Novel aromatic polyimides derived from benzofuro[2,3-b]benzofuran-2,3,8,9-tetracarboxylic dianhydride (BBTDA)

Benzofuro[2,3-b]benzofuran-2,3,8,9-tetracarboxylic dianhydride (BBTDA) is introduced as a monomer for the synthesis of a series of novel polyimides with enhanced high thermal stability. Polyimides derived from BBTDA and aromatic diamines showed high glass transition (T_g>296 °C) and degradation (T₅>455 °C) temperatures, and were soluble in organic solvents (i.e. N-methyl pyrrolidone (NMP), N,N^′-dimethylformamide (DMF), N,N^′-dimethylacetamide (DMAc)). The polymerization yielded high-molecular-weight polyimides with inherent viscosities ranging from 1.75 to 2.14 dl/g. The polymers were characterized by IR and elemental analysis.     

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.     

Molecular design, synthesis and electro-optic properties of novel Y-type polyurethanes with high thermal stability of second harmonic generation

2,4-Di-2^′-hydroxyethoxy)benzylidenemalononitrile (3) was prepared and condensed with 2,4-toluenediisocyanate and 3,3^′-dimethoxy-4,4^′-biphenylenediisocyanate to yield unprecedented novel Y-type polyurethanes (4-5) containing 2,4-dioxybenzylidenemalononitrile group as a nonlinear optical (NLO) chromophore, which constitutes a part of the polymer backbone. The resulting polyurethanes 4-5 were soluble in common organic solvents such as acetone and DMF. Polymers 4-5 showed a thermal stability up to 260 °C from thermogravimetric analysis (TGA) with differential scanning calorimetry (DSC) giving T_g values around 143-156 °C. The approximate lengths of aligned NLO-chromophores estimated from AFM images of poled polymer films were about 10 nm. The SHG coefficients (d₃₃) of poled polymer films were around 7.4 × 10⁻⁹ esu. These Poled polymers exhibited a greater thermal stability of dipole alignment even at 10 °C higher than T_g, and no SHG decay was observed below 155 °C due to the partial main chain character of the polymer structure and extensive hydrogen bonds between urethane linkage, which is acceptable for NLO device applications.     

Synthesis and nonlinear optical properties of novel Y-type polyimides with enhanced thermal stability of dipole alignment

2,3-Bis-(3,4-dicarboxyphenylcarboxyethoxy)-4′-nitrostilbene dianhydride (4) was prepared and reacted with 1,4-phenylenediamine, 4,4′-oxydianiline, 4,4′-diaminobenzanilide and 4,4′-(hexafluoroisopropylidene)dianiline to yield novel polyimides 5-8 containing 2,3-dioxynitrostilbenyl groups as NLO-chromophores, which constituted parts of the polymer backbones. The resulting polyimides 5-8 were soluble in polar solvents such as acetone and DMF. Polymers 5-8 showed a thermal stability up to 300 °C in TGA thermograms with T_g values obtained from DSC thermograms in the range of 135-160 °C. The SHG coefficients (d₃₃) of poled polymer films at the 1064 cm⁻¹ fundamental wavelength were around 5.26 × 10⁻⁹ esu. The dipole alignment exhibited exceptionally high thermal stability even at 30 °C higher than T_g and there was no SHG decay below 170-190 °C due to the partial main chain character of polymer structure, which was acceptable for NLO device applications.     

Synthesis and characterization of crosslinkable polyimides

A series of copolyimides were prepared from benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (BTDA) and various aromatic diamines which contain a fluorenyl group and/or alkyl substituents in ortho position to the amine groups. The effect of the chemical composition on the glass transition temperature (T_g), thermal stability as well as on the dielectric constant of these polymers was studied. High T_g polymers (T_g ranging from 260 °C to 370 °C), withstanding temperatures as high as 400 °C for 10 h and having a low dielectric constant (from 2.6 to 3.1) were successfully synthesized. All these polymers were able to crosslink under UV or thermal treatments.     

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.     

Novel polyimides with p-nitrophenyl pendant groups. Synthesis and characterization

Polyimides derived from a new dianhydride with p-nitrophenyl pendant groups have been synthesized and their properties compared with those of a reference series, without side groups. The polymers were obtained by combination of the novel monomer with aromatic diamines, in a two-step procedure that involved the synthesis of poly(amic acid) or poly(amic silyl ester) intermediates and the cyclization of them to polyimides by thermal treatment. The introduction of the polar nitro groups caused significant increase of the T_gs. On the contrary, the thermal stability was reduced because of the breakdown of C_Ar—NO₂ linkages around 400^oC. A slight decrease in mechanical properties was observed, due to the bulkiness of the side groups, that also produced an important decrease in the strength of the β relaxation, as determined by dynamic mechanical analysis. The solubility of the current polyimides in organic solvents was as poor as that of the parent unsubstituted polymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3377–3384, 1999     

Synthesis and characterization of novel polyimides derived from pyridine-bridged aromatic dianhydride and various diamines

A new kind of pyridine-bridged aromatic dianhydride monomer, 4-phenyl-2,6-bis[4-(3,4-dicarboxyphenoxy)phenyl]-pyridine dianhydride (PPDA), was successfully synthesized by modified Chichibabin reaction of benzaldehyde and substituted acetophenone, 4-(3,4-dicyanophenoxy)-acetophenone (DCAP), followed by acidic hydrolysis of the intermediate tetranitrile and cyclodehydration of the resulting tetraacid. The pyridine-bridged aromatic dianhydride was employed to synthesized a series of new pyridine-containing polyimides by polycondensation with various aromatic diamines in N-methyl-2-pyrrolidone (NMP) via the conventional two-step method, i.e. ring-opening polycondensation forming the poly(amic acid)s and further thermal or chemical imidization forming polyimides. The inherent viscosities of the resulting polyimides were in the range of 0.49-0.63 dL/g, and most of them were soluble in aprotic amide solvents and cresols, such as N,N-dimethylacetamide (DMAc), NMP, and m-cresol, etc. Meanwhile, strong and flexible polyimide films were obtained, which have good thermal stability with the glass transition temperatures (T_g) of 223-256 °C, the temperature at 5% weight loss of 523-569 °C, and the residue at 700 °C of 52.1-62.7% in nitrogen, as well as have outstanding mechanical properties with the tensile strengths of 70.7-97.6 MPa and elongations at breakage of 7.9-9.7%. Wide-angle X-ray diffraction measurements revealed that these polyimides were predominantly amorphous.     

Synthesis of novel Y-type polyurethane containing azomethine moiety, as non-linear optical chromophore and their properties

3,4-Di-(2′-hydroxyethoxy)-4′-nitrobenzylidene II was prepared by condensation reaction of 3,4-dihydroxy-4′-nitrobenzylidene I with 1-chloro-2-ethanol. Monomer II was reacted with p-phenylene diisocyanate to yield polyurethane containing the non-linear optical chromophore 3,4-di-(2′-hydroxyethoxy)-4′-nitrobenzylidene. Polymer III shows thermal stability up to 300 °C in TGA thermogram. T_g value of the polymer obtained from DSC thermogram was 110 °C. The resulting polyurethane III was soluble in common organic solvents such as acetone, DMF and DMSO. The values of electro optic coefficient d₃₃ and d₃₁ of the poled polymer film were 3.15 × 10 ⁻⁷ and 1.5 × 10 ⁻⁷ esu, respectively.     

Hydrolytic stability and high Tg of polyimides derived from the novel 4,9‐bis[4‐(3,4‐dicarboxyphenoxy)phenyl]‐diamantane dianhydride

This work reports the synthesis and characterization of diamantane‐based polyimides obtained from 4,9‐bis[4(3,4‐dicarboxyphenoxy)phenyl]diamantane dianhydride and various aromatic diamines. Interestingly, the diamantane‐based polyimides were very stable to hydrolysis. This novel polyimide exhibits a low dielectric constant (2.65–2.77), low moisture absorption (<0.67%), good solubility, high T_g and unusually high thermal stability. Dynamic mechanical analysis (DMA) reveals that the diamantane‐based polyimides have high T_g ranging from 281 to 379 °C. The high‐temperature β₁ subglass transition around 285 °C was observed in polyimide 6a derived from 2,2′‐bis(trifluoromethyl)benzidine. This class of novel diamantane‐based polyimide is very promising for electronic applications, because of its good mechanical properties, good thermal stability, low dielectric constant, excellent hydrolytic resistance, and low moisture absorption. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1673–1684, 2009     

Synthesis of soluble,thermosetting polymides derived from 1,4-phenylenebis(phenylmaleic anhydride) and aromatic diamines

The dianhydride monomer 1,4-phenylenebis(phenylmaleic anhydride) was polymerized with various aromatic diamines in a one-step solution polymerization to afford high molecular weight, soluble polyimides containing backbone phenylmaleimide structures. The polymides were soluble in amide solvents, chlorinated hydrocarbons, and tetrahydrofuran at 25°C at a concentration of 15% (w/v), displayed molecular weight distributions (M_w/M_n) of 2.0–2.2 as determined by absolute GPC and showed T_g values of 240°C and above as measured by differential scanning calorimetry. In addition, polyimide thermosets were prepared from these materials by thermal cure at 350–360°C. The crosslinked polyimides displayed T_gs 20–25°C higher than their soluble precursors, and chloroform extraction indicated gel fractions ranging from 74–100% after cure. © 1994 John Wiley & Sons, Inc.     

Structure‐property relationships for a series of amorphous partially aliphatic polyimides

High molecular weight, soluble, amorphous, partially aliphatic polyimides were successfully synthesized using an ester acid high‐temperature solution imidization route, which allows one to control desired glass‐transition (T_g) and processing temperatures. This method involves the prereaction of aromatic dianhydrides with ethanol and a tertiary amine catalyst to form ester acids, followed by the addition of diamines. Subsequent thermal reaction forms fully cyclized polyimides. This reaction pathway eliminates the need for anhydrous solvents and overcomes the problem of salt formation commonly observed for nucleophilic, more‐basic aliphatic amines when utilizing the traditional polyamic acid synthesis route. The molar ratio of aromatic‐to‐aliphatic diamines was varied to generate a series of copolyimides with the chosen dianhydride and tailor the physical properties for specific adhesive applications. This series of copolyimides was characterized by their molecular weight, T_g, thermal stability, coefficient of thermal expansion, refractive index, and dielectric constant. Structure‐property relationships were established. The γ and β sub‐T_g viscoelastic properties were researched to understand their molecular origins. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1503–1512, 2002     

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.     

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).     

Fully imidized soluble polyimides based on a novel dianhydride: 2,2′-dichloro-4,4′,5,5′-benzophenone tetracarboxylic dianhydride

We have synthesized a novel dianhydride, 2,2′-dichloro-4,4′,5,5′-benzophenone tetracarboxylic dianhydride (DCBTDA). Polyimides were synthesized with DCBTDA or 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) and several relatively rigid meta- and para- substituted mononuclear diamines. The BTDA based systems were insoluble in dipolar, aprotic solvents whereas the DCBTDA based polymers displayed enhanced solubility in these solvents. The thermal stability of these polyimides was excellent as measured by 5% weight loss decomposition. The T_g's of the polymers were all above 290°C.     

A new synthetic route of 4,4′-hexafluoroisopropylidene-2,2-bis-(phthalic acid anhydride) and characterization of 4,4′-hexafluoroisopropylidene-2,2-bis-(phthalic acid anhydride)-containing polyimides

The title product 4,4′-hexafluoroisopropylidene-2,2-bis-(phthalic acid anhydride) was prepared from hexafluoroacetone and o-xylene as the starting materials by condensation, oxidation and dehydration three-step reaction sequence. It reacted with diamines in DMF or xylene to give polyimides by condensation polymerization. Thermal and viscosity analyses show that these polyimides have lower molecular weight but excellent thermal stability.     

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.     

Synthesis and properties of polyimides from 4,4′-binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride

4,4′-Binaphthyl-1,1′,8,8′-tetracarboxylic dianhydride was synthesized from 4-chloro-1,8-naphthalic anhydride and polymerized with aromatic and pliphatic diamines in m-cresol or N-methyl-2-pyrrolidinone (NMP). The polyimides, except for two derived from p-phenylenediamine and hydrazine, are soluble in 1,1,2,2-tetrachloroethane and NMP. Their intrinsic viscosities ranged from 0.36 to 2.20 dL/g. The polymers showed excellent thermal and thermooxidative stabilities and displayed weak glass transition temperatures. Young's moduli of some polymer films were in the range of 2.5 and 5.4 GPa at 30°C. The aliphatic polyimides exhibited a stronger fluorescence than the aromatic polyimides. © 1995 John Wiley & Sons, Inc.     

Thermal behavior of copolyimides containing bisbenzoylamine groups

In an effort to improve the processibility of full aromatic polyimides, copolybisbenzoylamine imides were synthesized. As this study is a continuation of our work on flexibilization of the polyimide main chain, the bisbenzoylamine group was introduced stepwise into the polyimide main chain. Mixtures of pyromellitic anhydride, the rigid component, and a bisbenzoylamine-3,3′, 4,4′-tetracarboxylic acid dianhydride, the flexible component, were polymerized with aromatic diamines in a two-step procedure. The thermal stability of the four series of resulting copolyimides shows parallel changes that depend on the dianhydride ratio. The functional dependence of glass transition temperature (T_g) on copolymer composition differs for hydrogen or alkyl group substitution on the nitrogen in the bisbenzoylamine group. The solubility of the copolyimides in dimethylformamide changes from 0 to 33 wt %; there is a nonlinear dependence between solubility and the dianhydride ratio.     

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

A novel fluorinated aromatic dianhydride, 4,4′‐[2,2,2‐trifluoro‐1‐(3‐trifluoromethyl‐phenyl)ethylidene]diphthalic anhydride (TFDA) was synthesized by coupling of 3′‐trifluoromethyl‐2,2,2‐trifluoroacetophenone with o‐xylene under the catalysis of trifluoromethanesulfonic acid, followed by oxidation of KMnO₄ and dehydration. A series of fluorinated aromatic polyimides derived from the novel fluorinated aromatic dianhydride TFDA with various aromatic diamines, such as p‐phenylenediamine (p‐PDA), 4,4′‐oxydianiline (ODA), 1,4‐bis(4‐aminophenoxy)benzene (p‐APB), 1,3‐bis(4‐amino‐phenoxy)benzene (m‐APB), 4‐(4‐aminophenoxy)‐3‐trifluoromethylphenylamine (3FODA) and 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)benzene (6FAPB), were prepared by polycondensation procedure. 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 CHCl₃, THF, and acetone. Homogeneous and stable polyimide solutions with solid content as high as 35–40 wt % could be achieved, which were prepared by strong and flexible polyimide films or coatings. The polymer films have good thermal stability with the glass transition temperature of 232–322 °C, the temperature at 5% weight loss of 500–530 °C in nitrogen, and have outstanding mechanical properties with the tensile strengths of 80.5–133.2 MPa as well as elongations at breakage of 7.1–12.6%. It was also found that the polyimide films derived from TFDA and fluorinated aromatic diamines possess low dielectric constants of 2.75–3.02, a low dissipation factor in the range of 1.27–4.50 × 10^?3, and low moisture absorptions <1.3%. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4143–4152, 2004