Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
1074047
This invention relates to a process for polymerizing ~-alkenes to
form homopolymers or copolymers in the presence of a polymerization catalyst
comlrising a titanium-halide component supported on a water-free magnesium
halide or manganese-halide carrier, and an organoaluminum component; and
particularly relates to such polymerization processes having an improved
organo-aluminum component. The invention also provides shaped articles of
polymers thus prepared.
A known catalyst system includes a titanium-halide component con-
sisting of a titanium halide on a specially activated, water-free magnesium-
halide or manganese-halide carrier, the organoaluminum component being the
product of an addition reaction between a trialkyl-aluminUm compound and an
ester of an organic acid containing oxygen, and is usually a mixture of a
complex of the trialkyl-aluminium compound with the said ester and a free
trialkyl-aluminUm compound. A catalyst system of this type is particularly
useful in the polymerization of propene, butene-l, 4-methyl pentene-l and
other a-alkenes. However the stereospecificity of the polymer product with
such a catalyst leaves much to be desired.
The invention provides for the use of a catalyst system of the
type hereinbefore referred to, which when used for polymerizing a-alkenes
shows a particularly high activity together with a very high stereospecifi-
city. Another advantage is that a polymer product is obtained having a
large average particle size, which is advantageous when processing the pro-
duct to powder.
The invention provides a process for polymerizing an ~-alkene in
the presence of a catalyst system comprising a titanium-halide component sup-
ported on a water-free magnesium-halide or manganese-halide carrier, and an
organo-aluminum component that contains ~a) a complex of a trialkyl-aluminum
compound with an ester of a carboxylic acid, and ~b) the reaction product of
a dialkyl-magnesium compound and a monoalkyl-aluminùm dihalide.
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Th~ organo-aluminium component is preferably free of nol~-complexed
trialkyl-aluminium compound~ as the presence of non-complexed trialkyl-
aluminium compound detracts from the stereospecificity of the catalyst
system.
The process according to the in~ention is used in particular in
the stereospecific polymerization of C~-C~ oralkenes, e g. propene, butene-1,
4-methyl pentene-l and hexene, and in the copolymerization of such ~-alkenes
with each other and/or with ethene. Copolymers with a random distribution
of the various monomer units and block copolymers, may be thus prepared.
If ethene is used as comonomer it is usually incorporated in a minor propor-
tion e.g. up to 30 %, more particularly between 1 % and 15 ~ by weight,
based on the said ~-alkene.
The titanium halide is present in the titanium halide component
on a water-free magnesium halide or manganese-halide carrier. The titanium
compound used may be any halogenated compound of divalent, trivalent or
tetravalent titanium, including compounds in which part of the titanium
valences is utilized for compounds other than those with halogen atoms.
The halogen is preferably bromine, iodine and particularly chlorine. Specific
examples of such titanium compounds are TiC13, TiC13.1/3 AlC13, TiC14,
Ti~r4, TiI4 and Ti(isobutoxy)2C12.
The titanium halide is preferably present as a complex with
a Lewis base. The preferred Lewis base is an ester of a carboxylic acid,
more particularly esters of aromatic carboxylic acids e.g. ethyl benzoate,
ethyl-p-methoxy-benzoate, n-butyl benzoate, methyl toluate, and dimethyl
phthalate. Other examples of suitable esters are esters of saturated
aliphatic carboxylic acids, e.g. ethyl acetate, amyl propionate and methyl
butyrate, and esters of unsaturated aliphatic carboxylic acids, e.g.
methyl methacrylate, ethyl acrylate, and dimethyl maleinate. The acid
component of the ester usually contains from 1 to 9 carbon atoms per
molecule or is a natural fatty acid, while the alcohol component of the
ester usually contains from 1 to 6 carbon atoms per molecule. Other examples
of suitable Lewis bases are triethyl amine, pyridine, ethylene diamine,
nitrobenzene and diethylether.
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The titanium halide-Lewis base complexes can be obtained in any
known way, e.g. by putting together the components of the complex.
The carrier material used may be any water-Eree magnesium halide
or manganese halide, but in practice the ctlloride, particularly magnesium
chloride, is pre~erred.
Suitable water-free magnesium chloride can be prepared in known
manner by dehydration of MgC12.6 H~0.
Particularly good activity and stereospecificity are obtained in
the process of the invention using water-free magnesium halide or manganese
halide which has a surface area larger than 3 m /g, and/or shows broadened
diffraction lines in the X-ray spectrum compared to the normal, non-acti-
vated halide, and which has been activated, for instance as described in
the British Patent specification 1387890. Very favourable results are
obtained using a water-free magnesium dihalide that has been prepared by
making a dialkyl-magnesium compound react with an anhydrous hydrogen halide
in a suitable solvent, e.g. n-heptane or another liquid hydrocarbon.
The titanium halide may be put on the carrier for example by
simple admixture, preferably by grinding the mixture. If a titanium
halide-Lewis base complex is used, it is possible first to form the complex
and then to apply it to the carrier, or first to put the urcomplexed
titanium halide on the carrier and then to add the Lewis base, either
before or after the addition of the organoaluminium component. The
titanium content of the ready titanium halide component on the carrier
is preferably from-0.1 ~ to 10 % by weight. The Lewis base is present in
the titanium halide component in an amount of e.g. C-5 molecules per
titanium atom.
The organoaluminium component comprises a complex of a
trialkyl-aluminium compound with an ester of a carboxylic acid. Suitable
esters are the same esters as used in the titanium-halide component,
preferably esters oi aromatic carboxylic acids e.g. as hereinbefore des-
cribed. Particularly suitable trialkyl-aluminium compounds are triethyl
aluminium, tripropyl aluminium, triisobutyl aluminium, triisoprenyl
aluminium~ trihexyl aluminium and trioctyl aluminium. The Al/Ti ratio is
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preferably between 10 and 1000 and the molecule-atom ratio of the total
amount of bound Lewis base in the catalyst to Ti is preferably between
5 and 500.
As hereinbefore described, l;he organoaluminium compound is pre-
B 5 ferably free of uncomplexed trialkyl-aluminium compound, and thus ~_pre-
ferably a stoichiometric amount of ester with respect to the trialkyl-
aluminium compound is used, apart from the amount of ester used as a con-
stituent of the titanium-halide component in some instances.
The exact stoichiometric amount of ester with respect to the tri-
alkyl-aluminium compound can be determined by means of microwave titration
of the trialkyl-aluminium compound with the ester in the way described in
Analytical Chemistry 37 (1965), pp. 229-233.
The microwave titration is carried out by observing the change
in transmission of microwaves in a resonance cavity during the course of
the reaction of the trialkyl-aluminium compound with the ester. The mea-
sured energy loss is the sum of the individual losses of the components
present in the resonance cavity. One of these components is made up of the
new molecules thereby formed. By plotting the transmission potential ~ ,
which is defined as:
j 20 a =~ V - 1, where
VO = initial transmission potenti&l
V = transmission potential at the time of measurement,
against the concentration or the amount of reagent added, a curve is ob-
tained in which the sharp break indicates the composition of the complex.
This titration is particularly suitable for tha determination of
the stoichiometry of complexes, in particular, for the determination of the
stoichiometric amount of ester with respect to the trialkyl-aluminium com-
pound under the conditions of the polymerization reaction according to the
invention.
According to T. Mole and B.A. Jeffery, 'Organoaluminium compounds',
Elsevier Publ. Co., Amsterdam (1972), p. 302, a trialkylaluminium compound
.
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forms a 1 : 1 complex with an ester. It has been found however that by
means of microwave titration that under the polymerization conditions
used a normal value for the stoichiometric molar amount of ester with
_....
respect to the trialkyl-aluminium compound is 1 : l.S. The determined
value depends on the level of purity and the concentrations used and may
range for example from 1 : 1.0 to 1 : 2.0, in particular from 1 : 1.2
to 1 : 1.6.
It is to be considered surprising that the best combination
of activity and stereospecificity can be obtained with the stoichiometric
amount of ester with respect to the trialkyl-aluminium compound as
determined by the microwave titration, if use is made of an organoaluminium
component that also contains the reaction product of a dialkyl-magnesium
compound and a monoalkyl dihalide.
The organoaluminium component contains in addition to the
complex of trialkyl-aluminium compound and ester, the reaction product
of a dialkylmagnesium ¢ompound and a monoalkyl-aluminium dihalide. The
alkyl groups of the dialkyl-magnesium compound preferably contain 1-10
carbon atoms per molecule or form a palmityl or stearyl group. Examples
of suitable dialkylmagnesium compounds are diethyl magnesium, di-n-butyl
magnesium, di-n-hexyl magnesium and di-n-octyl magnesium. The monoalkyl-
aluminium dihalide is preferably a chloride or bromide. Ethyl-aluminium
dichloride or di-bromide are particularly suitable, but use may also
be made of other monoalkyl-aluminium dihalides, preferably with 1-10
carbon atoms in the alkyl group e.g. isopropyl-aluminium dichloride,
n-butyl-aluminium dibromide or n-octyl-aluminium dichloride. The reaction
product of the dialkyl-magnesium compound and the monoalkyl-aluminium
dihalide is preferably added to the reaction product of the titanium-halide
component and the complex of the trialkyl-aluminium compound with the
ester.
The molar ratio between the dialkyl-magnesium compound and the
monoalkyl-aluminium dihalide may for example be in the range 0.1 and 1,
preferably between 0.3 and 0.6. Too high molar ratios give rise to
~74~47
insufficiently stereospecific catalysts and too low ratios to insufficient
catalyst activity.
The conditions under which +he polym3ri~ation reaction by means of
the new catalysts is effected are similar to conditions conventionally used.
Thus the reaction may be carried out in the gaseous phase or in the presence
of a liquid vehicle, which may be inert or ~t may be a monomer in liquid form.
Examples of suitable vehicles are aliphatic, cycloaliphatic, aromatic and
mixed aromatic/aliphatic hydrocarbons with 3-8 carbon a-toms, for example
propene, butene-l~ butane, isobutane, n-hexane, n-heptane, cyclohexane,
benzene, toluene and the xylenes.
The polymerization temperature usually is within the range between
-80 and 150 C, preferably between ~0 and 100 C. The pressure may for
example be between 1 and 30 atmospheres.
If so desired the molecular weight of the polymer may be controlled
during the polymerization, e.g. by effecting the polymerization in the
presence of hydrogen or another well-known molecular-weight regulator.
To prepare block copolymers, the monomers may be added in any
desired order.
The process according to the invention is of particular importance
in the preparation of isotactic polypropene, random copolymers of propene
with minor amounts of ethene, and block copolymers of propene and ethene.
The following Examples of the invention are provided:
_etermination of the stoichiometrio amount of ester with respect to the
trialkyl-aluminium compound
50 ml of water-free gasoline were introduced into a mixing vessel
of the apparatus described in Analytical Chemistry 37 (1965), pp. 229-233.
3 ml of a 0.1 M solution of triethyl aluminium in gasoline were than added.
The titration was carried out with a 0.1 M solution of ethyl benzoate in
water-free ga~ollne. The scale of the millivolt recorder was set to 20 mV
~n / 0~ V~ D f
~ 30 The ~-value is plotted against the number of ~ ~ 5~.v~
; ethyl benzoate added (n), the break indicating the equivalence point, as
shown in the graph of the accompanying drawing. The ~ -value is defined as
`` 1~74~:)47
, where V denotes the initial transmission potential and V the
transmission potential at the time of measurement.
_ample I
6.5 ml of water-free ethyl ben~oate dissolved in 75 ml of water-free
gasoline were added at 0 C to a solution of 5 ml of TiCl4 in 125 ml of
gasoline that had been flushed with dry nitrogen, and the resulting complex
TiC14.C6H5COOC2H5 precipitated This precipitate was filtered, washed and
dried in a water-free nitrogen atmosphere.
0.348 g of the complex TiC14.C6H5COOC2H5 and 4.166 g of water-free
magnesium chloride thus obtained were ground together in an agate ball mill
for 16 hours in a nitrogen atmosphere. 0.448 g (containing 0.102 mmole of
titanium) of the ground mixture was suspended in a solution consisting of
1.23 ml of triethyl aluminium and 0.86 ml of ethyl ben~oate in 50 ml of water-
free gasoline and prepared under nitrogen and at room temperature five
minutes before (this solution contained amounts of triethyl aluminium and
ethyl benzoate corresponding to the stoichiometry determined by the micro-
wave titration).
1.8 litre of water-free gasoline were introduced into a stainless-
steel 3-litre autoclave equipped with a mechanical stirrer and having
previsously been flushed with dry nitrogen. 4.5 ml of a solution of gasoline
and the reaction product of 9 mmoles of di-n-butyl magnesium and 18 mmoles
of ethyl-aluminium di-chloride were then added, after which the suspension
thus obtained was added to the reaction system. The temperature of the
autoclave was raised to 65 C and propene introduced therein with
vigorous stirring. The propene pressure was controlled at 3 atmospheres
durlng the polymerization. After 1 hour the reaction was stopped and the
white powdery product filtered off.
The yield of polypropene was 59,000 g per g of titanium compound
used (calculated as titanium). The content of isotactic material that is
30 not soluble in gasoline of 65 C was 96.2 % by weight. 50 % by weight
of the polymer parti¢les had a diameter of over 220 ~ m. -
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1074047
Example II
The procedure of Example I was followed, except that only 3 mmoles
of di-n-butyl magnesium and 6 mmoles of ethyl-aluminium dichloride were
used, instead of 9 and 18 mmoles, respectively.
The yield of polypropene was 31,2~0 g per g of ti-tanium used.
The content of isotactic material that is not soluble in gasoline of 65 C
was 96.6 % by weight.
Comparative Experiments
The following comparative experiments were carried out in a way
analogous to that described in Example I, except for the alterations speci-
fied in the accompanying ~ ; wherein DBM denotes di-n-butyl magnesium;
MEAC denotes tmono)ethyl-aluminium dichloride and TEA denotes triethyl aluminium.
Exp. molar amount of amount of yield g isotactic ) molar TEA/ethyl
Al/Ti DBM mmoles ~ mmoles per g of % by w. benzoate ratio
ratio ~ titanium
A 180 0 0 41,500 87.4 3.4
B 76 0 0 11,500 92.4 1.5 )
C 76 9 0 13,900 65.4 1.52)
1) insoluble in gasoline of 65 C
2) stoichiometry determined by microwave titration.
Experiment A shows that a catalyst system that contains non-
complexed trialkyl aluminium but no reaction product of a dialkyl-magnesium
and a monoalkyl-aluminium dihalide, can provide a high catalyst activity
as manifested by the yleld per gram of titanium, but the stereo-specificity
of the catalyst is low. Almost 13 % of the propene monomer used was converted
into undesired atactic polymer.
In experiment B, the stoichiometric trialkyl-aluminium compound/
ester ratio is used, but the catalyst does not contain any reaction product
of a dialkyl-magnesium and a monoalkyl-aluminium dihalide. The activity o$
such a catalyst system is low.
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If a stoichiometric trialkyl-aluminium compound/ester ratio is
us~d, but only dialkyl magnesium is used instead of the reaction product
of a dialkyl-magnesium and a mono-alkyl-aluminium dihalide, the stereo-
specificity of the catalyst is very poor (Experiment C).
