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Recent years has witnessed a significant increase in the type of reactions driven by mechanical force, however, the number of methods for activating those mechanochemical reactions stays relatively limited.Furthermore, in situ characterization of a reaction is usually hampered by the inherent properties of conventional methods.In this study, we report a new method that utilizes mechanical force generated by the swelling of surface tethered weak polyelectrolytes.An initiator with Diels-Alder (DA) adduct structure was applied to prepare the polyelectrolyte-carboxylated poly(OEGMA-r-HEMA), so that the force could trigger the retro DA reaction.The reaction was monitored in real time by quartz crystal microbalance (QCM) and confirmed with AFM and XPS.Compared with the conventional heating method, the swelling-induced retro DA reaction proceeded rapidly with conversion ratio and selectivity.A 23.61 kcal/mol theoretical energy barrier supported the practicability of this retro DA reaction being triggered mechanically at ambient temperature.Duringswelling, the tensile force was controllable and persistent.This unique feature renders this mechanochemical method the potential to "freeze" an intermediate state of a reaction for in situ spectroscopic observations, such as SERS and SFG.