Catalyst component

A component for an olefin polymerisation catalyst which component is the product of treating a particulate support material with (a) an organomagnesium compound, (b) a transition metal compound of Groups IVA, VA or VIA, e.g. bis-butoxy titanium dichloride, (c) a pacifying agent, e.g. HCl and (d) optionally an aluminium compound, e.g. ethyl aluminium dichloride, an organometallic compound, e.g. zirconium tetrabenzyl, a halogenating agent e.g. silicon tetrachloride, or a Lewis Base compound, e.g. ethyl benzoate.

The present invention relates to a component of an olefin polymerisation 
catalyst, a process for the production thereof, polymerisation catalysts 
including the said component and an olefin polymerisation process using 
such catalysts. 
We have found that so-called Ziegler-Natta catalyst components obtained by 
treating a particulate support material with an organomagnesium compound 
and a compound of a transition metal of Groups IVA to VIA of the Periodic 
Table may be treated with a pacifying agent as hereinafter defined to 
reduce or remove the polymerisation activity of the catalyst component 
and/or to increase the activity of catalysts prepared therefrom. 
Accordingly, one aspect of the present invention provides a catalyst 
component which is the product of treating a particulate support material, 
preferably having a reactive surface (as hereinafter defined) with 
(a) at least one organomagnesium compound, 
(b) at least one transition metal compound of Groups IVA, VA or VIA of the 
Periodic Table, 
(c) at least one pacifying agent, and 
(d) optionally one or more compounds selected from the group consisting of 
(i) an aluminium compound of the general formula: 
EQU R.sub.n AlY.sub.3-n 
wherein 
R, each of which may be the same or different, represents a hydrocarbyl 
group, or substituted hydrocarbyl group, such as alkyl, aryl, cycloalkyl, 
aralkyl, alkenyl or alkadienyl, 
n is 0, 1, 2, 3 or a fraction less than 3, and 
Y is a singly charged ligand such as hydride, fluoride, chloride, bromide, 
iodide or oxyhydrocarbyl, 
(ii) an organometallic compound of the general formula: 
EQU R.sub.m.sup.1 MX.sub.p 
wherein 
M is a metal of Groups IA, IIA, IIB, IIIB, IVA, VA or VIA of the Periodic 
Table, 
R.sup.1 is a hydrocarbyl or a substituted hydrocarbyl group, 
X is a singly charged anionic ligand or a monodentate neutral ligand, 
m is an integer up to the highest valency of the metal M and 
p is 0 or an integer up to 2 less than the valency of the metal M, except 
when M is a metal from Group VIA p is always 0, and 
when M is a metal Groups IVA, VA or VIA m has a value from 2 to the highest 
valency of the metal and p has a value from 0 to a value of 2 less than 
the valency of the metal M, 
(iii) a halogen containing compound and 
(iv) a Lewis Base compound, with the proviso (i) that the particulate 
support material is treated with the at least one organomagnesium 
compound, the at least one transition metal compound of Groups IVA, VA or 
VIA, and the one or more compounds selected from the aforesaid group, 
where one or more is used, prior to being treated with the at least one 
pacifying agent, except that where (a) the pacifying agent is a hydrogen 
halide (b) the particulate support material is treated with an aluminium 
compound of general formula R.sub.n AlY.sub.3-n and (c) the particulate 
support material is treated with the aluminium compound of general formula 
R.sub.n AlY.sub.3-n and the at least one organomagnesium compound 
separately, the pacifying agent may be added to the support after the 
support has been treated with the at least one organomagnesium compound 
and the aluminium compound of general formula R.sub.n AlY.sub.3-n and 
before the support is treated with the at least one transition metal 
compound of Groups IVA, VA or VIA and (ii) that where the support is 
treated with two compounds selected from the aforesaid group they are not 
exclusively an aluminium compound R.sub.n AlY.sub.3-n and an 
organometallic compound R.sub.m.sup.1 MX.sub.p. 
Preferably the particulate support material is treated with an aluminium 
compound of general formula R.sub.n AlY.sub.3-n, more preferably prior to 
treatment with the at least one organomagnesium compound. Where the 
particulate support material is treated with an aluminium compound of 
general formula R.sub.n AlY.sub.3-n and the pacifying agent is a hydrogen 
halide it is preferred that the particulate support material is treated 
with the at least one transition metal compound of Groups IVA, VA or VIA 
of the Periodic Table prior to being treated with the pacifying agent. 
Where a halogen-containing compound is used, it is preferred that the 
support is treated with it prior to being treated with the at least one 
transition metal compound. 
Where a Lewis base compound is used, it is preferred that the support is 
treated with the organomagnesium compound prior to being treated with the 
Lewis base compound. 
All references to the Periodic Table are to the version of the Periodic 
Table of the Elements printed inside the back cover of "Advanced Inorganic 
Chemistry" by F. A. Cotton and G. Wilkinson 3rd Edition, Interscience 
Publishers, 1976. 
By a "reactive surface" we mean a plurality of sites on, and preferably 
attached to, the surface of the substantially inert particulate support 
material, which sites are capable of abstracting, e.g. a magnesium 
hydrocarbyl from a solution thereof. Preferably the said sites and OH 
groups chemically bonded to the surface of the particulate support 
material and the particulate support material is an inorganic material. 
Such a material will be "substantially inert" in that, whereas the said 
--OH groups are capable of reacting with, say, the organomagnesium 
compound and the organometallic compound R.sub.m.sup.1 MX.sub.p the bulk 
of the matrix material is chemically inert. Particularly good examples of 
such matrix materials are silica and alumina or mixtures thereof. These 
comprise a matrix of silicon or aluminium and oxygen atoms, to the surface 
of which --OH groups are attached, the hydrogen atoms of said groups 
having an acidic function. However, apart from the presence of these --OH 
groups, silica and alumina are generally regarded as chemically inert. 
Within the terms silica and alumina we include silica and alumina based 
materials containing small amounts of other suitable inorganic oxides, 
such as magnesium oxide and zinc oxide. The preferred matrices are silica 
and/or alumina. 
The at least one organomagnesium compound used for the preparation of the 
catalyst components according to the invention are compounds in which at 
least on hydrocarbyl group is directly bonded to magnesium through a 
carbon atom. Preferably two hydrocarbyl groups bonded in this way are 
present for each magnesium atom, which hydrocarbyl groups may be the same 
or different, although we do not exclude the possibility that one of the 
groups bonded to the magnesium may be halogen or oxyhydrocarbyl. The 
hydrocarbyl group may be an alkyl group, aryl group, cycloalkyl group, 
aralkyl group, alkadienyl group or an alkenyl group. The number of carbon 
atoms in the hydrocarbon group is generally between 1 and 30, but this 
number is not critical. Examples of magnesium compounds particularly 
suitable for use in the process according to the invention are diethyl 
magnesium, dipropyl magnesium, di-isopropyl magnesium, dibutyl or 
diisobutyl magnesium, butyl octyl magnesium, diamyl magnesium, dihexyl 
magnesium, diallyl magnesium, didecyl magnesium and didodecyl magnesium, 
dicycloalkyl magnesium with identical or different cyclo-alkyl groups 
containing 3 to 12 carbon atoms, preferably 5 or 6 carbon atoms. The 
magnesium may further carry an alkyl and a cyclo-alkyl group. 
Diphenylmagnesium is the preferred aromatic compound although e.g. 
ditolyl-dixylyl magnesium, and magnesium aryls derived from compounds with 
two or more condensed or non-condensed aromatic nuclei can also be used. 
Catalysts prepared with diaryl magnesium compounds may have a relatively 
lower activity. 
Preferably a dialkyl magnesium is used wherein the alkyl groups are C.sub.1 
-C.sub.10 groups, particularly preferably dibutyl magnesium which may be 
present as a mixture of dibutyl magnesiums, for example a mixture of 
di-n-butyl magnesium and di-iso-butyl magnesium. 
In the aluminium compound R.sub.n AlY.sub.3-n preferably R, where present, 
is alkyl, having 1 to 4 carbon atoms, more preferably ethyl or isobutyl, 
and preferably Y, where present, is a halide, particularly preferably 
chloride or bromide, more particularly preferably chloride. 
Suitable aluminium compounds R.sub.n AlY.sub.3-n include aluminium 
chloride, aluminium bromide, monoethyl aluminium dichloride, ethyl 
aluminium sesqui-chloride and diethyl aluminium chloride. 
Where an organometallic compound R.sub.m.sup.1 MX.sub.p is used and M is a 
metal from Groups IA, IIA, IIB or IIIB of the Periodic Table it is 
preferred that p is 0 and m is the highest valency of the metal. 
Preferred organometallic compounds R.sub.m.sup.1 MX.sub.p are those in 
which the metal M is a transition metal of Groups IVA, VA or VIA, more 
preferably titanium, vanadium, molybdenum, zirconium or chromium, and 
especially zirconium. The monovalent ligand X, where it is present, is 
preferably halogen. 
Hydrocarbyl groups of different types may be associated with a single metal 
atom M. 
Suitable hydrocarbyl groups R.sup.1 include alkyl and alkenyl groups 
(including .pi.-alkenyl groups such as .pi.-allyl) and substituted 
derivatives thereof. Examples of transition metal complexes include 
tetrakis (.pi.-allyl) zirconium or hafnium, tris (.pi.-allyl) chromium, 
tetrakis (.pi.-methallyl) zirconium or hafnium, tris (.pi.-methallyl) 
chromium and zirconium tris (.pi.-allyl) bromide. 
A preferred class of organometallic compounds R.sup.1 MX.sub.p are organic 
transition metal complexes in which some or all of the groups, or ligands, 
R.sup.1 are substituted alkyl groups of general formula --CH.sub.2 Z 
.sigma.-bonded to the transition metal through the carbon atom. In this 
general formula Z may represent a group capable of interaction with the 
vacant d-orbitals of the metal M. Preferably all the groups R.sup.1 have 
this formula, but it is possible for some of them to comprise other 
hydrocarbyl or substituted hydrocarbyl groups. 
Suitable substituent groups Z include aromatic and polyaromatic groups such 
as phenyl and naphthyl, giving rise in the formula --CH.sub.2 Z to the 
alkaryl groups benzyl and (1-methylene-1-naphthyl) and ring substituted 
derivatives thereof, for example p-methyl benzyl. 
Z may also be a cycloalkenyl group, such as a cyclooctenyl group. 
Z may also comprise a group of general formula: A(R.sup.2).sub.3 where A 
represents carbon, silicon, germanium, tin or lead, and each R.sup.2, 
which may be the same or different, represents a hydrocarbyl group or 
hydrogen; preferably at least one R.sup.2 is an alkyl group. 
Examples of this preferred class of organometallic compounds R.sup.1 
MX.sub.p include zirconium and titanium tetra(benzyl) 
tris(benzyl)zirconium chloride, zirconium tetrakis (p-methyl benzyl), 
zirconium and titanium tetrakis (1-methylene-1-naphthyl), zirconium 
tetrakis (trimethylsilylmethylene), zirconium tetrakis (neopentyl) and 
zirconium tetrakis (neophyl). 
Examples of preferred organometallic compounds R.sup.1 MX.sub.p containing 
monovalent ligands X include tris (.pi.-allyl) zirconium chloride, bromide 
or iodide and the equivalent .pi.-methyallyl and benzyl compounds. 
The halogen containing compound, where one is used, is preferably a 
halogenating agent and particularly preferably a chlorinating agent. 
Suitable halogenating agents include hydrogen halides such as hydrogen 
chloride, silicon halides of the formula R.sub.a.sup.3 Six.sup.1 (4-a) 
carboxylic acid halides of the formula R.sup.4 cox.sup.1 hydrocarbyl 
halides of the formula R.sup.5 x.sup.1 b, phosphorus pentachloride, 
thionyl chloride, sulphuryl chloride, phosgene, nitrosyl chloride, halides 
of mineral acids, chlorine, bromine, chlorinated polysiloxanes, 
hydrocarbyl aluminium halides, aluminium, chloride, boron halides and 
ammonium hexafluorosilicate. Wherein, in the formulas indicated, R.sup.3 
is a hydrogen or a hydrocarbyl group, preferably an alkyl group containing 
1 up to 6 carbon atoms or an aryl, alkaryl or aralkyl group containing 6 
up to 15 carbon atoms; R.sup.4 is a hydrocarbyl group, preferably an alkyl 
group containing 1 up to 4 carbon atoms or an aryl, alkaryl or aralkyl 
group containing 6 up to 12 carbon atoms; R.sup.5 is a hydrocarbyl 
residue; X.sup.1 is a halide; a is 0 or an integer from 1 up to 3; and b 
is an integer from 1 up to 10. 
The silicon halides of formula (A) include silicon tetrachloride, silicon 
tetrabromide and halosilanes such as trimethyl silicon monochloride, 
diethyl silicon dichlodride and monobutyl silicon trichloride. 
The carboxylic acid halides of formula (B) include acetyl chloride, benzoyl 
chloride and p-methylbenzoyl chloride. 
The hydrocarbyl halides of formula (C) include carbon tetrachloride, 
chloroform, ethyl chloride, ethylene dichloride and 1,1,1-trichloroethane. 
Halides of mineral acids include boron trichloride and antimony 
pentachloride. 
Hydrocarbyl aluminium halides include diethyl aluminium chloride and 
monoethyl aluminium dichloride. 
The quantity of the halogenating agent is conveniently sufficient to 
provide at least 0.1, and especially at least 1.0, halogen atom at every 
reactive site on the particulate support material. The treatment can be 
effected at ambient temperature or at an elevated temperature of up to 
100.degree. C. The preferred temperature is dependent on the particular 
halogenating agent used, for example, using silicon tetrachloride, the 
temperature is preferably at least 60.degree. C. The treatment is 
conveniently carried out by adding the halogenating agent to a stirred 
suspension of the support or of the support treated with the 
organomagnesium compound. Using a gaseous halogenating agent such as 
hydrogen chloride, the gas can be passed into the reaction medium until no 
further absorption is observed to occur. The treatment with the 
halogenating agent is conveniently effected for a time of at least 0.25 up 
to 10 hours, preferably from 1 up to 5 hours. 
After treatment with the halogenating agent, the solid reaction product is 
conveniently separated from the reaction medium and washed several times. 
The Lewis Base compound can be any organic Lewis Base compound which has 
been proposed for use in a Ziegler polymerisation catalyst and which 
affects either the activity or stereospecificity of such a system. Thus, 
the Lewis Base compound may be an ether, an ester, a ketone, an alcohol, a 
thioether, a thioester, a thioketone, a thiol, a sulphone, a sulphonamide, 
a fused ring compound containing a heterocyclic sulphur atom, an 
organo-silicon compound such as a silane or siloxane, an amide such as 
formamide, urea and the substituted derivatives thereof such as 
tetramethylurea, thiourea, an alkanolamine, an amine, a cyclic amine such 
as pyridine or quinoline, a diamine such as tetramethylethylenediamine or 
an organo-phosphorus compound such as an organo-phosphine, an 
organo-phosphine oxide, an organo-phosphite or an organo-phosphate. The 
use of organo Lewis Base compounds is disclosed, inter alia, in British 
patent specifications Nos. 803,198; 809,717, 880,998; 896,509; 920,118; 
921,954; 933,236; 940,125; 966,025; 969,074; 971,248; 1,013,363; 
1,017,977; 1,049,723; 1,122,010; 1,150,845; 1,208,815; 1,234,657; 
1,324,173; 1,359,328; 1,383,207; 1,423,658; 1,423,659 and 1,423,660. 
Preferred Lewis Base compounds are esters which may be represented by the 
formula R.sup.6 COOR.sup.7. 
R.sup.6 is a hydrocarbyl group which may be substituted by one or more 
halogen atoms and/or hydrocarbyloxy groups; and 
R.sup.7 is a hydrocarbyl group which may be substituted by one or more 
halogen atoms. 
The groups R.sup.6 and R.sup.7 may be the same or different. The group 
R.sup.6 is conveniently an alkyl or aryl group, for example a methyl, 
ethyl, phenyl or tolyl group. The group R.sup.7 is preferably an alkyl 
group containing up to 6 carbon atoms, for example an ethyl or a butyl 
group. It is particularly preferred that R.sup.6 is an aryl group and 
R.sup.7 is an alkyl group. 
A Lewis Base compound may be added to the support treated with the 
organo-magnesium compound and optionally with the one halogenating agent. 
This is conveniently effected by adding the Lewis Base compound to a 
suspension, in an inert liquid medium such as an inert liquid hydrocarbon 
or halohydrocarbon, of the support treated with the organomagnesium 
compound and optionally with the halogenating agent. The quantity of Lewis 
Base used is conveniently in an amount of up to 1 mole of Lewis Base 
compound for each gramme atom of magnesium which is present on the 
support. Preferred quantities of the Lewis Base are from 0.1 to 0.8 mole 
for each gramme atom of magnesium and especially at least 0.5 up to 0.8 
mole for each gramme atom of magnesium. 
The addition of the Lewis Base compound to the support may be effected at 
temperatures of from 0.degree. C. to 100.degree. C. and is very 
conveniently carried out at ambient temperature, that is from about 
15.degree. C. up to about 30.degree. C. After adding the Lewis Base 
compound to the support the materials are conveniently allowed to remain 
in contact for 0.1 up to 70 hours, especially 1 up to 20 hours. 
After the Lewis Base compound and the support treated with the magnesium 
compound have remained in contact for the desired period of time, the 
product thus formed is conveniently separated from the reaction medium and 
washed with an inert liquid. 
The at least one transition metal compound of Groups IVA, VA or VIA of the 
Periodic Table employed in the preparation of the catalyst component of 
the present invention may be any of the transition metal compounds, or 
mixtures thereof, known to be useful in forming Ziegler-Natta catalysts. 
The transition metal is preferably titanium, vanadium, molybdenum, 
zirconium or chromium, especially titanium. Suitable compounds include 
halides, halooxides, alkoxides, haloalkoxides, and acetyl acetonates, 
especially chlorides and alkoxides. The preferred compound is titanium 
tetrachloride. 
Suitable pacifying agents which may be employed in the preparation of 
catalyst components of the present invention include agents which, it is 
believed, are capable of breaking metal-carbon or metal-hydrogen bonds in 
the catalyst component but which do not have a deleterious effect on the 
catalyst component. Such agents include inter alia oxygen, carbon 
monoxide, carbon dioxide, esters and protic agents. Typically protic 
agents are hydrogen halides, carboxylic acids, alcohols, water, amines and 
acetylacetone. Preferably the pacifying agent is an aliphatic alcohol 
having from 1 to about 6 carbon atoms or an anhydrous hydrogen halide such 
as hydrogen fluoride, hydrogen chloride, hydrogen bromide or hydrogen 
iodide or a mixture thereof. Hydrogen halides, and particularly hydrogen 
chloride are preferred. 
The quantity of the at least one pacifying agent used is sufficient to 
break substantially all the metal-hydrocarbyl or metal-hydride bonds in 
the catalyst component. Conveniently excess hydrogen chloride gas is 
bubbled through a suspension of the treated support and excess removed by 
sparging with nitrogen. 
The molar ratio of the aluminium compound, where it is used, to the 
organomagnesium compound in the catalyst component of the present 
invention is preferably between 0.5 and 100, particularly between 1.0 and 
80 and more particularly preferably between 1.0 and 10.0. The molar ratio 
of aluminium compound to organometallic compound R.sub.m.sup.1 MX.sub.p is 
preferably between 0.1 and 100 and particularly between 1 and 20. The 
molar ratio of the aluminium compound to transition metal compound is 
preferably between 1 and 2000, particularly between 2 and 1500 and more 
particularly preferably between 2 and 100. 
Known magnesium containing Zeigler-Natta catalyst components are often so 
reactive that they cannot be mixed with an olefin containing stream prior 
to charging the said stream to a polymerisation zone. However, the 
catalyst components of the present invention are often of sufficiently low 
polymerisation activity or are substantially completely inactive such that 
they can be added to the polymerisation zone in the presence of an olefin 
containing stream. 
A further aspect of the present invention provides an olefin polymerisation 
catalyst which comprises 
(a) the catalyst component as hereinbefore defined and 
(b) an activator which is an organometallic compound of metals of Groups 
I-IV of the Periodic Table. 
Preferably the activator is an organometallic derivative of a metal of 
Groups IA, IIA, IIB, IIIB or IVB of the Periodic Table, particularly 
preferably the metal is aluminium and more particularly preferable the 
activator is a trialkyl aluminium, dihaloalkyl aluminium or halodialkyl 
aluminium. It will be appreciated that sufficient of the said activator is 
employed to transform the metal atoms of the transition metal compound 
known to be useful in forming Ziegler-Natta catalysts to an active state. 
The catalyst component of the present invention may be treated with the 
aforesaid activator by methods known in the art, for example, they may be 
reacted totally outside or inside the polymerisation vessel in which the 
catalyst is to be used or activation may be effected partially outside the 
polymerisation vessel and completed inside the said polymerisation vessel. 
A further aspect of the present invention provides a process for the 
polymerisation or copolymerisation of an olefinically unsaturated monomer 
which process comprises contacting, under polymerisation conditions, at 
least one olefin monomer with a catalyst in accordance with the present 
invention. 
The term "olefinically unsaturated monomer" is intended to include 
mono-olefins such as ethylene, propylene and 4-methylpentene-1. 
Our catalyst may also be used to initiate the copolymerisation of two or 
more olefinically unsaturated monomers. For example, ethylene may be 
copolymerised with a small amount of propylene, butene, hexene or decene, 
butadiene or styrene. 
Polymerisation processes according to the present invention may be carried 
out by techniques generally used for polymerisation processes of the type 
using Ziegler catalysts. 
The choice of conditions of pressure and temperature will vary with factors 
such as the nature of the monomer and catalyst and whether liquid, e.g. 
bulk or diluent, or gas phase polymerisation is used. 
For example, when ethylene is polymerised, pressures from sub-atmospheric 
to several thousand atmospheres may be used. Low pressure (say from 0.1 to 
30 atmospheres) and intermediate pressure (say from 30 to 300 atmospheres) 
polymerisation may be carried out using conventional equipment; but very 
high pressure polymerisation must be performed using suitable specialised 
reactors and pumping equipment. However, since, generally speaking, the 
higher the pressure the higher the activity, the use of such techniques 
may be justified. If very high pressures are used, it is preferred that 
conditions are such that the ethylene feed and polyethylene produced are 
maintained in a single fluid phase, i.e. the pressure should exceed 500 
Kg/cm.sup.2 preferably 1000 to 3000 Kg/cm.sup.2 and the temperature should 
be greater than 125.degree. C., say 140.degree.-300.degree. C. This type 
of process is usually operated in a continuous manner. 
A wide range of temperatures may be used, but in general low and 
intermediate pressure ethylene polymerisations are carried out at 
temperatures in the range 50.degree.-160.degree. C. 
When the process of our invention is used to polymerise propylene, it is 
preferred to operate under conditions commonly used for the polymerisation 
of propylene. However, polymerisation of propylene under other conditions, 
e.g. high pressure, is not excluded. 
It is also within the scope of our invention to use our compositions to 
initiate the copolymerisation of ethylene and propylene together and/or 
with other olefinically unsaturated monomers. 
The polymerisation process of the present invention may be carried out in 
the liquid or gaseous phase (i.e. in the essential absence of a liquid 
medium) and preferably in the gaseous phase. Where polymerisation is 
effected in the liquid phase, and the monomer is not liquid under the 
polymerisation conditions, the monomer may be dissolved in a suitable 
solvent. Examples of suitable solvents are aliphatic or aromatic 
hydrocarbons; for instance pentane, hexane, heptane, octane, decane, 
benzene, toluene and mixtures thereof. 
Polymerisation may be effected either in a batch manner or on a continuous 
basis, and the catalyst components of the present invention and the 
activator therefor may be introduced into the polymerisation vessel 
separately or the catalyst component and activator may be mixed together 
before being introduced into the polymerisation reactor. 
Preferably however, the polymerisation process of the present invention is 
effected as a continuous gas phase process such as a fluid bed process. A 
fluid bed reactor for use in the process of the present invention 
typically comprises a reaction zone and a so-called velocity reduction 
zone. The reaction zone comprises a bed of growing polymer particles, 
formed polymer particles and a minor amount of catalyst particles 
fluidised by the continuous flow of the gaseous monomer, and gaseous 
diluent to remove heat of polymerisation through the reaction zone. A 
suitable rate of gas flow may be readily determined by simple experiment. 
Make up of gaseous monomer to the circulating gas stream is at a rate 
equal to the rate at which particulate polymer product is withdrawn from 
the reactor and the composition of the gas passing through the reactor is 
adjusted to maintain an essentially steady state gaseous composition 
within the reaction zone. The gas leaving the reaction zone is passed to 
the velocity reduction zone where entrained particles are removed. Finer 
entrained particles and dust may be removed in a cyclone and/or fine 
filter. The said gas is compressed in a compressor and passed through a 
heat exchanger wherein it is stripped of the heat of polymerisation and 
then returned to the reaction zone. 
Chain transfer agents may be used in a polymerisation process according to 
our invention, and when ethylene is polymerised their use is normally 
desirable as the polyethylene produced is of very high molecular weight. 
Hydrogen may be conveniently used in accordance with usual practice. 
However, some solvents may act as chain transfer agents. 
Our process is preferably effected under an atmosphere free of oxygen, for 
example under an atmosphere of an inert gas, e.g. nitrogen, or of the 
monomer to be polymerised. It is also preferred to effect the process 
using apparatus and solvents which have been carefully freed from 
impurities, such as oxygen, water and other substances which would 
otherwise react with the catalysts.

The invention is illustrated by the following Examples. 
In the example, hexane and heptane were purified by passage through 
R.sub.3-11 copper catalyst and 5A molecular sieve and finally by sparging 
with pure nitrogen immediately before use. 
Ethylene was purified by passage through R.sub.3-11 copper catalyst and 5A 
molecular sieve. Hydrogen was purified by passage through a catalytic 
deoxygenation unit and 5A molecular sieve. 
EXAMPLE 1 
This example illustrates the improvement in catalyst activity obtained when 
an olefin polymerisation catalyst is prepared from a pacified catalyst 
compound. 
A particulate support material comprising microspheroidal silica (Grace 
Davidson 952) was dried by heating at 250.degree. C. for 2 hours under a 
flow of dry nitrogen. 
A portion of the dried silica (18.4 gms) was slurried in 150 mls of dry, 
deoxygenated hexane in an atmosphere of dry nitrogen. 36.8 mls of a 1.0 M 
solution of ethyl aluminium dichloride in hexane was added with stirring. 
After 15 minutes the slurry was filtered under dry nitrogen and the solid 
thoroughly washed with three 100 ml portions of hexane. The solid was then 
resuspended in 100 mls of hexane and 30 mls of 0.62 M dibutyl magnesium in 
Isopar E was added with stirring. After 15 minutes a second filtration 
under nitrogen, followed by washing with three 100 ml portions of dry 
hexane, was carried out and the solid suspended in 100 mls of hexane. 18.4 
mls of a 0.5 molar solution of bis-n-butoxy titanium dichloride in hexane 
was then added and the slurry heated to reflux for 30 minutes. The slurry 
was filtered and the resulting solid washed with hexane and then dried 
under vacuum. Analysis of the solid showed that it contained 0.355 
milliatoms of titanium per gram. 
A first sample of the Ti containing solid (2.9 gms) was slurried in 100 mls 
of heptane to give Slurry A. A second sample of the Ti containing solid 
(2.9 gms) was slurried in heptane, anhydrous hydrogen chloride gas was 
passed through the slurry for 1 minute followed by sparging with nitrogen 
for 15 minutes to give Slurry B. Slurries A and B were then tested as 
catalyst components in the polymerisation of ethylene. 
The polymerisation of ethylene was carried out as follows. A commercial 
hydrogenator (Hydrogenation Control Unit from Electrosound Supplies 
Limited) was adapted to deliver ethylene to a 500 ml vessel containing 200 
ml iso-octane at 20.degree. C. The vessel was stirred with a VIBRO-MIXER 
El. 2.0 ml of 0.8 M tri-n-octyl aluminium was added to the iso-octane 
which was then saturated with ethylene at 80.degree. C. and the 
polymerisation started by addition of 1.0 ml of Slurry A. The 
polymerisation was stopped after 1 hour and the activity of the catalyst 
prepared therefrom was found to be 250 gm polymer milliatom 
titanium.sup.-1 bar ethylene.sup.-1 hours.sup.-1. A similar experiment 
with Slurry B gave an activity of 436 gm polymer milliatom titanium.sup.-1 
bar ethylene.sup.-1 hours.sup.-1. These results indicate that a catalyst 
prepared from a pacified catalyst component of the present invention 
(Slurry B) is more active than catalyst prepared from an unpacified 
catalyst component (Slurry A).