Properties of dilute polymer solutions III: Intrinsic viscosity/temperature relationships for conventional polymethyl methacrylate

Abstract

Intrinsic viscosity/temperature relationships from 0° to 120°C determined in a variety of solvents on sixteen fractions of conventional polymethyl methacrylate ranging in molecular weight from 10 5 to 2.6 × 10 6 yield, through comparison with existing theory, information on both the intrachain forces and the thermodynamic interactions with the solvent, and their effect on the average dimensions of the polymer coil. The observation that the viscosity at the critical miscibility temperature Θ is 4.8 × 10 −4M 1 2 independent of temperature, from 30° to 70° at least, indicates an average linear dimension for the polymer coil twice that expected for free rotation about the chain bonds; the observed temperature independence indicates that the trans and gauche minima in the potential energy profile on rotation have the same energy. The heat of mixing and the Θ-temperature for polyisobutylene, polystyrene, and polymethyl methacrylate in different solvents are shown to be generally related to (and to increase with) the difference between the Hildebrand solubility parameters for the polymer and the solvent, and other unknown factors which in specific instances play a dominant role. The abnormally low entropy of mixing observed for these solutions indicates a high degree of local order in the packing of solvent molecules and polymer segments as a result of specific interactions dependent on the chemical and geometrical structure of the polymer-solvent pair.