Viscosity- and Hydrodynamic-Radius Expansion Factors of Oligo- and Poly(α-methylstyrene)s in Dilute Solution

Abstract

The intrinsic viscosity [η] was determined for 23 samples of atactic oligo- and poly(α-methylstyrene)s (a-PαMS), each with the fraction of racemic diads fr = 0.72, in the range of weight-average molecular weight Mw from 4.12 × 102 to 5.46 × 106 in three good solvents, toluene, 4-tert-butyltoluene, and n-butyl chloride, at 25.0 °C. The translational diffusion coefficient D was also determined from dynamic light-scattering measurements for 17 a-PαMS samples in the range of Mw from 1.04 × 103 to 3.22 × 106 under the same solvent conditions. It was found that the values of [η] in toluene and n-butyl chloride are appreciably smaller than the previous ones of [η]ϑ in cyclohexane at 30.5 °C (ϑ) in the oligomer region in which the intramolecular excluded-volume effect may be ignored, while those of [η] in 4-tert-butyltoluene are only slightly larger than the latter there because of the dependence on solvent of the hydrodynamic chain (bead) diameter. The disagreement in toluene and n-butyl chloride may be regarded as arising from the so-called specific interaction between polymer and solvent molecules, and therefore the viscosity-radius expansion factor αη in these solvents was calculated after removing its contribution. On the other hand, the values of the hydrodynamic radius RH defined from D in the three good solvents were found to agree well with the previous ones of RH,ϑ in cyclohexane at ϑ in the oligomer region, and therefore the hydrodynamic-radius expansion factor αH could be calculated straightforwardly. It was then found that both plots of αη and αH against the scaled excluded-volume parameter z̃ for a-PαMS in the three good solvents along with those for atactic polystyrene and atactic and isotactic poly(methyl methacrylate)s previously studied form their respective single-composite curves, confirming the validity of the quasi-two-parameter scheme that all expansion factors are functions only of z̃ irrespective of the differences in polymer species (chain stiffness and local chain conformation) and solvent condition.