Molecular structure, melting behavior, and crystallinity of 1‐octene‐based very low density polyethylenes (VLDPEs) as studied by fractionation and heat capacity measurements with DSC

Mathot, Vincent; Pijpers, M. F. J.

doi:10.1002/app.1990.070390416

Cited by 70 publications

(29 citation statements)

References 25 publications

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“…Some researchers assigned the additional reflection to the hexagonal mesomorphic phase which is not stable at room temperature and could probably be stabilized by the form of hexyl branches [26,27] and some others have assigned it to a monoclinic crystallization phase reflection [28]. As an overview, it is caused by bulky aliphatic branches which cannot be incorporated in an orthorhombic PE crystal and consequently form some other kinds of "crystal" with an order nature intermediate between crystalline and amorphous [19,29].…”

Section: Resultsmentioning

confidence: 99%

Shear effects on crystallization behavior of poly(ethylene-co-octene) copolymers

Wen

et al. 2011

J Polym Res

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Crystallization behavior of sheared polymer melts of a series of poly(ethylene-co-octene)s with different octene content was investigated by different scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD) and synchrotron small-angle X-ray scattering (SR-SAXS) techniques. The DSC results indicated that the hexyl branches content had dramatic effects on the thermal properties and crystallinity of polyethylene. It was also found that shear had no obvious effects on the size of either crystallite or lamellae. However, both crystallite and lamellae were oriented by shearing, especially for the lamellae. All obtained results indicate that the initial states of the polymer melt play an important role in affecting the crystallization behaviors. The difference of the shear-induced crystalline structure evolution and the orientation between crystallite and lamellae support the preordered mesomorphic phase of flexible polymer crystallization process proposed by Strobl.

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Section: Resultsmentioning

confidence: 99%

Shear effects on crystallization behavior of poly(ethylene-co-octene) copolymers

Wen

et al. 2011

J Polym Res

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“…Heterogeneous copolymers have a far more complex molecular structure [1,8,9,32,111]; LLDPE and VLDPE, for example, are blends [1,9,32,47,[111][112][113] of molecules which differ greatly in comonomer content, even at the same chain length. VLDPE molecules show exceptional behaviour: they crystallize and melt across a temperature range of about 200~ above the glass transition [1,35,72]. Therefore, in VLDPE we expect to find all types of crystallites: lamellae with folded ethylene sequences, fringed micelles with bundled ethylene sequences and clusters with loosely packed ethylene sequences.…”

Section: Discussionmentioning

confidence: 98%

“…The VLDPE is an intermolecularly heterogeneous copolymer [35], for it has been found that the copolymer with 8,5 mol % octene in Fig. 2 can be separated into molecules with greatly varying comonomer contents.…”

Section: Homogeneity and Heterogeneitymentioning

confidence: 99%

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Dynamic DSC, SAXS and WAXS on homogeneous ethylene-propylene and ethylene-octene copolymers with high comonomer contents

Mathot

Scherrenberg

Pijpers

et al. 1996

Journal of Thermal Analysis

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Ethylene-propylene (EP) and ethylene-octene (EO) copolymers polymerized with the aid of homogeneous vanadium and metallocene catalysts were compared by DSC and time-resolved simultaneous SAXS-WAXS-DSC at scanning rates of 10 and 20~ rain -1 using synchrotron radiation. An EP eopolymer with a density of 896 kg m -3 (about 89 mol% ethylene) after compression moulding gave orthorhombic WAXS reflections. The crystallinity as a function of temperature [wC(7)] calculated from these reflections using the two-phase model was in good agreement with we(T) calculated from Cp measurements using DSC. The Cp measurements also enabled calculation of the baseline Cp and the excess Cp. The SAXS measurements revealed a strong change in the long period in cooling and in heating. The SAXS invariant as a function of temperature showed a maximum in both cooling and heating, which could be explained from the opposing influences of the crystallinity and the electron density difference between the two phases. Two EO eopolymers with densities of about 871 kg m -3 (about 87 mol% ethylene) no longer showed any clear WAXS reflections, although DSC and SAXS measurements showed that these eopolymers did crystallize. The similarity between the results led to the conclusion that the copolymers, though based on different catalyst systems -vanadium and metallocene -did not have strongly different sets of propagation probabilities of chain growth during polymerization. On the basis of a Monte Carlo simulation model of crystallization and morphology, based on detailed knowledge of the mierochain structure, the difference between WAXS on the one hand and DSC and SAXS on the other could be explained as being due to loosely packed cryz,tallized ethylene sequences in clusters. These do cause the density and the electron density of the cluster to increase (which is measurable by SAXS) and the enthalpy to decrease (which is measurable by DSC) but the clusters are too small and/or too imperfect to give constructive interference in the case of WAXS. Of an EP copolymer with an even lower ethylene content (about 69 mol%), the crystallization and melting processes could still be readily measured by DSC and SAXS, which proves that these techniques are eminently suitable for investigating the crystallization and melting behaviour of the copolymers studied.

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“…[1][2][3][4][5]13 Here, we need to point out the shapes of the cooling curves which reveal a distinct heterogeneous transition behavior. Mathot et al [1][2][3] discussed the shape of the DSC curves in terms of intermolecular and intramolecular homogeneity of the distribution of the shortchain branches (SCB) but refer mainly to the heating scans, not the cooling scans.…”

Section: General Description Of Crystallization Andmentioning

confidence: 99%

A Study of Annealing of Poly(ethylene-co-octene) by Temperature-Modulated and Standard Differential Scanning Calorimetry

Androsch

Wunderlich

1999

Macromolecules

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Annealing of poly(ethylene-co-octene)s with 12-25 mass % 1-octene for 2.5-5250 min was carried out by approaching the annealing temperature through cooling at 10 K min -1 . Above the annealing temperature, primary crystallization was initiated. The analysis of the samples was performed during and after the annealing with temperature-modulated and standard differential scanning calorimetry, respectively (TMDSC and DSC). The irreversible annealing process consists of two different, exothermic events which are secondary crystallization and reorganization. The two processes were separated and quantitatively expressed by exponential laws with relaxation times of the order of 5 and 100 min, respectively. The two stages of crystallization and the reorganization produce a temperature-dependent, arrested, metastable, global structure of crystals and amorphous defects. Changing the annealing time can only partially compensate for changes in annealing temperature. Furthermore, TMDSC reveals a small amount of fully reversible melting. This reversible melting exists in addition to the well-known equilibrium of gauche-trans point defects in the crystal. Overall, there are thus at least five latent-heat contributions to the apparent heat capacity between the glass and melting transitions: primary and secondary crystallization, reorganization, locally reversible melting, and the gauche-trans equilibrium. For quantitative analysis of these latent-heat effects, they must be separated from the heat capacity of the melt, extrapolated from above the melting temperature, and the vibrational heat capacities of the crystal or glass.

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Molecular structure, melting behavior, and crystallinity of 1‐octene‐based very low density polyethylenes (VLDPEs) as studied by fractionation and heat capacity measurements with DSC

Cited by 70 publications

References 25 publications

Shear effects on crystallization behavior of poly(ethylene-co-octene) copolymers

Shear effects on crystallization behavior of poly(ethylene-co-octene) copolymers

Dynamic DSC, SAXS and WAXS on homogeneous ethylene-propylene and ethylene-octene copolymers with high comonomer contents

A Study of Annealing of Poly(ethylene-co-octene) by Temperature-Modulated and Standard Differential Scanning Calorimetry

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