Crystallization-induced microdomain coalescence in sphere-forming crystalline-amorphous diblock copolymer systems: Neat diblock versus the corresponding blends

Crystallization in the microdomains of crystalline-amorphous diblock copolymers may induce domain coalescence when the crystallization temperature lies above the T_g of the amorphous matrix. In this study, the perturbation of microdomain structure driven by isothermal crystallization and postannealing in a poly(ethylene oxide)-block-poly(1,4-butadiene) (PEO-b-PB) and PEO-b-PB/PB homopolymer (h-PB) blends consisting of spherical PEO domains in the melt state is systematically investigated to reveal whether the presence of homopolymer in the amorphous matrix would hinder or facilitate the microdomain coalescence driven by the crystallization. Three samples with nearly the same volume fraction and length of PEO block are adopted for the study; the first is an asymmetric PEO-b-PB that contains no h-PB, the second is a blend containing 12 wt % of h-PB, and the third is a blend consisting of 63 wt % of h-PB. Characterization of the domain structure after isothermal crystallization and postannealing treatment by SAXS and TEM indicates that the blend containing the higher h-PB content exhibits the stronger resistance against microdomain coalescence. The resistance is proposed to stem from the diffusion barrier associated with the rejection of a portion of h-PB originally dissolved in the coronal regions of the micelles during the coalescence process.