Method for preparing polyacrylonitrile spinning solution

The invention belongs to the field of organic polymers and particularly relates to a method for preparing polyacrylonitrile spinning solution. The method comprises the following steps of: mixing the dimethyl sulfoxide solution of acrylonitrile, itaconic acid and methyl acrylate which serve as comonomers with the dimethyl sulfoxide solution of azo-bis-iso-heptonitrile, wherein the concentrations of the comonomers are12-20%, the concentration of the azo-bis-iso-heptonitrile is 0.1-1%, and the molar ratio of the acrylonitrile, the itaconic acid and the methyl acrylate is (96-99):(0.5-3):(0.5-3); carrying out polymerization reaction at the temperature of 50-80 DEG C; controlling the temperature at 60-80 DEG C 5-10 hours later; continuing to stir and extracting a polymer solution in a polymerizing kettle in vacuum until the vacuum degree in the polymerizing kettle is -80kPa; increasing the vacuum degree in the polymerizing kettle to -98kPa after extracting for 1 hour; continuing to extract; feeding the polymer solution extracted in vacuum into a defoaming kettle; continuously defoaming under the condition of -80kPa and 60-80 DEG C; and carrying out tertiary filtering on a defoamed polymer. The method is simple in process and high in controllability, and the content of solid in the prepared spinning solution is large, and the content of residual monomers is low.