Quaternary ammonium salts (QAS) were covalently-bound to epoxy resins of different DP in two steps: addition of a N,N-dialkylaminoethanethiol followed by the quaternization of the tertiary amine by an alkylbromide. (C8H17Br to C14H29Br). The products were characterized by H-1 NMR spectroscopy; The QAS-containing oligomers were used as polyols to prepare polyurethane (PU) films by reaction with a triisocyanate. The films show a good bactericidal activity against Escherichia coli, which is preserved after 6 months of immersion in water.