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

Molecular orientation and mechanical properties of polystyrene/poly(vinyl methyl ether) (PS/PVME) miscible blends have been investigated in a broad range of compositions, taking as a reference the temperature of phase separation. Fourier transform infra-red spectroscopy and birefringence have been coupled to characterize the state of orientation of each component of the blend. It is found that the orientation decreases 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 overall 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 orientation is analysed using the rubber elasticity theory, whereas at larger deformations, the strain-orientation relation is properly modelled using a constitutive equation derived from the Doi-Edwards molecular theory.