A series of linear ionomeric polyurethanes were synthesized and obtained as stable aqueous dispersions using various amounts (ca. 6-20 %) of a diol functionalized polyhedral oligomeric silsesquioxane (POSS) comonomer. Polymers were characterized by GPC, XRD, DSC, dynamic rheology, and contact angle measurements. POSS macromonomers can be easily copolymerized, giving stable aqueous dispersions if the POSS content is <= 10 %. The X-ray diffraction analysis of cast films showed the presence of residual crystallinity even at the lowest nanofiller dosage. Dynamic mechanical analysis showed a reinforcement effect mainly when longer soft segments (poly(tetramethylene glycol) 2000) were used. Contact angle measurements indicated a significant surface hydrophobicity enhancement as well as reduction in surface energy components calculated according to the harmonic mean approximation.