Molecular and structural changes of the P(MAA-g-EG) hydrogels were investigated in their hydrated state using attenuated total reflectance Fourier transform infrared spectroscopy. FUR studies identified the formation of hydrogen-bonded complexes at low pH and polyelectrolyte complexes at high pH. Hydrogen bonding and electrostatic repulsion were not affected by the grafted PEG molecular weight in the hydrogels. Additionally, investigation of the macroscopic swelling properties showed that the presence of the grafted PEG chain in the P(MAA-g-EG) hydrogels contributed to the formation of hydrogen bonds. (C) 2003 Elsevier Science Ltd. All rights reserved.