The photo-induced copolymerization of dodecyl methacrylate (DDM) with five oxyethylene glycol dimethacrylates (OEGDM) was investigated. Effects of the monomer ratio and of the length of dimethacrylate spacer group on the polymerization kinetics, the extent of the after-effect and pendant double bond content in the polymerization product were studied and the reactivity ratios estimated. For systems containing OEGDM with short spacers between the methacrylate groups, R-p(max) reached the highest value at certain monovinyl/divinyl monomer ratio. This phenomenon was discussed in terms of the behavior of the reaction diffusion parameter (as a function of monomer ratio and conversion). Determination of the reactivity ratios by five calculation methods showed that r(1) (DDM) values were lower than 1 and the r(2) (OEGDM) values were higher than 1 indicating that the polymer formed at the beginning of the reaction is more densely cross-linked than that formed in the final reaction stages. (c) 2006 Elsevier Ltd. All rights reserved.