Session D40 - Poster Session I.
POSTER session, Monday afternoon, March 12
Exhibit Hall, Washington State Convention Center
The evolution of the morphology of a crystalline/amorphous diblock copolymer poly(ethylene oxide -b- 1,4 butadiene) (P(EO-b-BD)) upon crystallization in thin films was studied via interference optical microscopy. Two-dimensional crystallization confined within the PEO lamellar layers was observed with retention of the microphase separated lamellar morphology formed in the melt-state. The morphology was further characterized by TEM and electron diffraction which showed it to consist of alternating layers of PEO and PBD with PEO crystalline chains oriented perpendicular to the lamellar layers of the microphase separated structure. Multiple parallel layers of crystalline PEO were found by electron diffraction to be in crystallographic registry even though they were separated by approximately 10 nm thick layers of amorphous PBD. This behavior can only occur if the PEO crystals in adjacent layers originate from the same nucleus and there is an interconnection between layers. The strong immiscibility of PEO and PBD restricts layer interconnection to defect structures such as edge and screw dislocations that may provide connections for crystallites among different layers. Furthermore, the lamellar spacing and melting temperature increases as the degree of undercooling decreases as indicated by interference optical microscopy and atomic force microscopy. In contrast to the integral chain folding observed in PEO homopolymer, the increase in lamellar thickness with decreasing undercooling is continuous. This indicates that the PEO crystalline chains in P(EO-b-BD) were non-integral chain folded.