Analysis of branching distribution in polyethylenes by differential scanning calorimetry

Shanks, R, Chen, F and Amarasinghe, G 2003, 'Analysis of branching distribution in polyethylenes by differential scanning calorimetry', Chinese Journal of Polymer Science, vol. 21, pp. 231-239.

Document type: Journal Article
Collection: Journal Articles

Title Analysis of branching distribution in polyethylenes by differential scanning calorimetry
Author(s) Shanks, R
Chen, F
Amarasinghe, G
Year 2003
Journal name Chinese Journal of Polymer Science
Volume number 21
Start page 231
End page 239
Total pages 9
Publisher Springer
Abstract Short chain branching has been characterized using thermal fractionation, a stepwise isothermal crystallization technique, followed by a melting analysis scan using differential scanning calorimetry. Short chain branchingdistribution was also characterized by a continuous slow cooling crystallization, followed by a melting analysis scan. Four different polyethylenes were studied: Ziegler-Natta gas phase, Ziegler-Natta solution, metallocene, constrained-geometry single site catalyzed polyethylenes. The branching distribution was calculated from a calibration of branch content with melting temperature. The lamellar thickness was calculated based on the thermodynamic melting temperature of each polyethylene and the surface free energy of the crystal face. The branching distribution and lamellar thickness distribution were used to calculate weight average branch content, mean lamellar thickness, and a branch dispersity index. The results for the branch content were in good agreement with the known comonomer content of the polyethylenes. A limitation was that high branch content polyethylenes did not reach their potential crystallization at ambient temperatures. Cooling to sub-ambient was necessary to equilibrate the crystallization, but melting temperature versus branch content was not applicable after cooling to below ambient because the calibration data were not performed in this way.
Subject Physical Chemistry of Materials
Keyword(s) Branch distribution
Lamellar thickness
Short chain branching
Thermal fractionation
ISSN 0256-7679
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