Segmental Mobility of Polymer Chains under Molecular Confinement: Insights from Precision Molecular Bottlebrushes

Altering the properties of polymer chains under confinement represents fundamental challenges in polymer science. Molecular bottlebrushes (MBs), with their densely grafted architecture, create a unique constrained environment that serves as an ideal model system for exploring the structure–property relationships of confined molecular chains. In this work, we employed a Me6TREN/CuBr-catalyzed CuAAC click chemistry to synthesize precisely defined MBs with ultrahigh grafting densities (up to 6.2 side chains (SCs) per C–C repeating unit) via a reaction-enhanced reactivity of intermediates (RERI)-driven grafting-onto strategy. Using this approach, we prepared 65 MBs bearing tetraphenylethylene (TPE) units, a fluorescent moiety sensitive to mechanical strain, at tailored positions along poly(ethylene glycol) (PEG) SCs, including the interior segment, middle portion, and terminal end of the side chains. By systematically varying grafting density (Gdst), molecular weight, composition, and TPE location of SCs, as well as the backbone length, and correlating these with the luminescent behavior in both good and poor solvents, we elucidated the local segmental motion within the SCs. The results demonstrate that the mobility of the interior SC segments decreases initially in a linear manner with an increase of Gdst. Beyond a critical threshold, however, the decline in the mobility of segments follows a steeper linear trend. Moreover, the mobility of the SC segments away from the backbone increases significantly, even under dense grafting. This work not only clarifies how molecular parameters influence side-chain dynamics but also provides a theoretical basis for the design of advanced functional materials based on MBs.