Role of Monomer Sequence and Polymer Topology in Polymer Assembly

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PART 1: NON-TECHNICAL SUMMARYAs very long molecules, polymer chains can take on many shapes ranging from fully extended to collapsed. While the shape of some natural polymers, namely proteins, has evolved to be very complex and embeds significant functionality, synthetic polymer chain shapes are comparatively crude. Improved control of chain shape could, therefore, advance the design of materials for applications as diverse as organic electronics, structural plastics, and complex fluids. Recently, synthetic methods have improved to the point where we can make polymer chains with chemistry as complex as proteins, but the ability to design materials that attain specific shape remains out of reach. Taking inspiration from proteins, the PI's group will leverage these developments in polymer chemistry to determine the design rules controlling the chain shape and assembly of these polymers. Further, insights connecting the molecular design of a polymer to its three-dimensional shape will improve our understanding of natural protein folding and develop the tools necessary to synthesize materials with the complexity and function inherent in biology. An important component of the project focuses on broadening participation in polymer science at all levels including: (1) Engaging incoming community-college transfer students in research efforts, (2) A robust program of “Science Night” outreach activities, and (3) The training of undergraduate and graduate student researchers.PART 2: TECHNICAL SUMMARYMonomer sequence and polymer topology are two essential design handles to control polymer conformation and self-assembly. Recent advances in the gram-scale synthesis of sequence-controlled polypeptoids now make it possible to directly test predictions of how monomer sequence and polymer topology control chain collapse and leverage access to previously unrealized mesostructures. This project spans both chemical patterning and polymer topology as handles for fine-tuning material properties and, thus, builds a foundation for designing made-to-order soft materials and synthetic biological systems. Beyond precisely defined monomer sequence, junction location, and arm length, polypeptoids also provide user-defined chain stiffness, offering yet another handle to control chain shape and interfacial curvature. The PI's group will use this platform to explore how sequence and dynamic intramolecular interactions can be used to tune collapsed molecular structure, providing insight on protein folding and colloid design. In addition, they will synthesize polypeptoids with non-linear topologies and study their melt self-assembly, thus eliminating the dispersity effects intrinsic to most synthetic routes. In particular, the project will determine the role of interfacial curvature on resulting morphologies and explore how conformational asymmetry and complex topologies (graft and star architectures) can be combined to fine-tune self-assembly. Further, the PI's group will model polypeptoids as controlled platforms to generate insights for graft polymer design, beginning with systems to address two outstanding questions: (1) where does the limit between graft/star/bottlebrush lie? and (2) can the inherent competition between backbone orientation in inhomogeneous bottlebrushes be used to access new morphologies?.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.