Novel Phosphazene-Based flame retardant polyimine vitrimers with Monomer-Recovery and high performances

Novel polyimine vitrimers were constructed from cyclophosphazene bearing three aldehyde groups, CP-3AP, terephthalaldehyde, TPA, and diaminodiphenyl methane, MDA. Owing to the incorporation of phosphazene skeleton and high content of aromatic ring structure, the new vitrimers exhibit superior flame retardancy with UL-94 V0 level and high limiting oxygen index, LOI, of ∼ 40%, high thermostability with T 5% (5% weight loss) of ∼ 420 °C and ∼ 75% residues at 800 °C. Vitrimers owned high Tg of ca 146 °C, robust tensile strength of ∼ 56 MPa and excellent reprocessability with greater than 90% recycling efficiency of mechanical properties even when subjected to three recycling cycles based on imine dynamic covalent bond. Additionally, possible bond exchange mechanisms that are involved in the processability were systematically researched by model compounds using TOF-mass spectroscopy. CP-3AP could be recovered by acidolysis with high 81% efficiency. Such excellent comprehensive properties of phosphazene based polyimine vitrimers open new routes to a variety of high-performance vitrimers, especially in terms of thermal and flame retardancy properties.