Birefringence in solutions and films of poly(N-methyl-N-vinylacetamide) macromolecules

The flow birefringence of aqueous solutions of poly(N-methyl-N-vinylacetamide) macromolecules for samples of various molecular masses is studied. It is found that the sign of birefringence changes from positive to negative with a decrease in molecular mass in accordance with the manifestation of the macroform effect on condition that the value of the inherent optical anisotropy of macromolecules is negative. With the use of the macroform-effect theory in the Maxwell phenomenon of polymer solutions, the inherent optical anisotropy of the repeating polymer unit is estimated as (a (aEuro-)-a (aSyen)) = -(5 +/- 1) x 10(-25) cm(3). In turn, the value of (a (aEuro-)-a (aSyen)) makes it possible to separate structural and orientational contributions to the effect of spontaneous birefringence for films of various thicknesses that are cast from aqueous solutions of poly(N-methyl-N-vinylacetamide). The parameter of orientational order of chain fragments for this polymer in the near-surface layers of the films is -(0.05 +/- 0.01).