A complete 13C NMR characterization of two linear low-density polyethylenes (LLDPE), one highly branched and the other lowly branched, is presented. These LLDPE were synthesized with a new catalyst:  the [η3-methallyl-nickel-dad]PF6 complex by homopolymerization of ethylene, using different experimental conditions. Methyl, ethyl, propyl, butyl, amyl, and long branches were assigned and quantified.

SUMMARY:The behaviour of catalytic systems based on zirconium compounds for the copolymenzation of ethylene with 1-hexene and 1-octene is reported. The metallocenes (CH3),SiCp2-ZrCI,, Cp2ZrC1, (Cp = q5-cyclopentadienyl), (C2H, [Ind],ZrCl2 and [Ind],ZrCl, (Ind = qxindenyl) were chosen for this study. The bridged catalysts, (CH3),SiCp2ZrC1, and C,H,[Ind],ZrCl,, and the metallocene Cp2ZrCI2 showed similar catalytic activities for homo-and copolymerization of ethylene with 1-hexene. 13C NMR analysis showed that the composition of copolymerization products depends on the catalytic system, in other words, on the ligand structure of the transition metal. Copolymers obtained using the bridged catalysts have greater incorporation of comonomer. Thermal analysis and viscosity measurements demonstrated that an increase of the comonomer concentration reduces the melting point, the crystallinity and the molecular weight of the copolymer. Results from infrared spectroscopy showed that p-elimination is one of the possible termination reactions. The monomer reactivity ratios r were determined for all catalytic systems using Fineman-Ross and "C NMR methods. The values of r, (M, = ethylene) and r2 (M, = aolefin) showed an effect of the type of metallocene and of a-olefin on the structure of the copolymer obtained.

The products obtained with the system {[(ArNC(Me))2C5H3N]FeCl2}/MAO (Ar = 2-C6H4(Et)) (1) and the ones obtained by the use of 1 in conjunction with Me2SiInd2ZrCl2/MAO (2) or EtInd2ZrCl2/MAO (3) were completely characterized by 1H NMR and 13C NMR. Catalyst 1 gives mainly linear α-olefins of molecular weights close to 2000 g/mol and a low amount of alkanes. The use of 1 with 2 or 3 using only ethylene as monomer gives branched polyethylene with ethyl, butyl, and mainly long branches. Some amount of unreacted α-olefin was also found in some cases, especially in reactions where a high ratio Fe to Zr was used.

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In this study, we investigated the thermal, dynamic mechanical, mechanical, and electrical properties of polyethylene (PE)graphene nanosheet (GNS) nanocomposites, with GNS amounts from 0 to 20 wt %, prepared by in situ polymerization. The thermal stability was evaluated by thermogravimetric analysis (TGA) and showed that the addition of GNSs to the polyolefin matrix increased the onset degradation temperature by 30 C. The electrical conductivity, measured by the impedance technique, presented a critical percolation threshold of 3.8 vol % (8.4 wt %) of GNS. A slight decrease in the tensile strength was found. On the other hand, dynamic mechanical analysis showed an increase in the storage modulus of the nanocomposites compared with that of neat PE. The glass-transition temperature value increased from À111 C (neat PE) to À106 C (PE/6.6 wt % GNS). All of these results show that PE became stiffer and thermally more stable and could be transformed from an insulator to a semiconductor material in the presence of GNSs.

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The stoichiometric reactions of 5,6,7,8-tetrahydrocycloheptapyridin-9-one (cycloheptapyridin-9-one) with various anilines lead to corresponding mixtures of 9-aryliminocycloheptapyridine and the isomeric 9-arylamino-5,6,7-trihydrocycloheptapyridine derivatives; these compounds further reacted with nickel dichloride to form 9-aryliminocycloheptapyridyl nickel chlorides, respectively. The new organic compounds were analyzed by the NMR measurements, and all the organic and complex compounds were characterized by the FT-IR spectroscopy and elemental analysis. In addition, the molecular structures of representative nickel complexes and , determined by means of single-crystal X-ray diffraction, were found to be binuclear dimers with distorted square-pyramidal geometry around the nickel centers. On activation with either ethylaluminium sesquichloride (Et3Al2Cl3) or methylaluminoxane (MAO), all nickel complex pre-catalysts exhibited high activities of up to 7.80 × 10(6) g PE mol(-1) (Ni) h(-1) toward ethylene polymerization and produced highly branched polyethylenes in narrow polydispersity. The title nickel complexes showed comparable activities with 8-arylimino-5,6,7-trihydroquinolyl nickel analogues; whilst both exhibited higher activities than did the 2-iminopyridyl nickel analogues due to the enhancement of the ring-tension of cyclic-fused pyridine derivatives.

The synthesis of low-density polyethylene from ethylene as the only monomer feed has been investigated as an alternative route to branched polyethylene and to obtain new materials with different properties, avoiding the need to feed 1-alkenes into the polymerization process. The details of the evaluation of two combination catalyst systems based on single site catalysts are discussed. The {[(2-ArNdC(Me)) 2C5H3N]FeCl2} (Ar ) 2-C6H4(Et)) compound, designated as catalyst 1, oligomerizes ethylene to produce linear R-olefins with high selectivity, and Me2SiInd2ZrCl2 (2) or EtInd2ZrCl2 (3) are used as catalysts that incorporate the R-olefins in the polymer. For catalyst 1 in the presence of methylaluminoxane (MAO) and ethylene, a wide range of R-olefin products were found, both soluble and insoluble. Also, tandem catalyst combinations 1 and 2 or 1 and 3 in the presence of ethylene alone can readily produce branched polyethylene with levels of 1-4 branches per 100 units of ethylene. A change in activity was found for variations in the Fe/Zr ratio for both systems, with lower activity but higher frequency of branching in the polymer backbone for catalyst 2. The final product obtained by the 1/3/MAO systems, however, shows a more homogeneous structure as determined by DSC and GPC.