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.     

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.     

Synthesis and characterization of soluble polyimides derived from a novel unsymmetrical diamine monomer: 1,4-(2′,4″-diaminodiphenoxy)benzene

A new aromatic unsymmetrical diamine monomer, 1,4-(2′,4″-diaminodiphenoxy)benzene (OAPB), was successfully synthesized in three steps using hydroquinone as starting material and polymerized with various aromatic tetracarboxylic acid dianhydrides, including 4,4′-oxydiphthalic anhydride (ODPA), 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA), 2,2′-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride (6FDA) and pyromellitic dianhydride (PMDA) via the conventional two-step thermal or chemical imidization method to produce a series of the unsymmetrical aromatic polyimides. The polyimides were characterized by solubility tests, viscosity measurements, IR, ¹H NMR, and ¹³C NMR spectroscopy, X-ray diffraction studies, and thermogravimetric analysis. The polyimides obtained had inherent viscosities ranged of 0.38-0.58 dL/g, and were easily dissolved in common organic solvents. The resulting strong and flexible PI films exhibited excellent thermal stability with the decomposition temperature (at 5% weight loss) of above 505 °C and the glass transition temperature in the range of 230-299 °C. Moreover, the polymer films showed outstanding mechanical properties with the tensile strengths of 41.4-108.5 MPa, elongation at breaks of 5-9% and initial moduli of 1.15-1.68 GPa.     

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).     

An approach to the synthesis of chemically modified bisazocalix[4]arenes and their extraction properties

Bisazocalix[4]arenes [N,N′-bis(5-azo-25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene)benzene (1), N,N′-bis(5-azo-25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene)biphenyl (2) and N,N′-bis(5-azo-25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene)-2,2′-dinitro biphenyl (3)] have been synthesized from 25,26,27-tribenzoyloxy-28-hydroxycalix[4]arene by diazocoupling with the corresponding aromatic diamines (p-phenylenediamine, 4,4′-diamino biphenyl and 4,4′-diamino-2,2′-dinitrobiphenyl). Extraction studies of bisazocalix[4]arenes 1, 2, and 3 show no difference in their extraction behavior and selectivity, whereas azocalix[4]arenes are a poor extractant for heavy metal cations. The absorption spectra of the prepared bisazocalix[4]arenes are discussed, both the effect of varying pH and solvent upon the absorption ability of bisazocalix[4]arenes.     

Synthesis and characterization of new polyimides containing pendent pentadecyl chains

A new unsymmetrical aromatic diamine, viz., 4-pentadecylbenzene-1,3-diamine was synthesized through a series of reaction steps starting from 3-pentadecylphenol. 4-Pentadecylbenzene-1,3-diamine was employed to synthesize a series of new polyimides by one-step polycondensation in m-cresol with four commercially available aromatic dianhydrides, viz., 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA), 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), 4,4′-oxydiphthalic anhydride (ODPA) and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6-FDA). Inherent viscosities of resulting polyimides were in the range 0.33-0.67 dL/g and number average molecular weights were in the range 14,700-52,200 (GPC, polystyrene standard). Polyimides containing pendent pentadecyl chains were soluble in organic solvents such as chloroform, m-cresol, N,N-dimethylacetamide (DMAc), 1-methyl-2-pyrrolidinone (NMP), pyridine and nitrobenzene. Strong and flexible films of polyimides could be cast from their chloroform solutions. Polyimides exhibited glass transition temperature in the range 158-206 °C. The temperature at 10% wt. loss (T₁₀), determined by TGA in nitrogen atmosphere, of polyimides was in the range 470-480 °C indicating good thermal stability.     

Low dielectric constant polyimide nanomats by electrospinning

The proper combination of material (i.e. fluorinated polyimides) and processing technique (electrospinning) could lead to the formation of polyimides with low dielectric constant, high thermo‐oxidative stability and glass transition temperature, and high hydrophobicity. The polyimides in this work were based on 4, 4‐bis [3′‐trifluoromethyl‐4′ (4′‐amino benzoxy) benzyl] biphenyl (Q) and various fluorinated and non‐fluorinated dianhydrides namely benzene‐1,2,4,5‐tetracarboxylic dianhydride, 3,3′,4,4′‐biphenyltetracarboxylic dianhydride, benzophenone‐3,3′,4,4′‐tetracarboxylic dianhydride, and 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA). Processing of the polyimides was carried out in poly(amic acid) stage by two different methods—electrospinning and solution casting for comparison purposes. The processing of polyimides by electrospinning led to enhancement in mechanical properties (dianhydride‐structure dependent) and hydrophobicity without sacrificing thermo‐oxidative stability and glass transition temperatures significantly. Also, low dielectric constants (as low as 1.43) could be attained by suitable combination of dianhydride (6FDA) with 4, 4‐bis [3′‐trifluoromethyl‐4′ (4′‐amino benzoxy) benzyl] biphenyl diamine. Copyright © 2011 John Wiley & Sons, Ltd.     

PERVAPORATION SEPARATION FOR TOLUENE/n-HEPTANE MIXTURE BY POLYIMIDE MEMBRANES CONTAINING FLUORINE

Five kinds of polyimides were synthesized using five dianhydrides (including 2,2-bis[4-(3,4-dicarboxyphenoxy)- phenyl] propane dianhydride (BPADA),3,3',4,4'-diphenylsulfone-tetracarboxylic dianhydride (DSDA),4,4'- (hexafluoroisopropylidene)-diphthalic anhydride (6FDA),1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride (HQDPA), and 4,4'-oxydiphthlic dianhydride (ODPA)) and 2,2-bis[4-(4-aminophenoxy)phenyl] hexafluoropropane (BDAF) via the two- step method that included polyaddition to form the polyamic aci...     

Characterizations and thermal stability of soluble polyimide derived from novel unsymmetrical diamine monomers

Two kinds of novel aromatic, unsymmetrical diamines with ether-ketone group, 3-amino-4′-(4-amino-2-trifluoromethylphenoxy)-benzophenone and 3-amino-4′-(4-aminophenoxy)-benzophenone, was successfully synthesized by two different synthetical routes and polymerized with various aromatic tetracarboxylic acid dianhydrides, including 4,4′-oxydiphthalic anhydride, 3,3′,4,4′-benzophenone tetracarboxylic dianhydride, and 2,2′-bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride, via a conventional two-step thermal or chemical imidization method to produce a series of fluorinated polyimides. The polyimides were characterized with solubility tests, viscosity measurements, mechanical properties tests, IR-FT, and thermogravimetric analysis. The polyimides had inherent viscosities of 0.54-0.77 dL/g and were easily dissolved in both polar, aprotic solvents and common, low-boiling-point solvents. The resulting strong and flexible polyimide films exhibited excellent thermal stability, with decomposition temperatures (at 10% weight loss) above 573 °C and glass-transition temperatures in the range of 222-251 °C. Moreover, the polymer films showed outstanding mechanical properties, with tensile strengths of 86.5-121.6 MPa, elongations at break of 9-16%, and initial moduli of 1.26-1.97 GPa. These outstanding combined features ensure that the polymers are desirable candidate materials for advanced applications.     

Preparation and characterization of a novel polyimide liquid crystal vertical alignment layer

A series of diamines with a side chain containing rigid biphenyl unit and nonpolar alkoxy side end group [4-alkoxy-biphenol-3′,5′-diaminobenzoate] (Cm-BBDA, m = 4, 6, 12) were synthesized and their chemical structures were confirmed by Fourier Transform Infrared Spectroscopy (FT-IR) and nuclear magetic resonance spectroscopy (¹H NMR). Then three polyimides (PIs) were prepared by copolymerization of pyromellitic dianhydride (PMDA), 4,4′-methylenedianiline (MDA) and Cm-BBDA in N-methyl-2-pyrrolodone (NMP), and chemical structures of all PIs were confirmed by FT-IR. Structural identification of all poly(amic acid)s (PAA) was performed by ¹H NMR. Liquid crystal (LC) cells were fabricated using these PIs as the alignment layer for characterization of the alignment properties of LCs. It was found that the planar alignment was obtained when PI with side chain containing alkoxy side end group of 4 carbon atoms was employed and the vertical alignment was observed when alkoxy side end groups of 6 or 12 carbon atoms were included. A uniform vertical alignment was validated by polarizing microscopy. It was testified that LC vertical alignment possessed high thermal stability.     

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).     

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 novel sulfonated polyimides containing phthalazinone moieties for PEMFC

A novel sulfonated diamine, 1,2-dihydro-2-(3-sulfonic-4-aminophenyl)-4-[4-(3-sulfonic-4-aminophenoxy)-phenyl]-phthalazin-1-one(S-DHPZDA), was successfully synthesized and two series of six-membered sulfonated polyimides (SPIs) were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), S-DHPZDA, and nonsulfonated diamines DHPZDA or 4,4′-diaminodiphenyl ether (ODA). The chemical structure of the S-DHPZDA and the SPIs were characterized by ¹H NMR and FT-IR. Tough, brownish and transparent membranes were cast from SPIs’ solution in NMP. The water uptake, swelling ratio, chemical and thermal stability, hydrolytic and oxidative stability as well as proton conductivity of these new polymers were investigated systematically. Compared with Nafions, the obtained SPI membranes have onset decomposed temperatures of these two series SPIs were above 318 °C and decomposed temperature of main chain were 565 °C and excellent dimension stabilities on similar IECs. Introduction of phthalazinone moieties had improved the copolyimides’ solubility in polar aprotic organic solvents like m-cresol, NMP, DMSO, DMF etc. The SPIs had high proton conductivity (σ) in the order of magnitude of 10⁻³ to 10⁻² S cm⁻¹ depending on the degree of sulfonation (DS) of the polymers.     

Synthesis and characterization of novel fluorinated polyimides derived from 4-phenyl-2,6-bis[4-(4′-amino-2′-trifluoromethyl-phenoxy)phenyl]pyridine and dianhydrides

A series of organo-soluble polyimides were prepared from a novel fluorinated diamine monomer, 4-phenyl-2,6-bis[4-(4′-amino-2′-trifluoromethylphenoxy)phenyl]pyridine and various commercial aromatic dianhydrides. These polyimides had good solubility in common organic solvents. The obtained strong and flexible PI films exhibited excellent thermal stability with the decomposition temperature (at 5% weight loss) of above 561 °C and the glass transition temperature in the range of 258-312 °C. Moreover, the polymer films showed good electrical insulating property, low dielectric constant and low water uptake due to the introduction of fluorinated substitutes in the polymer backbone. The remarkable combined features ensure these polymers to be ideal candidate materials for advanced microelectronic industry and other related applications.     

Preparations of bis[2-(2-arylethynyl)-3-thienyl]arenes and bis[2-{2-(trimethylsilyl)ethynyl}-3-thienyl]arenes

4,4′-Bis[2-(2-phenylethynyl)-3-thienyl]biphenyl, 4,4′-bis[2-{2-(trimethylsilyl)ethynyl}-3-thienyl]biphenyl and their congeners were prepared and their properties were studied. Extension of π-system through the central benzene ring was suggested by UV-vis spectra. Connection of two 1,4-bis[2-{2-(trimethylsilyl)ethynyl}-3-thienyl]benzene units was exemplified.     

Pattern formation of polyimide by using photosensitive polybenzoxazole as a top layer

A versatile method for positive-type patterning of polyimide (PI) based on a two-layer photosensitive poly(benzoxazole) (PSPBO) and poly(amic acid) (PAA) film has been developed to provide a promising material in the field of microelectronics. This patterning system consisted of a pristine PAA thick bottom-layer and a poly(o-hydroxy amide) (PHA) thin top layer with 9,9-bis[4-(tert-butoxycarbonyl-methyloxy)phenyl]fluorene (TBMPF) as a dissolution inhibitor, and (5-propylsulfonyloxyimino-5H-thiophene-2-ylidene)-(2-methylphenyl)-acetonitrile (PTMA) as a photoacid generator (PAG). The PHA and PAA were prepared from 4,4′-(hexafluoroisopropylidene)-bis(o-aminophenol) and 4,4′-oxybis(benzoic acid) derivatives, and 3,3′,4,4′-biphenyltetracarboxylic dianhydride and 4,4′-oxydianiline, respectively, in N,N-dimethylacetamide. This two-layer system based on PHA (150-nm thickness) and PAA (1.5-μm thickness) showed high sensitivity of 35 mJ/cm² and high contrast of 10.3 when exposed to a 365 nm line (i-line), post-baked at 100 °C for 2 min, and developed in a 2.38 wt.% tetramethylammonium hydroxide aqueous solution/5 wt.% iso-propanol at 25 °C. A clear positive image of a 4-μm line-and-space pattern was printed on a film which was exposed to 100 mJ/cm² of i-line by a contact-printing mode and fully converted to the corresponding PBO/PI pattern upon heating at 350 °C, confirmed by FT-IR spectroscopy. This two-layer system could be applied to the patterning of various PAAs.     

Synthesis and gas transport property of polyimide from 2,2′-disubstituted biphenyltetracarboxylic dianhydrides (BPDA)

A series of dianhydride monomers, 2,2′-disubstituted-4,4′,5,5′-biphenyltetracarboxylic dianhydride (substituents = phenoxy, p-methylphenoxy, p-tert-butylphenoxy, nitro, and methoxy) were synthesized by the nitration of an N-methyl protected 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and subsequent aromatic nucleophilic substitutions with aroxides (NaOAr) or methoxide. These dianhydrides were polymerized with various aromatic diamines in refluxing m-cresol containing isoquinoline to afford a series of aromatic polyimides. The effects of varying 2,2′-substituents of the dianhydride (BPDA) moiety on the properties of polyimides were investigated. It was found that polyimides from the dianhydrides containing phenoxy, p-methylphenoxy, and p-tert-butylphenoxy side groups possessed excellent solubility and film forming capability whereas polyimides from 2,2′-dinitro-BPDA and 2,2′-dimethoxy-BPDA were less soluble in organic solvent. The soluble polymers formed flexible, tough and transparent films. The films had a tensile strength, elongation at break, and Young’s modulus in the ranges 102-168 MPa, 8-21%, 2.02-2.38 GPa, respectively. The polymer gas permeability coefficients (P) and ideal selectivities for N₂, O₂, CO₂ and CH₄ were determined for the -OAr substituted polyimides. The oxygen permeability coefficient (P_O2) and permselectivity of oxygen to nitrogen (P_O2/N2) of the films were in the ranges 3.4-11.3 barrer and 3.8-4.6, respectively. The gas permeability typically increased with increasing free volume in the order of tert-butylphenoxy substituted PI > methylphenoxy substituted PI > phenoxy substituted PI.     

Synthesis and properties of water stable poly[bis(benzimidazobenzisoquinolinone)] ionomers for proton exchange membranes fuel cells

A novel sulfonated tetraamine, di(triethylammonium)-4,4′-bis(3,4-diaminophenoxy)biphenyl-3,3′-disulfonate (BAPBDS), was successfully synthesized by nucleophilic aromatic substitution of 4,4′-dihydroxybiphenyl with 5-chloro-2-nitroaniline, followed by sulfonation and reduction. A high-temperature polycondensation of sulfonated tetraamine, non-sulfonated tetraamine (4,4′-bis(3,4-aminophenoxy)biphenyl) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (a) or 4,4′-binaphthyl-1,1′,8,8′-tetracarboxylic dianydride (b) gave the poly[bis(benzimidazobenzisoquinolinones)] ionomers SPBIBI-a(x) or SPBIBI-b(x), where x refers to the molar percentage of the sulfonated tetraamine monomer. Flexible and tough membranes of high mechanical strength were obtained by solution casting and the electrolyte properties of the polymers were intensively investigated. The ionomer membranes displayed excellent dimensional and hydrolytic stabilities. Moreover, these novel membranes showed proton conductivities comparable to that of Nafion 117, especially at high temperature. In addition, the proton conductivities of the SPBIBI-a ionomer membranes were found to be higher than those of the SPBIBI-b ones due to the weakened acid–base interactions between the pyridinone ring and the sulfonic acid groups. The highest proton conductivity (0.174 S/cm) was obtained for the SPBIBI-a(100) membrane at 100 °C, with an IEC of 2.65 mequiv./g. A combination of excellent dimensional and hydrolytic stabilities indicated that the SPBIBI ionomers were good candidate materials for proton exchange membrane in fuel cell applications.     

Effect of the SO2 group in the diamine fragment of polyimides on their structural, thermophysical, and mechanical properties

Experimental and theoretical investigations, including an all-atom computer simulation, are performed for block samples of thermoplastic polyimides, amorphous R-BAPS (based on R dianhydride 1,3-bis(3??,4-dicarboxyphenoxy)benzene and diamine BAPS 4,4??-bis(4??-aminophenoxy)biphenyl sulfone), and crystallizable R-BAPB (based on R dianhydride and diamine BAPB 4,4??-bis(4??-aminophenoxy)biphenyl), which differ in either the presence or absence of the sulfone group in the repeating unit of the polyimide macromolecule. The features of thermophysical, structural, and mechanical properties of R-BAPS and R-BAPB are related to the formation of associates from sulfur and oxygen atoms of the sulfone group that are stabilized by electrostatic interactions.     

Synthesis and characterization of organosoluble aliphatic-aromatic copolyimides based on cycloaliphatic dianhydride

A series of aliphatic-aromatic polyimides have been synthesized. These polyimides were prepared by high-temperature polycondensation of the aliphatic diamines: 1,4-diaminobutane, 1,6-diaminohexane, 1,7-diaminoheptane, 1,9-diaminononane, 1,10-diaminodecane, 1,12-diaminododecane and 4,4^′-methylenebis(2,6-dimethylaniline) with 1,2,3,4-cyclopentanetetracarboxylic dianhydride. Various ratios of diamines (aromatic:aliphatic) have been applied for preparation of copolyimides. Polycondensation proceeded at 190 °C and produced copolyimides with reduced viscosities up to 0.92 dl/g. The polyimides were soluble in a wide range of organic, common solvents and showed high-thermal stability. In most cases these polymers formed flexible films which presented excellent transparency.