Ranges for each element can be; Cl at
40.0-65.0%; Al at 0.0-6.0%; Mg at 6.0-15.0%; and Ti of
2.0-14.0%.
[0079] Table 1 lists the [Ti] measured from samples after the
TiCl4/Ti(OBu).sub.4 addition, three washes, a first TiCl.sub.4
addition, one wash and the second TiCl.sub.4 addition and three
subsequent washes. Decants 1-4 are following the
TiCl4/Ti(OBu).sub.4 addition. Decants 5 and 6 are following the
first TiCl.sub.4 addition. Decants 7-10 follow the second
TiCl.sub.4 addition.
1 TABLE 1 Decant Sample Ti (ppm) mmol/L 1 2.1 21000 306.9 2 0.8
8000 116.9 3 0.2 2000 29.2 4 0.1 1000 14.6 5 2 20000 292.3 6 0.4
4000 58.5 7 1.9 19000 277.7 8 0.4 4000 58.5 9 0.0925 925 13.5 10
0.0064 64 0.9
Comparative Example 1
[0080] Comparative Example 1 was prepared in a similar manner to
that of Example 1 except the third titanation was omitted and the
second titantion was carried out employing one fourth of the
quantity of TiCl.sub.4
Comparative Example 2
[0081] Comparative Example 2 was prepared in a similar fashion to
Example 1 except a second and third titantion step was performed
employing 0.5 equivalents of TiCl.sub.4 during each titanation
step.
Comparative Example 3
[0082] Comparative Example 3 was prepared in a similar manner to
Comparative Example 1 except the quantity of TiCl.sub.4 employed
during the second titanation was approximately four times that used
during Comparative Example 1. One hexane wash was performed
following the second titanation. In one embodiment the composition
in weight percent was: Cl at 57.0%; Al at 2.0%; Mg at 9.5% and Ti
at 10.0%. Ranges for each element can be; Cl at 55.0-57.0%; Al at
2.0-2.6%; Mg at 8.9-9.5%; and Ti of 10.0-11.0%.
Comparative Example 4
[0083] Comparative Example 4 was prepared in a similar manner to
Comparative Example 3 except two hexane washes were performed
following the second titanation. In one embodiment the composition
in weight percent was: Cl 53.0%; Al 2.3%; Mg 9.7% and Ti at 9.5%.
Ranges for each element can be; Cl at 52.6-53.0%; Al at 2.0-2.3%;
Mg at 9.7-10.6%; and Ti of 8.7-9.5%.
[0084] Table 2 lists the catalysts prepared.
2TABLE 2 Number of Number of Catalyst X washes Y washes Comparative
Example 1 0.5 0 0 NA Comparative Example 2 0.5 1 0.5 2 Example 1
1.0 1 1.0 2 Comparative Example 3 2.0 1 0 NA Comparative Example 4
2.0 2 0 NA
[0085] Table 3 gives the MWD data provided for polymers made with
Example 1 and Comparative Examples 1 to 4. For a given
catalyst/cocatalyst system, the data show that a narrower MWD can
be attained by increasing the numbers of washes or addition of a
third titanation step with TiCi.sub.4. In general, the polymer
resin intrinsic MWD increases in the following order Comparative
Example 1<Comparative Example 2<Comparative Example
4<Example 1<Comparative Example 3.
3TABLE 3 Number of Number of Washes Washes SR5 D Catalyst
Cocatalyst following X following Y (HLMI/MI.sub.5) (Mw/Mn)
Comparative Example 1 TEA1 0 0 10.9 6.2 Comparative Example 2 TEA1
1 2 10.9 NA Example 1 TEA1 1 2 12.6 6.8 Comparative Example 3 TEA1
1 NA 11.8-12.8 5.9-6.8 Comparative Example 4 TEA1 2 NA 10.8-12.0
6.0-6.3 Example 1 TIBA1 1 2 11.9 7.0 Comparative Example 3 TIBA1 1
NA 12.2-13.6 6.9-7.3 Comparative Example 4 TIBAl 2 NA 11.4-11.8
6.6-7.5
[0086] As shown in Table 4, each of the catalysts provides powder
with low levels of fines (particles less than 125 microns);
however, catalysts of the invention prepared with two titanation
steps consistently provide fluff with higher bulk densities.
4TABLE 4 D.sub.50 Fluff D.sub.50 % B.D. Catalyst (microns)
(microns) Fines (g/cc) Comparative Example 1 9.4 260 0.0 0.38
Comparative Example 2 7.8 237 0.6 0.40 Comparative Example 4 10.1
287 1.6 0.34 Example 1 9.2 264 0.6 0.38
[0087] These properties have substantial effects on the settling
efficiency of the polymer as demonstrated by the laboratory derived
settling efficiency curves provided in FIG. 1. The rapid
disappearance of the initial 10 ml of fluff from solution exhibited
by the inventive polymer made with the inventive catalyst of
Example 1 implies a greater settling rate and better polymer
morphology than that made with conventional catalyst of comparative
Example 4.
[0088] While the illustrative embodiments of the invention have
been described with particularity, it is understood that various
other modifications can be readily made by those skilled in the art
without departing from the scope of the invention.
* * * * *