Enhancing flame retardancy, mechanical durability, and anti-aging property of polyurethane foam via novel cyclic phosphonate

Incorporating flame retardants (FRs) is an essential way to enhance flame resistance of polymers. In an effort to obtain required flame retardancy, a large number of flame retardants are often needed, which inevitably deteriorate the mechanical properties, especially suffering from heat aging. To balance the flame retardancy and mechanical performance, herein, we designed and synthesized a cyclic phosphonate, denoted as TCDP, with high phosphorus content (20.1 %) for flexible polyurethane foam (FPUF). Notably, only 2.8 wt% TCDP addition can endow FPUF with self-extinguishing behavior when it is horizontally or vertically exposed to the flame for 10 s. High limiting oxygen index (LOI) of 26 % can be reached for the 12.6 wt% TCDP filled FPUF. In particular, the compression strength and resilience of the resulting FPUFs remain robust even under heat aging at 125 °C for 16 h, resulting from an energy dissipating network may be established by hydrogen bonding between the cyclic phosphonate and polyurethane. Additionally, the TCDP filled FPUFs exhibit an LOI loss of only 0.5 % after heat aging. This work presents a new strategy to do not sacrifice the mechanical properties even under heat aging but impart excellent flame retardancy to flammable polymers.