Synthesis of head-to-tail regioregular poly(3-hexylthiophene)s with controlled molecular weight via highly selective direct arylation polymerization (DArP)

In this study, we succeeded in controlling the molecular weight of head-to-tail (HT) regioregular poly(3-hexylthiophene) (P3HT) via palladium-catalyzed direct arylation polymerization (DArP). The key to success was using 2-phenylthiazole ( 2 ), which has a highly reactive C–H bond for direct arylation, as the end-capping reagent. The DArP of 2-bromo-3-hexylthiophene ( 1 ) in the presence of 2 ([ 1 ] 0 /[ 2 ] 0 = 10–80), Herrmann-Beller catalyst, and P( o -Me 2 NC 6 H 4 ) 3 ( L1 ) afforded HT-regioregular P3HT (HT = 99%) capped with a 2-phenylthiazole-5-yl group. The number-average molecular weight ( M n ) of P3HT agreed well with the value calculated by assuming formation of one polymer chain per molecule of 2 (polydispersity index: Ð = 1.8–2.1). Thus, the M n value could be controlled by adjusting the initial molar ratio of 1 to 2 . We also succeeded in controlling the molecular weight of poly(3-alkylthiophene)s (alkyl = butyl and octyl) with DArP using 2 as the end-capping reagent.