Determination of the molecular weight of polyacrylamide fractions by osmometry

The polymerization of acrylamide, initiated with permanganate/oxalic acid, has been studied at 35 ± 0.2 in an aqueous medium under nitrogen. Samples of polyacrylamide were fractionated by the triangular fractionation method using methanol as non-solvent. Molecular weights of the fractions have been determined by viscometry and osmometry. Integral and differential distribution curves were plotted using the fractionation data. The narrow molecular weight distribution for high conversion polymers has been discussed. For fractionated samples of polyacrylamide in water at 30°, the equation $\text{η]}{}_{\mathrm{ml/g}}\text{= 6.5 × 10}{}^{\mathrm{?3}}\text{M}{}_{\mathrm{n}}{}^{0.82}$ is applicable for the molecular weight range 4 × 10⁴ to 127 × 10⁴. This equation is very similar to the equation $\text{η]}{}_{\mathrm{ml/g}}\text{= 6.31 × 10}{}^{\mathrm{?3}}\text{M}{}_{\mathrm{/}}{}^{0.80}$ of Scholtan. Other parameters (osmotic second virial coefficient and unperturbed dimension) have also been evaluated.