Synthesis, morphology, and field-effect transistor characteristics of new crystalline-crystalline diblock copolymers of poly(3-hexylthiophene-block-steryl acrylate)

We report the synthesis, morphology, and charge-transporting characteristics of new crystallinecrystalline diblock copolymers, poly(3-hexylthiophene-block-stearyl acrylate) (P3HT-b-PSA). Three different diblock copolymers, P1, P2, and P3, with P3HT/PSA polymerization degree block ratios of 60/26, 60/50, and 60/360, respectively, were prepared for investigating the morphology-property relationship and the dependence of optoelectronic properties on the block copolymer structure. Small- and wide-angle X-ray scattering indicated the presence of both P3HT and PSA crystalline domains and the presence of microphase separation among blocks. The transmission electron microscopy and atomic force microscopy results revealed that the diblock copolymers cast from chlorobenzene, tended to form needle-like morphologies. The field-effect mobilities of the diblock copolymers deposited on untreated SiO2 substrates, decreased with increasing PSA block length. In a sharp contrast, the mobilities enhanced with increasing PSA content when the P3HT-b-PSA was deposited on phenyltrichlorosilane (PTS)-treated substrates. The copolymers with a 60/360 P3HT/PSA ratio showed a good mobility of 4 x 10(-3) cm(2) V-1 s(-1) and a high on/off ratio of 7 x 10(6) on PTS-treated substrates. This study highlighted the importance of the block ratio, the substrate and self-assembly structures on the charge transport characteristics of the crystallinecrystalline conjugated diblock copolymers. (c) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 686-695, 2012