Shape memory polymers (SMPs) have generated a great amount of interest due to their capacity to recover a programmable shape under an applied stimulus, such as temperature change or light irradation [1, 2]. The SMP is initially synthesized with a specific original shape. This shape can be deformed under a mechanical load and at a temperature (TH) greater than the glass transition temperature, Tg. The application of this deformation coupled with subsequent lowering of the temperature (TC) to below the Tg, can fix the polymer in the newly altered formation even after removal of the external load. Increasing the temperature again, to a point above Tg, then activates the shape memory effect, whereby the original shape can be recovered. This shape memory ability is a direct result of specific molecular architecture. Chemical and physical crosslinks and macromolecular chain entanglements are part of this structure. Chemical crosslinks between segments give form to the original shape. Some of these segments are stimuli-sensitive, in other words, segments can become increasingly elastic with the application of thermal energy. This application of energy causes the crystalline structure of these segments to melt and be easily deformed under external load. This temporary shape can now be maintained with the removal of thermal energy leading to re-crystallization. Recoil in this state is prevented by both the new crystalline structure and entanglements of the segments caused by deformation. Physical crosslinks give the architecture permanence, since the linkages do not degrade with stimulus . Different crosslinker formulations can result in varying types of chemical crosslinks. Variations in the structure lead to alterations in the material properties, such as mechanical characteristics and hydrophobicity.
- Bioengineering Division
Thermomechanical and Hydrophobic Characterization of Shape Memory Polymers
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Warren, PD, Bernal, RR, Harper, JL, Herlihy, RN, & Vande Geest, JP. "Thermomechanical and Hydrophobic Characterization of Shape Memory Polymers." Proceedings of the ASME 2009 Summer Bioengineering Conference. ASME 2009 Summer Bioengineering Conference, Parts A and B. Lake Tahoe, California, USA. June 17–21, 2009. pp. 69-70. ASME. https://doi.org/10.1115/SBC2009-206678
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