Electro-optical study of a polyelectrolytic graft copolymer

Abstract

Electro-optical experiments have been performed on a poly (styrene-co-N-ethyl-4-vinylpyridinium bromide) graft copolymer in water-methanol mixtures and in the absence of added salt. A positive electric briefringence was observed for the graft copolyme while the birefringence of the corresponding polyvinylpyridinium homopolymer was negative. This change of the sign of the optical anisotropy was discussedon the basis of the orientation of the pyridinium ring with respect to the main backbone and hence to the applied electric field.

We determined the electric polarizability parameter and the relaxation time of the birefringence. It was shown that the graft copolymer does not display the so-called polyelectrolytic effect, i.e. the pronounced extension of the chain with dilution. The conformation of the graft copolymer remains rather compact and much less extended than the corresponding homopolymer. The influence of the solvent composition was also investigated and the effects discussed in terms of preferential solvation of the styrene units by methanol.