Two different series of poly(ester imide)s, which are distinguished from each other in the orientation of the ester Linkages and show well-differentiated thermotropic behavior, are investigated by means of model calculations and dielectric relaxation spectroscopy. Model calculations show that the orientation of the ester linkages has a strong influence on the rotational energy barriers. The dielectric relaxation spectra of both series shows three relaxation regions in the temperature range between 100 and 400 K that have been identified as the alpha-, beta- and gamma-relaxation processes. A difference of about two orders of magnitude between the characteristic rates of the gamma-relaxation is the main feature observed in the dielectric response. However, the beta-relaxation shows very similar behavior for both series. The differences in the relaxation behavior in the solid state are interpreted on the basis of the rotational barriers deduced from the model calculation results.