Magnetoactive Thermoplastic Elastomers with Bottlebrush Strands: Switching and Programming of Mechanical Properties by a Magnetic Field

We report on a distinct class of magnetoactive thermoplastic elastomers (MATEs) based on A- g -B bottlebrush graft copolymers filled with magnetic carbonyl iron microparticles. The A- g -B copolymers form a solvent-free elastomeric matrix providing tissue-mimetic softness and strain-stiffening, along with the capability of molding above a specific flow temperature. In contrast to covalently cross-linked magnetoactive elastomers, the mechanical properties and magnetic response of MATEs can be altered through particle rearrangement in a magnetic field at enhanced temperatures. This thermo-magnetic processing transforms the MATE from an isotropic to anisotropic composite with near three-fold increase in elastic modulus, up to 25% decrease in the damping factor, and up to 7.5-fold enhancement of the magnetorheological effect. The ability to reprogram the shape and viscoelasticity of MATEs has vital implications for the future of biomedical devices and soft robotics.