Intramolecular branching distributions in metallocene short‐chain branched polyethylenes examined by crystallization and annealing at high pressure

Parker, J. A.; Olley, R. H.

doi:10.1002/polb.20482

Cited by 3 publications

(2 citation statements)

References 49 publications

(49 reference statements)

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“…Although such a low-temperature melting endotherm could be explained in terms of melting of a secondary crystalline phase, the exact assignment is not yet clear. In previous literature, ,,− the low-temperature endothermic peak was attributed to the melting of different types of crystalline phases or regions: (1) lamellar OCP with smaller thicknesses, (2) MCP, and (3) RCP. In our previous investigations on EVA, based on the NMR and DSC results, we attributed the low-temperature endothermic peak to the RCP …”

Section: Introductionmentioning

confidence: 97%

“…21 Corresponding to the multiple crystalline phases, multiple melting behaviors were commonly observed during DSC heating scans of ethylene-based copolymers. 5,14,[22][23][24][25][26][27][28][29][30][31][32] In general, except for the high-temperature melting endotherm of the orthorhombic phase, a low-temperature melting endotherm has been observed slightly above the room temperature. Although such a lowtemperature melting endotherm could be explained in terms of melting of a secondary crystalline phase, the exact assignment is not yet clear.…”

Section: Introductionmentioning

confidence: 99%

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Crystalline Phases in Ethylene Copolymers Studied by Solid-State NMR and DSC

et al. 2010

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The structures and thermal properties of the multiple ordered phases in ethylene−octene and ethylene−butene copolymers have been studied using a combination of solid-state NMR and DSC. Three types of the ordered phases, namely the orthorhombic, monoclinic, and rotator (or ordered mobile phase), have been found to coexist in these two ethylene copolymers. Our experimental results demonstrate that the slow-spinning solid-state CP/MAS 13C NMR provides a convenient method to discern the NMR signals of the three different ordered phases and to measure the 13C chemical shift tensors of orthorhombic and monoclinic phases. The measurements of 13C chemical shift tensors and magnetic relaxation times show that monoclinic and orthorhombic crystal phases have similar chemical shift anisotropy with 180° flip-flop segmental movement. The chemical shift anisotropy and segmental mobility in the rotator phase, on the other hand, are different from those in the orthorhombic and monoclinic phases. DSC results illustrate that a low-melting-point phase forms during room-temperature aging and melts at temperature slightly above the room temperature. The apparent correlation between the low-melting-point phase and the rotator structure is revealed by a combination of variable-temperature solid-state CP/MAS NMR spectra with a slow-spinning rate and DSC measurement. It is thus suggested that the rotator formation induced by room-temperature aging is a common phenomenon for the ethylene copolymers with different sizes of side groups.

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Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

Crystalline Phases in Ethylene Copolymers Studied by Solid-State NMR and DSC

et al. 2010

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New insights into the multiple melting behaviors of the semicrystalline ethylene‐hexene copolymer: Origins of quintuple melting peaks

Qiu

Zhao

et al. 2008

J Polym Sci B Polym Phys

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A semicrystalline ethylene‐hexene copolymer (PEH) was subjected to a simple thermal treatment procedure as follows: the sample was isothermally crystallized at a certain isothermal crystallization temperature from melt, and then was quenched in liquid nitrogen. Quintuple melting peaks could be observed in heating scan of the sample by using differential scanning calorimeter (DSC). Particularly, an intriguing endothermic peak (termed as Peak 0) was found to locate at about 45 °C. The multiple melting behaviors for this semicrystalline ethylene‐hexene copolymer were investigated in details by using DSC. Wide‐angle X‐ray diffraction (WAXD) technique was applied to examine the crystal forms to provide complementary information for interpreting the multiple melting behaviors. Convincing results indicated that Peak 0 was due to the melting of crystals formed at room temperature from the much highly branched ethylene sequences. Direct heating scans from isothermal crystallization temperature (Tc, 104–118 °C) were examined for comparison, which indicated that the multiple melting behaviors depended on isothermal crystallization temperature and time. A triple melting behavior could be observed after a relatively short isothermal crystallization time at a low Tc (104–112 °C), which could be attributed to a combination of melting of two coexistent lamellar stack populations with different lamellar thicknesses and the melting‐recrystallization‐remelting (mrr) event. A dual melting behavior could be observed for isothermal crystallization with both a long enough time at a low Tc and a short or long time at an intermediate Tc (114 °C), which was ascribed to two different crystal populations. At a high Tc (116–118 °C), crystallizable ethylene sequences were so few that only one single broad melting peak could be observed. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2100–2115, 2008

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New and Simple Staining Method for Visualizing UHMWPE Lamellar Structure in TEM

Stara

Šlouf

Lednický

et al. 2008

Journal of Macromolecular Science, Part B

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Ultra-high-molecular-weight polyethylene (UHMWPE) is used in arthroplasty as a key component of total joint replacements. In order to increase its wear resistance, the polymer is often cross-linked in a two-step procedure comprising irradiation and thermal treatment. Both modification steps impact UHMWPE lamellar structure. In this study we introduce a new staining method that makes it possible to visualize the UHMWPE lamellae by transmission electron microscopy (TEM). The method consists of one-step staining with oleum (H 2 SO 4 solution of SO 3 ) for 4 days and ultramicrotomy;this is significantly simpler than previously described techniques and yields micrographs of the same quality. The lamellar thicknesses from TEM correlated well with those from small-and wide-angle X-ray scattering and differential scanning calorimetry. It has also been demonstrated that the exact values of lamellar thicknesses obtained from TEM micrographs strongly depend on the place selected for image analysis.

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Intramolecular branching distributions in metallocene short‐chain branched polyethylenes examined by crystallization and annealing at high pressure

Cited by 3 publications

References 49 publications

Crystalline Phases in Ethylene Copolymers Studied by Solid-State NMR and DSC

Crystalline Phases in Ethylene Copolymers Studied by Solid-State NMR and DSC

New insights into the multiple melting behaviors of the semicrystalline ethylene‐hexene copolymer: Origins of quintuple melting peaks

New and Simple Staining Method for Visualizing UHMWPE Lamellar Structure in TEM

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