Process for the preparation of a polypropylene molding composition

A polypropylene molding composition which comprises:

• (1) 20 to 99% by weight of a crystalline polymer which comprises to the extent of at least 95% by weight of polymerized propylene and
• (2) 1 to 80% by weight of a non-crystalline ethylene-propylene copolymer having an ethylene content of 20 to 90% by weight,
• in which first the polymer (1) is prepared in one or more stages in liquid propylene over a residence time of 15 to 400 minutes under a pressure of 5 to 100 bar and at a temperature of 0.degree. to 100.degree. C., and the polymer (2) is prepared in a second stage over a residence time of 10 to 180 minutes, under a pressure of 5 to 49 bar and at a temperature of 0.degree. to 100.degree. C. in the presence of ethylene, in the presence of a catalyst which comprised of a transition metal compound and an organoaluminum compound, which comprises carrying out the polymerization in the second stage in solution or in suspension, and using a transition metal compound which is a metallocene of the formula I ##STR11## in which M.sup.1 is a metal of group IVb, Vb or VIb of the periodic table,
• R.sup.1 and R.sup.2 are identical or different and are a hydrogen atom, a C.sub.1 -C.sub.10 -alkyl group, a C.sub.1 -C.sub.10 -alkoxy group, a C.sub.6 -C.sub.10 -aryl group, a C.sub.6 -C.sub.10 -aryloxy group, a C.sub.2 -C.sub.10 -alkenyl group, a C.sub.7 -C.sub.40 -arylalkyl group, a C.sub.7 -C.sub.40 -alkylaryl group, a C.sub.8 -C.sub.40 -arylalkenyl group or a halogen atom,
• R.sup.3, R.sup.4, R.sup.5 and R.sup.6 are identical or different and are a hydrogen atom, a halogen atom, a C.sub.1 -C.sub.10 -alkyl group, --NR.sub.2.sup.10,, --SR.sup.10, --OSiR.sub.3.sup.10, --SiR.sub.3.sup.10 or PR.sub.2.sup.10, in which R.sup.10 is a halogen atom or a C.sub.1 -C.sub.10 -alkyl group, or in each case two adjacent R.sup.3, R.sup.4, R.sup.5 or R.sup.6 form a ring with the carbon atoms joining them,
• R.sup.7 is ##STR12## .dbd.BR.sup.11, .dbd.AlR.sup.11, --Ge--, --Sn--, --O--, --S--, .dbd.S.dbd.O, .dbd.SO.sub.2, .dbd.NR.sup.11, .dbd.CO, .dbd.PR.sup.11 or .dbd.P(O)R.sup.11, in which
• R.sup.11, R.sup.12, R.sup.13, R.sup.14 and R.sup.15 are identical or different and are a hydrogen atom, a halogen atom, a C.sub.1 -C.sub.10 -allyl group, a C.sub.1 -C.sub.10 -fluoroalkyl group, a C.sub.6 -C.sub.10 -aryl group, a C.sub.6 -C.sub.10 -fluoroaryl group, a C.sub.1 -C.sub.10 -alkoxy group, a C.sub.2 -C.sub.10 -alkenyl group, a C.sub.7 -C.sub.40 -arylalkyl group, a C.sub.8 -C.sub.40 -arylalkenyl group or a C.sub.7 -C.sub.40 -alkylaryl group, or R.sup.11 and R.sup.12 or R.sup.11 and R.sup.13 form a ring, in each case with the atoms joining them,
• M.sup.2 is silicon, germanium or tin,
• p is 1, 2 or 3,
• R.sup.8 and R.sup.9 are identical or different and are a group .dbd.CR.sup.11 R.sup.12, in which R.sup.11 and R.sup.12 have the above-mentioned meaning, and
• m and n are identical or different and are zero, 1 or 2, m+n being zero, 1 or 2, and an organoaluminum compound which is an aluminoxane of the formula II ##STR13## for the linear type and/or of the formula III ##STR14## for the cyclic type, in which R.sup.16 is a C.sub.1 -C.sub.6 -alkyl group and q is an integer from 2 to 50.