Study of the elastic constants of stressed poly(ethylene terephthalate) by the method of Mandel'shtam-Brillouin light scattering

The effect of tensile stress on the spectra of elastic vibrations of poly(ethylene terephthalate) was studied. Using data on the shift of hypersonic frequencies at various orientations of the wavevector with respect to the direction of loading, the stress dependence of the elastic rigidity constants was calculated. Young's modulus determined using the Mandel'shtam-Brillouin light scattering spectra of stressed PET films agree well with the values obtained on the basis of a nonlinear molecular-kinetic theory of polymer stretching.