The bulk morphology of poly(1,4-butadiene)-block-polystyrene-block-poly (ethylene oxide) (PB-b-PS-b-PEO) and polyethylene-block-polystyrene-block-poly (ethylene oxide) (PE-b-PS-b-PEO) triblock terpolymers is analyzed under a thermal protocol. This allows the investigation of the morphology during the occurrence of thermal transitions, such as crystallization and melting, which is a neat way of studying the competition between microphase separation and crystallization for the morphology formation. Only one of the studied systems presented a morphological transition upon melting of the PEO and the PE blocks, attributed to the crystallization of the PE block in finite interconnected domains. All the other systems presented no morphological transitions during the thermal scan. The results prove that the crystallization only disrupt the microphases generated in the molten state under very specific circumstances for these block copolymers. (c) 2007 Wiley Periodicals, Inc.