WO2009076152A1

WO2009076152A1 - Mixture of polyethylene-co-syndiotactic polypropylene block co-polymer and ultrahigh molecular weight polyethylene

Info

Publication number: WO2009076152A1
Application number: PCT/US2008/085484
Authority: WO
Inventors: Robert L. Jones, Jr.; Mahmoud Zohdi Armoush
Original assignee: The Polymer Technology Group, Inc.
Priority date: 2007-12-05
Filing date: 2008-12-04
Publication date: 2009-06-18

Abstract

A catalyst system is disclosed that comprises a heterogeneous catalyst and a single site catalyst impregnated on the surface of the heterogeneous catalyst. From this catalyst system, a pre-polymerized polyolefm catalyst can be produced by activating the catalyst system, adding a pre-polymerization monomer mix, and pre-polymerizing the catalyst system with the pre-polymerization monomer mix until 0.1 to 25.0 grams of polymer per gram of catalyst is deposited on the catalyst surface. A polymer is prepared by polymerizing the pre- polymerized catalyst with olefmic monomer.

Description

MIXTURE OF POLYETHYLENE-CO-SYNDIOTACTIC POLYPROPYLENE BLOCK CO-POLYMER AND ULTRAHIGH MOLECULAR WEIGHT

POLYETHYLENE

FIELD OF THE INVENTION

The present invention relates to a method of preparing a material consisting of a mixture of a co-polymer and ultrahigh molecular weight polyethylene. More particularly, the present invention relates to a method of preparing a material consisting of a mixture of polyethylene- co-syndiotactic polypropylene block co-polymer and ultrahigh molecular weight polyethylene.

BACKGROUND OF THE INVENTION

Pre-polymerization of supported polyolefm catalyst is an important method for improving the preparation and quality of material manufactured in commercial reactors. Generally, pre- polymerization consists of treating activated catalyst with a small amount of olefin with the intention of coating or containing the catalyst matrix (in what has been described as a micro- reactor) prior to introducing the catalyst into the main process stream. Catalyst treated in this fashion, when challenged with downstream reactor conditions, becomes less susceptible to fragmentation (which can produce undesirable fine particles known to plug and/or clog downstream processing equipment) and produces more uniform particles having better average particle size and polymer bulk densities. In addition, fouling due to agglomeration of the formed polymer particles is reduced, and operating conditions are generally improved.

It is known to those skilled in the art that pre-polymerization of catalyst used in polyolefm polymerization provides control over polymer particle morphology, less reactor fouling, and an improvement in post reactor processing of the material. Pre-polymerization of ethylene catalysts with higher molecular weight olefins such as propylene (or a combination of olefins or di-olefins) provide a protective coating of polymer around the catalyst particle which later serves the purpose of modifying ethylene gas diffusion to the catalyst sites and/or rapid expansion of the catalyst particle providing control over the reaction process. In this manner, the morphology of the catalyst particle is better preserved during the polymerization reaction.

Although pre-polymerization conditions can vary for type and amount of material being produced, polyolefins may or may not be of the same or similar polymer types. For example, pre-polymerization using propylene for making ultrahigh molecular weight polyethylene ("UHMWPE") polymer can be used as a method for controlling fouling and reactor-produced fines in commercial processes. Propylene is used because of the reduced activity compared to ethylene, allowing the polymerization to proceed at a slower rate, coating the catalyst particle and protecting it from fragmentation. In practice, a small coating of polypropylene (which is immiscible with polyethylene) encapsulates the catalyst particle and prevents catalyst particle fragmentation when it is introduced into the reactor system. Polypropylene residue remains as part of the pre-polymerization procedure using this monomer.

Loading an alternative catalyst onto the main catalyst support, in addition to the catalyst intended for the bulk polymerization processes, could produce polymer(s) by encapsulating the catalyst particle and make a polymer having properties sufficiently different than the target polymer. In this case, the pre-polymerization step could provide different structures and properties while still protecting the catalyst system. For example, a living single site catalyst system such as the phenoxy-imine (FI) catalyst loaded onto a classic Ziegler-Natta catalyst when pre-polymerized with propylene could produce a syndiotactic block, which would be followed with an ethylene block (due to the living nature of the catalyst system) when activation and polymerization with the Ziegler-Natta catalyst was carried out. The advantages of this polymer system would be similar to blends of ethylene/ethylene-co- syndiotactic polypropylene polymer systems, with the further advantage of being a molecular/reactor blend. Mixtures of syndiotactic polypropylene and homopolymer or copolymers for ethylene have been produced and shown to have improved properties according to International Publication No. WO/2005/012419. Copolymers have also been produced having improved mechanical properties (Ruokolainen, J.; Mezzenga, R.; Fredrickson, G. H.; Kramer, E. J.; Hustad, P. D.; Coates, G. W., "Morphology and Thermodynamic Behavior of Syndiotactic Polypropylene-Poly(ethylene-co-propylene) Block Polymers Prepared by Living Olefin Polymerization," Macromolecules 2005, 38, 851-860). However, the phenoxy-imine catalyst has the disadvantage of producing weakly syndiotactic homo-polymers when polymerized in propylene. The present invention addresses this disadvantage.

While pre-polymerization methods are known and well-described in the literature, the use of a single site catalyst impregnated on the surface of a heterogeneous catalyst for the purpose of pre-polymerization has not been described. Further, the use of a living single site catalyst having the ability to produce a block co-polymer or ter-polymer has not been described. In addition, a catalyst capable of tolerating monomers having functional groups are included as part of the present invention.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of preparing a material consisting of a mixture of a co-polymer and ultrahigh molecular weight polyethylene.

It is another object of the present invention to provide a method of preparing a material consisting of a mixture of polyethylene-co-syndiotactic polypropylene block co-polymer and ultrahigh molecular weight polyethylene.

It is yet another object of the present invention to provide a method for producing a pre- polymerized polyolefin catalyst.

These and other objectives of the present invention, and their preferred embodiments, shall become clear by consideration of the specification and claims taken as a whole.

As one embodiment, a polymer is prepared by first impregnating a living single site catalyst capable of synthesizing co-polymers into a silica-supported transition metal complex in order to create a catalyst system. Then, the catalyst system is activated and a pre-polymerization monomer mix is added. Next, the catalyst system and the pre-polymerization monomer is pre-polymerized until 0.1 to 25.0 grams of polymer per gram of catalyst is deposited on the catalyst surface to produce a pre-polymerized catalyst. Finally, the pre-polymerized catalyst is polymerized with olefinic monomer.

DETAILED DESCRIPTION OF THE INVENTION

As discussed above, a phenoxy-imine catalyst has the disadvantage of producing weakly syndiotactic homo-polymers when polymerized in propylene. The present invention relates to a catalyst system that takes advantage of the living character of a phenoxy-imine catalyst, making a polymer having a syndiotactic block and a miscible ethylene block. In fact, the polymer made in this fashion, as part of the pre-polymerization catalyst coating process, is also a compatibilizer.

The prepolymerization step when performed with a living catalyst will produce a polymeric coating formed from the initial monomers used for the pre-polymerization step and followed by the monomers used for the bulk polymerization. In essence, a block co-polymer chain is formed which is compatibilized with the bulk polymerization monomer. The elements of added mass (amount of pre-polymer) formed and the molecular weight of the pre- polymerization step create a catalyst and polymer particle having better material properties (bulk density, processability), as well as fusion and material properties (reduced grain boundaries, interparticle tension, and co-monomer compatibility when the material is used in master batches as a compatibilizer).

Similar (although not living) catalysts, which produce atactic high molecular weight polypropylene, could be added to a classic Ziegler-Natta system and pre-polymerized to a defined level, thereby providing a polymer mixture having high molecular weight atactic polypropylene as a micro-molecular mixture. In fact, metallocene catalysts having polymerization properties different from those of the classic Ziegler-Natta catalyst being used to produce the UHMWPE would be applicable.

Polymer compatibilizers have molecular characteristics and physical properties consisting of the materials to be mixed. Preparing a catalyst system having multiple catalyst components, one of which is a living catalyst capable of synthesizing co-polymers, preferably predominately syndiotactic polypropylene, followed by the "block" of polymer to be compatibilized (such as ethylene) either in a pre-polymerization step or in normal co- polymerization, produces a polymer having unique properties.

As one embodiment, a method of the present invention involves impregnating a suitable living syndio-specific polypropylene catalyst into a silica supported transition metal complex (for example, a classic Ziegler-Natta, titanium-impregnated silica or magnesium chloride). In standard fashion, the activated catalyst solution is added in such a manner as to prevent clumping and agglomeration of the material. The dried catalyst mixture is dried and can be stored as such.

Typically, a phenoxy-imine catalyst containing titanium, zirconium, or hafnium, which under normal polymerization conditions polymerizes propylene in predominately syndiotactic sequences, is activated with aluminum alkyl/alumoxane and then added to a pre-formed Ziegler-Natta catalyst. However, the phenoxy-imine catalyst produces weakly syndiotactic homo-polymers when polymerized in propylene

The pre-polymerization using the novel mixture described above is done with propylene to a pre-determined level in bulk, slurry, or gas phase polymerization, followed by polymerization (or co-polymerization) with ethylene or other suitable olefinic monomers.

The catalyst system of the present invention prepared above would consist of a polymer matrix consisting of a pre-determined amount of pre-polymerized syndiotactic polypropylene molecular chains having substantial polyethylene block mixed with polyethylene molecular chains. The polyethylene-co-syndiotactic polypropylene block co-polymers would provide anti-fouling properties such as those previously described for pre-polymerized polymers, while also providing a compatibilizing function for the subsequent materials produced by the classic Ziegler-Natta catalyst system. The ethylene can be polymerized to high molecular weight, thereby providing a polymer having properties comparable to those used in arthroscopic application. The properties attained by these polymers would encompass benefits of syndiotactic polypropylene (including greater modulus and flexibility), while improving the toughness and wear resistance normally experienced with UHMWPE.

The pre-polymerization process could be made without propylene but rather, alternatively, be made from any olefin for which the catalyst system loaded onto the supporting classic Ziegler-Natta catalyst system is active. In addition, combinations of olefins making co- or ter- polymers would impart unique and useful properties to the finished polymer particles including better fusibility and less grain boundary distributions in addition to imparting physical property enhancements.

As other embodiments of the catalyst of the present invention, a Ziegler-Natta catalyst may be added to a solution containing activated single site catalyst. The Ziegler-Natta catalyst may be a heterogeneous 5^th generation Ziegler-Natta catalyst. The activated single site catalyst may be 1) a Pd α-dnmine catalyst, T) pyridine-bisimine-based complexes of iron and cobalt with varying substituents on the imine carbon, 3) Bis(phenoxy-imine) group 4 metal catalyst, 4) Sita catalyst, or combinations thereof. The catalyst system may then be transferred to a polymerization vessel where pre-polymerization is accomplished. The catalyst is typically activated with a small amount of aluminum alkyl or is alkylated then activated with an aromatic boron salt such as tetrakis-pentafluorophenylboron-trityl complex. Then, pre-polymerization monomer mix may be added. Monomers can be added as a gas (such as with propylene, butene, or combinations thereof), a liquid (such as with butadiene, isoprene, decadiene, etc.), or both. Pre-polymerization may be carried out until such time as the desired amount of material is deposited on the catalyst surface. The desired amount is typically between 0.1 to 25.0 g polymer per gram of catalyst and preferably between 0.1 and 0.5 g polymer per gram of catalyst. After the pre-polymerization step is completed, the catalyst is transferred to polymerization conditions containing suitable olefmic monomer. Suitable olefmic monomer may be, for example, ethylene, a mixture of ethylene and propylene, a mixture of ethylene and hexene, or other suitable combinations of olefin, di- olefin or ter-monomer mixtures which provide a product having the desired end properties. EXAMPLES

All operations were carried out in a nitrogen glove box using anhydrous solvents as well as moisture-free and air-free conditions.

Example 1

Catalyst Preparation

In a 20 ml glass vial with a magnetic stirring bar was added 60 mg of ((Bis-(N-(3',5'-diiodo- salicylidene)-2,6-difluoroaniline)-titanium(IV)-dichloride) dissolved in 1.5 ml anhydrous toluene. A solution containing 5.5 ml of methylalumoxane (MAO) (-20 mmol, 30 wt % solution in toluene) was added. The mixture was stirred for 60 minutes. The color changed from light brown to dark red.

In a separate 250 ml Schlenk flask containing a magnetic stirring bar was placed 4.4 g of a commercially available Ziegler-Natta catalyst (used as an example in these experiments). The solution prepared above was added drop-wise to the Ziegler-Natta catalyst powder, and after each 0.5 ml of solution addition, the mixture was stirred with a spatula to prevent agglomeration and/or gel formation. The addition time was 10 minutes. After addition was completed, the material was dried under vacuum for 60 minutes at 50⁰C.

Catalyst Pre-Polymerization

In a 20 ml glass vial was added 65 mg of the catalyst prepared above dissolved in 10 ml toluene. Propylene was added as a gas; a total of 0.2 g was added (5 psi, 3 min).

Ethylene polymerization (with pre-polymerization)

The polymerization was carried out under standard conditions: 8O⁰C, 120 min, 80 psi in heptane. 0.78 g TiBAl (3.9 mmol; 1 ml in 10 ml toluene) was used as a scavenger/activator for the Ziegler-Natta catalyst. The polymer was collected from the reactor, dried in vacuo 90⁰C under vacuum for 6 hours.

Results: 35O g of the polymer was obtained. The molecular weight of the polymer (measured by IV: 16.3) was 3,445,782. The results are shown in Table 1.

Comparative Example 1

Ethylene Polymerization: Control (no propylene pre-polymerization)

All experimental conditions were carried out in the same fashion as Example 1 with the exception of the pre-polymerization step. 58 mg of catalyst was placed in a 20 ml glass vial. Toluene (10 ml) was added. Then, the mixture was cannulated into the polymerization reactor, and the polymerization was carried out as in Example 1.

Results: 298 g of the polymer was obtained. The molecular weight of the polymer (measured by IV: 16.8) was 3,600,042. The results are shown in Table 1.

Table 1

Example 1 having propylene-co-ethylene block co-polymer from the pre-polymerization provided a higher tensile strength than Comparative Example 1.

Example 2

Catalyst Preparation In a flask containing a heterogeneous 5^th generation Ziegler Natta catalyst is added a solution containing a Pd α-diimine catalyst, an activated single site catalyst (Living Polymerization of Ethylene Using Pd(II)-α-Diimine Catalysts. Gottfried, A. C; Brookhart, M. Macromolecules 2001, 1140-1142.). The catalyst system is transferred to a polymerization vessel where pre- polymerization is accomplished. The catalyst is activated with a small amount of aluminum alkyl. Then, pre-polymerization monomer mix is added. Monomers are added as a gas with propylene. Pre-polymerization is carried out until about 0.1 g polymer per gram of catalyst is deposited on the catalyst surface. After the pre-polymerization step is completed, the catalyst is transferred to polymerization conditions containing ethylene, an olefmic monomer.

Example 3

Catalyst Preparation

In a flask containing a heterogeneous 5¹ generation Ziegler Natta catalyst is added a solution containing pyridine-bisimine-based complexes of iron and cobalt with varying substituents on the imine carbon, an activated single site catalyst (Small, B. L.; Brookhart, M.; Bennett, A. M. A. J. Am. Chem. Soc. 1998, 120, 4049). The catalyst system is transferred to a polymerization vessel where pre-polymerization is accomplished. The catalyst is alkylated and then activated with tetrakis-pentafluorophenylboron-trityl complex, an aromatic boron salt. Then, pre-polymerization monomer mix is added. Monomers are added as a liquid with isoprene. Pre-polymerization is carried out until 0.5 g polymer per gram of catalyst is deposited on the catalyst surface. After the pre-polymerization step is completed, the catalyst is transferred to polymerization conditions containing a mixture of ethylene and propylene.

Example 4

Catalyst Preparation

In a flask containing a heterogeneous 5^th generation Ziegler Natta catalyst is added a solution containing Bis(phenoxy-imine) group 4 metal catalyst, an activated single site catalyst (Mitsui type catalysts: (a) Mitani, M.; Mohri, J.-L; Yoshida, Y.; Saito, J.; Ishii, S.; Tsuru, K.; Matsui, S.; Furuyama, R.; Nakano, T.; Tanaka, H.; Kojoh, S.-L; Matsugi, T.; Kashiwa, N.; Fujita, T. J. Am. Chem. Soc. 2002, 124, 3327-3336. (b) Mitani, M.; Nakano, T.; Fujita, T. Chem. Eur. J. 2003, 9, 2396-2403. (c) Suzuki, Y.; Terao, H.; Fujita, T. Bull. Chem. Soc. Jpn. 2003, 76, 1493-1517. (d) Makio, H.; Fujita, T. Bull. Chem. Soc. Jpn. 2005, 78, 52-66). The catalyst system is transferred to a polymerization vessel where pre-polymerization is accomplished. The catalyst is activated with a small amount of aluminum alkyl. Then, pre- polymerization monomer mix is added. Monomers are added as both a gas with butane and as a liquid with butadiene. Pre-polymerization is carried out until 25.0 g polymer per gram of catalyst is deposited on the catalyst surface. After the pre-polymerization step is completed, the catalyst is transferred to polymerization conditions containing a mixture of ethylene and hexane.

Example 5

Catalyst Preparation

In a flask containing a heterogeneous 5^th generation Ziegler Natta catalyst is added a solution containing Sita catalyst, an activated single site catalyst (Jayaratne, K. C; Keaton, R. J.; Hennmgsen, D. A.; Sita, L. R. "Living Ziegler-Natta Cyclopolymerization of Nonconjugated Dienes: New Classes of Microphase-Separated Polyolefin Block Copolymers via a Tandem Polymerization / Cyclopolymerization Strategy," J. Am. Chem. Soc. 2000, 122, 10490- 10491). The catalyst system is transferred to a polymerization vessel where pre- polymerization is accomplished. The catalyst is alkylated then activated with tetrakis- pentafluorophenylboron-trityl complex, an aromatic boron salt. Then, pre-polymerization monomer mix is added. Monomers are added as a gas with propylene and butene. Pre- polymerization is carried out until 0.4 g polymer per gram of catalyst is deposited on the catalyst surface. After the pre-polymerization step is completed, the catalyst is transferred to polymerization conditions containing a mixture of ethylene and hexane.

The advantages of the present invention are a result of the pre-polymer being made from a living catalyst and produced as a macromolecular chain having a block structure being compatible with the buly polymerization polymer. Reactor fouling is reduced, and the pre- polymerization polymer has preformed compatibilizer with less tendency to phase separate than heterogeneous polymer systems made without the benefit of this system.

While the invention has been described with reference to the preferred embodiments, it will be understood by those skilled in the art that various obvious changes may be made, and equivalents may be substituted for elements thereof, without departing from the essential scope of the present invention. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed but that the invention includes all equivalent embodiments.

Claims

What is claimed is:

1. A method of producing a pre-polymerized polyolefin catalyst, comprising the step of: impregnating a living single site catalyst capable of synthesizing co-polymers into a silica-supported transition metal complex to create a catalyst system.

2. The method according to claim 1, further comprising the steps of: activating the catalyst system; adding a pre-polymerization monomer mix; pre-polymerizing the catalyst system with the pre-polymerization monomer mix until 0.1 to 25.0 grams of polymer per gram of catalyst is deposited on the catalyst surface.

3. The method according to claim 1, wherein said co-polymers are syndiotactic polypropylene.

4. The method according to claim 1 , wherein said transition metal complex is a Ziegler-Natta catalyst.

5. The method according to claim 1, wherein said single site catalyst is at least one selected from the group consisting of a Pd α-diimine catalyst, pyridine-bisimine-based complexes of iron and cobalt with varying substituents on the imine carbon, Bis(phenoxy- imine) group 4 metal catalyst, and Sita catalyst.

6. The method according to claim 1, wherein said single site catalyst is a phenoxy-imine (FI) catalyst.

7. The method according to claim 2, wherein said activating step comprises activating the catalyst system with a small amount of aluminum alkyl.

8. The method according to claim 2, wherein said activating step comprises alkylating the catalyst system and then activating the catalyst system with an aromatic boron salt.

9. The method according to claim 8, wherein said aromatic boron salt is tetrakis- pentafluorophenylboron-trityl complex.

10. The method according to claim 2, wherein said pre-polymerization monomer mix is at least one selected from the group consisting of propylene, butane, butadiene, isoprene, and decadiene.

11. The method according to claim 2, wherein said pre-polymerizing step is carried out until 0.1 to 0.5 grams of polymer per gram of catalyst is deposited on the catalyst surface.

12. A catalyst system, comprising: a heterogeneous catalyst; and a single site catalyst impregnated on the surface of said heterogeneous catalyst.

13. The catalyst system according to claim 12, wherein said heterogeneous catalyst is a Ziegler-Natta catalyst.

14. The catalyst system according to claim 12, wherein said single site catalyst is a living catalyst.

15. The catalyst system according to claim 12, wherein said single site catalyst is an FI catalyst.

16. The catalyst system according to claim 12, wherein said single site catalyst is at least one selected from the group consisting of a Pd α-diimine catalyst, pyridine-bisimine- based complexes of iron and cobalt with varying substituents on the imine carbon, Bis(phenoxy-imine) group 4 metal catalyst, and Sita catalyst.

17. A polymer prepared by a process comprising the steps of: impregnating a living single site catalyst capable of synthesizing co-polymers into a silica-supported transition metal complex to create a catalyst system; activating the catalyst system; adding a pre-polymerization monomer mix; pre-polymerizing the catalyst system with the pre-polymerization monomer mix until 0.1 to 25.0 grams of polymer per gram of catalyst is deposited on the catalyst surface to produce a pre-polymerized catalyst; and polymerizing said pre-polymerized catalyst with olefinic monomer.

18. The polymer according to claim 17, wherein said polymer has a syndiotactic block and a miscible ethylene block.

19. The polymer according to claim 17, wherein said living single site catalyst is an FI catalyst.

20. The polymer according to claim 17, wherein said co-polymers are syndiotactic polypropylene.

21. The polymer according to claim 17, wherein said transition metal complex is a Ziegler-Natta catalyst.

22. The polymer according to claim 17, wherein said single site catalyst is at least one selected from the group consisting of a Pd α-diimine catalyst, pyridine-bisimine-based complexes of iron and cobalt with varying substituents on the imine carbon, Bis(phenoxy- imine) group 4 metal catalyst, and Sita catalyst.

23. The polymer according to claim 17, wherein said activating step comprises activating the catalyst system with a small amount of aluminum alkyl.

24. The polymer according to claim 17, wherein said activating step comprises alkylating the catalyst system and then activating the catalyst system with an aromatic boron salt.

25. The polymer according to claim 24, wherein said aromatic boron salt is tetrakis-pentafluorophenylboron-trityl complex.

26. The polymer according to claim 17, wherein said pre-polymerization monomer mix is at least one selected from the group consisting of propylene, butane, butadiene, isoprene, and decadiene.

27. The polymer according to claim 17, wherein said pre-polymerizing step is carried out until 0.1 to 0.5 grams of polymer per gram of catalyst is deposited on the catalyst surface.

28. The polymer according to claim 17, wherein said olefinic monomer is selected from the group consisting of ethylene, a mixture of ethylene and propylene, and a mixture of ethylene and hexane.