Multidirectional Triple-Shape-Memory Polymer by Tunable Cross-linking and Crystallization

Abstract

Medical fixing is one of the very important applications of the shape-memory polymer material, and the two important properties of the medical fixing material are that it perfectly fits the body during the fixing and easily detaches after being used. As the fixing and detachment are triggered by two independent stimuli in two opposite directions, it is necessary to develop multidirectional triple-shape-memory polymers. In this research, a series of polymer materials composed of trans-polyisoprene (TPI) and paraffin were prepared by melt blending and compression molding, and then the TPI was cross-linked by vulcanization. As a result of the large difference in the melting temperature and crystallization temperature between TPI and paraffin, the obtained polymer materials exhibit a triple-shape-memory behavior. According to the analysis of crystal behavior, microscopic morphology, and mechanical properties of the materials with different paraffin contents and TPI cross-linking density by differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and dynamic mechanical thermal analysis, the shape-memory behavior of the obtained materials was tunable by the cross-linking density of TPI and the crystallization degree of TPI or paraffin. Compared with the traditional triple-shape-memory material, our samples are prepared in a more facile way and can recover at human body temperature (37 °C). Moreover, our TPI/paraffin material can realize more flexible multidirectional recovery, as well as can be reprogramed and used multiple times. To the best of our knowledge, there are few polymer materials reported, which can realize multidirectional recovery. These unique multidirectional and reprogramable properties will enable the application of this polymer material, especially in the medical fixing materials.

High Energy Density Shape Memory Polymers Using Strain-Induced Supramolecular Nanostructures

“…SMPs reversibly alternate between a temporary deformed state and an initial undeformed state through application of a stimulus, such as heat or light. Stabilization (or fixing) of the temporary state requires a controllable molecular level change (e.g., glass or melting transition, − dynamic networks, − strain-induced crystallization, − or liquid crystal phase transition − ) that can be selectively activated and deactivated. Upon deactivation, SMPs return to their original undeformed state, driven by the relaxation of deformed chains between network junctions (e.g., topological entanglements, chemical cross-links, or secondary interpenetrating networks) that preserve the material’s memory of its initial state via stored entropic energy …”

Triple-Shape Memory Behavior of Modified Lactide/Glycolide Copolymers

“…The formed nanophases act as transition phases with variable transition temperatures, which can be adjusting by the St/MA ratio and are the cause of the observed phenomenon of multiple-shape memory. Similar material was obtained by a series of triple-shape memory polymer materials composed of paraffin and lightly cross-linked by vulcanization trans-polyisoprene (TPI) [13] As shown in the published literature, although the presence a chain cross-link is not necessary to obtain the shape memory effect, the simultaneous occurrence of both physical and chemical cross-links phenomena allows obtaining polymeric materials with especially high strain and multiple-shape memory [14].…”

Covalent crosslinks turn natural Eucommia ulmoides gum/polybutene‐1 composites into multiple shape memory materials

“…Meanwhile, more free radicals generated from the thermal decomposition of DCP would initiate more chain propagation, leading to a higher cross‐linking density of the EUG/PB‐1 composites with increasing DCP content. [ 36 ]…”