Note: Descriptions are shown in the official language in which they were submitted.
CA 02260891 1999-O1-19
WO 98/02469 PCT/EP97/03649
SYNDIOTACTIC/ATACTIC BLOCK POLYOLEFINS, CATALYSTS AND PROCESSES FOR
PRODUCING THE SAME
FIELD OF THE INVENTION:
The invention relates to a metallocene catalyst useful in preparing
syndiotactic/atactic block polyolefins and to the polymers so obtained.
The catalyst comprises a bridged monocyclopentadienyl metallocene in
which the cyclopentadienyl ring is substituted symmetrically with respect
to the active coordination positions. The invention further includes a
process of preparing syndiotactic/atactic block polyolefins that
comprises the use of the disclosed catalyst.
The present invention also provides for a process for polymerizing
olefins having three or more carbon atoms to produce polymers with
syndiotactic/atactic stereochemical configurations. The catalyst and
process of the invention are particularly useful in polymerizing
propylene to form a syndiotactic/atactic block polypropylene.
DESCRIPTION OF THE PRIOR ART:
As known in the art, syndiotactic polymers have a unique stereochemical
structure in which monomeric units having enantiomorphic configuration of
the asymmetrical carbon atoms follow each other alternately and regularly
in the macromolecular main chain. Syndiotactic polypropylene was first
disclosed by Natta et al. in U.S. Patent Number 3,258,455. The Natta
group obtained syndiotactic polypropylene by using a catalyst prepared
from titanium trichloride and diethyl aluminum monochloride. A later
patent to Natta et al., U.S. Patent Number 3,305,538, discloses the use
of vanadium triacetylacetonate or halogenated vanadium compounds in
combination with organic aluminum compounds for producing syndiotactic
polypropylene.
CONFIR>~AT!ON COr ~'
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WO 98/02469 PCT/EP97/03649
2
U.S. Patent Number 3,364,190 to Emrick discloses a catalyst system
composed of finely divided titanium or vanadium trichloride, aluminum
chloride, a trialkyl aluminum and a phosphorus-containing Lewis base as
producing syndiotactic polypropylene. U.S. Patent No. 4,892,851
disclosed a metallocene catalyst for producing highly crystalline
syndiotactic polyolefins.
As disclosed in these patent references and as known in the art, the
structure and properties of syndiotactic polypropylene differ
significantly from those of isotactic polypropylene. The isotactic
structure is typically described as having the methyl groups attached to
the tertiary carbon atoms of successive monomeric units on the same side
of a i-iypothetical plane through the main chain of the polymer, e.g., the
methyl groups are all above or below the plane. Using the Fischer
projection formula, the stereochemical sequence of isotactic
polypropylene is described as follows:
Another way of describing the structure is through the use of NMR.
Bovey's NMR nomenclature for an isotactic pentad is ...mmmm... with each
"m" representing a "meso" dyad or successive methyl groups on the same
side in the plane. As known in the art, any deviation or inversion in
the structure of the chain lowers the degree of isotacticity and
crystallinity of the polymer.
In contrast to the isotactic structure, syndiotactic polymers are those
in which the methyl groups attached to the tertiary carbon atoms of
successive monomeric units in the chain lie on alternate sides of the
plane of the polymer. Using the Fischer projection formula, the
structure of a syndiotactic polymer is designated as:
In NMR nomenclature, this pentad is described as ...rrrr... in which
each "r" represents a "racemic" dyad, i.e., successive methyl groups on
alternate sides of the plane.
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3
The percentage of r dyads in the chain determines the degree of
syndiotacticity of the polymer. Syndiotactic polymers are crystalline and,
like the isotactic polymers, are insoluble in xylene.
This crystallinity distinguishes both syndiotactic and isotactic polymers
from an atactic polymer that is soluble in xylene. Atactic polymer exhibits
no regular order of repeating unit configurations in the polymer chain and
forms essentially a waxy product. While it is possible for a catalyst to
produce all three types of polymer, it is desirable for a catalyst to produce
predominantly syndiotactic or isotactic polymer with some atactic block
fractions.
SUMMARY OF THE INVENTION
The invention provides for a new syndiotactic/atactic block homopolyolefins
and particularly a new syndiotactic/atactic block homopolypropylene.
The present invention also provides a catalyst and process for preparing
syndiotactic/atactic block polyolefins, and more particularly
syndiotactic/atactic block polypropylene. The catalyst and process can each
be adapted to produce a polymer with differing syndio-/atactic block ratios.
The catalyst comprises a metallocene, i.e., a metal derivative of a
cyclopentadiene, and an ionizing agent. The metallocene compound
contains only one substituted cyclopentadienyl ring derivative and is of the
general formula: R"(C4R'mCsC4R'a) XMeQ
wherein X is an hetero-atom ligand with one or two lone pair electrons and
selected from the elements of Group VA or VIA and is preferably nitrogen,
phosphorus, oxygen or sulfur, which can be substituted or non-substituted;
(C.~Rm'CsC4R~') is a fluorenyl or a symmetrically substituted fluorenyl or
cyclopentadienyl ring derivative; R' is
AMENDED SHEET
CA 02260891 1999-O1-19
.'
hydrogen or hydrocarbyl radical having from 1-20 carbon atoms, a halogen,
an alkoxy, and alkoxy alkyl or an alkylamino or alkylsilylo radical, each R'
may be the same or different and m and n independently are 0, 1, 2, 3 or 4,
with the proviso that the bilateraly symmetry is maintained ; R" is a
structural
bridge between the X and (C~R'mCsC.~R'~) ring to impart stereorigidity and,
preferably is a sdyl or a hydrocarbyl biradical having at least one silicon or
carbon atom to form the bridge; Q is a hydrocarbyl radical, such as an alkyl,
aryl, alkenyl, alkylaryl or arylalkyl radical having 1-20 carbon atoms or is a
halogen; Me is titanium; Me can be in any of its theoretically possible
oxidation states.
The term "symmetrically" shall mean that the local bilateral symmetry of the
active polymerization sites is essentially maintained.
The present invention further provides a process for producing
syndiotactic/atactic block polyolefins, particularly syndiotactic/atactic
polypropylene. The process comprises utilizing at least one of the catalysts
described by the above formula and introducing the catalyst into a
polymerization reaction zone containing an olefin monomer. In addition, a
cocatalyst such as alumoxane may be introduced into the reaction zone.
Further, the catalyst may also be pre-polymerized prior to introducing it into
the reaction zone and/or prior to the stabilization of reaction conditions in
the
reactor.
Metallocene catalysts are single site catalyst which, generally, produce
polymer having narrow molecular weight distribution.
While the present invention is mainly directed to a-olefin homopolymerization
it is obvious that copolymerization with other olefins can be obtained.
AMENDED SHEET
CA 02260891 2004-11-04
5
The present invention also provides for a new polymer comprising
alternating blocks of syndiotactic and atactic sequences, preferably
long syndiotactic and short atactic sequences, most preferably comprising
a fraction of syndiotactic triads (rr) of at least 70%.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete appreciation of the invention and many of the attendant
advantages thereof will be readily understood by reference to the
following detailed description when considered in connection with the
accompanying drawings wherein:
Figure 1 shows the structure of a catalyst precursor,
2,7-bis-tent-butyl-fluorenyl-9-dimethylsylyl-tert-butyl-amido
titanium dichloride.
Figure 2 shows the 1H NMR spectrum of the
2,7-bis-tert-butyl-fluorenyl-9-dimethylsilyl-cert-butyl-amido
titaniumdichloride
Figure 3 shows the 13C NMR spectrum of a syndiotactic/
atactic block copolymer of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
The present invention provides for a new polymer comprising alternating
blocks of syndiotactic and atactic sequences. The polymer of the
invention possesses particularly long sequences of syndiotactic species
and short sequences of atactic species. The syndio-/atactic ratio can
easily be modified by changing the polymerization conditions and/or the
catalyst structure within the invention. For example, as shown below,
increasing the polymerization temperature for a given catalyst decreases
the syndio-/atactic ratio. As also evidenced below, replacing a
dimethylsilyl bridge by a diphenylsilyl bridge also decreases the
syndio-/atactic ratio for identical polymerization conditions.
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WO 98/02469 PCT/EP97/03649
6
In the specific case of polypropylene, it has been noted that the new
polymer has elastomeric properties. Without being bound by the theory,
it may be considered that these properties are deriving from the
combination of the crystalline syndiotactic part and the amorphous
atactic part.
The polymer obtained has a molecular weight ranging from 100,000 to
1,000,000 depending on the polymerization conditions and on the catalyst
used in the process. For example, as shown below, replacing a
dimethylsilyl bridge by a diphenylsilyl bridge results in increased
molecular weight under identical polymerization conditions.
The present invention provides a catalyst and process for the production
of syndiotactic/atactic block polyolefins, particularly polypropylene.
The catalysts of the present invention produce a polymer with a
syndiotactic/atactic block microstructure.
The Applicants have now unexpectedly found that the catalyst of the
invention can be used for the production of high molecular weight
polyalphaolefin with stereoregular / stereoirregular block micro-
structure.
When propylene or other alpha-olefins are polymerized using a catalyst
consisting of a transition metal compound, the polymer product typically
comprises a random mixture (reactor blend) of amorphous atactic and
crystalline xylene insoluble fractions. The crystalline fraction may
contain either isotactic or syndiotactic polymer or a mixture of both.
The catalysts of the present invention have syndio-/atactic specificity
and produce polymeric chains with differing syndio-/atactic block ratios.
The metallocene catalysts of the present invention may be described by
the formula
R" (CqR'n,CSCqR'n) MeXQ
wherein X is an hetero atom Iigand with one or two lone pair electrons
and selected from the elements of Group VA or VIA and is preferably
nitrogen, phosphorus, oxygen or sulfur which can be substituted or not.
T
CA 02260891 1999-O1-19 - w
. . " ,
'S.
7
(C~R'mCsC~R'n) is a fluorenyl ring, substituted symmetrically; each R' is
hydrogen or hydrocarbyl radical having from 1-20 carbon atoms, a halogen,
an alkoxy, and alkoxy alkyl or an alkylamino or alkylsilylo radical, each R'
may be the same or different, m and n independently are 0, 1, 2, 3 or 4, and
with the proviso that the bilateral symmetry is maintained; R" is a structural
bridge between the hetero atom X and (C4R'mCsC.~R'n) ring to impart
stereorigidity, and preferably is a silyl or hydrocarbyl biradical having at
least
one silicon or carbon atom to form the bridge; Q is a hydrocarbyl radical,
such as an alkyl, aryl, alkenyl, alkylaryl or arylalkyl radical having 1-20
Carbon atoms or is a halogen; Me is titanium ; the titanium can adopt any of
the possible oxidation states.
(C~R'.~CsC4R'~) comprises hydrocarbyl biradicals bonded to two adjacent
carbon atoms in a cyclopentadienyl ring to form a fused ring.
In order to obtain syndiospecificity the cyclopentadienyl derivative or
fluorenyl
rings in the metallocene catalysts must be substituted in an essentially
symmetric manner with respect to the active coordination positions so that
the metallocene exibits bilateral symmetry at least around the active
coordination site. It has been unexpectedly noted that if in the original
syndiospecific catalysts described in US patent No.4,892,851 the non-
substituted cyclopentadienyl is replaced by a heteroatom ligand with one or
two lone pair electrons and selected from elements of Group V A or VI A, the
stereospecificty of catalyst will be periodically changed from
syndiospecificity
to aspecificity during the polymerization giving rise to the formation of
atactic
blocks within the predominantly syndiotactic chain.
Bilateral symmetry is defined as the condition in which there is no
substituents or one or more substituents on one side and no substituents or
one or more substituents on the other side in the same relative position such
that a mirror image is formed from one side to another. One preferred
example of such a compound is 2,7 di-tert-butyl-9-fluorenyl dimethyl silyl,
tert-butyl amido titanium dichloride.
AMENDED SHEET
CA 02260891 1999-O1-19
WO 98/02469 PCT/EP97/03649
8
An illustration of the ligands of this compound is shown below:
_-
R
1
X
1
R'
Bilateral symmetry is illustrated by a plane bisecting the fluorenyl and
the bridge resulting the right side of each ligand being a mirror image
of its left side. The numerical positions of the fluorenyl ring
represent the position of possible substituents on the fluorenyl ring, 9
being the position of the bridge.
Whilst not wishing to be bound by a theory and without intending to limit
the scope of the present invention as indicated by the claims, it is
believed that during the polymerization reaction the growing polymer
chain migrates from one coordination position to the other after each
monomer insertion as the catalyst simultaneously isomerizes and enchains
sequences of polymer of the syndiotactic structure; occasionally this
mechanism is disturbed by a haptocity change of the fluorenyl-transition
metal bonding or through inversion of the chiral nitrogen center,
leading to the loss of steric control and formation of short
sequences of atactic blocks whithin a predominantly syndiotactic polymer
chain. This mechanism differs from that put forward for syndiospecific
catalysts such as the active species formed from
isopropylidene [cyclopentadienyl-9-fluorenyl] zirconium dichloride as
disclosed in U.S. Patent no. 4,892,851 wherein the fluorenyl ring
exhibits mainly pentahapto bonding, i.e., all five carbon atoms of the
fluorenyl rings are coordinated with the zirconium atom.
SU8ST1TUTE SHEET (RULE 2fi)
CA 02260891 1999-O1-19 ' " "
,. . ,
It is believed that the catalysts of the present invention demonstrate a
reversible transformation of syndiospecific sites to atactic specific sites
through a haptocity change related stereoregulation/stereoderegulation
mechanism.
In theory, the steric condition for a preferred orientation of the growing
chain, adoption of one of the two possible conformation, intermittently
disappears and the coordination and insertion of either of the propylene
prochiral faces at both lateral coordination positions becomes accidental.
This mechanism enchains atactic sequences in a predominantly syndiotactic
polymer chain by a spontaneous change in haptocity of the bonding between
the fluorenyl and the transition metal from pentahapto to tri- and possibly
mono-hapto bonding which results in the loss of stereoregulating property of
the sites.
This electro-dynamic behavior of the active species provides in effect a
temporary transformation of enantiotopic, equivalent sites to non-
enantiotopic, non-equivalent environment at the lateral coordination
positions, atactic sequences being formed whenever this occurs.
Theoretically, only when both events, i.e., periodic loss of stereoregularity
and the stereospecific character of the catalyst occur simultaneously, is a
syndiotactic/atactic block homopolymer formed.
When catalysts of the present invention are used in polymerization of
olefins, the polymer which results is of a syndio-/atactic microstructure as
illustrated below:
In a preferred embodiment of the catalyst of the present invention
(C4R'mCsC4R'n) is preferably a substituted cyclopentadienyl ring derivative
with bulky substituents in 2 and 7 or positions ( combined 1,8 or 3,6 or 4,5
positions are also envisageble) such as tert-butyl and trimethylsilyl;
AMENDED SHEET
CA 02260891 1999-O1-19 ~ ..
.. ,
..
(C~R'mCsC.~R'~) is more preferably a substituted fluorenyl radical; Me is
titanium; Q is preferably a halogen and is most preferably chlorine; and R" is
preferably a silyl or hydrocarbyl biradical of at least one silicon or carbon
atom
which is coordinated with the heteroatom ligand and with (C~R'mCsC~R'n), most
preferably a silyl or hydrocarbyl biradical of at least one silicon or carbon
atom
being connected with heteroatom ligand and (C~R'mCsC4R'Rn) moiety.
Exemplary hydrocarbyl biradicals for the structural bridge include ethyl,
propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, and the like. Other
hydrocarbyl radicals useful as the structural bridge in the present catalysts
include linear alkyl radicals of 1-10 carbon atoms or branched alkyl radicals
of
1-20 carbon atoms, preferably one carbon atom, which may be substituted or
unsubstituted, preferably substituted.
Exemplary silyl biradicals for structural bridge include dimethylsilyl (which
is
preferred), diphenylsilyl of the general formula R2Si=, with each R
independently being any C 1-C20 hydrocarbyl or C 1-C20 mono-, di- or trialkyl
silyl radicals.
The catalyst may be prepared by any method known in the art. Generally, the
preparation of the catalyst complex consists of forming and isolating the
substituted cyclopentadienyl derivative or fluorenyl ligands which are then
reacted with a halogenated metal to form the complex. The preferred method
is that disclosed in U.S. Patent nos. 4,892,851. The catalyst may further be
supported on an organic or inorganic Garner. The synthesis process generally
comprises the steps of ( 1) preparing the halogenated or alkylated metal
compound, (2) preparing the ligand, (3) synthesizing the complex, and (4)
purifying the complex.
The metallocene catalysts of the present invention are useful in many of the
polymerization processes (solution, slurry or gas phase) known in the art
including many of those disclosed for the preparation of crystalline or
amorphous polypropylene. When the catalysts of the present invention are
used in these types of processes, the processes produce syndiotactic/atactic
block polymers.
AMENDED SHEET
I1
Further examples of polymerization processes useful in the practice of
the present invention include those disclosed in U.S. Patent No.
4,767,735 and European Patent Application Publication No. 310,734.
These
preferred polymerization procedures include the step of prepolymerizing
the catalyst and/or precontacting the catalyst with a cocatalyst and ~an
olefin monomer prior to introducing the catalyst into a reaction zone.
The ionizing agent is an alumoxane, an aluminum alkyl, other Lewis acid
or a combination thereof which will ionize a neutral metallocene compound
to form a cationic metallocene catalyst. Examples of such ionizing
agents are methyl alumoxane (MAO), triethyl aluminum (TEA1) and
tris(pentafluorophenyl)boron. Other ionizing agents are disclosed in
European Patent Publication Nos. 277003 and 277004.
The syndio-/atactic-specific catalysts of the present invention are
particularly useful in combination with an aluminum alkyl cocatalyst or
with an alumoxane, preferably with the latter.
In addition, a complex may be isolated between a metallocene catalyst as
described herein and an aluminum cocatalyst in accordance with the
teachings of European Patent Publication Number 226,463. As disclosed.
therein, a metallocene is reacted with an excess of alumoxane in the
presence of a suitable solvent. A complex of the metallocene and
alumoxane may be isolated and used as a catalyst in the present
invention.
The alumoxanes useful in combination with the catalysts of the present
invention, either in the polymerization reaction or in forming the
complex disclosed above, may be represented by the general formula
(R-A1-0-)n in the cyclic form and R(R-Al-0-)nALR2 in the linear form
wherein R is an alkyl group with one to five carbon atoms and n is an
integer from 1 to about 20. Most preferably, R is a methyl group and the
preferred alumoxane is methylalumoxane (MAO). The alumoxanes can be
represented structurally as follows:
CA 02260891 2004-11-04
CA 02260891 2004-11-04
12
CH3 CHg
A1 O-A1-O A1
CH3 CH3
n
CHg
n=15-20
The alumoxanes can be prepared by various methods.known in the art.
Preferably, they are prepared by contacting water with a solution of
trialkyl aluminum, such as trimethyl aluminum, in a suitable solvent
such as a benzene. Another preferred method includes the preparation of
alumoxane in the presence of a hydrated copper sulfate as described in
the U . S . Patent Number 4,404,344.
' This method comprises treating a dilute
solution of trimethyl aluminum in toluene with copper sulfate. The
preparation of other aluminum cocatalysts useful in the present invention
may be prepared by methods known to those skilled in the art.
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WO 98/02469 PCT/EP97/03649
13
The Examples given below illustrate the present invention and its various
advantages and benefits in more detail.
Example 1
The synthesis procedure was performed under an inert gas atmosphere using
a Vacuum Atmospheres glovebox or Schlenk techniques.
Step 1 Preparation of the
2,7-di-tert-butylfluorenyl-dimethylsilyl-chloride (1)
a) Aromatization of the fluorene: In a one liter flask equipped with
magnetic stirring bar, nitrogen inlet and reflux condenser, there was
added a solution of 0.1 mol 2,7-di-tert-butylfluorene in 300 cc of
diethyl ether. To this solution was added at room temperature dropwise
0.1 eguimol of methyllithium in ether (1.6 molar). The reaction was
completed after gas evolution stops. The orange solution was used in the
next step.
b) Reaction with dimethyldichlorosilane : The orange solution prepared
in step 1a was added dropwise to a solution of 0.1 mol of
dimethyldichlorosilane in 200 cc of ether. The mixture was stirred for
several hours at room temperature until the reaction was completed.
Step 2 . Preparation of tert-butyllithiumamide (2).
In a one liter flask eguipped with magnetic stirring bar, nitrogen inlet
and reflux condenser 0.1 mol of tert-butylamine was dissolved in 200 cc
of diethyl ether. The solution was cooled to -78'C. One equimol of
methyllithium in ether was added dropwise to the solution. The
temperature was increased to room temperature slowly. The reaction
mixture was stirred for several hours at room temperature until the
formation of the title compound was complete.
Step 3. preparation of
2,7-di-tert-butylfluorenyl-dimethylsilyl-tert-butylamine (3).
CA 02260891 1999-O1-19
1~
The reaction products prepared in step 2 and step 3 were added together and
stirred for several hours at room temperature. The LiCI formed as byproduct
was filtered off and the ether filterate was subjected to evaporation. The
title
compound was obtained as a yellow oil.
Step 4. Preparation of 2,7-di-tert-butyl-dimethyl-tert-butylamido titanium
dichloride (4).
a) Formation of dianion : 0.25 mol of 3 was dissolved in 200 cc of
diethylether. To this solution was added dropwise 0. S mol of methyllithium in
ether. The solution became red. The reaction was stopped after gas evolution
had stopped
b) Reaction of the dianion with TiCl4
The red powder obtained after evaporation of the ether from the solution
resulting from step 4b was washed several times with pentane and then
reacted with 0.25 mol of TiCl4 in 200 cc pentane. The mixture was stirred for
several hours at room temperature and filtered to separate the LiCI.
Evaporation of the solvent led to the isolation of a brown powder.
Recrystalization of the product from dichloromethane provided
spectroscopically pure product "4" (Cf Figure 2 HNMR).
Comparative Examples 2 and 3
2,7-di-tert-butyl-fluorenyl-dimethylsilyl-tert-butylamido-zirconium dichloride
("5") and the corresponding hafnium derivative ("6") were formed by repeating
example 1 while in step 4b respectively ZrCl4 or HfCl4 were used instead of
TiCl4.
Example 4 and comparative Examples 5 and 6
Examples 1 to 3 were repeated while using diphenyldichlorosilane instead of
dimethyldichlorosilane in step lb. The following metallocenes were formed
~,.~,"~i;p~~ SHEET
CA 02260891 1999-O1-19
2,7-ditert-butylfluorenyldiphenylsilyltertbutylamido titaniumdichloride
("7") .
2,7-ditert- butylfluorenyldiphenylsilyltertbutylamido zirconiumdichloride
("8").
2,7-ditert-butylfluorenyldiphenylsilyltertbutylamido hafniumdichloride
("9"~.
Examples 7-11, comparative Examples 12 and 13, and Example 14
Propylene was polymerized using the metallocenes produced by examples 1 to
4 and Comparative Examples 5 and 6. Two liters of liquid propylene were
introduced into a 4 liter bench reactor at room temperature. The metallocene
was placed in three milliliters of a 11% solution of MAO in toluene to form a
solution which was added to the reactor and the temperature increased to
40°C. The polymerization reaction was allowed to run for 60 minutes
during
which time the reactor was maintained at the temperature indicated in Tab. l
for each individual run. The reaction was terminated by venting the reactor of
monomer. The catalyst activity in grams of polypropylene per grams of
catalyst per hour was calculated. The molecular weight, molecular weight
distrubution and 13C NMR analysis of the polymer were determined. The
results are shown in Table 1.
Example 7
polymerization of propylene with "4" at 60 °C. Figure 3 shows the 13C
NMR
spectrum of the syndiotactic/atactic block polypropylene; signals at about
15.3, 17.5, 31.2 and 35.7 may be due to long-chain branching.
Example 8
polymerization of propylene with "4" at 80°C
AMENDED SHEET
CA 02260891 1999-O1-19
16
Example 9
polymerization of Propylene with "4" at 40°C
Exam 1~ a 10
polymerization of propylene with "4" at 60 °C in 1 liter of cyclohexane
Example 11
copolymerization of propylene and ethylene with "4" at 60°C
Comparative Example 12
polymerization of propylene with "S" at 60°C
Comparative Example 13
polymerization of propylene with "6" at 60°C
Example 14
polymerization of propylene with "7" at 60°C
The polymerization conditions and results are summarized in Table 1.
AMENDED SNEET
CA 02260891 1999-O1-19
WO 98/02469 PCT/EP97/b3649
17
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