Temperable Dynamic Covalent Networks

PART 1: NON-TECHNICAL SUMMARY Plastics are integral to our daily lives, but most are designed for a single purpose and discarded afterward. Nature offers a different approach through the concept of pluripotency. The term pluripotent is defined as “not fixed as to developmental potentialities”. Stem cells, for instance, are pluripotent because they can differentiate into various cell types based on chemical or mechanical cues. If a diverse range of materials can be accessed from a single “stem” plastic, it could revolutionize plastic sustainability. Imagine a world where all plastics are derived from a single source material. Recycling would become simpler and more cost-effective. In this research, we design and explore materials that can be tempered, (i.e., heating of a material at a given temperature below a critical point (e.g., melting point) before rapidly quenching) to allow access to a wide range of room-temperature materials properties dictated by the tempering temperature. The proposed research is a true mix of various disciplines within the polymer field, encompassing synthesis, polymer processing, and mechanical characterization. This integrated research approach aims to provide students, regardless of their level, with a comprehensive education covering these topics. Integrated high-school and undergraduate research and outreach activities are designed to broaden the participation of all students in science and engineering. Graduate students will participate in an innovative two-year training program to enhance their engagement and effective communication skills with the general public. Through this training, they will actively participate in various outreach events, such as Junior Science Cafés, the No Small Matter Molecular Engineering Fair, and programs tailored to reach students from local Chicago public schools. Notably, this approach fosters an engaging learning environment for participants while offering unique teaching opportunities for graduate researchers. PART 2: TECHNICAL SUMMARY Recent work by the PI'sgroup revealed that polymer networks formed through room-temperature dynamic thia-Michael (tM) bonds (based on benzalcyanoacetate Michael acceptors) result in mechanically robust polymer films that can be tempered. These films exhibit two thermal transitions: a glass transition temperature and a second transition temperature associated a hard phase formation of through a dynamic reaction-induced phase separation (DRIPS) process. By tempering these films between these two transitions, a wide range of room temperature material properties can be obtained, ranging from brittle and glassy to soft and extensible, simply by changing the tempering temperature. Studies indicate that the tempering temperature controls the amount of tM adduct formed, thereby determining the extent of crosslinking in the network. Building on these findings, the objective of this proposal is to establish fundamental structure/processing/morphology/property relationships in this class of pluripotent materials. The goal is to expand the range of material properties accessible, including toughness, elasticity, and more. To achieve this, the chemistry and architecture of the networks, as well as the type of dynamic tM bonds, will be varied to gain a better understanding of the parameters that influence the properties of these materials. Additionally, photo-responsive dynamic bonds will be developed by capitalizing on the inherent trans-cis isomerism of the benzalcyanoacetate-based Michael acceptor structure. This approach will enable access to a new class of dynamic materials that can be tempered using light instead of heat. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.