MULTI-STAGE PROCESS FOR THE (CO)POLYMERIZATION OF OLEFINS

Abstract: Multi-stage process for the polymerization of olefins CH2=CHR, where R is hydrogen or a C1-C10 alkyl, cycloalkyl or aryl radical, comprising: (I) a first polymerization stage carried out in the presence of a catalyst comprising the product of the reaction between an alkyl-A1 compound and a solid component comprising at least one compound of transition metal M<I> not containing M<I>- pi bonds, thus obtaining a porous polymer; (II) a treatment stage, wherein said porous polymer is contacted with a compound capable of deactivating the catalyst used in stage (I) and with a late transition metal complex; and (III) a second stage of polymerization, carried out in the presence of the product obtained from treatment stage (II).

Description: "MULTI-STAGE PROCESS FOR THE (CO) POLYMERIZATION OF OLEFINS" FIELD OF THE INVENTION The present invention relates to a multi-stage process for the homo or copolymenzation of olefϊn monomers, compnsmg (I) a first polymenzation stage in the presence of a Ti or V catalyst, thus obtaining a polymer that has particular values of porosity; (II) a treatment stage wherein the Ti or V catalyst is optionally deactivated and a late transition metal catalyst is supported on the porous polymer, optionally m the presence of a suitable cocatalyst; and (III) a final polymenzation stage, thus obtaining new polymer compositions directly from the reactors. BACKGROUND OF THE INVENTION Early transition metal catalysts for olefin polymenzation are well-known m the state of the art and compnse the traditional Ziegler-Natta catalysts based on Group 4 and 5 of the Penodic Table (IUPAC notation) and the newer metallocene catalysts, based on Group 4-6 metals. These catalysts systems have been widely used in single-stage processes for olefin polymenzation, as well as in multi-stage processes, the latter providing much greater flexibility in controlling the composition and the properties of the end product compared to the former ones. Multi-stage processes are generally earned out by using the same catalyst in the vanous stages/reactors, by utilizing tandem reactors operated m senes: the product obtained in one reactor is discharged and sent directly to the next stage/reactor, without altenng the nature of the catalyst. For example, broad or multi-modal molecular weight distnbution (MWD) polyethylenes are commonly prepared by employing a process, wherein ethylene is polymenzed in vanous reactors containing the same catalyst but in the presence of different concentrations of molecular weight regulators. Multi-stage processes are also used in the preparation of high-impact copolymers of propylene, by sequential polymenzation of propylene and of mixtures of propylene with ethylene. For instance, USP 4,521,566 descnbes the preparation of high impact strength polypropylene compositions m a multistage process which compnses at least one stage of homopolymenzation of propylene and at least one stage of polymenzation of ethylene/propylene mixtures in the presence, in both stages, of a catalyst compnsmg a compound of titanium supported on a magnesium halide. The international patent application WO 96/02583 descnbes a multi-stage process wherein different catalyst systems are used m the vanous stages, m order to allow the obtamment of a wide range of olefinic polymer compositions. More specifically, while in the first stage the polymenzation is earned out in the presence of a Ziegler-Natta catalyst system, m the second polymenzation stage a metallocene/alumoxane catalyst system is used, compnsmg a compound of a transition metal M selected from Ti, V, Zr and Hf, containing at least one M-π bond, and alkyl-Al compound. The international patent application WO 96/11218 descnbes a similar process, with the difference that the first polymenzation stage is followed by an intermediate stage wherein the catalyst used in the first stage is deactivated, before contacting the obtained polymer with the metallocene/alumoxane system of the second polymenzation stage. In the last years a new family of catalysts for olefin polymenzation, based on late transition metals, have been developed in the art; the new catalysts, containing complexes of metals belonging to Groups 8-11 of the Penodic Table of the Elements (new IUPAC notation), exhibit charactenstics different from those of transition metal metallocene catalysts or traditional Ziegler-Natta catalysts when used m olefin polymenzation. L. K. Johnson et al. (J. Am. Chem. Soc, 117: 6414-6415, 1995 and J. Am. Chem. Soc, 118: 267-268, 1996) descnbe the use of Ni and Pd complexes with bidentate α-diimine ligands, useful as catalyst components m ethylene, propylene or 1-hexene polymenzation; said complexes are activated with H + (OEt2)2[B(3,5-(CF3)2C6H3)4]", methylalumoxane (MAO) or Et2AlCl. These systems have the ability to produce highly branched polymers from ethylene and to copolymenze ethylene with polar monomers. A class of late transition metal complexes of bidentate α-diimine or β-diimine ligands was disclosed m WO 96/23010; said complexes, activated with halo-aluminum alkyl denvatives, MAO or alkylboronic acid derivatives, are used in the oligomerization and polymerization of α-olefϊns, and in particular of ethylene, and in the copolymenzation of ethylene with polar monomers. Bidentate ligands, which are useful in the preparation of Ni complexes active in the polymenzation of ethylene, norbornenes and styrenes, are described in the international patent application WO 97/02298; the corresponding complexes are used m association with acids of a non coordinating monoamon of formula HX, wherein the anion X is preferably BF4-, PFβ", BAF (i.e. tetrakιs[3,5- bιs(tnfluoromethyl)phenyl]borate) or SbFg". WO 98/40374 describes olefin polymenzation catalysts containing Group 8-10 metals and bidentate ligands having the following formula: A B R-N N-R wherein the substituents R can be hydrocarbyl, substituted hydrocarbyl or silyl; A and B are heteroatom connected monoradicals, wherein the connected heteroatom is selected from Group 15 or 16, and A and B may be linked by a bndging group; these catalysts optionally contain a Brønsted or Lewis acid as cocatalyst. Recently, Brooke L. Small et al. (J.Am.Chem.Soc. 120:4049-4050, 1998) disclosed Fe(II) and Co(II) catalyst systems incorporating tndentate pyndme dnmme ligands of the following general structure: wherein R is H, methyl or iso-propyl The active catalysts, generated by the addition of MAO, are able to convert ethylene to linear high density polyethylene; increasing the stenc bulk of the ortho aryl substituents increases molecular weight. The polymenzation of ethylene and propylene with the above-mentioned complexes of pyndme bis- lmine, and more specifically of 2,6-pyndmecarboxaldehyde bιs(ιmmes) and 2,6-dιacylpyndme bιs(ιmιnes), is descnbed m WO 98/27124 and WO 98/30612, wherein the above catalysts are activated with MAO, boron compounds and aluminum alkyl compounds. The above-descnbed late transition metal catalyst systems have also been used in association with conventional Ziegler-Natta catalysts. International patent applications WO 97/38024 descnbes polymenzation catalyst systems compnsmg (a) a cyclopentadienyl denvative of a Group 4 transition metal or a catalyst compnsmg magnesium, titanium and halogen; and (b) a complex of a bidentate ligand with a group 8-10 transition metal compound; m association with suitable cocatalysts. By using at the same time a mixture of the two different catalysts, olefin polymers having a broad molecular weight distnbution and excellent formability are obtained. Moreover, WO 97/48735 concerns a mixed olefin polymenzation catalyst system compnsmg- one late transition metal catalyst system, consisting of a Group 9-11 metal complex stabilized by a bidentate ligand; and at least one different catalyst system, selected from a Group 4 metallocene catalyst system and a Ziegler-Natta catalyst system. Because late transition metal catalysts may respond differently to reactor conditions than either metallocene or traditional Ziegler-Natta catalysts, by selecting the proper reactor conditions, polymer blends having the desired molecular weight distribution and composition distribution can be obtained. Also m this case, both the catalytic systems are used together in a single reactor. Finally, the above-mentioned late transition metal catalysts were also supported on inorganic carriers, such as Siθ2 and AI2O3, and the obtained supported systems were used in olefin polymenzation. For instance, WO 97/48736 descnbes late transition metal catalyst systems compnsmg a Group 9-11 metal complex immobilized on a solid metal or metalloid oxide particle support, particularly silica, and their use in heterogeneous polymenzation processes. Catalysts based on late transition metal complexes supported on fine particle earners consisting of inorganic oxides, such as AI2O3 and S1O2, for use in suspension and gas-phase polymenzation processes, were descnbed m JP 09-278821 and JP 09-278822 too; polymers having narrow composition distributions and supenor particle performances are obtained. Nevertheless, the supportation on silica and alumina of late transition metal catalyst leads to lower catalytic activities in companson with homogeneous polymenzation reactions; moreover, the supportation causes a substantial decrease of the branch-producing tendencies (branches/ 1000 carbon atoms) of these catalysts, thus leading to polymers having greater melting points and lower processabi ty, the branching decrease is estimated around 10-15% in the above-mentioned WO 97/48736 Therefore, it is felt the need of increasing the catalytic activity of late transition metal complexes with respect to the activities exerted m homogeneous polymenzations and in heterogeneous systems wherein silica or alumina catalysts are used, at the same time preserving the branching-tendency of these catalysts. SUMMARY OF THE INVENTION The applicant has now found that late transition metal catalysts can be advantageously used in a multistage process, said process compnsmg a first polymenzation stage using a Ziegler-Natta Ti or V catalyst to prepare an olefimc polymer endowed with a particular porosity value, and a second polymenzation stage, earned out in the presence of the thus obtained porous polymer on which is supported a late transition metal catalyst. By means of the above process, late transition metal systems exert an unexpectedly enhanced catalytic activity and the obtained polymers show an increased number of total branches. More specifically, the multi-stage process according to the present invention compnses: (I) a first polymenzation stage, wherein one or more olefins of formula CH>=CHR, wherein R is hydrogen or a linear or branched, saturated or unsaturated C1 -C10 alkyl, cycloalkyl or aryl radical, are polymenzed in one or more reactors, in the presence of a catalyst compnsmg the product of the reaction between an alkyl-Al compound and a solid component compnsmg at least one compound of a transition metal M* chosen between Ti and V, and not containing M - π bonds, and a halide of Mg, in order to produce an olefϊnic polymer having porosity, expressed as percentage of voids, greater than 5%; (II) a treatment stage, wherein the product obtained m said first polymenzation stage (I) is, in any order whatever: (a) optionally contacted with a compound capable of deactivating the catalyst used in stage (I); and (b) contacted with a late transition metal complex, optionally in the presence of a suitable activating agent; and (III) a second polymenzation stage, wherein one or more olefinic monomers are polymenzed in one or more reactors, in the presence of the product obtained from stage (II). Another object of the present invention is a catalyst component compnsmg a late transition metal complex supported on a polymenc porous support, having a porosity, expressed as percentage of voids, greater than 5%; said catalyst component may be suitably obtained by a process compnsmg: (I) a polymenzation stage, wherein one or more olefins of formula CH2=CHR, wherein R is hydrogen or a linear or branched, saturated or unsaturated Ci -Cjo alkyl, cycloalkyl or aryl radical, in the presence of a catalyst compnsmg the product of the reaction between one or more alkyl-Al compounds and a solid component compnsmg at least one compound of a transition metal M^ chosen between Ti and V, and not containing M^-π bonds, and a halide of Mg; (II) a treatment stage, wherein the product obtained in the polymenzation stage (I) is, m any order whatever: (a) optionally contacted with one or more compounds capable of deactivating the catalyst used m step (I); and (b) contacted with one or more late transition metal complexes, optionally in the presence of a suitable activating agent. DETAILED DESCRIPTION OF THE INVENTION The multi-stage process for the polymenzation of olefinic monomers and the supported catalyst component, according to the present invention, will be better descnbed in the following detailed descnption. Figure 1 shows three graphs wherein it is plotted the polymenzation activity of late transition metal catalysts vs. polymenzation time when used in the multi-stage process according to the present invention, when used unsupported in a homogeneous polymenzation and when used supported on silica, according to the processes known in the state of the art. In the first polymenzation stage (I) of the multi-stage process of the invention, one or more olefins of formula CH2=CHR, wherein R is hydrogen or a linear or branched, saturated or unsaturated C1-C10 alkyl, cycloalkyl or aryl radical, are homopolymenzed or copolymenzed m the presence of a Ziegler- Natta catalyst, thus obtaining a polymer having specified porosity values. The catalyst used m the first stage of polymenzation (I) compnses the product of the reaction between: (A) a solid component compnsmg a compound of a transition metal M. chosen between Ti and V and not containing M^-π bonds, supported on a halide of magnesium. The solid component can also compnse an electron-donating compound (internal donor). As a rule, the internal donor are useful when the solid component is used m catalysts for the stereospecific polymenzation of propylene, 1-butylene and similar α-olefins, where increased stereospecificity is necessary to obtain polymers with an index of isotacticity greater than 90; (B) an alkyl-Al compound and optionally an electron-donating compound (external donor). When stereoregular polymers are produced in the first stage of polymenzation (I), for example polymers of propylene with high index of isotacticity, one or more external donors are used in order to impart the necessary increased stereospecificity to the catalyst. However, when diethers of the type descnbed in patent EP-A-361493 or EP-A-728769 are employed as internal donors, the stereospecificity of the catalyst is sufficiently high and does not require the use of external donors. The catalyst must be capable of giving a polymer with porosity greater than 5%. The hahdes of magnesium, preferably MgC , and more preferably MgCl2 in active form, used as support for Ziegler-Natta catalysts, are widely known from the patent literature. For instance, USP 4,298,718 and USP 4,495,338 descnbe the use of these compounds m Ziegler-Natta catalysis. It is known to the skilled person that active forms of magnesium hahdes, commonly used as support or co-support in catalyst components for the polymenzation of olefins, are charactenzed by X-ray spectra wherein the most intense diffraction line appeanng in the spectrum of the non-active halide is diminished in intensity and is replaced by a halo, whose maximum intensity is shifted towards lower angles compared with those of the more intense line. Said compound of the transition metal M^ is preferably selected from the group consisting of hahdes of titanium, halo alkoxides of titanium, VCI3, VCI4, VOCI3 and halo alkoxides of vanadium. Among the compounds of titanium, those preferred are T1CI4, T1CI3 and the halo alkoxides of formula Tι(ORl) m X n , wherein RΪ is a C1-C12 hydrocarbon radical a -CORl group, X is halogen and (m+n) corresponds to the oxidation state of titanium. The catalytic component (A) can be advantageously employed in the form of sphencal particles having a mean diameter ranging from about 10 to 150 μm. Suitable methods for the preparation of said components are reported in EP-A-395083, EP-A-553805, EP-A-553806 and WO 98/44009. Suitable internal electron-donating compounds (internal donors) compnse ethers, esters (particularly esters of polycarboxyhc acids), amines, ketones and 1,3-dιethers as descnbed m EP-A-361493, EP-A- 361494, EP-A-362705, EP-A-451645 and EP-A-728769. By "alkyl-Al compound" is meant any compound in which at least one alkyl group is bound to an aluminum atom; said alkyl-Al compound (B) is preferably a tnalkylalummium, more preferably selected from the group consisting of tnethyl-Al, tnisobutyl-Al, tn-n-butyl-Al, tn-n-hexyl-Al and tn-n- octyl-Al. It is also possible to use mixtures of tnalkylAl's with alkyl-Al hahdes or alkyl-Al sesquichlondes, such as AlEt2Cl and A-2E.3CI3. Said external donor can be the same as or different from the internal donor When the internal donor is the ester of a polycarboxyhc acid, m particular a phthalate, the external donor is preferably a silicon compound having formula RHRIHSI(OR)2, where R^ and RlH are linear or branched, saturated or unsaturated Ci -Cis alkyl, cycloalkyl or aryl radicals. Examples of such silanes are methyl- cyclohexyldimethoxysilane, diphenyldimethoxysilane, methyl-t-butyldimethoxysilane, dicyclopentyl- dimethoxysilane and thexyl-tnmethoxy-silane. The first polymenzation stage (I) can be effected in liquid phase or m gas phase, working in one or more reactors The liquid phase can consist of an inert hydrocarbon solvent (suspension process) or of one or more olefins CH2=CHR (liquid monomer process). Gas-phase polymenzation can be effected using the known fluidized-bed technique or working in conditions in which the bed is mechanically stirred. Said olefin CH2=CHR, wherein R has the meaning reported above, is preferably selected from the group consisting of ethylene, propylene, 1-butene, 1-pentene, 4-methylpentene, 1-hexene, 1-octene and mixtures thereof. According to a preferred embodiment of the invention, the porous homopolymer or copolymer obtained m the first polymenzation stage (I) has a porosity, expressed as percentage of voids greater than 5%, and preferably greater than 10%. Porosity values of 35-40% or greater are particularly advantageous. It is moreover preferable that the polymers produced m the first stage of polymenzation (I) possess macroporosity. In general, more than 40% of the porosity of the said polymers is due to pores with diameter greater than 10,000 A. In the case where the porosity of the polymer produced in the first stage of polymenzation (I) is greater than 15%, the distnbution of pore radius is preferably such that more than 90% of the porosity is due to pores with diameter greater than 10000 A. The porosity, expressed as percentage of voids, and the distnbution of pore radius are determined by the mercury method descnbed later. The quantity of polymer produced in the first stage of polymenzation (I) is greater than 0.5 g/gof said solid component (A), preferably greater than 1000 g/g, and more preferably greater than 3000 g/g. The amount of polymer produced in the first polymerization stage (I) is preferably between 10 and 90% by weight relative to the total amount of polymer produced in stages (I) and (III), and more preferably is between 20 and 80%. The first stage of polymerization (I) is preferably preceded by a stage of prepolymerization in which propylene or its mixtures with one or more olefins CH2=CHR are polymerized in the presence of the catalyst described in (I) in a quantity of between 5 and 500 g/g catalyst. Prepolymerization is prefeBbly effected in liquid propylene or in an inert hydrocarbon solvent, for example propane. The first stage of polymerization (I) is preferably effected in one or more fluidized-bed reactors in the gas phase, into which the prepolymer produced is fed preferably continuously, recycled monomers and optionally a molecular weight regulator, an inert gas and an alkyl-Al compound are fed to the first stage of polymerization (I). According to an embodiment of the process of the invention, the first polymerization step (I) may comprise one or more steps, for instance a step (i) to form a crystalline polymer component and a step (ii) to form a low-crystalline, non-crystalline or elastomeric polymer component, said steps (i) and (ii) being carried out in an arbitrary order, so as to form a block polymer product. In the treatment stage (II), the product obtained in the first polymerization stage (I) is, in any order whatever: (a) optionally contacted with a compound capable of deactivating the catalyst used in stage (I); and (b) contacted with a late transition metal complex, optionally in the presence of a suitable activating agent. In step (a), the porous polymer produced in the first polymerization stage (I) is preferably contacted with a compound able to deactivate the catalyst used in said stage (I). Useful deactivating compounds have formula i s hydrogen or a CJ-CI Q hydrocarbon radical, X is O, N, or S, and y corresponds to the valence of X. Non-limiting examples of said deactivating compounds are alcohols, thioalcohols, mono- and di-alkylamines. Preferred deactivating compounds are those corresponding to the above formula, wherein X = O. According to a preferred embodiment of the process of the invention, said deactivating compound is selected from the group consisting of H2O, NH3, H2S, CO, COS, CS2, CO2 and O2; even more preferably, said deactivating agent is H2O. The molar ratio between said deactivating compound and the compound of the transition metal Ivf must ensure the substantial deactivation of the catalyst used in stage (I). The value of said ratio is preferably greater than 50, more preferably greater than 150, and even more preferably ranging from 250 to 1000. The deactivation treatment (a), wherein the deactivating compound is brought into contact with the polymer obtained from the first polymerization stage (I), can be effected in various ways. For instance, the polymer can be brought into contact, for a time ranging from 1 minute to some hours, with a hydrocarbon solvent containing said deactivating compound in solution, suspension or dispersion. An example of dispersion of the deactivating compound in a hydrocarbon solvent is represented by humidified hexane or propane. In treatment (b), the product obtained in the first stage of polymerization (I), and optionally treated according to step (a), is contacted with one or more late transition metal complexes, optionally in the presence of suitable activating agents. Said transition metal complex preferably corresponds to formula (I) or (II): LMXpX' s (I) LMA (II) wherein M is a metal belonging to Group 8, 9, 10 or 11 of the Periodic Table of the Elements (new IUPAC notation); L is a bidentate or tridentate ligand of formula (III): . B. (III) R 1 m -R 1 wherein: B is a C1-C50 bridging group linking E^ and E^, optionally containing one or more atoms belonging to Groups 13-17 of the Periodic Table; El and E the same or different from each other, are elements belonging to Group 15 or 16 of the Periodic Table and are bonded to said metal M; the substituents Rl, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C1 -C20 alkyl, C1 -C20 alkyliden, C3-C20 cycloalkyl, Cβ-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containingone or more atoms belonging to groups 13-17 of the Periodic Table of the Elements (such as B, Al, Si, Ge, N, P, O, S, F and Cl atoms); or two Rl substituents attached to the same atom E^ or E^ form a saturated, unsaturated or aromatic C4-C8 ring, having from 4 to 20 carbon atoms; m and n are independently 0, 1 or 2, depending on the valence of E and E^, so to satisfy the valence number of El and E^; q is the charge of the bidentate or tridentate ligand so that the oxidation state of MXpX'g or MA is satisfied, and the compound (I) or (II) is overall neutral; X, the same or different from each other, are monoanionic sigma ligands selected from the group consisting of hydrogen, halogen, -R, -OR, -OSO2CF3, -OCOR, -SR, -NR2 and -PR2 groups, wherein the R substituents are linear or branched, saturated or unsaturated, Q-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl or C7-C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Periodic Table of the Elements (new IUPAC notation), such as B, N, P, Al, Si, Ge, O, S and F atoms; or two X groups form a metallacycle ring containing from 3 to 20 carbon atoms; the substituents X are preferably the same; X' is a coordinating ligand selected from mono-olefins and neutral Lewis bases wherein the coordinating atom is N, P, O or S; p is an integer ranging from 0 to 3, so that the final compound (I) or (II) is overall neutral; s ranges from 0 to 3; and A is a π-allyl or a π-benzyl group. According to a preferred embodiment of the present invention, the bridging group B corresponds to a structural formula selected from the group consisting of: B-l B-2 B-3 B-4 B-5 B-6 B-7 B-S B-9 B-10 B-l l B-12 B-13 B-14 B-15 B-16 B-17 B-18 B-19 B-20 B-21 B-22 B-23 B-24 B-25 B-26 B-27 B-28 wherein G is an element belonging to Group 14 of the Periodic Table, and is preferably C, Si or Ge; r is an integer ranging from 1 to 5, E^ is an element belonging to Group 16 and E^ is an element belonging to Group 13 or 15 of the Periodic Table; the substituents R^, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C1-C20 alkyl, C1-C20 alkoxy, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Penodic Table (such as B, Al, Si, Ge, N, P, O, S, F and Cl atoms); or two R2 substituents form a saturated, unsaturated or aromatic C4-C8 nng, having from 4 to 20 carbon atoms, or they form a polycyclic nng system, optionally containing one or more Group 13-16 elements; a substituent Rl and a substituent R^ may form a substituted or unsubstituted, saturated, unsaturated or aromatic C4-C8 nng, having from 4 to 20 carbon atoms and optionally containing one or more Group 13-16 element. In the bidentate or ndentate ligand L of formula (III), E^ and E^ belong to Group 15 or 16 of the Penodic Table, and preferably are selected from the group consisting of N, P, O, and S. In the late transition metal compounds of formula (I) or (II), the substituents Rl, the same or different from each other, are preferably bulky groups; more preferably, they are C6-C20 aryl groups, and even more preferably are substituted in the 2 and 6 positions with a CI-CJO alkyl group. The substituents X are preferably hydrogen, methyl, phenyl, Cl, Br or I; p is preferably 1, 2 or 3. When X' is a neutral Lewis base wherein the coordinating atom is N, P, O or S, it is preferably selected from the group consisting of phosphines, amines, pyridines, nitriles, sulfides and ethers; even more preferably, it is selected from the group consisting of triphenylphosphine, tri(Cι-C6 alkyl)phosphines, tricycloalkyl phosphines, diphenyl alkyl phosphines, dialkyl phenyl phosphines, triphenoxyphosphine, pyridine, di(Cι -C3 alkyl) ether, tetrahydrofuran and nitriles, especially acetonitrile. When X' is a mono-olefin, it is a hydrocarbyl group having one carbon-carbon double bond, having from 2 to 20 carbon atoms; preferably is a substituted or unsubstituted C2-C6 alkene. The variable s is preferably 0 or 1. A is π-allyl or a π-benzyl group. By a π-allyl group is meant a monoanionic ligand with 3 adjacent sp2 carbon atoms bound to a metal center in an η3 fashion. The three sp2 carbon atoms may be substituted with other hydrocarbyl groups or functional groups. Typical π-allyl groups include: wherein R is hydrocarbyl. By a π-benzyl group is meant π-allyl ligand in which two of the sp2 carbon atoms are part of an aromatic ring. Typical π-benzyl groups include: and According to a prefened embodiment of the invention, the ligand of formula (III) is bidentate: the bridging group B corresponds to structural formula B-l, wherein G is C, E and E^ are N, m and n are 1 and q is 0; said neutral bidentate ligand has formula (V): wherein Rl and R^ have the meaning reported above. In formula (V), the substituents R^ are preferably the same and are selected from the group consisting of hydrogen, methyl, ethyl, n-propyl, i-propyl and benzyl, or the two substituents R^ form together a mono or polycyclic ring system. According to a particularly preferred embodiment of the invention, in formula (V) the two substituents R^ form an acenaphtenquinone group, thus resulting a ligand of formula (V)': wherein Rl has the meaning reported above. In formula (V), the substituents Rl are preferably C6-C20 aryl groups, optionally substituted in the 2 and 6 positions with a CI -CJO alkyl group; according to preferred embodiments of the invention, Rl is selected from the group consisting of phenyl, 2,6-dιmethyl-phenyl, 2,6-dιιsopropyl-phenyl and 2,4,6-tnmethyl-phenyl . When a catalyst system compnsmg a transition metal complex of (V) is used m the production of high molecular weight polymers, it is preferred that R is aryl substituted in the 2 and 6 positions, and optionally in the 4 position. Useful substituents include alkyl groups containing 1 to 20 carbon atoms, and halo such as chloro. The molecular weight of the polymer produced may be regulated to some extent by the nature of the substitution, if any, in the 2 and/or 6 positions. When the ligand L corresponds to formula (V), M preferably belongs to Group 10 of the Penodic Table, and even more preferably it is Ni or Pd; if the transition metal compound has formula (I), X radicals are preferably hydrogen, methyl, Cl, Br or I; p is preferably 2 or 3; s is preferably 0. The ligands of formula (V) and the corresponding complexes with late transition metals can be prepared according to methods known m the state of the art, for instance as described in the international patent application WO 96/23010. Prefened late transition metal compounds of formula (I), wherein the bidentate ligand L corresponds to formula (V), are reported in the following for illustrative purposes: [(2,6-.Pr 2 Ph)-N=C(H)-C(H)=N-(2,6-.Pr2Ph)]NιBr 2 [(2,6-.Pr2Ph)-N=C(Me)-C(Me)=N-(2,6-zPr2Ph)]NιBr2 [(2,6-.Pr2Ph)-N=C(An)-C(An)=N-(2,6-.Pr 2 Ph)]NιBr2 [(2,6-Me2Ph)-N=C(H)-C(H)=N-(2,6-Me 2 Ph)]NιBr 2 [(2,6-Me Ph)-N=C(Me)-C(Me)=N-(2,6-Me 2 Ph)]NiBr2 [(2,6-Me2Ph)-N=C(An)-C(An)=N-(2,6-Me2Ph)]NιBr2 [(2,6-Et 2 Ph)-N=C(An)-C(An)=N-(2,6-Et 2 Ph)]NιBr2 [(2,6-Et 2 Ph)-N=C(An)-C(An)=N-(2,6-Et2Ph)]Nι(OOCCF(CF3)OC3F7)2 [(2-Et-6-Me-Ph)-N=C(An)-C(An)=N-(2-Et-6-Me-Ph)]NιBr2 [(2-CF 3 -6-Me-Ph)-N=C(An)-C(An)=N-(2-CF3-6-Me-Ph)]NιBr 2 [(2,4,6-Me3Ph)-N=C(H)-C(H)=N-(2,4,6-Me 3 Ph)]NιBr 2 [(2,4,6-Me3Ph)-N=C(Me)-C(Me)=N-(2,4,6-Me 3 Ph)]NiBr 2 [(2,4,6-Me3Ph)-N=C(An)-C(An)=N-(2,4,6-Me 3 Ph)]NiBr 2 [(2,6-Cl2-4-MeO-Ph)-N=C(Me)-C(Me)=N-(2,6-Cl2-4-MeO-Ph)]NιBr2 [(2-Cl-4,6-Me 2 -Ph)-N=C(Me)-C(Me)=N-(2-Cl-4,6-Me2-Ph)]NiBr 2 [(2-Cl-4,6-Me 2 -Ph)-N=C(An)-C(An)=N-(2-Cl-4,6-Me 2 -Ph)]NιBr2 [(2,6-Me2-4-tBu-Ph)-N=C(An)-C(An)=N-(2,6-Me 2 -4-tBu-Ph)]NιBr2 or the conesponding LN1CI2, LNιMe2, LNiBrCl or LNiBrMe complexes, L being one of the ligands reported above, wherein An = acenaphtenquinone, Me = methyl, .Pr = .-.o-propyl, tBu = ter-butyl and Ph = phenyl. According to another preferred embodiment of the invention, the ligand of formula (III) is tndentate, B corresponds to the structure B-17 wherein the E4 IS N, E^ and E^ are N, m and n are 1, and q is 0; said neutral tndentate ligand has formula (VI): wherein the Rl and R^ groups, the same or different from each other, have the meaning reported above. According to a particularly preferred embodiment of the invention, in the tndentate ligand of formula (VI), the substituents R^ are hydrogen or methyl, and the substituents R' are aryl nngs. When a catalyst system compnsmg a transition metal complex of (VI) is used in the production of high molecular weight polymers, it is prefened that Rl IS aryl substituted m the 2 and 6 positions, and optionally in the 4 position. Useful substituents include alkyl groups containing 1 to 20 carbon atoms, and halo such as chloro. The molecular weight of the polymer produced may be regulated to some extent by the nature of the substitution, if any, m the 2 and/or 6 positions. When the tndentate ligand corresponds to formula (VI), the metal M preferably belongs to Group 8 or 9 of the Penodic Table, and even more preferably it is Fe or Co; if the transition metal compound has formula (I), the X radicals, the same or different from each other, are preferably hydrogen, methyl, Cl Br or I; p is preferably 2 or 3; s is preferably 0. The ligands of formula (VI) and the conesponding complexes with late transition metals can be prepared according to methods known m the state of the art, for instance as descnbed in the international patent applications WO 98/27124 and WO 98/30612. Prefened late transition metal compounds of formula (I), wherein the ligand L corresponds to formula (VI), are reported m the following for illustrative purposes: {2,6-[(2,6-.Pr 2 Ph)-N=C(Me)]pyndyl}FeBr2 {2,6-[(2,6-Me 2 Ph)-N=C(Me) jpyndyl } FeBr 2 {2,6-[(2,4,6-Me 3 Ph)-N=C(Me)]pyndyl}FeBr2 {2,6-[(2,6-.Pr 2 Ph)-N=C(Me)]pyndyl}CoBr2 {2,6-[(2,6-Me 2 Ph)-N=C(Me)]pyndyl}CoBr2 {2,6-[(2,4,6-Me3Ph)-N=C(Me)]pyndyl}CoBr 2 {2,6-[(2,6-.Pr 2 Ph)-N=C(Me)]pyndyl}FeBr3 {2,6-[(2,6-Me2Ph)-N=C(Me)]pyndyl}FeBr 3 {2,6-[(2,4,6-Me3Ph)-N=C(Me)]pyndyl}FeBr3 {2,6-[(2,6-.Pr 2 Ph)-N=C(Me)]pyndyl}CoBr 3 {2,6-[(2,6-Me 2 Ph)-N=C(Me)]pyndyl}CoBr 3 {2,6-[(2,4,6-Me3Ph)-N=C(Me)]pyndyl}CoBr 3 or the conesponding chloride complexes (LFeCl2, LC0CI2, LFeCl3 or LC0CI3, L being one of the ligands reported above) or methyl complexes, wherein Me = methyl, .Pr = ... o-propyl and Ph = phenyl. According to another embodiment of the invention, the ligand of formula (III) is bidentate: the bndgmg group B conesponds to the structural formula B-3, wherein G is C, E^ and E^ are N, m and n are 2 and q is 0, said neutral bidentate ligand has formula (VII): wherein R* and R2 have the meaning reported above. At least one substituent Rl linked to each N atom is preferably an aryl ring, more preferably substituted in the 2 and 6 positions, according to prefened embodiments of the invention, at least one Rl linked to each N atom is selected from the group consisting of phenyl, 2,6-dιmethyl-phenyl, 2,6- dnsopropyl-phenyl and 2,4,6-tnmethyl-phenyl The remaining R* ligand linked to N is preferably hydrogen, methyl or ethyl. The substituents R2 are preferably the same and are selected from the group consisting of hydrogen, methyl and phenyl, or two substituents R^ form together a mono or polycyclic nng system, optionally containing one or more Group 13-16 elements. When the bidentate ligand corresponds to formula (VII), M is preferably of Group 10, and even more preferably is Ni or Pd; if the transition metal compound has formula (I), X radicals are preferably hydrogen, methyl, Cl, Br or I; p is preferably 2 or 3; s is preferably 0. The ligands of formula (VII) and the corresponding complexes with late transition metals can be prepared according to methods known m the state of the art, for instance as descnbed in the international patent application WO 97/02298. According to another embodiment of the invention, the ligand of formula (III) is bidentate: the bndgmg group B conesponds to structural formula B-18, B-19 or B-20, wherein G is C, El and E^ are N, m and n are 1 and q is 0; said neutral bidentate ligands have formulae (VIII)-(XI): (VIII) (IX) (X) (XI) wherein Rl and R^ have the meaning reported above. The substituent Rl are preferably aryl groups, more preferably substituted in the 2 and 6 positions; according to prefened embodiments of the invention, Rl is selected from the group consisting of phenyl, 2,6-dιmethyl-phenyl, 2,6-dnsopropyl-phenyl and 2,4,6-tιmenthyl-phenyl The substituents R2 are preferably the same and are selected from the group consisting of hydrogen, methyl and phenyl, or two substituents R^ form together a mono or polycyclic ring system, optionally containing one or more Group 13-16 elements; or a substituent Rl and a substituent R2 form together a mono or polycyclic ring system, optionally containing one or more Group 13-16 elements. When the bidentate ligand conesponds to one of formulae (VIII)-(XI), M is preferably of Group 10, and even more preferably is Nι(II) or Pd(II); if the transition metal compound has formula (I), X radicals are preferably hydrogen, methyl, Cl, Br or I, p is preferably 2 or 3; s is preferably 0 The ligands of formulae (VIII)-(XI) and the conesponding complexes with late transition metals can be prepared according to methods known in the state of the art, for instance as described in the international patent application WO 98/40374. According to another prefened embodiment of the invention, the ligand of formula (III) is bidentate, B conesponds to the structure B-28 wherein G is C, E and E^ are N, a substituent Rl and a substituent R2 form a substituted nng, m and n are 1, and q is -1; said anionic bidentate ligand has formula (XII): (XII) wherein Rl and R^ have the meaning reported above and R!0-R12, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C1 -C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Penodic Table of the Elements (such as B, Al, Si, Ge, N, P, O, S, F and Cl atoms); or two adjacent substituents RlO- R 2 form a saturated, unsaturated or aromatic C4-C8 nng, having from 4 to 40 carbon atoms. According to a particularly preferred embodiment of the invention, m the bidentate ligand of formula (XII), the substituent R2 IS hydrogen or methyl; the substituents Rl and RlO are stenc bulky groups, preferably aryl nngs (more preferably substituted in the 2 and 6 positions with branched C3-C30 alkyl groups) or tertiary C3-C6 alkyl groups; the substituents RU and Rl2 are preferably hydrogen or methyl When the catalyst systems of the invention are used in the production of high molecular weight polymers, having low degrees of branching, Rl and RlO are preferably aryl nngs substituted in the 2 and 6 positions with a branched C3-C10 alkyl groups, having a secondary or tertiary carbon atom bonded to the phenyl group. When the catalyst systems of the invention are used m the production of lower molecular weight polymers or ohgomers, Rl and RlO are preferably aryl nngs substituted in the 2 and 6 positions with a linear or branched Cj-Ci o alkyl group, having a primary carbon atom bonded to the phenyl group. When the bidentate ligand conesponds to formula (XII), the metal M is preferably Fe, Co, Rh, Ni or Pd, if the transition metal compound has formula (I), X radicals, the same or different from each other, are preferably hydrogen, methyl, Cl Br or I, p is preferably 2 or 3; s is preferably 0 The ligands of formula (XII) and the conesponding complexes with late transition metals can be prepared according to methods known m the state of the art, for instance as descnbed in the international patent application WO 98/42665. Prefened late transition metal compounds of formula (I), wherein the ligand L conesponds to formula (XII), are reported in the following for illustrative purposes: [C4H 3 N-C(H)=N-(2,6-.Pr 2 Ph)]NiBr2 [C4H3N-C(Me)=N-(2,6-.Pr 2 Ph)]NιBr 2 [C4H 3 N-C(H)=N-(2,6-Me 2 Ph)]NιBr 2 [C4H 3 N-C(Me)=N-(2,4,6-Me3Ph)]NιBr2 or the corresponding dichlonde, dimethyl, monochloπde or monomethyl complexes, wherein Me = methyl, . Pr = .so-propyl and Ph = phenyl. According to another prefened embodiment of the invention, the ligand of formula (III) is bidentate, B conesponds to the structure B-12 wherein two vicinal substituent R2 form an aromatic nng, El and E^ are N, m and n are 1, and q is -1; said anionic bidentate ligand has formula (XIII): wherein Rl and R^ have the meaning reported above; the substituents Rl4 and Rl*>, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7- C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Penodic Table of the Elements (such as B, Al, Si, Ge, N, P, O, S, F and Cl atoms), the substituents R*3 and Rl5, the same or different from each other, have the same meaning of substituents Rl4 and Rl6, optionally forming with an adjacent substituent R 4 or Rl6 a saturated, unsaturated or aromatic C4-C8 ring, or they are electron withdrawing groups. According to a particularly prefened embodiment of the invention, in the bidentate ligand of formula (XIII), the substituents Rl are stenc bulky groups, preferably aryl nngs (more preferably substituted m the 2 and 6 positions with branched C3-C30 alkyl groups) or tertiary C3-C6 alkyl groups; the substituent R2 is hydrogen or methyl; the substituents Rl4 and R 6 are hydrogen or methyl; the substituent Rl3 IS a stenc bulky groups, preferably an aryl nng (more preferably substituted in the 2 and 6 positions with branched C3-C30 alkyl groups) or a tertiary C3-C6 alkyl group, or -NO2, Cl or Br; and R 5 IS an electron withdrawing group selected from -NO2, Cl, Br, I, -CF3, -SO3-, -SO2R and -COO". When the catalyst systems of the invention are used in the production of high molecular weight polymers, the substituents Rl are preferably aryl groups substituted m the 2 and 6 positions with a branched C3-C30 alkyl groups, more preferably having a secondary or tertiary carbon atom bonded to the phenyl group. When the bidentate ligand conesponds to formula (XIII), the metal M is preferably Fe, Co, Ni or Pd; if the transition metal compound has formula (I), X radicals, the same or different from each other, are preferably hydrogen, methyl, Cl Br or I; p is preferably 2 or 3; s is preferably 0. The ligands of formula (XIII) and the conesponding complexes with late transition metals can be prepared according to methods known in the state of the art, for instance as descnbed in the international patent application WO 98/42664. According to another prefened embodiment of the invention, the ligand of formula (III) is bidentate, the bridging group B conesponds to the structural formula B-12, wherein two vicinal substituent R2 form an aromatic ring, El is O and E^ is N, m = 0, n = 1, and q is -1; said anionic bidentate ligand has formula (XIV): (XIV) wherein Rl IS a stenc bulky group, preferably aryl (more preferably substituted in the 2, 6 and/or 4 positions with a substituent selected from halogen and linear or branched C1-C20 alkyl groups) or a tertiary C3- 3 alkyl group; the substituent R^ is hydrogen or methyl; the substituents R*4 and Rl6 are hydrogen, methyl or methoxy; the substituent R ^ is a stenc bulky groups, preferably an aryl ring (more preferably substituted in the 2 and 6 positions with branched C3-C30 alkyl groups) or a tertiary C3-C6 alkyl group, -NO2, or halogen (preferably Cl, Br or I); and Rl5 IS a stenc bulky group (preferably substituted aryl or a tertiary C3-C6 alkyl group) or an electron withdrawing group selected from -NO2, halo (preferably Cl, Br and I), -CF3, -SO3-, -SO2R and -COO". When the catalyst systems of the invention are used in the production of high molecular polymers, Rl IS preferably an aryl group substituted in the 2 and 6 positions with a branched C3-C20 alkyl group, preferably having a secondary or tertiary carbon atom bonded to the phenyl group. When the bidentate ligand conesponds to formula (XIV), the metal M preferably belongs to Group 10 of the Penodic Table, and even more preferably is Ni; if the transition metal compound has formula (I), X radicals, the same or different from each other, are preferably hydrogen, methyl, allyl, Cl, Br or I, p is preferably 1 and s is preferably 1; if the transition metal compound has formula (II), A is preferably a linear or branched C3-C5 allyl, more preferably allyl (C3) itself. The ligands of formula (XIV) and the conesponding complexes with late transition metals can be prepared according to methods known in the state of the art, for instance as described in the international patent application WO 98/30609 and WO 98/42664. Prefened late transition metal compounds of formula (I), wherein the ligand L conesponds to formula (XIV), are reported in the following for illustrative purposes: [ {2-0-3-Ph-C6H 3 } -CH=N-(2,6- Pr 2 -C 6 H 3 )]NiPh(PPh3) [ {2-0-3-(9-anthracenyl)C6H 3 } -CH=N-(2,6-. Pr2-C6H3)]NiPh(PPh3) [{2-0-3,5-tBu 2 -C6H2}-CH=N-(2,6-/Pr2-C6H 3 )]NiPh(PPh3) [{2-0-3,5-(N0 2 )2-C 6 H2}-CH=N-(2,6-/Pr 2 -C 6 H3)]NiPh(PPh3) [{2-0-3-Ph-C 6 H3}-CH=N-(2,6- Pr2-C 6 H3)]Ni(C 3 H 5 ) [{2-0-3-(9-anthracenyl)C6H 3 }-CH=N-(2,6-/Pr2-C 6 H3)]Ni(C3H5) [ {2-0-3 ,5-tBu2-C 6 H2}-CH=N-(2,6-jPr2-C6H3)]Ni(C 3 H5) [{2-0-3,5-(N0 2 )2-C6H2}-CH=N-(2,6-/Pr 2 -C 6 H3)]Ni(C3H5) [ {2-0-3-Ph-C 6 H 3 } -CH=N-(2,6-Me2-C 6 H 3 )]NiPh(PPh 3 ) [{2-0-3-(9-anthracenyl)C6H 3 }-CH=N-(2,6-Me2-C6H3)]NiPh(PPh3) [{2-0-3,5-tBu 2 -C 6 H 2 }-CH=N-(2,6-Me2-C6H3)]NiPh(PPh3) [{2-0-3,5-(N02)2-C6H 2 }-CH=N-(2,6-Me2-C 6 H3)]NiPh(PPh3) [ {2-0-3-Ph-C 6 H3 } -CH=N-(2,6-Me C 6 H 3 )]Ni(C3H5) [ {2-0-3-(9-anthracenyl)C6H 3 } -CH=N-(2,6-Me 2 -C 6 H3)]Ni(C3H 5 ) [{2-0-3,5-tBu 2 -C 6 H2}-CH=N-(2,6-Me2-C6H3)]Ni(C3H 5 ) [{2-0-3,5-(N0 2 )2-C 6 H 2 }-CH=N-(2,6-Me2-C 6 H3)]Ni(C3H 5 ) wherein Me = methyl, /Pr = /sø-propyl, tBu = ter-butyl and Ph = phenyl. According to another prefened embodiment of the invention, the ligand of formula (III) is bidentate, the bridging group B conesponds to the structural formula B-l, a substituent R and a substituent R^ form an aromatic ring, El and E^ are N, m and n are 1, and q is 0; said neutral bidentate ligand has formula (XV): (XV) wherein Rl, R^ and R13-R16 have the meaning reported above in connection with formula (XIII). When the bidentate ligand conesponds to formula (XV), the metal M preferably belongs to Group 10 of the Periodic Table, and even more preferably is Ni or Pd; if the transition metal compound has formula (I), X radicals, the same or different from each other, are preferably hydrogen, methyl, Cl, Br or I, p is preferably 2 or 3, and s is preferably 0. The ligands of formula (XV) and the conesponding complexes with late transition metals can be prepared according to methods known in the state of the art, for instance as described in the international patent application WO 98/49208. In treatment (b) of the process of the invention, the product obtained in the first stage of polymenzation (I) is contacted with one or more late transition metal complexes, optionally m the presence of a suitable activating agent. Said activating agent is preferably an alumoxane and/or a compound able to form an alkytnetal cation. Suitable activating agents are linear alumoxanes having formula: wherein the Rl 7 substituents, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated Cι -C20-alkyl, C3-C20-cycloalkyl, C6-C20-aryl, C7-C20-alkylaryl and C7-C2()-arylalkyl radicals, optionally containing Si or Ge atoms; and t is an integer ranging from 0 to 40 and Rl 7 has the meaning reported above; or cyclic alumoxanes having formula: R 17 I (Al— O) t wherein t is an integer ranging from 2 to 40 and Rl 7 has the meaning reported above. Examples of alumoxanes suitable as activating cocatalysts in the catalysts system according to the present invention are methylalumoxane (MAO), 2,4,4-tnmethyl-pentylalumoxane (TIOAO), 2-methyl- pentylalumoxane and 2,3-dιmenthyl-butylalumoxane. Mixtures of different alumoxanes can also be used. Activating cocatalysts suitable as component (B) m the catalysts of the invention are also the product of the reaction between water and an organometalhc aluminum compound; particularly suitable are the organometalhc aluminum compounds descnbed in the European patent application EP 0 575 875 (formula (II)) and m the international patent applications WO 96/02580 (formula (II)), WO 99/21899 (formula (II)) and in the European patent application no. 99203110.4 (formula (II)). Non-limiting examples of organometalhc aluminum compounds are: tns(methyl)alumιnum, tns(ιsobutyl)alummum, tns(2,4,4-tnmethyl-pentyl)alumιnum bιs(ιsobutyl)alummum hydnde, bιs(2,4,4-tnmethylpentyl)alumιnum hydnde ιsobutyl-bιs(2,4,4-tnmethyl-pentyl)alummum tπs(2,3-dιmethyl-hexyl)alumιnum tns(2,3,3-tnmethyl-butyl)alummum tπs(2,3-dιmethyl-butyl)alumιnum tns(2,3-dιmethyl-pentyl)alumιnum tπs(2-methyl-3-ethyl-pentyl)alummum tns(2-ethyl-3-methyl-butyl)alummum tns(2-ethyl-3-methyl-pentyl)alummum tns(2-ιsopropyl-3-methyl-butyl)alummum tns(2,4-dιmethyl-heptyl)alumιnum tπs(2-phenyl-propyl)alumιnιum tns[2-(4-fluoro-phenyl)-propyl]alummιum tns[2-(4-chloro-phenyl)-propyl]alumιmum tns[2-(3-ιsopropyl-phenyl)-propyl]alummιum tns(2-phenyl-butyl)alummιum tns(3-methyl-2-phenyl-butyl)alummιum tns(2-phenyl-pentyl)alumιnιum tns[2-(pentafluorophenyl)-propyl]alumιnιum tns[2,2-dιphenyl-ethyl]alummιum and tns[2-phenyl-2-methyl-propyl]alumιmum. Mixtures of different organometalhc aluminum compounds and/or alumoxanes can also be used. The molar ratio between aluminum and the metal M of the bndged metallocene compound is preferably compnsed between 10:1 and 50,000:1, and more preferably between 100:1 and 4,000:1. Further alumoxanes suitable as activating agents in the process of the present invention are alkylhaloalummoxanes, as descnbed in the US provisional application no. 60/104181, and m particular l,3-dιchloro-l,3-dιethyldιalumιnoxane [EtAlClføO and l,3-dιchloro-l,3-dιιsobutylalumιnoxane [iBuAlClfcO. The activating cocatalyst (B) of the catalyst system of the invention, can be a compound able to form an alkylmetallocene cation; preferably said compounds have formula Y+Z", wherein Y + is a Brønsted acid, able to donate a proton and to react meversibly with a substituent X of the metallocene compound of formula (I), and Z" is a compatible non-coordinatmg amon, able to stabilize the active catalytic species which results from the reaction of the two compounds and which is sufficiently labile to be displaceable by an olefin substrate. Preferably, the amon Z ~ consists of one or more boron atoms. More preferably, the amon Z" is an a on of the formula BAr4("), wherein the substituents Ar, the same or different from each other, are aryl radicals such as phenyl, pentafluorophenyl or bιs(tnfluoro- methyl)phenyl. Tetrakis-pentafluorophenyl borate is particularly prefened. Other useful non- coordmating anions Z" can be SbFg", PFβ", BF4", tnfluoromethanesulphonate and p-toluenesulphonate. Moreover, neutral Lewis acids such as BA13, SbF5 and BF3 can conveniently be used. According to a prefened embodiment of the multi-stage process of the invention, m the treatment stage (II), the product obtained m the first polymenzation stage (I) is, in the following order: (a) first contacted with a compound capable of deactivating the catalyst used in stage (I); and (b) then contacted with a late transition metal complex, optionally in the presence of a suitable activating agent. Preferably, before step (b), any excess of the deactivating compound is removed, according to procedures known m the state of the art. Step (b) can be advantageously effected by bnngmg the polymer produced in the first stage of polymenzation (I), optionally deactivated according to step (a), into contact with a solution of one or more late transition metal compounds in a solvent, preferably an hydrocarbon solvent selected from benzene, toluene, heptane, hexane, propane and mixtures thereof, in said solution can be dissolved a suitable activating agent as reported above. Treatment (b) can be earned out by suspending the polymer obtained from stage (I), optionally after the deactivation treatment (a), m a hydrocarbon solvent containing the dissolved compound of late transition metal and optionally a suitable activating agent, generally working at temperature between 0 and 100°C, preferably between 10 and 60°C, and removing the solvent at the end of the treatment. Alternatively, the polymer obtained from stage (I) can be brought into contact, dry, with a solutions of said late transition metal complex containing the minimum possible quartity of solvent necessary to solubihze said compound and wet the polymer When the deactivation treatment (a) is earned out after treatment (b), the deactivating agent must selectively deactivate the catalysts used in the first polymenzation stage (I), without affecting the catalytic activity of the late transition metal catalyst used in the second polymenzation stage (III) Stage (b) may be also earned out in the gas phase in a loop reactor, wherein the polymer produced m the first stage of polymenzation is circulated by a stream of inert gas Solitions of the deactivating compound and of the late transition metal complex can be fed successively, for example using a sprayer, to the loop reactor in the gas phase, and a free-flowing product is obtained at the end of the treatment It is an object of the present invention a catalyst component for the polymenzation of olefins compnsmg a late transition metal complex supported on a polymenc porous support, having a porosity, expressed as percentage of voids, greater than 5%, said catalyst component can be suitably used in a process for the polymenzation of olefins. It is another object of the present invention a catalyst component compnsmg a late transition metal complex supported on a polymenc porous support, having a porosity, expressed as percentage of voids, greater than 5%, said catalyst component being obtainable by a process compnsmg the following steps: (I) a polymenzation stage, wherein one or more olefins of formula CH2=CHR, wherein R is hydrogen or a linear or branched, saturated or unsaturated CI -CI Q. alkyl, cycloalkyl or aryl radical, in the presence of a catalyst compnsmg the product of the reaction between one or more alkyl-Al compounds and a solid component compnsmg at least one compound of a transition metal M* chosen between Ti and V, and not containing MΪ-π bonds, and a halide of Mg; (II) a treatment stage, wherein the product obtained in the polymenzation stage (I) is, in any order whatever: (a) optionally contacted with one or more compounds capable of deactivating the catalyst used (b) contacted with one or more late transition metal complexes, optionally m the presence of a suitable activating agent. The prefened embodiments of steps (I) and (II) have been descnbed above in details. The quantity of the late transition metal complex supported on said polymenc porous supportcan vary over a very wide range in relation to the late transition metal complex used and the relative amount of product that it produced in the vanous stages. Preferably, the amount of late transition metal complex ranges from 1.10" 7 to 1.10"! mmol per gram of polymenc porous support, more preferably from 1.10"6 to 1.10"3, and even more preferably from 1.10"^ to 1.10"4. Larger amounts are, however, possible. The polymenc porous support has a porosity, expressed as percentage of voids, greater than 5%, preferably greater than 10% and even more preferably ranging from 35 to 40%. Moreover, said polymenc porous support is preferably charactenzed by macroporosity, wherein more than 40% of the porosity is due to pores with diameter greater than 10,000 A, and more preferably wherein more than 90% of the porosity is due to pores with diameter greater than 10,000 A. The second stage of polymenzation (III) of the multi-stage process according to the present invention can be earned out m the liquid phase or in the gas phase, working m one or more reactors. The liquid phase can consist of an inert hydrocarbon solvent (suspension process) or of one or more olefinic monomers (liquid monomer process). The second stage of polymenzation (III) is preferably effected m one or more fluidized-bed reactors m the gas phase, into which the product that comes from stage (II) is fed, preferably continuously; recycled monomers, and inert gas and optionally a molecular weight regulator are fed to this stage of polymenzation. The polymenzation temperature is preferably compnsed between -20°C and 150°C, more preferably between 10°C and 100°C, and even more preferably between 40 and 90°C. The polymenzation pressure is preferably compnsed between 100 and 10,000 kPa, more preferably between 200 and 8,000 kPa, and even more preferably between 500 and 3,000 kPa. Reaction times of from 10 minutes to 2 hours have been found to be suitable, depending on the activity of the catalyst system and on the reaction conditions. The olefinic monomers that can be polymenzed in the second stage of polymenzation (III) are selected from the group consisting of ethylene, C3-C20 α-olefins, C4-C20 gem-substituted olefins, Cg-C20 aromatic substituted α-olefins, C4-C20 cyclic olefins, C4-C20 non conjugated diolefins and C20-C10OO vmyl and vmyhdene terminated macromers. Moreover, m view of the tolerance of the late transition metal catalysts to polar monomers, m the second polymenzation stage ethylenically unsaturated polar monomers can be additionally polymenzed or copolymenzed. Said prefened polar monomers include C4-C20 olefins containing functional groups such as esters, carboxylates, nitnles, amines, amides, alcohols, halide carboxylic acids and the like; said polar monomers are preferably vmyl esters, hahdes or nitnles. Not all of these olefins will polymenze with all of the above late transition metal complexes. Which combinations of monomer and complex will be active polymenzation catalysts may be found m the specific references cited above. By means of the process according to the present invention, the catalyst activity of late transition metal systems is unexpectedly enhanced with respect to the systems of the pnor art, wherein said catalysts are used in solution, m homogeneous polymenzation reactions, or supported on inorganic earners, as will be demonstrated m the following. Moreover, the polymers obtained with the multi-stage process of the invention unexpectedly evidence the complete retention of the branching tendency of the late transition metal catalysts, thus showing a good combination of rheological and physico-mechanical properties. The process of the invention can be used for prepanng a wide range of olefinic polymer compositions. In the first polymenzation stage (I) of the multi-stage process of the invention are preferably polymenzed olefins selected from the group consisting of ethylene, propylene, 1-butene, 1-pentene, 4- methyl-1-pnetene, 1-hexene and 1-octene; m the second polymenzation step (III), are preferably polymenzed α-olefins selected from the group consisting of ethylene, propylene, 1-butene, 1-pentene, 4-methyl-l-pnetene, 1-hexene and 1-octene, more preferably are obtained ethylene homo and copolymers, and even more preferably ethylene plastomers and elastomers According to a prefened embodiment of the multi-stage process of the invention, propylene and ethylene polymer compositions can be prepared: m the first polymenzation stage a homo or copolymer of propylene is obtained, having a content of propylene units greater than 80% wt. and cold xylene soluble fractions lesser than 40% wt., said homo or copolymer of propylene consisting of 10-90 %wt. of the total amount of polymer. In the second polymenzation stage it is produced non-crystalline polyethylene, having a number of total branching greater than 50 branches/1000 C, and preferably greater than 100 branches/1000 C, a density ranging from 0.830 and 0.880 g/crn^, and a Tg value lesser than -30°C, and more preferably lesser than -50°C. Due to the very low Tg obtainable in the second polymenzation stage, according to the multi-stage process of the invention, said polymer compositions show an improved balance between stiffness and impact resistance at low temperatures. According to another prefened embodiment of the process of the invention, polymer compositions can be prepared wherein, m the first polymenzation stage is produced polyethylene, polypropylene or propylene/ethylene copolymers, consisting of 10-90 %wt. of the total amount of polymer, while in the second polymenzation stage block polyethylene (having crystalline and non-crystallme blocks), having a melting point ranging from 100 to 130°C and a Tg value lesser than -30°C, is produced. These polymer compositions show a better balance of stiffness, elastomenc properties and resilience at low temperatures, thus allowing the use of these matenals in vanous applications. According to another prefened embodiment of the process of the invention, polymer compositions can be prepared wherein, in the first polymerization stage, a copolymer of ethylene with one or more α- olefins (LLDPE) is obtained, having a content of ethylene units of 80-99 %wt., said copolymer of ethylene consisting of 10-90 %wt. of the total amount of polymer; m the second polymenzation stage, polyethylene having a low degree of branching is produced, charactenzed by a number of total branching greater than 5 branches/1000 C, and preferably greater than 10 branches/1000 C, and a density greater than 0.880 g/cn- . The thus obtained polymer compositions show a better workability and are endowed with improved optical properties with respect to the blends LLDPE/LDPE known in the state of the art. According to a further embodiment of the process of the invention, the first polymenzation step (I) compnses a step (l) of homopolymenzation of propylene or of copolymenzation of propylene with another α-olefϊn to form a crystalline polypropylene component and a step (ii) of copolymenzation of ethylene with one or more α-olefins, optionally in the presence of a diene, to form a low-crystalline or non-crystalline ethylene/ α-olefin copolymer component, said steps (i) and (ii) being canied out in an arbitrary order, so as to form a propylene block copolymer product, for instance as descnbed m the Italian patent application MI98-A-001906. In the second polymenzation stage (III), it is produced amorphous polyethylene or block polyethylene, containing blocks of amorphous and crystalline polyethylene, or LLDPE. The following examples are given for illustrative and not limiting purposes. The properties stated are determined using the following methods: Melting Point: Tm values were measure by DSC analysis, using a Mettler instrument. The samples, sealed into aluminum pans, were first heated to 200°C at 20°C/mιn and kept at this temperature for 5 minutes. After cooling to 0°C at 20°C/mιn, the sample was left for 5 minutes at 0°C and finally heated to 200°C at 10°C/mιn. In this second heating run, the peak temperature was assumed as melting point (Tm). Intrinsic viscosity (IN.): the IN. of the polymer produced in the polymenzation stage (I) was measured in tefrahydronaphtalene (THN) at 135°C. The polymer molecular weights were determined from the viscosity values. The IN. of the polymer produced in the polymerization stage (III) was calculated from the IN. of the matrix produced in the polymerization stage (I), the IN. of the final product and the amount of polymer produced in stage (II). Melt Index L (MIL): determined according to ASTM-D 1238, method L. Content of comonomer: percentage by weight of comonomer determined from IR spectrum; IR analysis were performed on a Νicolet 20 instrument, on samples of 0.1 mm thickness. Polymer branching: the presence of branches was determined by l3 C-ΝMR analyses, which were performed on a Bruker DPX 400 MHz instrument, in tetrachlorodideuteroethane at 120°C. Porosity: the porosity expressed as percentage of voids is determined by absorption of mercury under pressure. The volume of mercury absorbed conesponds to the volume of the pores. For this determination, a calibrated dilatometer (diameter 3 mm) CD3 (Carlo Erba) connected to a reservoir of mercury and to a high- vacuum pump (1.10"2 mba) is used. A weighed amount of sample (about 0.5 g) is placed in the dilatometer. The apparatus is then placed under high vacuum (<0.1 mmHg) and is maintained in these conditions for 10 minutes. The dilatometer is then connected to the mercury reservoir and the mercury is allowed to flow slowly into it until it reaches the level marked on the dilatometer at a height of 10 cm. The valve that connects the dilatometer to the vacuum pump is closed and the apparatus is pressurized with nitrogen (2.5 kg/cm?). Under the effect of the pressure, the mercury penetrates into the pores and the level goes down according to the porosity of the material. Once the level at which the mercury has stabilized has been measured on the dilatometer, the volume of the pores is calculated from the equation V=R.2.π.ΔH, where R is the radius of the dilatometer and ΔH is the difference in cm between the initial and final levels of the mercury in the dilatometer. By weighing the dilatometer, dilatometer+mercury, dilatometer+mercury+sample, the value of the apparent volume Vi of the sample prior to penetration of the pores can be calculated. The volume of the sample is given by: V 1 =[P 1 -(P 2 -P)]/D where P is the weight of the sample in grams, Pj is the weight of the dilatometer+mercury in grams, P2 is the weight of the dilatometer+mercury+sample in grams, D is the density of ire rcury (at 25°C = 13.546 g/cmβ). The percentage porosity is given by the relation X=(100N)/Vj . CATALYST COMPONENTS [(2,6-Et 2 Ph)-N=C(An)-C(An)=N-(2,6-Et 2 Ph)]NiBr2 The catalyst was synthesized according to methods known in the state of the art, as described in the international patent application WO96/23010. [(2,4,6-Me3Ph)-N=C(An)-C(An)=N-(2,4,6-Me3Ph)]NiBr2 The catalyst was prepared as descnbed in Example 253 of the international patent application WO96/23010. MAO (methylalumoxane) A commercial (Witco) 10% w/w toluene solution of MAO (1JM) was used as such. M-MAO (modified methylalumoxane) Modified methylalumoxane MMAO-3A, containing 7 wt% Al in heptane, was purchased from Akzo Nobel. TIOA (Tris(2,4,4-trimethyl-pentyl)aluminum) TIOA was purchased from Witco as pure compound and diluted heptane to obtain a 1M solution. TIOAO (Tris(2,4,4-trimethyl-pentyl)aIuminoxane) TIOA, obtained as reported above, was diluted to a 1M solution m heptane. 3.45 ml of said solution were added at room temperature to 5 ml of toluene, previously deoxygenated and distilled over frnsobutylalummum. 0.031 ml of H2O were then added at room temperature with a synnge and the resulting solution was stmed for 10 minutes at room temperature. [iBu AlCl]2θ ( 1 -3-dichloro- 1 -diisobuty laluminoxane) l,3-Dichloro-l,3-dnsobutylalummoxane (0.34M Al in toluene) was supplied by Aldnch. EXAMPLE 1 Preparation of a homopolymer of propylene [stage (I)] In a 100 cπβ glass flask, treated beforehand in nitrogen at 90=C for three hours, 0 0098 g of a solid component containing titanium, prepared according to the procedure of Example 3 in patent EP-A- 395083, 0.76 g of tnethylalummum (TEAL) and 0 313 g of cyclohexylmethyldimethoxysilane (CMMS) were previously brought into contact in 10 cir of hexane for 5 minutes. The mixture was then fed into a four-liters steel autoclave, treated beforehand with nitrogen at 90°C for 3 hours. Feed was effected at 30°C in a propylene atmosphere. 1000 cm^ of H2 and 1.2 kg of propylene were then introduced and the autoclave was heated to 70°C. Polymenzation was effected for two hours, followed by degassing in a stream of N2 at 70°C for 1 hour. 238 g of sphencal polymer with the following charactenstics were obtained: MIL=3.5; porosity (% voids) = 24%. Treatment of the homopolymer with a deactivating agent [stage (II)(a)] After degassing propylene, the same reactor was charged with 1000 ml of hexane humidified with 0.513g of water. It was left m contact with the polymer at 50°C for 30 minutes, under nitrogen atmosphere. The liquid was eliminated by siphoning and some washings with cycles of vacuum/nitrogen were earned out at room temperature. Treatment of the deactivated homopolymer with M-MAO/[(2,6-Et2Ph)-N=C(An)-C(An)=N-(2,6- Et?Ph)1NiBr2 mixture [stage (II)(b)1 and ethylene polymenzation [stage (III)] 100 g of porous deactivated polypropylene, obtained as reported above, were loaded into a 2.6L stainless steel reactor. 500 ml of liquid propane were introduced into the reactor, maintained at 25°C, under a total pressure of 10.4 bar. At the same time, 4.5 mg (6J8 μ ol) of the catalyst [(2,6-Et2Ph)-N=C(An)-C(An)=N-(2,6- Et2Ph)]NιBr2 were dissolved in 10 ml of a solvent mixture consisting of 95%vol toluene and 5%vol. heptane, in a glass vessel, and to the solution was added M-MAO so to obtain a molar ratio Al/Ni = 167 (the catalyst concentration was 2.6 μmol/L); the obtained precontact mixture was maintained under stimng for 2 minutes, at room temperature. The obtained catalytic mixture was then loaded into the reactor with a nitrogen overpressure, and stmed for 2-3 minutes. The propane was flashed off in few minutes, while maintaining the temperature at 20-30°C. Then ethylene was fed all at once to a total pressure of 2,960 kPa (29.6 bar); ethylene concentration was 1.17 mol/L. The polymenzation was effected at 55°C for 2 hours, keeping the pressure constant. After stopping the polymenzation reaction by venting off ethylene, the reactor was cooled to room temperature and were obtained 94g of polymer composition, in the form of spheroid particles having good flowabihty and containing 30.9%wt. of ethylene polymer. In the second polymenzation stage (III) were produced 29g of ethylene polymer (activity of 72.8 KgPE/gNi), having Tm = 123.4°C (expeπmental) and IN =5 4 (calculated). Moreover, the branched polyethylene showed the presence of 30.2 CH3/IOOO C, determined by Ν.M.R. methods. COMPARATIVE EXAMPLE 1 Polymerization with unsupported catalyst in liquid phase. 1 L of heptane was loaded at room temperature, under ethylene atmosphere, into a purged 2.6 L stainless steel reactor. The temperature was raised to 50°C and ethylene was fed all at once to obtain a total pressure of 1,430 kPa (14.3 bar). At the same time, 7.42 μmol of the catalyst [(2,6-Et2Ph)-Ν=C(An)-C(An)=Ν-(2,6-Et2Ph)]ΝιBr2 were dissolved in 6 ml of toluene and 0.54 mmole of M-MAO were added, thus obtaining a molar ratio Al/Ni = 60; the mixture was then maintained under stirnng for few minutes, at room temperature. The obtained catalytic solution was injected into the reactor with an overpressure of ethylene, together with additional 0.54 mmole M-MAO, so to obtain m the reactor an overall molar ratio Al/Ni = 120 (the concentration of the catalyst was 7.42 μmol/L). After 30 minutes, at 50°C, the polymenzation reaction was stopped by venting off ethylene; the reactor was cooled to room temperature, thus collecting 22 g of a branched ethylene polymer, having IN. of 3.31 dl/g and a melting temperature Tm of 94J°C (activity = 41.4 KgPE/gΝi). The obtained ethylene polymer showed the presence of 27.7 CH3/IOOO C, determined by Ν.M.R. methods. COMPARATIVE EXAMPLE 2 Polymerization with silica-supported catalyst in liquid phase. Spherical silica (PQ MS 3040, purchased from P.Q. Corporation) with a mean diameter of 95 μm, a surface area of 197 m^/g and pores mean diameter of 131 A was used; said silica was heated at 250°C for 2 hours and subsequently at 500°C for 3 hours. 13.56g of the aforementioned silica were suspended in 100 ml of toluene containing 15.5 ml of a solution of M-MAO (6.78%wt. in heptane, 1.58g M-MAO), and the mixture was maintained under stirnng for 2 hours, at room temperature. The solid was then filtered, washed and dried under vacuum; the amount of fixed Al was 3.3%wt. Silica particles were suspended in a solution of 0.2 mmol of the catalyst [(2,6-Et2Ph)-N=C(An)- C(An)=N-(2,6-Et2Ph)]NιBr2 in 100 ml of toluene for 2 hours, at room temperature, thus obtaining a molar ratio Al/Ni = 138. 1 L of hexane was loaded at room temperature, under ethylene atmosphere, into a purged 2.6 L stainless steel reactor. Temperature was raised to 55°C and ethylene was fed all at once to a total pressure of 1,100 kPa (11 bar). The catalytic suspension obtained as reported above was added to the reactor with an overpressure of ethylene and the feeding banel was washed with 4 ml of hexane; finally, additional 0.2 mmol of M- MAO were added, so to obtain in the reactor an overall molar ratio Al/Ni = 175 (the catalyst concentration was 4.4 μmol/L) and an ethylene concentration of 1.17 mol/L. After 2 hours, at 55°C, the polymenzation reaction was stopped by venting off ethylene and the reactor was cooled to room temperature, thus collecting 10 g of a branched ethylene polymer, having IN. of 4.25 dl/g and melting temperature Tm of 120°C (activity = 33.4 KgPE/gΝi). The obtained ethylene polymer showed the presence of 17.8 CH3/IOOO C, determined by Ν.M.R. method. The above results demonsfrate that the polymenzation activities of the tested late transition metal catalysts decrease when the same catalyst is supported onto S1O2, even if the supportation confers stability along the time to the catalyst. Unexpectedly, by supporting the late transition metal catalysts on a polymenc porous support, according to the multi-stage process of the invention, the catalyst activity is dramatically increased, under exactly the same polymenzation conditions. In Figure 1 are plotted the polymenzation activities vs. time of late transition metal catalysts used in the 2 n " polymenzation stage of Example 1 , according to the invention, used m the unsupported state in homogeneous polymenzation (Comparative Example 1) and used supported on silica (Comparative Example 2). The figure clearly shows that, under exactly the same polymenzation conditions, late transition metal catalysts are much more active m olefin polymenzation when used in the multi-stage process according to the invention than when unsupported or supported on silica, according to pnor art processes. Moreover, as reported m the international patent application WO 97/48736, in companson with the products obtainable by homogeneous polymenzation processes, the immobilization of a late transition metal catalyst on silica leads to relevant modifications m the polymer charactenstics; in particular, silica supportation causes a decrease in branching (branches/ 1000 carbon atoms), leading to polymers having a much lesser number of total branches. On the opposite, the Applicant has unexpectedly found that the multistage process according to the present invention allows to obtain high polymenzation activities, much greater than the ones obtainable with homogeneous and silica-supported catalyst polymerizations, without affecting the branching tendency of the late transition metal catalysts. EXAMPLE 2 The procedure descnbed in Example 1 was repeated with the only difference that, m stage (II)(b), the catalyst [(2,6-Et2Ph)-N=C(An)-C(An)=N-(2,6-Et2Ph)]NιBr2 was dissolved in 10 ml of a solvent mixture containing 55%vol. toluene, 23%vol. methylene chlonde and 22%vol. heptane, in a glass vessel, and to this solution M-MAO was added together with 0.136 mmol of 1-hexene so to obtain a molar ratio Al/Ni = 710. The precontact mixture was injected into the reactor as descnbed in Example 1. Then polymenzation stage (III) was earned out at a total pressure of 2,500 kPa (25 bar) at 60C, for 2 hours, thus obtaining 175g of polymer composition, m the form of spheroid particles having good flowabihty and containing 42.9% wt. of ethylene polymer. The ethylene polymer produced in the second polymenzation stage (III), with an activity of 188 KgPE/gNi, had Tm = 119°C (expenmental), Tc = 103.7°C (expenmental) and I.V.=4.2 dl g (calculated). EXAMPLE 3 The procedure descnbed m Example 2 was repeated with the only difference that, in stage (II)(b), the precontact solution was prepared by dissolving 2.16 mg (3.39 μmol) of the catalyst [(2,4,6-Me3Ph)- N=C(An)-C(An)=N-(2,4,6-Me3Ph)]NιBr2 in 10 ml of a solvent mixture containing toluene (55% vol.), methylene chlonde (23% vol.) and heptane (22% vol.), and by adding M-MAO so to obtain a molar ratio Al/Ni = 710. The precontact mixture was treated and lqected into the reactor as descnbed m Example 1. Then polymenzation stage (III) was earned out at a total pressure of 2,500 kPa (25 bar) at 60°C, for 2 hours, thus obtaining 159g of polymer composition, m the form of spheroid particles having good flowabihty and containing 37.1% wt. of ethylene polymer. The ethylene polymer produced in the second polymenzation stage (III), with an activity of 296.2 KgPE/gNi, had Tm = 126.3°C (expenmental), Tc = 111°C (expenmental) and I V.=3 8 dl/g (calculated). EXAMPLE 4 The procedure descnbed in Example 3 was repeated with the only difference that, in stage (II)(b), to the precontact solution prepared by dissolving the catalyst [(2,4,6-Me3Ph)-N=C(An)-C(An)=N- (2,4,6-Me3Ph)]NιBr2 m 10 ml of a solvent mixture containing toluene (55% vol.), methylene chlonde (23% vol.), hexane (10.5% vol.) and heptane (11.5% vol.), were further added 0.17 mmol of 1-hexene and M-MAO so to obtain a molar ratio Al/Ni = 710. A polymer composition (150g), in the form of spheroid particles having good flowabihty and containing 30.7% wt. of ethylene polymer, was obtained. The ethylene polymer produced in the second polymenzation stage (III), with an activity of 231 KgPE/gNi, had Tm = 126.1°C (expenmental), Tc = 111 4°C (expenmental), density (calculated) =0.947 g/cm 3 and IN =2.4 dl g (calculated). EXAMPLE 5 The procedure descnbed m Example 1 was repeated with the only difference that, in the stage (II)(b) and m ethylene polymenzation [stage (III)], instead of MMAO, was used a mixture of MAO and TIOA, and [(2,4,6-Me3Ph)-Ν=C(An)-C(An)=Ν-(2,4,6-Me3Ph)]ΝιBr2 was used as the catalyst. More specifically, the precontact solution was prepared by dissolving 2.16 mg (3.39 μmol) of the catalyst [(2,4,6-Me3Ph)-N=C(An)-C(An)=N-(2,4,6-Me3Ph)]NιBr2 in 12 ml of a solvent mixture containing toluene (40% vol.) and heptane (60% vol.); to the obtained mixture were added 0.17 mmol of 1-hexene and a mixture of MAO and TIOA, at a molar ratio MAO/TIOA=4, so to obtain a molar ratio Al/Ni = 873. The precontact mixture was treated and lrjected into the reactor as descnbed in Example 1. Then polymenzation stage (III) was earned out at a total pressure of 2,500 kPa (25 bar) at 60°C, for 2 hours, thus obtaining 144g of polymer composition, in the form of spheroid particles having good flowabihty and containing 29.1% wt. of ethylene polymer. The ethylene polymer produced in the second polymenzation stage (III), with an activity of 211 KgPE/gNi, had Tm = 127°C (expenmental), Tc = 112°C (expenmental) and I.V.=3.3 dl/g (calculated). EXAMPLE 6 The procedure descnbed in Example 5 was repeated with the only difference that, in ethylene polymenzation [stage (III)], instead of a mixture of MAO and TIOA, was used a mixture of MAO and TIOAO at a molar ratio MAO/TIOAO=4, so to obtain a molar ratio Al/Ni = 873. A polymer composition (126g), m the form of spheroid particles having good flowabihty and containing 19% wt. of ethylene polymer, was obtained. The ethylene polymer produced in the second polymenzation stage (III), with an activity of 120.5 KgPE/gNi, had Tm = 126.6°C (expenmental) and Tc = 113°C (expenmental). EXAMPLE 7 The procedure descnbed m Example 5 was repeated with the only difference that, in ethylene polymenzation [stage (III)], instead of a mixture of MAO and TIOA, was used a mixture of MAO and TIBA at a molar ratio MAO/TIB A=5, so to obtain a molar ratio Al Ni = 852. A polymer composition (143.5g), in the form of spheroid particles having good flowabihty and containing 30.3% wt. of ethylene polymer, was obtained. The ethylene polymer produced in the second polymenzation stage (III), with an activity of 218.5 KgPE/gNi, had Tm = 126.5°C (expenmental), Tc = 112°C (expenmental) and I.V = 2.5 dl/g (calculated). EXAMPLE 8 The procedure descnbed in Example 2 was repeated with the only difference that, in ethylene polymenzation [stage (III)], [(2,4,6-Me3Ph)-N=C(An)-C(An)=N-(2,4,6-Me3Ph)]NιBr2 was used as the catalyst and was added an antistatic agent. More specifically, the precontact solution was prepared by dissolving 2.16 mg (3.39 μmol) of the catalyst [(2,4,6-Me3Ph)-N=C(An)-C(An)=N-(2,4,6-Me3Ph)]NιBr2 m 14 ml of a solvent mixture containing toluene (63% vol.), methylene chlonde (27% vol.) and heptane (10% vol.); to the obtained mixture were added 0.17 mmol of 1-hexene and M-MAO so to obtain a molar ratio Al/Nι= 900. The precontact mixture was treated and injected into the reactor as descnbed m Example 1. At the beginning of the polymenzation stage (III), the antistatic agent ATMER-163 (purchased from ICI; 100 ppm based on the PP produced in the first polymenzation stage) was fed along with the monomer as a hexane solution (2 ml) and the polymenzation was earned out at a total pressure of 2,500 kPa (25 bar) at 60°C, for 2 hours, thus obtaining 140g of polymer composition, m the form of spheroid particles having good flowabihty and containing 28.6% wt. of ethylene polymer. In the second polymenzation stage (III) an activity of 201 KgPE/gNi was observed. The above tnal demonstrated that the addition of 100 ppm of antistatic agent, based upon the polyolefin fed as a matnx, is sufficient to increase the final polymer flowabihty and to avoid the formation of electrostatic charges that may occur with large size reactors and may negatively affect the catalyst productivity. EXAMPLE 9 The procedure descnbed m Example 8 was repeated, with the only difference that polymenzation stage (III) was earned out in the presence of M-MAO at a molar ratio Al/Nι= 1200. A polymer composition (153g), in the form of spheroid particles having good flowabihty and containing 34.6% wt. of ethylene polymer, was obtained, in the second polymenzation stage (III) an activity of 266.3 KgPE/gNi was observed. EXAMPLE 10 Preparation of ethylene/ 1-butene copolymer (LLDPE) [stage (I)] The synthesis of LLDPE was performed with a catalyst prepared as descnbed m Example 2 of EP-A- 553806. 20,1 mg of said catalyst were reacted with 5 mmol of TEA at 25°C, for five minutes, and they were injected into a 4,2 L reactor, under propane atmosphere. After charging into the reactor 930g of propane, at 25°C, 178 g of 1-butene and lOOg of ethylene were charged to the reactor within few minutes. At the same time the temperature was raised up to 75°C and 6,5 normal liters of hydrogen were slowly added. The polymerization reaction was performed for 2 hours, keeping the pressure constant by feeding both the monomers at constant ratio. 439 g of LLDPE were obtained, having IN =2,07 and l-butene=9,l%wt. by IR. Treatment of the copolymer with a deactivating agent [stage (II)(a)] After degassing the reactor used in stage (I), the same reactor was charged with 1000 ml of hexane humidified with 0.513g of water. It was left m contact with the polymer at 50°C for 30 minutes, under nitrogen atmosphere. The liquid was eliminated by siphoning and some washings with cycles of vacuum/nitrogen were earned out at room temperature. Treatment of the deactivated copolymer with M-MAO[(2,4,6-Me3Ph)-Ν=C(An)-C(An)=Ν-(2,4,6- Me3Ph)]NιBr2 mixture [stage (II)(b)] and ethylene polymenzation [stage (III)] 58g of porous deactivated ethylene/1-butene copolymer, obtained as reported above, were loaded into a 2.6L stainless steel reactor. 500 ml of liquid propane were introduced into the reactor, maintained at 25°C, under a total pressure of 10.4 bar. At the same time, 2.16 mg (3.39 μmol) of the catalyst [(2,4,6-Me3Ph)-N=C(An)-C(An)=N-(2,4,6- Me3Ph)]NiBr2 were dissolved in 14 ml of a solvent mixture containing toluene (63% vol.), methylene chloride (27% vol.) and heptane (10% vol.), in a glass vessel; to the obtained mixture were added 0.17 mmol of 1-hexene and M-MAO so to obtain a molar ratio Al/Ni= 900. The obtained precontact mixture was maintained under stirring for 2 minutes, at room temperature, and was then loaded into the reactor with a nitrogen overpressure, and strrred for 2-3 minutes. The propane was flashed off in few minutes, while maintaining the temperature at 20-30°C. Then ethylene was fed up all at once to a total pressure of 2,500 kPa (25 bar) and 100 ppm of the antistatic agent ATMER-163 (purchased from ICI) were fed along with the monomer as a hexane solution (2 ml). The polymerization was effected at 60>C for 1 hour, keeping the pressure constant. After stopping the polymerization reaction by venting off ethylene, the reactor was cooled to room temperature and lOOg of polymer composition was obtained, in the form of spheroid particles having good flowabihty and containing 42% wt. of ethylene polymer produced in the second polymerization stage (III) (activity of 211 KgPE/gNi). EXAMPLE 11 Preparation of a propylene/ethylene copolymer [stage (I)] In a 100 cm 3 glass flask, treated beforehand in nitrogen at 9fr>C for three hours, 21 mg of a solid component containing titanium, prepared according to the procedure of Example 3 in patent EP-A- 395083, 1.14 g (10 mmol) of triethylaluminum (TEAL) and 114 mg (0.5 mmol) of dicyclooentyl- dimethoxy-silane were previously brought into contact in 10 cm 3 of hexane for 5 minutes. The mixture was then fed into a 4-liters steel autoclave, treated beforehand with nitrogen at 90°C for 3 hours. Feed was effected at 30°C in a propylene atmosphere. 2900 cm 3 of H2, 1280 g of propylene and 8.5 g of ethylene were then introduced and the autoclave was heated to 70°C. Polymerization was effected at a constant temperature of 70°C, at 31.2 barg and the pressure was kept constant by feeding 30 g of ethylene. After 30 minutes of polymerization, the autoclave was degassed with a stream of N?, at 70°C for 1 hour. 225 g of spherical propylene/ethylene polymer with the following characteristics were obtained: ethylene content = 3.1 %wt.; MIL=25.6; porosity (% voids) = 27%; IN. = 1.35 dl/g; solubility (in xylene, at 25°C) = 5 %wt. Treatment of the propylene/ethylene copolymer with a deactivating agent [stage (II)(a)] After degassing, the same reactor was charged with 1000 ml of hexane humidified with 0.52g of water. It was left in contact with the polymer at 50°C for 30 minutes, under nitrogen atmosphere. The liquid was eliminated by siphoning and some washings with cycles of vacuum/nitrogen were carried out at room temperature. C(An)=N-(2,4,6-Me3Ph)]NιBr2 mixture [stage (H)(b)] and ethylene polymenzation [stage (III)] 70 g of porous deactivated propylene/ethylene copolymer, obtained as reported above, were loaded into a 2.6L stainless steel reactor. 250 g of propane were introduced into the reactor, maintained at 30°C, under a total pressure of 10.4 bar; moreover, 3.39 mmol of M-MAO, diluted m 4 ml of heptane, were introduced m the reactor. At the same time, 2.16 mg of the catalyst [(2,4,6-Me3Ph)-N=C(An)-C(An)=N-(2,4,6-Me3Ph)]NιBr2 were dissolved in 6 ml of a solvent mixture consisting of 66%vol toluene and 34%vol. heptane, in a glass vessel, and to the solution was added M-MAO so to obtain a molar ratio Al/Ni = 100; the obtained precontact mixture was maintained under stirnng for 10 minutes, at room temperature. The obtained catalytic mixture was then loaded into the reactor with a mfrogen overpressure (thus obtaining a molar ratio Al/Ni =1100) and stined for 2-3 minutes. The propane was flashed off in few minutes, while maintaining the temperature at 20-30°C. Then ethylene was fed all at once to a total pressure of 2,500 kPa (25 bar); the polymenzation was effected at 60°C for 2 hours, keeping the pressure constant. After stopping the polymenzation reaction by venting off ethylene, the reactor was cooled to room temperature and were obtained 149g of polymer composition, in the form of sphencal particles having good flowabihty and containing 53%wt. of ethylene polymer. In the second polymenzation stage (III) were produced 79g of ethylene polymer (activity of 397 KgPE/gNi), having Tm = 130°C (expenmental) and I.V.=2.06 dl/g (calculated). EXAMPLE 12 The procedure descnbed m Example 11 was repeated with the difference that, in stage (II)(b), in the reactor were introduced 250 g of propane and [ιBuAlCl]2θ, diluted in 2 ml of heptane, instead of M- MAO. Moreover, m the precontact solution, 0.87 ml of [ιBuAlCl]2θ (0.34 M), diluted in 5.0 ml of toluene, were used instead of M-MAO, so to obtain a molar ratio Al/Ni = 200. The precontact mixture was treated and injected into the reactor, as descnbed in Example 11, so to obtain a molar ratio Al/Ni = 1100; polymenzation stage (III) was earned out as in Example 11, thus obtaining 116.5 g of polymer composition, in the form of sphencal particles having good flowabihty and containing 39.9% wt. of ethylene polymer. In the second polymenzation stage (III) were produced 46.5 g of ethylene polymer (activity of 234 KgPE/gNi), having Tm = 124°C (expenmental) and I.V.=1.83 dl/g (calculated). EXAMPLE 13 The procedure descnbed m Example 11 was repeated with the difference that, m stage (II)(b), m the reactor were introduced 250 g of propane and M-MAO, diluted in 5.3 ml of heptane. Moreover, in the precontact solution, 0.43 ml of [ιBuAlCl]2θ (0.34 M), diluted in 4.4 ml of toluene, were used instead of M-MAO, so to obtain a molar ratio Al/Ni = 100. The precontact mixture was treated and injected into the reactor, as descnbed m Example 11, so to obtain a molar ratio Al/Ni = 1100; polymenzation stage (III) was earned out as m Example 11, thus obtaining 155.7 g of polymer composition, in the form of sphencal particles having good flowabihty and containing 53.7% wt. of ethylene polymer. In the second polymenzation stage (III) were produced 85J g of ethylene polymer (activity of 431 KgPE/gNi), having Tm = 129°C (expenmental) and I.V.=1.95 dl g (calculated)

Claims: CLAIMS 1. A multi-stage process for the polymenzation of olefins compnsmg: (I) a first polymenzation stage, wherein one or more olefins of formula CH2=CHR- wherein R is hydrogen or a linear or branched, saturated or unsaturated -Cio alkyl, cycloalkyl or aryl radical, are polymenzed in one or more reactors, in the presence of a catalyst compnsmg the product of the reaction between an alkyl-Al compound and a solid component compnsmg at least one compound of a transition metal Ni chosen between Ti and V, and not containing Ml-π bonds, and a halide of Mg, in order to produce an olefinic polymer having porosity, expressed as percentage of voids, greater than 5%; (II) a treatment stage, wherein the product obtained in said first polymenzation stage (I) is, in any order whatever. (a) optionally contacted with a compound capable of deactivating the catalyst used in stage (I); and (b) contacted with a late transition metal complex, optionally in the presence of a suitable activating agent; and (III) a second polymenzation stage, wherein one or more olefinic monomers are polymenzed in one or more reactors, in the presence of the product obtained from stage (II). 2. The multi-stage process according to claim 1 wherein, in stage (I), said alkyl-Al compound is a tnalkyl-Al, an alkyl-Al halide or an alkyl-Al sesquichlonde, said halide of Mg is MgCb_ and said compound of a transition metal M is selected from the group consisting of hahdes of Ti, halo alkoxides of Ti, VCI3, VCI4, VOCI3 and halo alkoxides of V. 3. The multi-stage process according to claim 2, wherein said compound of a transition metal N IS selected from the group consisting of T1CI4, T1CI3 and halo alkoxides of the formula Tι(ORl) m X n , wherein R IS a Cj -C12 hydrocarbon radical or a -COR group, X is halogen and (m+n) corresponds to the oxidation state of Ti. 4. The multi-stage process according to claim 1 wherein, in stage (I) said solid component is m the form of sphencal particles having a mean diameter ranging from 10 μm to 150 μm. 5. The multi-stage process according to claim 1, wherein the catalyst used m stage (I) compnses the product of the reaction between an Al-alkyl compound, an electron-donating compound (external donor) and a solid component compnsmg at least one compound of a transition metal Ml selected from Ti and V and not containing MΪ-π bonds, a magnesium halide and an electron-donating compound (internal donor). 6. The multi-stage process according to claim 1, wherein the porosity of the olefinic polymer obtained in the first polymerization stage (I) is greater than 10%. 7. The multi-stage process according to claim 6, wherein more than 40% of said prosity is due to pores with diameter greater than 10,000 A. 8. The multi-stage process according to claim 1 wherein, in the treatment stage (II)(a), said compound capable of deactivating the catalyst used in stage (I) has formula RlVy.jXH, wherein Rl is hydrogen or a Cj-Cio hydrocarbon radical, X is O, N, or S, and y conesponds to the valence of X. 9. The multi-stage process according to claim 8, wherein said compound capable of deactivating the catalyst used in stage (I) is selected from the group consisting of HjO, NH3, H2S, CO, COS, CS2, CO2 and O2. 10. The multi-stage process according to claim 1 wherein, in the treatment stage (II)(b), said late transition metal complex has formula (I) or (II): LMXpX's (I) LMA (II) wherein M is a metal belonging to Group 8, 9, 10 or 11 of the Periodic Table; L is a bidentate or tridentate ligand of formula (III): q . B. R -1/ (HI) m -R 1 wherein: B is a C1-C50 bridging group linking El and E^, optionally containing one or more atoms belonging to Groups 13-17 of the Periodic Table; El and E^, the same or different from each other, are elements belonging to Group 15 or 16 of the Periodic Table and are bonded to said metal M; the substituents Rl, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C1 -C20 alkyl, -C20 alkyliden, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Periodic Table of the Elements (such as B, Al, Si, Ge, N, P, O, S, F and Cl atoms); or two Rl substituents attached to the same atom El or E^ form a saturated, unsaturated or aromatic C4-Csring, having from 4 to 20 carbon atoms; m and n are independently 0, 1 or 2, depending on the valence of El and E^, so to satisfy the valence number of El and E^; q is the charge of the bidentate or tridentate ligand so that the oxidation state of MXpX' s or MA is satisfied, and the compound (I) or (II) is overall neutral; X, the same or different from each other, are monoanionic sigma ligands selected from the group consisting of hydrogen, halogen, -R, -OR, -OSO2CF3, -OCOR, -SR, -NR2 and -PR2 groups, wherein the R substituents are linear or branched, saturated or unsaturated, C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl or C7-C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Periodic Table of the Elements (new IUPAC notation), such as B, N, P, Al, Si, Ge, O, S and F atoms; or two X groups form a metallacycle ring containing from 3 to 20 carbon atoms; the substituents X are preferably the same; X' is a coordinating ligand selected from mono-olefins and neutral Lewis bases wherein the coordinating atom is N, P, O or S; p is an integer ranging from 0 to 3, so that the final compound (I) or (II) is overall neutral; s ranges from 0 to 3; and A is a π-allyl or a π-benzyl group. 11. The multi-stage process according to claim 10, wherein said bridging group B is selected from the group consisting of: B-l B-2 B-3 B-4 B-5 B-6 B-7 B-8 B-9 B-10 B-l l B-12 B-13 B-14 B-15 B-16 B-17 B-18 B-19 B-20 R 2 R 2 R H_^ R 2 R 2__ E 3 R 2 R 2_^ E i_ R 2 R 2 E 4_ R 2 \ / \ / \ / \ // H G-G X v H / G-G X x H / , G_G v \ H / G~G x \ B-21 B-22 B-23 B-24 R 2_ R 2 G _ R 2 B-25 B-26 B-27 B-28 wherein G is an element belonging to Group 14 of the Periodic Table; r is an integer ranging from 1 to 5; E 3 is an element belonging to Group 16 and E^ is an element belonging to Group 13 or 15 of the Periodic Table; the substituents R2, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C1-C20 alkyl, C1-C20 alkoxy, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Periodic Table; or two R^ substituents form a saturated, unsaturated or aromatic C4-C8 ring, having from 4 to 20 carbon atoms, or they form a polycyclic ring system, optionally containing one or more Group 13-16 elements; a substituent Rl and a substituent R^ may form a substituted or unsubstituted, saturated, unsaturated or aromatic C4-C8 ring, having from 4 to 20 carbon atoms and optionally containing one or more Group 13-16 element. 12. The multi-stage process according to claim 10, wherein El and E^ are selected from the group consisting of N, P, O, and S. 13. The multi-stage process according to claim 10, wherein the substituents Rl are Cg-C20 aryl groups; the substituents X are selected from the group consisting of hydrogen, methyl, phenyl, Cl, Br and I; and p is 1, 2 or 3. 14. The multi-stage process according to claims 10 and 11, wherein said ligand L conesponds to formula (V): wherein Rl and R^ have the meaning reported in claims 10 and 11; M belongs to Group 10 of the Periodic Table; X radicals are hydrogen, methyl, Cl, Br or I; p is 2 or 3; and s is 0. 15. The multi-stage process according to claim 14, wherein the substituents Rl are C6-C20 aryl groups, optionally substituted in the 2 and 6 positions with alkyl groups containing 1 to 20 carbon atoms and/or halo groups; the substituents R2 are selected from the group consisting of hydrogen, methyl, ethyl, n-propyl, i-propyl and benzyl, or the two substituents R^ form together an acenaphtenquinone group. 16. The multi-stage process according to claims 10 and 1 1, wherein said ligand L conesponds to formula (VI): wherein the Rl and R2 groups have the meaning reported in claims 10 and 11, the metal M is Fe or Co; the X radicals are preferably hydrogen, methyl, Cl Br or I; p is 2 or 3; and s is 0. 17. The multi-stage process according to claim 16, wherein the substituents R^ are hydrogen or methyl, and the substituents Rl are aryl rings. 18. The multi-stage process according to claims 10 and 11, wherein said ligand L conesponds to formula (VII): wherein Rl and R2 have the meaning reported in claims 10 and 11, M belongs to group 10 of the Penodic Table, the X radicals are hydrogen, methyl, Cl, Br or I; p is 2 or 3; and s is 0. 19. The multi-stage process according to claims 10 and 11, wherein said ligand L conesponds to one of formulae (VIII)-(XI): (VIII) (DC) (X) (XI) wherein Rl and R^ have the meaning reported in claims 10 and 11, M belongs to Group 10 of the Periodic Table, the X radicals are hydrogen, methyl, Cl, Br or I; p is 2 or 3; and s is 0. 20. The multi-stage process according to claims 10 and 11, wherein said ligand L conesponds to formula (XII): (XII) wherein Rl and R^ have the meaning reported in claims 10 and 11; R!0-R12, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C1 -C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Penodic Table; or two adjacent substituents R!0-R1 form a saturated, unsaturated or aromatic C4-C8 nng, having from 4 to 40 carbon atoms; the metal M is preferably Fe, Co, Rh, Ni or Pd; the X radicals are hydrogen, methyl, Cl Br or I; p is 2 or 3; and s is 0. 21. The multi-stage process according to claims 10 and 11, wherein said ligand L conesponds to formula (XIII): Θ (XIII) wherein Rl and R^ have the meaning reported in claims 10 and 11; the substituents Rl4 and Rl6, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Periodic Table; the substituents Rl3 and Rl5, the same or different from each other, have the same meaning of substituents Rl4 and Rl6, optionally forming with an adjacent substituent Rl4 or Rl° " a saturated, unsaturated or aromatic C4-C8 ring, or they are electron withdrawing groups; the metal M is Fe, Co, Ni or Pd; the X radicals are hydrogen, methyl, Cl Br or I; p is 2 or 3; and s is 0. 22. The multi-stage process according to claims 10 and 11, wherein said ligand L conesponds to formula (XIV): (XIV) wherein Rl and R^ have the meaning reported in claims 10 and 11; Rl4 and Rl6, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C1 -C20 alkyl, C3-C20 cycloalkyl, C6-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radical, optionally containing one or more atoms belonging to groups 13-17 of the Periodic Table; Rl3 and Rl5 } the same or different from each other, have the same meaning of Rl4 and Rl6, optionally forming with an adjacent Rl4 or Rl6 a saturated, unsaturated or aromatic C4-C8 ring, or they are electron withdrawing groups; the metal M belongs to Group 10 of the Periodic Table, the X radicals are hydrogen, methyl, allyl, Cl, Br or I, A is a C3-C5 linear allyl, p is 1 and s is 1. 23. The multi-stage process according to claim 22 wherein, in said ligand of formula (XIV), Rl is aryl, substituted in the 2, 6 and/or 4 positions with a substituent selected from halogen and linear or branched C1 -C20 alkyl groups, or is a tertiary C3-C6 alkyl group; R2 is hydrogen or methyl; Rl4 and Rl6 are hydrogen, methyl or methoxy; Rl3 is selected from the group consisting of aryl, substituted in the 2 and 6 positions with branched C3-C30 alkyl groups, tertiary C3-C6 alkyl group, -NO2 and halo; and Rl5 is selected from the group consisting of aryl, tertiary C3-C6 alkyl group, -NO2, halo, -CF3, -SO3-, -SO2R and -COO'. 24. The multi-stage process according to claims 10 and 11, wherein said ligand L conesponds to formula (XV): (XV) wherein Rl and R^ have the meaning reported in claims 10 and 11; the substituents Rl4 and Rl6, the same or different from each other, are selected from the group consisting of hydrogen, linear or branched, saturated or unsaturated C1-C20 alkyl, C3-C20 cycloalkyl, Cg-C20 aryl, C7-C20 alkylaryl and C7-C20 arylalkyl radicals, optionally containing one or more atoms belonging to groups 13-17 of the Periodic Table; the substituents Rl3 and Rl5, the same or different from each other, have the same meaning of substituents Rl4 and Rl6, optionally forming with an adjacent substituent Rl4 or Rl6 a saturated, unsaturated or aromatic C4-C ring, or they are electron withdrawing groups; the metal M belongs to Group 10 of the Periodic Table; the X radicals are hydrogen, methyl, Cl, Br or I, p is 2 or 3, s is 0. 25. The multi-stage process according to claim 1 wherein, in the treatment stage (II)(b), said activating agent is an alumoxane and/or a compound able to form an alky ietal cation. 26. The multi stage process according to claim 1 wherein, in the treatment stag? (II), the product obtained in the first polymerization stage (I) is, in the following order: (a) first contacted with said compound capable of deactivating the catalyst used in stage (I); and (b) then contacted with said late fransition metal complex, optionally in the presence of a suitable activating agent. 27. The multi-stage process according to claim 26 wherein, before step (b), any excess of said compound capable of deactivating the catalyst used in stage (I) is removed. 28. The multi-stage process according to claim 1, wherein the polymerization stage (I) is carried out in liquid phase, said liquid phase consisting of a hydrocarbon solvent or of one or more olefins CH2=CHR, and the polymerization stage (III) is carried out in gas phase, in at least one reactor with a fluidized bed or a mechanically-agitated bed. 29. The multi-stage process according to claim 1, wherein both polymerization stages (I) and (III) are carried out in gas phase, in reactors with a fluidized bed or a mechanically-agitated bed. 30. A catalyst component for the polymerization of olefins comprising a late transition metal complex supported on a polymeric porous support having a porosity, expressed as percentage of voids, greater than 5%. 31. A catalyst component for the polymerization of olefins comprising a late transition metal complex supported on a polymeric porous support having a porosity, expressed as percentage of voids, greater than 5%, said catalyst component being obtainable by a process comprising: (I) a polymerization stage, wherein one or more olefins of formula CH2=CHR, wherein R is hydrogen or a linear or branched, saturated or unsaturated C1-C10 alkyl, cycloalkyl or aryl radical, in the presence of a catalyst comprising the product of the reaction between one or more alkyl-Al compounds and a solid component comprising at least one compound of a fransition metal Ml chosen between Ti and V, and not containing Ml-π bonds, and a halide of Mg; (II) a treatment stage, wherein the product obtained in the polymerization stage (I) is, in any order whatever: (a) optionally contacted with one or more compounds capable of deactivating the catalyst used in step (I); and (b) contacted with one or more late fransition metal complexes, optionally in the presence of a suitable activating agent. 32. The catalyst component according to claim 30 or 31, wherein said late transition metal complex is supported in a quantity ranging from 1.10" 7 to 1.10-1 mmol per gram of polymeric porous support. 33. The catalyst component according to claim 30 or 31, wherein said polymeric porous support has a porosity greater than 10%. 34. The catalyst component according to claim 33, wherein more than 40% of theporosity is due to pores with diameter greater than 10,000 A. 35. A polymer composition obtainable with the process of claim 1 , characterized in that: in said first polymerization stage a homo or copolymer of propylene is obtained, having a content of propylene units greater than 80% wt. and cold xylene soluble fractions lesser than 40% wt., said homo or copolymer of propylene consisting of 10-90 %wt. of the total amount of polymer; and in said second polymerization stage amorphous polyethylene is produced, having a number of total branching greater than 50 branches/1000 C, a density ranging from 0.830 and 0.880 g/cπ-2, and a Tg value lesser than -30°C. 36. A polymer composition obtainable with the process of claim 1 , characterized in that: in said first polymerization stage polyethylene, polypropylene or propylene/ethylene copolymer is produced, consisting of 10-90 %wt. of the total amount of polymer; and in said second polymerization stage block polyethylene is produced, having a melting point ranging from 100 to 130°C and a Tg value lesser than -30°C. 37. A polymer composition obtainable with the process of claim 1, characterized in that: in said first polymerization stage, a copolymer of ethylene with one or more α-olefins (LLDPE) is obtained, having a content of ethylene units of 80-99%wt., said copolymer of ethylene consisting of 10-90 %wt. of the total amount of polymer; in the second polymerization stage, polyethylene is produced having a number of total branching greater than 5 branches/1000 C and a density greater than 0.880 g/cirA

Inventors: BARUZZI GIOVANNI, CECCHIN GIULIANO, COLLINA GIANNI, COUGHLIN EDWARD BRYAN, FAIT ANNA, BARUZZI, GIOVANNI, CECCHIN, GIULIANO, COLLINA, GIANNI, COUGHLIN, EDWARD, BRYAN, FAIT, ANNA
Applicants: BARUZZI GIOVANNI, CECCHIN GIULIANO, COLLINA GIANNI, COUGHLIN EDWARD BRYAN, DU PONT, FAIT ANNA, MONTELL TECHNOLOGY COMPANY BV, BARUZZI, GIOVANNI, CECCHIN, GIULIANO, COLLINA, GIANNI, COUGHLIN, EDWARD, BRYAN, E.I. DU PONT DE NEMOURS AND COMPANY, FAIT, ANNA, MONTELL TECHNOLOGY COMPANY B.V.
Application year: 2000
Main classification: C08F10
IPC codes: C08F2, C08F4, C08F10, C08F110, C08F210, C08F297, C08L23