Chemical Modification of Polyisobutylene Succinimide Dispersants and Characterization of Their Associative Properties

The secondary amines found in b-PIBSI dispersants prepared by attaching two polyisobutylene chains to a polyamine core via two succinimide moieties were reacted with ethylene carbonate (EC). The reaction generated urethane bonds on the polyamine core to yield the modified b-PIBSI dispersants (Mb-PIBSI). Five dispersants were prepared by reacting 2 molar equivalent (meq) of polyisobutylene terminated at one end with a succinic anhydride moiety (PIBSA) with 1 meq of hexamethylenediamine (HMDA), diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), and pentaethylenehexamine (PEHA) to yield the corresponding b-PIBSI dispersants. Characterization of the level of secondary amine modification for the Mb-PIBSI dispersants with traditional techniques such as FTIR and (1)H NMR spectroscopies was greatly complicated by interactions between the carbonyls of the succinimide groups and unreacted secondary amines of the Mb-PIBSI dispersants. Therefore, an alternative procedure was developed based on fluorescence quenching of the succinimides by secondary amines and urethane groups. The procedure took advantage of the fact that the succinimide fluorescence of the Mb-PIBSI dispersants was quenched much more efficiently by secondary amines than by the urethane groups that resulted from the EC modification of the amines. While EC modification did not proceed for b-PIBSI-DETA and b-PIBSI-TETA certainly due to steric hindrance, 60 and 70% of the secondary amines found in the longer polyamine core of b-PIBSI-TEPA and b-PIBSI-PEHA had reacted with EC as determined by the fluorescence quenching analysis. Furthermore, the ability of the Mb-PIBSI dispersants to adsorb at the surface of carbon black particles used as mimic of the carbonaceous particles typically found in engine oils was compared to that of their unmodified analogues.