Miscibility behavior of metallocene polyethylene blends

Very-low-density polyethylenes (VLDPEs) with short branches, formed by meta llocene or Ziegler-Natta catalysts, were blended with low-density polyethyl enes (LDPEs) or VLDPEs with long branches. The crystallization and melting behavior of these blends were examined by differential scanning calorimetry (DSC). The blends of metallocene-catalyzed VLDPE1 and LDPEs showed a smooth change in both crystallization and melting peak temperatures, indicating t hat there was co-crystallization and, hence, partial miscibility at all com positions. However, the blends of VLDPE1 and long-chain branched VLDPE2 co- crystallized at 50% or less VLDPE2 content, whereas Ziegler-Natta-catalyzed VLDPE3-VLDPE2 blends showed co-crystallization at 50% or higher VLDPE2 com positions. It is concluded that either complete or partial miscibility has occurred between the two polyethylenes in each of the blends with VLDPE2. N evertheless, VLDPE2 did not cause a significant change in the morphology of VLDPE1, perhaps because of the reduced number of long branches present in VLDPE2 compared with LDPEs. The molar masses or melt flow indices of the po lyethylenes were not significant in controlling the morphology; only the di stribution of branches along the chains was important. (C) 2001 John Wiley & Sons, Inc.