i1i : Interfacial synthesis of 2D copolymers directed by noncovalent interactions

The correlation of polymer sequence and architecture to macroscopic properties represents a primary tenet of polymer chemistry. To date, researchers have focused on linear and branched polymers. Their studies have taken advantage of well- developed controlled polymerization reactions, and have provided both fundamental insight and commercially useful materials. In contrast, no one has performed such structure–property studies for two-dimensional (2D) organic polymers, defined as covalently bonded, monolayer structures with long-range order. Compared to the diversity of inorganic 2D materials (MoS2, WSe2, h-BN, borophene, silicene), graphene remains the only readily accessible and well-studied organic 2D polymer. The synthesis of well-defined organic 2D polymers suffers from significant challenges in synthesis and characterization. Current strategies rely on surface polymerization, which does not provide sufficient quantities of material, or dynamic covalent linkages, which suffer from hydrolysis and poor mechanical properties. Computational studies have predicted a wealth of remarkable properties for 2D structures that cannot be accessed by current approaches, motivating my group’s efforts to develop innovative strategies for their preparation. In particular, we are interested in materials predicted to be elastic in response to uniaxial strain, which couple mechanical stimulus to changes in optical, magnetic, or redox properties. Such materials serve as responsive fabrics, coatings, or membranes. To study the effect of sequence on the properties of this promising class of materials, an approach that marries self- assembly and reactivity is required. This proposal describes the electrostatically-driven self-assembly of rigid monomers at interfaces and externally triggered polymerization. Preliminary results demonstrate that the desired reactivity can be promoted by visible light in solution. The objectives of the proposed work include (1) developing conditions and small- molecule model systems for interfacial coupling; (2) designing monomers that self-assemble though noncovalent interactions at the air-water interface; (3) achieving interfacial polymerization; and (4) elucidating structure-property relationships for 2D materials. The proposed work will provide synthetic access to stable, structurally diverse 2D organic polymers in their monolayer form, a nearly unstudied class of materials. I anticipate that the proposed work will result in (a) fundamental insight into the properties of 2D materials, (b) design rules for the preparation of 2D copolymers with tailored responsiveness and mechanical properties, and (c) new lightweight, elastic materials with physical or chemical properties that respond to mechanical stress.