GB1574830A - Sabstantially agglomeration-free catalyst component - Google Patents

Description

(54) A SUBSTANTIALLY AGGLOMERATION-FREE CATALYST COMPONENT (71) We, STAUFFER CHEMICAL COMPANY, a corporation organised under the laws of the State of Delaware, United States of America, of Westport, Connecticut 06880, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to a substantially agglomeration-free catalyst component; more particularly, it relates to a substantially agglomeration-free, finely divided titanium trichloride-containing catalyst component which is suitable for use in the polymerization of alpha-olefins.

The present invention provides a catalyst component which comprises: (a) a titanium trichloride material; (b) an electron pair donor compound which is selected from organic oxygencontaining compounds, organic nitrogen-containing compounds, organic phosphorus-containing compounds, organic silicon-containing compounds and sulphur-containing compounds; and (c) an agglomeration control compound which is sodium bromide; (a), (b) and (c) being co-ground.

The present invention further provides a catalyst composition which comprises such a catalyst component and an organoaluminium compound.

The present invention further provides a process for the polymerization of an alpha-olefin which comprises effecting the polymerization in the presence of such a catalyst composition.

It is well known in the production of titanium trichloride catalyst components which are suitable for use in the production of polymers from alpha-olefins to add to the titanium trichloride material an effective amount of an electron pair donor to improve the stereospecificity or the stereospecificity and activity of the ultimate catalyst composition which contains the titanium trichloride/electron donor catalyst component. (see Keii, Kinetics of Ziegler-Natta Polymerization, Kodansha Ltd., Tokyo, 1972, pp. 163-173). Some recent examples of the use of such electron pair donor compounds as auxiliary components during the grinding or ball milling of titanium trichloride catalyst component compositions are described in U.S. Patent Nos. 3,639,375 and 3,701,763. When such electron pair donors and titanium trichloride are ground, it is not uncommon for agglomeration to occur. Such an agglomerated product has no substantial utility as a catalyst component in the polymerization of alpha-olefins.

The deleterious effect of agglomeration has been recognized. One solution that was proposed to control agglomeration was operating, during grinding, below the temperature at which agglomeration occurs, see Belgian Patent No. 800,057.

Another solution described in German Offenlegungsschrift No. 2,342,200, proposed grinding titanium trichloride with a metal hydroxide, sulphate, sulphite, phosphate, phosphite, carbonate, cyanide, thiocyanate, nitrate and/or nitrite.

However, it has been found that the use of these modifying agents alone does not produce satisfactory results when the catalyst is used in a solvent-containing polymerization system. The present invention is directed to another manner in which the problem of agglomeration may be controlled even though the grinding is carried out over a wide range of temperatures, by addition of a certain agglomeration control agent to produce a catalyst component in finely divided form which does not have the tendency to agglomerate; The present invention relies upon the presence during the milling or grinding operation of an effective amount for agglomeration control of a compound which is referred to herein as an "agglomeration control compound." This compound controls the aggregative behaviour of the finely divided particles produced during the grinding operation of the titanium trichloride catalyst component and ensures the formation of a powdery product by retaining the discreteness of the individual particles with substantially no agglomeration.

The term "agglomeration" as used herein is defined as the indiscriminate formation of aggregates or clusters of the finely divided particles due to the grinding of the titanium trichloride and one or more electron pair donor compounds. This undesired phenomenon, if present, will result in a reduction of the catalytic activity of the component.

Very small particles which are polar in nature, such as titanium trichloride, will, upon grinding, often agglomerate to a larger size. It is believed that the tendency to agglomerate is dependent upon both the repulsive electrostatic or coulombic forces between the particles and the mutual van der Waals force of attraction between the particles. Observations suggest that, for a given particle size distribution and environment, the degree of agglomeration may depend upon the combined potential of the mutual interactions between the particles and may be no more than the sum (V) of the repulsive electrostatic potential (Ve) and attractive van der Waals forces potential (via). For particles approximately spherical in shape, the mathematical expression of V6 and V6 is given by formulae (I) and (II), below.

Since the van der Waals forces of attraction operate at very short distances, these attractive forces will generally predominate over the repulsive electrostatic forces when the average particle size in the system decreases. Hence, fine particles that are polar in nature and which are obtained by intense and prolonged milling tend to agglomerate more readily than larger particles. It has been found in accordance with the present invention that the addition of an effective amount of an agglomeration control compound may control agglomeration in a titanium trichloride/electron pair donor mixture that has been ground and may thereby maintain the discreteness of the finely divided particles contained therein.

The agglomeration control compound which is used in accordance with the present invention, when adsorbed on the finely divided particles, may modify the mutual forces of interaction and thereby be effective in keeping the particles apart.

It is believed that the compound operates by increasing the surface potential (zeta potential) of the particles.

The type of titanium trichloride material which is suitable for use in accordance with the present invention is well known in the art. The titanium trichloride material used according to the present invention is a material of the type which may be obtained by: (a) reduction of titanium tetrachloride using a metal, such as aluminium or titanium, the reduced titanium material being either milled or unmilled; (b) reduction of titanium tetrachloride using hydrogen; (c) reduction of titanium tetrachloride using an organometallic compound, such as an aluminium alkyl; or (d) grinding a combination of titanium trichloride and a halide of a Group III metal, such as an aluminium halide.

Examples of suitable titanium trichloride starting materials are well known in the art and are described in a number of references including U.S. Patent Nos.

3,639,375 and 3,701,763 which describe a type of titanium trichloride starting material that may be used in accordance with the present invention. In any case, such a starting material is then ground with an electron pair donor compound and the agglomeration control agent to form the intended catalyst component.

The second material in the present composition is an effective amount of an electron pair donor compound, such as those described in U.S. Patent Nos.

3,639,375 and 3,701,763, to improve the stereospecificity or stereospecificity and activity of the resulting catalyst. Examples of suitable electron pair donor compounds which may be used in accordance with the present invention may be selected from the following: organic oxygen-containing compounds, such as aliphatic ethers, aromatic ethers, aliphatic carboxylic acid esters, cyclic esters of carbonic acid, aromatic carboxylic acid esters, unsaturated carboxylic acid esters, aliphatic alcohols, phenols, aliphatic carboxylic acids, aromatic carboxylic acids, aliphatic carboxylic acid halides, lactones, aromatic carboxylic acid halides, aliphatic ketones and aromatic ketones; organic nitrogen-containing compounds, such as aliphatic amines, aromatic amines, heterocyclic amines, aliphatic nitriles, aliphatic carbamates, aromatic nitriles, aromatic isocyanates and aromatic azo compounds; also mixed oxygen-nitrogen compounds, such as aliphatic and aromatic amides and guanidine and its alkyl substituted derivatives; organic phosphorus-containing compounds, such as aliphatic phosphines, aromatic phosphines, aliphatic phosphites and aromatic phosphites; also mixed phosphorus-nitrogen compounds, such as phosphoric amides; as well as mixed phosphorus-oxygen compounds, such as triphenyl-phosphine oxide; organic silicon-containing compounds including monomer-type compounds, such as tetrahydrocarbylsilanes, organohydrogenosilanes, organohalogenosilanes, organoaminosilanes, organoalkoxysilanes, organoaryloxysilanes, organosilicon isocyanates and organosilanol carboxylic acid esters; and polymer-type compounds, such as polysilalkylenes, organopolysilanes, organopolysiloxanes, CG,CL) dihalo-organopoly siloxanes, organocyclopolysiloxanes and polysilazanes; and sulphur-containing compounds, such as carbon disulphide, aliphatic thioethers and aromatic thioethers.

Generally, the dipole moment of the selected electron pair donor compounds will be in the range of from 0.5 to 6.0 Debye units. Examples of some particularly preferred electron pair donor compounds include: benzophenone, hexamethyl phosphoric triamide, dimethyl formamide, benzonitrile, y-butyrolactone, dimethyl acetamide, N-methyl pyrrolidone, triphenylphosphine oxide, N,N-dimethylpivalamide, toluene diisocyanate, dimethyl thioformamide, ethylene carbonate, trilauryltrithiophosphite, tetramethyl guanidine and methyl carbamate.

Other examples of particular electron pair donor compounds may be found in U.S. Patent Nos. 3,639,375 and 3,701,763.

The third essential component for the present composition is an agglomeration control compound which will prevent agglomeration of the titanium trichloride material and electron pair donor when these components are ground.

It is hypothesized that agglomeration will not occur if the following relationship is satisfied: 13+14 > k wherein: 13 represents the barrier distance afforded in the system by the electron pair donor compound; 14 represents the barrier distance afforded in the system by the agglomeration control compound; and k represents a constant which is obtained by setting the derivative of the mathematical expression for the total potential (V) of the system to zero.

The mathematical expression for the total potential of the system is merely the additive effects of the electrical repulsive potential (Ve) and the attractive potential (Va). Each may be expressed as follows: era252 Ve I R wherein: E represents the dielectric constant of the medium; R represents the distance between two adjacent particles; a represents the average radius of the particles in the medium; and g represents the zeta potential which is the surface potential of the spherical particle.

wherein A represents the Hamaker constant which may be calculated as described by Hamaker, H.C., Physica 4, 1058 (1937) and the references cited therein; and S represents R/a, wherein R and a are as defined above.

In order that the desired catalyst component be produced, it is preferred that the three components be present in certain amounts.

For example, the amount of electron pair donor compound should generally range from 2 to 150/,, preferably from 2.5 to 100/,, by weight of the titanium trichloride material. It is believed that the amount of electron pair donor compound should be present in an amount sufficient to form at least a monomolecular Izyer on the titanium trichloride particles. Thus, the preferred range is dependent upon the molecular weight of the electron pair donor compound and the effective surface area of the titanium trichloride material. Use of too much electron pair donor compound will poison the catalyst component, while use of too little will not result in the desired degree of improvement. It is well within the ability of those skilled in the art to approximate the weight amount of electron pair donor compound by realizing that about 6% by weight, of hexamethyl phosphoric triamide ([(CH3)2N]3PO), (HMPT) is needed for good results. The approximate amount of another selected electron pair donor compound (referred to as "Compound X", below) of similar molecular size as HMPT which should be used will be: 6% ( Compound X= xMol. Wt. Cpd. X Mol. Wt. HMPT Molecules having a smaller cross-section upon adsorption than HMPT will require correspondingly larger amounts to be equally effective in forming the monomolecular layer, while larger molecules will require less.

The amount of agglomeration control compound which is required is quite small. Generally, from 0.1 to 5%, based on the weight of electron pair donor compound, is usually effective in substantially preventing agglomeration. A preferred amount is from 0.6 to 3.0%. The amount of agglomeration control compound that is needed is dependent upon the nature and amount of the electron pair donor compound, as well as the average particle size of the titanium trichloride material. It is known that the average particle size of the titanium trichloride material is influenced by various factors such as milling time, grinding rate and the internal configuration of the grinding apparatus. Particles obtained by using a fast grinding rate tend to agglomerate more readily than larger particles obtained by using a slow grinding rate. For smaller particle size distributions a larger amount of agglomeration control compound is needed. The grinding rate, R, as defined by Berry et al., Proc. Intern. Cong. Surfact Activity, London, pp. 196-202 (1957), is related to the surface area, S, of the milled material and the time, t, of milling by the expression R=S/t.

The grinding operation according to the present invention may be performed by grinding the two aforementioned components with the agglomeration control compound under conventional conditions regarding temperatures and times. The grinding may be carried out in a ball mill or other suitable size reduction apparatus with the absence of diluents, under an inert atmosphere, such as nitrogen or argon, which is substantially free of oxygen, water and other catalyst poisons at a temperature and for a period of time which are suitable to reduce the mixture contained therein to a pulverulent composition which, when combined with organoaluminium compounds, produces a catalyst having good activity and stereospecificity in the polymerization of alpha-olefins.

Generally, when using a rotary ball mill, the grinding should take place for a period of from 30 to 90 hours preferably at a temperature of from 30 to 700 C.

However, in the case of some systems, shorter time periods are effective. Especially good results are obtained when the temperature is maintained at from 45 to 70"C., preferably from 50 to 600 C., and the grinding is carried out for from 40 to 80 hours.

One suitable apparatus for carrying out the grinding is described in U.S. Patent No.

3,688,992. In this particular apparatus, which has a fast grinding rate, shorter milling times, e.g. from 3 to 12 hours, may be used, although longer times may also be employed.

When measuring the temperature, the actual temperature in the interior of the ball mill is measured directly. Temperatures in excess of 70"C. should preferably be avoided since agglomeration of the catalyst component and subsequent deactivation of the final catalyst may result even when the agglomeration control compound used in accordance with the present invention is present.

As mentioned above and as shown in the Examples below, there are many factors involved in determining the quantity of the agglomeration control compound which will function well with a particular electron donor compound.

The data also shows that excess amounts of either or both of the electron donor compound and the agglomeration control compound may function to induce or increase agglomeration, although a certain level of the electron donor compound is required to provide the desired properties in the resultant polymer. Furthermore, milling conditions, such as temperature and amount of balls, have an effect on the phenomenon of agglomeration. These data indicate that an agglomeration control compound should be used in a commerical operation, to guard against agglomeration due to unexpected changes in milling conditions, even where initial laboratory data indicate agglomeration may not be a problem.

The product of the present invention which is produced by grinding the titanium trichloride material, electron donor compound and agglomeration control compound, may then be combined with conventional organoaluminium compounds for use in the polymerization of alpha-olefins using conventional reaction conditions for such a polymerization.

Suitable organoaluminium compounds are those conventionally used, particularly alkyl compounds of aluminium of which the following are examples: trimethyl aluminium, triethyl aluminium, tributyl aluminium, triisobutyl aluminium, methyl aluminium sesquichloride, ethyl aluminium sesquichloride, diethyl aluminium chloride, ethyl aluminium dichloride, dibutyl aluminium chloride and diethyl aluminium sesquibromide. Ethyl aluminium compounds, such as triethyl aluminium and diethyl - aluminium chloride, are preferred as organoaluminium compounds.

The product of the present invention may be used for the production of polymers of alpha-olefins having from 2 to 8 carbon atoms, including propylene homopolymers, copolymers of propylene and ethylene, ethylene homopolymers and polymers of butene-l, 3-methylbutene-l and 4-methylpentene-l. The polymerization of such monomers is generally carried out at temperatures of from 10 to 1500C. using pressures of from 0.5 to 100 atmospheres. The following Example illustrates the present invention: The indicated electron donor compound (ED) and the agglomeration control compound (AC) were mixed in the amounts stated. The mixture was then poured into an 11 cm. inner diameter, 15 cm. long stainless steel mill in a glove box operated under nitrogen with exclusion of air and moisture. The mill, which contained 875 grams of 1 cm. diameter magnetized stainless steel balls, was shaken so that a liquid film was formed around the balls and the inner walls of the mill. To this was then added 50 grams of titanium trichloride which has been obtained by reducing titanium tetrachloride using aluminium metal. It is a co-crystallized product corresponding to the formula 3TiCl3 . AlCI3 ("TiCl3A" from Stauffer Chemical Company, Speciality Chemical Division, Westport, Connecticut, U.S.A.). The mill was subsequently closed so as to be air-tight and was rotated at 110 rpm. for 48 hours at 500 C. The temperature was maintained via a system comprising a thermocouple inserted in an oil well inside the mill, a temperature controller and a temperature recorder. External heat was provided via infra-red radiation. At the end of the 48 hour period, the essentially agglomeration-free, finely divided catalyst component was transferred to a jar in the dry box and was tested, as outlined below, for activity and isotactic index.

The following sets forth the testing procedure that was utilized to determine the activity and isotactic index of the product formed using the type of catalyst components described above.

To a 1 gallon jacketed autoclave equipped with a stirrer that was set at 600 rpm. was charged 1 litre of dry heptane. About 0.3 grams of the above product was suspended in the heptane under a nitrogen atmosphere and 8 ml; of a 20% of weight solution of diethyl aluminium chloride in heptane was added. An additional 1 litre of dry heptane was charged into the autoclave and the autoclave was then closed.

The temperature was raised to 700 C., the autoclave was vented, hydrogen gas (3.2 Ibs/in2) was charged and propylene was fed at a constant pressure into the reactor at 142 lbs./in2. The propylene had been purified by being passed through a column of a copper-based catalyst to remove trace amounts of oxygen and through a molecular sieve resin (Linde (Registered Trade Mark) type 4A) to remove traces of water. The polymerization test was carried out for four hours. At the end of this period, the catalyst was destroyed by addition of a propanoVwater mixture, and the polymer product was filtered, dried at 700C. overnight and was weighed. About 6 grams of the dry polymer was extracted using heptane for three hours in a Soxhlet apparatus. The percentage amount of the non-extracted portion of the polymer was designated "C,i." From an aliquot of the filtrate was determined, via solvent evaporation, the amount of the soluble or atactic polymer that was produced.

The activity was defined as the amount of dry, solid polymer (obtained from the reaction) in grams per gram of TiCl3-containing catalyst preparation.

The isotactic index (II) was defined by the following formula: II=C7i X Wt. solid Polymer Wt. Total Polymer Produced The total polymer produced includes the above-described insoluble (isotactic) and soluble (atactic) polymer portions.

ED Wt. %* AC Wt. %** Activity II Triphenylphosphine oxide 9.0 Sodium bromide 2.3 1697 94.22 N,N-dimethylpivalamide 4.4 Sodium bromide 2.1 1336 94.22 Toluene diisocyanate (80% 2, 4 isomer; 20% 2, 6 isomer) - 6.2 Sodium bromide 1.9 1221 94.0 Dimethyl thioformamide 3.0 Sodium bromide 2.5 1146 93.0' Tetramethylguanidine 4.2 Sodium bromide 1.61 No agglomeration-not tested in polymerization Methyl carbamate 2.7 Sodium bromide 3.32 ,1 ,, * the weight percent is based on the weight of titanium trichloride material.

** the weight percent is based on the weight of electron pair donor compound.

1) the grinding was done in a laboratory ball mill containing 875 g. of l-cm balls.

2) the grinding was done in a laboratory ball mill containing 1750 g. of l-cm balls.

The following demonstrates that a change in milling conditions may induce agglomeration in a particular electron donor. It also compares a TiCI3 composition with a TiCl3 electron donor composition and with a TiCI3 electron donor agglomeration control compound composition. In the runs presented below in the Table, agglomeration was determined by sieving the milled catalyst component compositions; an increase in the percentage of the particles in the composition having a particle size less than 75 microns when an agglomeration control compound was used was considered as evidence of agglomeration control.

In all the runs, benzophenone was used as the electron donor and sodium bromide as the agglomeration control compound. The above general procedure was followed with exception that 1750 grams of 1 cm. diameter balls were used and a milling temperature of 55"C. was employed, since it had been determined that benzophenone did not appear to induce agglomeration at a milling temperature of 50"C. The polymerization and activity and II determination were carried out as described above. Unless otherwise indicated, all the data reported for activity and II represents an average for two polymerization runs.

Wt. of % Benzophenone Wt % NaBr Particle Distribution Activity II (% > 150 (% 75-150 (% < 75 Microns) Microns) Microns) 9 9 8 83 - - - 11 6 83 1075 91.5 - 6 9 85 1266 90.7 - 5 13 82 1166 91.6 - 6 8 86 1114 - 6 - 55 10 35 572 95.2 6 - 46 9 45 959 94.8 6 2.9 31 5 64 890 95.3 6 2.9 15 6 79 1025 92.7 6 3.9 25 4 71 830 95.3 6 3.9 13 5 82 1078' 94.9' 1) Represents the average of three polymerization runs.

For comparison purposes, the following illustrates the preparation of an electron donor-modified titanium trichloride catalyst component in the absence of an agglomeration control compound.

Pure hexamethyl phosphoric triamide (about 3.2 grams) was weighed into a small vial. This compound (hereinafter abbreviated HMPT) was added to the ball mill used above. Next, 50 g of TiCI3A was added to the mill and the mill was closed and rotated at 110 rpm for 48 hours at 500C. At the end of the milling period, the mill was opened under an inert atmosphere. The TiCIJHMPT mixture was lumpy and tended to adhere to the walls of the mill and the balls. The product was not a satisfactory catalyst component for propylene polymerization.

WHAT WE CLAIM IS: 1. A catalyst component which comprises: (a) a titanium trichloride material; (b) an electron pair donor compound which is selected from organic oxygencontaining compounds, organic nitrogen-containing compounds, organic phosphorous-containing compounds, organic silicon-containing compounds and sulphur-containing compounds; and (c) an agglomeration control compound which is sodium bromide; (a), (b) and (c) being co-ground.

2. A catalyst component as claimed in claim 1 comprising a titanium trichloride material obtained by: (a) reduction of titanium tetrachloride using a metal; (b) reduction of titanium tetrachloride using hydrogen; (c) reduction of titanium tetrachloride using an organometallic compound; or (d) grinding titanium trichloride and a halide of a Group III metal.

3. A catalyst component as claimed in claim 1 or claim 2 comprising a titanium trichloride material obtained by reducing titanium tetrachloride using aluminium.

4. A catalyst component as claimed in any of claims I to 3 comprising an electron pair donor compound in an amount of from 2 to 15%, by weight, based on the titanium trichloride material.

5. A catalyst component as claimed in claim 4 comprising an electron pair donor compound in an amount of from 2.5 to 10%, by weight, based on the titanium trichloride material.

6. A catalyst component as claimed in any of claims I to 5 comprising the agglomeration control compound in an amount of from 0. I to 5%, by weight, based on the electron pair donor compound.

7. A catalyst component as claimed in claim 6 comprising the agglomeration control compound in an amount of from 0.6 to 3.0%, by weight, based on the electron pair donor compound.

8. A catalyst component as claimed in any of claims 1 to 7 comprising a titanium trichloride material obtained by reducing titanium tetrachloride using aluminium; an electron pair donor compound which is benzophenone; and an agglomeration control compound which is sodium bromide.

9. A catalyst component as claimed in any of claims 1 to 7 comprising a titanium trichloride material obtained by reducing titanium tetrachloride using aluminium; an electron pair donor compound which is triphenylphosphine oxide; and an agglomeration control compound which is sodium bromide.

10. A catalyst component as claimed in claim 1 substantially as herein described.

11. A catalyst component as claimed in claim 1 substantially as herein described with reference to the Example.

12. A process for the production of a catalyst component as claimed in claim 1 which comprises co-grinding (a), (b) and (c).

13. A process as claimed in claim 12 substantially as herein described.

14. A process as claimed in claim 12 substantially as herein described with reference to the Example.

15. A catalyst component as claimed in claim 1 when produced by a process as claimed in any of claims 12 to 14.

16. A catalyst composition which comprises a catalyst component as claimed in any of claims 1 to 11 or 15 and an organoaluminium compound.

17. A catalyst composition as claimed in claim 16 substantially as herein described.

18. A process for the polymerization of an alpha-olefin which comprises effecting the polymerization in the presence of a catalyst composition as claimed in claim 16 or claim 17.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (20)

**WARNING** start of CLMS field may overlap end of DESC **. For comparison purposes, the following illustrates the preparation of an electron donor-modified titanium trichloride catalyst component in the absence of an agglomeration control compound. Pure hexamethyl phosphoric triamide (about 3.2 grams) was weighed into a small vial. This compound (hereinafter abbreviated HMPT) was added to the ball mill used above. Next, 50 g of TiCI3A was added to the mill and the mill was closed and rotated at 110 rpm for 48 hours at 500C. At the end of the milling period, the mill was opened under an inert atmosphere. The TiCIJHMPT mixture was lumpy and tended to adhere to the walls of the mill and the balls. The product was not a satisfactory catalyst component for propylene polymerization. WHAT WE CLAIM IS:

1. A catalyst component which comprises: (a) a titanium trichloride material; (b) an electron pair donor compound which is selected from organic oxygencontaining compounds, organic nitrogen-containing compounds, organic phosphorous-containing compounds, organic silicon-containing compounds and sulphur-containing compounds; and (c) an agglomeration control compound which is sodium bromide; (a), (b) and (c) being co-ground.

2. A catalyst component as claimed in claim 1 comprising a titanium trichloride material obtained by: (a) reduction of titanium tetrachloride using a metal; (b) reduction of titanium tetrachloride using hydrogen; (c) reduction of titanium tetrachloride using an organometallic compound; or (d) grinding titanium trichloride and a halide of a Group III metal.

3. A catalyst component as claimed in claim 1 or claim 2 comprising a titanium trichloride material obtained by reducing titanium tetrachloride using aluminium.

4. A catalyst component as claimed in any of claims I to 3 comprising an electron pair donor compound in an amount of from 2 to 15%, by weight, based on the titanium trichloride material.

5. A catalyst component as claimed in claim 4 comprising an electron pair donor compound in an amount of from 2.5 to 10%, by weight, based on the titanium trichloride material.

6. A catalyst component as claimed in any of claims I to 5 comprising the agglomeration control compound in an amount of from 0. I to 5%, by weight, based on the electron pair donor compound.

7. A catalyst component as claimed in claim 6 comprising the agglomeration control compound in an amount of from 0.6 to 3.0%, by weight, based on the electron pair donor compound.

8. A catalyst component as claimed in any of claims 1 to 7 comprising a titanium trichloride material obtained by reducing titanium tetrachloride using aluminium; an electron pair donor compound which is benzophenone; and an agglomeration control compound which is sodium bromide.

9. A catalyst component as claimed in any of claims 1 to 7 comprising a titanium trichloride material obtained by reducing titanium tetrachloride using aluminium; an electron pair donor compound which is triphenylphosphine oxide; and an agglomeration control compound which is sodium bromide.

10. A catalyst component as claimed in claim 1 substantially as herein described.

11. A catalyst component as claimed in claim 1 substantially as herein described with reference to the Example.

12. A process for the production of a catalyst component as claimed in claim 1 which comprises co-grinding (a), (b) and (c).

13. A process as claimed in claim 12 substantially as herein described.

14. A process as claimed in claim 12 substantially as herein described with reference to the Example.

15. A catalyst component as claimed in claim 1 when produced by a process as claimed in any of claims 12 to 14.

16. A catalyst composition which comprises a catalyst component as claimed in any of claims 1 to 11 or 15 and an organoaluminium compound.

17. A catalyst composition as claimed in claim 16 substantially as herein described.

18. A process for the polymerization of an alpha-olefin which comprises effecting the polymerization in the presence of a catalyst composition as claimed in claim 16 or claim 17.

19. A process as claimed in claim 18 substantially as herein described.

20. A polymer of an alpha-olefin when obtained by a process as claimed in claim 18 or claim 19.