Structure and properties of aromatic poly(benzimidazole‐imide) copolymer fibers

A series of co‐polyimide fibers were prepared by thermal imidization of copolyamic acids derived from 3,3′,4,4′‐biphenyltertracarboxylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA) in various molar ratios with 2‐(4‐aminophenyl)?5‐aminobenzimidazole (BIA). The dynamic mechanical behaviors of these polyimide (PI) fibers revealed that the glass transition temperature (T_g) was significantly improved upon increasing PMDA content. Heat‐drawing process led to dramatic change on the glass transition behavior of BPDA/BIA system, but had a small impact on BPDA/PMDA/BIA co‐polyimide fibers. This difference for PI fibers is attributed to the different degree of ordered structure of the fibers affected by heat‐drawing. The incorporation of PMDA obviously improved the dimensional stability against high temperature, due to the restricted movement of polymer chains. In addition, the obtained fibers show excellent mechanical and thermal properties because of the strong hydrogen bonding due to the incorporation of benzimidazole moieties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41474.     

Polyimide fibers prepared by a dry‐spinning process: Enhanced mechanical properties of fibers containing biphenyl units

Polyimide (PI) fibers with enhanced mechanical properties and high thermal and dimensional stability were prepared via a two‐step dry‐spinning process through the introduction of 3,3′,4,4′‐biphenyl tetracarboxylic dianhydride (BPDA) containing biphenyl units into rigid homopolyimide of pyromellitic dianhydride (PMDA) and 4,4′‐oxydianiline. The attenuated total reflectance–Fourier transform infrared spectra results imply that the incorporated BPDA moieties accelerate the imidization process and increase the imidization degree (ID) of the precursor fibers; this was attributed to the increased molecular mobility of the polymer chains. Two‐dimensional wide‐angle X‐ray diffraction spectra indicated that the prepared PI fibers possessed a well‐defined crystal structure and polymer chains in the crystalline region were highly oriented along the fiber axis. The PI fiber, with the molar ratio of PMDA/BPDA being 7/3, showed optimum tensile strength and modulus values of 8.55 and 73.21 cN/dtex, respectively; these were attributed to the high IDs and molecular weights. Meanwhile, the PI fibers showed better dimensional stability than the commercial P84 fiber, and this is beneficial for its security applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43727.     

Ortho alkyl substituents effect on solubility and thermal properties of fluorenyl cardo polyimides

Five fluorenyl cardo diamines containing different alkyl substituents were synthesized and characterized. A series of fluorenyl cardo polyimides were prepared by polycondensation of these cardo diamines with 4,4′-oxydiphthalic anhydride (ODPA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 3,3′,4,4′-biphenyl tetracarboylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA). Most of fluorenyl cardo polyimides exhibited excellent solubility in common organic solvents such as m-cresol, chloroform, tetrahydrofuran (THF), N-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAC) etc. and intrinsic viscosity in N,N-dimethylacetamide (DMAC) ranged from 0.31 to 0.92 dl/g. T_g of polyimides based on ODPA decrease with the number and size of alkyl substituents on fluorenyl cardo diamine. The results show that the incorporation of noncoplanar structure led by the introducing alkyl substituents on fluorenyl cardo diamines improves the solubility of cardo polyimides in organic solvents without sacrificing thermal properties.     

A study of the stabilization of vertical alignment for liquid crystals by increasing the side‐chain rigidity of polyimides

A series of polyimides (PIs) with various side‐chain structures were prepared via copolymerization of pyromellitic dianhydride, 3,3′‐dimethyl‐4,4′‐methylenediamine and three functional diamines: 4‐(4‐octyloxybenzoyloxy)biphenyl‐3′,5′‐diaminobenzoate (C8‐BPDA), 4‐octyloxybiphenyl‐3′,5′‐diaminobenzoate (C8‐PDA) and 4‐(4‐butoxybenzoyloxy)biphenyl‐3′,5′‐diaminobenzoate (C4‐BPDA). PIs derived from C8‐BPDA and C4‐BPDA exhibited excellent rubbing resistance in comparison with PI from C8‐PDA and the pretilt angle could be controlled over 89° after rubbing. Thermogravimetric analysis showed that the thermal degradation of PIs under nitrogen atmosphere occurred above 320 °C, and PI derived from C8‐BPDA showed the best thermal stability. Wide‐angle X‐ray diffraction patterns indicated an amorphous morphology of the PIs, and the PIs also had outstanding solubility in polar aprotic solvents. The resultant PI films were light colored and maintained high transparency in the visible light region. By increasing the rigidity of side‐chains, the rubbing resistance and the thermal stability of PIs could be promoted at the same time. © 2012 Society of Chemical Industry     

Electrically bistable digital memory behaviors of thin films of polyimides based on conjugated bis(triphenylamine) derivatives

Three functional polyimides (PIs) bearing conjugated bis(triphenylamine) (2TPA) derivatives with electron-donating and accepting groups were synthesized with reasonably high molecular weights. The PIs exhibited high thermal and dimensional stabilities and furthermore produced high-quality nanoscale thin films via conventional solution coating process. All of the PIs in the films were found to be amorphous, but they were oriented somewhat preferentially in the film plane, rather than randomly. Their film densities and interchain distances were measured, and the optical and electrochemical properties were determined. All of the PIs in the devices with aluminum top and bottom electrodes initially revealed a high resistance (OFF-state). However, under positive and negative voltage sweeps, the PIs demonstrated volatile or nonvolatile digital memory behavior, depending on the substituents of the 2TPA unit. The 2TPA-based PI, as well as the PI bearing 2TPA with electron-donating methoxy substituents showed unipolar write-once-read-many-times (WORM) memory behavior, whereas the 2TPA-based PI containing electron-accepting cyano groups exhibited unipolar dynamic random access memory (DRAM) behavior. All of the PI films revealed excellent retention abilities in both the OFF- and ON-state, even under ambient air conditions. Moreover, they all revealed high ON/OFF current ratios (10⁶–10¹⁰). All of the memory behaviors were found to be governed by a mechanism involving trap-limited space-charge limited conduction and local filament formation. Such memory behaviors were further investigated in detail with taking into consideration the PI components' chemical nature and molecular orbital levels, possible trapping sites, substituents' effect, and the metal electrodes' work function. Overall, this study demonstrated that the thermally, dimensionally stable PIs are highly suitable for the low-cost mass production of high performance, polarity-free digital memory devices that can be operated with very low power consumption. Moreover, the memory mode can be tuned by changing the substituent in the 2TPA unit.     

Imide oligomers having internal acetylene units in the backbone

Imide oligomers having internal acetylene groups in the backbone were prepared utilizing bis(3-aminophenyl)acetylene as an internal acetylene source. 2,2′-Bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), pyromellitic dianhydride (PMDA), 3,3′,4,4′-benzophenontetracarboxylic dianhydride (BTDA), and 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) were used as acid dianhydride monomers. Amine-terminated oligomers with average degree of polymerization (DP) of 3, 5, and I 1 were prepared by controlling the ratio of monomers, and were end-capped with phthalic anhydride. Anhydride-terminated oligomers were similarly prepared and were end-capped with aniline. Imidization was conducted by refluxing in toluene. The DSC of the oligoimides containing internal acetylene units showed exotherm due to the crosslinking reaction of acetylene units. Onset temperature of the exotherm was 300–370°C, depending on the chemical structure and DP of oligoimide. By the thermal cure at high temperatures, the amount of exotherm decreased and exotherm shifted to higher temperature. Melt-processing of the oligoimides was carried out using a hydraulic press at 400°C. Melt-processed films were dark brown, opaque, and somewhat brittle. The films became less brittle with the increase of the DP of the oligomers. The films showed excellent thermal properties; T_g's were above 375°C, and their films maintained their mechanical properties aboveT_g.     

Residual stress and mechanical properties of polyimide thin films

Four different structure polyimide thin films based on 1,4‐phenylene diamine (PDA) and 4,4′‐oxydianiline (ODA) were synthesized by using two different dianhydrides, pyromellitic dianhydride (PMDA) and 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), and their residual stress behavior and mechanical properties were investigated by using a thin film stress analyzer and nanoindentation method. The residual stress behavior and mechanical properties were correlated to the morphological structure in polyimide films. The morphological structure of polyimide thin films was characterized by X‐ray diffraction patterns and refractive indices. The residual stress was in the range of ?5 to 38 MPa and increased in the following order: PMDA‐PDA < BPDA‐PDA < PMDA‐ODA < BPDA‐ODA. The hardness of the polyimide films increased in the following order: PMDA‐ODA < BPDA‐ODA < PMDA‐PDA < BPDA‐PDA. The PDA‐based polyimide films showed relatively lower residual stress and higher hardness than the corresponding ODA‐based polyimide films. The in‐plane orientation and molecularly ordered phase were enhanced with the increasing order as follows: PMDA‐ODA < BPDA‐ODA < BPDA‐PDA ～ PMDA‐PDA. The PDA‐based polyimides, having a rigid structure, showed relatively better‐developed morphological structure than the corresponding ODA‐based polyimides. The residual stress behavior and mechanical properties were correlated to the morphological structure in polyimide films. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Properties of copolyimides prepared from different tetracarboxylic dianhydrides and diamines

Various copolymides were prepared from two acid dianhydrides (BPDA, 3,3′,4,4′-biphenyl tetracarboxylic dianhydride; PMDA, pyromelitic dianhydride) and two diamines (PPD, p-phenylene diamine; ODA, 4,4′-oxydianiline). The thermal and mechanical properties of these polyimides were examined in detail. By appropriately selecting the ratios of the acid dianhydride component and the diamine component, polyimide films having desirable mechanical and thermal characteristics can be obtained. Further, it was proved that there is a correlation between the properties and the compositions of the copolyimides and that the properties could be estimated from the compositions by the use of multiple regression analysis. © 1996 John Wiley & Sons, Inc.     

Novel polyimides derived from 2,3,3′,4′-benzophenonetetracarboxylic dianhydride

A series of polyimides (PIs) based on 2,3,3′,4′-benzophenonetetracarboxylic dianhydride (2,3,3′,4′-BTDA) and 3,3′,4,4′-BTDA were prepared by the conventional two-step process. The properties of the 2,3,3′,4′-BTDA based polyimides were compared with those of polyimides prepared from 3,3′,4,4′-BTDA. It was found that PIs from 2,3,3′,4′-BTDA have higher glass transition temperature and better solubility without sacrificing their thermal properties. Furthermore the rheological properties of PMR-15 type polyimide resins based on 2,3,3′,4′-BTDA showed lower melt viscosity and wider melt flow region (flow window) compared with those from 3,3′,4,4′-BTDA. The structure-property relations resulted from isomerism were discussed.     

Highly Thermal Stable Polyimides Applied in Flexible Resistive Memory

Flexible memory devices are one of the most crucial elements in the wearable electronics. In this work, polyimides (PIs)-based flexible resistive memory devices with an excellent thermal and mechanical durability are demonstrated. Four kinds of functional PIs are derived from the heterocyclic diamines including 2,6-diaminodibenzo-p-dioxin (OODA) and 2,6-diaminothianthrene, and dianhydrides including 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3′,4,4′-biphenyltetracarboxylic dianhydride. PI with diamine of OODA and dianhydride of 6FDA (PI(OODA_6FDA)) possesses outstanding thermal and mechanical properties with a high glass transition temperature of 352 °C, a low coefficient of thermal expansion of 28.1 ppm K⁻¹, and a high elongation at break of 10%. In addition, PI(OODA_6FDA)-based memory shows write-once-read-many behavior with a high on/off current ratio of 10⁶ and a stable data retention, attributed to the donor–acceptor charge transfer between the polymer chains. The retained current levels at a low resistive state can be observed even with thermal treatment at 200 °C for 24 h or 1000 times cyclic bending at a bending radius of 5 mm. These results demonstrate the potential of heterocyclic PIs for flexible resistive memory.     

Microstructure and properties of polyimide/poly(vinylsilsesquioxane) hybrid composite films

Polyimide (PI)/poly(vinylsilsesquioxane) (PVSSQ) (PI/PVSSQ) hybrid composite films were prepared from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)-4,4′-oxydianiline (ODA) polyamic acid and triethoxyvinylsilane (TEVS or VSSQ) via sol-gel process and thermal imidization. The presence of the PVSSQ showed a remarkable effect on the microstructure and properties of the polyimide based hybrid films. The transparency of the hybrid films decreased with increasing the content of the PVSSQ. The compatibility and interfacial interaction of the hybrid composites were evaluated by scanning electron microscope (SEM) and atomic force microscope (AFM), respectively. The PI/PVSSQ hybrids showed nanocomposite formation when the contents of PVSSQ was less than 20 wt%. It was found that the surface topography was influenced by the composition of the PVSSQ. Incorporating of the PVSSQ increased the thermal stability and T_g of hybrid composites. The dielectric constant of the hybrid composites was reduced by adding PVSSQ up to a certain content, showed a minimum and then found to be increased. The dielectric constant values of the hybrid composites ranged from 2.59 to 3.78. The presence of the PVSSQ also showed significant effects on the mechanical properties of the polyimide films.     

Synthesis and characterization of polyimides and co-polyimides having pendant benzoic acid moiety

A novel diamine monomer, 2,4-diamino-4′-carboxy diphenyl ether had been synthesized. Several polyimides were prepared by reacting this diamine with commercially available dianhydrides, such as benzophenone tetracarboxylic acid dianhydride (BTDA), 4,4′-bis{hexafluoroisopropylidene bis (phthalic anhydride)}(6-FDA), oxydiphthalic anhydride (ODPA) and 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (BPDA). Furthermore, copolymers from the resulting diamine and oxydianiline (ODA) with 6 FDA were also synthesized. The inherent viscosities of the polymers were 0.42-0.67 dl g⁻¹. The polymers have good solubility in polar aprotic solvents, high thermal stability up to 410 °C in nitrogen and high glass transition temperatures (T_g) ranging from 260-330 °C. These polymers formed tough flexible films by solution casting.     

Synthesis and properties of organosoluble polyimides based on 2,2′-diphenoxy-4,4′,5,5′-biphenyltetracarboxylic dianhydride

A novel method for the preparation of 2,2′-diphenoxy-4,4′,5,5′-biphenyltetracarboxylic dianhydride have been investigated. This new dianhydride contains flexible phenoxy side chain and a twist biphenyl moiety and it was synthesized by the nitration of an N-methyl protected 3,3′,4,4′-biphenyltetracarboxylic dianhydride and subsequent aromatic nucleophilic substitution with phenoxide. The overall yield was up to 75%. The dianhydride was polymerized with five different aromatic diamines to afford a series of aromatic polyimides. The polyimide properties such as inherent viscosity, solubility, UV transparency and thermaloxidative properties were investigated to illustrate the contribution of the introduction of phenoxy group at 2- and 2′-position of BPDA dianhydride. The resulting polyimides possessed excellent solubility in the fact that the polyimide containing rigid diamines such as 1,4-phenylenediamine and 4,4′-oxydianiline were soluble in various solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, dimethyl sulfoxide and chloroform. The glass-transition temperatures of the polymers were in the range of 255-283 °C. These polymers exhibited good thermal stability with the temperatures at 5% weight loss range from 470 to 528 °C in nitrogen and 451 to 521 °C in air, respectively. The polyimide films were found to be transparent, flexible, and tough. The films had a tensile strength, elongation at break, and Young's modulus in the ranges 105-168 MPa, 15-51%, 1.87-2.38 GPa, respectively.     

Effect of montmorillonite on thermal and moisture absorption properties of polyimide of different chemical structures

The thermal properties and the moisture absorption of three types of polyimide/montmorillonite nanocomposite were investigated: 3,3′,4,4′‐biphenyltetracarboxylic dianhydride‐4,4′‐oxydianiline (BPDA‐ODA); pyromellitic dianhydride‐ODA (PMDA‐ODA); and 3,3′,4,′‐benzophenone tetracarboxylic dianhydride‐ODA (BTDA‐ODA). The inhibition effect on in‐plane coefficients of thermal expansion (CTE) and moisture absorption of these polyimide nanocomposites by layered silicates from montmorillonite was found to decrease with the crystallinity in the pristine polyimides. The largest reduction, 30% in in‐plane CTE occurred in the case of amorphous BTDA‐ODA containing 5 wt % montmorillonite as compared with that of pure BTDA‐ODA, while the reduction in in‐plane CTE was 20% for the case of semicrystalline BPDA‐ODA. The maximum reduction in moisture absorption, 43%, also took place for the case of 3/97 ODA‐Mont/BTDA‐ODA as compared with that of pure BTDA‐ODA, whereas the semicrystalline 1/99 PPD‐Mont/BPDA‐ODA showed a 30% reduction as compared with that of pure BPDA‐ODA. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1742–1747, 2001     

Syntheses and properties of polyimides derived from diamines containing 2,5‐disubstituted pyridine group

A series of novel homo‐ and copolyimides containing pyridine units were prepared from the heteroaromatic diamines, 2,5‐bis (4‐aminophenyl) pyridine and 2‐(4‐aminophenyl)‐5‐aminopyridine, with pyromelltic dianhydride (PMDA), and 3,3′, 4,4′‐biphenyl tertracarboxylic dianhydride (BPDA) via a conventional two‐step thermal imidizaton method. The poly(amic acid) precursors have inherent viscosities of 1.60–9.64 dL/g (c = 0.5 g/dL in DMAC, 30°C) and all of them can be cast and thermally converted into flexible and tough polyimide films. All of the polyimides show excellent thermal stability and mechanical properties. The polyimides have 10% weight loss temperature in the range of 548–598°C in air. The glass transition temperatures of the PMDA‐based samples are in the range of 395–438°C, while the BPDA‐based polyimides show two glass transition temperatures (T_g1 and T_g2), ranging from 268 to 353°C and from 395 to 418°C, respectively. The flexible films possess tensile modulus in the range of 3.42–6.39 GPa, strength in the range of 112–363 MPa and an elongation at break in the range of 1.2–69%. The strong reflection peaks in the wide‐angle X‐ray diffraction patterns indicate that the polyimides have a high packing density and crystallinity. The polymer films are insoluble in common organic solvents exhibiting high chemical resistance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1844–1851, 2006     

Syntheses and properties of novel polyimides derived from 2‐(4‐Aminophenyl)‐5‐aminopyrimidine

2‐(4‐Aminophenyl)‐5‐aminopyrimidine (4) is synthesized via a condensation reaction of vinamidium salts and amidine chloride salts, followed by hydrazine palladium catalyzed reduction. A series of novel homo‐ and copolyimides containing pyrimidine unit are prepared from the diamine and 1,4‐phenylenediamine (PDA) with pyromellitic dianhydride (PMDA) or 3,3′,4,4′‐biphenyl tertracarboxylic dianhydride (BPDA) via a conventional two‐step thermal imidization method. The poly(amic acid) precursors had inherent viscosities of 0.97–4.38 dL/g (c = 0.5 g/dL, in DMAc, 30°C) and all of them could be cast and thermally converted into flexible and tough polyimide films. All of the polyimides showed excellent thermal stability and mechanical properties. The glass transition temperatures of the resulting polyimides are in the range of 307–434°C and the 10% weight loss temperature is in the range of 556–609°C under air. The polyimide films possess strength at break in the range of 185–271 MPa, elongations at break in the range of 6.8–51%, and tensile modulus in the range of 3.5–6.46 GPa. The polymer films are insoluble in common organic solvents, exhibiting high chemical resistance. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 5871–5876, 2006     

Synthesis and properties of fluorinated polyimides from 1,1‐bis(4‐amino‐3,5‐dimethylphenyl)‐1‐(3,4,5‐trifluorophenyl)‐2,2,2‐trifluoroethane and various aromatic dianhydrides

A novel aromatic diamine, 1,1‐bis(4‐amino‐3,5‐dimethylphenyl)‐1‐(3,4,5‐trifluorophenyl)‐2,2,2‐trifluoroethane, containing a pendant polyfluorinated phenyl group, a trifluoromethyl group, and methyl groups ortho‐substituted to the amino groups in the structure was synthesized and characterized. The diamine was polymerized with several aromatic dianhydrides, including 3,3′,4,4′‐biphenyltetracarboxylic dianhydride, 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride, 4,4′‐oxydiphthalic anhydride, and 4,4′‐hexafluoroisopropylidene diphthalic anhydride, via a high‐temperature one‐step procedure to afford four polyimides (PIs) with inherent viscosities of 0.47–0.70 dL/g. The PIs exhibited excellent solubilities in a variety of organic solvents. They were soluble not only in polar aprotic solvents but in many common solvents, such as cyclopentanone, tetrahydrofuran, and even toluene at room temperature. The tough and flexible PI films cast from the PI solutions exhibited good thermal stabilities and acceptable tensile properties. The glass‐transition temperatures were in the range 312–365°C, and the 5% weight loss temperatures were all higher than 480°C in nitrogen. The films had tensile strengths in the range 76–99 MPa, tensile moduli of 2.2–2.8 GPa, and elongations at break of 5–8%. In addition, the PI films exhibited excellent transparency in the visible light region with cutoff wavelength as low as 302 nm and transmittance higher than 88% at the wavelength of 450 nm. The PI films showed low dielectric constants ranging from 2.50–2.68 and low moisture absorptions of less than 0.56%. The good combined properties of the PIs mainly resulted from the synergic effects of the different substituents. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Copolyimides from 2,3,3′,4′-biphenyltetracarboxylic dianhydride and pyromellitic dianhydride with 4,4′-oxydianiline

A series of copolyimides were prepared via the polyamide acids (polyamic acids) from the reaction of 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA) and pyromellitic dianhydride (PMDA) with 4,4′-oxydianiline (4,4′-ODA) at dianhydride molar ratios of 9:1, 7:3, 1:1, 3:7 and 1:9. Homopolymers and a 1:1 polymer blend were also prepared. Films from the 7:3, 1:1 and 3:7 molar ratio polyamide acids reacted for 5-6 h at ambient temperature were brittle, whereas films from the same polyamide acids reacted for 24-48 h at ambient temperature were fingernail creaseable. The difference was apparently due to the initial formation of incompatible block domains that underway randomization upon longer reaction time. The differential scanning calorimetric (DSC) curves of some of the brittle films quenched after heating to 400 °C had two apparent glass transition temperatures (T_gs), indicative of two block domains. The creaseable films quenched after heating to 400 °C had single T_gs. Wide-angle X-ray diffraction showed all films to be amorphous even though the initial DSC curves showed strong endothermic peaks, generally associated with crystalline melts. These strong endotherms near the T_g region were thought to be due to relaxation of regions in the highly stressed films. Films of copolyamide acids from the reaction of 1:1 molar ratios of 3,3′,4,4′-oxydiphthalic anhydride/a-BPDA and 3,3′,4,4′-biphenyltetracarboxylic dianhydride/a-BPDA with 4,4′-ODA reacted for 6 h were fingernail creaseable. The chemistry and the properties of the copolymers are compared with those of the homopolymers.     

侧链含硫的联苯四酸二酐及其聚酰亚胺的合成

以3,3′,4,4′-联苯四酸二酐(BPDA)为原料合成了2,2′-苯硫醚-4,4′,5,5′-联苯四酸二酐,然后分别与对苯二胺和4,4′-二胺基二苯醚通过高温缩聚法制备出两种侧链含硫的新型聚酰亚胺(PI)(PI-1和PI-2).与文献报道的直接由BPDA为二酐制备的PI相比,PI-1和PI-2均表现出良好的有机可溶性...     

Resistive switching characteristics of polyimides derived from 2,2′‐aryl substituents tetracarboxylic dianhydrides

2,2′‐Position aryl‐substituted tetracarboxylic dianhydrides including 2,2′‐bis(biphenyl)‐4,4′,5,5′‐biphenyl tetracarboxylic dianhydride and 2,2′‐bis[4‐(naphthalen‐1‐yl)phenyl)]‐4,4′,5,5′‐biphenyl tetracarboxylic dianhydride were synthesized. A new series of aromatic polyimides (PIs) were synthesized via a two‐step procedure from 3,3′,4,4′‐biphenyl tetracarboxylic dianhydride and the newly synthesized tetracarboxylic dianhydrides monomers reacting with 2,2′‐bis[4′‐(3″,4″,5″‐trifluorophenyl)phenyl]‐4,4′‐biphenyl diamine. The resulting polymers exhibited excellent organosolubility and thermal properties associated with T_g at 264 °C and high initial thermal decomposition temperatures (T_5%) exceeding 500 °C in argon. Moreover, the fabricated sandwich structured memory devices of Al/PI‐a/ITO was determined to present a flash‐type memory behaviour, while Al/PI‐b/ITO and Al/PI‐c/ITO exhibited write‐once read‐many‐times memory capability with different threshold voltages. In addition, Al/polymer/ITO devices showed high stability under a constant stress or continuous read pulse voltage of ? 1.0 V. Copyright © 2011 Society of Chemical Industry