A method for increasing the melt strength and/or low shear viscosity of a polyethylene resin, the method comprising: a) providing a polyethylene composition comprising the reaction product of ethylene and optionally, one or more alpha-olefin comonomers, wherein the polyethylene composition comprises greater than 50 wt.% of the units derived from ethylene and less than 30 wt.% of the units derived from one or more alpha-olefin comonomers, wherein the polyethylene composition is characterized by the following properties: a density ranging from 0.900 g/cm 3 to 0.970 g/cm 3 measured in accordance with ASTM D792, a molecular weight distribution (Mw/Mn) ranging from 2.6 to 3.5 measured using high temperature GPC as set out in the description, and from 0.10 to 0.27 vinyl groups per 1,000 total carbon atoms measured as set out in the description; b) providing a masterbatch composition comprising 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 measured using DSC, and wherein the polyethylene resin has a density ranging from 0.900 g/cm 3 to 0.970 g/cm 3 measured in accordance with ASTM D792, melt index ranging from 0.01 g/10 min to 100 g/10 min measured in accordance with ASTM D 1238, Condition 190°C/2.16 kg, Procedure B; and c) reacting the polyethylene composition with the masterbatch composition to form a modified polyethylene composition, wherein the polyethylene composition and the masterbatch composition are subjected to a temperature above the softening point of the polymers for a sufficient period of time such that the reaction between the polyethylene composition and the free radical generator can take place. a) providing a polyethylene composition comprising the reaction product of ethylene and optionally, one or more alpha-olefin comonomers, wherein the polyethylene composition comprises greater than 50 wt.% of the units derived from ethylene and less than 30 wt.% of the units derived from one or more alpha-olefin comonomers, wherein the polyethylene composition is characterized by the following properties: a density ranging from 0.900 g/cm 3 to 0.970 g/cm 3 measured in accordance with ASTM D792, a molecular weight distribution (Mw/Mn) ranging from 2.6 to 3.5 measured using high temperature GPC as set out in the description, and from 0.10 to 0.27 vinyl groups per 1,000 total carbon atoms measured as set out in the description; b) providing a masterbatch composition comprising 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 measured using DSC, and wherein the polyethylene resin has a density ranging from 0.900 g/cm 3 to 0.970 g/cm 3 measured in accordance with ASTM D792, melt index ranging from 0.01 g/10 min to 100 g/10 min measured in accordance with ASTM D 1238, Condition 190°C/2.16 kg, Procedure B; and c) reacting the polyethylene composition with the masterbatch composition to form a modified polyethylene composition, wherein the polyethylene composition and the masterbatch composition are subjected to a temperature above the softening point of the polymers for a sufficient period of time such that the reaction between the polyethylene composition and the free radical generator can take place.