This project is concerned with the development of new chemical reactions for the repetitive formation of sp3-sp3 carbon-carbon bonds. The products of these reactions, carbon backbone polymers, comprise some of the most important synthetic materials known. Traditional methods for polymer synthesis involve polymerization of alkenes. The project will study new reactions involving the polymerization of ylides and diazoalkane monomers with Lewis acidic catalyst/initiators. These reactions build the carbon backbone one carbon at a time and provide exceptional control over molecular weight and polydispersity. Novel polymer topologies, not readily available by conventional olefin polymerization, will also be studied using these new reactions.
With this award, the Organic and Macromolecular Chemistry Program is supporting the research of Professor Kenneth J. Shea of the Department of Chemistry at the University of California, Irvine. Professor Shea's research efforts revolve around synthetic and mechanistic organic chemistry and span polymers, functional materials and catalysis. His research is of broad interest to polymer scientists for establishing structure/property relationships, for synthesizing polymer compatibilizing and blending agents, as standards for molecular weight calibration, and as surface modifiers for commodity plastics. His method can also be used to synthesize polymers for testing fundamental concepts of polymer physics such as the influence of topology on polymer diffusion, melt behavior, crystallization and solution viscosity. In addition, since many olefins do not readily polymerize, these alternative synthetic methods can serve as an entry to completely new substances and properties. Collaborations with the major producers of polyethylene have been established which will lead to extensive characterization of the properties of these materials.
NSF PH Project Outcome Report Synthetic polymers are ubiquitous and an essential part of contemporary society. It is inconceivable to think of the world without them. Their uses range from construction materials to replacements for arteries and hip joints. The importance of synthetic polymers stems from a combination of their physical, chemical, mechanical and biological properties. These variables are controlled by the chemical reactions that produce these materials. An extremely important development in synthetic polymer chemistry has been in the area of" living" or controlled polymerizations. These are reactions that permit control of molecular weight, polydispersity and functional groups in a way that has not been possible previously. These new synthetic methods have provided materials for new applications that have benefited society. Simple hydrocarbon polymers such as polyethylene and polypropylene are the world's most important synthetic polymers and are produced on an enormous scale. The polymerization reactions responsible for their production, although extraordinarily efficient, do not yet have the level of control of a "living" polymerization. Furthermore these hydrocarbon polymers are derived from petroleum, a feedstock that is not sustainable. The two objectives of our research have been to (1) develop" living" or controlled polymerization reactions for the synthesis of simple hydrocarbon polymers and (2) develop new chemistries to synthesize these important materials from non petroleum, more abundant or renewable feedstocks. To that end we have developed a controlled polymerization for the production of simple linear hydrocarbon polymers from C1 carbon sources. We have termed this polymerization reaction polyhomologation. Unlike traditional olefin polymerizations, the reaction builds the hydrocarbon chain one carbon at a time and uses an inexpensive, readily available organoborane as catalyst. The chemistry provides access to hydrocarbon polymers with control over composition, molecular weight, architecture and polydispersity (Figure 1). A significant recent finding has been our ability to introduce a variety of substituents on the linear hydrocarbon backbone. This provides controlled access to novel materials as well precision synthesis of important commodity materials. This has resulted in an active collaboration with Exxon Mobil. As part of this collaboration we have synthesized pure low molecular weight branched hydrocarbons and oligomeric polymethylene and very high molecular weight (> 1 million MW) star hydrocarbon polymers. Interest in the oligomeric polymethylenes and branchy derivatives stems from their ability to serve as excellent models for petroleum-derived waxes and have been evaluated for the kinetics of crystallization of well defined branched hydrocarbons and for the molecular weight and topological requirements for tie-chain molecules to serve as intercrystalline links to strengthen and toughen polyethylene (Figure 2). This collaboration resulted in my student being awarded an Exxon Mobile Fellowship where she spent the summer at Corporate Research Headquarters developing the polyhomologation reaction to synthesize polymers that are of interest to them. Not all outcomes of basic research are anticipated. Our expertise in the controlled synthesis of hydrocarbons led to a collaboration with Professor Tsutsui at U. C. Berkeley to identify the nestmate recognition cues of the Argentine ant (Linepithema humile). The Argentine ant is a major pest in California and in many parts of the South. The success of these non-native invaders stems from their ability to proliferate and produce huge "super colonies" that displace many native species. Unlike their native Argentina where colonies are small and inter colony warfare consumes a considerable fraction of their energy and resources, in California there is one major colony that controls most of the state, they behave as one big happy family. To learn how Argentine ants distinguish nestmates from non-nestmates we have been studying their chemical nestmate recognition cues. An understanding the factors that enable the Argentine ant to create such supper colonies, can lead to better control of this pest. We have identified and synthesized eight compounds (linear hydrocarbons!) that function as nestmate recognition cues (Figure 3). Our collaborators have also learned that the nestmate recognition cues of a homologous series elicit the same aggressive response because they convey the same information. This study contributes to our understanding of the chemical basis of nestmate recognition by showing that, similar to spoken language, the chemical language of social insects contains "synonyms," chemicals that differ in structure, but not meaning. The most significant development during this grant period has been the discovery that the polyhomologation reaction can be run in water using stable sulfonium salts as the C1 carbon source. This aqueous based chemistry is being developed to convert abundant C1 carbon sources to hydrocarbons ranging from fuels (C10-C15) to detergents (C12-C18) to waxes, all under sustainable conditions Figure 4. A patent application has been filed (Figure 4).
