Synthesis and Postfunctionalization of Rod–Coil Diblock and Coil–Rod–Coil Triblock Copolymers Composed of Poly(3-hexylthiophene) and Poly(4-(4′-N,N-dihexylaminophenylethynyl)styrene) Segments

Abstract

Poly(3-hexylthiophene) (P3HT) with a bromobutyl functional group at the ω-chain-end (P3HT-C4Br) and P3HT with bromobutyl functional groups at the α,ω-chain-ends (BrC4-P3HT-C4Br) were synthesized by selecting the appropriate initiators for the Grignard metathesis (GRIM) polymerization. The high end-functionality was confirmed by matrix assisted laser desorption-ionization time-of-flight (MALDI–TOF) mass spectrometry. These polymers were efficiently reacted with the living anionic polymers of 4-(4′-N,N-dihexylaminophenylethynyl)styrene (DHPS) to yield novel rod–coil diblock and coil–rod–coil triblock copolymers composed of rigid P3HT and flexible poly(4-(4′-N,N-dihexylaminophenylethynyl)styrene) (PDHPS) segments. The expected structures of the block copolymers were confirmed by size exclusion chromatography (SEC), proton nuclear magnetic resonance (1H NMR), and Fourier transform infrared (FT-IR) spectroscopies. Furthermore, the side chain alkynes of the PDHPS segments of both P3HT-b-PDHPS and PDHPS-b-P3HT-b-PDHPS were quantitatively functionalized by a [2 + 2] cycloaddition followed by a cycloreversion with tetracyanoethylene (TCNE), producing the corresponding block copolymers with donor–acceptor moieties in the flexible polystyrene segments. The formation of the new chromophores was confirmed by UV–vis spectroscopy and cyclic voltammetry (CV), which revealed strong intramolecular charge-transfer bands and redox activities ascribed to the formed donor–acceptor moieties. The thermal properties and surface morphology of the block copolymers were also evaluated by differential scanning calorimetry (DSC), atomic force microscopy (AFM) observations, and small-angle and wide-angle X-ray scattering (SAXS and WAXS). This is the first report about the development of P3HT-based block copolymers with tunable optoelectronic properties, which was achieved by the combined synthetic techniques of the GRIM polymerization, living anionic polymerization, and click postfunctionalization.