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

Quasiliving isobutylene polymerization initiated by 2-chloro-2,4,4-trimethylpentane/TiCl 4 /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 1 H and 13 C 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 PtO 2 in glacial acetic acid. Quantitative 1 H 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 BCl 3 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 BCl 3 systems, GPC analysis showed the product to be unimodal, indicating the absence of coupling through dialkylation of N -methylpyrrole.