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

Abstract

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 °C, giving the recovery ratio Rr as high as 80%. After a cold deformation, the copolymer could return to the original shape at about 60 °C, with a recovery ratio Rr 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) α form to iPP trigonal form under stretching, which rendered the materials with fixing ratio Rf of 70–80% and relatively stable recovery ratio Rr of 65–80% at 60 °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.