Synthesis and flame retardant properties of new boron-containing polyurethane

A novel boron-containing chain extender of diglyceride borate was synthesized and used to improve flame retardancy of polyurethane (PU). Diglyceride borate derived from boric acid with glycerin was synthesized by esterification reaction. The boron-containing polyurethanes were synthesized from polyether polyol, 4,4-diphenylmethane diisocyanate (MDI) and diglyceride borate through one-step method. The structure of diglyceride borate was fully characterized by Fourier transform infrared spectroscopy (FTIR), 1H-NMR. The thermal stability and fire behaviors of boron-containing PU were investigated by thermogravimetric analysis (TGA), limiting oxygen index (LOI), UL-94 rating and cone calorimeter (CCT). The LOI increased from 23.8% to 30.0%, with the content of diglyceride borate in the polymer chains increased from 13.6% to 25.7%, meanwhile char formation was enhanced and heat release reduced. Scanning electron microscope (SEM) images, residue digital photos, FTIR, Raman spectroscopy and X-ray diffraction (XRD) analysis of the char residues suggested the formation continuous compact char layer. The results showed that the flame retardancy of polyurethane was positively correlated with boron content.