Abstract: The invention relates to use of an additive as oxygen barrier in a plastic material wherein (a) the plastic material is a polyolefin, a polyolefin copolymer or a polystyrene, and the additive is (b) and optionally (c): (b) a compound of formula (I); wherein Ra represents C7-C20 alkyl, C6-C10 aryl, C4-C10 heteroaryl, wherein the heteroatoms are N, O and/or S, (C2-C6)-alkenylen-(C6-C10) aryl, C1-C6-alkylen-C6-C10-aryl, the aryl and heteroaryl radicals optionally being substituted by: hydroxyl, C1-C6-alkyl, C1-C6 alkoxyl, C6-C10 aryloxy, halogen, cyano, nitro, C6-C10-aryl, di(C1-C6)alkylamino, (C1-C6)alkylthio, C6-C10-arylthio, ?O, ?S, SO3H, SO2NR1R2, CO2R3, CONR1R2, NHCOR4, CO—C6-C10-aryl or a combination thereof, wherein R1, R2, R3, R4 are the same or different and independently represent hydrogen or Rb represents a group selected from the moieties of formula (II), (III), (IV), (V), (VI) and (VII); wherein each Rc can be the same or different and independently represents hydrogen, C1-C20