Viscometric study on the compatibility of polymer-polymer mixtures in solution

The viscosity behaviour of mixtures formed by two uncharged polymers in dilute solution has been studied at 25 degrees C. The ternary systems assayed, and denoted solvent (1)/ polymer (2)/ polymer (3), have in common the poly(ether sulphone) (PES) as polymer 2, and poly(vinylidene fluoride) (PVDF), poly(methyl methacrylate) (PMMA) or poly(styrene) (PS) as polymer 3. The intrinsic viscosity and the viscometric interaction parameters have been experimentally measured for the binary (solvent/polymer) as well as for the ternary systems, and also theoretically evaluated for the latter. The estimation of the compatibility degree of the above polymer pairs have been done by means of three criteria: (i) the sign of Delta b(m), according to the traditional formalism developed by Krigbaum and Wall: (ii) the sign of a new defined Delta b(m): and (iii) the sign of Delta[eta](m). The two last criteria are proposed in this work and are based on treating the viscosity interaction parameter and the intrinsic viscosity as excess properties by similarity with those of real solutions. Both methods provide compatibility predictions in agreement with those made with the traditional one but they are much more simple in handling the calculations. Finally, the observed compatibility behaviour follows the order: (PES + PMMA)much greater than(PES + PVDF)>(PES; PS), in dimethylformamide as solvent, at least in the assayed composition range. (C) 1998 Elsevier Science Ltd. All rights reserved.