Extraction of polyurethane block copolymers: effects on bulk and surface properties and biocompatibility

In order to study changes occurring in polyurethane block copolymers upon solvent extraction, a base polymer containing approximately 50% polyurethane hard segment based on 4,4'-bis(p-phenyl isocyanate), 1,4-butanediol, and poly(tetramethylene oxide) of MW 1000 was synthesized. Portions of this polymer were extracted using methanol, toluene, and acetone. Multidetector gel permeation chromatography was used to characterize the effect of extraction on molecular weight and molecular weight distribution. Extraction also affected bulk and surface properties and the blood compatibility as assessed using a canine ex vivo blood-contacting experiment. Extracted materials possessed a higher molecular weight than the base polymer and had narrower molecular weight distributions. Acetone extraction resulted in the polymer with the highest ultimate tensile strength. Contrary to expectations, the surface properties and blood compatibility of the material studied were affected minimally by extraction.