N-Methylpyrrole-Terminated Polyisobutylene through End-Quenching of Quasiliving Carbocationic Polymerization

Quasiliving isobutylene polymerization initiated by 2-chloro-2,4,4-trimethylpentane/TiCl₄/2,6-dimethylpyridine in 60/40 n-hexane/methyl chloride at −70 °C was allowed to reach 98+% monomer conversion and then reacted with N-methylpyrrole. All polyisobutylene (PIB) chains alkylated the N-methylpyrrole ring to form a mixture of 46% 2-PIB−N-methylpyrrole and 54% 3-PIB−N-methylpyrrole. GPC indicated the absence of coupled PIB, confirming that exclusively monosubstitution had occurred. Complete ¹H and ¹³C NMR chemical shift assignments were made for both isomers. The product was converted exclusively to mixed 2- and 3-PIB−N-methylpyrrolidine by catalytic hydrogenation using PtO₂ in glacial acetic acid. Quantitative ¹H NMR integration of PIB initiated from the difunctional aromatic initiator, 5-tert-butyl-1,3-di(2-chloro-2-propyl)benzene, showed exactly two N-methylpyrrole end groups per aromatic initiator residue. Quantitative reaction of PIB chains with N-methylpyrrole could not be obtained with BCl₃ systems. In methyl chloride diluent at −45 °C, <10% N-methylpyrrole capping was obtained after 70 min; in 1,2-dichloroethane at −10 °C, 77% of the PIB chains reacted with N-methylpyrrole after 15 min, and no further reaction was observed up to 18 h. In both BCl₃ systems, GPC analysis showed the product to be unimodal, indicating the absence of coupling through dialkylation of N-methylpyrrole.