Method for preparing high cis polyalkenamers

The method which comprises polymerizing a cycloolefin selected from the group consisting of cyclooctene and 1,5-cyclooctadiene to polyalkenamers having cis vinylene contents of at least 86% by means of a catalyst system comprising (A) an organosilicon compound of the formula R.sub.4 --nSi(Y).sub.n wherein R represents any hydrocarbon fragment from the group of an alkyl, alkenyl or aryl radical and Y is selected from the group consisting of vinyl alkylidenyl, alkoxy, aryloxy and aralkoxy radicals and n being at least 2 and (B) a tungsten halide salt of the general formula R.sub.m.sub.-n.sub.' WX.sub.n.sub.' wherein X represents chlorine or bromine and R is selected from the group consisting of alkoxy, aryloxy, haloalkoxy, alkaryloxy and acetyl acetonyl radicals m being 6 when X = Cl or 5 when X = Br and wherein n' is 3 to 6 inclusive when X = Cl or 3 to 5 inclusive when X = Br and (C) an organoaluminum compound of the formula ##EQU5## wherein R.sub.1, R.sub.2 and R.sub.3 may independently represent an alkyl, aralkyl radical or a halogen atom, and wherein the molar ratio of (A)/(B) ranges from 0.1/1 to 3/1 and the molar ratio of (C)/(B) ranges from 1/1 to 10/1.