Organic/inorganic hybrid bismaleimide resin with octa(aminophenyl)silsesquioxane

Octa(aminophenyl)silsesquioxane (OAPS) was prepared in two steps by the nitration of octaphenylsilsesquioxane (OPS) in fuming nitric acid to form octa(nitrophenyl)silsesquioxane (ONPS), followed by the mild reduction of ONPS with Pd/C as a catalyst. OPS, ONPS and OAPS were characterized by FTIR, ¹H NMR, and ²⁹Si NMR techniques. Modification of a bismaleimide (BMI) resin with OAPS and dipropargyl ether of bisphenol A (DPBPA) was investigated. The modified resins, OAPS/DPBPA/BMI, were characterized with DSC, FTIR and rheology analyses. The results showed that the modified resins have good processability. The DMA results indicated that the glass transition temperature (T_g) of the cured OAPS/DPBPA/BMI hybrid resins reached 350°C. The decomposition temperature (T_d5) of the cured resins decreased but the char yield (Y_c, 800°C) increased as the OAPS loading increased, especially in air. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

Synthesis and characterization of polyhedral oligomeric azido‐octaphenylsilsesquioxane

Polyhedral oligomeric azido‐octaphenylsilsesquioxane (N₃‐OPS) was synthesized from octaaminophenylsilsesquioxane (OAPS) via its diazonium salt. The synthesis included nitration of octaphenylsilsesquioxane (OPS) to octanitrophenylsilsesquioxane (ONPS), conversion of ONPS into octaaminophenylsilsesquioxane (OAPS), and conversion of OAPS into N₃‐OPS. The kinetics of the conversion of OAPS into N₃‐OPS were studied by recording the volume of N₂ gas released with the reaction time, which revealed it to be a 1st order reaction. The chemical structures of ONPS, OAPS and N₃‐OPS were characterized by ¹H‐NMR, GPC, FTIR, ²⁹Si solid NMR, ¹³C‐NMR, XRD, and elemental analysis. It is proposed that the diazonium salt of OAPS was substituted by the main ? N₃ group and a few of the ? OH groups. The ratio of ? N₃:? OH was calculated to be approximately 68:32 in N₃‐OPS on the basis of the elemental analysis and ¹H‐NMR. XRD suggested that N₃‐OPS was a kind of amorphous compound. The two‐step conversion mechanism of OAPS to N₃‐OPS was briefly discussed. TGA results showed that N₃‐OPS was stable at ambient temperature. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of a novel oligosiloxane containing alternative ladderlike structure via charge‐transfer interaction

A novel oligosiloxane containing alternative ladderlike structure involving viologen groups has been prepared via donor–acceptor interaction‐assisted template polymerization. The monomer used as the electron‐donor component, N,N ′‐bis(3‐methyldimethoxyl‐silylpropyl)‐4,4′‐bipyridinium dihexafluorophosphate and its precursor, N,N ′‐bis(3‐methyldimethoxyl‐silylpropyl)‐4,4′‐bipyridinium dibromide were first synthesized successfully in high yield. This oligosiloxane, which displays interesting electrochromic properties, has been characterized by FTIR, UV–vis, ¹H NMR, ²⁹Si NMR, X‐ray diffraction (XRD), and vapour pressure osmometry (VPO). © 2001 Society of Chemical Industry     

Preparation of poly(amic acid) and polyimide derived from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride with different diamines by microwave irradiation

Polycondensation‐type poly(amic acid) (PAA) was synthesized with 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride as a dianhydride monomer and 4,4′‐diaminodiphenylmethane and 4,4′‐oxydianiline as diamine monomers under microwave irradiation in dimethylformamide. Then, PAA was used to make polyimide (PI) by imidization at a low temperature. The structure and performance of the polymers were characterized with Fourier transform infrared (FTIR), proton nuclear magnetic resonance (¹H‐NMR), viscosity, X‐ray diffraction (XRD), and thermogravimetry (TG) curve analyses. The FTIR spectra of the polymers showed characteristic peaks of PI around 1779 and 1717 cm^?1. The ¹H‐NMR spectrum of PAA indicated a singlet at 6.55 ppm assigned to ? NHCO? and a singlet at 10.27 ppm assigned to carboxylic acid protons. The XRD spectrum demonstrated that the obtained PI had a low‐order aggregation structure with a d‐spacing of 0.5453 nm. The TG results revealed that the PI was thermally stable with 10% weight loss at 565°C in an N₂ atmosphere. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Synthesis and properties of elastic polyurethane‐imide

A new synthesis route for elastic polyurethane‐imides (EPUIs) has been established by a method involving the use of urea. Various EPUIs were synthesized from polyurethane‐urea, which was prepared from 4,4′‐diphenylmethane diisocyanate (MDI), polyoxytetramethylene glycol (PTMG) and 4,4′‐diphenylmethanediamine (MDA), and pyromellitic dianhydride in N‐methyl‐2‐pyrrolidone (NMP). Flexible films were cast from these solutions that had different inherent viscosities. Imidization of the EPUI films was completed at 200°C for 4 h in vacuo. The EPUIs were determined by FTIR, ¹H NMR, and ¹³C NMR spectra. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of novel optically active poly(ester imide)s by direct polycondensation reaction promoted by tosyl chloride in pyridine in the presence of N,N‐dimethyformamide

4,4′‐Hexafluoroisopropylidene‐2,2‐bis(phthalic acid anhydride) (1) was treated with L ‐methionine (2) in acetic acid and the resulting 4,4′‐(hexafluoroisopropylidene)‐N,N′‐bis(phthaloyl‐L ‐methionine) diacid (4) was obtained in high yields. The direct polycondensation reaction of this diacid with several aromatic diols, such as bisphenol A (5a), phenolphthalein (5b), 1,4‐dihydroxybenzene (5c), 4,4′‐dihydroxydiphenyl sulfide (5 d), 4,6‐dihydroxypyrimidine (5e), 4,4′‐dihydroxydiphenyl sulfone (5f), and 2,4′‐dihydroxyacetophenone (5g), was carried out in a system of tosyl chloride (TsCl), pyridine (Py), and N,N‐dimethylformamide (DMF). The reactions with TsCl were significantly promoted by controlling alcoholysis with diols, in the presence of catalytic amounts of DMF, to give a series of optically active poly(ester imide)s, (PEI)s, with good yield and moderate inherent viscosity ranging from 0.43 to 0.67 dL/g. The polycondensation reactions were significantly affected by the amounts of DMF, molar concentration of monomers, TsCl and Py, aging time, temperature, and reaction time. All of the aforementioned polymers were fully characterized by ¹H NMR, FTIR, elemental analysis, and specific rotation. Some structural characterization and physical properties of these optically active PEIs are reported. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 455–460, 2006     

Synthesis and characterization of polyimide/polyhedral oligomeric silsesquioxane nanocomposites containing quinolyl moiety

A series of functional polyhedral oligomeric silsesquioxane (POSS)/polyimide (PI) nanocomposites were prepared using a two‐step approach. First, octa(aminophenyl)silsesquioxane (OAPS) was mixed with poly(amic acid) (PAA) prepared by reacting bis(4‐amino‐3,5‐dimethylphenyl)‐3‐quinolylmethane and 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride. Second, the resulting solution was subjected to thermal imidization. The well‐defined ‘hard particles’ (POSS) and the strong covalent bonds in the amide linkage between the carbon atom of the carboxyl side group in PAA and the nitrogen atom of the amino group in POSS lead to a significant improvement in the thermal and mechanical properties. Homogeneous dispersion of POSS cages in the PI is evident from scanning electron microscopy, which further confirms that the POSS molecule becomes an integral part of the organic‐inorganic inter‐crosslinked network system. Differential scanning calorimetry and dynamic mechanical analysis show that the glass transition temperatures of the POSS‐containing nanocomposites are higher than that of the corresponding neat PI system, owing to the significant increase of the crosslinking density in the PI/POSS nanocomposites. Increasing the concentration of OAPS in the PI networks decreases the dielectric constant. Pure PI and PI/POSS systems have good antimicrobial activity. Copyright © 2011 Society of Chemical Industry     

八硝苯基笼型倍半硅氧烷改性丙烯酸酯乳液体系研究

采用半连续乳液聚合法，将八硝苯基笼型倍半硅氧烷（ONPS）掺入（甲基）丙烯酸酯乳液中，对其进行改性。透射电镜照片、粒径分布分析、DSC、拉伸强度的测量结果表明：ONPS的加入量低于3％时，明显提高了丙烯酸酯树脂的Tg，同时乳液涂膜的拉伸强度大幅上升，而断裂伸长率略有下降。     

Bis(nitrone) as crosslinking agent for unsaturated polyesters via 1,3‐dipolaric cycloaddition

The microwave‐assisted polycondensation of maleic anhydride and 1,6‐hexanediol was carried out using p‐toluenesulfonic acid as catalyst. The resulting unsaturated polyester was characterized using Fourier transform infrared (FTIR) and ¹H NMR spectroscopy, and the molecular weight determined using gel permeation chromatography. 4,4′‐Decanediyldioxydi(N‐methyl‐p‐phenylenenitrone) was chosen as a model compound for the crosslinking of the unsaturated polyester. The crosslinking, which is known to proceed via 1,3‐dipolaric cycloaddition, was followed using differential scanning calorimetry. Additionally, the kinetics of the cycloaddition was evaluated at 120 °C using FTIR spectroscopy. Copyright © 2012 Society of Chemical Industry     

Phosphorus‐containing epoxy resins: Thermal characterization

Three novel aromatic phosphorylated diamines, i.e., bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl} pyromellitamic acid (AP), 4,4′‐oxo bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl}phthalamic acid (AB) and 4,4′‐hexafluoroisopropylidene‐bis N,N′‐{3‐[(3‐aminophenyl)methyl phosphinoyl] phenyl}phthalamic acid (AF) were synthesized and characterized. These amines were prepared by solution condensation reaction of bis(3‐aminophenyl)methyl phosphine oxide (BAP) with 1,2,4,5‐benzenetetracarboxylic acid anhydride (P)/3,3′,4,4′‐benzophenonetetracarboxylic acid dianhydride (B)/4,4′‐(hexafluoroisopropylidene)diphthalic acid anhydride (F), respectively. The structural characterization of amines was done by elemental analysis, DSC, TGA, ¹H‐NMR, ¹³C‐NMR and FTIR. Amine equivalent weight was determined by the acetylation method. Curing of DGEBA in the presence of phosphorylated amines was studied by DSC and curing exotherm was in the temperature range of 195–267°C, whereas with conventional amine 4,4′‐diamino diphenyl sulphone (D) a broad exotherm in temperature range of 180–310°C was observed. Curing of DGEBA with a mixture of phosphorylated amines and D, resulted in a decrease in characteristic curing temperatures. The effect of phosphorus content on the char residue and thermal stability of epoxy resin cured isothermally in the presence of these amines was evaluated in nitrogen atmosphere. Char residue increased significantly with an increase in the phosphorus content of epoxy network. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2235–2242, 2002     

Synthesis and characterization of novel polyphenol species derived from bis(4‐aminophenyl)ether: Substituent effects on thermal behavior,electrical conductivity,solubility, and optical band gap

In this study, four different Schiff bases namely 4,4′‐oxybis[N‐(2‐hydroxybenzilidene)aniline] (2‐HBA), 4,4′‐oxybis[N‐(4‐hydroxybenzilidene)aniline] (4‐HBA), 4,4′‐oxybis[N‐(3,4‐dihydroxybenzilidene)aniline] (3,4‐HBA), and 4,4′‐oxybis[N‐(4‐hydroxy‐3‐methoxybenzilidene)aniline] (HMBA) were synthesized. These Schiff bases were converted to their polymers that have generate names of poly‐4,4′‐oxybis[N‐(2‐hydroxybenzilidene)aniline] (P‐2‐HBA), poly‐4,4′‐oxybis[N‐(4‐hydroxybenzilidene)aniline] (P‐4‐HBA), poly‐4,4′‐oxybis[N‐(3,4‐dihydroxybenzilidene)aniline] (P‐3,4‐HBA), and poly‐4,4′‐oxybis[N‐(4‐hydroxy‐3‐methoxybenzilidene)aniline] (PHMBA) via oxidative polycondensation reaction by using NaOCl as the oxidant. Four different metal complexes were also synthesized from 2‐HBA and P‐2‐HBA. The structures of the compounds were confirmed by FTIR, UV‐vis, ¹H and ¹³C NMR analyses. According to ¹H NMR spectra, the polymerization of the 2‐HBA and 4‐HBA largely maintained with C? O? C coupling, whereas the polymerization of the 3,4‐HBA and HMBA largely maintained with C? C coupling. The characterization was made by TG‐DTA, size exclusion chromatography and solubility tests. Also, electrical conductivity of the polymers and the metal complex compounds were measured, showing that the synthesized polymers are semiconductors and their conductivities can be increased highly via doping with iodine ions (except PHMBA). According to UV–vis measurements, the optical band gaps (E_g) were found to be 3.15, 2.06, 3.23, 3.02, 2.61, 2.47, 2.64, 2.42, 2.83, 2.77, 2.78, and 2.78 for 2‐HBA, P‐2‐HBA, 4‐HBA, P‐4‐HBA, 3,4‐HBA, P‐3,4‐HBA, HMBA, PHMBA, 2‐HBA‐Cu, 2‐HBA‐Co, P‐2‐HBA‐Cu, and P‐2‐HBA‐Co, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and characterization of poly(acrylate amic acid) and its application as negative‐tone photosensitive polyimides

The dianhydride monomer 3,3′,4,4′‐benzophenone tetracarboxylic acid dianhydride and two diamine monomers, 4,4′‐diamino‐3,3′‐biphenyldiol (HAB) and 2,4‐diaminophenol dihydrochloride (DAP), were used to synthesize a series of poly(hydroxyl amic acid). Further functionalization by grafting acrylate groups yields the corresponding poly(acrylate amic acid) that underwent a crosslinking reaction on exposure to UV‐light and was used as a negative‐tone photosensitive polyimide (PSPI). The analysis of chemical composition and molecular weight of these poly(amic acid)s determined by nuclear magnetic resonance (NMR) spectroscopy, Fourier transform infrared spectroscopy, and gel permeation chromatography revealed that the molecular weight of the poly(hydroxyl amic acid) increased with the molar content of HAB in the feedstock, because HAB exhibited higher polymerization reactivity than DAP. Moreover, the degree of grafting acrylate groups onto poly(hydroxyl amic acid) was determined by ¹H‐NMR spectroscopy. The photoresist was formulated by adding 2‐benzyl‐2‐N,N‐dimethylamino‐1‐(4‐morpholinophenyl) butanone (IRG369) and isopropylthioxanthone as a photoinitiator, tetra(ethylene glycol) diacrylate as a crosslinker, and tribromomethyl phenyl sulfone as a photosensitizer. The PSPI precursor exhibited a photosensitivity of 200 mJ/cm² and a contrast of 1.78. A pattern with a resolution of 10 μm was observed in an optical micrograph after thermal imidization at 300°C. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and characterization of conducting poly(aniline‐co‐diaminodiphenylsulfone) copolymers

Polyaniline, poly(aniline‐co‐4,4′‐diaminodiphenylsulfone), and poly(4,4′‐diaminodiphenylsulfone) were synthesized by ammonium peroxydisulfate oxidation and characterized by a number of techniques, including infrared spectroscopy, ultraviolet–visible absorption spectroscopy, ¹H‐NMR, thermogravimetric analysis, and differential scanning calorimetry. These copolymers had enhanced solubility in common organic solvents in comparison with polyaniline. The conductivities of the HCl‐doped polymers ranged from 1 S cm^?1 for polyaniline to 10^?8 S cm^?1 for poly(4,4′‐diaminodiphenylsulfone). The copolymer compositions showed that block copolymers of 4,4′‐diaminodiphenylsulfone (r₁ > 1) and aniline (r₂ < 1) formed and that the reactivity of 4,4′‐diaminodiphenylsulfone was greater than that of aniline. The results were explained by the effect of the ? SO₂? group present in the polymer structure. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2337–2347, 2003     

Synthesis and characterization of novel polyaspartimides derived from 2,2′‐dimethyl‐4,4′‐bis(4‐maleimidophenoxy)biphenyl and various diamines

A novel bismaleimide, 2,2′‐dimethyl‐4,4′‐bis(4‐maleimidophenoxy)biphenyl, containing noncoplanar 2,2′‐dimethylbiphenylene and flexible ether units in the polymer backbone was synthesized from 2,2′‐dimethyl‐4,4′‐bis(4‐aminophenoxy)biphenyl with maleic anhydride. The bismaleimide was reacted with 11 diamines using m‐cresol as a solvent and glacial acetic acid as a catalyst to produce novel polyaspartimides. Polymers were identified by elemental analysis and infrared spectroscopy, and characterized by solubility test, X‐ray diffraction, and thermal analysis (differential scanning calorimetry and thermogravimetric analysis). The inherent viscosities of the polymers varied from 0.22 to 0.48 dL g⁻¹ in concentration of 1.0 g dL⁻¹ of N,N‐dimethylformamide. All polymers are soluble in N‐methyl‐2‐pyrrolidone, N,N‐dimethylacetamide, N,N‐dimethylformamide, dimethylsulfoxide, pyridine, m‐cresol, and tetrahydrofuran. The polymers, except PASI‐4, had moderate glass transition temperature in the range of 188°–226°C and good thermo‐oxidative stability, losing 10% mass in the range of 375°–426°C in air and 357°–415°C in nitrogen. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 279–286, 1999     

Synthesis,characterization of novel dihydrazide containing polyurethanes based on N1,N2‐bis[(4‐hydroxyphenyl)methylene]ethanedihydrazide and various diisocyanates

Four novel types of polyurethanes (PUs) were prepared from N¹,N²‐bis[(4‐hydroxyphenyl)methylene]ethanedihydrazide with two aromatic diisocyanates (4,4′‐diphenylmethane diisocyanate and tolylene 2,4‐diisocyanate) and two aliphatic diisocyanates (isophorone diisocyanate and hexamethylene diisocyanate). The chemical structure of both diol and PUs was confirmed by UV–vis, fluoroscence, FTIR, ¹H NMR, and ¹³C NMR spectral data. DSC data show that PUs have multiple endotherm peak. X‐ray diffraction revealed that the PUs contained semicrystalline and amorphous regions that varied with the nature of the backbone structures. PUs were soluble in polar aprotic solvents. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and thermal property of hybrid nanocomposites by free radical copolymerization of styrene with octavinyl polyhedral oligomeric silsesquioxane

The poly(styrene‐co‐octavinyl‐polyhedral oligomeric silsesquioxane) (PS–POSS) organic–inorganic hybrid nanocomposites containing various percent of POSS were prepared via one‐step free radical polymerization and characterized by FTIR, high‐resolution ¹H NMR, ²⁹Si NMR, GPC, DSC, and TGA technologies. The POSS contents in these nanocomposites were determined using FTIR calibration curve. The result shows that the POSS contents in nanocomposites can be tailored by varying the POSS feed ratios. On the basis of the POSS contents in the nanocomposites and the ¹H NMR spectra, the number of reacted vinyl groups of each octavinyl‐POSS macromonomer were calculated to be 6–8. DSC and TGA measurements indicate that the incorporation of POSS into PS homopolymer can apparently improve the thermal properties of the polymeric materials. The dramatic T_g and T_dec increases are mainly due to the formation of star and low cross‐linking structure of the nanocomposites, where POSS cores behave as the joint points and hinder the motion and degradation of the polymeric chains. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis and characterization of a novel functional monomer containing cyano and propenylphenoxy groups and the properties of its copolymer with bismaleimide (BMI)

A novel functional monomer containing cyano and propenylphenoxy groups, 2,6‐di{2‐[(E)‐l‐propenyl]phenoxy}benzonitrile (DPPB) was prepared with high stereospecificity by the reaction of 2,6‐dichlorobenzonitrile and 2‐allylphenol in a mixed solvent system of N‐methylpyrrolidone (NMP)/toluene in the presence of anhydrous potassium carbonate. The chemical structure of the product was characterized by FTIR, ¹H NMR and ¹³C NMR. The monomer was then used to modify a popular commercial bismaleimide, 4,4‐bismaleimidodiphenylmethane (BMDPM), for improving the shear strength of the resin. The results showed that the modified resin could attain 4.7 times the shear strength of neat BMDPM and good heat resistance when the composition of DPPB in the modified resin was 45% (by weight). © 2002 Society of Chemical Industry     

Synthesis and characterization of novel polyurethanes based on N1,N4‐bis[(4‐hydroxyphenyl)methylene]succinohydrazide hard segment

This article deals with the synthesis and characterization of novel polyurethanes (PUs) by the reaction between two aromatic diisocyanates (4,4′‐diphenylmethane diisocyanate and tolylene 2,4‐diisocyanate) and two aliphatic diisocyanates (isophorone diisocyanate and hexamethylene diisocyanate) with N¹,N⁴‐bis[(4‐hydroxyphenyl)methylene]succinohydrazide, which acted as hard segment. UV–vis, FTIR, ¹H NMR, ¹³C NMR, and DSC/TGA analytical technique has been used to determine the structural characterization and thermal properties of the hard segmented PUs. X‐ray diffraction revealed that PUs contained semicrystalline and amorphous regions that varied depending upon the nature of the backbone structures. PUs were soluble in polar aprotic solvents. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Monomers and polymers of 4‐(N,N‐diallylamino)pyridine functions

4‐(N,N‐Diallylamino)pyridine (DAAP), N,N‐diallylaminobenzene (DAAB), N,N,N′,N′‐tetrallyl‐4,4′‐diaminobenzidine (AAB), N,N,N′,N′‐tetrallyl‐4,4′‐diaminodiphenyl sulfone (AABS), and N,N,N′,N′‐tetrallyl‐4,4′‐diaminodiphenyl ether (AABE) were prepared by sodium substitution and N‐allylation. Moreover, linear polyDAAP, poly(DAAP‐co‐DAAB), and network poly(DAAP‐co‐AAB), poly(DAAP‐co‐AABS), and poly(DAAP‐co‐AABE), all being polymers containing supernucleophilic groups, were synthesized in the cyclopolymerization. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 363–367, 2000     

Organosoluble polyimides derived from asymmetric 2‐substituted‐and 2,2′,6‐trisubstituted‐4,4′‐oxydianilines

We report a new method for the preparation of asymmetric diamines using 4,4′‐oxydianiline (4,4′‐ODA) as the starting material. By controlling the equivalents of bromination agent, N‐bromosuccinimide, we were able to attach bromide and phenyl substituents at the 2‐ or 2,2′,6‐positions of 4,4′‐ODA. Thus, four new asymmetric aromatic diamines, 2‐bromo‐4,4′‐oxydianiline (6), 2,2′,6‐tribromo‐4,4′‐oxydianiline (7), 2‐phenyl‐4,4′‐oxydianiline (8) and 2,2′,6‐triphenyl‐4,4′‐oxydianiline (9), were synthesized by this method. Their structural asymmetry was confirmed using ¹H NMR spectroscopy. Asymmetric polyimides (PI10–PI13) were prepared from these diamines and three different dianhydrides (pyromellitic dianhydride (PMDA), 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and 2,2‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride) in refluxing m‐cresol. The formed polyimides, except PI10a derived from 6 and PMDA, were all soluble in m‐cresol without premature precipitation during polymerization. These polyimides with inherent viscosity of 0.41–0.96 dL g^?1, measured at a concentration of 0.5 g dL^?1 in N‐methyl‐2‐pyrrolidone at 30 °C, can form tough and flexible films. Because of the structural asymmetry, they also exhibited enhanced solubility in organic solvents. Especially, polyimides PI11a and PI13a derived from 7 and 9 with rigid PMDA were soluble in various organic solvents at room temperature. The structural asymmetry of the prepared polyimides was also evidenced from ¹H NMR spectroscopy. In the ¹H NMR spectrum of PI11a, the protons of pyromellitic moiety appeared in an area ratio of 1:2:1 at three different chemical shifts, which were assigned to head‐to‐head, head‐to‐tail and tail‐to‐tail configurations, respectively. These polyimides also exhibited good thermal stability. Their glass transition temperatures ranged from 297 to 344 °C measured using thermal mechanical analysis. © 2013 Society of Chemical Industry