The intrinsic viscosity [η] was determined for 23 samples of atactic oligo-and poly(Rmethylstyrene)s (a-PRMS), each with the fraction of racemic diads fr ) 0.72, in the range of weightaverage molecular weight Mw from 4.12 × 10 2 to 5.46 × 10 6 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-PRMS samples in the range of Mw from 1.04 × 10 3 to 3.22 × 10 6 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 R η 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 RH could be calculated straightforwardly. It was then found that both plots of Rη and RH against the scaled excluded-volume parameter z ˜for a-PRMS 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 z ˜irrespective of the differences in polymer species (chain stiffness and local chain conformation) and solvent condition.

The intrinsic viscosity [η] was determined for 25 samples of atactic oligo- and poly(α-methylstyrene)s (a-PαMS), each with the fraction of racemic diads f r = 0.72, in the range of weight-average molecular weight M w from 2.94 × 102 (dimer) to 3.22 × 106 in cyclohexane at 30.5 °C (ϑ). The translational diffusion coefficient D was also determined from dynamic light-scattering measurements for 21 of them in the range of M w from 5.30 × 102 (tetramer) to 3.22 × 106 under the same solvent condition. It is found that the double-logarithmic plots of [η] and M w D against M w follow their respective asymptotic straight lines of slope 1/2 for M w ≳ 2 × 105, but deviate upward and downward, respectively, from them with decreasing M w for smaller M w. From an analysis of these transport coefficients on the basis of the helical wormlike (HW) chain model, it is shown that the above M w dependence of [η] and D may be well explained by the corresponding HW theories with the values of the model parameters consistent with those previously determined from the mean-square radius of gyration 〈S 2〉. A comparison is also made of the present results for [η] and D for a-PαMS with the previous ones for atactic polystyrene with f r = 0.59, atactic poly(methyl methacrylate) (a-PMMA) with f r = 0.79, and isotactic PMMA with f r ≃ 0.01. It confirms the previous conclusion derived from 〈S 2〉 concerning the chain stiffness and local chain conformations of the a-PαMS chain. That is, the a-PαMS chain tends to retain large and clearly distinguishable helical portions in dilute solution just as the a-PMMA chain, although the strength of helical nature is somewhat smaller for the former.