IE63110B1 - Catalytic solid which can be used for the stereospecific polymerization of alpha-olefins, process for the preparation thereof and process for the polymerization of alpha-olefins in the presence thereof - Google Patents

Abstract

Catalytic solids based on complexed titanium trichloride, which can be employed for the stereospecific polymerisation of alpha-olefins preactivated by being brought into contact with an organoaluminium preactivator comprising the product of reaction of a compound (a) chosen from organoaluminium compounds and of a compound (b) chosen from hydroxyaromatic compounds in which the hydroxyl group is sterically blocked. These solids enable propylene to be polymerised with an improved stereospecificity.

Description

The present invention relates to a catalytic solid which can be used for the stereospecific polymerization of alpha-olefins, to a process for the preparation of this solid and to a process for the polymerization of alphaolefins in the presence of this solid.

The stereospecific polymerization of alpha-olefins such as propylene using a catalytic system which comprises a titanium trichloride-based solid constituent and an activator which consists of an organometallic compound such as an al kyIaluminium chloride is known.

Hyperactive solid catalytic complexes based on TiClj with a high internal porosity which enable propylene polymers with very good stereoreguI arity to be obtained have been described in patent BE-A-78/0,758 (SOLVAY & Cie).

A preactivation treatment of these hyperactive solid catalytic complexes which enables them to be stored under hexane for long periods of time without losing their qualities has been described in patent BE-A-80/3,875 (SOLVAY & Cie). The preactivator employed may be chosen from amongst organoaIuminium compounds and in particular, depending on formula (I) which specifies their nature, from amongst hydrocarbyl hydrocarbyl oxyhalides of aluminium. However, diethylaluminium chloride, ethyI a Iuminium sesquichIoride, ethyI a Iuminium dichloride and triethylaluminium are used in practice.

Unfortunately, the stereospecificity of these catalytic complexes is not adequate under all conditions of polymerization under which they may be required to be used and is inadequate especially at the relatively high temperatures at which the polymerization of propylene in the gaseous phase is often carried out. In fact, when polymerization is carried out at relatively low temperatures, a significant decrease in prpductivity of the catalyst is observed.

Attempts have been made to overcome this disadvantage by carrying out the polymerization of propylene in the presence of catalytic systems which comprise the hyperactive solid catalytic complexes mentioned above, modified by the introduction of a third constituent, which is generally an electron donor compound (Lewis base), into the polymerization medium. A very large number of elect tron donor compounds of various types have already been proposed as the third constituents capable of increasing the stereospecificity of these catalytic systems (see for example patent 8E-A-82/2,941 (ICI)). Among this very large number of electron donor compounds which can be employed far this purpose, some phenolic compounds (European Pat10 ent Application EP-A-0,036,549 (BASF)) and some hydroxyaromatic compounds (US Patent Application US-A-4,473,939 (SHELL OIL)) have, in particular, been proposed. However, the improvement in stereospecificity obtained by the introduction of such electron donor compounds into the polymerization medium is significant only when the quantity of the electron donor compound is relatively high (the weight of electron donor compound is generally at least equal to the weight of the solid catalytic complex present in the medium and often much higher). As a re20 suit, deleterious secondary effects such as an unacceptable drop in the productivity of the catalyst and the appearance of interfering colours in the polymer collected, not to mention the complications which may be caused by the requirement to remove the residues of the third constituent from the polymer, are observed.

The present invention aims at providing a catalytic solid with a very high stereospecificity, without the need for introducing a third constituent into the polymerization medium.

To this end, the present invention relates to a complexed titanium trichIoride-based catalytic solid which can be used for the stereospecific polymerization of alpha-olefins, which has been preactivated by bringing it into contact with an organo aluminium preacti.vator and separated from its preactivation medium, the preactivator comprising the product of reaction between an organoaluminium compound (a) and a compound (b) chosen from amongst hydroxyaromatic compounds, the hydroxyl group of which is sterically hindered.

The complexed titanium trichloride-based solids employed as precursors for the preparation of the preactivated catalytic solids according to the present invention may be obtained by any known process. The use of solids obtained by processes which involve an initial reduction of titanium tetrachloride is generally preferred. This reduction may be carried out using hydrogen or metals such as magnesium and preferably aluminium. 8est results are obtained starting with solids produced by the reduction of titanium tetrachloride with an organometallic reducing agent. This may, for example, be an organomagnesium reducing agent. However, the best results are obtained with organoaluminium reducing agents ( 1 ) .

The organoaluminium reducing agents (1) which may preferably be employed are compounds which contain at least one hydrocarbon radical directly bound to the aluminium atom. Examples of compounds of this type are mono-, di- and tria IkyI a Iuminiurns , the alkyl radicals cf which contain from 1 to 12, and preferably from 1 to 6, carbon atoms, such as triethy I a Iuminium, isoprenyI a Iuminiums, diisobutylaluminium hydride and ethoxydiethy Ialuminium. With compounds of this type, best results are obtained with dia I kyI a Iuminium chlorides and, in particular, with diethy I a I uminium chloride.

In order to obtain the complexed titanium trichloride-based solids (hereinafter called precursors) which are employed for the preparation of the preactivated catalytic solids according to the present invention, the reduced solids mentioned above are subjected to a treatment with at least one complexing agent which is generally chosen from amongst organic compounds containing one or more atoms or groups having one or more free electron pairs capable of ensuring the coordination with the titanium or the aluminium atoms present in the titanium or aluminium halides. The complexing agent is preferably chosen from the group consisting of aliphatic ethers, and more particularly from amongst those of which the aliphatic radicals contain from 2 to 8 carbon atoms, and preferably 4 to 6 carbon atoms. A typical example - 4 of an aliphatic ether which gives very good results is diisoamyl ether.

These treatments with complexing agents, which are appropriate for stabilizing or for improving the pro5 ductivity and/or the stereospecificity of catalytic solids are well known and have been comprehensively described in the literature.

Thus, for the preparation of the precursor, the treatment with the complexing agent may consist of a grind ing of the reduced solid in the presence of the complexing agent. It may consist of a thermal treatment of the reduced solid in the presence of the complexing agent. It may also consist of washing the reduced solid extractively in the presence of mixed solvents containing a liquid hy15 drocarbon compound and an auxiliary polar solvent, for example an ether. The reduction of titanium tetrachloride may also be carried out with the organo-aIuminium reducing agent (1), in the presence of the complexing agent, for ex ample by adding, to the titanium tetrachloride, a hydro20 carbon-containing solution of the reaction product of the complexing agent with this reducing agent, and the reduced solid thus obtained may then be subjected to a thermal treatment in the absence of the complexing agent or in the presence of a fresh quantity of complexing agent, which may be identical to or different from the previous. The treatment with the complexing agent may also be carried out with a quantity of the latter which is sufficient to form a homogeneous solution of the titanium trichloridebased solid, and the solid thus dissolved may be repreci30 pitated by heating.

For the preparation of the precursor, the treatment with the complexing agent may be combined with or fol lowed by an activation treatment. These activation treatments are also well known and have also been described in the literature. They are generally carried out using at least one agent chosen from amongst inorganic halogenated compounds, organic halogenated compounds, interha Iogenated compounds and halogens. Among these agents, there may be mentioned: as inorganic halogenated compounds, halides of metals and non-metals, such as, for example, titanium and silicon halides; as organic halogenated compounds, halogenated hydrocarbons such as, for example, halogenated alkanes and carbon tetrahalides; as interha Iogenated compounds, for example iodine chloride and iodine bromide; and as halogen, chlorine, bromine and iodine.

Examples of agents which are very well suited for the activation treatment are titanium tetrachloride, silicon tetrachloride, iodobutane, monochloroethane, hexachloroethane, chIoromethyI benzene, carbon tetrachloride, iodine chloride and iodine. Best results were obtained with titanium tetrachloride.

The physical form of the complexing agents and the agents which are used for the optional activation treatment is not critical for the preparation of the precursor. These agents may be employed in gaseous form or in liquid form, the latter being the most common form in which they are present under usual temperature and pressure conditions. The treatment with the complexing agent and the optional activation treatment may also be carried out in the presence of an inert hydrocarbon diluent which is generally chosen from amongst liquid aliphatic, alicyclic and aromatic hydrocarbons such as liquid alkanes and isoalkanes and benzene.

Details on the most commonly used operating conditions for the complexation and activation treatments may be found especially in patent 8E-A-86/4,708 (SUMITOMO CHEMICAL COMPANY LTD), in patent US-A-4,295,991 (EXXON RESEARCH AND ENGINEERING CO) and in the documents mentioned in the latter.

At any time during its preparation, either after the reduction or the complexation stage, or after the optional activation stage, but preferably after the reduction stage, the precursor may be subjected to a treatment aimed at reducing the friability of the constituent particles thereof. This treatment, which is referred to as prepolymerization, consists in bringing the solid into contact with a lower a I pha-monooIefin such as ethylene, or preferably propylene, under polymerizing conditions so as to obtain a solid which generally contains between approximately 5 and 500% by weight of prepolymerized alpha-monoolefin. This prepolymerization may advantageously be carried out in a suspension of the solid in the inert hydrocarbon diluent as defined above for a period sufficient to obtain the desired quantity of the prepoIymerized alpha-monoolefin on the solid. The precursor obtained according to this variant is less friable and enables polymers with good morphology to be obtained even when the polymerization is carried out at a relatively high temperature.

For its conversion into preactivated catalytic solid, as described later, the precursor may be employed as such, i.e. without separating it from the medium in which it was prepared, or, preferably, after separation and optional washing with an inert hydrocarbon diluent as defined above.

A preferred method for the preparation of complexed titanium trichloride-based solids which can be used as precursors for the preparation of the preactivated catalytic solids according to the present invention has been described in patent BE-A-78/0,758. This method consists in the reduction of titanium tetrachloride using an organoaI urniniurn reducing agent (1) which, in this case, is preferably a dia IkyI a I urniniurn chloride, the alkyl chains of which contain from 2 to 6 carbon atoms, under mild conditions. After an optional thermal treatment of the reduced solid thus obtained, the latter is subjected to a treatment with a complexing agent as de'fined above. Finally, a treatment with titanium tetrachloride is carried out and the complexed titanium trichloride-based solid thus formed is separated and it is optionally washed with an inert hydrocarbon diluent as defined above, preferably chosen from amongst liquid aliphatic hydrocarbons containing from 3 to 12 carbon atoms and which is, moreover the diluent which may be employed throughout the - 7 preparation of the said solid.

The preferred preparation method defined in the preceding paragraph leads to the complexed titanium trichloride-based solid particles which are also described in patent BE-A-78/0,758. These particles are spherical and generally have a diameter of between 5 and 100 microns and most frequently between 10 and 50 microns. They consist of an agglomerate of microparticles, which are also spherical, which have a diameter of between 0.05 and 1 micron, most frequently between 0.1 and 0.3 micron and which are extremely porous. As a result, the particles have a specific surface area greater than 75 m^/g and most 2 frequently located between 100 and 250 m /g and a total porosity greater than 0.15 cm^/g and most commonly between 0.20 and 0.35 cm^/g. The internal porosity of the microparticles forms the most significant contribution to this total porosity of the particles, as evidenced by the high value for the pore volume corresponding to pores less than 200 A in diameter, which is greater than 0.11 cm^/g and most commonly between 0.16 and 0.31 cm\g.

The complexed titanium trichI oride-based solids (precursors) obtained according to the preparation method described in patent BE-A-78/0,758, choosing the preferred operating conditions, correspond to the formula: TiC13.( AIRC12)x·Cy in which R is an alkyl radical containing from 2 to 6 carbon atoms, C is a complexing agent as defined above, x is any number less than 0.20 and y is any number greater than 0.009 and generally less than 0.20.

As an alternative form of this preparation method, there may be mentioned that, mentioned above, which consists in prepolymerizing the reduced solid, after the optional thermal treatment and before treatment with the complexing agent, with a lower alpha-monoolefin (propylene) under polymerizing conditions. This prepolymerization is carried out in a suspension of the reduced solid in the inert hydrocarbon diluent as defined above, between approximately 20 and 80°C, for a period generally between 1 minute and 1 hour.

According to the invention, the precursor, which is prepared as described above, is brought into contact ·> 5 with an organoaIuminium preactivator comprising the product of reaction between an organoaIuminium compound (a) and a compound (b) chosen from amongst hydroxyaromatic compounds, the hydroxyl group of which is sterically hindered. 10 The organoaIuminium compound (a) is generally chosen from amongst compounds of formula: Al Rn X3-n in which R represents hydrocarbon radicals, which may be identical or different, containing from 1 to 18 carbon 15 atoms, chosen in particular from amongst alkyl, aryl, arylalkyl, alkylaryl, cycloalkyl, alkoxy and aryloxy radi cals; X is a halogen and n is a number such that 0 < n ✓ 7 20 > J In the above formula, R is preferably a straight- chain or branched alkyl radical containing from 2 to 8 carbon atoms, X is preferably chlorine and n is preferably such that 1 < n £ 3. 25 As examples of compounds (a), there may be mentioned: trialkylaluminiums such as trimethyl-, triethyl- tri-n-propyI-, tri-n-butyI-, tri-isobutyI-, tri-n-hexy1 -, tri-isohexyI-, tri-2-methyI pentyI- and tri-n-octyI a Iu- minium; dia IkyI a Iuminium monohalides such as diethyl-, 30 di-n-propyl- and di-iso-butyI a Iuminium monochlorides, ethylaluminium monofluorides, monobromides and monoiodides; a IkyI a Iuminium di- and sesquiha Iides such as methyl and ethylaluminium sesquichlorides and ethyl- and isobutyl a I um i n i um dichlorides; a I koxya Iuminium halides such • 35 I as methoxyaluminium and iso-butoxyaluminium dichlorides; a Ikoxya IkyI a Iuminiurns such as monoethoxydiethy1 a Iuminium, diethoxymonoethyI a Iuminium and dihexaneoxymono-n-hexyI- aluminium. Very good results were obtained with trialkylaluminiums and dia IkyI a Iuminium chlorides, in particular with triethyI a Iuminium and diethylaluminium monochloride. The compound (b) is chosen from amongst hydroxy- aromatic compounds, the hydroxyl group of which is sterically hindered. Hydrοxyaromatic compound, the hydroxyl group of which is sterically hindered refers to all hydroxyaromatic compounds which contain a secondary < or tertiary alkyl radical in the two ortho positions re5 lative to the hydroxyl group.

The compound (b) is generally chosen from amongst substituted mono- or polycyclic hydroxyarylenes as mentioned above, in particular from amongst hydroxybenzenes, hydroxynaphthalenes, hydroxyanthracenes and hydroxyphenan10 threnes thus substituted, and the aromatic rings of which may also carry other substituents.

As examples of compounds (b), there may be mentioned: monocyclic monophenols which are di-tert- and di15 sec-alkylated in the ortho positions relative to the hydroxyl group, such as 2,6-di-1ert-buty I pheno I , 2,6-ditert-butyl-4-methyI phenol, 3,5-tert-butyl-4-hydroxy-ahydroxybenzene, 2,6-di-tert-decyl-4-methoxyphenol , 2,6di-tert-butyl-4-isopropylphenol, 2,6-dicyclohexyl-420 methylphenol, 2,6-diisopropyl-4-methoxyphenol and 2,6di-tert-butyl-4-sec-butylphenol; 3-(3',5’-di-tert-butyl-4-hydroxyphenyl)propionic acid monoesters such as methyl, ethyl, n-propyl, n-butyl, n-octyl, n-dodecyl and n-octadecyl 3-(31,5'-di-tert25 butyl-4-hydroxyphenyl)propionates; polyphenols which are di-1ert-aIkyI ated in the ortho positions relative to the hydroxyl groups, such as 2,2-bis(2,6-di-tert-butylhydroxyphenyl)propane, b i s ( 3,5 di-tert-butyl-4-hydroxybenzyl)methane, 4,4’-methylene30 bis(2,6-di-tert-butyl)phenol, 2,2’-methylene-bis(4-ethyl6-tert-butyl)phenol, 1,3,5-trimethyl-2,4,6-bis(3,5-ditert-butyl-4-hydroxybenzy I )benzene and tris(2,6-di-terthexylhydroxyphenyl)benzene; 3-( 3 ' ,5'-d i - tert-bu ty I-4'hydroxypheny!) propionic acid polyesters such as tetrakisCmethylene-3-(3',5'-ditert-butyl-4'-hydroxyphenyl)propionate3methane; polycyclic monophenols which are di-tert- and disec-alkylated in the ortho positions relative to the hydroxyl group, such as 1,3-di-tert-butyl-2-hydroxyanthracene, - 10 1,3-di-tert-hexyl-2-hydroxyphenanthrene, 2,8-di-tert-butylnydroxynaphthalene, 1,3-di-tert-hexyl-2-hydroxynaphthalene and 1,3-diisoamyl-2-hydroxynaphthaIene .

Very good results were obtained with di-tert5 alkylated monocyclic monophenols, in particular with 2,6di-tert-butyl-4-methylphenol and with 3-(3',5'-d i-tertbutyl -4'-hydroxyphenyl)propionic acid monoesters, in particular with n-octadecyl 3-(3',5'-di-1ert-butyI-4,-hydrοxyphenyI)propion ate, the use of the latter giving an excellent stereospecificity to the catalytic solids prepared using it.

The general conditions under which compound (a) is brought into contact with compound (b) are not critical insofar as they induce a chemical reaction between these compounds. The reaction is generally carried out in the liquid phase, for example by mixing compound (b) and compound (a) in the absence of a liquid diluent, compound (a) often being liquid under normal temperature and pressure conditions. It is also possible to work in the presence of an inert hydrocarbon diluent as defined above.

The molar ratio in which compound (a) and compound (b) are brought into contact with each other may vary to a large extent. In general, 50 to 0.1 moles of compound (a) are employed per mole of compound (b); the quantity of compound (a) employed is preferably between 15 and 0.5 moles per mole of compound (b); very good results have been recorded for molar ratios of compound (a) to compound (b) of between approximately 3 and 1.

Compounds (a) and (b) may be brought into contact with each other at temperatures generally between approximately 0 and 90°C, preferably at a temperature in the vicinity of ambient temperature (25°C) and the mixture thereof is maintained for a period sufficient for them to chemically react with each other, which is generally between 5 minutes and 5 hours. This reaction is most often accompanied by a gas evolution which enables its progress to be monitored.

The exact chemical structure of the product of - 11 reaction between compounds (a) and (b) is not known with certainty. However, it is almost certain that this product corresponds at least partially to the empirical formula: Rp Al (OR 1)q X3-(p + q) in which: R, which has the meaning given above, represents the same hydrocarbon radical(s) as that (those) contained in the organoaIuminium compound (a); OR' represents the aryloxy group derived from compound ( b); X is a halogen; p is a number such that 0 < p < 3, preferably such that 0.1 < p < 2.5; q is a number such that 0 < q < 2, preferably such that 0.5 < q < 1.5; and the sum (p+q) being such that 0 < (p+q) < 3.

According to the invention, the organoaIuminium preactivator obtained as described above is brought into contact with the precursor.

The operating conditions under which the preactivator is brought into contact with the precursor are not critical insofar as they bring about at least a partial binding of the preactivator to the said precursor.

Providing this condition is met, this contacting may be carried out by any known process. This contacting may be carried out, for example, by grinding the precursor which is impregnated with a liquid phase containing the preactivator.

The preactivator is most often employed in the form of a solution of the following in the inert hydrocarbon diluent optionally employed for the preparation thereof : (1) the reaction product of compound (a) with compound (b) possibly accompanied by (2) the unreacted excess of compound (a) or of compound (b) employed.

In this case, it is preferable to introduce the preactivator solution containing ingredient (1) and possibly ingredient (2) into a suspension of the precursor in this same hydrocarbon diluent. This suspension is then generally maintained at a temperature between 0°C and the normal boiling point of the inert hydrocarbon diluent in which the preactivator was dissolved, preferably between approximately 20 and 40°C, for a period generally between approximately 5 and approximately 120 minutes, preferably between 15 and 90 minutes. The respective quantities of precursor and preactivator employed are such that the molar ratio between the total initial quantity of compound (a) employed and the quantity of TiCl3 present i.n the ,-3 precursor is ,-2 generally between 10 and 10, preferably between 10_£- and 1. Very good results are obtained when the molar ratio defined above is between 0.05 an-d 0.5.

At the end of this preactivation stage, the catalytic solid thus preactivated is separated from the preactivation medium and washed in order to remove the residues of unbound preactivator, preferably using an inert hydrocarbon diluent of the same type as those optionally employed for the preparation of the precursor and the preactivator solution.

The preactivated, separated and washed catalytic solid may then be dried, if required. For example, it may be dried until the residual liquid hydrocarbon diluent content thereof is less than 1% by weight, preferably less than 0.5% by weight relative to the weight of titanium trichloride it contains, according to the operating conditions described in the patent BE-A-84/6,911 (SOLVAY & Cie).

The preactivated catalytic solid thus obtained always contains a certain amount of preactivator which is bound to the solid and which cannot be dissociated from the latter by purely physical separation methods. The quantity of preactivator in this form is generally between 5 and 500 g per kg of TiCl3 present in the solid and preferably between 50 and 300 g/kg. Consequently, the preactivated catalytic solid according to the invention contains less TiCI3 per unit weight than the solid used as precursor for its preparation. Although the preactivated catalytic solid generally contains at - 13 Least 50% by weight of TiCl3 relative to the total weight, it rarely contains more than approximateIy 80% of the latter.

The external morphology of the preactivated catalytic solid particles according to the invention is no different from that of the particles of precursor used in their preparation. Thus, when they are prepared starting with spherical particles consisting of an agglomerate of porous spherical microparticles, they have substantially the same structure, the same dimensions and the same shapes as the particles used at the start. However, the preactivated catalytic solid particles, are less porous, i.e. they are no longer characterized by the high specific surface area associated with the high pore volume which characterizes the particles of the precursor.

After being washed and optionally dried, the preactivated catalytic solids according to the invention may immediately be brought into contact again with an inert hydrocarbon diluent such as those defined above, which can also be used as diluents in suspension polymerization. The preactivated catalytic solids according to the invention may also be subjected to a prepolymerization treatment as described above in connection with the precursor. They may be stored in hexane or in the dry form, preferably in the cold state, for long periods of time without losing their qualities.

For polymerization, the preactivated catalytic solid according to the invention is employed together with an activator chosen from amongst organometallic compounds of metals of groups Ia, Ila, lib and Illb of the Periodic Table (version published in Kirk-Othmer Encyclopedia of Chemical Technology, 2nd completely revised edition, volume 8, 1965, page 94) and preferably from amongst the compounds of formula: Al R'm Y3_m in which R''' is a hydrocarbon radical containing from to 18 carbon atoms and preferably from 1 to 12 carbon atoms, chosen from amongst alkyl, aryl, arylalkyl, alkylaryl and cycloalkyl radicals; best results are obtained when R''' is chosen from amongst alkyl radicals contain- i ng from 2 to 6 c a rbon atoms; Y is a halogen chosen from amongst fluorine. chlorine, bromine and iodine; bes t results are obtained when Y is chlorine; m is any number such that 0 < m < 3 and preferably such that 1.5 < m < 2.5; best resul ts are obta i ned when m i s equal to 2 .

Diethylaluminium chloride (DEAC) ensures maximum activity and maximum stereospecificity of the catalytic system.

The catalytic systems thus defined can be applied to the polymerization of olefins with terminal unsaturation, containing from 2 to 18 and preferably from 2 to 6 carbon atoms in the molecule, such as. ethylene, propylene, 1-butene, 1-pentene, methyl-1-butene, 1-hexene, 3and 4-methyl-1-pentenes and viny I cyc I ohexene. They are particularly useful in the stereospecific polymerization of propylene, 1-butene and 4-methyI- 1-pentene into highly isotactic, crystalline polymers. They can also be applied to the copolymerization of these alpha-olefins between one another as well as with diolefins containing from 4 to 18 carbon atoms. The diolefins are preferably unconjugated aliphatic diolefins such as 1,4-hexadiene, unconjugated monocyclic diolefins such as 4-vinyIcycIohexene, alicyclic diolefins having an endocyclic bridge, such as dicyclopentadiene, methylene- and ethylenenorbornene and conjugated aliphatic diolefins such as butadiene or isoprene.

They can also be applied to the manufacture of the so-called block copolymers which are formed starting with alpha-olefins and diolefins. These block copolymers consist of successions of chain segments of variable lengths; each segment consists of a homopolymer of an alpha-olefin or of a random copolymer containing an alphaolefin and at le-ast one comonomer chosen from amongst alpha-olefins and diolefins. The alpha-olefins and the diolefins are chosen from amongst those mentioned above.

The preactivated catalytic solids according to - 15 the invention are particut arty well suited to the manufacture of homopolymers of propylene and copolymers containing in total at least 50% by weight of propylene and preferably 75% by weight of propylene.

The polymerization may be carried out according to any known process: in solution or in suspension in a solvent or in an inert hydrocarbon diluent, such as those defined in connection with the preparation of the catalytic solid and which is preferably chosen from amongst butane, pentane, hexane, heptane, cyclohexane, methyIcycI ohexane or mixtures thereof. The polymerization may also be carried out in the monomer or with one of the monomers maintained in the liquid state or in the gaseous phase. The use.of the preactivated catalytic solids according to the invention is very advantageous in polymerization in the gaseous phase. In fact, insofar as the appearance of amorphous and sticky by-products is particularly harmful in this type of polymerization, the technology of which does not enable them to be removed, the use of highly stereospecific catalytic systems is particularly advantageous.

The polymerization temperature is chosen generally between 20 and 200°C and preferably between 50 and 90°C, the best results being obtained between 65 and 85°C. The pressure is chosen generally between atmospheric pressure and 50 atmospheres and preferably between 10 and 30 atmospheres. This pressure depends, of course, on the temperature employed.

The polymerization may be carried out in continuous or discontinuous fashion.

The preparation of the so-called block copolymers may also be carried out according to known processes.

The use of a two-stage process which consists in polymerizing an alpha-olefin, generally propylene, according to the method described above for homopolymerization, is preferred. The other alpha-olefin and/or diolefin, generally ethylene, is then polymerized in the presence of the homopolymer chain which is still active. This second polymerization may be carried out after the complete or the partial removal of the monomer which has not reacted during the first stage.

The organometallic compound and the preactivated catalytic solid may be added separately to the polymeriza tion medium. They may also be brought into contact with each other, at a temperature of between -40 and 80°C, for a period which depends on this temperature and which may range from an hour to several days, before introducing them into the polymerization reactor.

The total quantity of organometallic compound employed is not critical; it is generally greater than 0.1 mmol per litre of diluent, of liquid monomer, or of reactor volume, preferably greater than 0.5 mmol per litre.

The quantity of preactivated catalytic solid employed is determined according to the· TiCl3 content thereof. It is generally chosen so that the concentration of the polymerization medium is greater than 0.01 mmol of TiClj per litre of diluent, of liquid monomer or of reactor volume and preferably greater than 0.05 mmoI per litre.

The ratio between the quantity of organometallic compound and that of the preactivated catalytic solid is not critical either. It is generally chosen so that the molar ratio organometallic compound:TiC 13 present in the solid is between 0.5:1 and 20:1 and preferably between 1:1 and 15:1. Best results are obtained when the molar ratio is between 2:1 and 12:1.

The molecular weight of the polymers manufac30 tured according to the process of the invention may be adjusted by adding to the polymerization medium one or more molecular weight-adjusting agents such as hydrogen, diethyl zinc, alcohols, ethers and alkyl halides.

The stereospecificity of the preactivated cata35 lytic solids according to the invention is higher than that of the catalytic complexes described in patent BE-A78/0,758, when they are prepared from the latter. Additionally, this stereospecificity remains unchanged over very long periods of time, even when the preactivated - 17 catalytic solids are stored at a relatively high temperature. Therefore, when they are employed, there is no longer any need to add to the polymerization medium a third constituent which is conventionally known as improving this stereospecificity, such as, for example, an ether or an ester. It is self-evident that such addition of a third constituent to the polymerization medium containing a preactivated catalytic solid accordingto the invention does not constitute a departure from the scope of the latter; however, such an addition leads, at the very most, to only a marginal improvement in stereospecificity.

During the homopolymerization of propylene in the presence of the preactivated catalytic s ο I i ds.ac c,o r ding to the invention, the proportion of amorphous ..po l.ypropylene, determined by measuring the weight of polypropylene soluble in boiling heptane relative to the solid polypropylene manufactured during the polymerization, is almost always less than 3%. This property is conferred to the solid polypropylene manufactured, even when the preactivated catalytic solid has been stored at high temperature (45°C) for several weeks.

The following examples serve to illustrate the invention.

The symbols used in these examples have the following meanings: 1.1 = isotacticity index of the polymer, determined by the fraction of the latter, expressed as a percentage relative to the total quantity of solid polymer collected, which is insoluble in boiling heptane.

G = torsional modulus of rigidity of the polymer, determined at 100°C and at a torsion angle of 60° of arc, the temperature of the mould being fixed at 70°C and the period of conditioning at 5 minutes (standards BS 2782 - part I - method 150A; ISO 458/1, method B; DIN 53,447 and ASTM D 1043). This modulus is expressed in daN/cm^.

MFI = melt flow index determined under a load of 2.16 kg at 230°C and expressed in g/10 min (ASTM standard D 1238).

AD = ’ apparent density of the insoluble polymer fraction, determined by packing and expressed in g/l. a = catalytic activity, usually expressed in grams of insoluble polymer in the polymerization medium, obtained per hour and per gram of TiCl3 contained in the preactivated catalytic solid.

Example 1 A - Preparation of the precursor (complexed titanium trichloride-based solid) ml of dry hexane and 60 ml of pure TiCl4 are introduced, under a nitrogen atmosphere, into an 800-ml reactor equipped with a twin-blade stirrer, rotating at 400 rpm. This hexane-TiCl4 solution is cooled to 0 ( + 1)°C Within 4 h, a solution consisting of 190 ml of hexane and 70 ml of diethyI a Iuminium chloride (DEAC) is added thereto, while maintaining a temperature of 0 ( + 1)°C in the reactor .

After the addition of the DEAC-hexane solution, the reaction medium consisting of a suspension of fine particles is maintained stirred at 1 ( + 1)°C for 15 min and then heated, in the course of 1 h, to 25°C and maintained at this temperature for 1 h and then heated, in the course of 1 h, to approximately 65°C. The medium is maintained stirred for 2 h at 65°C.

The liquid phase is then separated from the solid and the solid product washed with 7 x 200 ml of dry hexane, the solid being resuspended during each washing.

The reduced solid thus obtained is suspended in 456 ml of diluent (hexane) and 86 ml of diisoamyl ether dded thereto. The suspension is stirred for The solid thus treated is then separated from the liquid phase.

The latter solid is resuspended in 210 ml of hexane and 52 ml of T iCL4 are added thereto; the suspension is maintained stirred (150 rpm) at 70°C for 2 h. The liquid phase is then removed by filtration and the com- 456 m I of (DIAE) are 1 h at 50° plexed titanium trichloride-based solid is washed with χ 270 ml of hexane.

B - Preactivation g of the complexed titanium trichloride-based solid (containing approximately 820 g of TiClj/kg) suspen5 ded in 280 ml of hexane are introduced into an 800-ml reactor equipped with a blade-stirrer rotating at 150 rpm. * 120 ml of a solution, in hexane, of a preactivator (hereinafter called preactivator A), prepared beforehand by mixing 80 g of DEAC (compound (a)) and 176.2 g of n-:octadecyl 3-(3 ' ,5 '-di-tert-butyl-4 1-hydroxyphenyl)propionate, mai . keted under the name Irganox 1076 by CIBA-GEIGY (compound (b)) per litre of hexane, are introduced slowly (30 minutes) into this reactor. Thus, the molar ratio between compounds (a) and (b) employed in preparing the preactiva15 tor is 2 and the molar ratio between the preactivator A and the complexed titanium trichloride-based solid (expressed as moles of compound (a) initially employed per mole of T1CI3 present in the solid) is 0.2.

The preactivator solution is introduced into the reactor only after 15 minutes from the time when the gas evolution observed during mixing compound (a) and compound (b) ceases .

The suspension to which the preactivator A has thus been added is maintained for 1 hour at 30°C, with stirring.

After decantation, the resulting preactivated catalytic solid is washed with 5 x 100 ml of dry hexane, the solid being resuspended during each washing, and then dried by sweeping with nitrogen in a fluidized bed for 2 hours at 70°C.

The preactivated catalytic solid thus obtained contains 641 g of Tid.3, 12 g of aluminium, 31 g of DIAE and a quantity, which is estimated to be approximately 250 g, of the preactivator A, per kg.

C - Polymerization of propylene in suspension in the « liquid monomer, in the presence of the preactivated catalytic solid The following are introduced, while being swept with nitrogen, into a 5-1i t re autoclave which has previously - 20 been dried and maintained under a dry nitrogen atmosphere: 400 mg of DEAC (in the form of a 200 g/l solution in hexane) marketed by SCHERING (the Cl : Al atom ratio is adjusted to 1.02 by adding ethyI a Iuminium dichloride) ; 100 mg of preactivated catalytic solid (the molar ratio between the DEAC and the TiCl3 present in the solid is thus approximately 8); hydrogen at a partial pressure of 1 bar; and I of liquid propylene.

The reactor is maintained at 65°C with stirring for 3 hours. The excess propylene is then degassed and the polypropylene (PP) formed, which amounts to 643 g of dry polypropylene, is collected.

The activity a of the preactivated catalytic solid is 3340; the productivity amounts to 6430 g of polypropylene/g of preactivated catalytic solid.

This polypropylene has the following characteristics : I. I = 98.1% G = 678 daN/cm2 MFI = 3.16 g/10 min AD = 510 g/l.

Examples 1R to 5R These examples are given by way of comparison. Example 1R A complexed titanium trichloride-based solid is prepared as described in Example 1, part A, without preactivating it as mentioned in part B of this example.

This solid, dried as mentioned in Example 1, contains 811 g of TiCl3, 2.8 g of aluminium and 61 g of DIAE.

A polymerization trial is carried out in the presence of the solid thus obtained, which is not preactivated, under conditions strictly comparable to those defined in Example 1, part C. 785 g of dry PP are collected at the end of this trial.

The activity a is therefore 3230 and the - 21 productivity amounts to 7850 g of PP/g of solid. this polypropylene has the following characterist i c s I . I G MFI AD = 94.9% = 572 daN/cm^ = 7.3 g/10 min = 490 g/l.

The significant differences in the fractions insoluble in boiling heptane and in the modules G respectively of the polymers obtained under comparable conditions according to Examples 1 and 1R are proof of the higher stereospecificity of the catalytic system which contains the preactivated catalytic solid of Example 1. Example 2R A complexed titanium trichloride-based solid prepared as described in Example 1, part A, is preactivated with a solution which contains only compound (b). A partial dissolution of the solid is observed, which solid is, moreover, in the form of very fine particles. The polymerization trial, carried out as mentioned in Example 1, part C, is repeated with a quantity of catalyst such that it contains approximately 70 mg of T7CI3. 535 g of PP are obtained, which corresponds to an activity a of only 2550. This PP is in the form of fine particles and its AD is only 100 g/l, which excludes the possibility of using it.

Example 3R Example 1, parts A and B, are repeated, the only exception being that the suspension of the complexed titanium trichloride-based solid is treated in sequence, first with a solution of compound (a) in hexane and then, 15 minutes after the addition of the solution of compound (a) is complete, with a solution of compound (b) in hexane. The values for the molar ratios between compounds (a) and (b), which are added separately, and between compound (a) and the quantity of TiClj present in the solid, are 2:1 and 0.2:1 respectively. The catalytic solid collected contains 757 g/kg of TiClj.

The polymerization trial, carried out as - 22 mentioned in Example 1, part C, only enables a polypropylene in the form of blocks, which cannot be used, to be collected with an activity a of 3090.

Example 4R Example 3R is repeated, but reversing the sequence of introduction of the solutions of c o m p:o u n d s (a) and (b). The same phenomenon as in Example 2R is observed, i.e. a partial dissolution of the solid.

The polymerization trial, carried out as described in Example 1, part C, only enables a polypropylene in the form of very fine particles, with an AD of only 200 g/l to be collected with an activity a of 3450, which excludes the possibility of using it.

Example 5R The complexed titanium trichloride-based solid prepared as described in Example 1R (i.e. not preactivated) is employed in a polymerization trial carried out as described in Example 1, part C, with the exception that in addition to DEAC, the solid, hydrogen and propylene, the product Irganox 1076 is introduced into, the polymerization medium in a quantity such that thei.molar ratio between this product and the T i C13 present in the solid is approximately 0.2.

A PP characterized by the following properties is obta i ned , with an I. I = 95. 2% G = 575 daN/c m^ MF I = 5.2 g/10 min AD 505 g/l. Ex amp I e 2 A preactivated catalytic solid is prepared as mentioned in Example 1, parts A and B, except that the product Irganox 1076 is replaced with 2,6-di-1ert-buty I4-methyI pheno I , marketed under the name Ionol CP by SHELL The preactivated catalytic solid thus obtained contains 632 g of TiCl3, 14 g of aluminium, 30 g of DIAE and a quantity of preactivat0r, which is estimated to be approximately 170 g, per kg. It is employed in carrying out a polymerization trial under the conditions of Example 1 , part C.

This trial enables a polypropylene with the following characteristics to be collected, with an activity a of 3230: I.I = 95.9% G = 653 daN/cm2 MFI = 9 g/10 min AD = 500 g/l.

Example 3 A preactivated catalytic solid prepared as mentioned in Example 1, parts A and B, is used in a trial for the polymerization of propylene in suspension in hexane under the operation conditions described below. litre of dry and purified hexane is introduced into a 5-litre stainless steel autoclave which has been purged several times with nitrogen. 400- mg of DEAC (in the form of a 200 g/l solution in hexane) and a quantity of catalytic solid equivalent to approximately 51 mg of TiCl3 are then introduced in sequence. The molar ratio DEAC:TiCl3 is therefore approximately 10.

The autoclave is heated to 65°C and the pressure is returned to atmospheric pressure by a slow degassing. An absolute hydrogen pressure of 0.3 bar is then set up therein and propylene is then introduced into the autoclave until a total pressure, at the temperature concerned, of 11.9 bars is obtained. This pressure is maintained constant during the polymerization by introducing gaseous propylene.

After 3 h, the polymerization is stopped by degassing the propylene.

The contents of the autoclave are poured onto a Buchner filter, rinsed with 3 x 0.5 I of hexane and dried under reduced pressure at 60°C. 251 g of hexane-insoIuble PP are collected. 0.75 g of soluble polymer, which corresponds to 0.3%, is found in the hexane used in the polymerization and in the washing. The activity a is 1643. The productivity amounts to’3157 g of PP/g of preactivated catalytic solid.

The hexane-insoluble PP has the following propert ies: I. I = 98. 2% G = 654 daN/ cij]2 MFI = 2.9 g/10 min AD = 503 g/l. Example 6R This example is given by way of comparison.

A polymerization trial is carried out under the same conditions as in Example 3 , in the presence of catalytic solid prepared as mentioned in Example 3, but leaving out the preactivation stage, and containing 735 g/kg of TiClj. A PP, 1% of which is soluble in the hexane used in the polymerization and in the washing, and the insoluble part of which has the following characteristics, is obtained, with an activity a of 1719: 1.1 = 95. 7% G 591 daN/cm^ MFI = 9.5 g/10 min AD = 479 g/l. Example 4 A preactivated catalytic solid is prepared according to the general conditions described in Example 1, parts A and B. However, after treatment of the suspension of the reduced solid with stirring for 2 hours at 65°C, this suspension is cooled to approximately 55°C; propylene is then introduced into the gaseous atmosphere in the reactor, at a pressure of 2 bars. This introduction is continued for a period sufficient (approximately 45 minutes) to obtain 100 g of polymerized propylene per kg of solid. The suspension of the solid thus prepolymerized is then cooled to 40°C and the preparation is then continued as mentioned in Example 1, part A.

The preactivated catalytic solid finally obtained contains 611 g of TiCl3, 9 g of aluminium, 14 g of DIAE and a quantity, which is estimated to be approximately 143 g, of preactivator A per kg.

This preactivated catalytic solid is employed in a propylene polymerization trial comprising a first stage which is carried out in the liquid monomer and a second stage which is carried out in the gaseous phase under the operating conditions detailed below.

The following are introduced, under a stream of nitrogen, into the 5—litre autoclave used according to Examples 1 and 3: 800 mg of DEAC a quantity of catalytic solid equivalent to 100 mg of T i C13.

The molar ratio DEAC:T iC13 is therefore approximately 10:1.

An absolute hydrogen pressure of 0.2 bar is set up in the autoclave. 2 I of liquid propylene are then introduced, with stirring, and the autoclave is heated to 60°C. Polymerization is carried out for 30 min at this temperature. The autoclave is then degassed to a pressure of 15 bars, while heating it to 70°C at the same time. An absolute hydrogen pressure of 1 bar is then set up therein and propylene is then introduced into the autoclave until a total pressure, at the temperature concerned, of 28 bars is obtained. After 3 hours, the polymerization is stopped by degassing the propylene, and the PP formed, which amounts to 1150 g of dry PP, is collected.

The activity a of the preactivated catalytic solid is therefore 3286 and the productivity amounts to 7027 g of PP/g of preactivated catalytic solid. This PP has the following characteristics: I . I = 97.9% G = 698 daN/cm2 MF I = 3 g/10 min AD = 520 g/l. Example 7R This example is given by way of comparison.

A preactivated catalytic solid is prepared according to the procedure in Example 4, but leaving out the preactivation stage. This solid contains 718 g of TiCl3, 3.8 g of aluminium and 84 g of DIAE per kg. When used in a polymerization trial carried out according to the conditions described in Example 4, it enables a PP, characterized by the following properties, to be obtained, with an activity a of 3168: 1.1 = 96.4% G 620 daN/cm2 MFI = 3 g/10 min AD = 516 g/l. Examples 5 to 7 Preactivated catalytic solids are prepared according to the conditions mentioned in Example 4, except that the molar ratio between compounds (a) and (b) employed in the preparation of the preactivator A (see Example 1, part B) (Examples 5 and 6) and the molar ratio between the preactivator A and the complexed titanium tri chloride-based solid (expressed as mole of compound (a) initially employed per mole of TiClj present in the solid) (see Example 1, idem) (Example 7) are modified.

These preactivated catalytic solids are employed in trials for the polymerization of propylene in suspension in hexane according to the general conditions mentioned in Example 3.

The operating conditions specific to the preparations of the catalytic solids and the results of the poly merization trials are collated in Table 1 which follows. - 27 Table I Example 5 6 7 Preparation of the preactivated catalytic solids Compound (a) 50 10 10 — — — — — — — — — — — — [Π 0 I 6 1 111 0 I € J Compound (b) Compound (a) 1 1 0.2 — — — — — — — — —— — < Π1 0 l β Z ul 0 l β / T i C 13 contained in the solid TiCl3 content of the preactivated catalytic solid (g/kg) 724 672 709 Results of polymerization Activity a (g PP/g TiCl3 x h) 2160 2160 2130 PP soluble in the hexane used in the polymerization (as % of total PP) 1.1 0.8 1 . 1 I.I (X) 97.3 98.2 97.4 G (daN/cm2) 678 688 689 MFI (g/10 min) 7.1 5.0 7.7 AD (g/l)502 502 504 Example 8 A preactivated catalytic solid is prepared according to the procedure in Example 4 and it is used in a polymerization trial carried out according to the conditions described in part C of Example 1, except that the reactor is maintained at 75°C with stirring for 2 hours .

Under these conditions, this preactivated catalytic solid enables a PP characterized by the following properties to be obtained, with an activity a of 5010: I. I = 98.1% G = 688 daN/cm2 MFI = 5.9 g/10 min AD = 510 g/l.

Examples 9 and 10 Preactivated catalytic solids are prepared according to the conditions mentioned in Example 1, parts A and B, except that t r i ethy I a I um i n i um (TEAL) (Example 9-) and ethylaluminium dichloride (EADC) (Example 10) are ent20 ployed as compounds (a) respectively.

These preactivated catalytic solids are used in trials for the polymerization of propylene in suspension in the liquid monomer, under the general conditions mentioned in Example 1, part C.

The characteristics of the preactivated catalytic solids employed and the results of these polymerization trials are collated in Table II which follows.

Table II 1 ί Example 9 10 Nature of compound (a) employed in the preparation of the preactivated catalytic solid TEAL EADC TiClj content of the preactivated catalytic solid (g/kg) 648 713 Activity a (g PP/g TiCl3 x h) 3136 2875 Propert ies of the PP I.I (X) 98.0 97.7 G (daN/cm2) 645 667 MFI (g/10 min) 3.4 3.7 AD (g/l) 504 490 CLAIMS • 5 1. Complexed titanium trichloride-based catalytic solid which can be

Claims (18)

CLAIMS • 5

1. Complexed titanium trichloride-based catalytic solid which can be used for the stereospecific polymerization of alpha-olefins, which has been preactivated by bringing it into contact with an organoa1uminium preactivator and separated from its preactivation medium, characterized 10 in that the said preactivator comprises the product of reaction between a compound (a) chosen from amongst organoaluminium compounds and a compound (b) chosen from amongst hydroxyaromatic compounds, the hydroxyl group of which is sterically hindered. 2. Solid according to claim 1, characterized in that the compound (a) is chosen from amongst compounds of formula: 15 A1 R n X 7 „ n 3-n in which: R represents hydrocarbon radicals, which may be identical or different, containing from 1 to 18 carbon atoms, 20 X is a halogen, and n is a number such that 0 < n 3. 25 3. Solid according to claims 1 and 2, characterized in that the compound (a) is chosen from amongst trialkylaluminiums and dialkylaluminium halides. 30 • 4.. Solid according to claim 1, characterized in that the compound (b) is chosen from amongst mono- or polycyclic hydroxyarylenes containing a secondary or tertiary alkyl radical in the two ortho positions relative to the hydroxyl group. 5. Solid according to claims 1 and 4, characterized in that the compound (b) is chosen from amongst di-tert-alkylated monocyclic monophenols and 3-(3 1 , 5'-di-tert-butyl-4'-hydroxyphenyl)propionic acid monoesters. ® 35 6. Solid according to claims 1 to 5, characterized in that the preactivator is prepared by bringing compound (a) and compound (b) into contact with each other in a molar ratio of between 50 and 0.1 moles of compound (a) per mole of compound (b). 7. Solid according to claim 6, characterized in that the preactivator is prepared by bringing into contact with each other a compound (a) chosen from amongst dialkylaluminium chlorides and a compound (b) chosen from amongst 3-(3 1 ,5'-di-tert-butyl-4'-hydroxyphenyl)propionic acid monoesters. 8. Solid according to claims 1 to 6, characterized in that the product of reaction between compound (a) and compound (b) corresponds to the empirical formula: R p AKOR-) q X 3 -(p+q) in which: R represents the same hydrocarbon radical(s) as that (those) contained in compound (a); OR' represents the aryloxy group derived from compound (b), X is the halogen optionally contained in compound (a); p is a number such that 0 < p < 3; q is a number such that 0 < q < 2; and the sum (p+q) is such that 0 < (p+q) < 3. 9. Solid according to claims 1 to 8, characterized in that the contacting with the preactivator is carried out by introducing the preactivator into a suspension of the solid to be preactivated in an inert hydrocarbon diluent. 10. Solid according to claims 1 to 9, characterized in that the preactivator is brought into contact with the solid to be preactivated, in a molar ratio between the total initial quantity of compound (a) employed and the quantity of TiCl 7 contained in the solid of between -2 ύ 10 and 1 mole/mole. 11. Solid according to claims 1 to 10, characterized in that it has been preactivated by bringing the preactivator into contact with a solid precursor corresponding to the formula: TiCl 3 .(AlRCl 2 ) x .C y in which R is an alkyl radical containing from 2 to 6 carbon atoms, C is a complexing agent chosen from amongst aliphatic ethers, the aliphatic radicals of which contain from 2 to 8 carbons atoms, x is any number less than 0.20 and y is any number greater than 0.009. 12. Solid according to claim 11, characterized in that the solid precursor is in the form of spherical particles of diameter between 5 and 100 microns, which consist of an agglomerate of microoarticles which are also spherical and which have a diameter of between 0.05 and 1 micron and the porosity of which is such that the

2. 5 specific surface area of the solid precursor is between 100 and 250 m 2 /g and that the total internal porosity is between 0.15 and 0.35 c m \ g. 13. Process for the preparation of a complexed titanium trichloride-based catalytic solid which can be used

3. 10 for the stereospecific polymerization of alpha-olefins, preactivated by bringing a complexed titanium trichloridebased solid precursor into contact with an organoaluminium preactivator, and separation of the preactivated solid from its preactivation medium, characterized in that the said preactivator comprises 15 the product of reaction between a compound (a) chosen from amongst organoaluminium compounds and a compound (b) chosen from amongst hydroxyaromatic compounds, the hydroxyl group of which is sterically hindered.

4. 14. Process according to claim 13, characterized in that the compound (a) is chosen from amongst compounds of formula: Al R n X 3 _ n in which: R represents hydrocarbon radicals, which may be identical or different, containing from 1 to 18 carbon 25 atoms. X is a halogen, and n isanumbersuchthat0 15. Process according to Claim 13, characterized in that the compound (b) is chosen from amongst mono- or 30 polycyclic hydroxyarylenes containing a secondary or tertiary alkyl radical in the two ortho positions relative to the hydroxyl group.

5. 16. Process according to Claims 13 to 15, characterized in that the preactivator is prepared by bringing 35 compound (a) and compound (b) into contact with each other in a molar ratio of between 50 and 0.1 moles of compound (a) per mole of compound (b).

6. 17. Process according to Claims 13 to 16, characterized in that the preactivator is brought into contact with the - 33 solid precursor in a molar ratio betueen the total initial quantity of compound (a) employed and the quantity of TiCl 3 contained in the precursor of between 10 -2 and 1 mo Ie/ mo Ie.

7. 18. Process according to Claims 13 to 17, characterized in that the contacting of the solid precursor with the preactivator is carried out by introducing the preactivator into a suspension of the precursor in an inert hydrocarbon diluent.

8. 19. Process according to Claims 13 to 18, characterized in that the solid precursor and the preactivator are maintained in contact with each other at a temperature between 20 and 40°C for a period between 15 and 90 minutes.

9. 20. Process according to Claims 13 to 19, characterized in that the preactivated catalytic solid is washed with an inert hydrocarbon diluent before being used in the polymerization.

10. 21. Process for the polymerization of alpha-olefins in the presence of a catalytic system containing an organometallic compound of metals of groups Ia, Iii a, lib and Illb of the Periodic Table and a complexed titanium trichloride-based catalytic solid characterized in that a catalytic solid according to any of claims 1 to 12 is employed.

11. 22. Process according to Claim 21, applied to the stereospecific polymerization of propylene.

12. 23. Process according to Claim 21, applied to the stereospecific polymerization of propylene in suspension in an inert hydrocarbon diluent.

13. 24. Process according to Claim 21, applied to the stereospecific polymerization of propylene in the monomer in the liquid state.

14. 25. Process according to Claim 21, applied to the -34stereospecific polymerization of propylene in the gaseous phase .

15. 26. A process according to claim 13 substantially as hereinbefore 5 described by way of Example.

16. 27. A complexed titanium trichloride-based catalytic solid whenever prepared by a process as claimed in any of claims 13 to 20 or 26.

17. 28. A process according to claim 21 substantially as hereinbefore described by way of Example.

18. 29. Alpha-olefins whenever prepared by a process as claimed in 15 any of claims 21 to 26 or 28TOMKINS & CO.