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The effect of temperature on nascent morphology of polyethylene polymerized over solution-phase flat model catalysts

✍ Scribed by Shidong Jiang; Bin Kong; Wei Han; Peter C. Thüne; Xiaozhen Yang; Joachim Loos; Shouke Yan


Book ID
104087877
Publisher
Elsevier Science
Year
2009
Tongue
English
Weight
741 KB
Volume
50
Category
Article
ISSN
0032-3861

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✦ Synopsis


The structure and morphology of polyethylene (PE) produced during solution polymerization using bis(imino)pyridyl metal catalysts supported by flat SiO 2 /Si(100) wafers were investigated by atomic force microscopy (AFM) and electron diffraction. Depending on the polymerization temperature, ranging from RT to 85 C, different morphologies of the nascent PE have been observed. ''Sea weed'' like supermolecular structures are the predominant nascent morphologies of the PE polymerized at low temperatures. This should be associated with the high PE yield and high nucleation rate at low temperature; the catalyst is highly active and the PE macromolecules have low solubility in toluene and nucleate immediately after formation. With increasing polymerization temperature, e.g. at 60 or 70 C, larger single crystals with roughly a lozenge shape but saw-tooth-like facets have been created. The multilayer overgrowth of the PE crystals demonstrates that the generated PE materials exceed what is required for single layer crystal growth. At 85 C, decreasing crystal growth rate results in the formation of small PE single crystals. At the same time, the high solubility of the PE in toluene results in continuous diffusion of the macromolecules to the existing PE crystals and therefore single crystals in regular truncated lozenge shape have been formed. Electron diffraction indicates that in the whole temperature range, PE crystallizes in flat-on crystals in chain-folded structure with different chain folding stem length.


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