Process for the preparation of branched low-pressure polyethylene, new low-pressure polyethylenes, and preformed bifunctional catalysts

A process for polymerizing ethylene to form branched low-pressure polyethylene having a main chain and side chains of different lengths, the side chains having lengths of 14-200 carbon atoms, which comprises reacting ethylene in the presence of a catalyst at a pressure of 1-1000 bar and at a temperature of 20-200 degrees C, the catalyst comprising a preformed bifunctional catalyst obtained by bonding in an inert reaction medium:

• i. a first catalyst comprising a chromium compound on a silica or aluminum oxide support, wherein the quantity of chromium compound, based on the quantity of the support, is from 0.1 to 3.5% by weight, the chromium compound being in the form of a coordinatively unsaturated chromium (II) and/or chromium (III) compound which is obtained by treating the support with an aqueous solution of a chromium (VI) compound, separating the solution from the impregnated support, drying the impregnated support and heating it at temperatures above 500.degree. C. in an oxygen stream for 1/2 to 3 hours and subsequently reducing the chromium (VI) compound with a gaseous reducing agent at 250.degree. to 500.degree. C. to yield a coordinatively unsaturated chromium (II) compound;
• with
• ii) a second catalyst comprising a nickel compound selected from the group consisting of:
• a) a nickel compound produced by reaction of a nickel (O) compound, or a nickel compound which can be converted into a nickel (O) compound in situ, with an adduct or a mixture of a quinoid compound and a tertiary phosphine and with a compound of the formula (I) ##STR5## in which R.sup.1, R.sup.2 and R.sup.3 , independently of one another, denote optionally halogen-, hydroxyl-, C.sub.1 -C.sub.20 -alkoxy-, nitro- or C.sub.6 -C.sub.12 -aryloxy-substituted C.sub.1 -C.sub.20 -alkyl, C.sub.2 -C.sub.20 -alkenyl, C.sub.6 -C.sub.12 -aryl or C.sub.3 -C.sub.8 -cycloalkyl, or denote C.sub.6 -C.sub.12 -aryl-C.sub.1 -C.sub.20 -alkyl, C.sub.1 -C.sub.20 -alkyl-C.sub.6 -C.sub.12 -aryl, C.sub.6 -C.sub.12 -aryl-C.sub.2 -C.sub.20 -alkenyl, C.sub.1 -C.sub.20 -alkyl-C.sub.3 -C.sub.8 -cycloalkyl and C.sub.6 -C.sub.12 -aryl-C.sub.3 -C.sub.8 -cycloalkyl, di-C.sub.1 -C.sub.4 -alkylamino, phenoxy, or alkoxy,
• X denotes 0, NR.sup.4 or ##STR6## R.sup.4, R.sup.5 and R.sup.6, independently of one another, denote hydrogen, acyl, silyl, halogen, cyano, nitrophenyl or R.sup.1 and
• n denotes zero or 1;
• and
• b) a nickel compound obtained by reacting a nickel (O) compound or a compound which can be converted into a nickel (O) compound in situ with compounds of the formulae (I) as defined above and (III) ##STR7## in which R.sup.10 -R.sup.14 represent, independently of one another, optionally halogen-, hydroxyl, C.sub.1 -C.sub.20 -alkoxy-, or C.sub.6 -C.sub.12 -aryloxy-substituted C.sub.1 -C.sub.20 -alkyl, C.sub.6 -C.sub.12 -aryl, C.sub.2 -C.sub.30 -alkenyl or C.sub.3 -C.sub.8 -cycloalkyl, C.sub.6 -C.sub.12 -aryl-C.sub.1 -C.sub.20 -alkyl, C.sub.1 -C.sub.20 -alkyl-C.sub.6 -C.sub.12 -aryl, halogen, hydroxyl, C.sub.1 -C.sub.20 -alkoxy, or C.sub.6 -C.sub.12 -aryloxy, in addition to which R.sup.13 may be hydrogen, and
• R.sup.14 may be hydrogen, acyl or sulphonate.