Covalently tethered, 1, 3, 5-benzenetricarboxamide helical stacks and novel, self-associating dynamic covalent polymers

Abstract

This thesis describes a new series of columnar, helical oligomers that have been synthesized. These oligomers utilize both covalent and non-covalent interactions to organize aromatic discs into discrete, stacked columnar structures of specific length. Specifically, aromatic discs with 1, 3, 5-benzenetricarboxamide side chains have been covalently tethered to a five atom spacer. The spacer is flexible enough to allow the cooperative hydrogen bonding from the amide side chains as well as π-π interactions to occur while also strengthening these interactions by covalently linking the discs together. The secondary structure of these oligomers is evidenced by 1 H NMR and circular dichroism (CD) spectroscopy. Vapor pressure osmometry (VPO) was performed in order to show that these oligomers do not aggregate in solution. The lack of aggregation between oligomers indicated that the 1 H NMR and CD data was a result of purely intramolecular hydrogen bonding and stacking interactions, and no supramolecular structures were assembled. Furthermore a self-complementary hydrogen bonding duplex, capable of dynamic covalent disulfide bonding was synthesized. This duplex was then attached on both ends of a rigid aromatic spacer to yield a functional unimer capable of both self-assembly and dynamic covalent polymerization. Cross-linking studies were performed on the unimer unit in an attempt to synthesis a novel polymer with both thermodynamically controlled non-covalent directionality, and with covalent linkages. An end-capping unit was also introduced into the polymerizations in an attempt to synthesis a mono-disperse polymer with the degree of polymerization controlled via the ratio of unimer to end-capper.