End-Quenching of Quasiliving Carbocationic Isobutylene Polymerization with Hindered Bases:  Quantitative Formation of exo-Olefin-Terminated Polyisobutylene

Abstract

Polyisobutylenes possessing exclusively exo-olefin end groups were created by end-quenching TiCl 4 -catalyzed quasiliving isobutylene (IB) polymerizations with a hindered base at -60 to -40 °C. Polymerizations were initiated from either 2-chloro-2,4,4-trimethylpentane (TMPCl) or 1,3-bis(2-chloro-2-propyl)-5-tert-butylbenzene, in 60/40 hexane/methyl chloride in the presence of 2,6-dimethylpyridine, allowed to reach 98+% isobutylene conversion, and then reacted with either 2,5-dimethylpyrrole, 1,2,2,6,6-pentamethylpiperidine, or 2-tert-butylpyridine for various times ranging from 10 to 170 min. Typical reaction molar concentrations were [IB] ) 0.5, [TMPCl] ) 0.014, [26Lut] ) 0.010, [TiCl 4 ] ) 0.083, and [hindered base] ) 0.02-0.04 M. In some cases, minor amounts of coupled PIB were produced through reaction of carbenium ions with exo-olefin. Coupling was suppressed by higher temperature and lower chain end concentration. 2,5-Dimethylpyrrole was the most effective quencher under the conditions studied, yielding the most rapid quenching and exhibiting the least tendency toward coupling.

Cationic polymerization of isobutylene at room temperature

“…The shoulder (4.82 ppm) to the downfield exo ‐olefin peak at 4.85 ppm (Fig. 1) was attributed either to the product of coupling of two PIB chains28 or rearrangements of growing cations 25…”

Primary Hydroxy-Terminated Polyisobutylene via End-Quenching with a Protected N-(ω-Hydroxyalkyl)pyrrole

“…Similarly, Ivan et al 11 described quenching with methallyltrimethylsilane to obtain PIB with exo-olefin end groups. As an alternative, Storey et al 12 have shown that deliberate addition of hindered amines to a TiCl 4 -catalyzed isobutylene polymerization induces β-proton elimination at the chain end for quantitative exo-olefin formation.…”

Synthesis, characterization and biological activity of C60 derivative

“…Additionally, there is a visible shoulder peak (e) at δ = 4.82 to the downfield exo ‐olefin peak (h 1 ) at δ = 4.84 even though MWD of PIB was narrow ( M w / M n = 1.22). This weak resonance at δ = 4.82 may be assigned either to C H 2  protons of internal vinylene resulting from carbenium ion rearrangements or to the two identical protons of C H 2  in the coupled PIBs formed by the addition of a growing PIB carbenium ion (I) to the exo ‐olefinic end group (A) in another PIB chain 29–32. The coupling reactions could not be avoided when β‐proton abstraction from the growing carbenium ions (I) was not sufficiently rapid.…”

“…On the basis of the integral calculation, the PIB chains obtained at −40 °C were only 6.2% of tert ‐Cl terminal groups, and the termination via chlorine transfer from counteranion did hardly take place during polymerization. Instead, the PIB obtained at −40 °C had another 61.9% of exo ‐ (δ f1,2 = 4.64, 4.85 ppm) terminal groups, 20.9% of endo ‐ (δ h = 5.15 ppm) terminal groups due to β‐proton elimination and 11.0% of isomer (δ = 4.82 ppm) C H 2  protons in internal vinylene mainly resulting from carbenium ion rearrangements or in the coupled PIBs formed by the addition of a growing PIB carbenium ion (I) to the exo ‐olefinic end group (A) in another PIB chain 29–32. The serious chain transfer to monomer did also simultaneously take place to form new polymer chains with 67.8% of tert ‐butyl head groups according to the characteristic resonance at δ = 0.99 ppm.…”