Ultrasound-Triggered Self-Immolation within Poly(benzyl ether)-Based Graft Copolymers Mediated Synergistically by Disulfide Mechanophore Activation and DBU Promotion

Self-immolative polymers that undergo extensive degradation in response to mechanical stimuli are promising candidates for applications ranging from controlled-release to plastic recycling. However, force-triggered polymer self-immolation has scarcely been reported. Herein, this paper describes the design of poly(benzyl ether) (PBE)-based graft copolymers bearing multiple disulfide (S–S) mechanophores attached with β-carbonate linkers at the backbone-arm junctions. The graft copolymers are capable of backbone self-immolation via mechanical cleavage of S–S bond, inducing spontaneous intramolecular cyclization alongside ring elimination and subsequent PBE backbone sequential depolymerization, triggered by ultrasound force stimulus. This process relies on both the sensitivity of S–S to mechanical force and the 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)-induced increase in electronegativity of phenolic oxygen linked on BE, leading to electronic rearrangement and further cascade reaction. The occurrence of self-immolation and the corresponding mechanisms were confirmed by combined experimental and DFT-simulated results. Additionally, several structure-mechanoresponse relationships have been identified, demonstrating the importance of disulfide presence, disulfide density, and multiple mechanophore incorporations on mechanical degradation characteristics. This work establishes a foundation for the rational design of potential mechanically responsive self-immolative polymers, and broadens the scope of both polymer mechanochemistry and polymer self-immolation, opening new avenues for potential biomedical and materials science applications.