AbstractPositive and negative secondary‐ion‐mass spectra of poly(2‐hydroxyethyl methacrylate), poly(2‐hydroxypropyl methacrylate) and both polymers after modification with D2O and propionyl chloride are presented. The spectra were obtained with a Time‐of‐Flight Secondary‐Ion‐Mass Spectrometer. The structures of typical ions in the mass range 10‐150 amu are given and the intensities of these ions were used to obtain quantitative information about the ion formation processes. Furthermore, the spectra of poly(2‐hydroxyethyl methacrylate), poly[2‐(propionyloxy)ethyl methacrylate] and four copolymers of 2‐hydroxyethyl methacrylate and 2‐(propionyloxy)ethyl methacrylate are compared to provide quantitative results on ion‐formation efficiency and/or stability. The results of this study can be used to study the kinetics of the reaction of propionyl chloride with poly(2‐hydroxyethyl methacrylate) at a surface.