DYNAMIC PROPERTIES OF LOW AND MODERATE MOLECULAR-WEIGHT POLYSTYRENES AT INFINITE DILUTION

Oscillatory flow birefringence (OFB) has been used to determine the dilute solution and infinite dilution conformational dynamics properties of four low molecular weight polystyrenes (PS) (M = 2.0 x 10(3), 5.5 x 10(3), 2.0 x 10(4), and 3.2 x 10(4)) in Aroclor 1248. These results are well-described by the bead-spring model (BSM) of Rouse and Zimm, using exact eigenvalue calculations and small values of the number of subchains, N. The initial concentration dependence of the relaxation times is in good agreement with the extension of Muthukumar and Freed. These results are predicated on the appropriate subtraction of the solvent contribution to the measured solution properties, which, in contrast to the conventional approach, is not given by the volume-fraction-weighted neat solvent birefringence. Additionally, pulsed-field-gradient NMR and forced Rayleigh scattering have been used to determine the infinite dilution diffusion coefficients for five PS samples (M = 2.0 x 10(3), 5.5 x 10(3), 9.0 x 10(3), 3.2 x 10(4), and 9.0 x 10(4)) in the same solvent. These results are well-represented by the Kirkwood-Riseman expression, using the same parameter values as used to interpret the OFB results. Furthermore, the diffusivities are equivalent to those reported for PS in toluene and cyclohexane, when scaled by the respective solvent viscosities. The OFB and diffusivity results have been combined with other literature data for PS in Aroclor 1248, including intrinsic viscosity, radius of gyration, and OFB properties for other molecular weights, to provide a stringent test of the BSM. All of the dynamic properties can be described quantitatively with one set of parameter values. This apparent success of the BSM is surprising, given the simplified description of the chain dynamics at the segmental level and the relatively low molecular weight samples examined. In particular, the OFB data suggest a distinct high-frequency end to the relaxation spectrum, corresponding to the relaxation of a ca. 50 monomer subchain.