Engineering Macromolecular Rigidity to Diversify Morphologies in Dendronized-Bottlebrush Block Copolymers

Ordered nanostructures exhibit great potential in various applications, including catalysts, functional membranes and photonic crystals. Bottlebrush block copolymers (BBCPs) offer a versatile platform for constructing complex nanostructures owing to their unique chain architectures and amplified conformational asymmetry. However, how macromolecular rigidity regulates chain conformation and subsequently dictates phase selection in highly asymmetric BBCPs remains elusive. Here, we establish a molecular rigidity engineering strategy to manipulate hierarchical self-assembly in dendronized-bottlebrush BBCPs. A series of asymmetric poly(norbornene benzyl)-block-poly(norbornene-graft-polydimethylsiloxane) (PNBn-b-PDMS) dendronized-bottlebrush BCPs were designed by integrating the dendronized PNBn block with the PDMS block, enabling systematic regulation of backbone rigidity. We reveal that the variation of macromolecular rigidity governs the competition among chain stretching, interfacial curvature, and packing frustration, leading to distinct phase-selection pathways. In particular, an intermediate rigidity window promotes balanced interfacial deformation and stabilizes a rich library of complex mesophases, including Frank Kasper A15, single diamond, and gyroid structures, whereas excessive rigidity or flexibility favors conventional morphologies. Furthermore, by extending the characteristic periodicities into the visible-light wavelength range, two-dimensional columnar photonic crystals with tunable structural colors were achieved. This work elucidates the pivotal role of macromolecular rigidity in directing self-assembly of asymmetric dendronized-bottlebrush BCPs and provides a molecular design principle for developing advanced photonic materials and functional nanostructures.