POLYACRYLAMIDE IN WATER - MOLECULAR-WEIGHT DEPENDENCE OF (R2) AND [ETA] AND THE PROBLEM OF THE EXCLUDED VOLUME EXPONENT

A commercial sample of polyacrylamide (CALGON) has been carefully purified, analysed and fractionated. With suitable care, the molecular characterization can be carried out by light scattering and viscosity measurements, without disturbances arising from microgels or aggregates. The molecular weight dependence of the radius of gyration and intrinsic viscosity are given by:. 〈R2〉 1 2 = 7.49 × 10- M0.64( A ̊)[η] = 9.33 × 10-3 M0.75(cm3/g). The value of the exponent ν = 0.64 in the 〈R2〉 1 2 equation has been cross-checked by a study of the asymptotic behaviour of the scattering envelope. Such a value is higher than that expected in a good solvent (ν = 0.60) and should lead to a higher exponent in the intrinsic viscosity dependence. However, it agrees more closely with the published dependence of sedimentation and diffusion coefficients. © 1979.