Formation of\nDisordered Cocontinuous Phases by Randomly\nLinked Star Copolymers

Cocontinuous polymeric nanostructures have garnered significant\ninterest due to their ability to combine different properties of two\nseparate polymer domains. Randomly linked copolymer networks have\nproven to be especially robust for formation of disordered cocontinuous\nphases across wide composition ranges (≈30 wt % or more). While\ntheoretical treatments of microphase-separated networks have focused\nprimarily on the role of random elastic forces imposed on the self-assembled\nnanostructures by virtue of the network architecture, experimental\nstudies seeking to disentangle these contributions from other potential\neffects, such as dispersity in preferred interfacial curvatures, have\nbeen scarce. To provide insight into this matter, we here study the\nself-assembly of randomly linked star copolymers (RSCs), constructed\nby linking premade polymer arms of polystyrene (PS) and poly(d,l-lactide) (PLA) using 3, 4, and 6-functional connectors.\nThis architecture yields similar distributions of preferred curvature\nas networks made using corresponding difunctional strands, but lacks\nthe elastic forces imposed by a network architecture. Gravimetry and\nsmall-angle X-ray scattering, coupled with scanning electron microscopy,\nwere performed to identify the percolation of PS/PLA RSCs. Remarkably,\nthe 4-arm RSC system exhibited a disordered cocontinuous window of\n≈25 wt %, indicating that dispersity in preferred curvature\ncan in some cases be sufficient to robustly drive formation of this\nmorphology. However, the other RSC architectures showed smaller cocontinuous\nranges, which we interpret in terms of the influence of homopolymer\nstars in the 3-arm case and the narrower distribution of preferred\ninterfacial curvatures in the 6-arm case. Finally, thin layers of\ninterconnected porous PS were achieved by solution-processing, suggesting\nthat RSCs have the potential to serve as a robust and easily processable\ncocontinuous polymeric nanomaterials in both bulk and membrane geometries.