| 摘要 |
A process for the preparation of propylene-ethylene block copolymers in which first (I) propylene is homopolymerised from the gas phase in a first polymerisation zone, and (II) a mixture of propylene and ethylene is polymerised onto the propylene homopolymer in a second polymerisation zone, characterised in that (a) (I) is carried out at a certain overall pressure, a certain temperature and a certain propylene:hydrogen partial pressure ratio (P/H-I) with a high space-time yield, (b) (II) is carried out at a certain overall pressure and a certain temperature, the propylene:ethylene partial pressure ratio and the propylene:hydrogen partial pressure ratio (P/H-II) having specific values, (c) the overall pressure in (I) is kept higher than in (II), (d) the temperature in (II) is chosen to be lower than that in (I), and (e) the P/H-I:P/H-II ratio has a specific value. The process gives polymers having improved physical properties. |
