The bulk morphology of a crystalline/amorphous diblock copolymer under different thermal, conditions was studied. The diblock copolymer, poly((ethylene oxide)-b-1,4-polybutadiene), forms a microphase-separated lamellar morphology in the molten state. For samples crystallized within the range of 20-50 degreesC, TEM coupled with electron diffraction revealed a microphase-separated, alternating lamellar morphology with the PEO crystalline chains oriented perpendicular to the interface between the PEO and PBD domains. A significant increase in the microphase-separated, lamellar domain spacing was observed upon crystallization. On the length scale of tens of microns, as probed by polarizing optical microscopy, a nonspherultic crystalline texture (with the absence of the Maltese cross), corresponding to the microphase-separated lamellar grain morphology, was observed. In contrast to the integral chain folding observed in PEO homopolymer, the increase in PEO lamellar thickness with decreasing undercooling is continuous in the block copolymer. In addition, the equilibrium melting temperature and lamellar spacing were determined.