Process for preparation and purification of material of a cycloolefin copolymer

A process for the preparation of a cycloolefin copolymer comprising the step of polymerization, without ring opening, of 0.1 to 100% by weight, based on the total amount of monomers, of at least one cycloolefin monomer of the formulae I, II, III, IV, V, or VI ##STR6## in which R.sup.1, R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7 and R.sup.8 are identical or different and are a hydrogen atom or a C.sub.1 C.sub.8 -alkyl radical, it being possible for the same radicals in the various formulae to have a different meaning,

• 0to 99.9% by weight, based on the total amount of monomers, of a cycloolefin of the formula VII ##STR7##
• in which n is an integer from 2 to 10, inclusive, and 0. 1 to 99.9% by weight, based on the total amount of monomers, of at least one open-chain olefin
• at temperatures of -78.degree. to 150.degree. C. under a pressure of 0.01 to 64 bar in the presence of a catalyst system comprising a metallocene and one or both of an aluminoxane or salt-like compound, wherein a portion of the metallocene catalyst is preactivated with a salt-like compound,
• in a cyclic olefin solution saturated with acyclic olefin by use of pressure, thereby forming a reaction solution comprising said cycloolefin copolymer and
• wherein the reaction solution is purified by a process comprising
• pouring the reaction solution into a liquid of a ketone, alcohol or ester,
• filtering the resulting mixture to give a filter cake,
• mixing the filter cake with decahydronaphthalene and diatomaceous earth to form a suspension,
• heating the suspension to dissolve said cycloolefin polymer, and
• filtering the resulting solution over a pressure filter with down to 0.3 .mu.m pore width to give a clear solution of said cycloolefin polymer.