Process for producing ethylene copolymers under high pressure

Details Process for producing ethylene copolymers under high pressure Process for producing ethylene copolymers under high pressure

1998-04-07

1999-10-19

Wu, David W.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Polymers from only ethylenic monomers or processes of...

526160, 526161, 526172, 5263481, 5263486, 526943, 502155, C08F 464

Patent

active

059690623

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for preparing copolymers of ethylene with C.sub.3 -C.sub.10 -alk-1-enes.
The present invention further relates to the use of the copolymers obtainable in this way for producing fibers, films and moldings and also to the fibers, films and moldings obtainable therefrom.
WO 91/04257 describes a process for preparing olefin polymers using monocyclopentadienyl(transition metal) complexes as catalysts, these complexes being activated with methylaluminoxane. A very high excess of methylaluminoxane is necessary to obtain a sufficiently high productivity, which results in undesirably high aluminum residues in the polymer and nonviable catalyst costs. In order to be able to achieve economically interesting conversions, the reactor temperature in high pressure processes has to be kept at above 200.degree. C. since the polymerization rate and thus also the productivity increase with rising temperature. The methylaluminoxane-activated catalyst systems mentioned in WO 91/04257 display a drastic fall in productivity and at the same time a decrease in the molecular weight of the polymers obtained even at temperatures above 180.degree. C.
WO 93/25590 describes a process for preparing polyolefins under high pressure and high temperature conditions, in which monocyclopentadienyl(transition metal) complexes which are activated with ionic compounds are used as catalysts. A disadvantage here is that at the polymerization temperatures of over 200.degree. C. which are necessary for economical conversions the polyolefins have relatively high densities, relatively low molecular weights or a broad molecular weight distribution.
The same disadvantages are displayed by the ethylene copolymers prepared in EP-A 612 768 and EP-A 612 769, in which the copolymers are obtained in a high pressure process at reaction temperatures above 200.degree. C. using biscyclopentadienyl(transition metal) complexes, ionic compounds and organoaluminum compounds as catalyst constituents.
U.S. Pat. No. 5,272,236 describes ethylene copolymers which are prepared in a solution process using monocyclopentadienyl(transition metal) complexes and ionic compounds as catalyst constituents.
These polymers too have a relatively high density at temperatures above 200.degree. C.
It is an object of the present invention to provide a process for preparing copolymers of ethylene with C.sub.3 -C.sub.10 -alk-1-enes which makes possible high conversions at a low catalyst consumption, which can be carried out simply in process terms and in which the resulting ethylene copolymers have low densities, high molecular weights and a narrow molecular weight distribution.
We have found that this object is achieved by a process for preparing copolymers of ethylene with C.sub.3 -C.sub.10 -alk-1-enes, wherein the polymerization is carried out at pressures in the range from 1000 to 3500 bar and at from 200 to 280.degree. C. in the presence of a catalyst system comprising as active constituents a donor-substituted monocyclopentadienylamido(transition metal) complex, a compound capable of forming metallocenium ions and, if desired, a trialkylaluminum compound.
Furthermore, we have found the use of the copolymers obtainable in this way for producing fibers, films and moldings and also the fibers, films and moldings obtainable therefrom.
In the process of the present invention, comonomers used are C.sub.3 -C.sub.10 -alk-1-enes, preferably propene, 1-butene, 1-hexene and 1-octene, in particular 1-butene and 1-hexene. A plurality of comonomers can also be used, but preference is given to using only ethylene and one comonomer. The amount of comonomers used can be in the range from 20 to 80% by weight, preferably in the range from 40 to 60% by weight. The sum of the percentages by weight of the ethylene and the comonomers used is always 100.
The process of the present invention is carried out at pressures in the range from 1000 to 3500 bar, preferably from 1200 to 3000 bar, and at from 200 to 280.degree. C., preferably from 220 to 260.degree. C. The reac

REFERENCES:
patent: 5241025 (1993-08-01), Hlatky et al.
patent: 5408017 (1995-04-01), Turner et al.

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