Synthesis and characterization of new imidazole and fluorene–bisphenol based polyamides: Thermal,photophysical and antibacterial properties

A new para-linked diether-diamine, 9,9-bis{4-[2-(4,5-diphenylimidazol-2-yl)-4-aminophenoxy] phenyl}fluorene (III), bearing fluorene–bisphenol and two ortho-linked diaryl-substituted imidazole rings were synthesized by the catalytic reduction of the nitro groups of compound (II), 9,9-bis{4-[2-(4,5-diphenylimidazol-2-yl)-4-nitrophenoxy]phenyl}fluorene, by using hydrazine monohydrate in the presence of Pd/C. Compound (II) was synthesized by the nucleophilic chloro displacement reaction of the synthesized 2-(2-chloro-5-nitrophenyl)-4,5-diphenyl-1H-imidazole with 9,9-bis(4-hydroxyphenyl)fluorene in refluxing DMAc in the presence of potassium carbonate. This diamine was condensed directly with aliphatic and aromatic diacids via the Yamazaki–Higashi phosphorylation method in the presence of triphenylphosphite (TPP), pyridine (Py) and halide salt to give high molecular polyamides (PAs). The synthesized PAs were obtained in quantitative yields with inherent viscosities between 0.51 and 0.76 dL g^?1. The structures of diamine and PAs were characterized by elemental analysis, FT-IR and NMR spectroscopy, and properties of PAs were investigated by using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and UV–visible and fluorescence spectroscopy. The PAs showed good solubility in aprotic and polar organic solvents, with high thermal stability exhibiting the glass transition temperatures (T_gs) and 10% weight loss temperatures (T_10%) in the range of 226–330 °C and 400–466 °C in air, respectively, and fluorescence emission with maximum wavelengths (λ_em) in the range of 417–473 nm with quantum yields (Φ_f) of 9–35%. Two of these polymers together with compounds (II) and (III) were also screened for antibacterial activity against Gram positive and Gram negative bacteria.     

Synthesis,microstructure and mechanical properties of lamellar YB2C2 – based ultra-high temperature ceramic composites

A significant improvement of the mechanical performance was observed following the introduction of rare earth oxides in ZrB₂-based ultra-high temperature ceramic matrix composites (UHTCMCs), resulting in the formation of ternary boro-carbides of general formula REB₂C₂, belonging to a new class of layered compounds akin to MAX phases. These layered phases possess high melting points and could be responsible for the toughening of UHTCMCs, but their formation, properties and role were never fully investigated. In this study we focused on the potential routes for the synthesis of YB₂C₂ phases at temperatures typical of UHTC sintering, starting from Y₂O₃, carbon and four different boron sources (B, B₂O₃, BN, B₄C) and their microstructure was analysed by SEM, XRD and TEM. The mixture with B₄C led to the highest selectivity towards the formation of YB₂C₂ and was selected to fabricate a long carbon fibre reinforced YB₂C₂ ceramic composite, which was mechanically tested displaying a flexural strength of 380 MPa. Finally, the chemical stability in air of these materials was assessed.     

A predesigned 1D chain of alternating di-μ1,1-azido bridged dinuclear Ni(II) and pyrazine: Synthesis,structure and magnetic properties

A new Ni(II) complex, [Ni₂(L)₂(μ_1,1-N₃)₂(pyz)]_n (1) (where pyz = pyrazine) has been synthesized using a dinuclear di-μ_1,1-azido bridged Ni₂ molecular building block derived from a tridentate NNO donor Schiff base ligand, HL (2-[(3-methylamino-propylimino)-methyl]-phenol) along with pyrazine as spacer. Single crystal X-ray analysis shows that complex 1 is a 1D chain in which dimeric Ni₂ units [Ni₂L₂(N₃)₂] are linked to each other by the bridging pyrazine ligand. Variable-temperature magnetic susceptibility studies indicate the presence of moderate ferromagnetic exchange coupling in complex 1 with J value of 53.54 cm^− 1.     

Preparation and properties of new π-conjugated polyquinoxalines with aromatic fused rings in the side chain

Summary New π-conjugated polyquinoxalines with aromatic fused rings in their side chain have been prepared. Dehalogenative organometallic polycondensation of 5,8-dibromo[2,3-b]-acenaphthenequinoxaline and 5,8-dibromo[2,3-b]phenanthrenequinoxaline with a zerovalent nickel complex afforded poly([2,3-b]acenaphthenequinoxaline-5,8-diyl) (P(5,8-Qx(ace))) and poly([2,3-b]phenanthrenequinoxaline-5-8-diyl) (P(5,8-Qx(phen))) in high yields. P(5, 8-Qx(ace)) had an [η] value of 0.23 dL g⁻¹ and showed absorption and photoluminescence peaks at 445 and 565 nm, respectively. (P(5,8-Qx(phen))) gave absorption and photoluminescence peaks at 400 and 514 nm, respectively. XRD data indicated formation of ordered structures of the polymers in the solid. Preparation of related copolymer with thiophene is also reported. Received: 15 February 2000/Accepted: 2 March 2000     

Synthesis,microstructure, and mechanical properties of WC–TiC–Co ceramic composites

A ceramic composite constituting the formula 78 wt% WC–16 wt% TiC–6 wt% Co denoted as the 78WC–16TiC–6Co ceramic composite was fabricated using a powder metallurgy process, by utilising commercially available WC and Co powders, and laboratory produced TiC powders. TiC powders were produced from machining chips of Grade 4 Titanium. Five different procedures were followed for the manufacturing process by altering the amount of the binding agent (stearic acid) and/or compacting pressure and/or sintering regime (temperature and time) and/or mixing process (dry mixing and mechanical alloying). Characterisation investigations conducted on the sintered samples revealed that stearic acid as the binding agent resulted in the decrease of the relative density while mechanical alloying (MA) induced finer microstructures. The 78WC–16TiC–6Co composites manufactured from commercially available and laboratory produced TiC powders using similar process procedures (including MA) exhibited similar characteristics in terms of relative density, hardness, and wear performance.     

Synthesis,characterization, and photophysical properties of covalent-linked ferrocene–porphyrin–single-walled carbon nanotube triad hybrid

The ferrocene–porphyrin–single-walled carbon nanotube (Fc–H₂P–SWCNT) triad hybrid was prepared by amidation reaction between carboxylated SWCNT and aminoporphyrin bearing an appended ferrocenyl substituent. The hybrid described here was fully characterized by a combination of analytical techniques such as Fourier transform infrared spectroscopy, Raman, absorption and emission spectroscopy, atomic force and scanning electron microscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy. The steady emission characteristics revealed the existence of the effective photoinduced electron transfer among ferrocene, excited porphyrin moiety and SWCNT, which was further confirmed by the results of time-resolved transient absorption spectra. The final lifetime of charge-separation state was observed to be 62.9 μs in N,N-dimethylformamide, which was significant increased compared to the reference nanohybrid porphyrin–SWCNT and the reported ferrocene–porphyrin–fullerene triad. Therefore, Fc–H₂P–SWCNT triad hybrid constructed by amidation is rationally expected to be an improved photon-to-electron conversion system.     

Double-linked chain in POM-based hybrids. Synthesis,crystal structure and properties of an inorganic–organic compound

An inorganic–organic compound, (H₂bipy)₃[(H₂O)₂Cu₂(bpy)₃(PMo₁₁CuO₃₉)₂]·8H₂O(1) (bpy = 4,4-bipyridine), has been prepared under mild hydrothermal conditions and has been structurally characterized by single-crystal X-ray diffraction. In compound 1 the polyoxoanion PMo₁₁CuO₃₉^5 − has a pseudo-Keggin structure since the Cu(II) atom replaces one Mo(VI) atom of Keggin anion. The polyoxoanions share their terminal oxygen atoms creating an anionic chain. Two adjacent anions in the chain coordinate to same one Cu ion forming a double-linked anionic chain, and then a railway-like chain is constructed by linkage of the bipy molecules to Cu atoms in which the double-linked anionic chains act as two rails of the railway and bipy molecules act as “crosstie”. The 3D supramolecular structure is formed from the railway-like chains through hydrogen bonds and strong π…π stacking interactions. The fluorescent emission of compound 1 from 4,4′-bipyridine ligand was detected and the photocatalysis property for degradation of methylene blue (MB) of compound 1 upon a UV irradiation was examined.     

Synthesis and photovoltaic properties of alternative copolymers of benzo[1,2-b:4,5-b′]dithiophene and thiophene

Two conjugated polymers containing benzodithiophene (BDT) unit and the unit of thiophene or thieno[3,2-b]thiophene, P(BDT-T) and P(BDT-TT), were synthesized by Pd-catalyzed Stille coupling method. The UV–Vis absorption, thermal, and electrochemical properties of the two polymers were characterized. Photovoltaic properties of the polymers were studied by using the polymers as donor and PC₇₀BM as acceptor with a weight ratio of polymer: PC₇₀BM of 1:1.5. The power conversion efficiencies of the PSC devices based on P(BDT-T) reached 2.05% with an open-circuit voltage of 0.75 V, a short-circuit current of 4.5 mA cm⁻², and a fill factor of 0.61, under the illumination of AM1.5, 100 mW cm⁻².     

Synthesis and characterization of β-TCP/CNT nanocomposite: Morphology,microstructure and in vitro bioactivity

In this study, β-TCP/CNT nanocomposite has been synthesized by solution precipitation method. Then, the effects of the different percentage of CNT (CNT1β-TCP, CNT3β-TCP, CNT5β-TCP) and surfactant (CNT1β-TCP1SDBS, CNT1β-TCP2SDBS, CNT1β-TCP3SDBS) on β-TCP/CNT nanocomposite powder were studied. The X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) analyses were used to characterize the samples. The observations revealed that the microstructure of 1 wt% CNT could provide dispersion without agglomeration in nanocomposite powder; however, a higher concentration of CNT powder in the nanocomposite resulted in the formation of Ca₂PO₇ phase. Implementing 2 wt% of SDBS as a surfactant modified the shape, size, and distribution of CNT particles on nanocomposites. Finally, the nanocomposite sample was immersed in simulated body fluid (SBF) to evaluate the in vitro bioactivity. It obviously showed an apatite layer on the surface after 7 days of immersion in SBF. Taken together, this nanocomposite might be potentially to be used as bone repair biomaterial.     

Blends of ethylene–octene copolymers with different chain architectures – Morphology,thermal and mechanical behavior

Blends of two elastomeric ethylene–octene copolymers with similar octene contents having a random (ORC) and a blocky architecture (OBC) are prepared by melt mixing. The thermal and mechanical properties of ORC, OBC and their blends are investigated by DSC, dynamic mechanical analysis and tensile tests. The morphology of the semi-crystalline samples is studied by AFM and WAXS. Two types of crystals have been observed: (i) Orthorhombic crystals forming lamellae with an estimated thickness of about 13 nm composed mainly of long polyethylene-like sequences of OBC that melt a temperature of about 120 °C and (ii) fringed micellar crystals with a thickness of 2–4 nm formed basically by short polyethylene-like sequences of ORC that have melting temperatures between 30 and 80 °C. The amorphous phase contains a relatively homogeneous mixture of segments of both components indicated by the relatively uniform shape of the loss modulus peaks from dymamic-mechanical measurements for all investigated copolymers and blends. ORC crystallization is hindered in blends as indicated by lower melting enthalpies. This might be related to the high octene content of the amorphous phase at the relevant crystallization temperature as well as geometrical constraints since ORC crystallization occurs in an already semi-crystalline polymer. The results of tensile tests show that the mechanical behavior can be tailored via blend composition and morphology of the semi-crystalline material. The findings clearly indicate that blending is a powerful strategy to optimize the properties of polyolefin-based copolymers.     

Nonoxide–boron nitride composites: in situ synthesis,microstructure and properties

Hexagonal graphitic boron nitride (h-BN) composites show excellent corrosion and thermal shock resistance, good mechanical tolerance and machinability, especially Si₃N₄–BN and Sialon–BN composites; they have already been used as break rings for horizontal continuous casting of steel. However, the strength of the conventionally processed BN composites were remarkably degraded by the addition of BN due to the poor densification behavior and the existence of large BN flakes or agglomerates of BN flakes that acted as fracture flaws. This means that BN dispersoids with fine particle size and homogeneous distribution are the key factors to obtain high strength composites. By in situ process, such microstructural features can be realized. In this work, by using the proposed in situ reactions, synthesis, microstructures and properties of various in situ nonoxide-boron nitride (Nobn) composites including SiC–BN, Si₃N₄–BN, AlN–BN, Sialon–BN and Alon–BN composites were investigated. For some Nobn composite systems, due to the large volume expansion during the reaction processes, near-net shape sintering can be realized. For example, the sintering shrinkage of AlN-30 vol.% BN was 3.1% and that of Alon-21 vol.% BN was 4.2%. This will be an advantage for the fabrication of large and complicated products.     

Synthesis of novel π-conjugated boron polymers containing transition metal in the main chain and their optical properties

Summary Novel π-conjugated boron polymers containing transition metals in the main chain were prepared by hydroboration polymerization between tetrayne monomer including metal complex and tripylborane. From gel permeation chromatographic analysis (THF, PSt standards), the number-average molecular weights of the polymers obtained were found to be 9,000. The polymers were soluble in common organic solvents such as THF, chloroform and benzene. The absorption peaks due to π-π^* transition were observed around 390nm in the UV-vis spectra of these polymers. The fluorescence emission spectra exhibited intense peaks at 490nm (in chloroform, room temperature, excitation wavelength at 390nm). Received: 16 April 2001/Accepted: 27 April 2001     

Synthesis, morphology and mechanical properties of linear triblock copolymers based on poly(α-methylene-γ-butyrolactone)

A series of well-defined triblock copolymers containing middle soft poly(n-butyl acrylate) (PBA) block and outer hard blocks of poly(α-methylene-γ-butyrolactone) homopolymer (PMBL) or random poly (α-methylene-γ-butyrolactone)-r-poly(methyl methacrylate) copolymer (PMBL-r-PMMA) were synthesized by atom transfer radical polymerization (ATRP). Phase separated morphologies of cylindrical or spherical hard block domains arranged in the soft PBA matrix were observed by atomic force microscopy and small-angle X-ray scattering. The mechanical and thermal properties of the copolymers were thoroughly characterized and their thermoplastic elastomer behavior was studied. Dynamic mechanical analysis (DMA) showed for all PMBL-b-PBA-b-PMBL copolymers a very broad rubbery plateau range extending up to temperatures of 300 °C. Replacement of the PMBL hard block with the less brittle PMBL-r-PMMA resulted in an improvement of the tensile properties, without compromising the very good thermal stability of the materials.     

Sol-gel–mediated synthesis of TiO2 nanocrystals: Structural,optical, and electrochemical properties

Nanoparticles of titanium dioxide were prepared using the sol-gel method without any impurity. Rietveld refinement of XRD data confirmed the anatase phase of synthesized nanoparticles with space group I4_1/amd (141). XRD pattern revealed the crystalline nature of synthesized nanopowder. The average crystallite size of synthesized nanoparticles was calculated 7.5 nm. The electrochemical performance of synthesized TiO₂ nanopowder was investigated as working electrode. The electrochemical reaction was found diffusion-controlled as observed from cyclic voltammetry (CV) studies at different scan rates. The diffusion-controlled charge storage mechanism also confirmed by charge transfer resistance and Warburg impedance, as calculated from the EIS analysis. SEM micrograph showed the plate-like structure grown in cluster cloud of particles of synthesized TiO₂ nanocrystals. Absorbance and optical bandgap were obtained using UV-Vis spectra. De-convoluted PL spectra provided the emission pattern from the ultra-violet region to green region due to the presence of interstitial oxygen vacancies. The tune bandgap with EIS measurements of synthesized TiO₂ nanoparticles offers its potential application in energy storage devices and photovoltaic applications.     

Novel 5-benzazolyl-10,15,20-triphenylporphyrins and β,meso-benzoxazolyl-bridged porphyrin dyads: Synthesis, characterization and photophysical properties

Novel 5-benzazolyl-10,15,20-triphenylporphyrins and β,meso-benzoxazole-linked diporphyrins were synthesized through La(OTf)₃ catalyzed reaction of newly prepared 5-(3,4-diaminophenyl)-10,15,20-triphenylporphyrin or 5-(3-amino-4-hydroxyphenyl)-10,15,20-triphenylporphyrin with aromatic aldehydes in 1,2-dichlorobenzene. On metalation with zinc acetate, freebase β,meso-benzoxazole-linked diporphyrin was successfully converted to the Zn-Zn diporphyrin complex in good yield. The synthesized porphyrin analogues were characterized using electronic absorption, IR and ¹H NMR spectroscopy in addition to mass and elemental analyses. The fluorescence studies of 5-benzazolyl-10,15,20-triphenylporphyrins showed efficient intramolecular energy transfer from the pyrene and fluorene subunits to the porphyrin core. In addition, the fluorescence quenching observed in β,meso-benzoxazolyl-bridged porphyrin dyads was attributed to the possible nonplanarity of a component of the diporphyrins. The freebase-Ni diporphyrin complex underwent strong emission quenching in comparison to that of freebase diporphyrin and dizinc diporphyrin analogues.     

ZnO – Yb2O3 composite optical ceramics: Synthesis,structure and spectral-luminescent properties

Zinc oxide optical ceramics containing 0–2 wt% ytterbium are prepared by uniaxial hot pressing of commercial oxides at 1150 and 1180 °C. The ceramics have the main crystalline phase of hexagonal wurtzite-type ZnO. Ytterbium ions do not enter the ZnO crystals but form a cubic sesquioxide phase of Yb₂O₃ located at the ZnO grain boundaries. Yb acts as an inhibitor for the ZnO grain growth. The ceramics exhibit transmittance up to 60 % in the visible. Their transmission in the infrared is determined by the free charge carrier absorption. The Yb³⁺ ions are found in C₂ and C_3i sites in Yb₂O₃ crystals. Under X-ray excitation, the ceramics exhibit intense luminescence bands in the blue (near-band-edge emission) and green (defect emission) whose positions, intensities and decay times depend on the Yb content. Yb₂O₃ causes a redistribution of luminescence intensity in favor of the near-band-edge emission and fastens the emission decay.     

No more ‘core-shell’ in binderjetting of bioceramics: Novel solution and experimental validation in microstructure and mechanical properties

During binderjetting of bioceramics, many commercial 3D printers dispense binder in a default ‘core-shell’ manner. Using such a conventional approach, more binder is dispensed at the periphery (shell) and less binder at the ‘core’ of the structure. The inhomogeneous binding of the powder particles from the shell to the core significantly impacts the microstructure and biomechanical properties. To address this, we hypothesised ‘segmentation’ of a 3D printable design file by slicing and discretising with an array of thin solid “segments”, separated with an infinitesimal gap in a periodic manner. In this novel approach, the printing software commands the printhead to print each of the “segments” individually. The inter-segment and intra-segment binder “bleeding” among the segments results in a printed part with a homogeneously bound cross-section, without any “core-shell” effect. This hypothesis was experimentally validated by better microstructure, improved density, and enhanced mechanical strength properties in binderjet printed 3 mol% yttria stabilised ZrO₂.     

3-D organic-inorganic hybrid architecture based on Tröger's Base: Synthesis,supramolecular structure,and aggregation-induced emission properties

An organic-inorganic hybrid solid (DMDP)[Hg(SCN)₄] (1) (DMDP = 2,8-(6H,12H-5,11-methanodibenzo[b,f]diazocineylene)-di(p-ethenyl-N-methyl-pyridinium)) was designed and synthesized. X-Ray structural analysis reveals that it comprises a 3-D interpenetrating superstructure that 1-D inorganic anionic chains {[Hg(SCN)₄]^2 −}_∞ penetrates into 2-D organic (DMDP)^2 + cationic network. Photoluminescence investigation show that compound 1 exhibits a typical aggregation-induced emission (AIE) properties.     

Synthesis and characterization of poly(ethyl vinyl ether) containing the NLO-phore 4′-oxy-4-nitrostilbene in the side chain

Summary 4-(2-Vinyloxyethoxy)-4-nitrostilbene 2 was prepared by the reaction of 4-hydroxy-4-nitrostilbene 1 with 2-iodoethyl vinyl ether. Monomer 2 was polymerized with cationic initiators to obtain a poly(ethyl vinyl ether) with the NLO-phore 4-oxy-4-nitrostilbene in the side chain. The resulting polymer 3 was soluble in common solvents such as chloroform and DMSO. The inherent viscosities of polymer 3 were in the range of 0.25–0.30 dL/g in chloroform. Polymer 3 showed a good thermal stability in TGA thermogram. Solution-cast films were cloudy and brittle with a T_g of 63°C.