Covalent Structurally Dynamic Polymers

Dynamic covalent bonds can be activated upon thermal, chemical, or light stimuli. The thermodynamics and kinetics of bond exchange reactions govern the material properties of polymeric materials containing dynamic covalent bonds. We aim to design novel smart materials for a variety of applications by investigating the effect of electronic structures on kinetics and material properties. 

The integration of dynamic covalent chemistries into networks has been previously shown to impart adhesive properties to systems that are traditionally incapable of adhesion. The addition of dynamic bonds enables a high degree of contact between the adhesive network and the surface of interest through the breaking and reforming of bonds under suitable bonding conditions (temperature, pressure, light exposure, etc). When combined with stiff fillers (such as cellulose nanocrystals) dynamic bonds offer an attractive avenue to strong, rebondable structural adhesives. The combination of thiol-modified cellulose nanocrystals and thiol-containing polymers resulted in dynamic disulfide composites with bonding strengths greater than conventional adhesives such as gorilla glue (see figure of 25 pound dumbbell supported by a 6x6 mm film of adhesive composite). Current research in the group seeks to expand the toolbox of dynamic bonds suitable for high-strength adhesives and creating multi-stage adhesives capable of markedly different adhesive properties depending on bonding conditions.

Another avenue of research pursued in the field of covalent structurally dynamic polymers by the Rowan group is their development as artificial muscles in soft robotics applications.  Just as 3D printing, a technology originally based in chemistry and materials science, has been adapted to the field of robotics for the fabrication of passive structural elements, more recently, shape memory materials have started to be developed as active components to afford movement in soft robots.  These materials serve as lighter and more easily miniaturized alternatives to the electric motors that roboticists traditionally use which are limited in their rigidity and achievable scale-down size. 

As a part of an international collaboration with groups at Case Western Reserve University and the University of Fribourg in Switzerland, the Rowan group is currently working to design and synthesize crosslinked shape memory materials that incorporate dynamic bonds to function as artificial muscles in soft wormlike robots.  Specifically, the development of these materials aims to enable the fabrication of soft robotic actuators in a variety of shapes and sizes without sacrificing the actuation properties of the base material.