Process for the preparation of ethylene polymers

A process for the preparation of ethylene polymers, 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 the general formula (I):
• SiR1R2LQMXp (I)
• wherein SiR1R2 is a divalent group bridging the moieties L and Q;
• R1 and R2, which may be the same or different, are selected from hydrogen, a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radical optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements;
• optionally R1 and R2 form a ring comprising from 3 to 8 atoms, which can bear substituents;
• Q is a moiety of formula (II):
• wherein A and B are selected from sulfur (S), oxygen (O) or CR5, R5 being selected from hydrogen, a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radicals optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements;
• either A or B being different from CR5, and wherein the rings containing A and B have a double bond in the allowed position having an aromatic character;
• if A is S or O, B is CR5 or if B is S or O, A is CR5;
• R3 and R4, which may be the same or different, are selected from hydrogen, a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements;
• L is a moiety of formula (III);
• wherein R6, R7, R8 and R9, which may be the same or different, are selected from C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-arylalkyl radicals optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements;
• and at least two adjacent R6 and R7 or R8 and R9 can form a ring comprising from 3 to 8 atoms, optionally bearing substituents and optionally containing heteroatoms belonging to groups 13 or 15-17 of the Periodic Table of the Elements;
• M is an atom of a transition metal selected from those belonging to group 3, 4, 5, 6 or to the lanthanide or actinide groups in the Periodic Table of the Elements,
• X, which may be the same or different, is a ligand selected from hydrogen, halogen, R10, OR10, OSO2CF3, OCOR10, SR10, NR102 or PR102 group, wherein R10 selected from hydrogen, a C1-C20-alkyl, C3-C20-cycloalkyl, C2-C20-alkenyl, C6-C20-aryl, C7-C20-alkylaryl or C7-C20-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 1to 3, being equal to the oxidation state of the metal M minus 2;
• and
• (B) at least one of an alumoxane and a compound capable of forming an alkyl metallocene cation.