The medical grade poly(vinylmethyl siloxane)(PVMS) and silica filled PVMS were crosslinked with benzoyl peroxide(BPO). The glass transition of the crosslinked silicone rubber was evaluated by measurment of thermally stimulated current(TSC). The releasing rate of 1 norgestrel(LNG) through the membrane of the vulcanized silicone rubber in saturated physiological salt solution and that from the intrauterine device(IUD) were determined. The results showed that the drug deli very behavour was influenced by the structure of PVMS molecules which were controlled by the content of BPO and silica used in vulcanization of PVMS. The burst effect at first stage of drug delivery was observed probably due to the interaction between LNG and macromolecules. The releasing curve of LNG from IUD could be kept constant for period of half a year.
