Abstract
A new AB2 monomer, 2,3-bis(3-amino-4-hydroxyphenyl)quinoxaline-6-carboxylic acid dihydrochloride, was synthesized in four steps starting from the double condensation of commercially available 3,4-diaminobenzoic acid and 4,4‘-dimethoxybenzil. It underwent facile polycondensation in polyphosphoric acid to afford the corresponding hyperbranched quinoxaline−benzoxazole polymer (PPQ−BO 5) with an intrinsic viscosity of 1.04 dL/g. It was end-capped with 2-thiophenecarboxylic acid, 3,5-dihydroxybenzoic acid, 3-sulfobenzoic acid, 4-sulfobenzoic acid, and 2,3-diphenylquinoxaline-6-carboxylic acid. These hyperbranched polymers displayed an unusual, nonlinear solution viscosity behavior at the concentrations below ∼0.25 g/dL. At these dilute concentrations, both reduced and inherent viscosities decreased precipitously (“inverse polyelectrolyte behavior”). The large numbers of o-aminophenol end groups were further chemically modified to afford hyperbranched PPQ−BO's with various functionalities. Similar to their line...
Published Version
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