Toheed Akhter

Enhancing the dielectric properties of highly compatible new polyimide/γ-ray irradiated MWCNT nanocomposites

Novel polyimide/γ-ray irradiated MWCNT (PI/γ-MWCNT) nanocomposites with improved dielectric properties were fabricated by casting and curing processes. The interfacial interactions between the two domains, i.e. PI and MWCNTs, were enhanced by hydrogen bonding between the hydroxyl groups present on PI and modified CNTs. A PI matrix having pendant phenolic hydroxyl groups was derived from pyromellitic dianhydride (PMDA) and diamine monomer 4,4′-diamino-4′′-hydroxytriphenylmethane. MWCNTs (5–20 wt%) were dispersed in the synthesized PI matrix. Before addition to PI, the surface of MWCNTs was equipped with hydroxyl and carboxylic groups by irradiating with γ-rays under a dry oxygen environment. Surface examination of PI/γ-MWCNTs composite films by scanning electron microscopy (SEM) revealed that MWCNTs are uniformly dispersed and completely wrapped by the PI matrix, most likely due to the hydrogen bonding. The influence of greater adhesion of MWCNTs with PI matrix on the dielectric, visco-elastic, and mechanical properties of final PI/γ-MWCNTs nanocomposites was explored using appropriate analytical techniques. The composite films exhibited high dielectric constant, a 7.6 fold improvement as compared to pristine PI. The storage modulus (E′) and glass transition temperature (Tg) demonstrated an improvement of 1.4 and 1.2 fold, respectively. Similarly, mechanical and thermal properties were also found to be improved remarkably. We believe that significant property enhancement of PI/γ-MWCNTs nanocomposites is the direct consequence of increased interface compatibility via hydrogen bonding between the polymer matrix and the carbon nano-filler.

Synthesis and characterization of novel coatable polyimide-silica nanocomposites

We report synthesis of a novel diamine 1,2-bis(4-(Hydrazonomethyl)phenoxy)ethane (bis- HPE) and a derived novel polyimide. The diamine was reacted with PMDA and ODA to synthesize copolyimide. Unmodified and modified silica particles were dispersed in the polyimide to prepare polyimide-silica hybrids: (a) unmodified (PSH-UM), and (b) modified (PSH-M). The PSH-UM were prepared by generating silica particles in situ in PI. In PSH-M, structural group identical to PI, 2,6- bis(3-(triethoxysilyl)propyl)pyrrolo[3,4-f]isoindole-1,3,5,7(2H,6H)-tetraone was introduced into silica nano-particles. The structural similarity enhanced compatibility between organic–inorganic components by like-like chemical interactions as both contain flexible alkyl groups. PSH-M have shown improved surface smoothness, hydrophobicity and thermal stability. Such properties are mandatory for stable coatings. The structure of silica and PI was affirmed by FTIR, EDX, and solid-state 29Si NMR spectroscopy. Morphological and thermal properties of the prepared PI-SiO2 nano-composites were investigated by field emission scanning electron microscopy, atomic force microscopy, contact angle measurement and thermogravimetric analysis.

Development of novel coatable compatibilized polyimide-modified silica nanocomposites

A series of novel coatable polyimide silica (PI-SiO2) nanocomposites have been synthesized. A new PI matrix, containing pendant hydroxyl groups, was prepared reacting diamine monomers (4,4’-diamino-4”-hydroxytriphenylmethane, and 4,4’-oxydianiline) and pyromellitic dianhydride (PMDA). Whereas, silica reinforcement was generated using TEOS. A coupling oligomeric species 2,6-bis(3-(triethoxysilyl)propyl)pyrrolo[3,4-f]isoindole-1,3,5,7(2H,6H)-tetraone (APA) was used to furnish silica nanoparticles with imide linkages and hydroxyl groups. As these groups are already present in PI matrix, so their presence in nanoparticles brought structural similarity, and hence enhanced phase connectivity among two phases. The resulting PI-SiO2 hybrids, with improved interfacial interactions through hydrogen bonding and like-like chemical interactions, displayed much enhanced morphological, thermomechanical, and thermal properties. The properties of resulting hybrids were studied by various advanced techniques and compared with PI-SiO2 hybrid system which was prepared from same polyimide and unmodified silica network.

Synthesis and characterization of blue light emitting redox-active polyimides bearing a noncoplanar fused carbazole–triphenylamine unit

A series of novel redox-active polyimides bearing unsymmetrical and noncoplanar carbazole units have been synthesized as future hole transporting materials. These polyimides were derived from a novel diamine monomer N1-(4-aminophenyl)-N1-(9-ethyl-9H-carbazol-3-yl)benzene-1,4-diamine, which was, in turn, synthesized by N-arylation of 9-ethyl-9H-carbazole-3-amine with 4-fluoro-1-nitrobenzene. The structures of the prepared monomer and polyimides were thoroughly characterized using CHNS, FTIR, and NMR spectroscopic techniques. Similarly, their thermal, optical, fluorescence, and electrochemical properties were measured using DSC, TGA, UV-Vis spectroscopy, photoluminescence spectroscopy, TCSPC and cyclic voltammetry, which revealed that the synthesized polyimides exhibit high lying HOMO levels, blue light emission, and stable electrochemical properties. Thus, these properties make our synthesized polyimides potential candidates for hole transporting materials in organic light emitting diodes (OLEDs).

4-(4-Nitro-phenoxy)biphen-yl.

The two phenyl rings of the biphenyl unit of the title compound, C18H13NO3, are almost coplanar [dihedral angle 6.70 (9)°]. The nitrophenyl ring, on the other hand, is significantly twisted out of the plane of the these two rings, making dihedral angles of 68.83 (4)° with the middle ring and 62.86 (4)° with the end ring. The nitro group is twisted by 12.1 (2)° out of the plane of the phenyl ring to which it is attached.

An investigation of physico-chemical properties of a new polyimide–silica composites

In the present study, a novel diamine 1,4-bis[4-(hydrazonomethyl)phenoxy]butane (4-BHPB) has been successfully synthesized by a facile method. 4-BHPB was reacted with pyromellitic dianhydride (PMDA) to derive a novel polyimide (PI). Highly compatibilized PI–SiO2 nanocomposites were tailored using synthesized PI matrix and modified silica nanoparticles. The compatibility between organic–inorganic (O–I) components was remarkably improved by charge transfer complex (CTC) formed between PI chains and modified silica nanoparticles. PI chains have electron donor and acceptor groups (diamine and dianhydride portion, respectively). These groups were generated in silica nanoparticles by the organic modification through 2,6-bis(3-(triethoxysilyl)propyl)pyrrolo[3,4-f]isoindole-1,3,5,7(2H,6H)-tetraone (M-SiO2), which in turn, was prepared reacting PMDA with 3-aminopropyltriethoxysilane. Sol–gel method was used for in situ synthesis of silica nanoparticles from a mixture of M-SiO2 and TEOS. The enhanced compatibility between O–I phases through CTC formation furnished PI–SiO2 nanocomposites (designated as OI-M) with improved thermal stability, hydrophobicity, and surface smoothness. For the comparison of properties, another series of PI–SiO2 composites (OI-UM) were prepared dispersing unmodified silica micro-particles into PI matrix. OI-UM hybrid system does not contain CTC between PI matrix and silica particles. The structure of the monomer, PI, and organically modified silica network was analyzed by FTIR, and NMR spectroscopy. Thermogravimetric analysis, FE-SEM, contact angle measurement, and AFM were used to study thermal and morphological properties of the synthesized PI–SiO2 hybrids.

4-Pheneth-oxy-aniline hemihydrate.

The crystal structure of the title compound, C14H15NO·0.5H2O, features N—H⋯O and O—H⋯N hydrogen bonds between the amino group and water molecule of crystallization, which generate a chain along the c axis. The water molecule lies on a twofold rotation axis. A C—H⋯π interaction is observed between the phenyl and aniline rings. The angle between the mean planes of the phenyl rings is 72.51 (7)°.

4-Nitro­phenyl 2-chloro­benzoate

The aromatic rings in the title compound, C13H8ClNO4, enclose a dihedral angle of 39.53 (3)°. The nitro group is almost coplanar with the ring to which it is attached [dihedral angle = 4.31 (1)°]. In the crystal, molecules are connected by C—H⋯O hydrogen bonds into chains running along [001].

1,10-Bis(4-nitro­phen­oxy)deca­ne

The title compound, C22H28N2O6, crystallizes with four half-molecules in the asymmetric unit: each molecule is located about a crystallographic inversion centre. The central methylene groups of two molecules are disordered over two sets of equally occupied sites. The crystal packing is characterized by sheets of molecules parallel to (14).