Synthesis and properties of polythiophenes bearing alkylsulfonic acid esters at the side chain

Abstract

Introduction of alkylsulfonic acid moieties into the side chain of polythiophene was carried out. Synthesis of 2,5-dihalothiophenes bearing alkylsulfonate groups at the 3-position was performed. The reaction of 2-chloro-5-iodothiophenes with Grignard reagents to form the organometallic monomers of the corresponding thiophenes followed by nickel(II)-catalyzed cross-coupling polymerization led to head-to-tail-type regioregular polythiophenes. The ester groups at the side chains were converted into alkali metal sulfonates by treatment with NaI or metal hydroxides (Li, Na, K). The obtained metal salts were successfully transformed into sulfonic acid groups by treatment with an ion exchange resin. The electric conductivity of the regioregular polythiophene bearing sulfonic acid groups was remarkably improved ca. 10² times compared to the corresponding metal salts (10⁶ times higher than the sulfonate ester).