Rate of Formation of Industrial Lubricant Additive Precursors from Maleic Anhydride and Polyisobutylene

The Alder-ene reaction of neat polyisobutylene (PIB) and maleic anhydride (MAA) to produce the industrially important lubricant additive precursor polyisobutylene succinic anhydride (PIBSA) is studied at 150-180 °C. Under anaerobic conditions with [PIB] ∼ 1.24 M (550 g mol^-1 grade, >80% exo alkene) and [MAA] ∼ 1.75 M, conversion of exo-PIB and MAA follows second-order near-equal rate laws with k _obs up to 5 × 10^-5 M^-1 s^-1 for both components. The exo-alkene-derived primary product PIBSA-I is formed at an equivalent rate. The less reactive olefinic protons of exo-PIB also react with MAA to form isomeric PIBSA-II (k _obs up to 6 × 10^-5 M^-1 s^-1). Some exo-PIB is converted to endo-PIB (containing trisubstituted alkene) in a first-order process (k _obs ∼ 1 × 10^-5 s^-1), while PIBSA-I is difunctionalized by MAA to bis-PIBSAs very slowly. The MAA- and PIB-derived activation parameter ΔG ^‡(150 °C) 34.3 ± 0.3 kcal mol^-1 supports a concerted process, with that of PIBSA-I suggesting a late (product-like) transition state.