Controlled Polymerization of Renewable Cyclic Esters: Catalyst Design and Polymerization Mechanisms William B. Tolman and Marc A. Hillmyer, Department of Chemistry, University of Minnesota, Minneapolis, MN 55455 We seek new and innovative methods for the conversion of molecules provided by plants into compounds that can be catalytically transformed into sustainable plastics. We integrate chemical synthesis and structural definition of new catalysts, monomers, and polymers, with particular emphasis on mechanistic studies of polymerization catalysis (right) and development of new materials with useful properties derived from biorenewable resources (below). A dizinc complex exists in equilibrium with a monomeric form that catalyzes the polymerization of caprolactone via a monomer-activated pathway. A triblock copolymer derived from the renewable cyclic esters lactide and menthide is a thermoplastic elastomer.