Structure and mechanical properties of thermoplastic polyurethane, based an hyperbranched polyesters

A series of hyperbranched polyurethane (HB-PU) were synthesized using hyperbranched polyester as a precursor. Morphology of these HB-PU films was investigated using atomic force microscopy and wide-angle X-ray diffraction; it's molecular dynamics was studied by dynamic mechanical analysis. FTIR studies showed that hard segments get more aggregated to form domains in the HB-PU block copolymer as hard segment content increases. Such domain formation has a significant influence on the mechanical and thermomechanical properties of HB-PU, such as maximum stress and elongation at break. Especially, maximum stress and elongation at break increased significantly at 25 wt % of hard segment content, and the highest loss tangent was observed at the same composition. Heat of crystallization as measured by differential scanning calorimetry is also dependent on the hard segment content, and the control of hard segment content in PU block copolymers is very important in determining their physical properties. (c) 2006 Wiley Periodicals, Inc.