C-13 MAGNETIC-RELAXATION STUDY OF THE INTERNAL MOTIONS OF POLY(4-VINYL-N-N-ALKYLPYRIDINIUM BROMIDES) IN METHANOL SOLUTIONS

The dynamical behavior of poly(4-vinylpyridine) quaternized by n-alkyl bromides of different chain length (x = 2, 4, 6, 8, 10) in methanol solution has been investigated by 13C longitudinal relaxation at 25 MHz with some subsidiary Tx and NOE measurements at 63 MHz. As in the case of poly(4-vinylpyridine) neutral or quaternized by HBr, the T1's in the macromolecular chain and in the pyridyl rings have been interpreted by a quasi-isotropic segmental motion and a jump oscillation about the C(α)-C(4') axis, respectively, assuming a distribution of correlation times. The influence of the coulombic and steric effects on the internal motions of these polymers has been examined by varying the length of alkyl side chains and the degree of quaternization. Both of these parameters have a marked effect on the flexibility of the main chain and side chains but not on the axial motion of pyridyl rings. For the internal motion of alkyl side chains, we have considered three basic models of rotation about N-C or C-C bonds and some of their combinations: rotational diffusion (A), jump among three equivalent sites corresponding to the t, g+, and g- conformers (B), and same as (B) with t unequivalent to g+, g- (C). The consistency between the T1 and NOE observed and computed for 25 and 63 MHz is achieved only for model C with W(g+ ⇄ g-) < W(t→ g±)≤0.5W (g±→t). © 1979, American Chemical Society. All rights reserved.