RHEOLOGICAL PROPERTIES OF SOLUTIONS OF BUTADIENE-STYRENE COPOLYMERS OF VARYING MICROSTRUCTURE

An experimental study of the non-Newtonian viscosity mu and the principal normal stress difference N//1 of solutions of polybutadiene, polystyrene, and their copolymers of varying microstructures has been carried out in decalin, decane, and their mixtures. For the homopolymers and random copolymers, the viscosity and Weissenberg number (N//1/ sigma //1//2) at a constant shear rate decrease as the nonsolvent is added. For block copolymers, the opposite is observed. The simple SB-block copolymers show thixotropic behavior with yield stress. This may be explained by the two-phase structure being in the form of micelles in which the polystyrene aggregates are solubilized by the polybutadiene segments.