Synthesis of phenolic resins with cyclotriphosphazene for enhancement of ablation and char yields

A novel phenolic resin with combined hydroxymethyl-substituted phosphazene unit as a part of cured network was prepared which exhibited excellent thermal properties and ablation resistance. The novel phenolic resin was synthesized via copolymerizing from hexa (4-hydroxymethylphenoxy) cyclotriphosphazene (CHPP), phenol and paraformaldehyde. The CHPP contains abundant –CH2OH groups, which can be a part of phenolic resin network through condensation reactions between the –CH2OH groups and active hydrogens on benzene rings of phenolic resins. The optimal curing temperature for the modified phenolic resins was determined using the non-isothermal DSC method. The ablation resistance was investigated using the oxyacetylene flame method. The char yield and linear ablation rate of the modified phenolic resins are 71.3 % and 0.0020 mm/s, respectively. The ablation resistance of the novel resin is significantly improved, compared with other phenolic resin composites. The modification method for the phenolic resin provides a novel pathway to improve the application prospects of phenolic resins in the field of thermal protective materials.