Photopolymerization of Acrylate Polymers Using Visible Light and Ethyl Cobalamin Mediator (2015)

Undergraduates: Laura Doherty, Zach Rodgers

Faculty Advisor: David Lawrence
Department: Biology

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The aim of this research is to use a vitamin B12 derivative, ethyl cobalamin, to control radical polymerization of acrylates in aqueous solution using visible green light. This enables the formation of polymers that have uniform size and molecular weight that can be tuned by changing the time length of light exposure. Ethyl cobalamin acts as a photoinitiator to begin the reaction, and it also serves to control the rate of propagation by reversibly binding to the growing polymer chain ends. The conversion was measured over time using proton nuclear magnetic resonance spectroscopy, and the molecular weight and polydispersity were measured with dynamic light scattering. When the light is on, the polymer conversion increases, and when the light is off, the conversion does not increase, indicating the cobalamin is reversibly capping the growing polymer chains. Furthermore, the vitamin B12 derivative can attach small molecules to the end of each polymer chain in the initiation step of the reaction. A fluorophore was covalently bound to the cobalamin, so that when it initiated polymerization, the fluorophore was bound to the end of the polymer. The initiator also controls the polymerizations of other monomers, so this technique can be used to make specific, functionalized block copolymers.