FIELD: production of thermal plastics. SUBSTANCE: proposed composition contains 62.0-71.2 % of crystalline polyolefin fraction, 2.6-14.4 % of fraction being insoluble in xylene, 18.2-32.6 % of fraction being insoluble in xylene. Mentioned above crystalline polyolefin fraction represents crystalline copolymer of propylene and ethylene (its quantity being 1.6-2.2 %) having isotactic index 91.0-92.5 %. Fraction being insoluble in xylene represents copolymer of ethylene with propylene (its quantity being 7.8-32.5 %). Fraction being soluble in xylene represents amorphous copolymer with 31.2-45.0 % of propylene. Proposed composition is prepared by two-stepped copolymerization. At the first step polymerization is carried out in gaseous phase at 54-70 C and 5.4-33 atm, ethylene is fed into gaseous phase at rate 150-500 kg/h in the presence of hydrogen. At the second step polymerization is carried out at 60-75 C and 6-14 atm in gaseous phase in the presence of product being prepared at the first step and in the presence of 1.8-8.0 mol % of hydrogen. Threethyl aluminium being solid component having specific surface 66.5 66,5 m2/g, porosity 0.261 cm3/g and bulk mass 0.44 g/cm3 is used as catalyst. Said catalyst comprises tetrahalide titanium compound and ester of dicarboxylic acid on activated adduct of magnesium chloride with alcohol (alcohol content is 1.5 moles per 1 mole of magnesium chloride) and donor of electrons (dicyclohexyldimethoxy silane and cyclohexyldimethoxy silane). EFFECT: improved quality of desired composition. 2 cl, 5 tbl
