Shape Memory Properties of Polystyrene-block-poly(ethylene-co-butylene)-block-polystyrene (SEBS) ABA Triblock Copolymer Thermoplastic Elastomers

This work demonstrates that neat polystyrene-block-poly(ethylene-co-butylene)-block-poly styrene (SEBS) displays thermally responsive shape memory properties. The shape memory properties were quantitatively investigated under uniaxial tension using a dynamic mechanical analyzer and manual stretching. The shape memory properties of SEBS were found to depend on both the molecular weight of the polymer and on the shape programming conditions, including the programming temperature, applied strain, and annealing time at elevated temperature under load. The shape memory mechanism is proposed to be a result of partial stress relaxation of the block copolymer network under load and the formation of a second network with a lower glass transition temperature. This second network counterbalances the initially stretched network producing fixity and weakens first on heating, allowing recovery. Due to the unique mechanism of shape memory where the secondary network is generated from the initial network, achieving higher fixity generally occurs at the expense of high recovery and vice versa.