Patent ID: 6864333

Claim:
A process for the preparation of polymers of ethylene comprising the polymerization reaction of ethylene and optionally one or more olefins in the presence of a catalyst comprising the product obtained by contacting: (A) a metallocene compound of formula (I): wherein the rings containing A and B have a double bond in the allowed position having an aromatic character; A and B are selected from sulfur (S), oxygen (O) or CR 9 , R 9 being hydrogen, a C 1 -C 20 -alkyl, C 3 -C 20 -cycloalkyl, C 2 -C 20 -alkenyl, C 6 -C 20 -aryl, C 7 -C 20 -alkylaryl, or C 7 -C 20 -arylalkyl radical, optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements, with the proviso that if A is S or O, B is CR 9 or if B is S or O, A is CR 9 , and A and B cannot simultaneously be CR 9; R 1 , R 2 , R 3 , R 4 , R 5 , R 6 , R 7 , and R 8 which may be the same as or different from each other, are hydrogen, a C 1 -C 20 -alkyl, C 3 -C 20 -cycloalkyl, C 2 -C 20 -alkenyl, C 6 -C 20 -aryl, C 7 -C 20 -alkylaryl, or C 7 -C 20 -arylalkyl radical, optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements, and at least two adjacent substituents R 1 and R 2 , R 3 and R 4 , or R 5 and R 6 can form a ring comprising 4 to 8 atoms; M is an atom of a transition metal selected from group 3, 4, 5, 6 or the lanthanide or actinide groups in the Periodic Table of the Elements, X, which may be the same as or different from each other, is hydrogen, halogen atom, a R 10 , OR 10 , OSO 2 CF 3 , OCOR 10 , SR 10 , NR 10 2 or PR 10 2 group, wherein the substituents R 10 are hydrogen, a C 1 -C 20 -alkyl, C 3 -C 20 -cycloalkyl, C 2 -C 20 -alkenyl, C 6 -C 20 -aryl, C 7 -C 20 -alkylaryl, or C 7 -C 20 -arylalkyl radical, optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements; p is an integer of from 1 to 3, being equal to the oxidation state of the metal M minus 2; with the proviso that at least one of R 7 and R 8 is not hydrogen; and (B) at least one member selected from the group consisting of an alumoxane and a compound of formula D + E − , wherein D + is a Brønsted acid, which gives a proton and reacts irreversibly with a substituent X of the metallocene of formula (I) and E − is a compatible anion, which stabilizes the active catalytic species originating from the reaction of the two compounds, and which is removed by an olefinic monomer.