Effects of molecular weight and concentration on flow properties of concentrated polymer solutions

Molecular weight (M) and concentration (c) dependencies of the viscosity were measured over wide ranges of M and c for concentrated solutions of linear and branched Poly(vinyl acetate) (PVAc) as well as of polystyrene (PS) in good and poor solvents, and the effect of branching and solvent on the flow properties was studied. The log η versus log M and log η versus log c curves for a given system can be superposed by the shift along the abscissa, giving smooth master curves. From the shift factors the ratio of the two exponents α and β, which appears in the following viscosity equation, can be evaluated: where η is the viscosity, p is the density of the solution, and K is a constant at constant temperature. The evaluated values of β/α for the several systems studied here ranged from 0.54 to 0.72. The log η versus log M curves cannot always be approximated by two straight lines, and therefore it was proposed to determine this critical molecular weight Mc an the lowest molecular weight above which the viscosity becomes proportional to M3.4 or M3.5. Then, the viscosity at Mc is constant independent of c, and the relation between Mc and c is given by (cp)Mβ/α = constant. The experimental values of β/α were compared with the theoretical values given by Bueche and Onogi et al.