Synthesis and Reactions of Strained Molecules and Polymers

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Professor Kenneth Shea, of the Department of Chemistry at the University of California, Irvine, is supported by the Organic Synthesis Program for his studies of the synthesis and reactions of strained molecules and polymers. Alkyl boranes initiate the polymerization of dimethylsulfoxonium methylide, resulting in the formation of perfectly linear polymethylene with an extremely narrow polydispersity index. Adjustment of the initial ratio of ylide to alkyl borane permits control of the molecular weight of the resulting polymethylene, while chemical transformations of the carbon-boron bonds of polyhomologated alkyl boranes allow the introduction of a variety of terminal functionalities. Extension of this polyhomologation chemistry to more complex alkyl borane initiators affords access to novel polymethylene architectures, including star, comb, and hyperbranched polymers. The chemistry may also be adapted to the formation of block copolymers which covalently link polymethylene with the incompatible polysiloxanes and polyethylene glycols. Development of control over the formation and structures of polymers, macromolecules comprised of chemically-linked repeating units derived from smaller molecules, is a central issue in the scientifically and technologically vital area of polymer chemistry. Professor Kenneth Shea exploits an unusual class of polymer-forming chemical reactions, wherein individual carbon atoms are added to a growing polymer chain one at a time. This chemistry affords synthetic access to a range of three-dimensional polymer structures, including circular-, comb-, and star-shaped materials, and will thereby permit the determination of the effects of such unusual structural motifs on the intrinsic and bulk properties of polymeric materials. Additional studies address the formation of block copolymers (two or more distinct polymers chemically linked to one-another) in which the linked polymers display drastically different properties. Unusual physical and chemical properties are expected to arise from such unions, including the formation of materials which can change their shapes and/or properties as a function of their environment.