Research Of Formation And Stability Of Polyimide Foam

In this paper a new kind of polyimide foam was successfully prepared using 3,3’,4,4’-benzophenone tetracarboxylic dianhydride（BTDA） and 4,4’-methylene dianiline （MDA） as main materials.The formation and stability of the foam were primarily studied, that is the preparation technology（esterification of anhydride,synthesis and foaming of polyamic ester precursor）,dimensional stability and thermal stability of the obtained polyimide foam.The optimal esterfying time for BTDA and 3,3’,4,4’-biphenyltetracarboxylic dianhydride（BPDA） were 1 h and 10 h respectively,determined by Fourier Transform Infrared Spectroscopy（FT-IR） and ¹H nuclear magnetic resonance（¹H NMR）.At the same time,the optimum foaming temperature was determined ranging from 100℃to 250℃using Thermogravimetic Analysis（TGA）.The morphology of foam cell,mechanical and endoenergic property,acoustical behavior,thermal properties and electrical performance of the foam were characterized by Scanning Electron Microscope（SEM）,Electronic Universal Testing Machine,Standing Wave Accelerator,thermal conductivity determinator,TGA,Differential Scanning Calorimetry（DSC） and resistance test instrument,respectively.The results show that the morphology of the polyimide foam cell are comparatively even which foamed by microwave than by heat.Along with increase of the foam density, the endergonic efficiency get bigger,and all the ideal endergonic efficiency can over 0.8, the foam is a kind of energy-absorption material.Between 63 Hz and 2000 Hz.the acoustic absorptivity of the foam can reach 0.8,and sound transmission loss 20 dB,the foam can be used as low frequency noise reduction material.All the thermal conductivity of the foam are low.which is 7.62×10^-3 W/（m·K） for microwave-foam and 6.168×10^-2 W/（m·K） for heated foam.The glass transition temperature（T_g） of the polyimide foam derived from PAE100,PAE90 and PAE75 are 328℃,321.8℃and 297.47℃,and T_d5（temperature for lost weight 5%） are 540℃,521℃and 517℃,separately.The results show that the polyimide foam is a type of heat protection material.Finally,the polyimide foam have an excellent insulating property,volume resistivity of which is 10¹⁶Ω·cm and surface resistivity 10¹⁵Ω.