A process for preparing thermically stable olefinic polymers

Claim 1

A process for the manufacture of thermically stable olefinic polymers which polymers are obtained by means of catalysts prepard by reaction of an Al-alkyl compound with a solid component selected from a product comprising a Titanium compound and a magnesium halide and a product formed by a tetravalent titanium compound which is supported onto a trivalent titanium halide having a surface area greater than 50 m /g which process consists in adding to the polymerization slurry during the polymerization or at the end of the polymerization a compound containing in the molecule one or more piperidinic groups that may be represented by the following general formula wherein: R 1 ,R 2 may be alkyl radicals containing from 1 to 4 carbon atoms or rings of 2,2,6,6-tetramethylpiperidine or together they may form with the piperidinic carbon atom they are bound to a cycloalkyl group containing from 5 to 10 carbon atoms, R 3 ,R 4 = alkyl radicals containing from 1 to 18 carbon atoms or together, they form with the piperidinic carbon atom they are bound to a cycloalkyl group containing from 5 to 10 carbon atoms, R 5 , R 6 , R 7 , R 8 , Rg, Z = hydrogen or an organic radical, preferably a C 1 -C 18 alkyl, C 3 -C 12 alkenyl, C 7 -C, 8 aralkyl radical.