Dynamic, reprocessable polymer networks.
The accelerating global accumulation of plastic waste is a pressing environmental issue. Major contributors to this problem are a class of compounds called thermosets, which consist of crosslinked polymer networks with a fixed structure. As their name implies, once thermosets are formed they typically cannot be reprocessed or recycled and their potential for reuse is limited. One way to address this is to incorporate dynamic bonds into the network structure. Under specific conditions, these bonds continuously break and re-form, enabling the network to flow and thus be remolded or recycled. We have discovered a new chemical reaction, which we call “thermal guanidine metathesis”, which can serve as the basis for dynamic polymer networks. Current projects in this area include exploring the effects of polymer structure on the properties of corresponding networks, synthesizing new types of guanidines to examine their influence on polymer dynamics, and in-depth examinations of the rheological behavior of these materials.
Degradable supramolecular guanidinium-carboxylate networks.
Guanidines are a common organic functional group that consists of three variously substituted nitrogens arrayed around a central carbon. By synthesizing molecules with two guanidine functional groups and combining these with molecules containing three carboxylic acid functional groups, we create networks based on electrostatic and hydrogen bonding – that is, noncovalent interactions. Prior experience in our lab has made us experts at making a variety of guanidines, so we can see how the properties of these networks change with guanidine structure. Because these materials are not held together by covalent bonds, we hope that they will be more easily degraded and recycled.
Ring-opening polymerization of iminooxazolidines.
Polyureas are a broadly useful class of materials that are traditionally made by step-growth polymerization, which inherently lacks easy control of polymer molar mass, endgroups, and dispersity. We are investigating a new, modular synthetic pathway to iminooxazolidine monomers and the corresponding polyureas made by chain-growth cationic ring-opening polymerization. The monomers derive from widely available amines or isothiocyanates and aldehydes, and the versatility of the synthetic approach is such that a variety of functionalities can be incorporated into the resulting polyurea.
