摘要：

The apparent specific volume of polystyrene was determined at 25.00°C. in chlorobenzene and bromobenzene. The results are compared with and discussed on the basis of recent density measurements of bulk polystyrene by Flory and Fox. It follows that at least 3% of the volume of solid bubble-free bulk polystyrene at room temperature consists of cavities and that the specific volume of bulk polystyrene at room temperature would be nearly the same as that of polystyrene dissolved in a good solvent if the apparent second-order transition could be avoided for the former. The results indicate that care must be taken in interpreting volume changes observed on mixing solid polymers with solvents. It is proposed to characterize the apparent second-order transition by an alternation of configurational probability in neighboring volume elements. The resulting "microstrain" and cavitation allow a simple explanation of phenomena associated with an apparent second-order transition such as brittleness. Slight divergencies between the apparent specific volume observed and expected in solution and an analysis of pertinent literature data show that the apparent specific volume changes appreciably with the nature of the solvent. It follows, in particular, that the number of vacant sites within a polystyrene molecule in solution is small in good solvents—where conceivably a slight solvation exists—and is very large in poor solvents. In the latter case, the free volume may exceed that found in bulk polystyrene at room temperature. The probable effect of molecular weight upon solution densities and the question of density measurements for rapid molecular weight determinations are discussed briefly by means of extrapolations from data obtained by Flory and Fox.

展开