Stereoselective Epoxide Polymerization: Exploring Isoselective Bimetallic Catalysts, Ionic Cocatalysts, And The Use Of Alcohols As Chain Transfer Agents
For over 50 years, researchers have attempted to create catalysts for stereoselectively polymerizing epoxides. Until very recently, catalysts for the polymerization of racemic epoxides gave mixtures of atactic and isotactic material or moderate tacticity polyethers. In 2008, the Coates Research Group reported a bimetallic catalyst system for enantioselectively polymerizing racemic epoxides to highly isotactic enantiopure polyethers. Catalyst simplification led to a highly active, isoselective catalyst. This catalyst is capable of quantitatively polymerizing racemic terminal epoxides to yield isotactic polyethers. Organic ionic compounds were synthesized and investigated as cocatalyts. The identities of both the cation and anion were systematically varied and subsequent polymerization reactivity was studied. The nature of the ionic cocatalyst dramatically impacted the rate and enantioselectivity of the catalyst system. The ionic cocatalyst [P(N=P(N(CH2)4)3)4+][tBuCO2-] produced a catalyst system that exhibited the greatest activity and selectivity for a variety of mono-substituted epoxides. The addition of alcohols to these bimetallic polymerization systems leads a lowering of molecular weight due to chain transfer. Polymer end-groups can be determined by choice of alcohol, addition of diols allows for the synthesis of isotactic telechelic poly(propylene oxide) diols.
Catalysis; Polyether; Stereoselective
Collum, David B; Sogah, Dotsevi Y
Chemistry and Chemical Biology
Ph. D., Chemistry and Chemical Biology
Doctor of Philosophy
dissertation or thesis