Living radical polymerization (LRP) can be used to create polymers with precise molecular weights and tailored architectures. The three most commonly used LRP techniques are nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP), and reversible addition/fragmentation chain transfer polymerization (RAFT). Each technique has both application-specific advantages as well as distinct requirements; fortunately, most monomers that are used with free radical polymerization can be used with LRP. NMP relies on alkoxyamines to function as the initiator as well as the stable, mediating nitroxide radical. ATRP relies on halogen-containing initiators and metal/ligand complexes that serve as catalysts. RAFT relies on chain transfer agents. The simplicity of adding these reagents to a polymerization reaction results in the ability to synthesize well-defined copolymers, functionalized polymers, and materials with specific architectures. Recent advances in each of the LRP techniques have continued to increase the diversity of resulting polymers.
The evolution of nanostructured materials that originate from the supramolecular assembly of macromolecular building blocks, from relatively simple overall shapes and internal morphologies to those of increasing complexity, is driving the development of synthetic methodologies that allow for the preparation of increasingly complex macromolecular structures. Moreover, the inclusion of functional units within selective compartments/domains is of great importance to create (multi)functional materials. We have a special interest in the study of nanoscopic macromolecules, with well-defined composition, structure and topology, as components that are programmed for the formation of sophisticated nanoscopic objects in solution. Combinations of controlled radical and ring opening polymerizations, chemical transformations, and supramolecular assembly are employed to construct such materials as functional entities. We employ a variety of multi-functional monomers, together with selective polymerization chemistries, to afford regiochemically-functionalized polymers and then further conduct supramolecular assemblies and chemical transformations upon those precursor materials. This presentation will provide an overview of living radical polymerization (LRP) chemistries and will then highlight our work to utilize LRP to prepare well-defined block copolymers, having controlled macromolecular architectures (linear vs. hyperbranched) and incorporating reactive functionalities. Transformation into three-dimensionally-controlled star-block or brush-block copolymer structures will also be described. A primary motivation is to take advantage of the effects of composition and structure on the solution-state supramolecular assembly behaviors of linear, branched, star and brush polymer architectures to afford unique nanostructures. Hierarchical assembly of nanostructures to create elaborate materials by simple processes will also be discussed.
Researchers and engineers interested in applying modern polymerization techniques for:
Professor Karen L. Wooley
Texas A&M University
W. T. Doherty-Welch Chair Department of Chemistry
Materials science and engineering
Research. Development. Production.
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