We report a novel method to prepare graft copolymers of PS-g-PEGM with controlled backbone length, grafting sites and spacing length. This method involves three steps: first step, styrene was controlled to insert into the main chain of polytrithiocarbonate at the trithiocarbonate sites, the experimental results show that not only the chain length of the backbone, but also the length of polystyrene (PS) space chain between neighboring trithiocarbonate units can be well-controlled; second step, 'grafting points' maleic anhydride units were inserted into the backbone chain between St unit and trithiocarbonate unit; third step, poly(ethylene glycol methyl ether) (PEGM) chains were grafted onto the main chain by esterification reaction of maleic anhydride with PEGM to form graft copolymers of PS-g-PEGM with controlled backbone length, spacing length and well-defined grafting sites. (C) 2004 Elsevier Ltd. All rights reserved.