Recovery as a measure of oriented crystalline structure in poly(ether ester)s based on poly(ethylene oxide) and poly(ethylene terephthalate) used as shape memory polymers

Poly(ether ester)s consisting of poly(ethylene oxide) and poly(ethylene ter ephthalate) segments, EOET copolymers, could be used as shape memory polyme rs (SMP). Crystalline structural characters of the copolymers during the me mory process were investigated by dynamic mechanical analysis, differential scanning calorimeter, wide-angle X-ray diffraction, polarizing microscopy, and recovery measurements. PEO crystals in stretched EOET copolymer prefer entially oriented along fiber ards or stretch direction. During stretching, the structure of the copolymer undertake a transformation from spherulite to fiber, resulting in a crystalline morphology similar to shish-kebab, and recovery properties of stretched EOET samples were dependent on as-describ ed crystalline structural characters that can be influenced by draw ratio. Driving forces for contraction come from the oriented chains, and only orie nted or extended chains can be contributive to the recovery of deformation; these extended chains involve both crystalline and amorphous segments. The recovery process in shape memory behavior was noticed to be deorientation of oriented chains due to thermodynamic entropy effect, and was divided int o three stages. (C) 1999 John Wiley & Sons, Inc.