Synthesis and Characterization of Carboxylic Acid-Terminated Polyisobutylenes

Abstract

tert-Chloride-terminated polyisobutylenes (PIB) (1020 \u3c= M-n \u3c= 6700 g/mol) were dehydrochlorinated nonregiospecifically using basic alumina, or regiospecifically either via potassium tert-butoxide or in situ quenching of quasiliving PIB. Olefin-terminated PIBs were quantitatively ozonized at -78 degrees C using hexane/methylene chloride/methanol, 62/31/7 (v/v/v) cosolvents, and an ozone generator, employing pure oxygen as source gas. The primary ozonides were reduced using trimethyl phosphite to yield pure PIB methyl ketone from exo-olefin PIB, and a mixture of PIB methyl ketone and PIB aldehyde from mixed olefin-PIB. PIB methyl ketone was oxidized to carboxylate via the haloform reaction; titration revealed near-quantitative functionalization, but the reaction was slow. Tetrahalomethane oxidation was identified as a preferred alternative method, and was conducted using either CCl4 as the reaction solvent, THF as the solvent with CCl4 in reagent amounts, or hexane as the solvent with a phase-transfer catalyst and CCl4 in reagent amounts. The system using hexane, with tetra-n-butyl ammonium chloride as phase-transfer catalyst, showed complete conversion in similar to 4 h. PIB carboxylic acid was recovered by acidification and isolation. (C) 2008 Wiley Periodicals, Inc