The Synthesis Of A Novel Phosphorus-containgning POSS Flame Retardant And Its Application In The Modification Of Bismaleimide Resin

Bismaleimide(BMI),as a typical thermalsetting resin,derives from polyimide resin and terminates with reactive maleimide radical.And bismaleimide is widely used in the fields of aerospace,aviation,electronics,transportation and construction industries for its high mechanical properties,outstanding thermalstability,good radiation resistance and flame retardancy.But with the extension of application fields and the developmentof exploration,the application environment of materials is becoming severer.Therefore,the application of BMI resin also faces great chanllenges.BMI resin presents a little flame retardancy for the nitrogen element in polymer chains,which can produce many nonflammable gases.But it is not enough to meet the requirement of practical application.Hence,seeking for the effective method to enhance the flame retardancy of BMI attracts researchers’attention.Currently,phosphorus-,silicon-and nitrogen-containing flame retardants were widely applied in the flame-retardant modification of polymers,for their high flame-retardant efficiency,environmental friendliness and low toxicity.In order to obtain preferable flame-retardant effect,milti-element synergistic flame retardants were usually employed.Especially the reactive synergistic flame retardants,it can not only give full use of the flame-retardant effects of each element and the synergistic effects among each element,but participate in the curing reaction of polymer matrixes,which will improve its compatibility with matrixes.But when more flame retardants are incorporated,the mechanical performances of polymeric matrixes generally deteriorate.Graphene presents unique two-dimensional molecular structure.It is usually used as flexibilizer to modify polymer matrix.And graphene has the similar structure as char layer,which can promote the formation of continuous,homogeneous and compact char layer in the combustion of polymers.So,the incorporation of graphene can also improve the flame retardancy of polymers.But there exist strong van der waals interaction among the graphene nanosheets,which leads the agglomeration of graphene sheets in polymeric meatrix.Therefore,effective method must be adopted to surface modify the graphene so as to improve the dispersion of graphene in polymeric matrix.In this study,two novel synergistic flame retardants were prepared according to the synergistic effects among phosphorus,silicon and graphene and the structure of BMI resin.Firstly,P-POSS was used to modify BMI resin to prepare P-POSS/DBMI composites,and the cure process,mechanical properties,thermalstability,flame retardancy and humidity resistance of the composites were characterized subsequently.For the synergistic effects among phosphorus,silicon and nitrogen elements,the P-POSS/DBMI composites exhibit preferable flame retardancy.With the incorporation of6.0 wt%P-POSS,the UL-94 rating of P-POSS/DBMI increased to V-0,and the LOI reached 35.4.Meanwhile,the mechanical performances of P-POSS/DBMI were also enhanced greatly for the increase of crosslinking density and the generation of micron-grade pores.But with the increase of P-POSS incorporation,the pores become lager,which deteriorate the toughness of P-POSS/DBMI composites.In order to improve the toughness and flame retardancy of P-POSS/DBMI futher,P-POSS/GO and 4.0 wt%P-POSS were used to modify BMI resin,and the P-POSS/GO/DBMI composites were obtaind.Subsequently,the mechanical properties,thermalstability,flame retardancy and humidity resistance of P-POSS/GO/DBMI composites were investigated in the same conditions.Under the synergistic effects of P-POSS/GO and P-POSS,the UL-94 level of P-POSS/GO/DBMI composites maintained V-0,and the LOI reached 39.4.We also observed that the graphene nanosheets captured the micron-grade pores.Precisely because of the capture and toughening effects,the flexural Strength and impact strength of 0.8 wt%P-POSS/GO/DBMI composites can respectively reach 139.4 MPa and 23.0 k J/m~2.In all,the test results indicated that P-POSS/GO/DBMI presented excellent comprehensive performance-outstanding mechanical properties,thermalstability and flame retardancy.