Synthesis and chain-end modification of a novel hyperbranched polymer containing alternating quinoxaline and benzoxazole repeat units
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- Synthesis and chain-end modification of a novel hyperbranched polymer containing alternating quinoxaline and benzoxazole repeat units
- Baek, Jong-Beom; Simko, Sharon R.; Tan, Loon-Seng
- Chain-end-modified polymers; Dihydroxybenzoic acid; Intrinsic viscosity
- Issue Date
- AMER CHEMICAL SOC
- MACROMOLECULES, v.39, no.23, pp.7959 - 7966
- A new AB 2 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 linear analogues, the T g's of all chain-end-modified polymers were not detected up to 450°C by DSC. PPQ-BO's had UV absorption maxima near 377 nm in basic NMP and 448 nm in MSA. Its emission maxima were at 467 nm in NMP and 475.5 and 767 nm in MSA.
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