Verfahren zur Stabilisierung der Schmelzeviskositaet von Zinn-, Titan- und/oder Zirkoniumverbindungen als Katalysator und/oder Initiator enthaltender aliphatischer oder aromatisch-aliphatischer Homo- oder Copolyester und Verwendung einer Verbindung, die mindestens einen Tropolonring aufweist als Maskierungsmittel in Polyesterschmelzen

Stabilising the melt viscosity of aliphatic or aromatic-aliphatic homo- or co-polyesters contg. Sn, Ti and/or Zr cpds. as catalysts/initiators involves adding a masking agent contg. a cpd. with at least one tropolone ring (I) to the melt obtd. in the synthesis or reprocessing of the polyester. Pref. masking agent (I) is alpha-tropolone, thujaplicin, purpurogallin or a mixt. thereof. The polyester is obtd. by ring-opening polymerisation or melt polycondensation in presence of initiators/catalysts. (I) is added in an excess of upto 2 wt% w.r.t. initiator/catalyst, opt. together with filler and/or reinforcing material and/or nucleating agent and/or delustering agent. (I) is intimately mixed with the polyester; in the case of reprocessing, (I) may be added to the melt obtd., or added before or during reprocessing. USE - Cpds. (I) are used as masking agents in polyester melts as above (claimed). ADVANTAGE - Stabilises (co)polyesters against thermal and/or thermo-oxidative degradation during melt processing to fibres, film or moulded prods. or during recycling by melt-sepn. processes.