FT-Raman investigation of the thermal curing of PMDA/ODA polyamic acids

The effect of solvent on the curing reactions of PMDA/ODA polyamic acids has been investigated using Fourier transform (FT)-Raman spectroscopy. Films of different thicknesses were cured by: (1) doctor blading 15% solids solutions onto glass slides, (2) removing all but the bound NMP, and (3) removing all the N-methypyrrolidinone (NMP). The rate of cure and final degree of conversion of the PMDA/ODA polyamic acid to polyimide increased substantially in the presence of NMP, and this effect was attributed to the plasticizing effect of the solvent. Below a critical solvent concentration, which was estimated to be approximately 40% of the NMP concentration in the bound-solvent limit, the rate of imidization slowed down considerably. Comparison of FT-Raman data for PMDA/ODA polyamic acid: (1) in solution in NMP, (2) complexed with NMP in the solid state, and (3) in the solid state after all the NMP had been removed with water, indicated that intermolecular interactions were greatest in the latter case and weakest in solution. Spectra of PMDA/ODA in NMP solution provide strong evidence for binding of NMP to the amide carbonyl in solution. © 1993 John Wiley & Sons, Inc.     

Molecular weight characterization of soluble high performance polyimides. 1. Polymer-solvent-stationary phase interactions in size exclusion chromatography

Soluble, fully cyclized m-amino phenyl acetylene terminated polyimides based on several anhydride/diamine monomers were prepared in N-methylpyrrolidine (NMP) and cyclized by solution imidization to controlled molecular weight. The polyimides and a polyamic acid precursor were successfully analyzed by size exclusion chromatography (SEC) utilizing online parallel coupled refractive index and differential viscometer detectors. The calculated M _nvalues were varied from 3,000 to 20,000 daltons. N-methylpyrrolidone (NMP), tetrahydrofuran (THF), and chloroform served as mobile phases for the cross-linked polystyrene gel packings. Normal retention behavior of the polyimides was observed in chloroform, THF, and NMP containing LiBr, or in NMP stirred over P₂O₅ before use. Values of Mark-Houwink-Sakurada exponents for narrow distribution linear polystyrene indicate that pure NMP and NMP with 0.06 M LiBr are good solvents for polystyrene standards at 60°C. In contrast, SEC behavior of polyimides in pure NMP leads to splitting of the peaks with the major portion observed to pass through the columns at the exclusion limit. In contrast to strong polymeric chain expansion of the polyamic acid in dilute solution, presumably due to a polyelectrolyte effect, no increase of intrinsic viscosity of polyimide samples in pure NMP was observed. This exclusion effect of polyimides analyzed in NMP is discussed in terms of possible ion-exclusion from pores of the stationary phase. Differences in polystyrene calibration in NMP with or without additives and the temperature dependence of calibration curves in these mobile phases is discussed as well. ©1995 John Wiley & Sons, Inc.     

Amine–quinone polyimide: A new high‐temperature polymer and its use to protect iron against corrosion

A new diamine monomer was synthesized by the Michael addition of 4,4′‐methylene dianiline with 1,4‐benzoquinone. The monomer was condensed with 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride to give a polyamic acid that was soluble in NMP. The polyamic acid was cast onto iron and thermally imidized to yield the amine–quinone polyimide (AQPI‐2). AQPI‐2 had a thermal decomposition temperature of 540 °C (10% TGA weight loss in N₂) and a glass transition at 292 °C, values typical of polyimides. The degradation of the coating on iron after exposure to 0.1 M NaCl electrolyte was followed by electrochemical impedance spectroscopy. Under these conditions a conventional polyimide failed after 3 days exposure, while AQPI‐2 survived more than 24 days exposure. The adhesive bond between the amine–quinone polyimide and the iron surface was so strong that it could not be broken by the electrolyte. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2893–2899, 2000     

Curing studies of a polyimide precursor

Complexes between diphenylcarbamido-dicarboxybenzene and 1-methyl-2-pyrrolidinone, 1/4 and 1/2 M, are obtained by reacting pyromellitic dianhydride with aniline in the solvent 1-methyl-2-pyrrolidinone. Decomplexation and imidization of this diamic acid are studied by thermogravimetric analysis, differential scanning calorimetry, Fourier transform infrared spectrometry, polarizing microscopy, and gas chromatography/mass spectrometry. Side reactions competing with the imide formation are discussed. The presence of solvent is found to markedly influence imidization.     

Mechanism and kinetics of the polymerization of thermoplastic polyimides. I. Study of the pyromellitic anhydride/aromatic amine system

We have synthesized model compounds representing the repeating units of a polyamic acid prepared from pyromellitic anhydride and an aromatic amine. They were characterized with HPLC, ¹H and ¹³C liquid and solid NMR and FTIR. The Kinetic study of the ring dehydration reaction of model compounds showed that the reaction paths were very different, depending on the experimental conditions (isotherms, liquid, or solid states). They could lead to a deterioration of the polyamic of the polyamic acid by the formation of side reactions. These reactions could predominate as a result of the existence of an equilibrium between the amic acid group and starting monomers.     

Spectrophotometric study of the complex formation of 3-(1-naphthyl)-2-mercaptopropenoic acid with nickel(II), palladium(II) and hydrogen ions

The equilibria between 3-(1-naphthyl)-2-mercaptopropenoic acid (H(2)NMP) and nickel, palladium and hydrogen ions at 25 degrees in aqueous 0.1 M NaClO(4) solution containing 1-2% ethanol have been studied spectrophotometrically. Protonation constants for the ligand and formation constants for the complexes Ni(NMP), Ni(NMP)(2-)(2), Pd(NMP) and Pd(NMP)(2-)(2), refined by the SQUAD program, are reported.     

Time resolved fluorescence spectroscopy of Eu(III) complexation with alpha-hydroxy isobutyric acid

Complexation of Eu(III) with alpha-hydroxy isobutyric acid (HIBA), a model compound of humic acid, has been studied by time resolved fluorescence spectroscopy. The ratio of fluorescence intensity of the two peaks at 616 and 592 nm (I(616/592)) was found to increase with increasing ligand to metal ratio. The I(616/592) data was used to deduce the stability constant of Eu-HIBA complexes of the type ML(i) (i=1-3). The formation of multiple ligand complexes was also corroborated by lifetime data which was found to increase with increasing [HIBA]/[Eu] ratio thus indicating replacement of coordinated water molecules by HIBA.     

Novel synthesis of polyimide with pendant 1-phenylethyl ester using DBU and its thermal acid-catalyzed deesterification

A model reaction of o-(N-phenylcarbamoyl)benzoic acid (amic acid) with threefold amounts of 1-phenylethyl bromide (PEB) and 1,8-diazabicyclo-[5,4,0]-7-undecene (DBU) was carried out in NMP. The reaction gave N-[m-(1-phenylethoxycarbonyl)phenyl]phthalimide in almost quantitative yield at room temperature for 2 h. Polyimide containing pendant 1-phenylethyl ester (P-1a) was also prepared from polyamic acid with PEB using DBU according to the model reaction. The obtained polymer was exactly consistent with P-1a synthesized stepwise from the esterification of the corresponding polyimide containing pendant carboxylic acid with PEB. Therefore, the reaction of polyamic acid bearing pendant carboxylic acid with alkyl bromide proceeded quantitatively to give polyimide containing pendant ester in the presence of DBU. Also, this method was applied to the synthesis of polyimide containing 1-phenylethyl ether. However, the polyimide with quantitative etherification was not synthesized. The acid-catalyzed deesterification of P-1a film was carried out by heating the irradiated polymer film containing 10 wt % of p-nitrobenzyl 9,10-diethoxyanthracene-2-sulfonate, which produced sulfonic acid by irradiation, at various temperatures. Although thermal deesterification of P-1a started at 220°C without any acid catalyst, the deesterification occurred when the irradiated film was heated at the lower temperature. The degree of esterification can be determined from the disappearance of absorption at 700 cm⁻¹. The deesterification obeyed first-order kinetics. © 1996 John Wiley & Sons, Inc.     

Solution properties of poly(amic acid)–NMP containing LiCl and their effects on membrane morphologies

Physical properties of poly(amic acid) (PAA) casting solutions in N-methyl-2-pyrrolidone (NMP) containing lithium chloride (LiCl) were characterized by viscometry and dynamic light scattering (DLS) and were related to the morphological properties of asymmetric membranes prepared from these solutions. At a fixed polymer concentration, the increase in viscosity of the PAA solutions with increasing LiCl content is mainly determined by the viscosity of the salt–solvent medium, implying that the LiCl–NMP interactions are stronger than those between LiCl and PAA. Because of the strong salt–solvent interactions, complexes between LiCl and NMP are formed. The complexes reduce the solvent power of NMP for PAA inducing polymer aggregation (clustering) and/or transient cross-links in the solutions. Dynamic light scattering results for salt-containing solutions at low PAA concentrations support the existence of these aggregations. Solutions without salt showed a single relaxation, but solutions with LiCl exhibit multiple relaxation modes; two diffusional modes of cooperative and aggregates, and one angle independent transient network mode. The polymer aggregates and transient cross-links form a gel-like structure in the casting solution film and hinder macrovoid formation during phase inversion, resulting in asymmetric membranes with a primarily sponge-like structure.     

Preparation,characterization, and properties of polyamic acid nano‐emulsion

A facile method was developed to prepare polyamic acid (PAA) nano‐emulsion using a non‐aqueous emulsification. The resultant PAA nano‐emulsion was characterized by light‐scattering particle size analysis, transmission electron microscopy (TEM), zeta potential, and conductivity analyses. It was found that polyamic acid salt (PAS), formed by partially neutralizing PAA at the carboxylic groups using triethyl amine (TEA), was of great importance for nano‐emulsification. The effect factors on the formation of PAA nano‐emulsion were investigated. To get a stable PAA nano‐emulsion in methanol (precipitant), the following ratios are required: amine/COOH (molar ratio) = 0.6–0.7, precipitant/solvent (mass ratio) = 1.5–2.25. A PAA nano‐emulsion with droplets ranging in size from 50 to 100 nm was obtained under optimized conditions. The driving force for the formation of PAA nano‐emulsion was also discussed. Copyright © 2011 John Wiley & Sons, Ltd.     

Fabrication of Porous Polyimide Membrane with Through-Hole via Multiple Solvent Displacement Method

Porous polyimide (PI) membranes are widely used in separation processes because of their excellent thermal and mechanical properties. However, the applications of porous PI membranes are limited in the nanofiltration range. In this study, porous PI membranes with through-holes have been successfully fabricated by the novel multiple solvent displacement method. This new method requires only a porous polyamic acid (PAA) membrane, which was prepared by immersing PAA film in N-methylpyrrolidoneebk; (NMP) prior to immersing it in a mixed solvent consisting of NMP and a poor solvent, followed by immersion only in poor solvent. The pore size, morphology, porosity, and air permeability demonstrated that the fabricated PI membranes had a uniformly porous structure with through-holes over their surface. This new method enabled control of pore size (3–11 μm) by selecting a suitable poor solvent. This multiple solvent displacement method is highly versatile and promising for the fabrication of porous PI membranes.     

Preparation and properties of aromatic polyimides from 2,2′-bis(p-aminophenoxy)biphenyl or 2,2′-bis)p-aminophenoxy)-1,1′-binaphthyl and aromatic tetracarboxylic dianhydrides

New aromatic polyimides containing a biphenyl-2,2′-diyl or 1,1′-binaphthyl-2,2′-diyl unit were prepared by a conventional two-step method starting from 2,2′-bis(p-aminophenoxy) biphenyl or 2,2′-bis(p-aminophenoxy)-1,1′-binaphthyl and aromatic tetracarboxylic dianhydrides. The polyimides having inherent viscosities of 0.69–0.99 and 0.51–0.59 dL/g, respectively, were obtained. Some of these polymers were readily soluble in a variety of organic solvents including N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), dimethyl sulfoxide, and pyridine. Transparent, flexible, and pale yellow to brown films of these polymers could be cast from the DMAc or NMP polyamic acid solutions. These aromatic polyimides containing biphenyl and binaphthyl units had glass transition temperatures in the range of 200–235 and 286–358°C, respectively. They began to lose weight around 380°C, with 10% weight loss being recorded at about 470°C in air. © 1993 John Wiley & Sons, Inc.     

Formation of a highly ordered poly (N,N'-bis-phenoxyphenylpyromellitimide) powder using a high pressure curing technique

A high-pressure curing technique was developed to help determine the effects of solvent presence during the thermal curing of the polyimide poly (N,N'-bis-phenoxyphenylpyro-mellitimide) (PMDA-ODA). A powder form of this aromatic polyimide was produced from a polyamic acid solution using the high-pressure thermal curing technique. Preliminary characterization of the powder indicates a high degree of crystallinity with a measured density of 1.46 ± 0.01 g/cm³ and a distinct melting point of 594°C. The addition of chemical curing agents to the polyamic acid solution prior to thermal treatment reduced the amount of crystallinity observed in the cured material. Molecular weight measurements of the polyamic acid precursor and powder suggest that the high degree of order observed in the powder is a result of degradation during cure. © 1994 John Wiley & Sons, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America

     

Preparation and properties of polyamides and polyimides derived from 1,3-diaminoadamantane

1,3-Diaminoadamantane (I) was used as a monomer with various aromatic dicarboxylic acyl chlorides and dianhydrides to synthesize polyamides and polyimides, respectively. Polyamides having inherent viscosities of 0.10–0.27 dL/g were prepared by low-temperature solution polycondensation. The polyamides were soluble in a variety of solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), pyridine, dioxane, and nitrobenzene. These polyamides had glass transition temperatures in the 179–187°C range and 5% weight loss temperatures occurred at up to 354°C. Polyimides based on diamine I and various aromatic dianhydrides were synthesized by the two-stage procedure that included ring-opening to form polyamic acids, followed by thermal conversion to polyimides. The polyamic acids had inherent viscosities of 0.14–0.38 dL/g. The glass transition temperature of these polyimides were in the 245–303°C range and showed almost no weight loss up to 350°C under air and nitrogen atmosphere. © 1996 John Wiley & Sons, Inc.     

Polyimide–silica hybrid coatings: morphological,mechanical, and thermal investigations

In this study, polyimide–silica (PI–silica) based hybrid coating compositions were prepared from tetraethoxysilane (TEOS), γ‐glycidyloxypropyl trimethoxy silane (GOTMS), and polyamic acid (PAA) via a combination of sol–gel and thermal imidization techniques. PAA was synthesized from 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) and 3,3'‐Diaminodiphenyl sulfone (DDS) in N‐Methyl‐2‐pyrrolidone (NMP). The silica content in the hybrid coatings was varied from 0 to 20 wt%. The structural characterization of the hybrid coatings was performed using FTIR and ²⁹Si‐NMR spectroscopies. Results from both pendulum hardness and micro indentation test show that the hardness of hybrid coatings improves with the increase in silica content. The tensile tests also demonstrated that the mechanical properties at low silica content are rather striking. Their surface morphologies were characterized by scanning electron microscopy (SEM). SEM studies revealed that inorganic particles were distributed homogenously through the PI matrix. It was also found that, incorporation of the silica domains increased the thermal stability of the hybrid coatings. Copyright © 2007 John Wiley & Sons, Ltd.     

Molecular engineering. 8. Kinetic and conformational studies of resorcin [4]arene-based C4 tetraoxatetrathiahemicarceplexes: carceroisomerism and twistomerism

New C(4v) tetraoxatetrathiahemicarcerands and their six hemicarceplexes containing DMF, DMA, DMSO, or NMP were synthesized and characterized. Their conformations, kinetic properties, carceroisomerism, and twistomerism were studied by VT, 2D COSY, NOESY, and ROESY (1)H NMR experiments. The decomplexation rates of DMF or DMA were very slow with high activation energy barriers (73 and 104 kJ mol(-1), respectively) and the complexed guests feel more constriction than their free liquid state. The largest isomerization energy barrier of carceroisomers was 15.4 kcal mol(-1), and the isomerization energy barriers of twistomers are significantly larger than those of carceroisomers.     

Aromatic polyimide-co-amides. I

A series of aromatic polyimide-co-amides of high thermal stability were synthesized. Low-temperature solution condensation involving aromatic diamines of varying basicity and bifunctional carboxylic acid chlorides containing performed imide rings was empolyed. This approach offers several advantages over the conventional polyamic acid route. The final polymers obtained are linear, soluble, and of high molecular weight. Solution of the final polymers are stable in contrast to polyamic acid solutions, which depolymerize hydrolytically due to the neighboring-group effect. Tough, flexible films were cast from solution and required no heat cure. The properties of one polymer made by the preformed ring approach were compared to its structurally related amide and imide homologs.     

Polyaniline emeraldine base in N‐methyl‐2‐pyrrolidinone containing secondary amine additives: A rheological investigation of solutions

From a rheological study of emeraldine base (EB)/N‐methyl‐2‐pyrrolidinone (NMP)/2‐methyl‐aziridine (2MA) solutions, a correlation between the solution concentration and solution viscosity was found. We investigated the rheokinetic mechanism of the EB dissolution process and determined the reaction rate, activation energy, equilibrium constant, and Gibbs free energy (ΔG_o) for the complexation between 2MA and EB tetrameric molecules ({EB}). The low rate constant (～3.0 × 10^?4 mol^?2 L² min^?1 at 298 K) indicates that the process of EB/NMP/2MA solution formation is slow. The {EB} and 2MA molecules need approximately 76 kJ/mol energy to form the complexes, and this implies that stable bonds may need to be broken before the complexes can form. Therefore, increasing the temperature can accelerate solution formation. The equilibrium constant increases with temperature, and this indicates that EB · 2MA complexation is endothermic. A positive value of ΔG_o (5.26 kJ/mol) indicates that EB · 2MA complexation is a thermodynamically unfavorable reaction; therefore, the concentrated EB/NMP/2MA solutions eventually gel. Furthermore, we find that the activation energy of EB/NMP viscous flow is 80 kJ/mol, which is about 3–4 times the energy of ? N? H? hydrogen bonding. This suggests that at least three hydrogen bonds can form between two {EB} molecules, which might be responsible for the poor solubility of EB in organic solvents. The effects of the temperature, EB concentration, and 2MA:{EB} molar ratio on the gelation process have also been investigated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2702–2713, 2002     

Decomplexing madder lakes using oxalic acid: A novel method coupled with microwave or ultrasound processes

The aim of the present study was to establish a mild extraction and universal method to characterize madder lakes of Rubia tinctorum by liquid chromatography coupled with a photodiode array detector . To analyze the lakes, anthraquinone molecules must be decomplexed of metal links. To this end, two processes, one ultrasound and the other microwave, were improved in association with two solutions, an oxalic acid solution (0.5 M in MeOH/H₂O 50/50) and an acetic acid buffer solution (1 M). First, the decomplexation of an alizarin experimental lake was optimized in comparison with a reference method using a strong acid. The microwave process used oxalic acid and increased the decomplexation yield of alizarin (71%) compared with the reference method (31%). Second, different madder experimental lakes, which were prepared using different metal salts, were decomplexed. The obtained results suggest that the use of microwave associated with oxalic acid solution is the most universal method providing a decomplexation of anthraquinones from lakes without hydrolysis of glycosidic compounds occurring.     

Stereoselective functionalization of 2-(1-aminoalkyl)aziridines via lithiation of aziridine-borane complexes

Highly selective functionalization of the aziridine ring of (2S,1'S)-2-(1'-aminoalkyl)aziridines 1, through successive formation of aziridine-borane complexes, lithiation, treatment with a variety of electrophiles and final decomplexation is described. The influence of the structure of the starting complexes 2 and of the electrophiles in the stereoselectivity of this process has been studied. Finally, successive double lithiation-electrophile reactions were carried out affording enantiopure 1,2,3,3-tetrasubstituted aziridine-borane complexes with high selectivity.