Effect of molecular weight on the partial specific volume of polystyrenes in solution

Abstract

The partial specific volume v ̄ 2 of linear and branched polystyrenes has been measured as a function of molecular weight (1300< M w <9×10 6). In the low molecular weight range, the effect of end-groups is predominant. In the high molecular weight range ( M w > about 20 000), we have detected small but significant variations due to the intramolecular segment-segment contacts within the coil. We have proposed an empirical relation between v ̄ 2 and the segment density of the macromolecule; this relation has been confirmed using highly branched polystyrenes. These results relative to dissolved polystyrenes are compared to experimental data obtained by different authors on pure liquid polystyrenes at different temperatures. Starting from simple additivity rules and from the known chemical composition of liquid polymers, we have shown that the variation of specific volume with high molecular weights is due to some phenomenon different from an effect of chain-ends.