Structure and thermomechanical properties of polyurethane block copolymerswith shape memory effect

Shape memory polyurethane (PU) block copolymers composed of 4,4 ' -methylen ebis-(phenylisocyanate), poly(tetramethylene glycol), and 1,4-butanediol as a chain extender were synthesized by a two-step process. FT-IR spectra sho wed that carbonyl peak appearing at 1700 cm(-1) increased with higher hard segment content, whereas another carbonyl peak at 1730 cm(-1) decreased. It suggests that hard segments get more aggregated to form domains in the PU block copolymer as hard segment content increases. Such domain formation ha s a significant influence on the mechanical and thermomechanical properties of PU, such as maximum stress, tensile modulus, and elongation at break. E specially, maximum stress, tensile modulus, and elongation at break increas ed significantly at 30 wt % of hard segment content, and the highest loss t angent was observed at the same composition. Heat of crystallization as mea sured by differential scanning calorimetry is also dependent on the hard se gment content. Finally, 80-95% of shape recovery was obtained at 30-45 wt % of hard segment content, and the control of hard segment content in PU blo ck copolymers is very important in determining their physical properties.