Method for producing propylene copolymers using a catalyst activated prior to copolymerization

A method for producing a crystalline copolymer consisting of 0.5-3% by weight of ethylene, 85-97% by weight of propylene and 2-11% by weight of another .alpha.-olefin having 4-12 carbon atoms, which comprises:

• (a) preparing a catalyst solution by mixing together
• (i) a titanium trichloride composition obtained by mixing and milling
• (1) a titanium trichloride obtained by reducing TiCl.sub.4 by metallic aluminum or by further milling the resulting reduction product, together with
• (2) a reaction product of a mixture of titanium tetrachloride with an ether,
• in a mixing ratio of said titanium trichloride (1) to said reaction product (2) of 1:0.001 to 0.3,
• (ii) a dialkylaluminum halide,
• (iii) an electron donor compound, and
• (iv) an inert solvent,
• (b) feeding propylene into the resulting catalyst solution at a temperature of 10.degree.-50.degree. C.
• (i) at a feeding rate in a ratio by weight of 0.02-1/said titanium trichloride composition/hr.
• (ii) in a feeding amount in a ratio by weight of 0.5-5/said titanium trichloride composition, and
• (iii) under a pressure of atmospheric pressure to 10 atmospheres,
• to obtain an activated catalyst solution containing polypropylene in an amount of 0.5-5 times the weight of the titanium trichloride composition contained in said catalyst solution, in advance of the subsequent copolymerization, and
• (c) feeding into a polymerization zone containing said activated catalyst solution,
• (1) 100 parts by weight of propylene,
• (2) 2 to 13 parts by weight of an .alpha.-olefin having 4 to 12 carbon atoms, and
• (3) 1 to 5 parts by weight of ethylene,
• said propylene and said .alpha.-olefin having 4-12 carbon atoms being fed into the catalyst solution at the same time and continuously,
• said ethylene being fed into the gas phase part of the polymerization zone intermittently at time intervals of 5 to 60 minutes, the once feeding time being 1 to 5 minutes, and the polymerization condition being under a temperature of 50.degree. to 75.degree. C. and a pressure of 5 to 40 kg/cm.sup.2.