A New Strategy to Prepare Polymer‐based Shape Memory Elastomers

Abstract

A new strategy that utilizes the microphase separation of block copolymer and phase transition of small molecules for preparing polymer-based shape memory elastomer has been proposed. According to this strategy, a novel kind of shape memory elastomer comprising styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) and paraffin has been prepared. Because paraffins are midblock-selective molecules for SEBS, they will preferentially enter and swell EB blocks supporting paraffins as an excellent switch phase for shape memory effect. Microstructures of SEBS/paraffin composites have been characterized by transmission electron microscopy, polarized light microscopy, and differential scanning calorimetry. The composites demonstrate various phase morphologies with regard to different paraffin loading. It has been found that under low paraffin loading, all the paraffins precisely embed in and swell EB-rich domains. While under higher loading, part of the paraffins become free and a larger-scaled phase separation has been observed. However, within wide paraffin loadings, all composites show good shape fixing, shape recovery performances, and improved tensile properties. Compared to the reported methods for shape memory elastomers preparation, this method not only simplifies the fabrication procedure from raw materials to processing but also offers a controllable approach for the optimization of shape memory properties as well as balancing the rigidity and softness of the material.

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“…Low temperature peaks around À 40°C correspond to the relaxation of EB segments. The higher peak at B60°C is attributed to the solid-liquid phase transition of paraffin 13 , since our paraffin melts at 53B57°C. As we previously mentioned, the maximum in tan d at the 8:2 weight ratio of wax:SEBS confirms the dominance of the wax-SEBS guest in determining the viscoelastic properties of the hybrid yarn.…”

“…The data show little dependence on paraffin wt% at both lower and higher paraffin concentrations. Interestingly, this transition in maximum torsional rotation occurs for paraffin levels (above 50 wt%) where transmission electron microscopy indicates a transition from wax completely confined within rubbery EB regions of the copolymer to a structure in which excess wax is no longer localized within this polymer block 13 . Based on this relationship between transition in maximum torsional actuation and structure change, it appears that nanocrystalline wax within the EB regions contributes little to the changes in guest volume that drives torsional actuation.…”

“…We synergistically combine the large thermally induced volume changes provided by paraffin wax with mechanical dampening that arises from the mixtures of this wax with a triblock copolymer. We build upon previous work that showed large peaks in mechanical dampening occur near the wax melting temperature for specific CNT-free mixtures of paraffin wax with polystyrene-poly(ethylene-butylene)-polystyrene (SEBS) triblock copolymer that have been used as shape memory elastomers 13 . SEBS is a classical phase-separating block copolymer, with a polystyrene (PS)-rich phase dispersed within the elastomeric ethylene-butylene (EB) continuous phase.…”

“…paraffin is confined to the EB regions 13 . For paraffin levels above 50 wt%, the excess wax is no longer completely confined within the EB regions.…”

Shape Memory Polymers from Blends of Elastomers and Small Molecule Additives

“…[28,29] The SEBS (Kraton G1654) used is a commercially available thermoplastic elastomer. Here, samples were prepared by solution blending and precipitation, without any additional crosslinking chemistry.…”