Near‐Ultraviolet Light Scattering for the Determination of Molecular Dimensions

Modification of a conventional light‐scattering photometer for measurements in the near ultraviolet is described. As a test of the instrument, unperturbed dimensions are determined for a series of polystyrene fractions covering a thirtyfold range of molecular weight. Values of the Flory hydrodynamic parameter are found to be nearly independent of molecular weight, averaging 10−21 Φ = 2.65±0.24, but there is a fairly definite indication that the polystyrene chain is non‐Gaussian for molecular weights below 3×105. Use of a 313‐mμ wavelength extends the measurement of radii of gyration of coiling molecules down to 100 A, which is about the upper limit which has been achieved by low‐angle x‐ray diffraction.