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Bulk and Solution Polymerization of Isobutene Using Tris(pentafluorophenyl)gallium and Tris(pentafluorophenyl)aluminum

Hand, Nathan, Mathers, Robert T., Damodaran, Krishnan, Lewis, Stewart P.
Industrial & Engineering Chemistry Research 2014 v.53 no.7 pp. 2718-2725
Bronsted acids, Lewis acids, aluminum, engineering, gallium, green chemistry, halides, molecular weight, polymerization, solvents, temperature, toxicity, zinc
From the standpoint of green chemistry, tris(pentafluorophenyl)gallium (7) and tris(pentafluorophenyl)aluminum (8) outperform all previously explored perfluoroarylated Lewis acids (PFLAs) for the polymerization of isobutene. In comparison to other PFLA based systems, 7 and 8 do not require ultrahigh purity monomer, toxic chlorinated solvents, or expensive and highly sensitive initiators (e.g., metallocenes). Moreover, compared to other PFLA based initiator systems they provide much larger yields of high to medium molecular weight polyisobutene even at polymerization temperatures up to ambient. Stopping experiments indicate that strong Brønsted acids formed in situ by reaction with adventitious moisture (9 and 10, respectively) induce cationic polymerization protonically. Unlike other PFLA compounds which require expensive and/or energetically unstable precursors, 7 and 8 are readily synthesized from their corresponding group 13 halides in conjunction with bis(pentafluorophenyl)zinc (6), thereby lending themselves to commercial implementation.