1,721,001 research outputs found
Kinetic investigation of syndiospecific styrene polymerization promoted by half titanocenes and novel complexes as models for the structural elucidation of the acticve species
No full textPolymerization of some hydrocarbon monomers in the presence of transition organometallic catalysts
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Simple trends in NMR spectra of vinyl polymers: the 1H NMR spectrum of poly(propylene)
No full textThe tacticity spreading of chemical shifts in the
proton NMR spectrum of poly(propylene) in solution has
been analyzed first qualitatively, taking advantage of known
trends in both proton chemical shift and conformational statistics
of vinyl polymers as summarized in the telephone rule,
and then quantitatively using ab initio computations, empirical
additivity schemes of proton chemical shifts, and conformational
averages according to models of different rotational
isomeric states. The very good results obtained, both qualitatively
and quantitatively, stem from the relatively easy
parametrization of proton chemical shift and establish a
successful application of the telephone rule, also for proton
NMR spectra
Single insertion of propene into a cationic zirconium(IV) complex: Isolation and X-ray crystal structure of [(C5Me5)Zr(CH2CHMeCH 2Ph)(CH2Ph)]-[B(CH2Ph)(C6F5)3]
No full textCopolymerization of Styrene and Isoprene - An Insight Into the Mechanism of Syndiospecific Styrene Polyinsertion
No full textSintesi e caratterizzazione di composti modello per lo studio di sequenze regioirregolari PEP in copolimeri etilene-propilene,
Full text linkSingle Insertion of Alpha-olefins Into the Cationic Complex [zr(ch2ph)3]+ Affording Isolable [zr(ch2ph)2(ch2chrch2ph)]+ Adducts - A Model For the Insertion Mechanism In Ziegler-natta Polymerization
No full textThe zwitterionic complex [Zr(CH2Ph)3{(eta6-PhCH2)B(C6F5)3}] (1) reacts smoothly at 25-degrees-C with propene and higher alpha-olefins, such as 4-methyl-1-pentene, 1-vinylcyclohexane, and allylbenzene, affording the single-insertion adducts [Zr(CH2Ph)2(CH2CHRCH2Ph)]+[B(CH2-Ph)(C6F5)3]- (R = Me, 2; R = CH2CHMe2, 4; R = C6H11, 5; R = CH2Ph, 6). Isolation and characterization of 2, 4, and 6 by NMR analysis reveal that the Zr cation is stabilized toward either further monomer insertion or beta-hydrogen elimination by back-biting eta(n)-coordination of the delta-Ph ring and by eta2-coordination of the two benzyl ligands. An analogous, less stable adduct deriving from single insertion of ethene (R = H, 3) has been detected at low temperatures by NMR. Thermolysis of 2 at 50-degrees-C, as well as addition of Lewis bases such as tetrahydrofuran, results in decomposition via beta-hydrogen elimination with formation of CH2=CMeCH2Ph. At 50-degrees-C, 2 reacts with an excess of propene affording a mixture of atactic and isotactic polypropylene, probably after beta-hydrogen elimination has occurred. In contrast, reaction of 2 with ethene proceeds already at 25-degrees-C, affording polyethylene, possibly through further insertion in 2. Compounds 2-6 are the first examples of adducts deriving from the insertion of olefins into the M-C bond of a group 4 metal complex which is an active Ziegler-Natta catalyst
Isolation of A Single-insertion Intermediate In the Catalytic Polymerization of Propene By A Cationic Tris(hydrocarbyl) Zirconium Complex
No full textPropene reacts smoothly with the alkene polymerization catalyst [Zr(CH2Ph)3{(eta6-PhCH2)B(C6F5)3)] 1 to give initially the single-insertion adduct [Zr(eta(n)-CH2Ph)2(CH2CHMeCH2Ph)]+[B(CH2Ph)(C6F5)3]- 2, which has been isolated and characterized
Syndiotactic-specific polymerization of propene with a Ni-based catalyst
No full textPolymerization of propene at -78 degrees C in the presence of a homogeneous catalytic system based on a Ni(II) diimine derivative and methylaluminoxane affords prevailingly syndiotactic crystalline poly(propylene) (rr triad content approximate to 80%). C-13 NMR analysis of the polymer microstructure indicates that the stereochemistry of the monomer insertion is controlled by the configuration of the methine carbon of the growing chain end (unlike-1,3 asymmetric induction). This is the first example of stereospecific homopolymerization of propene promoted by a late transition metal catalyst
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