DYNAMIC-MECHANICAL BEHAVIOR IN THE ETHYLENE TEREPHTHALATE ETHYLENE-OXIDE COPOLYMER WITH LONG SOFT SEGMENT AS A SHAPE-MEMORY MATERIAL

Several ethylene terephthalate-ethylene oxide segmented copolymers wit h long soft segments, in which poly(ethylene oxide) (PEG) chains serve as soft segments while poly(ethylene terephthalate) (PET) chains serv e as hard segments, were investigated by dynamic mechanical analysis ( DMA). The PET-PEG copolymers show three distinguishable relaxation pro cesses, alpha-, beta- and gamma-relaxation, within the examined concen tration range of PET in the copolymers, and alpha-relaxation was assoc iated with the glass transition of PEO segments in amorphous phase. Bo th longer PEO segments and higher PET content would tend to decrease t he alpha-relaxation temperature (T-alpha). The intensity of tan delta for alpha-relaxation reduced with the increase of soft segment length, and increased with PET content in the PET-PEG segmented copolymer. DM A measurements were carried out on the samples containing 2000, 4000, 6000 and 10,000 FED segments, respectively. Relations between the inte nsity of tan delta for alpha-relaxation and the maximum shape recovery (R-f) were also: discussed. Experiments revealed that small energy di ssipation and high physical crosslinking effects supplied by the PET c omponent in the copolymer would be favorable for the material to show a good shape recovery. (C) 1997 Elsevier Science Ltd.