Periodic Dynamic Polymers: Engineering Self-assembled Microstructures to Design Artificial Muscles and Underwater Adhesives

Polymer networks formed through dynamic noncovalent or covalent bonds exhibit robust and tunable mechanical properties (e.g., tough, elastic, self-healable, stimuli-responsive, and reconfigurable). In nature, these networks are often hierarchically-ordered to perform precise functions and assemble via cooperative interactions of many weak bonds as opposed to the independent association of a few strong bonds. Here, we use these principles to design linear polymers with periodically-placed dynamic bonds that collectively assemble into supramolecular nanofibers at equilibrium and under strain. We show that when the overall molecular weight (M_n) is below the polymer’s critical entanglement molecular weight (M_c), self-assembly of supramolecular nanofibers occurs, increasing the bulk film modulus by over an order of magnitude and delaying the onset of terminal flow by more than 100°C. We then design a periodic dynamic polymer with record-high shape memory recovery stress (12.8 MPa) and energy density (18.9 MPa) based on the formation of strain-induced supramolecular nanostructures. While initially, polymer chains adopt an amorphous structure (M_n &gt; M_c), during strain the polymers form nanostructures that trap the elongated backbones, enabling use as an artificial muscle. Finally, we design periodic dynamic polymers with a controlled nanophase morphology to enable high-strength underwater adhesives that can be reversibly adhered to a variety of substrates and fully recycled after use. These examples show how periodic dynamic polymers are a promising class of materials whose material properties arise from well-defined backbone periodicity.<br/><br/>Publication Reference:<br/>Using Periodic Dynamic Polymers to Form Supramolecular Nanostructures<br/>DOI: 10.1021/accountsmr.2c00101<br/> <br/>High Energy Density Shape Memory Polymers Using Strain-Induced Supramolecular Nanostructures<br/>DOI: 10.1021/acscentsci.1c00829<br/> <br/>Multivalent Assembly of Flexible Polymer Chains into Supramolecular Nanofibers<br/>DOI: 10.1021/jacs.0c07651