A study of the kinetics of the microwave cure of a phenylethynyl‐terminated imide model compound and imide oligomer (PETI‐5)

The kinetic mechanism of the microwave cure of a simple phenylethynyl‐terminated imide model compound, 3,4′‐bis[(4‐phenylethynyl)phthalimido]diphenyl ether (PEPA‐3,4′‐ODA) and a phenylethynyl‐terminated imide oligomer (PETI‐5, M_n 5000 g/mol) was studied. Dielectric properties of the model compound and PETI‐5 were measured in the microwave range from 0.4 GHz to 3 GHz. FTIR was used to follow the cure of the model compound (PEPA‐3,4′‐ODA), while thermal analysis (DSC) was used to follow the cure of the PETI‐5 oligomer. The changes in room temperature IR absorbance of phenylethynyl triple bonds at 2214 cm⁻¹ of PEPA‐3,4′‐ODA as a function of cure time were measured after cure temperatures of 300, 310, 320, and 330 °C. The changes in the glass‐transition temperature, T_g, of PETI‐5 as a function of cure time were measured after cure at 350, 360, 370, and 380 °C, respectively. The T_g 's were determined to calculated the relative extent of cure, x, of the PETI‐5 oligomer according to the DiBenedetto equation. For the model compound, the reaction followed first order kinetics, yielding an activation energy of 27.6 kcal/mol as determined by infrared spectroscopy. For PETI‐5, the reaction followed 1.5th order, yielding an activation energy of 17.1 kcal/mol for the whole cure reaction, as determined by T_g using the DiBenedetto method. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2526–2535, 2000     

Thermal analysis of phenylethynyl end-capped fluorinated imide oligomer afr-pepa-4

Thermal analysis of phenylethynyl end-capped imide oligomer AFR-PEPA-4 was performed to characterize cure reaction, thermal stabilities and semicrystalline behavior of AFR-PEPA-4 oligomer and its cured polyimide. Cured AFR-PEPA-4 polyimide showed high T _gs up to 418°C. Both AFR-PEPA-4 oligomer and polyimide exhibit excellent thermal stabilities comparable to PETI-5 polyimides. AFR-PEPA-4 imide oligomer has a T _m of 330°C and exhibits spherulite crystalline morphology in the film. The crystallinity in AFR-PEPA-4 films could not be regenerated under any annealing conditions after the initial melt.     

Imidization and interdiffusion of poly(amic ethyl ester) precursors of PMDA/3,4′-ODA

Para-, meta-, and mixed isomeric poly(amic ethyl ester) precursors of the polyimide based on pyromellitic dianhydride (PMDA) and 3,4′-oxydianiline (3,4′-ODA) were synthesized. The intrinsic viscosity of each of the isomers was measured in an NMP solution and found to be less than corresponding isomers derived from PMDA and 4,4′-oxydianiline (4,4′-ODA) precursors with comparable molecular weight. The imidization and solvent retention were measured as a function of imidization temperatures, T_i using forward recoil spectrometry (FRES). For samples cast from a single solvent, either N-methyl pyrrolidone (NMP) or dimethyl sulfoxide (DMSO), no difference was observed in the temperature-dependent imidization behavior between the isomers. In all cases the imide fraction f increased as T_i increased, and reached a value of unity, i.e., full conversion at 400°C. At the same T_i, samples cast from DMSO showed a slightly higher f than samples cast from NMP. FRES and time of flight FRES (TOF-FRES) were used to measure the interdiffusion distance, w, of deuterium-labeled tracers into nondeuterated base layers of the polyimide of PMDA/3,4′-ODA treated at various T_i. The primary determinant of w for all isomers was T_i, and the particular isomer used as either the base or the tracer molecule did not seem to affect w. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2247–2258, 1998     

Synthesis and thermal behavior of new poly(ethylene terephthalate‐imide)s

Copoly(ethylene terephthalate‐imide)s (PETIs) were synthesized by the melt copolycondensation of bis(2‐hydroxyethyl)terephthalate with a new imide monomer, N,N′‐bis[p‐(2‐hydroxyethoxycarbonyl)phenyl]‐biphenyl‐3,3′,4,4′‐tetracarboxydiimide (BHEI). The copolymers were characterized by intrinsic viscosity, Fourier transform infrared, ¹H NMR, differential scanning calorimetry, and thermogravimetric analysis techniques. Although their crystallinities decreased as the content of BHEI units increased, the glass‐transition temperatures (T_g) increased significantly. When 5 or 10 mol % BHEI units were incorporated into poly(ethylene terephthalate), T_g increased by 10 or 24 °C, respectively. The thermal stabilities of PETI copolymers were about the same as the thermal stability of PET, whereas the weight loss of PETIs decreased as the content of BHEI units increased. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 408–415, 2001     

One-pot Synthesis and Characterization of Poly(meta-aryl sulfide sulfone imide imide)

Poly(meta-aryl sulfide sulfone imide imide) (m-PASSII) was synthesized by one-pot process using 4-chlorophthalic anhydride, 3,3′-diamino diphenyl sulfone and sodium sulfide (Na₂S· xH₂O) as starting materials in N-methyl-2-pyrrolidone at atmospheric pressure. The intrinsic viscosity of m-PASSII was obtained with optimum synthesis conditions is 0.21-0.27 dl/g. The polymer and the separated intermediates which generated during the synthesis process were characterized by elemental analysis, FT-IR spectrum, ¹H-NMR spectrum, X-ray diffraction, DSC, TGA and dissolvability experiment. The polymer is found to have excellent thermal performance with glass transition temperature (T _g ) of 224°C and initial degradation temperature (T _d ) of 441°C. Moreover, the polymer is dissolvable in strong polar solvents.     

Preparation and properties of polybenzoxazine/poly(imide‐siloxane) alloys: In situ ring‐opening polymerization of benzoxazine in the presence of soluble poly(imide‐siloxane)s

Benzoxazine monomer (Ba) was blended with soluble poly(imide‐siloxane)s in various weight ratios. The soluble poly(imide‐siloxane)s with and without pendent phenolic groups were prepared from the reaction of 2,2′‐bis(3,4‐dicarboxylphenyl)hexafluoropropane dianhydride with α,ω‐bis(aminopropyl)dimethylsiloxane oligomer (PDMS; molecular weight = 5000) and 3,3′‐dihydroxybenzidine (with OH group) or 4,4′‐diaminodiphenyl ether (without OH group). The onset and maximum of the exotherm due to the ring‐opening polymerization for the pristine Ba appeared on differential scanning calorimetry curves around 200 and 240 °C, respectively. In the presence of poly(imide‐siloxane)s, the exothermic temperatures were lowered: the onset to 130–140 °C and the maximum to 210–220 °C. The exotherm due to the benzoxazine polymerization disappeared after curing at 240 °C for 1 h. Viscoelastic measurements of the cured blends containing poly(imide‐siloxane) with OH functionality showed two glass‐transition temperatures (T_g's), at a low temperature around ?55 °C and at a high temperature around 250–300 °C, displaying phase separation between PDMS and the combined phase consisting of polyimide and polybenzoxazine (PBa) components due to the formation of AB‐crosslinked polymer. For the blends containing poly(imide‐siloxane) without OH functionalities, however, in addition to the T_g due to PDMS, two T_g's were observed in high‐temperature ranges, 230–260 and 300–350 °C, indicating further phase separation between the polyimide and PBa components due to the formation of semi‐interpenetrating networks. In both cases, T_g increased with increasing poly(imide‐siloxane) content. Tensile measurements showed that the toughness of PBa was enhanced by the addition of poly(imide‐siloxane). Thermogravimetric analysis showed that the thermal stability of PBa also was enhanced by the addition of poly(imide‐siloxane). © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2633–2641, 2001     

Novel method for preparation of poly(benzoxazinone‐imide)

A novel method was developed to prepare poly(benzoxazinone‐imide) by the dealcoholization of poly(amide‐imide), having pendent ethoxycarbonyl groups, which was prepared from poly(amide acid). The poly(amide acid) was prepared from the reaction of pyromellitic dianhydride and 4,4′‐diamino‐6‐ethoxycarbonyl benzanilide. The curing behavior of the poly(amide acid) was monitored by DSC, which indicated the presence of two broad endotherms, one with maximum at 153 °C due to imide‐ring formation and the other with maximum at 359 °C due to benzoxazinone‐ring formation. The poly(amide acid) was thermally treated at 300 °C/1 h to get poly(amide‐imide) with pendent ester groups, then at 350 °C/2 h to convert into poly(benzoxazinone‐imide) by dealcoholization. Viscoelastic measurements of the poly(amide‐imide) showed that the storage modulus dropped at about 280 °C with glass‐transition temperature (T_g ) at about 340 °C. The storage modulus of poly(benzoxazinone‐imide), however, was almost constant up to 400 °C and no T_g was detected below 400 °C. Also, the tensile modulus and tensile strength of the poly(benzoxazinone‐imide) was much higher than that of the poly(amide‐imide). The 5% decomposition of poly(benzoxazinone‐imide) film was at 535 °C, which reflects its excellent thermal stability. Also, poly(benzoxazinone‐imide) showed more hydrolytic stability against alkali in comparison to polyimides. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1647–1655, 2000     

Synthesis and optical properties of novel soluble and optically transparent semifluorinated poly (ether imide)s

A fluorinated diamine monomer containing flexible ether linkage and bulky trifluoromethyl substituents, namely, bis(4‐amino‐2‐trifluoromethylphenyl) ether (a), is employed to react with nonfluorinated 1,4‐bis(3,4‐dicarboxyphenoxy) benzene dianhydride (3) and CF₃‐free 2,2‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl] propane dianhydride (4), respectively, to prepare 2 novel soluble and optically transparent semi‐fluorinated poly (ether imide)s (PEIs; 3a and 4a). Compared with the corresponding PEIs based on nonfluorinated 4,4′‐diaminodiphenyl ether (b) and CF₃‐free pyromellitic dianhydride (5), the novel semifluorinated PEIs 3a and 4a not only display better solubility in some organic solvents and higher optical transparency with cutoff absorption wavelength (λ₀) below 370 nm but also maintain outstanding mechanical properties and thermal stability. 3a and 4a have tensile strength beyond 80 MPa and possess glass‐transition temperatures (T_g) beyond 210°C, coupled with the temperatures of 5% weight loss (T_5%) exceeding 500°C. It is also found that 3a and 4a exhibit contact angles against water beyond 110° and water absorptions below 0.8% together with dielectric constants less than 3.2.     

Pore structure and glass transition temperature of nanoporous poly(ether imide)

The effect of nanopores on the glass transition temperature (T_g) of poly(ether imide) was studied with differential scanning calorimetry. Nanoporous poly(ether imide) samples were obtained through the phase separation of immiscible blends of poly(ether imide) and polycaprolactone diol and by the removal of the dispersed minor phase domains with a selective solvent. Microscopy and statistical methods were used to characterize the pore structure and obtain the pore structure parameters. The pore size was found to depend on the processing time and the initial blend composition, mainly because of phase-coarsening kinetics. A decrease in T_g was observed in the nanoporous poly(ether imide) in comparison with the bulk samples. The change in T_g was strongly influenced by the pore structure and was explained by the percolation theory. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3546–3552, 2006     

Phenylethynylnaphthalic endcapped imide oligomers with reduced cure temperatures

A series of 4-(2-phenylethynyl)-1,8-naphthalic anhydride (PENA) endcapped imide oligomers with different chemical backbones and calculated number average molecular weights (Calc’d M_n) were successfully synthesized and characterized. The PENA-endcapped imide oligomers were mixtures of mono- and double-endcapped imide oligomers with polymerization degree (P_n) of 1-5 and number average molecular weights (M_n) of 2515-3851 g/mol. determined by GPC. Study on effect of chemical structures on the curing behaviors of two model compounds: PENA-m based on PENA and PEPA-m derived from 4-phenylethynylphthalic anhydride (PEPA) revealed that PENA-m showed the cure temperature of 50 °C lower than PEPA-m and the activity energy of thermal curing reaction for PENA-m was also lower than that of PEPA-m. The PENA-endcapped imide oligomers could be melt at temperatures of >250 °C with the minimum melt viscosity of 1.2-230 Pa s at 275-301 °C and the widen melt processing windows, along with 10-40 °C lower cure temperature than the PEPA-endcapped analogue.The PENA-endcapped imide oligomers could be thermally cured at 350 °C/1 h to afford the thermally cured polyimides with good combined thermal and mechanical properties including T_g of 344-397 °C (DMA), T_d of 443-513 °C, tensile strength of as high as 54.7 MPa, flexural strength of as high as 126.1 MPa and modulus of as high as 2.3 GPa, respectively.     

Thermally stable and organosoluble poly(amide-imide)s based on the imide ring-preformed dicarboxylic acids derived from 3,4′-oxydianiline with trimellitic anhydride and 6FDA

A diimide-dicarboxylic acid (DIDA) (I) was prepared from the condensation reaction of trimellitic anhydride (TMA) and 3,4′-oxydianiline (3,4′-ODA) in a 2:1 molar ratio, and another new tetraimide-dicarboxylic acid (TIDA) (II) was synthesized by condensation from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), TMA, and 3,4′-ODA in a 1:2:2 molar ratio. Two series of aromatic poly(amide-imide)s (PAI) IVa-k and Va-k were synthesized by Yamazaki phosphorylation polyamidation reactions of DIDA I and TIDA II, respectively, with various aromatic diamines. Due to highly random segmental sequence for both series in the polymer chain and the incorporation of 6FDA moieties for the V series, all the polymers were readily soluble in many organic solvents and could be casted into transparent, flexible, and tough films with good mechanical properties. Glass-transition temperature (T_gs) of the IV series and V series were recorded in the range of 242–274°C and 264–295°C. In addition, almost all the polymers showed 10% weight loss temperatures higher than 500°C under a nitrogen or an air atmosphere.     

Design and characterization of thermosetting polyimide structural adhesive and composite matrix systems

Fully cyclized, organo soluble, phenylethynyl-terminated, ether-imide oligomers of 2–10,000 g/mol (M_n) were prepared by the reaction of 2,2′-bis[4-(3,4-dicarboxyphenoxy)phenyl]-propane dianhydride (bisphenol-A dianhydride, BPADA) with a stoichiometric excess of either para, meta, or isomeric mixtures of phenylene diamine and phenylethynylphthalic anhydride (4-PEPA) endcapper. High para-containing oligomers produced semicrystalline powders, but the all meta isomer was completely amorphous. The lower molecular weight oligomers displayed an attractive low viscosity melt and were cured to very high gel content networks at 350–380°C for 30–90 min. The cured 3000 g/mol oligomers showed a (DSC) glass transition temperature (T_g) of 267°C and produced tough, solvent-resistant films. Excellent adhesion to surface-treated titanium alloys was achieved, as judged by single-lap shear measurements. Resin infusion molding was conducted, which permitted low-void, graphite-fabric composite panels to be prepared. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2943–2954, 1997     

Synthesis and characterization of novel thermotropic liquid crystalline copoly(ester imide)s

Novel liquid crystalline copoly(ester imide)s were synthesized via polyesterification of triethyleneglycol bis(4-carboxyphenyl) ether ( 1e ), diacetoxybiphenyl, and diacids with imide moieties. The effects of composition on the changes of T_g, T_m, and T_i were examined by global TSC and DSC. Thermal gravimetric analyses (TGA) found that 4a–d and 5a–g possess higher thermal stability. Strong stir opalescence phenomenon and observations from polarized optical microscopy identified that 2b–e and 3a–d possess the typical schlieren texture of an enantiotropic nematic mesophase. The birefrigent melts of 4a–d and 5a–g, however, displayed particular liquid crystalline behavior. Copolymers with higher aromatic imide ring content ( 4a–d, 5a–g ) form a layered structure and an enantiotropic smectic mesophase in the melting state. The melt viscosity of the semetic mesophase was higher than the nematic mesophase which was observed by capillary rheometer. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1791–1803, 1998     

Synthesis and characterization of aromatic poly(ether sulfone imide)s derived from sulfonyl bis(ether anhydride)s and aromatic diamines

Two sulfonyl group-containing bis(ether anhydride)s, 4,4′-[sulfonylbis(1,4-phenylene)dioxy]diphthalic anhydride ( IV ) and 4,4′-[sulfonylbis(2,6-dimethyl-1,4-phenylene)dioxy]diphthalic anhydride (Me- IV ), were prepared in three steps starting from the nucleophilic nitrodisplacement reaction of the bisphenolate ions of 4,4′-sulfonyldiphenol and 4,4′-sulfonylbis(2,6-dimethylphenol) with 4-nitrophthalonitrile in N,N-dimethylformamide (DMF). High-molar-mass aromatic poly(ether sulfone imide)s were synthesized via a conventional two-stage procedure from the bis(ether anhydride)s and various aromatic diamines. The inherent viscosities of the intermediate poly(ether sulfone amic acid)s were in the ranges of 0.30–0.47 dL/g for those from IV and 0.64–1.34 dL/g for those from Me- IV. After thermal imidization, the resulting two series of poly(ether sulfone imide)s had inherent viscosities of 0.25–0.49 and 0.39–1.19 dL/g, respectively. Most of the polyimides showed distinct glass transitions on their differential scanning calorimetry (DSC) curves, and their glass transition temperatures (T_g) were recorded between 223–253 and 252–288°C, respectively. The results of thermogravimetry (TG) revealed that all the poly(ether sulfone imide)s showed no significant weight loss before 400°C. The methyl-substituted polymers showed higher T_g's but lower initial decomposition temperatures and less solubility compared to the corresponding unsubstituted polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1649–1656, 1998     

Glass‐transition temperature: Conversion relationship in the polycyclotrimerization of 4,4′‐thiodiphenylcyanate

Polycyclotrimerization of 4,4′‐thiodiphenylcyanate was adopted as a model system for general thermosetting polymers for studying the relationship between the glass‐transition temperature (T_g) and conversion (α) during network formation. Existing expressions for T_g‐α relationship were used and compared. The experimental T_g‐α data were well fitted to several one‐parameter equations although the physical significance of parametric values thus obtained could not be unambiguously identified. Among the two‐parameter models, both the Hale–Macosko–Bair equation and the so‐called “original” DiBenedetto equation were well fitted by experimental data (when the mean‐field crosslink density was used), yielding parametric values consistent with the original designated physical meanings within the corresponding theoretical frames. Relationships between the parameters in different theories were also discussed. Incidentally, a discontinuity of ΔC_pT_g at the gel point was observed (i.e., ΔC_pT_g is of different values in the pregel and postgel regimes, respectively). © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 726–738, 2000     

Phenylquinoxaline–Aryl ester block copolymers

Phenylquinoxaline–aryl ester block copolymers were synthesized using well-defined phenolic hydroxyl terminated oligomers via a monomers/oligomer approach. Phenylquinoxaline oligomers with molecular weights of 5600 and 12,900 g/mol were prepared from the condensation of 1,4-bis(phenylglyoxalyl)benzene and 3,3′-diaminobenzidine in the presence of 4-hydroxylbenzil. The oligomers were copolymerized with isophthaloyl chloride and bisphenol A in tetrachloroethane to afford the desired phenylquinoxaline–aryl ester block copolymers. Copolymers with polyester compositions ranging from 15–50 wt % were prepared by controlling the monomers/oligomer stoichiometry. The majority of the materials displayed single phase morphologies with T_gs intermediate to the T_gs for the poly (phenylquinoxaline) and polyester homopolymers. Plots of the reciprocal of the T_g of the copolymers versus composition agreed well with values predicted by the Fox equation. A multiphase morphology was obtained for the copolymer with the highest polyester block length (? 13,000 g/mol), which displayed a T_g at 190 and 300°C indicative of a glassy–glassy system. Significant improvement in the elongations were observed for the copolymers relative to the poly(phenylquinoxaline) homopolymer. The improved elongations were obtained with minimal sacrifice to the modulus. These materials represent the first example of poly(phenylquinoxaline) block copolymers from well-defined phenylquinoxaline oligomers.     

Wholly aromatic thermotropic liquid crystalline polyesters of 4,4′-biphenol,substituted biphenols,and 1,1′-binaphthyl-4,4′-diol with 3,4′-benzophenone dicarboxylic acid

Wholly aromatic, thermotropic homopolyesters, derived from 4,4′-biphenol, substituted biphenols, or 1,1′-binaphthyl-4,4′-diol and 3,4′-benzophenone dicarboxylic acid, and two copolyesters, each of which contained 30 mol % of 6-hydroxy-2-naphthoic acid, were prepared by acidolysis polycondensation reactions and characterized for their liquid crystalline properties. The solubility behavior of these polymers has also been investigated. The two homopolymers of phenyl-substituted biphenols with 3,4′-benzophenone dicarboxylic acid were soluble in many common organic solvents. All of the homopolymers had lower T_m/T_f values than those with terephthalic acid, which was attributed to the incorporation of the asymmetric 3,4′-benzophenone dicarboxylate units in a head-to-head and head-to-tail fashion along the polyester chain. Two copolymers had lower T_m values than those of the respective homopolymers, as expected. They formed nematic phases which persisted up to 400°C, except those of phenyl-substituted biphenols with 3,4′-benzophenone dicarboxylic acid. Each of these two polymers also exhibited an accessible T_i transition, and had a broad range of LC phase. They had glass transition temperatures, T_g, in the range of 139-209°C and high thermal stabilities in the temperature range of 465-511°C. © 1995 John Wiley & Sons, Inc.     

Glass transition temperature versus conversion relationships for thermosetting polymers

Owing to enthalpy relaxation, values of the glass transition temperature (T_g) for partially reacted polymers may depend on the thermal history of samples and the heating rate used for measurements. Use of theoretical relations between T_g and the extent of reaction (x) of a thermoset must take this fact into account. The original DiBenedetto equation has been reevaluated as a convenient constitutive equation for expressing T_g versus x. An extension of Couchman's approach for the expression of the compositional variation of T_g enabled us to derive the same functionality as given by the DiBenedetto equation. Thus, the DiBenedetto equation may be regarded as based on entropic considerations applied to a model of the thermosetting polymer consisting of a random mixture of a fully reacted network with the initial monomers in an amount which depends on the particular conversion level. These two equations have been applied with success to different diepoxy-diamine copolymers.     

Development of novel cardo‐containing phenylethynyl‐terminated polyimide with high thermal properties

A phenylethynyl‐terminated reactive diluent [Card‐4‐phenylethynylphthalic anhydride (PEPA)], which contained fluorenyl cardo structures, was successfully synthesized and used as a modifier for flexible phenylethynyl‐terminated imide oligomer (PEI‐PEPA). The chemical structure, crosslink characterization, molecular weights, and thermal properties of the products were characterized. The imide systems with addition of 10, 20, 30, and 40 wt% Card‐PEPA to PEI‐PEPA (PEI‐PEPA‐Card) and their cured resin systems were prepared. The thermal curing behaviors of imide systems at different heating rates were analyzed by using differential scanning calorimetry. Thermal properties such as glass transition temperature (T_g) and char yield at 800°C of the resultant resin systems were studied by differential scanning calorimetry, dynamic mechanical analysis, and thermogravimetric analysis. The rheological properties were also investigated using a dynamic rheometry. These properties were found to be outstanding compared with pure PEI‐PEPA. The uncured imide systems exhibited lower T_g and lower isothermal viscosity with addition of Card‐PEPA. Furthermore, the T_g and char yield of the cured resin systems increased with addition of Card‐PEPA. The cured resin systems containing 40 wt% Card‐PEPA exhibited the highest T_g of 359°C and char yield at 800°C of 66.5%. Copyright © 2016 John Wiley & Sons, Ltd.     

Preparation,characterization, and properties of poly(thioether ether imide)s from isomeric bis(chlorophthalimide)s and 4,4′‐thiobisbenzenethiol

A series of isomeric poly(thioether ether imide)s (PTEIs) containing both thioether and ether linkages were prepared by nucleophilic substitution reaction of isomeric bis(chlorophthalimide)s with 4,4′‐thiobisbenzenethiol. The inherent viscosities of these polymers were in the range of 0.40–0.56 dL/g in m‐cresol at 30°C. The T_g values of PTEIs were 196–236°C; T_5% values reached up to 509–529°C in nitrogen and 508–534°C in air, which indicated this kind of polyimide possessed excellent thermal stability. The hydrolytic stability was arranged in the order: a > b > c > d > e, and improved with increasing the content of 3‐substituted phthalimide unit in the polymer backbone. Flexible films could be cast from the polymer solution with a solid content of 10%. The PTEI films exhibited good mechanical properties with tensile strengths of 90–104 MPa, elongations at break of 6.6–7.9%, and tensile moduli of 2.3–2.6 GPa. The minimum complex viscosity of PTEIs c was about 100 Pa·s at 310°C and the minimum melt viscosity of PTEIs (a–e) decreased with increasing the content of unsymmetrical 3,4′‐substituted phthalimide units. Copyright © 2014 John Wiley & Sons, Ltd.