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

S.D. Jiang, B.L. Kong, W. Han, P.C. Thune, X.Z. Yang, J. Loos, S.K. Yan

Research output: Contribution to journalArticleAcademicpeer-review

3 Citations (Scopus)

Abstract

The structure and morphology of polyethylene (PE) produced during solution polymerization using bis(imino)pyridyl metal catalysts supported by flat SiO2/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.
Original languageEnglish
Pages (from-to)3810-3818
Number of pages8
JournalPolymer
Volume50
Issue number15
DOIs
Publication statusPublished - 2009

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