Macromolecules, Vol.34, No.18, 6402-6408, 2001
Gyration-radius expansion factor of oligo- and poly(alpha-methylstyrene)s in dilute solution
The mean-square radius of gyration was determined from small-angle X-ray scattering and light scattering measurements for atactic oligo- and poly(alpha -methylstyrene)s (a-P alpha MS) with the fraction of racemic diads f(r) = 0.72 in toluene at 25.0 degreesC, in 4-tert-butyltoluene at 25.0 degreesC, and in n-butyl chloride at 25.0 degreesC in the range of weight-average molecular weight from 1.04 x 10(-9) to 5.46 x 10(6). The gyration-radius expansion factor as was then evaluated from the values of < S2 > so determined along with those of < S2 > (Theta) previously determined for the same samples in cyclohexane at 30.5 degreesC (Theta). It is shown that the plots of as against the scaled excluded-volume parameter (z) over bar for a-P alpha MS 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 2 irrespective of the differences in polymer species (chain stiffness and local chain conformation) and solvent condition. The excluded-volume strength for a-P alpha MS in good solvents is also discussed in comparison with that for a-PS.