Synthesis of Thiophene- and Bithiophene-Based Alternating Copolymers via Pd-Catalyzed Direct C–H Arylation

Polycondensation via direct C-H arylation of thiophene derivatives gave thiophene- and bithiophene-based alternating copolymers in good yields. The optimization of the reaction conditions was investigated in terms of a catalytic system and reaction time. Under optimized conditions, the polycondensation reaction of 3,3',4,4'-tetramethylbithiophene with 2,7-dibromo-9,9-dioctylfluorene gave poly[2,7-(9,9-dioctylfluorene)-<i>alt</i>-5,5'-(3,3',4,4'-tetramethyl-2,2'-bithiophene)] with a molecular weight of 31 800 in 91% yield. The polycondensation reaction proceeded with 2 mol % of Pd(OAc)₂ without the addition of a phosphine ligand in a short reaction time (3 h). Six kinds of π-conjugated polymers were synthesized by the polycondensation reaction without the use of bifunctional organometallic reagents as monomers.