Microphase Separation in Melts of Copolymer Bottlebrushes with Alternating A- and B-Types of Side Chains

We investigated the self-assembly capabilities of comb-shaped macromolecules with alternating side chains of different chemical types (A and B) in melts using dissipative particle dynamics. Due to the variety in the number of parameters controlling architecture/composition, the molecular structure of such objects can be finely tuned, thereby programming their self-assembly in melts. In the current work, we confine ourselves by considering two macromolecular architectures: (i) equal fractions of A and B side chains so that the elementary “building block” (segment) of the brush represents a linear triblock copolymer (A- d -B, d being a dimer from the backbone) and (ii) unequal fractions of A and B side chains so that the elementary segment corresponds to a branched (star-like) motif (one arm of a minor component (A) and few arms of the major component (B), all being connected by the backbone fragment). In the linear elementary segment regime, the presence of a long backbone enables stabilization of not only conventional morphologies like lamellae, perforated lamellae, and cylinders, but also structures with three-dimensional percolation: the double gyroid with bicontinuous percolation and the novel cocontinuous M 15 morphology. In the star-like elementary segment regime, molecular brushes tend to form morphologies with spherical domain types. We observed the conventional spheres ordered with the symmetry of the body-centered cubic lattice as well as Frank-Kasper σ-type spheres. It was also shown that the backbone directly influences Frank-Kasper sphere packing types, since individual star-like macromolecules not connected by a backbone can form Frank-Kasper A15-type spheres. Furthermore, materials based on molecular brushes with star-like elementary segments can exhibit microphase separation with unique viscoelastic properties due to polymer bridge formation between the domains.