Melt grafting of acrylic acid (AA) and butyl acrylate (BA) (equal molar ratios) onto low-density polyethylene (LDPE) was carried out in Haake internal mixter by free radical grafting copolymerization. The graft degree of AA and BA in the grafted LDPE (LDPE-g-(AA+BA)) was determined by FTIR. The influences of initiator on the graft degree of AA and BA, melt flow rate (MFR), and gel content were investigated, and the optimum conditions were obtained. The successive self-nucleation/annealing (SSA) thermal fraction method was used to characterize the molecular structure and polydispersity of LDPE-g-(AA+BA) with various graft degrees. The effects of thermal fraction parameters on fraction of LDPE-g-(AA+BA) were investigated. On the basis of the results of SSA, the grafting reaction mechanism of AA and BA onto LDPE was proposed, i.e., grafting reaction preferentially occurred on the tertiary carbons of LDPE. The grafted LDPE possessed suitable reactivity and rheological property. (C) 2007 Wiley Periodicals, Inc.