Copolymerizations of ethylene with 1-hexene overansa-metallocene diamide complexes (original) (raw)
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Journal of Polymer Science Part A: Polymer Chemistry, 1999
Copolymerizations of ethylene with 1-hexene have been carried out by using two metallocenes: highly syndiospecific isopropylidene(1-5 -cyclopentadienyl)(1-5 -fluorenyl)-dimethylzirconium (Me 2 C(Flu)(Cp)ZrMe 2 , 1) and less syndiospecific (1fluorenyl-2-cyclopentadienylethane)-dimethylzirconium (Et(Flu)(Cp)ZrMe 2 , 2), in the presence of [Ph 3 C][B(C 6 F 5 ) 4 ] as a cocatalyst. The effect of different types of bridges on the catalytic activity and comonomer reactivity was reported. The ethano bridged 2 compound of a smaller dihedral angle showed much higher activity than the 1 compound in the ethylene homo-and copolymerizations. The catalytic activities of the two compounds were enhanced about twice when a suitable amount of 1-hexene comonomer is present in the feed. The copolymerization of ethylene with 1-hexene revealed a noticeable influence of the type of bridge on the relative reactivity of the 1-hexene. 13 C-NMR analysis of copolymers showed that compound 1 is characterized by lower r E , taken as an index of ethylene reactivity, and higher reactivity of 1-hexene. The bridge also affects the distribution of the 1-hexene along the copolymer chain, investigated through their product of reactivity ratios, r E r H . The thermal properties and the density of copolymers were not affected by the type of bridge of the metallocenes, but mainly depended on 1-hexene content in the copolymer.
Macromolecular Chemistry and Physics, 1995
The behaviour of catalytic systems based on zirconium compounds for the copolymerization of ethylene with 1-hexene and 1-octene is reported. The metallocenes (CH3)2SiCp2ZrCl2, Cp2ZrCl2 (Cp = η5-cyclopentadienyl), C2H4[Ind]2ZrCl2 and (Ind = η5-indenyl) were chosen for this study. The bridged catalysts, (CH3)2SiCp2ZrCl2 and C2H4[Ind]2ZrCl2, and the metallocene Cp2ZrCl2 showed similar catalytic activities for home- 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 β-elimination is one of the possible termination reactions. The monomer reactivity ratios r were determined for all catalytic systems using Fineman-Ross and 13C NMR methods. The values of r1 (M1 = ethylene) and r2 (M2 = α-olefin) showed an effect of the type of metallocene and of α-olefin on the structure of the copolymer obtained.
Polymer Bulletin, 1995
This study employed the~3C-NMR spectroscopy to investigate the influence of the increase of the comonomer concentration on the microstruture of ethylene/1hexene and ethylene/1-octene copolymers obtained by the use of MeSiCp2ZrC12, Cp2ZrC12,, Et[Ind]2ZrC12 and [Ind]2ZrCl2 catalysts. For both comonomers butyl or hexyl branches were isolated between ethylene blocks. As the ct-olefm concentration in the copolymer increased, butyl or hexyl branches became closer, some of them, separated by only one or two ethylene units. Incorporation of ct-olefm in the copolymer was higher for the bridged catalysts, MeSiCp2ZrCI2, and Et[Ind]2ZrC12 than for the unbridged ones. The ~-olefin size did not seem to effect its reactivity towards ethylene.
Model compounds and 13C NMR investigation of isolated ethylene units in ethylene/propene copolymers
Die Makromolekulare Chemie
The stereochemical environment of the isolated ethylene units, and the arrangement of the neighbouring propylene units, in ethylene/propene copolymers, prepared in the presence of syndiotactic‐specific and isotactic‐specific catalysts are investigated by comparing 13C NMR spectra of selectively 13C‐enriched copolymers and suitable model compounds. The implications of copolymer structure on polymerization mechanism are considered. In the presence of homogeneous syndiotactic specific catalyst systems both the regiospecificity and the stereospecificity are controlled by the last unit of the growing chain end. Regiospecificity and stereospecificity are unaffected by the ethylene units in the isotactic polymerization.
Polymer Bulletin, 2000
Methyl 2-cyano-3-dihalophenyl-2-propenoates, R2C6H3CH=C(CN)CO2CH3 (R2= 2,4-difluoro, 2,5-difluoro, 2,6-difluoro, 3,4-difluoro, 3,5-difluoro, and 2-chloro-6-fluoro), were prepared by the piperidine catalyzed Knoevenagel condensation of corresponding disubstituted benzaldehydes and methyl cyanoacetate. Novel copolymers of the propenoates and styrene were prepared at equimolar monomer feed by solution copolymerization in the presence of a radical initiator. The order of relative reactivity (1/r 1) was 2,5-difluoro (2.11) > 2,6-difluoro (1.84) > 3,5-difluoro (1.71) > 2,4-difluoro (1.4) > 3,4-difluoro (0.65) > 2-chloro-6-fluoro (0.59). The copolymers were characterized by IR, 1H and 13C NMR, GPC, DSC and TGA. High glass transition temperatures of the copolymers compared that of polystyrene indicates a substantial decrease in chain mobility of the copolymers due to the high dipolar character of the trisubstituted ethylene monomer unit.
Macromolecules, 2005
The copolymerization of ethylene and norbornene by catalytic systems composed of i-Pr-[(Cp)(Flu)]ZrCl2 (1) and methylaluminoxane was investigated. Ethylene-norbornene (E-N) copolymers with 40.2 mol % of norbornene are highly alternating (NENE 50 mol %) and contain a significant amount of racemic ENNE (8 mol %) and no ENNN sequences. The microstructural analysis by 13 C NMR of such copolymers was completely obtained at the tetrad level by a methodology that exploits all the peak areas of the spectra and accounts for the stoichoimetric requirements of the copolymer chain. The analysis at the tetrad level allowed us to test the statistical model best describing E-N copolymerization with Cssymmetric catalyst 1 and to study the polymerization mechanism. The root-mean-square deviations between experimental and calculated tetrads demonstrate that the first-order Markov model is sufficient to describe the microstructure of E-N copolymers with 1. It is concluded that in E-N copolymerizations with this catalyst both N and E are inserted according to a Cossee's migratory insertion, and backskips of the copolymer chain to its original position occur, causing the formation of both meso and racemic NEN sequences. The probability of chain backskip is relatively high with respect to that observed in syndiotactic propylene polymerization under the same polymerization conditions. This effect seems to be due to norbornene strong coordinating ability which can influence the competition between site epimerization and chain propagation.
Macromolecules, 2011
This work presents novel and, to some extent, surprising information on ethene/4-methyl-1-pentene (E/Y) copolymers prepared with C 2 symmetric single center metallocene catalysts: the moderately isopecific rac-ethylenebis-(tetrahydroindenyl)zirconium dichloride (EBTHI) and the highly isospecific rac-dimethylsilylbis(2-methyl-4-phenylindenyl)zirconium dichloride (MPHI). Blocky E/Y copolymers from EBTHI, with relatively long sequences of both comonomers, underwent a thorough structural and thermal characterization, performed by combining WAXD, DSC and SSA thermal fractionation. The presence of crystallinities arising from both comonomers, as a function of the copolymer composition led to figure out the simultaneous presence of two populations of thin and defective crystals due to sequences of both comonomers, in samples with almost equimolar composition. The most isospecific metallocene, MPHI, was used exactly with the aim of finally preparing block E/Y copolymers, with long crystalline sequences of both comonomers, whose simultaneous presence could be clearly detected. The easiest 1-olefin propagation ever observed in E/Y copolymerization was obtained with MPHI. However, surprisingly, short sequences of Y were detected in the presence of short E sequences as well. Chain generation, performed for copolymers from both EBTHI and MPHI, revealed, in the latter case, a novel and unique microstructure, with very short sequences of both comonomers almost randomly distributed along the polymer chain. An amorphous nature of these copolymers was revealed by thermal analysis. This paper proposes thus an apparent paradox: on one side, it is confirmed that the 1-olefin propagation becomes easier by increasing the catalyst isoselectivity and, on the other side, short 1-olefin sequences are formed with the most isospecific metallocene. A way to come out from this impasse is proposed, taking into consideration the low steric hindrance of the most isospecific metallocene and the consequent higher reactivity for the 1-olefin, that leads to a lower concentration of 1-olefin in the polymerization bath and of 1-olefin sequences in the copolymer chain. For the first time it seems possible to tell apart the influence of isoselectivity and steric hindrance of a single center C 2 symmetric catalyst on structure and properties of ethene/1-olefin copolymers. This work reveals the existence of unexpected degrees of freedom for tuning microand macro-structures of ethene/1-olefin copolymers from C 2 symmetric metallocenes and wants to be a contribution for developing polymerizations able to control the monomer sequences, proposed as the Holy Grail in polymer science.
Journal of Polymer Science Part A: Polymer Chemistry, 2004
Ethylene/1‐pentene copolymers were prepared using a [(CO)5W= C(Me)OZr(Cp)2Cl] (1)/MAO catalyst system. 1‐Pentene incorporation in the copolymer was monitored using 13C‐NMR spectroscopic methods. The weight average molecular weights (Mw) of the copolymers were between 142,000 and 629,000 g/mol, with polydispersity indexes (PDIs) ranging from ≈ 2 to 90, as analyzed by size exclusion chromatography (SEC). Melting and crystallization temperatures, determined using differential scanning calorimetry (DSC) and crystallization analysis fractionation (CRYSTAF), decreased linearly as the amount of 1‐pentene in the copolymer increased. SEC‐FTIR revealed that the 1‐pentene is predominantly incorporated in the low molecular weight fraction. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5121–5133, 2004
Structure characterization of copolymers of ethylene and 1-octadecene
Journal of Polymer Science Part B-polymer Physics, 2000
Four ethylene-1-octadecene copolymers and the corresponding polyethylene homopolymer, synthesized with a metallocene catalyst, have been analyzed by using three characterization techniques in the solid state: differential scanning calorimetry, wide-angle X-ray diffraction, and Raman spectroscopy. Very important annealing effects are observed in the copolymers with higher comonomer content while standing at room temperature, in such a way that the enthalpies of melting derived from the first and second melting are different. The X-ray diffractograms have been analyzed in terms of amorphous and crystalline components, determining both the crystallinity and the position of the different reflections. The variation of the unit cell parameters has been calculated from those reflections. No indication of a possible participation of the relatively long 1-octadecene branches in the crystallization can be deduced from the X-ray data. The degree of crystallinity has also been determined from the Raman spectra, following two procedures. The results indicate that the crystallinities deduced from the band at 1416 cm Ϫ1 are much lower than those derived from the other two characterization techniques. On the contrary, the data from the 1060 cm Ϫ1 band are practically coincident with the X-ray determinations.