Synthesis And Characterization Of A Novel Polyimide Material

Thermosetting polyimide(PI)composites have been playing a very important role in aerospace and aviation industry due to their outstanding combination properties,such as excellent mechanical properties,thermal stabilities and electronic properties at elevated temperature.However,there is still a need to develop the integration ability that would meet the thermal lightweight and multifunction requirements.The main goal of this work was to develop thermal stability of PI composite that would contribute to reducing the overall weight of a vehicle by eliminating or reducing the thermal protection required to protect the internal structural elements of the vehicle.The molecule design method was used to introducing bromine and ether into structure to improve potential thermal-oxidation degradation,dielectric performance and processability in this paper.Main contents and conclusions of this dissertation are as follows:1,A serial novel PI resin(BPI)including of bromine and ether linkage were synthesized by using 1,3-benzenediol(DB),N-(2,4,6-tribromophenyl)maleimide and N,N'-bismaleimido-4,4'-diphenylmethane(BDM).The best conditions of synthesizing resins were found.Their resins were characterized by FTIR,NMR, GC-MS,GPC,DMA,TGA et al.The results indicated that BPI exhibit excellent thermal stability with the glass transition temperature(Tg)up to 327℃and less than 5 wt%weight loss at 400℃.2,Rheological behavior of BPI resin was systemic studied.A rheological model based on Dual-Arrhenius equation wasη_t=5.05×10^-3exp[(4086.9/T)+exp (13.68-7904.96/T)t],The ideal temperature of processing window for the BPI composite was about 160℃;The cure kinetics of BPI resin was analyzed by DSC, The activation energy E of the BPI system is 93.14 kJ/mol,and the order of reaction n and the dynamic equation of the BPI are 0.913 and dct/dt = 3.617×10⁷ exp(-11202/T)(1-α)^0.913,respectively;Finally,the curing cycle for the BPI system was ascertained to be 190℃/1h+240～260℃/1h+270～290℃/2h.3,The graphite-reinforced BPI composite laminates(C/BPI)were made by autoclave techniques with the optimal cure processes and its properties were tested. The laminates of C/BPI exhibited high storage modulus and glass transition temperature(Tg)up to 425℃.The mechanical properties of C/BPI composite exhibit outstanding mechanical properties at room temperature and elevated temperature as high as 300℃.Compared with the room temperature,the retained rate of bending strength,bending modulus and shear strength were about 69.7%,95%and 53.7%.4,The quartz-reinforced composite laminates(Qz/BPI)were also made by autoclave techniques with the optimal cure processes,and its properties were tested subsequently.The laminates of Qz/BPI exhibited high storage modulus and glass transition temperature up to 330℃.The mechanical properties of Qz/BPI composite exhibit outstanding mechanical properties at room temperature and elevated temperature as high as 300℃.Compared with the room temperature,the retained rate of bending strength were about 66%.Qz/BPI composite also had excellent dielectric performance.The dielectric constant(ε)and loss tangent(Tanδ)were 3.54～3.55 and 8～9×10^-3at room temperature in the frequency of lKHz～20GHz,No significant changes were observe at elevated temperature up to 350℃.It was revealed that the Qz/BPI composite might be the candidate for broadband wavelength application.5,The molecule design method was used to synthesize the electron beam curing PI resin(EBBPI)by using BPI,trimethylolpropane trimethacrylate(TMPTMA)and N-Vinyl-2-pyrrolidone(NVP).Their resins were characterized by FTIR,DMA,et al. Experimental results indicate that EBBPI systems could be cured by EB with a Tg of 243℃.Furthermore,the curing reaction mechanism of the EBBPI system was discussed.