Browsing by Author "Sista, Prakash"
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Item Role of the Transition Metal in Grignard Metathesis Polymerization (GRIM) of 3-Hexylthiophene(2013-09-09) Bhatt, Mahesh P.; Magurudeniya, Harsha D.; Sista, Prakash; Sheina, E. E.; Jeffries-El, M.; Janesko, B. G.; McCullough, R. D.; Stefan, Mihaela C.; Stefan, Mihaela C.Regioregular poly(3-alkylthiophene)s are widely used in organic electronics applications such as solar cells and field effect transistors. Nickel, palladium, and platinum diphenylphosphinoethane complexes were tested as catalysts for the Grignard metathesis (GRIM) polymerization of 2,5-dibromo-3-hexylthiophene and 2-bromo-5-iodo-3-hexylthiophene. Nickel-mediated polymerization generated regioregular, low-polydispersity poly(3-hexylthiophene) with well-defined molecular weight consistent with a "living" chain-growth mechanism. By contrast, palladium-mediated polymerization proceeded by a step-growth mechanism and generated polymers with less than 80% head-to-tail couplings. Platinum-mediated polymerization gave very low molecular weight products. Kinetic and computational results suggested that the nickel catalyst acts as an initiator and remains associated with the growing polymer chain, while palladium dissociates from the growing chain. Computational and experimental evidence was provided for various side reactions of dissociated Pd(0) catalyst, which could yield a step growth mechanism and lower regioirregularity.Item Self-Assembly of a Conjugated Triblock Copolymer at the Air-Water Interface(2013-06-27) Zhao, L.; Feng, C.; Pang, X.; Jung, J.; Stefan, Mihaela C.; Sista, Prakash; Han, R.; Fang, N.; Lin, Z.; Stefan, Mihaela C.Controlling the self-assembly of highly luminescent conjugated polymers is essential for preparing various optoelectronic devices. In this study, a polyisoprene-b-polystyrene-b-poly(3-hexylthiophene) (PI-PS-P3HT) triblock copolymer was synthesized and readily self-assembled into network-like morphologies via dewetting at the air-water interface. Interestingly, the monolayer thick film displayed high photoluminescence (PL) as a result of successfully transferring the amorphous conjugated P3HT chains in the PI-PS-P3HT triblock copolymer from the solution state to the solid state. A model was proposed to illustrate the supramolecular organization of the PI-PS-P3HT monolayer. To the best of our knowledge, this is the first study of a hydrophobic conjugated block copolymer at the air-water interface, from which the conjugated polymer-based monolayer with highly efficient PL formed by dewetting was achieved.