Abstract The melt grafting of Glycidyl Methacrylate (GMA) onto Polyethylene in the presence of free radical initiators was conducted in a co-rotating twin screw extruder. Reaction kinetic parameters for the overall grafting and homopolymerization reactions were estimated in a batch melt mixer. Residence time distribution (RTD) in the extruder was determined and mean residence time and Peclet number (Pe) were estimated for different sets of reaction conditions. A twin screw simulation program was used to predict the flow characteristics along the length of the extruder. A modular reactor model consisting of plug flow and “axial dispersion” reactor cells was constructed and with the kinetic and transport information and the actual melt temperatures, the overall GMA conversion was predicted. In most cases the predicted conversion agreed well with experimentally determined values.