Light Scattering and Viscometric Study on Polyacrylonitrile in Dimethylformamide, Ethylene Carbonate/Water Mixture, and Aqueous Nitric Acid

Abstract

An attempt was made to determine the Flory theta solvents and the unperturbed chain dimension A of polyacrylonitrile (PAN). A sample of PAN, polymerized using redox catalyst and having isotactic triad of 26% and syndiotactic triad of 24%, was fractionated by successive solution fractionation method to give a series of fractions with the ratio of weight- to number- average molecular weight Mw/Mn of 1.15—1.41. A mixture of ethylene carbonate (EC) and water containing 85 wt% EC and aq. 55 wt% nitric acid was identified by the light scattering method to be Flory theta solvents at 25°C whose second virial coefficients were zero. The Mark–Houwink– Sakurada (MHS) equations were determined in various solvents. In the theta solvents, the radius of gyration 〈S2〉z1/2 was proportional to Mw1/2 and the exponent a in MHS equations was always 0.5. The Flory viscosity parameter Φ was 2.3×1023 in DMF and 2.8×1023 in theta solvents, independent of Mw. The unperturbed chain dimension parameter A, the conformation parameter σ and the characteristic ratio C∞ were determined by thermodynamic and hydrodynamic methods. Both methods gave consistent results. The solvent dependence of these parameters was demonstrated.