U.S. patent application number 10/792109 was filed with the patent office on 2004-12-09 for use and production of polypropylene.
This patent application is currently assigned to ATOFINA Research, S.A.. Invention is credited to Demain, Axel.
Application Number | 20040249094 10/792109 |
Document ID | / |
Family ID | 8237649 |
Filed Date | 2004-12-09 |
United States Patent
Application |
20040249094 |
Kind Code |
A1 |
Demain, Axel |
December 9, 2004 |
Use and production of polypropylene
Abstract
Use of isotactic polypropylene homopolymers or copolymers in
processes in which the polypropylene solidifies from a melt,
wherein for enhanced speed of solidification of the polypropylene
the polypropylene has a melt temperature and a crystallisation
temperature not more than 50.degree. less than the melt temperature
resulting from the polypropylene having been produced using a
metallocene catalyst component having the general formula as
described herein:
R"(C.sub.pR.sub.1R.sub.2R.sub.3)(C.sub.p'R.sub.n')MQ.sub.2 (I)
Inventors: |
Demain, Axel;
(Tourinnes-Saint-Lambert, BE) |
Correspondence
Address: |
FINA TECHNOLOGY INC
PO BOX 674412
HOUSTON
TX
77267-4412
US
|
Assignee: |
ATOFINA Research, S.A.
Seneffe (Feluy)
BE
|
Family ID: |
8237649 |
Appl. No.: |
10/792109 |
Filed: |
March 3, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10792109 |
Mar 3, 2004 |
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09939097 |
Aug 24, 2001 |
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6727332 |
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09939097 |
Aug 24, 2001 |
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PCT/EP00/01736 |
Feb 25, 2000 |
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Current U.S.
Class: |
526/160 ;
526/170; 526/351; 526/943 |
Current CPC
Class: |
C08F 110/06 20130101;
C08F 110/06 20130101; Y10S 526/943 20130101; C08F 110/06 20130101;
C08F 4/65912 20130101; C08F 2500/15 20130101; C08F 2500/12
20130101; C08F 4/65927 20130101; C08F 4/65927 20130101 |
Class at
Publication: |
526/160 ;
526/351; 526/943; 526/170 |
International
Class: |
C08F 004/44 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 26, 1999 |
EP |
99103803.5 |
Claims
1-10. Cancelled.
11. A process for producing an isotactic homopolymer of propylene
with enhanced speed of solidification when solidified from a melt,
having a melt temperature of from 139 to 144.degree. C. and a
difference between the melt temperature and the crystallisation
temperature of not more than 50.degree. C., the process comprising
homopolymerising propylene in the presence of a metallocene
catalyst of general formula:
R"(C.sub.pR.sub.1R.sub.2R.sub.3)(C.sub.p'R.sub.n')MQ.sub.2 (I)
wherein C.sub.p is a substituted cyclopentadienyl ring; C.sub.p' is
a substituted or unsubstituted fluorenyl ring; R" is a structural
bridge imparting stereorigidity to the component; R.sub.1 is a
substituent on the cyclopentadienyl ring which is distal to the
bridge, which distal substituent comprises a bulky group of the
formula XR*.sub.a in which X is chosen from Group IVA, a=2, and one
R* is chosen from hydrogen or hydrocarbyl of from 1 to 20 carbon
atoms and the other different R* is chosen from a substituted or
unsubstituted cycloalkyl where X is a carbon atom in the cycloalkyl
ring, R.sub.2 is a substituent on the cyclopentadienyl ring which
is proximal to the bridge and positioned non-vicinal to the distal
substituent and is of the formula YR#.sub.3 in which Y is chosen
from Group IVA, and each R# is the same or different and chosen
from hydrogen or hydrocarbyl of 1 to 7 carbon atoms, R.sub.3 is a
substituent on the cyclopentadienyl ring which is proximal to the
bridge and is a hydrogen atom or is of the formula ZR$.sub.3 in
which Z is chosen from Group IVA, and each R$ is the same or
different and chosen from hydrogen or hydrocarbyl of 1 to 7 carbon
atoms, each R'.sub.n is the same or different and is hydrocarbyl
having 1 to 20 carbon atoms in which 0.ltoreq.n.ltoreq.8; M is a
Group IVB transition metal or vanadium and each Q is hydrocarbyl
having 1 to 20 carbon atoms or is a halogen.
12. A process according to claim 11 wherein R.sub.1 is a
methyl-cyclohexyl group.
13. A process according to claim 12 wherein R.sub.2 is a methyl
group.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority of International
Application No. PCT/EP00/01736, entitled "USE AND PRODUCTION OF
POLYPROPYLENE, filed on Feb. 25, 2000. The above-listed application
is commonly assigned with the present invention and is incorporated
herein by reference as if reproduced herein in its entirety.
TECHNICAL FIELD AND SUMMARY OF THE INVENTION
[0002] The present invention relates to the use of homopolymers and
copolymers of propylene prepared with a metallocene catalyst
component in applications which require a low melting temperature,
a high crystallisation temperature and a high transparency. The
present invention also relates to a process for producing isotactic
polypropylene homopolymers.
BACKGROUND
[0003] It is known in the art to obtain polypropylene with low
melting temperature by inserting comonomers in the polymer chain
during polymerisation. With Ziegler-Natta catalysts, the addition
of ethylene (or other) comonomers in the growing chains of
polypropylene during polymerisation gives rise to a random
propylene copolymer that is characterised by a lower melting point,
a lower flexural modulus, lower rigidity and higher transparency
that the homopolymers of propylene. The cotnonomers generate
defects in the polymer chain which impede the growth of thick
crystalline structures and reduce the degree of crystallinity of
the overall polymer. The comonomers are not evenly distributed in
the polymer chains. Among the many comonomers that can be used in
the copolymerisation process, ethylene and butene have been most
frequently utilised. It has been observed that the melting
temperature of the propylene copolymers is reduced by about
6.degree. C. per wt % of inserted ethylene in the copolymer chain
or by about 3.degree. C. per wt % of inserted butene.
[0004] The addition of comonomer in industrial polymerisation
processes has however other impacts than just decreasing the
melting temperature of the polypropylene; it has both economical
and technical impacts.
[0005] These known random propylene copolymers also suffer from the
technical problem that the crystallisation temperature is
relatively low. This is technically disadvantageous when the
polypropylene is being processed since the low crystallisation
temperature increases the cycle time of any process where the
polypropylene is being solidified from the melt. With the lower
crystallisation temperatures, the period for solidification is
longer, thereby increasing the cycle time for injection moulding,
injection blow moulding and extrusion blow moulding and decreasing
the production line speed in film, tube, profile or pipe
extrusion.
[0006] EP-A-0881236 in the name of Fina Research S. A. and
EP-A-0537130 in the name of Fina Technology, Inc. each disclose a
metallocene catalyst component for use in producing isotactic
polypropylene.
[0007] EP-A-0870779 in the name of Fina Technology, Inc. discloses
metallocene catalysts for producing a blend of iso-and syndiotactic
polypropylene.
[0008] EP-A-0742227 in the name of Fina Technology, Inc. discloses
a metallocene compound for producing hemisotactic
polypropylene.
[0009] EP-A-0905173 discloses the production of biaxially oriented
metallocene-based polypropylene films.
[0010] Despite the disclosures of these prior Fina patent
specifications, there is a need in the art for polypropylene having
not only relatively low melting temperature but also relatively
high crystallisation temperature which enables the polypropylene to
be used more readily in processes requiring the polypropylene to be
solidified from the melt using shorter cycle times or higher film
speeds.
[0011] Accordingly, the present invention provides use of isotactic
polypropylene homopolymers or copolymers in processes in which the
polypropylene solidifies from a melt.
DETAILED DESCRIPTION
[0012] In a preferred embodiment, the present invention is directed
to the use of isotactic polypropylene homopolymers or copolymers in
processes in which the polypropylene solidifies from a melt,
wherein for enhanced speed of solidification of the polypropylene
the polypropylene has a melt temperature and a crystallisation
temperature not more than 50.degree. C. less than the melt
temperature resulting from the polypropylene having been produced
using a metallocene catalyst component having the general
formula:
R"(C.sub.pR.sub.1R.sub.2R.sub.3) (C.sub.p'R.sub.n')MQ.sub.2 (I)
[0013] wherein C.sub.p is a substituted cyclopentadienyl ring;
C.sub.p' is a substituted or unsubstituted fluorenyl ring; R" is a
structural bridge imparting stereorigidity to the component;
R.sub.1 is a substituent on the cyclopentadienyl ring which is
distal to the bridge, which distal substituent comprises a bulky
group of the formula XR*.sub.a in which X is chosen from Group IVA,
and when a=3 each R* is the same or different and chosen from
hydrogen or hydrocarbyl of from 1 to 20 carbon atoms, or when a=2
one R* is chosen from hydrogen or hydrocarbyl of from 1 to 20
carbon atoms and the other different R* is chosen from a
substituted or unsubstituted cycloalkyl where X is a carbon atom in
the cycloalkyl ring, R.sub.2 is a substituent on the
cyclopentadienyl ring which is proximal to the bridge and
positioned non-vicinal to the distal substituent and is hydrogen or
of the formula YR#.sub.3 in which Y is chosen from Group IVA, and
each R# is the same or different and chosen from hydrogen or
hydrocarbyl of 1 to 7 carbon atoms, R.sub.3 is a substituent on the
cyclopentadienyl ring which is proximal to the bridge and is a
hydrogen atom or is of the formula ZR$.sub.3 in which Z is chosen
from Group IVA, and each R$ is the same or different and chosen
from hydrogen or hydrocarbyl of 1 to 7 carbon atoms, each R'.sub.n
is the same or different and is hydrocarbyl having 1 to 20 carbon
atoms in which 0.ltoreq.n.ltoreq.8; M is a Group IVB transition
metal or vanadium and each Q is hydrocarbyl having 1 to 20 carbon
atoms or is a halogen.
[0014] The metallocene catalyst component may be employed either
alone or in a mixture of one or more metallocene catalyst
components.
[0015] In accordance with the invention, it has now been found that
homopolymers and copolymers of propylene obtained using these
metallocene catalysts have characteristics which are similar to and
better than those exhibited by random polypropylene (PP) copolymers
produced using Ziegler-Natta catalysts. These desired
characteristics are not only a low melting temperature and a high
transparency, but also a high crystallisation temperature. The
polymers usable in accordance with the invention can also tend to
have higher rigidity as compared to random PP copolymers produced
using Ziegler-Natta catalysts and higher flexibility than
homopolymers produced using Ziegler-Natta catalysts. As well as
having high transparency, the preferred polymers for use in the
invention also have low haze.
[0016] The present invention is predicated on the discovery by the
inventor that the use of particular metallocene catalysts enables
polypropylene homopolymers, or polypropylene copolymers with a
small amount of comonomer, to have a combination of relatively low
melting temperature and relatively high crystallisation temperature
which reduces the cycle time for processing the polymer from the
melt, for example in injection moulding and injection or extrusion
blow moulding. The amount of comonomer in the copolymers is not
more than 25 wt %, typically less than 10 wt %, more preferably
less than 5 wt % and yet more preferably less than 3 wt %. Typical
comonomers are ethylene and butene, but other alpha-olefins may be
employed. For extrusion processes, such as pipe, tube or profile
extrusion and for film production, the higher crystallisation
temperature permits higher line speeds. The film may be produced by
casting, a tenter frame process or blowing. Other polyolefin
processing methods exist for which the present invention has
utility in which the polypropylene is processed from the melt. The
combination of a low melting temperature and a high crystallisation
temperature provides a reduced temperature "window" between those
two temperatures, which enables the polypropylene to be more easily
and more quickly processed when the polypropylene is processed in
the melt and then solidified from the melt.
[0017] Thus the present invention further provides a process for
producing an isotactic homopolymer of propylene having a melt
temperature of from 139 to 144.degree. C. and a difference between
the melt temperature and the crystallisation temperature of not
more than 50.degree. C., the process comprising homopolymerising
propylene in the presence of a metallocene catalyst of general
formula:
R"(C.sub.pR.sub.1R.sub.2R.sub.3)(C.sub.p'R.sub.n')MQ.sub.2 (I)
[0018] wherein C.sub.p is a substituted cyclopentadienyl ring;
C.sub.p' is a substituted or unsubstituted fluorenyl ring; R" is a
structural bridge imparting stereorigidity to the component;
R.sub.1 is a substituent on the cyclopentadienyl ring which is
distal to the bridge, which distal substituent comprises a bulky
group of the formula XR*.sub.a in which X is chosen from Group IVA,
a=2, and one R* is chosen from hydrogen or hydrocarbyl of from 1 to
20 carbon atoms and the other different R* is chosen from a
substituted or unsubstituted cycloalkyl where X is a carbon atom in
the cycloalkyl ring, R.sub.2 is a substituent on the
cyclopentadienyl ring which is proximal to the bridge and
positioned non-vicinal to the distal substituent and is of the
formula YR#.sub.3 in which Y is chosen from Group IVA, and each R#
is the same or different and chosen from hydrogen or hydrocarbyl of
1 to 7 carbon atoms, R.sub.3 is a substituent on the
cyclopentadienyl ring which is proximal to the bridge and is a
hydrogen atom or is of the formula ZR$.sub.3 in which Z is chosen
from Group IVA, and each R$ is the same or different and chosen
from hydrogen or hydrocarbyl of 1 to 7 carbon atoms, each R'.sub.n
is the same or different and is hydrocarbyl having 1 to 20 carbon
atoms in which 0.ltoreq.n.ltoreq.8; M is a Group IVB transition
metal or vanadium and each Q is hydrocarbyl having 1 to 20 carbon
atoms or is a halogen.
[0019] The metallocene catalyst may be used either alone or in a
mixture of such metallocene catalysts.
[0020] In the bulky distal substituent group R.sub.1, X is
preferably C or Si. When a is 3, R* may be a hydrocarbyl such as
alkyl, aryl, alkenyl, alkyl aryl or aryl alkyl, preferably methyl,
ethyl, propyl, isopropyl, butyl, isobutyl, amyl, isoamyl, hexyl,
heptyl, octyl, nonyl, decyl, cetyl or phenyl. R.sub.1 may comprise
a hydrocarbyl which is attached to a single carbon atom in the
cyclopentadienyl ring or may be bonded to two carbon atoms in that
ring. Preferably, R.sub.1 is C(CH.sub.3).sub.3. When a is 2, one R*
is a substituted or unsubstituted cycloalkyl group, with X being C
and incorporated in the cycloalkyl ring. Thus R.sub.1 may comprise
an alkyl-cycloalkyl group, typically methyl-cyclohexyl.
[0021] The proximal substituents R.sub.2 and R.sub.3 are the same
or different and preferably CH.sub.3 or hydrogen.
[0022] R" is preferably isopropylidene in which the two C.sub.p
rings are bridged at position 2 of the isopropylidene.
[0023] M is preferably zirconium.
[0024] Q is preferably a halogen and more preferably C1.
[0025] The fluorenyl ring C.sub.p' can have up to 8 substituent
groups R'.sub.n, each of which is the same or different and may be
hydrogen or a hydrocarbyl selected from alkyl, aryl, alkenyl, alkyl
aryl or aryl alkyl, such as methyl, ethyl, propyl, isopropyl,
butyl, isobutyl, amyl, isoamyl, hexyl, heptyl, octyl, nonyl, decyl,
cetyl or phenyl. These substituents must be selected so that they
do not interfere with coordination of the monomer to the metal.
Preferably, therefore, the fluorenyl ring is unsubstituted at both
positions 4 and 5, these positions being distal to the bridge.
[0026] The metallocene catalyst component can be used to produce
isotactic polypropylene homopolymer, optionally with a small amount
of comonomer incorporated therein, i.e. a homopolymer with a low
degree of copolymer. Both types of polypropylene are characterised
by a low melting temperature and a high crystallisation
temperature.
[0027] In accordance with a preferred aspect of the invention, the
catalyst, which is selected from the cyclopentadienyl fluorenyl
family, is used in a homogeneous or heterogeneous (i.e. supported
catalyst) polymerisation for producing isotactic polypropylene
homopolymer. In one preferred embodiment, the catalyst is a methyl
cyclohexyl disubstituted cyclopentadienyl fluorenyl. Another
preferred catalyst is tertiary butyl disubstituted cyclopentadienyl
fluorenyl. In a further embodiment, the catalyst may be a tertiary
butyl monosubstituted cyclopentadienyl fluorenyl. Such
cyclopentadienyl fluorenyl metallocene catalysts enable relatively
low melting points to be achieved, typically lower than 145.degree.
C. for isotactic polypropylene.
[0028] By carefully selecting the catalyst formulation, isotactic
polypropylene having differing melting points can be obtained
without using any comonomer. A melting point as low as 120.degree.
C. is achievable using these catalysts in isotactic polypropylene
homopolymer. If a small concentration of comonomer for example
ethylene or butene, is added to the propylene during
polymerisation, a melting point lower than 120.degree. C. may be
achieved.
[0029] Compared to known polypropylene copolymers or homopolymers
fabricated using Ziegler-Natta catalysts, for a given melting
temperature higher crystallisation temperatures are achieved in
accordance with the invention. This provides for example a
significant reduction in the cycle time for injection moulding and
injection and extrusion blow moulding and higher line speeds for
production of film, together with reduced stickiness of the films
and higher production speeds for pipe, tube and profile extrusion.
The selection of a cyclopentadienyl metallocene catalyst also
provides improved mechanical properties, in particular flexural and
tensile properties, for the isotactic polypropylene. Furthermore,
the polypropylenes produced in accordance with the invention have
good light transmittance, including high transparency and low
haze.
[0030] When the polymers produced in accordance with the invention
are employed to produce articles by a processing technique, such as
injection moulding, injection or extrusion blow moulding, or
production of films, or extrusion of pipes, tubes or profiles, the
polypropylene can be employed either in its pure form, or in a
blend. When used pure, the polypropylene can be a layer of a
multilayer or any other type of construction.
[0031] In accordance with the invention, the provision of an
isotactic polypropylene homopolymer, optionally with a small degree
of copolymer therein, provides not only a relatively low melting
temperature of the polymer, but also a high crystallisation
temperature. This in turn reduces the temperature "window" between
those two temperatures to typically less than about 50.degree. C.
This greatly improves the processability of the polypropylene
polymer since not only is it possible to process the polymer melt
at lower temperatures, but also the speed of solidification of the
polypropylene from the melt is enhanced as a result of the
increased crystallisation temperature for a given melt
temperature.
[0032] When the catalyst is a tertiary butyl monosubstituted
cyclopentadienyl fluorenyl catalyst, the catalyst may comprise
isopropylidene (3-tert butyl-cyclopentadienyl-fluorenyl)
ZrCl.sub.2. The production of such a catalyst is disclosed in
EP-A-0537130. This catalyst produces isotactic polypropylene of low
isotacticity, typically having 75 to 80% mmmm and a melting point
of around 127 to 129.degree. C. The polymer produced has a low
molecular weight typically ranging from about 50,000 to 75,000
Mw.
[0033] When the catalyst comprises a tertiary butyl disubstituted
cyclopentadienyl fluorenyl metallocene catalyst, the catalyst may
particularly comprise isopropylidene (3-tert butyl-5-methyl
cyclopentadienyl-fluorenyl) ZrCl.sub.2. The synthesis of such a
catalyst is disclosed in EP-A-0881236. This catalyst has a higher
productivity than the corresponding monosubstituted catalyst
described above, and the polymer produced has a higher molecular
weight, a higher isotacticity and a higher melting point.
Typically, the tacticity ranges from about 83 to 86% mmmm and the
melting point ranges from about 139 to 144.degree. C. With the
additional hydrocarbyl group at the five position in the
cyclopentadienyl group, the amount of regio defects is reduced
below the limit of detection of the NMR, i.e. to less than 0.1%
regio defects.
[0034] The preferred methyl cyclohexyl disubstituted catalyst
incorporates a cycloalkyl group at the three-position of the
cyclopentadienyl ring. The synthesis of the methyl cyclohexyl
disubstituted cyclopentadienyl fluorenyl is similar to that of the
tertiary butyl disubstituted cyclopentadienyl fluorenyl catalyst
but cyclohexane is used instead of acetone in the synthesis of the
fulvene. Like the tertiary butyl disubstituted catalyst, the methyl
cyclohexyl disubstituted catalyst produces isotactic polypropylene
homopolymers having a high degree of tacticity, where mmmm is
typically around 80% and a low level of regio defects, typically
less than 0.1%. The melting point is around 140.degree. C.
Generally, the isotacticity and the melting point are slightly
lower for the methyl cyclohexyl disubstituted catalyst as compared
to the tertiary butyl disubstituted catalyst.
[0035] The catalyst may be a trisubstituted cyclopentadienyl
fluorenyl catalyst, with for example tertiary butyl or an
alkyl-cycloalkyl group at the three-position of the
cyclopentadienyl ring.
[0036] When copolymerisation is selected for lower the melting
temperature, metallocene catalysts offer two significant advantages
over the Ziegler-Natta catalysts. First, the insertion of comonomer
is more periodic, for all chain lengths, and therefore less
comonomer is required for a given decrease in the melting
temperature. Les comonomer is thus necessary in order to reach the
desired low melting temperature. The use of comonomer to lower the
melting point is thus more efficient. Second, the melting
temperature of the isotactic homopolymers of propylene produced
with metallocene catalysts is lower than that of the homopolymers
obtained with the Ziegler-Natta catalysts. The metallocene
catalysts used in accordance with the invention are Cp-Fluorenyl
metallocene catalysts which produce homopolymers with melting
temperatures of below 145.degree. C.
[0037] The catalyst system for use in preparing isotactic
polypropylene comprises (a) a catalyst component as defined above;
and (b) an aluminium- or boron-containing cocatalyst capable of
activating the catalyst component. Suitable aluminium-containing
cocatalysts comprise an alumoxane, an alkyl aluminium and/or a
Lewis acid.
[0038] The aluminoxanes usable as such cocatalysts are well known
and preferably comprise oligomeric linear and/or cyclic alkyl
alumoxanes represented by the formula: 1
[0039] for oligmomeric, linear alumoxanes and 2
[0040] for oligomeric, cyclic alumoxanes, wherein n is 1-40,
preferably 10-20, m is 3-40, preferably 3-20 and R is a
C.sub.1-C.sub.8 alkyl group and preferably methyl. Generally, in
the preparation of alumoxanes from, for example, aluminium
trimethyl and water, a mixture of linear and cyclic compounds is
obtained.
[0041] Suitable boron-containing cocatalysts may comprise a
triphenylcarbenium boronate such as
tetrakis-pentafluorophenyl-borato-tri- phenylcarbenium as described
in EP-A-0427696, or those of the general formula [L'-H]+[B
Ar.sub.1Ar.sub.2X.sub.3X.sub.4]--as described in EP-A-0277004 (page
6, line 30 to page 7, line 7).
[0042] The catalyst system may be employed in a solution
polymerisation process, which is homogeneous, or a slurry process
which is heterogeneous. In a solution process, typical solvents
include hydrocarbons with 4 to 7 carbon atoms such as heptane,
toluene or cyclohexane. In a slurry process it is necessary to
immobilise the catalyst system on an inert support, particularly a
porous solid support such as talc, inorganic oxides and resinous
support materials such as polyolefin. Preferably, the support
material is an inorganic oxide in its finely divided form.
[0043] Suitable inorganic oxide materials which are desirably
employed include Group 2a, 3a, 4a or 4b metal oxides such as
silica, alumina and mixtures thereof. Other inorganic oxides that
may be employed either alone or in combination with the silica, or
alumina are magnesia, titania, zirconia, and the like. Other
suitable support materials, however, can be employed for example,
finely divided functionalised polyolefins such as finely divided
polyethylene.
[0044] Preferably, the support is a silica having a surface area
comprised between 200 and 700 m.sup.2/g and a pore volume comprised
between 0.5 and 3 ml/g.
[0045] The amount of alumoxane and metallocenes usefully employed
in the preparation of the solid support catalyst can vary over a
wide range. Preferably the aluminium to transition metal mole ratio
is in the range between 1:1 and 100:1, preferably in the range 5:1
to 50:1.
[0046] The order of addition of the metallocenes and alumoxane to
the support material can vary. Alumoxane dissolved in a suitable
inert hydrocarbon solvent may be added to the support material
slurried in the same or other suitable hydrocarbon liquid and
thereafter a mixture of the metallocene catalyst component is added
to the slurry.
[0047] Preferred solvents include mineral oils and the various
hydrocarbons which are liquid at reaction temperature and which do
not react with the individual ingredients. Illustrative examples of
the useful solvents include the alkanes such as pentane,
iso-pentane, hexane, heptane, octane and nonane; cycloalkanes such
as cyclopentane and cyclohexane, and aromatics such as benzene,
toluene, ethylbenzene and diethylbenzene.
[0048] Preferably the support material is slurried in toluene and
the metallocene and alumoxane are dissolved in toluene prior to
addition to the support material.
[0049] The present invention will now be described in greater
detail with reference to the following non-limiting Example.
EXAMPLE 1
[0050] An isotactic polypropylene homopolymer was produced using,
as a metallocene catalyst, isopropylidene
(3-methylcyclohexyl-5-methyl
cyclopentadienyl-fluorenyl)ZrCl.sub.2.
[0051] The polymerisation was performed in a bench liquid full loop
reactor in the slurry phase by introducing the metallocene catalyst
precontacted with MAO (methylaluminoxane). The catalyst was
unsupported. The polymerisation temperature was 60.degree. C. The
productivity of the catalyst was 65,000 gPP/gcat/h. The fluff was
stabilised with conventional antioxidants and then extruded and
pelletised before being injection moulded into bars.
[0052] Isotactic polypropylene having a melt temperature of
142.degree. C. was obtained. The polypropylene obtained was
monomodal. The isotactic polypropylene had a tacticity of 80% mmmm,
with less than 0.1% regio defects. The tacticity was determined by
NMR analysis and the remaining NMR results are shown in Table
1.
[0053] The polymer was also subjected to differential scanning
calorimetry (DSC) to determine the melting temperature Tm and the
crystallisation temperature Tc of the polypropylene. The results
are shown in Table 2.
[0054] The polypropylene was also tested to determine its melt
index MI2. The melt index was determined using the procedure of
ASTM-A-1238 using a load of 2.16 kg at a temperature of 190.degree.
C. The melt index MI2 of the polypropylene was 1.5 g/10 min.
[0055] In addition, the flexural modulus of the polypropylene was
determined using the procedures of ISO R178 and the results are
shown in Table 2.
COMPARATIVE EXAMPLES 1 AND 2
[0056] As a comparison to the polypropylene homopolymer produced in
accordance with the invention, the corresponding properties
indicated in Table 2 for Example 1 were determined for a known
random PP copolymer produced using a Ziegler-Natta catalyst with
roughly the same melting point and MFI as for the polypropylene of
Example 1 (Comparative Example 1) and for a known PP homopolymer
using a Ziegler-Natta catalyst (Comparative Example 2). The sample
of Comparative Example 1 was a random copolymer containing about
3.5 wt % of ethylene monomer.
[0057] A comparison of the results for Example 1 and Comparative
Examples 1 and 2 shows that the melting point of the isotactic
polypropylene homopolymer is slightly larger than that of the
random polypropylene containing about 3.5 wt % of ethylene.
However, in accordance with the invention the crystallisation
temperature of the isotactic polypropylene is much higher, about
12.degree. C. higher, than that of the random polypropylene. The
isotactic polypropylene has a difference between Tm and Tc of less
than 50.degree. C. This is a significant reduction in the
temperature difference that can result in a dramatic improvement in
processing performance, leading to a decrease of cycle time for
injection moulding and injection and extrusion blow moulding, an
increase in the line speed and a reduction in the stickiness of the
film for extruding and blowing films, and an increase in the
production speed for pipe, tube and profile extrusion.
[0058] For the polypropylene homopolymer of Comparative Example 2,
the melting temperature is around 163.degree. C. which is higher
than for Example 1 and the crystallisation temperature is also
higher than for Example 1 and Comparative Example 1, being around
100.degree. C. This yields a temperature window between the melting
temperature and the crystallisation temperature which is more than
60.degree. C., i.e. significantly broader than that achievable in
accordance with the invention.
[0059] The flexural modulus of the isotactic polypropylene is about
20% larger than that of the random polypropylene of Comparative
Example 1. For the polypropylene homopolymer of Comparative Example
2, this had a higher flexural modulus as compared to the polymer of
Example 1. However the homopolymer of Comparative Example 2 has
lower transparency and requires higher processing temperatures than
the isotactic polymer of Example 1.
1 TABLE 1 mmmm 80.38 mmmr 6.04 rmmr 1.91 mmrr 5.43 rmrr + mrmm 0.88
mrmr 0.33 rrrr 1.30 mrrr 1.13 mrrm 2.61 mm 88.32 mr 6.64 rr 5.04 r
8.36
[0060]
2 TABLE 2 Comparative Comparative Units Example 1 Example 1 Example
2 MI2 g/10 min 1.5 3.9 13.4 Tm .degree. C. 142.1 138.7 163.1 Tc
.degree. C. 96.3 84.3 100.6 FLEXURAL MODULUS Flex. Mod. MPa 904 749
1209 at 0.25% Flex. Mod. MPa 868 718 1172 at 1%
* * * * *