Decoupling and Functionalization of Coupled Polyisobutylene via Alkoxybenzene Quenching
Polymers and High Performance Materials
During living polymerization of isobutylene, marginal conditions can lead to reaction of carbenium ions with exo-olefin and production of coupled polyisobutylene (PIB). When living PIB containing a coupled fraction is subjected to end-quenching with an alkoxybenzene compound in the presence of TiCl4, the coupling reaction is quantitatively reversed to form the two original chain ends, and the regenerated chains are observed to possess the desired alkoxyphenyl functionality. To demonstrate this phenomenon, various PIB samples were prepared to purposefully contain significant coupled fractions, from 10 to 55 mol %, by quenching living PIB with hindered nucleophiles under marginal conditions. The coupled fractions were quantified by 1H NMR and GPC. Coupled PIB samples were reacted with (3-bromopropoxy)benzene, methoxybenzene, or 4-phenoxy-1-butyl acrylate in the presence of TiCl4 and a source of protic catalyst. Various protic sources were found to be effective including externally added water, adventitious protic sources, and any finite fraction of tert-chloride chain ends. Decoupling did not occur in the presence of a proton scavenger such as 2,6-lutidine. The resulting PIB samples were quantitatively or nearly quantitatively decoupled, as determined by 1H NMR and GPC, and all of the chain ends visible by 1H NMR possessed the desired alkoxyphenyl end groups. Other π-nucleophile-type quenchers including N-methylpyrrole, 2-methylfuran, allyltrimethylsilane, and methallyltrimethylsilane were found to be ineffective under the same or similar conditions due apparently to reaction of the quencher with the necessary protic catalyst.
Storey, R. F.
(2016). Decoupling and Functionalization of Coupled Polyisobutylene via Alkoxybenzene Quenching. Macromolecules, 49(20), 7642-7652.
Available at: https://aquila.usm.edu/fac_pubs/17816