Thermoplastic polyesteramide elastomers with aromatic moieties were prepared and their structure-property relations were studied. The elastomers were synthesized by the polycondensation of 4,4'-methylenediphenyl diisocyanate, carboxylic acid-terminated poly(butylene adipate) oligomers and three different aliphatic dicarboxylic acids. Mixing between the hard and soft phases, examined by thermal and i.r. spectroscopic measurements, depended on the contents and the molecular weights of the poly(butylene adipate) oligomers and also on the types of the aliphatic dicarboxylic acids used. The dissolution of the hard polyamide segment into soft polyester domains increased with decreasing molecular weights of the constituent segments. The mixing was more effective when adipic acid, 1,10-decanedicarboxylic acid and azelaic acid (in increasing order of effectiveness) were used. A higher degree of phase mixing appeared to enhance the moduli of the elastomers but impair the tensile properties at high deformation. (C) 1997 Elsevier Science Ltd.