Two-Way Reversible Shape Memory in a Semicrystalline Network

作者：Taekwoong Chung, Angel Romo‐Uribe, Patrick T. Mather · 发表于：Macromolecules · 年份：2007 · 被引用次数：533 · 研究领域：Polymer composites and self-healing、Advanced Sensor and Energy Harvesting Materials、Advanced Materials and Mechanics

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 ( T c ) and contraction on heating ( T m ) 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...