Constructing 3D Polyphosphazene Nanotube@Mesoporous Silica@Bimetallic Phosphide Ternary Nanostructures via Layer-by-Layer Method: Synthesis and Applications

A novel ternary nanostructure polyphosphazene nanotube (PZS)@ mesoporous silica (M-SiO₂)@bimetallic phosphide (CoCuP) was facilely fabricated, using PZS as the template, where large amount of cetyltrimethylammonium bromide molecules were anchored to PZS via a similar layer-by-layer assembly strategy, and then uniform M-SiO₂ shells can be formed successfully by Hyeon's coating method. Subsequently, the three-dimensional (3D) nanostructure on the basis of bimetallic phosphide (CoCuP) interconnected with PZS@M-SiO₂ was synthesized via a convenient, mild hydrothermal route. It is noted that incorporating well-designed PZS@M-SiO₂@CoCuP led to significant decrease on fire hazard of thermoplastic polyurethane (TPU), that is, 58.2% and 19.4% reductions in peak heat release rate and total heat release, respectively, as well as lower toxic hydrogen cyanide and carbon monoxide yield accompanied by higher graphitized char layer. In the case of TPU/PZS@M-SiO₂@CoCuP system, the storage modulus at -97 °C was dramatically improved by 62.6%, and glass transition temperature was shifted to higher value, compared to those of pure TPU. The enhanced fire safety and mechanical property for TPU composites can be ascribed to tripartite cooperative effect from respective parts (CoCuP and M-SiO₂) plus the PZS.