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Ultra-high molecular weight polyacrylonitrile (UHMWPAN) powders were synthesized by aqueous suspension polymerization with different AN/IA ratios using α,α-azobisisobutyronitrile (AIBN) as initiator and Polyvinylalcohol (PVA) as the disperser at 70℃ for 2h.The thermal properties,structural characteristics,element component analysis and aggregation structure studies of the UHMWPAN samples were measured by thermal analyzer,differential scanning calorimeter,fourier transform infrared spectrometer,element analyzer and X-ray diffractometer.The addition of IA was found to be favorable to retard the concentrated heat release and improve the carbon yield in the process of preoxidation of the precursor.The main absorption peaks corresponding to C≡N,C=O,-CH2-,-OH,and etc.were observed in FI-IR spectra of the copolymers.As the content of IA increased,the intensity of the absorption peak at 1735cm-1 corresponding to C=O increased;the content of oxygenium in the copolymer increased first and then leveled off;the former crystal structure of PAN was destroyed which meaned the decline of the degree of crystallinity and the decrease of the grain size.