The chemistry of free radical graft copolymerization, initiated with t-butoxy radicals, has been investigated using ethylene glycol dibenzoate and diethylene glycol dibenzoate as models for polyethylene terephthalate (PET). Although diethylene glycol dibenzoate is more reactive than ethylene glycol dibenzoate the site of grafting from the polymer is determined by the concentration of ethylene glycol and diethylene glycol residues and the relative reactivity at these positions. Hence grafting occurs most frequently at the ethylene glycol positions. This study also suggests that PET is less reactive than the polyolefins LLDPE and polypropylene and that PET chain scission is possible using high t-butoxy radical concentrations in the presence of adventitious oxygen at relatively low temperatures. (C) 2000 Elsevier Science Ltd. All rights reserved.