Short chain branching has been characterized using thermal fractionation

a stepwise isothermal crystallizationtechnique

followed by a melting analysis scan using differential scanning calorimetry. Short chain branching distributionwas also characterized by a continuous slow cooling crystallization

followed by a melting analysis scan. Four differentpolyethylenes were studied: Ziegler-Natta gas phase

Ziegler-Natta solution

metallocene

constrained-geometry single sitecatalyzed 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.