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- PIBSA s very slowly. The MAA- and PIB- derived activation parameter Δ G ‡ (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.