Research

N-Heterocyclic carbene-carbodiimide (NHC-CDI) adducts have been used as catalysts, ligands, mechanophores, and (as demonstrated by our group) thermally-activated NHC precatalysts, in which the CDI electronic character was used to tune the adduct bond strength, and thus the thermal release profile of the NHC, allowing for controlled transformations in a triggerable fashion. Due to NHC-CDIs’ tunable structure, versatile reactivity, and synthetic accessibility, the Lamb lab explores their structure-property relationships under thermal, photochemical, and electrochemical conditions in efforts to expand their utility into new applications. For example, we demonstrated how selective structural changes of NHC-CDIs can have profound effects on their frontier molecular orbitals and their interactions with light. Furthermore, we disclosed how to tune NHC-CDIs to stabilize reactive organic intermediates including radical cations and dications. We continue to explore the different reactivity modes and applications of these versatile zwitterionic adducts.

Noncovalent interactions, such as dipole-dipole interactions, have a significant impact on the structure and properties of polymers, including industrially-relevant material properties, such as thermal stability and electronic properties. Despite their promise for controlling polymer properties, strong, non-ionic dipoles are understudied due to synthetic challenges. The Lamb group has approached this synthetic challenge by developing novel monomers amenable to ring-opening metathesis polymerization (ROMP) to access polymers containing polar heterocycles, particularly polyoxazolidinones (POxa). The polar heterocycles introduce strong, oriented dipoles embedded in the polymer backbone that can be systematically varied on the basis of monomer design and controlled polymerization conditions. Ring-closing metathesis (RCM) was shown to chemically recycle POxa to monomer, demonstrating a potential circular economy for these materials. The versatility of this synthetic system allows us to examine dipole effects – such as dipole strength, orientation, and density – on the tensile, rheological, and thermal properties of the resulting materials. Building on these more fundamental structure-property studies, we investigate the application of these polar-ring polymers, such as in electronics and adhesives.

The synthesis of block copolymers (BCPs) with a broad range of properties and chemical space can require the incorporation of diverse monomer classes that cannot be polymerized via a single mechanism; however, current methods to achieve materials from multiple mechanisms generally require tedious extra synthetic manipulations or an architecture-limiting multi-functional initiator. Universal mediators have emerged as a strategy to combine radical polymerization with either cationic or anionic polymerizations without the need for any intermediate synthetic steps, but compatibilization of cationic and anionic mechanisms using a universal mediator had previously been unreported. The Lamb lab has focused on thiocarbonyl thio compounds (TCTs) as universal mediators and developed a method to sequentially combine cationic and anionic group transfer polymerization mechanisms to synthesize novel poly(vinyl ether)-b-poly(thiirane) BCPs. This platform also allows for the simple addition of radical polymerization to ultimately synthesize novel three-mechanism, three-monomer-class triblock terpolymers. Through this system, we seek to expand the available chemical space of BCPs by incorporating disparate monomer classes, different tacticities, and post-polymerization modifications. We continue to utilize physical organic chemistry principles to improve universal mediator design, expand block compositions, explore the properties of the novel BCPs, and probe fundamental questions about BCP self-assembly.