The field strength dependence of the electric birefringence of poly-N-butyl-4-vinylpyridinium bromide in aqueous solution changes markedly with ]?__olymer concentration. Analysis of the orientation curves reveals that the mean electric polarizability A0c sharply increases when the concentration decreases, as a result of the extension of the chain, while the negative optical anisotropy factor remains unchanged. An empirical relationship, similar to that found for the reduced viscosity, is derived for the variation of electric polarizability with concentration.
Increasing the ionic strength produces a coiling of the polyelectrolytic chain and a decrease of A~. The replacement of the bromide ions by sulphate ions causes a conformational change evidenced by a decrease of A~ and of the relaxation time. This effect is interpreted by the formation of electrostatic bonding between the pyridinium rings on non-adjacent segments of the chain, and to a limited extend. by intermolecular bonding.
The dependence of the relaxation time, extrapolated to infinite dilution, on the molecular weight of the samples is analysed on the basis of a worm-like chain model. The persistent length obtained is found of the same order of magnitude as in the case of other semi-rigid polymers. The predominant influence of the segmental orientation on the optical, electric or conformational parameters is discussed in detail.