The phases behavior of poly(ester imide)s (PEI) based on trimellitic anhydride, 4-aminocinnamic acid and alpha,omega-dihydroxydodecane (n = 12) or alpha,omega-dihydroxyhexadecane (n = 16), resp., have been investigated by X-ray measurements employing synchrotron radiation. Both PEIs form monotropic LC phases which can be quenched into the glassy state. Due to the regular sequence of rigid, polar mesogens and flexible, non-polar spacers smectic phases are formed in the melt and in the solid state, giving rise to sharp X-ray reflections. During transition from the smectic LC phase to the higher ordered smectic crystalline phase these layer reflections shift towards larger scattering angles indicating a narrowing of the layers due to tilting of the mesogens with respect to the layer plane. X-ray fiber pattern indicate that this tilting already occurs in the Frozen LC phase (S-C). The chains are oriented preferably parallel to the fiber direction while the staggering of the mesogens orients the layers inclining an angle of about beta = 20 degrees. During crystallization the mesogens reptate longitudinally in order to fit the lateral lattice and the tilt angle increases up to 41 degrees (n = 12) and 35 degrees (n = 16) (S-H). Isothermal experiments reveal that PEI (n = 12) is capable of forming two different smectic-H phases depending on the thermal treatment. Above 130 degrees C S-H1(beta = 32 degrees, d = 27 Angstrom) is formed preferably whereas S-H2 (beta = 41 degrees, d = 24 Angstrom) dominates below 140 degrees C.