High-Performance Nonvolatile Organic Transistor Memory Devices Using the Electrets of Semiconducting Blends

Organic nonvolatile transistor memory devices of the <i>n</i>-type semiconductor <i>N</i>,<i>N</i>′-bis­(2-phenylethyl)-perylene-3,4:9,10-tetracarboxylic diimide (BPE-PTCDI) were prepared using various electrets (i.e., three-armed star-shaped poly­[4-(diphenylamino)­benzyl methacrylate] (N­(PTPMA)₃) and its blends with 6,6-phenyl-C₆₁-butyric acid methyl ester (PCBM), 6,13-bis­(triisopropylsilylethynyl)­pentacene (TIPS-pen) or ferrocene). In the device using the PCBM:N­(PTPMA)₃ blend electret, it changed its memory feature from a write-once-read-many (WORM) type to a flash type as the PCBM content increased and could be operated repeatedly based on a tunneling process. The large shifts on the reversible transfer curves and the hysteresis after implementing a gate bias indicated the considerable charge storage in the electret layer. On the other hand, the memory characteristics showed a flash type and a WORM characteristic, respectively, using the donor/donor electrets TIPS-pen:N­(PTPMA)₃ and ferrocene:N­(PTPMA)₃. The variation on the memory characteristics was attributed to the difference of energy barrier at the interface when different types of electret materials were employed. All the studied memory devices exhibited a long retention over 10⁴ s with a highly stable read-out current. In addition, the afore-discussed memory devices by inserting another electret layer of poly­(methacrylic acid) (PMAA) between the BPE-PTCDI layer and the semiconducting blend layer enhanced the write-read-erase-read (WRER) operation cycle as high as 200 times. This study suggested that the energy level and charge transfer in the blend electret had a significant effect on tuning the characteristics of nonvolatile transistor memory devices

Synthesis, Morphology, and Sensory Applications of Multifunctional Rod–Coil–Coil Triblock Copolymers and Their Electrospun Nanofibers

We report the synthesis, morphology, and applications of conjugated rod–coil–coil triblock copolymers, polyfluorene<i>-block-</i>poly­(<i>N</i>-isopropylacrylamide)<i>-block</i>-poly­(N-methylolacrylamide) (<b>PF</b><b>-</b><i><b>b</b></i><b>-</b><b>PNIPAAm</b><i><b>-b-</b></i><b>PNMA</b>), prepared by atom transfer radical polymerization first and followed by click coupling reaction. The blocks of PF, PNIPAAm, and PNMA were designed for fluorescent probing, hydrophilic thermo-responsive and chemically cross-linking, respectively. In the following, the electrospun (ES) nanofibers of PF-<i>b</i>-PNIPAAm-<i>b</i>-PNMA were prepared in pure water using a single-capillary spinneret. The SAXS and TEM results suggested the lamellar structure of the <b>PF</b><b>-</b><i><b>b</b></i><b>-</b><b>PNIPAAm</b><b>-</b><i><b>b</b></i><b>-</b><b>PNMA</b> along the fiber axis. These obtained nanofibers showed outstanding wettability and dimension stability in the aqueous solution, and resulted in a reversible on/off transition on photoluminescence as the temperatures varied. Furthermore, the high surface/volume ratio of the ES nanofibers efficiently enhanced the temperature-sensitivity and responsive speed compared to those of the drop-cast film. The results indicated that the ES nanofibers of the conjugated rod–coil block copolymers would have potential applications for multifunctional sensory devices

Room Temperature Synthesis of a Covalent Monolayer Sheet at Air/Water Interface Using a Shape-Persistent Photoreactive Amphiphilic Monomer

The shape-persistent monomer <b>3</b> with its three 1,8-diazaanthracene (DAA) units is spread and compressed at the air/water interface and the layer then converted into a 1.5 nm thick covalent monolayer sheet by photoirradiation under ambient conditions. The sheet obtained under these extremely mild conditions is mechanically stable to carry its own weight when spanned over TEM grids. While its molecular structure cannot be given yet with certainty, it is likely to be the result of [4 + 4]-cycloaddition dimerizations between the DAA units of neighboring monomers. Evidence is based on the wavelength of the monomer fluorescence emission, the kinetics of this emission’s intensity decay with irradiation time, and the mechanical sheet stability that suggests a surpassing of percolation threshold. Finally, the thermal stability of the sheet is investigated

B(C₆F₅)₃‑Catalyzed Group Transfer Polymerization of <i>N,N</i>-Disubstituted Acrylamide Using Hydrosilane: Effect of Hydrosilane and Monomer Structures, Polymerization Mechanism, and Synthesis of α‑End-Functionalized Polyacrylamides

The tris­(pentafluorophenyl)­borane- (B­(C₆F₅)₃-) catalyzed group transfer polymerization (GTP) of <i>N,N</i>-disubstituted acrylamide (DAAm) using a moisture-tolerant hydrosilane (H<i>Si</i>) as part of the initiator has been intensively investigated in this study. The screening experiment using various H<i>Si</i>s suggested that dimethylethylsilane (Me₂EtSiH) with the least steric bulkiness was the most appropriate reagent for the polymerization control. The chemical structure of the DAAms significantly affected the livingness of the polymerization. For instance, the polymerization of <i>N,N</i>-diethylacrylamide (DEtAAm) using Me₂EtSiH only showed better control over the molecular weight distribution, while that of <i>N</i>-acryloylmorpholine (MorAAm) with a more obstructive side group using the same H<i>Si</i> afforded precise control of the molecular weight as well as its distribution. Given that the entire polymerization was composed of the monomer activation, the <i>in situ</i> formation of a silyl ketene aminal as the true initiator by the 1,4-hydrosilylation of DAAm, and the GTP process, the polymerization mechanism was discussed in detail for each specific case, e.g., the B­(C₆F₅)₃-catalyzed polymerizations of DEtAAm and MorAAm and the polymerization of MorAAm using B­(C₆F₅)₃ and Me₃SiNTf₂ as a double catalytic system. Finally, the convenient α-end-functionalization of poly­(<i>N,N</i>-disubstituted acrylamide) (PDAAm) was achieved by the <i>in situ</i> preparation of functional silyl ketene aminals through the 1,4-hydrosilylation of functional methacrylamides, which has no polymerization reactivity in the Lewis acid-catalyzed GTP, followed by the Me₃SiNTf₂-catalyzed GTP of DAAms

Synthesis of α‑, ω‑, and α,ω-End-Functionalized Poly(<i>n</i>‑butyl acrylate)s by Organocatalytic Group Transfer Polymerization Using Functional Initiator and Terminator

The α-functionalized (hydroxyl, ethynyl, vinyl, and norbornenyl), ω-functionalized (ethynyl, vinyl, hydroxyl, and bromo), and α,ω-functionalized polyacrylates were precisely synthesized by the <i>N</i>-(trimethylsilyl)­bis­(trifluoroethanesulfonyl)­imide (Me₃SiNTf₂)-catalyzed group transfer polymerization (GTP) of <i>n</i>-butyl acrylate (<i>n</i>BA). The α-functionalization and ω-functionalization were carried out using the functional triisopropylsilyl ketene acetal as the initiator (initiation approach) and 2-phenyl acrylate derivatives as the terminator (termination approach) for the organocatalytic GTP, respectively. All the polymerizations precisely occurred and produced well-defined end-functionalized poly­(<i>n</i>-butyl acrylate)­s which had predictable molecular weights and narrow molecular weight distributions. High-molecular-weight polyacrylates were easily synthesized using both approaches. In addition, the α,ω-functionalized (hetero)­telechelic polyacrylates were synthesized by the combination of the initiation and termination approaches. The structure of the obtained polyacrylates and degree of functionalization were confirmed by the ¹H NMR and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS) measurements. The spectra of the ¹H NMR and MALDI-TOF MS showed that the end-functionalization quantitatively proceeded without any side reactions

Synthesis of Homopolymers, Diblock Copolymers, and Multiblock Polymers by Organocatalyzed Group Transfer Polymerization of Various Acrylate Monomers

The group transfer polymerization (GTP) with <i>N</i>-(trimethylsilyl)­bis­(trifluoromethanesulfonyl)­imide (Me₃SiNTf₂) and 1-methoxy-1-triisopropylsiloxy-2-methyl-1-propene (<i>i</i>Pr-SKA) has been studied using methyl acrylate (MA), ethyl acrylate (EA), <i>n</i>-butyl acrylate (<i>n</i>BA), 2-ethylhexyl acrylate (EHA), cyclohexyl acrylate (<i>c</i>HA), dicyclopentanyl acrylate (d<i>c</i>PA), <i>tert</i>-butyl acrylate (<i>t</i>BA), 2-methoxyethyl acrylate (MEA), 2-(2-ethoxyethoxy)­ethyl acrylate (EEA), 2-(dimethylamino)­ethyl acrylate (DMAEA), allyl acrylate (AlA), propargyl acrylate (PgA), 2-(triisopropylsiloxy)­ethyl acrylate (TIPS-HEA), and triisopropylsilyl acrylate (TIPSA). Except for <i>t</i>BA and DMAEA, the GTPs of all other monomers described above proceeded rapidly in a living manner and produced well-defined homo acrylate polymers. The living nature of the GTPs of such acrylate monomers was further applied to the postpolymerizations of MA, EA, <i>n</i>BA, and MEA and also to the sequential GTPs of diverse acrylate monomers for preparing di- and multiblock acrylate polymers. In greater detail, the AB and BA diblock copolymers, (ABC)₄ dodecablock terpolymer, (ABCD)₃ dodecablock quaterpolymer, and ABCDEF hexablock sestopolymer were synthesized by sequential GTP methods using various acrylate monomers

Synthesis of Linear, Cyclic, Figure-Eight-Shaped, and Tadpole-Shaped Amphiphilic Block Copolyethers via <i>t</i>‑Bu‑P₄‑Catalyzed Ring-Opening Polymerization of Hydrophilic and Hydrophobic Glycidyl Ethers

This paper describes the synthesis of systematic sets of figure-eight- and tadpole-shaped amphiphilic block copolyethers (BCPs) consisting of poly­(decyl glycidyl ether) and poly­[2-(2-(2-methoxyethoxy)­ethoxy)­ethyl glycidyl ether], together with the corresponding cyclic counterparts, via combination of the <i>t</i>-Bu-P₄-catalyzed ring-opening polymerization (ROP) and click cyclization. The clickable linear BCP precursors, with precisely controlled azido and ethynyl group placements as well as a fixed molecular weight and monomer composition (degree of polymerization for each block was adjusted to be around 50), were prepared by the <i>t</i>-Bu-P₄-catalyzed ROP with the aid of functional initiators and terminators. The click cyclization of the precursors under highly diluted conditions produced a series of cyclic, figure-eight-, and tadpole-shaped BCPs with narrow molecular weight distributions of less than 1.06. Preliminary studies of the BCPs self-assembly in water revealed the significant variation in their cloud points depending on the BCP architecture, though there were small architectural effects on their critical micelle concentration and morphology of the aggregates

Synthesis and Thermoresponsive Property of Linear, Cyclic, and Star-Shaped Poly(<i>N</i>,<i>N</i>‑diethylacrylamide)s Using B(C₆F₅)₃‑Catalyzed Group Transfer Polymerization as Facile End-Functionalization Method

The syntheses of linear, cyclic, and star-shaped poly­(<i>N</i>,<i>N</i>-diethyl­acrylamide)­s (PDEAAms) have been studied in order to clarify the topological effect on their thermoresponsive properties. For the group transfer polymerization of <i>N</i>,<i>N</i>-diethyl­acrylamide using tris­(pentafluoro­phenyl)­borane (B­(C₆F₅)₃) as the organocatalyst, the α-, ω-, and α,ω-end-functionalizations of the PDEAAms with well-controlled molecular weights and narrow polydispersities were quantitaively produced using the silyl ketene aminals with hydroxyl, ethynyl, and vinyl groups as functional initiators and 2-phenyl acrylate derivatives with hydroxyl, ethynyl, and bromo groups as functional terminators. The ω-end-functionalized PDEAAm with the azido group and the α,ω-end-functionalized PDEAAm with the ethynyl and azido groups were used as the starting materials for the inter- and intramolecular copper­(I)-catalyzed click reactions leading to the 3-armed star-shaped and cyclic PDEAAms (<i>s</i>₃-PDEAAm and <i>c</i>-PDEAAm, respectively). In order to eliminate the unit effect of the triazole (<i>taz</i>) group on the thermoresponsive behavior, the linear PDEAAm with the <i>taz</i> group at the center of the polymer chain (<i>l</i>-<i>taz</i>-PDEAAm) was prepared by the click reaction between the end-functionalized PDEAAm with the ethynyl group and that with the azido group. The thermoresponsive property of these PDEAAms with the DPs of 26–29, 50–52, and 78–80 was evaluated by the cloud point (<i>T</i>_c) determined by the turbidity measurements and the enthalpy changes (Δ<i>H</i>) of water molecules per molar monomer unit by highly sensitive differential scanning calorimetry (micro-DSC) measurements. The phase transition behavior of <i>s</i>₃-PDEAAm on the transmittance curve was similar to that of <i>l</i>-<i>taz</i>-PDEAAm, rather than <i>c</i>-PDEAAm. The <i>T</i>_c values decreased in the order of <i>l</i>-<i>taz</i>-PDEAAm > <i>c</i>-PDEAAm > <i>s</i>₃-PDEAAm. The Δ<i>H</i> values for <i>s</i>₃-PDEAAm were almost the same as those for <i>c</i>-PDEAAm, which were lower than those for <i>l</i>-<i>taz</i>-PDEAAm

Synthesis of Oligosaccharide-Based Block Copolymers with Pendent π‑Conjugated Oligofluorene Moieties and Their Electrical Device Applications

We report the synthesis and electric device applications of oligosaccharide-based diblock copolymers consisting of a maltoheptaose (MH) block and a poly­(4-oligofluorenyl­styrene) block (PStFl_<i>n</i>, <i>n</i> = 1 or 2), referred to as MH-<i>b</i>-PStFl_<i>n</i>. MH-<i>b</i>-PStFl_<i>n</i> was prepared by the Cu­(I)-catalyzed click reaction of azido-terminated PStFl_<i>n</i> (PStFl_<i>n</i>-N₃), which was obtained from the azidation reaction of the bromo-terminated PStFl_<i>n</i> (PStFl_<i>n</i>-Br), with excess ethynyl-terminated MH in the THF/DMF mixture solvent. The resulting diblock copolymers self-assembled to spherical microdomains with sub-10 nm sizes in both bulk and thin film state after annealing process. Thereafter, the MH-<i>b</i>-PStFl_<i>n</i> thin film (∼50 nm) with the self-assembled nanoscale spherical aggregates was used as the charge storage layer for the pentacene-based field-effect transistor type memory devices. The MH-<i>b</i>-PStFl_<i>n</i>-based devices had the excellent hole mobility (0.25–0.52 cm² V^–1 s^–1) and the high ON/OFF current (<i>I</i>_ON/<i>I</i>_OFF) ratio of 10⁷–10⁸, of which the MH-<i>b</i>-PStFl₁-based one had the higher mobility than that of the MH-<i>b</i>-PStFl₂-based one because the pentacene crystal in the former device possessed the larger grain size and fewer boundaries. On the other hand, the MH-<i>b</i>-PStFl₂-based device showed a larger memory window than the MH-<i>b</i>-PStFl₁-based one because the stronger electron-donating effect of the difluorenyl group in MH-<i>b</i>-PStFl₂ increased the charge storage capability of its related device. All the memory devices showed a long-term retention time over 10⁴ s with the high <i>I</i>_ON/<i>I</i>_OFF ratio of 10⁶–10⁸. Among these devices, the MH-<i>b</i>-PStFl₁-based device showed a good WRER endurance over 180 cycles. This work not only demonstrates the tunable electrical memory characteristics by adjusting the π-conjugation length of the oligofluorenyl side chain in the polymer electret but also provides a promising approach for developing the next-generation “green electronics” using natural materials

Stereoblock-like Brush Copolymers Consisting of Poly(l‑lactide) and Poly(d‑lactide) Side Chains along Poly(norbornene) Backbone: Synthesis, Stereocomplex Formation, and Structure–Property Relationship

Random and block copolymerizations of poly­(l-lactide) (PLLA) and poly­(d-lactide) (PDLA) macromonomers having an <i>exo</i>-norbornene group at the α- or ω-chain end (D/L ratio = 1/1, <i>M</i>_n = ca. 5000 g mol^–1) were performed via ring-opening metathesis polymerization to produce the brush random and block copolymers consisting of parallel or antiparallel aligned PLLA and PDLA side chains on a poly­(norbornene) backbone. The molecular weight and polydispersity index of the brush copolymers were in the range of 40 300–458 000 g mol^–1 and 1.03–1.14, respectively. Despite such high molecular weights, these brush copolymers formed a stereocomplex without homochiral crystallization. The melting temperature (<i>T</i>_m) and crystallinity (<i>X</i>) of the resulting stereocomplex varied depending on the backbone length, relative chain direction, and distribution of the PLLA/PDLA side chains. The parallel brush copolymers showed significantly higher <i>T</i>_m and <i>X</i> values than the antiparallel ones