A series of highly active ethylene polymerization catalysts based on bidendate α‐diimine ligands coordinated to nickel are reported. The ligands are prepared via the condensation of bulky ortho‐substituted anilines bearing remote push–pull substituents with acenaphthenequinone, and the precatalysts are prepared via coordination of these ligands to (DME)NiBr2 (DME = 1,2‐dimethoxyethane) to form complexes having general formula [ZN = C(An)‐C(An) = NZ]NiBr2 [Z = (4‐NH2‐3,5‐C6H2R2)2CH(4‐C6H4Y); An, acenaphthene quinone; R, Me, Et, iPr; Y = H, NO2, OCH3]. When activated with methylaluminoxane (MAO) or common alkyl aluminiums such as ethyl aluminium sesquichloride (EAS) all catalysts polymerize ethylene with activities exceeding 107 g‐PE/ mol‐Ni h atm at 30 °C and atmospheric pressure. Among the cocatalysts used EAS records the best activity. Effects of remote substituents on ethylene polymerization activity are also investigated. The change in potential of metal center induced by remote substituents, as evidenced by cyclic voltammetric measurements, influences the polymerization activity. UV–visible spectroscopic data have specified the important role of cocatalyst in the stabilization of nickel‐based active species. A tentative interpretation based on the formation of active and dormant species has been discussed. The resulting polyethylene was characterized by high molecular weight and relatively broad molecular weight distribution, and their microstructure varied with the structure of catalyst and cocatalyst. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1066–1082, 2008

A series of (imido)vanadium(V) dichloride complexes containing 1,3-imidazolin-2-iminato or 1,3-imidazolidin-2-iminato ligands of the type, V(NR')Cl2(L) [R' = 2,6-Me2C6H3, L = 1,3-R2(CHN)2C═N (1a-c,e) or 1,3-R2(CH2N)2C═N (2a-d), R = (t)Bu (a), 2,6-Me2C6H3 (b), 2,6-(i)Pr2C6H3 (c), C6H5 (d), 2,6-(Ph2CH)2-4-MeC6H2 (e); L = 1,3-(2,6-(i)Pr2C6H3)2(CHN)2C═N, R' = 1-adamantyl (Ad, 3c), C6H5 (4c); L = 1,3-(2,6-(i)Pr2C6H3)2(CH2N)2C═N, R' = Ad (5c)], were prepared and characterized. The molecular structures of 1a, 2a,c,d, 3c, 4c, and 5c were determined by X-ray crystallography. All complexes showed high catalytic activity for ethylene polymerization especially in the presence of Et2AlCl cocatalyst; the 2,6-R2C6H3 analogues (R = Me, (i)Pr; 1b,c, 2b,c) exhibited higher catalytic activities than the (t)Bu analogues (1a, 2a), which display rather unique (small) V-N-C(imido) bond angles in the solid state. A good correlation between the activity and the (51)V NMR chemical shift was found for the (arylimido)vanadium precatalysts (1a-c,e, 2a-d, and 4c). These complexes showed high catalytic activity for the copolymerization of ethylene with norbornene (NBE), affording ultrahigh molecular weight copolymers with uniform molecular weight distributions. The activities were affected by the imido ligand as well as by the substituents in the anionic ligand, and the 2,6-(i)Pr2C6H3 analogues (especially 2c and 4c) showed the higher activities. The complexes 2c and 4c also showed high activities with efficient comonomer incorporation for the ethylene copolymerization with 5-ethylidene-2-norbornene (ENB) in the presence of Et2AlCl; both the comonomer incorporation and the molecular weight in the resulting polymers were affected by the comonomer employed (NBE vs ENB).

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We report the preparation, characterization, and properties of polyaniline (PANI)/ phenothiazine (PTZ) blend with different concentration of titanium dioxide (TiO 2 ) nanoparticles. Formation of nanocomposites was monitored by Fourier transform infrared spectra, UV, X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), differential scanning calorimetry (DSC), and thermogravimetric analysis studies. Spectroscopic characterization confirmed the bonding structure of PANI/PTZ/TiO 2 composite through the shift in absorption peaks of nanocomposites compared to pure PANI/PTZ blend. XRD studies confirmed the presence of sharp crystalline peaks of TiO 2 in the blend system signifying good interaction among the adjoining molecular chain of polymer with the nanoparticles. Surface morphological details of the nanocomposites obtained using SEM and HR-TEM reveal the formation of hemispherical-like structures with a diameter of 15 to 30 nm. DSC measurements of these nanocomposites showed that the glass transition temperature was reduced as the concentration of TiO 2 increased into PANI/PTZ blend matrix. The influence of filler loading on thermal stability showed that the TiO 2 enhanced the thermal stability and reduced the rate of thermal degradation of polymer blend nanocomposites. Conductivity studies showed that both AC and DC conductivity, dielectric constant, and dielectric loss increase with an increase in the concentration of nano-filler TiO 2 up to 10 wt%. Similarly, the ammonia gas sensing behavior of nanocomposites was also improved by the addition of nanoparticles. From the characterization studies, it can be suggested that TiO 2 helps to achieve excellent thermophysical properties, gas sensing, electrical conductivity, and dielectric characteristics for PANI/ PTZ blend which can be used in the fabrication of electrical or nano-electronic devices.

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A series of (imido)vanadium(V) alkylidene complexes containing an imidazolidin-2-iminato ligand of the type V(CHSiMe3)(NR)(X)(PMe3) (R = 2,6-Me2C6H3 (Ar, 3a), 1-adamantyl (Ad, 3b), C6H5 (3c); X = 1,3-Ar′2(CH2N)2CN; Ar′ = 2,6- i Pr2C6H3) have been prepared in n-hexane in the presence of PMe3 from the corresponding dialkyl complexes V(NR)(CH2SiMe3)2(X) (2a–c). These alkylidene complexes (3a–c) exhibit catalytic activities for ring-opening metathesis polymerization (ROMP) of norbornene: the phenylimido analogue (3c) exhibits remarkable activity at 80 °C (e.g. a TOF value of 84800 h–1 (7070 turnovers after 5 min)), affording high-molecular-weight polymers with uniform molecular weight distributions. The reaction of the (arylimido)vanadium(V) dialkyl complex 2a with C6H6 afforded the phenyl complex V(NAr)(CH2SiMe3)(C6H5)(X) (4a) by 1,2-C–H activation via an alkylidene intermediate and the diphenyl complex V(NAr)(C6H5)2(X) as the final product. The activity by 3a–c for ROMP, the reactivity of 2a–c for formation of these alkylidenes by α-hydrogen elimination, and the reactivity of 2a–c toward benzene were highly affected by the nature of the imido ligand.