Abstract: The invention relates to a copolyether ester composition for products that show particularly good aging behaviour when exposed to dynamic deformation at elevated temperatures and in contact with greases. The copolyether ester composition comprises a mixture of at least 2 copolyether esters A and B, composed of hard segments derived from at least one alkylene diol and at least one aromatic dicarboxylic acid and soft segments derived from at least one polyalkylene oxide glycol and at least one aromatic dicarboxylic acid, in which the concentration of soft segments X in A and the concentration of soft segments Y in B lie between 30 and 65 wt. %, relative to the copolyether ester and the molecular weights of X and Y lie between 500 and 3000 and |Mx−My|≧400.

Abstract: The invention relates to a novel copolyester elastomer essentially made up of A: hard polyester segments made up of repeating units derived from an aliphatic diol and an aromatic dicarboxylic acid and B: soft polyester segments made up of repeating units derived from B1: an aliphatic carbonate and, if desired, up to 60% by weight of B, B2: an aliphatic diol and an aliphatic dicarboxylic acid or B3: a lactone, said hard and soft segments being bonded via ester bonds to form copolyesterester units and said copolyesterester units being connected to one another by a urethane group.The novel copolyester elastomer has an exceptionally high thermo-oxidative resistance and resistance to hydrolysis and is used, inter alia, in bellows, seals, pipes, hoses and cable sheathings.