Linear versus Helical Side Chains in Bottlebrush Polymers: Morphology and Mechanochemistry

Bottlebrush polymers (BBPs) present numerous intriguing properties, e.g., extended wormlike conformation and compact molecular dimension. Here, we customize BBPs’ architectures by manipulating the secondary structure of the side chains. Specifically, helical or random coil poly(γ-benzyl-glutamates) are grafted onto two chemically different polymeric scaffolds, poly(norbornene) and poly(cyclooctene), through controlled ring-opening polymerization of enantiopure (l-) or racemic (d/l-) amino acid N-carboxyanhydrides. The bulkier helical side chains induce stronger repulsion between each other, compelling the backbone to adapt a more extended conformation and leading to increased persistence lengths. This observation is further supported by comparing their mechanochemical responses. Subjecting these conformationally different BBPs to solvodynamic shear reveals that BBPs with helical side chains undergo accelerated backbone mechanochemistry, occurring up to two times faster than a typical BBP with unstructured side chains. Additionally, we find that the helical conformation of side chains can impart the mechanochemistry of mechanophores randomly embedded in the backbone, resulting in a very fast and high level of activation.