Supported catalyst system for polymerizing alk-1-enes

A process for preparing catalyst systems for polymerizing C2-C12-alk-1-enes comprising

• A) an organic or inorganic support,
• B) at least one metallocene complex,
• C) oligomeric aluminum oxide compounds and
• D) at least one boron compound of the formula I
• or a cyclic boron compound of the formula II
• or mixtures of boron compounds I and II,
• where, in the formulae I and II, the substituents have the following meanings:
• R1 to R4 are each
• a C1-C20-alkyl group which may bear halogen atoms, C6-C15-aryl groups and/or C1-C10-alkoxy groups as substituents,
• a C4-C7-cycloalkyl group which may bear halogen atoms, C1-C10-alkyl groups and/or C1-C10-alkoxy groups as substituents,
• a C1-C10-alkoxy or alkyl sulfide group which may bear halogen atoms, C1-C10-alkyl groups and/or C6-C15-aryl groups as substituents,
• a C6-C15-aryl group which may bear halogen atoms, C1-C10-alkyl groups, C1-C10-haloalkyl groups, C4-C10-cycloalkyl groups, C6-C15-aryl groups, C1-C10-alkenyl groups, amino groups, monoalkylamino or dialkylamino groups, nitro groups, formyl groups, acetamido groups and/or C1-C10-alkoxy groups as substituents or
• a saturated or unsaturated C3-C15-heterocycle which contains from one to three oxygen, sulfur and/or nitrogen atoms in the ring system and may bear halogen atoms, C6-C15-aryl groups, further C3-C15-heterocycles and/or C1-C10-alkyl groups as substituents,
• furthermore, R1 to R4 are as defined above and additionally bear from one to three further B(OR′)(OR″) groups or, if R1 to R4 contain an aromatic ring, this is part of a metallocene system,
• R′ and R″ are identical or different and are each hydrogen or a C1-C10-alkyl group, prepared by a process wherein the components A), B) and C), are first combined and secondly, the boron compound(s) of the formula I or II or a mixture of I or II are added.