Role of the in‐plane orientation of polyimide films in graphitization

Poly(amide acid) labeled with perylenetetracarboxydiimide (PEDI) was prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), p‐phenylenediamine (PDA), and diamino‐PEDI. Poly(amide acid) was then reacted with sodium hydride and various kinds of alkyl iodides for transformation into various poly(amide ester)s. The cast films were imidized while fixed on glass substrates to give BPDA/PDA polyimide films. The degree of in‐plane molecular orientation (f) of the polyimides and their precursors, poly(amide acid) and poly(amide ester)s, were determined via measurements of the visible dichroic absorption at an incidence angle for a rodlike dye (PEDI) bound to the main chain. All precursor films showed relatively low degrees of in‐plane orientation. After imidization of the precursors fixed on glasses, however, striking spontaneous in‐plane orientation behavior was observed. The f value for polyimide film from a poly(amide acid) precursor was as high as 0.7–0.8. The f value for polyimide film from a methyl ester precursor, however, was lowered to 0.4–0.5, but it increased with the increasing size of the alkyl groups. Good correlations of the in‐plane orientation of the polyimide films with the tensile modulus of the films and the in‐plane orientation of the graphitized films were observed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 3011–3019, 2001     

Effect of the Measurement Temperature on the Dispersive Component of the Surface Free Energy of a Heat Treated SiO2 Xerogel

The surface free energy of a monolithic silica xerogel treated at 1000°C has been measured by inverse gas chromatography in the temperature range 25–150°C using n-alkanes. Values of the dispersive component, _S ^D, vary from 49.07 mJ·m^–2 at 25°C to 17.20 mJ·m^–2 at 150°C. The _S ^D value obtained at 25°C is lower than that found for amorphous and crystalline silicas but higher than that found for glass fibres meaning that the heat treatment at 1000°C changes drastically the structure of the silica xerogel showing a surface similar to a glass. However, the higher value of _S ^D in comparison to glass fibres can be attributed to the mesoporous structure present in the silica xerogel. In the temperature range of 60–90°C there exists an abrupt change of the _S ^D values as well as in the dispersive component of the surface enthalpy, h _S ^D. Such abrupt change can be attributed to an entropic contribution of the surface free energy.     

Surface properties of cellulose modified by imidazolidinone

The influence of the modification of cellulose fibres by the imidazolidinone derivative 1,3-dimethyl-4,5-dihydroxyethylene urea (DMeDHEU) on fibre surface free energy and electrochemical potential was studied. The presence of DMeDHEU in the cellulose structure was confirmed by infrared spectral analysis. The surface free energy of untreated and treated cellulose fibres was determined from the results of thin-layer wicking, where the rate of liquid penetration into the cellulose fabric was measured. Using the van Oss-Chaudhury-Good theoretical approach, apolar, γ _S ^LW , polar electron-acceptor, γ _S ⁺, and electron-donor, γ _S ⁻, components of the surface free energy were calculated. The electrokinetic potential was determined from the results of steaming potential measurements. The results revealed that the incorporation of DMeDHEU into the cellulose structure lead to a decrease in the value of γ _S ⁻, whereas the values of γ _S ^LW and γ _S ⁺ remained almost unchanged. Despite their decreased γ _S ⁻ value, the treated cellulose fibres still represent a monopolar solid with a strongly expressed electron-donor component. The values of ΔG _iw and ΔG _iwi suggested that both untreated and treated cellulose samples could be considered hydrophilic substrates. The results of the electrokinetic potential measurements showed that the consumption of cellulose hydroxyl groups in the crosslinking reaction with DMeDHEU did not decrease the electrokinetic properties of the cellulose surface.     

The synthesis and characterization of polyimide homopolymers based on 5(6)‐amino‐1‐(4‐aminophenyl)‐1,3,3‐trimethylindane

The isomeric diamine monomer 5(6)‐amino‐1‐(4‐aminophenyl)‐1,3,3‐trimethylindane (DAPI) was successfully synthesized via the dimerization of α‐methylstyrene followed by nitration and reduction. High molecular weight, soluble polyimides were synthesized via ester–acid solution imidization techniques and had glass‐transition temperature values ranging from 247 to 369 °C. The polymers were soluble in common organic solvents because of the asymmetric and nonplanar nature of DAPI and displayed good short‐term thermal stability by thermogravimetric analysis, as shown by their 5% weight‐loss values above 500 °C in air. The DAPI/(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) polyimide also showed 2‐h thermal stability at 400 °C under nitrogen, despite the partial aliphatic character. Refractive index values as low as 1.571 were observed for DAPI/6FDA, which allows an estimated dielectric constant of 2.47 to be derived. The permeation of O₂ and N₂ was conducted on thin dense films. The bulky, bent, and isomeric nature of DAPI imparted film‐forming membranes that permitted high O₂ permeability. In combination with 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA), DAPI had a good combination of O₂ permeability and O₂/N₂ selectivity values of 2.8 Ba and 7.3, respectively. The polymerization method utilized to facilitate the cyclization of DAPI/BTDA to the polyimide affected the final thermal properties of the resulting polymer. The chemical imidization of DAPI/BTDA generated a polyimide with a glass‐transition temperature value of 311 °C and a 5% weight‐loss value in air of 457 °C. However, thermal and ester–acid imidization routes yielded an increase in the thermal properties. The ester–acid solution imidization of DAPI/BTDA produced a polymer glass‐transition temperature value of 333 °C and a 5% weight‐loss value of 525 °C in air. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2840–2854, 2000     

Transport properties of polyimides derived from benzophenonetetracarboxylic dianhydride and other diamines

Gas-separating membrane characteristics of polyimide films composed of the common fragment of benzophenone-3,3′,4,4′-tetracarboxylic dianhydride and diamines of varying structure were studied. Permeability coefficient P, diffusion coefficient D, and solubility coefficient S for H₂, CO, CO₂, and CH₄ were determined. The polyimide derived from m-phenylenediamine exhibited the best gas-separating properties. A relationship between the chain rigidity, free volume, and transport parameters (P, D, S, and selectivity) of polyimide was established on the basis of the data. It was shown that there is an optimal chain rigidity for the studied polyimides that results in polymer structurization during film preparation and corresponds to high separation selectivity.     

Structural characterization of silica modified polyimide membranes

Polyimide and hybrid polyimide‐siloxane were synthesized by polycondensation, imidization, and sol‐gel reaction. The polyimides were prepared from pyromellitic dianhydride (PMDA) and 4,4‐oxydianiline (ODA) in N‐methyl‐2‐pyrollidone (NMP). Trimethoxyvinyl silane (TMVS) was used as a source of silica. Their surface morphologies, structures and thermal performances were determined using scanning electron microscopy (SEM), infrared spectroscopy (IR), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results showed that the silica particles were finely and rather homogeneously dispersed in polymers. The glass transition temperature (T_g) of hybrid membrane materials increased with the increasing silica content. TGA analysis showed that polyimides were thermally stable with silica. Modified polyimide‐siloxane films, thermal characteristics were found to be better than the polyimide films without silica. Copyright © 2006 John Wiley & Sons, Ltd.     

Radiation effects in physical aging of binary As–S and As–Se glasses

Radiation-induced physical aging effects are studied in binary As _x S_100−x and As _x Se_100−x (30 ≤ x ≤ 42) glasses by conventional differential scanning calorimetry (DSC) method. It is shown that γ-irradiation (Co⁶⁰ source, ~3 MGy dose) of glassy As _x S_100−x caused a measurable increase in glass transition temperature and endothermic peak area in the vicinity of glass transition region, which was associated with acceleration of structural relaxation processes in these materials. In contrast to sulfide glasses, the samples of As–Se family did not exhibit any significant changes in DSC curves after γ-irradiation. The observed difference in radiation-induced physical aging between sulfides and selenides was explained by more effective destruction-polymerization transformations and possible metastable defects formation in S-based glassy network.     

Development of sulfide glass-ceramic electrolytes for all-solid-state lithium rechargeable batteries

Development of Li₂S–P₂S₅-based glass-ceramic electrolytes is reviewed. Superionic crystals of Li₇P₃S₁₁ and Li_3.25P_0.95S₄ were precipitated from the Li₂S–P₂S₅ glasses at the selected compositions. These high temperature or metastable phases enhanced conductivity of glass ceramics up to over 10⁻³ S cm⁻¹ at room temperature. The original (or mother) glass electrolytes itself showed somewhat lower conductivity of 10⁻⁴ S cm⁻¹ and have important role as a precursor for obtaining the superionic crystals, which were not synthesized by a conventional solid-state reaction. The substitution of P₂O₅ for P₂S₅ at the composition 70Li₂S·30P₂S₅ (mol%) improved both conductivity and electrochemical stability of glass-ceramic electrolytes. The all-solid-state In/LiCoO₂ cell using the 70Li₂S·27P₂S₅·3P₂O₅ (mol%) glass-ceramic electrolyte showed initial capacity of 105 mAh g⁻¹ (gram of LiCoO₂) at the current density of 0.13 mA cm⁻² and exhibited higher electrochemical performance than that using the 70Li₂S·30P₂S₅ glass-ceramic electrolyte.     

含硫醚结构均苯型聚酰亚胺的合成及表征

以4,4′-二氨基二苯硫醚(SDA)和均苯四酸酐(PMDA)为原料,通过溶液缩聚法-热酰亚胺/化学酰亚胺化的方法制备了一种含硫醚结构均苯型聚酰亚胺.利用高级旋转流变仪建立了在线跟踪反应进程的方法,采用热失重分析仪研究反应条件对热酰亚胺化及化学酰亚胺化法的影响,这些方法的建立为进一步制备高性能的聚酰亚胺提供有效的实验手段.采用小角激光光散射法、红外光谱、元素分析、接触角仪、DSC等方法对聚合物的结构与性能进行表征.结果显示,硫醚结构的引入,可有效改善聚合物薄膜的表面性能,其与铜箔之间的粘附功明显大于传统聚酰亚胺,在无胶挠性线路板应用方面显示出较好的应用前景.所获聚合物的Mw为(6.7±1.6)×104,分解温度均高于560℃;DSC的结果显示所制备的两种酰亚胺化聚合物均具有较高的玻璃化转变温度,相比之下,化学酰亚胺化更有利于获得高酰亚胺化程度的聚合物,产物的玻璃化转变温度也更高.     

Specific Structural Features of Langmuir-Blodgett Films of a Rigid-Chain Polyimide

Atomic-force microscopy, reflectometry, and ellipsometry were applied to analysis of ultrathin films (3.3–13.6 nm) of a rigid-chain polyimide, formed on the surface of a silicon substrate by thermal imidization of Langmuir-Blodgett films of polyamido acid derived from 3,3′,4,4′-diphenyltetracarboxylic acid and ortho-tolidine. __________ Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 9, 2005, pp. 1499–1503. Original Russian Text Copyright ? 2005 by Goloudina, Luchinin, Pasyuta, Rozanov, Sklizkova, Kudryavtsev, Levin, Mayer, Paufler.     

Metallized polyimide films: Metallization and mechanism of the process

The formation of metallized polyimide films in situ, namely, the alkaline hydrolysis of film surfaces, chelation of the modified surface with metal ions, and their chemical reduction giving rise to a metal layer, has been investigated. Initial polyimide films are cast from reaction solutions on a glass substrate. The solutions are prepared through the polycondensation of dianhydride of tricyclo[4.2.2.0^2.5dec-7-ene-3,4,9,10-tetracarboxylic acid and 4,4¹-diaminodiphenyl oxide in N-methyl-2-pyrrolidone at 160°C. It has been shown that alkaline water-alcohol solutions are optimal media for the hydrolysis of the film surface. The maximal exchange of alkali metal ions is achieved through formation of a more stable metal-ligand complex of poly(amido acid), with the chelation rate depending on the nature of a metal. The metal reduction proceeds rapidly; however, the mechanism of this process depends on the pH of a medium. The annealing of metallized films results in the imidization of poly(amido acid) and in the growth of metal grains on the material surface to yield a metal layer with good optical properties and high conductivity.     

Fabrication of highly refractive BaTiO3 nanocomposite films using heat resistant polymer as matrix

Highly refractive, heat-resistant BaTiO₃ nanocomposite films were fabricated via in situ polymerization to homogeneously disperse barium titanate (BT) nanoparticles into polyimide (PI) matrix. BT nanoparticles surface-modified with O-phosphorylethanol phthalimide (PPHI) were employed to the in situ polymerization in which condensation reactions of a diphthalic anhydride and a diamine were conducted to form the prepolymer of poly(amic acid) (PAA) that was thermally imidized in the following step. The nanoparticles surface-modified were added to PAA solution at different times in the polymerization to examine the effect of PAA molecular weight on the refractive index (RI) of the nanocomposite films, which indicated that relatively low molecular weights (<10,000) of PAA formed at the point of nanoparticle addition was appropriate for enhancement of nanocomposite RI. An additional treatment of chemical imidization using acetic acid anhydride and pyridine, which was followed by the thermal imidization, was performed to examine the effect of polyimide structure on RI of nanocomposite films. The RI of nanocomposite films with excellent thermal stability could be successfully enhanced to n = 1.88 by the chemical imidization.     

Residual stress and optical properties of fully rod-like poly(p-phenylene pyromellitimide) in thin films: Effects of soft-bake and thermal imidization history

A soluble poly(amic acid) precursor solution of fully rod-like poly(p-phenylene pyromellitimide) (PMDA-PDA) was spin cast on silicon substrates, followed by soft bake at 80–185°C and subsequent thermal imidization at various conditions over 185–400°C in nitrogen atmosphere to be converted to the polyimide in films. Residual stress generated at the interface was measured in situ during imidization. In addition, the imidized films were characterized in the aspect of polymer chain orientation and ordering by prism coupling and X-ray diffraction. The soft-baked precursor film revealed a residual stress of 16–28 MPa at room temperature, depending on the soft bake condition: higher temperature and longer time in the soft bake gave higher residual stress. The stress variation in the soft-baked precursor film was not significantly reflected in the final stress in the resultant polyimide film. However, the residual stress in the polyimide film varied sensitively with variations in imidization process parameters, such as imidization temperature, imidization steps, heating rate, and film thickness. The polyimide film exhibited a wide range of residual stress, −7 MPa to 8 MPa at room temperature, depending on the imidization condition. Both rapid imidization and low-temperature imidization generated high stress in the tension mode in the polyimide film, whereas slow imidization as well as high temperature imidization gave high stress in the compression mode. Thus, a moderate imidization condition, a single- or two-step imidization at 300°C for 2 h with a heating rate of < 10 K/min was proposed to give a relatively low stress in the polyimide film of < 10 μm thickness. However, once a precursor film was thermally imidized at a chosen process condition, the residual stress–temperature profile was insensitive to variations in the cooling process. All the films imidized were optically anisotropic, regardless of the imidization history, indicating that rod-like PMDA-PDA polyimide chains were preferentially aligned in the film plane. However, its degree of in-plane chain orientation varied on the imidization history. It is directly correlated to the residual stress in the film, which is an in-plane characteristic. For films with residual stress in the tension mode, higher stress films exhibited lower out-of-plane birefringence, that is, lower in-plane chain orienta-tion. In contrast, in the compression mode, higher stress films showed higher in-plane chain orientation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1261–1273, 1998     

Preparation and properties of thermally stable polyimides derived from asymmetric trifluoromethylated aromatic diamines and various dianhydrides

A novel method for the preparation of an asymmetric fluorinated aromatic diamine, 3,4′-bis(4-amino-2-trifluoromethylphenoxy)-benzophenone was investigated. This new diamine containing trifluoromethyl side group was synthesized from the nucleophilic substitution reaction of 2-chloro-5-nitrobenzotrifluoride and 3,4′-dihydroxybenzo phenone in the presence of potassium carbonate, followed by catalytic reduction with SnCl₂·6H₂O and concentrated hydrochloric acid. This novel diamine was used to react with different commercially available aromatic tetracarboxylic dianhydrides to prepare polyimides via thermal or chemical imidization. The polyimide properties such as inherent viscosity, solubility, thermal and surface properties were investigated to illustrate the contribution of the trifluoromethyl group and the asymmetry structure of the polyimide. The polyimides obtained had good thermal stability and the glass transition temperature values ranged from 225 to 267 °C. All of these novel polyimides held 10% weight loss at the temperature above 543 °C in air and left more than 47% residue even at 800 °C in nitrogen. The inherent viscosities of the obtained polyimides were above 0.73 dL/g and were easily dissolved in both polar, aprotic solvents and some low-boiling-point solvents. Moreover, these PI films had dielectric constants of 2.94-3.53 (1 kHz), with moisture absorption in the range of 0.07-0.34 wt%. In comparison of the PIs (5) series with the analogous symmetric PIs (6) series based on 4,4′-bis(4-amino-2-trifluoromethylphenoxy)-benzophenone, the (5) series revealed better solubility, low dielectric constant and moisture absorption.     

Characterization of wood fibers modified by phenol-formaldehyde

Wood-fiber phenol-formaldehyde-resin (PFR) modified surfaces, obtained from the adsorption of a PFR/water solution, are investigated as a function of the nature and the amount of PFR adsorbed. Surface are measurements are performed by using krypton adsorption at 77 K. Chemical modification is monitored by the electron spectroscopy for chemical analysis (ESCA) technique and the surface energy by the inverse phase gas chromatography (IPGC) method at infinite dilution. The London dispersive componentγ _S ^L of the surface energy shows a relationship to the concentration of carbon and oxgen at the fiber surface.γ _S ^L increases from 27.5 mN·m⁻¹ for the untreated fiber to 42.5 mN·m⁻¹ for the fibers treated with 20% high molecular-weight-grade phenol-formaldehyde. The surface atomic ratio O/C determined using the ESCA technique exhibits a decrease from 44% for untreated to 31% for treated samples. Surface area also decreases from 2.09 m²/g to 1.50 m²/g. The PFR adsorbed by wood fibers is observed as the dispersive component of surface energy starts to increase, as the surface oxygen concentration decreases, and on the surface area of the wood fiber.     

Structure and infrared emissivity of silicon-containing polyimide/BaTiO3 nanocomposite films

Silicon-containing polyimide/BaTiO₃ nanocomposite films were prepared by the direct mixing of silicon-containing polyamic acid and BaTiO₃ nanoparticles under ultrasonic wave irradiation, followed with thermal imidization. Structure and thermal properties were measured with FTIR, XPS, SEM, DSC and TGA. The results showed that the compatibility of BaTiO₃ and a polyimide might be improved by the introduction of dimethylsilylene groups into the backbone of a polyimide; and BaTiO₃ nanoparticles in the nanocomposites tended to form clusters. The clusters coalesced into a more uniform structure at a higher BaTiO₃ filling than at a lower one.The interfacial interaction between BaTiO₃ and the silicon-containing polyimide resulted in the increase of the glass transition and the thermal decomposition temperature. It was found that the nanocomposites exhibited lower infrared emissivity value than the pure polyimide and the magnitude of infrared emissivity value was related to the content of BaTiO₃ in the nanocomposites.     

In situ sol–gel fabrication of new poly(amide–ether–imide)/titania (TiO<Subscript>2</Subscript>) nanocomposite thin films containing <Emphasis Type="SmallCaps">l</Emphasis>-leucine moieties

In this study, the synthesis, morphology, and thermal properties of amino acid containing polyimide/titania nanohybrid films are investigated. At first, a chiral diamine containing l-leucine moieties in the structure (synthesized previously) was polymerized with 4,4′-oxydiphthalic anhydride in extremely dry conditions. Resulted poly(amic acid) (PAA) was mixed with a moisture-sensitive titania precursor (tetraethyl orthotitanate [Ti(OEt)₄]) and casted to a dust-free glass plate. The water derived from thermal imidization of PAA hydrolyzed Ti(OEt)₄ to titania nanoparticles with almost spherical shapes. The thermogravimetric analysis of various nanocomposites confirms the improvement in the thermal stability with the increase in the percentage of titania nanoparticle. The transmission electron microscopy of nanohybrid films with 3%, 5%, and 10% w/w of titania contents confirms well dispersion of nanoparticles in the polymer ground. The X-ray diffraction spectra showed that the titania contents have amorphous structure.     

Chemical Factors That Influence the Production of Conductive and/or Reflective Silver-Doped Polyimide Films

ABSTRACT

Doping a poly(amide acid) resin with a silver containing additive (1,5-cyclooctadiene-hexafluoroacetylacetonato)-silver(I) [Ag(COD) (HFA)] resulted, after thermal cure, in either a highly reflective or highly eléctrically conductive polyimide film. The combination of monomers, which render films with low T_g (~210°C), and contained sulfur, produced films with surface resistance in the range 10^1–10³ ohms. On the other hand, films with specular reflectivity (relative to a silver mirror) in the range of 65–48% were obtained using both high T_g polyimides and polyimides void of sulfur in the polyimide backbone with low T_g. Our understanding regarding the structure-property relationship on these polyimide films and also the characterization of the doped-films are discussed.     

Photon activation analysis of carbon in glasses for fiber amplifiers by using the flow method for the rapid separation of 11C

Summary We have studied the photon activation analysis of carbon in InF₃-based fluoride, chalcogenide and tellurite glasses for fiber amplifiers, and especially the nuclear interference from a matrix produced by (γ,n), (γ,2n), (γ,p) and (n,γ) reactions and a flow method for the rapid and simple separation of ¹¹C. A chemical separation technique is indispensable for determining carbon, because seventeen radionuclides are observed in these glasses. The flow method can sequentially be undertaken, the fusion of an irradiated sample with an oxidizer, the conversion of ¹¹C into ¹¹CO₂, and the absorption of ¹¹C in ethanolamine solution. We used a mixture of Pb₃O₄ and B₂O₃ as the oxidizer. There is interference with the ¹¹C measurement because ¹⁸F and ⁶⁸Ga are produced in fluoride and chalcogenide glasses by the ¹⁹F(γ,n), ²³Na(γ,αn) and ⁶⁹Ga(γ,n) reactions, respectively, and also absorbed in ethanolamine solution. Therefore, this flow method can only be applied to tellurite glasses. The chemical yield provided by the flow method was close to 100% when determining carbon in Japanese Iron and Steel Certified Reference Materials (JSS) by using lithium carbonate as a standard sample. We determined that the carbon concentrations in four kinds of tellurite glass were 7 to 14 ppm.     

Effect of ageing atmospheres on the changes in surface free energies of oxygen plasma-treated polyethylene films

The changes in the surface properties of oxygen plasma-treated polyethylene films during ageing in various atmospheres (water, dry nitrogen gas, and hexane) were studied from the viewpoint of the interaction of the surface functional groups formed on the films and the ageing media. The XPS (x-ray photoelectron spectroscopy) and the SSIMS (static secondary ion mass spectrometry) spectra indicated the formation of polar groups containing oxygen such as C=O on the film surface. The changes in the critical surface tension (_C) of the film with ageing time were largely affected by the ageing atmospheres: the _C value of the film aged in water increased, and those of the films aged in nitrogen gas and hexane decreased with an increase in ageing time. These different tendencies among the ageing media could be understood reasonably with examining the surface free energy ratios (the total energy, _S ^tot , the dispersion force component, _S ^d / _S ^tot , the polar component, _S ^p / _S ^tot , the hydrogen bonding component, _S ^h / _S ^tot ) of the films. The ageing in water of which _L is large gave the films with higher _S ^p / _S ^tot values, suggeting that the overturn and/or the orientation of the polar groups toward the water phase occurred so as to minimize the discrepancy of the surface free energy between the polymer surface and water. On the other hand, the ageing in nitrogen gas and hexane media of which _L are small gave the films with lower _S ^p / _S ^tot and _S ^h / _S ^tot values, suggesting the overturn and/or the orientation of the polar groups into the bulk polymer.