UNIAXIAL PLANAR DEFORMATION OF PET FILMS .2. CHARACTERIZATION OF THE ORIENTATION FROM MEASUREMENTS OF REFRACTIVE-INDEXES

Refractive indices along the three principal directions of uniaxial pl anar deformed poly(ethylene terephthalate) (PET) films have been used to calculate the second moments of the orientation distribution of the phenyl ring's normal with respect to the three principal directions o f the sample. Under our stretching conditions, the phenyl rings show a strong tendency to orient their plane parallel to the plane of the fi lms. The orientation of the chain axis can also be evaluated from the same data. A good correlation is observed between this indirect measur ement and direct, but more tedious, techniques such as infra-red dichr oism.