Intrinsic Viscosities of Polymer Blends and Polymer Compatibility: Self‐Organization and Flory–Huggins Interaction Parameters

The intrinsic viscosity of polymer blends in a common solvent may deviate markedly from additivity. Such behavior testifies favorable interactions between the two types of macromolecules. Under these conditions, isolated polymer coils contain one macromolecule of each species and represent the simplest possible case of self‐organization. The particular thermodynamic situation required for the occurrence of that phenomenon is being analyzed in terms of microphase equilibria by means of an approach, which subdivides the dilution process into two steps. The first step quantifies the opening of intersegmental contacts at constant conformations of the components and the second step the conformational relaxation required to attain equilibrium. The intrinsic viscosities resulting for the mixed isolated coils are normally smaller than calculated from additivity. However, the opposite behavior can also occur under special conditions. The possibilities to gain quantitative information on polymer/polymer interaction parameters from the intrinsic viscosities of polymer blends are being discussed. Solutions of two sufficiently compatible polymers (depicted in red and in green, respectively) form isolated coils upon dilution that contain one macromolecule of each type. Equilibrium is reached as µ 1, the chemical potential of the solvent inside the coil, equals that of the pure solvent surrounding it.