Construction of Phosphorus-Containing Polyimine Vitrimer Film by Incorporating Ionic Liquid Bmim∙Pf6 for Enhanced Mechanical, Flame-Retardant and Reprocessable Properties

Abstract

A composited flame-retardant phosphorus-containing polyimine vitrimer film (Ionic-PI) was 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, reprocessing, and flame retardancy were investigated. Compared to intrinsically phosphorus-containing polyimine film (PI), the composited Ionic-PI exhibited better mechanical strength and toughness. The hydrogen bonding interactions between BMIM∙PF6 and PI greatly increased their mechanical strength at a low addition of 1%, and the microphase separation caused by the aggregation of BMIM∙PF6 drastically enhanced their toughness as the addition increased. The prepared Ionic-PI 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-PI 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 fileds.

Keywords: Polyimine vitrimer film, ionic liquid, Flame retardancy, Mircophase separation, Reprocessing