POLYMER-POLYMER INTERACTION PARAMETERS OBTAINED FROM DIFFUSION-COEFFICIENTS OF TERNARY POLYMER-SOLUTIONS

Dynamic light scattering and pulsed field gradient nuclear magnetic re sonance were used to study ternary polymer solutions formed with poly( methyl methacrylate) and polystyrene dissolved in deuterated bromobenz ene and also in deuterated toluene. The self-diffusion coeffient of ea ch polymer and the slow mode diffusion coefficient were determined for each solution. These diffusion coefficients were then used to calcula te the polymer-polymer interaction parameter chi for each solution ass uming that the Borsali-Benmouna theory adequately described the dynami c light scattering observations. This procedure is complementary to th at introduced by Sun and Wang. Bath procedures recognize that addition al experimental information is required if the variation of chi with s olution composition is to be determined. Sun and Wang measured the dyn amic light scattering mode amplitudes; this work measures the polymer self-diffusion coefficients. The values of chi obtained from the bromo benzene solutions compare favorably with those obtained by Fukuda et a l. using classical light scattering under optical Theta conditions. Al so the variation of chi with minority polymer molar mass was similar t o the predicted variation of the critical value of chi. However, the v alues of chi obtained from the deuterated toluene solutions were large r and did not behave in a similar manner. This anomalous behavior is e xplained in terms of the phase stability of the deuterated toluene sol utions. However, the possibility that the Borsali-Benmouna theory is i nadequate for solutions formed with a solvent of unequal affinities fo r the two polymers when the solutions are close to phase separation is not discounted.