The melt grafting of glycidyl methacrylate (GMA) onto high-density polyethylene (HDPE) in the presence of free radical initiators was investigated in the batch mixer. The graft content was determined with the titration and FTIR spectroscopy. The graft content increased with the increase of peroxide and initially introduced GMA concentration. Increase of the grafted GMA content resulted in decrease of the melt index. Interestingly, there was a sudden drop of GMA grafting content with the reaction time. It is assumed that depolymerization of GMA have taken place over the ceiling temperature. The crystallinity of the prepared glycidyl methacrylate grafted high density polyethylene (HDPE-g-GMA) was determined by the measurement of the heat of fusion. GMA grafted site acted as defect and crystallinity of the HDPE-g-GMA decreased with the increase of grafting reaction. (C) 2008 Wiley Periodicals, Inc.