DD299651A5 - METHOD FOR GENERATING SYNDIOTACTIC POLYOLEFINES WITH A WIDE DISTRIBUTION OF THE RELATIVE MOLECULAR MATERIAL - Google Patents

Abstract

The invention relates to a process for the production of syndiotactic polyolefins having a broad distribution of the relative molecular masses. The catalyst used in the process according to the invention has two different bridging metallocenes. The catalyst is generally described by the formula R (CpRn) (CpRm) MeQk wherein Cp is each a cyclopentadienyl or a substituted cyclopentadienyl ring; Each of Rn and Rm is the same or different and is a hydrocarbyl radical having from 1 to 20 carbon atoms; R is a structural bridge between the two Cp rings, which gives the catalyst stereorigidity; Me is a metal of Group IVb, Vb or VIb of the Periodic Table of the Elements; Each Q is a hydrocarbyl radical of 1 to 20 carbon atoms or a halogen; 0k3; 0n4; 1m4; and wherein Rm is selected such that (CpRm) is a sterically different ring than (CpRn). This catalyst is introduced into a polymerization reaction zone containing an olefin monomer and the reaction zone maintained under polymerization reaction conditions. {Polyolefins, syndiotactic; polymerization; olefin polymerization; Molekuelmassenverteilung; Metallocene catalyst}

Description

The invention relates to a process for the production of syndiotactic polyolefins with a broad distribution of the molecular masses using one or more new catalysts.

As known in the art, syndiotactic polymers have a unique stereochemical structure in which monomeric units having enantiomorphous configuration of the asymmetric carbon atoms in the macromolecular backbone alternate and regularly follow one another. Syndiotactic polypropylene was first reported by Natta et al. in US 3,258,455. Natta's group obtained syndiotactic polypropylene using a catalyst made from titanium trichloride and di-ethylaluminum monochloride. A later patent to Natta et al., US Pat. No. 3,305,538, discloses the use of vanadium triacetylacetonate or halogenated vanadium compounds in conjunction with organic aluminum compounds for the production of syndiotactic polypropylene. U.S. 3,364,190 to Emrick discloses a catalyst system consisting of finely divided titanium or vanadium trichloride, aluminum chloride, a trialkylaluminum, and a phosphorus-containing Lewis base as a catalyst system that produces sydiotactic polypropylene. As disclosed in these patent references and 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 one in which the methyl groups are bonded to the tertiary carbon atoms of successive monomeric units on the same side of a hypothetical level throughout the main chain of the polymer; For example, the methyl groups are all above or below the level. Applying Fischer's projection formula, the stereochemical sequence of isotactic polypropylene is as follows:

Another way to describe the structure is to use NMR. Bovey's NMR nomenclature for an isotactic pentavalent pentad is ... mmmm ..., where "m" represents a "meso" dyad or consecutive methyl groups on the same side of the Ebono. As known in the art, any deviation or inversion in the structure of the chain reduces the degree of isotacticity and crystallinity of the polymer.

In contrast to the isotactic structure, syndiotactic polymers are those in which the methyl groups bound to the tertiary carbon atoms of successive monomeric units in the chain lie on alternate sides of the plane of the polymer. Syndiotactic polypropylene is zigzagged as follows:

Using Fischer's projection formula, the structure of a syndiotactic polymer is shown as follows:

I i

In NMR nomenclature, this pentad is described as ... rrrr ... where "r" represents a "racomic" dyad, i. successive methyl groups on alternate sides of the plane. The percentage of r dyads in the chain determines the degree of syndiotacticity of the polymer. Syndiotactic polymers are crystalline and, like the isotactic polymers, insoluble in xylene. This crystallinity distinguishes both syndiotactic and isotactic polymers from an atactic polymer that is soluble in xylene. An atactic polymer does not have a regular ordering of repeater unit configurations in the polymer chain and is essentially a waxy product.

While it is possible for a catalyst to produce all three types of polymers, it is desirable for a catalyst to produce predominantly isotactic or syndiotactic polymer with very little atactic polymer. Catalysts producing sotactic polyolefins are disclosed in co-pending U.S. Patents Nos. 034,472, filed April 3, 1987; 096,075, filed 9/11/87 and 095,755, filed 9/11/87. This application discloses chiral, stereorigid metallocene catalysts that polymerize olefins to form isotactic polymers, and that are particularly useful in the polymerization of a highly isotactic polypropylene. However, the present invention provides another class of metallocene catalysts which are useful in the polymerization of syndiotactic polyolefins and in particular syndiotactic polypropylene.

In addition to a newly discovered catalyst, the invention also provides syndiotactic polypropylene having a novel microstructure. It has been discovered that the catalyst structure not only affects the formation of a syndiotactic polymer as opposed to an isotactic polymer, but apparently also the type and number of deviations in the chain from the predominantly repeating units in the polymer. Previously it was believed that the catalysts used to make syndiotactic polypropylene exert chain-end control over the polymerization mechanism. These earlier known catalysts such as those of Natta et al. in the references given above predominantly produce syndiotactic polymers having the structure

Γ Ι Γ Μ

or in NMR nomenclature ... rrrrrmrrrrrr ... The NMR analysis for this structure of syndiotactic polypropylene is presented in Zambelli et al., Macromolecules, Vol. 13, pp. 267-270 (1980). Zambelli's analysis shows the supremacy of the individual

Meso-dyad about every other deviation in the chain. However, it has been discovered that the catalysts of this invention

produce a polymer having a microstructure different from that previously known and disclosed, and also a polymer having a high percentage of racemic dyads in the structure.

The invention provides a process for the polymerization of olefins having three or more carbon atoms for production

of a polymer having a syndiotactic stereochemical configuration with broad distribution of syndiotactic stereochemical configuration with broad distribution of molecular weights. The process of using a novel catalyst is particularly useful in the polymerization of propylene to form a highly crystalline, novel microstructure of syndiotactic polypropylene.

The present invention has for its object to provide a method for producing syndiotactic polyolefins with a broader To provide distribution of molecular weight. The object is achieved by a special catalyst, with the help of a polymer with a high

syndiotactic index and with a novel syndiotactic microstructure. In addition, syndiotactic polypropylene having a broad molecular weight distribution is obtained. Particularly advantageous is the

Ability to "tailor" the characteristics of the polymer, such as melting point, by varying the structure of the polymer Catalyst.

The catalyst used is a stereorigid metallocene catalyst which is described by the following formula. R "(CpR") (CpR ' _m ) Me0 _k

wherein Cp is a cyclopentadiene or a substituted cyclopentadienyl ring; R _n and R ' _{m are} each a hydrocarbyl radical having from 1 to 20 carbon atoms R i is a structural bridge between the two Cp rings which confers stereorigidity to the Cp rings, Me is a transition metal, and Q is each a hydrocarbyl radical or a halogen. Further, R ' _m is selected such that (CpR'J is a sterically different substituted cyclopentadienyl ring than (CpR _n ). It has been discovered that the use of a metallocene catalyst having sterically distinct cyclopentadienyl rings produces a predominantly syndiotactic polymer rather than an isotactic polymer.

The process of the present invention for producing syndiotactic polyolefins, and in particular syndiotactic polypropylene, consists in employing at least two of the catalysts described by the above formula and introducing the catalyst into a polymerization reaction zone containing an olefin monomer. In addition, an electron donor compound and / or a cocatalyst such as alumoxane can be introduced into the reaction zone. Furthermore, the catalyst can also be prepolymerized in the reactor before it is introduced into the reaction zone and / or before the reaction conditions are stabilized. Syndiotactic polyolefins having a broad distribution of molecular weights are obtained.

It was further found that the characteristics of the polymer produced by the polymerization process described by the heller could be controlled by varying the polymerization temperature or the catalyst structure. In particular, it was found that a higher polymerization temperature gave a syndiotactic polymer having a mixed microstructure. It has also been found that the melting points of the polymer are influenced by the reaction temperature, the catalyst-cocatalyst ratio and the structure of the catalyst. A higher reaction temperature generally produces a less crystalline polymer with a low melting point. Furthermore, polymer products having different melting points can be obtained by varying the catalyst structure.

The preparation of a bridge metallocene catalyst is accomplished by contacting a cyclopentadiene or a substituted cyclopentadiene with fulvene or a substituted fulvene under reaction conditions sufficient to produce a bridged dicyclopentadiene or a substituted dicyclopentadiene. The method further includes contacting bringing the bridge dicyclopentadiene with a metal compound of the formula MeQ _k as defined above under reaction conditions sufficient to complex the bridge dicyclopentadiene to produce a bridge metallocene.

The invention is explained in more detail by drawings

 Mean in it

FIG. 1: Illustration of the structure of a preferred catalyst of the invention, specifically iso

propyUcyclopentadienVIKfluorenyljhafniumdichlorid; 2: NMR spectrum for the polymer produced in Example 1 using iso

propyl (cyclopentadienyl) (fluorenyl) zirconium dichloride and one-time crystallization of the polymer from xylene; Fig. 3 and 4: IR spectra for the polymers produced in Example 7 or 8, when three times the crystallization of the polymer from xylene.

The invention provides a process for the production of syndiotactic polyolefins, in particular polypropylene. The catalysts used in the process of the present invention not only produce syndiotactic polypropylene but also produce a polymer having a novel microstructure.

When polymerizing propylene or other alpha-olefins using a transition metal compound catalyst, the polymer product typically comprises a mixture of amorphous atactic and crystalline xylene-insoluble fractions. The crystalline fraction may contain either isotactic or syndiotactic polymer or a mixture of both. Highly isospecific metallocene catalysts are disclosed in co-pending U.S. applications with application numbers 034,472; 096,075 and 095,755. In contrast to the catalysts disclosed in each application, the catalysts of this invention are syndiospecific and produce a polymer having a high syndiotactic index. It has been discovered that syndiotactic polymers generally have a lower heat of crystallization than the corresponding isotactic polymers. In addition, syndiotactic polymers have a higher melting point than isotactic polymers with the same number of defects in the polymer chain. The metallocene catalysts of the invention can be described by the formula _k R "(CpR") (CpR'JMeQ wherein Cp are each a cyclopentadienyl or substituted cyclopentadienyl ring; R _n and R _'m are hydrocarbyl radicals having 1 to 20 carbon atoms, wherein R _{n may} each be the same or different and each R ' _{m may} be the same or different, R "is a structural bridge between the two Cp rings which confers stereorigidity to the Cp rings within the catalyst, and R" is preferably selected from the group Me is a Group 4b, 5b, or 6b metal from the Periodic Table of the Elements; Q is a group consisting of an alkyl radical of 1 to 4 carbon atoms or a hydrocarbyl radical containing silicon, germanium, phosphorus, nitrogen, boron or aluminum; Is hydrocarbyl radical having from 1 to 20 carbon atoms or a halogen; 0sk <3; 0 <n <4 and 1 £ m <4. It has been discovered that to obtain the syndiospec if the Cp rings in the metallocene catalysts need to be substituted in a substantially different manner such that there is a steric difference between the two Cp rings, and therefore R ' _m is chosen such that (Cp R'J is a substantially different substituted ring is as (CpR _n ). To produce a syndiotactic polymer, the features of the groups substituted directly on the cyclopentadienyl rings appear to be important. Thus, as used herein, the terms "steric difference" or "sterically different" mean that a difference between the steric features of the Cp rings imp. Fourth, which controls the approach of each successive monomer unit added to the polymer chain. The steric difference between the Cp rings keeps the approaching monomer from a random approach and controls the approach so that the monomer can be added to the polymer chain in the syndiotactic configuration.

Without wishing to restrict the scope of the invention as defined by the claims, it is believed that in the polymerization reaction both the catalyst and the approaching monomer units will isomerize with each monomer added to the polymer chain. This isomerization of the monomer, which is controlled by the steric blocking of the differently substituted Cp rings, results in the alternating configuration of syndiotactic polymers and is in contrast to the chain end control of Natta et al. disclosed catalysts. The different reaction mechanism also results in a different structure for the polymer. In a preferred catalyst of the invention Me is titanium, zirconium or hafnium; Q is preferably a halogen and most preferably chlorine; and k is preferably 2, but it may also vary with the valency of the metal atom. Examples of hydrocarbyl radicals include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, amyl, isoamyl, hexyl, heptyl, octyl, nonyl, oecyl, cetyl, phenyl and the like. Other hydrocarbyl radicals useful in the catalysts include other alkyl, aryl, alkenyl, alkylaryl, or arylalkyl radicals. Additionally, R _n and R ' _{m may} comprise hydrocarbyl radicals attached to a single carbon atom in the Cp ring, as well as radicals attached to two Carbon atoms are bonded in the ring. Figure 1 shows the structure of a preferred catalyst, iso-propyl (fluorenyl cyclopentadienyl o-hafnium dichloride.) The zirconium analog of the catalyst shown in Figure 1 is likewise preferred.

The catalyst can be prepared by any method known in the art. The following examples disclose two methods of preparing the catalyst, with the second method being preferred because it provides a more stable and more active catalyst. It is important that the catalyst complex be "clean" since impure catalysts usually produce low molecular weight amorphous polymer, In general, the preparation of the catalyst complex consists of forming and isolating the Cp or substituted Cp ligands, which are then used to form the catalyst Formation of the complex can be reacted with a halogenated metal.

The catalysts of this invention are useful in many of the polymerization processes known in the art, including many of those disclosed for the production of isotactic polypropylene. When the catalysts of the present invention are used in these processes, syndiotactic polymers are more likely to be produced than isotactic polymers. Further examples of polymerization processes useful in the practice of the invention include those disclosed in U.S. Patents, Application Serial Nos. 009,712, filed on January 2, 1987, and Application Serial No. 095,775, filed on September 9, 1987, the disclosure of which is incorporated herein by reference is. These preferred polymerization processes include the step of prepolymerizing the catalyst and / or causing a pre-contact of the catalyst with a cocatalyst and an olefin monomer prior to introducing the catalyst into a reaction zone.

In accordance with the prior disclosures of metallocene catalysts for the production of isotactic polymers, the syndiospecific catalysts of the present invention are particularly useful in combination with an aluminum cocatalyst, preferably an alumoxane, an alkylaluminum, or a mixture thereof. In addition, a complex between a metallocene catalyst as described herein and an aluminum cocatalyst may be transferred in accordance with the teachings of EP Publication No. 226,463, published June 24, 1987, and Exxon Chemical Patents Inc., filed with Howard Turner as inventor, be isolated. As disclosed therein, a metallocene is reacted with an excess of alumoxane in the presence of a suitable solvent. A complex of the metallocene and alumoxane can be isolated and used as a catalyst in the present invention. The alumoxanes useful in combination with the catalysts of the invention, either in the polymerization reaction or in the formation of the complex disclosed by Turner, can be represented by the general formula (R-Al-O-) in the cyclic form and R (R-AI-O) _n -ALR 2 can be represented in the linear form, wherein R is an alkyl group having 1 to 5 carbon atoms and η is an integer of 1 to about 20. R is best a methyl group. The alumoxanes can be prepared by various methods known in the art. They are preferably prepared by water with a solution of trialkylaluminum such as. B. trimethylaluminum in a suitable solvent such as benzene is brought into contact. Another preferred method involves the preparation of alumoxane in the presence of hydrogenated copper sulfate as described in U.S. Patent No. 4,404,344, the disclosure of which is incorporated herein by reference. This method involves treating a dilute solution of trimethylaluminum in toluene with copper sulfate. The preparation of other aluminum cocatalysts useful in the invention can be accomplished by methods known to those skilled in the art.

embodiments

The following examples are intended to further illustrate the invention as well as its various advantages and advantages. Two different synthetic methods, designated A and B, are described for both zirconium and hafnium metallocene catalysts. The synthesis procedures were carried out in both methods under an inert gas atmosphere using a vacuum atmosphere glove box or Schlenk method. The synthesis process generally comprises the following steps: 1) preparation of the halogenated or alkylated metal compound, 2) preparation of the ligand, 3) synthesis of the complex, and 4) purification of the complex. The bridged substituted dicyclopentadienyl ligand was synthesized by contacting fulvene or a substituted fulvene with a cyclopentadienyl or substituted cyclopentadienyl under reaction conditions sufficient to produce a bridged dicyclopentadiene or substituted dicyclopentadiene. As known in the art, fulvene is Cp = C, wherein a carbon atom is bonded through a double bond to a cyclopentadienyl ring. Mean substituted fulvene as used herein is intended to (CpR) = CR _'b wherein fulvene is substituted either on the Cp ring or at the terminal carbon atom or both. R, and R ' _b are hydrocarbyl radicals wherein R 1 and R' _b are the same or different and 0 <a <4 and 0 <b <2. The other three synthetic steps may be as shown below or using other methods known in the art be executed. The general catalyst formula for the catalyst produced by these methods is iso-propyl-fluorenyl-cyclopentadiene-DMeClj, wherein Me is either zirconium or hafnium depending on the example. Figure 1 shows the structure of the hafnium catalyst, and the zirconium catalyst has substantially the same structure with Zr positioned at the site of the Hf atom.

Preparation of the catalyst - Method A

In Method A, the halogenated metal compound was prepared using tetrahydrofuran LTHF ") as a solvent, with the result that THF was bound to the final catalyst complex. Specifically, MeCl ₄ THF was prepared as described in Manzer, L., Inorg. Synth. , 21, 215-136 (1982). In the examples below, Me is zirconium and hafnium, but may also include titanium or other transition metals.

The substituted dicyclopentadienyl ligand can be prepared using various methods known in the art, depending on the choice of specific bridging or substituent substituents. In the in the. The preferred embodiment shown below is the ligand 2,2-isopropyl (fluorene) cyclopentadiene. To prepare this ligand, 44 g (0.26 mol) of fluorene in 350 ml of THF were dissolved in a round bottom flask equipped with side arm and dropping funnel. The funnel contained 0.25 mol of methyllithium (CH ₃ LI) in ether (1.4 M), CH ₃ Li was added dropwise to the fluorene solution, and the deep orange-red solution was stirred for several hours. After gas evolution ceased, the solution was cooled to -78 ° C and 100 ml of THF containing 26.5 g (0.25 mol) of 6,6-oimethylfulvene was added dropwise to the solution. The red solution was gradually warmed to room temperature and stirred overnight. The solution was treated with 200 ml of water and stirred for 10 minutes. The organic fraction of the solution was extracted several times with 100 ml portions of diethyl ether, and the combined organic phases were dried over magnesium sulfate. Removal of the ether from the organic phases gave a yellow solid which was dissolved in 500 ml of chloroform and recrystallized by addition of excess methanol at 2 ° C to yield a white powder. Elemental analysis of the ligand showed that carbon was 91.8 wt% of the compound and hydrogen was 7.4 wt%. This corresponds to the mass percentages for C ₂ IH ₂₀ of 92.6% carbon and 7.4% hydrogen. The NMR spectrum for the ligand proves that the structure includes a cyclopentadienyl ring linked by an isopropyl bridge to a second cyclopentadienyl ring which is substituted to form a fluorenyl radical.

A syndiospecific catalyst complex was synthesized using the ligand and the metal tetrachloride-THF complex. The catalyst was formed by adding 0.05 mol of n-butyllithium hexane (1.6M) dropwise to a 10OmI-THF solution containing 6.8 g (0.25 mol) of the Cp ligand described above. The solution was stirred at 35 ° C for twelve hours, after which 9.4 g (0.025 mol) of ZrCl ₄ -2THF contained in 200 ml of THF were quickly cannulated with the ligand solution into a 500 ml round bottom flask with vigorous stirring , The deep orange solution was stirred at reflux for twelve hours. A mixture of LiCl and a red solid was isolated by removal of the solvents under vacuum.

Catalyst complexes generated by Method A are reported to be slightly impure and extremely sensitive to air and moisture. As a result, you have purified catalysts of Method A in the examples below using one or more of the following purification procedures:

1. Extraction with pentane. Trace amounts of a yellow impurity contained in the solid red catalyst complex were repeatedly extracted with pentane until the pentane became colorless.

2. Fractionated recrystallization. DeV red complex was separated from the white LiCl by dissolving in 100 ml toluene, filtering through a fine porous sintered glass frit, and preparing a saturated solution by adding pentane. The red zirconium complex was isolated by crystallization I 3i -20 ° C.

3. Chromatography on organic beads. 50g Bio-beads SM-2 (spherical, macroreticular styrene-divinylbenzene copolymer with 20-50 mesh (= grain size, expressed by the mesh size of the sieve) from the Bio-Rad Laboratories) were placed under vacuum at 70 ° C for 48 hours in a Column of 30 x 1,5cm dried. The beads were then equilibrated with toluene for several hours. A concentrated solution of the red catalyst complex in toluene was eluted with 150 to 200 ml of Tcluen in the column. The complex was recovered by evaporation of the toluene under vacuum.

Catalyst Synthesis Procedures - Method B

As an alternative method of synthesis, Method B provides catalysts that are more stable, more active and produce a higher percentage of syndiotactic polypropylene. In this process, methylene chloride is used as a non-coordinating solvent. Hafnium is used as the transition metal in the process described below, but the process can also be adapted for use with zirconium, titanium or other transition metals. The substituted dicyclopentadienyl ligand was synthesized in THF in the same manner as described in Mothode A above. The red dilhhio salt of the ligand (0.025 mol) was isolated as disclosed in Method A by removing the solvents under vacuum and washing with pentane. The isolated red dilithio salt was dissolved in 125 mL of cold methylene chloride and an equivalent amount (0.025 mol) of HfCl ₄ slurried separately in 125 mL of methylene chloride at -78 ° C. The HfCU slurry was rapidly cannulated into the flask containing the ligand solution mixture for two hours at -78 ⁰ C was stirred, allowed to slowly to 25 ° C heat, and it was further stirred for 12 hours. an insoluble white salt (LiCl) was filtered off. A moderately air sensitive yellow powder was recovered by the The pale yellow product was washed on the sintered glass filter by repeatedly filtering off cold supernatant which had been back-cannulated over it Solvent isolated using a vacuum, and it was under tr ockenem, deoxidized argon stored. The process yielded 5.5 g of catalyst complex. The Elemsntaranalyse of hafnium catalyst complex prepared according to Method B showed that the catalyst of 48.79Ma .-% carbon, 3.4% hydrogen, 15.14% chlorine and 33.2% hafnium existed. These percentages are comparable to the theoretical analysis for C ₂₁ H ₁₈ HfCl ₂ , which is 48.39% carbon, 3.45% hydrogen, 13.59% chlorine and 34.11% hafnium. Similarly, zirconium catalysts produced by Method B show elemental analysis approaching the expected or theoretical values. Further, some of those illustrated in the examples below were used

Hafnium complexes prepared using 96% pure HfCl ₄ , which also contains about 4% ZrCl ₄ . Other catalyst samples were prepared using 99.99% pure HfCl ₄ , differences being seen in the molecular weight distributions of the polymers produced with the pure Hf catalyst as compared to the polymers produced using catalysts. which contain a small percentage of zirconium. The mixed catalyst produces a polymer having a broader molecular weight distribution than a pure catalyst system. The following examples further illustrate the invention and its various advantages. The results of the polymerization process and the analysis of the polymer are shown in Table 1 for Examples 1 to 17 and In Table 2 (for Examples 18 to 33).

example 1

The polymerization of propylene was carried out using 0.16 mg of isopropyl (cyclopentadienyl) (florenyl) zirconium chloride produced in accordance with method A described above. The catalyst was purified using fractional recrystallization. The catalyst was precontacted for 20 minutes with a toluene solution containing 10.7 mass% M, lalumoxane (MAO) with an average molecular weight of about 1300. The alumoxane serves as a cocatalyst in the polymerization reaction. 10 cm ^{3 of} the MAO solution was used in the polymerization. The catalyst and cocatalyst solution was then added to a Zipperclave reactor at room temperature, followed by the addition of 1.2 liters of liquid propylene. The reactor contents were then heated in less than about 5 minutes to the polymerization temperature, T in the tables Ί and 2, of 2O ⁰ C. During this time, the prepolymerization of the catalyst was carried out. The polymerization reaction was allowed to proceed for 60 minutes, during which time the reactor was maintained at the polymerization temperature. The polymerization was terminated by rapid venting of the monomer. The reactor contents were washed with 50% methanol in dilute HCl solution and dried in vacuo. The polymerization gave 14 g of polypropylene "in the polymerized state", ie no further isolation or purification was carried out.

Analysis of the polymer

The polymer was analyzed to determine the melting point Tm, the heat of crystallization Hc, the molecular weights Mp, Mw, and M _n, the percent of xylene insolubles XI, and the syndiotactic index Sl. Unless otherwise stated, analyzes were performed on the xylene-insoluble fraction of the polymer including the syndiotactic fraction and any isotactic polymer produced. The atactic polymer was removed by dissolving the polymer product in hot xylene, cooling the solution to ⁰ ° C., and precipitating the xylene-insoluble fraction. Successive recrystallizations carried out in this manner result in the removal of substantially all of the atactic polymer from the xylene-insoluble fraction.

Melting points Tm were derived using data from differential scanning calorimetry (DSC) known in the art. The melting points Tm 1 and Tm2 recorded in Tables 1 and 2 are not real equilibrium melting points but DSK peak temperatures. For polypropylene, it is not uncommon to obtain upper and lower peak temperatures, ie, two peaks, and both melting points are listed in Tables 1 and 2, with the lower melting point indicated as Tm 1 and the higher point as Tm2. True equilibrium melting points recovered over a period of several hours would most likely be a few degrees higher than the lower DSK peak melting points. As is known in the art, the melting points for polypropylene are determined by the crystallinity of the xylene-insoluble fraction of the polymer. This has been proven to be true by determining the DSC melting points before and after removal of the xylene-soluble or atactic form of the polymer. The results showed only a difference of 1 to 2 ⁰ C in the melting points after most of the atactic polymer was removed. As shown in Table 1, the melting points for the polymer produced in Example 1 were determined to be 145 ^° C. and 150 ^° C. The DSC data were also used to determine the heat of crystallization, given in Tables 1 and 2 as -Hc and measured in joules per gram (J / g). The melting points as well as -Hc were determined on the "as-polymerized" sample before the atactic polymer was removed The molecular weights of the polymer were determined using Gel Permeation Chromatography (GPC) analysis using an instrument of the Type Waters 15OC was calculated using a column of Jordi gel and an ultra-high molecular weight mixed bed The solvent was trichlorobenzene and the operating temperature was 140 ° C. From the GPC, for the xylene-insoluble fraction of the polymer produced: M _p , the maximum relative Molecular weight; M _n , the number average molecular weight, and M _w , the weight average molecular weight, The molecular weight distribution MWD is usually measured as M _w divided by M _n . The values determined for this sample are shown in Table 1. The GPC analysis was also used to calculate the syndiotactic index, SI%, which is shown in Tab listed in sections 1 and 2. The syndiotactic index is a measure of the percentage of syndiotactic structure generated in the polymerization reaction and was determined on the "polymerized state" samples from molecular weight data.

The NMR analysis was used to determine the microstructure of the polymer. A sample of the polymer produced above in a 20% solution of 1,2,4-trichlorobenzene / d _e was dissolved -benzene and using a spectrometer "om Bruker AM 300 WB using the inverter gate broadband decoupling method determined. The The test conditions were: transmitter frequency 75.47 MHz, decoupler frequency 300.3 MHz, pulse repetition time 12 seconds, detection time 1.38 seconds, pulse angle 90 ° (11.5 microseconds pulse width), memory size 74K points, spectral window, 12195 Hz, 7000 transient events were stored, and the probe temperature was set at 133 ^° C. The NMR spectrum for the polymer produced and once again recrystallized from xylene is shown in Figure 2. The calculated and observed values for the spectra are shown in Table 3, Example 1 being the data for the sample once recrystallized from xylene and Example 1-A the data for the sample recrystallized three times from xylene These values were derived using the Bernoulli Probabilistic Equations, as disclosed in Inoue, Y. et al., Polymer, Vol. 25, p. 1640 (1984) and known in the art.

The results show that in the sample once recrystallized from xylene, the percentage of racemic dyads (r) is 95%. For the sample recrystallized three times from xylene, the percentage of r dyads is 98%, indicating a polymer consisting of 2% or less of the meso (m) dyad. Further, the NMR spectrum shows that the meso-dyads are predominantly in pairs, i. as mm triads, in contrast to the previously known single-m-dyad structure in the chain, occur. Thus, the catalysts of the present invention produce a polymer product having a novel microstructure with respect to the previously known, novel microstructure.

Example 2

The procedures of Example 1 were repeated, except that 500 ml of toluene was used as co-solvent in the polymerization reaction. In addition, one gram of MAO was used in the polymerization, and the reaction temperature was 5O ⁰ C. There were combined with the polymeric product 15 grams of oil recovered. The polymer was analyzed in accordance with the procedures given above and the results are given in Table 1.

Example 3 The procedures of Example 2 were repeated, with the difference that hafnium in the catalyst as a transition metal

was used. The other reaction conditions were as shown in Table 1, and the analyzed properties of the resulting polymer are also shown in Table 1.

Figures 4 and 5 show the IR Spoktren for the polymer produced in Example 7 and 8, respectively. The characteristic gang at 977

and 962cm "for syndiotactic polypropylene are readily apparent The presence of this band again confirms the syndiotactic structure of the polymer The corresponding bands for isotactic polypropylene are 995 and 974, respectively.

Examples 4 to 8 The procedures of Example 1 were repeated, with the difference that different reaction conditions, as in Table 1

shown were applied. In addition, in Example 4, chromatography was used as the purification method and in

Example 5 no cleaning process performed. The results of the polymerization and the analysis of the polymer are in Table 1 listed. Figures 3 and 4 show the IR spectra for the polymers produced in Examples 7 and 8, respectively, where the polymer is repeated three times

crystallized out.

Examples 9 to 16

The procedures of Example 1 were repeated, with the difference that, as indicated in Table 1, changes were made in the catalyst and cocatalyst amounts. Further, the catalysts in Examples 9 to 13 and 15 were purified using both extraction with pentane and fractional recrystallization. In Example 14, extraction with pentane and chromatography were used as the purification method. In Example 16, no cleaning procedure was performed. ν

Example 17 The procedures of Example 1 were repeated except that hafnium was used as the transition metal for the catalyst

was used. The other reaction conditions were as shown in Table 1. The catalyst was through

Purification with pentane and fractionated recrystallization. The results of the polymerization are in Table 1

shown.

Examples 18 and 19

A hafnium metallocene catalyst was synthesized by the method B described above and using the 95% pure HfCl ₄ containing about 4% ZrCU. The polymerization was carried out using the polymerization methods of Example 1 under the conditions shown in Table 2. The polymers were analyzed in accordance with the procedures set forth in Example 1 and the results are given in Table 1.

Examples 20 to 31 A zirconium metallocene catalyst was prepared using Method B synthesis procedures, and the Polymerization of propylene was carried out under the conditions shown in Table 2 for each example. The Polymer products were analyzed in accordance with the procedures of Example 1 and the results are in Table 2

specified.

It should be noted that for Examples 20 to 22, the syndiotactic index S.I. for the xylene-insoluble fraction was determined. The syndiotactic index for these fractions was approximately 100%. The observed Df th NMR spectra for the Examples 20 and 22 are given in Table 4. The data given for Examples 20 and 22 were from those in the Examples 20 and 22 produced and once again re-crystallized from xylene polymer. Example 22-A is this Polymer of Example 22, which was recrystallized three times from xylene. Examples 32 and 33

A hafnium metallocene catalyst was prepared using Method B synthesis procedures. The catalyst for Example 32 was prepared using the 99% pure HfCl ₄ , while the catalyst in Example 33 was prepared from the 95% pure HfCl ₄ containing about 4% ZrCl ₄ . The polymerization was carried out in accordance with the procedures of Example 1 under the conditions shown for Examples 32 and 33 in Table 2. The results of the analysis of the polymer produced in these examples are shown in Table 2. The NMR data for Example 33 are given in Table 4 with the sample once recrystallized from xylene (Example 33) and with the sample recrystallized three times from xylene (Example 33A).

The data presented in Tables 1 to 4 and Figures 2 and 3 show that the catalysts of the present invention produce a predominantly syndiotactic polymer having high crystallinity and a novel microstructure. In particular, the NMR data presented in Tables 3 and 4 demonstrate that the Xy ion-insoluble fraction consists of a very high percentage of syndiotactic polymer, with very little, if any, isotactic polymer being produced. Furthermore, the syndiotactic polymer contains a high percentage of "r" groups and "rrr" pentads, indicating that there is only a small percentage of deviations from the "... rrrr .." structure in the polymer chain existing deviations are predominantly of the type "mm". In fact, the results for Example 1-A in Table 3 show that the only deviation in the chain is of the "mm" type. The other NMR samples show the predominance of the "mm" sweep over the "m" deviation. Thus, a novel microstructure for syndiotactic polypropylene was discovered. The data in Tables 1 and 2 show the high crystallinity of the polymer product. The relatively high melting points TM1 and TM2 and the relatively high heats of crystallization -Hc show that the polymers are highly crystalline. The data further show a correlation between the polymerization reaction temperature T and the melting points, the molecular weights and the crystallization heaters of the polymer. As the reaction temperature increases, all three of these properties drop off. There also appears to be a temperature range in which polymer yield is maximized. This temperature range will vary with the type of catalyst used, but is typically between 50 and 7O ⁰ C. The Konzentrat'on of methylalumoxane (MAO), the polymer yield also appears to influence. The data show that the greater the MAO concentration, the higher the polymer yield to some extent. The MAO concentration also appears to exert some influence on the amount of atactic polymer produced. MAO appears to act as a scavenger in terms of impurity and tends to reduce the amount of atactic polymer produced.

The data further shows a difference between the zirconium catalysts and the hafnium catalysts of the invention. The polymers produced with the hafnium catalysts tend to be less crystalline and have lower melting points than the polymers produced with the zirconium catalysts. The data in Table 4 also show that the hafnium catalyst produces a higher percentage of isotactic blocks in the polymer chain than is reflected by the presence of the isotactic pentad mmmm.

Examples 18, 19 and 33 show the possibility of achieving a broader molecular weight distribution, MWD = Mw / Mn, by using a mixture of two or more of the catalysts described by the invention. The catalysts in these examples were prepared using HfCl ₄ containing about 4% ZrCl ₄ . The MWD molecular weight distribution of the polymer in these examples is significantly higher than the MWD of the polymer produced by a substantially pure hafnium catalyst, see Example 32. Thus, a mixture of two different catalysts can be used to form a polymer to produce with a broad MWD value. It will be further understood that the syndiotactic catalysts of the present invention are not limited to the specific structures set forth in the examples, but rather include catalysts described by the general formula given herein wherein a Cp ring substitutes into a substantially different catfish Thus, in the examples described above, the rings included an N-substituted Cp ring and a Cp ring substituted to form a fluorenyl radical, but similar results are achievable using other ligands selected from bridged Cp Rings exist in which one of the Cp rings is substituted in a substantially different manner than the other Cp ring, e.g. As an indenyl radical and a Cp ring, a tetramethyl-substituted Cp ring and a Cp ring, a dialkyl-substituted Cp ring and a monoalkyl-substituted ring, etc. From the just given detailed description of the invention it is apparent that the invention provides a process for the preparation of syndiotactic polyolefins having a broad molecular weight distribution using a particular catalyst combination.

Although only a few embodiments have been described, those skilled in the art will recognize that various modifications and adaptations of the described catalysts and methods are possible without departing from the scope of the invention.

Table 1 method A

example metal Catalyst (mg) , MAO (cm ³ ) T ⁰ C (G) Yield TmI ⁰ C Tm 2 ⁰ C -Hc J / g Mp / 1000 Mw / Mn S.I.% 1 Zr 10.0 10.0 20 14 145 150 43 118 2.5 62 2 Zr 10.3 ig 50 26 129 137 45 57 1.9 68 3 Hf 10.3 1g 50 12 104 17 1222 46 4 Zr 5.0 10.0 50 130 132 138 37 61 87 6 Zr 5.1 10.0 50 83 131 138 38 62 84 6 Zr 5.0 0.3 g 70 22 115 127 34 71 83 7 Zr 5.1 5.0 50 68 131 140 37 60 38 8th Zr 5.1 10.0 50 110 132 140 38 60 42 9 Zr 5.1 1.0 50 14 114 126 21 58 24 10 Zr 5.0 2.5 50 34 111 122 14 60 23

Table 1 (continued) Example Metal Catalyst MAO (mg) (cm ³ )

T ⁰ C

Yield (g) Tm 1 ⁰ C

-Hc Tm 2 ⁰ CJ / g

Mp / 1000 Mw / Mn S.l.%

11 Zr 5.1 6.0 50 68 119 130 21 60 6.4 38 12 Zr 5.0 10.0 50 78 128 137 32 64 4.8 65 13 Zr 5.0 1.0 50 83 121 132 22 59 1.8 42 14 Zr 2.6 10.0 60 85 134 140 40 62 1.9 89 16 Zr 5.1 10.0 50 110 125 134 29 60 2.0 42 16 Zr 5.1 10.0 SO 115 131 138 38 62 1.9 84 17 Hf 10.3 ig 80 55 89 108 223 1.8 52 18 Hf 10.0 10 50 58 116 126 24 644 1.9 19 Hf 5.0 10 50 60 117 124 24 774 2.0 20 Zr 0.6 10 50 162 134 140 40 69 1.9 95 21 Zr 1.5 10 29 <1'J 142 146 45, 106 1.9 95 22 Zr 0.6 10 70 119 134 39 64 2.1 95 23 Zr 0.2 10 50 27 135 140 39 69 1.8 24 Zr 0.6 10 50 1P2 134 140 40 69 2.4 25 Zr 0.6 10 25 26 145 44 133 2.6 26 Zr 0.6 10 70 119 134 39 6-1 5.3 27 Zr 1.5 10 29 49 142 146 45 101) 28 Zr 2.5 10 60 141 136 141 40 70 29 Zr 5.0 10 28 152 128 137 43 88 30 Zr 0.5 10 60 185 128 137 37 52 31 Zr 0.5 5 70 158 120 134 36 55 32 Hf 2.5 10 70 96 103 19 474 33 Hf 10.0 60 ? 7 114 26 777

Table 3

Example 1 observed. % calculation. % Example 1A monitored. % calculation. % % r 95 95 98 98 mmmm 0.3 0.2 0 0 mmmr 0.3 0.6 0 0 rmmr 1.5 1.4 1.3 1.0 mmrr 2.4 2.9 1.9 2.1 rrmr + mmrm 1.5 1.6 0 0 mrmr 1.6 0.8 0 0 rrrr 88.0 89.1 94.7 94.7 mrrr 3.9 3.1 2.2 2.1 mrrm 0.4 0.4 0 0 dev. 0.2 0.1

Table 4

Example 20 observed%

Example 22 observed%

Example 22-A observed%

Example 33 observed%

Example 33-A observed%

mmmm 0 0.77 0.51 2.34 2.04 mmmr 0.23 0.45 0.31 0.73 0.76 rmmr 1.67 1.82 1.81 2.72 2.96 mmrr 3.58 4.25 4.06 5.72 6.44 mrmm + rmrr 2.27 3.23 3.57 2.87 3.12 mrmr 1.51 2.06 1.70 1.37 1.53 rrrr 82.71 77.58 78.12 75.7 74.55 mrrr 6.45 7.75 9.02 7.4 8.01 mrrm 0.68 0.73 0.93 1.08 0.55

Claims (8)

A process for producing syndiotactic polyolefins having a broad distribution of molecular weights, characterized by comprising a) the use of at least two different metallocene catalysts durch.die formula R "(CpR _n) (CpR _'m) MeQ k are described, wherein Cp is a respective Cyolopentadienyl- or a substituted cyclopentadienyl ring; R _n are identical or different and R ' _m is the same or different and represents a hydrocarbyl radical having from 1 to 20 carbon atoms; R "is a structural bridge between the two Cp rings which confers stereorigidity to the catalyst; Me is a metal of group 4 b, 5 b or 6 b from the table of the Periodic Table of the Elements; Each Q is a hydrocarbyl radical of 1 to 20 carbon atoms or a halogen; 0 <k <3, 0 <n <4; 1 <m <4; wherein R ' _m is selected such that (CpR' _m ) is a sterically different ring than (CpR _n ); and b) introducing the catalyst into a polymerization reaction zone containing an olefin monomer and maintaining the reaction zone under polymerization reaction conditions. 2. The method according to claim 1, characterized in that R "is a methyl, ethyl, ethylene, isopropylene, cyclopropyl, dimethylsilyl or a methylene radical. 3. The method according to claim 1, characterized in that η is 0. 4. The method according to claim 1, characterized in that R "(CpR _n ) (CpR ' _m ) forms an isopropyl (cyclopentadienyl-1-fluorenyl) radical. A process according to claim 1, characterized in that R _1n is selected such that (CpR ' _m ) forms a fluorenyl, indenyl, tetra, tri or dialkyl substituted cyclopentadienyl radical, and R _n is selected such that (CpR _n ) forms an alkyl-substituted or unsubstituted cyclopentadienyl radical. A method according to claim 1, characterized by further comprising an aluminum compound selected from the group consisting of alumoxanes, alkylaluminum and mixtures thereof. 7. The method according to claim 6, characterized in that it comprises an isolated complex of the metallocene catalyst and the aluminum compound. A process according to claim 1, characterized by further comprising prepolymerizing the catalyst prior to its introduction into the reaction zone, wherein the step of prepolymerizing comprises contacting the catalyst with an olefin monomer and an aluminum compound.