End-Quenching of TiCl₄-Catalyzed Quasiliving Polyisobutylene with Alkoxybenzenes for Direct Chain End Functionalization

Abstract

Alkoxybenzenes were used to end-quench TiCl 4 -catalyzed quasiliving isobutylene polymerizations initiated from 2-chloro-2,2,4-trimethylpentane or 5-tert-butyl-1,3-di(1-chloro-1-methylethyl)benzene at -70 °C in 40/60 (v/v) hexane/methyl chloride. The alkoxybenzene/chain end molar ratios were in the range 2.5-4. Effective alkoxybenzene quenchers included those with simple alkyl groups, such as anisole and isopropoxybenzene, haloalkyl tethers, such as (3-bromopropoxy)benzene and (2-chloroethoxy)benzene, and even those with hydroxyl and amine functionality, such as 4-phenoxy-1-butanol and 6-phenoxyhexylamine. Alkylation was generally quantitative and occurred exclusively in the para position; multiple alkylations on the same alkoxybenzene were not observed. The alkylation reactions were tolerant of temperatures ranging from -70 to -30 °C and were unimpeded by the presence of endo-or exo-olefin termini. In situ cleavage of the ether linkage of anisole and isopropoxybenzene termini allowed single pot syntheses of phenol-terminated polyisobutylenes.

Synthesis and characterization of polymer linked copper(I) bis(N‐heterocyclic carbene) mechanocatalysts

“…The synthesis of bromo‐telechelic poly(isobutylene) ( 1 ) was accomplished via living carbocationic polymerization (LCCP) according to common literature procedure of Binder et al . as well as Morgan and Storey using TMPCl/TiCl 4 as initiating system and 3‐(bromopropoxy)benzene (BPB) for termination. The pure product was obtained as a colorless, highly viscous polymer after drying in high vacuum.…”

Polyisobutylene containing covalently bound antioxidant moieties

“…Recently, our laboratory reported the cleavage/alkylation reaction of butyl rubber (F IP = 0.0230) using (3‐bromopropoxy)benzene . The latter is a versatile quencher that yields primary‐bromide functional groups along the PIB backbone for easy synthetic modification . The authors overviewed some general mechanistic considerations of the cleavage/alkylation process; however, their focus on achieving low‐molecular weight, difunctional PIB (~2000 < <5000 g/mol) deviated significantly from the goals of the present study.…”

“…Additionally, (3‐bromopropoxy)benzene has been reported to alkylate solely at the para‐ position relative to the alkoxy moiety, and there are no other substituents on the ring. This results in clearly defined doublets in the aromatic region . The use of DTP, however, results in a plurality of structures and a more complex 1 H NMR spectrum.…”

“…The use of DTP, however, results in a plurality of structures and a more complex 1 H NMR spectrum. As described in the publication on phenoxy quenching by Morgan et al ., the use of DTP to quench living PIB results in a combination of di‐ tert ‐butylated and mono‐ tert ‐butylated structures; the latter result from de‐ tert ‐butylation, which proceeds via a retro Friedel–Crafts mechanism. This combination of products results in multiple peaks in the aromatic region, ranging from 6.50 to 7.20 ppm and multiple peaks in the region of 4.5–5.1 ppm due to the resonance signals of the phenolic hydroxyl proton of various mono‐ and di‐alkylated phenolic species.…”

“…Isobutylene (IB, BOC gases) and methyl chloride (MeCl, gas and supply) were dried by passing the gas through a column of CaSO 4 /molecular sieves/CaCl 2 and condensing within a N 2 ‐atmosphere glovebox immediately prior to use. The monofunctional initiator, 2‐chloro‐2,4,4‐trimethyl‐pentane (TMPCl), was prepared via a previously described procedure . Butyl rubber (EXXON™ Butyl 068) was donated by ExxonMobil Corporation and used as received.…”