Hydrogen‐bonding,crystallinity, and morphological properties of poly(silicic acid)/waterborne polyurethane nanocomposites

Unique nanocomposites consisting of poly(silicic acid) nanoparticles (PNs) and waterborne polyurethane (WPU) were prepared. The aliphatic WPU prepared in this study was end‐capped with a silanol group, which could react with PNs via a sol–gel process. PNs were modified with phenyltrimethoxysilane (PTMS) and 3‐(trimethoxysilyl)propyl ester (TMPE) and then blended with WPU. The structure–property relationships were examined. Solid‐state ²⁹Si NMR spectra of WPU showed that structures T₁, T₂, and T₃ of WPU decreased and structures Q₃ and Q₄ of PN/WPU nanocomposites increased gradually. When the PN concentration increased to 10 wt %, PN/WPU nanocomposites exhibited the maximum fraction of hydrogen‐bonded carbonyl groups. In the PTMS–PN and TMPE–PN systems, the fraction of hydrogen‐bonded carbonyl groups fluctuated stably when the concentrations of PTMS–PN and TMPS–PN exceeded 5 wt %. The X‐ray diffraction results revealed that α‐form, γ‐form, or triclinic crystallization could be found in the WPU matrix. A differential scanning calorimetry spectrum showed that the crystalline structure of the hard segment of WPU was influenced by the nanoparticle concentration. The degrees of crystallinity were 88% for the PN/WPU nanocomposites, 41% for the PTMS–PN/WPU nanocomposites, and 54% for the TMPE–PN/WPU nanocomposites when the PN, PTMS–PN, and TMPE–PN concentrations were 5 wt %. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1076–1089, 2005     

Preparation of poly(methyl acrylate‐co‐itaconic anhydride)/SiO2 hybrid materials via the sol–gel process—The effect of the coupling agent,inorganic content,and nature of the catalyst

Transparent poly(methyl acrylate‐co‐itaconic anhydride)/SiO₂ hybrid materials were prepared from methyl acrylate‐itaconic anhydride copolymer and tetraethoxysilane (TEOS) with the coupling agent (3‐aminopropyl)triethoxysilane (APTES) via a sol–gel process. The covalent bonds between the organic and inorganic phases were introduced by the in situ aminolysis of the itaconic anhydride units with APTES forming a copolymer bearing a triethoxysilyl group. These groups subsequently were hydrolyzed with TEOS and allowed to form a network. These reactions were monitored by Fourier transform infrared analysis. The amount of APTES had a dramatic influence on the gel time and sol fraction. The effect of APTES, the inorganic content, and the nature of the catalyst on the thermal properties and morphology of the hybrid materials were studied by differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and atomic force microscopy. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 321–328, 2000     

Preparation and properties of silylated PTFE/SiO2 organic–inorganic hybrids via sol–gel process

A study on poly(tetrafluoroethylene) (PTFE) reinforced with tetraethoxysilanes (TEOS) derived SiO₂ is described. It included the manufacturing process of SiO₂‐reinforced PTFE and the effects of silylation agent on the properties of the hybrid material, such as porosity, hydrophobic, thermal resistance, dielectric and mechanical properties, and microstructure. PTFE/SiO₂ hybrids of 50 wt % SiO₂ loading were prepared via a sol–gel process and were shaped by a two‐roll milling machine. Trimethylchlorosilane and hexamethydisilazane were used as the silylation agents. Our results showed that the water absorption and dielectric loss of PTFE/SiO₂ hybrid had significantly improved with silylation agent. The silylation process replaced Si? OH with Si? CH₃ on the surface of the TEOS‐derived silica colloidal particle. The existence of trimethylsilyl [? Si(CH₃)₃] on the surface of the modified PTFE/SiO₂ hybrid was confirmed via infrared and solid‐state ²⁹Si magic‐angle spinning nuclear magnetic resonance spectra. Nitrogen‐sorption techniques were used to characterize the modified and unmodified PTFE/SiO₂ hybrids. The microstructure of SiO₂ in the matrix was also evaluated with scanning electron microscopy and transmission electron microscopy. Our results showed that the silylated sol–gel‐derived PTFE/SiO₂ hybrids had exhibited high porosity (53.7%) with nanosize pores (10–40 nm) and nanosize colloidal particles (20–50 nm). This manifests itself as have the ultralow dielectric properties (D_k = 1.9 and D_f = 0.0021), low coefficient of thermal expansion (66.5 ppm/°C), high tensile modulus (141 MPa), excellent thermal resistance (T_d = 612 °C), and an increased hydrophobia (θ = 114°); moreover, the hydrophobic property of the PTFE/SiO₂ hybrid was thermally stable up to 400 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1789–1807, 2004     

Preparation and characterization of some unusually transparent poly(dimethylsiloxane) nanocomposites

A technique was developed for preparing poly(dimethylsiloxane) nanocomposites having unusually high transparencies as quantitatively judged by ultraviolet–visible spectroscopy. The method was the in situ generation of silica particles by a two‐step sol–gel procedure in which the required water of hydrolysis was simply absorbed from the air, and the catalyst was generated in situ from a tin salt. Electron microscopy showed that the phase‐separated silica domains were very small (30–50 nm in diameter) and well dispersed, as expected from the transparency of the composites. Stress‐strain measurements in tension indicated that the particles provide very good reinforcement. Ultra‐small‐angle X‐ray scattering data showed that the domain morphology depends strongly on catalyst, but weakly on loading level. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1897–1901, 2003     

In situ polymerization of silicic acid in polyethylene–octene elastomer: Properties and characterization of the hybrid nanocomposites

Silicic acid produced from sodium metasilicate hydrate and metallocene polyethylene–octene elastomer (POE) were chosen as the ceramic precursor and the continuous phase, respectively, for preparation of new hybrids by an in situ sol–gel process. To obtain a better hybrid, the acrylic acid‐grafted polyethylene–octene elastomer (POE‐g‐AA) prepared in our laboratory and used as the continuous phase was also investigated. Characterizations of POE/SiO₂ and POE‐g‐AA/SiO₂ composites were performed by Fourier transform infrared spectroscopy, ²⁹Si solid‐state nuclear magnetic resonance (NMR) spectrometry, X‐ray diffractometry, differential scanning calorimetry, thermogravimetry analysis, and an Instron mechanical tester. The POE‐g‐AA/SiO₂ hybrid could give the positive effect on the properties of POE/SiO₂ hybrid because the carboxylic acid groups of acrylic acid should act as coordination sites for the silica phase to form chemical bonds. The result of ²⁹Si solid‐state NMR spectra showed that Si atom coordination around SiO₄ units is predominantly Q₃ and Q₄. Also, the POE‐g‐AA/SiO₂ hybrid with 15 wt % SiO₂ gave the maximum values of tensile strength and glass‐transition temperature because excess particles might cause the separation between the organic and inorganic phases when the silica content was beyond this point. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 351–359, 2003     

Silica/poly (N‐vinylimidazolium) nanospheres by combined RAFT polymerization and thiol‐ene click chemistry

We report a facile method that combined sol–gel reaction, reversible addition–fragmentation chain transfer (RAFT)/macromolecular design via interchange of the xanthates process and thiol‐ene click reaction to prepare monodisperse silica core‐poly(N‐vinylimidazole) (PVim) shell microspheres of 200 nm in average diameters. First, silica with C = C double bonds was prepared by the sol–gel reaction of 3‐(trimethoxysilyl)propyl methacrylates (MPS) with tetraethoxysilane in ethanol; SiO₂@PVim were subsequently prepared by grafting PVim chain (Mn = 9800 g/mol, polydispersity index = 1.22) to MPS‐SiO₂ via the thiol‐ene click chemisty. The obtained SiO₂@PVim microspheres show higher catalytic activity toward the hydrolysis of p‐nitrophenyl acetate compared with the PVim homopolymers. The as‐prepared composites have been characterized by scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis and Fourier transform infrared spectrometry analysis. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis of TiO2–SiO2/polymer core–shell microspheres with a microphase‐inversion method

A novel microphase‐inversion method was proposed for the preparation of TiO₂–SiO₂/poly(methyl methacrylate) core–shell nanocomposite particles. The inorganic–polymer nanocomposites were first synthesized via a free‐radical copolymerization in a tetrahydrofuran solution, and the poor solvent was added slowly to induce the microphase separation of the nanocomposite and result in the formation of nanoparticles. The average particle sizes of the microspheres ranged from 70 to 1000 nm, depending on the reaction conditions. Transmission electron microscopy and scanning electron microscopy indicated a core–shell morphology for the obtained microspheres. Thermogravimetric analysis and X‐ray photoelectron spectroscopy measurements confirmed that the surface of the nanocomposite microspheres was polymer‐rich, and this was consistent with the core–shell morphology. The influence of the synthetic conditions, such as the inorganic composition and the content of the crosslinking monomer, on the particle properties was studied in detail. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3911–3920, 2006     

Synthesis,structure, and morphology of polymer–silica hybrid nanocomposites based on hydroxyethyl methacrylate

Two types of polymer–silica nanocomposites have been prepared by undergoing free radical polymerization of 2-hydroxyethyl methacrylate (HEMA) either in the presence of HEMA-functionalized SiO₂ nanoparticles (Type 1) or during the simultaneous in situ growing of the silica phase through the acid-catalyzed sol–gel polymerization of tetraethoxysilane (TEOS) (Type 2). Relationships between synthesis conditions, chemical structure, and resulting morphology have been studied. Type 1 systems exhibit a classical particle-matrix morphology, but where particles tend to form aggregates. Type 2 systems possess a finer morphology characterized by a very open mass-fractal silicate structure, which is believed to be bicontinuous with the organic phase at a molecular level. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3172–3187, 1999     

The role of TEOS‐TIP within a pentablock ionomer: Morphology,physical properties,and ion transport

Inorganic–organic nanocomposites were created using tetraethylorthosilicate (TEOS), titanium isopropoxide (TIP), and poly(t‐butylstyrene‐b‐hydrogenated isoprene‐b‐sulfonated styrene‐b‐hydrogenated isoprene‐b‐t‐butylstyrene) or pentablock copolymer (PBC). A TEOS–TIP–H₂O ternary phase diagram was generated to create homogenous sol solutions with designable condensation reactions that led to controllable materials. An inorganic TEOS–TIP network was synthesized using sol–gel chemistry within the organic PBC domain. All TEOS–TIP–PBC films exhibited higher water sorption than unmodified PBC ionomer that was attributed to a change in morphology. Proton conductivity increased up to 80% due to TEOS–TIP within the nanocomposite film. This can be attributed to ion domain redistribution and partial charge transfer from the titanate's inorganic domains to sulfonate groups that promote acid dissociation. PBC had a microphase‐separated morphology that changed with increasing TIP concentration, which was observed from atomic force microscopy and small‐angle X‐ray scattering results. Finally, thermal gravimetric analysis revealed a decrease in degradation temperature, and dynamic mechanical analysis results demonstrated reduced polymer chain mobility caused by inorganic–organic interactions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 575–586     

Morphology and viscoelasticity of PP/TiO2 nanocomposites prepared by in situ sol–gel method

PP/TiO₂ nanocomposites were prepared from an original method based on the hydrolysis‐condensation (sol–gel method) reactions of titanium alkoxide inorganic precursor premixed with polypropylene (PP) under molten conditions. Nanocomposites with a mean diameter of primary particles lower than 5 nm were then prepared. The TiO₂ particle dispersion in the PP matrix was characterized over a wide length scale from the combination of small angle X‐ray scattering, transmission electron microscopy, and linear viscoelasticty of molten nanocomposites. As a result, a fractal structure of these particles was highlighted at the highest concentration (φ_r ≥ 0.014) with a characteristic aggregation size d_aggr ≈ 130 nm. The relationships between fractal structure and linear viscoelastic have been discussed from the main works of the literature on the reinforcement of nanocomposites. The drastic alteration of the terminal relaxation zone (solid‐like behavior) is correlated to the formation of an aggregate‐particle network. The study of the nonlinear viscoelastic behavior (Payne effect) agrees qualitatively with this reinforcement mechanism. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1213–1222, 2010     

Field effect conductance of conducting polymer nanofibers

We report on the electrical conductance of nanofibers of regioregular poly(3‐hexylthiophene) (RRP3HT) as a function of gate‐induced charge. Nanofibers of RRP3HT were deposited onto SiO₂/Si substrates by casting from dilute p‐xylene solutions. An analysis of the nanofibers by atomic force microscopy revealed fiber lengths of 0.2–5 μm, heights of 3–7 nm, and widths of approximately 15 nm. A field effect transistor geometry was used to probe the conductance of webs of nanofibers and single nanofibers; in these measurements, gold electrodes served as source and drain contacts, and the doped SiO₂/Si substrate served as the gate. Temperature‐dependent transport studies on webs of nanofibers revealed an activation energy of 108 meV at a gate‐induced hole density of 3.8 × 10¹² charges/cm². Pretreating SiO₂ with a hydrophobic hexamethyldisilazane (HMDS) layer reduced the activation energy to 65 meV at the same charge density. The turn‐on gate voltage on treated and untreated substrates increased in magnitude with decreasing temperature. Conductance measurements on single nanofibers on HMDS‐treated SiO₂ yielded hole mobilities as high as 0.06 cm²/Vs with on/off current ratios greater than 10³. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2674–2680, 2003     

Preparation and properties of poly(styrene-co-maleic anhydride)/silica hybrid materials by the in situ sol–gel process

Poly(styrene-co-maleic anhydride)/silica hybrid material has been successfully prepared from styrene–maleic anhydride copolymer and tetraethoxysilane (TEOS) in the presence of a coupling agent (3-aminopropyl)triethoxysilane (APTES) by an in situ sol–gel process. It was observed that the gel time of sol–gel solution was dramatically influenced by the amount of APTES. The hybrid material exhibits optical transparency almost as good as both silica gel and the copolymer. The covalent bonds between organic and inorganic phases were introduced by the aminolysis reaction of the amino group with maleic anhydride units of copolymer to form a copolymer bearing trimethoxysilyl groups, which undergo hydrolytic polycondensation with TEOS. The differential scanning calorimetry (DSC) showed that the glass transition temperature of the hybrid materials increases with increasing of SiO₂ composition. Photographs of scanning electron microscopy (SEM) and atomic force microscopy (AFM) inferred that the size of the inorganic particles in the hybrid materials was less than 20 nm. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1607–1613, 1998     

Preparation and characterization of epoxy/SiO2 nanocomposites by cationic photopolymerization and sol–gel process

Epoxy/SiO₂ nanocomposite materials were prepared by cationic photopolymerization and sol–gel process using a novel epoxy oligomer (EP‐Si(OC₂H₅)₃) prepared by 3‐isocyanatopropyltriethoxysilane (IPTS)‐grafted bisphenol A epoxy resin and tetraethyl orthosilicate as inorganic precursor. The chemical structures of EP‐Si(OC₂H₅)₃ were characterized by Fourier transformed infrared spectroscopy. Transmission electron microscopy showed that the in situ generated nano‐SiO₂ dispersed uniformly in the EP matrix, and its average diameter is around 40 nm. The relationship between nanocomposite materials' thermal/mechanical properties and nano‐SiO₂ introduced were studied by thermogravimetric analysis, dynamic mechanical analysis, and impact strength test. The results showed that the nanocomposite materials' thermal and mechanical properties improved a lot with increase of the SiO₂ content. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis and properties of silica/polystyrene/polyaniline conductive composite particles

In this study, silica/polystyrene/polyaniline (SiO₂/PS/PANI) conductive composite particles were synthesized by four sequential reactions. The nanosized SiO₂ particles were synthesized from tetraethoxysilane (TEOS) by a sol–gel process with water as the solvent medium, followed by a surface modification with triethoxyvinylsilane; then the surface modified SiO₂ particles were used as seeds to synthesize SiO₂/PS composite particles with soapless seeded emulsion polymerization. Finally, the SiO₂/PS particles were used as seeds to synthesize the SiO₂/PS/PANI conductive composite particles. The sol–gel process of SiO₂, the effect of surface modification, and several other factors that influenced polymerization of styrene in the soapless seeded emulsion polymerization will be discussed. Either potassium persulfate (KPS) or 2,2′‐azobis(isobutyramidine) dihydrochloride (AIBA) was used as the initiator to synthesize the uniform SiO₂/PS particles successfully, and the cross‐section morphology of the SiO₂/PS particles was found to be of a core–shell structure, with SiO₂ as the core, and PS as the shell. The SiO₂/PS particles were well dispersed in many organic solvents. In the following step to synthesize SiO₂/PS/PANI conductive composite particles, sodium dodecyl sulfate (SDS) played an important role, specifically, to absorb aniline onto the surfaces of the SiO₂/PS particles to carry out the polymerization of aniline over the entire surface of the particles. The conductivity of the SiO₂/PS/PANI composite particles approached that of semiconductive materials. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 342–354, 2005     

Preparation and properties of Nafion/SiO2 composite membrane derived via in situ sol–gel reaction: size controlling and size effects of SiO2 nano‐particles

A novel technique in controlling the size of SiO₂ nano‐particles in the preparation of Nafion/SiO₂ composite membranes via in situ sol–gel method, as well as the effects of nano‐particle size on membrane properties and cell performance, is reported in this paper. Nafion/SiO₂ composite membranes containing SiO₂ nano‐particles with four different diameters (5 ± 0.5, 7 ± 0.5, 10 ± 1, and 15 ± 2 nm) are fabricated by altering the reactant concentrations during in situ sol–gel reaction. Sequentially, size effects of SiO₂ nano‐particles on membrane properties and cell performance are investigated by SEM/EDAX, TEM, TGA, mechanical tensile, and single cell tests, etc. The results suggest that 10 nm is a critical diameter for SiO₂ incorporated into Nafion matrix, exhibiting desirable physico‐chemical properties for operation at elevated temperature and low humidity. At 110°C and 59% RH, the output voltage of the cell equipped with Nafion/SiO₂ (10 nm) obtains an output voltage of 0.625 V at 600 mA/cm², which is 50 mV higher than that of unmodified Nafion. Copyright © 2010 John Wiley & Sons, Ltd.     

Real‐time Fourier transform infrared study of the free‐radical ultraviolet‐induced polymerization of a hybrid sol–gel. II. The effect of physicochemical parameters on the photopolymerization kinetics

Free‐radical photocurable hybrid sol–gel materials have gained special interest during the last decades. Compared to thermally processed materials, they present the advantages of fast curing, low energy consumption, and spatiotemporal control of the reaction. Although comprehension of the photochemical step is fundamental, little is known about the characteristic of photochemistry in this kind of material. Real‐time Fourier transform infrared spectroscopy was used to study the photopolymerization of a hybrid sol–gel upon ultraviolet irradiation. Various photoinitiator systems were tested for their efficiency in inducing the polymerization of pendant polymerizable moieties anchored on a partially condensed silicate network. The presence of O₂ and the nature of the polymerizable function were shown to be crucial factors in the photoinduced process. The effects of the photoinitiator concentration and light intensity were also studied. These results were explained in terms of classical kinetic models developed for all‐organic photopolymers to point out the distinctive aspects related to the use of photoinitiated polymerization in hybrid sol–gel materials. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 831–840, 2003     

Fabrication of Fe3O4@SiO2 nanocomposites to enhance anticorrosion performance of epoxy coatings

SiO₂‐coated Fe₃O₄ (Fe₃O₄@SiO₂) nanocomposites were prepared by sol–gel method, and the anticorrosion performance of composite coatings was discussed. The structure of the Fe₃O₄@SiO₂ nanocomposites was verified through Fourier transform infrared, X‐ray diffraction, and scanning electron microscopy. Composite epoxy coatings with same concentrations of Fe₃O₄ and Fe₃O₄@SiO₂ were measured by scanning electron microscopy contact angle meter. More importantly, the Fe₃O₄@SiO₂ nanocomposites not only obtained a homogeneous dispersion and compatibility in epoxy resin but also exhibited an obvious superiority in enhancing the anticorrosion performance of epoxy coatings. Furthermore, the anticorrosion mechanism of Fe₃O₄@SiO₂/epoxy composite coating was tentatively discussed. Copyright © 2015 John Wiley & Sons, Ltd.     

Confined crystallization behaviors in polyethylene/silica nanocomposites: Synergetic effects of interfacial interactions and filler network

The confinement effects introduced by nanoparticles have been reported to influence the phase behaviors thus the properties of polymer nanocomposites. In this study, molecular dynamics and crystallization behaviors of polyethylene (PE) composited with three types of silica (SiO₂) nanoparticles, namely unmodified SiO₂, hydrophobically modified SiO₂, SiO₂‐APTES (3‐aminopropyltriethoxysilane) and SiO₂‐PTES (n‐propyltriethoxysilane), were systematically investigated via a combination of DSC, XRD and ¹H solid‐state NMR measurements. The suppressions in crystallization and chain mobilities of PE rank in the order of unmodified SiO₂ < SiO₂‐APTES < SiO₂‐PTES due to the increasing interfacial interactions between PE and SiO₂ nanoparticles. Additionally, independent of polymer–nanoparticle interactions, a silica network forms for all three kinds of nanocomposites when SiO₂ content reaches 83 wt %. The mobilities of polymer chains are severely restricted by such a percolated network structure, leading to a turning point in the crystallization ability of nanocomposites and a new crystallization peak at 45 °C lower than that of pure PE. The synergetic effects of interfacial interactions and filler network on polymer crystallization have been thoroughly studied in this work, which will provide guidance on modifying and designing nanocomposites with controlled properties. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 498–505     

Synthesis of polyethylene‐octene elastomer/SiO2‐TiO2 nanocomposites via in situ polymerization: Properties and characterization of the hybrid

In this study, a silicic acid and tetra isopropyl ortho titanate ceramic precursor and a metallocene polyethylene‐octene elastomer (POE) or acrylic acid grafted metallocene polyethylene‐octene elastomer (POE‐g‐AA) were used in the preparation of hybrids (POE/SiO₂? TiO₂ and POE‐g‐AA/SiO₂? TiO₂) using an in situ sol‐gel process, with a view to identifying a hybrid with improved thermal and mechanical properties. Hybrids were characterized using Fourier transform infrared spectroscopy, ²⁹Si solid‐state nuclear magnetic resonance (NMR), X‐ray diffraction, differential scanning calorimetry, thermogravimetry analysis, dynamic mechanical thermal analysis, and Instron mechanical testing. Properties of the POE‐g‐AA/SiO₂? TiO₂ hybrid were superior to those of the POE/SiO₂? TiO₂ hybrid. This was because the carboxylic acid groups of acrylic acid acted as coordination sites for the silica‐titania phase to allow the formation of stronger chemical bonds. ²⁹Si solid‐state NMR showed that Si atoms coordinated around SiO₄ units were predominantly Q₃ and Q₄. The 10 wt % SiO₂? TiO₂ hybrids gave the maximum values of tensile strength and glass transition temperature in both POE/SiO₂? TiO₂ and POE‐g‐AA/SiO₂? TiO₂. It is proposed that above this wt %, excess SiO₂? TiO₂ particles caused separation between the organic and inorganic phases. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 1690–1701, 2005     

Gel–sol transition for soluble polyimide solution

Copolyimides were synthesized in N‐methyl‐2‐pyrrolidone (NMP) to prepare polyimide (PI) solutions with various concentrations, and gels can form in PI/NMP solution with a suitable concentration or at a low temperature. Gel–sol transition in the PI/NMP solution has been investigated through a combination of polarized optical microscope, differential scanning calorimeter measurement, and rheological measurements. According to Winter–Chambon theory, the critical gel point is 12 wt %, and the loss tangent (tan δ) shows frequency independence. Gel–sol transition temperature (T_gel) for the 13 wt % solution is around 65 °C. Below the T_gel, the gel exhibits strong optical planar texture, indicating the formation of a fully anisotropic phase, which has a great importance for the fabrication of PI fibers by gel‐spinning. Dynamic temperature sweep measurements show that the formation of the gel from solution is thermoreversible and is significantly delayed in the cooling process. Under the favorable conditions, the tensile strength and modulus of the fibers derived from the solution are about 0.7 and 12.5 GPa using gel‐spinning method, which is believed to afford broad application potential in preparing high‐performance PI fibers. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 450–459