EFFECT OF POLYOL TYPE ON THE SURFACE-STRUCTURE OF SULFONATE-CONTAINING POLYURETHANES

Polyurethanes based upon polytetramethylene oxide (PTMO) as the polyol and derivatized with propyl sulfonate functionality pendant from the urethane nitrogen have previously been shown to possess good blood-con tacting properties. Other investigators have shown that sulfonated pol yurethanes containing polyethylene oxide (PEO) as the soft segment are much more thrombogenic than those containing PTMO as the soft segment . In this article, the surface properties of sulfonated polyurethanes based upon either PTMO or PEO are compared. Dynamic contact angle meas urements show a significant decrease in the receding angles of the sul fonated PTMO-containing polyurethane as compared to its nonsulfonated precursor polymer. No significant difference is seen between the reced ing contact angles of either the sulfonated PEO-based polyurethane or its nonsulfonated analog. Variable-angle electron spectroscopy for che mical analysis (ESCA) studies of sulfonated PTMO-based polyurethane pe rformed at room temperature show that there is a significant decrease in sulfur content at the surface. In contrast, the sulfonated PEO-base d polyurethane showed little change in sulfur content with take-off an gle. Finally, ESCA studies of freeze-dried surfaces show a significant increase in sulfur near the surface of the sulfonated PTMO-based poly mer as compared to vacuum-dried samples but show no such increase for the sulfonated PEO-based polyurethane. It is suggested that the abilit y of the sulfonate functionality to be expressed at the surface may ex plain the observed differences in blood compatibility between the sulf onated polyurethanes based upon polyols of varying hydrophilicity.