The present invention relates to a mixture comprising the components (A) and (B) and optionally the further component (C). Component (A) comprises at least one bismuth- containing catalyst which is defined by the general formula (I) detailed in the subsequent text. The bismuth-containing catalyst comprises at least one radical R1, which comprises a carboxyl fragment according to the general formula (II), wherein a 10 first carbon atom (α-carbon) is bonded to the carbon atom of the carboxyl group, which in turn is directly substituted with at least one aromatic system. Component (B) of the inventive mixture is at least one hydrocarbon compound containing two hydroxyl groups ("diol"). The optionally present component (C) is at least one solvent.