PROCESS FOR THE MANUFACTURE OF RANDOM COPOLYMERS OF PROPYLENE AND OTHER MONO-OLEFINS

The continuous preparation of random copolymers of propylene by polymerisation of a monomer mixture by means of a Ziegler-Natta catalyst system in the gas phase in a central stirred bed of finely divided polymer with dissipation of the heat of polymerisation by evaporation cooling, the monomer mixture being introduced continuously into the polymerisation zone and the polymer being discharged continuously from the polymerisation zone, with the provisos that (a) the pressure and the temperature in the polymerisation zone are kept within a range which corresponds to the gaseous state of the monomer mixture, (b) gaseous, unconsumed monomer mixture is discharged from the polymerisation zone and reintroduced in liquid form into the polymerisation zone, (c) the temperature in the polymerisation zone is regulated by means of the amount of liquid monomer mixture introduced per time unit, and (d) the monomers consumed by the polymerisation are replaced, characterised in that the residence time of the monomer mixture in the polymerisation zone is kept very short, the monomer mixture employed comprising principally propylene, a little ethylene and very little hydrogen.