Expanding Polymer Design Tools: Molecular Fluxionality and Topological Crosslinks for Novel Polymer Networks

Abstract

Polymer materials have profoundly transformed our lives over the past century. While we derive significant benefits from their convenience, the escalating plastic waste crisis necessitates a deeper comprehension of the molecular structure-property correlation inherent in plastic materials. Consequently, it is imperative to devise novel motifs and building blocks for sustainable polymers that will shape the materials of the future. In this dissertation, I expanded polymer design toolkit by introducing two novel motifs. Starting with the first incorporation of molecular ball joint, bullvalene, into polymer networks. Since its initial conception, bullvalene has captivated scientists due to its remarkable fluxionality. It undergoes rapid low barrier sigmatropic rearrangements, resulting in a molecule devoid of a permanent structure at room temperature. Recent breakthroughs in synthesis have reignited the interest in its application in the solution state. I explored bullvalene’s fluxionality in bulk polymer materials using dynamic mechanical analysis. Through this research, we demonstrated bullvalene as a unique low-force covalent mechanophore. Its introduction enhanced the polymer’s energy dissipating mechanism and facilitated the formation of stronger glass structures during the glass transition process. Furthermore, I investigated the interplay between polymer topology and network hierarchy to devise a class of material that has not yet been officially defined by IUPAC. This network was constructed using cyclic polymers as topological crosslinks to toughen existing polymer materials. By employing ring expansion metathesis polymerization process, I successfully synthesized cyclic polymers at scale. These cyclic polymers were subsequently dissolved along with linear polymer precursors and cured into unique semi-interpenetrating polymer networks. The bulk properties of these networks were assessed through mechanical testing and molecular dynamic simulations. The results demonstrated that the networks consisted of cyclic polymers exhibiting enhanced toughness and stiffness compared to control networks composed of linear polymers. This dissertation presents two distinct pathways for designing novel polymer materials that hold great promise for the development of next-generation energy dissipating and robust polymer materials.