The utilization of ultrasound to assess mechanically induced chain scission remains an emerging field of study in polymer science, as many of the conditions leading to bond breakage have yet to be elucidated. While work on linear polymers has established a link between an increased rate of scission to longer chain lengths, minimal work has been conducted on more complex polymer architectures. As a result, the contributions of structural factors unique to nonlinear polymers on mechanochemical response (i.e., contour length, side chain length and composition) have yet to be definitively established. Herein, this work systematically investigates the role of topologically asymmetric linear-bottlebrush diblock copolymers to elucidate the role of increasing bottlebrush composition on mechanochemical chain scission kinetics. Specifically, a small library of poly(norbornene polystyrene)-b-poly(norbornene dimethyl ester) (PNBPS-b-PNDME) linear-bottlebrush block copolymers were generated with variable block composition (10, 30 and 50% bottlebrush) and overall backbone length (DPn = 75 or 150). Norbornene-functionalized polystyrene macromonomers (3 kDa) were prepared via reversible addition-fragmentation chain-transfer (RAFT) polymerization. Sequential ring-opening metathesis polymerization (ROMP) of NDME and NBPS a generated the linear-bottlebrush diblock copolymer. Through the aid of a coumarin tag located on the chain end, the location of the scission events along the backbone of the polymer were discerned using size-exclusion chromatography. Importantly, this work demonstrates the influence of complex topology on mechanochemical response that has not yet been extensively explored.

Role of length in the ultrasonication of asymmetric polymer topologies

ACS Spring Meeting 2021

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