Nitrogen-phosphorus flame retardant and preparation method thereof

The invention belongs to the technical field of flame retardants, and particularly relates to a nitrogen-phosphorus flame retardant and a preparation method thereof. The nitrogen-phosphorus flame retardant is polyalcohol phosphate ester ammonium salt with a structural formula as shown in the specification, and R-O-P is phosphate ester formed by esterifying at least one hydroxy of polyalcohol and phosphate. A plurality of ammonium phosphate molecules are bridged to form macromolecules by P-O-C ester, the nitrogen-phosphorus polyalcohol phosphate ester ammonium salt flame retardant is an upgrade product of nitrogen-phosphorus flame retardants such as APP (ammonium polyphosphate) and MP (melamine phosphate), is used for preparing waterborne coatings and has the advantages of homogeneous dispersibility, storage stability, excellent flame resistance, compatibility with macromolecule base materials and avoidance of corrosion, damping, precipitation and frosting. The preparation method of the nitrogen-phosphorus fla