Ring-opening metathesis copolymerization of norbornene ethyl polyhedral oligomeric silsesquioxane monomer (NBEPOSS) and 2-endo-3e-vo-5-norbornene-2,3-dicaboxylic acid trimethyl ester (NBETMS) was performed using a Ru-based catalyst, RuCl2(=CHPh)(PCY3)(2). The block copolymers poly(NBETMS-b-NBEPOSS) were then converted to poly(NBECOOH-b-NBEPOSS) by hydrolysis and precipitation. The polymers were characterized by NMR and GPC and the actual NBEPOSS contents were found in good correspondence with the theoretical values. A linear dependence Of M-n on conversion and a linear dependence of ln([M-0]/[M]) on reaction time observed in the polymerization of NBETMS suggest that chain breaking reactions such as termination and chain transfer are minimal. Low PDI values and smooth GPC peak shifts during polymerization after addition of a second batch of the same monomer or a NBEPOSS monomer also reflect a living process. (c) 2007 Elsevier Ltd. All rights reserved.