Preparation Of Side Chain Fluorenyl Benzoxazine Monomers And Study On Polymerization Properties

Polybenzoxazine is a new type of thermosetting resin that shows good application prospects.Compared with traditional phenolic resin,it not only has the characteristics of easy curing,almost zero volume shrinkage during curing,and strong molecular design flexibility,but also exhibits excellent mechanical properties and higher thermal stability.Therefore,it is used in aerospace materials,Electronic sealing materials,supercapacitor materials,ablation resistant materials and other fields are widely used.Fluorene derivatives have become one of the most commonly used materials in organic electroluminescent materials and two-photon absorption materials due to their strong electron delocalization,high luminous efficiency,good photothermal stability and rigid planar structure.Therefore,the introduction of fluorenyl units into the benzoxazine molecular structure to prepare fluorenyl benzoxazine resins will help to enhance the thermal stability and mechanical properties of the benzoxazine resins and expand its application fields.In this thesis,fluorene is used as the initial raw material to obtain 2-aminofluorene through nitration and reduction,and then 2-aminofluorene,p-ethylphenol,p-tert-amylphenol,o-ethoxyphenol,2-methoxy-4-Using methyl phenol and paraformaldehyde as raw materials,four fluorenyl benzoxazine monomers with pendant side chains were prepared,and their curing kinetics and thermal properties of their polymers were systematically studied.In the synthesis of monomers,fluorene is first used as a raw material,reacted with nitric acid to form 2-nitrofluorene,and then reduced with zinc powder in ethanol to obtain 2-aminofluorene.Four kinds of fluorenyl benzoxazine monomers were prepared by the solution method of 2-aminofluorene and four different structures of phenol and paraformaldehyde,namely 3-fluorenyl-6-ethyl-3,4-dihydro-1,3-benzoxazine(FBOZ-1),3-fluorenyl-6-(1.1-dimethyl-propyl)-3,4-dihydro1,3-benzoxazine(FBOZ-2),3-fluorenyl-8-ethoxy-3,4-dihydro-1,3-benzoxazine(FBOZ-3)and 3-fluorenyl-8-methoxy-6-methyl-3,4-Dihydro-1,3-benzoxazine(FBOZ-4).The monomer structure was characterized by infrared spectroscopy(FT-IR),high-resolution mass spectrometer(MS),and nuclear magnetic resonance spectroscopy(NMR).The results proved that the four monomers were successfully synthesized.Differential scanning calorimetry(DSC)was used to study the curing kinetics of four monomers.The Kissinger method,Ozawa method and Flynn-Wall-Ozawa method were used to calculate FBOZ-1,FBOZ-2,FBOZ-3,and FBOZ-4 activation energy,and verified by Friedman ’ s method that the curing mechanism is autocatalytic thermal ring-opening curing reaction;the thermal properties of four monomers and their polymers are analyzed by thermal weight loss analysis(TGA),FBOZ-1,FBOZ-2,FBOZ-3,and FBOZ-4 all show typical thermal open loop curing characteristics,and the exothermic peak top temperature(10℃/min heating rate)is 259.4℃,258.1℃,258.4℃ and 251.9℃,respectively,The initial decomposition temperature(thermal weight loss of 5%)of the corresponding polymer reached 290℃,296℃,271℃ and 299℃;the carbon residue rate at 850℃ was41.4.%,40.7.%,41.9% and 44.1%.The limiting oxygen index(LOI)is 34.06,33.78,34.26 and 35.14,respectively.Using the best curing conditions,the four monomers FBOZ-1～FBOZ-4 were thermally polymerized to prepare benzoxazine resins.The thermal stability and flame retardancy of the resins were studied by TG and DSC,and simultaneously measured Fluorescence properties of monomers and polymers in solution.Four monomers FBOZ-1～FBOZ-4 were blended with epoxy soybean oil(ESO)to prepare composite resins with different ESO content.Through dynamic thermomechanical analysis(DMA)test,the dynamic thermomechanical properties of composite resins were further studied.performance.