Study On Synthesis And Properties Of Highly Isotactic Polyacrylonitrile

Properties of carbon fiber is directly influenced by the quality of polyacrylonitrile (PAN) precursor, the factors that affet on he quality of PAN precursor, such as the type of polymerization monomer in the polymer, molecular weight, stereoregularity, clean level, spinning method and technique, tensile technique, compacting level by drying, the type of oil and oiling technique and so on, must be paid great attention to prepare the PAN precursor with good properties. The stereoregularity of PAN precursor influences properties of carbon fiber. In this paper highly isotactic(mm>0．50) PAN by anionic polymerization using dibutylmagnesium and triethylaluminum as initiator were synthesized, by means of ¹³ C nuclear magnetic resonance(¹³ C-NMR), differential scanning calorimeter(DSC), Fourier transform infrared ray(FT-IR), X-ray diffraction(XRD), highly isotactic PAN and atatic PAN abtained by free-radical polymerization were studied. The process of the preparation consists of: 1,The effects of different reaction conditions on PAN were investigated, the best condition for synthesis of PAN was ascertained: reaction time for 7h; mole ratio of dibutylmagnesium to AN was 1:150; reaction temperature was 130℃.2,isotacticity of PAN were researched through the reaction in the solvent at 130℃. The results show that isotacticity of PAN is different in the different solvent when other conditions are consistent, isotactic content of PAN increased in the nonpolar solvent putted in the appropriate polar solvennt such as diethylene glycol dimethyl ether(2G) and dioxane.3,the triad tacticities of PAN obtained was analyzed by ¹³ C-NMR, the triad isotactic content of synthesized PAN can achieve 56．5%, the triad syndiotactic content of synthesized PAN is 18．0%,the triad atactic content of synthesized PAN is 15．5%. the triad isotactic content of synthesized PAN increase 31 % comparing with PAN attained by free-radical polymerization.4,By means of DSC,FT-IR and XRD, it is discovered that isotactic PAN releases greater quantity of heat than atactic PAN during the preliminary heat treatment in oxi-dizing and it is prone to Cyclization, accordingly , isotactic PAN form ladder-shaped reticular structure easily; cyano group in the isotactic PAN molecular reacts easily each other to form ladder-shaped reticular structure .