The photopolymerization of four dimethacrylate monomers under different irradiating conditions was followed in situ by H-1 stray-field magnetic resonance imaging (H-1 STRAFI-MRI). This technique is capable of discriminating local changes at a spatial resolution of tens of micron and is suitable for studying larger samples than infrared spectroscopy and photocalorimetry. The evolution of proton magnetization with irradiation time and intensity was recorded and correlated with volumetric polymerization shrinkage, extent of reaction and spatially resolved reaction rates. (c) 2005 Elsevier Ltd. All rights reserved.