Novel donor–acceptor rod–coil diblock copolymers of regioregular poly(3‐hexylthiophene) (P3HT)‐block‐poly(2‐phenyl‐5‐(4‐vinylphenyl)‐1,3,4‐oxadiaz‐ole) (POXD) are successfully synthesized by the combination of a modified Grignard metathesis reaction (GRIM) and atom transfer radical polymerization (ATRP). The effects of the block ratios of the P3HT donor and POXD pendant acceptor blocks on the morphology, field effect transistor mobility, and memory device characteristics are explored. The TEM, SAXS, WAXS, and AFM results suggest that the coil block fraction significantly affects the chain packing of the P3HT block and depresses its crystallinity. The optical absorption spectra indicate that the intramolecular charge transfer between the main chain P3HT donor and the side chain POXD acceptor is relatively weak and the level of order of P3HT chains is reduced by the incorporation of the POXD acceptor. The field effect transistor (FET) hole mobility of the system exhibits a similar trend on the optical properties, which are also decreased with the reduced ordered P3HT crystallinity. The low‐lying highest occupied molecular orbital (HOMO) energy level (–6.08 eV) of POXD is employed as charge trap for the electrical switching memory devices. P3HT‐b‐POXD exhibits a non‐volatile bistable memory or insulator behavior depending on the P3HT/POXD block ratio and the resulting morphology. The ITO/P3HT44‐b‐POXD18/Al memory device shows a non‐volatile switching characteristic with negative differential resistance (NDR) effect due to the charge trapped POXD block. These experimental results provide the new strategies for the design of donor‐acceptor rod‐coil block copolymers for controlling morphology and physical properties as well as advanced memory device applications.

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b S Supporting Information ' INTRODUCTION DonorÀacceptor (DÀA) polymer systems have widely investigated for organic electronics, such as light-emitting diodes, 1,2 photovoltaic cells, 3À16 field-effect transistors, 11À18 and memory devices. 19À21 They provide the advantages of flexibility, low cost, solution processability, and three-dimensional stacking capability as compared with inorganic counterparts. 1À21 Because of the stable electron-donating nitrogen atom in the triphenylamine (TPA), 22,23 the TPA-based DÀA polymers were developed for various electronic applications. 24À33 In addition, the energy level of TPA-based polymers can be chemically tuned through the different strength of electron acceptors to meet the requirement of original molecular design for specific organic electronics. For example, functional polyimides (PIs) containing electrondonating TPA moieties and electron-withdrawing phthalimide moieties were demonstrated for the device application of dynamic random access memory (DRAM), static random access memory (SRAM), write-once-read-many times (WORM), and flash memory via an external voltage bias or pulse. 24À28 Soluble TPA-based polyazomethine grafted with graphene oxide acceptors was prepared for bistable flash memory device. 29 Besides, side-chain TPAÀ perylene block copolymers influenced the HOMO energy level and microphase-separated morphologies, which affected the solar cell performance significantly. 30,31 We are particularly interested in the design and synthesis of DÀA polymer systems for resistive-type memory device applications. 27,34À37 The reported DÀA materials system for the volatile and nonvolatile memory devices included small molecules, 38,39 conjugated polymers, 40À42 nonconjugated polymers with D/A chromophores (functional polyimide 24À29,34 or pendent polymers 36,43,44 ), and polymer nanocomposites (metal nanoparticle, 45,46 fullerene, 37,47 carbon nanotube, 48 or graphene oxide 29 embedded). The original switching mode of memory devices were operated through several proposed mechanisms such as the trapping/detrapping of charges, charge transfer effect, and filamentary conduction, as summarized by Kang and co-workers. 19

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