CRITICAL CONCENTRATION EFFECTS IN POLYMER–POLYMER–SOLVENT SYSTEMS

In various ternary systems of the type polymer A – polymer B – solvent S, a dip or peak has been observed in the [η] – cB curve at the critical concentration of polymer B. ([η] is the intrinsic viscosity of A in mixed solvent consisting of B and S, and cB is the concentration of B in this mixed solvent.) It is shown that such a critical concentration effect is most likely to occur when the solvent is poor for polymer B, and will be the larger the poorer the solvent.Evidence is also presented in support of the hypothesis that if, as is usual, the two polymers repel each other, the effect is a dip if the solvent is good for polymer A and is a peak if the solvent is sufficiently poor for polymer A.Critical concentrations of polystyrene, polyvinyl acetate, and polymethyl methacrylate (five different samples) have been measured in this way in 12 different ternary systems. These observed critical concentrations are in good agreement with values calculated using the equation previously described, according to which the critical concentration of a polymer is inversely proportional to its intrinsic viscosity in the solution.