Polyimide nanocomposites prepared from high-temperature, reduced charge organoclays

Montmorillonite clays modified with the dihydrochloride salt of 1,3-bis(3-aminophenoxy)benzene (APB) were used in the preparation of polyimide/organoclay hybrid films. Organoclays with varying surface charge based upon APB were prepared and examined for their dispersion behavior in the polymer matrix. High molecular weight poly(amide acid) solutions were prepared in the presence of the organoclays. Films were cast and subsequently heated to 300 °C to cause imidization. The resulting nanocomposite films, containing 3 wt% of organoclay, were characterized by transmission electron microscopy and X-ray diffraction. The clay's cation exchange capacity (CEC) played a key role in determining the extent of dispersion in the polyimide matrix. Considerable dispersion was observed in some of the nanocomposite films. The most effective organoclay was found to have a CEC of 0.70 meq/g. Nanocomposite films prepared with 3-8 wt% of this organoclay were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and thin-film tensile testing. High levels of clay dispersion could be achieved even at the higher clay loadings. Results from mechanical testing revealed that while the moduli of the nanocomposites increased with increasing clay loadings, both strength and elongation decreased.     

Effects of thermal imidization on mechanical properties of poly(amide‐co‐imide)/multiwalled carbon nanotube composite films

In this study, experimental and numerical studies were performed to investigate the relationship among the functionalization method, weight fraction of MWCNTs, thermal imidization cycle, and mechanical properties of various PAI/MWCNT composite films. Poly(amide‐co‐imide)/multiwalled carbon nanotube composite films were prepared by solution mixing and film casting. The effects of chemical functionalization and weight fraction of multiwalled carbon nanotubes on thermal imidization and mechanical properties were investigated through experimental and numerical studies. The time needed to achieve sufficient thermal imidization was reduced with increasing multiwalled carbon nanotube content when compared with that of a pure poly(amide‐co‐imide) film because multiwalled carbon nanotubes have a higher thermal conductivity than pure poly(amide‐co‐imide) resin. Mechanical properties of pure poly(amide‐co‐imide) and poly(amide‐co‐imide)/multiwalled carbon nanotube composite films were increased with increasing imidization time and were improved significantly in the case of the composite film filled with hydrogen peroxide treated multiwalled carbon nanotubes. Both the tensile strength and strain to failure of the multiwalled carbon nanotube filled poly(amide‐co‐imide) film were increased substantially because multiwalled carbon nanotube dispersion was improved and covalent bonding was formed between multiwalled carbon nanotubes and poly(amide‐co‐imide) molecules. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polyimide/organo‐montmorillonite nanocomposites: A comparative study of the organoclays modified with aromatic diamines

Six organophilic clays have been obtained through cation‐exchange between sodium montmorillonite (Na^+‐Mt) and the hydrochloride salts of aromatic diamines (DA1–6). The results obtained by thermogravimetric analysis (TGA) showed that the organophilic clays start to decomposition within 150–340°C, which shows that they are thermally stable compared with conventional montmorillonite modified with aliphatic long‐chain quaternary alkyl ammonium salts. The highest thermal stability and interlayer basal spacing were observed for the organoclay obtained from 3,3′‐sulfonyl dianiline (DA2), and therefore it was chosen for preparing clay/polymer nanocomposite materials (CPN). Polyimide/clay nanocomposite materials consisting of benzophenone‐3,3′,4,4′‐tetracarboxylic dianhydride (BTDA) and 2‐(5‐(3,5‐diaminophenyl)‐1,3,4‐oxadiazole‐2‐yl)pyridine (POBD) were also obtained by an in situ polymerization reaction through a thermal imidization. DA2‐Mt was used as filler at different concentrations. Both the thermal stability and the glass transition temperature (T_g) are increased with respect to pure polyimide (PI) at low clay loadings. At high clay concentrations, the organoclay particles make aggregate and as results of this phenomena T_g and thermal stability are decreased. POLYM. COMPOS., 36:613–622, 2015. © 2014 Society of Plastics Engineers     

Photosensitive poly(amic acid)/organoclay nanocomposites

A project was carried out aimed at reducing the coefficient of thermal expansion (CTE) of photosensitive polyimide formulations (photoresists) through the incorporation of small amounts of an organoclay. The organoclay was formed by a cation exchange reaction between a NA⁺-montmorillonite clay and an ammonium salt of dodecylamine. Two polyimide precursors, a poly(amic ester) (PAE) and a poly(amic acid) (PAA), were used in this study. The PAE was prepared by direct polymerization of 2,2′-bis-(3-amino-4-hydroxyphenyl)hexafluoropropane and bis(n-butyl)ester of pyromellitic acid in the presence of phenylphosphonic dichloride as an activator. The polymer had an inherent viscosity of 0.23 dL/g. The PAA copolymer was prepared by polymerization of pyromellitic dianhydride, oxydiphthalic anhydride and oxydianiline. The polymer had an inherent viscosity of 1.00 dL/g. Two photosensitive resin/clay formulations were prepared from these two PI precursors using 2,3,4-tris(1-oxo-2-diazonaphthoquinone-5-sulfonyloxy)-benzophenone as the photosensitizer and 3 wt% organoclay. The films obtained from the PAA formulation were transparent and tough, while the films prepared from the PAE formulation were opaque and brittle. Both X-ray diffraction and transmission electron microscope analyses showed that, although the organoclay was not dispersed well in the PAE matrix, it was dispersed in the PAA matrix on a nanometer scale. The clay particles remained well dispersed after the PAA film was thermally imidized. The CTE of the polyimide film obtained was 23% lower than that of a similar film that did not contain the organoclay. The temperature at which the polyimide underwent a 5% weight loss when subjected to TGA in nitrogen was also increased by 13%. The photosensitive PAA/clay nanocomposite showed a sensitivity of 301 mJ/cm² and a contrast of 1.66 when a 0.2 wt% tetramethylammonium hydroxide developer was used. A line/space pattern with a resolution of 10 μm was obtained from this formulation.     

Poly(amide‐imide)/organoclay nanocomposites using glycine as a natural amino acid: study on fire and thermal behavior

In the present study, new functional poly(amide‐imide)/organoclay nanocomposite films were successfully fabricated through the solution intercalation technique. New poly(amide‐imide) (PAI) containing glycine was synthesized via solution polycondensation of 1,1',3,3'‐tetraoxo(5,5'‐biisoindoline‐2,2'‐diyl)diacetic acid with 4,4′‐diaminodiphenylsulfone. The synthesized PAI was characterized by ¹H NMR, Fourier transform infrared (FTIR) spectroscopy, gel permeation chromatography, elemental analysis and inherent viscosity. Then, PAI/organoclay nanocomposite films containing 4 and 8 wt% of organoclay were prepared via solution intercalation through blending of organoclay 30B with the PAI solution. The nanostructures and properties of the PAI/organoclay were investigated using FTIR spectroscopy, XRD, transmission electron microscopy (TEM), TGA, DSC and microscale combustion calorimetry. XRD and TEM revealed the good dispersion of organoclay in the polymer matrix. TGA indicated that the addition of organoclay into the PAI matrix increases the thermal decomposition temperatures and char yields of the nanocomposites. Organoclay shows a positive effect in improving the flame retardancy of the PAI, reflecting the decrease in heat release rate, the total heat release and the heat release capacity of the PAI nanocomposites, while the thermal stability of the PAI nanocomposites only increased slightly compared with the neat polymer. © 2013 Society of Chemical Industry     

Effects of dispersion and arrangement of clay on thermal diffusivity of polyimide‐clay nanocomposite film

Polymer‐clay nanocomposites are well‐known high‐performance materials with a superior tensile modulus. However, in the case of composites with polyimide (PI), additional functions require study because PI is a high‐performance material in itself. Significant enhancement of thermal conductivity, which is closely related to the state of clay dispersion, is expected for a polymer‐clay nanocomposite. In this study, variations in the thermal diffusivity of PI‐clay nanocomposite films prepared by different methods were investigated. The thermal diffusivity of PI‐clay nanocomposite film increased at low clay content only when unmodified clay was used, where the clay morphology was a layered structure dispersed on a nanometer scale. Moreover, the thermal diffusivity could be enhanced by controlling the tensile stress induced by spontaneous shrinkage of the film during thermal imidization. These results demonstrated that the thermal diffusivity of PI‐clay nanocomposite films is significantly affected by the dispersion and/or arrangement states of the clay. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Novel POBD‐modified organoclay and its polyimide nanocomposites for removal of the Co(II) ion

An organophilic clay has been obtained via cation exchange reaction between sodium montmorillonite and the hydrochloride salt of 2‐(5‐(3,5‐diaminophenyl)‐1,3,4‐oxadiazole‐2‐yl)pyridine, POBD. Thermogravimetric analysis (TGA) showed that thermal decomposition of the organophilic clay starts at about 350°C, which shows that it is quite thermally stable compared with conventional montmorillonite modified with aliphatic long chain surfactants. POBD‐modified organoclay almost quantitatively removed the Co(II) ion from aqueous solution at pH = 10.0 (Q_t = 3.00 mg g⁻¹, R = 98.2%). A series of polyimide/clay nanocomposite materials (PCNs) consisting of POBD and benzophenone‐3,3′,4,4′‐tetracarboxylic dianhydride, BTDA were also prepared by an in situ polymerization reaction via thermal imidization. POBD‐modified organoclay was used as a surfactant at different concentrations. Intercalation of polymer chains within the organoclay galleries was confirmed by WXRD. Both the glass transition temperature and thermal stability are increased with respect to pristine PI at low clay concentrations. At high clay loadings, the aggregation of organoclay particles results in a decrease in T_g and thermal stability. In the SEM images of PCN 1 and 3%, too many micro cracks are observed in the background, and a flower‐shape pattern spreads uniformly over the entire surface. The maximum Co(II) uptake capacity and efficiency were observed at pH 10.0 within a 40‐h period for both PI and PCN films. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Interfacial polyfunctional condensation: Curing reaction

Heat treatment of films obtained by interfacial condensation of 4,4′-methylene dianiline (MDA) or ethylene diamine (EDA) in water and 1,2,4,5-benzenetetra acyl chloride (BTAC) in dichloromethane were studied by Fourier transform infrared spectroscopy (FTIR), ¹H-and ¹³C-nuclear magnetic resonance (NMR), fast atom bombardment mass spectrometry (FABMS), an elemental analyzer, and differential scanning calorimetry (DSC). The reaction scheme for forming the polyimide is presented. Films were synthesized from the aromatic diamine and from the aliphatic diamine system. Both must go through two-stage thermal treatment to form the structure of the imide. The first stage of this reaction is the imidization of the polyamic acid, and the second is the reaction to imidization of the functional amide group linked to the neighboring carbon on the benzene ring. After thermal treatment, the films will maintain good heat resistance. The difference between the mentioned interfacial synthetic polyimide and the conventional synthetic polyimide is that no isoimide and anhydride groups are found in the former. But the thickness of the film is limited by the nature of interfacial polymerization. In our reaction system, the maximum thickness of the film did not exceed 20 μm.     

Synthesis and Characteristics of Novel Poly(Imide Siloxane) Segmented Copolymers

New poly(imide siloxane) copolymers for possible use as tough environmentally stable structural matrix resins and structure adhesives have been prepared. Thus, 3,3'-4,4'-benzophenone tertracarboxylic dianhydride was reacted with various Mn aminopropyl-terminated polydimethylsiloxane oligomers and a meta-substituted diamine “chain-extender” such as 3,3'-diaminodiphenyl sulfone or 3,3'-diaminobenzophenone to produce the siloxane-modified poly(amic acid). Thin films were cast from the reaction mixtures and subsequent thermal dehydration produced the poly(imide siloxane) block or segmented copolymers. Upper “cure” temperatures of 300°C were used to insure complete imidization. By varying the amount and molecular weight of the siloxane oligomer, a variety of novel copolymers of controlled composition have been synthesized. Tough, transparent, flexible soluble films were produced by this method. The thermal and bulk properties of films having low to moderate siloxane content closely resemble those of the unmodified polyimide controls. However, toughness and surface behavior can be enhanced.     

Synthesis and properties of BCDA‐based polyimide–clay nanocomposites

Bicyclo[2.2.2]oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride (BCDA)‐based polyimide–clay nanocomposites were prepared from their precursor, namely polyamic acid, by a solution‐casting method. The organoclay was prepared by treating sodium montmorillonite (Kunipia F) clay with dodecyltrimethylammonium bromide at 80 °C. Polyamic acid solutions containing various weight percentages of organoclay were prepared from 4,4′‐(4,4′‐isopropylidenediphenyl‐1,1′‐diyldioxy)‐dianiline and BCDA in N‐methyl‐2‐pyrrolidone containing dispersed particles of organoclay at 20 °C. These solutions were cast on a glass plate using a Doctor's blade and then heated subsequently to obtain nanocomposite films. The nanocomposites were characterized using Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal mechanical analysis, dynamic mechanical analysis, polarizing microscopy, scanning electron microscopy, transmission electron microscopy, wide‐angle X‐ray diffraction (WAXD) and thermogravimetric analysis. The glass transition temperature of the nanocomposites was found to be higher than that of pristine polymer. The coefficient of thermal expansion of the nanocomposites decreased with increasing organoclay content. WAXD studies indicated that the extent of silicate layer separation in the nanocomposite films depended upon the organoclay content. Tensile strength and modulus of the nanocomposite containing 1% organoclay were significantly higher when compared to pristine polymer and other nanocomposites. The thermal stability of the nanocomposites was found to be higher than that of pristine polymer in air and nitrogen atmosphere. Copyright © 2007 Society of Chemical Industry     

Novel nanocomposites based on reactive organoclay of l-tyrosine and amine end-capped poly(amide–imide): Synthesis and characterization

In the present study, a series of nanocomposite materials were successfully prepared using a poly(amide–imide) (PAI) matrix and novel reactive organoclay as a reinforcing agent. The organoclay was synthesized from Cloisite Na⁺ and protonated form of l-tyrosine amino acid via ion-exchange reaction. It was confirmed by Fourier transform infrared spectroscopy, X-ray powder diffraction, field emission scanning electron microscopy, transmission electron microscopy and thermogravimetry analysis techniques. An optically active PAI was synthesized via solution polycondensation reaction of N,N′-(pyromellitoyl)-bis-phenylalanine diacid chloride and 4,4′-diaminodiphenylether. Then it was end-capped with amine end groups near the completion of the reaction to interact chemically with organoclay. Organoclay/PAI nanocomposite films containing different amounts of organoclay were prepared via solution intercalation method through blending of organoclay with the PAI solution. The nanostructures and properties of the organoclay/PAI hybrids were investigated using different techniques. Thermogravimetry analysis results indicated that the addition of organoclay into the PAI matrix increased the thermal decomposition temperatures of the resulting hybrid materials. The presence of amino acids as a biodegradable segment in both novel organoclay and optically active PAI, made the resulting nanostructure materials susceptible for biodegradation.     

Synthesis and properties of hydrogen‐bonded poly(amide‐imide) hybrid films

Poly(amide‐imide), PI, hybrid films are prepared by using sol–gel techniques. First, the poly(amide amic acid) with controlled block chain length of 5000 and 10,000 g/mol and uncontrolled chain length are synthesized by condensation reaction with 4,4′‐diaminodiphenyl ether (ODA), 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), trimellitic anhydride chloride (TMAC) and terminated with p‐aminopropyltrimethoxysilane (APrTMOS). And then the imidization reactions of poly (amide amic acid) are proceeded to obtain the poly (amide‐imide) hybrid film. Hybrid films with 5000 g/mol block chain length possess higher storage modulus, lower glass transition temperature and damping intensity comparing to films with 10,000 g/mol block chain length. The addition of TMAC to the poly(amide‐imide) hybrids is due to the increase of toughness and intermolecular hydrogen bonding, which is the average strength of intermolecular bonding and studied by the hydrogen‐bonded fraction (f_bonded), frequency difference (Δν) and shiftment. Meanwhile, PI hybrid films containing more APrTMOS and TMAC content possess higher thermal and mechanical properties. On the other hand, hybrid films with 10,000 g/mol block chain length and more TMAC content have higher gas permeabilities than other films. The degradation temperatures of 5 wt % loss of all hybrid films are all higher than 540°C and increased as the increase of TMAC content. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effect of clay surface modification and organoclay purity on microstructure and thermal properties of poly(l-lactic acid)/vermiculite nanocomposites

Vermiculite (VMT) was successfully modified by cationic exchange of hexadecyltrimethyl ammonium ions, covalent grafting of glycidoxypropyl trimethoxy silane, and combining grafting and intercalation. The complete removal of excess surfactant from VMT resulted in a change in the interlayer structure and higher thermal stability of the organoclay mineral. The organosilane grafted on the clay mineral edges improved the thermal stability of the organoclay mineral. The organoclay minerals were melt compounded with poly(l-lactic acid) (PLLA), and the effect of the nanofiller concentration, type of modification and organoclay mineral purity on the nanostructure and thermal properties of nanocomposites was investigated. The removal of excess surfactant and organosilane functionalization enhanced the dispersion level of the organoclay mineral. PLLA degradation that occurred during nanocomposite processing depended on the clay mineral concentration, the extent of clean surface and the clay mineral dispersion state. The removal of excess surfactant and organosilane functionalization improved the thermal stability of nanocomposites.     

Synthesis and properties of polyimide (containing naphthalene) nanocomposites with organo‐modified montmorillonites

2,7‐Bis(4‐aminophenoxy) naphthalene (BAPN), a naphthalene‐containing diamine, was synthesized and polymerized with a 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) to obtain a polyimide (PI) via thermal imidization. To enhance the thermal and mechanical properties of the polymer, PI–Montmorillonite (MMT) nanocomposites were prepared from a DMAc solution of poly(amic acid) and a DMAc dispersion of MMT, which were organo‐modified with various amounts of n‐dodecylamine (DOA) or cetylpyridium chloride (CPC). FTIR, XRD, and TEM (transmission electron microscopy) were used to verify the incorporation of the modifying agents into the clay structure and the intercalation of the organoclay into the PI matrix. Results demonstrated that the introduction of a small amount of MMT (up to 5%) led to the improvement in thermal stability and mechanical properties of PI. The decomposition temperature of 5% weight loss (T_d,5%) in N₂ was increased by 46 and 36°C in comparison with pristine PI for the organoclay content of 5% with DOA and CPC, respectively. The nanocomposites were simultaneously strengthened and toughened. The dielectric constant, CTE, and water absorption were decreased. However, at higher organoclay contents (5–10%), these properties were reduced because the organoclay was poorly dispersed and resulted in aggregate formation. The effects of different organo‐modifiers on the properties of PI–MMT nanocomposite were also studied; the results showed that DOA was comparable with CPC. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Preparation,structure, and pervaporation performance of poly(amide–imide)-sulfonated polyimide composites

Poly{[4,4′-bisdiphenyl-2,2′-disulfonic acid]imide-1,3-bis(3,4-dicarboxyphenoxy)benzene} was synthesized via polycondensation and subsequent thermal imidization in m-cresol:triethylamine. The obtained polymer and its composites with aromatic poly(amide–imide) obtained through polycondensation of 4-chloroformyl-(N-p-chloroformylphenyl)phthalimide and 4,4′-diaminodiphenyl ether were investigated by use of nuclear magnetic resonance, thermogravimetric analysis, dynamic mechanical analysis, differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction analysis. Transport properties of composite films were studied during pervaporation of water–alcohol mixtures. On the basis of the data obtained, suggestions on the structure of materials and its influence on transport and other physical properties were made. The addition of 30 wt % of sulfonated polyimide to the poly(amide–imide) matrix enhances its separation factor in the process of separation of an azeotrope water/ethanol mixture by four times while permeability remains unchanged. The methanol permeability increases with an increase of the mass fraction of sulfonated polyimide in the composite film. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48197.     

Preparation and characterization of silica/polyimide nanocomposite films based on water‐soluble poly(amic acid) ammonium salt

In this article, a series of new silica/polyimide (SiO₂/PI) nanocomposite films with high dielectric constant (>4.0), low dielectric loss (<0.0325), high breakdown strength (288.8 kV mm⁻¹), and high volume resistivity (2.498 × 10¹⁴ Ω m) were prepared by the hydrolysis of tetraethyl orthosilicate in water‐soluble poly(amic acid) ammonium salt (PAAS). The chemical structure of nanocomposite films compared with the traditional pure PI was confirmed by Fourier transform infrared spectroscopy and X‐ray diffraction patterns. The results indicated that both the PAAS and the polyamide acid (PAA) material were effectively converted into the corresponding PI material through the thermal imidization and the amorphous SiO₂ was embedded in the nanocomposite films without structural changes. Thermal stability of the nanocomposite films was increased though mechanical property was generally decreased with increasing the mass fraction of SiO₂. All the nanocomposite films exhibited an almost single‐step thermal decomposition behavior and the average decomposition temperature was about 615°C. It was concluded that the effective dispersion of SiO₂ particles in PI matrix vigorously improved the comprehensive performance of the SiO₂/PI nanocomposite films and expanded their applications in the electronic and environment‐friendly industries. POLYM. COMPOS., 38:774–781, 2017. © 2015 Society of Plastics Engineers     

Polyimide nanocomposite with a hexadecylamine clay: Synthesis and characterization

A poly(amic acid) was prepared by the reaction of 3,3′‐dihydroxybenzidine and pyromellitic dianhydride in N,N‐dimethylacetamide. Hexadecylamine was used as an organophilic alkylamine in organoclay. Cast films were obtained from blend solutions of the precursor polymer and the organoclay. The cast film was heat treated at different temperatures to create polyimide (PI) hybrid films. We set out to clarify the intercalation of PI chains to hexadecylamine–montmorillonite (C₁₆–MMT) and to improve thermal and tensile properties and the gas barrier. It was found that the addition of only a small amount of organoclay was enough to improve both the thermal and the mechanical properties of PIs. Maximum enhancement in the ultimate tensile strength for PI hybrids was observed for the blends containing 4% C₁₆–MMT. The initial modulus monotonically increased with further increases in C₁₆–MMT content. Water vapor permeability was decreased with increasing clay loading from 1 to 8 wt %. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2294–2301, 2002     

Positive‐working aqueous base developable photosensitive polybenzoxazole precursor/organoclay nanocomposites

Positive‐working aqueous base developable photosensitive polybenzoxazole (PBO) precursor/organoclay nanocomposites have been prepared through the addition of an organoclay to a PBO precursor. The organoclay was formed by a cation exchange reaction between a Na⁺‐montmorillonite clay and an ammonium salt of dodecylamine. The PBO precursor used in this study was a polyhydroxyamide that was prepared from a low‐temperature polymerization of 2′2′‐bis(3‐amino‐4‐hydroxyphenyl) hexafluoropropane and 4,4′‐oxydibenzoyl chloride with an inherent viscosity of 0.3 dL/g. The photosensitive resin/clay formulations were prepared from the precursor with 2,3,4‐tris(1‐oxo‐2‐diazonaphthoquinone‐5‐sulfonyloxy)‐benzophenone photosensitive compound and 3–5 wt % organoclay. The PBO precursor/clay was subsequently thermally cured to PBO/clay at 350°C. Both X‐ray diffraction and transmission electron microscope analyses showed that the organoclay was dispersed in the PBO matrix in a nanometer scale. The thermal expansion coefficient of PBO/clay film, which contained 5 wt % organoclay, was decreased 33% compared to the pure PBO film. The PBO/clay nanocomposite films also displayed higher thermal stability, glass transition temperature, and water resistance than the pure PBO film. The photosensitive PBO precursor/clay nanocomposite showed a line/space pattern with a resolution of 5 μm and its sensitivity and contrast were not affected by the organoclay. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2350–2356, 2005     

Processing of continuous poly(amide‐imide) nanofibers by electrospinning

Continuous poly(amide‐imide) nanofibers were fabricated using a novel electrospinning method with rotating and re‐collecting cylindrical collectors. The nanofilaments were modified using various post‐treatments, i.e. glycerol treatment and thermal imidization under tension, for possible application as high‐performance reinforcements. Morphological and mechanical properties of continuous poly(amide‐imide) nanofibers prepared by the electrospinning process and various post‐treatments were measured. Severe adhesion between individual nanofibers within fiber bundles was inhibited through surface treatment of the electrospun nanofiber bundles by spraying with glycerol. The morphological and mechanical properties of the continuous poly(amide‐imide) nanofibers and thermal stability were improved using thermal imidization at high temperature under tension. The morphological and mechanical properties of the continuous electrospun nanofibers were improved significantly by post‐treatments after electrospinning because uniform and complete thermal imidization occurred through the core region of the nanofibers. Copyright © 2009 Society of Chemical Industry     

Synthesis and characterization of colorless polyimide nanocomposite films

A poly(amic acid) was prepared through the reaction of 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride and 2,2′‐bis(trifluoromethyl) benzidine in N,N‐dimethylacetamide. Hybrid films were obtained from blend solutions of the precursor polymer and the organoclay dodecyltriphenylphosphonium–mica, with the organoclay content varying from 0 to 1.0 wt %. The cast films of poly(amic acid) were heat‐treated at different temperatures to create polyimide (PI) hybrid films. These PI hybrid films showed excellent optical transparency and were almost colorless. The intercalation of PI chains in the organoclay was examined with wide‐angle X‐ray diffraction and electron microscopy. In addition, the thermomechanical properties were tested with differential scanning calorimetry and thermogravimetric analysis, and the gas permeability was determined. The addition of only a small amount of the organoclay was sufficient to improve the thermal and mechanical properties of the PI, with the maximum enhancement being observed with 0.5 wt % organoclay. However, the water vapor permeability decreased with the clay loading increasing from 0 to 0.5 wt %. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007