Preparation of a copolyether ester

The invention relates to an improved process for the preparation of a copolyether ester. Copolyether esters are thermoplastic elastomer polymers built up of hard polyester segments of repeating units derived from at least one alkylene glycol and at least one aromatic dicarboxylic acid or an ester thereof and soft segments derived from a polyalkylene oxide glycol. Such a copolyether ester is generally prepared by a process involving the combining in the melt of at least one alkylene glycol, at least one aromatic dicarboxylic acid or an ester thereof and the polyalkylene oxide glycol. If an ester of an aromatic dicarboxylic acid is started from, for instance the dimethyl ester of terephthalic acid, then first a transesterification reaction takes place upon which the alkylene glycol and the polyalkylene oxide glycol take the methyl position in the aromatic dicarboxylic acid ester, with the methanol, which is volatile under the transesterification reaction conditions, being separated off. If the aromatic dicarboxylic acid is present in place of the ester, then esterification with the glycols takes place directly. Subsequently, polycondensation of the ester to yield polyester, in the case specified here copolyether ester, takes place under reaction conditions that are generally different from those of the transesterification or esterification. The polycondensation in the melt is then continued until a polycondensate with the desired molecular weight is obtained. The invention relates to a process for the preparation of a copolyether ester built up of hard polyester segments of repeating units derived from at least one alkylene glycol and at least one aromatic dicarboxylic acid or an ester thereof and soft segments derived from at least one polyalkylene oxide glycol, which comprises polymerization by condensation in the melt of at least one aromatic dicarboxylic acid, at least one alkylene glycol and at least one polyalkylene oxide glycol, in the presence of a catalyst based on a combination of titanium and a bivalent metal in a single compound or several compounds, characterized in that the molecular ratio of Ti:bivalent metal is at most 1.6, preferably at most 1.5.The invention leads to a substantial shortening of the polycondensation time in the melt or a higher degree of polymerization of the copolyether ester. The solid-phase post-condensation can also be shortened substantially.The process is effective in particular for copolyether esters with a high soft