Preparation And Properties Of Thermally Conductive Polyimide/Inorganic Composites

With the development of the high power,high integration and miniaturization of microelectronic devices,the components will result in the accumulation of heat in a confined space,and solving the problems of heat dissipation are the key factors to ensure their safe and stable working.Polymer matrix composites combine excellent performance with high thermal conductivity,electrical insulation and easy forming process,which have been widely used in the fields of aerospace,auto mechanics,interlayer dielectrics and packaging materials,etc.Polyimide(PI)has unique properties of excellent thermal stability,mechanical properties,high electrical insulation and low dielectric constant.Hexagonal boron nitride(BN)and nano-diamond(ND)both have ultra-high thermal conductivity,and low dielectric properties and thermal expansion coefficient,which make BN and ND as the ideal fillers for preparing polymer composites with enhanced thermal conductivity.Polyimide/inorganic fillers' composites combine the polyimide polymer and thermally conductive inorganic filler's advantages.In this study,PI/BN composites and PI/(BN+ND)composites were prepared by dispersing single BN fillers or both BN and ND particles into polyimide by in-situ polymerization.The preparation of PI/BN composites is discussed firstly.In order to improve organic-inorganic interface compatibility and enhance wettability of BN surface,the BN fillers were modified with mixed acid to introduce sufficient hydroxyl groups,and then the BN micro-particles were further functionalized with a silane coupling agent,3-glycidyloxypropyltrimethoxy silane(?-MPS).The modified BN particles were used to fabricate PI/BN composites with enhanced thermal conductivity by in situ polymerization.The FTIR,XRD,SEM,TEM and contact angle measurements showed that the silane coupling agent was successfully grafted to the BN surfaces.The addition of BN fillers can effectively improve the thermal conductivity of composites.The composites presented a thermal conductivity of 0.677 W/(m·K)with loading of 40wt% BN particles.Whereas a higher thermal conductivity value of 0.768 W/(m·K)was obtained by adding the same content of modified BN fillers,4.6 times higher than that of pure polyimide.The glass transition temperature and tensile strength of composites decreased slightly with the increase of the modified BN content.Meanwhile,the composites fabricated retained excellent thermal stability and electrical insulation.For the composites filled with BN and ND hybrid fillers into polyimide system,BN fillers were functionalized with hyperbranched aromatic polyamide(HBP)and ND particles with 4,4'-oxybisbenzenamine(ODA)firstly,and then were characterized by fourier transform infrared(FTIR)spectra,thermo-gravimetric analysis(TGA)and scanning electron microscopy(SEM)tester.Meanwhile,the effects of BN and ND surface modification and loading level of BN and ND particles on thermal conductivity,thermal stability,electrical insulation and dynamic mechanical properties of the fabricated composites were investigated.The results indicated that the different sizes thermal conductive fillers filled in polyimide matrix could promote the fillers' dispersion,increase the packing density,and present a noticeable synergistic effect on reducing the interfacial thermal resistance and forming thermal conductive networks.When the filler content was 30wt% with the modified BN and ND particles in mass ratio of 9:1,the thermal conductivity of the composite was 0.598 W/(m·K),which was 3.5 times higher than that of the pure polyimide.Meanwhile,the composites fabricated possessed excellent electrical insulation and thermal stability,and are appropriate for the application of packaging materials.