Effects of the phase-separated melt on crystallization behavior and morphology in short chain branched metallocene polyethylenes

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Abstract
Some metallocene catalyst synthesized short chain branched polyethylene (SCBPE) samples have been found to possess at least intermolecular heterogeneity in the SCB. As-received SCBPE samples are molecularly homogeneous in the isotropic melt. However, phase separation due to the intermolecular heterogeneity can be found via molecular segregation processes induced by multiple-step isothermal crystallization experiments. When the phase-separated SCBPE samples are reheated above their melting temperatures, the phase-separated (heterogeneous) melt is maintained for an extended period of time (at least 20 h at 150°C). Neither phase mixing in the melt nor significant changes in molecular weight, molecular weight distribution, comonomer content, or sequence have been found during the high-temperature treatment. Comparisons of overall crystallization kinetics and morphology of the SCBPE samples obtained from the homogeneous and heterogeneous melts exhibit substantially different behavior which indicates that the phase-separated melt exists and can be identified.
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