Research On Structure Control And Preparation Of Heat-resistant And Flame-Retardant Polyphosphazene Elastomers

Traditional rubber is usually flammable and lack of heat resistance.To realize the application of elastomers in high-temperature environments,it is of great significance to synthesize heat-resistant flame-retardant elastomers.Different from traditional rubber,the main chain of polyphosphazene elastomers contains phosphorus and nitrogen atoms,and the properties of polyphosphazene are influenced by the side groups.The polyphosphazene with silicon-containing side groups and phenoxy groups has an enhanced heatresistant,flame-retardant and tensile properties,due to the synergistic effect of side groups and the main chain have.A halogen-free heat-resistant flameretardant phosphazene elastomers with high elongation can be obtained.In this paper,three types of polyphosphazene derivatives have been synthesized:phenoxy polyphosphazene elastomers,trimethylsilylethoxy/phenoxy polyphosphazene elastomers,and dimethylhydroxysiloxy/phenoxy polyphosphazene elastomers.The crosslinked behavior of dimethylhydroxysiloxy/phenoxy polyphosphazene elastomers was studied.The main research results are as follows:1.The intermediate,linear polydichlorophosphazene was synthesized by ring-opening polymerization in solution with hexachlorocyclotriphosphazene.Then a series of polyphosphazene elastomers were synthesized.The number average molecular weight of polyphosphazene is between 1.5×105 and 1.7×105 with a narrow molecular weight distribution.2.The thermal properties of polyphosphazene elastomers were explored.As the ratio of the trimethylsilyl ethoxy group to trimethylsilyl ethoxy group/phenoxy polyphosphazene increases,the Tg value of polyphosphazene decreases.The maximum weight loss rate temperature of phenoxy polyphosphazene and dimethylhydroxysiloxy/phenoxy polyphosphazene s is above 420℃ the residual rate is above 50%.These two types of polyphosphazenes have excellent heat resistance.3.The tensile properties of polyphosphazene with different side group types,different side group ratios,and different crosslinking ratios were explored.The break elongation of dimethylhydroxysiloxy/phenoxy polyphosphazene can reach 1900%.The maximum tensile strength of cross-linked dimethylhydroxysiloxy/phenoxy polyphosphazene can reach 1.14 MPa.4.The flame-retardant properties of polyphosphazene elastomers were explored.The phenoxy polyphosphazene,dimethylhydroxysiloxy/phenoxy polyphosphazene,and cross-linked dimethylhydroxysiloxy/phenoxy polyphosphazene can reach UL-94 V-0 rating,and all the LOI of them are more than 27%.