ORCID
https://orcid.org/0000-0002-5235-2644
Date of Award
12-18-2024
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Catenanes are a subset of mechanically interlocked molecules (MIMs) and are composed of interlocked rings that can be oriented linearly, radially, or branched. A defining feature of all MIMs is that they are bound through their architectures consisting of mechanical bonds, leading to unique topologies. Catenanes have attracted interest due to their stimuli-responsive behavior and the degrees of freedom afforded by the mechanical bond, a feature which is absent with standard covalent bonds. The stimuli responsiveness of catenanes arises from their templated syntheses, where two or more pre-macrocycles are brought together by a driving force. Various templation strategies rely on different forms of molecular recognition, such as donor-acceptor interactions, hydrogen bonding, and anionic templation, however, metal templation has been shown to be the most efficient. Recently, research has shifted towards higher-order linear catenanes, as these structures maximize the system's degrees of freedom, making them promising candidates for creating more flexible materials when integrated into polymer networks. While bottom-up approaches have been employed to successfully synthesize shorter discrete oligo[n]catenanes (where n refers to the total interlocked rings), these structures typically lack the ability to be extended further. In contrast, top-down approaches have produced higher molecular weight 17 molecules with fewer synthetic steps, but often suffer from impure linear products that are difficult to isolate from branched and cyclic byproducts. This dissertation aims to bridge the gap between top-down and bottom-up catenane syntheses while also exploring the integration of bottom-up discrete catenanes in materials. Chapter 2 explores a strategy to expand upon bottom-up approaches, focusing on the synthesis of record-length discrete linear catenanes. The chapter details the syntheses of [7]- and [8]catenanes using orthogonal metal templation and the ‘zip-tie’ approach. Both MIMs retain the potential for further extension due to bis-functional ligand terminal macrocycles, which serve as functional handles. However, as the bottom-up 'zip-tie' approach is expanded to produce higher-order structures, diminishing yields are observed. Through the production of these higher order structures, we learned various nuances (ring closing concentration, stoichiometry) in the syntheses of catenanes and found methods to produce shorter linear oligo[n]catenanes in large scales. Thus, while both top-down and bottom-up methods have their advantages and disadvantages, the bottom-up approach has shown greater promise in the synthesis of shorter, unimolecular linear catenanes. The bottom-up approach could therefore be adapted to produce relatively large scales of discrete catenane crosslinkers. While significant research has been conducted on catenane and MIM-based gels, there is a noticeable gap in studies examining the role of catenanes in bulk materials, such as thermosets, that do not contain any solvent. Chapter 3 addresses this by detailing the synthesis of [3]catenane cocrosslinked thermosets using a modified FROMP procedure. My expectation in carrying out this study was that the unique catenane architecture would exhibit an increase in elasticity due to the inherent freedom of the mechanical bond; furthermore, this architecture should influence the relaxation of the materials and increase the rate of stress relaxation. However, we found significant aggregation of the demetalated catenanes. The disorder that the aggregates imparted into the network thus resulted in slower relaxation rates; furthermore, the aggregates also likely had a strong influence on the tensile properties of the materials. The resulting catenane cocrosslinked materials exhibited greater strength, stiffness, and elasticity compared to controls lacking the catenane co-crosslinkers. I hypothesize that the enhanced strength and stiffness result from catenane aggregation within the network, while the increased elasticity is due to the inherent flexibility of the MIMs. The research described in this dissertation describes how unique topological architectures such as linear oligo[n]catenanes can be used to tune the properties (e.g., relaxation rate, strength, stiffness, elasticity) of densely crosslinked networks (i.e. thermosets).
Language
English (en)
Chair and Committee
Jonathan Barnes
Committee Members
Chenfeng Ke; Chris Cooper; Kevin Moeller; Vladimir Birman
Recommended Citation
Harlan, Gray, "Synthesis of Higher-Order Catenanes and Catenane-based Materials" (2024). Arts & Sciences Electronic Theses and Dissertations. 3373.
https://openscholarship.wustl.edu/art_sci_etds/3373