Quasielastic light scattering and viscometric measurements on dilute ionomer solutions

Abstract

The hydrodynamic radius and intrinsic viscosity of a number of dilute solutions containing lightly sulfonated polystyrene ionomers and its unmodified analog have been measured in both polar and nonpolar solvents. Since these ionic interactions are known to significantly modify the physical properties of a polymer through relatively strong intra- and intermolecular interactions, it is important to examine how the individual chain characteristics of a charged polymer are influenced with changes in solvent quality and sulfonation level. In a polar solvent, such as dimethylsulfoxide, a short and a long correlation time is observed indicative of at least two relaxation processes. The long correlation time is attributed to the translational motion of the entire polymer chain, while the short relaxation process is correlated with the motion of the polystyrene segments situated between ionic groups. This result may be due to the ability of dimethylsulfoxide to dissolve lightly sulfonated polystyrene, but not its nonionic analog. On the contrary, in a relatively nonpolar solvent, such as cyclohexanone, only a single correlation function is noted. Again correlation with viscometric measurements shows that this is entirely due to translational motion of the individual coil. In this particular solvent, both polystyrene and sulfonated polystyrene are soluble. These results are useful as a basis for interpreting similar measurements in the semidilute region where the ‘‘universal’’ solution characteristics of associating polymers more specifically ionomers, may be observed.