Precursor-driven bcc-fcc order-order transition of sphere-forming block copolymer/homopolymer blend

Yen Yu Huang, Jen Yung Hsu, Hsin Lung Chen*, Takeji Hashimoto

*Corresponding author for this work

Research output: Contribution to journalJournal Article peer-review

31 Scopus citations


We disclose a precursor-driven order-order transition (OOT) between bcc and fee lattices in a sphere-forming blend of a poly(ethylene oxide)-block-poly(1, 4-butadiene) (PEO-b-PB) and a PB homopolymer (h-PB). The blend as cast from toluene exhibited a metastable trapped fcc (t-fcc) phase, which showed no sign of transformation into bcc phase on heating to 260°C. Annealing the as-cast blend at -20°C disturbed the long-range order of t-fcc due to crystallization of PEO within the spherical microdomains. A significant portion of the rather disorderly arranged crystalline domains relaxed to grains having the equilibrium bcc lattice, when the PEO crystals were melted at elevated temperatures. The bcc grains thus developed then acted as the precursor to induce a transformation of t-fcc phase to bcc phase on heating up to 205°C. Since the t-fcc phase was not completely wiped out through this process, a bcc-to-fcc OOT assisted by the residual t-fcc precursor set in on heating from 205 to 260°C where fee became the stable packing symmetry. Subsequent cooling from 260°C recovered the bcc phase and the blend cooled to 110°C was essentially fee free. Because of the absence of fcc grain, the thermodynamically prescribed bcc-to-fcc OOT could no longer take place on reheating. Our results revealed the necessity of bcc or fee precursor for initiating the relevant OOT and hence implied a high activation barrier associated with the transition. The activation barrier was proposed to be entropie in origin stemming from the deformations of PB blocks and h-PB chains in the lattice transition proceeding through the Bain distortion mechanism.

Original languageEnglish
Pages (from-to)3700-3707
Number of pages8
Issue number10
StatePublished - 15 05 2007
Externally publishedYes


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