Degradable Schiff base benzoxazine thermosets with high glass transition temperature and its high‐performance epoxy alloy: Synthesis and properties

Abstract

Benzoxazines have been widely used in many fields, such as the aerospace, electronics, and automotive industries; however, these resins exhibit nonrecyclable nature and limited strength (for their brittleness). Introducing reversible covalent bonds in benzoxazines is expected to address these issues. Herein, two-benzene-ringconjugated Schiff-base benzoxazine was successfully synthesized using a designed strategy. Using this strategy, possible side reactions, such as the transimination of the Schiff-base, were prevented when preparing the target product via the traditional Mannich reaction. The cured benzoxazine could chemically degrade under acidic conditions and it undergoes controllable degradation when the temperature, acidity, and solvent are changed. The synthesized benzoxazine forms noticeable liquid crystals

Exploring the Limits of High-Tg Epoxy Vitrimers Produced through Resin-Transfer Molding

“…For some aeronautical applications, a high glass transition temperature (≥200 °C) is one of the most important characteristics to consider. However, only a few recent reports fulfill this criterion, , with most of the reports exhibiting T g below 170 °C, − or using other polymer matrices such as benzoxazines. − Ruiz de Luzuriaga and co-workers recently developed a high- T g epoxy vitrimer based on commercial resins TGMDA (MY21) and DGBF (PY306) and compared its properties to those of aerospace-certified resin Hexcel HexFlow RTM6, which is widely used in industry for many decades and is especially designed for resin-transfer molding (RTM) process. , However, the resulting resin afforded a glass transition of 176 °C still well below the T g of 220 °C of the RTM6-based thermoset benchmark. In addition, the optimization of the composite manufacturing process RTM was not investigated.…”

Solvent-free preparation of imine vitrimers: leveraging benzoxazine crosslinking for melt processability and tunable mechanical performance

“…The inclusion of a miscible organic solvent is often employed to promote solution ingress into the network and to aid in solubilizing the resulting macromolecular depolymerization products. 60,84 All p(iBOX) networks underwent full dissolution in the 1 M HCl/THF solution at 25 °C and yielded homogenous transparent solutions (Fig. 9b).…”

“…Synthesis of the mono-functional aldehyde-containing benzoxazine monomer (HBA-BA) was achieved by modifying previously reported procedures. 60,62 Aqueous formalin (180 g, 2.2 mol) was added to a 1 L one-neck round bottom flask and alkalized to pH 9 using 1 M NaOH. Toluene (400 mL) was added and stirred to form a heterogeneous solution prior to the dropwise addition of BA (107 g, 1.0 mol) at 25 °C.…”

“…52–54 Following these initial reports of BOX-derived vitrimers, the field has grown rapidly to incorporate alternative dynamic chemistries including transacetalation, 55,56 transcarboamoylation, 57 and boronic ester exchanges. 58 Several studies have reported the incorporation of imine bonds into BOX to impart unique properties such as shape memory, 59 liquid crystalline behavior, 60 and nitrogen doping upon pyrolysis. 61 Recently, Liu et al demonstrated the hydrolytic degradation of an imine-containing BOX network; however, the conjugated aromatic imine monomer had limited melt processability and required copolymerization with epoxides to achieve manufacturability.…”

“…61 Recently, Liu et al demonstrated the hydrolytic degradation of an imine-containing BOX network; however, the conjugated aromatic imine monomer had limited melt processability and required copolymerization with epoxides to achieve manufacturability. 60 Despite the demonstrated successful incorporation of imine bonds into BOX networks, no investigations have reported the dynamic behavior and potential recyclable characteristics of the resulting polymers.…”