Catalyst for the polymerization of olefins

A supported solid component of catalyst, for the stereospecific polymerization of propylene and other .alpha.-olefins, is obtained by making a non-activated silica interact in succession with: (i) a magnesium dialkyl or halide of magnesium alkyl; (ii) a halogenating agent selected from silicon, tin and antimony halides; (iii) a titanium tetrahalide; and (iv) a Lewis base. A catalyst for the stereospecific polymerization of propylene and other .alpha.-olefins is composed of: (A) the solid component of catalyst; (B) an aluminium trialkyl or aluminium alkyl halide; and (C) an electron donor compound, capable of forming a complex compound with component (B).

DESCRIPTION 
The present invention relates to a procedure for the production of a 
component of catalyst for the polymerization of .alpha.-olefins, the 
catalyst which incorporates the component thus obtained and a procedure 
for the polymerization of .alpha.-olefins using this catalyst. 
Olefinic monomers such as ethylene, propylene and higher .alpha.-olefins 
can be polymerized using Ziegler-Natta catalysts, i.e. catalytic systems 
obtained by the combination of an organometallic compound of elements from 
groups IA to IIIA and a compound of a transition metal belonging to groups 
IVA to VIA of the Periodic Table (Boor Jr., "Ziegler-Natta Catalysts and 
Polymerization", Academic, New York, 1979). 
When these catalysts are used in the polymerization of propylene and higher 
.alpha.-olefins there is the formation of a mixture of isotactic and 
atactic polymers, the isotactic polymer being the more valuable material 
for commercial purposes. The first problem consequently consists of 
orienting the polymerization of the olefin towards the prevalent or 
exclusive formation of the isotactic polymer. Another problem consists of 
reducing the content of catalytic residues obtained in the polymer to 
lower levels than those which can cause harmful effects in the subsequent 
processing and transformation phases. 
Various proposals have been made in the art for improving the 
stereospecificity and the activity of the catalytic system. These 
proposals are generally based on a modification of the components of the 
catalytic system by introducing further components and typically Lewis 
bases and using a support for the transition metal, and typically a halide 
of a bivalent metal. 
According to U.S. Pat. No. 4,252,670, a component of catalyst for the 
polymerization of olefins is obtained by treating an organic compound of 
magnesium with a halogenating agent, and adding a Lewis base and titanium 
tetrachloride to the reaction product thus obtained. According to U.S. 
Pat. No. 5,006,620 a component of catalyst for the polymerization of 
olefins is obtained by treating a silica in succession with an organic 
compound of magnesium, a gaseous chlorinating agent selected from chlorine 
and hydrochloric acid, a derivative of phthalic acid, a C.sub.1-8 alkanol 
and titanium tetrachloride. 
It has now been found according to the present invention, that a 
non-activated silica can interact with an organic compound of magnesium to 
give an activated support which can be easily halogenated with a silicon, 
tin or antimony halide. It has also been found that this activated and 
halogenated support can interact with titanium tetrachloride and 
particular Lewis bases to give, in a simple and economical way, a solid 
component of catalyst which is highly active in the polymerization of 
.alpha.-olefins in stereoregular polymers. 
In accordance with this the present invention relates to a procedure for 
the preparation of a solid component of catalyst, active in the 
polymerization of propylene and other .alpha.-olefins into stereoregular 
polymers, composed of a silica support and a catalytically active part 
including magnesium, halogen, titanium and a Lewis base, said procedure 
comprising: 
(i) the treatment of a non-activated silica support by contact of said 
silica with a solution, in an inert hydrocarbon solvent, of a magnesium 
dialkyl or halide of magnesium alkyl, operating with a weight ratio 
between the magnesium compound and the silica of 0.1/1 to 10/1, at a 
temperature ranging from 20.degree. C. to the boiling point of the liquid 
phase, for a period which is sufficient to completely, or almost 
completely, deposit the magnesium compound on the silica; 
(ii) the halogenation of the support treated in (i) by contact of said 
activated support with a solution, in an inert hydrocarbon solvent, of a 
halogenating agent selected from silicon, tin or antimony halides, 
operating with a molar ratio between the halogenating agent and the 
magnesium compound deposited in step (i) of 0.1/1 to 100/1, at a 
temperature of -20.degree. to 100.degree. C. and for a period of 0.5 to 
5.0 hours; 
(iii) the titanation of the support halogenated in step (ii) by contact of 
said halogenated support with an excess of a titanium tetrahalide either 
liquid or in solution in an inert, hydrocarbon solvent, operating at a 
temperature of 80.degree. C. to 100.degree. C. and for a period of 0.5 to 
5.0 hours; 
(iv) the formation of the solid component of catalyst by contact of the 
support titanated in (iii) with a Lewis base either liquid or in solution 
in an inert hydrocarbon solvent, operating with a molar ratio between said 
Lewis base and the magnesium compound absorbed in step (i) of 0.05/1 to 
0.5/1, at a temperature of 80.degree. to 120.degree. C. for a period of 
0.5 to 5.0 hours; and 
(v) the recovery of the solid component of catalyst from the reaction 
products of step (iv). 
The silica suitable as a support for the catalyst of the present invention 
is preferably a microspheroidal, porous silica, with a particle size of 20 
to 100 .mu.m, with a surface area of 150 to 400 m.sup.2 /g, a pore volume 
of 1.3 to 1.8 ml/g and an average pore diameter of 20 to 30 A (angstrom). 
This silica has not been pre-activated and consequently contains hydroxyls 
and water in a total quantity which is generally higher than 1% by weight 
up to a maximum value of 5% by weight. 
In step (i) of the procedure of the present invention, the silica support 
is suspended in a solution, in an inert organic solvent, of a magnesium 
dialkyl or halide of magnesium alkyl. 
The magnesium compounds suitable for the purpose are those which can be 
defined with the formulae MgRR' or MgR"X, wherein R, R' and R", each 
independently, represent an alkyl group, linear or branched, containing 
from 1 to 12 carbon atoms and X represents a halogen atom preferably 
chlorine. Specific examples are magnesium diethyl, magnesium ethyl butyl, 
magnesium dihexyl, magnesium butyl octyl and magnesium dioctyl, the 
corresponding chloroderivatives and a mixture thereof. 
Examples of inert hydrocarbon solvents suitable for the purpose are 
aliphatic hydrocarbon solvents such as pentane, isopentane, hexane, 
heptane and octane. 
In practice the support is added to the solution of the magnesium compound 
or preferably the support is suspended in an inert organic solvent, 
selected from those mentioned above and the solution of the magnesium 
compound in the same or other inert hydrocarbon solvent is slowly added to 
the suspension thus obtained. 
The resulting suspension is kept at a temperature ranging from 20.degree. 
C. to the boiling point of the liquid phase and preferably at a 
temperature of 50.degree.-70.degree. C. 
In this step the magnesium compound is deposited onto the silica support 
and, to ensure success in the following step (ii), it is important to use 
a quantity of magnesium compound which is not higher than the absorption 
capacity of the support. For this purpose the weight ratio between the 
magnesium compound and the silica may be 0.1/1 to 10/1 and preferably 
0.2/1 to 1.5/1 and in the very preferred form with a value of about 1/1. 
Under the above conditions, the time necessary for the complete, or almost 
complete, absorption of the magnesium compound varies from 10 minutes to 2 
hours, depending on the temperature chosen and in the preferred method is 
about 0.5-1.0 hours. 
At the end of the treatment the solid is separated from the suspension, for 
example by sedimentation, filtration or centrifugation and is washed with 
an inert solvent, such as a liquid aliphatic hydrocarbon and possibly 
dried. 
In step (ii) of the procedure according to the present invention, the 
support treated as described above is put in contact and interacted with a 
halogenating agent selected from silicon, tin and antimony halides. 
The silicon halides suitable for the purpose are silicon chlorides and 
bromides and chloro and bromo silanes. Specific examples of these 
compounds are silicon tetrachloride, silicon tetrabromide, 
trichlorosilane, vinyl trichlorosilane, trichlorethoxy silane and 
chloroethyl trichlorosilane. Among these silicon tetrachloride is 
preferred. 
Other suitable halogenating agents are tin and antimony chorides and 
bromides, such as tin tetrachloride, which is preferred, and antimony 
pentachloride. 
In step (ii) the treated support is suspended in an inert organic solvent 
and generally an aliphatic hydrocarbon solvent, such as pentane, 
isopentane, hexane, heptane and octane. The halogenating agent is added to 
the suspension thus obtained and the resulting suspension is heated to a 
temperature of -20.degree. C. to 100.degree. C., for a period of 0.5 to 5 
hours. It is preferable to operate at 70 -95.degree. C. for 1-2 hours. 
As previously specified, in step (ii) the molar ratio between the 
halogenating agent and the magnesium compound is 0.1/1 to 100/1, the best 
results being obtained with a value of said ratio of about 10/1. 
At the end of the halogenation treatment, the solid is separated from the 
suspension, for example by sedimentation, filtration or centrifugation and 
is washed with a solvent, such as a liquid aliphatic hydrocarbon solvent 
and possibly dried. 
In step (iii) of the procedure according to the present invention, the 
halogenated support of step (ii) is submitted to titanation by interaction 
with a titanium tetrahalide and preferably titanium tetrachloride. 
More specifically, the procedure is carried out with an excess of titanium 
tetrahalide by suspending the halogenated support in the liquid titanium 
tetrahalide or in solution in one of the above-mentioned inert hydrocarbon 
solvents. The operating temperature varies from 80.degree. to 120.degree. 
C. for a period which, depending on the temperature chosen, can vary from 
0.5 to 5.0 hours. In the preferred embodiment the temperature is about 
95.degree. C. for a period of about 1 hour. 
Under these conditions a quantity of titanium of about 3-7% by weight is 
fixed onto the chlorinated support. 
According to the procedure of the present invention in step (iv) the 
support which has been titanated in step (iii) is put in contact with a 
Lewis base. Lewis bases (or internal electron donors) which can be used 
are ethers, amines, esters, alcoholates, silanic compounds, ketones and 
phosphoramides. The esters used can be of the organic or inorganic type. 
Aromatic esters such as diisobutylphthalate , alkyl esters of benzoic 
acid, p-methoxybenzyl acid and p-toluic acid, and aliphatic esters such as 
diethyl carbonate, ethyl pivalate, ethyl acetate and dimethyl maleate are 
particularly suitable for the purpose. Other compounds which can be used 
for the purpose are alkyl aryl silanes and alkoxysilanes. 
In the preferred embodiment the Lewis base is added to the reaction mixture 
obtained at the end of titanation step (iii) and the molar ratio between 
said Lewis base and the magnesium compound absorbed in step (i) varies 
from 0.05/1 to 0.5/1, the temperature ranges from 80.degree. to 
120.degree. C. for a period of 0.5 to 5.0 hours. In the preferred 
embodiment the molar ratio is 0.1/1 to 0.3/1, the temperature about 
95.degree. C. for a period of about 1 hour. 
In this way the solid component of catalyst is obtained and is recovered in 
step (v) of the procedure and washed with a hydrocarbon solvent and 
possibly dried. 
The solid component of catalyst thus obtained is submitted to one or more 
treatments with titanium tetrahalide, carried out under the above 
conditions, to purify the catalyst so that the whole catalytic complex is 
structurally homogeneous, in order to have stereospecific active centres 
of the same kind in the polymerization phase. 
In another embodiment, the solid component of catalyst is heated in the 
presence of a liquid aliphatic hydrocarbon to dissolve and remove any 
possible titanium tetrachloride which has been absorbed on the active 
surface or on the titanium complex. 
In all cases, by operating as described above, a solid component of 
catalyst is obtained, which is composed of a silica support (10-90% by 
weight) and a catalytically active part containing magnesium, halogen and 
titanium, as well as the Lewis base selected. The catalytically active 
component of the solid catalyst according to the present invention usually 
contains: 4-8% by weight of magnesium, 20-35% by weight of chlorine, 3-7% 
by weight of titanium and 1-15% by weight of the Lewis base, wherein the 
titanium is partly in its trivalent state and partly in its tetravalent 
state, with a ratio Ti(III)/Ti(IV) generally varying from 0.05/1 to 1/1. 
In terms of molar ratios said active part has a composition within the 
following ranges: 
EQU Mg.sub.(1) Cl.sub.(2-4) Ti.sub.(0.1-0.5) LB.sub.(0.01-0.1) 
wherein LB=Lewis base. 
It has now been experimentally found that the reaction between a magnesium 
dialkyl and silicon tetrachloride, in a molar ratio of 0.5/1 to 20/1, 
carried out without the silica support, produces a magnesium chloride 
solid mixed with greater or lesser quantities of an unknown product, as 
revealed by X-ray diffraction analysis. More specifically the magnesium 
chloride thus formed is present in alpha and gamma crystalline forms 
(considered to be scarsely active), with a limited presence of the delta 
form (which constitutes the active form). When the magnesium dialkyl is 
deposited on a silica with a certain content of water and/or hydroxyls 
(step (i) of the present invention), the treatment with silicon 
tetrachloride (according to step (ii) produces a very disorderly dispersed 
phase of magnesium chloride, practically without the peak at 15.degree. in 
the X-ray spectrum, in the form of random oriented lamellae. This 
magnesium chloride, in its maximum state of disorder, is highly active 
from a catalytic point of view. 
It has now been found, according to the present invention, that useful 
results are not obtained by first depositing the silicon tetrachloride on 
the silica containing water and/or hydroxyls and then treating with a 
magnesium dialkyl, as described in a comparative example. This would seem 
to indicate that the magnesium dialkyl deposited in step (i) of the 
present invention, is grafted to the silica (probably by Mg--O--Si type 
bonds) and that this grafted form is essential for the formation of the 
highly dispersed magnesium chloride of chlorination step (ii) with 
titanium tetrachloride. This seems to be confirmed by the fact that useful 
results are not obtained by using a pre-activated silica, from which the 
water and hydroxyls have been substantially removed. As shown in a further 
comparative example, useful results are not obtained by depositing the 
magnesium chloride onto the silica before treatment with the magnesium 
dialkyl, and this confirms how critical steps (i) and (ii) are according 
to the present invention. When tin tetrachloride is used in step (ii) of 
the present invention, the interaction between this halogenating agent and 
the magnesium dialkyl seems to lead to the formation of both alkyl 
compounds of tin, and also to polymer aggregates of an unspecified nature, 
which however have proved to be useful in the preparation of component of 
catalyst which is highly active and stereospecific in the polymerization 
of olefins. It has also been noted that contact between antimony 
pentachloride and silica containing water and/or hydroxyls, when there is 
no magnesium dialkyl, causes reduction to metallic antimony. On the other 
hand, in the presence of magnesium dialkyl, in step (ii) of the present 
invention, the halogenating agent is reduced from pentavalent to 
trivalent, and this again proves how critical steps (i) and (ii) of the 
present invention are. 
The present invention also relates to a catalyst for the stereospecific 
polymerization of propylene and other .alpha.-olefins which is composed 
of: (A) the solid component of catalyst described above; (B) an aluminium 
trialkyl or halide of aluminium alkyl; and (C) an electron donor compound, 
capable of forming a complex compound with component (B). 
Component (B) of the catalyst is conveniently selected from aluminium 
trialkyls and halides (especially chlorides) of aluminium alkyl, which 
contain from 1 to 6 carbon atoms in the alkyl portion. Among these 
aluminium trialkyls are preferred, such as aluminium triethyl, aluminium 
tributyl, aluminium triisobutyl and aluminium trihexyl. 
Component (C) of the catalyst is conveniently selected from alkoxy silanes 
which can be defined with the formula R.sup.1 R.sup.2 
Si(OR.sup.3)(OR.sup.4) wherein R.sup.1 and R.sup.2 are phenyl groups and 
R.sup.3 and R.sup.4 are C.sub.1 -C.sub.4 alkyl groups. A specific example 
of component (C) is dimethoxy diphenyl silane. 
In the catalysts of the present invention the atomic ratio between the 
aluminium (present in component (B)) and the titanium (present in 
component (A)), may generally vary from 10/1 to 1,000/1 and will 
preferably be within the range of 50/1 to 150/1. Moreover the molar ratio 
between components (B) and (C) may generally vary from 5/1 to 20/1 and 
will preferably be about 10/1. 
The catalyst of the present invention is highly active in procedures for 
the polymerization of propylene and other .alpha.-olefins in highly 
stereospecific polymers. In particular in the polymerization of propylene, 
polypropylenes are obtained having an isotactic index equal to or higher 
than 95%. Examples of other .alpha.-olefins which can be polymerized using 
the catalyst of the present invention are butene-1, 4-methylpentene-1 and 
hexene-1. 
The polymerization reaction may be carried out with the suspension 
technique in an inert diluent, with the loop reactors technique without 
solvents or diluents, or with the gas-phase technique. The polymerization 
may generally be carried out at a temperature ranging from room 
temperature to 120.degree. C. and under a pressure of 1 to 100 
atmospheres. 
In all cases, operating with the catalyst of the present invention, 
olefinic polymers are obtained with a particle size which are a precise 
replica of the solid component used. It is thus possible to produce 
polymers having the desired particle size of the granules based on the 
choice of the size and size distribution of the support. 
The experimental examples which follow provide a better illustration of the 
invention.