Two symmetrical imide diacids were prepared from trimellitic anhydride and two alpha,omega-diamines containing ether linkages, namely 1,8-diamino-3,6-dioxaoctane and 1,12-diamino-4,9-dioxadodecane. Polycondensations in the melt of the imide diacids and diacetyl bisphenols yielded the corresponding series of poly(ester imide)s (PEIs), characterized by an alternating sequence of stiff. aromatic imide units and ether-containing aliphatic spacers. The presence of -O- linkages within the flexible spacers greatly affected the thermal transitions and the thermotropic behaviour of the PEIs. Comparison with homologous PEIs without ether linkages revealed lower glass transition temperatures and a weaker tendency to form liquid crystal mesophases. Only the PEIs from 4,4’-dihydroxybiphenyl showed a regular thermotropic behaviour, as could be proved by optical microscopy with crossed polarizers, by d.s.c. and by synchrotron radiation measurements at variable temperature. These PEIs form layer structures in the solid and liquid state. The textures suggest the formation of a smectic-A phase.