| abstract |
BLENDS OF ETHYLENE POLYMERS HAVING IMPROVED STRESS CRACK RESISTANCE COMPRISING A HIGH DENSITY, HIGH MOLECULAR WEIGHT POLYETHYLENE AND A COPOLYMERIC CONSTITUENT CONTAINING AS AN ESSENTIAL INGREDIENT AT LEAST ONE BLOCK COPOLYMER OF POLYETHYLEN AND A POLYMER OF BUTENE-1. A METHOD FOR THE PREPARATION THEREOF WHICH COMPRISES (1) POLYMERIZING ETHYLENE TO HIGH DENSITY, HIGH MOLECULAR WEIGHT POLYETHYLENE IN THE PRESENCE OF A HETEROGENEOUS CATALYST SYSTEM, SUCH AS A MIXTURE OF TRIISOBUTYL ALUMINUM AND TITANIUM TETRACHLORIDE, AND A MOLECULAR WEIGHT CONTROL AGENT, SUCH AS HYDROGEN; (2) WITHDRAWING A MAJOR PART OF THE RESULTING POLYMER SLURRY FROM THE POLYMERIZATION ZONE; (3) INTRODUCING A GASEOUS ALPH-OLEFIN, SUCH AS BUTENE-1, INTO THE REMAINING PORTION OF THE STILL CATALYTICALLY ACTIVE POLYMER SLURRY AND POLYMERIZING THE RESULTING MIXTURE TO OBTAIN A BOLCK COPOLYMER OF POLYETHYLENE AND A POLYMER OF BUTENE-1; AND (4) ADMIXING THE WITHDRAWN POLYMER SLURRY WITH THE REMAINING POLYMER SLURRY. |