Provided is a method for increasing the melt strength and/or low shear viscosity of a polyethylene resin. The method includes: a) providing a polyethylene composition including the reaction product of ethylene and optionally, one or more alpha-olefin comonomers, wherein the polyethylene composition is characterized by the following properties: a density ranging from 0.900 g/cm3 to 0.970 g/cm3, a molecular weight distribution (Mw/Mn) ranging from 2.6 to 3.5, and from 0.10 to 0.27 vinyl groups per 1,000 total carbon atoms; b) providing a masterbatch composition including a free radical generator and a polyethylene resin, wherein the free radical generator has a half-life at 220° C. of less than 200 seconds, and a decomposition energy higher than −250 kJ/mol, and wherein the polyethylene resin has a density ranging from 0.900 g/cm3 to 0.970 g/cm3, melt index ranging from 0.01 g/10 min to 100 g/10 min; and c) reacting the polyethylene composition with the masterbatch composition to form a modified polyethylene composition.