Dynamic Depolarized Light Scattering by Oligo- and Poly(α-methylstyrene)s in Dilute Solution

Abstract

ABSTRACT:The power spectrum J À of the excess depolarized component of scattered light was determined from frequency-domain dynamic depolarized light scattering measurements for 10 samples of atactic oligo-and poly(-methylstyrene)s (a-PMS), each with the fraction of racemic diads f r ¼ 0:72, in the range of weight-average degree of polymerization x w from 2 to 67.1 in cyclohexane at 30.5 C (Â). It is found that, as in the cases of atactic polystyrene (a-PS), atactic poly(methyl methacrylate) (a-PMMA), and isotactic (i-) PMMA, J À may be well represented in terms of a single Lorentzian independently of x w , and that the relaxation time À as defined as the reciprocal of the half-width at half-maximum of J À evaluated at infinite dilution increases with increasing x w and levels off to its asymptotic value in the limit of x w ! 1, being consistent with the theoretical prediction on the basis of the helical wormlike (HW) chain model. A comparison is made of the present data for À 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 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 À . From a comparison of the present results for À for a-PMS with previous ones for a-PS and a-and i-PMMAs, it is shown that there is good correlation between static and dynamic chain stiffness, the latter being defined as the ratio of the relaxation time associated with the local motion of the long chain to that of its isolated repeat unit (monomer), as predicted by the HW theory.

Nuclear Magnetic Relaxation of Oligo- and Poly(α-methylstyrene)s in Dilute Solution

“…The spin-lattice relaxation time T 1 and nuclear Overhauser enhancement NOE determined from nuclear magnetic relaxation measurements may also be written in terms of the time-correlation functions of the same class 2(1), 2,4,5 and therefore have a close relation to À . In the present paper as a continuation of the preceding one, 1 we report results of a nuclear magnetic relaxation study of a-PMS.…”

“…1 In Table I are reproduced the values of the weight-average molecular weight M w , weight-average degree of polymerization x w , ratio of M w to the number-average molecular weight M n , and fraction of racemic diads f r for the three samples from Table I The solvent cyclohexane used for nuclear magnetic relaxation measurements was purified according to a standard procedure prior to use.…”

“…1 Thus the purpose of the present paper is to examine whether such a close correlation holds also for a-PMS.…”

“…In the preceding paper, 1 we have examined the behavior of the relaxation time À defined by the reciprocal of the half-width at half-maximum of the spectrum J À of the excess depolarized component of the light scattered by atactic oligo-and poly(-methylstyrene)s (a-PMS) in cyclohexane at 30.5 C (Â). The quantity À represents a mean of relaxation (correlation) times of time-correlation functions of the spherical tensor components of the polarizability tensor affixed to the repeat unit of a polymer chain.…”

Fine characterization of oligomers and polymers in dilute solution

“…Fig. 17 shows double-logarithmic plots of t G =t 0 G against x w for a-PaMS in cyclohexane at 30.5 1C ðYÞ [33] and a-PS in cyclohexane at 34.5 1C ðYÞ [34], where t 0 G is the t G of cumene, which may be regarded as corresponding to the monomer of each of a-PaMS and a-PS. From this figure, it is seen that t G =t 0 G for each of the polymers first increases with increasing x w and seems to level off in the limit of x w !…”