Excluded-Volume Effects on the Hydrodynamic Radius of Atactic and Isotactic Oligo- and Poly(methyl methacrylate)s in Dilute Solution

Abstract

The translational diffusion coefficient D was determined from dynamic light scattering measurements for atactic (a-) and isotactic (i-) oligo- and poly(methyl methacrylate)s (PMMA) in acetone at 25.0 °C in the range of weight-average molecular weight Mw from 1.83 × 103 to 9.52 × 105 for the former and from 3.04 × 103 to 9.78 × 105 for the latter. For each PMMA, the values of the (perturbed) hydrodynamic radius RH (defined from D) in acetone were found to agree with those of the radius RH,ϑ previously (and presently) obtained in the unperturbed (ϑ) state (i.e., in acetonitrile at 44.0 °C for a-PMMA and at 28.0 °C for i-PMMA) in the oligomer region. The hydrodynamic-radius expansion factor αH was then determined correctly from the values of RH and RH,ϑ. The results for αH as a function of the scaled excluded-volume parameter z defined in the Yamakawa−Stockmayer−Shimada theory for the helical wormlike chain with excluded volume are consistent with the previous results for atactic polystyrene, poly(dimethyls...