Interpenetrating polymer networks (IPNs) combining polyisobutene (PIB) and poly(cyclohexyl methacrylate) (PCHMA), networks were prepared using an in situ strategy. PIB networks were formed by alcohol-isocyanate addition between the hydroxyl end groups of telechelic dihydroxypolyisobutene and an isocyanate cross-linker, catalyzed by dibutyltindilaurate (DBTDL). PCHMA networks were obtained from free-radical copolymerization of cyclohexyl methacrylate (CHMA) with ethylene glycol bismethacrylate (EGDM) in the presence of dicyclohexyl peroxydicarbonate (DCPD) as the-initiator. The network formations into the IPN architecture were followed by FTIR spectroscopy. In a large composition range, transparent IPNs exhibit two mechanical relaxation temperatures as determined by dynamic mechanical thermal analysis (DMTA), corresponding to those of a PIB enriched phase and of one interpenetrating phase containing the PCHMA network. This morphology was confirmed by IPN surface analysis by AFM. As expected, mechanical properties of PIB networks are improved by the presence of PCHMA network in such IPN architectures. (c) 2006 Elsevier Ltd. All rights reserved.