Better Living Through Chloride

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Science  30 Nov 2012:
Vol. 338, Issue 6111, pp. 1128-1129
DOI: 10.1126/science.338.6111.1128-d

Conjugated polymers are used as the active element in many flexible optoelectronics devices, including thin-film transistors and light-emitting diodes, and as such, versatile routes to their preparation are in demand. Bonillo and Swager report a distinct method for the synthesis of conjugated polymers with thiophene backbones, a class of materials currently accessed through oxidative and cross-coupling techniques. Their starting point was the previously reported observation that 3-alkoxy-2-bromothiophenes undergo a violent autopolymerization that proceeds through a cationic mechanism with the elimination of HBr. The authors show that the chloro variant of this reaction proceeds in a more controlled manner. They used chlorodibutylpropylenedioxythiophene as a model monomer and studied the promotion of the reaction by different Lewis acids and solvents: Tin tetrachloride in o-dichlorobenzene proved the optimal combination. End-capping by nucleophiles could stop the reaction on account of the chain-growth nature of the mechanism; moreover, the “living” character of the process not only led to products with a low polydispersity index but also enabled the synthesis of block copolymers. In this vein, the authors prepared rod-coil copolymers comprising thiophene and ethyl vinyl ether blocks. They further suggest that the ionic addition/elimination scheme could generalize, offering access to a range of other polyaromatic systems.

J. Am. Chem. Soc. 134, 10.1021/ja308498h (2012).

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