Process for producing heterophasic propylene resin

A process for the preparation of a heterophasic polypropylene resin in a multistage polymerisation process in the presence of a metallocene catalyst, said process comprising:

• (I) in a first polymerisation step, polymerising propylene and optionally at least one C2-10 alpha olefin comonomer to a obtain polypropylene matrix phase (A);
• and subsequently
• (II) in a second polymerisation step, polymerising propylene, ethylene and optionally at least one C3-10 alpha olefin comonomer, in the presence of the metallocene catalyst and polymer from step (I) to obtain an ethylene-propylene copolymer phase (B) dispersed in the matrix phase (A);
• wherein said metallocene catalyst comprises a metallocene complex of Formula I
• wherein Mt is Zr or Hf;
• each X is a sigma-ligand;
• E is a —CR12—, —CR12—CR12—, —CR12—SiR12—, —SiR12— or —SiR12—SiR12— group chemically linking the two cyclopentadienyl ligands;
• The R1 groups, which can be the same or can be different, are hydrogen or C1-20 hydrocarbyl groups, optionally containing up to 2 silicon, oxygen, sulphur or nitrogen atoms, and optionally two R1 groups can be part of a C4-C8 ring,
• R2 and R2′ are the same or different from each other;
• R2 is a —CH2R group, with R being H or a linear or branched C1-6 alkyl group, C3-8 cycloalkyl group, C6-10 aryl group;
• R2′ is a C1-20 hydrocarbyl group;
• preferably, R2 and R2′ are the same and are linear or branched C1-6 alkyl groups;
• each R3 and R4 are independently the same or can be different and are hydrogen, a linear or branched C1-6 alkyl group, a C7-20 arylalkyl, a C7-20 alkylaryl group, C6-20 aryl group, an OY group wherein Y is a C1-10 hydrocarbyl group, and optionally two adjacent R3 or R4 groups can be part of a ring including the phenyl carbons to which they are bonded;
• each R5, R5′, R6 and R6′ are independently hydrogen or a C1-20 hydrocarbyl group, optionally containing up to 2 silicon, oxygen, sulphur or nitrogen atoms, or an OY group wherein Y is a C1-10 hydrocarbyl group, and can be —CH═, —CY═, —CH2—, —CHY— or —CY2— groups that are part of a cyclic structure of 4 to 7 atoms, including the carbon atoms at positions 5 and 6 and/or 5′ and 6′ of the corresponding indenyl ligand;
• R7 and R7′, same or different from each other, are H or an OY group or a C1-20 hydrocarbyl group optionally containing up to two silicon, oxygen, sulphur or nitrogen atoms, with the proviso that when R7═H, then both R5, R6≠H, and when R7′═H, then both R5′,R6′≠H, and with the additional proviso that R5 and R6 can be hydrogen only when R7 is different from hydrogen and that R5′ and R6′ can be hydrogen only when R7′ is different from hydrogen;
• and
• wherein step (II) takes place in at least one gas phase reactor operating at a pressure of at least 26 bar.