Poly(ethylene glycol) dimethacrylates (PEGDMA) were synthesized by esterification reaction of different molecular weight poly(ethylene glycol) with methacrylic acid in presence of acid catalyst. Their degrees of acrylation were found to be in the range of 93-95%, using nuclear magnetic resonance (NMR) spectroscopy. PEG dimethacrylates of molecular weight ranging from 400 to 4000 and methacrylic acid were further copolymerized to obtain pH sensitive crosslinked hydrogel microparticles. The diameters of poly(PEGDMAMAA) microparticles increased with increasing molecular weight of the poly(ethylene glycol) dimethacrylates and was found to be in the range of 0.4-2.7 mu m at pH 7.4 and 5.2-25.3 mu m at pH 2.5 in aqueous solution. Surface morphology of various polymeric samples were observed using SEM, which showed partial aggregation of particles at pH 2.5 but microparticles coalesce with each other and appeared like a continuous film at pH 7.4. In vitro insulin release studies were performed by simulating the condition of gastrointestinal tract, which showed only 18-25% insulin release into the aqueous medium at pH 2.5 in 90 min, while significantly higher release was observed at pH 7.4. In studies with diabetic rabbits, the blood glucose levels were lower for animals that received the insulin loaded hydrogel microparticles and the effect lasted for 8-10 h. (C) 2007 Wiley Periodicals, Inc.