Interpenetrating　polymer　network　(IPN)　hydrogels　were　prepared　by　grafting　of　acrylamide　(AAm),　N-methylol　acrylamide　(NMA)　and　acrylic　acid　(AAc)　onto　preirradiated　polypropylene　(PP)　membrane.　To　obtain　PP-g-AAc/AAm/NMA　IPN　hydrogels,　at　first,　AAc　were　grafted　onto　preirradiated　PP　and　then　AAm　were　grafted　onto　the　PP-g-AAc　membranes.　Finally　NMA　were　grafted　onto　PP-g-AAc/AAm　membranes.　In　the　different　stages　of　grafting　under　different　reaction　conditions,　trapped　radicals　in　the　membrane　samples　were　probed　by　electron　spin　resonance　(ESR).　The　temperature　response　behaviors　of　the　IPN　hydrogels　were　studied.　Reversible　behavior　and　controlled　release　of　drug　tests　made　reflecting　the　switching　to　＂on＂　state　at　higher　temperatures　and　to　＂off＂　state　at　lower　temperatures　were　achieved.　By　increasing　the　grafted　content　of　NMA,　higher　transition　temperature　of　the　hydrogel　could　be　attained.