Transport Coefficients of oligo-and Poly(#alpha#-methylstyrene)s in Dilute Solution

摘要

The intrinsic viscosity [17] was detennined for 25 samples of atactic oligo- and poly(a- methylstyrene)s (a-PaMS), each with the fraction of racemic diads fr = 0.72, in the range of weight- average molecular weight Mw from 2.94 x 102 (dimer) to 3.22 x 106 in cyclohexane at 30.5 °C (8). The translational diffusion coefficient D was also determined from dynamic light-scattering measurements for 21 of them in the range ofMw from 5.30 x 102 (tetramer) to 3.22 x 106 under the same solvent condition. It is found that the double-logarithmic plots of [17] and MwD against Mw follow their respective asymptotic straight lines of slope 1/2 for Mw ~ 2 x 105, but deviate upward and downward, respectively, from them with decreasing M w for smaller Mw. From an analysis of these transport coefficients on the basis of the helical wormlike (HW) chain model, it is shown that the above Mw dependence of [17] and D may be well explained by the corresponding HW theories with the values of the model parameters consistent with those previouslydetennined from the mean-square radius of gyration (82). A comparison is also made of the present results for [11] and D for a-PaMS with the previous ones for atactic polystyr.ene with fr = 0.59, atactic poly(methylmethacrylate) (a-PMMA) with fr =0.79, and isotactic PM11A with fr ~ 0.01. It confirms the previous conclusion derived from (82) concerning the chain stiffness and .local chain conformations of the a-PaMS chain. That is, the a-PaMS 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 fonner.