Method for synthesizing polymethylene polyphenyl multielement benzoxazine resin

The invention discloses a method for synthesizing polymethylene polyphenyl multielement benzoxazine resin, which comprises the following steps: firstly, adopting an aniline and a formaldehyde as reactants to synthesize the polymethylene polyphenyl polyamine under the action of an acidic catalyst, then carrying out Mannich polycondensation reaction on the synthesized polymethylene polyphenyl polyamine serving as an amine source, with a phenolic compound and a formaldehyde source to prepare the polymethylene polyphenyl multicomponent benzoxazine resin. In the synthesis method of the method for synthesizing polymethylene polyphenyl multielement benzoxazine resin, acid catalytic condensation is firstly carried out to obtain a mixture of the 2 nuclear methylene diamine isomer and the polymethylene polyphenyl polyamine, which destroys the regularity of the molecular structure of the benzoxazine resin, reduces the softening point of the polymer and improves the storage stability of the benzoxazine resin; on the othe