As one of emerging layered nanomaterials, the potential of black phosphorous nanosheets (BP) for fabricating high performance polymer composites was seriously confined by incompatible interface. Herein, interfacial engineering between BP nanosheets and polyurethane (PU) matrix was rationally designed, where employing polymerized ionic liquid as linking bridge between robust BP nanosheets and soft TPU. The ionic liquid (IL) was firstly confined onto the surface of BP nanosheets with the combination of electrostatic-driving self-assembly process and in situ radical polymerization was then performed. The successful preparation of IL-functionalized BP (IL-BP) nanosheets was confirmed by a series of analytic methods, incluing TEM, XPS, FTIR, and so on. The resultant IL-BP nanosheets imparted well mechanical performance and flame retardancy to TPU composites. Compared to the mechanical enhancement reported by other literatures, the break strength of TPU/IL-BP-1.0 was significantly increased by 50%, attributing to strong interfacial regulation of polymerized IL and mechanically robust BP nanosheets, generated by the similar polarity. Meanwhile, significant decreases of 38.2% and 19.7% in peak values of heat release rate and total heat release were achieved for TPU/IL-BP-2.0. With the investigation of combustion residue and pyrolysis products, it was found that a mass of pyrolysis products reacted with IL-BP nanosheets to form mechanically robust protective char and solid products, being no longer used as fuel to support combustion. Meanwhile, the maximum concentration of CO2 and highly toxic CO of TPU/IL-BP-2.0 were effectively decreased by 36.9% and 26.5%, compared to the pure TPU. Such a design route effectively regulates the interfacial interaction between BP nanosheets and polymer matrix and offers a practical route for preparing high performance materials. (C) 2019 Elsevier Inc. All rights reserved.