Various poly(ester-imide)s of N-(4-carboxyphenyl)trimellitimide were prepared by transesterification of its dimethyl ester with various aliphatic diols. The following spacers were used : combinations of different alpha,omega-dihydroxyalkanes, mixtures of 1,12-dihydroxydodecane and tetraethylene glycol, neat di-, tri-, and tetraethylene glycol, and diols containing sulfide groups. Poly(ester-imide)s containing alkane spacers form layer structures in the solid state but neither monotropic nor enantiotropic liquid-crystalline (LC) phases. The three different kinds of solid state observed for these poly(ester-imide)s were interpreted as frozen smectic-A, -B, and -E phases. Spacers containing sulfide bonds yield poly(ester-imide)s which may form two different smectic crystal modifications but again no enantiotropic LC phase. Poly(ethylene oxide) spacers tend to suppress the crystallization and prevent the formation of layer structures. Taking also into account further results from the literature, we interpret the formation of layer structures as a phase separation on the nanometer level.