MOF-based porous liquids towards a highly stressed and chemically resistant fire-safety polyurea elastomer

Metal-organic framework (MOF)-based functionalized porous liquids are promising candidates for efficient functional species, owing to their better storage stability, higher dispersibility, and convenient processing properties than solid MOF-based fillers. However, the structural design and synthesis strategy for such porous liquids have been a challenge so far. Herein, a porous flame retardant (UiO-66-NH₂@PA@OAPS, U@PA@OA) was designed using UiO-66-NH₂ as a precursor, 3-phosphonopropanoic acid (PA) as a flame-retardant ligand, and octa(aminophenyl) polyhedral oligomeric silsesquioxane (OAPS) as a modifier through post-synthesis modification strategies, such as ligand replacement, defect engineering, and surface modification. Later, it was utilized as a rigid guest and polysiloxane was employed as a mobile phase and a hydrophobic component to manufacture functionalized porous liquids (UiO-66-NH₂@PA@OAPS PLs, U@PA@OA PLs). Advanced U@PA@OA PLs present favorable storage stability as well as compatibility with polyurea components. Impressively, U@PA@OA PLs with a 10 wt% loading (2 wt% U@PA@OA content) in polyurea can improve the limiting oxygen index value of the composites to 26.9% and pass the V-0 rating in the UL-94 test. Moreover, the peak of heat release rate, total heat release, and total smoke production of the polyurea composites are reduced by around 53.7, 36.3, and 34.0%, respectively, compared to neat polyurea. Moreover, the mechanical properties, impact resistance, and chemical resistance of PLs modified polyurea composites are also significantly enhanced. This work not only motivates researchers to design functionalized porous liquids rationally, but it is also expected to expand the application of composites in other potential fields.