Dynamic Viscoelastic Properties of Segmented Polyurethanes

Four types of segmented polyurethanes with systematically varying blockness of hard segment were prepared. The dynamic viscoelastic properties of the segmented polyurethanes were studied in a wide range of temperature. These segmented polyurethanes were prepared by prepolymer technique using polyoxy tetramethylene glycol (PTMG) (Mn=1000 and 2000) and 4, 4'-diphenylmethanediisocyanate as starting materials and hydrazine and ethylenediamine as chain extenders. The samples were studied at a frequency of 110 Hz by Vibron DDV III-B. Differential scanning calorimetry (DSC) and infrared spectroscopy were also studied. These segmented polyurethanes showed tanδ maxima at two temperatures (-120℃ and -50℃). As the hard segment concentration was increased, main dispersion shifted to a lower temperature, its height of tanδ peak decreased and its width widened. As the moleculare weight of PTMG was increased, main dispersion shifted to a lower temperature. Storage modulus E' in a series of PTMG 1000-HD was increased as hard segment concentration was increased, but E' in a series of PTMG 2000-HD and -EDA were not affected. The dispersions were interpreted in terms of molecular motion and the difference of composition of segmented polyurethanes