Preparing flame-retardant poly(phenylene oxide)/polyurea nanocomposite foam with excellent heat-resistance and shape memory performance

Superlight polymer foams with excellent heat resistance and flame retardancy are highly expected in many application fields. However, the challenge for preparing polymer foams with the required performances by green method needs to be overcome. Here, using "Plasticizing-Foaming-Reinforcing" (PFR) strategy, we combined poly (phenylene oxide) (PPO) and polyurea (PUA) to fabricate intrinsic fire-retardant PPO/PUA nanocomposite foam with excellent heat resistance and solvent resistance and shape memory. The supercritical CO2 (sc-CO2) foam processing was realized at a much lower temperature, stemming from the fact that the monomer of PUA, polymeric methylene diphenyldiisocyanate (PMDI), acted as a reactive plasticizer for PPO during the foaming process, and the expansion ratio of the resultant PPO/PUA foams was greatly increased. The in-situ formation of nanostructure in the cell wall during the crosslinking of PMDI takes place, in which the PUA is the dispersed phase with 10-40 nm in the matrix of PPO. Compared to the PPO foam and PPO/polystyrene blend foam, the PPO/PUA nanocomposite foam has excellent heat resistance and solvent resistance. Furthermore, the PPO/PUA nanocomposite foam also has excellent shape memory performance at high temperature.