The molar stoichiometry and the crystal structure of four molecular complexes between poly(ethylene oxide) (PEO) and p-dichlorobenzene (PDCL), resorcinol (RES), hydroquinone (HYD) and p-nitrophenol (PNP) are compared. Even with a polymer weight fraction of 0.5, these molecular compounds form lamellar crystals when crystallized from the melt. The morphology of the lamellar crystals of these four PEO molecular complexes has been investigated in the early stages and after prolonged times of crystallization from the melt by time-resolved small-angle X-ray scattering coupled with wide-angle X-ray diffraction and differential scanning calorimetry. Non-integral-folded chain (NIFC) crystals are observed in the early stage of crystallization of PEO-RES and PEO-PNP molecular complexes from the melt. NIFC crystals of PEO-RES transform into integral-folded chain (IFC) and extended chain (EC) lamellar crystals with time. NIFC, 1-IFC and EC crystals can coexist in a sample of PEO-RES molecular complex. NIFC crystals of PEO-PNP do not transform into IFC or EC crystals even after long crystallization times or after heating until they melt. Stacks of IFC and EC crystals are present in the early stage of crystallization of PEO-HYD complexes at all the range of crystallization temperatures studied. The relative proportion of EC crystals of PEO-HYD increases with the crystallization temperature. PEO-PDCL forms only EC crystals at high crystallization temperatures (T-c > 50 degrees C). The type and magnitude of the interactions between host and guest molecules account for the different lamellar morphologies of these four molecular complexes. PEO-RES forms banded and unbanded spherulites in the temperature range 20 to 55 degrees C. Banded spherulites are metastable and transform into unbanded spherulites through a solid-phase transition.