High Temperature Shape Memory Polymers

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TECHNICAL SUMMARY: The objectives of the NSF-funded research are to develop and understand the structure and properties of high temperature shape memory polymers (HTSMPs) based on mixtures of an ionomer and a low molecular weight crystalline compound (LMWC). This includes developing a fundamental understanding of the molecular origin of shape memory in these two-component systems. The permanent crosslink in these materials is based on microphase separation of ionic nanodomains in the ionomer or covalent crosslinks, and the advantages/disadvantages of each design will be assessed. The temporary network derives from strong intermolecular interactions between the ionomer and the LMWC dispersed phase, and the switching temperature, Tc, is controlled by the melting point of the LMWC. The experimental work includes preparing HTSMPs by melt compounding and the characterization of their morphology, physical properties and mechanical properties. Shape memory characteristics will be assessed by shape memory cycles measured by dynamic mechanical analysis and the sustainability of the shape reversibility will be evaluated from cyclic testing experiments using larger prototype samples. The initial focus of the research will be mixtures of partially sulfonated poly(ether ether ketone) and sodium oleate with a targeted Tc ~ 200°C, but other systems based on high temperature ionomer matrices derived from polysulfones and polyimides and other LMWCs such as fatty acids, eutectic mixtures, fusible metals, ionic liquids, high melting point organic compounds, tin alloys and phosphate glasses will be considered to assess the efficacy of the ionomer/LMWC shape memory polymer design. NON-TECHNICAL SUMMARY: Shape memory polymers (SMP) are materials that have the capability of changing shape when exposed to an external stimulus (e.g., temperature, light or electrical or magnetic fields). Applications of these smart materials include orthodontic wires, polymer stents, biodegradable implants, artificial muscles, actuators, sensors, switches and smart textiles. Most SMPs are soft, thermally-activated materials with shape-switching temperatures lower than 100°C. Higher temperature applications, such as expandable structures with high strength and stiffness (e.g., deployable solar arrays, antennas and reflectors) and shape morphing surfaces and structures (e.g., airplane wings) require higher operating and switching temperatures. This NSF award supports research on the development of high temperature shape memory polymers made from mixtures of a thermoplastic polymer containing bonded ionic groups and a low molecular weight additive that interacts strongly with the ionic polymer. In addition to the development of new materials for high-performance applications, such as aerospace components, this project will include training scientists to work in the emerging field of smart materials. The research will involve graduate, undergraduate and high school students and high school science teachers. Special efforts will be made to recruit students form under-represented STEM groups to participate in the research. Collaborations will be sought with private industry and national laboratories to develop new fundamental knowledge of the subject materials and advance the development of new commercial applications. The scientific results from the research will be broadly disseminated through rapid publications in major scientific journals and presentations by the PI and students at national scientific meetings.