POLYOLEFIN PRODUCTION

Abstract: Provided is a catalyst for the polymerisation of olefins of general formula: R"(C4R'mC5C4R'n)XMeQ wherein X is a hetero-atom ligand with one or two lone pair electrons selected from the elements of Group VA or VIA which can be substituted or non-substituted: (C4Rm'C5C4Rn') is a symmetrically substituted, 3,6-substituted fluorenyl; R' is hydrogen or hydrocarbyl radical having from 1-20 carbon atoms, a halogen, an alkoxy, an alkoxy alkyl or an akylamino or aklylsilylo radical, each R' may be the same or different and m and n independently are 1, 2, 3, or 4, with the proviso that the bilateral symmetry is maintained; R" is a structural bridge between X and the (C4R'mC5C4R'n) ring to impart stereorigidity; Q is a hydrocarbyl radical having 1-20 carbon atoms or is a halogen; Me is a Group IIIB, IVB, VB, or VIB metal as positioned in the Periodic Table of Elements; and Me can be in any of its theoretically possible oxidation states. Also provided are olefin monomers (particularly propylene) polymerised using these catalysts to form syndiotactic/atactic block polymers of high molecular weight and comprising at least 70% of syndiotactic triads.

Description: POLYOLEFLN PRODUCTION FIELD OF THE INVENTION The invention relates to a metallocene catalyst useful in preparing syndiotactic/atactic block polyolefms and to the polymers so obtained The catalyst comprises a bridged monocyclopentadienyl metallocene m which the cyclopentadienyl is part of a fluorene ligand which is substituted symmetrically with respect to the active coordination position and is 3,6 substituted. The invention further includes a process of preparing syndiotactic/actactic block polyolefms that comprises the use of the present catalyst. The present invention also provides a process for polymerising olefins having three or more carbon atoms to produce polymers with syndiotactic/atactic stereochemical configurations. The catalyst and process of the invention are particularly useful in polymerising propylene to form a syndiotactic/atactic block polypropylene. BACKGROUND TO THE INVENTION AND PRIOR ART DISCUSSION As known in the art, syndiotactic polymers have a unique stereochemical structure m which monomenc units having enantiomorphic configuration of the asymmetrical carbon atoms follow each other alternately and regularly m the macromolecular mam chain. Syndiotactic polypropylene was first disclosed by Natta et al. in U.S. Patent 3,258,455. The Natta group obtained syndiotactic polypropylene by using a catalyst prepared from titanium trichloride and dietyl aluminium monochloπde. A later patent to Natta et al., U.S. Patent 3,305,538, discloses the use of vanadium triacetylacetonate or halogenated vanadium compounds in combination with organic aluminium compounds for producing syndiotactic polypropylene. U.S Patent 3,364,190 to Emrick discloses a catalyst system composed of finely divided titanium or vanadium trichloride, aluminium chloride, a trialkyl aluminium and a phosphorus-contammg Lewis base as producing syndiotactic polypropylene. U.S. Patent 4,892,851 discloses a metallocene catalyst for producing highly crystalline syndiotactic polyolefms. As disclosed m these patent references and as known in the art, the structure and properties of syndiotactic polypropylene differ significantly from those of isotactic polypropylene. The isotactic structure is typically described as having the methyl groups attached to the tertiary carbon atoms of successive monomeπc units on the same side of a hypothetical plane through the mam chain of the polymer, e.g., the methyl groups are all above or below the plane Using the Fischer projection formula, the sterochemical sequence of isotactic polypropylene is described as follows: Another way of describing the structure is through the use of NMR. Bovey's NMR nomenclature of an isotactic pentad is ...mmmm ... with each "m" representing a "meso" dyad or successive methyl groups on the same side m the plane. As known m the art, any deviation or inversion m the structure of the chain lowers the degree of isotacticity and crystallmity of the polymer. In contrast to the isotactic structure, syndiotactic polymers are those m which the methyl groups attached to the tertiary carbon atoms of successive monomeπc units m the chain lie on alternate sides of the plane of the polymer. Using the Fischer projection formula, the structure of a syndiotactic polymer is designated as: In NMR nomenclature, this pentad is described as ... rrrr .. m which each "r" represents a "racemic", i.e., successive methyl groups on alternate sides of the plane. The percentage of r dyads m the chain determines the degree of syndiotacticity of the polymer Syndiotactic polymers are crystalline and, like the isotactic polymers, are insoluble m xylene. This crystallmity distinguishes both syndiotactic and isotactic polymers from an atactic polymer that is soluble m xylene. Atactic polymer exhibits no regular order of repeating unit configurations m the polymer cham and forms an essentially waxy product. While it is possible for a catalyst to produce all three types of polymer, it is desirable for a catalyst to produce predominantly syndiotactic or isotactic polymer with some atactic block fractions. WO 98/02469 discloses use of metallocene catalysts m the formation of syndiotactic/atactic block homopolyolefms. The catalyst is a monocyclopentadienyl type catalyst. The cyclopentadienyl may be part of a fluorene ligand which is symmetrically substituted. The document is specifically concerned with 2,7 substituted fluorene hgands. However, the polymers produced using these catalysts do not have a melt temperature and are thus very sticky. This greatly reduces the utility of these polymers. EP-A-0,931 ,814 discloses production of syndiotactic/atactic block polypropylene. The catalyst used m the production of the syndiotactic/atactic block polypropylene is a monocyclopentadienyl type catalyst. The cyclopentadienyl may be part of a fluorene ligand which is symmetrically substituted. The application is specifically concerned with 2,7 substituted fluorene hgands WO 96/00734 relates to group IV metal diene complexes and addition polymerisation catalysts produced therefrom. The document is particularly concerned with metallocenes having a cyclopentadienyl ligand and additionally a chelatmg alkenyl ligand. Shiomura et al disclose, m Macromol. Rapid Commun., 17, 9-14, (1996), inversion of stereoregulaπty m a metallocene catalyst This document relates to an inversion of stereoselectivity of a particular metallocene from syndiospecific into isospecific by changing the cocatalyst. In particular, the document relates to an unsubstituted fluorene-contammg metallocene. EP-A-0,628,577 relates to fluorenyl-contammg silyl bridged metallocenes, processes of using such metallocene to polymerise olefins and the syndiotactic polypropylene so produced. This document refers specifically to a 2, 7 -substituted fluorenyl type catalyst. WO 93/19103 relates to a process and a metallocene catalyst system for the production of stereoregular polyolefms. The process permits improved control over tacticity, molecular weight and molecular weight distribution. In one example, the document relates to a polymerisation process employing a catalyst comprising an unsubstituted fluorene type ligand. SUMMARY OF THE INVENTION It is an object of the present invention to overcome the above and other problems associated with the prior art catalysts. Accordingly, the present invention provides a catalyst for the polymerisation of olefms of general formula: R"(C4R' m C5C 4 R' n )XMeQ wherein X is an hetero-atom ligand with one or two lone pair electrons selected from the elements of Group VA or VIA which can be substituted or non-substituted; (C4R m 'C5C4R n ') is a symmetrically substituted, 3,6-substιtuted fluorenyl; R' is hydrogen or hydrocarbyl radical having from 1-20 carbon atoms, a halogen, an alkoxy, an alkoxy alkyl or an alkylammo or alkylsilylo radical, each R' may be the same or different and m and n independently are 1 , 2 3 or 4, with the proviso that the bilateral symmetry is maintained; R" is a structural bridge between X and the (C4R' rn C5C4R' n ) ring to impart stereoπgidity ; Q is a hydrocarbyl radical having 1 -20 carbon atoms or is a halogen; Me is a Group IIIB, IVB, VB, or VIB metal as positioned m the Periodic Table of Elements, and Me can be in any of its theoretically possible oxidation states. The present invention further provides a process for preparing syndiotactic/atactic block polyolefms, and more particularly syndiotactic/actactic block polypropylene using the above catalyst The catalyst and process can each be adapted to produce a polymer with differing syndιo-/atactιc block ratios. The invention also provides syndiotactic/atactic block homopolyolefms and particularly a syndiotactic/atactic block homopolypropylene, obtainable using the present catalysts. One advantage of the present catalysts is that they are capable of producing syndiotactic/actactic block homopolyolefms which are not sticky and which exhibit a melt temperature, unlike polymers produced using prior art catalysts. In addition, the present catalysts show good activity as compared with prior art catalysts. DETAILED DESCRIPTION OF THE INVENTION The catalyst comprises a metallocene, i.e., a metal derivative of a cyclopentadiene, and an ionising agent. The metallocene compound contains only one substituted cyclopendadienyl ring and is of the general formula: R"(C4R' m C 5 C4R' n )XMeQ wherein X is an hetero-atom ligand with one or two lone pair electrons and selected from the elements of Group VA or VIA and is preferably nitrogen, phosphorus, oxygen or sulfur, which can be substituted or non-substituted, (C4R m 'C5C4R n ) is a symmetrically substituted fluorenyl which is 3,6-substιtuted hydrogen or hydrocarbyl radical having from 1-20 carbon atoms, a halogen, an alkoxy, and alkoxy alkyl or an alkylammo or alkylsilylo radical, each R' may be the same or different and m and n independently are 0, 1 , 2, 3 or 4, with the proviso that the bilateral symmetry is maintained; R' is a structural bridge between the X and (C4R m 'C5C4R n ') ring to impart stereorigidity and, preferably is a silyl or hydrocarbyl biradical having at least one silicon or carbon atom to form the bridge, Q is a hydrocarbyl radical, such as an alkyl, aryl, alkenyl, alkylaryl or arylalkyl radical having 1-20 carbon atoms or is a halogen; Me is a Group IIIB, IVB, VB, or VIB metal as positioned in the Peπdic Table of Elements; Me can be m any of its theoretically possible oxidation states Preferred metals for the catalyst of the invention are Zr, Ti, and Hf. It is particularly preferred that the fluorenyl group is 3,6 substituted and not substituted at any other position. The term "symmetrically" shall mean that the local bilateral symmetry of the active polymerisation sites is essentially maintained. The present invention further provides a process for producing syndiotactic/atactic block polyolefms, particularly syndiotactic/atactic polypropylene. The process comprises utilising at least one of the catalysts described by the above formula and introducing the catalyst into a polymerisation reaction zone containing an olefin monomer. In addition, a co-catalyst such as alumoxane may be introduced into the reaction zone. Further, the catalyst may also be pre-polymeπsed prior to introducing it into the reaction zone and/or prior to the stabilisation of reaction condition in the reactor. Metallocene catalysts are single site catalysts which, generally, produce polymers having a narrow molecular weight distribution. While the present invention is mainly directed to α-olefm homopolymerisation, co-polymeπsation with other olefms can be carried out. The present invention also provides for a new polymer comprising alternating blocks of syndiotactic and atactic sequences, preferably long syndiotactic and short atactic sequences, most preferably comprising a fraction of syndiotactic triads (rr) of at least 70% A more complete appreciation of the invention and may of the attendant advantages thereof will be readily understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: Figure 1 shows the structure of a catalyst precursor, 3,6-bιs-tert-butyl-fluorenyl-9- dimethylsylyl-tert-butyl-amido titanium dichloπde. The present invention provides a polymer comprising alternating blocks of syndiotactic and atactic sequences. The polymer of the invention possesses particularly long sequences of syndiotactic species and short sequences of atactic species. The syndio- /atactic ratio can easily be modified by changing the polymerisation conditions and/or the catalyst structure withm the invention. For example, as shown below, increasing the polymerisation temperature for a given catalyst decreases the syndιo-/atactιc ratio. As also evidenced below, replacing a dimethylsilyl bridge by a diphenylsilyl bridge also decreases the syndιo-/atactιc ratio for identical polymerisation conditions. In the specific case of polypropylene, it ahs been noted that the polymer has elastomeπc properties Without being bound by the theory, it may be considered that these properties are deriving from the combination of the crystalline syndiotactic part and the amorphous atactic part. The polymer obtained has a molecular weight ranging from 50,000 to more than 1,000,000 depending on the polymerisation conditions and on the catalyst used in the process For example, as shown below, replacing a dimethylsilyl bridge by a diphenylsilyl bridge results m increased molecular weight under identical polymerisation conditions. The present invention provides a catalyst and process for the production of syndiotactic/atactic block polyolefms, particularly polypropylene. The catalysts of the present invention produce a polymer with a syndiotactic/atactic block microstructure. The applicants have now unexpectedly found that the catalyst of the invention can be used for the production of high molecular weight polyalphaolefm with stereoregular/stereoirregular block micro-structure. When propylene or other alpha-olefms are polymensed using a catalyst consisting of a transition metal compound, the polymer product typically comprises a random mixture (reactor blend) of amorphous atactic and crystalline xylene insoluble fractions. The crystalline fraction may contain either isotactic or syndiotactic polymer or a mixture of both. The catalysts of the present invention have syndιo-/atactιc specificity and produce polymeric chains with differing syndιo-/atactιc block ratios. The metallocene catalysts of the present invention may be described by the formula: R"(C4R' m C5C 4 R' n )XMeQ wherein X is an hetero atom ligand with one or two lone pair electrons and selected from the elements of Group VA or VIA and is preferably nitrogen, phosphorus, oxygen or sulfur which can be substituted or not. (C4R' m C5C4R' n ) is a fluorenyl ring, substituted symmetrically and substituted at the 3 and 6 positions each R' is hydrogen or hydrocarbyl radical having form 1-20 carbon atoms, a halogen, an alkoxy, and alkoxy alkyl or an alkylammo or alkylsilylo radical, each R' may be the same or different, m and n independently are 0, 1, 2, 3 or 4, and with the proviso that the bilateral symmetry is maintained; R" is a structural bridge between the hetero atom X and (C4R' m C5C4R' n ) ring to impart stereorigidity, and preferably is a silyl or hydrocarbyl biradical having at least one silicon or carbon atom to form the bridge; Q is a hydrocarbyl radical, such as an alkyl, aryl, alkenyl, alkylaryl or arylalkyl radical having 1-20 carbon atoms or is a halogen- Me is a Group IIIB, IVB, VB, or VIB metal as positioned in the Periodic Table of Elements, the transion metal can adopt any of the possible oxidation states. Preferred metals for the catalysts of the invention are Ti, Zr, and Hf A particularly suitable metal is Ti (C4R' m C5C4R'4) compπses hydrocarbyl biradicals bonded to two adjacent carbon atoms m a cyclopentadienyl ring to form a fused ring In order to obtain syndiospecificity the cyclopentadienyl or fluorenyl rings m the metallocene catalysts must be substituted m an essentially symmetric manner with respect to the active coordination positions so that the metallocene exhibits bilateral symmetry at least around the active coordination site. It has been unexpectedly noted that if in the original syndiospecific catalysts described in US patent 4,892,851 the non-substituted cyclopentadienyl is replaced by a heteroatom ligand with one or two lone pair electrons and selected from elements of Group VA or VI A, the stereospecificity of catalyst will be periodically changed from syndiospecificity to aspecificity during the polymerisation giving rise to the formation of atactic blocks withm the predominantly syndiotactic chain Bilateral symmetry is defined as the condition m which there is no substituent or one or more substituents on one side and no substituent or one or more substituents on the other side m the same relative position such that a mirror image is formed from one side to another. One preferred example of such a compound is 3,6-dι-tert-butyl-9-fluorenyl- dimethylsilyl-tert-butylamido titanium dichloπde. An illustration of the hgands of this compound is shown m Figure 1. Bilateral symmetry is illustrated by a plane bisecting the fluorenyl and the bridge resulting the right side of each ligand being a mirror image of its left side The numerical positions of the fluorenyl ring represent the position of possible substituents on the fluorenyl ring, 9 being the position of the bridge. Whilst not wishing to be bound by a theory and without intending to limit the scope of the present invention as indicated by the claims, it is believed that during the polymerisation reaction the growing polymer chain migrates from one coordination position to the other after each monomer insertion as the catalyst simultaneously isomerises and enchains sequences of polymer of the syndiotactic structure; occasionally this mechanism is disturbed by a haptocity change of the fluorenyl-transition metal bonding or through inversion of the chiral nitrogen center, leading to the loss of steric control and formation of short sequences of atactic blocks withm a predominantly syndiotactic polymer chain This mechanism differs from that put forward for syndiospecific catalysts such as the active species formed from isopropylidene [cyclopentadιenyl-9-fluorenyl] zirconium dichloπde as disclosed m U.S Patent 4,892,851 wherein the fluorenyl ring exhibits mamly pentahapto bonding, i.e.. all five carbon atoms of the fluorenyl rings are coordinated with the zirconium atom. It is believed that the catalysts of the present invention demonstrate a reversible transformation of syndiospecific sites to atactic specific sites through a haptocity change related stereoregulation/stereoderegulation mechanism. In theory, the steric condition for a preferred orientation of the growing chain, adoption of one of the two possible conformations, intermittently disappears and the coordination and insertion of either of the propylene prochiral faces at both lateral coordination positions becomes accidental. This mechanism enchains atactic sequences in a predominantly syndiotactic polymer chain by a spontaneous change m haptocity of the bonding between the fluorenyl and the transition metal from pentahapto to tri- and possibly mono-hapto bonding which results in the loss of stereoregulatmg property of the sites. This electro-dynamic behaviour of the active species provides m effect a temporary transformation of enantiotopic, equivalent sites to non-enantiotopic, non-equivalent environment at the lateral coordination positions, atactic sequences being formed whenever this occurs. Theoretically, only when both events, i.e. periodic loss of stereoregulaπty and the stereospecific character of the catalyst occur simultaneously, is a syndiotactic/atactic block homopolymer formed When catalysts of the present invention are used m polymerisation of olefins, the polymer which results is of a syndιo-/atactιc microstructure as illustrated below In a preferred embodiment of the catalyst of the present invention (C4R' m C5C4R' n ) is preferably a substituted fluorenyl ring with bulky substituents m 3 and 6 positions such as tert-butyl and tπmethylsilyl; Me is preferably titanium, zirconium or hafnium, more preferably ;zιrcomum or titanium and most preferably titanium; Q is preferably a halogen and is most preferably chlorine; and R" is preferably a silyl or hydrocarbyl biradical of at least one silicon or carbon atom which is coordinated with the heteroatom ligand and with (C4R' m C5C4R'4), most preferably a silyl or hydrocarbyl biradical of at least one silicon or carbon atom being connected with heteroatom ligand and the (C4R' m C5C4R'R n ) moiety. Exemplary hydrocarbyl biradicals for the structural bridge include ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, and the likes. Other hydrocarbyl radicals useful as the structural bridge m the present catalysts include linear alkyl radicals of 1-10 carbon atoms or branched alkyl radicals of 1-20 carbon atoms, preferably one carbon atom, which may be substituted or unsubstituted, preferably substituted. Exemplary silyl biradicals for a structural bridge include dimethylsilyl (which is preferred), diphenylsilyl of the general formula R2Sι=, with each R independently being any C1 -C20 hydrocarbyl or C1 -C20 mono-, di- or tπalkyl silyl radicals. The catalyst may be prepared by any method known m the art Generally, the preparation of the catalyst complex consists of forming and isolating the substituted cyclopentadienyl 01 fluoienyl hgands which are then reacted with a halogenated metal to form the complex The preferred method is that disclosed in U S Patent No 4,892,851 The catalyst may furthei be suppoited on an oigamc or inorganic carriei The synthesis process generally compπses the steps of (1 ) preparing the halogenated oi alkylated metal compound, (2) preparing the ligand, (3) synthesizing the complex, and (4) purifying the complex The metalocene catalysts of the present invention are useful m many of the polymeπsation processes (solution, slurry or gas phase) known m the art including many of those disclosed foi the preparation of ciystalhne oi amorphous polypropylene When the catalysts of the present invention are used m these types of processes, the processes produce syndiotactic/atactic block polymers Further examples of polymerisation processes useful m the practice of the present invention include those disclosed m US Patent 4,767,735 and European Patent Application 310,734, the disclosure of which are hereby incorporated herein by reference Those pieferred polymerisation procedures include the step of prepolymeπsmg the catalyst and/or precontactmg the catalyst with a cocatalyst and an olefm monomer prior to introducing the catalyst into a reaction zone The ionising agent is an alumoxane, an aluminium alkyl, other Lewis acid or a combination thereof which will ionise a neutral metallocene compound to form a catiomc metallocene catalyst Examples of such ionising agents are methyl alumoxane (MAO), tπ ethyl aluminium (TEA1) and tπs (pentafluorophenyl)boron Othei ionising agents aie disclosed m European Patents 277003 and 277004 which are hereby incorporated by reference The syndιo-/atactιc-specιfιc catalysts of the present invention are particularly useful combination with an aluminium alkyl cocatalyst or with an alumoxane, preferably with the latter In addition, a complex may be isolated between a metallocene catalyst as described herein and an aluminium cocatalyst m accordance with teachings of European Patent 226,463. As disclosed therein, a metallocene is reacted with an excess of alumoxane m the presence of a suitable solvent. A complex of the metallocene and alumoxane may be isolated and used as a catalyst m the present invention The Alumoxanes useful in combination with the catalysts of the present invention, either m the polymerisation reaction or in forming the complex disclosed above, may be represented by the general formula (R-Al-O-) n m the cyclic form and R(R-Al-O-) n AlR2 m the linear form, wherein R is an alkyl group with one to five carbon atoms and n is an integer from 1 to 20 Most preferably, R is a methyl group and the preferred alumoxane is mefhylalumoxane (MAO). The alumoxanes can be represented structurally as follows - n = 15-20 The alumoxanes can be prepared by various methods known in the art. Preferably, they are prepared by contacting water with a solution of tπalkyl aluminium, such as tnmethyl aluminium, in a suitable solvent such as benzene. Another preferred method includes the preparation of alumoxane m the presence of a hydrated copper sulfate as described in US Patent 4,404,344 the disclosure of which is hereby incorporated by reference. This method comprises treating a dilute solution of tnmethyl aluminium in toluene with copper sulfate. The preparation of other aluminium cocatalysts useful in the present invention may be prepared by methods known to those skilled in the art. The Examples given below illustrate the present invention and its various advantages and benefits m more detail EXAMPLES Example 1 The synthesis procedure was performed under an inert gas atmosphere using a Vacuum Atmospheres glovebox or Schlenk techniques. Step 1 . Preparation of 3,6-dι-tert-butylfluorenyl-dιmethylsιlyl-chlorιde (1 ) a) Aromatisation of the fluorene: In a one liter flask equipped with a magnetic stirring bar nitrogen mlet and reflux condenser, there was added 0.1 mol of a solution of 3,6-dι-tert-butylfluorene m 300 cc of dietyl ether. To this solution was added at room temperature dropwise 0.1 equimol of methyllithium in ether (1 6 molar). The reaction was completed after gas evolution stops The orange solution was used m the next step. b) Reaction with dimethyl dichlorosilane: The orange solution prepared in step l a was added dropwise to a solution of 0.1 mol of dimethyldichlorosilane m 200 ml of ether. The mixture was stirred for several hours at room temperature until the reaction was completed. Step 2 Preparation of tert-butylhthiumamide (2)- In a one liter flask equipped with magnetic stirring bar nitrogen mlet and reflux condenser, 0.1 mol of tert-butylamme was dissolved m 200 ml of diethyl ether. The solution was cooled to -78°C One equimol of methyllithium m ether was added dropwise to the solution The temperature was increased to room temperature slowly. The reaction mixture was stirred for several hours at room temperature until the formation of the title compound was complete. Step3. Preparation of 3,6-dι-tert-butylfluorenyl-dιmethylsιlyl-tert-butylamιne (3): The reaction products prepared m step 1 and step 2 were added together and stirred for several hours at room temperature. The LiCl formed as byproduct was filtered off and the ether filterated was subjected to evaporation. The title compound was obtained as a yellow oil Step 4 Preparation of 3,6-dι-tert-butyl-dιmethyl-tert-butylamιdo titanium di chloride (4) a) Formation of diam on: 0.25 mol of (3) was dissolved in 200 ml of diefhyl ether. To this solution was added dropwise 0.5 mol of methyllithium m ether The solution became red. The reaction was stopped after gas evolution had stopped b) Reaction of the diamon with T1CI4 The red powder obtained after evaporation of the ether from the solution resulting from step 4a was washed several times with pentane and then reacted with 0.25 mol of T1CI4 in 200 ml pentane. The mixture was stirred for several hours at room temperature and filtered to separate the LiCl . Evaporation of the solvent led to the isolation of a brown powder. Recrystalhsation of the product from dichloromethane provided spectroscopically pure product (4) Example 2 Propylene was polymensed using the metallocenes produced by example 1. Two litres of liquid propylene were introduced into a 4 1 bench reactor at room temperature. The metallocene was placed m three milhhtres of 1 1 % solution of MAO m toluene to form a solution which was added to the reactor and the temperature increased to 40°C the polymerisation reaction was allowed to run for 60 minutes during which time the reactor was maintained at the temperature indicated m Table 1 for each individual run. The reaction was terminated by venting the reactor of monomer. The catalyst activity m grams of polypropylene per grams of catalyst per hour was calculated. The molecular weight, molecular weight distribution and ^C NMR analysis of the polymer were determined. The results are shown m Table 1. The further examples below were carried out using a process analogous to that of Example 2. Exampe 3 polymerisation of propylene with (4) at 60°C. Example 4: polymerizartion of propylene with (4) at 80°C. Example 5: polymerisation of Propylene with (4) at 40°C, in the presence of 3 N 1 of H . The polymerisation conditions and results are summarized m Table 1. The variation of pentad stereosequence intensity distribution with polymerisation temperature for the above examples is shown m Table 2. Table 1 Polymerization conditions and results for Pol. Tem p A ctivity M p rrrr w rr (°C) (kg/g) (°C) (%) (%) [kDa] 40 222 703 2.9 123 81.6 90.3 40(*) 157 733 2.9 121 82.0 91.0 60 181 765 2.7 105 74.0 85.9 80 271 700 3.3 N o p e a k 62.8 78.8 Polymerization were performed in a pressure reactor in iquid propylene with 850ppm MAO; (*) : 0.3 N1 H2 Table 2 Variation of pentad stereosequence intensity distributions with polymerization temperature for μ -(Me 2 Si)(3,6di-tBuFlu)(tBuN)TiCI 2 - MAO system Pol. Temp. m m m m m m m r rm m r m m rr rm rr + m rm r rrrr m rrr m rrm ( β C) (%) (%) (%) (%) m rm m (%) (%) (%) (%) 40 0.1 0.3 1.6 3.5 3.6 0.6 81.6 7.9 0.9 40(*) 0.0 0.3 1.5 3.4 3.4 0.5 82.0 7.8 1.2 60 0.1 0.7 1.7 4.1 6.5 1.0 74.0 10.6 1.3 70 0.1 0.8 1.7 4.2 8.3 1.2 69.4 12.7 1.5 80 0.2 1.2 2.2 5.0 10.6 1.9 62.8 14.4 1.6 Polymerization condition I 11 pro pyl ene; 5 mIMAO (1 l t% in toluene); 60min.; (* r ) : 0.3 Nl H2

Claims: CLAIMS: 1 A catalyst for the polymerisation of olefins of general formula. R"(C4R' m C 5 C4R' n )XMeQ wherein X is an hetero-atom ligand with one or two lone pair electrons selected from the elements of Group VA or VIA which can be substituted or non-substituted' (C4R m 'C5C4R n ') is a symmetrically substituted, 3,6-substιtuted fluorenyl; R' is hydrogen or hydrocarbyl radical having from 1-20 carbon atoms, a halogen, an alkoxy, an alkoxy alkyl or an alkylammo or alkylsilylo radical, each R' may be the same or different and m and n independently are 1, 2 3 or 4, with the proviso that the bilateral symmetry is maintained; R" is a structural bridge between X and the (C4R' m C5C4R' rι ) ring to impart stereorigidity; Q is a hydrocarbyl radical having 1-20 carbon atoms or is a halogen; Me is a Group IIIB, IVB, VB, or VIB metal as positioned in the Periodic Table of Elements; and Me can be in any of its theoretically possible oxidation states. 2. A catalyst according to claim 1 , wherein the substituent of the fluorenyl radical is 3,6 dι-tert-butyl-9-fluorenyl. 3. A catalyst according to claim 1 or claim 2, wherein the heteroatom ligand is selected from the group consisting of N, P, O and S. 4. A catalyst according to any of claims 1-3, wherein Me is selected from the group consisting of Ti, Zr and Hf. 5. A catalyst according to any preceding claim, wherein R" is preferably a silyl or hydrocarbyl biradical having at least one silicon or carbon atom to form the bridge. 6. A catalyst according to claim 5, wherein R" is dimethylsilyl. 7. A catalyst according to any preceding claim, wherein Q is selected from the group consisting of alkyl, aryl, alkenyl, alkylaryl and arylalkyl radicals. 8. A process for polymerising an olefm monomer to form a syndiotactic/atactic block polyolefm comprising: a) selecting a catalyst according to any one of claims 1 to 7 b) introducing the catalyst into a polymerisation reaction zone containing an olefm monomer and maintaining the reaction zone under polymerisation reaction conditions; and c) extracting a syndiotactic/atactic block polymer. 9. A process according to claim 8, wherein the monomer is propylene. 10. A syndiotactic/actactic block homopolymer of a α-olefin having 3 or more carbon atoms, obtainable according to a process as defined in claim 8 or claim 9. 11. A syndiotactic/atactic block homopolymer according to claim 10, which comprises a polypropylene. 12. A syndiotactic/atactic block homopolymer according to claim 10, or claim 11 wherein the fraction of the syndiotactic triads is at least 70%. 13. A syndiotactic/atactic block copolymer of two or more α-olefin monomers obtainable by polymerising the α-olefm monomers m the presence of a catalyst as defined in any of claims 1-7.

Inventors: RAZAVI ABBAS, RAZAVI, ABBAS
Applicants: FINA RESEARCH, RAZAVI ABBAS, FINA RESEARCH S.A., RAZAVI, ABBAS
Application year: 2000
Main classification: C08F10
IPC codes: C08F4, C08F10, C08F110