ABSTRACT
Ionic elastomers are characterized by a strong physically cross-linked network resulting from a phase separation of ionic-rich nano-domains. (Holden, 2004) Ionic domains are formed by the association of ionic groups that act as cross-links, promoting the elastic behaviour of these polymers. In addition, trapped glassy rubber around ionic associations can form its own thermal transition, the ionic transition (Ibarra, 2007). Therefore, this highly restricted polymer improves physical properties of these materials below ionic transition, acting as reinforcing points of the soft rubbery matrix. These materials are considered as thermoplastic elastomers because of the thermo-labile nature of ionic associations; however, this property limits their potential applications at elevated temperatures. In order to overcome with this disadvantage, some permanent covalent crosslinks have been formed in the ionic structure, improving their properties at high temperature (Mora-Barrantes, 2012). On the other hand, the versatility of the network microstructure allows the design of shape memory materials with tuneable properties. In this case, novel smart rubbers based on a commercial Carboxylated Nitrile Rubber (XNBR) have been used with enhanced shape-memory properties. Its structure allows its cross-link via metallic oxides, resulting on a controlled ionic network responsible of the transitory shape achieved during the shape memory cycle further described. In this case, ionic transition from ionic nano-domains (characterized by the ionic temperature Ti) is the thermal process acting as the shape memory switch.
