Polythiophene-block-Polyfluorene and Polythiophene-block-Poly(fluorene-co-benzothiadiazole): insights into the self-assembly of all-conjugated block copolymers

Journal Article · Sat Jan 01 00:00:00 EST 2011 · Macromolecules

DOI:https://doi.org/10.1021/ma102728z· OSTI ID:1081639

Verduzco, Rafael ^[1]; Botiz, Ioan ^[2]; Dimasi, Elaine ^[3]; Pickel, Deanna L ^[1]; Hong, Kunlun ^[1]; Darling, Seth B. ^[2]

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1. ORNL
2. Argonne National Laboratory (ANL)
3. Brookhaven National Laboratory (BNL)

Block copolymers made by covalently linking two or more conjugated polymers have significant potential for organic optoelectronic applications, particularly those requiring a p/n junction. Herein, we report the structure of all-conjugated diblock copolymers poly(3-hexylthiophene)-block-poly(9,9-dioctylfluorene) and poly(3-hexylthiophene)-block-poly(9,9-dioctylfluorene-co-benzothiadiazole) in thin films and in the bulk. The diblock copolymers are prepared using a combination of Grignard metathesis polymerization and Suzuki polycondensation and purified using solvent extraction and column chromatography. 1H NMR, SEC, and UV/Visible absorbance measurements are used to characterize the materials and quantify the amount of homopolymer impurities. Thin films and bulk structure are characterized using a combination of differential scanning calorimetry, x-ray diffraction, small-angle x-ray scattering, and atomic force microscopy. Atomic force microscopy images reveal nanoscale lamellar domains in solvent-annealed diblock copolymer thin films, and peaks in x-ray diffraction data correspond to poly(3-hexylthiophene) crystallites. On cooling from temperatures above the crystallization temperature to below the crystallization temperature, two peaks appear in temperature-dependent small-angle x-ray scattering traces - one associated with poly(3-hexylthiophene) crystallites and a second low-angle peak indicative of a self-assembled nanostructured. These measurements show all-conjugated diblock copolymers self-assemble into nanoscale crystalline domains present throughout the bulk samples which may be useful for improving the performance of organic photovoltaics and organic light-emitting diodes.

• Research Organization: Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Sciences (CNMS)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: DE-AC05-00OR22725
• OSTI ID: 1081639
• Journal Information: Macromolecules, Vol. 44, Issue 3; ISSN 0024--9297
• Country of Publication: United States
• Language: English