This study assesses how the physical characteristics of styrene‐divinylbenzene (PS‐DVB) resins affect the extent to which they are modified when they are functionalized, and how they affect recoveries in on‐line solid‐phase extraction (SPE) of some polar phenolic compounds, pesticides, and metabolites from water samples which were analyzed by liquid chromatography and UV detection. For this purpose, three commercial PS‐DVB resins with different physical characteristics (Amberchrom GC‐161m and two different PLRP‐S resins) were chemically modified by placing a hydrophilic group, an o‐carboxybenzoyl moiety, on their surface; although the physical characteristics are different, the extent of modification did not vary significantly. The results from the SPE process with each sorbent were related to their physical and chemical properties. The polymers with higher surface area provided better recoveries. Moreover, the recoveries for these analytes were better with the chemically‐modified polymers due to the higher polarity of these sorbents. The best recovery values were with the sorbent obtained from the chemical modification of Amberchrom GC‐161m, the commercial sorbent with higher surface area. For instance, in the analysis of 50 mL of a sample of 2 μg L–1, the recovery of phenol was 40% with Amberchrom GC‐161m and 65% with the chemically‐modified Amberchrom GC‐161m.