The mean-square optical anisotropy (T2) was determined for 10 samples of atactic oligo-and poly(methyl methacrylate)s (a-PMMA), each with the fraction of racemic diads f, = 0.79, in the range of weight-average molecular weight Mw from 3.02 X 102 to 2.95 X 103 in acetonitrile at 44.0 °C (0) and also for methyl isobutyrate (MIB) (the monomer of PMMA) in acetonitrile at 44.0 °C and in carbon tetrachloride at 25.0 °C, from anisotropic light scattering measurements with a photometer equipped with a Fabry-Perot interferometer. The determination was also made for three samples of atactic oligo-and polystyrenes (a-PS) used in the previous study of (T2) along with cumene in carbon tetrachloride at 25.0 °C in order to compare the present procedure for determining (T2) with the previous one. A comparison is made of the present data with the helical wormlike (HW) chain theory with the values of the model parameters determined previously from the mean-square radius of gyration (S2) and with the local polarizability tensor ao properly assigned on the basis of the group polarizability tensor for the ester group of the a-PMMA chain evaluated from the polarizability of methyl acetate or MIB. The HW theoretical value of the ratio (/xw)/(

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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, -0.59, in the range of weight-average molecular weight Mw from 3.70 x 102 (trimer) to 1.01 X104 and also for cumene in cyclohexane at 34.5 °C (6) and in carbon tetrachloride at 25.0 °C. The spin-lattice relaxation time 7\ was also determined for the trimer through pentamer and the sample with the highest Mw, and the nuclear Overhauser enhancement NOE, for the trimer and the sample with the highest Afw, both in cyclohexane at 40 °C. It is found that Jr may be well represented in terms of a single Lorentzian independently of Mw and solvent and that the relaxation time rr as defined as the reciprocal of the half-width at half-maximum of Jr evaluated at infinite dilution increases with increasing M" and levels off to an asymptotic value in the limit of Mm 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^Trrhc with k% the Boltzmann constant, T the absolute temperature, and t)o the solvent viscosity is found to be almost independent of solvent for each sample, its asymptotic value in the limit of Mw -*• ® being ca. 4 x 103 A3. A comparison is made of the present data for rr, T\, and NOE with the HW chain theory, and it is shown that the theory may explain satisfactorily the data in the range of Afw S 103 except for NOE. For Mv 5 10s, 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 rr.

The (excess) power spectrum J Γ of the depolarized component of scattered light intensity was measured for eight samples of isotactic oligo- and poly(methyl methacrylate)s (i-PMMA), each with the fraction of racemic diads f r ≃ 0.01, in the range of weight-average degree of polymerization x w from 4 to 70.1 in acetonitrile at 28.0 °C (ϑ). The spin−lattice relaxation time T 1 was also determined for the three samples with x w = 4, 5, and 70.1, and the nuclear Overhauser enhancement NOE, for the two samples with x w = 4 and 70.1, all in acetonitrile at 35 °C. As in the cases of atactic (a-) polystyrene (a-PS) and a-PMMA previously studied, it is found that J Γ may be well represented in terms of a single Lorentzian independently of x w and that the relaxation time τΓ defined from J Γ at infinite dilution increases with increasing x w and levels off to its asymptotic value in the limit of x w → ∞, being consistent with the recent theoretical prediction on the basis of the helical wormlike (HW) chain model. A comparison is made of the present data for τΓ, T 1, and NOE with the HW theory, and it is shown that the theory may explain satisfactorily the data in the range of x w ≳ 10, although semiquantitatively for τΓ. For x w ≲ 10, 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 τΓ but not of T 1, indicating that the dynamic depolarized light scattering and nuclear magnetic relaxation cannot be described in terms of a common single relaxation time. However, there is shown to be an effective (mean) magnetic relaxation time τM approximately equal to 0.6τΓ. From a comparison of the present results for τΓ for i-PMMA with the previous ones for a-PS and a-PMMA, it is shown that there is good correlation between the static and dynamic chain stiffness, the latter being defined as the ratio of the value of τΓ in the limit of x w → ∞ to that of the corresponding isolated repeat unit (monomer), as predicted by the HW theory.

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