Chain branching agent and polyamide composition containing the same

The invention relates to a chain branching agent containing anhydride groups, which chain branching agent contains. (a) 5-75 mass % of a copolymer of at least an unsaturated dicarboxylic acid or a derivative thereof and a vinyl aromatic monomer; (b) 5-75 mass % of a copolymer of acrylonitrile and a vinyl aromatic monomer, (c) 0-80 mass % of an inert processing aid; and (d) 0-10 mass % customary additives; and in which (a) and (b) are miscible, the ratio (a)/(b) is from 1/3 to 3/1, and the total of (a)+(b)+(c)+(d) is 100%. Advantages of this chain branching agent in the preparation of, for instance, a polyamide composition with non-Newtonian melt flow behaviour include better reproducibility and strongly decreased formation of gel particles. The invention also relates to processes for the preparation of a chain branching agent and of a polyamide composition with non-Newtonian melt flow behaviour as well as to the use of such a polyamide composition for the manufacture of moulding articles.