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Chitosan‐functionalized graphene oxides (FGOCs) were successfully synthesized. FGOCs were found to significantly improve the solubility of the GO in aqueous acidic media. The presence of organic groups was confirmed by means of XPS and TGA. Restoration of the sp2 carbon network and exfoliation of graphene sheets were confirmed by Raman spectroscopy, UV‐visible spectroscopy and WAXD. The SEM and AFM investigations of the resultant FGOCs showed that most of the graphene sheets were individual and few were layered. Controlled release behavior of Ibuprofen and 5‐fluorouracil was then investigated. We found that FGOCs are a promising new material for biological and medical applications. magnified image

Transparent polyimides (PIs) that have a high refractive index and low birefringence as well as good thermal and mechanical stability were synthesized by the judicious introduction of di-and tetrachlorinated aromatic diamines with aromatic/aliphatic dianhydrides. All the PI films, except for the PI derived from aromatic dianhydride and dichlorinated diamine (BPDA/2DCDB and BPDA/3DCDB), exhibited high optical transparency over the entire visible region. In particular, tetrachlorinated, fully aromatic polyimide (BPDA/TCDB) with a highly distorted conformation of the main chain exhibited excellent optical transparency in the visible range that was comparable to highly fluorinated aromatic PIs. This was attributed to the effective suppression of intra-and intermolecular charge transfer (CT) interactions by steric hindrance between the five-membered imide rings and chlorine atoms attached directly to the adjacent benzene rings as well as between chlorine atoms in the diamine molecules. A high transmittance of 82% at 400 nm with an average transmittance >90% in the visible region and strong fluorescent emission were achieved in a fully aromatic PI (BPDA/TCDB). In addition, the chlorinated aromatic PIs exhibited high average refractive indices (1.702-1.732), suitable for applications as optical materials, such as microlens, and low birefringences (0.028-0.091) at 633 nm, due to the high atomic polarizability of chlorine and the bulky molecular structure of chlorinated PIs. In particular, a mean refractive index of 1.7018 was observed for BPDA/TCDB PI, which is extraordinarily high for a colorless PI.

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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.

Two new perfluorodecylthio substituted aromatic diamines, namely 2,4-diamino-1-(1H,1H,2H,2H-perfluorodecathio)benzene (DAPFB) and 2,2'-Bis((1H,1H,2H,2H-perfluorodecyl)thio)[1,1'-biphenyl]4,4'-diamine (BPFBD) were synthesized and polycondensed with 4,4 0 -(hexafluoroisopropylidene)diphthalic anhydride (6FDA) to produce two new perfluorinated polyimides (PI2 and PI4). The chemical structures of these polyimides were confirmed by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. Two other polyimides (PI1 and PI3) were also synthesized from 6FDA and analogous perfluorodecylthio unsubstituted diamines to investigate the incorporation effect of perfluorodecylthio group on various physical and chemical properties of the synthesized PIs. Compared with PI1 and PI3, PI2 and PI4 exhibited improved solubility, optical transparency, and hydrophobicity, lower moisture absorption, dielectric constant, and thermo-mechanical stabilities owing to the presence of the perfluorodecylthio side group in the polymer chain. Even though thermo-mechanical properties of PI2 and PI4 (T 5 d : 413 and 404 C, T g : 220 and 209 C, tensile strength of 101 and 76 MPa, tensile modulus of 1.7 and 1.5 GPa and elongation at break of 8 and 10%, respectively) were reduced in comparison to PI1 and PI3 but still were good enough for most of the practical applications. Most importantly, the presence of the perfluorodecylthio side group in BPFBD considerably reduced the dielectric constant of PI4 to 2.71 which was quite low as aromatic polyimide. V C 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 479-488

Cover: The cover illustrates a rolled polyimide (PI)/graphene carboxylic acid (GCA) nanocomposite film. In the image, wrinkled graphene sheets are 2D‐aligned and well‐dispersed in a PI matrix with no covalent interaction, highlighted by the blue fluorescent bonds. The PI/GCA nanocomposite film may have application as a gas barrier, an anti‐corrosion material, or a flame retardant material. Further details can be found in the article by G. Y. Kim, M.‐C. Choi, D. Lee, and C.‐S. Ha* .