<i>N</i>-Methylpyrrole-Terminated Polyisobutylene through End-Quenching of Quasiliving Carbocationic Polymerization
2005-05-31T00:00:00Z (GMT) by
Quasiliving isobutylene polymerization initiated by 2-chloro-2,4,4-trimethylpentane/TiCl<sub>4</sub>/2,6-dimethylpyridine in 60/40 <i>n</i>-hexane/methyl chloride at −70 °C was allowed to reach 98+% monomer conversion and then reacted with <i>N</i>-methylpyrrole. All polyisobutylene (PIB) chains alkylated the <i>N</i>-methylpyrrole ring to form a mixture of 46% 2-PIB−<i>N</i>-methylpyrrole and 54% 3-PIB−<i>N</i>-methylpyrrole. GPC indicated the absence of coupled PIB, confirming that exclusively monosubstitution had occurred. Complete <sup>1</sup>H and <sup>13</sup>C NMR chemical shift assignments were made for both isomers. The product was converted exclusively to mixed 2- and 3-PIB−<i>N</i>-methylpyrrolidine by catalytic hydrogenation using PtO<sub>2</sub> in glacial acetic acid. Quantitative <sup>1</sup>H NMR integration of PIB initiated from the difunctional aromatic initiator, 5-<i>tert</i>-butyl-1,3-di(2-chloro-2-propyl)benzene, showed exactly two <i>N</i>-methylpyrrole end groups per aromatic initiator residue. Quantitative reaction of PIB chains with <i>N</i>-methylpyrrole could not be obtained with BCl<sub>3</sub> systems. In methyl chloride diluent at −45 °C, <10% <i>N</i>-methylpyrrole capping was obtained after 70 min; in 1,2-dichloroethane at −10 °C, 77% of the PIB chains reacted with <i>N</i>-methylpyrrole after 15 min, and no further reaction was observed up to 18 h. In both BCl<sub>3</sub> systems, GPC analysis showed the product to be unimodal, indicating the absence of coupling through dialkylation of <i>N</i>-methylpyrrole.