Gas‐transport properties of indan‐containing polyimides

A series of indan‐containing polyimides were synthesized, and their gas‐permeation behavior was characterized. The four polyimides used in this study were synthesized from an indan‐containing diamine [5,7‐diamino‐1,1,4,6‐tetramethylindan (DAI)] with four dianhydrides [3,3′4,4′‐benzophenone tetracarboxylic dianhydride (BTDA), 3,3′4,4′‐oxydiphthalic dianhydride (ODPA), (3,3′4,4′‐biphenyl tetracarboxylic dianhydride (BPDA), and 2,2′‐bis(3,4′‐dicarboxyphenyl) hexafluoropropane dianhydride (6FDA)]. The gas‐permeability coefficients of these four polyimides changed in the following order: DAI–BTDA < DAI–ODPA < DAI–BPDA < DAI–6FDA. This was consistent with the increasing order of the fraction of free volume (FFV). Moreover, the gas‐permeability coefficients were almost doubled from DAI–ODPA to DAI–BPDA and from DAI–BPDA to DAI–6FDA, although the FFV differences between the two polyimides were very small. The gas permeability and diffusivity of these indan‐containing polyimides increased with temperature, whereas the permselectivity and diffusion selectivity decreased. The activation energies for the permeation and diffusion of O₂, N₂, CH₄, and CO₂ were estimated. In comparison with the gas‐permeation behavior of other indan‐containing polymers, for these polyimides, very good gas‐permeation performance was found, that is, high gas‐permeability coefficients and reasonably high permselectivity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2769–2779, 2004     

Dielectric properties of oxydianiline‐based polyimide thin films according to the water uptake

For polyimide thin films, the dielectric properties were investigated with the capacitance and optical methods. The dielectric constants of the 4,4′‐oxydianiline (ODA)‐based polyimide thin films varied from 2.49 to 3.10 and were in the following decreasing order: 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA)–ODA > 1,2,4,5‐benzenetetracarboxylic dianhydride (PMDA)–ODA > 4,4′‐hexafluoroisopropylidene diphthalic dianhydride (6FDA)–ODA. According to the absorption of water, the diffusion coefficients in the films varied from 4.8 × 10^?10 to 7.2 × 10^?10 cm²/s and were in the following increasing order: BPDA–ODA < PMDA–ODA < 6FDA–ODA. The dielectric constants and diffusion coefficients of the polyimides were affected by the morphological structures, including the molecular packing order. However, because of the water uptake, the changes in the dielectric constants in the polyimide thin films varied from 0.49 to 1.01 and were in the following increasing order: BPDA–ODA < 6FDA–ODA < PMDA–ODA. Surprisingly, 6FDA–ODA with bulky hexafluoroisopropylidene groups showed less of a change in its dielectric constant than PMDA–ODA. The total water uptake for the polyimide thin films varied from 1.43 to 3.19 wt % and was in the following increasing order: BPDA–ODA < 6FDA–ODA < PMDA–ODA. This means that the changes in the dielectric constants in the polyimide thin films were significantly related to the morphological structure and hydrophobicity of hexafluoroisopropylidene groups. Therefore, the morphological structure and chemical affinity in the polyimide thin films were important factors in controlling the dielectric properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2190–2198, 2002     

Packing density and gas permeability of copolyimides containing bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride constituent

Packing density and gas permeability of two copolyimide series containing an alicyclic monomer, bicyclo[2,2,2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCDA), and a fluorinated monomer, hexafluoroisopropylidene,2,2-bis(phthalic acid anhydride) (6FDA), were measured. Incorporation of a rigid BCDA segment in 6FDA polyimides either increases gas permeability or improves gas selectivity, depending on the base 6FDA polyimide. In the case of the highly gas permeable 6FDA polyimide, introduction of BCDA further increases gas permeability despite a loss in the amount of free volume. In the moderately gas permeable 6FDA polyimide, on the other hand, the introduction improves gas selectivity. © 1995 John Wiley & Sons, Inc.     

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.     

Synthesis and properties of poly(amic acid)s and polyimides based on 2,2′,6,6′‐biphenyltetracarboxylic dianhydride

Poly(amic acid)s (PAAs) having the high solution stability and transmittance at 365 nm for photosensitive polyimides have been developed. PAAs with a twisted conformation in the main chains were prepared from 2,2′,6,6′‐biphenyltetracarboxylic dianhydride (2,2′,6,6′‐BPDA) and aromatic diamines. Imidization of PAAs was achieved by chemical treatment using trifluoroacetic anhydride. Among them, the PAA derived from 2,2′,6,6′‐BPDA and 4,4′‐(1,3‐phenylenedioxy)dianiline was converted to the polyimide by thermal treatment. The heating at 300 °C under nitrogen did not complete thermal imidization of PAAs having glass‐transition temperatures (T_g)s higher than 300 °C to the corresponding PIs. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6385–6393, 2006     

Nanoindentation studies of polyimide thin films with various internal linkages in the diamine component

Polyimide thin films were synthesized from 3,3′,4,4′‐biphenyltetracarboxylic acid dianhydride (BPDA) and four different diamines (p‐phenylene diamine, 4,4′‐oxydiphenylene diamine, 4,4′‐biphenylene diamine, and 4,4′‐sulfonyldiphenylene diamine). The nanoindentation behavior of the resulting polyimides, namely, poly(p‐phenylene biphenyltetracarboximide) (BPDA‐PDA), poly(4,4′‐biphenylene biphenyltetracarboximide) (BPDA‐BZ), poly(4,4′‐oxydiphenylene biphenyltetracarboximide) (BPDA‐ODA), and poly(4,4′‐sulfonyldiphenylene biphenyltetracarboximide) (BPDA‐DDS), were investigated. Also, the morphological properties were characterized with a prism coupler and wide‐angle X‐ray diffraction and were correlated to the nanoindentation studies. The nanoindentation behavior and hardness varied quite significantly, depending on the changes in the chemical and morphological structures. The hardness of the polyimide thin films increased in the following order: BPDA‐DDS < BPDA‐ODA < BPDA‐BZ < BPDA‐PDA. For all the polyimide thin films, except that of BPDA‐BZ, the hardness decreased with an increase in the load. The birefringence, a measure of the molecular in‐plane orientation, increased in the following order: BPDA‐DDS < BPDA‐ODA < BPDA‐PDA < BPDA‐BZ. The X‐ray diffraction studies revealed that the crystallinity of the polyimide thin films varied with the changes in the chemical structure. The studies showed that the indentation response with an applied load and the hardness by nanoindentation for the BPDA‐based polyimides were closely related to the morphological structure. The nanoindentation and birefringence results revealed that the mechanical properties of the polyimide thin films were dependent on the crystallinity, which arose because of the chain order along the chain axis and the molecular packing order. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 861–870, 2004     

Organosoluble polyimides and copolyimides based on 1,1‐bis[4‐(4‐aminophenoxy)phenyl]‐1‐phenylethane and aromatic dianhydrides

1,1‐Bis[4‐(4‐aminophenoxy)phenyl]‐1‐phenylethane (BAPPE) was prepared through nucleophilic substitution reaction of 1,1‐bis(4‐hydroxyphenyl)‐1‐phenylethane and p‐chloronitrobenzene in the presence of K₂CO₃ in N,N‐dimethylformamide, followed by catalytic reduction with hydrazine and Pd/C. Novel organosoluble polyimides and copolyimides were synthesized from BAPPE and six kinds of commercial dianhydrides, including pyromellitic dianhydride (PMDA, I_a ), 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA, I_b ), 3,3′,4,4′‐ biphenyltetracarboxylic dianhydride (BPDA, I_c ), 4,4′‐oxydiphthalic anhydride (ODPA, I_d ), 3,3′,4,4′‐diphenylsulfonetetracarboxylic dianhydride (DSDA, I_e ) and 4,4′‐hexafluoroisopropylidenediphthalic anhydride (6FDA, I_f ). Differing with the conventional polyimide process by thermal cyclodehydration of poly(amic acid), when polyimides were prepared by chemical cyclodehydration with N‐methyl‐2‐pyrrolidone as used solvent, resulted polymers showed good solubility. Additional, I_a,b were mixed respectively with the rest of dianhydrides (I_c–f) and BAPPE at certain molar ratios to prepare copolyimides with arbitrary solubilities. These polyimides and copolyimides were characterized by good mechanical properties together with good thermal stability. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 2082–2090, 2000     

Synthesis and properties of aromatic polyimides derived from 2,2,′3,3′‐biphenyltetracarboxylic dianhydride

2,2,′3,3′‐Biphenyltetracarboxylic dianhydride (2,2,′3,3′‐BPDA) was prepared by a coupling reaction of dimethyl 3‐iodophthalate. The X‐ray single‐crystal structure determination showed that this dianhydride had a bent and noncopolanar structure, presenting a striking contrast to its isomer, 3,3,′4,4′‐BPDA. This dianhydride was reacted with aromatic diamines in a polar aprotic solvent such as N,N‐dimethylacetamide (DMAc) to form polyamic acid intermediates, which imidized chemically to polyimides with inherent viscosities of 0.34–0.55 dL/g, depending on the diamine used. The polyimides from 2,2,′3,3′‐BPDA exhibited a good solubility and were dissolved in polar aprotic solvents and polychlorocarbons. These polyimides have high glass transition temperatures above 283°C. Thermogravimetric analyses indicated that these polyimides were fairly stable up to 500°C, and the 5% weight loss temperatures were recorded in the range of 534–583°C in nitrogen atmosphere and 537–561°C in air atmosphere. All polyimides were amorphous according to X‐ray determination. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1425–1433, 1999     

Synthesis and characterization of novel fluorinated aromatic polyimides derived from 1,1‐bis(4‐amino‐3,5‐dimethylphenyl)‐1‐(3,5‐ditrifluoromethylphenyl)‐2,2,2‐trifluoroethane and various aromatic dianhydrides

A novel fluorinated aromatic diamine, 1,1‐bis(4‐amino‐3,5‐dimethylphenyl)‐1‐(3,5‐ditrifluoromethylphenyl)‐2,2,2‐trifluoroethane (9FMA), was synthesized by the coupling reaction of 3′,5′‐ditrifluoromethyl‐2,2,2‐trifluoroacetophenone with 2,6‐dimethylaniline under the catalysis of 2,6‐dimethylaniline hydrochloride. A series of fluorinated aromatic polyimides were synthesized from 9FMA and various aromatic dianhydrides, including pyromellitic dianhydride, 3,3′4,4′‐biphenyl tetracarboxylic dianhydride, 4,4′‐oxydiphthalic anhydride, 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA), and 4,4′‐hexafluoroisopropylidene diphthalic anhydride, via a high‐temperature, one‐stage imidization process. The inherent viscosities of the polyimides ranged from 0.37 to 0.74 dL/g. All the polyimides were quickly soluble in many low‐boiling‐point organic solvents such as tetrahydrofuran, chloroform, and acetone as well as some polar organic solvents such as N‐methyl‐2‐pyrrolidinone, N,N′‐dimethylacetamide, and N,N′‐dimethylformamide. Freestanding fluorinated polyimide films could be prepared and exhibited good thermal stability with glass‐transition temperatures of 298–334 °C and outstanding mechanical properties with tensile strengths of 69–102 MPa and elongations at break of 3.3–9.9%. Moreover, the polyimide films possessed low dielectric constants of 2.70–3.09 and low moisture absorption (<0.58%). The films also exhibited good optical transparency with a cutoff wavelength of 303–351 nm. One polyimide (9FMA/BTDA) also exhibited an intrinsic negative photosensitivity, and a fine pattern could be obtained with a resolution of 5 μm after exposure at the i‐line (365‐nm) wavelength. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2665–2674, 2006     

Analysis of dimensionally stable copolyimide with a low‐level residual stress

Copolyimide thin film, which has low‐level stress and stress relaxation induced by water sorption, was characterized for potential applications as an encapsulant, a stress‐relief buffer, and in interlayer dielectrics. The polyimides examined were poly(p‐phenylene pyromellitimide) (PMDA‐PDA) and poly(p‐phenylene biphenyltetracarboximide) (BPDA‐PDA) as well as their random copolyimides with various compositions. These copolyimide films exhibited good combinations of physical and mechanical properties with low thermal expansion coefficients, residual stress, and moisture‐induced stress–relaxation behavior by appropriately selecting the ratios of the dianhydride component. For these polyimides, the residual stress increased in the range of −8.1–7.5 MPa, whereas stress relaxation induced by water uptake decreased in the range of 10.3–4.7 MPa with increasing BPDA contents, respectively. The major factor in determining the magnitude of the stress behavior induced by both the thermal mismatch and water uptake in films should be the morphological factors such as chain rigidity, chain orientation, crystallinity, and microvoids. Their morphological structures were examined by wide angle X‐ray diffraction and a prism coupler, and the thermal properties were measured using a dynamic mechanical thermal analyzer as well as thermomechanical analysis. Overall, the candidate for the low level stress buffer application from the PMDA/BPDA‐PDA copolyimide was the 30/70 (= PMDA/BPDA in molar ratio) copolyimide. This copolyimide showed no residual stress after curing at 400 °C and relatively insensitive stress relaxation to ambient humidity. © 2001 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 796–810, 2001     

New concept of positive photosensitive polyimide: Reaction development patterning (RDP)

A soluble multiblock copolyimide without specific functional groups such as OH and COOH was prepared by a direct one‐pot polycondensation of two types of dianhydrides and diamines in the presence of γ‐valerolactone/pyridine catalyst using N‐methylpyrrolidone (NMP)/toluene mixture as a solvent. The polyimide film containing the photosensitive agent diazonaphthoquinone (DNQ) compound gave positive‐tone behavior by UV irradiation, followed by development in a mixture of ethanolamine/NMP/H₂O (1/1/1 by weight). The scanning electron microscopic photograph of the resultant image showed fine patterns with about 20 μm film thickness. Its pattern forming was based on the photorearrangement of diazonaphthoquinone, a process in which the ring‐opening reaction of imide units of the polyimide with the amine used as a developer and the following degradation of the polymer are induced. Such a new imaging technique combines principles of photolithography and etching of a polyimide to give, what we call, reaction development patterning in which the main chemical reactions directly related to the pattern formation occur during development. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3451–3463, 2001     

Synthesis and properties of fluorinated polyimides. 1. Derived from novel 4,4″‐bis(aminophenoxy)‐3,3″‐trifluoromethyl terphenyl

A new diamine monomer, 4,4″‐bis(aminophenoxy)‐3,3″‐trifluoromethyl terphenyl (ATFT) was synthesized that led to a number of novel fluorinated polyimides by solution as well as thermal imidization routes when reacted 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 ATFT/BTDA and ATFT/6FDA derived from both routes were soluble in several organic solvents such as N,N‐dimethylformamide, N,N‐dimethylacetamide, and dimethyl sulfoxide. The polyimide ATFT/PMDA was only soluble in N‐methylpyrollidone. The polyimide films had low water absorption of 0.3–0.7%, low dielectric constants of 2.72–3.3 at 1 Hz, refractive indices of 1.594–1.647 at 589.3 nm, and optical transparency >85%. These polyimides showed very high thermal stability with decomposition temperatures (5% weight loss) up to 532 °C in air and good isothermal stability; only 7% weight loss occurred at 400 °C after 7 h, and less than 0.6% weight loss was observed at 315 °C for 5 h. Transparent thin films of these polyimides exhibited tensile strengths up to 112 MPa, a modulus of elasticity up to 3.05 GPa, and elongation at break up to 21% depending on the repeating unit structure. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1016–1027, 2002     

Synthesis and characterization of polyimides derived from (3‐amino‐2,4,6‐trimethylphenyl)‐(3′‐aminophenyl)methanone and aromatic dianhydrides

A series of new polyimides were prepared via the polycondensation of (3‐amino‐2,4,6‐trimethylphenyl)‐(3′‐aminophenyl)methanone and aromatic dianhydrides, that is, 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), 4,4′‐oxydiphthalic anhydride, 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride, and 2,2′‐bis(3,4‐dicarboxyphenyl) hexafluoropropane dianhydride. The structures of the polyimides were characterized by Fourier transform infrared and NMR measurements. The properties were evaluated by solubility tests, ultraviolet–visible analysis, differential scanning calorimetry, and thermogravimetric analysis. The two different meta‐position‐located amino groups with respect to the carbonyl bridge in the diamine monomer provided it with an unsymmetrical structure. This led to a restriction on the close packing of the resulting polymer chains and reduced interchain interactions, which contributed to the solubility increase. All the polyimides except that derived from BPDA had good solubility in strong aprotic solvents, such as N‐methyl‐2‐pyrrolidinone, N,N′‐dimethylacetamide, N,N‐dimethylformamide, and dimethyl sulfone, and in common organic solvents, such as cyclohexanone and chloroform. In addition, these polyimides exhibited high glass‐transition values and excellent thermal properties, with an initial thermal decomposition temperature above 470 °C and glass‐transition temperatures in the range of 280–320 °C. The polyimide films also exhibited good transparency in the visible‐light region, with transmittance higher than 80% at 450 nm and a cutoff wavelength lower than 370 nm. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1291–1298, 2006     

Atomistic models of three fluorinated polyimides in the amorphous state

Molecular models of three fluorinated polyimides based on the 4,4′‐(hexafluoroisopropylidene)diphthalic dianhydride (6FDA) have been studied using molecular dynamics (MD) simulations. The respective diamines were 4,4′‐hexafluoroisopropylidene dianiline (6FpDA), 3,3′‐hexafluoroisopropylidene dianiline (6FmDA), and 2,4,6‐trimethyl‐1,3phenylenediamine (DAM). Thirty independent samples were prepared using a hybrid pivot Monte Carlo‐MD generation technique and average densities were found to be in very good agreement with experiment. Model structures also agreed with available wide‐angle X‐ray scattering data. Cohesive energies, Hildebrand solubility parameters, fractional free volumes (FFV), void space distributions and intermolecular as well as intramolecular interactions were analyzed. The differences in bulk properties between both 6FDA‐6FpDA and 6FDA‐6FmDA isomers remain fairly small, although the configurations of the former are more extended. 6FDA‐DAM has a lower density, larger intermolecular distances, and higher free volume than the other two polyimides. Results are discussed with respect to their use as matrices for gas separation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1166–1180, 2009     

Synthesis and properties of novel triptycene‐based polyimides

Two new triptycene‐containing bis(ether amine)s, 1,4‐bis(4‐aminophenoxy)triptycene ( 4 ) and 1,4‐bis(4‐amino‐2‐trifluoromethylphenoxy)triptycene ( 6 ), were synthesized, respectively, from the nucleophilic chloro‐displacement reactions of p‐chloronitrobenzene and 2‐chloro‐5‐nitrobenzotrifluoride with 1,4‐dihydroxytriptycene in the presence of potassium carbonate, followed by palladium‐catalyzed hydrazine reduction of the dinitro intermediates. The bis(ether amine)s were polymerized with six commercially available aromatic tetracarboxylic dianhydrides to obtain two series of novel triptycene‐based polyimides 8a – f and 9a – f by using a conventional two‐step synthetic method via thermal and chemical imidizations. All the resulting polyimides exhibited high enough molecular weights to permit the casting of flexible and strong films with good mechanical properties. Incorporation of trifluoromethyl groups in the polyimide backbones improves their solubility and decreases their dielectric constants. The fluorinated polyimides 9d and 9f derived from diamine 6 with 4,4′‐oxydiphthalic anhydride and 2,2‐bis(3,4‐dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), respectively, could afford almost colorless thin films. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis and properties of novel photosensitive polyimides containing chalcone moiety in the main chain

Two chalcone-derivative isomers, 4,4′-diaminochalcone ( 4DAC ) and 3,3′-diaminochalcone ( 3DAC ), were synthesized and used as monomers together with tetracarboxylic dianhydrides to prepare novel photosensitive polyimides that contain a chalcone moiety in the main chain. The polyimides were characterized and their photochemical behavior was investigated as thin films and in solutions with the aid of ultraviolet and infrared spectroscopy. Compared with 4DAC -based polyimides, the 3DAC -based polyimides exhibited lower glass transition temperatures and higher photocrosslinking rates of the carbon–carbon double bond as well as higher photosensitivities obtained from the exposure characteristic curves, suggesting that an increase in the photoreactivity of the 3DAC -based polyimides might arise from the improved flexibility of their backbones. The polyimide from 3DAC and 6FDA (2,2-bis[3,4-dicarboxypheny]hexa-fluoropropane dianhydride) showed a photosensitivity of 33 mJ/cm² with a contrast of 1.5 upon light irradiation using a Xenon lamp. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 685–693, 1998     

Novel Non‐Coplanar and Tertbutyl‐Substituted Polyimides: Solubility,Optical, Thermal and Dielectric Properties

A novel aromatic diamine monomer bearing tertbutyl and 4‐tertbutylphenyl groups, 3,3′‐ditertbutyl‐4,4′‐diaminodiphenyl‐4′′‐tertbutylphenylmethane (TADBP), was prepared and characterized. A series of non‐coplanar polyimides (PIs) were synthesized via a conventional one‐step polycondensation from TADBP and various aromatic dianhydrides including pyromellitic dianhydride (PMDA), 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), 4,4′‐oxydiphthalic anhydride (OPDA), 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) and 4,4′‐(hexafluoroisopropylidene)dipthalic anhydride (6FDA). All PIs exhibit excellent solubility in common organic solvents such as N,N‐dimethylformamide (DMF), N,N‐dimethylacetamide (DMAc), N‐methyl‐2‐pyrrolidone (NMP), dimethyl sulfoxide (DMSO), chloroform (CHCl₃), tetrahydrofuran (THF), and so on. Furthermore, the obtained transparent, strong and flexible polyimide films present good thermal stability and outstanding optical properties. Their glass transition temperatures (T_gs) are in the range of 298 to 347°C, and 10% weight loss temperatures are in excess of 490°C with more than 53% char yield at 800°C in nitrogen. All the polyimides can be cast into transparent and flexible films with tensile strength of 80.5–101 MPa, elongation at break of 8.4%–10.5%, and Young's modulus of 2.3–2.8 GPa. Meanwhile, the PIs show the cutoff wavelengths of 302–356 nm, as well as low moisture absorption (0.30% –0.55%) and low dielectric constant (2.78–3.12 at 1 MHz).     

Polyimides with alicyclic diamines. II. Hydrogen abstraction and photocrosslinking reactions of benzophenone-type polyimides

Photosensitive polyimides with alicyclic diamines and benzophenone moiety were prepared by reactions of 3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA) with diamines in aprotic solvents, followed by thermal or chemical imidizations. Among them the polyimide from BTDA and bis(4-amino-3-methylcyclohexyl) methane (DMDHM) can be dissolved in several organic solvents such as dichloromethane, tetrachloroethane, and N-methyl-2-pyrrolidone (NMP). In order to compare properties of the polyimides with alicyclic diamines with those of corresponding aromatic polyimides, the UV absorption spectra and fluorescence spectra of these polyimides and their model compounds were investigated. No occurrence of charge transfer at photoexcited states was ascertained for the polyimides with alicyclic diamines. The hydrogen abstraction and crosslinking during photoirradiation have been studied to learn the influence of the elimination of charge transfer process in these photosensitive polyimides. The quantum yield of hydrogen abstraction for the model compound of alicyclic polyimides is 0.56 in THF measured with HPLC. The quantum yield for the photocrosslinking reaction of the solvent-soluble polyimide with alicyclic diamine, PI(BTDA/DMDHM), was determined to be 0.004 in air from gel permeation chromatography (GPC) measurement, which is four times higher than that for photosensitive polyimides with aromatic diamines. © 1994 John Wiley & Sons, Inc.     

Improvement of thermoplasticity for s‐BPDA/PDA by copolymerization and blend with novel asymmetric BPDA‐based polyimides

Asymmetric biphenyl type polyimides (PI) derived from 2,3,3′,4′‐biphenyltetracarboxylic dianhydride (a‐BPDA) and p‐phenylenediamine (PDA) or 4,4′‐oxydianiline (ODA) show higher T_gs, and much better thermoplasticity than the corresponding isomeric PIs from symmetric 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (s‐BPDA). In addition, a‐BPDA‐derived PIs are completely amorphous owing to their bent chain structures and highly distorted conformations, whereas the PIs from s‐BPDA are semicrystalline. a‐BPDA‐derived PIs possessing these properties or the a‐BPDA monomer were used as a flexible blend component or a comonomer to improve the insufficient thermoplasticity of semirigid s‐BPDA/PDA homo polymer. The blends composed of s‐BPDA/PDA (80%) with a‐BPDA‐derived PIs (20%), as well as the s‐BPDA/PDA‐based copolymer containing 20% a‐BPDA, showed a certain extent of thermoplasticity above the T_gs without causing a decrease in T_g. In addition, these blends and copolymer provided comparatively low thermal expansion coefficient (ca. 18 ppm). The improved film properties for the blends are related to good blend miscibility. On the other hand, when s‐BPDA/ODA was used as a flexible matrix polymer instead of a‐BPDA‐derived PIs, the 80/20 blend film annealed at 400°C exhibited no prominent softening at the T_g. This result arises from annealing‐induced crystallization of the flexible s‐BPDA/ODA component. Thus, these results revealed that a‐BPDA‐derived PIs are promising candidates as matrix polymers for semirigid s‐BPDA/PDA for the present purpose. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2499–2511, 1999     

Synthesis and Characterization of Fluorinated Polyimide Derived from 3,3′‐Diisopropyl‐4,4′‐diaminodiphenyl‐3′′,4′′‐difluorophenylmethane

A novel aromatic diamine monomer, 3,3′‐diisopropyl‐4,4′‐diaminodiphenyl‐3′′,4′′‐difluorophenylmethane (PAFM), was successfully synthesized by coupling of 2‐isopropylaniline and 3,4‐difluorobenzaldehyde. The aromatic diamine was adopted to synthesize a series of fluorinated polyimides by polycondensation with various dianhydrides: pyromellitic dianhydride (PMDA), 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA), 4,4′‐oxydiphthalic anhydride (ODPA) and 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride (BTDA) via the conventional one‐step method. These polyimides presented excellent solubility in common organic solvents, such as N,N‐dimethylformamide (DMF), N,N‐dimethyl acetamide (DMAc), dimethyl sulfoxide (DMSO), N‐methyl‐2‐pyrrolidone (NMP), chloroform (CHCl₃), tetrahydrofuran (THF) and so on. The glass transition temperatures (T_g) of fluorinated polyimides were in the range of 260–306°C and the temperature at 10% weight loss in the range of 474–502°C. Their films showed the cut‐off wavelengths of 330–361 nm and higher than 80% transparency in a wavelength range of 385–463 nm. Moreover, polymer films exhibited low dielectric properties in the range of 2.76–2.96 at 1 MHz, as well as prominent mechanical properties with tensile strengths of 66.7–97.4 MPa, a tensile modulus of 1.7–2.1 GPa and elongation at break of 7.2%–12.9%. The polymer films also showed outstanding hydrophobicity with the contact angle in the range of 91.2°–97.9°.