Study On Preparation And Performance Of PI-EP Nanocomposite

Polyimide （PI） and epoxy resin （EP） have their respective advantages, twokinds of materials were bonded together using a reasonable method, andmodified nanoparticles were evenly dispersed in the matrix, the nanocompositewhich had excellent comprehensive properties of both inorganic material andpolymer advantages would be prepared.In this paper, polyamide acid （PAA） was synthesized by3,3’-diethyl-4,4’-diamino diphenyl methane （DEDADPM） and3,3’,4,4’-benzophenone tetracarb-oxylic dianhydride （BTDA） in the solvent which was N, N’-dimethylacetamide（DMAc）, then the prepolymer were prepared through adding epoxy resion （E-51）into PAA. The surface of nano-TiO₂and nano-Al₂O₃was modified by silanecoupling agent （KH550）. Nanoparticles were doped into the prepolymer throughin situ polymerization, the PI-EP nanocomposites was prepared through thesystem was cured in gradient temperature.The chemical structure, microstructure, grafting rate and dispersion ofnanoparticles were studied by Fourier transform infrared spectrometer （FT-IR）,Scanning electron microscope （SEM）, gravimetric method and sedimentationexperiment，respectively. The results showed that the surface of the modifiedparticles have grafted KH550, reunion phenomenon was abated, particle size wasnanometer level, grafting rates of KH550-TiO₂and KH550-Al₂O₃modified byKH550were2.76%and3.05%, respectively, dispersion and stability of modifiednanoparticles in DMAc were improved. Chemical structure and microstructure ofPI-EP nanocomposites were studied by FT-IR, X-ray diffractometer （XRD），SEM and Atomic force microscopy （AFM）, the heat-resistant, dielectricproperties, shear strength and adhesion level were tested by Thermal gravimetricanalysis （TGA）, precision impedance analyzer, universal electronic tensilemachine and adhesion tester, respectively. The results indicated that the reaction of EP and PAA through the epoxy group formed prepolymer, PI-EP matrix wasprepared when thermal imidization of prepolymer was complete, solid content ofPI-EP matrix was25wt%. Modified particle and matrix produced chemicalbonding through KH550, which improved the compatibility of two phase,reunion phenomenon was abated, dispersed more uniformity. With the increase ofinorganic particle doping amount, molecular order of resin matrix reduced,material suppleness increased, the heat resistance of material increased, and theinfluence of KH550-TiO₂was the most obvious, the Onset temperature wasincreased22℃, when the content of inorganic component was5wt%. Thedielectric properties of material slightly decreased, but dielectric constant anddielectric loss of all samples were lower in the low frequency, and closed tomatrix (ε≈3.3, tanδ≈1.64×10^-3), fully met the application index of impregnatingvarnish in insulating material. With the increase of particle doping amount, shearstrength of materials increased, then decreased, when the shear strength of8wt%-KH550-Al₂O₃composite achieved maximum10.64MPa, which was156%ofpure PI （6.8MPa）. The adhesive forces of all materials were at one or two level.