FIELD: chemistry.
SUBSTANCE: invention relates to a moulding composition prepared from polyethylene with multimodal molecular weight distribution for making pipes, as well as a method of preparing said moulding composition via a multi-step sequence of reactions, comprising a sequence of polymerisation steps in the presence of a catalyst system, including a Ziegler catalyst and a cocatalyst. The composition contains 45-55 wt % ethylene homopolymer A with low molecular weight, 20-40 wt % high-molecular copolymer B consisting of ethylene and another olefin with 4-8 carbon atoms in amount of 1-8 wt % per weight of the high-molecular copolymer, and 15-30 wt % ethylene copolymer C with ultra-high molecular weight, containing 1-8 wt % of the weight of the ultra-high molecular weight copolymer C, ethylene and one or more olefins with 4-8 carbon atoms.
EFFECT: during storage, the composition has high processability as starting material for making pipes, has a good combination of properties, such as resistance to stress cracking caused by external conditions and mechanical strength, especially during a long period of time.
5 cl, 2 tbl, 2 ex
