Radical melt graft polymerizations of low-density polyethylene (PE) during reactive extrusion were investigated. In the absence of any reactive monomer, effects of peroxide initiator concentration and type, reaction temperature, and rotor speed of reactive extrusion on the polymer reactions were studied by monitoring mixing torque, and proper reaction conditions for the grafting reaction were proposed. Afterward, radical melt graft polymerizations of PE with several amide monomers including methacrylamide (MAM), N-tert-butylacrylamide (NTAAM), and N-tert-butylmethacrylamide (NTMAM) were continued. Fourier transform spectroscopy (FTIR) analysis and nitrogen analysis confirmed that MAM and NTAAM were successfully grafted onto PE. Monomer structures affected grafting efficiency and polymer chain combination. After exposure to chlorine bleach, the graft modified products exhibited powerful antibacterial properties against Escherichia coli and Staphylococcus aureus.