Lösungseigenschaften von polymethylmethacrylat und polystyrol aus Röntgenkleinwinkelmessungen

Light scattering investigations of solutions of polymethylmethacrylat (PMMA) and polystyrene (PST) are extended to low molecular weights by small-angle X-ray scattering. In a medium range of molecular weights (M = 10³ to 3·10⁴) the radius of gyration is proportional to M^0.5 even in good solvents. For M < 3·10⁴ the radii of gyration of PMMA found in the good solvent acetone are equal to those in the used Θ-solvent within the limits of error. In the case of PST in toluene this is not valid. From the relations α⁵ - α³ ～ z and α³ - 1 ～ z graphical methods were derived for the determination of r²₀/M from measurements in goods solvents by extrapolation to M = 0. For these extrapolation procedures it is necessary to perform measurements in the range between M = 10⁴ and M = 10⁵. The dependence of the second osmotic virial coefficient on the molecular weight in the low molecular range can be interpreted by Monte Carlo calculations on model compounds.