FIELD: chemistry.
SUBSTANCE: described is a composition for making tubes, which contains an ethylene polymer and 0.5-5 wt % C4-C8-alpha-olefin. The composition has natural density of 935-956 kg/m3 and melt index MI5 of 0.15-0.5 g/10 min. Dynamic complex viscosity at 100 rad/s and 190°C (η100) is not greater than 2500 Pa·s. The composition has a relationship between η100 and dynamic complex viscosity defined in Pa·s at 0.01 rad/s and 190°C (η0.01) and determined by the equation η0.01>115000+30·η100. Resistance to cracking due to external loads, which is determined by testing tubes with an incision in accordance with ISO 13479:1997 on 11 110-millimetre tubes with standard dimension ratio (SDR) at 80°C and under pressure of 9.2 bars is greater than 1000 h. A Ziegler-Natta catalyst is used. C4-C8-alpha-olefin is 1-hexene, 1-pentene or 1-octene. Described also is a method of preparing the composition.
EFFECT: obtaining resins with high sag resistance and processability, excellent resistance to cracking under a load.
15 cl, 1 dwg, 2 tbl, 6 ex
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