Catalyst masterbatch

1. A catalyst masterbatch for cross-linking a polyolefin comprising cross-linkable silicon-containing groups comprising

a Brønsted acid and/or Brønsted acid anhydride (A); and

a polyolefin (B) containing Brønsted acid anhydride groups,

wherein the Brønsted acid and/or Brønsted acid anhydride (A) are selected from carboxylic acids, carboxylic acid anhydrides, sulphonic acid and/or sulphonic acid anhydrides;

wherein (A) is present in an amount of from 0.5 to 20 wt %, and

wherein (B) is present in an amount of from 15 to 99 wt % based on the total weight of the catalyst masterbatch.

2. The catalyst masterbatch according to claim 1 , wherein component (B) is an ethylene homo- or copolymer or propylene homo- or copolymer.

3. The catalyst masterbatch according to claim 1 , wherein component (B) contains Brønsted acid anhydride groups in a total amount of 0.01 to 20 wt. % based on the total amount of component (B).

4. The catalyst masterbatch according to claim 1 , wherein the catalyst masterbatch contains Brønsted acid groups and/or Brønsted acid anhydride groups in a total amount of 0.2 to 25 wt. % based on the total amount of the catalyst masterbatch.

5. The catalyst masterbatch according to claim 1 , wherein the sulphonic acid comprises the structural element (II)

aromatic organic sulphonic acid comprising the structural element (II)

Ar(SO 3 H)x   (II)

with Ar being an aryl group which may be substituted or non-substituted, and x being at least 1.

6. The catalyst masterbatch according to claim 5 , wherein the sulphonic acid is selected from the following compounds:

(i) an alkylated naphthalene monosulfonic acid substituted with 1 to 4 alkyl groups wherein each alkyl group is a linear or branched alkyl with 5 to 40 carbon atoms with each alkyl group being the same or different and wherein the total number of carbon atoms in the alkyl groups is in the range of 20 to 80 carbon atoms;

(ii) an arylalkyl sulfonic acid wherein the aryl group is phenyl or naphthyl and is substituted with 1 to 4 alkyl groups wherein each alkyl group is a linear or branched alkyl with 5 to 40 carbon atoms with each alkyl group being the same or different and wherein the total number of carbon atoms in the alkyl groups is in the range of 12 to 80;

(iii) an alkylated aryl disulfonic acid selected from the group consisting of the structure (III):

or the structure (IV):

wherein each of R 1 and R 2 are the same or different and is a linear or branched alkyl group with 6 to 16 carbon atoms, y is 0 to 3, z is 0 to 3 with the proviso that y+z is 1 to 4, n is 0 to 3, X is a divalent moiety selected from the group consisting of

—C(R 3 )(R 4 )—, wherein each of R 3 and R 4 is H or independently a linear or branched alkyl group of 1 to 4 carbon atoms and n is 1;

—C(═O)—, wherein n is 1;

—S—, wherein n is 1 to 3 and

—S(O)2—, wherein n is 1.

7. The catalyst masterbatch according to claim 6 , wherein the sulphonic acid is selected from compounds of group (ii).

8. The catalyst masterbatch according to claim 7 , wherein in the sulphonic acid of group (ii) the aryl group is phenyl and is substituted with 1 to 2 alkyl groups wherein each alkyl group is a linear or branched alkyl with 8 to 25 carbon atoms with each alkyl group being the same or different and wherein the total number of carbon atoms in the alkyl groups is in the range of 12 to 40.

9. The catalyst masterbatch according to claim 5 , wherein the sulphonic acid is selected from the following compounds:

(ii) an arylalkyl sulphonic acid wherein the aryl group is phenyl or naphthyl and is substituted with 1 to 4 alkyl groups wherein each alkyl group is a linear or branched alkyl with 5 to 40 carbon atoms with each alkyl group being the same or different and wherein the total number of carbon atoms in the alkyl groups is in the range of 12 to 80; or

(iv) an alkylated aryl disulphonic acid selected from the group consisting of the structure (III):

or the structure (IV):

wherein each of R 1 and R 2 are the same or different and is a linear or branched alkyl group with 6 to 16 carbon atoms, y is 0 to 3, z is 0 to 3 with the proviso that y+z is 1 to 4, n is 0 to 3,

X is a divalent moiety selected from the group consisting of —C(R 3 )(R 4 )—,

wherein each of R 3 and R 4 is H or independently a linear or branched alkyl group of 1 to 4 carbon atoms and n is 1;

—C(═O)—, wherein n is 1;

—S—, wherein n is 1 to 3 and

—S(O)2—, wherein n is 1.

10. A method for cross-linking a polyolefin with cross-linkable silicon-containing groups (C) comprising adding the masterbatch according to claim 1 , to the polyolefin (C) to form a polyolefin composition; and treating the polyolefin composition under cross-linking conditions.

11. A cable layer comprising the catalyst masterbatch according to claim 1 .