[Abstract unavailable

Current progress in understanding the dynamics of associating polymers is reviewed, with examples including both ionic and hydrogen bonding associations. A particular emphasis is placed on quantification of the strength of the interaction that sets the association lifetime. Knowledge of the interaction energy and the number density of associating groups allows a rational understanding of the linear viscoelastic response of many associating polymers.

Linear viscoelasticity (LVE) of low-ion-content and lowmolecular-weight (nonentangled) randomly sulfonated polystyrene shows a sol−gel transition when the average number of ionic groups per chain approaches unity. This transition can be well understood by regarding the number of ionizable sites over a chain as the relevant functionality for crosslinking. For ionomers below but very close to the gel point, the LVE shows power law relaxation similar to gelation of chemical cross-linking. Nevertheless, ionomers near and beyond the gel point also show terminal relaxation not seen in chemically cross-linking systems, which is controlled by ionic dissociation. Careful analysis of the power law region of the frequency dependence of complex modulus close to the gel point shows a change in exponent from ∼1 at high frequency to ∼0.67 at low frequency, which strongly suggests a transition from mean-field to critical percolation known as the Ginzburg point. A mean-field percolation theory by Rubinstein and Semenov for gelation with effective breakup has been modified to include critical percolation close to the gel point and predicts well the observed LVE of lightly sulfonated polystyrene oligomers.