Patent ID: 7084236

Claim:
A polymer with structural units in accordance with formula I, in which Ar is an aromatic cyclic system with 4 to 20 carbon atoms with optionally a single or multiple substitution with a group consisting of a non-branched C 1 –C 20 -alkyl, C 3 –C 20 -alkoxy, C 1 –C 20 -alkylsulphate, a branched C 3 –C 20 -alkyl, phenyl, or benzyl group, and which may optionally comprise up to 4 hetero atoms selected from the group consisting of oxygen, sulfur, and nitrogen in the aromatic cyclic system, R 2 and R″ 2 are selected from a the group consisting of a C 1 –C 20 -alkyl and a C 4 –C 20 -aryl group, which groups may optionally comprise substituents, characterized in that the polymer has a number average molecular weight which is below 300×10 3 g/mole, and in that the polymer has a weight average molecular weight which is below 500×10 3 g/mole.