Molecular Design of Novel Polymer Materials Based onBottlebrush Macromolecules

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Significant progress in polymerization techniques allows synthesis of hyperbranched architectures with precisely controlled molecular dimensions and well-defined shapes. One of the most distinctive examples of highly-branched macromolecules are molecular bottlebrushes composed of many polymer sidechains densely grafted to a linear chain (backbone). Strong steric repulsion between densely grafted branches affects stiffness and ensures highly extended conformations of individual bottlebrushes and reduces overlap between molecules in concentrated solutions and melts. These remarkable features provide access to fabrication of bottlebrush based materials with physical properties that are distinct from conventional materials composed of linear polymers. The goal of this project is to develop analytical and numerical models of bottlebrush polymers that will provide guidelines for designing novel super-soft and super-tough materials. Softness of polymers can be greatly enhanced by disentanglement of molecules. In melts, bottlebrush architecture promotes disentanglement resulting in unusual rheological properties, i.e. plateau modulus is 2-3 orders of magnitude lower than typically observed in linear chain melts. We propose to study the relationship between architecture of cross-linked bottlebrushes and softness of the resulting elastomer. It has been demonstrated that properties of polymer gels can be improved by synthesizing networks with different stiffness. Stiffness of bottlebrushes can be controlled by varying their thickness. We propose to study properties of interpenetrating networks composed of cross-linked bottlebrushes with different stiffness. Our approach is a combined study using molecular dynamics and Monte-Carlo simulation techniques as well as scaling and mean-field concepts to develop a theoretical understanding of bottlebrush melts and networks.