Architecturally Semiflexible Bottlebrush-Based Block Copolymers

For block copolymer (BCP) self-assembly, classical understanding is that domain spacing is limited by the contour length of the polymer backbone. We discover that this molecular picture does not hold for architecturally semiflexible block copolymers. For strongly segregated linear–semiflexible bottlebrush–linear triblock copolymers, the bottlebrush can rearrange its constituent linear side chains to form domains remarkably larger than the contour length of the bottlebrush backbone. Moreover, the semiflexible bottlebrush widens the regime for the cylinder morphology that is associated with the volume fraction of the end blocks f_C^SFB ∈ (0.10, >0.41), much wider than that for flexible linear BCPs, f_C^F ∈ (0.14, 0.35). Further, we propose a modified Halpin-Tsai model to describe the shear modulus G of polymers with cylinder morphology:G = G_m(1+ζf)/(1–f), in which G_m is the shear modulus of bottlebrush matrix and ζ is an adjustable parameter that describes the grain size relative to the fiber diameter.. Our results not only reveal previously unexplored molecule-structure-property relation of self-assembled bottlebrush polymer networks, but also provide a new class of soft, solvent-free, and reprocessable polymeric materials with a wide range of controllable stiffnesses.