The benzene ring structure is conducive to improving the heat resistance of cyclophosphazene. Cyclophosphazenes with phenyl, phenoxy or aniline groups are not only heat-resistant and hydrolysis-resistant, but also have high LOI and low smoke emission, and are suitable for use in coatings, foam plastics, fibers and other materials. Phenoxycyclotriphosphazene (PCPZ) is a cyclic phosphazene compound, which is a light yellow or white powder or product. It can be directly added to polyethylene to prepare flame-retardant polyethylene materials, and the LOI of the material can reach 30.0%~33.0%. It can also be directly prepared into an emulsion and used for flame-retardant finishing of fibers, yarns and fabrics by impregnation-drying, spraying or coating methods. It can be added to viscose fiber spinning solution to obtain flame-retardant viscose fibers with an LOI of 25.3%~26.7%. This is a very important type of fine chemical intermediates, which has good flame retardant properties. If other functional groups are further introduced into the side chain and heat-treated, it can be made into resins. This type of resin can be made into high-temperature composite materials when compounded with glass fibers.

Compared with other phosphorus-containing flame retardants with other chemical structures, the advantages of phenoxy cyclotriphosphazene are its excellent heat resistance, acid and alkali resistance, hydrolysis resistance and low water absorption.

The phosphorus atom on the hexachlorocyclotriphosphazene ring has an empty 3d orbital and is electrophilic, so the chlorine on the phosphorus atom is very active and easy to undergo electrophilic substitution reactions. In the phenol molecule, the valence electrons of the oxygen atom participate in bonding with sp hybrid orbitals. The p orbital where a pair of unshared electron pairs on the oxygen atom in the phenolic hydroxyl group is located is parallel to the p orbital of the six carbon atoms in the benzene ring. They are conjugated, and part of the negative charge on the oxygen atom is delocalized and dispersed in the entire conjugated system, so the electron cloud density on the oxygen atom is reduced, which weakens the O-H bond energy and is conducive to the dissociation of hydrogen atoms into protons and phenoxy anions. Therefore, it can be seen that phenoxy anions are strong nucleophiles. When hexachlorocyclotriphosphazene comes into contact with phenoxy anions, the phenoxy anions attack the phosphorus atom as a nucleophile, and substitution reactions are easily induced to generate cyclotriphosphazenes containing substituted phenoxy groups.

At present, the preparation process of hexaphenoxy cyclotriphosphazene (HPCTP) is mainly divided into two categories: one is to use inorganic bases such as NaOH and potassium carbonate (K2CO3) as acid binding agents, add phase transfer catalysts, and make phenol and hexachlorocyclotriphosphazene undergo nucleophilic substitution reaction. The other is to react metal Na, sodium hydride (NaH) and phenol under N2 protection to generate sodium phenolate solution, and the sodium phenolate solution then undergoes nucleophilic substitution reaction with hexachlorocyclotriphosphazene. The synthesis of hexaphenoxy cyclotriphosphazene is divided into two steps. The first step is to generate hexachlorocyclotriphosphazene from PCl5 and NH4Cl under the action of catalyst, and the second step is to generate hexaphenoxy cyclotriphosphazene from hexachlorocyclotriphosphazene and phenol under the action of alkali. The key to the synthesis reaction of hexaphenoxy cyclotriphosphazene lies in the synthesis of hexachlorocyclotriphosphazene in the first step, because the conversion rate of the reaction can only reach 50%~60%, which is seriously low, and a large amount of hydrochloric acid and phosphorus and nitrogen by-products will be generated during the reaction, which is troublesome to post-process and has great environmental pollution. The second step reaction is easier to achieve, with a conversion rate of more than 90%. Due to the low conversion rate of the first step reaction, the troublesome post-processing, and the high production cost of the intermediate hexachlorocyclotriphosphazene, the price of hexaphenoxycyclotriphosphazene remains high, which to some extent limits the development and promotion of hexaphenoxycyclodiphosphazene flame retardants.