Chung, Taekwoong Romo-Uribe, Angel Mather, Patrick T. Two-Way Reversible Shape Memory in a Semicrystalline Network Cooling-induced crystallization of cross-linked poly(cyclooctene) films under a tensile load results in significant elongation and subsequent heating to melt the network reverses this elongation (contracting), yielding a net two-way shape memory (2W-SM) effect. The influence of cross-linking density on the thermal transitions, mechanical properties, and the related 2W-SM effect was studied by varying the concentration of cross-linking agent dicumyl peroxide (DCP) and using differential scanning calorimetry (DSC), gel fraction measurements, dynamic mechanical analysis (DMA), and customized 2W-SM analysis. The latter showed that there is crystallization-induced elongation on cooling and melting-induced shrinkage on heating (2W-SM), with lower cross-link density leading to higher elongation at the same applied stress. For a given cross-link density, however, increasing the tensile stress applied during cooling resulted in greater stress-induced crystallization. We further observed that the onset temperatures for elongation on cooling (<i>T</i><sub>c</sub>) and contraction on heating (<i>T</i><sub>m</sub>) shifted to higher temperatures with decreasing cross-link density. Similarly, the degree of molecular orientation achieved upon deformation was found to increase with decreasing cross-link density. The impact of stress on the 2W-SM effect was examined using wide-angle X-ray diffraction (WAXD), revealing a transition from bimodal to unimodal orientation. As the crystalline structure evolves from bimodal (low stress) to unimodal (high stress), the crystallization occurs along a single preferred orientation thus inducing greater elongation along the stretching direction. We anticipate that the observed 2W-SM property in a semicrystalline network will enable applications heretofore possible only with costly shape memory alloys and liquid crystalline elastomers. density;DCP;load results;semicrystalline network;WAXD;DSC;heating;DMA;scanning calorimetry;crystallization;onset temperatures;cooling;unimodal orientation;stress;shape memory alloys;elongation 2008-01-08
    https://acs.figshare.com/articles/journal_contribution/Two_Way_Reversible_Shape_Memory_in_a_Semicrystalline_Network/2964199
10.1021/ma071517z.s002