Swelling behaviour of hydrogels from methacrylic acid and poly(ethylene glycol) side chains by magnetic resonance imaging

The swelling behaviour of hydrogels of methacrylic acid and poly(ethylene glycol) monomethyl ether monomethacrylate macromonomer, P[(MAA)-co-(PEGMEMA)], copolymers was investigated. Under pH 7, characteristic sigmoidal swelling appears depending on composition. This anomalous swelling phenomenon is related to the ability of moieties in the comonomeric units -COOH and -[-O-CH2-CH2-]- to form complexes by hydrogen bonding, stabilized by hydrophobic interactions. The swelling was followed using magnetic resonance imaging (MRI) providing spatial and temporal resolution. Data from MRI are compared with gravimetric results and photographs during swelling. In the MRI images two processes were distinguished, corresponding to a swollen external region in contrast to a rigid core which starts to swell after a lag time depending on sample composition. Microscopic and macroscopic results are in good agreement. (C) 2007 Society of Chemical Industry.