Extinction angles, intrinsic viscosities, and molecular weights of polystyrene in solution

Abstract

Experimental measurements of the extinction angle of polystyrene fractions were made concurrently with intrinsic viscosity and sedimentation measurements. Data so obtained have been used to examine the Kuhn theory of streaming birefringence and also to calculate rotatory diffusion constants. A combination of intrinsic viscosity and rotatory diffusion constant was used to calculate molecular weights, and these were compared with previously calculated data from osmotic pressure, sedimentation, and intrinsic viscosity measurements on the same fractions. Furthermore, this pair measurement was used according to the Kirkwood-Riseman (K-R) theory to compute the fundamental molecular parameters b and ζ which were compared with the results from sedimentation measurements. The root mean square end-to-end distance is determined from the experimental values of b and compared with the analogous values from sedimentation and with the length obtained from a direct application of the Kuhn theory. In addition the following information was obtained: 1. 1. The changes in the extinction angle from solvent to solvent can be interpreted in a manner analogous to the intrinsic viscosity and sedimentation data as being connected with the average changes in shape (molecular dimensions). Thus the extinction angle is found to be lower in chloroform than in toluene, corresponding to the higher intrinsic viscosity in the former. 2. 2. Molecular-weight measurements are readily made from the pair measurement of intrinsic viscosity and rotatory diffusion constant in direct analogy to the pair measurement of sedimentation constant and translational diffusion constant. 3. 3. Sizes computed from the direct application of the Kuhn theory are several fold too low as compared with the values customarily found from light-scattering, sedimentation, and intrinsic viscosity. 4. 4. Sedimentation constants calculated from the b and ζ values of extinction angle measurements are in satisfactory agreement with those previously reported for the same fractions. 5. 5. Extinction angles near 45° were found up to gradients of 5 × 10 3 sec. −1 for polystyrene molecular weights up to 8 × 10 5, in agreement with those calculated from the rotatory diffusion constant according to Riseman and Kirkwood.