Dr. Yoan Simon
School of Polymer Science and Engineering
University of Southern Mississippi
Friday, April 22, 2022 - 11:00am
Prof. Chris Bates
The past decade has seen a regain of interest for polymeric networks on account of their unique properties (e.g. resistance to solvents, durability) which makes them suitable for a variety of applications ranging from coatings to insulating foams to structural materials in transport applications. Fueled by concerns of sustainability, covalent adaptable networks, whereby reversible covalent bonds, aka dynamic covalent chemistry, enable the rearrangement of bonds and ultimately reprocessability of the materials have blossomed. Motivated by these attributes, we set out on a journey to unravel the governing principles of associative dynamic exchanges by modulating the chemistry of uncatalyzed exchanges in diketoenamines and diketoxime structures by utilizing orthogonal thiol-ene photopolymerization. Specifically, we will broach the topics of chemical exchange and chain dynamics and their overall impact on the rheological properties of the materials. We will also discuss counterintuitive behavior that we discovered in the photopolymerization of thiol-ene networks in the presence and absence of solvent, wherein solvent-cured systems repeatedly exhibited both a higher glass transition temperature (Tg) and a lower elastic modulus above said Tg. This unexpected behavior appeared to be amplified for higher-functionality and more rigid monomers and drastically impacted the thermal expansion of the materials, suggesting a complete different topological connectivity of the networks despite apparent full monomer conversion. We believe that these findings can have huge impacts on the transport properties, the reprocessability and the performance of such systems and could be used as an additional handle to tune materials properties.