Some aromatic polyimides based on diamines containing hydrazo group and ether linkages

Three new hydrazo-bridged diamines, 4,4′-bis [4-(4-aminophenyloxy) phenylhydrazyl] biphenyl (BPD-2), 4,4′-bis [4-(4-aminophenyloxy) phenylhydrazyl] biphenyl ether (SPD-2) and 4,4-bis [4-(4-aminophenyloxy) phenyl] hydrazine (APD-2), were synthesized by the reduction of three azo-diols, 4,4′-bis (4-azo-1-hydroxyphenyl) biphenyl (BPD), 4,4′-bis (4-azo-1-hydroxyphenyl) biphenyl ether (SPD) and azo-4-hydroxybenzene (APD), and polymerized with pyromellitic dianhydride (PM), 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BP) and 3,4,9,10-perylenetetracarboxylic acid dianhydride (PR) either by one-step solution polymerization or by two-step procedure which includes ring-opening polyaddition to give poly(amic acid) followed by cyclic dehydration to polyimide. The monomers and polyimides were characterized by their elemental analyses, FTIR and ¹H NMR spectroscopy. Glass transition temperatures of the polymers are quite high (175-310 °C), characteristic of polyimides. The decomposition temperatures for 10% weight loss fall in the range of 280-575 °C in nitrogen. Activation energies of pyrolysis for each of the polymers calculated from Horowitz and Metzger's method are also high (52.54-95.28 kJ mol⁻¹). The inherent viscosities of the polyimides at a concentration of 0.5 g/dl in DMF range from 0.94 to 1.93 dl/g.     

Synthesis and properties of polyimides derived from bis-(Aminophenoxy) containing naphthalene, [Phenyl] propane and [Methyl] cyclohexane segment and 4, 4′-carbonyldiphthalic anhydride

ABSTRACT

Three wholly, semi aromatic and aliphatic-aromatic polyimides containing bis(phenoxy) naphthalene, bis[(phenoxy) phenyl] propane and bis(phenoxy-methyl) cyclohexane segments by the two-step procedure from 2, 7-bis(4-aminophenoxy) naphthalene (BAPON), 2, 2-bis[4-(4-aminophenoxy)phenyl]propane (BAPOP), 1, 4-bis (4-aminophenoxy methyl) cyclohexane (BAPMC) as a diamine and 4,4′-carbonyldiphthalic anhydride (CDPA) were prepared. The first step of this procedure including ring-opening polyaddition in a polar solvent to give poly(amic-acid)s, second step containing cyclodehydration reaction to form polyimides. Synthesized monomer and polyimides were characterized by FT-IR, ¹H NMR spectroscopy and elemental analyses (CHN) that obtained results gave the most powerful evidence. The polyimide synthesized from BAPON was characterized as semi-crystalline, whereas the other polyimides showed amorphous patterns by the x-ray diffraction studies. The inherent viscosity was ranging between 0.87–1.01 dL/g. Tensile strength, initial moduli, and elongation at break of the polyimide films ranged from 88–117 MPa, 1.98–2.32 GPa, and 5–8%, respectively. Thermogravimetric analysis in nitrogen atmosphere shows that these polymers having good stability, so 10% weight will be lost in the range of 500–630°C. The point of polyimide with BAPMC segment, is “adding of good thermal stability and processability” lower moisture absorption and dielectric constant (0.75% and 2.90).     

Poly(1,3,4-oxadiazole-ether-imide)s and their polydimethylsiloxane-containing copolymers

Poly(1,3,4-oxadiazole-ether-imide)s were prepared by thermal imidization of poly(amic-acid) intermediates resulting from the solution polycondensation reaction of a bis(ether-anhydride), namely 2,2′-bis-[(3,4-dicarboxyphenoxy)phenyl]-1,4-phenylenediisopropylidene dianhydride, with different aromatic diamines containing 1,3,4-oxadiazole ring, such as 2,5-bis(p-aminophenyl)-1,3,4-oxadiazole, 2,5-bis[p-(4-aminophenoxy)phenyl]-1,3,4-oxadiazole, 2-(4-dimethylaminophenyl)-5-(3,5-diaminophenyl)-1,3,4-oxadiazole. Poly(1,3,4-oxadiazole-ether-imide)-polydimethylsiloxane copolymers were prepared by polycondensation reaction of the same bis(ether-anhydride) with equimolar quantities of an aromatic diamine having 1,3,4-oxadiazole ring and a bis(aminopropyl)polydimethylsiloxane oligomer of controlled molecular weight. A solution imidization procedure was used to convert quantitatively the poly(amic-acid) intermediates to the corresponding polyimides. All the polymers were easily soluble in polar organic solvents such as N-methylpyrrolidone and N,N-dimethylacetamide. The polymers showed good thermal stability with decomposition temperature being above 400 °C. Solutions of some polymers in N-methylpyrrolidone exhibited blue fluorescence, having maximum emission wavelength in the range of 370-412 nm.     

Synthesis and characterization of soluble polyimides based on a new fluorinated diamine: 4-Phenyl-2,6-bis[3-(4′-amino-2′-trifluoromethyl-phenoxy) phenyl] pyridine

A new kind of pyridine-containing aromatic diamine monomer, 4-phenyl-2,6-bis[3-(4′-amino-2′-trifluoromethyl-phenoxy) phenyl] pyridine (m-PAFP), was successfully synthesized by a modified Chichibabin reaction of 3-(4′-nitro-2′-trifluoro-methyl-phenoxy)-acetophenone with benzaldehyde, followed by a catalytic reduction. A series of fluorinated pyridine-bridged aromatic poly(ether-imide)s were prepared from the resulting diamine monomer with various aromatic dianhydrides via a conventional two-step thermal or chemical imidization method. The inherent viscosities values of these polyimides were in the range of 0.56-1.02 dL/g, and they could be cast and thermally converted into transparent, flexible, and tough polyimide films. The polyimides displayed higher solubility in polar solvents such as NMP, DMSO and m-cresol. The polyimides had good thermal stability, with the glass transition temperatures (T_g) of 187-211 °C, the temperatures at 5% weight loss of 511-532 °C, and the residue at 800 °C in air was higher than 50%. These films also had dielectric constants of 2.64-2.74 at 10 MHz and low water uptake 0.53-0.66%. Wide-angle X-ray diffraction measurements revealed that these polyimides were predominantly amorphous. Moreover, the polymer films of these novel polyimides showed outstanding mechanical properties with the tensile strengths of 90.1-96.6 MPa, elongations at breakage of 8.9-10.7% and tensile modulus of 1.65-1.98 GPa.     

One-pot synthesis of polyimides via Ni-catalyzed coupling of bis(chlorophthalimide)s

A one-pot synthesis method for the preparation of polyimides containing biphenyl units was developed via nickel-catalyzed coupling reaction of bis(chlorophthalimide)s which were prepared from chlorophthalic anhydrides and diamines in xylene. The resulting polyimides had inherent viscosities of above 0.60 dL g⁻¹. In the meantime, the copolymerizations from a mixture of three isomeric bis(chlorophthalimide)s gave the polymers with inherent viscosities of 0.36-0.55 g dL⁻¹. The solubility and film formability of the copolymers were better than those of homopolymers from bis(4-chlorophthalimide). The 10% weight loss of these polyimides was between 470 and 531 °C.     

Synthesis and characterization of fluorinated polyimides for pervaporation of n-heptane/thiophene mixtures

Soluble fluoro-polyimides have been synthesized by reacting of a fluorine-containing aromatic dianhydride, 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride, with aromatic diamine to yield poly(amic acid)s which were then cyclized to yield polyimide by chemical imidization method. The polyimides have excellent solubility both in strong bipolar solvents, such as NMP and DMAc, and in common organic solvents, such as THF and dioxane, etc. The glass transition temperature of these polyimides were determined by DSC and ranged from 281 to 289 °C. Thermogravimetric analysis indicated that these polyimides have good thermal stability with initial thermal decomposition temperature of 520-526 °C. The polyimide asymmetric membranes were prepared by phase inversion method and the inner structure was observed by method of SEM. The pervaporation properties of the prepared polyimides asymmetric membranes for n-heptane/thiophene mixtures were investigated at 40-77 °C and the permeation flux and the sulfur enrichment factor of the polyimide membranes are in the range of 0.56-1.68 kg/m² h and 3.12-2.24, respectively. The result demonstrated that the pervaporation method could be very effective method for desulfurization by polyimides asymmetric membranes with ultrathin skin.     

Synthesis and characterization of polyimides based on novel isomeric perfluorinated naphthylenediamines

Novel highly fluorinated polyimides containing hexafluoronaphthylene fragment in the main chain were prepared by the two-stage polymerization of 2,7- and 2,6-diaminohexafluoronaphthalenes with 4,4′-oxydiphthalic anhydride: polycondensation in a solution at 80 °C followed by high-temperature solid-state chain extension. The influence of hexafluoronaphthylene fragment isomerism on the key polyimide features - molecular weight, thermal stability, solubility, optical properties - was characterized. Polyimides based on 2,7-diaminohexafluoronaphthalene or easily accessible mixture of isomeric diamines formed the flexible, transparent, and thermostable films.     

Synthesis and characterization of fluorinated polyimides derived from novel unsymmetrical diamines

Two kinds of aromatic, unsymmetrical diamines with ether-ketone group, 3-amino-4′-(4-amino-2-trifluoromethylphenoxy)-benzophenone and 4-amino-4′-(4-amino-2-trifluoromethylphenoxy)-benzophenone, were successfully synthesized with two different synthetic routes. Then, they were polymerized with 4,4′-oxydiphthalic anhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, and 2,2′-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride to form a series of fluorinated polyimides via a conventional two-step thermal or chemical imidization method. The resulting polyimides were characterized by measuring their solubility, viscosity, mechanical properties, IR-FT, and thermal analysis. The results showed that the polyimides had inherent viscosities of 0.48-0.68 dl/g and were easily dissolved in bipolarity solvents and common, low-boiling point solvents. Meanwhile, the resulting strong and flexible polyimide films exhibited excellent thermal stability, e.g., decomposition temperatures (at 10% weight loss) are above 575 °C and glass-transition temperatures in the range of 218-242 °C. The polymer films also showed outstanding mechanical properties, such as tensile strengths of 86.5-132.8 MPa, elongations at break of 8-14%, and initial moduli of 1.32-1.97 GPa. These outstanding combined features ensure that the polymers are desirable candidate materials for advanced applications.     

Formation of ordered macroporous films from fluorinated polyimide by water droplets templating

Preparation of honeycomb-patterned films from one of soluble fluorinated polyimides in a humid atmosphere was reported in this paper. This polyimide was synthesized from 2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (BDAF) by two-steps method, which has excellent solubility both in strong bipolar solvents or in common low boiling-point solvents. The glass transition temperature of 6FDA-BDAF polyimide was determined by DSC and as 238 °C. Thermogravimetric analysis indicated that soluble fluoro-polyimide has good thermal stability with maximum thermal decomposition temperature of 545 °C in nitrogen atmosphere. The honeycomb-patterned films were obtained by casting a drop of polymer solution on a solid substrate in a humid atmosphere. Some influence factors, such as the solution concentration, the type of the solvent and the humidity, were also tested.     

Synthesis and properties of novel organosoluble polyimides derived from bis[3-(4-amino-2-trifluoromethylphenoxy) phenyl] ether

A new aromatic ether diamine, bis[3-(4-amino-2-trifluoromethylphenoxy) phenyl] ether, was successfully synthesized via nucleophilic substitution reaction of 3,3′-oxydiphenol and 2-chloro-5-nitrotrifluoromethylbenzene, followed by a catalytic reduction. A series of new polyimides were synthesized from the diamine with various commercially available aromatic dianhydrides via a conventional two-stage process, i.e. ring-opening polyaddition forming the poly(amic acid)s and further thermal or chemical imidization forming polyimides. The resulting polyimides exhibited good solubility in polar solvents, such as N,N-dimethylacetamide, N,N-dimethylformamide, N-methyl-2-pyrrolidinone and common solvents such as chloroform, tetrahydrofuran upon heating and possessed the inherent viscosities of 0.51-0.68 dL/g. The resulting strong and flexible films exhibited excellent thermal stability with the temperature at 10% weight loss is above 502 °C and the glass transition temperature in the range of 191-232 °C. The polyimides also were found to possess high optical transparency.     

Synthesis and characterization of novel polyimides derived from pyridine-bridged aromatic dianhydride and various diamines

A new kind of pyridine-bridged aromatic dianhydride monomer, 4-phenyl-2,6-bis[4-(3,4-dicarboxyphenoxy)phenyl]-pyridine dianhydride (PPDA), was successfully synthesized by modified Chichibabin reaction of benzaldehyde and substituted acetophenone, 4-(3,4-dicyanophenoxy)-acetophenone (DCAP), followed by acidic hydrolysis of the intermediate tetranitrile and cyclodehydration of the resulting tetraacid. The pyridine-bridged aromatic dianhydride was employed to synthesized a series of new pyridine-containing polyimides by polycondensation with various aromatic diamines in N-methyl-2-pyrrolidone (NMP) via the conventional two-step method, i.e. ring-opening polycondensation forming the poly(amic acid)s and further thermal or chemical imidization forming polyimides. The inherent viscosities of the resulting polyimides were in the range of 0.49-0.63 dL/g, and most of them were soluble in aprotic amide solvents and cresols, such as N,N-dimethylacetamide (DMAc), NMP, and m-cresol, etc. Meanwhile, strong and flexible polyimide films were obtained, which have good thermal stability with the glass transition temperatures (T_g) of 223-256 °C, the temperature at 5% weight loss of 523-569 °C, and the residue at 700 °C of 52.1-62.7% in nitrogen, as well as have outstanding mechanical properties with the tensile strengths of 70.7-97.6 MPa and elongations at breakage of 7.9-9.7%. Wide-angle X-ray diffraction measurements revealed that these polyimides were predominantly amorphous.     

Phenylethynyl terminated oligoimides derived from 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride and their adhesive properties

A series of phenylethynyl terminated oligoimides based on 3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA), m-phenylene diamine (m-PDA) or/and 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (6FAPB) with calculated molecular weight of 5000 g mol⁻¹ were synthesized. The effect of molecular structure on solubility and melt viscosity of oligoimides as well as the thermal properties of cured polyimide resins was investigated. Experimental results indicated that the oligoimides have good solubility in strong polar solvents to afford homogeneous solutions with the solid content as high as 50 wt%. The oligoimides exhibited better solubility and lower minimum melt viscosity at relatively lower temperature with the incorporation of flexible 6FAPB. These oligoimides could be thermally cured at 320-380 °C to give thermosetted resins. The cured resins have good thermal stability with the glass transition temperatures of 278-329 °C and the onset decomposition temperatures higher than 500 °C. Adhesive properties of polyimides adhered to stainless steel at various conditions were evaluated by lap shear strength test. It was found that the LSS at room temperature increased with the molar ratio of 6FAPB increasing. The polyimides with combination of rigid and flexible structures exhibited good adhesive properties. With the increasing of curing temperature, the lap shear strength of polyimides at elevated temperature maintained at a high level due to the formation of strong bond.     

Synthesis and properties of organosoluble polyimides based on novel perfluorinated monomer hexafluoro-2,4-toluenediamine

New highly fluorinated aromatic polyimides based on hexafluoro-2,4-toluenediamine and commercially available dianhydrides (6FDA and ODPA) were synthesized by one-pot high temperature polycondensation in benzoic acid melt. Owing to the CF₃ group and fluorine atoms in the meta-linked phenylenediamine fragment, these polyimides combine good solubility in organic solvents including such a low boiling point solvent as chloroform with high glass transition temperatures (330-345 °C), thermal and thermooxidative stability (T₅ is >500 °C). The highly fluorinated polyimide films (hydrogen content is ≤1%) exhibit good dielectric properties and low water absorption as well as excellent optical transparency in the UV-vis region (cut-off wavelength is 311 nm for 6FDA-based and 357 nm for ODPA-based polyimides), which is very important for optoelectronic materials.     

Synthesis and properties of soluble aromatic polyimides from 2,2′-bis(3,4-dicarboxyphenoxy)-1,1′-binaphthyl dianhydride and aromatic diamines

Aromatic tetracarboxylic dianhydride having crank and twisted noncoplanar structure, 2,2′-bis(3,4-dicarboxyphenoxy)-1,1′-binaphthyl dianhydride, was synthesized by the reaction of 4-nitrophthalonitrile with 2,2′-dihydroxy-1,1′-binaphthyl, followed by alkaline hydrolysis of the intermediate bis(ether dinitrile) and subsequent dehydration of the resulting bis(ether diacid). Binaphthyl-2,2′-diyl–containing novel aromatic polyimides having inherent viscosities up to 0.67 dL/g were obtained by the one-step polymerization process starting from the bis(ether anhydride) and various aromatic diamines. All the polyimides showed typical amorphous diffraction patterns. Most of the polyimides were readily soluble in common organic solvents such as N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), and pyridine. These aromatic polyimides had glass transition temperatures in the range of 280–350°C, depending on the nature of the diamine moiety. All polymers were stable up to 400°C, with 10% weight loss being recorded above 485°C in air. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1937–1943, 1998     

Synthesis,Characterization and Comparison of Properties of Novel Fluorinated Polyimides Derived from Bisphenol–A‐di(phthaleic anhydride)

Four new poly(etherimide)s have been synthesized by reaction with commercially available bisphenol‐A‐(diphthaleic anhydride) (BPADA) with four different kinds of diamines, namely 4,4′‐bis(p‐aminophenoxy‐3,3″‐trifluoromethyl) terphenyl,4,4′‐bis(3″‐trifluoromethyl‐p‐aminobiphenyl ether)biphenyl,2,6‐bis(3′‐trifluoromethyl‐p‐aminobiphenyl ether)pyridine, 2,5‐bis(3′‐trifluoromethyl‐p‐aminobiphenylether)thiopene. The poly(etherimide)s are named as 1a, 1b, 1c and 1d, respectively. The synthesized polyimides show good solubility in various organic solvents. The polyimide films had low water absorption of 0.19–0.30% and low dielectric constant of 2.79–3.1 at 1 MHz. These polyimides showed very high thermal stability with decomposition temperature (5% wt loss) up to 522°C in nitrogen. Transparent thin films of these polyimides exhibited tensile strength up to 97 MPa, a modulus of elasticity up to 1.56 GPa and elongation at break up to 20%.     

Synthesis and characterization of novel fluorinated polyimides derived from 1,1′-bis(4-aminophenyl)-1-(3-trifluoromethylphenyl)-2,2,2-trifluoroethane and aromatic dianhydrides

A novel fluorinated aromatic diamine 1,1′-bis(4-aminophenyl)-1-(3-trifluoromethylphenyl)-2,2,2-trifluoroethane (6FDAM) was synthesized in a simple procedure, which was then employed to prepare a series of fluorinated polyimides with commercial aromatic dianhydrides, such as pyromellitic dianhydride (PMDA), 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane (6FDA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) and 4,4′-oxydiphthalic anhydride (ODPA). The polyimides exhibited good solubility in strong dipolar solvents such as NMP, DMAc, DMF and m-cresol as well as some of low boiling point organic solvents of THF and CHCl₃, etc. Experimental results indicated the polyimides possessed low moisture adsorptions of 0.42-0.95%, low dielectric constant of 2.71-2.95 at 1 MHz, high dielectric strength of 92.0-122.6 kV/mm and good optical transparency with cutoff wavelengths of UV-vis at 330-375 nm. The polyimides also exhibited good mechanical properties as well as excellent thermal and thermo-oxidative stability. The fluorinated polyimides possessed better solubility, lower dielectric constant and water adsorption as well as higher optical transparency than the representative non-fluorinated polyimide derived from PMDA and 4,4′-oxydianiline (ODA).     

Synthesis and characterization of novel fluorinated polyimides derived from 1,3-bis(4-amino-2-trifluoromethylphenoxy)naphthalene and aromatic dianhydrides

A new structurally asymmetric diamine monomer containing flexible ether linkages and bulky trifluoromethyl substituents, namely 1,3-bis(4-amino-2-trifluoromethylphenoxy)naphthalene, was prepared from 1,3-dihydroxynaphthalene and 2-chloro-5-nitrobenzotrifluoride. New series of fluorinated polyimides were synthesized from the diamine with six commercially available aromatic tetracarboxylic dianhydrides using a conventional two-stage process with thermal or chemical imidization. The resulting polyimides were highly soluble in a variety of organic solvents and could afford transparent and tough films via solution casting. These polyimides exhibited moderately high glass-transition temperatures (by DSC) of 236-268 °C and softening temperatures (by thermomechanical analysis) of 231-250 °C, and they did not show significant decomposition before 500 °C under either nitrogen or air atmosphere. Also, they revealed low moisture absorptions (0.32-0.78%), low dielectric constants (2.81-3.24 at 10 kHz), and high optical transparency (ultraviolet-visible absorption cutoff wavelengths of 377-426 nm).     

Synthesis and characterization of some novel aromatic polyimides

Three new diamines 1,2-di(p-aminophenyloxy)ethylene, 2-(4-aminophenoxy)methyl-5-aminobenzimidazole and 4,4-(aminopheyloxy) phenyl-4-aminobenzamide were synthesized and polymerized with 3,3′,4,4′-benzophenone tetracarboxylic acid dianhydride (BP), 4,4′-(hexafluoroisopropyledene)diphthalic anhydride (HF) and 3,4,9,10-perylene tetracarboxylic acid dianhydride (PD) either by one step solution polymerization reaction or by two step procedure. The later includes ring opening poly-addition to give poly(amic acid), followed by cyclodehydration to polyimides with the inherent viscosities 0.62-0.97 dl/g. Majority of polymers are found to be soluble in most of the organic solvents such as DMSO, DMF, DMAc, m-cresol even at room temperature and few becomes soluble on heating. The degradation temperature of the resultant polymers falls in the ranges from 240 °C to 550 °C in nitrogen (with only 10% weight loss). Specific heat capacity at 300 °C ranges from 1.1899 to 5.2541 J g⁻¹ k⁻¹. The maximum degradation temperature ranges from 250 to 620 °C. T_g values of the polyimides ranged from 168 to 254 °C.     

Adhesive and dielectric properties of novel polyimides with bis(3,3′-aminophenyl)-2,3,5,6-tetrafluoro-4-trifluoromethyl phenyl phosphine oxide (mDA7FPPO)

Polyimides with a low dielectric constant and excellent adhesion were prepared from a diamine containing phosphine oxide and fluorine groups, bis(3,3′-aminophenyl-2,3,5,6-tetrafluoro-4-trifluoromethyl phenyl phosphine oxide (mDA7FPPO), and rigid-rod type dianhydride containing fluorine groups, such as 3,6-di(3′,5′-bis(trifluoromethyl)-phenyl)pyromellitic dianhydride (12FPMDA). The polyimides were synthesized via the known two-step process, preparation of poly(amic-acid) followed by solution imidization, and characterized by FT-IR, NMR, DSC, TGA and TMA. In addition, their solubility, intrinsic viscosity, dielectric constant and adhesive property were also evaluated. For comparison, 3,6-di(4′-trifluoromethylphenyl) pyromellitic dianhydride (6FPMDA) and 3,6-diphenylpyromellitic dianhydride (DPPMDA) were also utilized. The prepared polyimides exhibited high T_g (276-314 °C), excellent thermal stability (>500 °C in air), good adhesive property (104.7-126.3 g/mm), good solubility, and very low dielectric constant (2.34-2.89).     

Synthesis and properties of new polyimides derived from 1,5-bis(4-aminophenoxy)naphthalene and aromatic tetracarboxylic dianhydrides

Novel aromatic polyimides containing bis(phenoxy)naphthalene units were synthesized from 1,5-bis(4-aminophenoxy)naphthalene (APN) and various aromatic tetracarboxylic dianhydrides by the usual two-step procedure that included ring-opening polyaddition in a polar solvent such as N,N-dimethylacetamide (DMAc) to give poly(amic acid)s, followed by cyclodehydration to polyimides. The poly(amic acid)s had inherent viscosities between 0.72 and 1.94 dL/g, depending on the tetracarboxylic dianhydrides used. Excepting the polyimide IVb obtained from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), all other polyimides formed brown, flexible, and tough films by casting from the poly(amic acid) solutions. The polyimide synthesized from BPDA was characterized as semicrystalline, whereas the other polyimides showed amorphous patterns as shown by the x-ray diffraction studies. Tensile strength, initial moduli, and elongation at break of the APN-based polyimide films ranged from 105–135 MPa, 1.92–2.50 GPa, and 6–7%, respectively. These polyimides had glass transition temperatures between 228 and 317°C. Thermal analyses indicated that these polymers were fairly stable, and the 10% weight loss temperatures by TGA were recorded in the range of 543–574°C in nitrogen and 540–566°C in air atmosphere, respectively. © 1993 John Wiley & Sons, Inc.