(718c) Dynamic Networks As Multi-Stimuli Responsive Actuating Adhesives

An enduring challenge in polymer science is to create materials endowed with the inherent ability to react to a multitude of stimuli, with each eliciting a unique macroscopic physical response. However, the design of these smart materials requires judicious selection of which combination of chemical functionalities to embed within the material. We have created a family of liquid crystalline elastomer networks (LCNs) that can respond reversibly to a number of different stimuli (UV and visible light, metal ions, and heat). These materials are synthesized using a facile two-step process where thiol telechelic preopolymers are first prepared in a step-growth polymerization and subsequently oxidized in the presence of a tetrathiol crosslinker. The presence of disulfide bonds (dynamic at T > 150 °C or upon exposure to UV light) at the junctions of the network makes these materials adhesives that are both self-healing and reprocessable. Additionally, the incorporation of one or more liquid crystal mesogens in the backbone of the preopolymer causes network to adopt an ordered liquid crystalline phase, with a melting temperature and liquid crystal to isotropic transition temperature dependent on the structure of the preopolymer used. I will demonstrate how changes to the mesogen or combination of mesogens in the preopolymer can be used to tune the thermal, mechanical, and rheological properties of the LCN, and will discuss how this knowledge can be used to design advanced materials tailor-made for specific applications. As a specific example, I will describe a shape-memory elastomer that can be used as a reversible actuating adhesive with heat as the only external trigger.