Zur unverträglichkeit von polymergemischen. III. Lichtstreuungsmessungen an hochmolekularen polystyrolen in polymethylmethacrylat/benzol

Polystyrenes of high molecular weight were investigated by means of light scattering in the isorefractive polymer/solvent mixture polymethylmethacrylate/benzene. It was found, that the second osmotic virial coefficient, A₂, was strongly dependent on the molecular weight and the concentration of polymethylmethacrylate (PMMA) but neglegibly on the molecular-weight of polystyrenes (PS) or on the temperature between 20 and 60°C. A plot of A₂/A vs. c_PMMA/c_Θ revealed that all points fall on a common line for all molecular weights of PS and PMMA. Herein A means the second osmotic virial coefficient of PS in pure benzene, c_PMMA the concentration of PMMA, and c_Θ the concentration of PMMA at the Θ-point (A₂ + 0). This result could be theoretically interpreted in terms of the STOCKMAYER light scattering theory for multicomponent systems. The radii of gyration of PS in PMMA/benzene decrease with increasing concentration of PMMA. Furthermore, these radii increase slightly with increasing molecular weight of PMMA at the Θ-point. The coil dimensions, however, are generally bigger than those found in binary Θ-systems. For the measured radii of gyration of PS in PMMA/benzene a common line for all molecular weights of PS and PMMA could be found by normalizing with respect to both the radii of gyration and the concentration of PMMA.