Donor-acceptor copolymers containing phthalazinone-thiophene structure synthesized by low-cost copper-catalyzed Ullmann polymerization

Herein, we present low-cost copper-catalyzed Ullmann polycondensation of phthalazinone based monomers containing both OH and NH groups, which provides access to polyarylethers and conjugated polymers. The synthesis of the polymers was accomplished by a combination of low activity thiophene and carbazole monomers. In particular, it was shown that a stronger base (Cs2CO3 > K2CO3) can efficiently polymerize the low activity thiophene monomer with the phthalazinone based monomer, to obtain high number-average molecular weight, up to 17.9 kDa (PDI = 2.43). Moreover, in this study, the result of reaction process monitoring revealed that the Ullmann polymerization was in favour of the radical mechanism. The reaction activity of di-halogenated monomers was found to be a crucial factor for achieving a high molecular weight polymer. Thus, the number-average molecular weight of donor-acceptor copolymers containing the phthalazinone-thiophene structure ranged from 2.2 to 9.6 kDa. The new copolymer structures were confirmed by H-1-NMR, FT-IR and GPC. Their thermal, optical, electrochemical and X-ray diffraction (XRD) properties, and density functional theory (DFT) calculations, were investigated in detail. The results show that the thiophene unit is beneficial to the pi-pi interaction between the polymer chains, compared to carbazole and phthalazinone units.