Process for the polymerization of olefins

1. A process for the polymerization of olefins comprising contacting one or more olefins under polymerization conditions in the presence of a catalyst system comprising the product obtained by contacting:

(A) at least one transition metal organometallic compound, pyrolidyl bis(η-cyclopentadienyl)methylzirconium being excluded, and

(B) an organometallic compound obtained by contacting:

(a) a Lewis base having formula (I):

 wherein R a , R b , R c and R d , equal to or different from each other, are selected from the group consisting of hydrogen, halogen, linear or branched, saturated or unsaturated, C 1 -C 10 alkyl, C 6 -C 20 aryl, C 7 -C 20 arylalkyl and C 7 -C 20 alkylaryl groups, optionally containing O, S, N, P, Si or halogen atoms, or two or more adjacent substituents R a , R b , R c and R d form one or more C 4 -C 7 rings, optionally containing O, S, N, P or Si atoms, that can bear substituents; with

b) a Lewis acid of formula (II)

MtR 1 3   (II)

 wherein Mt is a metal belonging to Group 13 of the Periodic Table of the Elements; R 1 , equal to or different from each other, are selected from the group consisting of halogen, halogenated C 6 -C 20 aryl and halogenated C 7 -C 20 alkylaryl groups; two R 1 groups optionally form with the metal Mt one condensed ring; and

(C) optionally an alkylating agent.

2. The process according to claim 1 wherein ethylene is homopolymerized or copolymerized with a comonomer of formula CH 2 ═CHR′, wherein R′ is a linear, branched or cyclic C 1 -C 20 alkyl radical, or with a cycloolefin.

3. The process according to claim 2 wherein propylene is homopolymerized.

4. The process according to claim 2 for the preparation of elastomeric copolymers of ethylene with α-olefins of formula CH 2 ═CHR″, wherein R″ is a C 1 -C 10 alkyl radical, optionally contain minor proportions of units deriving from polyenes.