Strictly alternating polyesteramides consisting of 1,4-butylene terephthalamide diester and mixtures of aliphatic diols have been synthesised in the melt in the presence of a titanium catalyst. To increase the molecular weight a solid state post condensation was applied. The composition was determined with H-1 NMR. The thermal properties were analysed with differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). With the mixture of diols the structural regularity of the diester part in polymers was disturbed. Although this disturbance caused the polymers to be fast crystallising (Delta T < 32 degrees), highly crystalline polymers. It was found that the melting temperature decreased linearly with increasing length of the diols in the mixture. The melting temperatures with the mixtures of diols were lower than with a single diol. The reason for this is probably thinner lamella. Mechanical tests on the melt processed polyesteramides showed high glass transition temperatures and a high modulus above the glass transition temperature. These polyesteramides have a T-g/T-m ratio of 0.70-0.72. This high ratio is probably due to the relatively low melting temperatures. The water absorption, is close to the values for polyesters (1.3-1.7 wt%). Disturbing the alternating structure of the polyesteramide by esteramide interchange reactions resulted in a loss of the thermal and mechanical properties. (C) 1997 Elsevier Science Ltd.