Influence of molecular weight distribution on the intrinsic viscosity‐molecular weight relationship

Polystyrene made by polymerization at 140° (polymer yield 18.9%) was fractionated successively into a number of fractions of increasing homogeneity. Intrinsic viscosity and osmotic molecular weight of the unfractionated polymer and of the fractions were determined. In the relation between them the constant K was found to decrease from K 0 = 14.2 X 10 −7 for the unfractionated polymer to K 0 = 6.8 X 10 −7 for the most homogeneous fractions. The distribution function of G. V. Schulz for the polymer and a Gaussian function for the most homogeneous fractions are discussed. From the ratio K 0 / K 0 K ∞ = 2.09 (±0.15) we draw conclusion on the mechanism of polymerization under assumption of the validity of [η] = K M α instead of the simple Staudinger equation. A possible explanation for the deviation of the experimental value 2.09 from the theoretical 1.877 is given.