Synthesis and characterization of novel fluorinated polyimides derived from 4,4′-[2,2,2-trifluoro-1-(3,5-ditrifluoromethylphenyl)ethylidene]diphthalic anhydride and aromatic diamines

A novel fluorinated aromatic dianhydride, 4,4′-[2,2,2-trifluoro-1-(3,5-ditrifluoromethylphenyl) ethylidene] diphthalic anhydride (9FDA), was synthesized, which was employed to polycondense with various aromatic diamines, including 4,4′-oxydianiline, 1,4-bis(4-aminophenoxy) benzene, 3,4′-oxydianiline and 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene to produce a series of fluorinated aromatic polyimides. The fluorinated polyimides obtained had inherent viscosities ranged of 0.61-1.14 dL/g and were easily dissolved both in polar aprotic solvents and in low boiling point common solvents. High quality polyimide films could be prepared by casting the polyimide solution on glass plate followed by thermal baking to remove the organic solvents and volatile completely. Experimental results indicated that the fluorinated polyimides exhibited good thermal stability with glass transition temperature ranged of 245-283 °C and temperature at 5% weight loss of 536-546 °C. Moreover, the polyimide films showed outstanding mechanical properties with the tensile strengths of 87.7-102.7 MPa and elongation at breaks of 5.0-7.8%, good dielectric properties with low dielectric constants of 2.71-2.97 and low dissipation factor in the range of 0.0013-0.0028.     

Synthesis and characterization of novel polyimides derived from 2-amino-5-[4-(4′-aminophenoxy)phenyl]-thiazole with some of dianhydride monomers

A new kind of aromatic unsymmetrical diamine monomer containing thiazole ring, 2-amino-5-[4-(4′-aminophenoxy)phenyl]-thiazole (APPT), was synthesized. A series of novel polyimides were prepared by polycondensation of APPT with various aromatic dianhydrides via one-step process. The resulting polyimides held inherent viscosities of 0.40-0.71 dL/g and were easily dissolved in strong dipolar solvents. Meanwhile, strong and flexible polyimide films were obtained, which had thermal stability with the glass transition temperatures (T_g) of 268.2-328.8 °C in nitrogen, the temperature at 5% weight loss of 452-507 °C in nitrogen and 422-458 °C in air, and the residue at 800 °C of 54.18-63.33% in nitrogen, as well as exhibited outstanding mechanical properties with the tensile strengths of 105.4-125.3 MPa, elongations at breakage of 6-13%. These films also held dielectric constants of 3.01-3.18 (10 MHz) and showed predominantly amorphous revealed by wide-angle X-ray diffraction measurements.     

Synthesis and characterization of highly optical transparent and low dielectric constant fluorinated polyimides

Multitrifluoromethyl-substituted aromatic diamines, 1,1-bis[4-(4′- amino-2′-trifluoromethylphenoxy)phenyl]-1-(3″-trifluoromethylphenyl)-2,2,2-trifluoroethane (12FDA) and 1,1-bis[4-(4′-amino-2′-trifluoromethylphenoxy)phenyl]-1-[3″,5″-bis (trifluoromethyl)phenyl]-2,2,2-trifluoroethane (15FDA) were synthesized, which were employed to react with various aromatic dianhydrides to yield a series of highly fluorinated polyimides. The fluorinated polyimides synthesized showed great solubility with inherent viscosities of 0.47-0.69 dL/g. The strong and tough polyimide films exhibited good thermal stability with the glass transition temperature (T_g) of 209-239 °C and outstanding mechanical properties with the tensile strengths of 88-111 MPa and tensile modulus of 2.65-3.17 GPa. Dielectric constants of as low as 2.49 and low moisture absorptions (0.17-0.66%) were measured. The fluorinated polyimide films (7-10 μm in thickness) also showed highly optical transparency with light transmittance at 450 nm of as high as 97.0% and cutoff wavelength of as low as 298 nm. The average refractive indices and birefringence of the fluorinated polyimide films were measured in the range of 1.5060-1.5622 and 0.0036-0.0095, respectively. PI-7 and PI-8 exhibited low light-absorption in the near-infrared region, especially at the optocommunication wavelength of 1310 nm and 1550 nm.     

Synthesis and characterization of highly refractive polyimides derived from 2,7-bis(4′-aminophenylenesulfanyl)thianthrene-5,5,10,10-tetraoxide and aromatic dianhydrides

New polyimides (PIs) containing thioether and sulfonyl groups in their main chains have been developed. These PIs were synthesized by a two-step polycondensation procedure from several dianhydrides such as 4,4′-[p-thiobis(phenylenesulfanyl)] diphthalic anhydride (3SDEA), 4,4′-oxydiphthalic anhydride (ODPA), 4,4′-[sulfonylbis(phenylenesulfanyl)] diphthalic anhydride (pDPSDA) and a new sulfonyl and sulfur-containing aromatic diamine, 2,7-bis(4′-aminophenylenesulfanyl)thianthrene-5,5,10,10-tetraoxide (APTTT). All of the PIs show good thermal and optical properties such as optical transparency higher than 80% at 450 nm for a thickness of ca. 10 μm, glass transition temperatures higher than 250 °C, thermal decomposition temperatures (T_10%) in the range of 504-514 °C. Because of the two sulfonyl groups at each monomer unit in the polymer main chain, all of the PIs show good transparency maintaining relatively high refractive index.     

Synthesis and properties of soluble polyimides based on isomeric ditrifluoromethyl substituted 1,4-bis(4-aminophenoxy)benzene

A new fluorinated diamine monomer, [1,4-bis(4-amino-3-trifluoromethylphenoxy)benzene (2)], and a known isomeric analog 1,4-bis(4-amino-2-trifluoromethylphenoxy)benzene (3) were synthesized. A series of organosoluble polyimides Ia–d and IIa were prepared from the diamines (2, 3) and dianhydrides (a–d) by a high-temperature one-step method. The effects of the trifluoromethyl substituents on the properties of polyimides were evaluated through the study of their soluble, thermal, optical, and gas permeability properties. Polyimides (Ia–d) had glass transition temperatures between 229 and 279 °C, and the temperatures at 5% weight loss ranged from 510 to 533 °C under nitrogen. These polyimides could be cast into flexible and tough membranes from DMAc solutions. The membranes had tensile strengths in the range of 137–169 MPa, tensile modulus in the range of 1.6–2.2 GPa and elongations at break from 11% to 14%. The polyimide Ia with trifluoromethyl groups ortho to the imide nitrogen exhibited enhanced gas permeability, solubility, transparency, and thermal stability compared with the isomeric polyimide IIa with the CF₃ group meta to the imide nitrogen. Thus, the effect of substituents in the ortho-positions of nitrogen on properties was greater than the effect of substituents in the meta-positions.     

Synthesis and properties of fluorinated polyimides. 3. Derived from novel 1,3-bis[3′-trifluoromethyl-4′(4″-amino benzoxy) benzyl] benzene and 4,4-bis[3′-trifluoromethyl-4′(4-amino benzoxy) benzyl] biphenyl

Novel diamine monomers, 1,3-bis[3′-trifluoromethyl-4′(4″-amino benzoxy) benzyl] benzene (IV) and 4,4-bis[3′-trifluoromethyl-4′(4-amino benzoxy) benzyl] biphenyl (V) have been synthesized. These monomers lead to several novel fluorinated polyimides on reaction with different commercially available dianhydrides like pyromellatic dianhydride (PMDA), benzophenone tetracarboxylic acid dianhydride (BTDA) or 2,2-bis(3,4-dicarboxyphenyl) hexafluoropropane (6FDA). The polyimides prepared from above two monomers on reaction with 6FDA are soluble in several organic solvents such as N,N-dimethyl formamide (DMF), N,N-dimethyl acetamide (DMAc) and tetrahydrofuran (THF). The polyimides prepared from PMDA/IV is soluble in DMF and N-methyl pyrollidone (NMP) on heating, whereas V/PMDA is insoluble in all solvents. BTDA/IV polyimide is also soluble in NMP, DMF and DMAc. These polyimide films have low water absorption rate 0.2-0.7% and low dielectric constant 2.74-3.2 at 1 MHz. These polyimides showed very high thermal stability even up to 531 °C for 5% weight loss in synthetic air and glass transition temperature up to 316 °C (by DSC) in nitrogen. All polyimides formed tough transparent films, with tensile strength up to 148 MPa, a modulus of elasticity up to 2.6 GPa and elongation at break up to 31% depending upon the exact repeating unit structure.     

Organosoluble and optically transparent fluorine-containing polyimides based on 4,4′-bis(4-amino-2-trifluoromethylphenoxy)-3,3′,5,5′-tetramethylbiphenyl

A novel fluorinated diamine monomer, 4,4′-bis(4-amino-2-trifluoromethylphenoxy)-3,3′,5,5′-tetramethylbiphenyl, was prepared by a nucleophilic chloro-displacement reaction of 3,3′,5,5′-tetramethyl-4,4′-biphenol with 2-chloro-5-nitrobenzotrifluoride and subsequent reduction of the intermediate dinitro compound. The diamine was reacted with aromatic dianhydrides to form polyimides via a two-step polycondensation method; formation of poly(amic acid)s, followed by thermal imidization. All the resulting polyimides were readily soluble in many organic solvents and exhibited excellent film forming ability. The polyimides exhibited high T_g (312-351 °C), good thermal stability, and good mechanical properties. Low moisture absorptions (0.2-1.1 wt%), low dielectric constants (2.54-3.64 at 10 kHz), and low color intensity were also observed.     

Synthesis and characterization of novel polyimides derived from 1,1-bis[4-(4′-aminophenoxy)phenyl]-1- [3″,5″-bis(trifluoromethyl)phenyl]-2,2,2-trifluoroethane

A novel fluorinated aromatic diamine monomer, 1,1-bis[4-(4′-aminophenoxy)phenyl]-1-[3″,5″-bis(trifluoromethyl)phenyl]-2,2,2-trifluoroethane(9FTPBA), was synthesized by coupling 3′,5′-bis(trifluoromethyl)-2,2,2-trifluoroacetophenone with 4-nitrophenyl phenyl ether under the catalysis of trifluoromethanesulfonic acid, followed reduced by reductive iron and hydrochloric acid. A series of new fluorine-containing polyimides having inherent viscosities of 0.96-1.23 dl/g was synthesized from the novel diamine with various commercially available aromatic dianhydrides using a standard two-stage process with thermal imidization and chemical imidization of poly(amic acid) films. All the fluorinated polyimides were soluble in many polar organic solvents such as NMP, DMAc, DMF, and m-cresol, as well as some of low boiling point organic solvents such as chloroform and acetone. The polymer films have good thermal stability with the glass transition temperature of 223-225 °C, the temperature at 5% weight loss of 535-568 °C in nitrogen, and have outstanding mechanical properties with the tensile strengths of 68-89 MPa, initial moduli of 2.14-2.19 GPa, and elongations at breakage of 3.2-10.5%.     

Synthesis and properties of soluble poly[bis(benzimidazobenzisoquinolinones)] based on novel aromatic tetraamine monomers

Four aromatic tetraamine monomers possessing flexible ether linkages were successfully synthesized by nucleophilic aromatic substitution of hydroquinone, 4,4′-dihydroxybiphenyl, 2,2′-bis(4-hydroxyphenyl)propane, and 2,7-dihydroxynaphthalene with 5-chloro-2-nitroaniline, followed by reduction, respectively. With these monomers, a new class of soluble poly[bis(benzimidazobenzisoquinolinones)] was prepared by a one-step, high-temperature solution polycondensation. The resulting polymers were completely soluble in phenolic solvents and had high inherent viscosities ranging from 1.2 to 1.5 g dL⁻¹. These polymers had glass transition temperatures in the range of 427-449 °C. Thermogravimetric analysis showed that all polymers were thermally stable, with 5% weight loss recorded above 510 °C in nitrogen. The tough polymer films, obtained by casting from solution, had tensile strength, elongation at break, and tensile modulus values in the range of 79.5-114.5 MPa, 10.3-23.0%, and 1.1-1.7 GPa, respectively. It is demonstrated that these semiladder polymer membranes displayed high CO₂ permeability coefficients (P₂CO=31.6−96.5barrer) and permeability selectivity of CO₂ to CH₄(P₂CO/P₄CH=30.6−43.4).     

Electrochemically and electrochromically stable polyimides bearing tert-butyl-blocked N,N,N′,N′-tetraphenyl-1,4-phenylenediamine units

A new class of electrochemically active polyimides with di-tert-butyl-substituted N,N,N′,N′-tetraphenyl-1,4-phenylenediamine units was prepared from N,N-bis(4-aminophenyl)-N′,N′-bis(4-tert-butylphenyl)-1,4-phenylenediamine and various aromatic tetracarboxylic dianhydrides via a conventional two-step procedure that included a ring-opening polyaddition to give poly(amic acid)s, followed by chemical or thermal cyclodehydration. Most of the polyimides are readily soluble in many organic solvents and can be solution-cast into tough and amorphous films. They had useful levels of thermal stability, with relatively high glass-transition temperatures (276-334 °C), 10% weight-loss temperatures in excess of 500 °C, and char yields at 800 °C in nitrogen higher than 60%. Cyclic voltammograms of the polyimide films cast on the indium-tin oxide (ITO)-coated glass substrate exhibited two reversible oxidation redox couples at 0.70-0.74 V and 1.05-1.08 V vs. Ag/AgCl in acetonitrile solution. The polyimide films revealed excellent stability of electrochromic characteristics, with a color change from colorless or pale yellowish neutral form to green and blue oxidized forms at applied potentials ranging from 0.0 to 1.3 V. These anodically coloring polymeric materials exhibited high optical contrast of percentage transmittance change (Δ%T) up to 44% at 413 nm and 43% at 890 nm for the green coloration, and 98% at 681 nm for the blue coloration. After over 50 cyclic switches, the polymer films still exhibited good redox and electrochromic stability.     

Synthesis of novel sulfonated polybenzimidazole and preparation of cross-linked membranes for fuel cell application

A novel sulfonated polybenzimidazole, sulfonated poly[2,2′-(p-oxydiphenylene)-5,5′-bibenzimidazole] (SOPBI), was successfully prepared by post-sulfonation reaction of the parent polymer, poly[2,2′-(p-oxydiphenylene)-5,5′-bibenzimidazole] (OPBI), using concentrated and fuming sulfuric acid as the sulfonating reagent at 80 °C, and the degree of sulfonation (DS) could be regulated by controlling the reaction conditions. No significant polymer degradation was observed in the post-sulfonation processes. Direct polymerization of 4,4′-dicarboxydiphenyl ether-2,2′-disulfonic acid disodium salt (DCDPEDS) and 3,3′-diaminobenzidine (DABz), however, resulted in insoluble gels either in polyphosphoric acid (PPA) or in phosphorus pentoxide/methanesulfonic acid (PPMA) in a ratio of 1:10 by weight reaction medium. The SOPBIs prepared by the post-sulfonation method showed good solubility in dimethyl sulfoxide (DMSO), high thermal stability, good film forming ability and excellent mechanical properties. Cross-linked SOPBI membranes were successfully prepared by thermal treatment of phosphoric acid-doped SOPBI membranes at 180 °C in vacuo for 20 h and the resulting cross-linked membranes showed much improved water stability and radical oxidative stability in comparison with the corresponding uncross-linked ones, while the proton conductivity did not change largely. Highly proton conductive (150 mS cm⁻¹, 120 °C in water) and water stable SOPBI membrane was developed.     

Synthesis and characterization of poly(aryl ether ketone) copolymers containing (hexafluoroisopropylidene)-diphenol moiety as proton exchange membrane materials

Sulfonated poly(aryl ether ketone)s (SPAEK) copolymers were synthesized by aromatic nucleophilic polycondensation from 4,4′-(hexafluoroisopropylidene)-diphenol, 1,3-bis(4-fluorobenzoyl)benzene and di-sulfonated difluorobenzophenone. The copolymers exhibited good thermal and oxidative stability. The SPAEK membranes with sulfonic acid content (SC) ranging from 0.6 to 1.16 maintained adequate mechanical strength after immersion in water at 80 °C for 24 h. The proton conductivities of the SPAEK films increased with SC and temperature, reaching values above 3.3×10⁻² S/cm at 80 °C for SC≥0.76. Tensile strength measurement indicated that SPAEK membranes with SC 0.76, 0.98 and 1.16 are tough and strong at ambient conditions. Consequently, these materials are promising as proton exchange membranes (PEM) for fuel cells operated at medium temperatures.     

A positive type alkaline developable thermally stable and photosensitive polymer based on partially O-methylated poly(2,6-dihydroxy-1,5-naphthylene), an acidolytic de-cross-linker, and a photoacid generator

A positive working and chemically amplified photosensitive polymer based on partially (30%) O-methylated poly(2,6-dihydroxy-1,5-naphthylene) [PMPDHN (30)], 1,3,5-tris[(2-vinyloxy)ethoxy]benzene (TVEB) as an acidolytic de-cross-linker, and a photoacid generator (5-propylsulfonyloxyimino-5H-thiophen-2-ylidene)-(2-methylphenyl)acetonitrile (PTMA) has been developed. Poly(2,6-dihydroxy-1,5-naphthylene) (PDHN) with a number-average molecular weight of 33,000 was prepared by oxidative coupling polymerization of 2,6-dihydroxynaphthalene (2,6-DHN) using di-μ-hydroxo-bis-[(N,N,N′,N′-tetramethylethylenediamine)copper(II)] chloride [CuCl(OH)TMEDA] as the catalyst in 2-methoxyethanol at room temperature. PDHN was converted to PMPDHN by treating with iodomethane. The resist showed a sensitivity of 19.4 mJ cm⁻² and a contrast of 7.5 when it was exposed to 436 nm light, followed by post-baking at 120 °C for 5 min and developing with 2.38 wt% aqueous tetramethylammonium hydroxide (TMAH) solution at 25 °C. A fine positive image featuring 6 μm line and space patterns was obtained on the film exposed to 20 mJ cm⁻² of UV-light at 436 nm by the contact-printed mode. The optically estimated dielectric constants (at 1 MHz) of PMPDHN (30) with and without TVEB and PTMA are 3.03 and 3.01, respectively. The moisture absorption (1.7 wt%) of the resist system based on PMPDHN (30) and TVEB is very low compared to that (4.3%) of the resist system consisting of PDHN and 4,4′-methylenebis[2,6-bis(hydroxymethyl)]phenol (MBHP).     

Color lightness and highly organosoluble fluorinated polyamides, polyimides and poly(amide-imide)s based on noncoplanar 2,2′-dimethyl-4,4′-biphenylene units

A new diamine monomer containing noncoplanar methyl substitution, 2,2′-dimethyl-4,4′-bis(2-trifluoromethyl-4-aminophenoxy)biphenyl (DBTFAPB) was successfully synthesized and used in the preparation of a series of polyamides and polyimides by direct polycondensation with various aromatic dicarboxylic acids and tertacarboxylic dianhydrides. A new noncoplanar dicarboxylic acid monomer containing noncoplanar methyl substitution, 2,2′-dimethyl-4,4′-bis(2-trifluoromethyl-4-trimellitimidophenoxy)biphenyl (DBTFTPB) was also successfully synthesized by refluxing the diamine, DBTFAPB, with trimellitic anhydride in glacial acetic acid. A series of new poly(amide-imide)s were prepared directly from DBTFTPB with various diamines in N-methyl-2-pyrrolidinone (NMP). All the polymers exhibited excellent solubility in solvents, such as N-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), pyridine, tetrahydrofuran (THF), cyclohexanone and γ-butyrolactone at room temperature or upon heating at 70 °C. Inherent viscosities of the polymers were found to range between 0.60 and 1.34 dL g⁻¹. Gel permeation chromatography (GPC) of the polymers showed number-average and weight-average molecular weight up to 7.3×10⁴ and 17.9×10⁴, respectively. These polymers showed that the glass transition temperatures were between 230 and 265 °C, and the 10% mass loss temperatures were higher than 460 °C in nitrogen atmosphere. All the polymers could be cast into flexible and tough films from DMAc solutions. They had a tensile strength in the range of 82-124 MPa and a tensile modulus in the range of 1.9-2.9 GPa. These polymers exhibited low dielectric constants ranging from 2.87 to 4.03, low moisture absorption in the range of 0.29-3.20%, and high transparency with an ultraviolet-visible absorption cut-off wavelength in the 347-414 nm range.     

Synthesis and characterization of polyimides and co-polyimides having pendant benzoic acid moiety

A novel diamine monomer, 2,4-diamino-4′-carboxy diphenyl ether had been synthesized. Several polyimides were prepared by reacting this diamine with commercially available dianhydrides, such as benzophenone tetracarboxylic acid dianhydride (BTDA), 4,4′-bis{hexafluoroisopropylidene bis (phthalic anhydride)}(6-FDA), oxydiphthalic anhydride (ODPA) and 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (BPDA). Furthermore, copolymers from the resulting diamine and oxydianiline (ODA) with 6 FDA were also synthesized. The inherent viscosities of the polymers were 0.42-0.67 dl g⁻¹. The polymers have good solubility in polar aprotic solvents, high thermal stability up to 410 °C in nitrogen and high glass transition temperatures (T_g) ranging from 260-330 °C. These polymers formed tough flexible films by solution casting.     

Synthesis and properties of novel organosoluble polyimides derived from 1,4-bis[4-(3,4-dicarboxylphenoxy)]triptycene dianhydride and various aromatic diamines

A novel triptycene-based dianhydride, 1,4-bis[4-(3,4-dicarboxylphenoxy)]triptycene dianhydride, was prepared from 4-nitro-N-methylphthalimide and potassium phenolate of 1,4-dihydroxytriptycene (1). The aromatic nucleophilic substitution reaction between 4-nitro-N-methylphthalimide and 1 afforded triptycene-based bis(N-methylphthalimide) (2), which hydrolyzed and subsequently dehydrated to give the corresponding dianhydride (3). A series of new polyimides containing triptycene moieties were prepared from the dianhydride monomer (3) and various diamines in m-cresol via conventional one-step polycondensation method. Most of the resulting polyimides were soluble in common organic solvents, such as chloroform, THF, DMAc and DMSO. The polyimides exhibited excellent thermal and thermo-oxidative stabilities with the onset decomposition temperature and 10% weight loss temperature ranging from 448 to 486 °C and 526 to 565 °C in nitrogen atmosphere, respectively. The glass transition temperatures of the polyimides were in the range of 221-296 °C. The polyimide films were found to be transparent, flexible, and tough. The films had tensile strengths, elongations at break, and tensile moduli in the ranges 95-118 MPa, 5.3-16.2%, and 1.03-1.38 GPa, respectively. Wide-angle X-ray diffraction measurements revealed that these polyimides were amorphous.     

Semi-interpenetrating polymer networks of Nafion and fluorine-containing polyimide with crosslinkable vinyl group

Fluorine-containing polyimide with crosslinkable vinyl group (FPI) was synthesized from 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (PFMB), and 4-amino styrene (AS). The reinforced composite membranes based on semi-interpenetrating polymer networks (semi-IPN) were prepared via solution casting of FPI and Nafion^®212, and crosslinking thereafter. The water uptake, swelling ratio, mechanical properties, thermal behavior, proton conductivity, and oxidative stability of the composite membranes were investigated. Compared with the recast Nafion^® 212, the composite membrane shows better mechanical properties and improved dimensional stability. The tensile strength of the composite membranes ranges from 39.0 MPa to 80.0 MPa, which is higher than that of the recast Nafion^® 212 membrane (26.6 MPa). The dimensional stability of the composite membranes increases with increasing FPI content in the membranes, whereas the proton conductivity decreases. The composite membranes show considerable proton conductivity from 2.0 × 10⁻² S cm⁻¹ to 8.9 × 10⁻² S cm⁻¹ at a temperature from 30 °C to 100 °C, depending on the FPI contents. The composite membranes with semi-IPN from FPI and Nafion^®212 have considerable high proton conductivity, excellent mechanical properties, thermal and dimensional stabilities.     

Organosoluble and light-colored fluorinated polyimides derived from 2,3-bis(4-amino-2-trifluoromethylphenoxy)naphthalene and aromatic dianhydrides

A novel fluorinated bis(ether amine) monomer, 2,3-bis(4-amino-2-trifluoromethylphenoxy)naphthalene, was prepared through the nucleophilic aromatic substitution reaction of 2-chloro-5-nitrobenzotrifluoride and 2,3-dihydroxynaphthalene in the presence of potassium carbonate, followed by catalytic reduction with hydrazine and Pd/C. A series of new fluorine-containing polyimides having inherent viscosities of 0.54 to 1.10 dl/g were synthesized from the diamine with various commercially available aromatic dianhydrides using a standard two-stage process with thermal imidization of poly(amic acid) films. These polyimides were highly soluble in a variety of organic solvents, and most of them afforded transparent, light-colored, and tough films with good tensile strengths. These polyimides exhibited glass transition temperatures (T_gs) of 247-300 °C and showed no significant decomposition below 500 °C under either nitrogen or air atmosphere. Except for the polyimide derived from pyromellitic dianhydride, the polyimide films were almost colorless, with an ultraviolet-visible absorption cutoff wavelength below 400 nm and low b∗ values (a yellowness index) of 10.7-41.9. These polyimides had dielectric constants of 3.09 to 3.65 (1 MHz) and moisture absorptions in the range of 0.2-0.3 wt%.     

Synthesis and properties of organosoluble polyimides based on 2,2′-diphenoxy-4,4′,5,5′-biphenyltetracarboxylic dianhydride

A novel method for the preparation of 2,2′-diphenoxy-4,4′,5,5′-biphenyltetracarboxylic dianhydride have been investigated. This new dianhydride contains flexible phenoxy side chain and a twist biphenyl moiety and it was synthesized by the nitration of an N-methyl protected 3,3′,4,4′-biphenyltetracarboxylic dianhydride and subsequent aromatic nucleophilic substitution with phenoxide. The overall yield was up to 75%. The dianhydride was polymerized with five different aromatic diamines to afford a series of aromatic polyimides. The polyimide properties such as inherent viscosity, solubility, UV transparency and thermaloxidative properties were investigated to illustrate the contribution of the introduction of phenoxy group at 2- and 2′-position of BPDA dianhydride. The resulting polyimides possessed excellent solubility in the fact that the polyimide containing rigid diamines such as 1,4-phenylenediamine and 4,4′-oxydianiline were soluble in various solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, dimethyl sulfoxide and chloroform. The glass-transition temperatures of the polymers were in the range of 255-283 °C. These polymers exhibited good thermal stability with the temperatures at 5% weight loss range from 470 to 528 °C in nitrogen and 451 to 521 °C in air, respectively. The polyimide films were found to be transparent, flexible, and tough. The films had a tensile strength, elongation at break, and Young's modulus in the ranges 105-168 MPa, 15-51%, 1.87-2.38 GPa, respectively.     

Polyimides based on “multiring” flexible diamines

The five benzene rings-containing (hereafter for convenience, referred to as five-ringrd) diamines ad-bis[4-(4-aminophenoxy)phenyl]-1,4 (or 1,3)-diisopropylbenzene (p- or m-3) were prepared by a nucleophilic substitution of ,-bis(4-hydroxyphenyl)-1, 4 (or 1,3)-diisopropylbenzene (p- or m-1) with p-chloronitrobenzene in the presence of K₂CO₃ and then hydro-reduced. The polyimides were synthesized from diamine 3 and various aromatic dianhydrides via the two-stage procedure that include ring-opening polyaddition in DMAc to give poly(amic acid)s, followed by thermal conversion to polyimides. The poly(amic acid)s had inherent viscosities of 0.63–1.54 dL/g depending on the dianhydrides used. Almost all the poly(amic acid)s could be solution-cast and thermally converted into transparent, flexible, and tough polyimide films. These polyimides have glass transition temperatures in the range of 186–290°C and almost no weight loss up to 500°C in air or nitrogen atmosphere. The polyimide obtained from pyromellitic dianhydride and diamine m-3 showed two endothermic peaks of 270 and 300°C on the diagram of differential scanning calorimetry (DSC), and the other polyimides showed no endotherms on their DSC traces.