Phase Behavior of Star-Shaped Polystyrene-block-poly(methyl methacrylate) Copolymers

The phase behavior of 18-arm star-shaped polystyrene-block-poly(methyl methacrylate) copolymers ((PS-b-PMMA)18) with various volume fractions of PMMA block (fPMMA) was investigated by transmission electron microscopy and small-angle X-ray scattering. (PS-b-PMMA)18 was synthesized by atom transfer radical polymerization from α-cyclodextrin (α-CD) having 18 functional groups for the initiation. We also prepared the corresponding linear PS-b-PMMAs by cutting the ester groups connecting α-CD and PS chains in (PS-b-PMMA)18 through the hydrolysis. The microdomains of (PS-b-PMMA)18 changed from body-centered-cubic spheres (BCC), hexagonally packed cylinders (HEX), perforated lamellae (PL), and lamellae (LAM), with increasing fPMMA from 0.3 to 0.8. Interestingly, (PS-b-PMMA)18 with fPMMA of 0.77 showed highly asymmetric lamellar microdomains, while the corresponding linear PS-b-PMMA with the same volume fraction should not have lamellar microdomains. Thus, the microdomains are highly affected by the molecular arc...