Disclosed herein is a polyethylene. The polyethylene has a melt flow index of about 0.4 g/10 min to about 0.6 g/10 min, a weight average molecular weight of about 500,000 g/mol to about 700,000 g/mol, and a molecular weight distribution of about 3 to about 5 and is prepared by polymerization in the presence of a catalyst retaining at least about 50% of an initial reactivity level (during initial 30 minutes) for a period of time exceeding about 4 hours.