Synthesis and Chain-End Modification of a Novel Hyperbranched Polymer Containing Alternating Quinoxaline and Benzoxazole Repeat Units

Abstract

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 3,4diaminobenzoic 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.

New series of AB2‐type hyperbranched polytriazoles derived from the same polymeric intermediate: Different endcapping spacers with adjustable bulk and convenient syntheses via click chemistry under copper(I) catalysis

“…This was reasonable. As mentioned in the introduction part, some properties of hyperbranched polymers were dominated by the nature of their large amount of end groups in the periphery,46–52 similar to those in dendrimers,6 the different absorption behavior of P1 – P6 just proved this point on one aspect.…”

“…As we know, unlike linear polymers bearing only two end‐groups, the number of end groups in hyperbranched polymers are very large, and the end‐groups frequently become the primary interface between the hyperbranched polymers and the environment 12–20. As a result, some properties of hyperbranched polymers (e.g., solubility, processability, chemical reactivity, glass transition temperature) were dominated by the nature of their large amount of end groups in the periphery,46–52 similar to those in dendrimers 8. For example, the recent work of Bunz and coworkers demonstrated that hyperbranched polymer with large amount of end‐groups was a universal conjugated polymer platform, and through postfunctionalization strategies, different functional groups end‐capped hyperbranched polymer intermediate to afford new properties 47.…”

“…For example, the recent work of Bunz and coworkers demonstrated that hyperbranched polymer with large amount of end‐groups was a universal conjugated polymer platform, and through postfunctionalization strategies, different functional groups end‐capped hyperbranched polymer intermediate to afford new properties 47. Baek et al designed and synthesized a series of novel AB 2 ‐type of hyperbranched polymers, and they also explored the structure–property–processing relationships with respect to tailoring the end‐group functionality 48–50. Thus, we wondered if it was possible to improve the processability of HP1 and HP2 by changing the end‐capping groups.…”

Synthesis of hyperbranched polybenzoxazoles and their molecular composites with epoxy resins

“…16,17 The introduction of hyperbranched structure constitutes another facilitate approach to tailor the physicochemical properties of linear polymers. [27][28][29] For instance, Kudo et al synthesized HBPBOs in two steps via the thermal cyclodehydration of a hyperbranched poly(o-hydroxyamide), which was preprepared by A 2 1B 3 strategy. [18][19][20] Owing to their globular and porous structure, HBPs generally exhibit better solubility and processibility than their linear counterparts because such configuration could lower the entanglement or packing of polymer chains.…”

“…28,29 However, the synthesis of AB 2 monomers generally involves multistep reaction sequences. The HBPBOs or modified HBPBOs thus obtained were soluble in most of polar aprotic solvents.…”