Poly(N-isopropylacrylamide) microgel with functional benzo-18-crown-6 group was synthesized by modifying a parent poly(Nisopropylacrylamidecoacrylic acid) microgel with 4′-aminobenzo18-crown-6 under EDC catalysis.The introduction of the functional groups was confirmed by IR and NMR.The resultant microgel is still thermosensitive

but the volume phase transition temperature shifts from 30℃ to 42℃.The swelling degree of the microgels increases too

indicating the 4′-acrylamidobenzo-18-crown-6 monomer acts as an hydrophilic one.The effects of Na+ and Pb 2+ on the microgel size were studied by dynamic light scattering.When ionic strength is not controlled

the microgel size decreases with increasing ［NaCl］

but first decreases followed by increasing with increasing ［Pb(NO3)2］.When ionic strength is kept constant

increasing ［Na+］ has little effect on microgel size.In contrast

microgel size expands significantly with increasing ［Pb2+ ］.In this case

the effect of ionic strength was avoided.Because of its high affinity to 18-crown-6

the binding of Pb2+ with crown ether further increases its hydrophilicity

so the microgels swell to a larger extent.However the binding constant between Na+ and 18-crown-6 is small

therefore it induces little swelling of the microgel particles.The light scattering results also show a narrow size distribution of the microgels.The monodisperse

lead-sensitive microgel may find application for the fabrication of new lead sensors.