Note: Descriptions are shown in the official language in which they were submitted.
CA 02406602 2002-10-24
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PROCESS FOR PREPARATION OF BUTYL RUBBER HAVING
BROAD MOLECULAR WEIGHT DISTRIBUTION
In one of its aspects, the present invention relates to m improved, catalytic,
solution process
for preparing butyl rubber polymers. More particularly, the present invention
relates to such a
process for preparing butyl rubber polymers with good isobutylene conversions,
such polymers
having a broad molecular weight distribution (MWD), at polymerization
temperatures of -100°C
to +50°C.
Canadian patent application S.N. 2,252,295 discloses a process for the
preparation of butyl
rubber using a catalyst system comprising a dialkyl aluminum halide, a
monoalkyl aluminum halide
and an aluminoxane or water. Surprisingly, it has now been found that, when
aluminoxane is used
in such a process, the butyl rubber so-produced has a broad molecular weight
distribution.
The physical properties and polymer processing characteristics are well known
to depend on
weight average molecular weight (MW), and number average molecular weight
(M,~. In general, the
tensile strength and modulus of vulcanizates are dependent on number average
molecular weight.
The processability of elastomers is dependent on both MW and Mw/M" (molecular
weight distribution
or MWD). For example, the mill behaviour of several types of rubber has been
classified relative
to Mw/Mn. [J. Appl. Polym. Sci., vol. I2, pp.1589-1600 (I968).]
Butyl rubber having a broad molecular weight distribution has been found to
exhibit
excellent Banbury mixing characteristics and is very resistant to flow under
storage conditions (cold
flow). The molecular weight distribution of butyl rubber also controls the
extent of extrusion die
swell. Therefore, to produce fabricated articles that are of constant size and
shape, it is highly useful
to have a control over MW and MW/M".
Butyl rubbers with broad molecular weight distribution also have enhanced
green strength
over narrower molecular weight distribution rubbers. The improved green
strength or uncured stock
strength results in improved manufacturing operations (e.g. inner tube
manufacture) in that the
uncured rubber articles are much stronger and less subject to distortion.
United States patent 3,780,002 teaches a method of preparing a broad molecular
weight
distribution butyl rubber in methyl chloride as the diluent. This is
purportedly accomplished by
utilising a mixed catalyst system (e.g., A1C13 and TiCl4 or AlCl3 and SnCl4)
where each of the metal
compounds is an active catalyst independently capable of initiating
polymerization. The molecular
weight distribution of the so-obtained butyl rubber purportedly was greater
than 5.0 and up to about
7.6.
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Despite the advances in the art, there is still a need for a convenient method
for producing
butyl rubber having a broad molecular weight distribution.
It is the object of the present invention to provide a novel method for the
manufacture of
butyl rubber.
Accordingly, the present process provides a process for preparing a butyl
polymer having a
broad molecular weight distribution, the process comprising the step of
contacting a C4 to C8 monoolefm monomer with a C4 to C,~ multiolefin monomer
at a
temperature in the range of from about -100°C to about +50°C in
the presence of a diluent and a
catalyst mixture comprising a major amount of a dialkylaluminum halide, a
minor amount of a
monoalkylaluminum dihalide, and a minute amount of an aluminoxane.
More specifically, the present invention is directed to the preparation of
butyl rubber
polymers having a molecular weight distribution greater than 4.0 by reacting a
C4 to C8 olefin
monomer, preferably a C4 to C8 isomonoolefm with a C4 to C14 multiolefin
monomer, preferably a
C4 to Cto conjugated diolefin monomer, at temperatures ranging from -100
°C to +50 °C, preferably
from -80 °C to -20 °C, in the presence of a diluent, preferably
an aliphatic hydrocarbon diluent, and
a catalyst mixture comprising: (A) a major amount, e.g., 0.01 to 2.0 wt.
percent of a
diallcylaluminum halide, (B) a minor amount, e.g., 0.002 to 0.4 wt. percent of
a monoall~ylaluminum
dihalide (the weight percent being based on the total of the polymerizable
monomers present) with
the monoalkylaluminum dihalide always representing no more than about 20 mole
percent of the
catalyst mixture (based on monohalide plus dihalide) and (C) a minute amount
of an aluminoxane
purposely added to activate the catalyst.
As mentioned hereinabove, the present process relates to the preparation of
butyl rubber
polymers. The term "butyl rubber" as used throughout this specification is
intended to denote
polymers prepared by reacting a major portion, e.g., from about 70 to 99.5
parts by weight, usually
80 to 99.5 parts by weight of an isomonoolefin, such as isobutylene, with a
minor portion, e.g., about
to 0.5 parts by weight, usually 20 to 0.5 parts by weight, of a multiolefin,
e.g., a conjugated
diolefin, such as isoprene or butadiene, for each 100 weight parts of these
monomers reacted. The
isoolefin, in general, is a C4 to C8 compound , e.g., isobutylene, 2-methyl-1-
butene, 3-methyl-1-
butene, 2-methyl-2-butene, and 4-methyl-1-pentene.
30 Those of skill in the art will recognize that it is possible to include an
optional third
monomer to produce a butyl terpolymer. For example, to possible to include a
styrenic monomer
in the monomer mixture, preferably in an amount up to about 15 percent by
weight of the monomer
mixture. The preferred styrenic monomer may be selected from the group
comprising p-
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methylstyrene, styrene, a-methylstyrene, p-chlorostyrene, p-methoxystyrene,
indene (including
indene derivatives) and mixtures thereof. The most preferred styrenic monomer
may be selected
from the group comprising styrene, p-methylstyrene and mixtures thereof: Other
suitable
copolymerizable tennonomers will be apparent to those of skill in the art.
The present process is conducted in a diluent. While the diluent may be
conventional (e.g.,
methyl chloride) it is particularly preferred to utilize an aliphatic
hydrocarbon diluent. Suitable
aliphatic hydrocarbon diluents which can be used in accordance with the
present process include,
but are not limited to, the following: C4 to C$ saturated aliphatic and
alicyclic hydrocarbons, such
as pentane, hexane, heptane, isooctane, methylcyclohexane, cyclohexane, etc.
Preferably the CS to
C6 normal paraffins are used, e.g., n-pentane and n-hexane. The same saturated
hydrocarbons serve
as "solvent"' for the catalyst mixture. The concentration of diluent during
polymerization may range
from 0 to about 50 volume percent, and more preferably from 0 to about 25
volume percent.
The catalyst mixture used in the present process comprises a mixture of from
about 1 to
about 20 mole percent of a monoalkylaluminum dihalide, from about 80 to about
99 mole percent
of a dialkylaluminum monohalide and minute amounts of aluminoxane. Usually the
catalyst
mixture will contain from about 1 to about 15 mole percent of the
monoalkylaluminum dihalide and
from about 85 to about 99 mole percent of the dialkylaluminum monohalide.
Preferably, however,
and in order to achieve the most advantageous combination of ease of
polymerization coupled with
catalyst efficiency and good temperature control over the polymerization
reaction the catalyst
mixture contains from about 2 to about 10 mole percent of the
monoalkylaluminum dihalide and
from about 90 to 98 mole percent of the dialkylaluminum monohalide.
Usually the dialkylaluminum monohalide employed in accordance with this
invention will
be a CZ to C16 low molecular weight dialkylaluminum monochloride, wherein each
alkyl group
contains from 1 to 8 carbon atoms. Preferably, Cz to C8 dialkylaluminum
chlorides are used, wherein
each alkyl group contains from 1 to 4 carbon atoms. Suitable exemplary
preferred dialkylalumimun
monochlorides which can be used in accordance with this invention include, but
are not limited to,
a member selected from the group comprising dimethylaluminum chloride,
diethylaluminum
chloride, di(n-propyl)aluminum chloride, diisopropylaluminum chloride, di(n-
butyl)aluminum
chloride, diisobutylaluminum chloride, or any of the other homologous
compounds.
The monoalkylaluminum dihalides employed in accordance with the present
process may
be selected from the Cl to C8 monoalkylaluminum dihalides, and preferably are
C, to Cø
monoalkylaluminum dihalides independently containing essentially the same
alkyl groups as
mentioned hereinabove in conjunction with the description of the
dialkylaluminum monochlorides.
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Suitable exemplary preferred C1 to C4 monoalkylaluminum dihalides which can be
employed
satisfactorily in accordance with the present process include, but are not
limited to, the following:
methylalumilzum dichloride, ethylalumimum dichloride, propylaluminum
dichlorides, butylaluminum
dichlorides, isobutylaluminum dichloride, etc.
As stated hereinabove, the present process is conducted in the presence of an
aluminoxane.
The aluminoxane component useful as a catalyst activator typically is an
oligomeric aluminum
compound represented by the general formula (Rz-Al-O)", which is a cyclic
compound, or R2(RZ-Al-
O)"A1R22, which is a lineax compound. In the general aluminoxane formula, RZ
is independently a
C, to C,° hydrocarbyl radical (for example, methyl, ethyl, propyl,
butyl or pentyl) and n is an integer
of from 1 to about 100. R2 may also be, independently, halogen, including
fluorine, chlorine and
iodine, and other non-hydrocarbyl monovalent ligands such as amide, alkoxide
and the like, provided
that not more than 25 mol % of Rz are non-hydrocarbyl as described here. Most
preferably, Rz is
methyl and n is at least 4.
Aluminoxanes can be prepared by various procedures known in the art. Fox
example, an
aluminum alkyl may be treated with water dissolved in an inert organic
solvent, or it may be
contacted with a hydrated salt, such as hydrated copper sulfate suspended in
an inert organic solvent,
to yield an aluminoxane. Generally, however prepared, the reaction of an
aluminum alkyl with a
limited amount of water yields a mixture of the linear and cyclic species, and
also there is a
possibility of interchain complexation (crosslinking). The catalytic
efficiency of aluminoxanes is
dependent not only on a given preparative procedure but also on a
deterioration in the~catalytic
activity ("ageing") upon storage, unless appropriately stabilized,
Methylaluminoxane and modified
methylaluminoxanes are preferred. For further descriptions, see, for example,
one or more of the
following United States patents:
4,665,208 4,952,540 5,041,584
5,091,3 52 5,206;199 5,204,419
4,874,734 4,924,018 4,908,463
4,968,827 5,329,032 5,248,801
5,235,081 5,157,137 5,103,031
In the present invention,it is preferred oxane is added to the catalyst
that alumin solution in such an
amount that the reactionfeed contains 0.3 to about 3.0 weight percent,
from about more preferably
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WO 01/85810 PCT/CA01/00602
from about 1.0 to about 2.5 weight percent of aluminoxane, based on the total
weight of the
aluminum-containing components of the catalyst system.
The application of the present process results in the production of butyl
rubber polymers
having a broad MWD. Preferably, the MWD is greater than about 3.5,
more'preferably greater than
about 4.0, even more preferably in the range of from about 4.0 to about 10.0,
most preferably in the
range of from about 5.0 to about 8Ø Thus, it has been unexpectedly observed
that, when minute
amounts of aluxninoxanes are present in the reaction feed, the resulting butyl
rubber polymer will
have a broad MWD.
Embodiments of the present invention will be illustrated with reference to the
following
Examples, which should not be use to construe or limit the scope of the
present invention.
EXAMPLE 1
To a 50 mL Erlenmeyer flask, 3.75 mL of distilled hexane, 4.62 mL Et~AlCl (1.0
M solution
in hexanes) and 0.38 mL EtA1C12 (1.0 M solution in hexanes) were added at room
temperature
forming a catalyst solution.
To a 250 mL 3-neck flask equipped with an overhead stirrer, 40.0 mL of
isobutylene at -
75°C were added, followed by 8.0 mL hexane at room temperature and 1.0
mL isoprene at room
temperature. The reaction mixture was cooled down to -75°C and 1.8 mL
of the catalyst solution was
added to start the reaction.
The reaction was carried out in an MBRAUNTM dry box under the atmosphere of
dry
nitrogen. The temperature changes during the reaction were followed by a
thermocouple. After 20
minutes, the reaction was terminated by adding 5 mL of ethanol into the
reaction mixture.
The polymer solution was poured on an aluminum tray lined with Teflon and the
solvent and
unreacted monomers were allowed to evaporate in a vacuum oven at 70°C.
The gravimetrically determined yield was 14.8 wt. percent, M" = 46 200, MW =
126 500,
MW/M"= 2.7, and isoprene content was 1.3 mol percent.
This Example represents a conventional method for production of butyl rubber
(United
States patent 3,361,725 [Parker] and is provided for comparative purposes.
5
CA 02406602 2002-10-24
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EXAMPLE 2
The methodology of Example 1 was repeated except 25 L of MAO was added
directly to
the catalyst solution. After stirring, 1.8 mL of this solution was immediately
used to start the
reaction.
The polymer yield was 33.8 wt. percent, M" = 139 400, MW = 506 100, M,~/M" =
3.6, and
isoprene content was 1.6 mol percent.
EXAMPLE 3
The methodology of Example 1 was repeated except 75 L of MAO was added
directly to
the catalyst solution. After stirring, 1.8 mL of this solution was immediately
used to start the
reaction.
The polymer yield was 55.3 wt. percent, M" = 117 200, MW = 514 300, MW/Mn =
4.4, and
isoprene content was 1.8 mol percent.
EXAMPLE 4
The methodology of Example 1 was repeated except 100 L of MAO was added
directly to
the catalyst solution. After stirring, 1.8 mL of this solution was immediately
used to start the
reaction.
The polymer yield was 54.5 wt. percent, Mn = 83 800, MW = 523 900, M,~IM" =
6.3, and
isoprene content was 1.9 mol percent.
EXAMPLE 5
The methodology of Example 1 was repeated except 175 L of MAO was added
directly to
the catalyst solution. After stirring, 1.8 mL of this solution was immediately
used to start the
reaction.
The polymer yield was 57.1 wt. percent, Mn = 67 900, MW = 517 500, M,~/M" =
7.6, and
isoprene content was 1.9 mol percent.
The results from Examples 1-5 are presented in Table 1. These results
illustrate the
advantageous combination of yield, MWD and isoprene content in Examples 2-5,
particularly in
Examples 3-5, compared to those properties for the polymer of Example 1.
While this invention has been described with reference to illustrative
embodiments and
examples, the description is not intended to be construed in a limiting sense.
Thus, various
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CA 02406602 2002-10-24
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modifications of the illustrative embodiments, as well as other embodiments of
the invention, will
be apparent to persons skilled in the art upon reference to this description.
It is therefore
contemplated that the appended claims will cover any such modifications or
embodiments.
All publications, patents and patent applications referred to herein are
incorporated by
reference in their entirety to the same extent as if each individual
publication, patent or patent
application was specifically and individually indicated to be incorporated by
reference in its entirety.
7
CA 02406602 2002-10-24
WO 01/85810 PCT/CA01/00602
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