Process for producing propylene-ethylene block copolymer.

摘要

A propylene-ethylene block copolymer is produced in the presence of a catalytic system essentially comprising an organoaluminum compound and a solid titanium trichloride catalytic complex having an atomic ration of Al to Ti of less than 0.15:1 and including a complexing agent, in three stages of polymerization; (a) a first stage in which propylene is polymerized in the presence of liquid propylene and hydrogen to produce a propylene homopolymer having a melt flow index of 1 to 60 at a ratio of 70 to 90% by weight based on the total polymers; (b) a second stage in which the resulting polypropylene is copolymerized propylene and ethylene in the presence of hydrogen and liquid propylene, at a concentration of propylene in the vapor phase, based on the total of propylene and ethylene in the vapor phase, of 50 to 85 mol %, to produce a propylene-ethylene copolymer having a melt flow index of less than 0.1 at a ratio of 3 to 20% by weight based on the total polymers; and (c) a third stage in which the resulting copolymer is polymerized with ethylene or with and propylene in the presence of hydrogen, with liquid propylene or in the absence of any substantial amount of liquid hydrocarbon, at a concentration of propylene in the vapor phase, based on the total of propylene and ethylene in the vapor phase, of less than 75 mol % and less than the corresponding ratio in said second stage, to produce an ethylene-propylene copolymer having a melt flow index of less than 1 at a ratio of 5 to 20% by weight based on the total polymers.