WO2001012684A1

WO2001012684A1 - Polymerisation process

Info

Publication number: WO2001012684A1
Application number: PCT/GB2000/002806
Authority: WO
Inventors: Marc John Payne
Original assignee: Bp Chemicals Limited
Priority date: 1999-08-02
Filing date: 2000-07-20
Publication date: 2001-02-22
Also published as: AU6005000A; GB9918189D0

Abstract

A process for the polymerisation or copolymerisation of 1-olefins is disclosed, comprising contacting the monomeric olefin under polymerisation conditions in the gas phase with a polymerisation catalyst comprising a complex of formula (I) wherein Y?1 and Y2¿ are each independently S, O or N-R; Z is N or P; A1 to A3 are each independently N, P or C-R8; and each R, each R?8 and R4 and R6¿ are all independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl; M is Fe, Co, Ru or; X represents an atom or group covalently or ionically bonded to the metal M; T is the oxidation state of the metal; and b is the valency of the atom or group X; wherein the partial pressure of the 1-olefin under the polymerisation conditions is from 11 to 20 bar. An improved activity and activity profile is shown compared with the prior art.

Description

POLYMERISATION PROCESS

The present invention relates to a process for the polymerisation and copolymerisation of 1-olefιns, specifically to such processes utilising polymerisation catalysts based on certain transition metal complexes.

The use of certain transition metal compounds to polymerise 1-olefιns, for example, ethylene or propylene, is well established in the prior art. The use of Ziegler- Natta catalysts, for example, those catalysts produced by activating titanium halides with organometallic compounds such as triethylaluminium, is fundamental to many commercial processes for manufacturing polyolefins. Over the last twenty or thirty years, advances in the technology have led to the development of Ziegler-Natta catalysts which have such high activities that olefin polymers and copolymers containing very low concentrations of residual catalyst can be produced directly in commercial polymerisation processes. The quantities of residual catalyst remaining in the produced polymer are so small as to render unnecessary their separation and removal for most commercial applications. Such processes can be operated by polymerising the monomers in the gas phase, or in solution or in suspension in a liquid hydrocarbon diluent. Polymerisation of the monomers can be carried out in the gas phase (the "gas phase process"), for example by fluidising under polymerisation conditions a bed comprising the target polyolefin powder and particles of the desired catalyst using a fluidising gas stream comprising the gaseous monomer. Our own WO99/12981 discloses that 1-olefins may be polymerised by contacting it with certain transition metal, particularly iron, complexes of selected 2,6- pyridinecarboxaldehydebis(imines) and 2,6-diacylpyridinebis(imines). Gas phase polymerisations using an ethylene partial pressure of 8 bar are exemplified. It is an object of the present invention to provide an improved gas phase polymerisation process using such catalysts.

Accordingly, the present invention provides a process for the polymerisation and copolymerisation of 1-olefins, comprising contacting the monomeric olefin under polymerisation conditions in the gas phase with a polymerisation catalyst comprising a complex of the formula

Formula (I)

wherein Y¹ and Y² are each independently S, O or N-R; Z is N or P; A¹ to A³ are each independently N, P or C-R⁸; and each R, each R⁸ and R⁴ and R⁶ are all independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl; M is Fe, Co, Ru or ; X represents an atom or group covalently or ionically bonded to the metal M; T is the oxidation state of the metal; and b is the valency of the atom or group X; wherein the partial pressure of the 1 -olefin under the polymerisation conditions is from 11 to 20 bar.

We have discovered that operating at higher pressures than 8 bar results in a substantial increase in activity per unit pressure of the catalyst. The time to reach maximum activity after commencement of polymerisation (induction period) can also be significantly increased compared with operation at lower pressures of the 1 -olefin: this provides well-known advantages of improved mixing in the reactor prior to commencement of polymerisation and better fragmentation characteristics of the catalyst, and also improved particle morphology and reduced fines. A preferred range of pressures is from 12 to 18 bar, and more preferably from 14 to 16 bar. A preferred process comprises the steps of : a) preparing a prepolymer-based catalyst by contacting one or more 1-olefιns with a catalyst, and b) contacting the prepolymer-based catalyst with one or more 1-olefιns, wherein the catalyst is as defined above.

In the text hereinbelow, the term "catalyst" is intended to include "prepolymer- based catalyst" as defined above.

Particularly preferred conditions are partial pressures of 1 -olefin between 12 and 15 bar. Preferred catalysts for use in the present invention comprise a complex having the formula

Formula (II)

wherein R¹ to R⁷ are each independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl or SiR'₃ where each R' is independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl.

R⁵ and R⁷ are preferably independently selected from substituted or unsubstituted alicyclic, heterocyclic or aromatic groups, for example, phenyl, 1-naphthyl, 2-naphthyl, 2-methylphenyl, 2-ethylphenyl, 2,6-diisopropylphenyl, 2,3-diisopropylphenyl, 2,4-diisopropylphenyl, 2,6-di-n-butylphenyl, 2,6-dimethylphenyl, 2,3-dimethylphenyl, 2,4-dimethylphenyl, 2-t-butylphenyl, 2,6-diphenylphenyl, 2,4,6-trimethylphenyl, 2,6- trifluoromethylphenyl, 4-bromo-2,6-dimethylphenyl, 3,5 dichloro2,6-diethylphenyl, and 2,6,bis(2,6-dimethylphenyl)phenyl, cyclohexyl and pyridinyl. In a preferred embodiment R⁵ is represented by the group "P" and R⁷ is represented by the group "Q" as follows:

wherein R¹⁹ to R²⁸ are independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl; when any two or more of R¹ to R⁴, R⁶ and R¹⁹ to R²⁸ are hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl, said two or more can be linked to form one or more cyclic substituents.

The ring systems P and Q are preferably independently 2,6-hydrocarbylphenyl or fused-ring polyaromatic, for example, 1 -naphthyl, 2-naphthyl, 1-phenanthrenyl and 8- quinolinyl. Preferably at least one of R¹⁹, R²⁰, R²¹ and R²² is hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl. More preferably at least one of R¹⁹ and R²⁰, and at least one of R²¹ and R²², is hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl. Most preferably R¹⁹, R²⁰, R²¹ and R²² are all independently selected from hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl. R¹⁹, R²⁰, R²¹ and R²² are preferably independently selected from methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, tert.- butyl, n-pentyl, neopentyl, n-hexyl, 4-methylpentyl, n-octyl, phenyl and benzyl. R\ R², R³, R⁴, R⁶, R¹⁹, R²⁰, R²¹, R²², R²³, R²⁵, R²⁶ and R²⁸ are preferably independently selected from hydrogen and Ci to C₈ hydrocarbyl, for example, methyl, ethyl, n-propyl, n-butyl, t-butyl, n-hexyl, n-octyl, phenyl and benzyl.

In an alternative embodiment R⁵ is a group having the formula -NR²⁹R³⁰ and R⁷ is a group having the formula -NR³¹R³², wherein R²⁹ to R³² are independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl; when any two or more of R¹ to R⁴, R⁶ and R²⁹ to R³² are hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl, said two or more can be linked to form one or more cyclic substituents. Each of the atoms Y\Y² and Z (preferably nitrogen atoms) is coordinated to the metal by a "dative" bond, i.e. a bond formed by donation of a lone pair of electrons from the nitrogen atom. The remaining bonds on each of these atoms are covalent bonds formed by electron sharing between the atoms and the organic ligand as shown in the defined formula for the metal complex illustrated above. The atom or group represented by X in the compounds of Formula (I) and (II) can be, for example, selected from halide, sulphate, nitrate, thiolate, thiocarboxylate, BF₄ ^", PFβ^", hydride, hydrocarbyloxide, carboxylate, hydrocarbyl, substituted hydrocarbyl and heterohydrocarbyl, or β-diketonates. Examples of such atoms or groups are chloride, bromide, methyl, ethyl, propyl, butyl, octyl, decyl, phenyl, benzyl, methoxide, ethoxide, isopropoxide, tosylate, triflate, formate, acetate, phenoxide and benzoate. Preferred examples of the atom or group X in the compounds of Formula (I) are halide, for example, chloride, bromide; hydride; hydrocarbyloxide, for example, methoxide, ethoxide, isopropoxide, phenoxide; carboxylate, for example, formate, acetate, benzoate; hydrocarbyl, for example, methyl, ethyl, propyl, butyl, octyl, decyl, phenyl, benzyl; substituted hydrocarbyl; heterohydrocarbyl; tosylate; and triflate. Preferably X is selected from halide, hydride and hydrocarbyl. Chloride is particularly preferred.

The catalysts utilised in the present invention can if desired comprise more than one of the above-mentioned compounds. The catalysts can also include one or more other types of catalyst, such as those of the type used in conventional Ziegler-Natta catalyst systems, metallocene-based catalysts, monocyclopentadienyl- or constrained geometry based catalysts, or heat activated supported chromium oxide catalysts (e.g. Phillips-type catalyst).

In addition to the above complex, preferred catalysts for use in the process of the present invention additionally comprise an activator compound. The activator is suitably selected from organoaluminium compounds and hydrocarbylboron compounds. Suitable organoaluminium compounds include compounds of the formula A1R₃, where each R is independently Ci-Cπ alkyl or halo. Examples include trimethylaluminium (TMA), triethylaluminium (TEA), tri-isobutylaluminium (TIBA), tri-n-octylaluminium, methylaluminium dichloride, ethylaluminium dichloride, dimethylaluminium chloride, diethylaluminium chloride, ethylaluminiumsesquichloride, methylaluminiumsesquichloride, and alumoxanes. Alumoxanes are well known in the art as typically the oligomeric compounds which can be prepared by the controlled addition of water to an alkylaluminium compound, for example trimethylaluminium. Such compounds can be linear, cyclic or mixtures thereof. Commercially available alumoxanes are generally believed to be mixtures of linear and cyclic compounds. The cyclic alumoxanes can be represented by the formula [R¹⁶AlO]_s and the linear alumoxanes by the formula R¹⁷(R¹⁸AlO)_s wherein s is a number from about 2 to 50, and wherein R¹⁶, R¹⁷, and R¹⁸ represent hydrocarbyl groups, preferably Ci to Cβ alkyl groups, for example methyl, ethyl or butyl groups. Alkylalumoxanes such as methylalumoxane (MAO) are preferred.

Mixtures of alkylalumoxanes and trialkylaluminium compounds are particularly preferred, such as MAO with TMA or TIBA. In this context it should be noted that the term "alkylalumoxane" as used in this specification includes alkylalumoxanes available commercially which may contain a proportion, typically about 10wt%, but optionally up to 50wt%, of the corresponding trialkylaluminium; for instance, commercial MAO usually contains approximately 10wt% trimethylaluminium (TMA), whilst commercial MMAO contains both TMA and TIBA. Quantities of alkylalumoxane quoted herein include such trialkylaluminium impurities, and accordingly quantities of trialkylaluminium compounds quoted herein are considered to comprise compounds of the formula A1R₃ additional to any A1R₃ compound incorporated within the alkylalumoxane when present. Examples of suitable hydrocarbylboron compounds are boroxines, trimethylboron, triethylboron, dimethylphenylammoniumtetra(phenyl)borate, trityltetra(phenyl)borate, triphenylboron, dimethylphenylammonium tetra(pentafluorophenyl)borate, sodium tetrakis[(bis-3,5-trifluoromethyl)phenyl]borate, H^*(OEt₂)[(bis-3,5- trifluoromethyl)phenyl]borate, trityltetra(pentafluorophenyl)borate and tris(pentafluorophenyl) boron. In the preparation of the catalysts utilised in the present invention the quantity of activating compound selected from organoaluminium compounds and hydrocarbylboron compounds to be employed is easily determined by simple testing, for example, by the preparation of small test samples which can be used to polymerise small quantities of the monomer(s) and thus to determine the activity of the produced catalyst. It is generally found that the quantity employed is sufficient to provide 0.1 to 20,000 atoms, preferably 1 to 2000 atoms of aluminium or boron per atom of metal M in the compound of Formula (I).

An alternative class of activators comprise salts of a cationic oxidising agent and a non-coordinating compatible anion. Examples of cationic oxidising agents include: ferrocenium, hydrocarbyl-substituted ferrocenium, Ag⁺, or Pb²⁺. Examples of non- coordinating compatible anions are BF ^', SbClβ^', PFβ^", tetrakis(phenyl)borate and tetrakis(pentafluorophenyl)borate.

The catalyst may also comprise a neutral Lewis base. Neutral Lewis bases are well known in the art of Ziegler-Natta catalyst polymerisation technology. Examples of classes of neutral Lewis bases suitable for the present invention are unsaturated hydrocarbons, for example, alkenes (other than 1 -olefins) or alkynes, primary, secondary and tertiary amines, amides, phosphoramides, phosphines, phosphites, ethers, thioethers, nitriles, carbonyl compounds, for example, esters, ketones, aldehydes, carbon monoxide and carbon dioxide, sulphoxides, sulphones and boroxines. Although 1 -olefins are capable of acting as neutral Lewis bases, for the purposes of the present invention they are regarded as monomer or comonomer 1 -olefins and not as neutral Lewis bases per se. However, alkenes which are internal olefins, for example, 2-butene and cyclohexene are regarded as neutral Lewis bases in the present invention.

Preferred monomers for homopolymerisation processes are ethylene and propylene. Suitable other monomers copolymerisation with ethylene or propylene are, for example, C_2-20 α-olefins: specifically 1-butene, 1-pentene, 1-hexene, 4- methylpentene-1, 1-heptene, 1-octene, 1-nonene, 1-decene, 1-undecene, 1-dodecene, 1- tridecene, 1-tetradecene, 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1- nonadecene, and 1-eicosene. Other monomers include methyl methacrylate, methyl acrylate, butyl acrylate, acrylonitrile, vinyl acetate, and styrene.

Irrespective of the polymerisation or copolymerisation technique employed, polymerisation or copolymerisation is typically carried out under conditions that substantially exclude oxygen, water, and other materials that act as catalyst poisons. Also, polymerisation or copolymerisation can be carried out in the presence of additives to control polymer or copolymer molecular weights.

The use of hydrogen gas as a means of controlling the average molecular weight of the polymer or copolymer applies generally to the polymerisation process of the present invention. For example, hydrogen can be used to reduce the average molecular weight of polymers or copolymers prepared using gas phase, slurry phase, bulk phase or solution phase polymerisation conditions. The quantity of hydrogen gas to be employed to give the desired average molecular weight can be determined by simple "trial and error" polymerisation tests.

The polymerisation process of the present invention provides polymers and copolymers, especially ethylene polymers, at remarkably high productivity (based on the amount of polymer or copolymer produced per unit weight of complex employed in the catalyst system). This means that relatively very small quantities of transition metal complex are consumed in commercial processes using the process of the present invention. It also means that when the polymerisation process of the present invention is operated under polymer recovery conditions that do not employ a catalyst separation step, thus leaving the catalyst, or residues thereof, in the polymer (e.g. as occurs in most commercial slurry and gas phase polymerisation processes), the amount of transition metal complex in the produced polymer can be very small.

The gas phase polymerisation conditions of the invention are particularly useful for the production of high or low density grades of polyethylene, and polypropylene. In these processes the polymerisation conditions can be batch, continuous or semi- continuous. Furthermore, one or more reactors may be used, e.g. from two to five reactors in series. Different reaction conditions, such as different temperatures or hydrogen concentrations may be employed in the different reactors. In the gas phase process, the catalyst is generally metered and transferred into the polymerisation zone in the form of a particulate solid either as a dry powder (e.g. with an inert gas) or as a slurry. This solid can be, for example, a solid catalyst system formed from the one or more of complexes of the invention and an activator with or without other types of catalysts, or can be the solid catalyst alone with or without other types of catalysts. In the latter situation, the activator can be fed to the polymerisation zone, for example as a solution, separately from or together with the solid catalyst. Preferably the catalyst system or the transition metal complex component of the catalyst system employed in the gas phase polymerisation is supported on one or more support materials. Most preferably the catalyst system is supported on the support material prior to its introduction into the polymerisation zone. Suitable support materials are, for example, silica, alumina, zirconia, talc, kieselguhr, or magnesia. Impregnation of the support material can be carried out by conventional techniques, for example, by forming a solution or suspension of the catalyst components in a suitable diluent or solvent, and slurrying the support material therewith. The support material thus impregnated with catalyst can then be separated from the diluent for example, by filtration or evaporation techniques. Once the polymer product is discharged from the reactor, any associated and absorbed hydrocarbons are substantially removed,- or degassed, from the polymer by, for example, pressure let-down or gas purging using fresh or recycled steam, nitrogen or light hydrocarbons (such as ethylene). Recovered gaseous or liquid hydrocarbons may be recycled to the polymerisation zone.

Methods for operating gas phase polymerisation processes are well known in the art. Such methods generally involve agitating (e.g. by stirring, vibrating or fluidising) a bed of catalyst, or a bed of the target polymer (i.e. polymer having the same or similar physical properties to that which it is desired to make in the polymerisation process) containing a catalyst, and feeding thereto a stream of monomer at least partially in the gaseous phase, under conditions such that at least part of the monomer polymerises in contact with the catalyst in the bed. The bed is generally cooled by the addition of cool gas (e.g. recycled gaseous monomer) and/or volatile liquid (e.g. a volatile inert hydrocarbon, or gaseous monomer which has been condensed to form a liquid). The polymer produced in, and isolated from, gas phase processes forms directly a solid in the polymerisation zone and is free from, or substantially free from liquid. As is well known to those skilled in the art, if any liquid is allowed to enter the polymerisation zone of a gas phase polymerisation process the quantity of liquid in the polymerisation zone is small in relation to the quantity of polymer present. This is in contrast to "solution phase" processes wherein the polymer is formed dissolved in a solvent, and "slurry phase" processes wherein the polymer forms as a suspension in a liquid diluent. The gas phase process can be operated under batch, semi-batch, or so-called

"continuous" conditions. It is preferred to operate under conditions such that monomer is continuously recycled to an agitated polymerisation zone containing polymerisation catalyst, make-up monomer being provided to replace polymerised monomer, and continuously or intermittently withdrawing produced polymer from the polymerisation zone at a rate comparable to the rate of formation of the polymer, fresh catalyst being added to the polymerisation zone to replace the catalyst withdrawn form the polymerisation zone with the produced polymer.

For typical production of impact copolymers, homopolymer formed from the first monomer in a first reactor is reacted with the second monomer in a second reactor. For manufacture of propylene/ethylene impact copolymer in a gas-phase process, propylene is polymerized in a first reactor; reactive polymer transferred to a second reactor in which ethylene or other comonomer is added. The result is an intimate mixture of a isotactic polypropylene chains with chains of a random propylene/ethylene copolymer. A random copolymer typically is produced in a single reactor in which a minor amount of a comonomer (typically ethylene) is added to polymerizing chains of propylene.

Methods for operating gas phase fluidised bed processes for making polyethylene, ethylene copolymers and polypropylene are well known in the art. The process can be operated, for example, in a vertical cylindrical reactor equipped with a perforated distribution plate to support the bed and to distribute the incoming fluidising gas stream through the bed. The fluidising gas circulating through the bed serves to remove the heat of polymerisation from the bed and to supply monomer for polymerisation in the bed. Thus the fluidising gas generally comprises the monomer(s) normally together with some inert gas (e.g. nitrogen or inert hydrocarbons such as methane, ethane, propane, butane, pentane or hexane) and optionally with hydrogen as molecular weight modifier. The hot fluidising gas emerging from the top of the bed is led optionally through a velocity reduction zone (this can be a cylindrical portion of the reactor having a wider diameter) and, if desired, a cyclone and or filters to disentrain fine solid particles from the gas stream. The hot gas is then led to a heat exchanger to remove at least part of the heat of polymerisation. Catalyst is preferably fed continuously or at regular intervals to the bed. At start up of the process, the bed comprises fluidisable polymer which is preferably similar to the target polymer. Polymer is produced continuously within the bed by the polymerisation of the monomer(s). Preferably means are provided to discharge polymer from the bed continuously or at regular intervals to maintain the fluidised bed at the desired height. The process is generally operated at temperatures for example, between 50 and 120 °C. The temperature of the bed is maintained below the sintering temperature of the fluidised polymer to avoid problems of agglomeration.

In the gas phase fluidised bed process for polymerisation of olefins the heat evolved by the exothermic polymerisation reaction is normally removed from the polymerisation zone (i.e. the fluidised bed) by means of the fluidising gas stream as described above. The hot reactor gas emerging from the top of the bed is led through one or more heat exchangers wherein the gas is cooled. The cooled reactor gas, together with any make-up gas, is then recycled to the base of the bed. In the gas phase fluidised bed polymerisation process of the present invention it is desirable to provide additional cooling of the bed (and thereby improve the space time yield of the process) by feeding a volatile liquid to the bed under conditions such that the liquid evaporates in the bed thereby absorbing additional heat of polymerisation from the bed by the "latent heat of evaporation" effect. When the hot recycle gas from the bed enters the heat exchanger, the volatile liquid can condense out. In one embodiment of the present invention the volatile liquid is separated from the recycle gas and reintroduced separately into the bed. Thus, for example, the volatile liquid can be separated and sprayed into the bed. In another embodiment of the present invention the volatile liquid is recycled to the bed with the recycle gas. Thus the volatile liquid can be condensed from the fluidising gas stream emerging from the reactor and can be recycled to the bed with recycle gas, or can be separated from the recycle gas and then returned to the bed.

The method of condensing liquid in the recycle gas stream and returning the mixture of gas and entrained liquid to the bed is described in EP-A-0089691 and EP-A- 0241947. It is preferred to reintroduce the condensed liquid into the bed separate from the recycle gas using the process described in our US Patent 5541270, the teaching of which is hereby incorporated into this specification.

When using the catalysts of the present invention under gas phase polymerisation conditions, the catalyst, or one or more of the components employed to form the catalyst can, for example, be introduced into the polymerisation reaction zone in liquid form, for example, as a solution in an inert liquid diluent. Thus, for example, the transition metal component, or the activator component, or both of these components can be dissolved or slurried in a liquid diluent and fed to the polymerisation zone. Under these circumstances it is preferred the liquid containing the component(s) is sprayed as fine droplets into the polymerisation zone. The droplet diameter is preferably within the range 1 to 1000 microns. EP-A-0593083, the teaching of which is hereby incorporated into this specification, discloses a process for introducing a polymerisation catalyst into a gas phase polymerisation. The methods disclosed in EP-A-0593083 can be suitably employed in the polymerisation process of the present invention if desired. Although not usually required, upon completion of polymerisation or copolymerisation, or when it is desired to terminate polymerisation or copolymerisation or at least temporarily deactivate the catalyst or catalyst component of this invention, the catalyst can be contacted with water, alcohols, acetone, or other suitable catalyst deactivators a manner known to persons of skill in the art.

The present invention is illustrated in the following Examples. EXAMPLES Catalyst Preparation EXAMPLE 1 Preparation of 2.6-diacetylpyridinebis(2.4.6-trimethylaniD

To a toluene (150 ml) solution of 2,6-diacetylpyridine (2g; 12.3mmol) in a single neck 250cm³ round bottom flask was added 2,4,6-trimethyl aniline (5.16cm³; 36.8mmol). Toluene sulphonic acid-monohydrate (0. lg) was added to the solution and the flask connected in series to a Dean-Stark apparatus and water cooled condenser. The reaction mixture was refluxed for 20 hours during which the produced water from the condensation reaction was collected in the Dean-Stark apparatus. Upon cooling to room temperature the volatile components of the reaction mixture were removed in vacuo and the product crystallised from methanol. The product was filtered, washed with cold methanol and dried in a vacuum oven (50°C) overnight. NMR and IR revealed the product to be exclusively 2,6-diacetylpyridinebis(2,4,6-trimethylanil). The yield was 4.23g (87 %). EXAMPLE 2

Preparation of 2.6-diacetylpyridinebis⁽2.4.6-trimethylaniπFeCl₂.

FeCl₂ (3.19g; 25.2mmol) was dissolved in hot n-butanol (400ml) at 80°C and the 2,6-diacetylpyridinebis(2,4,6-trimethylanil) (lO.Og; 25.2mmol) added as a solid portion wise. The reaction mixture turned blue. After stirring at 80°C for 60 minutes the reaction was allowed to cool down to room temperature and stir for 16 hours. The resultant suspension was filtered and the blue precipitate washed with toluene (2 x 200cm³) and pentane (1 x 100cm³) and dried in vacuo. The yield of 2,6- diacetylpyridinebis(2,4,6-trimethylanil)FeCl₂ was 12.87g (97 %). EXAMPLE 3 Preparation of Supported Catalyst

The preparation of 2,6-diacetylpyridinebis(2,4,6-trimethylanil)FeCl₂ is described above. Silica (Crosfield grade ES70X) was heated under flowing nitrogen at 200 °C for 16 hours. A sample of this silica (2.0g) was placed in a Schlenk tube with dried toluene (10 ml) and had 2.81 ml of 1.78M methylaluminoxane, MAO (supplied by Albemarle) added to it to form a slurry. The slurry was heated for 1 hour at 80°C with periodic agitation before adding a slurry of 2,6-diacetylpyridinebis(2,4,6-trimethylanil)FeCl₂ (0.026 g) in dried toluene (10 ml). The mixture was heated at 80 °C for a further hour with periodic agitation. The now clear supernatant was decanted off and the silica/MAO Fe complex was dried in vacuo until all signs of fluidisation stopped to leave an orange/brown free flowing solid. Analysis of the catalyst gave a nominal composition of 0.12%w/w Fe and 5.8%w/w Al.

EXAMPLE 4

GAS PHASE POLYMERISATION TESTS

The reagents used in the polymerisation tests were: hydrogen Grade 6.0 (supplied by Air Products): ethylene Grade 3.5 (supplied by Air Products): dried pentane (supplied by Aldrich): and methylaluminium (2M in hexanes, supplied by Aldrich). A 3 litre reactor was heated to 80°C before being pressured to 10 bar with nitrogen and vented to

1 bar. The pressure purge cycle was repeated 8 times before powdered sodium chloride charge powder (300g, predried under vacuum, 160°C, >4 hours) was added under a stream of nitrogen. The sodium chloride was used as a fluidisable stirrable start-up charge powder for the gas phase polymerisation. Trimethyl aluminium (4 ml, 2 molar in hexanes) was added to the reactor and was boxed in under nitrogen (1.5 bar). The alkyl aluminium was allowed to scavenge for poisons in the reactor for between 2 and 3 hours before being vented at 80°C using 8 x 10 bar nitrogen purges. The gas phase composition to be used for the polymerisation was introduced into the reactor and preheated to 78°C prior to injection of the catalyst composition. The catalyst (0.05 -

0.22 g) was injected under nitrogen and the temperature then adjusted to 80°C. The polymerisation tests were allowed to continue for 1 hour before being terminated by purging the reactants from the reactor with nitrogen and reducing the temperature to < 30°C. The produced polymer was washed with water to remove the sodium chloride, then with acidified methanol (50 ml HC1/2.5 litres methanol) and finally with water/ethanol (4: 1 v/v). The polymer was dried under vacuum, at 40 °C, for 16 hours. The polymerisation tests were carried out at a polymerisation temperature of 80 °C and at an ethylene pressure of 8 to 15 bar. The polymerisation conditions and catalyst activities are set out in the following Table.

1. "Comp" Denotes Comparative Example

2. Activity is expressed as g/mmol^"1

3. Productivity is expressed in g polymer/g catalyst

Plots of catalyst activity against time for the above polymerisations are shown in Figure 1. These plots show that both with and without pentane, an increase in the partial pressure of ethylene results in a substantial increase in activity. Furthermore, there is a much greater delay before the maximum level of activity is reached. In the two runs without pentane (Examples 4.1 and 4.3) this delay increases from less than one minute after commencement to greater than 15 minutes. With pentane, the delay increases from about 2 minutes to almost 10 minutes.

Claims

Claims:

1. Process for the polymerisation or copolymerisation of 1 -olefins, comprising contacting the monomeric olefin under polymerisation conditions in the gas phase with a polymerisation catalyst comprising a complex of the formula

Formula (I)

2. Process according to claim 1, wherein the preferred partial pressure of the 1 -olefin is from 12 to 18 bar, preferably from 12 to 15 bar.

3. Process according to any preceding claim comprising the steps of : a) preparing a prepolymer-based catalyst by contacting one or more 1 -olefins with a catalyst, and b) contacting the prepolymer-based catalyst with one or more 1 -olefins, wherein the catalyst is as defined above.

4. Process according to any preceding claim wherein the complex of formula (I) comprises a complex having the formula

Formula (II)

wherein R¹ to R are each independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl or SiR'₃ where each R' is independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl.

5. Complex according to claim 4 wherein R⁵ and R⁷ are each independently selected from phenyl, 1-naphthyl, 2-naphthyl, 2-methylphenyl, 2-ethylphenyl, 2,6-diisopropylphenyl, 2,3-diisopropylphenyl, 2,4-diisopropylphenyl, 2,6-di-n- butylphenyl, 2,6-dimethylphenyl, 2,3-dimethylphenyl, 2,4-dimethylphenyl, 2-t- butylphenyl, 2,6-diphenylphenyl, 2,4,6-trimethylphenyl, 2,6-trifluoromethylphenyl, 4- bromo-2,6-dimethylphenyl, 3,5-dichloro-2,6-diethylphenyl, 2,6,bis(2,6- dimethylphenyl)phenyl, cyclohexyl or pyridinyl.

6. Complex according to claim 4 wherein R⁵ is represented by the group "P" and R⁷ is represented by the group "Q" as follows:

7. Process according to claim 6 wherein R¹, R², R³, R⁴, R⁶, R¹⁹, R²⁰, R²¹, R²², R²³, R²⁵, R²⁶ and R²⁸ are independently selected from hydrogen and Ci to Cg hydrocarbyl.

8. Process according to claim 6 or 7 wherein R¹⁹, R²⁰, R²¹ and R²² are independently selected from methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, tert. -butyl, n-pentyl, neopentyl, n-hexyl, 4-methylpentyl, n-octyl, phenyl and benzyl.

9. Process according to claim 4 wherein R⁵ is a group having the formula -NR²⁹R³⁰ and R is a group having the formula -NR R , wherein R to R are independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl; when any two or more of R¹ to R , R⁶ and R²⁹ to R³² are hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl or substituted heterohydrocarbyl, said two or more can be linked to form one or more cyclic substituents.

10. Process according to any preceding claim wherein X is selected from halide, sulphate, nitrate, thiolate, thiocarboxylate, BF₄ ^', PFβ^", hydride, hydrocarbyloxide, carboxylate, hydrocarbyl, substituted hydrocarbyl and heterohydrocarbyl, and β- diketonates.

11. Process according to claim 10 wherein X is selected from chloride, bromide, methyl , ethyl, propyl, butyl, octyl, decyl, phenyl, benzyl, methoxide, ethoxide, isopropoxide, tosylate, triflate, formate, acetate, phenoxide and benzoate.

12. Process according to any preceding claim wherein M is Fe or Co.

13. Process according to any preceding claim wherein the 1 -olefin is additionally contacted with an activator comprising trimethylaluminium (TMA), triethylaluminium (TEA), tri-isobutylaluminium (TIBA), tri-n-octylaluminium, methylaluminium dichloride, ethylaluminium dichloride, dimethylaluminium chloride, diethylaluminium chloride, ethylaluminiumsesquichloride, methylaluminiumsesquichloride, or an alumoxane.

14. Process according to any preceding claim wherein the 1 -olefin is additionally contacted with a neutral Lewis base.

15. Process according to any preceding claim wherein the catalyst is supported on a support material comprising silica, alumina, MgCl₂ or zirconia, or on a polymer or prepolymer comprising polyethylene, polypropylene, polystyrene, or poly(aminostyrene).

16. Process according to any preceding claim wherein the polymerisation is conducted in the presence of hydrogen as a molecular weight modifier.

17. Process according to any preceding claim wherein the polymerisation conditions are solution phase, slurry phase or gas phase.

18. Process according to claim 17 wherein the polymerisation is conducted under gas phase fluidised bed conditions.

19. Process according to claim 17 wherein the polymerisation is conducted in slurry phase in an autoclave or continuous loop reactor.