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

摘要

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 degrees 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.