EFFECT OF POLYOL MOLECULAR-WEIGHT ON THE PHYSICAL-PROPERTIES AND HEMOCOMPATIBILITY OF POLYURETHANES CONTAINING POLYETHYLENE OXIDE MACROGLYCOLS

The physical properties and haemocompatibility of polyurethanes contai ning polyethylene oxide (PEG) of varying molecular weights but constan t weight fraction of hard segment are investigated. The PEO molecular weights studied were 600, 1450 and 8000. Analysis of polyurethane phas e separation and crystallinity using dynamic-mechanical analysis and d ifferential scanning calorimetry show that the degree of phase separat ion and crystallinity increase with polyol molecular weight, but level off at the highest molecular weights. The degree of water absorption increases substantially with increasing PEO molecular weight, levellin g off at the highest molecular weight. Tensile data show a maximum in extensibility at a polyethylene glycol (PEG) molecular weight of 1450, while ultimate strength increases with increasing segment length. Whe n the materials are hydrated, there is a significant drop in the modul us, ultimate stress and ultimate elongation. Dynamic contact angle mea surements show that surface hydrophobicity decreases as the soft segme nt molecular weight increases. Using electron spectroscopy for chemica l analysis (ESCA) to determine the surface composition of these polyur ethanes, it was found that the hard segment content at the surface inc reases as the polyol block length decreases. The haemocompatibility of these polyurethanes was investigated in an ex vivo canine blood-conta cting model. Only for the shortest block length studied, PEG-BOG, are differences in blood compatibility observed. This material was found t o be the most thrombogenic. The PEG-1450 sample shows comparable blood compatibility to PEG-8000.