Ethylene/1-olefin copolymer with improved combination of stiffness, environmental stress crack resistance and impact strength is obtained using a specially prepared chromium catalyst

摘要

An ethylene/1-olefin copolymer has the following properties (A) density 0.940-0.955 g/cm 3; (B) vinyl end group content above 0.5 per 1000C atoms; (C) an impact strength a tnas per DIN EN ISO 8256 (1997)/1A at -30[deg]C of =145 kJ/m 2; and (D) a comonomer side-chain content C xper 1000C atoms given by C x= 128.7 - 134.62d where d = the copolymer density in g/cm 3. An independent claim is also included for preparation of the copolymer by polymerization of ethylene with a 3-12C 1-alkene at 80-125[deg]C/0.2-20 MPa with a chromium catalyst obtained by (1) drying a silicon oxide-containing hydrogel to a liquid residue below 50 wt.% at 200-600[deg]C within 300 seconds to form a xerogel which is optionally sieved; (2) adding a chromium salt (0.01-5 wt.%) capable of being converted by calcination to chromium trioxide; and (3) calcining the obtained solid at 400-950[deg]C under oxidative conditions.