Molecular orientation in stretched poly(vinyl alcohol). I. NMR anisotropy and birefringence

The second and fourth moments of the proton resonance line in stretched poly(vinyl alcohol) samples have been measured by a pulse technique. Their anisotropy has been analyzed at different elongation ratios λ. The use of the second and fourth moments gives an interesting cross‐check on the reliability of the results. Despite the fact that the lattice sums required for absolute determination of the orientation cannot be calculated, coefficients related to the second and fourth moments of the orientation distribution function can be compared to the prediction of the quasiaffine orientation scheme for the crystalline phase and to the experimental values of the birefringence as a function of λ. It is shown that NMR clearly detects the onset of the orientation of the amorphous chains above λ ≈ 4.