Solubility control of regioregular 3-substituted polythiophenes bearing 2-phenylnaphthalene side chain by copolymerisation

Two types of 2,5-dibromothiophene monomers having a dodecyl chain and a 2-phenylnaphthalene one were randomly copolymerised in different feed molar ratio by Ni-catalysed chain-growth polymerisation method. Regioregularity of all polymers were sufficiently high (88-97%). Absorption λ_max due to π-π* transition of polythiophene backbones in solutions were observed at 444-451 nm for all polymers, which were almost similar to each other and typical of the optical characteristics of regioregular poly(3-alkylthiophene)s. The homopolymer of the latter monomer that had the phenylnaphthalene side group showed poor solubility to common organic solvents, i.e., it was insoluble in chloroform at room temperature and could dissolve only in hot solvents above 100 °C. The copolymers, which had higher number average molecular weights (M_n), had better solubility than that of the homopolymer.