Process for the production of a thermoplastic polymer comprising segments of a diamide, the process comprising: 1) a first step of preparing a reaction mixture comprising a diamine H2N—Y—NH2 Form. (I), and a diester of a dicarboxylic acid Form. (II) 2) a second step of heating the reaction mixture to a temperature at least 5° C. above the crystallization temperature of the diester and a least 5° C. below the melting temperature of the formed amide (formula III) in the presence of an alkaline or earth alkaline alkoxy catalyst Form. (III) wherein X and Y are the same or different and are an aliphatic group comprising 2-12 carbon atoms or an aromatic group comprising 6-20 carbon atoms, R1 and R2 are the same or different and are an aliphatic group comprising 2-15 carbon atoms and wherein R equals R1 or R2 and are the same or different. 3) optionally a third step of quenching the catalyst of the reaction mixture obtained in the second step by adding an acid to the reaction mixture and 4) a fourth step of adding further components to the reaction mixture obtained in the second step, or if the third step has been applied to the reaction mixture obtained in the third step, and so producing the thermoplastic polymer comprising the segments of the diamide.