MICRODYNAMICS OF REVERSE MICELLES OF OMEGA-METAL AND ALPHA,OMEGA-METAL SULFONATO POLYSTYRENE IN TOLUENE

Reverse micelles of omega- and alpha,omega-metal sulfonato polystyrene s in toluene have been investigated by Li-6, Li-7, and pulsed field gr adient NMR. Micelles are found to be of a narrow size distribution and to consist of roughly spherical ionic cores shielded from the solvent by a polystyrene shell. The nature of the ion pair is found to influe nce significantly the micellar size. The correlation time characterist ic of lithium relaxation is faster than the reorientational correlatio n time of the aggregates, which means that lithium relaxation essentia lly takes place within the ionic cores. The effective relaxation mecha nism is consistent with a fast exchange of lithium ions between differ ent coordination sites within the aggregates. In concentrated solution s, the equilibrium between aggregated polymer chains and unassociated chains is essentially shifted toward the aggregated species. This tend ency is reversed upon dilution. Below a critical micellar concentratio n of ca. 0.01 g/dL, only ''free'' chains persist in solution. Temperat ure has no significant effect on the position of the aggregation equil ibrium. The aggregates are dissociated by the addition of a polar coso lvent, such as methanol, which solvates the ion pairs. The MeOH/Li+ mo lar ratio must, however, be higher than 100 to perturb significantly t he ion pair aggregation. Up to a MeOH/Li+ ratio of 10 000, part of the chains remain aggregated, and the lithium spin-lattice relaxation is dominated by the aggregates. Above a MeOH/Li+ ratio of 10 000, the agg regates are almost completely disrupted. Self-diffusion coefficients o f the difunctional chains are not dramatically smaller compared to the monofunctional counterparts, even when solutions of difunctional comp ounds form a gel. This behavior might be explained by the percolation model applied to the aggregation process, with the pulsed field NMR ex periment probing only the selfdiffusion of the clusters in the sol pha se of the gel.