WO2010136173A1

WO2010136173A1 - Polyolefin doped with a stabilizer

Info

Publication number: WO2010136173A1
Application number: PCT/EP2010/003169
Authority: WO
Inventors: Katrin Schuhen; Markus Enders
Original assignee: Aesculap Ag; Ruprecht-Karls- Universität Heidelberg
Priority date: 2009-05-26
Filing date: 2010-05-25
Publication date: 2010-12-02
Also published as: DE102009023651A1; DE102009023651B4

Abstract

The invention relates to a process for preparing a polyolefin doped with a stabilizer, preferably an antioxidant, wherein a polymerization of an olefin is performed in the presence of a stabilizer, preferably an antioxidant, and of a catalyst.

Description

description

Polyolefin doped with a stabilizer

The present invention relates to a production process for a polyolefin which is doped with a stabilizer, a polyolefin produced or preparable by the process and a corresponding medical article.

To increase the life of implants based on polyolefins, the polyolefins are usually additized with stabilizers. However, as the example of ultra-high-molecular-weight polyethylene (UHMWPE) will explain in more detail below, such additive preparation can often only be achieved by complicated processes in which there is the risk of only uneven distribution of the stabilizers in the polyolefins.

Ultra high molecular weight polyethylene (UHMWPE, ultra-high molecular weight polyethylene) is used extensively for the production of orthopedic implants. For example, about 70% of all hip and knee endoprostheses in the world have sliding surfaces made of UHMWPE. Although these have been proven in everyday clinical practice for more than 30 years, their lifespan is usually limited to 10 to 15 years. The reasons for the limited lifespan are oxidative damage mechanisms of the UHMWPE ₁ which take place in the body of a patient. As a result, the abrasion of the polymer material can increase dramatically. In addition, inflammation may occur in the environment of the implant. In many cases, therefore, expensive revision operations are required.

EP 1 161 489 B1 describes a process for the preparation of a UHMWPE doped with a stabilizer such as α-tocopherol described. The method is based on the diffusion principle, wherein the stabilizer is pressed by means of supercritical carbon dioxide in a UHMWPE cube. A corresponding diffusion method for crosslinked UHMWPE is known from EP 1 624 905 B1. A disadvantage of these diffusion methods, however, is that they are expensive and, in particular, expensive. A particular problem is that in reasonable times virtually no reasonable penetration depths of the stabilizer in UHMWPE can be realized. Although the solubility of the stabilizer in UHMWPE can in principle be increased by increasing the temperature. However, there is a risk here that the polymer will be "overloaded" with the stabilizer, with the result that excess stabilizer is "sweated out" again after the end of the diffusion process. In order to achieve a uniform distribution of the stabilizer in UHMWPE, a heat treatment step is therefore proposed in EP 1 624 905 B1. The disadvantage, however, is that this long annealing times are required, which lead to a significant overall extension of the production time for a UHMWPE, which is doped with a stabilizer lead.

It is therefore an object of the present invention to provide an alternative preparation process for a polyolefin provided with a stabilizer or doped polyolefin, which effects the most homogeneous possible distribution of the stabilizer in the polyolefin, is simple to carry out and inexpensive, and in particular due to shorter production times distinguished.

This object is achieved by a manufacturing method having the features of independent claim 1. Preferred embodiments of the manufacturing method are the subject of dependent claims 2 to 20. Another object of the invention is a polyolefin according to independent claim 21. A preferred embodiment of the polyolefin is the subject of dependent claim 22. A further aspect of the invention relates to a medical device according to independent claim 23. Embodiments of the medical device article are shown in the dependent claims 24 and 25.

The process according to the invention is a process for the preparation of a polyolefin (polyalkene), preferably polyethylene, which is provided with a stabilizer, preferably antioxidant (antioxidant or oxidation inhibitor), in which a polymerization of an olefin, preferably of Ethylene, in the presence of a stabilizer, preferably antioxidant, and a catalyst is performed.

In contrast to the processes known from the prior art, which provide a subsequent additive with a stabilizer, the present invention proposes to carry out a so-called in-situ polymerization to produce stabilized, in particular stabilized by an antioxidant, polyolefins. In other words, the stabilizer or the antioxidant is preferably incorporated into the forming polyolefin during the polymerization process ("in situ additive").

As a result, a uniform or homogeneous distribution of the stabilizer in the polyolefin can be achieved with particular advantage without tedious and cumbersome aftertreatment steps, in particular in the form of tempering, being necessary. This leads to a considerable shortening of the production time and to a reduction of the thermal load of the polyolefin material. Furthermore, material properties of the polyolefin to be produced can be regulated in a simple manner, for example by selecting the reaction time, the reaction temperature and / or the reaction pressure.

In a preferred embodiment, the polymerization is carried out as a solution polymerization. In principle, however, the polymerization can also be carried out as suspension polymerization, slurry polymerization or gas phase polymerization. For the polymerization, the olefin is preferably first passed into a solution which contains the stabilizer, the catalyst and a suitable solvent or solvent mixture. For example, to prepare the solution, first the catalyst and then the stabilizer can be dissolved in the solvent or solvent mixture. Expediently, solvents or solvent mixtures are used which are inert to the respective polymerization conditions. Aliphatic hydrocarbons, aromatic hydrocarbons, halogenated hydrocarbons or mixtures thereof can in principle be used as the solvent. Examples of aliphatic hydrocarbons may be selected from the group consisting of pentane, hexane, heptane, octane, decane, kerosene, cyclobutane, methylcyclobutane, cyclohexane, methylcyclohexane, and mixtures thereof. Suitable aromatic hydrocarbons may be selected from the group consisting of benzene, toluene, ortho-xylene, meta-xylene, para-xylene, ethylbenzene, cumene, cymene and mixtures thereof. Suitable halogenated hydrocarbons may, for example, be selected from the group consisting of aliphatic fluorohydrocarbons, aromatic fluorohydrocarbons, chlorobenzene, dichlorobenzene, trichlorobenzene and mixtures thereof. As a rule, dried, ie essentially anhydrous, solvents are used.

In a further preferred embodiment, the olefin is selected from the group consisting of ethylene, propylene, 1-butene, 2-butene, isobutene, hexene, in particular 1-hexene, 1, 3-butadiene, isoprene (2-methyl-1, 3 Butadiene), cycloolefins and combinations thereof.

As already mentioned above, the olefin is preferably ethylene (ethene).

As a stabilizer, it is preferable to use a compound which does not substantially impair the activity of the catalyst. In front- Preferably, the stabilizer is used in a molar amount which does not substantially affect the activity of the catalyst.

In a further embodiment, a molar ratio of the stabilizer to the catalyst is from 10000: 1 to 1: 1, preferably 1000: 1 to 10: 1, more preferably 250: 1 to 20: 1, most preferably 100: 1 to 50: 1, used. The catalyst may be present in particular as a so-called precatalyst. This will be discussed in more detail below.

In principle, the stabilizer may be a synthetic or artificial stabilizer. However, in the present invention, it is particularly preferable to use as a stabilizer a naturally occurring stabilizer, a derivative thereof, a salt thereof, or combinations thereof.

In a particularly preferred embodiment, an antixoxidant is used as stabilizer, as already mentioned. The antioxidant usually acts as a radical scavenger. In principle, synthetically produced antioxidants can be used. Suitable antioxidants may be selected, for example, from the group consisting of ascorbates, ascorbic esters, gallates, isoascorbic acid, butylhydroxyanisole (BHA), butylhydroxytoluene (BHT), derivatives thereof, salts thereof, and combinations thereof.

Preferably, however, a naturally occurring antioxidant, a derivative thereof and / or a salt thereof is used as the stabilizer. Suitable antioxidants may be selected from the group consisting of vitamin E, vitamin C (ascorbic acid), carotenoids, flavonoids, tannins, derivatives thereof, salts thereof, and combinations thereof. Examples of possible carotenoids may be selected from the group consisting of astaxanthin, β-carotene, canthaxanthin, capsanthin, capsorubin, cryptoxanthin, lutein, luteoxanthin, lycopene, zeaxanthin, derivatives thereof, salts thereof, and combinations thereof. When Flavonoids can be used in principle flavones, flavonols, flavanols, flavonones, flavanonols, isoflavones, anthocyanidins or anthocyanins, derivatives thereof, salts thereof and / or combinations thereof. Examples of possible flavones are luteolin, apigenin, derivatives thereof, salts thereof and / or combinations thereof. Examples of suitable flavonols are morin, quercetin, rutin, kaempferol, myricetin, isorhamnetin, fisetin, derivatives thereof, salts thereof and / or combinations thereof. As suitable flavanols, for example, catechin, gallocatechin, epicatechin, epigallocatechin gallate, theaflavin, thearubigin, derivatives thereof, salts thereof and / or combinations thereof can be selected. Examples of possible flavanones are hesperetin, nahngenin, eriodictyol, derivatives thereof, salts thereof and / or combinations thereof. An example of a flavanoneol is taxifolin. As possible isoflavones, genistein, daidzein, licoricidin, derivatives thereof, salts thereof and / or combinations thereof may be used. Possible anthocyanidins or anthocyanins are, for example, cyanidin, delphinidin, malvidin, pelargonidin, peonidine, petunidin, derivatives thereof, salts thereof and / or combinations thereof.

According to the invention, the use of vitamin E as stabilizer is preferred. The vitamin E can be selected from the group consisting of α-tocopherol, β-tocopherol, γ-tocopherol, δ-tocopherol, α-tocotrienol, β-tocothenol, γ-tocotrienol, δ-tocothenol, α-tocomonoenol, β-tocomono. enol, γ-tocomonoenol, δ-tocomonoenol, derivatives thereof, salts thereof, and combinations thereof. More preferably, the vitamin E is selected from the group consisting of α-tocopherol, γ-tocopherol, δ-tocopherol, derivatives thereof, salts thereof, and combinations thereof. Most preferred is the use of α-tocopherol as a stabilizer.

In a further suitable embodiment, the preparation of the polyolefin takes place by means of a so-called coordination polymerization or coordinative insertion polymerization. This is understood to mean a polymerization of olefins on Lewis acid-metal complex complexes. bonds. Suitable catalysts may be Ziegler-Natta catalysts, metallocene catalysts or non-metallocene catalysts. The catalyst used is preferably a mixed catalyst, preferably comprising a precatalyst and a cocatalyst or activator. Under Ziegler-Natta catalysts are generally organometallic mixed catalysts of compounds of IV. To VI. Subgroup of the Periodic Table of the Chemical Elements and organometallic compounds of I. to III. Main group of the Periodic Table understood. In the compounds of IV. To VI. Subgroup are in particular titanium, vanadium and / or zirconium compounds. Suitable titanium compounds may, for example, be selected from the group consisting of titanium tetrachloride, titanium tetrabromide, ethoxy titanium trichloride, isobutoxy titanium trichloride and combinations thereof. In the organometallic compounds of I. to III. The main group is preferably aluminum-organic compounds, in particular aluminum alkyls, aluminum alkyl halides and / or alkyl aluminoxanes. According to the invention, the Ziegler-Natta catalysts may also comprise carrier components, in particular magnesium compounds, for example magnesium dichloride, and / or silica gel.

In a further suitable embodiment, the catalysts used are chromium catalysts, in particular heterogeneous chromium catalysts, i. Chromium catalysts on suitable support materials, preferably so-called Phillips catalysts (chromium salts on silica gel) or on-carbide catalysts (chromocene on silica gel) used.

Suitable metallocene catalysts can be selected from the group consisting of bis-cyclopentadienyl compounds, bis-indenyl compounds, substituted bis-cyclopentadienyl compounds and substituted bis-indenyl compounds of the elements titanium, zirconium, hafnium, scandium and / or lanthanides. In a particularly preferred embodiment, a non-metallocene or non-metallocene is used as catalyst, in particular precatalyst. Non-metallocenes (non-metallocenes) are molecular catalysts that contain ligands other than metallocene catalysts. Preferred non-metallocenes are mono-cyclopentadienyl complexes, derivatives of mono-cyclopentadienyl complexes and a variety of complexes with one or more heteroatom donor ligands. Examples of suitable donor ligands are nitrogen- and / or oxygen-containing chelate ligands. Non-metallocene catalysts preferably have a metal center whose metal is selected from the group consisting of scandium, titanium, zirconium, hafnium, vanadium, niobium, chromium, molybdenum, tungsten, iron, cobalt, nickel, palladium, platinum and lanthanides is. According to the invention, the use of chromium-containing non-metallocenes, in particular of 2,3,4-trimethyl-i- (8-quinolyl) trimethyl-silyl-cyclopentadienyl-chromium (III) chloride, is preferred.

Metallocene catalysts and non-metallocene catalysts are generally used as precatalysts in combination with a suitable cocatalyst or activator. According to the invention, it is therefore particularly preferred for the catalyst according to the invention to be a mixed catalyst comprising a metallocene or a non-metallocene as precatalyst and a suitable cocatalyst or an activator. The cocatalyst or activator is preferably an alkylaluminoxane, particularly preferably methylaluminoxane (MAO) or polymethylenealuminoxane (PMAO). Other suitable activators or cocatalysts can be selected from the group consisting of aluminum alkyls, mixed haloaluminum alkyls, metal alkyls, metal aryls and combinations thereof. Suitable metal alkyls and / or metal aryls can be selected from the group consisting of lithium alkyls, sodium alkyls, potassium alkyls, magnesium alkyls, lithium aryls, sodium aryls, potassium aryls, magnesium maryls, and combinations thereof. Activation in the presence of weakly coordinating anions such as tetraarylborates, fluorinated tetraarylborates or tetraalkoxyalumina- It is also possible. Particularly preferred according to the invention is a mixed catalyst comprising a chromium-based or chromium-containing non-metallocene catalyst (non-metallocene catalyst), in particular 2,3,4-trimethyl-1- (8-quinolyl) trimethylsilyl-cyclopentadienyl chromium ( III) chloride, as a precatalyst, and methylaluminoxane (MAO) as a cocatalyst.

The catalyst is used in a further embodiment in a concentration between 0.1 .mu.mol and 400 .mu.mol, in particular 1 .mu.mol and 200 .mu.mol, preferably 10 .mu.mol and 100 .mu.mol, based on 1 liter of a solvent or solvent mixture used for the polymerization. Preferably, for the preparation of the catalyst, a molar ratio of a precatalyst to an alkylaluminoxane cocatalyst, preferably to a methylaluminoxane cocatalyst (MAO cocatalyst), from 1:20 to 1: 20,000, preferably 1: 100 to 1: 5,000, more preferred 1: 200 to 1: 2,000, most preferably 1: 500 to 1: 1,000, based on the aluminum atoms of the alkylaluminoxane cocatalyst, preferably methylaluminoxane cocatalyst.

Conveniently, the polymerization of the olefin is carried out in a suitable reaction vessel, in particular in a Schlenk flask or polymerization reactor.

The polymerization is preferably carried out in a temperature range between 0 ^° C. and 120 ^° C., in particular 20 ^° C. and 110 ^° C., preferably 25 ^° C. and 100 ^° C. Furthermore, the polymerization can be carried out under normal pressure or overpressure, in particular in an autoclave. Preferably, the polymerization is carried out at an overpressure between 0.1 MPa and 10 MPa.

With particular advantage, the polymerization can be carried out for a reaction time of between 10 minutes and 240 minutes, in particular 10 minutes and 180 minutes, preferably 10 minutes and 60 minutes. In general, the catalyst is destroyed after preparation of the polyolefin, for example by adding a methanol-hydrochloric acid mixture. If a solvent or solvent mixture is used, it is usually removed in a subsequent drying step, for example by applying a negative pressure or vacuum, preferably a high vacuum. Alternatively or in combination, drying in a drying oven can be carried out.

With the aid of the process according to the invention, it is possible in principle to prepare any desired polyolefin. The polyolefin may be present as homo- or copolymer. For the purposes of the present invention, a copolymer is to be understood as meaning a polymer which has at least two different monomer units. Accordingly, the polyolefin according to the invention may also be a terpolymer or tetrapolymer. The polyolefin can be present in particular as a random copolymer, alternating copolymer, grafted copolymer or as a block copolymer. The polyolefin may further be present as an isotactic, syndiotactic or atactic polymer.

In a further embodiment, the polyolefin is a polyolefin which is selected from the group consisting of polyethylene, polypropylene, polybutene, in particular poly-1-butene, polyhexene, in particular poly-1-hexene, polybutadiene, in particular 1, 2 Polybutadiene and / or 1,4-polybutadiene, polyisoprene, polycycloolefins, copolymers thereof, and combinations thereof. In the case of polypropylene, it is preferably isotactic polypropylene or syndiotactic polypropylene.

The production of polyethylene, in particular polyethylene homopolymers and / or polyethylene copolymers, is particularly preferred according to the invention. The polyethylene is preferably selected from the group consisting of high density polyethylene (HDPE), low density polyethylene (LDPE), ₁ high molecular weight polyethylene (HMWPE), uitra high molecular weight polyethylene (UHMWPE), copolymers thereof and combinations thereof. The mentioned hochmolekula in this _section: re polyethylene (HMWPE) preferably has a molecular weight between 10 ⁵ and 10 ⁶ g / mol. The ultra-high molecular weight polyethylene (UHMWPE) mentioned in this section preferably has a molecular weight between 10 ⁶ and 10 ⁷ g / mol.

Optionally, it may be provided in a further embodiment that the produced, doped with a stabilizer polyolefin is crosslinked in a subsequent step. By crosslinking the polyolefin, in particular of ultra-high molecular weight polyethylene (UHMWPE), its abrasion behavior can be significantly improved. The crosslinking can be done chemically or physically. A chemical crosslinking of the polyolefin can be done for example by a peroxide treatment. A physical crosslinking of the polyolefin is preferably carried out by irradiation, in particular by ionizing irradiation. For example, the polyolefin may be crosslinked by treatment with γ-rays, β-rays, X-rays, ultraviolet rays, neutron rays, proton rays and / or electron rays.

In another possible embodiment, the polyolefin doped with a stabilizer is subjected to tempering. On the one hand, tempering can serve to reduce possible stresses in the polyolefin. This is especially true with regard to crosslinked ultra-high molecular weight polyethylene (UHMWPE). On the other hand, the mobility of radicals which may be present in the polyolefin is increased by means of tempering, which increases their recombination probability and their saturation by the stabilizer. Alternatively, or in combination, the polyolefin may also be treated with micro and / or ultrasonic waves to achieve increased radical saturation. Another aspect of the present invention relates to a polyolefin which is produced or preparable by a process according to the invention. The polyolefin preferably has a stabilizer content of between 0.01% by weight and 0.5% by weight, based on the total weight of the polyolefin. Preferably, the polyolefin is selected from the group consisting of polyethylene, polypropylene, polybutene, in particular poly-1-butene, polyhexene, in particular poly-1-hexene, polybutadiene, in particular 1, 2-polybutadiene and / or 1,4-polybutadiene, polyisoprene, Polycycloolefins, copolymers thereof, and combinations thereof. Polyethylene is preferred, wherein the polyethylene is preferably selected from the group consisting of high density polyethylene (HDPE), low density polyethylene (LDPE), high molecular weight polyethylene (HMWPE) _1, preferably ultra high molecular weight polyethylene (UHMWPE), especially crosslinked ultra high molecular weight polyethylene (UHMWPE), copolymers thereof, and combinations thereof.

With regard to further features and advantages of the polyolefin according to the invention, in particular with regard to the preparation process for the stabilizer-doped polyolefin, reference is made in full to the previous description.

The present invention also encompasses a shaped body, preferably a medical article, comprising a polyolefin, which can be produced or produced by the process according to the invention. The medical article is preferably designed as an implant, epithesis or orthosis. Preferably, the medical article is selected from the group consisting of catheter, trocar, surgical suture, medical net, in particular heroin mesh or prolapse mesh or prolapse band, urinary incontinence band and prosthesis. Particularly preferably, the medical device object is designed as a prosthesis, in particular an endoprosthesis. According to a further embodiment, the medical article is a joint prosthesis, preferably selected from the group consisting of hip joint prosthesis, knee joint prosthesis, ankle joint prosthesis, elbow joint prosthesis, temporomandibular joint prosthesis, shoulder joint prosthesis, finger joint prosthesis and spinal articulation prosthesis.

In a further advantageous embodiment, the medical article is designed as a component, in particular in the form of a sliding surface, an insert or an insert, for a joint prosthesis. With regard to the joint prostheses in question, reference is made in particular to the abovementioned joint prostheses. Furthermore, the medical article may be a prosthetic bearing component.

With regard to further features and advantages of the medical article, in particular with regard to the production process for the stabilized polyolefin doped polyolefin and / or the polyolefin itself, reference is also made entirely to the previous description.

Finally, the present invention also relates to the use of a polyolefin, which is produced or preparable by a process according to the invention, for the production of a medical device. For further features and advantages of use, reference is also made to the previous description.

Further features and advantages of the invention will become apparent from the following description of preferred embodiments in the form of examples in combination with the subclaims. In these embodiments, individual features of the invention may be implemented alone or in combination with other features. The described preferred embodiments are merely descriptive, not to be understood as a limiting revelation in any way.

Examples

1. General:

All experiments were carried out using the Schlenk technique and predried argon as a shielding gas. The polymerization gas used was commercially available ethylene 3.0 without further purification. Toluene was anhydrous and obtained in 99.9% purity from Sigma-Aldrich and further dried with a solvent drying apparatus from VAC up to a water content of <5 ppm. The cocatalyst PMAO (polymethylenealuminoxane) was purchased from AKZO as a 7% solution in toluene. All other commercially available chemicals were used as received.

As precatalysts, 2,3,4-trimethyl-1- (8-quinolyl) trimethylsilyl-cyclopentadienyl-chromium (III) chloride catalyst, hereinafter abbreviated as KAT 1, and zirconocene dichloride were used. Α-tocopherol was used as vitamin E (purity> 96%, CAS No. 10191-41-0, Sigma-Aldrich).

2. Polvmerisation experiment 1

In a 25 mL Schlenk flask 3.60 mg (8.38 x 10 ^"6 mol) of the pre-catalyst KAT was dissolved in 10 ml of toluene. 1 in a second 250 ml_- Schlenk flask, 100 ml of toluene were charged and is 0 , 31 g (7.17 x 10 ^"4 mol, corresponding to 85 eq. based on KAT 1) vitamin e dissolved. The Präkataiysator KAT 1 was charged with 3.23 g (8:38 x 10 ^"3 mol) PMAO (1000 eq Al, based on the catalyst) into the activated species and added by means of a syringe in the polymerization vessel. Ethylene was introduced via the Schlenk connection and the reaction mixture was stirred at the highest stage. The batch was cooled in a water bath. To terminate the polymerization was terminated with methanol / HCl. The reaction was due to a strong increase in viscosity in the piston, due to precipitated polymer, already terminated after 13 min. The resulting product was washed in acetone for 2 hours and dried at 80 ^° C. overnight.

3. Polvmerisation experiment 2

In a 25 mL Schlenk flask 4.20 mg (9.78 x 10 ^"6 mol) of the precatalyst KAT was dissolved in 10 ml of toluene. 1 in a second 250 ml_- Schlenk flask 100 mL of toluene was charged therein and 0 , 86 g (1.99 x 10 ^-3 mol, corresponding to 205 eq, based on CAT 1) of vitamin E. The precatalyst KAT 1 was treated with 3.77 g (9.78 x 10 ^-3 mol) of PMAO (1000 eq Al ₁ based on the catalyst) was transferred into the activated species and added by means of a syringe into the polymerization vessel via the Schlenk connection, ethylene was introduced and the reaction mixture was stirred at the highest stage.The total was stirred for 3 hours, the approach The polymerization was terminated with methanol / HCl and the resulting polymer was washed in acetone for 2 hours and dried at 80 ^° C. overnight.

4. Polvmerisation experiment 3

In a 25 mL Schlenk flask 7.70 mg (2.63 x ^{10 -5} mol) were dissolved the precatalyst zirconocene dichloride in 10 mL of toluene. In a second 250 ml Schlenk flask, 100 ml of toluene were introduced and 0.91 g (2.11 × 10 ^-3 mol, corresponding to 80 eq, based on zirconocene dichloride) of vitamin E were dissolved therein. The precatalyst zirconocene dichloride was charged with 10.15 g (2.63 x 10 ^-2 mole) PMAO (1000 eq Ai, based on the Catalyst) into the activated species and added with the aid of a syringe into the polymerization vessel. Ethylene was introduced via the Schlenk connection and the reaction mixture was stirred at the highest stage. In total, the reaction was run for 20 minutes while cooling the batch with a water bath. To terminate the polymerization was terminated with methanol / HCl. The resulting polymer was washed in acetone for 2 hours and dried at 80 ° C. overnight.

The polymers obtained after carrying out the polymerization experiments described above were colored, which confirmed the incorporation of vitamin E into the polymers or the doping of the polymers with vitamin E.

The results obtained are summarized in Table 1 below, where experiments K1 and K2 represent control experiments without stabilizer.

Table 1: Data from the polymerization experiments

5. Summary

Overall, the experiments described above show that the synthesis of polyethylene in the presence of an antioxidant is possible. Furthermore, even in the presence of the antioxidant, the catalyst activities were sufficiently high to allow satisfactory catalysis. The experiments also show that it is possible to produce polyethylene doped with an antioxidant under mildly gentle reaction conditions. A particular advantage relates to the considerably shortened compared to the known from the prior art method reaction time (time for the preparation of a doped with a stabilizer polyolefin). The molecular weight of the polymers produced was about 1.6 × 10 ⁶ mol / g.

Claims

claims

1. A process for the preparation of a stabilizer, preferably antioxidant, doped polyolefin, characterized in that a polymerization of an olefin is carried out in the presence of a stabilizer, preferably antioxidant, and a catalyst.

2. The method according to claim 1, characterized in that the polymerization is carried out as a solution polymerization.

3. The method according to claim 1 or 2, characterized in that the olefin for polymerization in a solution containing the stabilizer bilisator, the catalyst and a solvent or solvent mixture is passed.

4. The method according to claim 3, characterized in that for the preparation of the solution, first the catalyst and then the stabilizer are dissolved in the solvent or solvent mixture.

5. The method according to any one of the preceding claims, characterized in that the stabilizer substantially does not affect the activity of the catalyst or the stabilizer is used in a molar amount which does not substantially affect the activity of the catalyst.

6. The method according to any one of the preceding claims, characterized in that a molar ratio of the stabilizer to the

Catalyst of 10,000: 1 to 1: 1, preferably 1000: 1 to 10: 1, more preferably 250: 1 to 20: 1, most preferably 100: 1 to 50: 1 is used.

7. The method according to any one of the preceding claims, characterized in that a naturally occurring antioxidant and / or a salt thereof is used as the stabilizer.

8. The method according to any one of the preceding claims, characterized in that as stabilizer an antioxidant from the group consisting of vitamin E, vitamin C, carotenoids, flavonoids, tannins, salts thereof and combinations thereof is used.

9. The method according to claim 8, characterized in that the vitamin E is selected from the group consisting of α-tocopherol, β-tocopherol, γ-tocopherol, δ-tocopherol, salts thereof and combinations thereof.

10. The method according to any one of the preceding claims, characterized in that the preparation of the polyolefin takes place by means of a coordination polymerization.

11. The method according to any one of the preceding claims, characterized in that the catalyst is a Ziegler-Natta catalyst, metallocene catalyst or a non-metallocene catalyst is used.

12. The method according to any one of the preceding claims, characterized in that the catalyst is a mixed catalyst, preferably comprising a pre-catalyst and a cocatalyst tor used.

13. The method according to claim 12, characterized in that as precatalyst, a non-metallocene, preferably a chromium-containing non-metallocene, in particular 2,3,4-trimethyl-1- (8-quinolyl) trimethyl-silyl-cyclopentadienyl-chromium (lll ) chloride, and as cocatalyst preferably an aluminoxane, in particular an alkyl luminoxane, preferably methylaluminoxane (MAO) is used.

14. The method according to any one of the preceding claims, characterized in that the catalyst in a concentration between 0.1 .mu.mol and 400 .mu.mol, in particular 1 .mu.mol and 200 .mu.mol, preferably 10 .mu.mol and 100 .mu.mol, based on 1 liter of one used for the polymerization Solvent or solvent mixture is used.

15. The method according to any one of the preceding claims, characterized in that for preparing the catalyst, a molar ratio of a precatalyst to a methylaluminoxane cocatalyst of 1: 20 to 1: 20,000, preferably 1: 100 to 1: 5,000, more preferably 1: 200 bis 1: 2,000, most preferably 1:

500 to 1: 1000, based on the aluminum atoms of the methylaluminoxane cocatalyst.

16. The method according to any one of the preceding claims, characterized in that the polymerization in a temperature range between 0 ⁰ C and 120 ⁰ C, in particular 20 ⁰ C and 110 ⁰ C, preferably 25 ⁰ C and 100 ⁰ C, is performed.

17. The method according to any one of the preceding claims, characterized in that the polymerization at atmospheric pressure or

Overpressure is performed.

18. The method according to any one of the preceding claims, characterized in that the polymerization is carried out at an overpressure between 0.1 MPa and 10 MPa.

19. The method according to any one of the preceding claims, characterized in that the polymerization during a Reacti- onszeit between 10 min and 240 min, in particular 10 min and 180 min, preferably 10 min and 60 min, is performed.

20. The method according to any one of the preceding claims, characterized in that the polyolefin is selected from the group consisting of polyethylene, polypropylene, polybutene, in particular poly-1-butene, polyhexene, in particular poly-1-hexene, 1, 2-polybutadiene, 1,4-polybutadiene, polyisoprene, polycycloolefins and copolymers thereof.

21. Polyolefin, produced or producible by a process according to one of the preceding claims.

22. A polyolefin according to claim 21, comprising a stabilizer proportion between 0.01 wt .-% and 0.5 wt .-%, based on the total weight of the polyolefin.

23. A medical device comprising a polyolefin according to claim 21 or 22.

24. Medical device according to claim 23, characterized in that it is designed as a prosthesis, in particular endoprosthesis.

25. Medical device according to claim 23 or 24, characterized in that it is designed as a joint prosthesis, in particular selected from the group consisting of hip joint prosthesis, knee joint prosthesis, ankle joint prosthesis, elbow joint prosthesis, temporomandibular joint prosthesis, shoulder joint prosthesis, finger joint prosthesis and vertebral articular surface prosthesis.