DEPOLARIZED RAYLEIGH-SCATTERING FROM SHORT-CHAIN POLYSTYRENE IN A THETA-SOLVENT

Five different polystyrene samples with a narrow molecular weight distribution were investigated in dilute solution in bicyclohexyl by depolarized light scattering using interferometric techniques. Bicyclohexyl was found to be a theta-solvent at 61-degrees-C. The chain length of the polystyrene samples varied from approximately 10 to 100 monomer units. We investigated the temperature range from 20 to 90-degrees-C whereby the solution concentrations were in the nonoverlap region (c[eta] much less than 1). The depolarized Rayleigh spectra were well-represented by a single Lorentzian line shape which was assigned to the overall reorientational motion of the chains. The reorientational relaxation times fit to the modified Stokes-Einstein-Debye relation, yielding hydrodynamic volumes of the oligomers. The reorientation motion of polystyrene in bicyclohexyl reflects, with increasing molecular weight, a tendency to coil formation of the molecules beginning at a nominal molecular weight of 2000. Using the Perrin relation we were able to calculate the axial ratios of the oligomers at the theta-point assuming a prolate ellipsoid of revolution.