AIE Bottlebrush Polymers: Verification of Internal Crowdedness in Bottlebrush Polymers Using the AIE Effect

Bottlebrush polymers, characterized by densely grafted side chains along a central backbone, have gained significant interest due to their unique properties in bulk and solution states. Despite extensive research, a comprehensive understanding of the internal crowdedness within single polymer chains in dilute solutions remains challenging, and direct evidence to visualize and manifest this effect is scarce. Aggregation-induced emission (AIE) offers a novel method to address this challenge. To achieve this, a vinyl-derivatized AIE monomer was polymerized using atom transfer radical polymerization (ATRP) in a controlled way. Afterward, the end group of the synthesized polymer chain was transformed to azide, which was coupled with an alkyne-derivatized norbornene unit using click chemistry to produce the macromonomer. Ring-opening metathesis polymerization (ROMP) of the norbornenyl macromonomer using Grubbs catalyst, (H₂IMes)(pyr)₂(Cl)₂Ru = CHPh (G3), resulted in well-defined bottlebrush polymers in a highly efficient way. We studied the polymerization behavior and characterized the single chain conformation of the bottlebrush polymers in dilute solution together with coarse-grained molecular dynamics (CG-MD) simulation. Photoluminescence investigation of the bottlebrush polymers in dilute solution revealed the expected AIE phenomenon, thus verifying the steric crowding effects within bottlebrush polymers. This work bridges AIE technology with polymer science and especially bottlebrush polymers. By doing this, our research not only broadens the bottlebrush polymer library but also provides insights into bottlebrush polymer chain study for potential applications.