Abstract: As an intermediate in the preparation of ashless dispersant, the structure and properties of polyisobutylene succinic anhydride (PIBSA) were the critical factor of subsequent amination reactions. The structures of polyisobutylenes with different activities prepared by two catalytic processes (BF3和AlCl3) and of PIBSA prepared by different alkylation processes (chlorination and thermal addition) were characterized by IR and 1H NMR to study the systhetic reaction mechanism. The ashless dispersants were prepared by further amination of two PIBSAs. The dispersity of low temperature sludge, high temperature cleanness and soot dispersability of the ashless dispersants were compared and analyzed. The results indicated that the structures of PIBSAs prepared by two alkylation processes were great different due to the difference of polyisobutylene structures and reaction principles. The end of PIBSA prepared by thermal addition method was mainly composed of grafted monopentacyclic anhydride structure, while at the end of PIBSA prepared by chlorination method, phthalic anhydride structure was predominant. Two different structures had a great influence on the performance of ashless dispersants. The ashless dispersant DL prepared by chlorination of PIBSA and the ashless dispersant DR prepared by thermal addition of PIBSA had a similar low-temperature oil sludge dispersibility. The high temperature detergency of DL was better than that of DR, while the soot dispersibility was slightly worse than that of DR.

Key words: polyisobutylene succinic anhydride, ashless dispersant, synthetic mechanism, detergency