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Linear Polyethylene (linear + polyethylene)
Selected AbstractsO -Acylated 2-Phosphanylphenol Derivatives , Useful Ligands in the Nickel-Catalyzed Polymerization of EthyleneEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 9 2009Dmitry G. Yakhvarov Abstract The title ligands were prepared by O -acylation of 2-diphenylphosphanyl-4-methylphenol (1) or directly by double lithiation of 2-bromo-4-methylphenol and stepwise coupling with ClPPh2 and ClP(O)Ph2 or RC(O)Cl (R = Me, tBu, Ph, 4-MeOC6H4) to afford diphenylphosphinate 2 and carboxylic esters 3a,d. X-ray crystal structure analyses of 3b,d show conformations in which the P -phenyl substituents are rotated away from the ester group and the C(O)O , planes are nearly perpendicular to the phenol ring , plane. O -Acylated phosphanylphenols 2 and 3a,d form highly active catalysts with Ni(1,5-cod)2 (as does 1) for polymerization of ethylene, whereas phosphanylphenyl ethers do not give catalysts under the same conditions. The reason is the cleavage of the O -acyl bond upon heating with nickel(0) precursor compounds in the presence of ethylene. The precursors are P-coordinated Ni0 complexes, which are formed at room temperature, such as 4d obtained from 3d and Ni(cod)2 (in a 2:1 molar ratio), and characterized by multinuclear NMR spectroscopy. Upon heating in the presence of ethylene, the precatalysts are activated. Catalysts 2Ni and 3a,dNi convert ethylene nearly quantitatively, 2Ni slowly, and 3a,dNi rapidly, into linear polyethylene with vinyl and methyl end groups, and in the latter case, C(O)R end groups are also detectable. This proves insertion of Ni0 into the O,C(O)R bond of 3a,d ligands for formation of the primary catalyst. Termination of the first chain growing cycle by ,-hydride elimination changes the mechanism to the phosphanylphenolate,NiH initiated polymerization providing the main body of the polymer. A small retardation in the ethylene consumption rate with 3a,dNi catalysts relative to that observed for 1Ni and stabilization of the catalyst, which gives rise to reproducibly high ethylene conversion, is observed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Anomalous rheological response for binary blends of linear polyethylene and long-chain branched polyethyleneADVANCES IN POLYMER TECHNOLOGY, Issue 3 2007Naoya Mieda Abstract The rheological properties are studied for binary blends composed of a low-density polyethylene (LDPE) and a linear polyethylene. It is found that some blends exhibit higher oscillatory shear moduli and drawdown force than the individual pure components, demonstrating that relaxation mechanism with longer characteristic time appears in the blend. The anomalous rheological behavior is detected more clearly for the blends with autoclave-LDPE than those with tubular-LDPE. Furthermore, the number of short-chain branches in a linear polyethylene has no influence on the rheological properties of the blends, suggesting that the phase separation will not be responsible for the anomalous behavior. It is also found that blends of autoclave-LDPE and tubular-LDPE show no synergetic effect. © 2008 Wiley Periodicals, Inc. Adv Polym Techn 26:173,181, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/adv.20100 [source] Synthesis of a linear polyethylene macromonomer and preparation of polystyrene- graft -polyethylene copolymers via grafting-through atom transfer radical polymerization,JOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2007Hiromu Kaneyoshi Abstract A vinyl-terminated linear polyethylene (number-average molecular weight = 1800, weight-average molecular weight/number-average molecular weight = 1.7, functionality = 92%) prepared by ethylene coordination polymerization was transformed into a monohydroxy-terminated linear polyethylene by hydroalumination of the vinyl group with diisobutylaluminum hydride and subsequent oxidation and hydrolysis. This monohydroxy-terminated linear polyethylene was quantitatively converted into a linear polyethylene macromonomer with a terminal ,-methacrylate group through esterification followed by dehydrobromination. A grafting-through atom transfer radical polymerization of the ,-methacrylate-terminated polyethylene and styrene was performed to yield a well-defined polystyrene- graft -polyethylene copolymer. The number-average molecular weight of the graft copolymers, measured by gel permeation chromatography, was lower than the predetermined number-average molecular weight, presumably because of the intramolecular aggregation of polyethylene side chains. The ,-methacrylate-terminated polyethylene content and number-average molecular weight of polystyrene- graft -polyethylene were determined by 1H-NMR. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 105: 3,13, 2007 [source] Synthesis and reactivity of allyl nickel(II) N -heterocyclic carbene enolate complexesJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 16 2007Stefan Benson Abstract Two new N -heterocyclic carbene enolate nickel(II) allyl complexes have been prepared and their activity towards ethylene polymerization was investigated. It was found that in the presence of diethyl zinc, the carbene enolate complex bearing a nitro substituent produces highly linear polyethylene of modest molecular weight and high polydispersity. The influence of the reaction parameters on catalytic activity and the characteristics of the resulting polymer were investigated through systematic variation of the time, temperature, and diethyl zinc concentration. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45:3637,3647, 2007 [source] Bis(salicylaldiminate)copper(II)/methylaluminoxane catalysts for homo- and copolymerizations of ethylene and methyl methacrylateJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 6 2007Anna Maria Raspolli Galletti Abstract Bis(salicylaldiminate)copper(II) complexes, when activated with methylaluminoxane, catalyzed the homo- and copolymerizations of ethylene and methyl methacrylate (MMA). The activity in the MMA homopolymerization was influenced by the electronic and steric characteristics of the Cu(II) precursors as well as the cocatalyst concentration. The same systems revealed modest activity also in the homopolymerization of ethylene, giving a highly linear polyethylene, and in its copolymerization with MMA. These copolymers exhibited a very high content of polar groups (MMA units > 70 mol %) and were characterized by a high molecular weight and polydispersity. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1134,1142, 2007 [source] Grafting of maleic anhydride onto linear polyethylene: A Monte Carlo studyJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 22 2004Yutian Zhu Abstract Monte Carlo simulation was used to study the graft of maleic anhydride (MAH) onto linear polyethylene (PE-g-MAH) initiated by dicumyl peroxide (DCP). Simulation results revealed that major MAH monomers attached onto PE chains as branched graft at higher MAH content. However, at extremely low MAH content, the fraction of bridged graft was very close to that of branched graft. This conclusion was somewhat different from the conventional viewpoint, namely, the fraction of bridged graft was always much lower than that of branched graft under any condition. Moreover, the results indicated that the grafting degree increased almost linearly to MAH and DCP concentrations. On the other hand, it was found that the amount of grafted MAH dropped sharply with increasing the length of grafted MAH, indicating that MAH monomers were mainly attached onto the PE chain as single MAH groups or very short oligomers. With respect to the crosslink of PE, the results showed that the fraction of PE-(MAH)n -PE crosslink structure increased continuously, and hence the fraction of PE-PE crosslink decreased with increasing MAH concentration. Finally, quantitative relationship among number average molecular weight of the PE, MAH, and DCP contents was given. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5714,5724, 2004 [source] | |||||||||||||