Preparation of ultra high molecular weight polyethylene

Abstract

The invention relates to a process for the preparation of a particulate ultra high molecular weight polyethylene (UH-MWPE), comprising the steps of preparing a magnesium containing carrier, loading the carrier with a organometallic compound forming a supported catalyst and contacting the supported catalyst with at least ethylene under polymerization conditions, wherein the organometallic compound is of the formula R.sup.3.sub.3P═N—TiCpX.sub.n.

Claims

1. A process for preparing a particulate ultra high molecular weight polyethylene (pUHMWPE), comprising the steps of: a) preparing a magnesium containing carrier by interaction of a solution of an organomagnesium compound having composition MgR.sup.1.sub.2.nMgCl.sub.2.mR.sup.2.sub.2O where n=0.37-0.7, m=1.1-3.5, R.sup.1 is each an aromatic or aliphatic hydrocarbyl residue and R.sup.2.sub.2O is an aliphatic ether, with a chlorinating agent at a molar ratio Mg/Cl of at most 0.5, wherein Mg represents the Mg of the organomagnesium compound and Cl represents the Cl of the chlorinating agent; b) loading the magnesium containing carrier with a organometallic compound forming a supported catalyst, and c) contacting the supported catalyst with at least ethylene under polymerization conditions, wherein the organometallic compound is a compound of the formula
R.sup.3.sub.3P═N—TiCpX.sub.n, wherein each R.sup.3 is independently selected from the group consisting of: a hydrogen atom, a halogen atom, a C.sub.1-20 hydrocarbyl radicals optionally substituted by at least one halogen atom, a C.sub.1-8 alkoxy radical, a C.sub.6-10 aryl or aryloxy radical, an amido radical, a silyl radical of the formula —Si—(R.sup.4).sub.3 and a germanyl radical of the formula —Ge—(R.sup.4).sub.3, and wherein each R.sup.4 is independently selected from the group consisting of: hydrogen, a C.sub.1-8 alkyl or alkoxy radical, C.sub.6-10 aryl or aryloxy radicals, Cp is a cyclopentadienyl ligand, X is an activatable ligand and n is 1 or 2, depending upon the valence of Ti and the valence of X.

2. The process of claim 1, further comprising the step of treating the magnesium containing carrier or the organometallic compound with an activator selected from the list of alumoxanes, alkyl aluminiums, alkyl aluminum halides, anionic compounds of boron or aluminum, trialkylboron compounds, triarylboron compounds, borates, and mixtures thereof.

3. The process according to claim 1, wherein the magnesium containing carrier has a D50 of 2 to 30 μm.

4. The process according to claim 1, wherein step c) comprises contacting ethylene and at least one alpha-olefin with the supported catalyst.

5. The process according to claim 1, wherein the chlorinating agent is a chlorine-containing compound of composition Y.sub.kACl.sub.4-k, where Y=OR.sup.5 or R.sup.5 group with R.sup.5 being a C.sub.1-20 hydrocarbyl radicals optionally substituted by at least one halogen atom, A is a Si or C atom and k=0 to 2.

6. The process according to claim 1, wherein the organometallic compound is of the formula .sup.tBu.sub.3P═N—TiCp*X.sub.2, wherein Cp* is pentamethylcyclopentadienyl and X is selected from the group consisting of Cl, Br, Me and Et.

7. The process of claim 1, wherein X is selected from the group consisting of Cl, Br, Me and Et and n=2.

8. The process of claim 1, wherein X is a substituted or unsubstituted butadiene and n=1.

Description

EXPERIMENTAL

(1) The organometallic compound Cp*Ti[(t-Bu).sub.3PN]Cl.sub.2 (I) was produced according to the method described in Douglas W. Stephan et al in Organometallics, 2003, 22, 1937-1947, which is hereby included by reference.

(2) Preparation of Magnesium Containing Carrier and Supported Catalyst.

Example 1: Preparation of the Magnesium Containing Carrier

(3) In a 1 L reactor equipped a thermostat, internal temperature control and a mechanical stirrer. 130 mL of PhMgCl in dibutylether (0.53 mol Mg/L) was stirred at 500 rpm at 10° C. 75 mL of a 3.7 M solution of PhSiCl.sub.3 in PhCl was added drop wise at a rate of 75 ml/hour. The reaction mixture was stirred for 30 minutes at 10° C., then heated at a rate of 1° C./min to 60° C., and finally stirred for a further 30 minutes at 60° C. Heptane washings were then performed until the supernatant is clean. The support obtained has a median particle size 10.2 μm of and a span of 0.96 as measured by Malvern Laser light scattering.

Example 2: Pre-Treatment of the Magnesium Containing Carrier by an Alkyl Aluminum Compound

(4) A toluene suspension of the MgCl.sub.2 support from Example 1 and MAO.sub.10% wt (0.138 mol in toluene) was stirred at 300 rpm and 60° C. for 1 hour. The resulting solid was washed thoroughly with toluene at 60° C. until the supernatant is clean.

Example 3: Supporting of the Organometallic Compound

(5) In a 1 L reactor, ˜5 g of solid from Example 2 in toluene is stirred at 300 rpm and at room temperature. 40 mL of 0.02 M toluene solution of compound (I) is added and the mixture is allowed to react for 1 hour. Toluene washings are then performed until the supernatant is colorless. The solid is finally slurried in 250 mL of heptane.

Example 4

(6) In a 100 mL reactor, ˜250 mg of solid from Example 2 in toluene is contacted at room temperature with 20 mL of 0.015 M toluene solution of compound (I) for 1 hour. Toluene washings are then performed until the supernatant is colorless. The solid is finally slurried in 2 mL of heptane.

Example 5

(7) Supported catalyst is prepared as described in example 3 from a support with a d50 of 5.5 μm obtained by the process of example 1 at a higher stirring rate.

Example 6

(8) Supported catalyst is prepared as described in example 3 from a support with a d50 of 3.2 μm.

Example 7: Preparation of the Magnesium Containing Carrier

(9) The process of Example 1 is repeated with the difference that the PhMgCl was at a molar rate of 1.0 mol Mg/L. The support obtained has a median particle size 6.5 μm of and a span of 0.92 as measured by Malvern Laser light scattering.

Example 8

(10) A supported catalyst is prepared as described in Example 3 from a support prepared as described in Example 9.

Example 9

(11) A supported catalyst is prepared as described in Example 3 from a support with a d50 of 11.9 μm obtained by the process of Example 9 whereby the stirring rate is 250 rpm.

Example 10

(12) Supported catalyst is prepared as described in Example 3 from a support with a d50<2 μm obtained by the process of Example 9 whereby the stirring rate is 1400 rpm.

(13) Comparative Experiment A:

(14) Catalyst prepared as described in example 4 except that the solution of compound (I) is replace by 20 mL of a 0.0125 M toluene solution of CpTiCl.sub.3.

(15) Comparative Experiment B:

(16) Catalyst prepared as described in example 4 except that the solution of compound (I) is replace by 20 mL of a 0.015 M toluene solution of Me.sub.5CpTiCl.sub.2(NC(2,6-F.sub.2Ph)(.sup.iPr.sub.2N) prepared as described in WO2005/090418.

(17) Comparative Experiment C:

(18) A MgCl.sub.2 support is prepared as described in example 18 of U.S. Pat. No. 7,528,091B2. The resulting d50 was 12.5 μm. 250 mg of the resulting solid in toluene is contacted at room temperature with 20 mL of 0.015 M toluene solution of compound (I) for 1 hour. Toluene washings are then performed until the supernatant is colorless. The solid is finally slurried in heptane.

(19) Comparative Experiment D:

(20) A MgCl.sub.2 support prepared as described in Example 1 slurried in heptane is contacted at 60° C. with 0.09 mol TiCl.sub.4 for 1 h. Heptane washings were then performed until the supernatant is clean.

(21) General Polymerization Procedure:

(22) Unless otherwise specified, batch polymerizations were carried out in a stirred 2 L or 10 L reactor. The reaction temperature was set to the required temperature and controlled by a Lauda thermostat. The feed streams (solvent and ethylene) were purified with various adsorption media to remove catalyst killing impurities such as water, oxygen and polar compounds as is known by someone skilled in the art. In an inert atmosphere the previously dried reactor is filled with 1 L of heptane (or 4.5 L for Experiments IV and VI). After the solvent has reached the desired temperature, the scavenger components are added and after 5 minutes the supported catalyst is added. Next the ethylene stream is fed into the reactor to reach and maintain a total pressure of 0.5 or 1.0 MPa. After the desired polymerization time, the contents of the reactor is collected, filtered and dried under vacuum at 50° C. for at least 12 hours. The polymer is weighted and samples are analyzed.

(23) TABLE-US-00001 Scavenger Reaction Polymerization Cat TEA Temperature Pressure Time Yield Cat Yield Productivity D50 Reaction Catalyst [mg] [mmol/L] [° C.] [MPa] [h:m] [g] [gpol/gcat] [gpol/gcat*h*barg] [μm] A C.Exp. A 250 1.00 60 0.5 2:04 196 787 76 105.9 B C.Exp. B 250 1.00 60 0.5 2:00 35 140 14 C C.Exp. C 250 1.00 60 0.5 2:00 55 220 22 618.0 D C.Exp. D  15 0.92 60 0.5 2:00 98 6528 653 171.9 I Ex. 3 100 1.00 60 0.5 2:00 259 2589 259 165.4 II Ex. 4 250 1.00 60 0.5 1:34 358 1437 184 129.2 III Ex. 5 100 0.92 60 0.5 2:00 301 3009 301 89.2 IV Ex. 5 110 4.6 70 1.0 3:53 1720 15686 145.1 V Ex. 6  15 0.92 60 0.5 1:00 266 17686 3537 57.6 VI Ex. 6  50 4.6 60 0.5 7:00 1325 26225 93.5 VII Ex. 8  15 0.92 60 0.5 2:00 147 9737 974 101.6 VIII Ex. 9  15 0.92 60 0.5 2:00 79 5204 520 166.4 IX Ex. 10  15 0.92 60 0.5 2:00 340 22603 2260 41.5 Calculated Bulk Ti Ash Polymerization density content Content DF ES IV Mn Mw Mw/Mn Reaction SPAN [g/L] [ppm] [ppm] [s] [N/mm.sup.2] [dL/g] [kg/mol] [kg/mol] [—] A 0.74 284 1271 45 0.379 360 3000 8.2 B 193 7143 380 2400 6.3 C 1.94 4545 430 2400 5.7 D 1.12 321 153 30 0.423 470 3000 6.3 I 0.8  340 386 28 20.8 960 3100 3.2 II 0.73 346 4.5 696 31 0.433 1100 2800 2.5 III 0.82 360 332 35 — — — — IV 0.83 456 64 25 0.488 — — — — V 0.98 298 57 45 1100 3400 2.9 VI 0.92 418 38 32 3800 1500 2.5 VII 0.90 370 <1.7 103 38 VIII 0.82 362 1.9 192 22 IX 1.04 320 0.4 44 0.469
Test Methods
SEC-MALS:

(24) The molecular mass distributions (Mn, Mw, Mz, Mw/Mn) were measured using a PL-210 Size Exclusion Chromatograph coupled to a refractive index detector (PL) and a multi-angle light scattering (MALS) detector (laser wavelength 690 nm) from Wyatt (type DAWN EOS). Two PL-Mixed A columns were used. 1,2,4-trichlorobenzene was used as the solvent, the flow rate was 0.5 ml/min, and the measuring temperature was 160° C. Data acquisition and calculations were carried out via Wyatt (Astra) software. The UHMWPE should be completely dissolved under such conditions that polymer degradation is prevented by methods known to a person skilled in the art.

(25) Bulk density is determined according to DIN 53466; ISO 60 at 23° C. and 50% relative humidity.

(26) Particle Size and Span:

(27) The average particle size (d50) of the polymer is determined in accordance with ISO 13320-2, using a Malvern™ LLD particle size analyzer. The span defined as (d90−d10)/d50 was also determined using the Malvern™ LLD particle size analyzer.

(28) The average size of the catalyst is determined using a Malvern™ LLD particle size analyzer.

(29) Dry Flow (DF):

(30) The dry flow in seconds was measured according to the method described in ASTM D 1895-69, Method A; 23° C. and 50% relative humidity.

(31) Intrinsic Viscosity (IV):

(32) The Intrinsic Viscosity is determined according to method PTC-179 (Hercules Inc. Rev. Apr. 29, 1982) at 135° C. in decalin, the dissolution time being 16 hours, with BHT (Butylated Hydroxy Toluene) as anti-oxidant in an amount of 2 g/l solution, by extrapolating the viscosity as measured at different concentrations to zero concentration;

(33) Elongational Stress (ES)

(34) of UHMWPE is measured according to ISO 11542-2A.