The research focus of the Coates Group is the development of new synthetic strategies for producing polymers of defined structure. The control of polymer composition, architecture, stereochemistry, and molecular weight allows the indirect control of polymer properties via polymer morphology. Our research projects are interdisciplinary, addressing problems at the interface of organic, inorganic, organometallic, and polymer chemistry. Described below is a selected compilation of research topics that are being investigated in the group.

Enantioselective Epoxide Polymerization

Two major goals of catalysis are the efficient preparation of enantiopure small molecules and stereoregular polymers. Our group recently reported a cobalt-based bimetallic catalyst for the enantioselective polymerization of epoxides that achieves both objectives at the same time. Starting from racemic terminal epoxides the catalyst produces isotactic polyethers and enantiopure epoxides in high yields and short reaction times. The polyethers formed are highly isotactic (> 99% mm), and the selectivity factors (s-factor, k_fast/k_slow) most often exceed 50, which makes this system useful for the synthesis of highly enantioenriched epoxides.

These new isotactic polyethers have numerous potential applications. For example, they could help improve everyday foams, sealants, surfactants, elastomers, and biomedical components, which currently are based on atactic polyethers. Futhermore, enantiopure epoxides are important building blocks for pharmaceuticals and other stereoregular polymers.

1. Hirahata, W.; Thomas, R. M.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2008, 130, 17658-17659.
2. Thomas, R. M.; Widger, P. C. B.; Ahmed, S. M.; Jeske, R. C.; Hirahata, W.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2010, 132, 16520-16525.
3. Widger, P. C. B.; Ahmed, S. M.; Hirahata, W.; Thomas, R. M.; Lobkovsky, E. B.; Coates, G. W. Chem. Commun. 2010, 46, 2935-2937.

Carbonylation

Carbon monoxide (CO) is a readily available building block that introduces valuable functional groups into organic molecules. Our group has focused on the catalytic carbonylative ring-expansion of heterocycles, foremost the carbonylation of epoxides to beta-lactones and succinic anhydrides. The resulting products are important monomers in the synthesis of biodegradable polymers, and have emerging applications as fine chemicals and building blocks in pharmaceutical syntheses.

Our main objective is the development and mechanistic understanding of highly active and selective carbonylation catalysts. Over the years our group has introduced several catalytic systems of the general form [Lewis Acid]+[Co(CO)4]- that show unique reactivity for different substrate classes and applications. We also apply our carbonylation catalysts to current challenges in polymer synthesis. Examples include a highly efficient one-pot synthesis of the commercially relevant polymer poly(3-hydroxybutyrate) (PHB), and control over the microstructure of poly(beta-hydroxalkanoate)s through carbonylation.

1. Rowley, J. M.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2007, 128, 4948-4960.
2. Church, T. L.; Getzler, Y. D. Y. L.; Coates, G. W. J. Am. Chem. Soc. 2006, 128, 10125-10133.
3. Schmidt, J. A. R.; Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2005, 127, 11426-11435.

Biodegradable Polymers

1. Poly(hydroxyalkanoates)

Poly(hydroxyalkanoate)s (PHA)s are naturally-occurring biodegradable polyesters made by bacterial fermentation. Our goal is to develop an alternative synthetic route that consists of carbonylation of epoxides to beta-lactones, followed by ring-opening polymerization to yield PHAs. Recently, we reported a one-pot carbonylative polymerization method that makes poly(3-hydroxybutyrate) (PHB) from propylene oxide and carbon monoxide.

1. Dunn, E. W.; Coates, G. W. J. Am. Chem. Soc. 2010, 132, 11412.

2. Polycarbonates

Poly(hydroxyalkanoate)s (PHA)s are naturally-occurring biodegradable polyesters made by bacterial fermentation. Our goal is to develop an alternative synthetic route that consists of carbonylation of epoxides to beta-lactones, followed by ring-opening polymerization to yield PHAs. Recently, we reported a one-pot carbonylative polymerization method that makes poly(3-hydroxybutyrate) (PHB) from propylene oxide and carbon monoxide.

1. Jeske, R. C.; Rowley, J. M.; Coates, G. W. Angew. Chem. Int. Ed. 2008, 47, 6041.

3. Polyesters

Traditional methods to synthesize biodegradable polyesters are often energy intensive and not atom economical. To establish a more efficient route, our group designed a discrete (BDI)ZnOAc catalyst for the ring-opening copolymerization of epoxides and cyclic anhydrides. This approach replaces the energy intensive step-growth mechanism with an efficient chain growth mechanism, and gives access to new aliphatic polyesters with high molecular weights. We also discovered a chromium salen-based catalyst that incorporates maleic anhydride into the polymer backbone. The resulting unsaturated polyesters find use in numerous applications such as composite materials or biomedical devices.

1. Jeske, R. C.; DiCiccio, A. M.; Coates, G. W. J. Am. Chem. Soc. 2007, 129, 11330. 

Polyolefins

Our research in polyolefins focuses on the design of homogeneous polymerization catalysts, and the characterization of the polymer architectures they produce. Our primary goal is to control polymer structure through the rational design of catalysts. The design and synthesis of such catalysts requires working at the interface of organic, organometallic and inorganic chemistry. The extensive characterization of the materials produced by these catalysts provides insight into their polymerization mechanism and guides the design of new and improved catalysts.

1. Hotta, A.; Cochran, E.; Ruokolainen, J.; Khanna, V.; Fredrickson, G. H.; Kramer, E. J.; Shin, Y.-W.; Shimizu, F.; Cherian, A. E.; Hustad, P. D.; Rose, J. M.; Coates, G. W. Proc. Natl. Acad. Sci. U. S. A. 2006, 103, 15327-15332.
2. Edson, J. B.; Wang, Z.; Kramer, E. J.; Coates, G. W. J. Am. Chem. Soc. 2008, 130, 4968-4977.
3. Rose, J. M.; Cherian, A. E.; Coates, G. W. J. Am. Chem. Soc. 2006, 128, 4186-4187.

Fuel Cells

Fuel cells are electrochemical devices that efficiently produce energy, offering advantages such as low emissions and high power density. Currently, most commercially available systems employ proton exchange membranes (PEMs) as electrolytes and operate under acidic conditions. However, these systems suffer from sluggish reduction kinetics and require costly platinum as electrode material, which limits widespread use of PEM-based fuel cells. To bypass the obstacles associated with PEMs, research interest recently focused on alkaline fuel cells (AFCs) that utilize anion exchange membranes (AEMs). This approach avoids the use of precious metals and would make devices more affordable, but the development of efficient alkaline AEMs remains a major challenge.

To date, our group has designed three polyelectrolyte membranes for AFCs that exhibit competitive properties with other materials in the field. We take advantage of the functional group tolerance of Grubbs’ 2nd generation catalyst for ring-opening metathesis polymerizations (ROMP) of functionalized monomers. This approach provides well-defined polymers containing cationic moieties without the need for post- polymerization modification.

1. Clark, T. J.; Robertson, N. J.; Kostalik IV, H. A.; Lobkovsky, E. B.; Mutolo, P. F.; Abruna, H. D.; Coates, G. W. J. Am. Chem. Soc. 2009, 139, 12888.
2. Kostalik IV, H. A.; Clark, T. J.; Robertson, N. J.; Mutolo, P. F.; Longo, J. M.; Abruna, H. D.; Coates, G. W. Macromolecules 2010, 43, 7147.
3. Robertson, N. J.; Kostalik IV, H. A.; Clark, T. J.; Mutolo, P. F.; Abruna, H. D.; Coates, G. W. J. Am. Chem. Soc. 2010, 132, 3400.