The Effect of Amide Solvent Structure on the Direct Arylation Polymerization (DArP) of 2-Bromo-3-hexylthiophene

In this work, we investigate the influence of the amide solvent chemical structure on the properties of poly(3-hexylthiophene) (P3HT) prepared via direct arylation polymerization (DArP). Our findings indicate that for successful polymerization the amide must possess an acyclic aliphatic structure since cyclization of an amide results in a complete shutdown of DArP reactivity as evidenced by failed polymerization in N-methylpyrrolidone, whereas the presence of an aromatic motif renders the amide solvent susceptible to C-H activation and leads to incorporation of the solvent structure into the P3HT backbone, as demonstrated on the example of N, N-diethylbenzamide. Additionally, we observed that the steric bulk of alkyl substituents on both the nitrogen atom and the carbonyl group within the amide structure has to be delicately balanced for optimal DArP reactivity. In the optimal cases, P3HT is obtained in high yield, with high molecular weight and contains a minimal amount of structural defects. The obtained polymer samples were comprehensively studied in terms of their chemical structure, optical, thermal and solid-state properties in thin films using GPC analysis, H-1 NMR, MALDI, UV-vis, GIXRD spectroscopy, and DSC. We additionally note a drastic difference of the amide solvent effect between DArP and Stille polymerization. (C) 2015 Wiley Periodicals, Inc.