Effects of the acceptor conjugation length and composition on the electrical memory characteristics of random copolyimides

Resistive‐switching memories based on copolyimides (coPIs), PI‐NTCDIX and PI‐BTCDIX , with different compositions of 4,4′‐diamino‐4″‐methyltriphenylamine ( AMTPA ), 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride, and N,N′‐bis‐(4‐aminophenyl)‐1,8:4,5‐naphthalenetetracarboxydiimide ( NTCDI ) or N,N′‐bis‐(4‐aminophenyl)‐1,2:4,5‐benzenetetracarboxydiimide ( BTCDI ) have been developed. By varying the feed ratio of monomers, PI‐NTCDIX and PI‐BTCDIX showed tunable optical and electronic properties through the charge transfer (CT) between AMTPA and NTCDI or BTCDI . The memory devices based on PI‐NTCDIX exhibited the tunable electrical bistability from the volatile dynamic random access memory to nonvolatile write once read many memory characteristics as the NTCDI composition increased. The OFF/ON electrical switching transition was mainly attributed to the CT mechanism for the charge separated high conductance, based on the analysis of model compounds and density functional theory calculation. Also, the volatility of the memory device depended on the stability of CT complex. The long conjugation and high electron affinity of the NTCDI moiety stabilized the radical anion generated in the CT complex and prevented the recombination of segregated radical species even through applying the high positive or negative voltage. On the other hand, the memory devices based on PI‐BTCDIX showed a rather unique behavior compared with those based on PI‐NTCDIX . At the low BTCDI composition, the device exhibited volatile memory property. However, no switching behavior was observed at the high BTCDI composition due to the low highest occupied molecular orbital energy level of BTCDI . Combining these results and our previous study on perylenebisimide ( PBI ), we concluded that memory characteristics could be tailored by changing the conjugation length ( PBI > NTCDI > BTCDI ) and the acceptor composition in random coPIs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Synthesis and characterization of polyaniline doped with organic acids

Spectroscopic [UV–visible and Fourier transform IR (FTIR)] and thermal properties of chemically synthesized polyanilines are found to be affected by varying the protonation media (acetic, citric, oxalic, and tartaric acid). The optical spectra show the presence of a greater fraction of fully oxidized insulating pernigraniline phase in polyaniline doped with acetic acid. In contrast, the selectivity in the formation of the conducting phase is higher in oxalic acid as a protonic acid media. The FTIR spectra of these polymers reveal a higher ratio of the relative intensities of the quinoid to benzenoid ring modes in acetic acid doped polyaniline. Scanning electron micrographs revealed a sponge‐like structure derived from the aggregation of the small granules in acetic acid and oxalic acid doped polyaniline. A three‐step decomposition pattern is observed in all the polymers, regardless of the protonic acid used for the doping. The second step loss related to the loss of dopant is found to be higher in the oxalic acid doped polymer. In accordance with these results the conductivity is also found to be higher in oxalic acid doped material. The temperature dependent conductivity measurements show the thermal activated behavior in all the polymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2043–2049, 2004     

Synthesis,identification and study of electrical conductivity of the doped poly aniline

Poly aniline and poly aniline doped with 2,5-dimethyl benzene sulfonic acid (PXSA), 4-hydroxy-m-benzene disulfonic acid (PDSA), 3-chloro-4-hydroxybenzene sulfonic acid (OCPSA) were prepared. The polymers are identified by FT-IR and UV–vis spectroscopy. The ionic conductivities of poly aniline and poly aniline doped with 2,5-dimethyl benzene sulfonic acid (PXSA), 4-hydroxy-m-benzene disulfonic acid (PDSA), 3-chloro-4-hydroxybenzene sulfonic acid (OCPSA) were studied as a function of weight of the dopant compounds. It is noted that an increase of the conductance of poly aniline by doping with OCPSA, and became equal to 0.001321 Ω^?1 for 1 g higher than the conductance for the poly aniline when it is doped with OCPSA.     

Facile synthesis and optimization of conductive copolymer nanoparticles and nanocomposite films from aniline with sulfodiphenylamine

A new series of electrically conductive pure copolymer nanoparticles was facilely synthesized by using oxidative polymerization of aniline (AN) and sodium diphenylamine-4-sulfonate (SDP) in acidic media in the absence of stabilizer. The variation of the structure of the copolymer particles was comprehensively studied by carefully choosing several important parameters, such as the comonomer ratio, oxidant/monomer ratio, polymerization time and temperature, monomer concentration, acidic medium, and oxidant species. Analytical techniques used include IR and UV-visible spectroscopy, X-ray diffraction, laser particle analysis, atomic force microscopy, and transmission electron microscopy. It was found that the particle size varied significantly with the above-mentioned polymerization parameters, only changes in the salt concentration in the aqueous testing solution had no noticeable effect. The polymerization conditions were optimized for the formation of copolymer nanoparticles with sought-after properties. The doped copolymer particles of AN/SDP (50:50) at an oxidant/monomer molar ratio of 0.5 exhibit a minimum length of 50 nm and a minimum diameter of 44 nm. The bulk electrical conductivity of the copolymer particles increases greatly from 5.90x10(-4) to 1.15x10(-2) S cm(-1) with increasing AN content. Compared with barely soluble polyaniline, the copolymers exhibit a remarkably enhanced solubility in most solvents, including NH4OH and even water, due to the presence of the hydrophilic sulfonic groups. Nanocomposite films of the nanoparticles and cellulose diacetate exhibit a percolation threshold of down to 0.1 wt %, at which the film retains 98% of the transparency, 94% of the strength, and 5x10(7) times the conductivity of a pure cellulose diacetate film.     

Structural effect of polymeric acid dopants on the characteristics of doped polyaniline composites: Effect of hydrogen bonding

The conductivities of polyaniline (PANi) composites doped with the copolymeric acids such as poly(methyl methacrylate-co-p-styrenesulfonic acid) (PMMA-co-SSA), poly(styrene-co-p-styrenesulfonic acid) (PS-co-SSA), and poly(methyl methacrylate-co-2-acrylamido-2-methyl-1-propanesulfonic acid) (PMMA-co-AMPS) were investigated as a function of the acid content in the copolymeric acid dopants. With the fixed ratio of acid to aniline (1/1) in the PANi composites, the conductivities of the copolymeric acid-doped PANis decreased as the acid content in the copolymeric acids decreased. This could be attributed to the nonacidic units in the copolymeric acids which seemed to prevent adjacent acid groups from doping the PANi. Among the three kinds of copolymeric acid dopants, the PMMA-co-SSA series doped the PANi most effectively, and consequently, the PMMA-co-SSA-doped PANi composites showed the highest conductivities. The lack of conductivities of the PMMA-co-AMPS-doped PANi composites seems to be due to the doping ability of the AMPS groups. The higher conductivities of the PMMA-co-SSA-doped PANi composites rather than the PS-co-SSA-doped ones were attributed to the hydrogen bonding formed between the carbonyl groups in MMA and the amine groups in aniline which may hinder the phase separation and induce more homogeneous mixing and efficient doping. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1431–1439, 1998     

硫化聚并苯导电材料结构的理论化学研究

采用量子化学从头算方法和AM1半经验方法,探讨了聚并苯导电聚合物硫掺杂前后结构和电子性质的变化,提出了硫化聚并苯导电材料的“双层夹心”分子结构模型.研究表明,硫化后的聚并苯材料,S原子位于两层聚并苯分子平面中间,并与两个聚并苯分子平面中相应的两个C原子相键合,形成C—S—C“桥式”共价单键;并解释了硫化聚并苯导电材料比本征态聚并苯材料作电极时可逆容量增大的原因.     

Mechanistic studies on the catalytic reaction of piperidine with formaldehyde

Reaction of piperidine with formaldehyde over HY, -Al₂O₃ and acetic acid under liquid phase and/or gas phase conditions lead to picolines and higher alkylpyridines. Mechanistic aspects of the reaction are discussed.     

Electrochemical and spectroelectrochemical studies on aniline in organic medium and its antiknock mechanism

Electrochemical properties of aniline in 1,2-dichloroethane are investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and in situ UV-vis spectroelectrochemistry. Aniline is an additive in gasoline, whose antiknock mechanism is extrapolated on the basis of its electrochemical properties and its reaction with hydrogen peroxide. The experimental results indicate that for aniline low parent concentration and non-protonic solvents are in favor of producing benzidine by tail-to-tail coupling of cation radicals, the nature of the reaction between aniline and hydrogen peroxide is in that the proton released from electrooxidation can interact with hydrogen peroxide. Hydrogen peroxide can reduce the resistance of the electrochemical reaction and also has an inhibiting effect on the transmission of ion from solution to the electrode surface. The results offer significant evidence and a new method for studying antiknock mechanism of aromatic amines. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 9, pp. 1071–1076. The text was submitted by the authors in English.     

Preparation and properties of aniline chain-extended thermoplastic epoxy resin using triphenylphosphine as catalyst

Thermoplastic resins have been widely used in fiber reinforced polymer composites because of its recyclability and short cycle times. However, the high viscosity after heating and melting restricts its infiltration on the surface of fiber. In this study, a series of thermoplastic epoxy resins were prepared via the chain extension reaction of epoxy groups with liquid aniline using triphenylphosphine (TPP) as catalyst. The relationship between polymer network structure and performance was comprehensively investigated. The solubility tests indicated that excessive aniline or TPP facilitated the crosslinking of resins. Besides, on the premise of thermoplasticity, appropriate TPP could increase the degree of chain extension, molecular weight, and glass transition temperature of resins. Furthermore, the in-situ polymerization process facilitated infiltration between epoxy resin and the fibers before chain extension reaction. The bending test showed that the flexural performance of the sample with 2 phr of TPP was improved by 38.8%. Therefore, this work provides a feasible method to prepare the thermoplastic epoxy resins and its fiber-reinforced composites with good mechanical properties.     

甲醛光催化降解反应机理的量子化学研究

分别采用B3LYP,MP2方法在6-311++G(2df,pd)水平研究了甲醛光催化降解反应的微观机理,找到了可能的反应通道,预测反应产物为HCOOH与H2O.并得到了各反应通道的反应物、中间体、过渡态和产物的优化构型、谐振频率.成功地解释了实验结论.从键长和能量的变化角度,讨论了化学反应过程中化学键的变化规律,整个反应通道中各势能面均较低,从理论角度分析该反应室温下能够进行,为空气中的甲醛降解反应的实验研究提供理论依据.     

Electrical and humidity sensing properties of synthesized hydrophosphoric acid doped polyaniline

H₃PO₄ doped polyaniline was synthesized by a single‐step chemical polymerization method using ammonium persulfate as an oxidizing agent. The material characterization was done by SEM, UV–vis spectroscopy and thermogravimetric analysis (TGA). The pellets of the synthesized material were used to study the electrical properties, using a four‐probe method. The room temperature electrical conductivity is found to be 0.2201 S/cm. The electrical resistance in response to the varying humid environment (ranging between 20 and 100% RH) is recorded to evaluate the sensitivity of the H₃PO₄ polyaniline samples toward humidity. The resistance of the samples is found to vary by three orders of magnitude for 20–100% RH and is found to decrease with increasing humidity. The response and recovery time are observed to be 12–14 and 26–30 sec, respectively. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of aromatic substitution in aniline on the properties of polyaniline

Substitution in aniline has tremendous effect in the synthesis of poly(substituted anilines) as well as in their properties. In this investigation polyaniline (PANI), poly(m-nitro aniline) (PMNA), poly(m-amino phenol) (PMAP) and poly(o-ethyl aniline) (POEA) were synthesized by oxidative polymerization under identical conditions. Different properties were measured and compared with PANI to find out the presence of electron donating -OH group, electron withdrawing -NO₂ group and less effecting ethyl group on the properties of poly(substituted anilines). It was found that presence of any type of substitution in the benzene ring of aniline increases the solubility of the resulted polymer but reduces the yield, degree of polymerization, thermal stability, electrical and thermal conductivity. The colors, bulk density, particle size, percentage of crystallinity vary considerably depending on the nature of substitution.     

Contradictory ageing behaviour and optical property of iodine doped and H2SO4 doped pulsed DC plasma polymerized aniline thin films

Polymerization of aniline in the presence of H₂SO₄ and iodine vapour is carried out using pulsed DC glow discharge plasma. The as prepared iodine doped plasma polymerized aniline films are found to be highly crystalline due to some crystal structure formed by the iodine incorporated into the film and the ex-situ H₂SO₄ doped films are found to be amorphous. However, the structure of the iodine doped films transforms to amorphous one while that of the ex-situ H₂SO₄ doped films transforms to crystalline one due to the effect of ageing. The optical band gap of the samples decreases depending upon the level of doping and annealing, having minimum optical band gap for iodine doped plasma polymerized aniline. Due to ageing, the optical property of the H₂SO₄ doped film is found to become superior while for iodine doped films a negligible change of the optical property has been noticed even after six months of ageing.     

Crystal structure and luminescence of antimony(III) bromide with aniline

The atomic structure of antimony(III) bromide crystals with anilinium was determined by X-ray diffraction analysis of (C₆H₅NH₃)₂SbBr₅ (a = 19.704(3) Å, b = 7.914(1) Å, c = 25.556(4) Å; space group Pbca, Z = 8, ρ_calc = 2.365 g/cm³). The crystal structure consists of infinite chains of [SbBr₅]^2? complex anions formed by sharing six vertices and the anilinium (C₆H₅NH₃)⁺ cations, through which the chains are linked in layers by N-H...Br hydrogen bonds. The geometrical aspects that determine the luminescent spectral properties of the complex are discussed.     

Preparation and characterization of hexadecane microcapsule with polyurea--melamine formaldehyde resin shell materials

<正>This paper gives a brief report of the preparation of hexadecane microcapsule with polyurea-melamine formaldehyde resin shell materials(HMPM).The sealing performance and thermal stability of HMPM was enhanced much more effectively than that of microcapsule with polyurea shell material(HPM).The results of microscopical imaging analysis system,DSC,TG,and laser particle analyzer were briefly introduced.     

Chemical synthesis and electric properties of the conducting copolymer of aniline and o‐aminophenol

A copolymer, poly(aniline‐co‐o‐aminophenol), was prepared chemically by using ammonium peroxydisulfate as an oxidant. The monomer concentration ratio of o‐aminophenol to aniline strongly influences the copolymerization rate and properties of the copolymer. The optimum composition of a mixture for the chemical copolymerization consisted of 0.3 M aniline, 0.021 M o‐aminophenol, 0.42 M ammonium peroxydisulfate, and 2 M H₂SO₄. The result of cyclic voltammograms in a potential region of ?0.20 to 0.80 V (vs.SCE) indicates that the electrochemical activity of the copolymer prepared under the optimum condition is similar to that of polyaniline in more acid solutions. However, the copolymer still holds the good electrochemical activity until pH 11.0. Therefore, the pH dependence of the electrochemical property of the copolymer is improved, compared with poly(aniline‐co‐o‐aminophenol) prepared electrochemically, and is much better than that of polyaniline. The spectra of IR and ¹H NMR confirm that o‐aminophenol units are included in the copolymer chain, which play a key role in extending the usable pH region of the copolymer. The visible spectra of the copolymers show that a high concentration ratio of o‐aminophenol to aniline in a mixture inhibits the chain growth. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5573–5582, 2007     

Structural characteristics of phenol formaldehyde novolak resin depending on polycondensation type using molecular simulation

Phenol formaldehyde novolak resins have various structures depending on the polycondensation types. Their structures were characterized using molecular mechanics and molecular dynamics. Dimer, tetramer, hexamer, octamer, and decamer of the resins with the ortho–ortho, ortho–para, and para–para sequences were calculated. The ortho–ortho resins have the structural characteristics of intramolecular hydrogen bonds between hydroxyl groups of the adjacent phenolic units. For the ortho–para and para–para resins, the intramolecular hydrogen bonds are formed mainly between hydroxyl groups of the backbone phenolic units. The para–para resins also have intramolecular hydrogen bonds between hydroxyl groups of the branched phenolic units. A factor determining the structural characteristics of the resins was found to be the geometry of the basic unit (dimer). The order of the end‐to‐end distances between hydrogen atoms on the para‐position of the basic units of the resins is ortho–ortho resin < ortho–para resin < para–para resin. The calculational results were found to be consistent with the gel permeation chromatography (GPC) analysis. Copyright © 2001 John Wiley & Sons, Ltd.