Sulfonated naphthalene dianhydride based polyimide copolymers for proton‐exchange‐membrane fuel cells. I. Monomer and copolymer synthesis

A novel sulfonated diamine, 3,3′‐disulfonic acid‐bis[4‐(3‐aminophenoxy)phenyl]sulfone (SA‐DADPS), was prepared from m‐aminophenol and disodium‐3,3′‐disulfonate‐4,4′‐dichlorodiphenylsulfone. The conditions necessary to synthesize and purify SA‐DADPS in high yields were investigated in some detail. This disulfonated aromatic diamine, containing ether and sulfone linkages, was used to prepare N‐methyl‐2‐pyrrolidinone‐soluble, six‐membered ring polyimide copolymers containing pendent sulfonic acid groups by a catalyzed one‐step high‐temperature polycondensation in m‐cresol. These materials showed much improved hydrolytic stability with respect to phthalimides. High‐molecular‐weight film‐forming statistical copolymers with controlled degrees of disulfonation were prepared through variations in the stoichiometric ratio of disulfonated diamine (SA‐DADPS) in its soluble triethylamine salt form to several unsulfonated diamines. Three unsulfonated diamines, bis[4‐(3‐aminophenoxy)phenyl] sulfone, 4,4′‐oxydianiline, and 1,3‐phenylenediamine, were used to prepare the copolymers. The characterization of the copolymers by ¹H NMR, Fourier transform infrared, ion‐exchange capacity, and thermogravimetric analysis demonstrated that SA‐DADPS was quantitatively incorporated into the copolymers. Solution‐cast films of the sulfonated copolymers were prepared and afforded tough, ductile membranes with high glass‐transition temperatures. Methods were developed to acidify the triethylammonium salt membranes into their disulfonic acid form, this being necessary for proton conduction in a fuel cell. The synthesis and characterization of these materials are described in this article. Future articles will describe the performance of these copolymers as proton‐exchange membranes in hydrogen/air and direct methanol fuel cells. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 862–874, 2004     

3‐Phenylethynyl phthalimide end‐capped imide oligomers and the cured polymers

In the past decades, 4‐phenylethynyl phthalic anhydride (4‐PEPA) has been the most important endcapper used for thermoset polyimide. As the isomer of4‐PEPA, 3‐phenylethynyl phthalic anhydride (3‐PEPA) has attracted our interest. In this article, 3‐PEPA was synthesized and a comparative study with 4‐PEPA on curing temperature, curing rate, thermal and mechanical properties of oligomers and cured polymers was presented. The new phenylethynyl endcapped model compound, N‐phenyl‐3‐phenylethynyl phthalimide, was synthesized and characterized. The molecular structure of model compound was determined via single‐crystal X‐ray diffraction and the thermal curing process was investigated by Fourier transform infrared. Differential scanning calorimetry clearly showed that the model compound from 3‐PEPA had about 20 °C higher curing onset and peak temperature than the 4‐PEPA analog. This result was further proved by the dynamic rheological analysis that the temperature of minimum viscosity for oligomers end‐capped with 3‐PEPA was above 20 °C higher than that of the corresponding 4‐PEPA endcapped oligomers with the same calculated number average molecular weight. The cured polymer from 3‐PEPA displayed slightly higher thermal oxidative stability than those from 4‐PEPA by thermogravimetric analysis. The thermal curing kinetics of 3‐PEPA endcapped oligomer (OI‐5) and 4‐PEPA endcapped oligomer (OI‐6) fitted a first‐order rate law quite well and revealed a similar rate acceleration trend. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4227–4235, 2008     

Solubility and transport of water vapor in some 6FDA-based polyimides

Permeability, diffusion, and solubility coefficients for H₂O vapor in four different 6FDA-based polyimides were determined at temperatures between 25 and 45°C and over a wide range of relative humidities. The solubility of H₂O vapor in some of the polyimides studied can be described by the “dual-mode sorption” model whereas in other polyimides it is represented by the Flory-Huggins equation, which suggests that the latter polymers are plasticized by H₂O. The solubility of H₂O vapor in the polyimides decreases as the temperature is raised and increases with increasing polarity of the polymer. The diffusion coefficients for H₂O in the polyimides studied either increase or pass through a weak maximum with increasing H₂O activity, or concentration in the polymers. The latter behavior is probably due to a clustering of H₂O molecules in the polyimides at higher H₂O activities or concentrations. The diffusion coefficients for H₂O decrease as the chain-packing density of the polyimides increases. The permeability coefficients for H₂O vapor in 6FDA-based polyimide membranes either increase slightly or are constant as the H₂O activity is increased. The experimental values of the permeability coefficients are consistent with the values determined from diffusion and solubility coefficients. The permeability of the polyimides to H₂O vapor appears to be controlled by the solubility of H₂O in the polymers. The polyimides studied exhibit a very high selectivity for H₂O vapor relative to CH_4, and therefore are potentially useful membrane materials for the dehydration of natural gas. ©1995 John Wiley & Sons, Inc.     

Investigation of the role of the pyrimidine ring in the main chain of polyamido acids and polyimides. 2. Characteristics of the thermocyclization of polypyromellitamido acids based on 2,5-bis(p-aminophenyl)pyrimidine and 4,4′-diaminoterphenyl

The thermocyclization of polypyromellitamido acids based on 2,5-bis(p-aminophenyl)pyrimidine and 4,4-diaminoterphenyl was investigated by thermogravimetric and mass spectrometric analysis. Characteristics of the thermocyclization of pyrimidine-containing polyamido acids due to the presence of a basic nitrogencontaining ring in the main macrochain were revealed. The hypothesis advanced in Part 1, that the pyrimidine ring displaces solvent molecules bound to the polyamido acid, was confirmed. The hypothesis of the presence of shift packing in a pyrimidine-containing polyamido acid was confirmed by its greater kinetic homogeneity in comparison with the completely aromatic analog.Institute of High-Molecular-Weight Compounds Russian Academy of Sciences, 199004 St. Petersburg. Novosibirsk Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, 630090 Novosibirsk. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2297–2301, October, 1992.     

The influence of surface treatment on the tensile and tribological properties of wood fiber‐reinforced polyimide composite

In this paper, the effect of coupling agent surface treatment of wood fiber on tensile and tribological property of wood fiber‐reinforced thermoplastic polyimide (PI) composites was experimentally investigated. Experimental results revealed that coupling agent surface treatment could effectively improve the interfacial adhesion between wood fiber and PI matrix. Compared with the untreated wood fiber/PI composite, the coupling agent‐treated composite had better interfacial adhesion. The fracture surfaces and worn surface of samples were investigated by scanning electronic microscopy to analyze the effects of surface treatment methods.     

Ionic effects on electro-optics and residual direct current voltages of twisted nematic liquid crystal cells

By using electro-optical and dielectric absorption [1–4] measurements, we report our investigations of ionic effects on electro-optics and residual direct current voltages (VrDCs) of two polyimide (PI)-aligned twisted nematic (TN) cells with same liquid crystal mixture but different PI-alignment materials. We have also carried out new experimental methods to find out that the observed VrDCs were caused by LC-PI-interfacial trapped ions generated and transported from the LC medium for one TN cell, and from the PI layers for the other TN cell. Our measured VrDCs indicated that the former had two different exponential-decay rates similar to the published results by M. Mizusaki et al. [2] but the latter had only a single exponential-decay rate.     

The alignment of nematic liquid crystal by the Ti layer processed by nonlinear laser lithography

It is well known that the alignment of liquid crystals (LCs) can be realised by rubbing or photoalignment technologies. Recently, nonlinear laser lithography (NLL) was introduced as a fast, relatively low-cost method for large area nano-grating fabrication based on laser-induced periodic surface structuring. In this letter for the first time, the usage of the NLL as a perspective method of the alignment of nematics was presented. By NLL, nanogrooves with about 0.92 μm period were formed on Ti layer. The nanostructured Ti layer (NSTL) was coated with oxidianiline-polyimide film with annealing of the polymer followed without any further processing. Aligning properties of NSTLs were examined with combined twist LC cell. The dependencies of the twist angle of LC cells and azimuthal anchoring energy (AE) of layers on scanning speed and power of laser beam during processing of the Ti layer were the focus of our studies as well. The maximum azimuthal AE, obtained for pure NSTL, is comparable with photoalignment technology. It was found that the deposition of polyimide film on NSTL leads to the gain effect of the azimuthal AE. Also, atomic force microscopy (AFM) study of aligning surfaces was carried out.     

Synthesis and characterization of thermally stable and flame retardant hexakis(4-aminophenoxy)cyclotriphosphazene-based polyimide matrices

A new approach to the preparation of hexakis(4-aminophenoxy)cyclotriphosphazene (HACTP) based polyimide (PI) matrices is proposed, for improved thermal and flame retardant properties. HACTP was synthesized with good yield. The structure of HACTP was confirmed by various characterization techniques, such as FTIR, NMR, and mass Spectroscopy. Polyimide matrices were prepared by thermal imidization process using HACTP and dianhydrides using N-methyl pyrrolidone as a solvent. The successful formation of HACTP-based polyimide matrices was confirmed by the FTIR. Thermal properties of the PI were analyzed using DSC and TGA techniques. Data obtained from the thermal studies indicate that the HACTP-based PI possesses better thermal and flame retardant properties.     

Preparation of A New Fiber by Sol-gel Technology in Solid-phase Microextraction （SPME）

The sol-gel technology is applied for the preparation of solid-phase microextraction (SPME) fiber. The fiber demonstrates high thermal stability, efficient extraction rate and the selectivity for non-polar or low-polar analytes. Efficient SPME-GC-FID analyses of benzenetoluene-ethylbenzene-xylenes (BTEXs) and low-polar halocarbon were achieved by the sol-gel coated DSDA-DDBT-TiO2 fiber. Some parameters of the SPME fiber for the determination of halocarbon in aqueous sample were investigated.     

3,3′-二氨基查尔酮的合成

由硝基苯甲醛和硝基苯乙酮经C laisen-Schm idt缩合制得3,3′-二硝基查尔酮,再用FeC l3-NH2NH2.H2O-C体系将其还原成3,3′-二氨基查尔酮。所得产品经元素分析、熔点、IR和1H NMR测试确认,讨论了影响产品收率的因素。收率为78.6%。