Construction of phosphorus-containing polyimine vitrimer film by incorporating ionic liquid BMIM∙PF6 for enhanced mechanical, flame-retardant and reprocessable properties

A composited flame-retardant phosphorus-containing polyimine vitrimer films (Ionic-PIs) were synthesized by using ionic liquid BMIM∙PF6 containing flame retardant elements N, P and F as the regulator. The effects of the addition amount of BMIM∙PF6 on the mechanical properties, degradation, recycling, and flame retardancy were investigated. Compared to intrinsically phosphorus-containing polyimine film (PI), the composited Ionic-PIs exhibited better mechanical strength and toughness. Hydrogen bonding interactions between BMIM∙PF6 and polyimine network greatly increased Ionic-PI's mechanical strength at a low addition of 1 wt%, and the microphase separation caused by the aggregation of BMIM∙PF6 drastically enhanced their toughness as the addition increased. Ionic-PIs exhibited excellent reprocessability at 85 °C and degradable recyclability under acidic conditions. In addition, due to the synergistic effect of condensed-phase and gas-phase flame-retardant mechanisms, the Ionic-PIs possessed good flame retardancy with LOI above 27 % and a UL-94 test reaching VTM-0 grade, which was important for the high-fire safety of polyimine vitrimer. This work is helpful to provide a simple and feasible strategy to modulate the comprehensive properties of cross-linked polyimine vitrimer film and to expand their applications in many fields.