Effect of Polyether Components on Surface Composition and Blood Compatibility of Segmented Polyurethaneureas

DSC, water absorption test, and X-ray photoelectron spectroscopy (XPS) were carried out in order to characterize the surface composition and microphase separated structure of segmented polyurethaneureas (SPUU's) composed of diphenylmethane-4,4'-diyl diisocyanate ethylenediamine, and polyethers with different surface free energies and also various molecular weights, M_n. Polyethers used were poly (ethylene glycol) (PEG), poly (propylene glycol) (PPG), and poly(tetramethylene glycol) (PTMG). DSC measurements revealed that the phase mixing between the hard and soft segments proceeded with a decrease in Mn of polyether. The water absorption tests clarified the relative magnitude of surface free energy of each segment. The surface free energy increased in the order of PTMG≈PPG<hard segment<PEG. XPS revealed that an anisotropic distribution of the hard and soft segments existed on the air and substrate facing surfaces due to the difference in surface free energy of each component. This anisotropic composition became more distinct with an increase in degree of microphase separation. The concentration of the component with lower surface free energy increased with a decrease in sampling depth of XPS from the air facing surface. This result indicates that the interfacial free energy between polymer surface and air is minimized by concentrating the component with lower surface free energy on the air facing surface. Blood compatibility of SPUU's was evaluated from the degree of interaction between blood platelets and the surface of SPUU. Blood compatibility of SPUU was better than those of homopolymers composed of hard and soft segments. This means that the microphase separated structure may affect blood compatibility of SPUU. The M_n and surface concentration of polyether of SPUU, at which the minimum number of adhered and deformed platelets were observed, increased with a decrease in the magnitude of the surface free energy pf the polyether components. It is concluded from the surface characterization and the test of blood compatibility that the blood compatibility of SPUU was affected mainly by the state of microphase separation, the surface composition, and the surface free energy of each segment.