Resistance switching memory devices with the configuration of poly(ethylene naphthalate)(PEN)/Al/polyimide (PI) blend/Al are reported. The active layers of the PI blend films were prepared from different compositions of poly[4,4'-diamino-4″-methyltriphenylamine-hexafluoroisopropylidenediphthalimide] (PI(AMTPA)) and polycyclic aromatic compounds (coronene or N,N-bis[4-(2-octyldodecyloxy)phenyl]-3,4,9,10-perylenetetracarboxylic diimide (PDI-DO)). The additives of large π-conjugated polycyclic compounds can stabilize the charge transfer complex induced by the applied electric field. Thus, the memory device characteristic changes from the volatile to nonvolatile behavior of flash and write-once-read-many times (WORM) as the additive contents increase in both blend systems. The main differences between these two blend systems are the threshold voltage values and the additive content to change the memory behavior. Due to the stronger accepting ability and higher electron affinity of PDI-DO than those of coronene, the PI(AMTPA):PDI-DO blend based memory devices show a smaller threshold voltage and change the memory behavior in a smaller additive content. Besides, the memory devices fabricated on a flexible PEN substrate exhibit an excellent durability upon the bending conditions. These tunable memory performances of the developed PI/polycyclic aromatic compound blends are advantageous for future advanced memory device applications.

Cross-linked liquid crystalline (LC) polyimides with siloxane units have been developed as high thermally conductive materials. The relationship between their thermal diffusivities and film morphologies was investigated. The crosslinking reaction of the LC polyimides was monitored by Fourier transform infrared spectroscopy and differential scanning calorimetry. It was found that the cross-linked LC polyimides successfully maintained their LC structures at room temperature as confirmed by polarized optical microscopy and wide-angle X-ray diffraction (WAXD). The thermal diffusivity of the films in the thickness direction measured by a temperature wave analysis method increased gradually from 0.116 to 0.185 mm 2 s −1 with the increasing extent of the crosslinking. In the detailed WAXD study, the obtained cross-linked LC polyimide films showed that the polymer chains vertically aligned in the thickness direction of the films, and the increase in the extent of the cross-linking expanded the areas of chain alignment. Such a chain alignment plays an important role in the phonon conduction in the thickness direction of the films.

Novel siloxane-containing liquid crystalline (LC) polyimides with methyl, chloro, and fluoro substituents on mesogenic units have been developed from siloxane-containing diamines with pyromellitic dianhydride (PMDA) or 3,3 0 ,4,4 0 -tetracarboxybiphenyl dianhydride (BPDA), and their thermotropic LC behavior was examined. Among these, chloro and fluoro substituents are effective for the formation of LC phases, particularly when those are substituted away from the center of the mesogenic unit: the isotropization temperature is not much affected, but the crystal-LC transition temperatures are significantly decreased. On the other hand, the methyl substituent tends to interrupt liquid crystallization as well as crystallization. Thus, the fluoro-substituted polyimide derived from BPDA exhibited the lowest crystalline-LC transition temperature (T cr-lc = 134 °C) among all polyimides, showing a wide liquid crystal temperature up to 238 °C. From the X-ray diffraction measurement conducted for the oriented mesophases of fibrous polyimides, they were found to form SmA and SmC as high-and low-temperature mesophases, respectively.

Running Head: Synthesis of PolyimidesSynthesis and characterization of 1b-1c, 2b-2e, 3b-3e, and 6a-6j. Synthesis of 4-(5-Hexenyloxy)nitrobenzene (1b).The title compound, 1b, was synthesized by the same procedure as 1a performed with 2.79 g (20.0 mmol) of 4-nitrophenol, 4.15 g (30.1 mmol) of K 2 CO 3 , 4.01 g (24.6 mmol) of 6-bromo-1-hexene, and 40 mL of CH 3 CN. The compound, 1b, (4.11 g, 93% yield) was then isolated as a yellow oil after the vacuum.

The synthesis of poly(m‐phenyleneisophthalamide) was performed by thermal solid‐phase polymerization from isophthalic acid and m‐phenylenediamine without using any solvents or condensation agents. The two‐stage heating process was conducted. The oligo(m‐phenyleneisophthalamide) was first synthesized at a relatively low temperature (260 °C for 1 h), followed by the polycondensation at 400 °C for 1 min under reduced pressure to produce the aramid with an inherent viscosity of 0.55 dL/g.

Hexagonal boron nitride (h-BN) composites with the oriented cross-linked liquid crystalline (LC) polyimide have been developed as high thermally conductive materials. Well-dispersed h-BN composite films were obtained, as observed by scanning electron microscopy. The morphology of the composite films was further investigated in detail by the wide-angle X-ray diffraction. The obtained composite films based on the cross-linked LC polyimide showed that the polymer chains vertically aligned in the direction parallel to the films, while those based on the amorphous polyimide showed an isotropic nature. Moreover, the alignment of the cross-linked LC polyimides was maintained, even after increasing the volume fraction of h-BN. This alignment plays an important role in the effective phonon conduction between h-BN and the matrices. Indeed, the thermal diffusivity in the thickness direction of the composite films based on the LC polyimide measured by a temperature wave analysis method was increased to 0.679 mm(2) s(-1) at a 30 vol % h-BN loading, which was higher than that based on the amorphous polyimide.

Thermotropic liquid crystalline (LC) semi-aliphatic polyimides have been developed from 3,3′,4,4′-tetracarboxybiphenyl dianhydride (BPDA) and diamines containing siloxane spacer units. These polyimides exhibited high thermal stability and lower transition temperature compared to the corresponding polyimides containing alkyl or oxyethylene spacer units.

We investigated the phase transition behavior and liquid-crystalline structure for main-chain liquidcrystalline polyimides with aromatic imide cores and alkyl and dimethyl siloxane spacers, BPDA/ 3SiO4-3F. They formed crystal, smectic C (S C ), smectic A (S A ), and isotropic phases in order of increasing temperature. The characteristic structures of the S A and S C phases were extracted with wideangle X-ray diffraction (WAXD) and Fourier transform infrared (FTIR) spectroscopy measurements. In the S C phase, the mesogenic groups were tilted by approximately 40 to the smectic layer and the unusual quasi two-dimensional structural order exists irrespective of the liquid-like packing of aromatic cores within a layer. On heating, the S C phase transformed into the S A phase with a nature of first-order transition. The resulting S A structure was also unusual. The orientational order parameter was 0.43, which was lower than 0.71 in the S C phase. This indicates that a ''de Vries''-type of smectic A is formed in which the mesogenic groups are tilted away from the optic axis, but in azimuthally random directions. The average tilt angle was estimated to be 42 . These characteristics were produced because of the strong segregation effect of the dimethyl siloxane spacer groups with a relatively larger molecular area compared to alkyl chain and aromatic imide cores.BPDA/3SiO4-3F, which has an F-substituted BPDA mesogenic unit. In this paper, we report the nature of the S A -S