Nanostructure Formation in Poly(3-hexylthiophene-block3-(2-ethylhexyl)thiophene)s

A series of conjugated, highly regioregular poly(3-hexylthiophene-block-3-(2-ethylhexyl)thiophene)s (P(3HT-b-3EHT)s) were synthesized by nickel-catalyzed quasi-living polymerization. H-1 NMR spectra and GPC charts showed that the synthesized P(3HT-b-3EHT)s have well-controlled block ratios and molecular weights with narrow polydispersity indices, which enable the systematic study of the correlation between the polymer structure and nanostructures of P(3HT-b-3EHT) films. AFM observation revealed that P(3HT-b-3EHT)s self-organized into thin films after thermal annealing to spontaneously form clear microphase-separated nanopatterns whose size depends oil the block ratio. The temperature for the nanopattern formation correlated to the transition temperature of the polymers that were investigated by DSC. In contrast, only featureless patterns were observed in the films of random copolymers and physical mixtures of homopolymers with the corresponding unit ratios, indicating that well-defined diblock copolymers are essential for spontaneous nanopattern formation. The UV-vis absorption spectra and XRD patterns obtained showed that highly crystalline P3HT blocks stacked with their pi-planes and alkyl side chains aligned in the thin films in an orientation normal to the substrate.