Coil Dimensions of Polystyrenes in Isorefractive Viscous Solvents by Small-Angle Neutron Scattering

The radii of gyration of perdeuterated polystyrenes with molecular weights ranging from 10000 to 104 000 have been determined at infinite dilution in Aroclor 1248 and tricresyl phosphate by small-angle neutron scattering. Measurements were carried out at the National Bureau of Standards, the Oak Ridge National Laboratory, and the University of Missouri. The coherent scattering in all cases is well described by the Debye function. The radii are very close in magnitude to those obtained in cyclohexane at the θ temperature, although for these solvents all indications are that the solvent quality is intermediate to good. This result is interpreted as another manifestation of the solvent dependence of the unperturbed dimensions of polystyrene. Remarkably, however, literature values of the intrinsic viscosity of polystyrenes in these two solvents are considerably higher than those reported in cyclohexane. Thus, in these particular systems the scattering and viscosity experiments are apparently sensitive to quite different properties of the chain, and extraction of coil dimensions directly from intrinsic viscosity data should be performed with caution.