Experimental and Theoretical Investigations of PAN Molecular Weight Increase in Precipitation Polymerization as a Function of H2O/DMSO Ratio
The precipitation polymerization of acrylonitrile (AN) was carried out in a mixture solution of dimethyl sulfoxide (DMSO) and water at <TEX>$50{\sim}65^{\circ}C$</TEX> using <TEX>${\alpha},{\alpha}'$</TEX>-azobisisobutyronitrile (AIBN) as an initiator. The increased molecular weight polyacrylonitrile (PAN) was prepared with increasing the <TEX>$H_2O$</TEX>/DMSO ratio from 10/90 to 80/20. The viscosity average molecular weight of <TEX>$H_2O$</TEX>/DMSO solvent was 4.4 times larger than that of <TEX>$H_2O$</TEX>/DMF solvent, and precipitation polymerization was accelerlated due to the far decreased chain transfer effect of DMSO. Based on the experimental results, the increased PAN molecular weight was regarded as the summation of two mechanisms: i) particle-particle aggregation and ii) particle-radical attachment. The theoretical equation derived from the mechanisms was well coincided with the experimental results showing the linear relationship between the viscosity average molecular weight and the H2O/DMSO ratio.