Process for the Production of Powdery, Thermoplastic Copolymers From Ethylene and Butene-(1)

The invention concerns a process for the production of thermoplastic low density copolymers of ethylene as workable powders with relatively high bulk densities through the copolymerization of ethylene and butene-(1) with the help of vanadium containing Ziegler catalysts.

The production of ethylene polymers of a low density is customarily effected by the polymerization of ethylene with radical initiation under high pressures of 1,000 bar to 3,000 bar. These processes have, on the one hand, the disadvantage that the production of high pressures is technically cumbersome and expensive. Another disadvantage consists of the fact that no polymerisates can be produced according to such high pressures with such high molecular weights that they have satisfactory properties, such as, for example, a good tension crack resistance vis-a-vis surface-active media or high breaking strength with alternating bending stress and others. Therefore, the ethylene polymerisates produced according to the high pressure process cannot be applied in all fields of utilization due to their relatively low molecular weights.

Additionally, a process has become known for the production of low-density polyethylene with densities of 0.915 g/cm.sup.3 to 0.930 g/cm.sup.3 by means of copolymerization of ethylene with (1)-olefins in hexane at temperatures >130.degree. C. This process has the disadvantage that the polymerisate is obtained dissolved in hexane and must be separated from the solvent.

Recently, a process has become known through the Belgian Pat. No. 862,697 with which powdery polymers with excellent properties for continued processing into finished parts can be produced from ethylene and, possibly, (1)-olefins as comonomers through polymerization with vanadium-containing catalysts in inert liquid hydrocarbons at temperatures of 50.degree. C. to about 95.degree. C. and pressures of 10 bar to 100 bar. Liquid inert hydrocarbons, preferably a hexane cut with a boiling range of 63.degree. C. to 80.degree. C., were mentioned as diluting medium for the polymerization. However, when using such diluting media, no powdery polymers of ethylene and butene-(1) can be produced with densities of about 0.900 g/cm.sup.3 to about 0.930 g/cm.sup.3. The polymers are actually obtained as chunks and lumps and cannot be handled in a technical system.

On the other hand, it has now been determined that copolymers of low densities of ethylene and butene-(1) can also be produced as fluid powder with relatively high bulk densities when using liquid butene-(1) as the diluting medium which can, possibly, also contain inert saturated and/or unsaturated C.sub.4 hydrocarbons.

Therefore, the object of the invention is a process for the production of powdery, thermoplastic copolymers from ethylene and butene-(1) with densities of about 0.900 g/cm.sup.3 up to about 0.930 g/cm.sup.3, good fluidity of the powder, mean grain diameters of up to 1,000 .mu.m and practically without fine grain portions, through polymerization of ethylene and butene-(1), if necessary, in the presence of hydrogen, in inert liquid hydrocarbons at temperatures between 50.degree. C. and about 95.degree. C. and pressures of 10 bar to 100 bar, preferably 20 bar to 60 bar, according to a discontinuous or continuous process by means of Ziegler catalysts, produced in inert liquid hydrocarbons through the reaction of chlorine- and alkoxy-containing vanadyl(V) compounds with aluminum-organic compounds, separation of the insoluble reaction product and activation with aluminum-organic compounds whereby, as a vanadyl(V) compound, a reaction product of vanadyl(V)-chloride and a vanadyl(V)-alcoholate is used at a mole ratio of 1 to 2 up to 2 to 1 or directly the reaction product of vanadyl(V)-chloride with an alcohol, preferably ethanol, propanol-(1), butanol-(1) in mole ratios of 1 to 2 up to 1 to 1 is used, and, as aluminum-organic compound for the reduction, is used ethylaluminum dichloride and/or diethylaluminum chloride, isobutyaluminum dichloride and/or diisobutylaluminum chloride in mole ratios of aluminum compounds to vanadium compounds of 1 to 1 up to 3 to 1 and the reaction of the vanadium compounds with the aluminum-organic compounds is effected by agitation with specific agitation outputs of 0.1 to 20,000 watts/m.sup.3, preferably 1 to 5,000 watts/m.sup.3, and the activation is effected with aluminumalkyl compounds of the formula AlR.sub.3, whereby R represents hydrocarbon radicals with 2 to 8 C-atoms, or with alkylaluminum sesquichloride and/or alkylaluminum dichloride, particularly ethylaluminum sesquichloride and/or ethylaluminum dichloride, characterized by the fact that the polymerization is effected in liquid butene-(1), if necessary in the presence of additional inert, saturated and/or unsaturated C.sub.4 hydrocarbons.

FIG. 1 is a microphotograph of the powdery polymerisate produced in Example 3. Illustration Scale 16:1.

Preferably, according to the invention, the polymerization is effected using pure butene-(1). The commercial purity amounts of 99 percent. However, according to the invention, a C.sub.4 cut can also be used which, for example, can contain, besides butene-(1), trans- and cis-butene-(2), isobutene, n-butane and isobutane. It is important that the added substances have an inert behavior towards the polymerization catalyst. Thus, the mixture should, for example, not contain any butadiene-(1,3) if possible which proved to be a catalyst poison. It goes without saying that attention is to be paid that the mole ratio of butene-(1) to ethylene, required for the desired density of the copolymers be maintained during the polymerization.

The process according to the invention under consideration offers, surprisingly, the possibility of also producing copolymers of ethylene and butene-(1) with the catalyst system known from the Belgian Pat. No. 862,697 having considerably lower densities than they are described in the Belgian Patent whereby the polymers are obtained suspended in the diluting medium and, after their separation from the suspension, are suitable for further processing into finished plastic parts after having added thereto the customary additives so that the otherwise necessary processing of the polymers into granulated material can be omitted. Since high outputs can be obtained with the catalysts used according to the invention, measures for the removal of the catalysts from the polymers can be omitted. Due to their high molecular weight, the low density copolymers produced according to the invention have excellent properties for technical applications. Thus, tubes produced from the copolymers obtained according to the invention have, besides their high flexibility required for certain applications, a high bursting strength and an excellent alternating bending strength. Sprayed die castings show an excellent surface gloss and have no inclination to shrink and distort. Sheeting made from the copolymers produced according to the invention shows a superior impact strength and stretch expansion.

The process according to the invention under consideration is illustrated by means of the following examples:

(a) Catalyst production

122.3 g (705.7 mMole) vanadyl(V)-chloride and 172.3 g (705.7 mMole) vanadyl(V)-n-propylate were heated together for 2 hours to 55.degree. C. in 1.7 l of a hexane cut 63/80.degree. C. under nitrogen. After the mixture had cooled down, a solution of 358.2 g (2,822.8 mMole) ethylaluminum dichloride in 1.43 l of the hexane cut 63/80.degree. C., at 20.degree. C. to 25.degree. C., was added in the course of 2 hours by stirring with a flat blade paddle agitator and a specific agitation output of 126 watts/m.sup.3. The suspension obtained was, subsequently, stirred for another 2 hours at 55.degree. C. with the same specific agitation output. After it had cooled down, the solid substance was separated and washed five times, each time with 5 l of the hexane cut.

(b) Copolymerization of ethylene and butene-(1)

4 ml of a solution of triisobutylaluminum in hexane with a concentration of 100 g/l were pipetted into a 2-liter steel autoclave, under nitrogen. With water cooling, 600 g butene-(1) were pressed into the autoclave through a cartridge filled with a molecular sieve 3 A (manufacturer: Union Carbide). Now the heating to the polymerization temperature is effected. For the removal of the nitrogen, 4 liters of gas were released through a gas meter. Then, hydrogen was pressed on and, subsequently, ethylene was added while stirring (1,000 rpm). A suspension of the catalyst components, described under (a), with a concentration of 10 g solid substance per liter hexane was charged into the autoclave through a sluice. With the completion of the polymerization time during which the polymerization temperature as well as the pressure were kept on a constant level by adding ethylene, the substance was cooled to room temperature and the excessive butene was released. Further details concerning the different examples can be taken from the following Tables 1 and 2.

(a) Copolymerization of ethylene and butene-(1) according to the invention.

It was carried out analogous to Example 10. In deviation from it, a mixture of 79 g butene-(1), 228 g n-butene, 214 g trans-butene-(2), 148 g cis-butene-(2) was used a diluting agent. The quantity of the solid catalyst components amounted to 44 mg. The polymerization was already stopped after one hour. 55 g of a fluid powdery polymer were obtained. The properties are listed in Table 3.

(b) Comparative test

It was carried out as under 11(a) but with the difference that hexane 63/80.degree. C. was used as diluting agent. The quantity of butene-(1) used amounted to 72 g, the ethylene partial pressure, as in Example 11(a) was 4.5 bar. The yield of polymer was 79 g and consisted of rough chunks or lumps.

It was carried out analogous to Example 1. Instead of triisobutylaluminum, tri-n-octylaluminum was, however, used as co-catalyst. 2.2 ml of a solution in hexane were used with a concentration of 167 g tri-n-octylaluminum per liter. The quantity of the solid catalyst components amounted to 20 mg, the hydrogen partial pressure to 1.0 bar, the total pressure to 33 bar. The polymerization was effected over a period of 4 hours at 60.degree. C. The polymer consisted of a fluid powder. Further details are contained in Table 4.

It was carried out as for Example 12. Instead of tri-n-octylaluminum, diethylaluminum chloride was, however, used, namely 2.2 ml of a solution in hexane with a concentration of 112 g diethylaluminum chloride per liter. The polymer consisted of a fluid powder. Further details are contained in Table 4.