Primary Halide-Terminated Polyisobutylene: End-Quenching of Quasiliving Carbocationic Polymerization with N-(omega-Haloalkyl)pyrrole
Polymers and High Performance Materials
N-(omega-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)/TiCl(4) or 5-tert-butyl-1,3-di(2-chloro-2-propyl)benzene (t-Bu-m-DCC)/TiCl(4) at -70 degrees C in hexane/CH(3)Cl (60/40, v/v). Prechilled N-(omega-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-(omega-haloalkyl)pyrrole] = 2[CE] and [TiCl(4)] = 1.5[N-(omega-haloalkyl)pyrrole]. (1)H NMR analysis revealed mixed isomeric end groups in which polyisobutylene (PIB) was substituted at either C(2) or C(3) of the pyrrole ring. The isomer ratio C(2)/C(3) was observed to be effected by the alkylene tether length. N-(2-Haloethyl)pyrroles yielded isomer ratios C(2)/C(3) in the range 0.26/0.74 to 0.29,10.71; 1-(3-bromopropyl)pyrrole yielded C(2)/C(3) 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 (1)H and (13)C NMR chemical shift assignments were made for both isomers produced from each of the three quenchers. (1)H NMR integration of PIB initiated from the difunctional aromatic initiator, t-Bu-m-DCC, showed two N-(omega-haloalkyl)pyrrole end groups per aromatic initiator residue.
Morgan, D. L.,
Storey, R. F.
(2009). Primary Halide-Terminated Polyisobutylene: End-Quenching of Quasiliving Carbocationic Polymerization with N-(omega-Haloalkyl)pyrrole. Macromolecules, 42(14), 4963-4971.
Available at: http://aquila.usm.edu/fac_pubs/1336