A weak polyelectrolyte coating, carboxylated poly(oligo(ethylene glycol)methacrylate-co-2-hydroxyethylmethacrylate), was prepared viasurface initiated polymerization (SIP) from initiators immobilized to gold surface through the Au–S bonds. When dry thickness increased up to 75 nm, this polyelectrolyte coating was pulled off the Au substrate by simply exposing to phosphate buffer saline (PBS, pH = 7.4, [Na⁺] = 150 mM). This covalent bond breaking (CBB) behavior was monitored in situ using a quartz crystal microbalance (QCM) and CBB was associated with the swelling of the anchored polyelectrolyte chains.