Unprotected exo,exo-5-norbornene-2,3-dicarboxylic acid and exo,exo-7-oxa-5-norbornene-2,3-dicarboxylic acid were polymerized via ring-opening metathesis polymerization. This reaction yielded polymers with molecular weights (M-n from GPC) ranging from 31 to 242 kg/mol and polydispersity indices between 1.05 and 1.12, using Grubbs' third generation catalyst. The water solubility as a function of pH value of the polymers was investigated by dynamic light scattering (DLS). DLS and acid-base titration revealed that the oxanorbornene polymer was water soluble over a wider pH range than its norbornene analog. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1266-1273, 2009