WO2000009583A1

WO2000009583A1 - Catalyst composition and process for the preparation of copolymers of carbon monoxide and an olefinically unsaturated compound

Info

Publication number: WO2000009583A1
Application number: PCT/EP1999/005823
Authority: WO
Inventors: Jan Karel Frederik Buijink; Eit Drent; Jacoba Catherina Lucia Johanna Suykerbuyk
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 1998-08-14
Filing date: 1999-08-10
Publication date: 2000-02-24
Also published as: AU5513399A

Abstract

A catalyst composition which is based upon (a) a source of nickel cations and (b) a bidentate ligand of the general formula (I): R?1R2M1-R-M2R3R4¿ wherein M?1 and M2¿ represent independently phosphorus, nitrogen, arsenic or antimony, R?1, R2, R3 and R4¿ independently represent optionally substituted aliphatic or alicyclic groups and R represents a bivalent bridging group of which the bridge which extends directly between the atoms M?1 and M2¿ consists of at most two bridge atoms; and a process for the preparation of copolymers of carbon monoxide and an olefinically unsaturated compound comprising contacting the monomers in the presence of the said catalyst composition.

Description

CATALYST COMPOSITION AND PROCESS FOR THE PREPARATION OF

COPOLYMERS OF CARBON MONOXIDE AND AN OLEFINICALLY

UNSATURATED COMPOUND

The invention relates to a catalyst composition and a process for the preparation of copolymers of carbon monoxide and one or more olefinically unsaturated compounds . Linear copolymers of carbon monoxide with one or more olefinically unsaturated compounds can be prepared by contacting the monomers in the presence of a Group VIII (Groups 8, 9 and 10 in modern notation) metal containing catalyst. The copolymers can be processed by means of conventional techniques into films, sheets, plates, fibres and shaped articles for domestic use and for parts in the car industry. They are eminently suitable for use in many outlets for thermoplastics . In the copolymers in question the units originating from the carbon monoxide on the one hand and the units originating from the olefinically unsaturated compound (s) on the other hand occur in an alternating or substantially alternating arrangement .

So far, the preparation of the copolymers by using catalysts based on palladium as the Group VIII metal has been studied extensively because palladium based catalysts provide a high polymerization rate. However, a disadvantage of using palladium based catalysts is the high palladium price. This high price is to be accepted as a matter of fact because it is caused by the limited natural availability of this metal. Methods for the extraction of palladium remnants from the copolymers which allow the recycle of palladium are available, but these methods introduce additional process steps which complicate the total polymerization process scheme. Another disadvantage is that palladium based catalysts have a tendency to plate-out, i.e. to convert into the zero-valent metallic state. Plating-out during the copolymer work-up and further processing may cause some grey discoloration of the copolymer, in particular when its content of catalyst remnants is high. Plating-out may also occur during the catalyst preparation or the storage of the catalyst composition prior to its use in the copolymerization process. The tendency to plate-put is associated with the noble-metal character of palladium based catalysts. It would be desirable to find an alternative to palladium based catalysts.

Many patent applications filed in relation to linear copolymers of carbon monoxide with one or more olefinically unsaturated compounds present a list of possible Group VIII metals. For example EP-A-585493 mentions ruthenium, rhodium, palladium, osmium, iridium, platinum, iron, cobalt and nickel. The great majority of such patent applications state that palladium is the catalytic metal of choice, and include examples only of palladium.

There are, thus, few earlier patent applications which place emphasis on or exemplify the use of nickel in catalysts for the copolymerization of carbon monoxide with olefinically unsaturated compounds. One is

US-A-3, 984, 388 which exemplifies the use of nickel cyanide based catalysts. These catalysts, however, displayed a low polymerization activity despite the application of a high polymerization temperature. Moreover, copolymers made with these catalysts contain cyanides as catalyst remnants. It would then be likely that cyanide containing compounds, for example hydrogen cyanide, are being released from the copolymer during its end-use application. This is in particular undesirable when the copolymer is used as a packaging material in contact with food. A second patent application which exemplifies the use of a nickel containing catalyst is EP-A-121965. This suggests the use of catalysts containing nickel, cobalt or, preferably, palladium, in each case complexed with a ligand which is defined as a bidentate ligand of the general formula R¹R²-M-R-M-R³R⁴ in which M represents phosphorous, arsenic or antimony, R represents a divalent organic bridging group having at least 2 carbon atoms in the bridge, none of these carbon atoms carrying substituents that may cause steric hindrance and in which R1, R², R3 and R⁴ are identical or different hydrocarbyl groups. In the examples the divalent bridging group R is a 1,3-propane or 1,4-butane group. However, in those examples of EP-A-121965 in which the copolymer' s molecular weight was determined it was lower than desirable for many applications. Moreover, the polymerisation rates obtained still leave substantial room for further improvements. These comments apply particularly to the single example, test 16, which employed a nickel containing catalyst.

A third patent application which exemplifies a nickel containing catalyst is EP-A-470759. This discloses the use of catalysts based on nickel complexed with a mercaptocarboxylic acid. From the working examples in the latter application it can be comprehended that the polymerization rates achieved were again low.

A fourth patent application which exemplifies nickel containing catalysts is WO 97/00127. In this case more promising nickel containing catalysts were found. They were based upon (a) a source of nickel cations, and (b) a bidentate ligand of the general formula R¹R²M¹-R-M²R³R⁴ wherein M^- and M² represent independently phosphorous, nitrogen, arsenic or antimony, Rl, R², R3 _and R⁴ represent independently optionally substituted hydrocarbyl groups on the understanding that at least one of R¹, R², R3 and R⁴ represents a substituted aryl group, and R represents a bivalent bridging group of which the bridge consists of at most two bridging atoms. The reason for the requirement that at least one of Rl, R², R3 _Qr R⁴ represents a substituted aryl group can be found in the examples; comparison example 2 in which each of Rl, R²,

R or R⁴ represents a phenyl group shows very poor yield of the copolymer.

It is thus believed that whilst there are many prior art documents making mention of nickel in lists of possible catalytic metals, but emphasising and exemplifying palladium, there is little by way of useful practical disclosure of the use of nickel. The single specification which appears to disclose nickel catalysts of apparent practical value is the somewhat restricted disclosure of WO 97/00127.

However, we have now determined further nickel containing catalysts which give good copolymerization rates and/or copolymers of useful molecular weight, of the same order of magnitude as those described in the examples of WO 97/00127. We regard this finding as very surprising, having regard to the prior art, in particular to WO 97/00127 and EP-A-121965. Advantages of this finding are that in a simple and efficient manner copolymers can be prepared using a further cyanide free, non-plating metal containing catalysts. Further, the copolymers thus prepared can have a very low content of catalyst remnants and a good colour performance. The copolymers are in principle free of cyanides. Accordingly the invention relates to a catalyst composition which is based upon

(a) a source of nickel cations and

(b) a bidentate ligand of the general formula _R1_R2_M1-_R-M R3R4 (I) wherein M^- and M² represent independently phosphorous, nitrogen, arsenic or antimony, R^, R², R3 and R⁴ independently represent optionally substituted aliphatic or alicyclic groups, and R represents a bivalent bridging group of which the bridge which extends directly between the atoms M^- and M² consists of at most two bridge atoms.

The invention also relates to a process for the preparation of copolymers of carbon monoxide and an olefinically unsaturated compound comprising contacting the monomers in the presence of a catalyst composition according to this invention.

In addition this invention relates to a linear copolymer of carbon monoxide and an olefinically unsaturated compound which copolymer comprises nickel in a quantity of up to 500 ppmw relative to the weight of the copolymer and which copolymer is free or substantially free of palladium.

As the source of nickel cations conveniently a nickel salt, such as a nickel (II) salt, is used. Suitable salts include salts of mineral acids such as sulphuric acid, nitric acid, phosphoric acid and sulphonic acids, and organic salts, such as nickel acetylacetonate . Preferably, a nickel salt of a carboxylic acid is used, for example a carboxylic acid with up to 8 carbon atoms, such as formic acid, acetic acid, trifluoroacetic acid, trichloroacetic acid, propionic acid and citric acid. Other preferred nickel salts are nickel halogenates, such as nickel (II) bromide and nickel (II) iodide. Nickel (II) acetate represents a particularly preferred source of nickel cations. Another very suitable source of nickel cations is a compound of nickel in its zero-valent state, i.e. nickel (0), complexed with an organic ligand, such as a diene or a phosphene . Examples of complexes are nickel (0) tetracarbonyl, nickel (0) bis ( triphenyl- phosphine)- dicarbonyl and nickel (0) dicyclooctadiene, from which cationic species may be formed by reaction, e.g., with a strong acid, such as acids as defined herein, e.g. trifluoroacetic acid.

In the ligands of formula (I) M^ and M² preferably represent phosphorous atoms. When any or all of R¹, R², R³ and R⁴ represent optionally substituted aliphatic groups suitable aliphatic groups include alkyl and alkenyl groups. Suitably such groups have up to 20 carbon atoms, preferably 2-12 carbon atoms, most preferably 3-8 carbon atoms.

In addition to hydrogen and carbon atoms aliphatic groups may contain heteroatoms, for example sulphur, oxygen or nitrogen atoms, either as substituents of the aliphatic group or as atoms in the backbone of the chain. When present there may suitably be 1-3 heteroatoms.

Preferably there are no heteroatoms in the backbone of the chain of aliphatic groups R¹, R², R , or R⁴.

Preferred aliphatic groups are branched.

Preferred aliphatic groups are alkyl groups, especially branched alkyl groups, for example t-butyl and i-butyl .

Suitable substituents of aliphatic groups include halogen, especially fluorine, chlorine or bromine atoms, and nitro, cyano, hydroxyl, C__4 alkoxy, C_]__4 haloalkoxy, (^cl-4 alkoxy) carbonyl groups, amino, C]__4 alkylamino, di(Cι__4 alkyl) amino groups and phenyl groups (whereby groups Rl, R², R3 and R⁴ may be aralkyl, for example benzyl, groups). When an aliphatic group is substituted 1-3 substituents may suitably be present. It is preferred, however, that aliphatic groups are unsubstituted.

By alicyclic we mean having a ring or rings of atoms but not being an aryl or heteroaryl group, for example phenyl, naphthyl, phenanthrenyl, pyridyl, pyrollyl, furyl or thienyl . More generally we may define an alicyclic group as a group comprising a ring or rings of atoms but not complying with Hϋckel's rule (that is, not having 4n+2 π electrons where n is an 0 or an integer) .

When any or all of R¹, R², R³ or R⁴ represent optionally substituted alicyclic groups suitable alicyclic groups include cycloalkyl and cycloalkenyl groups. They may be single rings or polycyclic systems. Suitably such groups have 3-20 ring atoms, preferably 3-14 ring atoms, most preferably 6-12 ring atoms. In addition to hydrogen and carbon atoms alicyclic groups may contain heteroatoms, for example sulphur, oxygen or nitrogen atoms, either as substituents of the alicyclic group or as ring atoms. When present there may suitably be 1-3 heteroatoms. Preferably there are no heteroatoms present as ring atoms of such alicyclic groups .

Preferred alicyclic groups are cycloalkyl groups, especially cyclohexyl, cyclooctyl and norbornyl .

Suitable substituents of alicyclic groups include Cχ_4 alkyl, C2-4 alkenyl and Cχ_4 haloalkyl groups, halogen, especially fluorine, chlorine or bromine atoms, and nitro, cyano, hydroxyl, C _4 alkoxy, Cχ_4 haloalkoxy,

(Cχ_4 alkyl) carbonyl, (C _4 alkoxy) carbonyl groups, amino, C _4 alkylamino or di(Cχ_4 alkyl) amino groups. When an alicyclic group is substituted 1-3 substituents may suitably be present. It is preferred, however, that alicyclic groups are unsubstituted.

Conveniently R^ or R² are identical to each other, but this is not essential. Conveniently R3 and R⁴ are identical to each other, but this is not essential.

Conveniently R^- and R are identical to each other, but this is not essential.

Conveniently R² and R⁴ are identical to each other, but this is not essential. Thus, preferably R¹, R², R³ and R⁴ are all identical groups .

The bridging group R of the ligands of formula (I) has two bridge atoms (by which we mean atoms in the direct chain between the atoms M^ and M² ) , preferably both carbon atoms. However, in total the bridging group R preferably has up to 10 carbon atoms, and, optionally, one, two or three heteroatoms, such as silicon, oxygen or nitrogen atoms. The bridging group R may be aliphatic, olefinic or aromatic of nature. However, it is preferably a 1,2-alkylene group, for example a 1, 2-propylene, a 2,3-butylene group or a 1, 2-cyclohexylene group. R represents most preferably an ethylene group (-CH2-CH2-) • The amount of bidentate ligand supplied may vary considerably, but is usually dependent on the amount of nickel present in the catalyst composition. Preferred amounts of bidentate ligands are in the range of from 0.1 to 8, more preferably in the range of from 0.5 to 2 moles per gram atom of nickel, most preferably 1.0-1.5 moles per gram atom of nickel.

The nickel containing catalyst compositions may be based on another additional component which functions during the copolymerization as a source of anions which are non- or only weakly co-ordinating with nickel under the conditions of the copolymerization. Typical additional components are, for example, protic acids, salts of protic acids, Lewis acids, acids obtainable by combining a Lewis acid and a protic acid, and salts derivable from such combinations. Suitable are strong protic acids and their salts, which strong protic acids have in particular a pKa of less than 6, more in particular less than 4, preferably less than 2, when measured in aqueous solution at 18 °C . Examples of suitable protic acids are the above mentioned acids which may also participate in the nickel salts, e.g. perchloric acid and trifluoroacetic acid. Other suitable protic acids are adducts of boric acid and 1,2-diols, catechols or salicylic acids. Salts of these adducts may be used as well. Suitable Lewis acids are, for example, BF3, SnCl2,

SnF2, AIF3, ASF5, Sn(CF3S03)2, Sn(CH3S03)2, and also hydrocarbylboranes, such as triphenylborane, tris-

(perfluorophenyl) borane and tris [bis-3, 5- (trifluoro- methyl) phenyl] borane . Protic acids with which Lewis acids may be combined are for example sulphonic acids and hydrohalogenic acids, in particular HF. A very suitable combination of a Lewis acid with a protic acid is tetrafluoroboric acid (HBF4) or hexafluorophosphoric acid

(HPFg) . Other compounds which function during the copolymerization as a source of anions which are non- or weakly co-ordinating with nickel are salts which contain one or more hydrocarbylborate anions or carborate anions, such as sodium tetrakis [bis-3, 5- (trifluoromethyl) - phenyl] borate, lithium tetrakis (perfluorophenyl) borate .and cobalt carborate (Co (Bχ CH 2) 2' • Again other compounds which may be mentioned in this context are aluminoxanes, in particular methyl aluminoxanes and t-butyl aluminoxanes.

The amount of the additional component which functions during the copolymerization as a source of anions which are non- or only weakly co-ordinating with nickel is preferably selected in the range of 0.1 to 50 equivalents per gram atom of nickel, in particular in the range of from 0.5 to 25 equivalents per gram atom of nickel. However, the aluminoxanes may be used in such quantity that the molar ratio of aluminium to nickel is in the range of from 4000:1 to 10:1, preferably from 2000:1 to 100:1.

The amount of catalyst composition used in the process of the invention may vary between wide limits. Recommended quantities of catalyst composition are in the range of 10-^ to 10^~2, calculated as gram atoms of nickel per mole of olefinically unsaturated compound to be copolymerised with carbon monoxide. Preferred quantities are in the range of 10^"^ to 10^"3 on the same basis. The performance of nickel containing catalyst compositions in the copolymerization process may be improved by introducing an organic oxidant, such as a quinone or an aromatic nitro compound. Preferred oxidants are quinones selected from the group consisting of benzoquinone, napththoquinone and anthraquinone. When the process is carried out as a gas phase process, the quantity of oxidant is advantageously in the range of from 1 to 500, preferably in the range of from 1 to 100 mole per gram atom of nickel.

The copolymerization process is usually carried out at a temperature between 20 and 200 °C, preferably at a temperature in the range of from 30 to 150 °C, and usually applying a pressure between 0.1 and 20 MPa, pressures in the range of from 1 to 10 MPa being preferred. Olefinically unsaturated compounds which can be used as monomers in the copolymerization process of the invention include compounds consisting exclusively of carbon and hydrogen and compounds which in addition comprise hetero atoms, such as unsaturated esters, ethers and amides. Unsaturated hydrocarbons are preferred.

Examples of suitable olefinic monomers are lower olefins, such as ethene, propene and butene-1, cyclic olefins such as cyclopentene, aromatic compounds, such as styrene and α-methylstyrene and vinyl esters, such as vinyl acetate and vinyl propionate. Preference is given to mixtures of ethene with another olefinically unsaturated compound, in particular an α-olefin, such as butene-1, or, especially, propene, and, especially, to ethene as the sole olefinically unsaturated compound. The term "lower" used in this document to specify an organic compound has the meaning that the organic compound contains up to 6 carbon atoms .

Generally, the molar ratio of on the one hand carbon monoxide and on the other hand the olefinically unsaturated compound (s) used as monomer is selected in the range of 1:10 to 10:1. Preferably the molar ratio is in the range of 1:5 to 5:1, more preferably in the range 1:2 to 2:1. Substantially equimolar ratios are most preferred. Hydrogen may be present in processes employing the catalyst compositions of the invention. Hydrogen may act as a chain transfer agent and so play a part in controlling the molecular weight of the copolymers formed. However, hydrogen is not needed for a reaction to take place with good yield. Accordingly, for simplicity at least it is preferred in many embodiments to employ the catalyst compositions in such processes in the absence of hydrogen.

The process of the invention is conveniently carried out in the presence of a diluent. Preferably a diluent is used in which the copolymers are insoluble or virtually insoluble so that they form a suspension upon their formation. Aromatic solvents, such as alkylbenzenes, for example toluene and xylenes, may be used. Halogenated alkanes may be used, for example dichloromethane .

Recommended diluents are polar organic liquids, such as ketones, for example acetone, and ethers, esters or amides. Protic liquids are favoured for many embodiments, for example monohydric and dihydric alcohols, in particular alcohols having at most 4 carbon atoms per molecule, such as methanol and ethanol . Protic liquids may advantageously contain a minor quantity of water, for example 0.1-10 %vol, preferably 0.2-5 %vol, based on the total volume of the protic liquid. The process of this invention may also be carried out as a gas phase process, in which case the catalyst is typically used deposited on a solid particulate material or chemically bound thereto. The process may also be carried out as an emulsion polymerisation reaction.

When a diluent is used in which the formed copolymer forms a suspension it is preferred to have a solid particulate material suspended in the diluent before the monomers are contacted with the catalyst composition. Suitable solid particulate materials are silica, polyethene and a copolymer of carbon monoxide and an olefinically unsaturated compound, preferably a copolymer which is based on the same monomers as the copolymer to be prepared. The quantity of the solid particulate material is preferably in the range of from 0.1 to 20 g, particularly from 0.5 to 10 g per 100 g diluent. The copolymers can be recovered from the polymerization mixture by using conventional techniques. When a diluent is used the copolymers may be recovered by filtration or by evaporation of the diluent. The copolymer may be purified to some extent by washing. Copolymers are suitably prepared in which the units originating from carbon monoxide on the one hand and the units originating from the olefinically unsaturated compound (s) on the other hand occur in an alternating or substantially alternating arrangement. The term "substantially alternating" will generally be understood by the skilled person as meaning that the molar ratio of the units originating from carbon monoxide to the units originating from the olefinically unsaturated compound (s) is above 35:65, in particular above 40:60. When the copolymer ratio is 50:50, as is preferred, the copolymers are believed to be perfectly alternating.

A high Limiting Viscosity Number (LVN) , or intrinsic viscosity, of the copolymers is indicative of a high molecular weight. The LVN is calculated from determined viscosity values, measured for different copolymer concentrations in m-cresol at 60 °C . It is preferred to prepare copolymers having an LVN in the range of from 0.1 to 10 dl/g, in particular from 0.2 to 8 dl/g, more preferably from 0.5 to 6 dl/g, and especially 0.6 to 3 dl/g. It is also preferred to prepare copolymers which have a melting point above 150 °C, as determined by

Differential Scanning Calorimetry (DSC) . For example, linear copolymers of carbon monoxide and ethene and linear copolymers of carbon monoxide, ethene and another α-olefin which are alternating or substantially alternating fall into this category.

Furthermore, for practical reasons the nickel content of the copolymers will typically be above 0.01 ppmw, relative to the weight of the copolymer. It is preferred to prepare copolymers which have a nickel content in the range of from 0.05 to 300 ppmw, in particular from 0.1 to 200 ppmw, relative to the weight of the copolymer. The copolymers are preferably substantially free, and more preferably entirely free, of palladium. "Substantially free of palladium" means to the skilled person that the palladium content is lower than the value normally achieved when a palladium based catalyst is employed in the copolymerization, for example less than 1 ppmw, in particular less than 0.1 ppmw, relative to the weight of the copolymer. Alternatively it is preferred that, if palladium is present, the weight ratio of palladium to nickel is less than 1:50, especially less than 1:100, most preferably less than 1:200.

Preferably the copolymers are entirely free or substantially free of inorganic cyanides. Substantially free of organic cyanides may be considered copolymers of which the content of inorganic cyanide, measured as the weight of CN, is less than 10 ppm, especially less than 1 ppm, most preferably less than 0.1 ppm, relative to the weight of the copolymer. The copolymer' s content of cyanide can be determined by bringing the cyanide into an aqueous solution, for example by dissolving the copolymer in a suitable polar solvent, such as hexafluoroiso- propanol, and adding water, after which the cyanide content of the aqueous solution can be determined using standard methods. The process of the invention may be carried out as a batch process or as a continuous process.

The invention is illustrated by the following examples of the preparation of linear alternating carbon monoxide/olefin copolymers. Example 1

A carbon monoxide/ethene copolymer was prepared as follows .

A stirred 200 ml autoclave was dried overnight at 100 °C at a reduced pressure. After cooling down to ambient temperature the autoclave was pressurised 3 times with 70 bar of nitrogen, each time followed by release of the pressure. The autoclave was then charged with a catalyst solution consisting of 50 ml of methanol, 0.1 mmol of [1, 2-bis (dicyclohexylphosphino) ethane] nickel (II) dimethyl and 0.1 mmol of trifluoromethane- sulfonic acid.

The catalyst solution was prepared separately in a Schlenk flask under nitrogen and transferred to the autoclave with a syringe while slowly purging the autoclave with nitrogen. The autoclave was then pressurized with carbon monoxide to 5 bar and additionally with 40 bar of ethene, i.e. a total of ethene and carbon monoxide of 45 bar. Subsequently the autoclave was heated to 80 °C . The autoclave was then pressurised 8 times at intervals of 0.05 hrs with 5 bar additional carbon monoxide. After 0.5 hrs the polymerization was terminated by cooling to ambient temperature and subsequently releasing the pressure. The copolymer was recovered by filtration, washing with methanol and drying at 60°C in nitrogen at a reduced pressure . The yield was 24.4 g of a copolymer having an LVN of 0.8 dl/g, which corresponds to a number average molecular weight of 12000. Example 2 A carbon monoxide/ethene copolymer was prepared as follows :

A 250 ml Hastelloy C (Trademark) autoclave was charged with a catalyst solution of 50 ml methanol containing 0.1 mmol nickel (II) acetate, 0.12 mmol 1, 2-bis (dicyclohexylphosphino) ethane and 1.0 mmol trifluoroacetic acid.

The air in the autoclave was removed by evacuation and subsequently pressurized by 20 bar of ethene, 20 bar of carbon monoxide and 5 bar of hydrogen. The autoclave was heated to 85 °C and kept at that temperature for

1.5 hr. The autoclave was cooled to ambient temperature and the pressure was released. The copolymer was recovered by filtration and dried. The yield of copolymer was 8.8g and its LVN was 1.0 dl/g, which corresponds to a number average molecular weight of 15000. Example 3

Example 2 was repeated with the following differences :

0.12 mmol of 1, 2-bis (diisobutylphosphino) ethane was used instead of 1, 2-bis (dicyclohexylphosphino) ethane and 1.0 mmol tetrafluoroboric acid instead of 1.0 mmol of trifluoroacetic acid. At ambient temperature 20 bar of ethene, 5 bar of carbon monoxide, 5 bar of hydrogen and 10 ml of liquid propene were introduced. The autoclave was heated to 75 °C . After 0.25 hr again 5 bar of carbon monoxide was introduced. After 1.5 hr the reactor was cooled to ambient temperature and 6.6 g of copolymer was recovered. The LVN of the copolymer was 1.2 which corresponds to a number average molecular weight of 18000. Propene incorporation was approximately 0.2 wt% of the total weight of the copolymer. Example 4

Example 2 was repeated with the following differences :

0.12 mmol of 1, 2-bis (dinorbornylphosphino) ethane was used instead of 1, 2-bis (dicyclohexylphosphino) ethane and 1.0 mmol of tetrafluoroboric acid instead of 1.0 mmol trifluoroacetic acid. At ambient temperature 30 bar of ethene, 5 bar of carbon monoxide and 5 bar of hydrogen was introduced and the contents were heated to 112 °C . After 0.25 hr a further 10 bar of carbon monoxide was introduced; a further 5 bar of carbon monoxide was admitted after a further 2.25 hr and this was again repeated after a further 0.75 hr. After a total of 4 hrs the autoclave was cooled to ambient temperature and 8.2 g of a white polymer was recovered with an LVN of 0.5 dl/g, which corresponds to a number average molecular weight of 7500. Example 5

Example 3 was repeated with the following differences:

1.0 mmol tetrafluoroboric acid was used instead of 1.0 mmol trifluoroacetic acid. The reactor was pressurized by 30 bar of ethene and 10 bar of carbon monoxide and subsequently heated to 85 °C . After 0.25 hrs all carbon monoxide was consumed and the autoclave was cooled to ambient temperature. 5.7 g of ethene/carbon monoxide copolymer was recovered. The LVN was 1.4 dl/g, which corresponds to a number average molecular weight of 21000. Example 6 (for comparison)

A 250 ml Hastelloy C (Trade Mark) autoclave was charged with a catalyst solution of 50 ml methanol containing 0.1 mmol nickel acetate, 0.12 mmol 1,3-bis- (dicyclohexyl-phosphino) propane and 1.0 mmol tetra- fluoroboric acid. The air in the autoclave was removed by evacuation and subsequently pressurized by 30 bar of ethene and 10 bar of carbon monoxide. The autoclave was heated to 85 °C and kept at that temperature for 2 hrs. The autoclave was cooled to ambient temperature and the pressure was released. Only a trace of copolymer had been formed.

Example 7 (for comparison)

Example 6 was repeated with the difference that 5 bar of hydrogen was additionally present. Only a trace of copolymer was formed. Example 8

Example 2 was repeated with the difference that 0.12 mmol of 1, 2-bis (diethylphosphino) ethane was used instead of 0.12 mmol of 1,2- bis (dicyclohexylphosphino) ethane. The yield of ethene/carbon monoxide copolymer after

6 hours at 85 °C was 3.1 g.

In all of the Examples in which LVN was determined, it was determined in m-cresol as solvent at 60 °C .

Claims

C L A I M S

1. A catalyst composition which is based upon

(a) a source of nickel cations and

(b) a bidentate ligand of the general formula

_R1_R2_M1__R__M2_R3_R4 (x) wherein M^ and M² represent independently phosphorous, nitrogen, arsenic or antimony, R1, R², R3 and R⁴ independently represent optionally substituted aliphatic or alicyclic groups, and R represents a bivalent bridging group of which the bridge which extends directly between the atoms M¹ and M² consists of at most two bridge atoms .

2. A catalyst composition as claimed in claim 1, characterized in that the source of nickel cations comprises a nickel salt or a compound of nickel (0) complexed with an organic ligand.

3. A catalyst composition as claimed in claim 1 or 2, characterized in that M^ and M² represent phosphorous atoms . . A catalyst composition as claimed in any preceding claim, characterized in that R¹, R², R³ and R⁴ independently represent an optionally substituted alkyl, alkenyl, cycloalkyl or cycloalkenyl group having up to 20 carbon atoms.

5. A catalyst composition as claimed in claim 4, characterized in that at least one of R¹, R², R³ and R⁴ represents a branched C3_g alkyl group.

6. A catalyst composition as claimed in claim 4, characterized in that at least one of R¹, R², R3 and R⁴ represents a cycloalkyl group having 3-14 ring atoms. 7. A catalyst composition as claimed in any of claims 1-6, characterized in that the bivalent bridging group R is a 1,2-alkylene group, preferably an ethylene group.

8. A process for the preparation of copolymers of carbon monoxide and an olefinically unsaturated compound comprising contacting the monomers in the presence of a catalyst composition as claimed in any of claims 1-7.

9. A process as claimed in claim 8, characterized in that the olefinically unsaturated compound is an unsaturated hydrocarbon, especially ethene. 10. A process as claimed in claim 8 or 9, characterized in that the contacting is carried out in a diluent in which the copolymers are insoluble or virtually insoluble, such as methanol or ethanol, so that they form a suspension upon their formation, using such an amount of the catalyst composition that the amount of nickel present is in the range of from 10-^ to 10^~2 gram atom, preferably 10^~' to 10^~3 gram atom, per mole of olefinically unsaturated compound to be copolymerized, and applying a molar ratio of carbon monoxide to the olefinically unsaturated compound (s) in the range of from 1:5 to 5:1, preferably from 1:2 to 2:1, a temperature between 20 and 200 °C, in particular between 30 and 150 °C, and a pressure between 0.1 and 20 MPa, in particular between 1 and 10 MPa. 11. A linear copolymer of carbon monoxide and an olefinically unsaturated compound prepared by a process as claimed in any preceding claim, which copolymer comprises nickel in a quantity of up to 500 ppmw relative to the weight of the copolymer and which copolymer is free or substantially free of palladium.

12. A copolymer as claimed in claim 11, characterized in that the copolymer has a nickel content in the range of from 0.05 to 300 ppmw, in particular from 0.1 to 200 ppmw, relative to the weight of the copolymer. 13. A copolymer as claimed in claim 11 or 12, characterized in that if palladium and/or inorganic cyanide are present, the content of palladium is less than 1 ppm and the content of inorganic cyanide is less than 10 ppm, calculated as with weight of CN, both contents being relative to the weight of the polymer. 14. A copolymer as claimed in any of claims 11-13, characterized in that the copolymer is a linear alternating copolymer of carbon monoxide and ethene or a linear alternating copolymer of carbon monoxide, ethene and another -olefin.