A new method for poly(p-phenylene sulfide) (PPS) molecular mass characterization by size exclusion chromatography (s.e.c.) at 75 degrees C based on a derivatization procedure, improving the polymer solubility, is proposed. This procedure leads to the preparation of a poly(p-phenylene sulfoxide) (PPSO) polymer. As complete oxidation is achieved, the reproducibility of the chemical modification is ensured as well as the increase of molecular mass. Furthermore, the molecular mass distribution is preserved for all that the PPS macromolecule only contains sulfide linkages and halogenoaryl chain ends. Molecular characterization of PPSO by light scattering, viscometry and s.e.c. is described. A Mark-Houwink-Sakurada relationship in m-cresol + 0.1 M LiBr is established. From specific and universal calibrations, absolute molecular masses of PPSO are obtained by s.e.c. The study of PPSO conformation in dilute solution reveals that the PPSO macromolecule can be considered as a freely rotating chain with ca 104-110 degrees valence angles. The sigma factor is close to 1.