Computational and Experimental Design of Associating Bottle Brush Mesostructures

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With this award, the Macromolecular, Supramolecular and Nanochemistry Program in the Division of Chemistry is funding Professors Douglas H. Adamson and Elena Dormidontova at University of Connecticut to study the behavior of well-defined polymeric structures at the mesoscale. Matter at the mesoscale, with characteristic length between the nanoscale (proteins, DNA, viruses) and macroscale (bacteria, chromosomes, human hair) typically exhibit fundamentally different interactions and properties than at larger or smaller length scales. At the mesoscale, materials are held together not only by the chemical bonds found in small molecules, but by additional associative and dissociative forces or interactions. Much of biology operates at the mesoscale with these additional bonding interactions. Examples include protein folding, virus encapsulation, mollusk shell formation, and transport between cellular membranes. In this research, chemical reactions are used to prepare polymer brushes or worm-like molecules in which the main polymer chain is grafted with additional polymer chains of varying density. These side polymer chains contain different associating groups, including DNA strands and small molecules that can bind metals. Computer modeling and a variety of other measurement techniques are then used to predict, guide and characterize assemblies of polymer brushes at the mesoscale. Benefits to the broader society include the potential for accelerated the development of inorganic/organic and bioinspired materials based on controlled and predictable mesoscale structures. Human resource and training benefits arise through the training of a diverse group of undergraduate and graduate students, as well as through the support of the Chemistry Wizards program. The Chemistry Wizards program works with high school students in under-represented populations and uses a competition-based approaches to increase interest in STEM-based careers.Guided by computer modeling, this research is developing unique building blocks for mesoscopic assembly. Polymer bottlebrushes functionalized by different associating groups, including DNA strands and ligands for metal-ligand complexation with different densities and distributions of associating groups, are systematically prepared using a combination of established and modified synthetic approaches. Self-assemblies of bottlebrush polymers are characterized and studied using transmission electron microscopy and scattering approaches, as well as by Monte Carlo and coarse-grained Molecular Dynamics simulations. The effect of bottlebrush architecture (rigidity, length of grafts, distribution, and density of functional groups), association strength, and nature of functional group interaction (self-interaction and complementary assembly) on the dynamics and outcomes of self-assembly in solution are also systematically investigated. This work addresses many challenges pertaining to polymeric materials which assemble at the mesoscale, including lack of theoretical framework, gaps in understanding collective interactions and motions from which structures emerge, challenges in modeling and measuring metastable states, and difficulty in controlling these states experimentally. Results associated with this award could be valuable in the development of novel polymeric structures for biology, medicine, and materials chemistry.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.