Polydispersity Stabilized Complex Morphologies in Poly(styrene-b-methyl methacrylate) Diblock Copolymers

Block copolymers have the unique property to self-assemble into ordered microstructures with well-defined periodicity. Among the various attainable microdomain morphologies, complex bicontinuous morphologies are highly desirable due to their inherent structural connectivity. While such complex structures are difficult to obtain in monodisperse block copolymers, they may be stabilized by increasing block dispersity. In this study, we synthesized a series of poly(styrene-b-methyl methacrylate) (PS-PMMA) diblocks where dispersity of both blocks were systematically varied. The domain morphologies of the resulting diblocks were examined by combination of small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). At fixed volume fraction of the PS block, dispersity dictated phase transition was observed. In particular, in the case where dispersity of both blocks were high, the polymers were found to exhibit perforated lamellae (PL) and disordered bicontinuous (BIC) morphologies. These results showed that dispersity control can be used to widen the accessibility window for complex morphologies in block copolymers.