Structural assignment of commercial polyisobutylene succinic anhydride-based surfactants

Abstract

Concentration of the surface active agents in industrial products is a common source of error. In order to compare the efficiency of a number of polyisobutylene succinic anhydride (PIBSA) based surfactants, their concentration needs to be determined with a fair degree of accuracy. Industrial samples of the monoethanolamine adduct of PIBSA (PIBSA-MEA) concentrate were used for chromatographic separation of the functionalized surfactant from the sample matrix. Complete spectroscopic assignments were based on detailed analysis of all the precursors and of the purified mixture of structural isomers. The structures of the double bond isomers were consistent with the expected addition products of the classic Alder-ene reaction-derived PIBSA. The carbon–carbon connectivity of the succinamide head group to the bulky polymer tail of PIBSA-MEA was more complicated than previously thought, pointing towards regioselectivity in the nucleophilic substitution of PIBSA. By analogy, further structural assignments of two other surfactants, branded as PIBSA-IMIDE and PIBSA-UREA were made from the spectroscopic data recorded on crude industrial samples. Detailed nuclear magnetic resonance (NMR) assignments for all three surfactants reported here were utilized to develop a semi-quantitative 13C-NMR based method for the estimation of the amount of the functionalized surfactant relative to the total PIB content in the industrial concentrates. The results highlight common sources of structure- and concentration-dependent errors in high internal phase emulsion formulations