Synthesis of π-conjugated block copolymer containing poly(3-hexylthiophene) and bent-core liquid crystal

Abstract

Conjugated polymers consist of organic macromolecules, of which the polymer backbones are comprised of alternating double- and single-bonds. Conjugated polymers have high conductivity and chemical stability due to an overlap of π-molecular orbitals. Conjugated polymer-based materials have various advantages such as lightweight, low cost, flexibility, and processability. Polythiophene (PT) is an important conjugated polymer. PT has excellent thermal stability, environmental stability, and good conductivity, but has poor solubility. To improve the solubility of PT, flexible side chains were attached onto the backbone. Poly(3-alkylthiophene) (P3AT) can dramatically improve the solubility. The properties of a conjugated polymer are strongly dependent on the morphology of the material in the solid-state.

The aim of study was to investigate the morphologies formed self-assembly of block copolymers containing P3HT. We synthesized ethynyl-terminated P3HT by Grignard Metathesis polymerization (GRIM method) and characterized it. The ethynyl-terminated P3HT was reacted with azide-terminated PS or PEG via Cu(I)-catalyzed cycloaddition (click chemistry). The self-assembly behavior of P3HT-b-PS in a thin film was studied by treating the thin films with solvent annealing using chloroform or toluene as a solvent. The self-assembly behavior of P3HT-b-PEGs in aqueous solution was studied. The resulting block copolymers self-assembled into nanofibers in solution presumably due to the crystallization of the core-forming P3HT block.

Liquid crystals (LCs) are materials in a state that has properties between those of a conventional liquid and those of a solid crystal. Bent-core LCs have special features of the LC phases formed by banana-shaped molecules (with a bend angle of ~120°). The well-defined morphologies of bent-core LC have exotic physicochemical properties.

We synthesized two chiral bent-core mosogens (P8-O-PIMB6* and P9-O-PIMB7*) and an achiral bent-core mesogen (P8-O-PIMB6) in order to obtain well-defined morphologies in the 60 nm AAO nanochannel. The structures of bent-core mesogens were confirmed by NMR and EI-mass spectrometry. The transition temperatures of bent-core mesogens were measured by DSC. The morphologies of bent-core liquid crystals in the 60 nm AAO nanochannel were studied by depolarized reflected light microscopy (DRLM), scanning electron microscopy (SEM), and grazing incidence X-ray diffraction (GIXD).