Excluded-Volume Effects on the Hydrodynamic Radius of Oligo- and Polyisobutylenes in Dilute Solution

Abstract

The translational diffusion coefficient D was determined from dynamic light scattering measurements for oligo- and polyisobutylenes in isoamyl isovalerate (IAIV) at 25.0 °C (ϑ) and in n-heptane at 25.0 °C in the range of weight-average molecular weight Mw from 1.01 × 103 to 1.76 × 106. The values of the unperturbed and perturbed hydrodynamic radii RH,ϑ and RH defined from D in IAIV and in n-heptane, respectively, were found to agree with each other in the oligomer region, indicating that the values of RH,ϑ may be adopted as those of the unperturbed hydrodynamic radius RH,0 in n-heptane at 25.0 °C. The values of the hydrodynamic-radius expansion factor αH in n-heptane at 25.0 °C are then obtained as the ratio RH/RH,ϑ from those values thus determined. The data for RH,ϑ are analyzed as usual by the use of the corresponding (unperturbed) helical wormlike (HW) chain theory. The results for αH as a function of the scaled excluded-volume parameter z defined in the Yamakawa−Stockmayer−Shimada theory for the HW ...