2,2′-Bis­(thiophenyl)­benzidine (BTPB) and 2,2′-bis­(4-chlorothiophenyl)­benzidine (BCTPB) were synthesized via a benzidine rearrangement reaction of the corresponding hydrazobenzene derivatives obtained after the reduction of (3-nitrophenyl)­(phenyl)­sulfane and (4-chlorophenyl)­(3-nitrophenyl)­sulfane, respectively. Transparent polyimides (PIs) with high refractive indices and small birefringences as well as good thermomechanical stabilities were synthesized by the conventional two-step thermal polycondensation of BTPB and BCTPB with five different dianhydrides in N-methyl-2-pyrrolidone. 3,3′,4,4′-Biphenyltetracarboxylic dianhydride (BPDA)/BCTPB PI, a fully aromatic and non-fluorinated PI, with a highly distorted noncoplanar conformation of the main chain was transparent and colorless with a transmittance of ∼83% and >88% at 450 nm and in the visible region, respectively. In addition, all six non-fluorinated sulfur-containing aromatic PIs exhibited high average refractive indices (1.7112–1.7339), and small birefringences (0.0007–0.0022) at 633 nm, because of the high atomic polarizability of sulfur and the rigid bulky molecular structure of BTPB and BCTPB. The more effective steric effect caused by bulky 4-chlorothiophenyl in BCTPB improved the optical transparency but decreased the average refractive indices of BCTPB-based PIs compared to BTPB-based PIs.

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In recent years, many researchers have been studied and developed the nanofibers which have a large specific surface area and a small pore size. The polymer nanofibers are being used or finding uses in filtration, biomedical applications including wound dressings as structural elements in artificial organs, and reinforced composites. Thus these special needs have stimulated recent studies and renewed interest in the process, quantitative technical and scientific information regarding process and product characterization are extremely limited. The electrospinning can allow producing and encouraging the utilization of nanofibers. The surface morphology of e-spun fiber is affected by many variables that involve polymer concentration, applied voltage, spinning distance, air friction, gravity and ambient parameters. This study shows the effect of relative humidity on the microstructures of the e-spun Polystyrene (PS) fiber.A PS solution is prepared from PS pellet (Aldrich, molecular weight 170,000 g/mol) which is dissolved with Tetrahydrofuran and Dimethylformamide (Junsei Co.) in the ultrasonicator. The concentration of the PS solution was 7 weight%. The Spinning occurs from the droplet of solution protruding from the 0.7 mm internal diameter of the tip. A positive electric potential is applied to the polymer blend solution by attaching the lead to the variable high voltage power supply (Chungpa EMT Inc.). It was directly connected to the copper wire located in the inside of the solution. A drum collector covered with aluminum foil is placed 10 cm vertically from the tip of the syringe as a grounded collector. The relative humidity was changed with four steps from 10 to 70%. All experiments were performed at the constant temperature-humidity chamber. The surface morphology and the diameter of the e-spun fiber were investigated by the Scanning Electron Microscope (AMRAY model 1400), Atomic force Microscope (PSIA XE-100) and the image processor (GAIA Blue).The relative humidity has shown a great influence on the fiber diameter in terms of the analysis of SEM and measurement of fiber diameter which are given in FIG. 1 and TABLE 1. When the relative humidity was 10%, e-spun fibers have the average diameter of 130 nm (FIG. 1-a), but as the relative humidity increased to 70%, the fiber diameter gradually thickened to 380 nm (FIG. 1-d). The higher relative humidity makes thicker fiber because the higher electrostatic charge on the fiber surface has the opportunity to split the fibers more. Thus it results in producing thinner fibers in the travel of the fibers towards the target. In other words, the higher moisture can produce thicker fiber due to more discharge of electrostatics on the surface of the polymer solution.

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A new diamine containing an imidazole structure, 4,4′-(4,5-diphenyl-1H-imidazole-1,2-diyl)dianiline (DIMA), was synthesized to prepare photoconductive polyimides (PIs) with four types of dianhydrides such as 3,3′,4,4′-biphenyltetracarboxylic dianhydride, 4,4′-oxyduphthalic anhydride, 4,4′-(hexafluoroisopropylidene) diphthalic anhydride, and cyclobutane-1,2,3,4,-tetracarboxylic dianhydride, based on the fact that the imidazole ring is a useful n-type block with high electron-donating property and good thermal stability. The imidazole-containing diamine possesses high electron-donating properties due to the lone pair electrons at nitrogen, which affords a high hole-transport property. All the PIs prepared from DIMA were amorphous due to the large side group and kink structure of the diamine, optically transparent (transmittances of 92–98% at 450 nm), and exhibited high thermal stability (10% weight loss temperatures ranged 453–558°C).

The effects of crosslinking agents (crosslinkers) on polyimide (PI)/graphene oxide (GO) hybrid films were extensively investigated. The surface of GO was modified with amino groups using 4‐aminobenzylamine to improve compatibility with pyromellitic dianhydride/4,4′‐oxydianiline PI, and two kinds of crosslinkers were used: tris(4‐aminophenyl)amine and 1,3,5‐triazine‐2,4,6‐triamine (melamine). The mechanical, thermal and optical properties of the PI hybrid films were investigated. In particular, the transparency and physical properties of the PI hybrid films containing amino‐functionalized GO with homogeneous dispersion were improved. As the content of the crosslinker increased, a crosslinking network was formed between the PI chains, and the stiffness of the hybrid films was increased. The glass transition temperature, heat resistance and mechanical properties were also enhanced. The PI hybrids prepared with a rigid crosslinker exhibited higher optical transparency due to the reduction of the intermolecular charge transfer interactions with increasing interchain spacing between the PI chains. © 2018 Society of Chemical Industry

Polyimide (PI)/silica hybrid films were prepared from tetraethyl orthosilicate (TEOS) using a sol‐gel process as well as pyromellitic dianhydride and 4,4‐oxydianiline. 1,4‐Cyclohexanedicarboxylic acid (1,4‐CHDA) was added as a coupling agent. The PI/silica hybrid films were characterized by Fourier transform infrared spectroscopy, field emission scanning electron microscopy, differential scanning calorimetry and wide‐angle X‐ray diffraction. The thermal, tensile and dielectric properties of the hybrid films were measured. The results showed that the tensile and dielectric properties of the hybrid films improved with increasing silica concentration and 1,4‐CHDA content in the PI matrix. Covalent ester bonds were formed between SiOH groups of silica and carboxyl groups of 1,4‐CHDA. As a result, the silica particle size was reduced and dispersed homogeneously in the PI matrix, leading to increased tensile strength and tensile modulus of the typical hybrid film with 1,4‐CHDA (PI‐2), when compared with the PI/silica hybrid film without 1,4‐CHDA at the same silica contents. The presence of an alicyclic moiety containing silica in PI reduced the dielectric constant considerably to 2.83, which was lower than that of pristine PI. Copyright © 2016 John Wiley & Sons, Ltd.

We aimed at enhancing interaction in the polyimide/sepiolite hybrid films with the loading of sepiolite in the polyimide matrix ranged from 0 to 8 wt% via acid activating and polydopamine doping. First, sepiolite was treated with a 3M HCl solution under reflux conditions. Then the acid-activated sepiolite was coated by mussel-inspired polydopamine under alkaline conditions.The coated polydopamine was found to successfully enhance dispersibility of sepiolite in the polyimide matrix. The modification of the sepiolite in the hybrid films was investigated by Fourier transform infrared spectroscopy, wide-angle X-ray diffraction, field emission scanning electron microscopy, thermogravimetric analysis, and transmission electron microscope. The results indicated that polydopamine coating could increase interaction between the polyimide matrix and sepiolite. KEYWORDS acid activation, polydopamine, polymer/clay nanocomposite, pyromellitic dianhydride-4,4′oxydianiline polyimide, sepiolite