Multidimensional Synthesis of Organic Materials
- Author(s): Sample, Caitlin Sarah
- Advisor(s): Hawker, Craig J
- Bates, Christopher M
- et al.
At the core of materials science is a simple but essential rule: structure informs function. It follows, then, that the ability to control the structure of organic molecules is key to the development of highly functional organic materials. At the small-molecule level, this means taking advantage of the diversity of synthetic transformations available to control the spatial arrangements of atoms within the molecular structure. For example, the synthesis of asymmetric perylene diimides for organic semiconductors is realized by choosing a naphthalic starting material over the traditional perylene core, and the substitutions made possible by this approach have a dramatic effect on the electronic and optical properties as well as the potential for subsequent functionalization. Small-molecule functionality becomes of great important as we move to higher dimension systems, such as polymers. Macromolecular synthesis requires a careful selection of functional monomer and appropriate catalyst. The synthetic route demonstrated herein shows that the polyaddition of bis(silanes) and diketones can be achieved via borane-catalyzed hydrosilylation to generate poly(silyl ethers) with varied thermal properties and degradation behavior. By exchanging one of the small-molecule starting components —bis(silanes)—for hydrosilane-containing polymers, we shift from the synthesis of discrete polymer chains to unimolecular silicone networks, in which chemical crosslinks give the resultant thermosets the mechanical integrity needed to perform as engineering materials. As a further handle for structural manipulation, triggers for external stimuli can be used to give spatiotemporal control over material properties. In the final case study discussed in this dissertation, the combination of two forms of stimuli is demonstrated. Light is used to spatially program the macroscopic structure of thiol–ene networks, while the inclusion of dynamic boronic ester bonds allows for thermal relaxation at the nanoscopic scale. The interplay between these stimuli allows for 3D printing of objects that can relax stress, self-heal, and be reprocessed into entirely new parts. In each of the examples presented, we harness fundamental concepts from organic chemistry to gain control over chemical and physical structure, enabling the generation of functional organic materials across multiple length scales.