Rubber-like composites with tunable thermal- and photo-responsive shape memory properties

Shape memory polymers (SMPs) are crosslinked networks with molecular switches to control network mobility and thus macroscopic deformation. The network crosslinking and the molecular switches make most SMPs behave like hard plastics, with very few exceptions whose extensibilities are comparable to rubbers and elastomers. Here we report a class of composites that comprise polystyrene-b-ethylene-co-butylene-b-styrene (SEBS) as elastic matrices and azobenzene derivatives (ADs) as molecular switches. The incorporation of the ADs does not impair the extensibility of the SEBS substrates, and the tensile strains of the prepared composites can exceed 900% even when the content of the ADs reaches 30 wt%. The thermal- and photo-responsive solid-liquid transitions of the ADs are responsible for the shape memory effects of the composites. The photo-responsive shape recovery process can be completed within 2 s, and 2D-to-3D shape transformations are realized on the samples fixed with tensile strains by spatiotemporal control of UV irradiation. On another aspect, the chemical structures of the ADs can be tailored to regulate their melting points and thus the thermal responsive shape memory properties of the composites. Furthermore, different pieces of composites can be combined by hotpressing to exhibit spatially tailorable thermal responsive shape recovery behaviors. The facile preparation and interesting shape memory properties of the rubber-like composites can inspire the design of soft SMPs with more promising applications.

Automated summary

This research reports a new type of composite material with rubber-like shape memory properties. The composite material consists of a polymer matrix and molecular switches, which do not affect the stretchability of the matrix. The composite material exhibits thermal and photoresponsive shape recovery properties, and shape transformations can be achieved by controlling UV irradiation. Furthermore, the thermal responsive properties of the composite material can be adjusted by tailoring the chemical structure of the molecular switches, allowing for spatially tailorable shape recovery behaviors between different fragments.