STUDY OF ORIENTATION IN POLYSTYRENE POLY(VINYL METHYL-ETHER) RELATIVETO THE TEMPERATURE OF PHASE-SEPARATION

Molecular orientation and mechanical properties of polystyrene/poly(vi nyl methyl ether) (PS/PVME) miscible blends have been investigated in a broad range of compositions, taking as a reference the temperature o f phase separation. Fourier transform infra-red spectroscopy and biref ringence have been coupled to characterize the state of orientation of each component of the blend. It is found that the orientation decreas es progressively with an increase in the amount of PVME in the blend, and that a close relation holds between the Young's modulus and the ov erall orientation. The results are interpreted in terms of free-volume variations with the distance to the glass transition temperature. At the initial stage of deformation, the relation between modulus and ori entation is analysed using the rubber elasticity theory, whereas at la rger deformations, the strain-orientation relation is properly modelle d using a constitutive equation derived from the Doi-Edwards molecular theory.