Polypeptoids as model materials for studying the role of monomer sequence and chain shape on block copolymer self-assembly

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PART 1: NON-TECHNICAL SUMMARYPolymers that form patterns on the nanometer scale are important components of adhesives and next-generation flexible and rubbery materials. Being able to control this patterning in next-generation polymers is important for applications such as nanolithography, flexible electronics, and biomedicine. These polymers have much more complicated chemical structures and molecular-scale shapes than typical polymer molecules. This project is targeted at understanding how complexity in the molecule's chemical structure and shape affects its ability to form patterns involving the mutual packing of many molecules. To do this, molecules will be designed and studied that are inspired by biological polymers (proteins) but allow for tuning of their shape, stiffness, and chemical structure. Undergraduate and graduate student researchers will be trained at national research user-facilities, participate in local and national scientific meetings, and interact closely with research collaborators. Combining both research and learning to interact in the broader scientific community comprises an integral part of the educational experience for graduate students bound for either industrial careers or the academic world. Furthermore, the PI will partner with the UCSB Center for Science and Engineering Partnerships to incorporate a diverse cadre of incoming community-college transfer students into the research group to both ease transfer shock and provide research experience. A robust program of "Science Night" outreach activities at Santa Barbara/Goleta elementary and middle schools will continue to generate excitement in STEM fields among a new generation of students. PART 2: TECHNICAL SUMMARYEquilibrium self-assembled mesostructures in block copolymers arise from the competition between enthalpic segregation of dissimilar blocks, liquid crystalline interactions, composition, and the mismatch in scaling dimensions between blocks. The ability to synthesize sequence-specific polypeptoids at gram scale presents a unique opportunity to directly test predictions of copolymer self-assembly that suggest both 'blockiness' and gradient strength in a copolymer sequence impacts the chain's ability to minimize free energy by sorting monomers to the preferred side of the interface. Furthermore, the chain persistence length is tunable on a single chemical platform by controlling the sequence, side chain chirality, and bulkiness. This platform provides the conformational (persistence length) control necessary to explore the continuum of semiflexible chain shapes between the rod and coil limits. In addition, the fundamental role of asymmetry in contributing long-range entropic effects to the free energy of mixing will be explored. The goal of this project is to develop a deep understanding of how sequence and chain shape impact the free energy contributions to block copolymer self-assembly. It is expected that this fundamental understanding will guide the design of semiflexible and sequence-defined block copolymers and ultimately impact fields as diverse as organic optoelectronics and biomaterials.