Architectural Control of Bottlebrush Polymers for Tuning Rheology of Polylactic Acid Blends

A series of polylactic acid (PLA)-based bottlebrush polymers (BBPs) with controlled grafting ratios were synthesized and blended with linear PLA to examine the role of bottlebrush architecture in governing melt rheology. The blends exhibited a nonmonotonic dependence of complex viscosity on the grafting ratio: increasing the grafting ratio up to 50% reduced viscosity, whereas higher grafting ratios resulted in an increase in viscosity. Molecular dynamics simulations revealed corresponding changes in chain conformation and mobility, indicating that compact bottlebrush structures at low grafting density promoted chain relaxation, whereas densely grafted architectures suppressed molecular mobility at higher densities. Extensional viscosity also increased with grafting density, although no pronounced strain hardening was observed under the measurement conditions. These results identify grafting density as a key structural parameter for tuning the viscoelastic response of PLA blends and provide molecular-level insights into the role of BBP additives in modulating melt behavior.