Gyration-Radius Expansion Factor of Oligo- and Poly(α-methylstyrene)s in Dilute Solution

Abstract

The mean-square radius of gyration 〈S2〉 was determined from small-angle X-ray scattering and light scattering measurements for atactic oligo- and poly(α-methylstyrene)s (a-PαMS) with the fraction of racemic diads fr = 0.72 in toluene at 25.0 °C, in 4-tert-butyltoluene at 25.0 °C, and in n-butyl chloride at 25.0 °C in the range of weight-average molecular weight from 1.04 × 103 to 5.46 × 106. The gyration-radius expansion factor αS was then evaluated from the values of 〈S2〉 so determined along with those of 〈S2〉ϑ previously determined for the same samples in cyclohexane at 30.5 °C (ϑ). It is shown that the plots of αS against the scaled excluded-volume parameter z for a-PαMS along with those for atactic polystyrene (a-PS) and atactic and isotactic poly(methyl methacrylate)s previously studied form a single-composite curve, 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 loc...