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.     

Novel fluorinated polyimides derived from 9,9-bis(4-amino-3,5-difluorophenyl)fluorene and aromatic dianhydrides

Novel fluorinated polyimides (PIs) were prepared from 9,9-bis(4-amino-3,5-difluorophenyl)fluorene with three aromatic dianhydrides via a one-step high-temperature polycondensation procedure. These obtained PIs showed excellent solubility and could be readily soluble in a variety of organic solvents such as NMP, DMAc, DMF, CHCl₃, CH₂Cl₂ and THF. All the PIs could afford flexible and strong films with low dielectric constants (2.62-2.79 at 1 MHz) and low moisture absorptions (0.18-0.41%). Thin films of these PIs exhibited high optical transparency and light color, with the cutoff wavelength at 341-355 nm and transmittance higher than 80% at 450 nm. Meanwhile, these PIs possessed eminent thermal stability, with decomposition temperatures (T_d) above 570 °C in both air and nitrogen atmospheres and glass transition temperatures (T_g) beyond 376 °C. Moreover, these fluorinated PI films showed low surface free energy and hydro-oleophobic character. The contact angles on the films for water and glycerol were in the range of 102.3-107.9° and 94.0-100.3°, respectively. In comparison with the analogous PI non-containing fluorine group, these fluorinated PIs showed better solubility, higher optical transparency, lower dielectric constants and lower surface free energy.     

Synthesis of novel polyimides with (tert-butyldimethylsiloxy)biphenyloxy groups and the effect of side-chains content on their properties

A novel aromatic diamine 4′-(tert-butyldimethylsiloxy)biphenyl-4-yl 3,5-diaminobenzoate (DPA) was synthesized through three steps including monoesterification, silylation and hydrogenation. DPA with different ratios was copolymerized with 4,4′-diaminodiphenyl ether (ODA) and 3,3′,4,4′-biphenyl dianhydride (BPDA) to give poly(amic acid)s which were converted into polyimides (PIs) by thermal imidization. The effect of side-chain content on the thermal stability, optical transparency and surface energies was investigated by DSC, TGA, UV-vis spectra and contact angle measurement. With the content of side-chains increasing, the PIs revealed lower thermal stability, higher optical transparency and lower surface energies. The pretilt angles of 4-pentyl-4′-cyanobiphenyl (5CB) on the PI films were measured by a crystal rotation method. For the same rubbing strength, the pretilt angles increased with the increasing of the content of side-chains. When the content of side-chains rose from 5% to 20%, the pretilt angles increased from 2.8° to 15.0° under 28.5 mm of rubbing strength. When the content of side-chains increased to 70%, 80%, 90%, and 100%, the pretilt angles was 75.0°, 82.9°, 87.0°, and 87.7°, respectively, under 28.5 mm rubbing strength.     

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 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 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.     

Spontaneous molecular orientation of polyimides induced by thermal imidization (4): Casting- and melt-induced in-plane orientation

Driving forces of in-plane chain orientation of polyimides (PIs) and their precursors were discussed and the mechanisms were proposed. A polyimide precursor, poly(amic acid) (PAA) derived from 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) with p-phenylenediamine (PDA) showed a certain degree of in-plane orientation in its solution-casting process and clear molecular weight dependence. The results allowed us to propose the casting-induced in-plane orientation mechanism of the rigid PAA chains. The imidization-induced in-plane orientation mechanism was also discussed by investigating how residual solvent content influences the degree of in-plane orientation of resultant PI films. The results suggested that the magnitudes of the PI chain in-plane orientation are dominated by a combined effect of the initial PAA orientation, apparent stretching based on a great thickness decrease, and the molecular mobility during thermal imidization. In a system derived from s-BPDA with 2,2′-bis(trifluoromethyl)benzidine (TFMB), the effect of molecular mobility during thermal imidization was predominant when cured under usual thermal conditions owing to the presence of the trifluoromethyl groups contributing to weakened intermolecular interaction. In s-BPDA/TFMB and s-BPDA/m-TOL systems (m-TOL = m-tolidine), a melt-induced in-plane orientation phenomenon was observed at temperatures corresponding to their T_g’s when the extents of in-plane chain orientation (f values) were monitored as a function of temperature in the stepwise heating process. This behavior is very curious because there are no appreciable dimensional, morphological, and structural changes as some driving forces just above the T_g of s-BPDA/TFMB.     

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 polyamides containing pendant pentadecyl chains

A new aromatic diacid monomer viz., 4-(4′-carboxyphenoxy)-2-pentadecylbenzoic acid was synthesized starting from cardanol and was characterized by FTIR, ¹H- and ¹³C NMR spectroscopy. A series of new aromatic polyamides containing ether linkages and pendant pentadecyl chains was prepared by phosphorylation polycondensation of 4-(4′-carboxyphenoxy)-2-pentadecylbenzoic acid with five commercially available aromatic diamines viz., 1,4-phenylenediamine, 4,4′-oxydianiline, 4,4′-methylenedianiline, 1,3-phenylenediamine, and 4,4′-(hexafluoroisopropylidene)dianiline. Inherent viscosities of the polyamides were in the range 0.45-0.66 dL/g in N,N-dimethylacetamide at 30 ± 0.1 °C. The introduction of ether linkages and pendant pentadecyl chains into polyamides led to an enhanced solubility in N,N-dimethylacetamide and 1-methyl-2-pyrrolidinone at room temperature or upon heating. The polyamides could be solution-cast into tough, flexible and transparent films from their N,N-dimethylacetamide solution. Wide angle X-ray diffraction patterns exhibited broad halo indicating that the polymers were essentially amorphous in nature. X-Ray diffractograms also displayed a diffuse to sharp reflection in the small-angle region (2θ = ∼2-5°) for the polyamides characteristics of formation of loosely to well-developed layered structure arising from packing of flexible pentadecyl chains. The glass transition temperature observed for the polyamides was in range 139-189 °C. The temperature at 10% weight loss (T₁₀), determined by TGA in nitrogen atmosphere, of the polyamides was in the range 425-453 °C indicating their good thermal stability.     

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 poly(amideimide)s containing pendent flexible alkoxy chains

A series of aromatic diacylhydrazides containing pendent flexible alkoxy chains, viz., 5-butyloxyisophthalicacid dihydrazide, 5-octyloxyisophthalicacid dihydrazide, 5-dodecyloxyisophthalicacid dihydrazide and 5-hexadecyloxyisophthalicacid dihydrazide were synthesized by the hydrazinolysis reaction of the corresponding aromatic esters with hydrazine hydrate. Diacylhydrazides were each polycondensed with aromatic dianhydrides, viz., 4,4′-oxydiphthalic anhydride (ODPA), 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) and pyromellitic dianhydride (PMDA) to obtain new poly(amideimide)s. Poly(amideimide)s had inherent viscosity in the range 0.55-0.88 dL/g in N,N-dimethylacetamide (DMAc) at 30 ± 0.1 °C. Poly(amideimide)s were found to be soluble in DMAc, N,N-dimethylformamide (DMF), 1-methyl-2-pyrrolidinone (NMP) and pyridine and could be cast into tough, flexible and transparent films from a solution in DMAc. X-ray diffractograms revealed that poly(amideimide)s with longer alkoxy chains had layered structures. Glass transition temperature of poly(amideimide)s containing pendent flexible alkoxy chains were in the range 215-245 °C. Temperature at 10% weight loss was in the range 380-410 °C in nitrogen atmosphere indicating good thermal stability of poly(amideimide)s.     

Poly(ester imide)s possessing low coefficients of thermal expansion (CTE) and low water absorption (III). Use of bis(4-aminophenyl)terephthalate and effect of substituents

A variety of poly(ester imide)s (PEsIs) were prepared using bis(4-aminophenyl)terephthalate (BPTP) and substituted BPTP (BPTP series) for applications to novel base film materials in flexible printed circuit boards (FPC). BPTP series were all highly reactive with various tetracarboxylic dianhydrides and led to considerably high molecular weights of PEsI precursors. The thermally imidized BPTP-based PEsI films achieved lower extents of water absorption (W_A) than the corresponding 4-aminophenyl-4′-aminobenzoate (APAB)-based PEsI systems while keeping other target properties, in particular, the linear coefficient of thermal expansion (CTE) much lower than that of copper foil as a conductive layer in FPC. The lower W_A is attributed to the decreased imide contents in the structure by using BPTP. The considerably low CTE can be explained in terms of intimate stacking between the p-aromatic ester fragments with an extended conformation. The BPTP-based PEsI system also exhibited a considerably low dissipation factor (tan δ = 1.91 × 10⁻³) at a high-frequency electric field of 18.3 GHz, comparable to a liquid-crystalline polyester. An effect of substituents on the film properties was also investigated in this work. Incorporation of methyl substituents on BPTP was very effective for property improvement, whereas methoxy substituents on BPTP, as well as methyl substituents onto hydroquinone bis(trimellitate anhydride) (TAHQ), showed a trend to significantly increase the CTE. Copolymerization with an adequate amount of a typically flexible monomer, 4,4′-oxydianiline (4,4′-ODA), allowed the CTE matching with copper foil and the film toughness improvement at the same time. The PEsI copolymer prepared from TAHQ (10 mmol) with methyl-substituted BPTP (7 mmol) and 4,4′-ODA (3 mmol) achieved excellent combined properties, namely, a very high T_g at 410 °C, a slightly lower CTE (10.0 ppm/K) than that of copper foil, suppressed water absorption (0.35%), an extremely low linear coefficient of humidity expansion (CHE = 3.4 ppm/RH%), and good film toughness (the elongation at break, ε_b = 50.7%). Thus, BPTP- and methyl-substituted BPTP-based PEsI systems can be promising candidates as a next generation of FPC base film materials.     

Synthesis and characterization of new aromatic polyesters containing cardo decahydronaphthalene groups

Three cardo bisphenols containing decahydronaphthalene group viz., 4,4′-(octahydro-2(1H)-naphthylidene)bisphenol, 4,4′-(octahydro-2(1H)-naphthylidene)bis-3-methylphenol and 4,4′-(octahydro-2(1H)-naphthylidene)bis-3,5-dimethylphenol were synthesized starting from commercially available 2-naphthol and were utilized for synthesis of new aromatic polyesters by phase transfer-catalyzed interfacial polycondensation with isophthaloyl chloride, terephthaloyl chloride and a mixture of isophthaloyl chloride and terephthaloyl chloride (50:50 mol %). Inherent viscosities and number average molecular weights (M_n) of polyesters were in the range 0.35-0.84 dL/g and 13,300-48,500 (Gel Permeation Chromatography, polystyrene standard), respectively. Polyesters were readily soluble in organic solvents such as dichloromethane, chloroform, tetrahydrofuran, meta-cresol, pyridine, N,N-dimethylformamide, N,N-dimethylacetamide, and 1-methyl-2-pyrrolidinone at room temperature and could be cast into tough, transparent and flexible films from their chloroform solutions. Wide-angle X-ray diffraction measurements revealed the amorphous nature of polyesters. The glass transition temperature of polyesters was in the range 207-287 °C. The temperature at 10% weight loss (T₁₀), determined from thermogravimetric analysis of polyesters, was in the range 425-460 °C indicating their good thermal stability.     

High strength electrospun polymer nanofibers made from BPDA-PDA polyimide

A series of high molecular weight PI precursors, poly(p-phenylene biphenyltetracarboxamide acid), were synthesized from 3,4,3′,4′-biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA) by using intense mechanical stirring at −15 to 0 °C for 48-72 h. The as-synthesized PI precursor solution was used to make BPDA/PDA polyimide thin films and electrospun nanofibers. IR, Ostward Viscometer, CMT-8102 Electromechanical Universal Testing Machine and scanning electron microscope (SEM) were used for the characterizations of the as-synthesized PI precursor, PI films and nanofiber sheets. The high molecular weight BPDA/PDA PI thin films and electrospun nanofiber sheets possess excellent mechanical properties of up to 900 MPa tensile strength with up to 18.0 GPa E-modulus and up to 210 MPa tensile strength with up to 2.5 GPa E-modulus, respectively.     

Organo-soluble and transparent polyimides containing phenylphosphine oxide and trifluoromethyl moiety: Synthesis and characterization

A series of aromatic polyimides (PI-II_a-d) containing lateral phenylphosphine oxide (PPO) and trifluoromethyl (-CF₃) moiety were prepared from an aromatic diamine, 2,5-bis[(4-amino-2-trifluoromethylphenoxy)phenyl]diphenyl-phosphine oxide (BATFDPO) and various aromatic dianhydrides via a two-step chemical imidization procedure. In parallel, for comparison, another series of polyimides (PI-I_a-d) without trifluoromethyl were synthesized from a diamine, 2,5-bis[(4-aminophenoxy)-phenyl]diphenylphosphine oxide (BADPO) and the same dianhydrides. It was found that both of the two series of polyimides (PIs) were soluble in polar aprotic solvents, such as N-methyl-2-pyrrolidinone (NMP) and the solubility of PI-II_a-d was highly enhanced by the introduction of the bulky -CF₃ group. Flexible and tough PI films with tensile strengths higher than 70 MPa were cast from the PI solution. The introduction of -CF₃ moiety slightly sacrificed the thermal stability and mechanical properties of the PI films. For example, PI-II_a-d showed 5% weight loss at 472-476 ^°C, which was about 50 ^°C lower than those of their PI-I_a-d analogues. However, -CF₃ group apparently improved the optical transparency and decreased the refractive indices of the PI films. PI-II_d derived from BATFDPO and 4,4’-hexafluoroisopropylidenediphthalic anhydride (6FDA) exhibited the highest optical transparency with the transmittance of 90% at 400 nm and the refractive index as low as 1.5511 at 1310 nm.     

Regularly alternating poly(amideimide)s containing pendent pentadecyl chains: Synthesis and characterization

Two new aromatic diamines containing preformed amide linkages, viz., N,N′-(4-pentadecyl-1,3-phenylene)bis(4-aminobenzamide) I and N,N′-(4-pentadecyl-1,3-phenylene)bis(3-aminobenzamide) II, were synthesized by reaction of 4-pentadecylbenzene-1,3-diamine with 4-nitrobenzoylchloride and 3-nitrobenzoylchloride, followed by reduction of the respective dinitro derivatives. A series of new poly(amideimide)s was synthesized by polycondensation of I and II with four commercially available aromatic dianhydrides, viz., pyromellitic dianhydride (PMDA), 4,4′-biphenyltetracarboxylic dianhydride (BPDA), 4,4′-oxydiphthalic anhydride (ODPA), and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6-FDA) in N,N-dimethylacetamide (DMAc) employing conventional two step method via poly(amic acid) intermediate followed by thermal imidization. Reference poly(amideimide)s were synthesized by polycondensation of N,N′-(1,3-phenylene)bis(4-aminobenzamide) and N,N′-(1,3-phenylene)bis(3-aminobenzamide) with the same aromatic dianhydrides. Inherent viscosities of poly(amideimide)s containing pendent pentadecyl chains were in the range 0.37-1.23 dL/g in N,N-dimethylacetamide at 30 ± 0.1 °C indicating the formation of medium to high molecular weight polymers. The poly(amideimide)s containing pendent pentadecyl chains were found to be soluble in N,N-dimethylacetamide, N,N-dimethylformamide, 1-methyl-2-pyrrolidinone and pyridine and could be cast into transparent, flexible and tough films from their N,N-dimethylacetamide solution. Wide angle X-ray diffraction patterns exhibited broad halo indicating that the polymers were essentially amorphous in nature. X-ray diffractograms also displayed sharp reflection in the small angle region (2θ ≈ 3°) for poly(amideimide)s containing pentadecyl chains indicating the formation of layered structure arising from packing of flexible pentadecyl chains. The glass transition temperatures observed for reference poly(amideimide)s were in the range 331-275 °C and those for poly(amideimide)s containing pendent pentadecyl chains were in the range 185-286 °C indicating a large drop in T_g owing to the “internal plasticization” effect of pentadecyl chains. The temperature at 10% weight loss (T₁₀), determined by TGA in nitrogen atmosphere, were in the range 460-480 °C indicating their good thermal stability.     

Microstructure and properties of organosoluble polyimide/silica hybrid films

Organosoluble polyimide/silica hybrid materials were prepared via the sol-gel process and their pervaporation properties were studied. The organosoluble polyimide (PI) was based on 4,4′-oxydiphthlic dianhydride (ODPA) and 4,4′-diamino-3,3′-dimethyldiphenylmethane (DMMDA). The surface chemical structure of polyimide/silica films was analyzed by Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) and the results show that the completely hydrolysis of alkoxy groups of precursors and formation of the three-dimensional Si-O-Si network in the hybrid films. The morphology and the silica domain thus obtained were studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM), respectively. The silica particle size in the hybrid is in the range of 40-100 nm for the hybrid films when the amount of silica is less than 20 wt%. The strength and the modulus of the hybrid films are improved and the mechanical properties were found to be strongly dependent on the density of the crosslink. The glass transition temperature (T_g) of the hybrid films was determined by dynamic mechanical analysis (DMA) and the value increased 15-20 °C as the silica content increased. Furthermore, the pervaporation performances of the prepared hybrid films were also investigated for the ethanol/water mixtures at different temperature.     

Novel thermally stable and chiral poly(amide-imide)s bearing from N,N′-(4,4′-diphthaloyl)-bis-l-isoleucine diacid: Synthesis and characterization

Novel optically active aromatic poly(amide-imide)s (PAIs) were prepared from newly synthesized N,N′-(4,4′-diphthaloyl)-bis-l-isoleucine diacid (3) via polycondensation with various diamines. The diacid was synthesized by the condensation reaction of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (1) with l-isoleucine (2) in a mixture of acetic acid and pyridine (3:2 v/v). All the polymers were obtained in quantitative yields with inherent viscosities of 0.20-0.43 dL g⁻¹. All the polymers were highly organosoluble in solvents like N-methyl-2-pyrrolidinone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran, γ-butyrolactone, cyclohexanone and chloroform at room temperature or upon heating. These poly(amide-imide)s had glass transition temperatures between 198 and 231 °C, and their 10% weight-loss temperatures were ranging from 368 to 398 °C and 353 to 375 °C under nitrogen and air, respectively. The polyimide films had tensile strengths in the range of 63-88 MPa and tensile moduli in the range of 0.8-1.4 GPa. These poly(amide-imide)s possessed chiral properties and the specific rotations were in the range of −3.10° to −72.92°.     

Synthesis and characterization of soluble polyimides based on a new fluorinated diamine: 4-Phenyl-2,6-bis[3-(4′-amino-2′-trifluoromethyl-phenoxy) phenyl] pyridine

A new kind of pyridine-containing aromatic diamine monomer, 4-phenyl-2,6-bis[3-(4′-amino-2′-trifluoromethyl-phenoxy) phenyl] pyridine (m-PAFP), was successfully synthesized by a modified Chichibabin reaction of 3-(4′-nitro-2′-trifluoro-methyl-phenoxy)-acetophenone with benzaldehyde, followed by a catalytic reduction. A series of fluorinated pyridine-bridged aromatic poly(ether-imide)s were prepared from the resulting diamine monomer with various aromatic dianhydrides via a conventional two-step thermal or chemical imidization method. The inherent viscosities values of these polyimides were in the range of 0.56-1.02 dL/g, and they could be cast and thermally converted into transparent, flexible, and tough polyimide films. The polyimides displayed higher solubility in polar solvents such as NMP, DMSO and m-cresol. The polyimides had good thermal stability, with the glass transition temperatures (T_g) of 187-211 °C, the temperatures at 5% weight loss of 511-532 °C, and the residue at 800 °C in air was higher than 50%. These films also had dielectric constants of 2.64-2.74 at 10 MHz and low water uptake 0.53-0.66%. Wide-angle X-ray diffraction measurements revealed that these polyimides were predominantly amorphous. Moreover, the polymer films of these novel polyimides showed outstanding mechanical properties with the tensile strengths of 90.1-96.6 MPa, elongations at breakage of 8.9-10.7% and tensile modulus of 1.65-1.98 GPa.     

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.