Raita Goseki

Nonvolatile organic field-effect transistor memory devices using polymer electrets with different thiophene chain lengths

We report the synthesis of poly(5-hexyl-2-vinylthiophene) (PVT) and poly(5-hexyl-5′′-vinyl-2,2′:5,2′′-terthiophene) (PVTT) as charge storage electrets for nonvolatile organic field effect transistor (OFET) memory devices of n-type semiconducting N,N′-bis(2-phenylethyl)perylene-3,4,9,10-bis(dicarboximide) (BPE-PTCDI). The effects of the conjugated thiophene chain length on the morphology, OFET mobility and memory characteristics are explored and compared to those of the styrene or fluorene side chain. The mobility of the OFET memory device using PVTT as an electret is significantly smaller compared with that of PVT because its large torsional angle hinders the molecular packing of BPE-PTCDI. However, the OFET memory device using the PVTT electret has the largest hysteresis window of 81 V, compared to PVT, polystyrene (PS), and poly(styrene) para-substituted with fluorene (PSt-Fl). The highest HOMO energy level of PVTT facilitates the charge transfer from BPE-PTCDI and leads to the largest memory window. The backbone non-coplanarity prevents the back transfer of the charge for the nonvolatile memory characteristics. The device shows excellent nonvolatile behavior for bistable switching and the write–read–erase–read (WRER) cycles are operated over 100 cycles. The shifted threshold voltages of the OFET memory devices using PVTT are stable over 104 s, and the ON and OFF states could maintain 104 s with the Ion/Ioff current ratios of 103. This study suggests that the pendent conjugation length and the backbone coplanarity of polymer electrets significantly affect the charge mobility and electrical characteristics of OFET memory devices.

Chain-end- and in-chain-functionalized AB diblock copolymers as key building blocks in the synthesis of well-defined architectural polymers

This paper reviews the precise synthesis of architectural polymers by methodologies utilizing either chain-end- or in-chain-functionalized AB diblock copolymers as efficient key building blocks. Architectural polymers herein synthesized are miktoarm star-branched polymers, exact graft copolymers, high-density comblike polymers, and alternative and sequential multiblock copolymers. Chain-end- and in-chain-functionalized AB diblock copolymers and, in some cases, core-functionalized ABC star-branched polymers utilized as building blocks are prepared by living anionic polymerization in conjunction with specially functionalized agents and linked in manners suitably designed for each architectural polymer to successfully synthesize such structurally complex polymers. The resulting polymers are all well-defined in structure and precisely controlled in chain length.

Synthesis of well-controlled graft polymers by living anionic polymerization towards exact graft polymers

This article reviews the synthesis of well-controlled graft polymers by living anionic polymerization towards exact graft polymers. The structure of a graft polymer is defined by the following three parameters: (1) molecular weight of the main chain, (2) molecular weight of the graft chain, and (3) placement of the graft chain. Based on these three parameters, the extent of the structural control of the graft polymers synthesized so far is described. Finally, the recently synthesized exact graft (co)polymers by stepwise iterative methodologies are introduced. In their structures, the three parameters are perfectly controlled.

Dynamic covalent diarylbibenzofuranone-modified nanocellulose: mechanochromic behaviour and application in self-healing polymer composites

The surface of cellulose nanocrystals (CNCs) was modified with a scissile but reversibly recombinable dynamic covalent mechanophore, and the activation of the mechanophore on the CNC surface in bulk was investigated. The recombination behaviour of the activated surface-modified mechanophore exhibited high sensitivity to mechanical stress because of the limited molecular mobility. The modified CNCs could be used to effectively reinforce a self-healable polymer containing similar dynamic covalent linkages through the formation of reversible covalent bonds between the CNC surfaces and the polymer matrix, while the nanocomposite retained the ability to heal. The results of the present study appear to be broadly useful for designing composite materials with fascinating functional properties such as damage self-reporting and self-healing.

Thermally Adjustable Dynamic Disulfide Linkages Mediated by Highly Air-Stable 2,2,6,6-Tetramethylpiperidine-1-sulfanyl (TEMPS) Radicals

Intrinsically exchangeable dynamic covalent bonds that can be triggered by readily usable stimuli offer easy incorporation of their dynamic properties in various molecular systems, but the library of such bonds is still being developed. Herein, we report the dynamic covalent chemistry of 2,2,6,6-tetramethylpiperidine-1-sulfanyl (TEMPS) dimers derived from thermally reversible homolytic dissociation of disulfide linkages. High air stability of TEMPS was observed even at 100 °C, affording facile employment of thermal dissociation-association equilibria and adjustable bond exchange properties under atmospheric conditions. We also established an efficient synthetic route for a modifiable derivative of the dimer that enabled incorporation of dynamic properties into linear and network polymer structures. The obtained polymers showed controllable molecular weights, temperature-dependent swelling properties, healing ability, and recyclability, reflecting the thermally tunable dynamics of the dimer.

Precise Synthesis of Macromolecular Architectures by Novel Iterative Methodology Combining Living Anionic Polymerization with Specially Designed Linking Chemistry

This article reviews the development of a novel all-around iterative methodology combining living anionic polymerization with specially designed linking chemistry for macromolecular architecture syntheses. The methodology is designed in such a way that the same reaction site is always regenerated after the polymer chain is introduced in each reaction sequence, and this “polymer chain introduction and regeneration of the same reaction site” sequence is repeatable. Accordingly, the polymer chain can be successively and, in principle, limitlessly introduced to construct macromolecular architectures. With this iterative methodology, a variety of synthetically difficult macromolecular architectures, i.e., multicomponent μ-star polymers, high generation dendrimer-like hyperbranched polymers, exactly defined graft polymers, and multiblock polymers having more than three blocks, were successfully synthesized.

Facile synthesis of multiarmed and multicomponent star polymers by a new iterative methodology using (formyl-protected 1,3-dioxolane)-end-functionalized polymer anions

A new and efficient iterative methodology using (formyl-protected 1,3-dioxolane (DOL))-end-functionalized polymer anions was carried out for the facile synthesis of multiarmed and multicomponent μ-star polymers. Using this methodology, both the arm introduction and DOL reintroduction steps are simultaneously performed by the linking reaction of the DOL-end-functionalized polymer anion with the formyl group regenerated from the DOL reintroduced in advance and repeated several times. By combining the DOL-end-functionalized polymer anions with non-DOL-functionalized polymer anions in the linking reaction, synthetically-difficult and well-defined complex μ-star polymers ranging from the ABC, ABCD, ABCDE, and ABCD2, to the ABCD2E2 types were successfully obtained. Moreover, synthesis of A3B2 and A3B2C4 star polymers was also achieved with the same methodology using (DOL)2-end-functionalized polymer anions. The arm segments were polystyrene, polystyrene derivatives, polyisoprene, poly(2-vinylpyridine), and poly(alkyl methacrylate(s)), which were introduced into the μ-star polymers via the formyl or α-phenylacrylate reaction site(s).

Living Anionic Polymerization of 1‐Adamantyl 4‐vinylphenyl ketone

The anionic polymerization of 1-adamantyl 4-vinylphenyl ketone (1), a styrene derivative carrying an electrophilic carbonyl group, is carried out in tetrahydrofuran (THF). Although no polymerization of 1 occurs with sec-BuLi at −78 °C for 48 h, a polymeric product of 1 is obtained with diphenylmethyllithium in 10% yield under similar conditions. The resulting poly(1) has a very broad molar-mass dispersity (Đ M = M w/M n = 1.72) and a molecular weight higher than the calculated value based on the molar ratio of the monomer and initiator and the conversion. On the other hand, the polymerization of 1 with diphenylmethylpotassium or diphenylmethylcesium quantitatively proceeds in THF at −78 °C within 48 h to form the polymers with predicted molecular weights and narrow molecular weight distributions (M w/M n < 1.1). The stability of the propagating carbanion derived from 1 is demonstrated by the quantitative efficiency of the postpolymerization (sequential monomer addition). The reaction of the adamantyl ketone moieties of poly(1) with methylmagnesium iodide quantitatively proceeds in THF/diethyl ether at room temperature, indicating the high electrophilicity of ketone groups. The resulting poly(1) has a high glass transition temperature at 193 °C, indicating the effect of the bulky adamantyl substituent.

Facile modification and fixation of diaryl disulphide-containing dynamic covalent polyesters by iodine-catalysed insertion-like addition reactions of styrene derivatives to disulphide units

We report the modification of diaryl disulphide-containing dynamic covalent polyesters (DADS-PEs) via an iodine-catalysed addition reaction with styrene derivatives that proceeds in an insertion-like manner. The simple procedure of these reactions enabled facile control of the primary structure and physical properties of DADS-PEs by using various styrene derivatives with several polar substituents, flexible oligomeric chains, and two vinyl functionalities that work as a cross-linker. The addition reactions were also found to be an efficient method for “fixing” the polymer structure via conversion of dynamic diaryl disulphide bonds, which are susceptible to bond exchange reactions under photo-irradiation.

Iron Oxide Arrays Prepared from Ferrocene- and Silsesquioxane-Containing Block Copolymers

Arrays of iron oxides as precursors of iron clusters were prepared by oxygen plasma treatment of block copolymer microphase-separated nanostructures in thin films. Block copolymers composed of ferrocene-containing and silsesquioxane-containing polymethacrylate (PMAPOSS-b-PMAHFC) were successfully prepared, with different molecular weights and compositions and narrow molecular weight distributions, by living anionic polymerization. The formed microphase-separated nanostructures in the bulk were characterized by wide- and small-angle X-ray scattering (WAXS and SAXS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Thin films were prepared from a solution of PMAPOSS-b-PMAHFC in tetrahydrofuran by spin coating onto silicon wafers. Fingerprint-type line nanostructures were formed in the PMAPOSS-b-PMAHFCs thin films after solvent annealing with carbon disulfide. Oxygen plasma treatment provided the final line arrays of iron oxides based on the formed nanostructural patterns.