EFFECTS OF THE PHASE-SEPARATED MELT ON CRYSTALLIZATION BEHAVIOR AND MORPHOLOGY IN SHORT-CHAIN BRANCHED METALLOCENE POLYETHYLENES

Some metallocene catalyst synthesized short chain branched polyethylen e (SCBPE) samples have been found to possess at least intermolecular h eterogeneity in the SCB. As-received SCBPE samples are molecularly hom ogeneous in the isotropic melt. However, phase separation due to the i ntermolecular heterogeneity can be found via molecular segregation pro cesses induced by multiple-step isothermal crystallization experiments . When the phase-separated SCBPE samples are reheated above their melt ing temperatures, the phase-separated (heterogeneous) melt is maintain ed for an extended period of time (at least 20 h at 150 degrees C). Ne ither phase mixing in the melt nor significant changes in molecular we ight, molecular weight distribution, comonomer content, or sequence ha ve been found during the high-temperature treatment. Comparisons of ov erall crystallization kinetics and morphology of the SCBPE samples obt ained from the homogeneous and heterogeneous melts exhibit substantial ly different behavior which indicates that the phase-separated melt ex ists and can be identified.