Study On The Relationship Between The Chemical Structure Of Polyphosphazene And Its Mechanical Properties

A polyphosphazene elastomer is a type of polymer material in which a main chain is composed of a single-double bond alternating phosphorus-nitrogen element.Because its main chain has a high phosphorus and nitrogen content,and the structure of side group can be regulated by nucleophilic substitution,it has good thermal and chemical stability,and has a wide range of applications in aerospace and biomedicine.Fluoroalkoxy polyphosphazenes have excellent hydrophobic and oil resistance,acid and alkali corrosion resistance,fire retardant and other important application properties due to their high fluorine content and phosphazene backbone properties,but the mechanical properties of oxypolyphosphazenes are somewhat different from those of other dielectric materials this paper aims to explore the optimal conditions for the mechanical properties of fluoroalkoxy polyphosphazenes by adjusting the structure and vulcanization process of PTFEP.Linear polydichlorophosphazene was synthesized by thermal ring opening of hexachlorocyclotriphosphazene solution,and nucleophilic substitution reaction was carried out by using sodium trifluoroacetate,sodium octafluoropentaoxide and a double bond reactive group.The type and amount of the nucleophile are controlled to finally obtain the designed amorphous fluoroalkoxy polyphosphazene structure.The relationship between the mechanical properties and the ratio of the side groups was explored,and it was determined that R1 is the most suitable crosslinking reactive group for PTFEP.After the vulcanization process and formulation were investigated,it was determined that the perfect amount of vulcanizing agent was 0.5 phr,the vulcanization temperature was 140 °C,and the mass-to-volume ratio of the solution mixing method was 1:20 g/ml,and the tensile strength of PTFEP can reached 9.3 MPa.The elongation at break was 215%,at a higher level,and the minimum glass transition temperature was-69?.As a new type of flexible thermal insulation material,aryloxy polyphosphazene has a very broad application prospect in the internal thermal insulation layer of rocket engines.To enhance the advantage of polyphosphazene as a flexible insulating material in ablation performance.We introduced the nitro group into the aryloxy polyphosphazene to further reduce its line ablation rate.When the content of the nitro group introduced into the aryloxy polyphosphazene is 10%,the residual carbon at 800 ? can reach 51.4%,which is much higher than the conventional aryloxy polyphosphazene.And the line ablation rate is also as low as 0.1183 mm/s,which is a significant reduction compared to the conventional aryloxy polyphosphazene.It is indicated that the nitro group can greatly improve the ablation performance and thermal stability of the aryloxy polyphosphazene.