POLYETHYLENE COMPOSITIONS, HAVING IMPROVED PROPERTIES

摘要

FIELD: chemistry. ^ SUBSTANCE: polyethylene composition contains ethylene and butene and has long-chain branching index (g'av.) from 0.5 to 0.9; melt flow index (MFI) higher than (49.011ùIR(-0.4304)), where IR is melt index; and ratio of weight-average molecular weight to number-average molecular weight Mw/Mn less than or equal to 4.6. The method for gas-phase polymerisation of olefins to obtain said composition is realised in the presence of a catalyst system containing an achiral cyclic bridge metallocene catalytic compound and an activator - aluminoxane, modified aluminoxane or mixture thereof. Films containing said composition have good optical and shrinking properties. In particular, a film can have one or more of the following characteristics: longitudinal plastic shrinkage stress (MD) ëñ0.08 MPa; Retromat surface shrinkage >60%; transparency >60%; relative internal turbidity ëñ1.0%/mil (i.e. %/0.001 inch); turbidity <20%. ^ EFFECT: improved properties. ^ 31 cl, 5 dwg, 10 tbl, 5 ex