Characterization of engine motor oils dispersants of the polybutenylsuccinimide type by saponification, methylation and size exclusion chromatography

Characterization of the molecular weight distribution (MWD) of the starting polybutene (PBU) used in the synthesis of dispersants of the polybutenylsuccinimide type used in lubricants can be achieved through size exclusion chromatography after a preliminary chemical treatment consisting of saponification followed by acidification and methylation with diazomethane. This treatment can be checked by Fourier transform infrared spectrometry since each compound — the original dispersant, the PBU succinic acid derivative and the corresponding methyl ester — has typical absorption bands. The method was tested with model dispersants synthesized from known starting PBUs and applied to dispersants contained in commercial engine motor oils.