Temperature coefficients of unperturbed chain dimensions for polystyrene and poly(α-methylstyrene)

The temperature coefficient d In (R-2)(0)/dT of the unperturbed mean-square end-to-end distance (R-2)(0) with T the absolute temperature was determined from light scattering measurements for atactic polystyrene (a-PS) with the fraction of racemic diads f(r) = 0.59 and atactic poly(alpha-methyl styrene) (a-P alpha MS) with f(r) = 0.72, both in toluene (good solvent) and in the range of temperature 15.0-55.0 degrees C, on the assumption that the binary-cluster integral and hence the gyration-radius expansion factor do not depend on T. It is then found that d In (R-2)(0)/dT is definitely negative for a-PS with a weak helical nature but almost vanishes for a-P alpha MS with a strong helical nature. The results are consistent with the helical wormlike chain theory prediction.