Attachment of amino groups to polymer surfaces by radiofrequency plasmas

Abstract Low temperature gaseous plasmas of ammonia or nitrogen–hydrogen mixtures contain NH 2 groups, or precursors thereof, formed in the plasma, which experimental evidence strongly suggests, can add to various polymer surfaces. The plasmas were established in the 0.3–1.5 torr range by radiofrequency (13.56 MHz) electrodeless excitation at powers ranging from 50 to 500 W. Samples of polypropylene, poly(vinyl chloride), polytetrafluorethylene, polycarbonate, polyurethane, and poly(methl methacrylate) were investigated. All these polymers added amino groups to varying degrees of amino site densities depending on the choice of plasma parameters and the reactivity of the polymer itself. In every instance the polymer was rendered more wettable, although no quantitative wettability measurements were made. Following the plasma treatment, degrees of amino attachment to the polymer were followed radiometrically and reported in terms of “heparin thicknesses” resulting from ionic heparin  35 S attachment to quaternary sites produced from the amino groups. Two implications of such a surface modification are to adhesion and blood compatible materials preparation.