Morphology of a crystalline/amorphous diblock copolymer: Poly((ethylene oxide)-b-butadiene)

The bulk morphology of a crystalline/amorphous diblock copolymer under diff erent thermal, conditions was studied. The diblock copolymer, poly((ethylen e oxide)-b-1,4-polybutadiene), forms a microphase-separated lamellar morpho logy in the molten state. For samples crystallized within the range of 20-5 0 degreesC, TEM coupled with electron diffraction revealed a microphase-sep arated, alternating lamellar morphology with the PEO crystalline chains ori ented perpendicular to the interface between the PEO and PBD domains. A sig nificant increase in the microphase-separated, lamellar domain spacing was observed upon crystallization. On the length scale of tens of microns, as p robed by polarizing optical microscopy, a nonspherultic crystalline texture (with the absence of the Maltese cross), corresponding to the microphase-s eparated lamellar grain morphology, was observed. In contrast to the integr al 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 wer e determined.