Primary Halide-Terminated Polyisobutylene: End-Quenching of Quasiliving Carbocationic Polymerization with N-(ω-Haloalkyl)pyrrole

Abstract

N-(ω-Haloalkyl)pyrroles (1-(2-chloroethyl)pyrrole, 1-(2-bromoethyl)pyrrole, and 1-(3-bromopropyl)pyrrole) were used to end-quench quasiliving isobutylene (IB) polymerizations initiated from 2-chloro-2,2,4-trimethylpentane (TMPCl)/TiCl4 or 5-tert-butyl-1,3-di(2-chloro-2-propyl)benzene (t-Bu-m-DCC)/TiCl4 at −70 °C in hexane/CH3Cl (60/40, v/v). Prechilled N-(ω-haloalkyl)pyrrole, either neat or in a solution of the reaction solvents, was charged to the polymerizations at full (>98%) IB conversion. In all cases, quantitative end-capping of about 0.03 M chain ends (CE) was achieved within 4 min using [N-(ω-haloalkyl)pyrrole] = 2[CE] and [TiCl4] = 1.5[N-(ω-haloalkyl)pyrrole]. 1H NMR analysis revealed mixed isomeric end groups in which polyisobutylene (PIB) was substituted at either C2 or C3 of the pyrrole ring. The isomer ratio C2/C3 was observed to be effected by the alkylene tether length. N-(2-Haloethyl)pyrroles yielded isomer ratios C2/C3 in the range 0.26/0.74 to 0.29/0.71; 1-(3-bromopropyl)pyrrole yielded C2/C3 in the range 0.38/0.62 to 0.40/0.60. GPC indicated the absence of coupled PIB, confirming exclusive monosubstitution on each pyrrole ring. Complete 1H and 13C NMR chemical shift assignments were made for both isomers produced from each of the three quenchers. 1H NMR integration of PIB initiated from the difunctional aromatic initiator, t-Bu-m-DCC, showed two N-(ω-haloalkyl)pyrrole end groups per aromatic initiator residue.