Study On The Synthesis And Properties Of Polyphosphazene With Mixed Substituted Side Group Based On Aryloxy Polyphosphazene

Poly(diaryloxyphosphazene)elastomers are widely used in fireproofing,heat insulation,electrical insulation applications and many other aspects due to its unique flame retardant elements of phosphorus and nitrogen main chain and the existence of aromatic oxygen side groups.However,the glass transition temperature(Tg)of poly(diaryloxy-phosphazene)is too high(Tg is close to 0?),which greatly limits its practical application as elastomers under extremely cold environments.The diversity and adjustability of polyphosphazene side groups make it have a variety of unique properties to meet many applications in many fields.The target Tg of polyphosphazene can be obtained by adjusting the type and content of side groups.In the thesis,two kinds of polyphosphazene elastomer materials,poly[(ethoxy)/(aryloxy)phosphazenes](PEPP)and poly[(butoxy)/(aryloxy)phosphazenes](PBPP),were prepared by introducing ethoxy or n-butoxy into the phosphorus site containing aromatic side group polyphosphazene by stepby-step substitution method.The effect of side group content on polymer Tg was analyzed,and its application in the field of thermal protection and electrical insulation was evaluated.At the same time,the polyhedral oligomeric silsesquioxane(POSS)was attempted to introduce into the side groups of polyphosphazenes to explore its effect on the thermal properties of polyphosphazenes.Three kinds of PEPP were synthesized.When the content of ethoxy group is 55.12%,the Tg of PEPP reaches-41.25?.Thermogravimetric analysis shows that the three kinds of PEPP have good thermal stability,and the carbon residue rate is higher than 30%.Three kinds of PEPP were prepared into thermal insulation materials for ablation resistance test.The results show that PEPP polymer is a kind of elastomer with excellent cold resistance and have the potential to be used as thermal insulation material.Six kinds of PBPP were synthesized.The Tg of PBPP is decreased significantly from-13.9? to-63.4? with the increase of the ratios of nbutoxy side groups.Subsequently,the ablative properties of the PBPP composites were examined by oxy-acetylene ablation tests to exhibit excellent linear ablation rates(0.14 mm·s-1 after a 20 s ablation test),which is better than those of synthetic organic rubbers.Meanwhile,the mechanism of outstanding ablation resistance was further clarified by TGA,DSC,XRD,XPS and SEM.After that,the electrical insulation performance of PBPP composites was evaluated by testing their breakdown strength(26.99 kV·mm-1)and flashover voltages under AC voltages(14.90 kV).All results indicate that these lowtemperature elastomers have a great potential for fabricating thermal and electrical insulation materials under extremely low-temperature environment.Through the exploration of synthesis conditions,the hybrid material of POSS-polyphosphazene was synthesized.And its thermal properties and flame retardancy were analyzed by TGA and micro-calorimetric combustion tests,respectively.The introduction of POSS improved the thermal stability and flame retardancy of PBPP.