A process for the preparation of an ultra-high molecular weight ethylene homopolymer having a MFR21 of 0.01 g/10 min or less, said process comprising:



(I) prepolymerising at least ethylene at a temperature of 0 to 90° C. in the presence of a heterogeneous Ziegler Natta catalyst to prepare an ethylene prepolymer having an Mw of 40,000 to 600,000 g/mol; and thereafter in the presence of the prepolymer and said catalyst;
(II) polymerising ethylene at a temperature of 55° C. or less, such as 20 to 55° C., to prepare said UHMW ethylene homopolymer;

wherein the UHMW ethylene homopolymer comprises up to 8 wt. % of said prepolymer.