High molecular weight polyether urea copolymers were synthesized using perfectly difunctional aromatic amine terminated polypropylene oxide (PPO) (2800 <Mn>) prepared via aluminum porphorin initiated coordination polymerization. The resulting segmented copolymer showed much higher tensile strength and better thermal stability than polyureas based on commercial PPO which contains some terminal unsaturation. This was attributed to the achievement of both higher molecular weight and to more extensive microphase separation between the segments. In addition, the surface structure of segmented polyether urea and polyurethane urea copolymers were modified in two ways: siloxane urea segmented copolymers were synthesized and physically blended into the system, and siloxane oligomers of controlled molecular weight and composition were incorporated into the copolymer backbone as a part of the soft segment. X-ray photoelectron spectroscopy (XPS) was used to obtain surface compositional information, while differential scanning calorimetry (DSC) and stress-strain analysis were used to characterize the bulk properties. In general, the surface enrichment of siloxane was observed in both solvent cast blends and siloxane incorporated systems. The surface siloxane concentration showed a small increase with siloxane segment length, content, and surface sensitive angle. Surface segregation of these systems was suppressed to a certain extent due to phase mixing within the copolymer bulk and by the anchoring of both ends of the siloxane segment with urea components. The bulk properties of these copolymer systems were not affected greatly when small amounts of siloxane ureas were added or when small amounts of siloxane blocks were incorporated. / Master of Science