13C NMR determination of the microstructure of polypropylene obtained with the DADNi(NCS)2/methylaluminoxane catalyst system (original) (raw)
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Propylene polymerization with nickel-diimine complexes containing pseudohalides
Journal of Polymer Science Part A: Polymer Chemistry, 2006
DADNiX 2 nickel-diimine complexes [DAD ¼ 2,6-iPr 2 À ÀC 6 H 3 À ÀN¼ ¼C(Me)À À C(Me)¼ ¼NÀ À2,6-iPr 2 À ÀC 6 H 3 ] containing nonchelating pseudohalide ligands [X ¼ isothiocyanate (NCS) for complex 1 and isoselenocyanate (NCSe) for complex 2] were synthesized, and the propylene polymerization with these complexes and also with the Br ligand (X ¼ Br for complex 3) activated by methylaluminoxane (MAO) were investigated (systems 1, 2, and 3/MAO). The polypropylenes obtained with systems 1, 2, and 3 were amorphous polymers and had high molecular weights and narrow molecular weight distributions. Catalyst system 1 showed a relatively high activity even at a low Al/Ni ratio and reached the maximum activity at the molar ratio of Al/Ni ¼ 500, unlike system 3. Increases in the reaction temperature and propylene pressure favored an increase in the catalytic activity. The spectra of polypropylenes looked like those of propylene-ethylene copolymers containing syndiotactic propylene and ethylene sequences. At the same temperature and pressure, system 2 presented the highest number of propylene sequences, and system 3 presented the lowest. V V C 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 458-466, 2006
Journal of Polymer Research, 2012
Ethylene (E), propylene (P), and 1-pentene (A) terpolymers differing in monomer composition ratio were produced, using the metallocenes rac-ethylene bis(indenyl) zirconium dichloride/methylaluminoxane (rac-Et(Ind) 2 ZrCl 2 /MAO), isopropyl bis(cyclopentadienyl)fluorenyl zirconium dichloride/methylaluminoxane (Me 2 C(Cp)(Flu)ZrCl 2 /MAO, and bis(cyclopentadienyl)zirconium dichloride, supported on silica impregnated with MAO (Cp 2 ZrCl 2 /MAO/SiO 2 /MAO) as catalytic systems. The catalytic activities at 25 8C and normal pressure were compared. The best result was obtained with the first catalyst. A detailed study of 13 C NMR chemical shifts, triad sequences distributions, monomer-average sequence lengths, and reactivity ratios for the terpolymers is presented. V V C 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 947-957, 2008
Polymer, 2005
A new siloxy-substituted a-diimine compound and its corresponding Ni(II) complex, {bis[N,N 0 -(4-tert-butyl-diphenylsiloxy-2,6dimethylphenyl)imino]acenaphthene}dibromonickel (6), were successfully synthesized and the molecular structure of 6 characterized by Xray crystallography. The precatalyst 6 activated by methylaluminoxane (MAO) or diethylaluminum chloride (DEAC) was tested in the polymerization of ethylene, showed to be highly active (e.g. 2.2!10 7 and 1.8!10 7 g polymer (mol Ni.h.bar) K1 , respectively) and led to a branched polyethylene (ca. 35-55 branches/1000 C). The catalyst system 6/methylaluminoxane (MAO) catalyzes, at K11 8C, living polymerization of propylene, to a polypropylene showing a syndiotactic-rich microstructure (P r Z0.74). 1-Hexene was also successfully polymerized via a living process, both at K11 and C16 8C. The 13 C NMR spectra of the poly(1-hexene)s obtained at room temperature show a microstructure almost exclusively composed by n-butyl and methyl branches, the latter being present in a much higher number. Diblock polypropylene-block-poly(1-hexene) and triblock poly(1-hexene)-block-poly(propylene-ran-1-hexene)-block-poly(1-hexene) copolymers have also been synthesized and characterized by GPC/SEC, DSC and NMR. q
Polymer, 2004
Homopolymerization of hexene-1 with nickel(a-diimine) catalyst forms poly(hexene-1) containing different types of branches and varying number of methylene units in the backbone. Types of branches identified by NMR spectroscopy include, butyl (C 4), longer than butyl (.C 4) and methyl (isolated and meso and racemic head-to-head). Formation of ethyl (C 2) and propyl (C 3) branches were not observed. The migration of the nickel during polymerization not only causes the formation of branches other than C 4 , but also the runs of methylene units in the backbone due to complete 1,6-enchainment (chain running). The formation of regio-irregular methyl branches required an insertion of hexene-1 in the nickel-secondary carbon. Formation of methyl branches and (1, v) enchainment has also been observed during the polymerization of octene-1, decene-1, tetradecene-1 using the same catalyst system. The extent formation of these subunits in the polymer depends on polymerization temperature. A plausible explanation for the formation of different branches is discussed.
Polymer Bulletin, 2013
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2017
The study of the polymer blend composed of isotactic polypropylene (i-PP) and ethylene-propylene-diene terpolymer and of the components of this blend was made with the use of the broad line H nuclear magnetic resonance technique. Experiments were carried out within the broad temperature range of 160 – 370 K that covers the glass transition regions of all investigated polymers. Interpretation of the experimental results is based on analysis of the variation of the second moments M2 with temperature and on decomposition of the NMR spectra into elementary components related to the amorphous, intermediate and crystalline regions of partially crystalline polymers. The temperature dependences of the second moment of the spectra measured on the terpolymer and iPP show drops in the temperature ranges 200 – 250 K and 270 – 320 K, respectively, which are related to the glass transitions of the particular polymers. A double glass transition was revealed on the blend by means of the second mome...
Propylene Polymerization with α-Keto-β-Diimine Initiators Proceeds via Enantiomorphic Site Control
Macromolecules, 2012
13 C NMR spectroscopy is used to characterize the microstructure of polypropylene (PP) obtained using a nickel α-keto-β-diimine initiator activated with methylaluminoxane (MAO) at different reaction temperatures (T rxn ). The product prepared at −20°C has structural features that resemble an ethylene-propylene copolymer. We find that the main sequences present in this sample arise as a result of normal 1,2-insertion and that propylene sequences are predominantly isotactic (m = 88%, mmmm = 63%). There is also evidence of ethylene-like sequences as a result of 3,1-enchainment, and from 2,1-insertion. A reduction in T rxn to −60°C results in a polymer that has undetectable regioirregularities and is highly isotactic (m = 93%, mmmm = 85%). Moreover, the application of stereo propagation models gives indication that the isospecificity is a result of enantiomorphic site control.