Structure and properties of ultralow density polyethylenes

Woo, Lecon; Westphal, Stanley P.; Ling, T.K.

doi:10.1016/0040-6031(93)80209-s

Cited by 10 publications

(2 citation statements)

References 6 publications

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“…2) was highly branched, and references 1 and 2 have clear β transitions between −45 and −20 °C. The appearance of a β transition is typical for SCB polyethene 17, 18. The intensity of the β relaxation is thus rather high for low density polyethylenes (LDPEs) and low or even absent for high density polyethylenes (HDPEs) (see reference 3).…”

Section: Resultsmentioning

confidence: 99%

Molecular structure determination of Ni(II) diimine complex and DMA analysis of Ni(II) diimine‐based polyethenes

Liimatta¹,

Löfgren²,

Miettinen³

et al. 2001

J. Polym. Sci. A Polym. Chem.

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Dynamic mechanical thermoanalysis showed that polyethene, prepared under suitable polymerization conditions with the Brookhart‐type catalyst dibromo‐N,N′‐1,2‐acenaphthylenediylidenebis[2,6‐bis(1‐methylethyl)benzeneamine]Ni(II)/methylaluminoxane (MAO), behaved like an elastomer, even though no comonomer was added. A structural characterization showed that the polymers contained methyl to hexyl branches and some longer branches. The effect of the polymerization conditions on branching was investigated through variations in the pressure and temperature of the polymerization. Depending on the degree and type of branching, polyethene was either quite amorphous or highly crystalline with a high melting temperature. The solid‐state structure of the catalyst dibromo‐N,N′‐1,2‐acenaphthylenediylidenebis[2,6‐bis(1‐methylethyl)benzeneamine]Ni(II) consisted of two centrosymmetrically related monomeric moieties, where Ni atoms were bridged by two bromide ligands. The Ni atom was five‐coordinated, with a square pyramidal coordination polyhedron. The sixth coordination site of the octahedral geometry was effectively blocked by the isopropyl groups of the 2,6‐C6H3(i‐Pr) substituents of the diimine ligand. In solution in the presence of MAO, the longer bridging NiBr bonds broke, and the complex dissociated to a monomeric species. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1426–1434, 2001

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Section: Resultsmentioning

confidence: 99%

Molecular structure determination of Ni(II) diimine complex and DMA analysis of Ni(II) diimine‐based polyethenes

Liimatta¹,

Löfgren²,

Miettinen³

et al. 2001

J. Polym. Sci. A Polym. Chem.

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“…[17,18] The a transition is located in the range 20-70 8C, and it is related to the molecular motion of the crystalline phase. In particular, by increasing the density and decreasing the branching, higher values of the a peak intensity, [19] and temperature [20] are generally observed.…”

Section: Crosslinking Of Linear Low Density Polyethylene (Lldpe)mentioning

confidence: 98%

Modulated Crosslinking of Polyolefins through Radical Processes in the Melt

Passaglia

Coiai

Giordani

et al. 2004

Macro Materials & Eng

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Summary: The possibility to submit a semi‐crystalline polyolefin (or a mixture of different polyolefins) to a phase selective crosslinking process, in order to produce a material with unchanged crystallinity but a partially crosslinked amorphous fraction, has been investigated. The crosslinking process has been performed in the melt in the presence of radical initiators. Three different polymer systems have been considered: a LLDPE sample (an ethylene‐1‐butene 91/9 w/w copolymer), two EVA samples (ethylene‐vinyl acetate copolymers containing a different amount (10 and 15 wt.‐%) of acetate monomer units), and mixtures of LLDPE with polybutadiene (BR) (90/10 w/w). All the reaction products have been characterized by selective solvent extractions to determine the gel content, by analysis with different spectroscopies (IR and NMR) and by viscosity measurements to evaluate changes of the structure and the molecular weight (MW) of the partially crosslinked samples. Finally DSC and DMTA analyses have been used to correlate the variations of the macromolecule structure to the thermo‐mechanical properties and, in the case of the mixtures, TEM analysis has been carried out to gather information about the morphology.TEM micrograph of the partially crosslinked polyethylene/polybutadiene blend 90/10 (w/w).magnified imageTEM micrograph of the partially crosslinked polyethylene/polybutadiene blend 90/10 (w/w).

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Polymerization and characterization of ethylene/propylene and ethylene/1‐octene copolymers produced with bridged Zr‐ and Hf‐based metallocenes

Starck¹,

Lehtinen²,

Löfgren³

1997

Angew. Makromol. Chem.

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Ethylene/propylene (EP) and ethylene/l -octene (E/O) copolymers were polymerized with two bridged metallocene catalyst systems, Et(Ind)2ZrC12/MA0 and Et(Ind),HfCI,/MAO, respectively. The copolymers produced and some commercial reference copolymers were characterized by DSC, SEC, DMA and 13C NMR.The Hf-catalysed E P polymerizations showed much lower activities than the corresponding Zr-catalysed polymerizations but gave polymers with high molar mass. The Hf-based copolymers also showed two melting peaks which may be indicative of several active sites of the catalyst. A comparison of E P copolymers, containing about 20 mol-% propylene and produced with Zr, Hf and homogeneous V-catalysts, respectively, indicated that the Hf and V-catalysts gave material more similar to each other.The E/O copolymers produced with Zr-catalysts gave very low molar masses and the reactivity ratios, calculated from the NMR data, indicated that the Hf-catalyst has a slightly higher reactivity for 1-octene and the Zr-catalyst some better reactivity for ethylene. Segregation fractionation studies by DSC indicated that a lower l-octene feed gives more heterogeneous copolymers and the DMA measurements reveal the existence of a linear correlation between the 1-octene content and the intensity of the tan 6 , , ,ZUSAMMENFASSUNG: Ethylen/Propylen(E/P)-und Ethylerdl -octen(E/O)-Copolymere wurden mit zwei verschiedenen Katalysatorsystemen, Et(Ind)2ZrC12/MA0 und Et(Ind)2HfC12/MA0, hergestellt und mittels DSC, SEC, DMA und 13C-NMR charakterisiert. Die E P -Polymerisationen mit Hf ergaben niedrigere Katalysatoraktivitaten, jedoch zeigten die erhaltenen Polymeren eine hohere Molmasse und zwei verschiedene Schmelzpunkte, was auf unterschiedliche aktive Zentren des Katalysators hindeutet. E/O-Copolymere mit sehr niedrigen Molmassen wurden mit dem Zr-Katalysator hergestellt. Die Hf-Katalysatoren ergaben Copolymere mit hoheren Molmassen, je-

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Structure and properties of ultralow density polyethylenes

Cited by 10 publications

References 6 publications

Molecular structure determination of Ni(II) diimine complex and DMA analysis of Ni(II) diimine‐based polyethenes

Molecular structure determination of Ni(II) diimine complex and DMA analysis of Ni(II) diimine‐based polyethenes

Modulated Crosslinking of Polyolefins through Radical Processes in the Melt

Polymerization and characterization of ethylene/propylene and ethylene/1‐octene copolymers produced with bridged Zr‐ and Hf‐based metallocenes

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