Macromolecular Metamorphosis: Transformable Polymeric Materials

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NON-TECHNICAL SUMMARY:This project seeks to develop a new paradigm in the area of materials science by considering the effects of transformable molecular shape on final materials properties. The architecture of a polymer molecule directly affects the properties of the materials they are used to prepare. Polymers are designed to have a characteristic and static molecular structure selected for a specific application. This project involves the development and investigation of polymers composed of reversible bonds that enable dramatic transformations in their architecture when triggered. This concept introduces a new paradigm in the field of responsive polymeric materials. The resulting polymers will be structurally robust while also allowing themselves to be healed when damaged. Applications of stimuli-responsive materials are continually being developed, with significant promise having been demonstrated in the area of drug delivery, smart coatings, and self-healing materials. Polymers that undergo architectural transformations in solution may have potential utility as additives in motor oil or personal care products. Materials that demonstrate self-healing and recyclability before being fixed at elevated temperatures could address one of the fundamental limitations of many materials constructed via reversible linkages, namely their propensity to slowly deform over time. The project also includes outreach and education activities directed toward local K-12 students and training of graduate and undergraduate students in emerging areas of chemistry and polymer science.TECHNICAL SUMMARY:Currently, most examples of stimuli-responsive polymers derive their response from changes in molecular size through alterations of chain conformation or changes in polymer-solvent or polymer-polymer interactions. However, the fundamental characteristic of molecular architecture has not typically been considered a variable because a macromolecule's topology is "locked" by its covalent primary structure. This project challenges this convention by investigating materials that transform their covalent architecture when triggered by an external stimulus. By preparing polymers capable of exchanging irreversible bonds for reversible bonds, a new class of responsive materials that adapt to their surroundings by transitions in their covalent architecture can be achieved. Specifically, three systems are being considered: (1) macromolecules capable of topological transformations in solution; (2) adaptable organogels that modify their covalent structure; and (3) transformable bulk materials with "switchable" crosslinks. The first system involves polymers with complex chain architectures that irreversibly transform into new architectures when triggered. The second and third systems involve reversibly-crosslinked polymer networks that are structurally-dynamic, meaning they can be triggered to significantly rearrange their internal structure to become irreversibly crosslinked (i.e., "fixed"). These three areas have been chosen to investigate the potential of this approach across a wide spectrum of sizes (nano to macro) and material states (solution, gels, and bulk) and to dramatically expand the definition of stimuli-responsive materials.