Polethylene composition having high swell ratio

A polyethylene composition having the following features:

• 1) density from 0.940 to 0.955 g/cm3 determined according to ISO 1183 at 23° C.;
• 2) ratio MIF/MIP from 12 to 30, where MIF is the melt flow index at 190° C. with a load of 21.60 kg and MIP is the melt flow index at 190° C. with a load of 5 kg, both determined according to ISO 1133;
• 3) Mz from 2,000,000 to 4,500,000 g/mol, where Mz is the z-average molecular weight measured by GPC;
• 4) η0.02 from 160,000 to 300,000 Pa·s wherein η0.02 is the complex shear viscosity at an angular frequency of 0.02 rad/s, measured with dynamic oscillatory shear in a plate-plate rotational rheometer at a temperature of 190° C.;
• and
• 5) long-chain branching index, LCBI, equal to or greater than 0.75, wherein LCBI is the ratio of the measured mean-square radius of gyration Rg, measured by GPC-MALLS, to the mean-square radius of gyration for a linear PE having the same molecular weight.