Elucidation of the Mechanisms of the Yamamoto Polymerizations
Thieo Hogen-Esch is a professor of organic and polymer chemistry in the department of chemistry in the
USC College of Letters, Arts, and Sciences. His research interests include polymerization mechanisms
and the synthesis of polymers with well-defined architectures. Polymerization - the science of
creating polymers, or chain molecules containing many identical units, from small molecules - has
many industrial, medical, and advanced material-science applications. Hogen-Esch's work involves "living"
polymerizations, in which conditions are created that allow the polymer to grow under controlled
conditions without termination. Recent mechanistic work of this type has demonstrated that phosphor
ylides, or neutral molecules, can mediate living polymerizations of methacrylate monomers, which
are key components of polyacrylates, or thermoplastic engineering resins.
These methods allow the synthesis of polymers with well-defined architectures, including block
copolymers in which the chain is composed of two or more different blocks that confer properties of
each of the blocks to a single chain. Such chains tend to assemble into materials having nanosized
domains corresponding to each of the blocks. Another focus of his group is the synthesis of
fluorocarbon (RF) functionalized polymers with self-assembling properties. These polymers and
their blends display nanoscale morphologies observable by atomic force microscopy (AFM), transmission
electron microscopy (TEM), and other methods. His research also includes the synthesis of conjugated
polymers, which have potential applications in light-emitting and light-harvesting devices.
Recently, Hogen-Esch and his colleague Jun Ling, Ph.D., have used HPCC-supported density functional
(DFT) calculations on the mechanisms of the formation of polyfluorenes. These calculations allow the
evaluation of the role of chain-end nickel complexes acting as catalysts and support the idea that
these polymerization rates increase as polymers grow longer. Related calculations designed to
elucidate the shape of polyfluorenes in dilute solution allow a better insight into the shapes of
these polymers in solution and in the solid state. These findings are of significance for the
technology of light-emitting and solar energy-harvesting devices.
