High-strength–high-modulus polyimide fibers I. One-step synthesis of spinnable polyimides

Polyimides with aromatic links are synthesized usually in two steps, but a series of aromatic polyimides with large molecular weights sufficient to produce strong fibers were prepared in one step by the reaction of 3,3′, 4,4′-biphenyltetracarboxylic dianhydride (BPDA) with various aromatic diamines. The one-step polycondensation was possible even when BPDA was replaced to some extent by pyromellitic dianhydride, which is a basic component in the conventional two-step method. The copolyimides based on BPDA and mixtures of aromatic diamines were also synthesized in similar manner. For the one-step polycondensation, phenol and some of its derivatives were found to be suitable solvents, while the typical solvent employed in the two-step method, such as N-methyl-2-pyrrolidone, could not be used because of the precipitation of low-molecular weight polyimides. p-Hydroxybenzoic acid proved to be a very efficient accelerator for the conversion of polyamic acids to polyimides.     

Preparation and properties of organo‐soluble polyimides based on 4,4′‐diamino‐3,3‐dimethyldiphenylmethane and conventional dianhydrides

4,4′‐Diamino‐3,3′‐dimethyldiphenylmethane was used to prepare polyimides in an attempt to achieve good organo‐solubility and light color. Polyimides based on this diamine and three conventional aromatic dianhydrides were prepared by solution polycondensation followed by chemical imidization. They possess good solubility in aprotonic polar organic solvents such as N‐methyl 2‐pyrrolidone, N,N‐dimethyl acetamide, and m‐cresol. Polyimide from 4,4′‐diamino‐3,3′‐dimethyldiphenylmethane and diphenylether‐3,3′,4,4′‐tetracarboxylic acid dianhydride is even soluble in common solvents such as tetrahydrofuran and chloroform. Polyimides exhibit high transmittance at wavelengths above 400 nm. The glass transition temperature of polyimide from 4,4′‐diamino‐3,3′‐dimethyldiphenylmethane and pyromellitic dianhydride is 370°C, while that from 4,4′‐diamino‐3,3′‐dimethyldiphenylmethane and diphenylether‐3,3′,4,4′‐tetracarboxylic acid dianhydride is about 260°C. The initial thermal decomposition temperatures of these polyimides are 520–540°C. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1299–1304, 1999     

Soluble aromatic polyimides and polyamides based on 4,4′-diaminotriphenylmethane

Aromatic polyamides and polyimides were synthesized from 4,4′-diaminotriphenylmethane (DA-TPM) for studying their solubility, thermal, and mechanical properties. The polymers were found to be soluble in amide solvents and pyridine, and this could be attributed to the practically free rotation of the polymer chain segments around the bridging group within the DA-TPM and the effect of its pendant phenyl ring. The polyimides and polyamides exhibited well-distinguished glass transition in the range of temperatures, which is typical for flexible-chain polymers. For the polyimides, significant differences in solubility and mechanical properties were observed between the samples prepared by chemical and thermal imidization of poly(amic acids). Thermal imidization brought about remarkably less soluble brittle films. © 1995 John Wiley & Sons, Inc.     

Preparation and properties of melt‐processable polyimides based on fluorinated aromatic diamines and aromatic dianhydrides

Two series of melt‐processable polyimides were prepared from 4,4′‐bis(3‐amino‐5‐trifluoromethylphenoxy)biphenyl (m‐6FBAB) and 4,4′‐bis(4‐amino‐5‐trifluoromethylphenoxy) biphenyl (p‐6FBAB) with various aromatic dianhydrides. The effects of the chemical structures of the polyimides on their properties, especially the melt processability and organic solubility, were investigated. The experimental results demonstrate that some of the fluorinated aromatic polyimides showed good melt processability at elevated temperatures (250–360°C) with relatively low melt viscosities and could be melt‐molded to produce strong and tough polyimide sheets. Meanwhile, the polyimides showed excellent organic solubility in both polar aprotic solvents and common solvents to give stable polyimide solutions with high polymer concentrations and relatively low viscosities. Thus, we prepared high‐quality polyimide films by casting the polyimide solutions on glass plates followed by baking at relatively low temperatures. The polyimides derived from m‐6FBAB showed better melt processability and solubility than the p‐6FBAB based polymers. The melt‐processable polyimides showed a good combination of thermal stability and mechanical properties, with decomposition temperatures of 547–597°C, glass‐transition temperatures in the range 205–264°C, tensile strengths of 81.3–104.9 MPa, and elongations at break as high as 19.6%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis and properties of polyimides from isomeric bis(dicarboxylphenylthio)diphenyl sulfone dianhydrides

4,4′-Bis(3,4-dicarboxyphenylthio)diphenyl sulfone dianhydride(4,4′-PTPSDA) and 4,4′-bis(2,3-dicarboxyphenylthio)diphenyl sulfone dianhydride(3,3′-PTPSDA) were synthesized from chlorophthalic anhydrides and bis(4-mercaptophenyl)sulfone. Their structures were determined via IR spectra, ¹H NMR and elemental analysis. A series of polyimides were prepared from isomeric PTPSDAs and aromatic diamines in 1-methyl-2-pyrrolidinone (NMP) via the conventional two-step method. Polyimides based on 4,4′-PTPSDA and 3,3′-PTPSDA have good solubility in polar aprotic solvents and phenols. The 5% weight-loss temperatures of isomeric polyimides were near 500 °C in N₂. DMTA and DSC analyses indicated that the glass-transition temperatures of polyimides from 3,3′-PTPSDA are higher than those of polyimides from 4,4′-PTPSDA. The wide-angle X-ray diffraction showed that all polyimides are amorphous. The polyimides from 3,3′-PTPSDA showed higher permeability but lower permselectivity compared with those from 4,4′-PTPSDA.     

Synthesis of aliphatic–aromatic polyimides by two-step polymerization of aliphatic dianhydride and aromatic diamine

Aliphatic-aromatic polyimides were synthesized by polycondensation reaction in solvent. The effects of variables such as the kind of solvent, reaction time and temperature, and monomer concentration were investigated in detail on the reaction of 1,2,3,4-butanetetra-carboxylic dianhydride and 4,4′-diaminodiphenylmethane. The viscos-ities of polyimides were between 0.22 and 0.46 dL/g. The polyimides were soluble in some aprotic polar solvents, such as N,N′-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), dimethylsulfoxide (DMSO), and N,N′-dimethylformamide (DMF). They began to decompose at 380–410°C in air, and 10% weight loss temperatures were 430–450°C. © 1996 John Wiley & Sons, Inc.     

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     

Synthesis and properties of polyimides derived from cis- and trans-1,2,3,4-cyclohexanetetracarboxylic dianhydrides

Cis-1,2,3,4-cyclohexanetetracarboxylic dianhydride (cis-1,2,3,4-CHDA) was synthesized. It was found that under such conditions as heating or boiling in acetic anhydride, cis-1,2,3,4-CHDA could be converted to its trans-isomer. The process of thermal isomerization was monitored by ¹H NMR spectra and the mechanism of conversion was proposed. Their absolute structures of cis- and trans-1,2,3,4-CHDAs were elucidated by single crystal X-ray diffraction. The polycondensations of cis- and trans-1,2,3,4-CHDAs with aromatic diamines such as 4,4′-oxydianiline (ODA), 4,4′-methylenedianiline (MDA), 4,4′-diamino-3,3′-dimethyldiphenylmethane (DMMDA), 4,4′-bis(4-aminophenoxy)benzene (TPEQ), 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) were studied. It is easy to obtain higher molecular weight polyimides from trans-1,2,3,4-CHDA using conventional one-step or two-step methods. However, higher molecular weight polyimides derived from cis-1,2,3,4-CHDA could not be prepared by the usual methods (solid content ca. 10%) owing to the trend of forming cyclic oligomers. Increasing the concentration of monomers could give higher molecular weight cis-polymers. All of the cis-polyimides were soluble at room temperature in aprotic polar solvents and phenolic solvents and some of them even soluble in chloroform and tetrahydrofuran, while the corresponding trans-polymers showed poor solubility as compared to cis-polymers. All of the polyimides showed good thermal stability with the 5% weight loss temperatures in air over 415 °C. Furthermore, polyimides derived from cis-1,2,3,4-CHDA have higher glass transition temperatures (T_gs) than corresponding trans-polyimides. The flexible polyimide films possessed a tensile modulus range of 2.1-3.6 GPa, a tensile strength range of 42-116 MPa, an elongation at break of 4-18%. These polyimides exhibited cutoffs at wavelengths around 270 nm and were entirely colorless. All the polyimides showed amorphous pattern according to Wide angle X-ray diffraction measurements. The differences of polymerization and properties were explained by the structural changes resulted from isomerism.     

Synthesis and characterization of fluorine and nitrile containing polyimides

A series of polyimides were synthesized from new diamine, Bis [4,4′‐amino‐5,5′ trifluoromethyl phenoxy‐(hexafluoro isopropylidine) phenoxy phenyl] benzonitrile [BATFB] and various aromatic tetracarboxylic anhydrides by thermal and chemical imidization routes. The BATFB was synthesized in two steps by nucleophilic displacement reaction of 2,6‐dichloro benzonitrile, 4,4′‐(hexafluoro isopropylidine) diphenol and 2‐amino‐5‐fluoro benzotrifluoride in the presence of anhydrous potassium carbonate in N,N′‐dimethyl acetamide (DMAc) and the structure was confirmed by FTIR spectroscopy and CHNSO analyzer. The polymers were characterized by FTIR spectroscopy and thermal analysis were performed by differential scanning calorimetry and thermogravimetric analysis methods. The prepared polyimides had glass transition temperatures between 230 and 290°C and their 10% weight loss were recorded in the range 550–590°C in N₂ atmosphere. Majority of polymers are found to be soluble in most of the organic solvents such as DMSO, DMF, DMAc, m‐cresol, and THF even at room temperature and few becomes soluble on heating. The prepared polyimides showed water uptake values 0.34–0.54 wt % at room temperature. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3455–3461, 2006     

Organosoluble and light-colored fluorinated semialicyclic polyimide derived from 1,2,3,4-cyclobutanetetracarboxylic dianhydride

In this study, the alicyclic dianhydrides 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA) was polymerized with seven kinds of fluorinated aromatic diamines, 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (1), 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (2), 1,4-bis(4-amino-2-trifluoromethylphenoxy)diphenyl (3), 1,4-bis(4-amino-2-trifluoromethylphenoxy) diphenyl ether (4), 2,2-bis[4-(4-amino-2-trifluoromethylphenoxy)phenyl]hexafluoropropane (5), 4,4′-bis(4-amino-2-trifluoromethylphenoxy)diphenyl sulfone (6), and 2,7-bis(4-amino-2-trifluoromethylphenoxy)naphthalene (7), via a two-step polycondensation procedure to prepare seven kinds of fluorinated semialicyclic polyimides (PI) PI-1 ∼ PI-7. The structures of these polyimides were confirmed by infrared spectroscopy (IR). Solubility of the polyimides was tested in various organic solvents and their thermal properties were investigated by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA). Ultraviolet-visible spectra (UV-vis) and near infrared absorption spectra (NIR) were obtained to evaluate the optical properties of these polyimides. The obtained polyimides PI-1 ∼ PI-7 displayed excellent solubility in a variety of organic solvents; they were readily soluble in amide-type polar solvent. These polyimide films exhibited good optical transparency in the visible light region (400–700 nm) with the transmittance higher than 80% at 450 nm, and these polyimide films showed little absorption at the optocommunication wavelengths of 1.30 and 1.55 μm. These polyimides showed good thermal stability with the 10% thermal decomposing temperatures higher than 443°C in nitrogen and the glass transition temperatures higher than 265°C. In addition, the effect of the structure of fluorinated diamines on the properties of polyimide films was also compared. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and characterization of polyamide-imides

A series of thermally stable, tough, linear polyimides containing amide linkages was prepared. The new polyamide-imides were synthesized by reacting a group of isomers of diaminobenzanilide (DABA) with various dianhydrides, such as 4,4′-oxydiphthalic anhydride (ODPA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), and 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA). The resulting polyamide-acids were thermally or chemically converted to the polyamide-imide (PAI). Twelve polyimides were synthesized from unsubstituted and N-methyl substituted amide diamines and their properties were compared with previously made polyamide-imides and the polyimide LARC-TPI. These polyimides exhibited high inherent viscosities and glass transition temperatures. They were made into tough, flexible films of which some showed good thermal stability and resistance to organic solvents. Overall, the mechanical properties of the PAI films were comparable to those of LARC-TPI with the 4,4′-systems exhibiting exceptional properties and crystallinity. These materials have potential as high temperature films, coatings and fibers, as well as molding and laminating resins.     

Dendronized Polyimides Bearing Long-Chain Alkyl Groups and Their Application for Vertically Aligned Nematic Liquid Crystal Displays

Polyimides having dendritic side chains were investigated. The terphenylene diamine monomer having a first-generation monodendron, 3,4,5-tris(n-dodecyloxy)-benzoate and the monomer having a second-generation monodendron, 3,4,5-tris[-3’,4’,5’-tri(n-dodecyloxy)benzyloxy]benzoate were successfully synthesized and the corresponding soluble dendritic polyimides were obtained by polycondensation with conventional tetracarboxylic dianhydride monomers such as benzophenone tertracarboxylic dianhydride (BTDA). The two-step polymerizations in NMP that is a general method for the synthesis of soluble polyimides is difficult; however, the expected dendritic polyimides can be obtained in aromatic polar solvents such as m-cresol and pyridine. The solubility of these dendoronized polyimides is characteristic; soluble in common organic solvents such as dichloromethane, chloroform, toluene and THF. These dendronized polyimides exhibited high glass transition temperatures and good thermal stability in both air and under nitrogen. Their application as alignment layers for LCDs was investigated, and it was found that these polyimides having dendritic side chains were applicable for the vertically aligned nematic liquid crystal displays (VAN-LCDs).     

Novel partially bio-based fluorinated polyimides from dimer fatty diamine for UV-cured coating

A series of novel partially bio-based fluorinated polyimides with double-bond end groups (BGPIs) from 4,4′-(hexafluoroisopropylidene) diphthalic anhydride, 4,4′-(hexafluoroisopropylidene) dianiline, Priamine 1074, 4-aminobenzoic acid, and glycidyl methacrylate were synthesized via a copolycondensation method in m-cresol. The chemical structure and performances of BGPIs were fully characterized by Fourier transform infrared spectroscopy, proton nuclear magnetic resonance, gel permeation chromatography, solubility test, X-ray diffraction, and differential scanning calorimetry. It was determined that the prepared BGPIs were in the amorphous phase and readily soluble in conventional aprotic polar solvents. Additionally, the properties of as-prepared UV-cured coatings based on BGPIs were also evaluated by real-time Fourier transform infrared, thermogravimetric analysis, UV–Vis spectroscopy, and so on. Results revealed that all coatings exhibited satisfactory curing, higher adhesion, lower water uptakes, outstanding optical transparency, and fairly favorable thermal stability under a high content of biomass up to 48.9%. Therefore, these bio-based polymers could be considered as a potential sustainable candidate for high-temperature UV-curable coatings in the microelectronic field.     

Preparation and properties of novel fluorinated polyimides based on 2,2′,6,6′-tetrafluorobenzidine

Fluorinated polyimides were prepared from 2,2′,6,6′-tetrafluorobenzidine and four conventional dianhydride monomers by a solution polycondensation reaction followed by a chemical imidization. Polyimide based on 2,2′,6,6′-tetrafluorobenzidine and hexafluoroisopropylidene bis(3,4-phthalic anhydride) (6FDA) is soluble in organic solvents such as NMP, DMA, DMF, THF, chloroform, and acetone while those based on 2,2′,6,6′-tetrafluorobenzidine and pyromellitic dianhydride (PMDA), benzophenone-3,3′,4,4′-tetracarboxylic acid dianhydride (BTDA), diphenylether-3,3′,4,4′-tetracarboxylic acid dianhydride (ETDA) are not. Polyimide from 2,2′,6,6′-tetrafluorobenzidine and 6FDA possesses high optical transparency at 350–700 nm and has a in-plane refractive index of 1.558 at 632.8 nm. All polyimides exhibit glass transition temperatures above 350°C. They also possess very high thermal stability. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1605–1609, 1998     

Synthesis and Characterisation of Polyamides and Polyimides from Amino/Methylene bis[Benzenamine] Styryl Pyridines

Polyamides and polyimides containing diamines, with potential non-linear optical characteristics, were prepared using (E)-4,4′-[[[2-(4-pyridinyl)ethenyl]phenyl]amino]bis[benzenamine] and (E)-4-4′-[[[2-(4-pyridinyl)ethenyl]2-methyl phenyl]amino]bis[benzenamine] condensed with pyromellitic dianhydride to obtain poly(amic acid)s. The poly(amic acid)s were soluble in polar aprotic solvents, such as dimethylformamide, dimethylsulphoxide and dimethylacetamide, and could be cast into transparent, tough, flexible films. Amorphous thermally stable polyimides were formed by cyclodehydration. Similarly, (E)-4,4′-[[[2-(4-pyridinyl)ethenyl]phenyl]methylene]bis[benzenamine] and (E)-4,4′-[[[2-(4-pyridinyl)ethenyl]phenyl]methylene]bis[N-ethylbenzenamine] were condensed with 3-methyladipoyl chloride to obtain other new polyamides. Characterisation using infra-red and nuclear magnetic resonance spectroscopy, X-ray diffraction and thermogravimetric analysis are reported. © 1997 SCI.     

Synthesis and properties of organosoluble polyimides derived from 2,2′‐dibromo‐ and 2,2′,6,6′‐tetrabromo‐4,4′‐oxydianilines

Two new aromatic diamines, 2,2′‐dibromo‐4,4′‐oxydianiline (DB‐ODA 4 ) and 2,2′,6,6′‐tetrabromo‐4,4′‐oxydianiline (TB‐ODA 5 ), have been synthesized by oxidation, bromination, and reduction of 4,4′‐oxydianiline (4,4′‐ODA). Novel polyimides 6a–f and 7a–f were prepared by reacting DB‐ODA ( 4 ) and TB‐ODA ( 5 ) with several dianhydrides by one‐step method, respectively. The inherent viscosities of these polyimides ranged from 0.31 to 0.99 dL/g (0.5 g/dL, in NMP at 30°C). These polyimides showed enhanced solubilities compared to those derived from 4,4′‐oxydianiline and corresponding dianhydrides. Especially, polyimides 7a , derived from rigid PMDA and TB‐ODA ( 5 ) can also be soluble in THF, DMF, DMAc, DMSO, and NMP. These polyimides also exhibited good thermal stability. Their glass transition temperatures measured by thermal mechanical analysis (TMA) ranged from 251 to 328°C. When the same dianhydrides were used, polyimides 7 containing four bromide substituents had higher glass transition temperatures than polyimides 6 containing two bromide substituents. The effects of incorporating more polarizable bromides on the refractive indices of polyimides were also investigated. The average refractive indices (n_av) measured at 633 nm were from 1.6088 to 1.7072, and the in‐plane/out‐of‐plane birefringences (Δn) were from 0.0098 to 0.0445. It was found that the refractive indices are slightly higher when polyimides contain more bromides. However, this effect is not very obvious. It might be due to loose chain packing resulted from bromide substituents at the 2,2′ and 2,2′,6,6′ positions of the oxydiphenylene moieties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of thermostable polyamideimides and their properties

Thermostable polyamideimides with inherent viscosity of 1.02–1.50 dL/g were synthesized from reacting of diamine-terminated aromatic amide prepolymer with various diisocyanate terminated imide prepolymers. The imide prepolymer was prepared by using 4,4′-diphen-ylmethane diisocyanate to react with 3,3′,4,4′ benzophenonetetracarboxylic dianhydride, 3,3′,4,4′ sulfonyl diphthalic anhydride, or 4,4′-oxydiphthalic anhydride using the direct one-pot method to improve their solubility. Almost all of the polyamideimides were generally soluble in a wide range of organic solvents such as N,N-dimethylformamide, N,N-dimeth-ylacetamide, N-methyl-2-pyrrolidone, dimethyl sulfoxide, and pyridine at room temperature. Polymers with high imide content required high temperatures to dissolve. All polyamide-imides had a glass transition temperature of 223–352°C and showed a 10% weight loss temperature of 415–575°C in air and 424–583°C in nitrogen atmosphere. The tensile strength, elongation at break, and initial modulus of polymer films ranged from 61 to 108 MPa, 5 to 10% and 1.54 to 2.50 GPa, respectively. These copolymers were partly crystalline in structure as shown by X-ray pattern. © 1996 John Wiley & Sons, Inc.     

Heat stable and organosoluble polyimides containing laterally-attached phenoxy phenylene groups

In this research a diamine monomer containing two phenoxy phenylene lateral groups, 2,2′-bis[(p-phenoxy phenyl)]-4,4′-diaminodiphenyl ether (PPAPE) was used to prepare novel wholly aromatic polyimides by thermal or chemical two-step polycondensation reactions. Comonomers including pyromellitic dianhydride (PMDA), 4,4′-oxydiphthalic anhydride (ODPA), and 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) were used for the polyimidization reactions. A reference polyimide was also prepared by the reaction of 4,4′-diaminodiphenyl ether (DADPE) with pyromellitic dianhydride (PMDA). The limited viscosity numbers as well as [`(M)]<sub>n</sub> \overline{M}_n and [`(M)]_w \overline{M}_w values of the resulting polymers were determined. All PPAPE-resulted polyimides had excellent organosolubility in common polar solvents. A low crystallinity extent was only observed using their wide-angle X-ray diffractograms (WAXD). The prepared hinged polyimides could also be cast into transparent and flexible films. The glass transition temperatures of the resulting polyimides were determined by differential scanning calorimetry (DSC) analyses. The thermograms obtained from thermogravimetric analyses (TGA) showed that the phenoxy phenylene lateral groups attached to the macromolecular backbones had no substantial diminishing effect on the thermal stability of these structurally-modified polyimides.     

A solid-state NMR study of aromatic polyimides based on 4,4′-diaminotriphenylmethane

The effect of different synthesis routes on the chemical and molecular order of polyimides based on 4,4′-diaminotripenylmethane (DA-TPM) and various aromatic dianhydrides (PI-TPM) was studied by solid-state carbon-13 nuclear magnetic resonance (¹³C-NMR). Polyimides were prepared by three different methods including a two-step procedure with either thermal or chemical imidization of precursor poly(amic acid)s (PAA) and one-step high-temperature polycondensation in phenolic solvents. Model compounds were also obtained and used in the assignment of the NMR signals. The NMR spectra for PI-TPMs obtained by one-step high-temperature polycondensation and—to a lesser extent—by thermal imidization of PAA, show sharper lines than those observed in the spectra of polymers prepared from PAA via chemical imidization. These differences are due mainly to the lower degree of ordering of the latter polyimides. WAXD patterns of polyimide films also indicated a less-ordered structure of the polymers resulting from the chemical imidization of PAA. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 1053–1064, 1998     

Preparation,Characterization and H<Subscript>2</Subscript>O<Subscript>2</Subscript> Selectivity of Hyperbranched Polyimides Containing Triazine

Novel polyimides based on aromatic dianhyride and various hexahydrotriazine monomers were synthesized via two-stage solution polycondensation method. The resulting polyimides were characterized by solubility, viscosity, density, spectroscopic and thermal analysis methods. The results showed that polyimides soluble in polar solvents and had inherent viscosities ranging from 1.92 to 2.32 dL/g. The glass transition temperatures were 315 and 344 ^○C, and the 10% weight loss temperatures were above 604 and 628 ^○C. Then, polyimide-modified electrodes were prepared for the selective determination of hydrogen peroxide. The electrochemical behavior of the resulting polyimide film electrodes to the electroactive and non-electroactive species such as ascorbic acid, oxalic acid, hydrogen peroxide, lactose, sucrose and urea was examined by CV, DPV and TB techniques. From the obtained findings, it was shown that polyimide-coated electrode (PI-2) was only permitted to hydrogen peroxide among the species examined. As a result, it is claimed that polyimide electrode could be used as a selective membrane for hydrogen peroxide.