The (excess) power spectrum Jr of the depolarized component of scattered light was measured for 10 samples of oligo- and polystyrenes, each with the fraction of racemic diads f(r) = 0.59, in the range of weight-average molecular weight M(W) from 3.70 x 10(2) (trimer) to 1.01 X 10(4) and also for cumene in cyclohexane at 34.5-degrees-C (theta) and in carbon tetrachloride at 25.0-degrees-C. The spin-lattice relaxation time T was also determined for the trimer through pentamer and the sample with the highest M(W), and the nuclear Overhauser enhancement NOE, for the trimer and the sample with the highest M(W), both in cyclohexane at 40-degrees-C. It is found that J(GAMMA) may be well represented in terms of a single Lorentzian independently of M(W) and solvent and that the relaxation time Tr as defined as the reciprocal of the half-width at half-maximum of J(GAMMA) evaluated at infinite dilution increases with increasing M(W) and levels off to an asymptotic value in the limit of M(W) --> infinity in each solvent, being consistent with the recent theoretical results on the basis of the helical wormlike (HW) chain model. The reduced relaxation time k(B)Ttau(GAMMA)/eta0 with k(B) the Boltzmann constant, T the absolute temperature, and eta0 the solvent viscosity is found to be almost independent of solvent for each sample, its asymptotic value in the limit of M(W) --> infinity being ca. 4 x 10(3) angstrom3. A comparison is made of the present data for tau(GAMMA), T1, and NOE with the HW chain theory, and it is shown that the theory may explain satisfactorily the data in the range of M(W) greater than or similar to 10(3) except for NOE. For M(W) less-than-or-similar-to 10(3), the rigid sphere model having the radius equal to the apparent root-mean-square radius of gyration of the HW chain may give a good explanation of all the data. An analysis of the interrelation between these three quantities leads to the simple picture that the nuclear magnetic relaxation is also governed, although approximately, by a single relaxation time identical with tau(GAMMA).