Preparation of ultra high molecular weight polyethylene

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 1 2 .nMgCl 2 .mR 2 2 O where n=0.37-0.7, m=1.1-3.5, R 1 is each an aromatic or aliphatic hydrocarbyl residue and R 2 2 O 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 3 3 P═N—TiCpX n , wherein

each R 3 is independently selected from the group consisting of:

a hydrogen atom,

a halogen atom,

a C 1-20 hydrocarbyl radicals optionally substituted by at least one halogen atom,

a C 1-8 alkoxy radical,

a C 6-10 aryl or aryloxy radical,

an amido radical,

a silyl radical of the formula —Si—(R 4 ) 3 and

a germanyl radical of the formula —Ge—(R 4 ) 3 , and wherein

each R 4 is independently selected from the group consisting of:

hydrogen,

a C 1-8 alkyl or alkoxy radical, C 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 k ACl 4-k , where Y=OR 5 or R 5 group with R 5 being a C 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 t Bu 3 P═N—TiCp*X 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.