GB2045779A - Copolymerisation of ethylene and a di- or polyunsaturated hydrocarbon - Google Patents

Abstract

Ethylene is copolymerised with a polyunsaturated hydrocarbon, e.g. butadiene, using a catalytic system comprising (a) an organometallic compound of a metal of Group III of the Periodic Table, preferably aluminium, and (b) a component which is obtained by reacting magnesium or manganese vapour with a titanium compound and a halogen donor.

Description

SPECIFICATION Process for the copolymerisation of ethylene with polyunsaturated hydrocarbons This invention relates to a process for the preparation of copolymers of ethylene (or ethylene and one or more alpha-olefins) and a compound containing two or more unsaturated olefinic bonds, which compound can be conjugated. The copolymers obtained by the copolymerisation of ethylene alone with the polyunsaturated compound are in the form of crystalline polymers.

We are aware of various processes for preparing crystalline copolymers by the polymerisation of ethylene with a conjugated or non-conjugated polyolefin, in particular butadiene and ethylidenenorbonene (see for example, British Patent Specification No. 1,519,472 and 1,519,474 and British Patent Applications Nos. 28622/77, 7935802 and 7935803).

These processes are based on vanadium-based coordinated anionic catalysts which, although giving high polymerisation yields, do not attain catalytic activity levels such as to obviate the need for the difficult purification of the copolymer from the transition metal residues, which residues damage the oxidation stability of the copolymer and produce an undesirable colour.

We are also aware of British Patent Application No. 3437/77, Serial No. 1576431 which relates to a catalytic composition which is extremely active in polymerising and copolymerising mono-a-olefins, and is prepared by reacting an organometallic compound of Group Ill of the Periodic Table with a composition prepared by (i) vaporising or subliming magnesium in vacuo, and (ii) condensing the vapour into a condensed phase comprising a titanium tetrahalide and a halogen donor.The application states that the activity of the catalytic composition in the homopolymerisation and copolymerisation of a-olefins is extremely high when the quantity of magnesium metal vaporised is such as to give an atomic Mg:Ti ratio greatly exceeding 0.5 in the condensed phase, and there is present a compound which is able to yield halogen to the magnesium metal in excess of the atomic Mg:Ti ratio of 0.5 corresponding to the complex MgX2.2TiX3 (X=halogen). In this manner, there is further formation of MgX2, which interacts with the stoichiometric compled to give a new and more active complex containing titanium.

We have now discovered that by suitably modifying the magnesium vaporisation conditions and choosing the reagents and reaction conditions, it is possible to copolymerise ethylene, either alone or in admixture with other a-olefins, with a compound containing one or more unsaturated olefinic bonds to give copolymers (which are highly crystalline copolymers if ethylene is used alone). Manganese, in addition to magnesium, can be used for preparing the catalytic system.

According to the present invention, there is provided a process for the copolymerisation of ethylene (or ethylene and one or more a-olefines) with a polyunsaturated hydrocarbon containing conjugated or non-conjugated unsaturated bonds, which process comprising copolymerising the ethylene, the polyunsaturated hydrocarbon and, if used, the a-olefin(s) in the presence of a catalytic system comprising (1 ) a component prepared by reacting magnesium vapour or manganese vapour with a titanium compound and a halogen donor, and (2) an organometallic compound of aluminium or other Group Ill element.

The activity of the catalytic system is usually such as to produce a quantity of copolymer, per gram of titanium, of at least 50 kg. Component (1 ) of the catalytic system may be prepared by vaporising the magnesium or manganese, either in their metallic state or in the form of one of their alloys, and condensing the vapour into a cold solution prepared by dissolving a titanium compound and a halogen donor in an inert diluent. The metal can be used in powder form, in the form of granules or in lumps, and is preferably vaporised under vacuum by sublimation. In the case of magnesium, for a pressure of from 2 to 10-4 Torr, the temperature varies, as a function of the pressure, between about 650 and 300"C. Manganese may require more severe conditions, e.g. 800-100"C at 1 of1 to 10-4 Torr.If the operation is carried out at a higher temperature, the metal can be vaporised from its molten state even at atmospheric pressure. The solution into which the vapour is condensed is usually kept stirred at a low temperature. Depending upon the solvent used, this temperature is usually from -120 to 0 C, and generally -80 to -20 C. The use of an inert diluent selected from low volatility hydrocarbon solvents of low freezing point (e.g. n-heptane, n-octane and toluene) is not necessary, as the reaction can be carried out even within the titanium compound and the halogen donor in their pure state.

Titanium tetrachloride is a liquid titanium compound preferred for this purpose, and alkyl halides are preferred as the halogen donors, their measured excess then constituting the reaction medium. Examples of alkyl halides which can be used are 1-chiorobutane, 1-chlorohexane and 1bromohexane, but secondary or tertiary alkyl halides and aryl or alkylaryl halides are also reactive. The most suitable inorganic halides are SnC14, SbCI5, GeCI4 and POCI3.

With regard to the titanium compounds, in addition to the tetrachloride, effective use can be made of other halides (including trivalent halides), alcoholates, halogen alcoholates, chelates and all organometallic derivatives. In practice, any titanium compound can be used, the difference between them being only the rate of reaction.

In order to prepare extremely active catalytic systems, the M:Ti ratio (wherein M is Mg or Mn) exceeds 0.5:1, and in particular is equal to or greater than 4:1. The preferred value for this ratio is from 15:1 to 30:1, and a further excess of M does not give rise to any advantage.

The quantity of the halogen donor present in the reaction may be adjusted according to the quantity of M used, with respect to which it is preferably present in a ratio greater than or equal to 2:1 in the case of mono-halogenated organic compounds, and greater than or equal to 1:1 in the case of inorganic compounds able to yield more than one halogen atom per molecule.

The reaction between the M vapour, the titanium compound and the halogen donor partly takes place at the aforesaid low temperature. For its completion, it is preferred to use either a long period (some days) of standing at ambient temperature, or heating for a few hours (1-5), depending upon the chosen temperature (50-180"C). The reaction is faster when the halogen donor is inorganic.

The halogen donor is not strictly required to be present in the low temperature-maintained solution into which the metal vapour is condensed. It can be added later, but before the solution is raised to a higher temperature for completing the reaction.

The fine suspension prepared as heretofore described is usually used directly as a catalytic component for the copolymerisation, provided neither any excess of one of the reagents nor any reaction by-products substantially constitute disturbing agents in the formation of the catalyst. Alternatively, the suspension can be filtered and the solid resuspended in the dispersing agent considered most suitable, generally the same as that in which the copolymerisation is carried out. Again, the solid compound can be dispersed on an inert solid support, constituted for example by the actual polymer which is to be produced.

As stated, the other catalytic component is an organometallic compound of an element of Group Ill of the Periodic Table. Aluminium is generally used for reasons of effectiveness and convenience. Examples of such compounds are trialkyl and triaryl aluminium compounds such as Al(C2H5)3, Al(i-C3H7)3 and Al(C5H5)3, alkylaluminium hydrides such as Al(H)(i-C3H7)2, and alkyl and arylaluminium halides such as Al(C2H5)2CI and Al(C2H5)CI2. Trialkyl derivatives are preferred, these derivatives also being very effective in mixture with halogenated derivatives.

The molar ratio of the organometallic compound to the titanium compound preferably exceeds 3:1 in order to attain maximum specific activity. For practical reasons, the ratio is very high, for example from 100:1 to 500:1, due to the fact that extremely small quantities of the titanium compound are used in the copolymerisation.

The copolymerisation process according to the present invention is preferably a copolymerization of ethylene with a conjugated or non-conjugated polyolefin, using the aforesaid catalytic components in the presence of an inert diluent, and using a temperature of from 40 to 1 200C and a pressure of from 1 to 20 kg/cm2. In batch processes, the reagents may be fed into the reactor such that the catalyst either forms in the presence of the mixture of the two monomers or comes into contact with it. In practice, there are two methods of operation, both of which are effective. In the first, the catalytic component containing the titanium is introduced last, while in the second the reaction between the catalytic components to be added successively to the monomer mixture is carried out separately.In this latter case, there is a precontact time which, although not critical, should not be very prolonged, in particular when the Al :Ti ratio is high.

Aliphatic hydrocarbons are preferably used as the inert diluents. However, the presence of a diluent is not strictly necessary during the copolymerisation, as it is possible to operate in the gaseous state by introducing the catalyst dispersed in a small quantity of the low boiling solvent.

The monomers which we have chosen for exemplifying the copolymerisation are those listed below.

The conditions detailed heretofore are absolutely general, and all types of ethylene copolymers can be prepared by applying the method of the present invention on the basis of the detailed teachings for the copolymers listed hereinafter. The person skilled in the art will be able to choose the most suitable operating conditions in relation to the required copolymer.

The monomers are ethylene on the one hand, and a cyclic or alicyclic hydrocarbon containing more than one unsaturated bond, which can be conjugated, on the other. Examples of such hydrocarbons preferred for their reactivity and low cost are 1,3butadiene and 5-ethylidene-(2.2.1)-dicyclohepta-2- ene (i.e. ethylidenenorbonene). They have a reactivity in copolymerisation which is less than that of ethylene, because of which they are normally used in excess (50 times or more) with respect to the quantity thereof which it is desired to be present in the copolymer. This excess may be utilised by recycling its solution.

The practically useful ethylene comonomer content ofthe copolymer may be just a few per cent (less than 10 mol %).

The molecular weight of the copolymer can be controlled by introducing hydrogen, in addition to varying the reaction coditions.

The copolymers prepared by the process according to the present invention have properties which depend upon their composition. Ethylene-butadiene copolymers contain trans unsaturated bonds, while cis and vinyl unsaturated bonds are absent or practically absent, as shown by the 1,4-trans addition of the butadiene units. Ethylenebutadiene copolymers rich in ethylene are usually characterised by densities between 0.940 and 0.960, melting points around 1300C and an unsaturated bond distribution (as shown by the accompanying drawing which is the 13C-NMR spectrum of a copolymer containing 12.3 mol % of butadiene) in which three peaks, attributable to differently structured butadiene units along the polymer chain, can be seen, i.e.

peaks attributable to methylene groups in the butadiene units at a (32.6ppm) b (32.7 ppm) and c (32.9 ppm). It should be noted that analogous copolymers prepared by the prior art have only two of the said three peaks in their 13C-NMR spectrum.

It is known that crystalline poly-a-olefins such as polyethylene, isotactic polypropylene and isotactic polybutene, have been available commercially for some time. These poly-a-olefins are either homopolymers or copolymers containing small quantities of a second a-olefin in order to solve certain technical problems. The quantity of the second olefin is normally so low as not to excessively reduce the crystallinitywith respect to the homopolymer, as certain important mechanical characteristics such as modulus and ultimate tensile strength are associated with the high crystaliinity.

The copolymers of ethylene and butadiene, the compatibility of units of the two types in the same crystai enables substantially crystalline polymers to be obtained over the entire range of composition from pure polyethylene to pure trans-po lybutadiene.

In this case, there is therefore not the limitation, which exists in the case of copolymers of mono-aolfins, that the olefin must be present in a very small quantity in the copolymer in order to maintain the crystallinity at a high level. An extremely important advantage of the copolymers prepared according to the process of the present invention is the fact that they contain unsaturated bonds (either in the main chain as in the case of, for example, butadiene, or in the side chains as in the case of, for example, ethylidenenorbonene). By means of these unsaturated bonds, the copolymer can be easily crosslinked (with sulphur or other reagents) to further improve its technical characteristics such as thermal resistance, impact strength and resistance to agents which induce the formation of environmental stress cracking.The unsaturated bonds also allow certain transformations which would otherwise be difficult if not impossible, such as foaming and thermoforming of sheets.

The invention will now be illustrated by the following Examples.

Example 1 A catalytic component containing titanium was prepared in a 1 litre horizontally disposed rotating glass flask, at the centre of which was placed an aluminium crucible heated electrically by means of a tungsten filament. In the flask, 240 ml of n-heptane and 0.2 ml of TiCI4 were places, and 0.9 g of magnesium shavings were placed in the crucible.

The solution was cooled to -70 C. After reducing the pressure in the flask to 10-3 Torr, the crucible was heated by applying, across the ends of the filament, an electrical voltage of sufficient intensity to heat it to red heat. Vaporisation of the magnesium led to the formation of a brown suspension, to which 8.2 ml of n-butyl chloride were added after releasing the vacuum by introducing nitrogen. The suspension was then heated for 3 hours at 80"C, using a reflux condenser.

A stainless steel autoclave having a capacity of 5 litres and fitted with a mechanical stirrer and controlled electrical heating device was put under vacuum, and the following solution was then introduced by suction: anhydrous n-heptane 2200 ml butadiene 200 9 Al(C2H5)3 - 15 mmol15 mmol The temperature of the autoclave was controlled at70 C, and hydrogen and ethylene at partial pressures of 3.5 and 4.5 kg/cm2, respectively, were then introduced. A quantity of 10 ml of the heptane suspension prepared as described above and containing 0.075 mmol of titanium was fed into the autoclave, at an ethylene overpressure, using a 100 ml steel phial provided with a feed valve and discharge valve.A solution of Al(C2H5)CI2 (7.5 mmol) in heptane (50 ml) was then added to the mixture present in the autoclave, using a piston pump, during the first five minutes of reaction. An immediate absorption of ethylene was observed. Ethylene was fed in continuously so as to maintain constant the initial pressure, the temperature being kept at 70 C. After 3 hours it was found that the ethylene was still being absorbed at an intensity approximately equal to the initial intensity. The reaction was however interrupted, and the suspension contained in the autoclave was discharged and filtered. There were obtained 388 g of dry polymer having a melt flow index MFI12.16 of 49.5, a butadiene unit content of 3.3 mol % and a melting point (Tm), determined by differential thermal analysis, of 131 C.

The polymer, which had the appearance of a white solid very similar to the appearance of polyethylene, was mixed with the following compounds (grams per 100 g of polymer): zinc oxide................................... oxide 5 g stearic acid ........................................ 1 g 2,2'-methylene-bis(4-methyl-terbutylphenol) (A.O.2246) 1 g N-oxydiethylbenzothioazole-2-sulphenamide (NOBS special) 1.5 9 dibenzothiazyl disulphide (Vulkacit DM) .............0.5 0.5 9 sulphur 3 9. 3g.

The mixture was treated in a press at 180 for 30 minutes to give a product leaving 40% of residue after extraction with boiling xylols (the polymer as such was completely soluble).

Example 2 A reaction was carried out at 850C using the autoclave and method described in Example 1. In this case, the partial pressures of ethylene and hydrogen were 5 and 3 kg/cm2 respectively, and 250 g of butadiene were introduced. All of the other quantities were as in Example 1.

After 3 hours of polymerisation, there were obtained 250 g of dry copolymer having a butadiene unit content of 3.3 mol %, a melt flow index MFl2.16 of 0.84, a melt flow index ratio MFI216/MFI2.16 of 32.5:1, a melting point of 129 C, and an impact strength of 13.7 kg/cm2.

When cross-linked as described in Example 1,the product obtained has an impact strength of 50.4 kg/cm2.

Example 3 A polymerisation reaction was carried out employing the same apparatus and method of the preceding Examples, using the following reagents: n-heptane ........................................ 1840 ml butadiene ........................................ 102g Al(C2H5)3 .................................. 17.6 mmol H2 -------------------------------- ---- 3.5 kg/cm ethylene ........................................ 5.0 kg/cm2 Ti complex (see Example 1)................. 1) 0.06 mmol.

The autoclave was maintained at 850C both during gas introduction and during polymerisation, in the course of which the consumed ethylene was replaced by fresh ethylene.

After 4 hours the reaction was interrupted, and the product was filtered off and dried to give 285 g of a copolymer having a butadiene unit content of 1.5 mol %, a melt flow index MFl2.16 of 0.99 g/10 min., a melt flow index MF121.6 of 27.4, and a melting point Tm (DSC) of 133 C.

Example 4 A solution prepared from 400 ml of n-heptane and 40 ml of bicyclo-(2.2.1 )-5-ethylidene-2-heptane (ethylidenenorbornene) was drawn into a stainless steel autoclave of the type described in Example 1, but having a capacity of 2 litres. The autoclave was temperature controlled at 85"C, and ethylene and hydrogen were then introduced at partial pressures of 5 and 3 kg/cm2, respectively. A catalyst, consisting of a suspension in heptane of the product obtained by reacting 5 mmol ofAl(i-C4H9)3with 0.012 mmol of titanium in the form described in Example 1 for 60 minutes at ambient temperature, was then introduced using a steel phial and a N2 overpressure. The reaction lasted for one hour, during which the consumed ethylene was made up with fresh ethylene so as to maintain constant its partial pressure.

The solid product obtained by filtering the suspension and drying weighed 35 g. It has an ethylidenenorbornene content of 3.3% by weight, a meitfiow index MFI2.16 of 3.4 9/10 min., a melt flow index MFl21.6 of 33, and a 620 min of 0.9633 g/cm3.

Example 5 A catalytic component containing titanium was prepared in a manner similarto that described in Example 1, but starting from the following reagents: l-chlorooctane 120 ml TiCI4 0.088 ml manganese metal................................... metal 1.5 g.

The solution was cooled to -50 and a vacuum of 10-4Torr was applied, after which the manganese was vaporised and condensed. A dense dark brown suspension was obtained. This suspension was then heated to 100C for one hour. Chemical analysis showed that the homogenised suspension contained 5.10 mmol per litre of Ti, 186.2 mmol per litre of Mn, and 390.0 mmol per litre of Cl.

A copolymerisation reaction between butadiene and ethylene was carried out using the apparatus described in Example 1. The solution fed into the reactor consisted of: n-heptane 2200 ml butadiene 250 g Al(i-C4H9)3 22.5 mmol After controlling the temperature at 85 C, the autoclave was pressurised with 3 kg/cm2 of hydrogen and 5 kg/cm2 of ethylene. Then, 15 cm3 of the suspension containing the titanium complex, prepared as described above, were introduced. Further ethylene was added for 3 hours in order to maintain the pressure at the initial value of 10 kg/cm2 at 85"C, after which the reaction was interrupted, and the product filtered off and dried.There were obtained 200 g of polymer having a 1,4-trans butadiene unit content of 5.15 mol %, a melt flow index MFl2.16 of 0.05 g/10 min., a melting point Tm (DSC) of 132"C, and [rlj (in decalin at 105 ) of 1.75.

Example 6 A catalytic component containing titanium was prepared in an apparatus analogous to that described in Example 1,from: n-octane 300 mi TiC4 ........................................ 0.187 ml SnCI4 8 ml Mg 1.2 9.

The magnesium was vaporised at 5 x 10-2 Torr and condensed into the solution, which was maintained at about -50 C. The suspension obtained was raised to ambient temperature. After 24 hours, the solution above the decanted solid was free from titanium, whereas the homogenised suspension contained 6.32 mmol per litre of Ti, 187 mmol per litre of Mg, 207 mmol per litre of Sn and 863 mmol per litre of CI.

Copolymerisation was carried out in the autoclave described in Example 1 at 85 C, using the same method and the same reagents as Example 5, with the exception of the catalytic component containing titanium, which this time consisted of 11.85 ml of the above suspension. The polymer obtained weighed 180 g and had a melt flow index MFl2.1s of 0.1 g/10 min., a melting point Tm of 131 C (DSC), and a butadiene unit content of 3.3 mol %.

Claims (28)

1. A process for the copolymerisation of ethylene (or ethylene and one or more a-olefins) with a polyunsaturated hydrocarbon containing conjugated or non-conjugated unsaturated bonds, which process comprising copolymerising the ethylene, the polyunsaturated hydrocarbon and, if used, the a-olefin(s) in the presence of a catalytic system comprising (1) a component prepared by reacting magnesium vapour or manganese vapour with a titanium compound and a halogen donor, and (2) an organometallic compound of aluminium or other Group Ill element.

2. A process as claimed in claim 1, component (1) of the catalytic system having been prepared by vaporising magnesium or manganese or an alloy thereof, and by condensing the vapour in a diluent containing the titanium compound and, if desired, the halogen donor,

3. A process as claimed in claim 1 or 2, component (1) of the catalytic system having been prepared by subliming magnesium at a vacuum offrom 2to 10-4 Torr and art a temperature of from 300 to 6500C.

4. A process as claimed in claim 1 or 2, component (1) of the catalytic system having been prepared by subliming manganese at a vacuum of from 10- to 10-4 Torr and at a temperature of from 800 to 1100"C.

5. A process as claimed in any of the preceding claims, component (1) the the catalytic system having been prepared by condensing the metal vapour in an inert solvent selected from aliphatic and aromatic hydrocarbons and maintained at a temperature of from -120to 0 C.

6. A process as claimed in any of the preceding claims, component (1) of the catalytic system having been prepared by a reaction which has been completed at a temperature of from 20 to 1800C.

7. A process as claimed in any of the preceding claims, component (1) of the catalytic system having been prepared by the use of a halide, alcoholate, haloalcoholate or organometallic derivative of trivalent or tetravalent titanium as the titanium compound.

8. A process as claimed in any of the preceding claims, component (1) the catalytic system having been prepared by the use of an organic or inorganic halide as the halogen donor.

9. A process as claimed in claim 8, component (1) of the catalytic system having been prepared by the use of a chloroalkane, bromoalkane, chloroarene or bromarene as the halogen donor.

10. A process as claimed in claim 8 or 9, component (1) of the catalytic system having been prepared by a reaction wherein the molar ratio of the organic halogen donor to the vaporised metal is equal to or greater than 2:1.

11. A process as claimed in claim 8, component (1)of the catalytic system having been prepared by the use of SnCl4, Sic4, GeCI4 or POCI3 as the halogen donor.

12. A process as claimed in claim 10 or 11, component (1) of the catalytic system having been prepared by a reaction wherein the molar ratio of the inorganic halogen donor to the vaporised metal is equal to or greater than 1:1.

13. A process as claimed in any of the preceding claims, component (1) of the catalytic system having been prepared by reacting the vaporised metal with the titanium compound in a metal:titanium ratio equal to or greater than 4:1.

14. A process as claimed in claim 13, component (1) of the catalytic system having been prepared by reacting the vaporised metal with the titanium compound in a metal: titanium ratio of from 15:1 to 30:1.

15. A process as claimed in any of the preceding claims, wherein the copolymerisation is carried out in the presence of an inert solvent.

16. A process as claimed in claim 15, wherein the inert solvent is the same as that in which component (1) of the catalytic system has been prepared.

17. A process as claimed in any of claims 1 to 14, wherein the ethylene, the polyunsaturated hydrocarbon and, if used, the a-olefin are reacted in the gaseous state and in the absence of a solvent.

18. A process as claimed in any of the preceding claims, wherein the catalytic system is disposed on an inert support.

19. A process as claimed in any of the preceding claims, wherein the copolymerisation is carried out at a pressure of from 1 to 30 atmospheres.

20. A process as claimed in claim 20, wherein the copolymerisation is carried out at a pressure of from 1 to 20 atmospheres.

21. A process as claimed in any of the preceding claims, wherein the copolymerisation is carried out at a temperature between ambient temperature and a temperature slightly less than the melting point of the copolymer.

22. A process as claimed in claim 21, wherein the copolymerisation is carried out at a temperature of from 40 to 120"C.

23. A process as claimed in any of the preceding claims, wherein the polyunsaturated hydrocarbon is 1,3 butadiene.

24. A process as claimed in any of claims 1 to 22, wherein the polyunsaturated hydrocarbon is ethylidenenorbornene (i.e. 5-ethylidene (2.2.1)bicylohepta-2-ene).

25. A process for the copolymerisation of ethylene with a polyunsaturated hydrocarbon, substantially as described in any of the foregoing Examples.

26. A copolymer of ethylene and a polyunsaturated hydrocarbon, when prepared by a process as claimed in any of the preceding claims.

27. A copolymer of ethylene, a polyunsaturated hydrocarbon and one or more a-olefins, when prepared by a process as claimed in any of claims 1 to 24.

28. An ethylene-butadiene copolymer having a 13C-NMR spectrum with three peaks at 32.6,32.7 and 32.9 ppm pertaining to the methylene groups of the butadiene units thereof.