Au-Catalyzed Bromination Enables Access to Hypercomb Libraries with Uniform Branching Subchains and Diverse Functionalities: From Flexible Backbone to Rigid Architecture

The integration of rigidity into hyperbranched polymers represents a frontier in manipulating their conformation and properties, yet it remains challenging due to the lack of a robust functionalization platform that preserves structural integrity. This study establishes a versatile Au-catalyzed C–H bromination platform for long-subchain hyperbranched polystyrene (LH-PS), enabling precise side-chain postpolymerization modification. We systematically evaluated three functionalization pathways, revealing that the Au/NBS system is incompatible with sensitive click-chemistry handles (alkyne, azide) in linear precursors (synthetic pathways 1 and 2). Crucially, a postpolymerization bromination strategy (pathway 3) was developed, successfully modifying preformed LH-PS scaffolds to generate a well-defined brominated product, i.e., LH-PS-Br. This key intermediate served as a springboard for diverse C–C couplings to introduce functional groups (X), i.e., LH-PS-X. Through a combined Sonogashira and click-coupling approach, the polystyrene side chains can be introduced to yield a novel architecture termed Hypercomb, and this postpolymerization approach circumvents the excessive azidation and gelation side reactions that can arise from copolymerization methods. Based on the results of light scattering on the fractionated product and computational simulation on the model system, it was revealed that side-chain grafting of PS 10 dramatically increases backbone rigidity, leading to significant segment interpenetration: the Mark–Houwink exponent α plummeted from 0.72 (linear chain) to 0.59 (flexible hyperbranched chain), and to 0.27 ( Hypercomb ), corresponding to the fractal dimension ( D f ) of 2.4, signifying a transition to a more condensed conformational state with segment interpenetration feature. This work provides a general strategy for designing hyperbranched materials with increased rigidity, tailored side-chain structures and functions.