a composition comprising in admixture with a polymer , preferably a polyurethane , and a compatible surface - modifying macromolecule having a central portion of a segmented block oligomeric copolymer comprising at least one polar hard segment , and ∝- ω terminal polyfluoro oligomeric groups , in a surface modifying enhancing amount . the composition is of use in providing articles having improved surface properties , particularly , medical devices having improved resistance to enzyme degradation with acceptable blood compatibility .