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Home  >  Journal list  >  Polymer Journal  >  Vol.49  No.9 (2017)  >  pp.649-654

Polymer Journal
<<Previous article Vol.49  No.9 (2017)   pp.649 - 654 Next article>>

Regioselective halogen–magnesium exchange reaction of a bithiophene derivative bearing methoxy and pyridine groups at the β-position and Kumada coupling polymerization

Koji Takagi1, Ryo Kouchi1 and Junpei Kawai1
1Life Science and Applied Chemistry, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya, Japan

We have previously reported the synthesis of a polythiophene derivative (P2′) bearing pyridine and methoxy groups at the β-position, but the halogen–magnesium exchange reaction of the monomer did not proceed in a regioselective manner and resulted in a twisted polymer conformation. In the present paper, the halogen–magnesium exchange reaction of 4-(5″-hexylpyridine-2″-yl)-3-methoxy-2-(5′-bromothiophene-2′-yl)-5-bromothiophene (M3) and its Kumada coupling polymerization and optoelectronic characterization were investigated. The reaction of M3 with i-PrMgCl·LiCl gave a Grignard monomer (GM3a) in 79% yield, with the halogen–magnesium exchange reaction occurring exclusively at the bromine atom neighboring the pyridine group. Reflux temperature was required for the Kumada coupling polymerization of GM3a using Ni(dppp)Cl2 to proceed smoothly (72% conversion after 24h) due to the sterically hindered monomer structure. On the other hand, the conversion of GM3a remained at 15% without the addition of LiCl. The number-average molecular weight of the tetrahydrofuran-soluble fraction of the regiocontrolled oligo(bithiophene) (P3′) was 2900 because of its poor solubility. Ultraviolet–visible and cyclic voltammogram measurements indicated that compared with P2′, P3′ has a more planar conformation, an increased highest occupied molecular orbital energy level and a narrower bandgap energy. A non-covalent S···O interaction was assumed to cause the planar conformation, which was supported by theoretical density functional theory calculations.

Received: April 29, 2017 , Revised: June 08, 2017
Accepted: June 08, 2017 , Published online: July 19, 2017
© 2017 The Society of Polymer Science, Japan

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