Thermoplastic polyolefins with high flowability and excellent surface quality produced by a multistage process

1. A catalyst system, comprising:

(i) a Ziegler-Natta procatalyst which contains a trans-esterification product of a lower alcohol and a phthalic acid ester and

(ii) an organometallic cocatalyst and

(iii) external donor represented by the formula

Si(OCH 2 CH 3 ) 3 (NR x R y )

wherein R x and R y can be the same or different a represent a hydrocarbon group having 1 to 12 carbon atoms,

suitable for producing a reactor grade thermoplastic polyolefin in a multistage process with at least 3 polymerization steps,

said reactor grade thermoplastic polyolefin having an MFR (230° C.) of greater than 30 g/10 min and comprising

(A) 40-90 wt % of a propylene homo- or copolymer matrix with an MFR 2 in accordance with ISO 1133 (230° C., 2.16 kg load) of 200 g/10 min and

(B) 2-30 wt % of an elastomeric ethylene-propylene copolymer having an intrinsic viscosity IV (according to ISO 1628 with decalin as solvent) of ≤2.8 dl/g and an ethylene content of in the range of 50 to 75 wt % and

(C) 15-27 wt % of an elastomeric ethylene-propylene copolymer having an intrinsic viscosity IV (according to ISO 1628 with decalin as solvent) of 3.0-6.5 dl/g and a propylene content of 50 to 80 wt %.

2. The catalyst system according to claim 1 , wherein the Ziegler-Natta procatalyst (i) has been prepared by

a) reacting a spray crystallized or emulsion solidified adduct of MgCl 2 and a C 1 to C 2 alcohol with TiCl 4

b) reacting the product of stage a) with a dialkylphthalate of formula (I)

wherein R 1 ′ and R 2 ′ are independently at least a C 5 alkyl

under conditions where a transesterification between said C 1 to C 2 alcohol and said dialkylphthalate of formula (I) takes place to form an internal donor

c) washing the product of stage b) and

d) optionally reacting the product of step c) with TiCl 4 .

3. The catalyst system according to claim 2 , wherein the dialkylphthalate of formula (I) is dioctylphthalate and that the C 1 to C 2 alcohol is ethanol.

4. The catalyst system according to claim 1 , wherein the organometallic cocatalyst (ii) is selected from the group consisting of trialkylaluminium, dialkyl aluminium chloride and alkyl aluminium sesquichloride.

5. The catalyst system according to claim 4 , wherein the organometallic cocatalyst (ii) is triethylaluminium.

6. The catalyst system according to claim 1 , wherein the external donor (iii) is diethylaminotriethoxysilane.

7. The catalyst system of claim 1 , further comprising the reaction grade thermoplastic polyolefin produced by the catalyst system and said at least 3 polymerization steps.

8. The catalyst system of claim 2 , further comprising the reaction grade thermoplastic polyolefin produced by the catalyst system and said at least 3 polymerization steps.

9. The catalyst system of claim 3 , further comprising the reaction grade thermoplastic polyolefin produced by the catalyst system and said at least 3 polymerization steps.

10. The catalyst system of claim 4 , further comprising the reaction grade thermoplastic polyolefin produced by the catalyst system and said at least 3 polymerization steps.

11. The catalyst system of claim 5 , further comprising the reaction grade thermoplastic polyolefin produced by the catalyst system and said at least 3 polymerization steps.

12. The catalyst system of claim 6 , further comprising the reaction grade thermoplastic polyolefin produced by the catalyst system and said at least 3 polymerization steps.