THERMODYNAMICS OF THE AGGREGATION PHENOMENON IN ASSOCIATING POLYMER-SOLUTIONS

The effect of temperature on the extent of aggregation, in dilute solution, of sodium sulfonated polystyrene ionomers in xylene has been determined by using small-angle neutron scattering (SANS). The data are described by using the open association model in which it is assumed that an equilibrium is eventually formed between single chains and aggregates of all sizes. The extent of aggregation was found to be temperature independent which suggests that there is no change in enthalpy on forming aggregates. It was therefore suggested that on aggregation intramolecular ion pair associations are broken and the same number of intermolecular associations formed. Intramolecular ion pair associations in the ionomer solutions were shown to collapse the single-chain radius of gyration (Rg) at infinite dilution to a value less than half the single chain dimension of normal polystyrene in this solvent and also smaller than for polystyrene in θ solvents. The temperature dependence of the second virial coefficient for the ionomers was determined and compared with values for polystyrene. It was also found that 2% by volume of methanol was enough to almost completely solvate all the ionic groups and prevent both inter- and intramolecular ion pair associations in dilute solution. © 1990, American Chemical Society. All rights reserved.