Synthesis and nonvolatile memory characteristics of thermally, dimensionally and chemically stable polyimides

High-performance non-volatile resistive switching memory based on a polyimide/graphene oxide nanocomposite

Chemical structure of PI-GO, schematic structure of the ITO/PI-GO/Al device and its memory characteristics.

Fabrication and characterization of a high performance polyimide ultrafiltration membrane for dye removal

Membrane separation technology is one of the cost effective and most efficient technologies for treatment of wastewater from textile industry. However, development of membranes with better performance and thermal stability is still a highly challenging task. In this study, successful preparation of a novel thermally stable polyimide (PI) polymer was demonstrated using 2,4,6-trimethyl-1,3-phenylenediamine, 4,4'-diaminodiphenylmethane and 1,2,4,5-benzenetetracarboxylic dianhydride components. PI was selected as representative candidate because of its excellent thermal stability (decomposition temperature of 529 °C), as revealed by thermogravimetric analysis. Furthermore, PI polymer was used to fabricate ultrafiltration (UF) membrane by phase inversion process. This UF membrane is especially interesting as it allowed for almost complete penetration of monovalent (NaCl) and divalent (Na₂SO₄) inorganic salts because of its molecular weight cut off of 9320 Da. Moreover, the membrane exhibited very good surface hydrophilicity with the water contact angle of 67.6°. This PI-based UF membrane was found to be substantially effective as it showed high pure-water and dye-permeation fluxes of 345.10 and 305.58 L m^-2 h^-1 at 0.1 MPa, respectively. Besides, the membrane exhibited a rejection of 98.65% toward the direct red 23 dye (100 ppm) at 0.1 MPa. Thus, this PI-based UF membrane is highly beneficial and acts as a potential candidate for dye removal from wastewater produced by textile industry.

Fabrication of low dielectric constant polyimide/TiO2 nanofibers with enhanced UV-light shielding properties

Polyimide (PI)/titanium dioxide (TiO2) composite nanofibers (NFs) with average diameters of 200–250 nm were synthesized via electrospinning. The total number density of dipoles decreased significantly, owing to the porous structures and compact interface between TiO2 NPs and PI matrix. All PI/TiO2 NFs maintain low dielectric constants and losses. For example, the dielectric constants of PI/TiO2-6% NFs are all lower than 2.6, being exposed to temperatures from 25°C to 200°C. Meantime, the dielectric losses of PI/TiO2-6% NFs are below 0.005. For ultraviolet (UV)-light shielding performance, the PI/TiO2 NFs exhibited good UV-light shielding and corresponding anti-photoaging properties. The reason can be ascribed from high UV-light absorption and scattering ability in the TiO2 NPs. The best UV-light absorption (average: 3.71) and corresponding absorption decay (15.13%) were achieved for optimized PI/TiO2-6% NFs. Other fundamental characteristics, such as the thermal stability, mechanical tensile property, and hydrophobicity, were also investigated. Such low dielectric constant PI/TiO2 composite NFs can be alternatively chosen under a longtime UV-light exposing condition.

Preparation and properties of highly organosoluble polyimides derived from 2,2′-disubstituted-4,4′-oxydianilines

Four novel aromatic, symmetrical ether diamines (2,2′-bis(biphenyl)-4,4′-oxydianiline, 2,2′-bis[4′-(3″,4″,5″-trifluorophenyl)phenyl]-4,4′-oxydianiline, 2,2′-bis[4-(naphthalene-1-yl)phenyl]-4,4′-oxydianiline, and 2,2′-bis[4″-(diphenylamino)phenyl]-4,4′-oxydianiline), were successfully synthesized through four steps using p-chloronitrobenzene as a starting material. Highly organosoluble polyimides were obtained by the reaction of these diamines with 2′2 ′-bis[4′-(3″,4″,5″-trifluorophenyl)phenyl]-4,4′,5,5′-biphenyltetracarboxylic dianhydride via a conventional two-step chemical imidization method. All the polyimides were thoroughly characterized by Fourier transform infrared, ultraviolet, fluorescence, gel permeation chromatography, and thermogravimetric analysis. The effect of the fluorine atoms directly linked to the lateral phenyl rings showed excellent dissolution and strong fluorescence. The polyimides exhibited excellent thermal stability, with decomposition temperatures (at 10% weight loss) above 530°C and glass transition temperatures in the range of 258–320°C. These outstanding combined features ensured that these polyimides could be used as memory materials for advanced microelectronic applications.

Highly transparent and organosoluble polyimides derived from 2,2′-bis[4-(5-amino-2-pyridinoxy) phenyl] propane

Two new isomers containing pyridine ring diamine monomers, 2,2′-bis[4-(5-amino-2-pyridinoxy)phenyl] propane (1b) and 2,2′-bis[4-(6-amino-3-pyridinoxy)phenyl] propane (2b), were prepared via a simple nucleophilic reaction of 2-chloro-5-nitropyridine and 5-bromo-2-nitropyridine with bisphenol A in the presence of potassium carbonate, respectively. A series of polyimides (PIs) were obtained from the heterocyclic diamine with various commercially available aromatic dianhydrides via the conventional two-step method. These obtained PIs were investigated in aspects of their solubility, thermal, mechanical, and optical properties for studying the effects of the heteroaromatic rings into the main chain. At the same time, the impact of the two isomers introduced into the PI was discussed in detail.

Linkage and donor–acceptor effects on resistive switching memory devices of 4-(N-carbazolyl)triphenylamine-based polymers

In order to gain deeper insight about the linkage effect and donor–acceptor effect on memory behavior (from DRAM to WORM), 4-(N-carbazolyl)triphenylamine-based polyimides and polyamides were synthesized and their memory behaviours were investigated.

Clues to the electrical switching mechanism of carbazole-containing polyimide thin films

The mechanism behind electrical memory behavior of carbazole-containing polyimides (PIs) in nanoscale thin films was investigated. For this investigation, a series of poly(3,3'-dihydroxy-4,4'-biphenylene-co-3,3'-bis(N-ethylenyloxycarbazole)-4,4'-biphenylene hexafluoro-isopropylidenedi-phthalimide)s (6F-HAB-HABCZn PIs) with various compositions was synthesized as a model carbazole-containing polymer system. The thermal properties, band gaps, and molecular orbital levels of the PIs were determined. Furthermore, the chemical compositions, as well as the nanoscale thin film morphologies and electron densities, were analyzed, providing detailed information on the population and positional distribution of carbazole moieties in thin films of the PIs. PI Devices were fabricated with aluminum electrodes and tested electrically. The PI thin film layers in the devices exhibited electrically permanent memory behavior, which was driven by trap-limited space-charge limited conduction and ohmic conduction. The permanent memory characteristics were found to be attributed to the incorporated carbazole moieties rather than from the other chemical components. Furthermore, the memory characteristics depended significantly on the population and positional distribution of carbazole moieties in the PI layer, as well as the film thickness. Considering that the backbone is not conjugated, the present results collectively indicate that the electrical switching behavior of the PI films is driven by the carbazole moieties acting as charge traps and a hopping process using the carbazole charge-trap sites as stepping-stones.

Synthesis and characterization of ternary copolyimides derived from aromatic dianhydride and aromatic diisocyanates

A series of polyimide (PI) copolymers were synthesized via a one-step polycondensation procedure from benzophenone-3,3′,4,4′-tetracarboxylic acid dianhydride, toluene diisocyanate (TDI), and 4,4′-methylene bis(phenyl isocyanate) (MDI) with various mole ratios of TDI and MDI ranging from 70:30 to 100:0. The inherent viscosities of the resulting PIs were in the range of 0.51–0.80 dL g−1. The prepared PIs showed good solubility in common organic as well as in less polar solvents. All copolymers afforded tough and flexible films that had good thermal stability with glass transition temperature of 308–325°C and the temperatures of 5% weight loss in air and nitrogen being 420 and 460°C, respectively. The resultant PI films with thickness about 15 μm exhibited high transparency (>88%) in visible region (400–700 nm). Also, the cured PI films possessed good mechanical properties with tensile strength of 60.52–69.31 MPa and tensile modulus of 0.98–1.30 GPa.

Polymer-based resistive memory materials and devices

Due to the advantages of good scalability, flexibility, low cost, ease of processing, 3D-stacking capability, and large capacity for data storage, polymer-based resistive memories have been a promising alternative or supplementary devices to conventional inorganic semiconductor-based memory technology, and attracted significant scientific interest as a new and promising research field. In this review, we first introduced the general characteristics of the device structures and fabrication, memory effects, switching mechanisms, and effects of electrodes on memory properties associated with polymer-based resistive memory devices. Subsequently, the research progress concerning the use of single polymers or polymer composites as active materials for resistive memory devices has been summarized and discussed. In particular, we consider a rational approach to their design and discuss how to realize the excellent memory devices and understand the memory mechanisms. Finally, the current challenges and several possible future research directions in this field have also been discussed.