GB2099836A - Process for the preparation of ethylene-propylene-1,4-hexadiene terpolymers - Google Patents

Abstract

Ethylene/propylene/1,4- hexadiene terpolymers are prepared by polymerization of a mixture of the three monomers in the presence cf a catalyst comprising: (a) a metalorganic aluminium compound selected from Al- trialkyls and Al-alkyl monohalides; and (b) a titanium halide, in particular a tetrahalide of titanium, supported on an anhydrous magnesium dichloride or magnesium dibromide in activated form, and the X-ray spectrum of which is characterized in that the line of maximum intensity appearing in the spectrum of the Mg-dihalide of normal type is not present and that in its place there is a halo with its maximum intensity displaced with respect to that line. p

Description

SPECIFICATION Process for the preparation of ethylene-propylene-i 4-hexadiene terpolymers The present invention relates to a process for the preparation of ethylene-propylene-l ,4- hexadiene terpolymers, and more particularly to a process for the preparation of elastomeric, vulcanizable terpolymers of ethylene with propylene and 1,4-hexadiene.

It is known to prepare elastomeric terpolymers, vulcanizable with sulphur, of ethylene with propylene and dienic, cyclic or with open chain monomers (such as dicyclopentadiene, ethylidennorbornene, 1,4-hexadiene, butadiene, vinylcyclohexene) by polymerization of mixtures of the three monomers, carried out in the presence of catalysts consisting of a vanadium salt (acetylacetonate, oxychloride) and Al-alkyl compounds.

Preparations of this kind have been described, for example, in U.S. Patent Nos. 3 000 866, 3 063 973 and 3 093 621. The terpolymers thus obtained appear to be completely amorphous, with "green strength" values of from 0 to 60 kg/sq.cm when the content of copolymerized propylene is from 30 to 70% by weight, while they are semi-crystalline, with "green strength" values greater than 60 kg/cm2 when having a content of propylene below 30% by weight.

By using the above-mentioned catalysts it is, however, impossible to obtain terpolymers with a high molecular weight, corresponding to values of [X7] (in tetrahydronaphthalene at 1 250C) equal to 2-3, when the content of propylene in the terpolymer exceeds 50% by weight, and when the preparation is carried out at temperatures greater than room temperature in order to obtain high yields of polymer, and in particular when operating at temperatures greater than 250C.

The present invention provides a process for the preparation of ethylene-propylene-1,4-hexadiene terpolymers, comprising polymerizing a mixture of ethylene, propylene and 1,4-hexadiene in the presence of a catalytic system comprising the following components: (a) a metalorganic aluminium compound selected from one or more Al-trialkyls and Al-alkyl monohalides; and (b) a titanium halide, supported on an anhydrous magnesium dichloride or magnesium dibromide in activated form, wherein the X-ray spectrum of the magnesium dichloride or dibromide is characterized in that the line of maximum intensity appearing in the spectrum of the normal type magnesium dihalide, as defined in ASTM 3-0854 and ASTM 1 5-836, is not present, and that in its place there is a halo with its maximum intensity displaced with respect to the distance dof the said line. The titanium halide is preferably a titanium tetrahalide. In the case of MgCl2, the maximum intensity of the halo is comprisec between d = 2.44 A and 2.97 A. In the case of MgBr2, the maximum intensity of the halo is comprised between d= 2.80 A and 3.24 A.

In general the composition of the component (b) of the catalyst may be expressed as formed by 7090% by weight of Mg dichloride or dibromide, the balance being represented by the Ti-compound.

The component (b) may be prepared according to a variety of methods. One of these comprises bringing the Ti compound into contact with pre-activated Mg halide having the X-ray spectrum characteristics previously specified.

Another method of preparing the component (b), which is also the preferred method, comprises grinding a mixture of Mg halide with the Ti-compound, operating under conditions (grinding time, type of mill) at which in the X-ray spectrum of the ground product there appears the change or modification of the above indicated spectrum.

Still another method of preparing the component (b) comprises reacting an adduct between the Mg-halide and an alcohol with an Al-alkyl, and then treating the product of the reaction with an excess of TiCI4, at a temperature from 600C to the boiling temperature of the TiCI4.

The Al-alkyl compound is used in such a case in a ratio to the adduct at least sufficient to react with the alcohol present in the adduct.

The metalorganic compounds of Al, usable as component (a), preferably consist of Al-trialkyl compounds such as Al-triethyl, Al-tripropyl and Al-triisobutyi compounds or compounds of the formula

The copolymerization of ethylene with propylene and 1,4-hexadiene utilizing the previously defined catalyst may be carried out in the liquid phase, optionally in the presence of an inert hydrocarbon diluent such as hexane, heptane or cyclohexane, or in the gaseous phase in the presence of a mixture of component (a) and (b) of the catalyst.

In the mixture of the components (a) and (b) of the catalyst the ratio between the components is not critical; preferably, however, the components (a) and (b) are employed in weight ratios of 200:1 to 3000:1.

The polymerization temperature is generally maintained at OOC to 1 500C, preferably at OOC to 500 C, more preferably at a temperature greater than 250 C. The operationai pressure may be either atmospheric or a pressure greater than atmospheric pressure.

The ethylene, the propylene and the 1,4-hexadiene are preferably polymerized with each other in such ratios as to obtain terpolymers containing from 30% to 70% by weight of ethylene, from 70% to 30% by weight of propylene, and from 0.1 to 2 mols of 1,4-hexadiene based on 100 mols total of copolymerized ethylene and propylene.

Tlie terpolymers thus obtained by the process of the invention and containing from 30 to 50% by weight of copolymerized propylene are semi-crystalline, while those containing from 50 to 70% by weight of propylene are substantially amorphous, and show values of [77] in tetralin (THN) at 1 250C equal to or greater than 2, while behaving as normal elastomers vulcanizable with sulphur.

The invention will be further described with reference to the following illustrative Examples.

In the preparations described in the Examples, the catalytic component (b), used in the polymerization, was prepared by grinding in a nitrogen atmosphere 60 g of anhydrous MgCIz with 4 g of TiCI4 for a period of 90 hours in a vibrating mill of the VIBRATOM type produced by N. V. TEMA's GRAVENHAGE of Holland, having a total volume of one litre and containing 3 kg. of stainless steel balls of 1 6 mm diameter.

The grinding was carried out assuming a filling coefficient equal to 1 35 g/lt of total (empty) volume, at a temperature inside the grinder of about 400C, with grinding times of from 25 to 1 50 hours.

EXAMPLE 1 Into a 7 litre autoclave, provided with a comb stirrer and maintained at a temperature of 300 C, there were introduced 5,000 cc of propylene and then 300 cc of technical 1 ,4-hexadiene (containing 79% by weight of 1 ,4-hexadiene in the transform and 21% by weight of 1 ,4-hexadiene in the cis form).

The pressure was then brought up to 12.1 atmospheres with ethylene (3.3 atmospheres of overpressure), and to the mixture was then added a mixture of Al-triisobutyl and Al-tri-n. butyl as component (a) of the catalyst dissolved in n-hexane in a quantity of 12.5 millimols/litre of total monomers, whereupon component (b) of the catalyst dispersed in toluene in a total quantity of 1 50 mg was added.

During the reaction the pressure in the reactor was maintained constant by replenishing with ethylene the reacted quantity. The reaction was interrupted after 60 minutes by the addition of acetone while the mixture of monomers was de-gassed and the polymer subjected to stripping by steam.

The yield amounted to 230 kg of terpolymer/g of metal titanium. In Table I below are given some of the polymerization conditions and the characteristics of the terpolymer obtained.

EXAMPLES 2-5 Into a 1.5 litre autoclave, maintained at 300 C, there were introduced 1 ,000 cc of propylene and technical 1 ,4-hexadiene and ethylene in the quantities and respectively at the pressures indicated in Table I below, besides component (a) of the catalyst of the same type as that of Example 1 and in an amount ranging from 1 5 to 40 millimols/litre of monomers, and component (b) of the same type as that of Example 1 in a total quantity of 98 mg.

The reaction was interrupted after 60 minutes, in the usual way. The characteristics of the terpolymers thus obtained, their yields and some operational conditions are given in Table I.

TABLE I

Examples l 2 3 4 5 Total pressure in reactor (atm) 12.1 i 12.1 11.1 10.8 10.8 1,4-hexadiene in reactor (cc) 300 80 80 80 120 CHARACTERISTICS OF TERPOLYMER bound propylene, (% by weight) 39 42.6 70 50 54 bound 1,4-hexadiene (trans form), (% in mols) 0.73 0.58 0.92 1.0 1.2 Mooney viscosity ML1+4 not 1210C 87 94 35 50 determined [#] in tetralin at 121 C 1.92 2.69 2.05 2.05 2.06 Yield in kg/g of titanium 230 240 84 91 100 Polyethylenic crystallinity (%) 7 7 absent 4 2 Polypropylenic crystallinity (%) absent absent absent absent absent The terpolymers obtained according to Examples 1 to 5 were used for preparing mixes of the following composition by weight:: Parts by Weight Terpolymer 100 ZnO 5 Sulphur 1.5 Stearic acid 1 Carbon black 55 CORTIS 100/M (paraffinic oil) (by TOTAL) 30 Tetramethylthiuram monosulphide 1.5 Mercaptobenzothiazol 0.75 The mixes were then vulcanized in a plate press at a temperature of 1 600C for 30 minutes.

In Table II below are given the characteristics of the vulcanized mixes of each terpolymer of Examples 1 to 5.

TABLE II

Examples 1 2 3 4 5 Breaking load (kg/cm2) 115 105 130 112 121 Elongation at break (%) 890 645 620 625 450 Elastic modulus 100 (kg/cm2) 17 23 28 19 23 Elastic modulus 200 (kg/cm2) 29 37 50 36 51 Elastic modulus 300 (kg/cm2) 43 52 73 54 80 Tension set 200% (%) 30 29 32 17 11 Shore A hardness 62 68 68 61 64

Claims (7)

1. A process for the preparation of ethylene-propylene-1 ,4-hexadiene terpolymers, comprising polymerizing a mixture of ethylene, propylene and 1,4-hexadiene in the presence of a catalytic system comprising the following components: (a) a metalorganic aluminium compound selected from one or more Al-trialkyls and Al-alkyl monohalides; and (b) a titanium halide, supported on an anhydrous magnesium dichloride or magnesium dibromide in activated form wherein the X-ray spectrum of the magnesium dichloride or dibromide is characterized in that the line of maximum intensity appearing in the spectrum of the normal type magnesium dihalide, as defined in ASTM 3-0854 and ASTM 1 5-836, is not present, and that in its place there is a halo with its maximum intensity displaced with respect to the distance d of the said line.

2. A process as claimed in Claim 1, wherein the titanium halide is a titanium tetrahalide.

3. A process as claimed in Claim 1 or 2, wherein the polymerization is carried out at a temperature greater than 250C.

4. A process as claimed in any of Claims 1 to 3, wherein the weight ratio of the said catalyst component (a) to the said catalyst component (b) is 200:1 to 3000:1.

5. A process according to Claim 1 for the preparation of ethylene-propylene-1 ,4-hexadiene terpolymers, substantially as herein described in any of the foregoing Examples.

6. An ethylene/propylene/1 4-hexadiene terpolymer prepared by the process as claimed in any of Claims 1 to 5 and containing from 30% to 70% by weight of ethylene, from 70% to 30% by weight of propylene and from 0.1 to 2 mols of 1 ,4-hexadiene based on 100 mols total of copolymerized ethylene and propylene.

7. A terpolymer as claimed in Claim 6, which contains from 50% to 70% by weight of copolymerized propylene.