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Enthalpy-Driven Polyisobutylene Depolymerization

Author:
Watson, Christopher B., Tan, Dustin, Bergbreiter, David E.
Source:
Macromolecules 2019 v.52 no.8 pp. 3042-3048
ISSN:
1520-5835
Subject:
Bronsted acids, ambient temperature, benzene, cleavage (chemistry), depolymerization, polymers, solvents, thermodynamics, toluene
Abstract:
Polyisobutylene (PIB) oligomers containing terminal alkene groups depolymerize rapidly at room temperature in the presence of trifluoromethanesulfonic acid and an arene solvent like benzene. This dramatically lower temperature depolymerization behavior is due to an enthalpically driven process wherein the isobutylene groups formed by a chain scission event after reacting a strong Brønsted acid with alkene groups at the polyisobutylene oligomer terminus are trapped by the solvent. In an arene solvent like benzene or toluene, tert-butyl carbocations formed from this isobutylene group rapidly react with benzene or toluene in a thermodynamically favorable process to form tert-butylarene products. This process is presumably favored in part because the Cₛₚ₂–Cₛₚ₃ bond that forms tert-butylarene is stronger than the Cₛₚ₃–Cₛₚ₃ bonds in the polyisobutylene polymer. These studies show that polyisobutylene oligomers depolymerize in only a few minutes at ambient or even sub-ambient temperature using this chemistry.
Agid:
6377140