Process for preparing propylene polymer compositions

An olefin polymerization process, wherein propylene and C4 to C10 α-olefin and optionally ethylene are reacted in the presence of a Ziegler-Natta catalyst so as to obtain a propylene polymer composition,

• wherein the polypropylene comprises C4 to C10 α-olefin-derived comonomer units in an amount of from 0.5 wt % to 15 wt % and ethylene-derived comonomer units in an amount of 0 wt % to 3 wt %, and
• the Ziegler-Natta catalyst comprises:
• i) an external donor of the following formula (I):
• (R3)z(R2O)ySi(R1)x (I)
• wherein:
• x is 1 or 2;
• y is 2 or 3;
• and z is 0 or 1;
• under the provision that x+y+z=4;
• R1 is an organic residue of the following formula (II)
• wherein,
• the carbon atom bonded to the Si atom is a secondary carbon atom and the residues R4 and R5 bonded to the secondary carbon atom are, independently from each other, a C1-2 alkyl group,
• R2 is a linear C1-4 alkyl and
• R3 is a linear C1-4 alkyl, and
• ii) a solid Ziegler-Natta catalyst component, which is free of any external carrier material;
• wherein the solid Ziegler-Natta catalyst component ii) is prepared according to the procedure comprising:
• a) providing a solution of
• a1) at least a Group 2 metal alkoxy compound (Ax) being the reaction product of a Group 2 metal compound and an alcohol (A) comprising in addition to the hydroxyl moiety at least one ether moiety optionally in an organic liquid reaction medium;
• or
• a2) at least a Group 2 metal alkoxy compound (Ax′) being the reaction product of a Group 2 metal compound and an alcohol mixture of the alcohol (A) and a monohydric alcohol (B) of formula ROH, with R being a straight-chain or branched C2-C16 alkyl residue, optionally in an organic liquid reaction medium;
• or
• a3) a mixture of the Group 2 metal alkoxy compound (Ax) and a Group 2 metal alkoxy compound (Bx) being the reaction product of a Group 2 metal compound and the monohydric alcohol (B), optionally in an organic liquid reaction medium;
• or
• a4) Group 2 metal alkoxy compound of formula M(OR1)n(OR2)mX2-n-m or mixture of Group 2 alkoxides M(OR1)n′X2-n′ and M(OR2)m′X2-m′, where M is Group 2 metal, X is halogen, R1 and R2 are different alkyl groups of C2 to C16 carbon atoms, and 0≤n<2;
• 0≤m<2 and n+m≤2, provided that both n and m≠0, 0<n′≤2 and 0<m′≤2;
• and
• b) adding said solution from step a) to at least one compound of a transition metal of Group 4 to 6 and
• c) obtaining the solid catalyst component particles, and
• adding a non-phthalic internal electron donor at any step prior to step c).