Enthalpy-Driven Polyisobutylene Depolymerization

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 C sp2 −C sp3 bond that forms tertbutylarene is stronger than the C sp3 −C sp3 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.

Reversed Controlled Polymerization (RCP): Depolymerization from Well-Defined Polymers to Monomers

“…A lower energy route to depolymerization via cationic depropagation has also been reported by treatment with Lewis acids . A cationic pathway was utilized by Bergbreiter and co-workers in 2019 to give efficient poly­(isobutylene) depolymerization at room temperature . Poly­(isobutylene) oligomers synthesized via living cationic polymerization with functionalized chain-ends were protonated with the strong Brønsted acid CF 3 SO 3 H to give a macromolecular cation capable of depropagation to give isobutylene.…”

“…75 A cationic pathway was utilized by Bergbreiter and co-workers in 2019 to give efficient poly(isobutylene) depolymerization at room temperature. 76 Poly(isobutylene) oligomers synthesized via living cationic polymerization with functionalized chain-ends were protonated with the strong Brønsted acid CF 3 SO 3 H to give a macromolecular cation capable of depropagation to give isobutylene. Unsaturated chain-ends were found to give the highest extent of depolymerization (Figure 10B).…”

Depolymerization of Cross-Linked Polybutadiene Networks in Situ Using Latent Alkene Metathesis

“…16−22 Polyamides and polyurethanes have also been catalytically depolymerized under a limited set of conditions, as summarized in a relevant review. 22 Similarly, Campbell and Storey 23 and Watson et al 24 showed that butyl rubber and polyisobutylene can be depolymerized by Lewis and Brønsted acids, respectively, with appropriate choice of solvent/ additives.…”

“…Polyesters and polycarbonates, of course, are readily depolymerized by several routes, including hydrolysis, transesterification, or even catalytic cleavage of C–O bonds. − Polyamides and polyurethanes have also been catalytically depolymerized under a limited set of conditions, as summarized in a relevant review . Similarly, Campbell and Storey and Watson et al showed that butyl rubber and polyisobutylene can be depolymerized by Lewis and Brønsted acids, respectively, with appropriate choice of solvent/additives.…”

Capsules of the Poly(α-olefin) PAO432 for Removal of BTEX Contaminants from Water

“…2 Prior work by the Bergbreiter group demonstrated that PAO solutions can be used to recycle hydrocarbon-soluble catalysts or to sequester organic small molecules from polar solutions. For example, in a PAO medium, polyisobutylene (PIB) bound sulfonic acids were useful as esterification catalysts, 7 and the ester products could be isolated by vacuum distillation, quantitatively recycling the catalyst and the PAO solvent. In other chemistry, a PIB bound dimethylaminopyridine (DMAP) analog functioned as a recyclable nucleophilic catalyst in a PAO solvent system for reactions that included protection of phenols, Knoevenagel condensations, and cyanosilylations of an aldehyde.…”