Synthesis and polymerization of 3,4-dialkoxy thiophene

Abstract

Poly(3,4-ethylenedioxythiophene) is acknowledged for its high electrical conductivity but insoluble in common organic solvents, leading to difficulties in fabrication process. In attempts to solve this problem, new monomers were synthesized by modifying the substituents on the thiophene rings. They were used to prepare polythiophene via chemical, thermal solid or liquid state polymerization techniques. Brominations of 3,4-ethylenedioxythiophene, 3,4-dimethoxythiophene, and 2'-hydroxymethyl-3,4-ethylenedioxythiophene provided 2,5-dibromo-3,4-ethylenedioxythiophene, 2,5-dibromo-3,4-dimethoxythiophene, and 2'-hydroxymethyl-2,5-dibromo-3,4-ethylenedioxythiophene in 85, 80 and 72% yields, respectively. Subsequent substitutions with 2-bromoethanol on 2,5-dibromo-3,4-ethylenedioxythiophene yielded the crown-ether fused thiophene derivative 2 in 22% yield. When, using 3,4-dimethoxythiophene as the precursor in other substitutions, 2'-hydroxymethyl-3,4-ethylenedioxythiophene 3 and 3,4-dibenzoyloxythiophene 6 could be obtained both in 20% yields. Finally, chemical polymerization of 3,4-dihydroxythiophene 5 and thermal polymerization of 2'-hydroxymethyl-2,5-dibromo-3,4-ethylenedioxythiophene provided their corresponding polymers in 98% and 54% yield, respectively