Interpenetrating Polymer Networks of Porous Organic Polymers and Polyurethanes for Flame Resistance and High Mechanical Properties

An approach was developed to simultaneously improve the fire retardancy and the mechanical strength of polyurethane (PU) elastomer through the formation of interpenetrating polymer networks (IPNs) between PU and porous organic polymer containing phosphorus and nitrogen elements (PNPOP). The PNPOP with high fire retardant ability was synthesized from hexachloro­cyclotri­phosphazene and 3,3′-diamino­benzidine to achieve a specific surface area of 457 m2·g–1 and a total pore volumes of 0.27 cm3·g–1. Polyester diol as the PU monomer was then impregnated into the pores of the PNPOP through a diffusive process and finally PNPOP/PU composites with IPN structure were prepared by in situ polymerization. The PNPOP/PU composites possessed high thermal stability, enhanced mechanical strength, and rigidity in comparison with the PU sample. The fire safety of PNPOP/PU composites was greatly improved with the increase of PNPOP contents. For instance, the reduction of peak heat release rate and total heat release for the PNPOP/PU composite with 10 wt % PNPOP were 46% and 36%, respectively, which is more significant than the samples prepared by simply blending the same amount of PNPOP or a generally used fire retardant, ammonium polyphosphate, with PU. The miscibility between PNPOP and PU was greatly enhanced through the formation of IPNs, endowing the facile formation of flame retardant condensed phase on the PU matrix. Overall, our research provides a promising strategy to prepare flame retardant polymer composites with high performance.