Synthesis of regioblock copolythiophene by Negishi catalyst-transfer polycondensation using tBu2Zn·2LiCl

Poly(3-hexylthiophene) with head-to-head/tail-to-tail regioregularity (HHTT-P3HT), controlled molecular weight and low molecular weight distribution was synthesized by Negishi catalyst-transfer polycondensation (NCTP) using tBu2Zn·2LiCl. The conditions to achieve controlled polymerizations of HHTT-P3HT were studied by optimizing the Ni catalyst, reaction concentrations and temperature. Furthermore, regioblock copolythiophenes consisting of HHTT-P3HT and P3HT segments with head-to-tail regioregularity (HT-P3HT) were synthesized by NCTP, in which the monomer addition sequence, that is, HHTT-P3HT block (1st) and HT-P3HT block (2nd), was firstly adopted. The decent yield (54–65%) of the regioblock copolythiophene was an advantageous point for the NCTP system. This decent yield was presumably derived from the carefully optimized conditions to form the quasi-living polymer of HHTT-P3HT with a stable chain end, –C–Ni(dcpe)–Br (dcpe = 1,2-bis(dicyclohexylphosphino)ethane), suited for the smooth crossover reaction and polymerization to the 2nd monomer for HT-P3HT. The obtained regioblock copolythiophene showed phase separation between the crystalline HT-P3HT domains and exclusive amorphous domains, as characterized by grazing-incidence X-ray scattering and atomic force microscopy.