A new strategy to prepare polymer composites with versatile shape memory properties

A new strategy to prepare multi-shape memory polymers, which utilizes the confined co-crystallization characteristics of small molecules to construct tunable switch, has been proposed. On the basis of this strategy, a novel shape memory polymer comprising paraffin molecules with different chain lengths and styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) was prepared. As paraffin molecules tend to form continuous series of solid solution over a wide range of chain lengths, deemed as co-crystallization, a broad thermal transition may be obtained through mixing paraffin molecules with distinct melting points, and for our shape memory composites, a broad transition is essential for tunable abilities. Thermal properties of the SEBS-paraffin composites have been characterized by differential scanning calorimetry, suggesting excellent confined co-crystallization characteristics, and such characteristics have been further verified by wide angle X-ray diffraction and successive self-nucleation and annealing thermal fractionation analysis. The results of a series of shape memory testing demonstrate that the composites possess versatile shape memory properties, such as temperature memory and multi-shape memory effect. Compared with the reported methods to prepare multi-shape memory polymers, this method not only simplifies the fabrication procedure from raw materials to processing, paving the way for large-scale fabrication, but also offers a controllable approach for adjusting the mechanical properties as well as tailoring the transition temperature.