Thermo-responsive shape memory effect in isotactic propylene/1-butene copolymers

This paper reported a thermo-responsive shape memory effect in common isotactic propylene/1-butene copolymer (iPPBu) synthesized by Ziegler-Natta catalyst. The deformation principle in the copolymer was cold deformation, and the recovery temperature was around 60 degrees C, giving the recovery ratio R-r as high as 80%. After a cold deformation, the copolymer could return to the original shape at about 60 degrees C, with a recovery ratio R-r of up to 80%. The crystal structures of the copolymer during deformation and recovery were investigated by WAXS measurements, and the shape memory effect mechanism in such materials was proposed. The mechanism varied according to the copolymer composition, but the crystal transformation always played a key role in the shape memory behavior. iPPBus with about 30-60 mol% of 1-butene exhibited unique crystal transition from isotactic polypropylene (iPP) alpha form to iPP trigonal form under stretching, which rendered the materials with fixing ratio R-f of 70-80% and relatively stable recovery ratio R-r of 65-80% at 60 degrees C owing to the constant melting point of trigonal crystal. This work provided a potential application of these common propylene copolymers in shape memory materials.