Temperature Coefficients of Unperturbed Chain Dimensions for Flexible Polymers*

Until now, we have made a series of experimental studies of dilute solution behavior of typical flexible polymers on the basis of the helical wormlike (HW) chain model. From an analysis of experimental data obtained for the polymers including their oligomers in their respective $\Theta $ states, we have shown that atactic poly($\alpha $-methylstyrene) (a-P$\alpha $MS) with the fraction of racemic diads $f_{r}$=0.72 tends to retain large and clearly distinguishable helical portions in dilute solution while atactic polyetyrene (a-PS) with $f_{r}$=0.59 does not. In this study, we determined the temperature coefficient d ln$_{0}$/d $T$ of the unperturbed mean-square end-to-end distance $_{0 }$with $T$ the absolute temperature from light scattering measurements for a-PS and a-P$\alpha $MS. It has then been found that d ln$_{0}$/d $T$ is definitely negative for a-PS but almost vanishes for a-P$\alpha $MS. The results are consistent with the HW theory prediction.