Radiation induced polymerization of styrene (St), methyl methacrylate (MMA) and n-butyl methacrylate (BMA) is carried out in a room temperature ionic liquid (RTIL), [Me3NC2H4OH](+)[ZnCl3](-) and in its mixed solutions with THF. The presence of ionic liquid (IL) leads to a significant increase in monomer conversion and polymer's molecular weight. Molecular weight distribution (MWD) of resulting polymer varies with the IL fraction in the RTIL/THF solutions and is also dependent on the monomer used. For polystyrene (PSt) and poly(n-butyl methacrylate) (PBMA), multi-modal broad MWD is observed at IL > 50 v% while single-modal narrow MWD is observed at IL < 40 v%. For poly(methyl methacrylate) (PMMA), however, nearly a single-modal MWD is observed at THF > 20 v%. The measured miscibility of polymer with RTIL is in the order: PMMA > PBMA > PSt. Here we propose that the difference in MWD is due to the inhomogeneous nature of the ionic liquid in micro-region and the immiscibility of polymer with medium. (c) 2005 Elsevier Ltd. All rights reserved.