Surface tethered weak polyelectrolyte, carboxylated poly(OEGMA-r-HEMA), was prepared viasurface initiated polymerization (SIP) from metal (Au, Pt and Ag) surfaces functionalized with initiators through metal–S bonds. The swelling behavior of carboxylated poly(OEGMA-r-HEMA) in phosphate buffered saline (PBS) was studied by quartz crystal microbalance (QCM) and was found to obey the following equation: T_eff = (0.32ln([Na⁺]) + 2.53) × T_COOH,dry, where T_eff and T_COOH,dry are the thicknesses of carboxylated poly(OEGMA-r-HEMA) in PBS measured by QCM and in air measured by ellipsometry, respectively. We also confirmed that the event of covalent bond breaking (CBB) of Au–S bonds occurred at a certain critical T_eff, i.e. ∼255 nm. Thus, one could predict the CBB of Au–S or other metal–S bonds from the swelling behavior of surface tethered carboxylated poly(OEGMA-r-HEMA).