Diffusion measurements on low molecular weight polystyrenes

Abstract

Abstract Measurements of diffusion, viscosity, and cryoscopic determinations of molecular weight were carried out in benzene on eight fractions of polystyrene with low molecular weight (up to about 3,000). These indicate that there is a linear relation between MD and M 1/2 . This relationship corresponds to the Einstein‐Stokes equation in which the equivalent radius is replaced by the gyration radius. The value of the rotation hindrance factor A calculated from the results of diffusion measurements on polystyrenes with low molecular weights was found to be equal to that calculated from the viscosity data on polymers of high molecular weight in θ solvents, where the swelling effect is nil. This confirms, therefore, that this factor is constant over a wide range of molecular weights. The viscosity data on low molecular weight polystyrene in benzene at 20°C. are very similar to those for samples of high molecular weight in θ solvents. The molecular dimensions of polystyrenes with low molecular weight are therefore unaffected by the swelling effect. The Flory constant Φ, deduced from cryoscopic, diffusion, and viscosity measurements, for the values of M , (h̄ 2 ) 1/2 , and [η], respectively, assumes a value of 3 × 10 21 . The results have been briefly discussed, from the point of view of the Kirkwood‐Riseman and Debye‐Bueche theories.